European coal geology and technology

European Coal Geology and Technology

Geological Society Special Publications Series Editor A. J. FLEET

GEOLOGICAL SOCIETY SPECIAL PUBLICATION NO. 125

European Coal Geology and Technology

EDITED BY

R. GAYER Department of Earth Sciences, University of Wales, Cardiff AND

J. PESEK Charles University, Prague, Czech Republic

1997 Published by The Geological Society London

THE GEOLOGICAL SOCIETY The Society was founded in 1807 as The Geological Society of London and is the oldest geological society in the world. It received its Royal Charter in 1825 for the purpose of 'investigating the mineral structure of the Earth'. The Society is Britain's national society for geology with a membership of around 8000. It has countrywide coverage and approximately 1000 members reside overseas. The Society is responsible for all aspects of the geological sciences including professional matters. The Society has its own publishing house, which produces the Society's international journals, books and maps, and which acts as the European distributor for publications of the American Association of Petroleum Geologists, SEPM and the Geological Society of America. Fellowship is open to those holding a recognized honours degree in geology or cognate subject and who have at least two years' relevant postgraduate experience, or who have not less than six years' relevant experience in geology or a cognate subject. A Fellow who has not less than five years' relevant postgraduate experience in the practice of geology may apply for validation and, subject to approval, may be able to use the designatory letters C. Geol. (Chartered Geologist). Further information about the Society is available from the Membership Manager, The Geological Society, Burlington House, Piccadilly, London W1V 0JU, UK. The Society is a Registered Charity, No. 210161. Published by The Geological Society from: The Geological Society Publishing House Unit 7, Brassmill Enterprise Centre Brassmill Lane Bath BA1 3JN UK (Orders: Tel. 01225 445046 Fax 01225 442836)

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Contents

Preface

Regional coal reserves, coal basin tectonics and stratigraphy DORUSKA, J. The Czech Republic Energy Policy: conception and implementation in a market economy PEgEK, J. & DOPITA, M. Coal production and usage in the Czech Republic KUMPERA, O. Controls on the evolution of the Namurian paralic basin, Bohemian Massif, Czech Republic KRS, M., PEgEK, J., PRUNER, P., SKO~EK, V. & SLZPI~KOVA, J. The origin of magnetic remanence components of Westphalian C to Stephanian C sediments, West Bohemia: a record of waning Variscan tectonism DREESEN, R., BOSSIROY, D., SWENNEN, R., THOREZ, J., FADDA, A. OTTELLI, L. & KEPPENS, E. A depositional and diagenetic model for the Eocene Sulcis coal basin of SW Sardinia INANER, H. & NAKOMAN, E. Turkish lignite deposits KARAYIGIT, A. I. & WHATELEY, M. K. G The origin and properties of a coal seam associated with continental thin micritic limestones, Selimoglu-Divrigi, Turkey KARAYIGIT, m. I. & WHATELEY, M. K. G. Chemical characteristics, mineralogical composition and rank of high sulphur coking coals of Middle Miocene age in the G6kler coal field, Gediz, Turkey TICLEANU, N. & DIACONITA, D. The main coal facies and lithotypes of the Pliocene coal basin, Oltenia, Romania SI~KOV, G. D. Bulgarian low rank coals: geology and petrology STUKELOVA,I. E. Coal petrology and facies associations of the South Yakutian Coal Basin, Siberia

Coal petrology and palaeontology GAYER, R. A., FOWLER, R. & DAVIES, G. Coal rank variations with depth related to major thrust detachments in the South Wales coalfield: implications for fluid flow and mineralization DvoIL~K, J., HON~K, J., PE~EK, J. & VALTEROVA, P. Deep borehole evidence for a southward extension of the Early Namurian deposits near N6m~i6ky, S Moravia Czech Republic: implication for rapid coalification KOSTOVA, I., MARKOVA, K. & KUNTSCHEV, K. M6ssbauer spectroscopic investigation of low rank coal lithotypes PREMOVIC, P. I., NIKOLIC, N. D. & PREMOVIC, M. P. Comparison of solid state ~3C NMR of algal coals/anthracite and charcoal-like fusinites: further evidence for graphitic domains SYKOROVA, I., (~ERN~', J., PAVLIKOVA, H. & WEISHAURTOV~,, Z. Composition and properties of North Bohemian coals STEFANOVA, M. & MAGNIER, C. Aliphatic biological markers in Miocene Maritza-Iztok lignite, Bulgaria SYBRYAJ,S. Floristic characters of the upper coal-bearing formation in the Transcarpathians

vii

1 3 13 29

49

77 101 115

131 141 149

161

179

195 201 207 219 229

vi

CONTENTS

Mineral matter in coal and the environment

BAQR1, S. R. H. The distribution of sulphur in the Palaeocene coals of the Sindh province of Pakistan CAVENDER,P. F. & SPEARS,D. A. Sulphur distribution in a multi-bed seam BOUSKA, V., PESEK, J. & ZAK, K. Values of ~34S in iron disulphides of the North Bohemian lignite basin, Czech Republic JANKES, G., CVETKOVIC, O. & GLUMICIC, T. Determination of different forms of sulphur in Yugoslav soft brown coals PREMOVI(~, P. I., NIKOLIC, N. D., PAVLOVIC, M. S., JOVANOVIC, LJ. S. & PREMOVIC, M.P. Origin of vanadium in coals: parts of the western Kentucky (USA) No. 9 coal rich in vanadium SPEARS, D. A. Environmental impact of minerals in UK coals

237 245 261 269 273 287

Mining geophysics

GREGOR, V. & TI~2KY, A. A well logging method for the determination of the sulphur contents in coal seams by means of deep gammaspectrometry MACH, K. A logging correlation scheme for the main coal seam of the North Bohemian brown coal basin, and the implications for the palaeogeographical development of the basin HOLU~, K. Seismic monitoring for rock burst prevention in the Ostrava-Karvinfi coalfield, Czech Republic KALA~, Z. An analysis of mining induced seismicity and its relationship to fault zones OPLU~TIL, S., PE~EK, J. & SKOPEC, J. Comparison of structures derived from mine workings and those interpreted in seismic profiles: an example from the Ka~ice deposit, Kladno Mine, Bohemia

297 309 321 329 337

Coal technology and coalbed methane

BARRAZA, J., CLOKE, M. & BELGHAZI, A. Improvements in direct coal liquefaction using beneficiated coal fractions ALEKSI(~, B. R., ERCEGOVAC, M. D., CVETKOVlC, O. G., MARKOVlC, B. Z., GLUMI(~IC, T. L., ALEKSIC, B. D. & VITOROVIC, D. K. Conversion of low rank coal into liquid fuels by direct hydrogenation ASMATULU, R., ACARKAN, N., ONAL, G. & CELIK, M. S. Desulphurization of low-rank coals by low-temperature carbonization WHATELEY, M. K. G., GENCER, Z. & TUNCALI, E. Amelioration of high organic sulphur coal for combustion in domestic stoves STANOJEVI(~,P., JANKES,G., KUBROVIC,M., STANOJEVI(~,M. & BLAGOJEVI(~,P. The use of pulverized lignite/natural gas mixed fuels in the high-temperature process of a cement rotary kiln DOUCHANOV, D. & MINKOVA, V. The possibility of underground gasification of Bulgarian Dobrudja's coal BOARDMAN, E. L. & RIPPON, J. H. Coalbed methane migration in and around fault zones HOLUB, V., ELIAg, M., HRAZD[RA, P. & FRANCU, J. Geological research into gas sorbed in the coal seams of the Carboniferous in the Mgeno-Roudnice basin, Czech Republic GRZYBEK, I., GAWLIK, L., SUWALA, W. & KUZAK, R. Estimation method for methane emission from Polish coal mining TAKLA, G. & VAVRUS~.K, Z. Methane emissions and its utilization from Ostrava-Karvinfi collieries in the Upper Silesian coal basin, Czech Republic

349

Index

441

357

365 371 379

385 391 409 425 435

Preface Despite the major reduction in the coal mining industry that has taken place in Europe over the last decade, most European countries remain strongly dependent on utilizing coal for both power production and in the steel industry. There is an increasing tendency to import cheaper coal from sources outside Europe and this trend is likely to continue and even expand. However, the need to use indigenous coal is essential and by improving knowledge of coal geology and technology, more efficient and competitive use of existing proven and indicated reserves will be possible. This volume contains some 40 papers describing new research into coal geology and coal technology. These have been grouped into five sections dealing with separate aspects of the subject, so that related papers are placed together in the volume. However, some important coal basins have been researched by several different techniques, and papers on these topics have been included in the appropriate different sections. For example, the Upper Silesian basin, one of the most important Upper Palaeozoic coal basins in Europe, is covered by six papers in four of the sections of the volume. Similarly, the North Bohemian lignite basin is described in four papers placed in four different sections. Coal deposits from twelve countries are covered in the volume, with the majority of papers (34) covering deposits in Central and Eastern Europe. Nevertheless, the geology and technology described, despite having a geographical bias, is of general applicability. The deposits together with the associated concepts and methods may not be well known in the west so that the papers and included references should provide an invaluable data source. Thus the volume can be seen as a companion volume to European Coal Geology (Whateley & Spears 1995) which concentrated on coal deposits in western Europe. The present volume also describes new and important research in western Europe, updating the coal geology provided in the earlier volume. Section One includes 11 papers describing regional coal reserves, coal basin tectonics and stratigraphy. The regions covered include Bulgaria, the Czech Republic, Romania, Sardinia, Siberia, and Turkey. Amongst these interesting accounts are a paper by the late Professor Otto Kumpera, which relates the coal accumulation in the Upper Silesian basin to processes related to foreland basin tectonics, and a paper by Krs et ai. documents the waning effects of the Variscan orogeny in the Bohemian Massif by a detailed study of palaeomagnetism. Dreesen et al. describe an unusual coal basin in Sardinia in which coal forming environments are closely associated with carbonates and evaporites. The section also contains an important paper by Pesek & Dopita discussing the present and future energy requirements and associated environmental issues of the Czech republic, as an example of one of the developing eastern European countries. Section Two covers various aspects of coal petrology and palaeontology in seven papers. These include papers describing unusual variations of coal rank with depth in Moravia (Dvorak et al.) where coals remain at relatively low rank despite being buried beneath the Carpathian thrust sheets, and in South Wales (Gayer et al.), where high levels of heat flow and reversals in rank increase with depth are attributed to fluid flow within the basin. Other authors describe the results of various analytical approaches to the study of coal petrology, including solid state 13C NMR studies of fusinites (Premovic et al.), M6ssbauer spectroscopy of low rank coal lithotypes (Kostova et al.), and biochemical analysis of lignite (Stefanova & Magnier). Section Three deals with mineral matter in coal and the environment. The six papers include the sulphur contents of Pakistan coals (Baqri), of Yugoslavian lignites

viii

PREFACE

(Jankes et ai.) and of a multi bed coal in the UK (Cavender & Spears). Bouska et aL discuss the sulphur isotopic composition of North Bohemian lignites and Premovic et aL present the results of vanadium analysis in Kentucky coals. Section Four contains five papers concerned with mining geophysics. These include well logging techniques applied to the North Bohemian lignite basin (Mach) and the use of a deep gamma spectrometer (Gregor & Tezky). Seismic monitoring for rock bursts (Holub) and mining induced seismicity (Kalab) are two aspects of seismic investigation covered in the section. The final Section Five includes papers describing coal technology and coalbed methane. Liquefaction is discussed in two papers; one by Aleksic et aL using direct hydrogenation of low rank coals and the other describing experiments on beneficiated coal fractions (Barraza et aL). Desulfurization is also covered in two papers; one by Asmatulu et al. and the other by Whateley et aL, both dealing with unusual techniques to treat high sulphur Turkish coals. Gassification and coalbed methane generation from mines is covered by Douchanov & Minkova, Gryzbek et aL and Holub et aL, whilst Boardman & Rippon present an analysis of the influence of faults in coalbed methane production. The editors would like to thank all the authors for submitting the papers which represent a selection of those originally presented at the Second European Coal Conference in 1995 in Prague. We would also like to thank the many geologists who reviewed the papers: Mesdames & Messieurs Austin, Bouska, Brabham, Bright, Bryant, Cloke, Cole, Cornford, Davidson, Davies, Dopita, Drozdzewski, Ellison, Frodsham, Gayer, Gillespie, Glover, Goulty, Guion, Harris, Hathaway, Hemsley, Holub, Honek, Jelinek, Jones, Juch, Karayigit, Konecny, Kostova, Kropacek, Kumpera, McLean, Malan, Martinec, Miliorizos, Moore, Oplustil, Patrick, Pesek, Premovic, Querol, Rhodes, Rippon, Rosa, Simunek, Skocek, Spears, Spiker, Thomas, Turner, Wagner, Wakefield, Whateley. Many of the papers were written by authors whose first language is not English and this represented a problem not only for the authors but also for the reviewers. Both worked very hard to produce the present results. We have been continually amazed at the language skills of European geologists and hope that any slight errors remaining in the texts do not detract from the value of the volume. Sadly, one of the authors, Professor Kumpera, died before completing the final version of his major work on the geology of the Upper Silesian basin. Although his widow, Anna Kumperova, continued with the drafting of the diagrams, the conclusions have been added by the editors who accept responsibility for any errors inadvertently produced. We would also like to thank David Ogden, the staff editor at the Geological Society Publishing House for his continuing support and editing of this volume. Dr Rod Gayer, Cardiff Professor Jiri Pesek, Prague

Reference WHATELEY, M. K. G. & SPEARS, D. A. (eds) 1995. European Coal Geology. Geological Society, London, Special Publication, 82.

Preface Despite the major reduction in the coal mining industry that has taken place in Europe over the last decade, most European countries remain strongly dependent on utilizing coal for both power production and in the steel industry. There is an increasing tendency to import cheaper coal from sources outside Europe and this trend is likely to continue and even expand. However, the need to use indigenous coal is essential and by improving knowledge of coal geology and technology, more efficient and competitive use of existing proven and indicated reserves will be possible. This volume contains some 40 papers describing new research into coal geology and coal technology. These have been grouped into five sections dealing with separate aspects of the subject, so that related papers are placed together in the volume. However, some important coal basins have been researched by several different techniques, and papers on these topics have been included in the appropriate different sections. For example, the Upper Silesian basin, one of the most important Upper Palaeozoic coal basins in Europe, is covered by six papers in four of the sections of the volume. Similarly, the North Bohemian lignite basin is described in four papers placed in four different sections. Coal deposits from twelve countries are covered in the volume, with the majority of papers (34) covering deposits in Central and Eastern Europe. Nevertheless, the geology and technology described, despite having a geographical bias, is of general applicability. The deposits together with the associated concepts and methods may not be well known in the west so that the papers and included references should provide an invaluable data source. Thus the volume can be seen as a companion volume to European Coal Geology (Whateley & Spears 1995) which concentrated on coal deposits in western Europe. The present volume also describes new and important research in western Europe, updating the coal geology provided in the earlier volume. Section One includes 11 papers describing regional coal reserves, coal basin tectonics and stratigraphy. The regions covered include Bulgaria, the Czech Republic, Romania, Sardinia, Siberia, and Turkey. Amongst these interesting accounts are a paper by the late Professor Otto Kumpera, which relates the coal accumulation in the Upper Silesian basin to processes related to foreland basin tectonics, and a paper by Krs et ai. documents the waning effects of the Variscan orogeny in the Bohemian Massif by a detailed study of palaeomagnetism. Dreesen et al. describe an unusual coal basin in Sardinia in which coal forming environments are closely associated with carbonates and evaporites. The section also contains an important paper by Pesek & Dopita discussing the present and future energy requirements and associated environmental issues of the Czech republic, as an example of one of the developing eastern European countries. Section Two covers various aspects of coal petrology and palaeontology in seven papers. These include papers describing unusual variations of coal rank with depth in Moravia (Dvorak et al.) where coals remain at relatively low rank despite being buried beneath the Carpathian thrust sheets, and in South Wales (Gayer et al.), where high levels of heat flow and reversals in rank increase with depth are attributed to fluid flow within the basin. Other authors describe the results of various analytical approaches to the study of coal petrology, including solid state 13C NMR studies of fusinites (Premovic et al.), M6ssbauer spectroscopy of low rank coal lithotypes (Kostova et al.), and biochemical analysis of lignite (Stefanova & Magnier). Section Three deals with mineral matter in coal and the environment. The six papers include the sulphur contents of Pakistan coals (Baqri), of Yugoslavian lignites

viii

PREFACE

(Jankes et ai.) and of a multi bed coal in the UK (Cavender & Spears). Bouska et aL discuss the sulphur isotopic composition of North Bohemian lignites and Premovic et aL present the results of vanadium analysis in Kentucky coals. Section Four contains five papers concerned with mining geophysics. These include well logging techniques applied to the North Bohemian lignite basin (Mach) and the use of a deep gamma spectrometer (Gregor & Tezky). Seismic monitoring for rock bursts (Holub) and mining induced seismicity (Kalab) are two aspects of seismic investigation covered in the section. The final Section Five includes papers describing coal technology and coalbed methane. Liquefaction is discussed in two papers; one by Aleksic et aL using direct hydrogenation of low rank coals and the other describing experiments on beneficiated coal fractions (Barraza et aL). Desulfurization is also covered in two papers; one by Asmatulu et al. and the other by Whateley et aL, both dealing with unusual techniques to treat high sulphur Turkish coals. Gassification and coalbed methane generation from mines is covered by Douchanov & Minkova, Gryzbek et aL and Holub et aL, whilst Boardman & Rippon present an analysis of the influence of faults in coalbed methane production. The editors would like to thank all the authors for submitting the papers which represent a selection of those originally presented at the Second European Coal Conference in 1995 in Prague. We would also like to thank the many geologists who reviewed the papers: Mesdames & Messieurs Austin, Bouska, Brabham, Bright, Bryant, Cloke, Cole, Cornford, Davidson, Davies, Dopita, Drozdzewski, Ellison, Frodsham, Gayer, Gillespie, Glover, Goulty, Guion, Harris, Hathaway, Hemsley, Holub, Honek, Jelinek, Jones, Juch, Karayigit, Konecny, Kostova, Kropacek, Kumpera, McLean, Malan, Martinec, Miliorizos, Moore, Oplustil, Patrick, Pesek, Premovic, Querol, Rhodes, Rippon, Rosa, Simunek, Skocek, Spears, Spiker, Thomas, Turner, Wagner, Wakefield, Whateley. Many of the papers were written by authors whose first language is not English and this represented a problem not only for the authors but also for the reviewers. Both worked very hard to produce the present results. We have been continually amazed at the language skills of European geologists and hope that any slight errors remaining in the texts do not detract from the value of the volume. Sadly, one of the authors, Professor Kumpera, died before completing the final version of his major work on the geology of the Upper Silesian basin. Although his widow, Anna Kumperova, continued with the drafting of the diagrams, the conclusions have been added by the editors who accept responsibility for any errors inadvertently produced. We would also like to thank David Ogden, the staff editor at the Geological Society Publishing House for his continuing support and editing of this volume. Dr Rod Gayer, Cardiff Professor Jiri Pesek, Prague

Reference WHATELEY, M. K. G. & SPEARS, D. A. (eds) 1995. European Coal Geology. Geological Society, London, Special Publication, 82.

The Czech Republic energy policy: conception and implementation in a market economy JOSEF DORUSKA

Ministry of Industry and Trade of the Czech Republic, 11015 Prague 1, Czech Republic Abstract: In 1992 the government of the Czech Republic approved the 'Energy Policy of the

Czech Republic'. It was directed to the legislative and ecological respects which are compatible with European Union countries.

In the period since February 1992, when the energy policy was approved by the Government of the Czech Republic there have been many changes. For example, in July 1992 the Government approved its programme; the former Czech and Slovak Federal Republic was divided into the Czech and Slovak Republics; a major part of the energy companies was privatized; price adjustment of a considerable part of the energy commodities was abrogated and the Ingoldstadt oil pipeline construction was started. The Government has considered many other aspects which have a substantial influence on the energy sector including documents on: Governmental policy concerning the environment of the Czech Republic, of principles of the governmental mineral policy; European agreement on incorporation of the Czech Republic into the European Union; European Energy Charter; results of the Uruguay round of GATT; Convention on climatic change; and others. Because of the changes and new agreements there is a need to update the energy policy of the Czech Republic. The updated energy policy that is being elaborated by the Ministry of Industry and Trade, is created in such a way that the transition of the power industry would lead t o - i n technical, legislative and ecological respects - a compatibility with the power industries of the advanced countries of the European Union. The basic long-term objectives of the updated energy policy are: 9 to ensure sufficient energy supplies for the economy at acceptable prices; 9 to minimize negative impacts of energy production, distribution and consumption on the environment in order to reach a common level in the countries of the European Union; 9 to prepare the power economy of the Czech Republic for entry into the European Union in legislative and technical respects.

With respect to the above-mentioned principles, a programme of desulphurization of power plants has been accepted. By 1998 the following power plants will be equipped with machinery for flue gas desulphurization:

Tugimice II Prun6~ov Po6erady Tisovfi Chvaletice M~lnik II M61nik III D6tmarovice

800 MW 1490 MW 1000 MW 110 MW 600 MW 220 MW 500 MW 800 MW

The realization of this programme will significantly contribute to improvement of the environment. The government of the Czech Republic realizes the importance of: 9 ensuring the energy for the national economy 9 sustaining ecological limits resulting from the impacts on the environment 9 ensuring the permanently sustainable development of the national economy 9 fulfilling obligations of the Czech Republic resulting from the Energy Charter. The government is ready to react to changing conditions in energy supplies. The government realizes that with respect to: (1) the level of national reserves of fossil energy sources, and (2) the negative impacts of utilization of fossil energy sources on the environment; it is necessary to develop ways that will respect both the Energy Charter and conditions of permanently sustainable development of the national economy. The Czech Republic is one of a group of countries of Central and Eastern Europe where the transition process is taking place. In historical times the territory of the Czech Republic was part of the Roman Empire, whereas in the Middle Ages borders were

From Gayer, R. & Pe~ek, J. (eds), 1997, European Coal Geology and Technology, Geological Society Special Publication No. 125, pp. 1-2.

output output output output output output output output

2

J. DORUSKA

difficult to define between dozens of kingdoms and principalities. At the beginning of the 21st century we are on the threshold of transnational integration of the energy sector. The basis of the economic prosperity of the European Union countries was in steel and coal, but the development of human knowledge has extended this to include information and communication areas. In these areas the Czech Republic is ready to play its full role.

References Resolution of the Government of the Czech Republic on the Power Policy of the CR, Prague, February 1992. Updated Energy Policy of the CR, Ministry of Industry and Trade of the Czech Republic, Prague, June 1994. The Basic Principles of the Governmental Mineral Policy of the CR (work version), Ministry of Economy of the Czech Republic, Prague, 1994.

Coal production and usage in the Czech Republic J. P E S E K 1 & M . D O P I T A ~

1Faculty of Science, Charles University, 128 43 Praha 2, Albertov 6, Czech Republic 2 Vysok{l s~kola bgt~skgt, 708 O00strava-Poruba, ti.17, listopadu, Czech Republic Abstract: Coal mining in the industrialized countries of Europe including the Czech Republic is witnessing a prolonged recession in the production of bituminous coal and lignite in particular due to reduced demands. Recession in numerous fields of industry has resulted apparently in lower production of metallurgical coke as well as in power generation. In addition, some countries have substituted the burning of solid fossil fuels with petroleum or natural gas or with other energy sources such as nuclear power, hydroenergy or geothermal energy. The Czech Republic is facing similar problems.

Judging from various scenarios presented by different institutions, it is becoming apparent that the production of bituminous coal in the Czech Republic even after the year 2000 will not drop dramatically below the level of production during 1993 and 1994. It is expected that about 14-16 x 106 metric tons of bituminous coal will be extracted in the year 2000 while the production in 1994 was about 17 x 106metric tons. Limited coal reserves in the workable levels of coal mines which will still be in operation in 2000 and whose prospects are promising, will require the development of new mine levels (e.g. Darkov and CSM mines in the Upper Silesian basin) and, around the year 2010, even the sinking of some new shafts in the Beskydy piedmont part of the Upper Silesian basin. Financial and time demands will play an important role when establishing such a scenario. The cost of developing a new mine level, taking into account the extent of the mining space required, the depth and the mining method, may be from 1.5 to 3 x 109 K6 at the current prices. Costs in developing a new mine can be as much as 20 x 109 K~ (see the Frengtfit mine) but the anticipated output from such a mine can only be achieved 10 to 15 years after commencing its construction. Some extra time is also required for conceptual issues, designing and for negotiations with legal entities operating in the region. These delaying factors argue for an intensification of studies to produce a long-term plan for solid and other fuel consumption in the Czech Republic in order to provide alternatives in the time span of 25 to 30 years. We consider the role of government to be paramount in this issue which is supported by numerous documents from industrialized European countries as well as from the USA. Our view, similar to that of Formfinek (1994) is that the role and importance of coal in the structure of primary energy sources has been underestimated. It is to be

noted that the Czech Republic always has been and will continue be more dependent on the output of coal in power generation in the year 2000 than any neighbouring country.

Electric power generation vs coal production and coal reserves The whole spectrum of problems related to coal mining can be divided basically in two groups. The first involves issues related to mining and necessary protection of coal reserves, whereas the second group involves issues related to improvement of the environment badly affected by mining operations. The policy to develop heavy industry following the communist coup d'gtat in February 1948, resulted in considerable increase in pig iron, steel and other energy demanding products. This resulted in a rather high consumption of electricity by the former Czechoslovakia (Fig. 1). As more than 90% of Czechoslovakia electricity was generated from lignite in the early 1960s, lignite production in the years 1946 through 1984 increased from 19.5 x 106metric tonnes to more than 101 x l06., and generation of electricity increased from 5.6 x 109 kWh in 1946 to 89 x 109kWh in 1989. Nuclear power stations at Jaslovsk6 Bohunice and Dukovany came into operation in the 1970s. The gradual introduction of nuclear power supplied only a part of the increase in energy demands of the former Czechoslovakia. However, in the 1980s, the * Similar considerable increase in production of lignite after World War II was recorded in former Yugoslavia, and in production of bituminous coal in former USSR, Poland and Australia. By contrast, a completely opposite trend in mining for coal in the same period of time was recorded for instance in the USA, Great Britain, France and Spain.

From Gayer, R. & Pe~ek, J. (eds), 1997, European Coal Geology and Technology, Geological Society Special Publication No. 125, pp. 3-12.

4

J. PESEK & M. DOPITA 1001

2 ......... 8Q-

..~ 60QO0e

t,..O 40-

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O. 1935

4'0 4's

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~0 ~9'95

Fig. 1. Electrical power generation in the period 1937-1994 (1) in Czechoslovakia; (2) in the Czech Republic. Note: Czech Republic constituted about two thirds of the territory of former Czechoslovakia.

patterns of production of electricity and coal (particularly lignite) began to differ considerably (see Figs 1-3). Whereas production of lignite reached its peak in 1985, the power generation culminated later in 1989. The relatively great difference between the decreasing coal production but continuing increase in power generation up to 1989 can be attributed to the electricity supply from nuclear power stations. Apart from the major decrease in demand for solid fuels in the former Czechoslovakia which is also evident in the Czech Republic, the coal mining industry remains the largest and most

important sector of the mineral raw materials mining industry. Coal has a prominent position among fossil fuels because natural hydrocarbon resources in the Czech Republic are negligible. Extraction of coal and its utilization has had a continuingly harmful influence on the environment, not only in coal mining districts (Ostrava region, Kru~n6 hory piedmont basin) but also in areas where its consumption has been concentrated such as around large coal-burning power stations and in large cities (e.g. North Bohemian basin, the M6lnik region, Prague agglomeration and other large cities).

120 2 .........

100

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~- 6o-

20

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9'0 19'95

Fig. 2. Production of lignite (in metric tonnes) in the period 1937-1994 (1) in Czechoslovakia; (2) in the Czech Republic.

COAL PRODUCTION IN THE CZECH REPUBLIC

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8's

ag'gs

Fig. 3. Production of bituminous coal both in former Czechoslovakia and in the Czech Republic (in metric tonnes) in the period 1937-1994.

It is obvious that the high coal consumption in former Czechoslovakia has resulted in a significant depletion of coal reserves with associated adverse impacts. Economic reform introduced after 1989 accelerated further reduction in demand for bituminous coal and lignite (Figs 2 & 3). This trend led to a decrease in coal production to economically and technically feasible levels and also to an abandonment of selected (and by that time) inefficient mines. The intentions of the Czech Government and pressure by local authorities are oriented towards a reduction of the negative impacts of both coal mining and its combustion on the environment (cf. Formfinek 1994, Reichmann 1994, Spousta 1995). These factors are reflected in the present position of the coal mining industry and in its search for the most suitable methods for a rapid inprovement of its situation. The solution lies not only in economical, technical and technological parameters, but also in averting potentially grave social and thus political consequences. The decrease in production of fossil fuels in the Czech Republic has resulted not only from the above factors but also from the restructuring of the economy which has led to a gradual reduction of metallurgical production and a concentration on the manufacturing of energetically less demanding products. However, it should be noted that the decline in industrial production in the Czech Republic and in the former Czechoslovakia in the years 1990-1993 has not been matched as yet by a similar decrease in the power demands. To manufacture products worth 1 USD, Austria and France needed in 1990, 0.18 and 0.2 kg of oil equivalent

respectively, whereas in the former Czechoslovakia the equivalent requirement was 1.6kg! These figures perhaps do not need any comment.

Durability of workable coal reserves in mined levels of the Ostrava-Karvinfi coal district and of other bituminous coal basins The Czech coal mining industry has reacted to reduced demand for bituminous coal and lignite in the same way as any other country's mining industry. Several underground mines have already been abandoned with the result that in the Rosice-Oslavany, Plzefi and Intra Sudetic basins, mining activities have ceased completely. Lignite production in the single underground mine in the Sokolov region as well as extraction of bituminous coal in the Ostrava part of the Upper Silesian basin has also terminated. Reduction of coal mining in the Peffvald part of the Upper Silesian basin is scheduled to commence during 1995. Various volumes of workable reserves were left behind in all the above-mentioned mines (Table 1). If these volumes are included in an overall diminution of workable coal reserves in the Czech Republic and when taking into consideration minimum profit achieved by the coal mining companies, it is necessary to discuss again the fate of workable reserves which our country has currently at its disposal. Ostravsk6 doly a.s., our largest bituminous coal mining company which together with the Dill CSM mine produce more than 90% of the annual output in the Czech Republic showed a profit of only

J. PESEK & M. DOPITA Table 1. Workable reserves in 10 6 t o n n e s left in abandoned bituminous coal mines due to closure programmes in the years 1990 through 1995 Sverma mine (OKR) Hehnanice mine Ostrava mine Odra mine J. Fu6ik mine Krimich mine Dobr6 ~t6sti mine Jind~ich mine Z. Nejedl2~ mine J. Sverma mine (VUD) Kate~ina mine

32.002 26.863 30.496 25.284 13.727 2.5 0.5 7.2 121.14 8.12 46.5

by January by January by January by January an estimate an estimate by January by January by January by January by January

147 x 106K6 (approximately 5.5 x 106USD) in 1992, and 31.4 x 106K6 (approx. 1.2 x 106USD) in 1993. The company applied selective but not always well-advised mining measures to improve mining methods. Nevertheless, it is necessary to separate strictly workable reserves which occur in the operating levels of existing mines from those whose development and extraction would require huge investment, particularly in the Czech part of the Upper Silesian basin (Table 2). However, individual mines of the Ostrava-Karvinfi coal district (OKR) have not at present sufficient financial resources for the required investment. It should be noted that one more underground bituminous coal mine in the Kladno region is still in operation. Its coal reserves, however, constitute less than 10% of workable reserves occurring in mined and developed levels of the Ostrava-

l, 1994 l, 1994 1, 1994 1, 1994 by the date of expected shut-down in 95 by the date of expected shut-down in 95 1, 1991 1, 1994 1, 1994 1, 1992 1, 1994

Karvinfi coal district. Table 2 shows that the coal reserves in currently operating mines will last without any large investment on average until 2010 or 2016, depending on the percentage lost during recovery, unless some unexpected event in the mining industry occurs in the Ostrava region e.g. abandonment of more mines, isolation of currently workable reserves due to regional or ecological limitations (see intensions of local authorities to outline a safety pillar under the city of Karvinfi and/or under the spa of Darkov). Introduction of these or other measures would reduce the lifespan of workable coal reserves in the Czech Republic (Pe~ek & Pe~kovfi 1993; Pe~ek et al. 1993). It is to be hoped that these alarming figures should provoke the relevant authorities into appropriate action. Almost 130 x 106 metric tonnes of workable reserves have been left in

Table 2. Workable reserves of bituminous coal in I06 tonnes in operating mines in the Czech Republic registered by December 31, 1994, and their duration in operating and developing levels Upper Silesian basin

total workable reserves of which confined to: operating levels developing levels designed levels total

586.6 149 164 164 454

Kladno basin

workable reserves in the Kladno mine Total workable reserves confined to operating and developing levels Anticipated output in the Czech Republic in 1995 (sine 1992)

19 332 16.4-16.7 i.e. average about 16.5 anticipated recovery factor 60% 100%

Decline in reserves of operating mines in 1995 Anticipated production in CR in 2000 (sine 1992) Decline in reserves of operating mines in 1996 through 2000 Anticipated volume of reserves by January 1, 2001 Life of mineable reserves in operating mines in operating and developing levels at the yearly anticipated output of 14.5 x 10 6 i.e. till the year

-23.1 14.5 -101.5 201.8

-16.5 14.5 -76.5 239.0

9.9 years 2010

16.4 years 2016

COAL PRODUCTION IN THE CZECH REPUBLIC prematurely closed mines of the O K R which represents 6 to 8 years of coal production in the Czech Republic. Further reserves appear to be irretrievably lost in the Rosice-Oslavany basin (RUD mines) and particularly in mines of the Intra Sudettic basin (VUD).

Issues related to profitability of underground coal mining with particular reference to bituminous coal Termination of bituminous coal production in the Rosice-Oslavany basin, then in NE Bohemia, and abandonment of coal mines in the Ostrava region and in western Bohemia (see above) was motivated either by reduced consumption or by unprofitability of underground mining. To date it has been questionable whether discussion of profitability (i.e. not subsidized) of coal production is meaningful under regulated (until recently) prices of coal and the still regulated prices of energy. This is the major issue from which the majority of partial problems are derived. According to an EC commission report, the average expenditure related to extraction of 1 metric ton of bituminous coal in EC countries in 1990 was equal to 200DM (3460K6, i.e. 102ECU). Expenditure in Germany was 260DM (132ECU). In 1994, their figures were 289 DM (147 ECU) in the Ruhr basin and 265DM (135ECU) in the Saar basin but the price of 1 metric tonne of an equivalent of bituminous coal imported into Germany was 70 DM (36 ECU) in 1994. Expenditure in Great Britain as only 150DM (76ECU) in 1994. Consequently, prices in Germany were subsidized by 54.5 ECU per metric tonne, i.e. about 1853 K6 (1 E C U = 3 4 K 6 ) . In Spain the equivalent subsidy was 26.4 ECU per tonne. However, in 1993 the subsidy in Germany increased to 69.5 ECU per tonne, and in 1994 to 215 DM (109ECU) per tonne in the Ruhr basin and 210DM (107ECU) in the Saar basin which is K6 3720 and 3633 respectively. In contrast, expenditure related to the extraction of 1 tonne of bituminous coal in Spain were reduced to ECU 19.8 per tonne in 1993, when numerous unprofitable mines were shut down. Comparing geological and mining conditions, the Ruhr basin appears to be unambiguously very similar to the OKR. Thus the intention to make underground mining bituminous coal in the Czech Republic profitable, seems to be highly problematic. It may be too late to reverse, but closing so-called non-profitable mines remains

7

highly questionable from the viewpoint of a long-term mineral policy. It may have been more realistic to compare the costs involved in closing selected mines with those related to subsiding operating mines. There can be no doubt that if underground mining for bituminous coal had been subsidized at a comparable rate to that applied in countries of the European Economic Community (see above) the so-called unprofitable Czech mines could have continued to operate. It is obvious that outlay of capital related to the development of new levels and/or a new mine would be higher than any mining company could afford. The question is whether it is more rewarding to extract the easily accessible coal reserves in mines scheduled to be shut down, but in which some investment has already been made and operation costs incurred, in order to develop some part of the mining space. The relatively small volume of workable reserves of bituminous coal should provoke the country's planner to reconsider the future of coal mining and to assess if, within the next ten to fifteen years, there will be any coal left to be extracted. There is no doubt that in the long term some revitalization of coal demand will occur. Coal should be considered not only as a traditional fuel for energy generation and production of coke but also and in particular as an irreplaceable raw material for the chemical industry. There is a requirement for the thoughtful manipulation of the coal reserves because present mining methods do not allow the remaining coal to be extracted from prematurely abandoned mines. Consequently, coal reserves of abandoned basins (coal districts) are lost forever including elimination of mining skills in the region. Reference to abandonment of numerous mines in industrialized western countries appears to be irrelevant when considering our specific situation. The fundamental difference between the Czech Republic and for instance Great Britain, Germany and/or other countries is in the fact that some of these countries including USA and Canada have considerably larger yet untouched coal reserves which can be exploited in the event of revitalized demands for bituminous coal.

Where to obtain energy after exhaustion of coal reserves? A considerable reduction in coal mining (e.g. France) or even its complete liquidation (e.g. Belgium) has taken place in several west European countries. The generation of electricity from classical sources is either substantially

8

J. PESEK & M. DOPITA

(France) or partially (.numerous west European countries) replaced by nuclear energy, indigenous or imported noble fuels or the partial substitution of indigenous coal by imported cheaper coal. The absence of large deposits of crude oil and gas in the Czech Republic, the slow and expensive construction of the Temelin nuclear power plant which, together with the high level waste repository, is opposed by both the Czech and foreign public, suggest that the Czech Republic could in the future be dependent on importing a large volume of coal for the generation of electricity, once the domestic fossil fuels have been exhausted. Consequently, prior to the complete exhaustion of the Czech coal reserves, the republic should either plan the construction of further nuclear power stations or make advance arrangements with potential coal exporting countries (such as Poland) for the supply of the necessary volume of coal. These negotiations should involve not only contracts containing long-term financial guarantees but also specifications and data on basic technological parameters of the imported coal including limits on harmful substances, etc. Published data suggest that coal from the Polish part of the Upper Silesian basin has for instance a higher content of sulphur. It is also necessary to determine the volume of coal that can be imported via the international transport network, particularly through the present railroad system, and also to consider boat transport, etc. However, if the coal is imported from other than neigbouring countries, then its import will be limited by the transport capacity of the transit countries and would also incur transit charges which show an increasing trend. Another issue involves payments for imported electricity or fuels. The administration would need to consider the financial sources required to pay for them. Such considerations are not premature for longterm planning. The future price of imported electricity or fuels should also be considered. The republic's present trade balance is static and the import of large volume of coal could seriously destabilize the situation. Despite the short-term fluctuations of prices we consider that the risk of a significant rise in price of coal and/or other fossil fuels should not be underestimated. This reasoning is especially pertinent in the event of further reductions or a complete shut down of coal mining in central and western Europe, bearing in mind that the present low wage manpower in South African Republic, Ukraine and other countries will not last much longer. In the case of Ukraine the present problems in coal mining may lead to a reduction of exported coal, particularly if Ukraine meets

its obligations and shuts down the Chernobyl nuclear power station by the year 2000. It is anticipated that this nuclear capacity will be replaced by the construction of new coal burning power stations.

Is coal a strategic raw material for the Czech Republic? We believe that this question deserves an unambiguous positive answer. Provided that more than 30-35% electricity requirement is generated by combusting mostly lignite from opencast mines (in the year 2000 still about 48%), then there can be no other answer. We recall the economic break-down resulting from the sudden extreme drop in temperature which occurred between December 31, 1978 and January 1, 1979. If we look at coal from another angle, the Czech administration should at least create the conditions and apply appropriate measures to secure enough coal reserves for operating power and heating plants at large agglomerations. This is required to prevent a reduction in power and heat generation leading to a complete breakdown of the whole economy because of, for instance, extreme climatic changes or other reasons such as long-lasting strikes of miners or railroad workers.

Regional and enviromental limitations stimulated by the Czech administration The Government of the Czech Republic has since 1991 passed several decrees constraining the limits of mining within the current coal mining areas particularly in the Kru~n~ hory piedmont coal basins (see e.g. S~korova et al. this volume, Bou~ka et al. this volume). The mining areas are delimited, according to law No. 44/1988 Coll. of the Czech National Council and in the wording of decree No. 172/92 from 16 March 1992 of the Czech Board of Mines, by the district Boards of Mines. The new mining law under preparation will attempt to reflect this situation. In our view, the situation is paradoxical, as the Government of the Czech Republic in order to reduce the negative impacts of coal mining on the population and environment, has developed its own decrees on the regional and ecological limits before making laws. There is no doubt that the destruction of tens of communities after 1948, including the ancient town of Most in northern Bohemia, resulted from originally useful objectives, i.e. making coal

COAL PRODUCTION IN THE CZECH REPUBLIC reserves available for mining (as we now know, wanton coal mining), but it also essentially affected the destiny of thousands of families that had to abandon their homes and native land. The current protection of other communities against liquidation unfortunately leads to other paradoxes. On the one hand, everyone, particularly the citizens in the North Bohemian basin, are right in calling for improvement of the environment in the basin area, but on the other hand, mining for coal with the lowest sulphur content in the North Bohemian basin at Chaba~ovice has been rather prematurely reduced. The same aspect applies to the activity of the 'rescuers' of the Libkovice village, considering that it is the underground mines in the North Bohemian basin which usually extract essentially better-quality coal than do the open cast mines (the coals from the former show usually lower sulphur and ash contents). The most controversial decision in this respect is the decree No. 441 from 1991 of the Government of the Czech Republic which constrains the development of the CSA open cast mine in the North Bohemian basin. This decree confines the extraction in this mine to the limits of the so-called first phase of its development. This reduces its reserves to such an extent that extraction will come to an end in 2007. The original mining scheme suggested that it would operate until about 2050, which was projected for the second phase of its development. The scheme would, nevertheless, entail the destruction of the villages of Ji~etin and t~ernice. The problem of a shorter or longer life for this mine, however, requires that its solution cannot be postponed until the first years of the next century, when a qualified decision could be taken based on actual needs. Extraction technology (turning of a face) requires the problem to be solved before the end of 1996. If the Government of the Czech Republic changes its earlier decision, not to allow the second phase, after this date the second phase would only be possible (if at all?) with huge financial losses and with considerable losses in coal recovery. The fact that the sterilization of these reserves will not only reduce the life of the mine by more than 40 years, but will also markedly influence that of the whole Basin should also be taken into consideration. We are of the opinion that the problems associated with destroying the communities were unnecessarily politicized. None of the large-scale open cast mining in densely populated Europe could have taken place without destroying those communities that were in the path of the mine developments. For instance, the Lower Rhine

9

basin in Germany, where more than ten communities had to give way to coal mining is not different from the CSA mine. Unlike the common practice introduced in former Czechoslovakia after 1948, the stoped out workings are immediately restored after abandonment, completely new villages are built and the inhabitants of the abandoned communities are offered adequate housing.

The problem of improvement of the environment Emissions of sulphur and nitrogen oxides that often exceed the limits from time to time give rise to air conditions approaching smog. This is particularly frequent in many of the densely populated towns where it has caused a reduction in life expectancy and calls for a radical solution that has been the subject of a number of crucial government decrees. It is a very serious problem with political overtones. The measures aimed at mitigating the negative influences on the environment should take place at two parallel levels. Whereas some solutions can be put into practice almost 'from day to day', the second group of problems can be solved only within a longer time interval and at considerably higher costs.

The medium- to long-term solutions Desulphurization of thermal power plants. According to the agreement on the atmosphere, all power plants in the Czech Republic will have to comply with emission limits that correspond to European standards by 1998. Until then, the Czech Energy Company must shut down in the thermal power plants obsolete units with a capacity totalling 2280 MW. Until now, 11 units with an output of 1225MW have been shut down. In five smaller power plants efficient fluid bed boilers will be installed, whereas the remaining 31, with a total output of 5730 MW, will be desulphurized by 1998 (Otava 1994). Installations of desulphurization systems in Czech thermal power stations will require extraction, preparation and transportation of a relatively large quantity of limestone (wet limestone washing), for the treatment. This will have a harmful influence on both the environment elsewhere, and also the limestone reserves. It will also be necessary to establish a market for the gypsum bi-product generated by the treatment, whose annual production will be 5 x 10 6 metric tonnes (M. Ku~vart pets. comm.), which is around five times the country's current consumption of gypsum.

10

J. PESEK & M. DOPITA

Fluid combustion of medium- to high-ash coals or high-sulphur coals. Fluid combustion (particularly under circulation or under pressure) would result in higher efficiency, and the use of reserves of coal with a heating value equal to or greater then 6 MJ kg -1 . These coals have not been considered for suitable mining due to their low quality. This could markedly extend the length of life not only of some of the mines, but of whole districts (basins) where these reserves are currently not extracted. There would also be an associated negative impact on the environment elsewhere resulting from the extraction and transportation of limestone which needs to be mixed with the high-sulphur coal prior to burning. Use of natural gas in major towns and power stations. A substantial or complete substitution of coal combustion by gas in the thermal power plants, heating plants and in the domestic heating in major towns in the Czech Republic provides a real possibility of reducing harmful emission in the most exposed regions. This concept has been both approved and initiated within an environmental program supported by 6.1 • 109K~ of government finance. It is, however, necessary to bear in mind the long-term dependence on natural gas from Russia with 37% of the world gas reserves. The construction of a new gas pipeline through Byelorus and Poland to western Europe, planned to transport 2-3 • 109m 3 gas to Frankfurt an der Oder by 1996, confirms a necessary diversification of gas sources as a safeguard against possible changing attitudes in the transit states. It will be necessary to explore the possibility of linking into this gas pipeline, whose capacity, however, is not planned to increase until long after the year 2000. We are not the only ones who take the view that, in the longer term, the prices of natural gas on the world markets will increase. If gas subsidies in the Czech Republic are completely removed by 1998, it may put a considerable financial strain on consumers. Should the prices of gas be higher for smallscale consumers than for large-scale consumers, as is suggested in some reports, we would consider this approach to be unjustfied.

Relatively short-term solutions Obligatory preferential supplies to large-scale consumers in major towns and in the North Bohemian basin with low-sulphur fuel. In the immediate future, we will only be able to monitor but not solve the major problem of S- and

N-oxide pollution that causes smog. Nevertheless, the problem could be solved by suitable legislative measures. The creation of suitable reserves of low-sulphur coal at the thermal power stations and urban heating plants would preclude unforeseen shutdowns of these facilities (see above). Alternatively, it might be possible to substitute high-sulphur lignite by the lowersulphur bituminous coal. This would, however, be possible only after the costly upgrading of furnaces in the heating plants and power stations. This would, nevertheless, bring some benefits. Owing to the higher heating value and lower ash content of the bituminous coal, the volume of the combusted bituminous coal would be lower as would be the volume of ash and/or clinker. Neither would it be necessary to carry out a costly desulphurization of the emissions from medium-size consumers (50 to 300 MW), since the sulphur contents in the coals used in power plants usually does not exceed 0.6%

Conclusions Public opinion in the Czech Republic, as in most developed countries is more and more concerned to see a rapid improvement in the environment. This should provide a driving force for change. It is clear that many of the current ecological problems are linked with coal mining and the burning of solid fuel. Therefore many countries are interested in developing new technologies for coal use covered under the heading of clean coal technology. Its principal goal is to make the use of coal more environmentally friendly and at the same time to increase the efficiency of its combustion. Several technologies have been industrially established, others are being tested. In the USA, which has the largest viable bituminous coal reserves in the world, a great deal of attention is paid to the problems of bituminous coal liquefaction and to the production of coal bed methane. It has been estimated that about 20 to 25% of coal reserves in the USA are high sulphur coals (1.5% and more). In our opinion, coal liquefaction is not an option in the Czech Republic in the foreseeable future. This paper therefore, has concentrated on several solutions which should be adopted in a systematic way. Some of these would lead to an improvement in the environment and to an increase of reserves of a material that might already be exhausted by 2020. As reserves dwindle coal will no longer be the principal source of environmental pollution, but will remain an important raw material for the chemical industry.

COAL P R O D U C T I O N IN THE CZECH REPUBLIC Everyone of us should bear in m i n d that this will be the time of our children's generation. We do not want them to deplore the imprudence of their parents! But we must not be unrealistic in thinking that whatever our e c o n o m y will need, can be easily bought or imported. This raw material (as well as others) will be hard to pay for and it will be necessary to create (and finance) the conditions enabling to realize this idea.

References FORMANEK,V. 1994. The need for well-advised energy policy in the Czech Republic. (In Czech). UhliRudy-Geologickf~ prdzkum, 1, 405-408. OTAVA, B. 1994. Clear clouds of Po6erady made by CEZ (Czech Energy Company). (In Czech). Koruna, LN III, 3 (Dec. 8, 1994).

11

PEgEK,J. & PESKOV~,,J. 1993. Prospects of mining and decline in coal reserves of the Czech Republic. (In Czech). Uhli-Rudy, 41, 136-138. & 1995. Coal production and coal reserves of the Czech Republic and former Czechoslovakia. In: WHATELEY, M. K. G. & SPEARS, D. A. (eds) European Coal Geology. Geological Society, London, Special Publication, 82, 189-194. - - , DOPITA, M., OPLUSTIL,S., PEgKOV.A,,J., KOULA,J. & ZELENKA,O. 1993. Real volume of coal reserves to be extracted in operating mines of the Czech Republic. Part I. Bituminous coal. (In Czech). Uhli-Rudy, 41, 307-316. REICHMANN,F. 1994. Ecology and mining for mineral raw materials. (In Czech). Uhli-Rudy-Geologick) prdzkum, 1, 414-416. SPOUSTA, Z. 1995. A commentary to the document: "The role of coal industry in energy policy and the role of state in mining". (In Czech). UhliRudy-Geologick~ pr~zkum, 2, 20-21. -

-

Controls on the evolution of the Namurian paralic basin, Bohemian Massif, Czech Republic O. K U M P E R A

VSB-Technical University of Ostrava, Institute of Geological Engineering, Ostrava-Poruba, tK17.listopadu, 708 33, Czech Republic Abstract. The Namurian A paralic molasse deposits of the Upper Silesian Coal Basin form erosion remnants of an extensive foreland basin located in the eastern part of the Bohemian Massif. This basin represents the latest stage of development of the Moravian-Silesian Paleozoic Basin (Devonian-Westphalian). The paralic molasse stage of the foreland basin evolved from foreland basins with flysch and with marine molasse. The deposition of the thick paralic molasse (Ostrava Formation) started in the Namurian A. In comparison with other coal-bearing foreland basins situated along the Variscan margin in Europe, this is characterized not only by earlier deposition, but also by a different tectonic setting. It is located in the Moravian-Silesian branch of the Variscan orocline striking NNE-SSW, i.e. perpendicularly to the strikes of more western European foreland basins. In the Vis6an and Namurian, the foreland basin developed rapidly under the influence of the western thrustfold belt in the collision zone. The deposition was influenced by contrasting subsidence activities of the youngest and most external trough - Variscan foredeep - and the platform. The Upper Silesian Basin shows therefore a distinct W-E lithological and structural polarity and zonation.

The Upper Silesian Coal Basin (Fig. 1) represents one of the most important European paralic and limnic hard coal basins. The boundaries of the basin are not completely known as its coal-bearing sediments are mostly covered with younger sediments and can be seen only in small outcrops. The rocks are mainly known either from deep exploration and/or structural boreholes or from mines. The total known area of the basin is approximately 6500km 2, of which more than two thirds are situated in Poland. The Czech part of the basin, the Ostrava-Karvinfi coalfield (Dopita & Kumpera 1993a), is located in the southern parts of the basin with a known area of around 2000km 2. However, the actual extent of the Czech part of the basin is far greater as shown by prognostic studies (Zeman 1977) and paleogeographic analyses (Turnau 1962, 1970; Dopita & Kumpera 1993b). Coal-beating sediments in the south of the district were found at mineable depths in deep boreholes only in the area shown in Fig. 4. According to geophysical data, further south they plunge steeply south under the nappes of the Outer Carpathians in the zone of the E - W striking Sulov faults, where they have been found in the Jablfinka 1 borehole at a depth of 2985-3870m under the nappes northwest of Vsetin (Polick~, & Hon6k 1984). The extent of the Upper Carboniferous coal-bearing sediments beneath the Carpathians nappes must be even greater as proved by deep boreholes in the

surroundings of N~m6i6ky in Southern Moravia (Purkyfiovfi 1978). In these boreholes, the coalbearing Carboniferous formations were shown to be below mineable depths with the top of the formations being at 2711 m and the base greater than 4787m. These data suggest that before denudation, the Czech part of the Upper Silesian Basin covered a great area in the south and southeast, which was not limited by the Czech boundary, and that the erosional remnants of the coal-bearing Carboniferous formations are preserved in half-grabens south of the zone of the Sulov faults, buried beneath the nappes of the Outer Carpathians.

The paralic molasse (Ostrava Formation Namurian A) in the framework of the Moravian-Silesian Paleozoie Basin The molasse formations of the Upper Silesian Paleozoic Basin form part of the thick DevonianCarboniferous accretionary wedge, which is preserved as erosional remnants of a large basin at the eastern margin of the Bohemian Massif (Fig. 1). The basin formed as a result of a continental plate collision at the eastern border of the Bohemian Massif from Devonian through Westphalian times (Kumpera & Foldyna 1992). In the collision zone several units of the Czech Massif meet. These units are defined in the

From Gayer, R. & Pe~ek, J. (eds), 1997, European Coal Geologyand Technology, Geological Society Special Publication No. 125, pp. 13-27.

14

O. KUMPERA

Fig. 1. Schematic geological map of the Moravian-Silesian Paleozoic Basin (compiled after J. Dvo~fik, A. Kotas, M. Dopita, O. Kumpera, J. Foldyna) 1, Devonian; 2, Permian; 3, plutonic complex of Brunovistulian basement; 4, crystalline complex of Brunovistulian basement; 5, Namurian A-predominantly coal-bearing paralic molasse; 6, Namurian B-Westphalian-predominantely coal-bearing continental molasse; 7, Lower Carboniferous; 8, remnant basin relic; 9, borehole Krfisnfi; 10, locality of Fig. 3.

Report of the Working Group for Regional Geological Classification of the Bohemian Massif at the former Czechoslovak Stratigraphic Commission (Chulpa6 & Vrfina 1994). In the west, internal orogenic zones of the Bohemian Massif are interpreted as the hangingwall to this collision zone (Fritz et al. 1993). The eastern Cadomian block of the Brunovistulian basement formed the footwall which gradually disintegrated and subsided (Kumpera 1988) during an oblique collision (Grygar 1992). The deeply eroded roots of the collision suture are located in the Silesian and Lugian units in the north and in the Moravian and Moldanubian units in the south. The collision of the two plates of a contrasting crustal character resulted in a rapid uplift in the central parts of the Bohemian Massif and the formation and evolution of subsiding and migrating foreland basins, the final basin being located on Brunovistulian basement (Fig. 2). This consequently led to the development of a thick sedimentary accretionary

wedge with a complex composition and structure. The preserved filling of the basin represents a rather small erosional remnant of a far larger basinal structure. The Moravian-Silesian Paleozoic Basin underwent a complicated evolution in the course of the collision covering several types of basins (Klein 1987). These are described by Kumpera (1983), Hladil (1988), Dopita & Kumpera (1993a), and Kumpera & Martinec (1995). Carboniferous foreland basins with molasse represent development during the latest stage of oblique collision.

Partial troughs within the Moravian-Silesian Paleozoic Basin The basin depocentre migrated from the collision zone towards the foreland (Kumpera 1971; Dvo~fik 1973). The sedimentary wedge mainly consists of siliciclastic flysch and molasse sediments (a smaller part belongs to platform

NAMURIAN PARALIC MOLASSE IN BOHEMIAN MASSIF

15

Fig. 2. Schematic conception of the partial flysch troughs and molasse fordeep and of the surrounding source areas in the Moravian-Silesian Paleozoic Basin during the Late Vis6an and Namurian A stages of development. Two of the troughs and depressions are in Fig. 3. carbonates and rift d e p o s i t s - K u m p e r a & Martinec 1995). The total thickness of the Carboniferous sedimentary wedge (after compaction) is more than 12km, although, due to the prograding wedge, this is never developed in one location. The average rate of sedimentation is therefore about 270 m Ma -1 . The accretionary wedge has its greatest thicknesses in the west, in the vicinity of a broad collision zone, and above all in the northwest. The preserved maximum thickness is about 6 km, whereas the total thickness decreases gradually to 200 m in the extreme eastern parts of the basin. The decrease is not continuous, but the thickness distribution varies within narrow partial troughs and forebulges (Figs 2 & 3) which developed during the Carboniferous (Kumpera 1983). Some of these troughs and elevations have been proved conelusively by isopach studies. Two partial basins

and forebulges of different ages are well documented in the eastern part of the Paleozoic basin (Fig. 3). In the western trough (eastern flysch basin in Fig. 3), the thickness of Upper Vis6an flysch is reduced from 2500m in the western part to 100m, or less, in the eastern part. In the eastern elevation, stratigraphic gaps at different Vis6an levels have been even observed. The eastern trough is filled with thick uppermost Vis6an and Upper Carboniferous molasse deposits.

The Variscan foredeep and platform in the development of the Upper Silesian Coal Basin The initial ideas of uniform geotectonic development of the Upper Silesian Basin have been

w

E

FORELAND BASIN EASTERNFLYSCH BASIN Budi~ov

PLATFORM

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FOREDEEP Odry-Hranice ; ......

,

._.;

Vala~sk~ Mezi~I~f

..

FOREBULGE I " Orlov~ s t r u c t u r e Fren~t~t p. Radh.

;

" i - . 9~ 9. . . . . . , . 9 ,..~r

am " ur

i

,

]

A ~-.~-~

~

I

2

3

4

5

Fig. 3. Palinspastic cross section showing the thickness of stratigraphic units at the transition from the foreland basin with flysch to the foreland basin with molasse in the Moravian-Silesian Paleozoic Basin during Late Visban (Goa-~) and Namurian A. l, carbonates; 2, predominantly shaly deposits; 3, predominantly graywackes; 4, conglomerates; 5, coal-bearing paralic molasse.

16

O. KUMPERA

modified in terms of a polytype basin (Havlena 1982) as a result of deep exploration boreholes. The first boreholes sunk in the southern and southeastern parts of the basin within the coalbearing Carboniferous showed considerable differences between the area of active mining in the north and areas under exploration in the south. With continual exploration, it has been determined that thicknesses of parts of the Carboniferous sequence diminish towards the east and southeast. In addition, their coal capacity and the thickness and number of seams also decrease. Extensive borehole exploration throughout the area of the basin together with new data from the deeper levels of the mines has proved that in the course of the Carboniferous development, the coal basin was divided into two parts with distinct developments and structures (Fig. 3): 9 The younger Variscan foredeep, represented by a narrow mobile zone along the western margin of the basin. 9 The Upper Silesian stable block, an extensive platform in the eastern part of the basin. This division is only apparent in the Upper Vis~an and Upper Carboniferous levels of the basin. During the Devonian and the earliest Carboniferous, the whole preserved part of the basin was a platform. Thus, the Devonian and Lower Carboniferous carbonates have a similar thickness throughout the basin (up to 700 m in the south and up to 1100m in the northern parts of the basin in Poland). By Early Vis~an time, Variscan deformation had reached the eastern boundary of the basin. It is only the Upper Vis6an formations that are largely of a clastic character. Their thickness reaches 1000-1500 m in the foredeep but eastwards, towards the platform, decreases to 100m (in the Krfisn~, 1 borehole- Roth 1979). Correlated stratigraphical units of the molasse vary considerably in thickness across the basin. The foredeep is filled with marine and paralic molasse sediments, whose compacted thickness is up to 4500m (before compaction, the thickness may have reached more than 6000m) in the depocentre, whereas it decreases to 200m or less over the easternmost platform forebulge. In addition to variations in thickness, the foredeep and platform differ markedly, especially in the development of the paralic molasse (Ostrava Formation - lower Namurian - Ez zone). The main feature of the coal-bearing paralic molasse deposition was that subsidence was compensated by clastic supply. Nevertheless, the sedimentation was influenced by the

contrasting subsidence rates of the foredeep and the platform (Fig. 4). Thus the foredeep is characterized by a full subsidence compensation and the platform by a retarded subsidence.

The main lateral changes in the iithological development of the Namurian paralic molasse (Ostrava Formation) See Table 1 of Dvo~ik et al. this volume, for the stratigraphic classification of the mollasse-filled foreland basin.

Thickness of the Ostrava Formation First of all, the foredeep and the platform differ in the thickness of the paralic molasse. In the foredeep, the thickness of the Ostrava Formation reaches up to 3200 m and decreases to about 100m or less in the platform forebulge (in the vicinity of the Kop~ivnice-T~inec anticlinorium). These changes are well illustrated on isopach maps of the total thicknesses of individual lithostratigraphic units of the Ostrava Formation, namely the Pet~kovice and Jaklovec Members (Figs 5 & 6). All members show maximum thicknesses in the foredeep (especially in the north), but thicknesses decrease to the east, particularly the southeast, in the area of the forebulge. This contrast in thickness gradually diminishes in successively younger stratigraphic units, from the oldest (Peffkovice Member) to the youngest fully preserved unit (Jaklovec Member). The youngest unit of the Ostrava F o r m a t i o n Poruba Member - has not been studied because the upper part of the member is nowhere preserved. Estimates of sediment accumulation rates across the whole basin vary from 250350 m Ma -1 in the Late Vis6an flysch depression, through a surprisingly high 9 0 0 m M a -1 in the foredeep during Namurian A, to zero in the platform forebulge.

Lateral changes in coal accumulation The foredeep and the platform differ not only in the thickness of the paralic molasse, but also in the number and thickness of coal seams developed. Coal accumulation decreases markedly towards the platform (Dopita & Kumpera 1993b). The Ostrava Formation contains more than 170 coal seams with an average thickness of 73 cm in the foredeep, whereas the number of coal seams in the same stratigraphic interval

N A M U R I A N PARALIC MOLASSE IN BOHEMIAN MASSIF

17

OL4N b " " -lZ N

/ ,~,j-,-,.,--~.,~

|

~J

I, - - . . .

.9

\ ," ..."~

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1

o-'*

7n j"

FB

~

a b c

"- .'7'.

o,,

:'"..

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~

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!---

~

.No.

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:.'|

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-

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,.

,

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-

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~,

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>

>

10 11

|

12

13 I~

os-

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~

50km

14

Fig. 4. Outline of the early Namurian palaeogeography in the Czech part of the Upper Silesian Coal Basin. 1, paralic molasse in known regions (with compensated subsidence); 2, postulated pre-erosional extent of paralic molasse; 3, paralic molasse in regions with retarded subsidence; 4, source areas (a-lowlands, b-hills, c-mountains), ZN-prograding thrust zones; 5, present erosional limits of the known basinal regions; 6, postulated original limits of the basin; 7, depocentre axis; 8, postulated forebulges; 9, directions of marine trangressions; 10, directions of clastic transport; 11, rivers and deltas; 12, humid climate; 13, postulated volcanic centres; 14, state boundaries, FB-postulated forebulge. decreases to 40, or even 20, in the platform, where some parts of the Ostrava Formation are even non-productive. This is illustrated in the maps of total coal accumulation of the Pettkovice Member (Fig. 7) and the Jaklovec Member (Fig. 8) with maximum values in the foredeep and minimum values in the vicinity of the platform forebulge. These maps show the division of the basin into sub-areas, where subsidence was more or less compensated by sedimentation. Spatial variations in coal accumulation in the sub-areas are thought to have been controlled by the interplay between tectonics and clastic supply. The isopach maps suggest a slight shift of the maximum coal accumulation eastwards with the younger units, probably due to an eastward migration of the depocentre. As with total sediment thickness, the contrast between the foredeep and the

platform diminishes towards the younger stratigraphic units, particularly in the southern areas, where an extensive platform forebulge was gradually uplifted in the vicinity of the present Koptivnice-Ttinec anticlinorium.

Lateral changes in the distribution of other lithotypes Simultaneous changes in the number, thickness and character of various correlatable stratigraphic units can be observed between the foredeep and platform. Up to 80 marine and brackish bands, representing marine transgressions, have been recorded altogether in the northern part of the foredeep (Reho~ & l~eho~ov~ 1972) These show progressively less

18

O. K U M P E R A

2F,

0I,

!

1(2

20 ,,I

km

Fig. 5. Isopach map of the Pet~kovice Member (lower part of the Ostrava Formation, Czech part of the Upper Silesian Coal Basin). 1, present limits of the basin; 2, limit of the Frengt~tt relic of the Karvinfi Formation; 3, isopach in metres. marine influence or disappear towards the platform so that only the four most important, thick bands are present in the eastern part of the platform. The thickness of those bands with the most stable areal distribution is up to 180 m in the foredeep but is markedly reduced towards the platform. The faunal content changes significantly also from north to south in the area of the foredeep. Towards the south, elements of a brackish fauna, or even a freshwater fauna, occur more often at the expense of elements of a marine fauna in a considerable number of marine bands (l~eho~ & l~eho~ovfi 1972). These changes are even more marked in a W - E direction. This indicates that marine

conditions transgressed from north to south and west to east through the foredeep and, from time to time, even reached the area of the Upper Silesian platform block. The foredeep, in which each marine transgression resulted in at least 22m of accumulated clastic sediments, represents an area regularly flooded by the sea, whereas the platform was an area only sometimes flooded (Havlena 1982). In addition, volcanoclastic rocks present in the f o r e d e e p altered tuffites in terrigenous siliclastic sediments, kaolinite tonsteins in coal seams (up to 16 beds in the f o r e d e e p - Dopita & Krfilik 1977), and kaolinized tuffites redeposited as 'whetstone' rocks (30 beds in the western part)

NAMURIAN PARALIC MOLASSE IN BOHEMIAN MASSIF

Q

10 -,

i

19

20 km

Fig. 6. Isopach map of the Jaklovec Member (Upper part of the Ostrava Formation, Czech part of the Upper Silesian Coal Basin). For 1-3, see Fig. 5.

disappear towards the platform. This can be seen in the isopach map (Fig. 9) of the s.c. Main Ostrava Whetstone, which forms an important marker bed in the lower part of the Ostrava Formation over large areas of the basin. Figure 9 shows a decrease in its thickness from 12m in the west to 0 m in the east. It also shows marked

local variations in the thickness of the Main Whetstone that probably represent a combination of subsidence and fluvial control. Volcanic material was largely redeposited into the foredeep from the platform by complex sedimentary processes. A map of composite thickness of all the volcanogenic beds in the Ostrava Formation

20

O. KUMPERA

?'g'l

-/ /

0

z9

Fig. 7. Total coal accumulation map of the Pet~kovice Member (lower part of the Ostrava Formation, Czech part of the Upper Silesian Coal Basin). For 1-3 see Fig. 5. (not shown), shows a similar pattern. It must be stressed that some of these beds have an areal extent ranging from 102-103 km 2. The thickness of individual cyclothems, the grain size and the number of sandstone and conglomerate layers increase towards the southeastern part of the platform indicating a source area in the vicinity of the Kop~ivnice-T~inec anticlinorium - Fig. 10 (Jansa 1967).

A similar pattern of the main trends in the development of the basin is given by the distribution of coalification intensity (Adamusovfi et al. 1992). The more modern methods of coal quality determination have not been sufficiently and equally applied to the whole area of the Czech part of the Upper Silesian Coal Basin so that the degree of coalification has been characterized by volatile matter V aaf. The map

N A M U R I A N PARALIC MOLASSE IN BOHEMIAN MASSIF

21

2#";71 F"-t //

/ ,o

I

i

I

,o 1

0

10

20kin

Fig. 8. Total coal accumulation map of Jaklovec Member (Upper part of the Ostrava Formation, Czech part of the Upper Silesian Coal Basin). For 1-3 see Fig. 5.

of coalification of the upper surface of the Ostrava Formation again illustrates the basic difference between the area of the Variscan foredeep and the Upper Silesian platform. In the area of the Variscan foredeep on its west margin, the V daf values fall to less than 10~ whereas the

lowest V daf values in the area of the Upper Silesian platform are only 20% and the maximum is more than 35% V daf in the youngest part of the paralic molasse sequence. Generally, the degree of coalification is controlled by stratigraphy; the coalification is lower

22

O. KUMPERA

,t _l

/

0

10

.I__

2,0kin

i.,

Fig. 9. Isopach map of the Main Ostrava whetstone horizon (lower part of the Ostrava Formation, Czech part of the Upper Silesian Coal Basin),For 1-3 see Fig. 5.

in the younger members of the formation. However, at the same time, the intensity of coalification depends on the thickness of the basin fill in any region. At comparable stratigraphic levels, the degree of coalification in the Upper Silesian platform is lower than that in the Variscan foredeep. The lowermost degree

of coalification occurs in the Namurian A in South Moravia (up to 40.9% Vaaf). Doubtless, this is connected with a generally low subsidence rate in the southern areas of the MoravianSilesian Paleozoic Basin. By contrast, the highest degree of coalification in the western part of the foredeep is probably

NAMURIAN PARALIC MOLASSE IN BOHEMIAN MASSIF

23

9

4r,-

I--3 1 2 P _z, l

-,

L..._./

0 I

10 I

20 km ,.J

Fig. 10. Isolines of sandstone index in the Jaklovec Member (Upper part of the Ostrava Formation, Czech part of the Upper Silesian Coal Basin).l, limits of the basin; 2, limits of the Fren~tfit relic of the Karvinfi Formation; 3, sandstone index (%).

partly a result of the deepest burial of coalbearing strata during the coalification processes, and partly due to the greatest heat flow at the Variscan front in the west of the basin. This is in good agreement with the results from the whole Moravian-Silesian Paleozoic Basin (Sko6ek 1976).

Structural zonation The Upper Silesian Basin is stratigraphically and paleogeographically (e.g. Havlena 1982) as well as geotectonically and structurally (Kumpera 1971, 1980; Kotas 1985) asymmetric. The main manifestation of tectonic asymmetry in a

24

O. KUMPERA

W - E direction is the greater intensity of folding and the development of more complex structures in the western part of the basin. In the eastern part of the basin within the area of the Upper Silesian platform, the prevailing structures are taphrogenic. Structural asymmetry parallel to the Variscan orogenic trend is expressed in somewhat more complicated tectonic styles in northern areas. Thus, the regional tectonic scheme, like the other features described above, prove a generally greater mobility of the basin in the west and in the north. A detailed analysis of basinal tectonic structures indicates the presence of structural zonality within the foredeep area. Here, parallel to the axis of the foredeeep, narrow zones trending in a NNE-SSW direction and characterized by unusual fold-fault structures are present. Thus, it is possible to delineate a zone containing a holomorphic style of folding along the western margins of the basin. To the east, this zone is fringed by the zone of western brachystructures. After that, the area of idiomorphic (ejective) folds follows, within which the parallel narrow zones of the Mich~ilkovice-Rybnik and OrlovfiBohugovice anticlinal fold-fault structures are developed. Between these two anticline-fault structures, the zone of eastern brachystructures is located. The tectonic zones are characterized by specific fold-fault structures (Foldyna & Kumpera 1991).

The main vertical changes in the development of the paralic molasse (Ostrava Formation) Vertical changes in some lithological parameters point to important processes in the development of the basin as well as to the changing basinal regime.

The abundance of marine facies Marine conditions greatly influenced the sedimentation of the lower part of the Ostrava Formation but became less significant upwards. This can be demonstrated by the number of marine units in successive members of the Ostrava Formation. In the Pet~kovice Member, up to 32 bands with marine or brackish faunas are known, in the Hrugov Member 26 and in the Jaklovec Member, marine or Lingula-bearing bands are represented only by the Susta marine band and the Barbora group of 4 bands. Marine influence increased again in the Poruba Member, where up to 20 bands (Reho~ & l~eho~ov~ 1972) have been found. By comparing the maximum

thickness of a member with the maximum number of marine occurrences documented by bands in that member with a marine or brackish fauna, the frequency of marine influence can be quantified. The greatest effects occur in the Peffkovice Member (1 transgression per 22m thickness of sediments). Lesser effects are recorded in the Hru~ov and Poruba Members (1 transgression per 94 m and 49 m of sediments, respectively). These data indicate that although considerable variations in subsidence rate occurred (as shown by the thick nonproductive sequences with a prevailing marine influence upon the megacycle boundaries), the rate of subsidence gradually decreased.

Periodical variation between marine molasse and paralic molasse Thick and laterally extensive marine units occur, widely separated by 300 to 500 m thick sequences of paralic molasse containing great coal accumulations. The most important are the marine bands associated with the seams Naneta, Franti~ka, Enna, Barbora, Roemer and Gaebler. These marine bands have a rather constant faunal content over the whole Czech part of the basin and have a considerable thickness up to 180 m. Periods of extensive marine flooding are associated with considerable falls in coal accumulation or even in the development of barren measures (Dopita & Havlena 1980). Closely associated with the most stable faunal bands in the Ostrava Formation are nonproductive or only weakly coal-bearing sequences, whose thickness varies between 100-240m. They divide the richly coal-bearing sequences of the Ostrava Formation. The lithological nature and mainly a marine origin of nonproductive parts of the sequence indicate periods, when subsidence remained uncompensated over almost the whole of the Czech part of the basin. Thus the Ostrava Formation can be classified as a polyfacial sequence, in which the prevailing paralic molasse was several times interrupted by the development of marine molasse. The marine molasse was formed, in contrast to the paralic molasse, during periods of uncompensated subsidence. This suggest changes in subsidence rates and tectonic activity both within the basin and in the source area.

Changes in volcanic activity The layers of volcanogenic sediments reflect intensive volcanic activity in volcanic centres, which have yet to be identified in detail, although

NAMURIAN PARALIC MOLASSE IN BOHEMIAN MASSIF they are probably in the western source area. The most important is the Ostrava Whetstone, whose thickness is up to 12 m, and which is developed over almost the whole area of the Czech part of the basin with the exception of the easternmost areas. Another important unit is the stratigraphically lower whetstone of the Leonard seam. The early Namurian A was the most volcanically active period in the near source area, producing frequent and thick layers of whetstone in the paralic basin. Later, the volcanic activity waned and mostly only produced layers of tonstein in the swamps and peat moors which were quiet sedimentary environments protected from resedimentation. Thin pyroclastic layers falling into a high energy environment would have been kaolinized and dispersed amongst clastic materials. Nevertheless, in the lower Namurian A sequence up to 46 units of volcanogenic sediments have been preserved at various stratigraphic levels. Their maximum total thickness is 16 m indicating that the Namurian A represents a period of strong and frequent volcanic activity in the Variscides of Central Europe. The diminution in the total thickness of volcanogenic sediments to the east suggests their redeposition from the platform to the foredeep.

Changes in the petrographic and geochemical composition Changes can also be observed in the petrographic composition of psammites through the stratigraphic sequence. Among them, graywacke sandstones prevail. In the upper part of the paralic molasse, the number of graywacke layers, arkosic sandstones and arkoses increase (Fialovfi et al. 1978). This relates to important changes in the source area. Whereas in the lower part of the Ostrava Formation, the major source lay in the western orogenic area together with resedimentation of older Carboniferous clastics; in the upper part, the influence of the eastern source area of the stable Upper Silesian block (e.g. from the area of the forebulge) gradually manifested itself. This is also indicated by the geochemistry of some claystones suggesting an increasing supply from morphologically flatter source areas which were exposed to long-term chemical weathering.

The influence of eustatic movements upon sedimentation Some major changes in the lithology of the Namurian paralic sequence can be related to

25

glacio-eustatic changes of the sea level as well as to climatic oscillations during the Late Carboniferous. They can be correlated with the mesothems described by Ramsbottom (1979) from northwestern Europe (Sko6ek 1991). A shortage of radiometric age data makes it difficult to interpret the influence of climatic changes on sedimentation in the Carboniferous of the Upper Silesian Basin. However, it would expected that these changes could contribute to lithological changes in cyclothems, or they could be reflected in marine transgressions which might result in a complex interplay with tectonics.

Some paleogeographic features of the basin As with the earlier stages of the development of the Moravian-Silesian Basin, the Namurian A paralic molasse basin developed on continental crust in the foreland under a compressional regime. Therefore, the basin was filled by erosion of rocks of the overthrust lithospheric plate both in the inner parts of the Bohemian Massif and in the foreland thrust zone. This latter consisted of the waning collision zone and also the western areas of the Paleozoic rocks in the Moravian-Silesian Basin, which were, progressively, included into the thrust-fold zone. Also sedimentation in the paralic molasse took place partly at the expense of synsedimentary uplift within the platform foreland. Active tectonic development both in the source area and in the area of the basin itself, resulted in a significant resedimentation of elastics connected with the processes of basinal cannibalism (Kumpera & Martinec 1994). The Czech part of the Upper Silesian Basin that is preserved today, represents an erosional remnant of the former basinal structure that was originally substantially larger than today. The western part of the basin-fill had been already eroded by the end of the development of the Variscan fold-thrust structure and the uplifts of the Rheno-Hercynian and Sub-Variscan zones. The axis of the maximum compensated subsidence is thought to be situated to the west of the existing erosional western boundary of the basin. This axis plunged to the north. Towards the western margin of the basin, all indications of mobility become more marked: thicknesses of stratigraphic units (Figs 5 & 6), coal accumulation (Figs 6 & 7), degree of coalification, thickness and number of faunal bands, etc. Along its western boundary, the basin is amputated by tectonics and erosion. It can be assumed that within the early Namurian, the basin extended

26

O. KUMPERA

along the whole eastern margin of the Bohemian Massif (Fig. 4). The original southern margin of the basin is not known, but on the evidence from deep boreholes located at Nrm~i~ky (Dvo~fik et al. 1997) as well as an analysis of the tectonic position, it is probable that the basin extended originally as far as the Austrian border, where its remnants are still preserved. Likewise, it is possible that the coal-bearing deposits covered a considerable area to the southeast and east beneath rocks of the Styrian (Carpathian) nappes (Dopita & Kumpera 1993b). As described above various source areas can be postulated for the basin fill. The western source area comprised both the areas formed by the crystalline complex and cover sediments. The geological composition of the denuded surface changed in the course of sedimentation during the Namurian A. A great amount of arkosic sandstones and arkoses in psammites in the upper part of the Ostrava Formation and a considerable content of K feldspars indicate that the level of erosion had cut down into the larger granitoid bodies. During the later Namurian A eastern source areas joined those in the west. In contrast to the orogenic western source, these less extensive source areas were intraplatform elevations in the foreland. Their intermittent influence was first seen in the sedimentation of the Hru~ov Member by the Kopfivnice-Tfinec uplift. In the later Namurian A low elevations within the platform areas sourced short streams that fed the more eastern part of the basin. The relief of source areas became gradually less and less flat and produced more chemically mature solid products of weathering (Kumpera & Martinec 1993).

onto the forebulge; (b) the development of marine bands and the degree of marine influence diminish, indicating marine transgression towards the south and east; (c) the thickness of volcanogenic coal tonsteins and whetstonesboth show a decrease in thickness towards the forebulge; (d) the development of individual cyclothems, showing a general increase in both grainsize and number of sandstone and conglomerate beds towards the forebulge indicating a source area in the southeast; (e) degree of coalification, which decreases at any one stratigraphic level from west to east and southeast, attributable to a combination of shallower burial and lower heatflow in the stable area of the forebulge; and (f) intensity of fold/fault structure with a generally asymmetric pattern developed, verging to the east. 4. Vertical changes in the sediment fill of the foreland basin reflect a diminishing tectonic source from the Variscan hinterland in the west. These are documented as: (a) diminution in the number of marine occurrences upwards, indicating a decreasing subsidence rate with time; (b) common interruptions of marine conditions by coal-rich parallic molasse suggesting intermittently changing subsidence rates and tectonic activity in the source areas; (c) decrease in total thickness of volcanogenic ash, suggesting a waning volcanic activity in the mountain belt from Namurian A times; and (d) changing geochemistry of claystones, indicating a gradual lowering of relief in the source area.

Conclusions

References

1. The Visran Upper Carboniferous coalbearing molasse of the Upper Silesian Coal Basin represents the latest and most eastward development of a Variscan foreland basin, formed as a result of oblique continental collision in the west. 2. The molasse-filled foreland basin is divided into a western foredeep with up to 4.5km of sediment and an eastern platform (forebulge) with less than 200m of sediment. Decreasing thickness from foredeep to forebulge is recorded for each of the stratigraphic units but younger units show less marked thickness changes. 3. Contrasts between foredeep and forebulge are documented in: (a) coal accumulationboth the number of coal seams and the total coal thickness diminish towards the east and south

ADAMUSOVA, M., DOPITA, M., FOLDYNA, J., KALENDOVA, J., KUMPERA, O. (~ STRAKOS, Z. 1992. The isopachous and coalification maps of coal-bearing molasses in the Czechoslovak part of the Upper Silesian black coal basin. Sbor. Vdd. Praci Vys. Sk. Bdfi, Ostrava, 28, 1~. HG. (1), 27-38. CrtLUPA~, I. & VRANA, S. (eds) 1994. Regional Geological Subdivision of the Bohemian Massif on the Territory of the Czech Republic. Journal of the Czech Geological Society, 39, 127-144. DOPITA, M. & HAVLENA, V. 1980. Geology and mining in the Ostrava-Karvin6 Coalfield. OKD, Ostrava. -& KRALiK, J. 1977. Coal tonsteins in OstravaKarvin6 Coal Basin. OKD, Ostrava, 1-213. - - & KUMPERA,O. 1993a. Geology of the OstravaKarvinfi coalfield, Upper Silesian Basin, Czech Republic, and its influence on mining. International Journal of Coal Geology, 23, 291-321.

Professor Kumpera died before corrections to the manuscript had been completed. Final corrections were made by the editors

N A M U R I A N P A R A L I C MOLASSE IN B O H E M I A N MASSIF & - - 1 9 9 3 b . Contribution to the Paleogeography of Namurian A in the Bohemian Massif (Czech). Sbor. v6d. Praci Vys. Sk. bfin, Ostrava, 39, R. HG, 1104, 41-51. Dvo0akK, J. 1973. Synsedimentary tectonics of the Palaeozoic of the Drahany Upland (Sudeticum, Moravia, Czechoslovakia). Tectonophysics, 17, 359-391. --, HONEK, J., PESEK, J. & VALTEROVA, P. 1997. Deep borehole evidence for a southward extension of the Early Namurian deposits near Nemcicky, S. Moravia, Czech Republic: implication for rapid coalifaction. This volume. FIALOVA, V., POLICK~(, J. & HONI~K, J. 1978. Petrography and lithology of the Jaklovec Member (in Czech.). Ostrava, Sbor. GPO, 16, 5-38. FOLDYNA, J. & KUMPERA, O. 1991. Tectonic zones and areas in Subvariscan Zone of the Bohemian Massif (Upper Silesian Basin). Acta Univers. Carol. Kettner, Praha, 3-4, 165-281. FRITZ, H., DALLMEYER, R. D., NEUBAUER, F. & URBAN, M. 1993. Thick-skinned versus thinskinned thrusting: Mechanism for the formation of inverted metamorphic section in the SE Bohemian Massif. Journal of the Czech Geological Society 38, 33-34. GRYGAR, R. 1992. Kinematics of Lugosilesian orocline accretion wedge in relation to the Brunovistulian foreland. Sbor. Vdd. Praci Vys. Sk. bdd, Ostrava, I~. HG, 38, 1, 49-72. HAVLENA, V. 1982. The Namurian deposits of the Upper Silesian Coal Basin. Rozpr. Cs. Akad. V(d., R. mat. p(ir. vdd, 92, 7, 1-79. HLADIL, J. 1988. Zonality in the Devonian carbonate sediments in Moravia (CSFR). Proc. 1st Int. Conf. Bohemian Massif, Praha, 121-126. JANSA, L. F. 1967. Sedimentological evolution of Carboniferous strata in southern part of Upper Silesian Coal Basin. PhD Thesis, Charles University, Praha, MS, (in Czech). KLEIN, G. DE V. 1987. Current aspects of basin analysis. Sedimentary Geology, 50, 95-118. KOTAS, A. 1985. Structural Evolution of the Upper Silesian Coal Basin (Poland). C. R. 10. Congr. Int. Strat. Geol. Carb., Madrid, 3, 459-469. KUMPERA, O. 1983. Lower Carboniferous geology of Jesenlky Block (in Czech). Knih Ust[. Ust. geol. 59, Praha.

--,

27

1988. Brunovistulicum in Variscan development (in Czech). Acta Univ. Carolinae, Geol. Praha, 401-410. - - & FOLDYNA,J. 1992. Development of MoravianSilesian Paleozoic Basin. Sbor. Vdd. pracl, Vys. Sk. b6~. Ostrava, I~. HG, 38. -& MARTINEC, P. 1993. V~voj sedimentfi karbonsk6ho akre6niho klinu moravskoslezsk6 pfinve. Sbor. 1. desko-polskO konf. o sedimentol. karbonu, UG Ak. Vfid CR, Ostrava, 125-166. & 1994. The development of the Carboniferous accretionary wedge in the Moravian-Silesian Paleozoic Basin. Journal of the Czech Geological Society, 39, 1, 63-64. POLICK~/, J. & HONI~K,P. 1984. Produktivni karbon ve vrtu Jablfinka 1. Gas. Mineral. Geol., Praha, 29, 4, 445. PURKYlqOVA, M. 1978. Fl6ra svrchniho karbonu (namuru A) v paleozoiku JV svahfi Cesk6ho masivu u N6m6i6ek na ji~ni Morav~. Gas. Slez. Muzea, Opava, A 27. RAMSHOTTOM, W. H. C. 1979. Rates of transgression and regression in the Carboniferous of NW Europe. Journal of the Geological Society, London, 136, 147-153. ROTH, Z. 1979. The Krfisn~i 1 borehole in the central part of the Moravskoslezske6 Beskydy Mountains. Vdst. (Jstf . (lst. geol. Praha, 55, 2, 75-83. ]~EHOI~, F. & I~EHOI~VA, M. 1972. Makrofauna uhlonosn~ho karbonu deskoslovenskd (6sti hornoslezsk~ phnve, Ostrava, Profil. SKO~EK, V. 1975. Regional and geological interpretation of organic matter coalification in the late Palaeozoic sediments of the Bohemian Massif. Vdst. (Jst(. Ust. geol. Praha, 51, l, 13-25. 1991. Indications of the Late Carboniferous eustatic and climatic oscillations in the Upper Silesian Basin. Vdst. (lst(. tQst. geol. Praha, 66, 2, 85-96. TURNAU, E. 1962. The Age of Coal Fragments from the Cretaceous Deposits in the Outer Carpathians, Determined on Microspores. Bull. Acad. Polonaise Sci. Krak6w, gOol.-g~ogr., 10, 2, 85-89. 1970. Mikroflora i paleogeografia karbonu produktywnego v polskiej czesci Karpat. Biul. Ins. geol., Warszawa, 235, 13, 163-229. ZEMAN, J. 1977. Progn6za roz~i~eni uhlonosnOho karbonu pod vn6jgim flygem Z/tpadnich Karpat. Geol. Prdzk., Praha, 19, 12, 353-357.

The origin of magnetic remanence components of Westphalian C to Stephanian C sediments, West Bohemia: a record of waning Variscan tectonism M I R O S L A V K R S ~, JIt~I P E S E K 2, P E T R P R U N E R ~, V L A D I M [ R

SKO(~EK 2

& JANA SLEPICKOVA 2

1 Geological Institute, Academy of Sciences of the Czech Republic, Rozvojov6 135, 165 O0 Prague 6, Czech Republic 2 Faculty o f Sciences, Charles University, Albertov 6, 128 43 Prague 2, Czech Republic Abstract. Petromagnetic and magnetomineralogical investigations of Westphalian C to

Stephanian C rocks from the Central and Western Bohemian Late Palaeozoic Basins were undertaken to determine the origin of magnetic remanence components and of ferrimagnetic minerals - carriers of respective remanence components in a variety of rock types including tufts, tuffites, siltstones, sandstones, grey and red claystones. Multi-component analysis allowed the separation of remanence components and a selection of petromagnetic and/or magnetomineralogical methods were used to determine the ferrimagnetic minerals. Magnetite was found to be the principal carrier of Variscan remanence components in most non-red-coloured rocks and haematite in red claystones originated during diagenesis in the Carboniferous period. In several samples, haematite, goethite and other Fe-oxides were found to result from recent weathering. In some samples, the Variscan remanence components were separated at relatively low temperatures, from about 150 ~ onwards. Variscan virtual pole positions have been derived from relatively small sets of samples. Nevertheless, they show that the rocks of the Westphalian C and D ages were more intensively deformed than those of the Stephanian, agreeing with an overall decrease in intensity of deformation in the final stages of the Variscan orogeny. This paper aims to establish a geologicalhistorical succession for the generation of the remanence components in Carboniferous rocks of the Late Palaeozoic Basins in Central and Western Bohemia and to determine the minerals - carriers of their respective remanence

components. Distinguishing epigenetic remanence components from those of a syngenetic origin on the basis of a multi-component analysis is possible only where these components mutually differ in direction. A Variscan overprint took place in the Bohemian Massif in the Latest

Table 1. Units of Central and Western Bohemian Late Paleozoic Basins Age

Formation C

Member

Lin6 Otruby Slan~,

B

Stephanian

Malesice Jelenice

Carboniferous

,

A?

T~nec

Cantabrian o

9

e

e

.

~

9

o

t

9

9

.

e

n

9

o

e

9

9

,,

D

.

9

9

9

o

N2;'~any

:

Kladno

Westphalian C (1) Double line indicates gap in sedimentation

From Gayer, R. & Pegek, J. (eds), 1997, European Coal Geology and Technology, Geological Society Special Publication No. 125, pp. 29-47.

Radnice

,

30

M. K R S E T AL.

k~

0


Q~--._.100o C~r " 1 unit=239x1(55Alm S

No. 7 2 5 0 A 3

200

400

500oc

..... 400

150

No. 7 2 5 6 A 4

--~t

200

210 ~ S

200

,

,~n.70•

5OO~

200

~t

400

~ o ~

600o(2 -',-t

5 s r] 400

600% --"- t

Fig. 4. Bilfi Hora near Plzefi. Westphalian C, laminated sandstone, reddish claystone. See caption to Fig. 2.

Bohemian Basins, subsidence faults predominate and generally strike N W - S E to N N E SSW and E-W. In the Ohe River district the Carboniferous is cut by NE to SW trending faults parallel to the Litom6f'ice Deep Fault. Furrow-like depressions owe their origin to recurrent movements that took place along N N E - S S W trending basement faults. All basins exhibit, besides disjunctive tectonic structures, conjuctive phenomena. A close relationship exists between these two types of tectonic factors. Some faults were produced by displacement along one plane, while others form zones up to several hundred metres wide. The faults trend in a curved pattern; the throw and dip vary. The fault throw ranges from several cm to several hundreds of metres. Most frequently movements along the faults are of

the order of l0 -~ to 102m. Fault planes are estimated to dip on average 65 ~ to 70 ~, but very low angle faults dipping about 10~ to 25 ~ are also present together with steep to vertical faults. Faults often virgate and vicariate, the isolated fractures becoming Y-shaped. A number of faults were active in both synsedimentary and postsedimentary conditions, while others formed after the termination of deposition.

Laboratory procedures Laboratory procedures were combined in a way that enabled the derivation of both the palaeomagnetic directions and the determination of the m i n e r a l s - carriers of the respective

36

M. KRS E T AL.

Mtl~..~J n=7719x 165Aim ' 1-"~H"N--~| 4, , ~ 0.5t 56.5x 166Aim

No.7244A2

o...xz

N I

.T /

'260'

e...XY 200oc

~NS

3oooc..~c~ 3o~

60o 8oooc "-"" t

/

_

:

/

/

7oooc

//o~

~

~

"k.~o

L~s-52ooc/

w-I'""

' " : + ! ' " " " ~E -I /

U/5zooc E \ W___~F_! ; : I I I '. : \ -4 / Up ~ B50~ Down 2 4 0 ~ 4 ~ 68/0~ ">-~\ ',LZ...-'C l~ j680~ S lunit=Tg6xl()6AIm 210 ~ " 150 No. 7240 A1 M t . l ~ _ j s = 1091x,(]4Aim

i

200

1

i

1

i

I

I

I

I

No. 7244A1 Nt'ls]~-~ " Js=17432x ,(]4Alrn

--I-

400 600~ 200 400 600~ ~r _ ~m.m~o --4- t --4. t ~'t I~,n 2 t ~ 2 gtn=8X1()6 [ S,] I (~6[SI l ltt~m-11"~4~~ 200 400 600 oC 200 400 600 ~ I

1

---'-- t

i

i

1

I

I

1

--"

t

Fig. 5. Mirogov, 'Lomy na JanovE. Westphalian D, grey siltstone. See caption to Fig. 2.

remanence components. This method provides data to be used for the reconstruction of the history of the origin of the magnetization components. The following approach was adopted: Hand samples were collected in the field from the localities mentioned in Table 2 and at locations shown in Fig. 1. Laboratory specimens in the form of small cubes were prepared from the hand samples to be measured on spinner magnetometers JR-4 and JR-5 (Jelinek 1966). The hand samples are designated by both numbers and by the letter A, e.g. 7190A. Laboratory specimens are designated by indexes 1, 2, 3, etc., for example 7190A1, 7190A2, 7190A3, etc. Laboratory rock specimens in their natural state were subjected to progressive thermal demagnetization by using the MAVACS equip-

ment (P[ihoda et al. 1989) securing generation of a high magnetic vacuum in a medium of thermally demagnetized specimens. The remanent magnetization of specimens in their natural state is identified by the symbol Jn, the corresponding remanent magnetic moment by the symbol Mn. The remanent magnetic moment of the rock specimen demagnetized at temperature t~ is denoted by Mt. Graphs of normalized values of M t / M n = ~ ( t ) were constructed for each analyzed specimen and they provided primary information on the unblocking temperatures of the minerals - carriers of remanent magnetization. The directions of Jn and those of the remanent magnetization of the thermally demagnetized specimens in the course of a progressive thermal demagnetization are shown in stereographic projection. The orthogonal projection of the

MAGNETIC REMANENCE COMPONENTS

100[ % ]

~

9ao ~

Roudn6 near Plze6

37

o,-' * ' ~ * ~

0/o"

271100[pT1

No. 7217A3

l

l

1

2

I

' [

| I

-'

I

4 6 810

"nil

20

tIu|'l

4060

'

I

II

Ill'l

n

100 200 4(33 1000[rnT] 80 600 800

fi___.

lOO-%] 90" 80I 70"

Pit between Ledce end Zitov

~'13413[nT]

/

60~" SO"

No.7335A5 ~IRM/t~H

-~ 4o30" 20" 10I

I

1

2

, , ~

'

,,

4 6 810

'

I

20

''I

'I'I

I

'

I

'I

I

'l'l'

40 60 100 200 4.00 lO00[mT] 80 600 800

Fig. 6. Isothermal remanent magnetization (IRM) in dependence on direct magnetic field (H). No. 7217A3: a sample of grey claystone from the Roudn/t locality near Plzefi; No. 7335A5: a sample of red claystone from a pit between Ledce and Zilov.

remanent magnetization vectors is shown by the Zijderveld's diagram, where a full circle indicates projection onto a horizontal plane (XY) and a blank circle indicates projection onto a north-south vertical plane (XZ). The natural state of the specimens is designated by NS. Phase or mineralogical changes of magnetically active (mostly ferrimagnetic) minerals frequently occur during the laboratory thermal tests. These changes can be clearly derived from the graphs of the normalized values of ~,/~t =f(t), where Jg, designates the volume magnetic susceptibility of specimens in the natural state and ~ t the susceptibility of samples demagnetized at temperature t~ The 9 and ~ , values were measured on a kappabridge KLY-2 (Jelinek 1973). Because of an excessive number of data, these graphs are not shown in the present paper, only typical examples of pilot specimens are presented. In order to determine the unblocking temperatures of minerals in low magnetic rocks (with a low content of ferrimagnetic minerals)

with appropriate accuracy, pilot samples were selected for the respective localities. They were subjected to isothermal progressive magnetization by a direct magnetic field up to the saturation state with the use of a direct field with a maximum intensity of 1000mT (10 000 Oe). Dependence of the isothermal remanent magnetization (IRM) on the direct magnetic field (H) was tested for 28 specimens. Again, owing to the large amount of data these graphs are not shown here. However, this information will be used for data interpretation, see below. The specimens with the saturated remanent magnetization Js and with the corresponding remanent saturation moment Ms, were subjected to a progressive thermal demagnetization by using the MAVACS equipment. The plots of the normalized values Mr,s~ Ms in relation to the temperature t~ of the demagnetization for the pilot specimens are shown in Figs 2 to 5 and in Figs 7 to 12. The symbol Mt,s indicates the moment of a specimen that had a remanent magnetic saturation

M. KRS ET AL.

38

H

~

Mr/ ?n+~---~k J n :555 x 10 5A/m

,\

No. 7222 A3 E

N

W

I

I

I

/

~5.5x10

Aim

I

'Oo n

540oC

L

,

,

200

;'--s

N

400

600~

-----300oC

V

S

Q,..XY 210 ~

Mt,s/MsNO. 7217A3_L

150

S

1unit = 79.6 xlOSA/m--

~,,t,s/MsNO.7219 A1-4

/--

/ \

o

2 0 0 ~ 400

t

~t/~n 1

500~

--~'t

x16 s [,Sll i

200

i

400

200

~t/~n

400

600%

----~ t

1 :.~ i

600~ -'~t

i

i

200

i

i

400

i

i

600~ --~t

Fig. 7. Roudnfi near Plzefi. Westphalian D, grey claystone. See caption to Fig. 2.

moment of Ms in the initial state and was subsequently demagnetized at temperature t~ Separation of the remanent magnetization components was carried out by using the multi-component analysis of Kirschvink (1980). The statistics of Fisher (1953) were used for both the derivation of mean palaeomagnetic directions from the data of progressive thermal demagnetization for selected sets of rocks with suitable physical properties and for calculation of mean directions of the pertinent remanence components derived by the multi-component analysis.

Results of laboratory measurements The heterogeneous petrographic rock types selected for laboratory treatment represent a natural material with a wide spectrum of

magnetic properties, with varied geological history, origin of the remanence components, and with variable magnetically active minerals. This paper describes typical examples of the measurement results.

Bil5 Hora near Plzefi, 7198A-7201A, tuffite, Westphalian C Various Fe-oxides with markedly unstable properties were identified. Specimen No. 7199A3 shows a single-component remanence with haematite generated by recent weathering as its carrier. This specimen with recently generated haematite shows a narrow spectrum of microcoercive forces, the saturation state was reached in a high field of 900 mT in intensity. Another investigated specimen No. 7201A2 with various Fe-oxides shows a wide spectrum of micro-

MAGNETIC REMANENCE COMPONENTS Mt/Mn

.+"+~.

I \ Jn=84 * I(]4Alm~.

NO. 7 2 0 6 A1

0.54

I

12"8x1()4A/m~--~ I

o...xz

N

I

200

!

!

I

|

N 400

600~

e...XY 200~ 300~ \,.,

--

660~

.

~'+-+._

1-.~-+/

t

39

o

".1~ 450~ S ,, 585oC ~ -~-,,.-, -o'--\ 100~

/ft /

: 71

"~-%oooc , ooc

: : :_: : : : : Ej

Up lunit=Zg6xl(~4Ai m

Down

MLslM s No. 7 2 0 2 A 2

I

I

2 ~/~n 200/

J

I

! _ 200

400

210 " ' - - ' r " ' S

500~ "-~'t

150

MI,slMs N o . 7 2 0 6 A 2

I C 215-~ ~

400 "-~'t 600~

1

J

~

it/~r

I

-

200 400.,, 600~ /L~" --~'t

/ 200

400

600~ "-~'t

Fig. 8. Rad6ice near Plzefi. The Westphalian D/Earliest Stephanian, grey claystone. See caption to Fig. 2.

coercive forces, the saturation state was reached at 200mT. Samples of this group did not preserve their Variscan magnetic directions owing to intensive weathering. Some samples also revealed a conspicuous instability during their thermal treatment (Fig. 2).

Tlustice near Zebrdk, 7190A-7197A, tuff- tuffite, Westphalian C Two-component magnetization predominates. Goethite is the carrier of the remanent magnetization with the direction of the recent geomagnetic field (influence of weathering). The carrier of the characteristic magnetization is a minor magnetite proportion. The Variscan remanence component is well separable at an interval of 250~176 In four samples the increase in

IRM on a magnetizing field H was investigated and in three samples a saturation state was reached in a direct magnetic field of 700mT, which is characteristic of magnetically hard samples. Unblocking temperatures for goethite _%._Z_.--~,=~ =,u / ~S 200~

Mt.s/M s

200 400 600~ ~'t/~n ---"t 2t ~'n=151x166 Is1] I

i

S

S 150oC 1unit =7g.6 x 106Aim

Mr,sIMs

\

i

I

No.7228A2 Js :4768x1154A/rn

200 400 600~ ~t/a'n -'-'- t 2t ~n=18xld6[sl] i

600~ " "

I~

,-,~

i

'1

200

t

I

400

i

!

600~ "-'-t

Fig. 10. Dolni Vtk~. Stephanian B, siltstone. See caption to Fig. 2.

proved, the proportion of magnetite is low. Ferrimagnetic minerals are represented by Fe-oxides, by goethite and probably by one of the "r-Fe203 or rl-Fe203. The Variscan remanence component is separable at a relatively low temperature, within the interval of (100) 150~176 (Fig. 7).

Raddice near PlzetL 7202A-7207A, grey claystone, Westphalian D/the Earliest Stephanian Multi-component remanence is caused by syngenetic magnetite and by secondary Feoxides, ranging from goethite to haematite, formed by recent weathering (specimen No 7206A1). Magnetite is the carrier of the

Variscan remanence component, being separable within a temperature range 250~176 Samples containing exclusively haematite, generated by recent weathering, show a narrower spectrum of microcoercive forces and they reach the saturation state in high intensity magnetic fields (Fig. 8).

Rad~ice near Plzeti, 7208A-7216A, green siltstone, Stephanian A No haematite was detected in this sample group. Otherwise, magnetic properties similar to samples from the previous locality have been proved. Magnetite is, again, the carrier of the Variscan remanence component, which is separable in the temperature interval 250~ (Fig. 9).

42

M. K R S E T AL.

Dolni Vlkf~Y, 7224A-7231A, siltstone, Stephanian B Mostly minerals with a low unblocking temperature below 300~ are the remanence carriers. The saturation state was reached at a field intensity of 350 mT; these are therefore mediummagnetic-hardness minerals. Graphs of Mt,s/Ms plotted against temperature show a higher proportion of minerals with a lower unblocking temperature, but even a lower content of magnetite has been proved with unblocking temperature below 580~ The Variscan remanence component is already separable at relatively low temperatures, within an interval of 150~ to 300~ (Fig. 10).

Zihle, a red claystone pit, 7260A-7272A, red claystone, Stephanian C The remanence consists of two components, a smaller proportion represented by viscous magnetization. The carrier of the principal remanence component is an extraordinarily stable

haematite with unblocking temperature below 680~ Three sites were sampled at this locality. The group of samples 7263A-7272A shows palaeomagnetic directions that correspond well to those from the clay pit between the villages of Ledce and Zilov (samples No. 7232A-7235A), see below. The high stability of palaeomagnetic remanence is also well documented by the results of progressive thermal demagnetization of the specimens (Table 3). The structure of Zijderveld's diagrams, graphs of Mt/Mn and Mt,s/Ms plotted against temperature, and the extraordinary stability of magnetic susceptibility vs. the thermal fields from the Zihle locality (Fig. 11) entirely correspond to the values established for the clay pit locality between the villages of Ledce and Zilov (cf. Fig. 12).

A red claystone pit between the villages of Ledce and Zilov, 7232A-7235A, red claystone, Stephanian C The two-component remanence is due to a small proportion of viscous (recent) component

Table 3. Results of progressive thermal demagnetization using the MAVACS apparatus. A red claystone pit, locality Zihle. Stephanian C, red claystone, Nos of samples 7263A-7267A Temperature (~

20 100 150 200 250 300 350 400 450 500 540 580 620 650 680 700

Mean direction of remanent magnetization D(~

I(~

215.5 206.5 206.4 206.5 206.1 206.2 205.6 205.5 205.3 204.5 204.7 204.6 203.4 208.6 176.9 .

19.9 11.1 9.8 9.0 9.2 8.7 8.6 8.2 8.9 8.7 8.4 8.2 8.3 8.0 - 1.2 .

.

.

a9s (~

k

11.8 10.6 10.4 10.6 10.7 10.6 9.8 9.9 9.6 10.1 10.9 10.7 10.2 12.9 12.5

43.2 52.8 54.6 52.9 51.7 53.5 61.7 60.6 64.2 58.8 50.5 52.1 57.7 35.9 38.2

5 5 5 5 5 5 5 5 5 5 5 5 5 5 5 5

D, I, declination, inclination of the remanent magnetization after dip correction; a9s, semi-vertical angle of the cone of confidence calculated according to Fisher (1953) at the 950 probability level; k, precision parameter; n, number of the samples analyzed.

MAGNETIC REMANENCE COMPONENTS

Mt/~In

W

I

:

I

650~

0.5x 164Aim

1'

:

Up 700oC~ 680~ /

43

'o'

~

/

58~c4 500~

\

NS ~,, c -~-~_ 400~ [-

300~

b'~200oC 100~ 1 unit =15.9xl(~4A/m /M NO.7263A2

!

|

200

!

i

!

!

400

S

MtdM s NO. 7 2 7 0 A 2

200 400 600~ n =221x10-6[SI] --"t

aft/~'n

21U~_----q'50

'

600~ --"t

200 400 600% ~ft~.n.~_~n=249x166 [sI] --"- t !

!

200

i

i

400

i

i

600~ "----t

Fig. 11. Zihle, a red claystone pit. Stephanian C, red claystone. See caption to Fig. 2.

and to a prevailing Variscan component brought about by syngenetic haematite. The haematite is characterized by a narrow spectrum of micro-coercive forces and by high magnetic hardness (the lower part of Fig. 6). The stability of palaeomagnetic directions is extraordinarily high. Table 4 shows the mean remanence directions using Fisher's (1953) statistics of four samples submitted to progressive thermal demagnetization. The Variscan remanence directions are derivable within an interval of 150~176 and optimum cleaning was achieved at a temperature of 620~ (Fig. 12).

Palaeomagnetic directions and virtual pole positions The objective of our work was not merely to increase the data base of palaeomagnetic

directions, but to determine on several representative rock samples, the genetic history of the remanence components or the overprint components. This approach has, nevertheless, partially verified the results of previous palaeomagnetic measurements (Krs 1968) by using a refined methodology, particularly by introducing the multi-component analysis of remanence and by using the thermal demagnetizaion in a high magnetic vacuum. Table 5 summarizes the derived palaeomagnetic directions and the corresponding virtual pole positions. Higher values of palaeomagnetic declination have been proved at several localities (Rad6ice near Plzefi- grey claystone, Bil~ Hora near Plzefi and also at the red claystone localities between the villages of Ledce and Zilov, Zihle). Similar higher values of palaeomagnetic declination in western Bohemia were reported earlier (Birkenmajer et al. 1968). The data presented here indicate that the higher values

44

M. KRS E T AL. MtlMn

11~"+'~, -4 I\ 'N-,,.~.~.0.8x10 Aim

NO. 7232AI

w

u#

: " =~f' "~0o~o/ 7 ~ 6sooc

" / . . . .

200

o...xz

f

o...XY

/

~

/ ~ , T 585o C

\

150~C S 1unit = 23.9 x 1()4A/rn

~

.

,/'g~

600

800~

:

uu/

hoooc,l

.,

-

/

"k,,~u

:

210 ~

/

150 S

No.7235A5 Mr,s/Ms 1 1 ~ ~ 1 ~ 4 0 2 3 x 1(}4A/m

200

~tlMn

!

i

200

400

!

i

400

600~ ~ t

I

!

600~ --~.f

Fig. 12. Between villages Ledce and 7,ilov, a red claystone pit. Stephanian C, red claystone. See caption to Fig. 2.

for palaeomagnetic declination in the Carboniferous are not constant across the studied area, but differ from one locality to another. On the other hand, the palaeomagnetic directions for Early Permian rocks are homogeneous in the territory of the Bohemian Massif, indicating an extraordinary tectonic stability (consolidation of blocks of the newly forming supercontinent Pangea, Krs & Pruner 1995). Figure 13 shows the virtual pole positions for the studied Westphalian and Stephanian rocks. Although the pole positions have been calculated from a small number of samples, the Westphalian rocks exhibit a higher scatter of palaeomagnetic data than do those of the Stephanian. For rocks of the Westphalian the ~,p = 36.25 ~N; Ap : 164.87 ~ E; Q{95: 15.4~ k=36.4; N = 4 ; for rocks of the Stephanian

qap = 37.46 ~N; Ap--163.76 ~ E; 0 { 9 5 = 6.7~ k = 132.7; N - 5 . The difference in magnitude of the precision parameter k is significant. The mean pole positions calculated in this paper correspond well to those derived on a larger data set for the whole Bohemian Massif, on rocks dated biostratigraphically (Krs & Pruner 1995).

Conclusions Palaeomagnetic, petromagnetic, magnetomineralogic analyses and the multi-component analyses of remanence of rocks of Westphalian C to Stephanian C ages in the Central and Western Bohemian Late Palaeozoic Basins have provided the following information:

MAGNETIC

REMANENCE

COMPONENTS

45

Table 4. Results of progressive thermal demagnetization using the MAVACS apparatus. A red claystone pit, between villages Ledce and Zilov. Stephanian C, red claystone, Nos of samples 7232A-7235A Temperature (~

20 100 150 200 250 300 350 400 450 500 540 580 620 650 680 700

Mean direction of remanent magnetization D(~

I(~

208.8 206.8 206.3 206.1 205.7 205.8 205.5 205.4 204.6 204.9 204.9 205.0 204.3 204.9 177.4 38.2

-9.9 -12.9 - 14.4 - 14.4 - 13.9 - 14.1 -12.5 - 11.8 - 10.0 -10.1 -8.3 -7.1 -5.2 - 5.3 -2.9 -35.5

o~95 (~

k

14.0 14.4 14.5 14.3 14.2 14.3 14.4 14.4 14.0 13.6 13.9 13.3 12.8 13.2 5.2 49.4

44.3 41.6 40.9 42.1 42.7 42.4 41.7 41.9 44.2 46.4 44.8 48.8 52.3 49.2 307.8 4.4

4 4 4 4 4 4 4 4 4 4 4 4 4 4 4 4

D, I, declination, inclination of the remanent magnetization after dip correction; a95, semi-vertical angle of the cone of confidence calculated according to Fisher (1953) at the 95% probability level; k, precision parameter; n, number of the samples analyzed. Table 5. Virtual pole positions, mean palaeomagnetic directions. Plzet[ Basin, Westphalian C to Stephanian C,

cf Table 2 Site

Locality

Mean palaeomagrnetic directions

Dp (o)

a95 (~

k

n

Virtual pole positions

/p (~

1

Bilfi Hora near Plzefi

unstable sample

2

Tlustice near Zebrfik

201.4

18.6

Ovals of confidence

~p(~

Ap(~

dm (~

dp (~

27.69

169.89

10.93

5.68

3 10.5

34.2

7

3

Bil~i Hora near Plzefi

218.5

-12.8

19.7

162.3

2

36.04

143.52

20.07

10.23

4

Miro~ov 'Lomy na Janov6'

200.8

2.8

10.5

131.8

3

36.27

167.51

10.50

5.25

5

Roudnfi near Plzefi

190.7

-5.7

6.5

87.1

7

42.22

178.90

6.52

3.27

6

Rad6ice near Plzefi

212.2

-10.8

3.6

653.8

4

38.07

150.98

3.65

1.85

7

Rad6ice near Plzefi

196.5

3.0

14.4

15.7

8

36.81

172.56

14.41

7.21

8

Dolni V l k ~

197.4

-0.6

6.8

79.1

7

38.32

170.88

6.80

3.40

9

Zihle, a red claystone pit in operation

205.0

2.3

7.2

45.6

10

34.40

162.57

7.20

3.60

10

A red claystone pit, between Ledce and Zilov

204.3

-5.2

12.8

52.3

4

38.47

161.66

12.84

6.44

Dp, Ip, mean palaeomagnetic declination, inclination; a95, semi-vertical angle of the cone of confidence calculated at the 95% probability level; k, precision parameter; n, number of the samples analyzed; ~p, Ap, palaeolatitude, palaeolongitude of the virtual pole position; dm, dp, ovals of confidence calculated at the 95% probability level.

M. KRS E T AL.

46

Westphalian

Step hanian

Fig. 13. Stereographic projection of virtual pole positions. Virtual pole positions are denoted by small full circles. The mean pole position calculated from virtual pole positions is denoted by a crossed small full circle, it is circumscribed by a circle of confidence calculated according to Fisher (1953) at the 95% probability level. Westphalian: 2, Tlustice near Zebr~k, Westph. C; 3, Bil~ Hora near Plzefi, Westph. C; 4, Miro~ov, 'Lomy na Janov6', Westph. D; 5, Roudnfi near Plzefi, Westph. D. Stephanian: 6, Rad6ice near Plzefi, the Westph. D/Earl. Steph.; 7, Rad6ice near Plzefi, Steph. A; 8, Dolni Vlk~,~, Steph. B; 9, Zihle, a red claystone pit, Steph. C; 10, Between villages Ledce and Zilov, a red claystone pit, Steph. C.

(1) Magnetite is the principal carrier of the Variscan remanence component in most nonred-coloured rocks. In tufts and tuffites the magnetization is of thermoremanent and detrital origin, and it is also of detrital origin in grey, green claystones and siltstones. In these cases, magnetite is syngenetic with the rock, i.e. the direction of its Variscan palaeomagnetic remanence component corresponds to the time of deposition and compaction of the rock. (2) In the red-coloured rocks, haematite is the carrier of palaeomagnetization which clearly originated during the diagenesis of the rock (red claystone). Haematite of this type is physically stable; it has been proved to contain a slightly viscous component and its spectrum of unblocking temperatures is wide. (3) In some rocks other than red, e.g. in the grey siltstone from the Miro~ov locality, in the 'Lomy na Janov6' quarries and in the grey claystone from the Rad6ice near Plzefi locality, haematite has been found to be a product of weathering. Haematite of this type shows a narrow spectrum of unblocking temperatures;

its direction of remanent magnetization corresponds to that of the field of a recent (theoretical, co-axial, geocentric) magnetic dipole. (4) Except for the Bilfi Hora locality near Plzefi (highly weathered tuffite), all rocks of the localities studied (Tables 2 and 5) show a multicomponent remanence and some of them also a Variscan remanence component. (5) In some rocks, the Variscan remanence component was already separable at low temperatures, e.g. in the grey claystone from Roudnfi near Plzefi from (100) 150~ upwards, and in a claystone from Dolni V l k ~ from 150~ In red claystones from the localities of 2;ihle and from the clay pit between the villages of Ledce and Zilov, the Variscan component was separable from (100) 150~ upwards. These data indicate that these localities were not significantly reworked chemically, thermally or by other processes in postVariscan times. It was the recent rock weathering that caused either a partial or a complete obliteration of the Variscan remanence component in some of the rocks.

MAGNETIC REMANENCE COMPONENTS (6) Virtual pole positions have been derived from relatively small sets of data. Nevertheless, the Westphalian rocks seem to have undergone palaeotectonic deformation more intensively than those of the Stephanian. This is in accordance with an overall decrease in palaeotectonic deformation in the final phase of the Variscan orogeny, which finally terminated by Early Permian times (Krs & Pruner 1995). The authors wish to thank Professor R. Gayer and Dr. V. Kropfirek for reviewing the paper and suggestions. They are also grateful to Professor R. Gayer for improvement of the English. The authors would like to thank Mrs. Marta Krsov/t and RNDr. Daniela Venhodovfi for their help in laboratory works. They also acknowledge the financial support through the Grant No. 113/94 of the Charles University in Prague.

References BIRKENMAJER,K., KRS, M. & NAIRN,A. E. M. 1968. A palaeomagnetic study of Upper Carboniferous rocks from the Inner Sudetic Basin and the Bohemian Massif. Bulletin of the American Geological Society, 79,589-608.

47

FISHER, R. 1953. Dispersion on a sphere. Proceedings of the Royal Society, A217, 295-305. JELiNEK, V. 1966. A high sensitivity spinner magnetometer. Studia geophysica et geodaetica, Praha, 10, 58-78. - - 1 9 7 3 . Precision A.C. bridge set for measuring magnetic susceptibility and its anisotropy. Studia geophysica et geodaetica, Praha, 17, 36-48, KIRSCHVINK, J. L. 1980. The least-squares line and plane and the analysis of palaeomagnetic data. Geophysical Journal of the Royal Astronomical Society, 62, 69%718. KRS, M. 1967. Research Note: On the palaeomagnetic stability of Red sediments. Geophysical Journal of the Royal Astronomical Society, 12, 313-317. 1968. Rheological aspects of palaeomagnetism? International Geological Congress Prague, XXXIII Session, 19-28 August 1968, Proceedings, Section 5, 87-96. & PRUNER, P. 1995. Palaeomagnetism and palaeogeography of the Variscan formations of the Bohemian Massif, comparison with other European regions. Journal of the Czech Geological Society, Praha, 40/1-2, 3-46. PI~iHODA, K., KRS, M., PESINA,B. & BLAHA,J. 1989. MAVACS- a new system creating a non-magnetic environment for palaeomagnetic studies. Special Issue Cuadernos de Geologia Ibdrica, Madrid, 12, 223-250.

A depositional and diagenetic model for the Eocene Sulcis coal basin of SW Sardinia ROLAND

DREESEN'*,

DOMINIQUE

B O S S I R O Y ~, R U D Y S W E N N E N ~,

JACQUES

T H O R E Z 3, A U R E L I O

F A D D A 4,

LUCIANO

OTTELLI 5 & EDDY

KEPPENS 5

l Institut Scientifique de Service Public, 200 Rue du Chdra, B-4000 Li@e, Belgium 2 Katholieke Universiteit Leuven, Afdeling Fysico-chemische Geologie, Celestijnenlaan 200 C, B-3001 Leuven, Belgium 3 Universit~ de Lidge, Service de G~ologie GOnOrale, GOologie des Argiles et Sddimentologie des Silicoclastiques, AllOe du 6 Aofft, B18, B-4000 Sart Tilman par Lidge 1 Belgium 4 Carbosulcis, Miniera Monte Sinni, 1-09010 Cortoghiana (Ca), Sardinia, Italy 5 Vrije Universiteit Brussel, Eenheid Geochronologie, Laboratorium voor Stabiele Isotopen Geochemie, Pleinlaan 2, B-1050 Brussels, Belgium * Current address." VITO, Boeretang 200, 2400 Mol, Belgium

Abstract: Detailed sedimentological, mineralogical and petrographical analysis of closely

spaced cored boreholes has enabled the development of a revised depositional model for the early Eocene coal-bearing Produttivo Formation of the Sulcis Basin. The deposition of autochthonous-hypautochthonous palustrine-lacustrine coals and associated carbonates was interrupted episodically by sedimentation of allochthonous lithocalcirudites and lithocalcarenites. The latter clastics display characteristic upward shoaling tidal flat sequences related to marine incursions. This interpretation is in contrast to the previously accepted fluvial origin of the detrital episodes. The coarse basal transgressive lag deposits consist of various carbonate intraclasts, dolosparite, grains consisting of calcite cement and euhedral-subhedral evaporite-bearing quartz grains. Combined stable isotope and cathodoluminiscence analysis has revealed a complex diagenetic history for the clastic deposits. The potential extrabasinal or intrabasinal provenance of the clasts, in particular the origin of the evaporite relicts, is discussed. The subtropical-tropical coastal marshes of the Florida Everglades (USA) are proposed as a possible modern analogue for the subbituminous Sulcis coals.

The Sulcis coal basin in southwest Sardinia (Fig. 1) represents the only subbituminous coal deposit in Italy. Between 1979 and 1992 over two hundred exploration boreholes were drilled from the surface and from underground galleries by Carbosulcis S.p.A. Recently, a number of these cored drillholes have been reinvestigated as part of an international research project funded by the European Commission (ECSC). The main objective of this work is to enhance the resolution or reliability of intrabasinal lithostratigraphical correlations of coal seams through an integrated sedimentological and sequence stratigraphical approach. Previous sedimentological analyses include scientific case studies conducted under the supervision of Italian universities (Siena, Cagliari) and consultancy studies completed by national or international experts. The former dealt with micropaleontological, palaeoecological or microfacies characteristics of the marine and lacustrine

carbonates, which are closely associated with the coals. The latter concentrated on the search for local lithological and palaeontological marker beds. Most of these data are unpublished and were made available to us by courtesy of the Board of Directors of Carbosulcis. The coal-bearing sequence (the so-called 'Produttivo') displays complex interfingering of marine-influenced and non-marine sediments, including coals, carbonaceous mudstones, marls, brackish to fresh-water limestones, and carbonate-rich detrital rocks. The latter 'hybrid' clastic rock types (quartz-rich lithocalcirudites, lithocalcarenites) represent minor or major clastic intercalations, which can be used for subdividing the coal-bearing sequence into successive lithological intervals. This paper will focus on the origin and the role of the latter 'detrital' intervals in the context of a revised depositional model for the coal-bearing deposits of the Sulcis Basin.

From Gayer, R. & Pegek, J. (eds), 1997, European Coal Geology and Technology, Geological Society Special Publication No. 125, pp. 49-75.

50

R. DREESEN E T AL.

Fig. 1. Location map of Sulcis mining project area (dark shaded area) in SW Sardinia.

Regional geological setting, palaeogeography and stratigraphy The coal-bearing Sulcis Basin formed during early Tertiary times as a result of extensional tectonic events which affected the south-eastern edge of the Iberian Plate (Assorgia et al. 1992). After an initial sea level rise at the base of the Palaeogene, a sea level fall was induced in the early Eocene by the Pyrenean orogeny in the western Mediterranean area. Subsequently, the synsedimentary graben-like Sulcis Basin was formed and reached equilibrium between subsidence and infill (Fadda et al. 1994). The Sulcis Basin was infilled by various sedimentary and volcano-sedimentary deposits: Palaeogene marine, brackish and continental (coal-bearing) deposits, Oligo-Miocene calc-alkaline volcanics (ignimbrites); and Neogene fluviatile and fluviolacustrine deposits. The aeral extent of the Sulcis Basin is estimated at about 200 km 2. It is bordered to the east by Palaeozoic basement outcrop and to the west by the sea (Fig. 2). The Eocene coalbearing formation ('Formazione produttiva a lignite' or 'Produttivo') has a known subsurface areal extent of more than 100 km 2. It dips to the SSW with an average dip of 8-10 ~. The thickness of the Produttivo and the number and thickness of the coal seams gradually increase to the SSW. The Produttivo Formation reaches a maximium thickness of 70 m. In the mining project area of Monte Sinni (Fig. 1) its

average thickness is 40-50 m at depths between 200 and 400m. The estimated coal reserves exceed some 250 million tons. The Sulcis coal can be classified as a low rank non-caking coal with very high volatile matter, low reflectance and calorific values (sub-bituminous A-B coal; Glanzbraunkohle). The heterolithic coal-bearing Caenozoic sediments of the Sulcis Basin have been affected by E-W and N N W - S S E oriented block faults (Fig. 2), which can be related to the anticlockwise rotation of the Corso-Sardinian microplate (Orsini et al. 1980) during successive tectonic phases of the Alpine orogeny. Eocene normal growth (listric) faults created halfgraben structures and were responsible for thickness variations of the coeval sedimentary deposits (Assorgia et al. 1992). The coal seams and the associated 'barren rocks' (mostly limestones and marls) are often affected by smallscale folds. The latter occur in narrow belts and they originated as a result of differential lateral movements (gravitational sliding or slumping; Bandelow & Gangel 1993) related to rollover phenomena (Cocozza et al. 1989; Fadda et al. 1994). According to Plaziat's (1981) palinspastic palaeogeographic reconstruction of the periPyrenean region, the Sulcis area represented a coastal embayment during early Eocene times. This area was bordered by a shallow sea in the SE and was intermittently affected by terrigenous influxes derived from a continental source, supposedly located in the NW. The latter

EOCENE SULCIS COAL BASIN

51

Fig. 2. Simplified geological map of the Sulcis Basin, SW Sardinia (modified after Fadda et al. 1994). Heavy lines correspond to major faults.

Fig. 3. Palaeogeographical map of the peri-Pyrenean region during Ilerdian (Ypresian; early Eocene) times (modified after Plaziat 1981). source area would correspond to the PyreneoProvengal mountain chain (Fig. 3). Tambareau et al. (1989) have stressed the analogies between the continental microfaunas and palynofloras of the Ilerdian (Ypresian) deposits of Sardinia

and the Pyrenean foreland (Languedoc area) which corroborate the continental continuity between the Pyrenean area and Sardinia. The Palaeogene deposits of the Sulcis Basin reach a maximum thickness of 140m and

52

R. DREESEN E T A L . DEPOSITIONAL

STAGES

FORMATIONS

MAJOR

LITHOLOGIES

COCOZZA et al. 1989

CONSULTANCY STUDIES

ASSORGIA et al. 1991 FADDA et al. 1994 tu u

......

O z

Volcano sedimentary

~ ......

pyroclastlcs

volcanics interbedded within continental terdgenous successiona

'

.............

rhyolitic Ignlmbrttas

.............

andesitic basaits

complex 0

I

~_) . . . ~ .

0

polygenic cong,o.~

Cixerri Fm.

alluvial fans

claystones

~ t o ~ o ~ .,

..........

Fm.

'1r 7~ rr. ~ Miliolitic

-

,-

30- 40 m B~S~L CONGLO.U.., --

PALAEOZOIC~ BASEMENT

~ custdne

freshwater Iimest. marls claystones

parallc lagoonal

~

~-=-

PERMO- " ~ J f / J \ TRIAS.~C ~ v j / / /

.

.

.

.

.

.

.

littoral

~

hypersaline & mesohallne lagoons

marls

-

.

.

.

.

w

......

lacustrine palustrine episodically interrupted by channellized tidal clastic deposits reworking pseudomorphosed

fluvial channels supralittoral paludal lagoonal

fluvial channels

b i o - calcarenites

~

Limestone Fm. P-,-~_':-CF.~

cgl.

"-" siltat. ~ r . ~ L

Produttivo

i ~

not studied

braided plains

alltatones

i

not studied

alluvial fans

sandstones

LU

0

THIS PAPER

450 m ,~, b . . , h . . ,, ,,., ,~

0 ~

Z

ENVIRONMENT

lag

folded metasedl.,mentary

evaporites

sublittoral

\ \ '

notstudied

restricted marine with fluctuating salinities to

ah\...allowmarine ~

\

Fig. 4. Stratigraphic scheme, major lithologies and depositional settings of the Palaeogene deposits in the Sulcis area. display a characteristic transgressive-regressive megasequence with marine carbonates above a polymict conglomerate at the base; paraliccontinental heterolithic sediments in the middle; and continental facies at the top of the sequence (Fig. 4). A marked reduction in diversity of the microfaunas and an inferred salinity anomaly about 35m above the base of the marine carbonates marks the onset of a regression, which reached its acme with the deposition of continental coal-bearing sediments. The resulting heterolithic paralic formation, the so-called 'Produttivo' is sandwiched between shallow marine limestones ('Calcare a Miliolidi') at the base and coarse detrital fluvial deposits at the top ('Cixerri Formation') (Fig. 4). Most of the boreholes drilled by Carbosulcis reached the top of the Miliolitic Limestones Formation only. Good biostratigraphic markers are restricted to the marine carbonates. The basal part of the Miliolitic Limestones contains large foraminifera (Alveolinids and Orbitolitids) which suggest an Ilerdian age (early Ypresian, Early Eocene; Cherchi 1983). The age of the coal-bearing formation is more difficult to determine due to obvious palaeoecological constraints. However, the lowest coal-bearing strata yield charophytes

and palynomorphs suggesting a Cuisian (late Ypresian) age (Pittau 1977; Salvadori 1979). The Produttivo Formation is unconformably overlain by the Cixerri Formation, the basal part of which has been assigned to the earliest Lutetian (Middle Eocene) on the basis of palynomorph and charophyte content (Pittau Demelia 1979).

Previous work The first detailed sedimentological-palaeoecological work on the coal-bearing Tertiary Sulcis Basin was an unpublished study conducted by the University of Siena (Cocozza et al. 1989). In this study, four major lithostratigraphical units were recognized within the 'Eocene series'. The basal unit corresponds to the shallowingupward coastal-lagoonal carbonates of the Miliolitic Limestone Formation (Fig. 4). The second and third units roughly correspond to the coal-bearing ('Produttivo') sequence. The second unit was interpreted as a gradual transition from coastal-lagoonal carbonates through brackish-lagoonal and heterolithic coal-bearing lacustrine-palustrine facies. The latter unit is interrupted by an important fining-upward clastic deposit, which has been interpreted as

EOCENE SULCIS COAL BASIN fluvial in origin. The third unit is lithologically similar to the second, but the coals tend to be thicker. Its upper limit is marked by a second clastic episode. The fourth and final unit corresponds to the Cixerri Formation (partita) and is characterized by the lack of coal and by the dominance of coarse clastics. The latter have been interpreted as braided fluvial channel deposits. The carbonates of the basal unit comprise a variety of microfacies types, indicating lowenergy, shallow lagoonal environments of a tropical to subtropical arid coastal zone (Cocozza et al. 1989). The benthic foraminiferal faunas indicate dominant hypersaline lagoonal conditions, with intermittent freshwater influxes (temporary hyposaline conditions; Cocozza etal. 1989). Foraminiferal wacke/packstones with ostracodes, molluscs, green algae and echinoderms are the dominant microfacies type. Crossbedded grainstones with peloids, low-energy fibro-radiated ooids, intraclasts and cyanobacterial oncoids are less frequent. The latter grainstones enclose corroded larger foraminifera with open-marine affinities (Alveolina, Orbitolites), the presence of which can been related to storm-induced transport. All microfacies types show more or less important bioturbation. Near-emergence is indicated by plant rootlets, incipient pedogenesis, and mottling whereas micro-karst phenomena suggest temporary subaerial exposure. The carbonates in the second and third unit comprise freshwater-influenced restricted-marine ('paralic') and lacustrine limestones (Cocozza et al. 1989). The paralic mud/ wacke/packstones contain abundant smoothshelled ostracodes, brackish foraminifera (e.g. Ammonia), freshwater molluscs, charophytes and dwarf miliolinids. Rare gastropod-bivalve coquinas (Cyrena, Potamides) occur in their basal part. The lacustrine limestones consist of mudstones, wackestones and (pseudo) packstones with variable amounts of skeletal grains such as those of freshwater gastropods, freshwater bivalves and charophytes. Plant root pedoturbation and other pedogenetic features are common. The clastic or detrital facies consist of finingupward sequences of rudites, arenites and siltstones. These strata have been related to braided fiver deposits in a distal alluvial plain setting (Cocozza et al. 1989). Other unpublished reports (e.g. by RIMIN 1990-1991) contain less sedimentological information. These studies focussed on the stratigraphical framework of the Produttivo. The clastic episodes have been again interpreted as channelized fluvial deposits. A major result of these

53

studies has been the subdivision of the coalbearing sequence into informal lithostratigraphic units, and the regrouping of the numerous tiny coal layers into 10-12 multi-seam coal horizons. This lithostratigraphic scheme was based on lithological predominance criteria and on the presence of local marker beds. However, bed-bybed correlation is not generally possible, except in the case of closely spaced boreholes. Even then, correlation of individual coal seams is problematic because of marked seam irregularities. The wedge-shaped sandstones which erode underlying coals, were interpreted as fluvial channels. The coarser clastics of the overlying Cixerri Formation were attributed to alluvial fan deposits. A stratigraphical study recently conducted by Montan Consulting GmbH (Bandelow & Gangel 1993) lead to similar conclusions. Although potential marker beds were identified (including questionable bentonite layers) and the correlation of coal seams over larger distances between closely spaced boreholes was possible, a bedby-bed correlation of the coal seams remained uncertain, due to the combined effect of synsedimentary tectonics (difference in thickness of coeval strata) and sedimentological events (e.g. wash-out phenomena).

Facies spectrum and distribution The 40-70 m thick heterolithic sequence of the Produttivo Formation is subdivided into four informal lithostratigraphic units, based on a detailed study of 50 closely spaced cored boreholes in the area of Monte Sinni (Fig. 1). Each unit contains one or more parasequences, bounded by unconformities which correspond to the erosional bases of the 'detrital episodes' (Fig. 5). The boundary between the Miliolid Limestones and the Produttivo is not clear-cut, but consists of a gradual transition from restricted marine to lacustrine-palustrine limestone facies. This boundary represents not an unconformity but rather a palaeoecological/palaeoenvironmental change within the coastal lagoon setting. The sudden occurrence of 'paralic' microfaunas (mixohaline or hyposaline conditions) and the first occurrence of (autochthonous) coal seams, can be used as criteria for defining the base of the Produttivo Formation. This event is characterized by the mass occurrence of (pyritized) smooth-shelled ostracodes and by an important decrease or even disappearance of miliolinids (dwarf forms). The Cixerri Formation which unconformably overlies the Produttivo consists of conglomerates, coarse sandstones and var-

54

R. DREESEN E T A L .

Fig. 5. Ideal parasequence within the Produttivo Formation, with evolution of relative water depth and relative sea level (MFS: marine flooding surface; TST: transgressive system tract; HST: highstand system tract; LST: lowstand system tract; EV: evaporite; PAL/LAC: palustrine / lacustrine; TF: tidal flats. Not to scale.

iegated mudstones. The lack of coals and limestones is used here as a criterion to distinguish it from the Produttivo, although a gradual transition cannot be excluded. The ideal parasequence or depositional unit within the Produttivo Formation is an upwardshoaling unit, several metres to about 10 metres thick. It is bounded by marine flooding surfaces, coinciding with an erosional unconformity (Fig. 5) and marking the base of a 'detrital' episode. This depositional unit corresponds to a parasequence, in the sense of Van Wagoner et al. (1988, 1990), and the Produttivo Formation is composed of a parasequence-set formed by

the stacking of analogous parasequences. In contrast with the unpublished reports referred to earlier, we consider the detrital episodes not as fluvial deposits but rather as marine sediments. They are interpreted as shallow marine tidal deposits, displaying characteristic subtidalintertidal-supratidal upward-shoaling sequences (Fig. 6). The 'detrital' sediments represent the lowermost part of each parasequence. The upper part consists of 'continental' supratidal deposits, which grade vertically (and laterally) into lacustrine and palustrine coal-bearing facies. The tidal character of the clastics is indicated by a vertical suite of characteristic sedimentary structures, whereas tidal subenvironments may be distinguished on the basis of lithologies and associations of structures (Terwindt 1988). Marine fossils are apparently lacking in the studied shallow marine tidal deposits, despite indirect evidence for in-situ organic activity such as intense bioturbation and the presence of escape structures. Reworked cyanobacterial mats or oncoids (stromatolites) and fragmented thick-shelled (mixohaline?) molluscs occur in the basal part of each parasequence. We suggest that this apparent lack of in situ organisms must be related to the extreme harsh environmental conditions (abnormal salinities) during deposition of the subtidal and intertidal sediments. Analogous observations have been made in tidal sequences from the Late Devonian Psammites du Condroz Group of the Ardennes in Belgium (Thorez et al. 1988). The subtidal facies is represented by relatively thin (5-20cm) coarse-grained lag deposits ('microconglomerates') overlaying erosional unconformities. The lags are composed of grey quartz-rich (litho-)calci-dolorudites and (litho-) calci-doloarenites displaying some grading and oblique or cross stratification. The subangular, strongly packed pebbles or granules include various intraclasts such as grains consisting of calcite and dolomite cement, lacustrine mud/ wackestones, pedogenic carbonates, black pebbles, oncoids, stromatolitic crusts, chert, coal and mollusc fragments. Euhedral quartz grains are common and locally abundant. This subtidal facies is interpreted as a thin transgressive unit. It coincides with a transgressive lag, which resulted from the reworking of underlying or lateral deposits, i.e. the winnowing of finegrained sediments and the accumulation of coarse-grained sediments on the ravinement surface, during shoreface erosion (Swift 1975). The ravinement surface corresponds here to the flooding surface (MFS; Fig. 5). Because of the reduced sediment influx (as the shelf area expands the volume of sediment being supplied

EOCENE SULCIS COAL BASIN

55

Fig. 6. Borehole 67-91: Lithologies, sedimentary structures and inferred tidal subenvironments within clastic deposits of the Produttivo Formation. Logs a and b refer to basal parts of lithostratigraphic intervals D and C respectively (see Fig. 7). per unit area decreases) one of the principal sources of coarse material for transgressive deposition is cannibalization of previously deposited sediments (Arnott 1995). The intertidal facies consist of a sequence, a few to several metres in thickness, of grey

'sandstones', 'siltstones' and 'mudstones', which correspond to intensly bioturbated, alternating calcarenites and carbonaceous calcilutites. Individual beds are between ten and several tens of cm in thickness, not exceeding 1 m. The latter calcarenites and calcilutites vertically grade into

56

R. DREESEN E T AL.

dolarenites and dololutites: stained acetate peels (Friedman 1959; Katz & Friedman 1965; Dickson 1966) and X-ray diffraction indicate nonferroan and ferroan dolomite (the latter as a cement) increasing from bottom to top (Fig. 7). Kaolinite is omnipresent. Lenticular, flaser and ripple bedding are most common, whereas pervasive pedoturbation (due to plant roots?) frequently induces destratification. Lower and upper intertidal subenvironments can be distinguished on the basis of sedimentary structures (Fig. 6). Vertically recurrent microconglomeratic or litharenitic levels suggest stacking of the tidal sand bodies. The supratidal facies consist of a sequence, several meters in thickness, of grey dololutites displaying a rather massive aspect due to intense bio- and pedoturbation. Palaeosols are present as proved by the occurrence of mottling and illuviation-oxidation phenomena along rootlets and by the presence of caliche nodules. The change from marine to continental supratidal conditions is marked by a change in colour (grey versus tan/beige) and by pedogenetic features: incipient calcretes, rootlets or seatearths related to overlying coals. The overlying palustrine-lacustrine facies are characterized by irregularly alternating coals, carbonaceous mudstones, freshwater limestones and marls. The beige to characteristically hazelnut-brown coloured ('nocciola') limestones have been deposited in shallow, nearshore lacustrine environments (littoral carbonates). They consist of bioclastic and phytoclastic material: plant remains and skeletal debris of fresh-water molluscs (including limnic gastropods e.g. Planorbis, Paludina, Melanopsis; Cocozza et al. 1989), smooth-shelled ostracodes and charophyte gyrogonites. Lignite laminae are common and all intermediate lithologies exist between relatively pure, non-carbonaceous limestones and impure coals. Staining shows that the limestones consist exclusively of non-ferroan calcite. Strongly packed monospecific mollusc shell debris may account for the characteristic pseudopackstone texture. Although deep water facies have not been recorded, some limestones are poor in skeletal debris and display a varvoid texture. Dissolution residues reveal only a subordinate amount or even a lack of siliciclastic material (Fig. 7). The limestones contain numerous roots and there is evidence for subaerial exposure, such as the presence of rhizoliths, Microcodium, desiccation cracks, micro-karst phenomena and nodular fragmentation or 'micro-brecciation'. Marls are interbedded with the limestones. They are generally dark-coloured, carbonaceous, rooted and contain occasional shells (mollusc,

ostracodes) as well as pyritized charophyte gyrogonites. Individual coal seams never exceed lm in thickness, but coal-limestone associations build up sequences several metres thick. The coals are composed of leaf cuticles, spores, pollen and sub-ordinate algae. Petrographic analysis of several hundreds of samples gives an average of 73.3% vitrinite, 11% liptinite, and 5% inertinite (Fadda et al. 1994). The liptinites frequently contain alginite, whereas fusinite and semifusinite are common in the inertinites of the lower coal seams. Other physico-chemical parameters include: volatile matter content of 42%, vitrinite reflectance values of 0.45 to 0.5%, fixed carbon of 48 to 52%, average ash content of 10% and average S content of 6% (Fadda et al. 1994). The ash analysis shows a low silica ratio with high iron (24%) and sulphate (17%) content. The general lack of well-developed seatearths or rooted horizons and stump or stem horizons (Fadda et al. 1994) suggests that some of the Produttivo coals are allochthonous: they result from the reworking of plant remains from swampy-marshy zones into subaqueous, nearshore lacustrine areas. Moreover, the presence of alginite in most of the coal seams would indicate a partial algal origin. The palynomorph content of the coal-bearing strata is rather poor and badly preserved. The associations are dominated by herbaceous plant pollen typical of both warm palustrine-savanna and moderate steppe-prairie type environments (Cocozza et al. 1989). The good preservation of fresh-water mollusc shells and charophyte gyrogonites in the coals and the close association with carbonates suggest that water acidity was very low. Decimetric coquinas are sometimes interbedded with the coal-limestone sequence in the lowermost part of the Produttivo. These coarse mollusc packstones locally display erosional bases and contain coal clasts. They are almost exclusively composed of gastropod (Potamides) and bivalve (Cyrena) packstones, suggesting mixohaline environments (Cocozza et al. 1989). The scoured bases, orientation of the shells and indistinct grading of the coquinas point to a possible storminduced origin. For four selected lithostratigraphical intervals (A through D), cumulative thicknesses of lithology classes have been processed into isopach maps, using simple kriging contour routines. The contour maps (Fig. 8) cover an area of about 16 km 2, which approximately corresponds to the mining project area (Fig. 1). The following lithologies have been selected and grouped for processing: coals (including all dirty

Fig. 7. Borehole 67-91: Lithological-sedimentological log showing mineralogy, clay minerals (right) and interpreted depositional environment (left). A-D: lithostratigraphical intervals; S.M.: shallow-marine, R.M.: restricted marine; SB: subtidal; SB/IT: subtidal/intertidal, IT: intertidal, SP (m): (marine) supratidal, PL/LC: palustrine/lacustrine, PS: palaeosol; Ca: Calcite; Do: Dolomite; Qtz: Quartz; Cl: Clays; KF: K-Feldspar; K: Kaolinite; I: Illite; C: Chlorite; Sm: Smectite; (10-14C) and (10-14Sm): irregular mixed layers. Shaded lines represent allochtonous coals. Arrows correspond to upward shoaling trends. Left-hand side of log corresponds to carbonates, right-hand side of log to clastics and coals.

58

R. D R E E S E N E T AL.

o

,,.._.,,

o

8 o

e.-.

ff ..=

o

8

8~

EOCENE SULCIS COAL BASIN

59

60

R. DREESEN E T AL.

coals and carbonaceous mudstones), lacustrine limestones (including all marly limestones), and the clastics (including 'siltstones', 'sandstones' and 'conglomerates'). The regressive trend of the Produttivo is evidenced by a progradation, in time, of coal from the SW to the NE. Furthermore, a comparison of the coal and the limestone isopach maps reveals a good correlation between both lithologies, except for the earliest interval A. This suggests that the limestones are genetically related to the coals (corroborating the inferred lacustrine-palustrine environment). However, the limestones of interval A are not true lacustrine but rather paralic in origin: i.e. they were deposited under hyposaline, restricted marine conditions indicated by their microfacies and microfaunal content. Their maximum thickness shows a N N W - S S E to N N E - S S W orientation, which parallels or corresponds to the former coastline. The coals and the clastics are mutually exclusive, as shown by the location and orientation of their zones of maximum thickness. The area of maximum development of the clastics roughly corresponds to that of the paralic belt, which would corroborate their relation with the marine environment. The stacking of zones of maximum thickness of clastic rocks in the NW corner of the studied area (compare the successive siltstone/sandstone/conglomerate isopach maps in Fig. 8) might indicate the existence of a narrow depression or a preferential pathway, such as a channel or a 'slough', for the clastics in this area. The clastic bodies have a variable

thickness and lateral extent (Fig. 9): the small and thin lenticular sand bodies are interpreted as shallow marine channel or gully fills whereas the larger sand bodies correspond to stacked sand sheets. The latter have a lateral extent up to 1 km and a maximum thickness of 5 m.

Petrography and geochemistry Methods More than 100 thin-sections have been studied with conventional and cathodoluminescence (C.L.) petrography. C.L. petrography was carried out with Technosyn Cold Cathodo Luminescence Model 8200 Mark II. Operating conditions were 16-20 kV gun potential, 420 #A beam current, 0.05 Torr vacuum and 5 m m beam width. After careful petrographic characterization of individual authigenic minerals, a microscope mounted micro-drill assembly (with a drill-bit of 0 . 5 - 1 m m ) was used to obtain carbonate powders of 1-10mg for isotopic analysis. However, complete separation of individual phases was not always possible. Isotopic analysis of carbon and oxygen was performed on a Finnigan Mat delta E stable isotope ratio mass spectrometer. Carbonate powders were dissolved in >100% orthophosphoric acid at 25~ All data have been corrected following procedures modified from Craig (1957). The isotopic compositions are expressed as 0 values in per mil (%0) difference from the PDB

Fig. 10. (1) Photomicrograph of non-stained calci-dolomite. Dolomite and monocrystalline quartz rock. Locally a chert particle (ch) as well as some spherical chalcedony bioclasts (s) occur. Scale = 160 #m; PPL; (borehole 4/B 76~tr-47.50 m). (2) Photomicrograph of an euhedral quartz particle with carbonate (c) and lath shaped anhydrite (A) inclusions, surrounded mainly by monocrystalline quartz and algal micrites (M) particles. Notice that the latter are severely affected by compaction. Scale = 80 #m; PPL; (borehole 4/B 76~tr-38.30 m). (3) Photomicrograph of quartz particles consisting of different phases which locally possess a euhedral outline. A lath shaped internal arrangement is accentuated by the presence of elongated calcite inclusions. Locally some minute lath shaped anhydrite inclusions (A) occur. This particle is surrounded by micritic algal clasts. Scale = 80 #m; PPL; (borehole 43/90-433.25 m). (4) Photomicrograph of quartz particles with ghosts of pseudomorphosed lath shaped crystals displaying a felted texture. This particle is dominantly surrounded by dolomite as well as quartz particles. Notice that some of the latter possess a euhedral to subhedral outline. Furthermore some micrite algal particles (M) are present. Scale = 80 #m; NPL; (borehole 43/90-447.70 m). (5) Photomicrograph of different types of particles, namely a length slow chalcedony particle (CH) with dolomite inclusions (D), a laminated micritic algal particle (M) and a micrite particle with relict sponge spines (S). Scale = 80#m; PPL; (borehole 43/90-433.25 m). (6) Photomicrograph of well-rounded polycrystalline quartz particle surrounded by dolomite. Typical is the undulose extinction as well as the trails of minute inclusions within the quartz phases. In the lower left corner part of a monocrystalline quartz grain with sometimes lath shaped calcite inclusions occurs. Scale = 20 #m; PPL; (borehole 47/90-477.60 m). (7) Photomicrograph of intensely compacted micritic algal clasts next to dolomite and quartz particles. Notice the microsparitic nature (MS) of the algal clast on the left side of the picture. Scale = 85 #m NPL; (borehole 67/91-377.30 m). (8) Cathodoluminescence photomicrograph of Fig. 10.7. The fine tubular texture within the algal clast as well as recrystallisation textures become more apparent. Notice the presence of a zoned calcite particle with truncated edges between the algal clasts. Furthermore dull red dolomite particles are easily distinguishable from the non- to darkbrown luminescing quartz particles. Around some of the dolomite particles a dull luminescing cement (D1) is present. It precedes a deep red phase (D2). Scale = 85#m; CL; (borehole 67/91-377.30 m).

EOCENE SULCIS COAL BASIN

61

62

R. DREESEN ET AL.

international standard. Reproducibility, determined by replicate analysis of samples NBS 19 and NBS 20, is better than 0.1%o for oxygen and 0.05%o for carbon. No correction for dolomite or siderite dissolution by phosphoric acid has been applied.

Petrography of sedimentary particles A detailed study of the (litho-)calci-dolorudites and (litho-)calci-doloarenites of the Produttivo Formation revealed that the detrital grains mainly consist of quartz and carbonate (dolomite and calcite) particles (Fig. 10.1). Well rounded chert as well as feldspar particles (K-feldspar and subordinate plagioclase) are present in low concentrations (300 #m) pores.

Stable isotopes Table 1 is split in two parts, and gives the 013C and 0180 of the analysed samples. Part A groups all the samples which consisted of rather pure sedimentary or diagenetic phases, or where based on microscopic examination, the relative proportions of different contributing phases can be estimated. It was not possible to sample calcite I and the non-ferroan dolomite I seperately. In part B samples are grouped where such an estimation could not be carried out due to the presence of too many different components. An essential first step in diagenetic studies is the estimation of the original isotopic composition of marine water. This starting composition

67

can serve as a standard value against which the diagenetic products can be evaluated. Reported estimates for Lower Eocene marine carbonates vary around +0.5 + 5%o Ox80 and +2.3 • 0130 (bulk sediment data reported by Shackleton 1986). The coquina debris and its marine limestone matrix (Miliolitic Formation) which possess values of 0i80 of -5.0 + 0.3%0 and 013C of -1.30+0.05%o are clearly depleted with respect to Lower Eocene marine values. This also accounts for stable oxygen and carbon data from the Miliolitic Limestone of the Sulcis Basin reported by Perna et al. (1994) ( 0 1 8 0 : - 5 . 7 to -9%o and 013C: -0.6 to -3.3%o). Recrystallization by meteoric and/or warm fluids with involvement of depleted CO2, most likely derived either from soil-gas CO2 or from decarboxylation reactions within the coal layers of the Produttivo Formation are possible explanations. This seems also to account for most isotopic signatures of the calcarenites and other detrital calcite/dolomite dominated lithologies sampled in this study. These strata cluster within an area defined by 013C of -4.5 • and 0180 of -7.2 +0.8%o. Sample 400.00m however is more depleted in 0180 (-9.82%0). This may relate to the presence of minute calcite II veinlets and possibly to recrystallization due to interaction with calcite II bearing solutions. One of the larger calcite II veins analysed was collected from this sample. 013C and 0180 values of the glaebules respectively plot around -9.2%o and -5.4%o (Table 1 and Fig. 13). The influence of soil-gas CO2 in the soil formation is clearly reflected in the depleted 013C of these pedogenic carbonates (Salomons et al. 1978; Cerling 1991). The oxygen isotope signature is in agreement with a meteoric water dominated system. The few sampled siderites are characterized by a 013C varying between -0.5 to +2.8%0 and 0180 varying between -4.9 to -8.0%0. The carbon signature could be interpreted to reflect siderite formation in equilibrium with atmospheric CO2. However, based on the bacterial micro-textures observed under high magnification as well as on literature data (e.g. Curtis et al. 1986; Moore et al. 1992), this signature most likely reflects a mixture of different CO2 sources of which atmospheric CO2 could be one source. A depleted sulphate reduction CO2 type is less likely to be involved since these siderites occur in unit D where marine incursions less frequently occurred. This is also deduced from the virtual absence of framboidal pyrite. CO2 derived from bacterial fermentation could be involved, however this is not the only CO2 source since the carbon isotopic composition is less enriched in comparison to the + 15%o which

R. D R E E S E N E T AL.

68

Table 1. Oxygen and carbon isotope data of diagenetic and sedimentary components of the Eocene Sulcis Basin (FD: ferroan dolomite; NFD: non-ferroan dolomite)

013C

PART A

0180

Glaebules in claymatrix 374.00 Glaebules (pure)

-9.25 -9.29

-5.57 -5.35

Siderite (nodule centre) 359.9 Siderite (nodule edge) 358.90 Siderite nodule

+2.78 +2.38 -0.47

-7.98 -6.38 -4.97

400.00 Calcite vein 403.35 Calcite vein (with pyrite)

-4.51 -4.05

-10.46 - 11.16

403.35 400.00 394.80 394.80 390.40 383.20 377.60 363.38 355.70 355.40

-6.05 -2.30 -1.35 -1.25 -3.88 -2.67 -5.89 -4.45 -4.43 -3.59

-7.78 -9.82 -4.68 -5.29 -8.06 -7.13 -6.42 -7.10 -6.55 -6.42

+0.11 -8.34 +0.68 -8.82 -1.58 -1.81 -0.87 +0.11 -0.86 -0.70 -9.04 -10.96

-4.14 -7.95 -7.42 -7.62 -6.97 -7.44 -6.04 -5.62 -7.55 -8.56 -8.13 -8.33

-3.63 -4.16 -6.11 -4.40 -2.34 -3.67 -4.54 -3.44 -5.43 -5.78 6.69 -7.54 -3.05 -4.60

-6.13 -5.33 -6.44 -6.40 -4.21 -5.26 -7.62 -8.04 -7.01 -7.07 -8.34 -7.29 -7.57 -6.50

-3.30 -0.66 -1.87 -2.07

-7.01 -8.97 -5.10 -6.88

Ferroan limestone matrix Limestone matrix Bivalve shells + limestone (70% + 30%) Limestone around bioclasts Limestone matrix Limestone matrix Limestone components Limestone matrix Limestone matrix + < F D Limestone matrix, slightly ferroan

Ferroan dolomite matrix 360.30 Ferroan dolomite matrix 359.89 Ferroan dolomite matrix 357.70 Ferroan dolomite matrix (>80% FD) 355.40 Ferroan matrix between FD vein 355.00 Ferroan dolomite matrix (>90% FD) 355.00 Ferroan dolomite vein + 20% matrix 355.00 Ferroan dolomite vein (pure) 355.00 Ferroan dolomite vein (pure) 354.00 (Ferroan) dolomite vein 362.70 Non ferroan + ferroan dolomite vein 359.89 Non ferroan § ferroan dolomite vein PART B Limestone/dolomite matrix + FD 377.30 Dominantly FD+limestone/dolomite matrix 377.30 Limestone/dolomite + FD + NFD? 377.30 Dominantly FD + limestone/dolomite 377.10 Dominantly FD + matrix 377.10 FD + limestone § NFD? 375.29 Limestone matrix with FD vein 365.90 Dominantly limestone/dolomite matrix + FD 363.16 Dominantly limestone/dolomite matrix 362.70 Dominantly FD 361.75 Dominantly FD + dolomite matrix 358.90"Dominantly FD + limestone/dolomite matrix 358.25 Dominantly FD in organic rich mud 354.00 Dominantly FD + limestone/dolomite matrix ML-1 ML-2 ML-3 ML-4

Miliolitic Miliolitic Miliolitic Miliolitic

limestone limestone limestone limestone

(Perna (Perna (Perna (Perna

et et et et

al. al. al. al.

1994) 1994) 1994) 1994)

EOCENE SULCIS COAL BASIN

69 a13C

/

FERROAN DOLOMITE (GROUP 1)

SIDERITE T+2

_[+,

a180

-11

-10

-4

MILIOLITIC LIMESTONE

%

11"

.

-3

-2

-1

11=

CALCARENITE (CALCITE& DOLOMITEGRAINS)

A, 4, 9

CALCITEVEINS

FERROAN+ NON FERROAN DOLOMITE (GROUP2) ~

.~...- GI.AEBULES 9-10 9 ~= 9 A ~k 9 X 1~ 9

GLAEBULES SIDERITES CALCITEVEINS CALCARENITE FERROANDOLOMITE NON-FERROANDOLOMITE MILIOLITICLIMESTONE MILIOLITICLIMESTONESULClS BORENOLES MIXEDSAMPLES

Fig. 13. Plot of carbon and oxygen stable isotope data from the Produttivo Formation. is typical for the anaerobic (bacterial) carbonate reduction and fermentation processes (Irwin et al. 1977; Irwin 1980 and others). Ferroan dolomite veins as well as intensively ferroan dolomitized strata have been sampled at different stratigraphic levels within the Produttivo Formation. Their 013C-0180 plot into two distinct areas. Group I clusters around a 013C of - 1 +2%o and 9180 o f - 6 4 - 2 % 0 . The second group is characterized by depleted 013C values varying around -8.5 4- 0.5%o and 9180 values of -7.8 + 0.3%o. In fact this group clusters close to the values of the sampled non-ferroan dolomites II with even more depleted 013C values down to -10.96%o and with rather similar olSO-values. Whether both dolomite types are genetically

linked is not yet clear. It is therefore proposed that at least two post-compactional dolomitization stages should be differentiated. Both could be related to circulation of meteoric water, however their ferroan post-compactional and dolomitizing nature point to circulation of evolved fluids. According to their 013C signature depleted CO2 was not or only slightly involved in the group I ferroan dolomites, whilst in the group II ferroan + non ferroan dolomites, CO2 derived from decarboxylation reactions should be taken into consideration. The calcite II cements and veins are characterized by moderately depleted 013C values (-4.254-0.30%o) and highly depleted 9180 values (-10.80 + 0.40%o). Such depleted oxygen

70

R. DREESEN E T AL.

values are characteristic of high temperature fluids. However, fluid inclusion data are needed to correctly evaluate the significance of their isotopic signature.

Depositonal setting The Sulcis coals most probably originated as a response to rising sea level. They represent in fact the upper end member of a highstand system tract (Fig. 5). The coarse lag at the base of each clastic episode corresponds to a transgressive system tract followed by the intertidal-supratidal lower member of the highstand system tract. The lag is composed of reworked material, including various limestone intraclasts, silicified evaporites and dolomites. The latter possibly represent the only relicts of a lowstand system tract, which has been completely eroded and winnowed by hurricanes (?) before the next marine flooding event. A working model illustrating the successive stages in the development of the ideal parasequence of the Produttivo Formation is depicted in Fig. 14. It is interesting to note that the successive flooding events ('detrital episodes') within the Produttivo Formation apparently coincide with the main transgressive cycles (3th order cycles 2.3 to 2.6) of Haq et al. (1988) for the Lower Eocene (Ilerdian/Cuisian). Alternatively, the silicified evaporites have been eroded and reworked from emerged Palaezoic rocks (Cambro-Silurian basement) or Triassic rocks in the near hinterland and episodically swept into the fresh-water marsh. Within the Produttivo Formation two lithology types can be differentiated. Within the first type the allochthonous calci/doloarenites dominate. Here, particles clearly have been transported, however, most of them only over limited distances. The second autochthonous

lithology-type is dominated by the pure palustrine/lacustrine carbonates. Most of the coal layers do not occur in situ but limited transport is indicated (hypautochthonous coals). The absence of in situ evaporites, the limited development of microkarst and desiccation cracks and the fact that the successions are capped with coal horizons point towards sub-humid climatic conditions (Platt & Wright 1992). Root development within the autochthonous carbonates is extensive. The limited pedogenetic features, such as glaebules and 'micro-nodular' structures indicate occasional emergence but they become more frequent in the upper part of the Produttivo Formation. Well developed calcretes, terrestrial gastropods and desiccation breccias which reflect prolonged exposure are absent. All these features point towards a complex environment of marginal marine, brackish and fresh-water settings. The Florida Everglades provides a potentially useful modern analogue. This area is characterized by intensely vegetated fresh-water marshland, swamp and fresh-water to brackish lagoons. The coastal mangrove region may provide an analogue for the Sulcis coal swamp. The Everglades has a very low topographic gradient and minimal relief (1000 1001-1500 1501-2000 2001-2500 2501-3000 3001-3500 3501-4000 4001-4500 >4501 Total

123.2 4367.1 870.3 674.0 927.0 324.4 4.3 11.8 36.9 7339.0

1.6 59.5 11.9 9.2 12.6 4.4 0.1 0.2 0.5 100.0

265.7 4519.1 972.2 932.2 1105.3 401.0 28.5 31.8 118.6 8374.4

3.2 54.0 11.6 11.1 13.2 4.8 0.3 0.4 1.4 100.0

TURKISH LIGNITE DEPOSITS

99

Table 6. Areas of utilization for the Turkish/ignites

References

Consumption

%

Thermal power stations Domestic heating Industrial factories Internal consumption

67.4 16.5 15.7 0.4

AKGUN,F. & AKYOL,E. 1992. Palynostratigraphy of the coal-bearing Neogene deposits in Bfiyfik Menderes Graben, Western Anatolia. 1st. International symposium on Eastern Mediterranean Geology, Proceedings and Abstracts, Adana, Turkey. ALTAr, M., (~ELEBI, E. & FIKRET, H. 1994. Development of energy sector of Turkey and projections of supply and demand (1970-2010), 6th National Energy Congress. izmir, Turkey (in Turkish). INANER, H. 8r NAKOMAN,E. 1993. Lignite deposits of the western T~irkiye, Bulletin of the Geological Society of Greece, 28]2, 493-505. KAYA, O. & DiZER, A. 1984. Stratigraphy of Mengen Coal Basin, MTA Publication, No. 97/98 Ankara, Turkey (in Turkish). KOKTORK, A. 1994. Lignite Sources and Utilization in Turkey, Turkish Energy Day, 6th National Energy Congress, Izmir, Turkey (unpublished, in Turkish). MTA, 1993. Turkish Coal Inventory, Ankara (in Turkish). NAKOMAN E. 1971. Coal, MTA Educational Series No. 8, Ankara (in Turkish). - - 1 9 8 8 . Coal Deposits of Turkey, Postgraduate Lecture Notes, Izmir (unpublished, in Turkish).

machinery and equipment used in open cast operations mostly reflects the latest technologies. Draglines of various capacities are utilized in major open cast operations. Lignite is used mainly to generate electricity in thermal power station (67.4%), for domestic heating (16.5%), industrial factories (15.7%), and internal consumption (0.4%) (Alta~ et al, 1994). The lignites with low calorific values are generally consumed in power plants under state ownership. Private lignite companies usually supply lignite for domestic and industrial uses (Table 6).

The origin and properties of a coal seam associated with continental thin micritic limestones, Selimoglu-Divrigi, Turkey A. I. K A R A Y I G I T 1 & M. K. G. W H A T E L E Y 2

1Department of Geological Engineering, Hacettepe University, Beytepe-Ankara, Turkey 2Department of Geology, University of Leicester, University Road, Leicester LE1 7RH, UK Abstract: The Selimoglu coalfield is situated at the southeastern part of Divrigi, which is geographically distinct from the major coalfields of Turkey. A number of thin and lenticular coal seams and sedimentary rocks occur in the Selimoglu unit of the Ogulbey Formation of Upper Miocene age. Only one seam, which is produced by an underground method, is associated with continental thin micritic limestones that have a total thickness of about 150 cm. It has a macroscopically bright appearance and a working thickness of 50-90 cm (70 cm average). A total of 32 channel samples were collected from the mined seam for proximate, mineralogical and petrographic analyses. The results of proximate analyses on an air-dried basis show that the coal is characterized by low moisture content (1.68% average), high ash yield (24.04% average), high total sulphur content (up to 8.92%) and high calorific value (5606kcalkg-1 average). The coals average 65.5% vitrinite, 4.5% liptinite, 2.5% inertinite and 27.4% mineral matter. Desmocollinite is the dominant maceral in the vitrinite group and calcites in the whole-coal minerals. Carbonate minerals with irregular shapes are in general early-diagenetic, and occur in desmocollinites in all the samples. The micritic texture of the limestone shows both diagenetic and authigenic origin in subaquatic conditions with high pH, but organic debris is allochthonous in origin. The reflectance values of telocollinite (0.77% Rr) show a high volatile bituminous coal rank. The random reflectance of telocollinite and spectral maxima (625-661 nm) of sporinites, and proximate analyses reveal that the thermal history may have been affected by volcanic activity that occurred in the coal field.

Most Miocene coals in Turkey are of lignite or subbituminous coal rank and are generally associated with claystone, marl and rarely sandstone. However, there is a lack of information about this type of formation in Turkey. The coal seam, which is produced in an underground mine, forms a useful example to assess the formation of coal associated with continental micritic limestones in the Selimoglu coal field. This paper summarizes the geological setting and stratigraphy of the coal field, and presents proximate analyses, the mineralogicpetrographic composition, spectral properties of some liptinite macerals and the rank of the coal seam. The Selimoglu coal field is geographically remote from the major coalfields of Turkey, and is situated 20 km southeast from Divrigi (Fig. 1). About 30-50 t/day of coal is produced in Coal Mine II (for location see Fig. lb and lc). The region containing the coal field was first investigated by Wedding (1965), who studied the stratigraphy of the region. This was followed with studies by Keskin et al. (1984), who revised the geological map and determined a similar stratigraphy for the coal field as that of Wedding

(1965). The basic geological characteristics of the Divrigi region, including the northern small part of the study area have been investigated by Tunc et al. (1991). This present paper represents an extension of a preliminary study by Karayigit (1993).

Methods of study Representative rock, coal and coaly bituminous shale samples were collected; from which thin sections of rock samples were prepared to determine the petrographic composition. X-ray powder diffraction (XRD) analyses were performed to determine the mineralogical composition of limestones. In addition, for age determination, limestones, marls and claystones were sieved for ostracoda, and palynological investigations were made on coals and coaly bituminous shale. A total of 32 (31 samples from Coal Mine II and 1 sample from Coal Mine I for locations see Fig. lc) fresh, channel coal samples that represent the full thickness, including dirt bands ( < l c m thick) within the seam, were

From Gayer, R. & Pe~ek, J. (eds), 1997, EuropeanCoalGeologyand Technology, Geological Society Special Publication No. 125, pp. 101-114.

102

A. I. K A R A Y I G I T

& M. K. G. W H A T E L E Y

Fig. 1. (a) The stratigraphical sequence of the Selimoglu coal field, (b) simplified geological map around the coal mines, (e) some macroscopical seam sections, lateral extend of the mining seam and the underground map on a more detailed geological map (modified after Karayigit 1993).

CONTINENTAL MICRITIC LIMESTONES, TURKEY collected from the coal seam for proximate, mineralogical and petrographic analyses. Proximate analyses (moisture, ash, volatile matter) as well as total sulphur analyses and calorific values of all samples were performed and the reported results expressed as weight percentages, except calorific values, and made in accordance with the ASTM (1991) procedure. The whole-coal minerals of all coal samples were identified by X-ray powder diffraction (XRD). After identifying all peaks on the every X R D diagram, the net area under each diagnostic peak was determined and converted to a percentage for each mineral. In order to determine the chemical composition of carbonates and some silicate minerals, two coal briquettes were selected and examined on a JEOL 8250 electron microprobe. Maceral analyses were determined using a reflected light microscope (Leitz MPV II) with a 32x objective and oil immersion (noil :1.518) on polished briquettes. Ordinary white light from a tungsten lamp and blue light, K510 barrier filter for determination of liptinite macerals were used for illumination. The analyses are based on counting 500 points on each sample and the reported results are expressed as volume percentages of the various macerals and minerals. Petrographic constituents of the coals were determined using the information given by ICCP (1963; 1971) and Stach et al. (1982). Random reflectances of vitrinite (telocollinite and desmocollinite) were measured with a minimum of 50 points on every briquette using the same microscope with a 50• oil immersion objective, sapphire (0.551%R) and glass (1.23% R) standards for calibration. During spectral fuorescence emission measurements of liptinite mecerals, a Leitz MPVSP microscope fitted with a high-pressure 100WHg light source, a BG38 and a BG1 filter, and a K460 barrier filter was used. Spectral intensities in the range of 460-700 nm were measured and corrected spectral intensities were automatically produced using a connected computer. Some numerical parameters, such as relative intensities, wavelength of maximum intensity ()~max) and the logarithmic ratio (Q) of the relative intensity of red (650nm) and green (500nm), were then generated from them. The principles, basic calibration techniques and some applications of measuring fluorescence in geological samples are documented in the work of Jacob (1964; 1973), Pflug (1966), Ottenjann et al. (1975), Teichmtiller & Ottenjann (1977), Teichmiiller & Wolf (1977), Robert (1981), Crelling (1983), and Teerman et al. (1987).

103

Geological setting and stratigraphy The location map of the study area, the stratigraphical sequence of the coal field and simplified geological map around the coal mines are shown in Fig. 1. The Giines ophiolite forms the basement in the coal field (Fig. la). It is of Upper Cretaceous age and contains generally serpentinized rocks (Tunc et al. 1991). The Ogulbey Formation rests unconformably on the basement. It has an extensive areal distribution and is subdivided into three informal units; from base upward, Hantepe unit, coal-bearing Selimoglu unit and Hanioglu unit (Fig. 1a). The Hantepe unit, which has an average thickness of 90m, contains mainly thin bedded lacustrine micritic limestones (Fig. la) that are composed of calcites. The Selimoglu unit only hosts coal seams throughout the coal field and the thickness can reach up to a maximum of 295 m. In the lower part of the unit, reddish mudstones and minor sandy limestones and thin sandstones (=4o-~30n~ 2 0 -

rr 20

100

0 450

5O0

550

6O0

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450

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Fig. 5. Typical examples of fluorescence spectral curves of some liptinite macerals from the mining seam in the Selimoglu coal field.

Most Miocene coals in Turkey are of lignite or subbituminous coal rank, whereas the investigated coals have a high volatile bituminous rank. The results obtained from %Rr of telocollinite and spectral maxima (625-661 nm) of sporinites, the low moisture content (1.68% average), high calorific values (5606kcalkg -1 average) and agglomerating characters of the coals suggest that the thermal history may

have been affected by the volcanic activity that occurred in the coal field.

Conclusions In the Selimoglu coal field, only one coal seam, which is associated with thin continental micritic limestones, is exploited by underground mining.

112

A. I. KARAYIGIT & M. K. G. WHATELEY

It has a macroscopically bright appearance and a working thickness of 50-90cm (70 cm average), and it was probably accumulated in a small, shallow lake or pond on an alluvial plain. The coal seam is characterized by low moisture content (1.68% average), high ash yield (24.04% average), high total sulphur content (up to 8.92%) and high calorific value (5606kcal kg -1 average). The maceral and mineral matter contents on a mineral-matter free basis average 90.5% vitrinite, 6.0% liptinite and 3.5% inertinite. It is thought that peat formation may have been developed in subaquatic conditions with high pH and low Eh and an accelerated bacterial activity. Most Miocene coals in Turkey are of lignite or subbituminous coal rank, whereas the investigated coals are of a high volatile bituminous rank. It is possible that the thermal history may have been affected by volcanic activity that occurred in the coal field. We acknowledge the Turkish Scientific and Research Council (TUBITAK) for supported first writer's research project (TBAG/YBAG-948), the British Council of Turkey who supported Karayigit's expenses in UK and for the help given by S. Toprak with the microscope for spectral analyses and C. Tunoglu with osctracod studies. Our thanks also to R. Wilson for the help with the electron microprobe studies.

References ASTM 1991. Annual Book of A S T M Standards, Gaseous Fuels; Coal and Coke. 1916 Race Street, Philadelphia, PA 19103, 05.05. CASAGRANDE, D., SIEFERT, L., BERSCHINSKI, C. & SUTTON, N. 1977. Sulfur in peat forming systems of Okefenokee Swamp and Florida Everglades: Origins of sulfur in coals. Geochimica et Cosmochimica Acta, 41, 161-167. COHEN, A. O., SPACKMAN, W. & DOLSEN, P. 1984. Occurrence and distribution of sulfur in peatforming environments of southern Florida. International Journal of Coal Geology, 4, 73-96. CRELLING, J. C. 1983. Current uses of fluorescence microscopy in coal petrology. Journal of Microscopy, 132, 132-147. GIERLOWSKI-KORDESH, E., GOMEZ FERNANDEZ,J. C. & MELI~NDEZ, N. 1991. Carbonate and coal deposition in an alluvial-lacustrine setting: Lower Cretaceous (Weald) in the Iberian Range (east-central Spain). International Association of Sedimentology, Special Publication, 13, 109-125. GIVEN, P. H. & MILLER, R. N. 1985. Distribution of forms of sulfur in peat from saline environments in the Florida Everglades. International Journal of Coal Geology, 5, 397-409. HAGEMANN, H. W. & WOLF, M. 1989. Paleoenvironments of lacustrine coals- the occurrence of algae in humic coals. In: LYONS, P. C. & ALPERN, B.

(eds) Peat and CoaL" Origin, Facies, and Depositional Models. International Journal of Coal Geology, 12, 511-522. ICCP, 1963; 1971. Internationales Lexikon Ffir Kohlenpetrologie. Centre National de la Recherche Scientifique 15, Quai-Anatole-France, Paris. JACOB H. 1964. Neue Erkenntnisse auf dem Gebiet der Lumineszenmikroskopie fossiler Brennstoffe.Fortschr. Geol. Rheinld. u. Westf. 12, 569-588, Krefeld. 1973. Kombination yon Fluoreszenz-und Reflexions-Mikroskopphotometrie der organischen Stoffe yon Sedimenten und Boden.-Leitz-Mitt. Wiss. u. Techn. VI, 1 21-27, Frankfurt. KARAYIGIT, A. I. 1993. Geological and sedimentological investigation of the Selimoglu (Divrigi-Sivas) basin, and chemical-petrographic properties of the coals. Project no: TBAG 948/YBAG 15, TUBITAK, Earth Sciences Research Grant Committee [in Turkish]. KESKIN, E., GI3RSOY, N. & GI2RSOY, B. 1984. Geology of the Sivas-Divrigi (Selimoglu-Mursal) area. MTA Report No: 7616. [In Turkish] OTTENJANN, K., TEICHMOLLER,M. & WOLF, M. 1975. Spectral fluorescence measurements of sporinites in reflected light and their applicability for coalification studies. In: ALPERN, B. (ed.) P~trographie de la MatiOre Organique des Sediments, Relation avec la Paleotemperature et le Potentiel Petrolier, Paris, 67-95. PFLUG, H. D. 1966. Fluoreszenzmessungen an Gesteinen und Fossilien.-Leitz-Mitt. Wiss. u. Techn. II, 6 Frankfurt, 183-188. ROBERT, P. 1981. Classification of organic matter by means of fluorescence; application to hydrocarbon source rocks. #International Journal of Coal Geology, l, 101-137. ROBERTS, D. L. 1988. The relationship between macerals and sulphur content of some South African Permian coals. International Journal of Coal Geology, 10, 399-410. STACH, E., MACKOWSKY,M.-TH., TEICHMULLER,M., TAYLOR, G. H., CHANDRA,D. & TEICHMf3LLER,R. 1982. Stach's Textbook of Coal Petrology. Gebruder Borntraeger, Berlin. TEERMAN, S. C., CRELLING,J. C. & GLASS, G. B. 1987. Fluorescence spectral analysis of resinite macerals from coals of the Hanna Formation. Wyoming, USA. International Journal of Coal Geology, 7, 315-334. TEICHM(]LLER, M. 1974. Uber neue Macerale der Liptinit-Gruppe und die Entstehung des Micrites.Fortschr. Geol. Rheinld. u. Westf 24, 37-64. OTTENJANN, K. 1977. Liptinite und lipoide Stoffe in einem ErdO'lmuttergestein.-ErdG1 u. Kohle, 30, 387-398. -~ WOLF, M. 1977. Application of fluorescence microscopy in coal petrology and oil exploration. Journal of Microscopy, 109, 49-73, London. TUNG, M., OZCELIK, O., TUTKUN, Z. & GOKCE, A. 1991. Basic geological characteristics of the Divrigi-Yakuplu-Ilic-Hamo (Sivas) area. Doga Turkish Journal of Engineering and Environmental Sciences, 15:2, 225-245. [In Turkish]

C O N T I N E N T A L MICRITIC LIMESTONES, T U R K E Y UNSWORTH, J. F., BARRATT, D. J. & ROBERTS, P. T. 1991. Coal quality and combustion performance. An International Perspective. Coal Science and Technology, 19, Elsevier, Amsterdam.

113

WEDDING, E., 1965. A report on the Divrigi (Sivas) lignite basin. Directorate of Mineral Research and Exploration, Report No: 3774, [in Turkish translation].

Chemical characteristics, mineralogical composition and rank of high sulphur coking coals of Middle Miocene age in the G6kler coal field, Gediz, Turkey A. I. K A R A Y I G I T l & M. K. G. W H A T E L E Y 2

1Department of Geological Engineering, Hacettepe University, Beytepe-Ankara, Turkey 2 Department of Geology, University of Leicester, University Road, Leicester LE1 7RH, UK Abstract: Most Miocene coals in Turkey are of subbituminous to lignite rank. The G6kler

coal field in the western part of Turkey contains mainly high sulphur coals of bituminous rank. The chemical characteristics, mineralogical composition and rank of high sulphur coking coals of Middle Miocene age in the coal field are investigated for the first time. A total of 46 channel and core samples were collected from underground mine workings and from boreholes drilled in the coal field. The results of the proximate analyses as well as total sulphur analyses and calorific values on an air-dried basis show on average 1.2% moisture, 22.9% ash, 34.6% volatile matter, 6.9% total sulphur contents and 5850kcalkg -1 calorific value. X-ray powder diffraction studies of the coal samples on an air-dried basis show quartz, pyrite and calcite to be the dominant minerals; kaolinite, hydromuscovite, dolomite, gypsum, iron sulphate hydrate and rarely illite/smectite and feldspar constitute the remainder. Secondary calcite in random fractures surfaces of the coals is especially abundant in samples obtained from an area adjacent to the fault zones. The mean random reflectance values (%Rr) of telocollinite vary between 0.50 and 0.95%. These values show that the rank can be determined as a high volatile bituminous stage. In addition, these coals can form isotropic coke. Fluorescence intensities of sporinite are weak to very weak. The mean random vitrinite reflectance values within the coal field generally increase towards southern parts of the coal field. It is thought that this increase can be related to the recent hydrothermal antimony mineralization in the southeastern parts of the coal field.

The coal field is located east of Gediz in the northwestern part of the Muratdagi region (Fig. 1). In Turkey, the coal and coal-bearing strata have been studied extensively by the General Directorate of Mineral Resource and Exploration (MTA) and Turkish Coal Enterprise. Most Miocene coals of Turkey, for example Krtahya-Seyit6mer and Tuncbilek, Canakkale-Can, Manisa-Soma, Mugla-Yatagan and Ankara-Beypazari are of subbituminous to lignite coal rank depending on their chemical properties with calorific values which range from 1900 to 3500kcalkg -1. The investigated G6kler coals have a calorific value greater than 5200kcalkg-aand sulphur contents of more than 5% according to unpublished reports prepared by MTA. The Gediz region contains important mineral deposits like borax and antimony, as well as coal deposits. Some studies on the regional geology, coal geology and antimony mineralization have been made by Atabek (1939), Kalafatcioglu (1961), Akkus (1962), Lebktichner (I965), G6kmen (1970), Grin (1975), Bing61 (1977), K6ksoy & Ileri (1977), G6kce (1987), K6ksoy et al. (1987) and Aral (1989). The stratigraphy, petrological properties and geochronology of

rocks of the Muratdagi region were investigated by Bing61 (1977) in detail, and also, for the first time, Bing61 determined the age of the G6kler coals as Middle Miocene age using palynological studies. G6kce (1987) investigated the geology of the antimony mineralization found in the Muratdagi region. He proposed that the antimony mineralization formed from the hydrothermal solutions which are still precipitating antimony at the present time. Aral (1989) indicated that all host rocks were first strongly silicified and open spaces were lined with crystalline quartz prior to mineralization. Mineralization is of two types: antimonite with pyrite and marcasite as in the G6yntik mine, and antimonite with no other sulphides as in the Derek@ mine including the Sakarciburnu and Karciolukpinari mineralizations (Fig. 1). Mercury minerals are absent. Trace amounts of arsenopyrite and sphalerite are present at the G6ynfik mine. Gangue minerals observed in both mineralization stages are quartz, chalcedony, opal, calcite, clay minerals, and fuchsite. Major secondary antimony minerals are antimony oxides such as valentinite, cervantinite, kermesite, and metaantimonite (Aral 1989). The detailed geology and economic potential of the

From Gayer, R. & Pe~ek, J. (eds), 1997, European Coal Geology and Technology, Geological Society Special Publication No. 125, pp. 115-130.

116

A. I. K A R A Y I G I T

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HIGH SULPHUR COKING COALS, TURKEY northeastern part of the coal field was studied by K6ksoy et al. (1987), and they proposed the generalized stratigraphical sequence of the coal field (Fig. 2). In the coal field, total coal production is about 1 Mt per year, which is sold mainly to cement

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factories. The overall objective of this study was to determine the chemical properties, mineralogical composition and rank of the high sulphur G6kler coals, and explain why this coal, which has high calorific values and swelling indices between 5 and 8.5, is used for industrial purposes.

EXPLANATION Alluvium Gray-white sandstone with cross-bedding and sericites UNCONFORMITY

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118

A. I. KARAYIGIT & M. K. G. WHATELEY

Geological setting Rocks which range in age from Jurassic to Quaternary crop out in the Muratdagi region. In this region (Fig. 1), the Asagibelova Formation of Jurassic age, Muratdagi Melange of Cretaceous age, Paleocene Baklan Granite, Miocene Karacahisar volcanics (mainly rhyolite) and coal-bearing G6kler Formation, Pliocene Karsakatepe deposits and Quaternary G6cfiktepe sediments and alluvium were identified by G6kce (1987). The Karacahisar volcanics were also considered as Middle Miocene age and were deposited contemporaneously with the coalbearing sediments in the Muratdagi region (G6kce 1987). However, our field studies have failed to locate the volcanics in the coal field. In the basement immediately below the coal field, serpentinized mafic and ultramafic rocks, metadetrital rocks, that consist mainly of quartz and muscovite, and different types of limestone

and marble of the Muratdagi Melange crop out. The bedding dips of the G6kler Formation are 30-50 ~ at the boundary of basement rocks, and 10-15 ~ below the Karsakatepe deposits. All the basement rocks and the coal-bearing G6kler Formation were cut by a number of normal faults which strike NW-SE, and by less frequent strike-slip faults cutting the normal faults (Fig. 1) (G6kce 1987). In the northeastern part of the coal field a small syncline and anticline were determined from underground maps and shown on iso-reflectance map (see Fig. 8). Tectonically the area is still active as evidenced by the occurrence of strong earthquakes in the region; the last one occurred on March 28, 1970. The coal seams are located at the base of the G6kler Formation (Fig. 2), and examples of their macroscopic seam sections are shown in Fig. 3. There are two coal seams, the upper Bfiyfik and the lower Kticfik seams. They are separated by about 3 m of black claystone and

(roof)

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HIGH SULPHUR COKING COALS, TURKEY brown to dark brown clayey dolomitic limestone with ostracode that is laterally extensive and 50-100 cm thick (Fig. 2). The presence of clayey dolomitic limestone as an intra-seam unit is some indication of limited acid conditions during peat accumulation. Towards the coal field margins this parting interval gradually decreases and the coal seams amalgamate into a single coal seam. In this study, this single seam, coal seams in some boreholes and some undefined coal seams in the underground mines which cannot clearly be differentiated are referred to as the unnamed seam (Fig. 3). The B~iyiik seam appears to be dull because of black claystone partings in the seam (Fig. 3). The Kticfik seam is bright and contains less mineral partings than the Btiytik seam (Fig. 3). The Biiytik and Kfictik seams average 170 cm and 120 cm thick, respectively. The floor rock of the Ktictik seam is green claystone that includes rare sericites. The roof rock of the Bfiyiik seam is claystone-marl with common sericite.

Methods A total of 46 channel and core coal samples were collected from the Grkler coal field (for sample locations, see Fig. 8). Thirty seven samples were collected from the underground mine workings and 9 from core samples from the 6 boreholes. All samples were mechanically crushed to 1 mm size and split into two subsamples (ASTM 1991). One sample was used for petrographic briquette preparation and embedded in cold setting epofix resin, and then polished. The other was further reduced to 60 mesh (250#m) for proximate analysis (moisture, ash and volatile matter) as well as total sulphur analysis and calorific value of all samples on an air-dried basis. In addition, for some evaluations, volatile matter and calorific values on a dry, ash-free basis were calculated from the results on an airdried basis. Sulphur forms and Free Swelling Index (FSI) tests were determined on only six samples selected from the samples. The analyses were made according to the ASTM (1991) procedure and presented as weight percentages, except calorific values. Random reflectances of the maceral vitrinite group telocollinite were measured at a minimum of 50 points on every coal polished briquette (ICCP 1963; 1971; Stach et al. 1982). A Leitz MPV II microscope with a 50x oil immersion (n:1.518) objective, sapphire (0.551%R) and glass (1.23%R) standards for reflectance calibration were used. During spectral fluorescence measurements of some liptinite macerals, a Leitz

119

MPV-SP microscope equipped with a highpressure 100WHg light source, a BG38 and a UG 1 filter, and a K460 barrier filter was used. This microscope system was computerised so that spectral intensities in the range of 460-700nm could be measured and corrected spectral intensities automatically produced. Some numerical parameters, such as relative intensities, wavelength of maximum intensity (Amax) and the logarithmic ratio (Q) of the relative intensity of red (650nm) and green (500 nm), were then generated from them. The principles, basic calibration techniques and some applications of measuring fluorescence in geological samples are given by Jacob (1964; 1973), Ottenjann et al. (1975), Teichmtiller & Ottenjann (1977), Teichmtiller & Wolf (1977), Crelling (1983) and Teerman et al. (1987). All coal samples on an air-dried basis, except two samples with insufficient coal, were analysed by X-ray powder diffraction (XRD) methods. After identification of the whole-coal minerals on each XRD diagram, the nett area under each diagnostic peak for every mineral was determined and then the nett area value was converted to a percentage. In order to determine the chemical composition of some silicate minerals, two coal polished briquettes were selected, one from the Btiyfik (sample no: GM-10) and one from the Kticfik (sample no: C-94) seams, which were examined on JEOL8250 electron microprobe. The mineralogic composition (by weight percentage) determined on the electron microprobe was grouped according to our interpretation of the minerals. The information given by Newman & Brown (1987) was used for interpretation of the clay minerals by their chemical composition.

Results and discussion Chemical character&tics

Table 1 summarizes the results of the chemical characteristics and XRD analyses on an airdried basis and random reflectance measurements of all coal samples. In addition, the histograms of some analytical results are shown in Fig. 4. The moisture contents of the coals on an airdried basis are low and average 1.2% (Table 1). In addition, it was determined that the moisture content of the coals on an as-received basis is less than 5% according to unpublished reports of the coal mining companies. The ash yields show a broad variation ranging from 10.951.2% but they are generally less than 40%. The

120

A. I. KARAYIGIT & M. K. G. WHATELEY

Table 1. The chemical characteristics, mineralogical composition and vitrinite reflectance measurements of the Bfiyfik, Kficfik and unnamed seams in the G6kler coalfield ii

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0.76-0.74% Rr at 86-3; for location see Fig. 8). This shows that the parting sediments (3 m thick) between the two coal seams do not clearly influence the reflectance values. Figure 8 shows the iso-reflectance map of the coal field. Sample locations, reflectance values, faults and folds,

which are determined from a number of underground mine maps, and antimony mineralization in the Deliktas and Karacatepe areas also illustrated on the map. The iso-reflectance values for the seams over the whole coal field in general increase toward southern parts of the

128

A. I. K A R A Y I G I T & M. K. G. W H A T E L E Y

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PLIOCENE COAL FACIES AND LITHOTYPES IN ROMANIA

135

forest areas are dominated by Salix, Populus, Alnus and Betula, the Pliocene swamps forest

Table 1. The main physical and chemical characteristics of the lithotypes of the Olternia.

palaeophytocoenoses

Lithotype

were

dominated

by

Byttneriophyllum tiliaefolium, Salix ssp., Glyptostrobus europaeus, as well as other tree species. Because rainfall distribution controls various factors (such as swamp bottom morphology, annual rainfall quantity, evapotranspiration etc.), the areas occur as more or less parallel bands. The general aspect of the vegetation was that of a huge mosaic such as that presented by McCaffrey & Hamilton (in Cohen et al. 1984), for the Okefenokee swamp map of the southeast United States.

The main coal facies and the lithotypes According to Ticleanu & Biloianu (1989) the Pliocene coals in Oltenia contain the following facies: Sequoia abietina forest, swamp deciduous forest, Carex spp. grassy marsh, swamps with Glyptostrobus, reed swamps, floating vegetal formation and aquatic vegetation. Considering the fact that the first facies played an insignificant role in the coal-generating phytomass constitution and the sixth one led only to coaly clays, in this study we shall refer only to the remaining facies which constitute those of real significance, together with an addititional facies - aquatic macrophyte prarie. To describe the primary characteristics of coal layers in each coal facies we have used Teichmfiller's method (in Stach et al. 1982).

The coal faciesmgrassy marsh Carex ssp. Plant communities: palaeophytocoenoses with Carex ssp. (Carex flagellata, Carex cf nigra etc.) Associated dements: Scirpus rnaeotica, Cladium mariscus, Cladium palaeomariscus, Sparganium neglectum, Najas pliocenica, Butomus umbelatus, Oenanthe aquatica, Trichosanthes fragilis, Pedicularis sp., Lythraceae ( ?Lythrum salicaria), etc. Most of these taxa are still living today and examples are found in actual Carex ssp. swamps in Romania (Pop 1960). In the palustrian vegetation in the Danube Delta, Popescu et al. (1981) have identified the association with

Aanh (%)

Vd (%)

Xylite 1.26-3.35 47.7-68.4 Xylitic coal 8.58-17.82 39.0-52.2 Weak xylitic 16.79-28.0 36.2-46.9 coal Detrital coal 22.11-48.45 27.8-38.8

Qd (kcal/kg) 5042-6034 4340-5378 3874-4871 2503-4012

Aanh, Anhydrous ash; V~ Volatile matter (air-dried basis); Qa Upper calorific value. In the first stages of the evoluion of the Carex swamp's vegetal cover, there were only small clumps of bushes of Salix cinerea and Salix pliocenica distant from the open water but they developed into bigger and bigger clusters, as they grew nearer to the central open water area of the swamp where they occurred beside Byttneriphyllum tiliaefolium, Nyssa, Glyptostrobus, etc. Palaeobiotope: floodable areas, but only in the first stages of vegetation evolution. Type of deposition: mainly autochthonous, partially hypautochthonous by vegetable remains brought by floods and less allochthonous (pollen, leaves fragments and fruits brought by wind). Depositional milieux: telmatic. Environmental characteristics: the peat is generated especially by roots and less by aerial remains of plants, deposited under aerobicanaerobic conditions with a moderate to weakly acid pH(5.0-6.8), rarely from weak acid to neutral (6.0-7.2), and extremely rarely in an alkaline environment. Lithotype: detrital coal, i.e. a groundmass with a fine detritic texture, more or less layered, more than 50mm thick, frequently with more than 30% ash content (Table 1). According to Pop (1960) the actual Carex peat contains more than 10% ash, and where flooded, this percentage increases because of the mineral material suspended in water. We consider that transformation of peat into lignite can lead to a relative enrichment of the ash content up to 30%. The petrographical composition of the detrital coal lithotype shows its high humodetrinite content (Table 2).

Claudietum mirisci. The presence of taxa that generate actual phytocoenoses ( Carecetum, Scirpetum and Claudictum) and the relatively high density of their seeds in the clays and the clayey silts that accompany the coal layers prove the development on large areas of coal facies of swamps with sedge (Carex ssp.).

The coal facies---deciduous forest Plant communities: Palaeophytocoenoses with Byttneriophyllum tiliaefolium, Byttneriophyllium tiliaefolium-Glyptostrobus europaeus, Salix ssp.Glyptostrobus europaeus, Salix ssp. (Salix abla, Salix fragilis, Salix grandifolia, etc.).

136

N. TICLEANU & D. DIACONITA,

Table 2. Petrographical composition of the Pliocene coals between the Danube and the Amaradia Valley after Bitoianu (in Ticleanu et al. 1989, 1992).. Group of macerals Ubgroup of erals

Huminite % Humotelinite

Humodetrinite Humocollinite

68.2-87.0 49.0-49.6 22.0-27.8 8.0-18.5

8.0-12.7 25.8-32 51.8-54 59.0-61.7

Liptinite (%)

Inertnite (%)

0.15-0.20 1.30-3.0 1.80-3.5 1.10-1.5

0.31-1.2 2.40-3.2 2.70-4.4 2.07-4.2

Lithotype xylite xylitic coal weak xylitical coal detrital coal

Associated elements: Acer tricuspidatum, Populus populina, Nyssa disseminata, Liquidambar europaeum and Carya cf. aquatica. Palaeophytocoenoses with Byttneriophyllum tiliaefolium, Glyptostrobus europaeus and Nyssa were located in the central areas of the swamp, and Salix ssp. in the marginal ones. Palaeobiotope: seasonally flooded areas. Type of deposition: frequently autochthonous, rarely hypautochthonous, and extremely rarely allochthonous (pollen, flying fruits). Depositional milieux: telmatic. Environmental characteristics: acid pH (3.5-5), deposited in aerobic-anaerobic conditions, to explain the rapid loss of most of the cellulose. Lithotypes: detrital coal, weak xylitical coal and rarely xylite coal. The weak xylitic coal was probably generated in the internal part of the seasonally flooded area, to the limit of the almost permanently flooded area, from palaeophytocoenoses with Byttneriophyllum tiliaefolium-Glyptostrobus europaeus and Salix ssp.-Glyptostrobus europaeus. In the same areas a very small part of the lithotype xylite also accumulated, included in detrital coal, resembling rare xylite lenses and bands with more than 50 mm thick. Generally, the ash content is relatively low, because of the protection granted by the surrounding palaeophytocoenoses against water with suspended clay content. The coal facies--forest swamp with Glyptostrobus Plant communities: palaeophytocoenoses with Glyptostrobus europaeus. Associated elements: very rare Taxodium dubium and Nyssa disseminata representing Miocene relicts. In open horizontal structured palaeophytocoenoses, trees were scarce, and between them were areas covered by water, even when the water level was at its lowest. In these prairie

0.1-0.13 0.6-0.7 0.3-1.3 0.2-3.7

areas occasional Stratiotes dacicus were found. This explains the relatively high frequency of seeds of this species in the xylitic coal. Surrounding Glyptostrobus europaeus trunks, and between these trunks and pneumatophores fern bushes (Osmunda regalis) were growing similar to Osmunda lignitum (Petrescu & Givulescu 1986), in Chattian swamps in the Petro~ani Basin. The role of Glyptostrobus europaeus species in the genesis of coals, has been treated in many papers. The most recent is the paper by Boulter et al. (1993). Palaeobiotope: almost permanently flooded areas, where water withdraws for only one or two months in a year. Type of deposition: mainly autochthonous. Depositional milieux: telmatic to subaquatic (limnic). Environmental characteristics: in closed horizontally structured palaeophytocoenoses (pure Glyptostrobus forest) the pH was probably low (3.5-5) and in open structured ones the pH was higher but still weakly acidic (5.6--6.6) and less probably neutral (6.8-7.2), as in modern swamps with Stratiotes aloides, the modern equivalent of Stratiotes dacicus species. Considering that the palaeophytocoenoses with Glyptostrobus europaeus were covered by water between ten and eleven months in a year, the plant material accumulated under mostly anaerobic conditions. Lithotypes: xylitic coal, xylite and weak xylitical coal. The xylitic coal lithotype is composed of alternating bands of fine coal mass, weakly banded, and bands and lenses of fossil wood (xylite) both less than 50 mm thick. The xylitic coal is second in importance (30% of the entire reserves) after detrital coal in the soft brown coals in Oltenia. Many coal layers consist only of this lithotype. Pieces of charcoal (inertinite) with a variety of different sizes occur relatively frequently, in the detrital of xylitic coal. In our opinion, these

PLIOCENE COAL FACIES AND LITHOTYPES IN ROMANIA show the presence of frequent natural fires in the forest swamp. These fires have played the same role in the Pliocene swamps as they do in modern swamps for the vegetation in Okefenokee, as shown by Izlar (in Cohen et al. 1984). The ash content of the xylitic coal lithotype is relatively low, because the clayey material is kept out by the surrounding palaeophytocoenoses. The ash content of the xylitic coal lithotype is also proportional to the amount of xylite. The ash content xylite is very low (Aanh: 1.26-3.35%) and is of primary origin (Table 1). Another important lithotype generated in the same facies is xylite that represents between 5 and 20% of entire coal volume, and is represented by lenses and bands that can reach up to a few meters long and 50-350 mm thick, sometimes even more. More than 80% of the xylite represents branches, trunks and roots of Glyptostroboxylon tenerum, identified by Petrescu (oral communication). The xylite lithotype is characterized by the highest humotelinite content (Table 2).

The coal facies--reed swamp Plant communities: palaeophytocoenoses with Phragmites oeningensis and with Typha latissima. Associated elements: Sparganium noduliferum, Stratiotes dacicus, Butomus umbelatus, Najas lanceolata, Equisetum sp., Carex ssp. Palaeobiotope: permanently covered by water with a depth of less than 2 m, at maximum. In deeper water the plants are drowned. Type of deposition: autochthonous, partially hypautochthonous up to the limit with the aquatic macrophyte prairie, because of the action of streams and storm waves. Depositional milieux: subaquatic (limnic). Environmental characteristics: similar to modern swamps with Phragmites australis, where the pH is mainly neutral to alkaline. The plant material accumulates in anaerobic conditions. Modern peats with Phragmites contain from 15 to 20% ash content. By residual enrichment, the resulting coals could reach between 30-50% ash content. Ph. australis, is growing today in the Danube Delta on a surface of more than 20000 ha, in which a surface of more than 100000ha is covered by 'plaur', a floating vegetal mass, mainly generated by the rhyzome of this species. Lithotype: detrital coal. Distinguished from the detrital coal from swamps with sedge (Carex ssp.) and from hygrophite deciduous forest,

137

because this facies contains frequent seeds of

Stratiotes dacicus. The quantity of this coal shows the importance of palaeophytocoenoses with Phragmites in coal generating phytomass constitution.

Aquatic macrophyte prairie Plant communities: palaeophytocoenoses dominated by one of the main taxa: Stratiotes dacicus, Trapa urceolata, Trapa expectata, Myriophyllum nagavicum, Hydrocharis morsus-renae, Potamogeton corniculatus, Ceratophyllum demersum, Ceratophyllum submersum, Nymphaea alba, Nuphar pliocenicum and Nelumbo protospeciosa. The relative high number (68) of AFVR of aquatic plants, and their palaeocarpological content has helped us to identify 15 palaeophytocoenoses in the Pliocene swamps. From the 27 aquatic plant associations found by Popescu et al. (1981) in the Danube Delta, at least eight also existed as such in the Pliocene

(Hydrocharitetum morsus-ranae, Stratiotetum, Cerato_phylletum demersi, Myriophyllo-Potametum, Najadetum, Myriophyllo-Nupharetum, Trapo-Nymphoidetum and Trapetum). Associated elements: Salvinia sp., Spirematospermum wetzleri, Brasenia tanaitica, Myriophyllum spinosum, Trapa givulescui, Trapa victoriae, Trapa horrida, which could also generate monocoenoses. The aquatic macrophyte prairies are the first in an ecological succession (Fig. 3). Vertically, in the genetical series, the aquatic macrophyte prairies are replaced by swamps with Phragmites, and these by forest swamps. Such successions can be foune in many of the coal open-pit mines in Oltenia. Palaeobiotope: permanently flooded areas, with a depth of more than 2 m (in the initial stage of the vegetation evolution the depth can be between 0 and 3 m). Type of deposition: autochthonous, but in many ways hypautochthonous because of water currents and storm waves than move the plant material from low deep swamps. Depositional milieux: subaquatic (limnic). Environmental characteristics: Similar to swamp lakes in the Danube Delta and the Romanian Plain where the water is introduced into the lake via rivers, but almost double the rainfall and with a pH from neutral to alkaline. The plant remains accumulated in an anaerobic environment. Lithotypes: frequently, in this environment coaly clays and clayey coals were generated. Nevertheless, the frequency of Nelumbo leaves, strictly

138

N. T I C L E A N U & D. DIACONIT-~

autochthonous on the X layer level in Pinoasa and Plo~tina open-pit mines, lead us to the conclusion that this species has played an important role in the phytomass constitution. In the same way that in the Okefenokee swamp (Cohen et al. 1984) Nymphaea peat together with Taxodium peat constitutes more than 80% of this peat. Palaeophytocoenoses with Stratiotes and with Trapa could generate such peats and also detrital coals.

Conclusions The Pliocene coals in Oltenia were generated in five distinct coal facies (grassy marsh Carex ssp., swamp deciduous forest, swamp with Glyptostrobus, reed swamps and aquatic macrophyte prairie) with a time and spatial distribution controlled, first of all, by the hydrological level, which has generated palaeobiotopes with different environmental factors (pH, Eh, etc.). Each facies has a characteristic plant community, composed of one or more palaeophytocoenoses generated by plants belonging to major taxonomic groups (angiosperm, mono and dicotyledon and gymnosperm) distinguished by the content in the main coal-generating substance (cellulose, pentosane, lignin, etc.). In the primary peat swamps different environmental conditions from one palaeobiotope to another and important quantities of vegetal phytomass with different chemical composition accumulated. This determined the development of distinct lithotypes, characterised by physicalchemical properties (Table 1) and certain petrographical characteristics (Table 2), that enabled differentiation of the main lithotypes detrital coal, xylite and xylitic coal. Phytogeographical considerations indicate that the coal-generating flora are distinguished by a strong Pliocene characteristic feature determined by: the fact that corresponding modern plant assemblages are prevalent in the eutrophical low moors in Romania, the important role of species Glyptostrobus europaeus and Byttneriophyllum tiliaefolium; the sporadic presence (relict) of the species:

Taxodium dubium, Nyssa disseminata, Acer tricuspidatum, Carya cf aquatica and Liquidambar europaeum, all of them characteristic of the Miocene flora in Europe, and with modern correspondents in the south-east of North America.

References ANDREESCU, I., TICLEANU, N., PANA, I., PAULIUC, S., PELIN, M. & BARUS, T. 1985. Stratigraphie des d6p6ts pliocenes a charbons. Zone est d'Oltenie (Secteur Olt-Jiu). Analele Universitdlii Bucure~ti, Geologie, 34, 87-96. BITOIANU, C. & ILIE, S. 1967. Contribu~ii la studiul petrografic al c~trbunilor de la Valea Motrului (Oltenia). Studii tehnice #i economice, 7, A, 165-173. BOULTER, M. C., HUBBARD, N. L. B. R. & KVACEK,Z. 1993. A comparison of intuitive and objective interpretations of Miocene plant assemblages from north Bohemia. Palaeogeography, Palaeoclimatology, Palaeoecology, 101, 81-96. COHEN, A. D., CASAGRANDE,D. J., ANREJKO, M. J. & BEST, G. R. 1984. The Okefenokee Swamp: its natural history, geology and geochemistry. Wetland Surveys, 709. ILIE, S. & BITOIANU, C. 1967. Studiul petrografic al c~rbunilor de la Rovinari. Studii tehnice #i economice, 7, A, 177-185. PETRESCU, I. tYr GIVULESCU, R. 1986. Flore et vegetation de la Valea du Jiu (Basin Petro~ani). Revue de Palaeobiologie continentale XIV, 2, 385-395. PoP, E. 1960. Mla~tinile de turb~ din R. P. Romgm~t. Editura Academiei, 511. POPESCU, A., SANDA, V. & NEDELCU, G. A. 1981. Allgemeine Ubersicht fiber die Vegetation des Donaudeltas. Horti Bucurestiensis, Acta Botanica, 175-191. RUDESCU, L., NICULESCU, C. & CHIVU, I. P. 1965. Monorafia stufului din Delta Dun~rii. Editura Academiei Romdne Bucure~ti. STACH, E., MACKOWSKY, M. Th., TAYLOR, G. H., CHANDRA, D., TEICHMULLER, M. t~r TEICHMULLER, M. & TEICHMI~ILLER,R. 1975. Coal Petrology, Berlin. TEICHMIJLLER, M. 1958. Rekonstruktionen verschidener Moor typen Hauptfl6zes der Niederrheinischen Braunkohlen. Fortschritte in der Geologie yon Rheinland und Westfalen, 2, 599-612. TICLEANU, N. 1986. Date preliminare privind studiul palaeobotanic al unor foraje de referin~t, 70-71/ 3, Palaeontologie, 235-248. 1992a. Studiul genetic al principalelor zficfiminte de cfirbuni neogeni din Romfinia pe baza palaeofitocenozelor caracteristice, privire speciafft la Oltenia. Tezd de doctorat, 339. Universitatea Bucureqti, Romfinia. - - 1 9 9 2 b . Main coal-generating palaeophytocoenoses in the Pliocene of Oltenia. Romanian Journal of Palaeontology, 75, 75-80. 1995a. An Attempt to Reconstitute the Evolution of the Mean Annual Temperature in the Neogene of Romania. Romanian Journal of Palaeontology, 76/3, 137-144. - - - 1 9 9 5 b . Taphonomic Researches on the Fossil Plants from the Pliocene Coal Deposits in Oltenia. Romanian Journal of Palaeontology, 75/3, 153-160. - - 1 9 9 5 c . Utilisation of the Palaeobotanical Data in the Study of the Coal Deposits. Romanian Journal of Palaeontology, 76/3, 145-152.

PLIOCENE COAL FACIES A N D LITHOTYPES IN R O M A N I A & ANDREESCU, [. 1988. Considerations on the development of Pliocene coaly complexes in the Jiu-Motru Sector (Oltenia). Ddri de searnd, Institutul de Geologie l'i Geofizicd, 72-73/2. Zdcdminte, 227-244. & BITOIANU,C. 1989. Coal Facies, Characteristic Palaeophytocoenoses and Lithotypes of Pliocene from Oltenia. Studia Universitatis Babeq - Bolyai, 34, 2, 89-93. - - , ANDREESCU, l., BITOIANU, C., PAULIUC, S., NICOLAE, Gh., NI[COLAE,V., POPESCU,A., BARUS, T., PASLARU,T., GRIGORESCU, Gh. & TICLEANU, M. 1988. Remarks on the relationship between the spatial distribution of the coal complexes in -

-

-

-

139

the Olt-Jiu sector and the structural-genetic factors. Ddri de seamd, Institutul de Geologie ~i Geofizicd, 72-73/2. Z&'dminte, 215-226. - - - , BITOIANU,C., MUNTIU, O. & NAGAT, F1. 1989. Palaeofitocenozele carbogeneratoare, petrografia ~i chimismul litotipilor din c~rbunii plioceni dintre Valea Jiulu ~i Valea Amaradiei. Ddri de seamd. Institutul de Geologie ~i Geofizicd, 74/2, Zdcdrninte-Geochimie, 115-129. TICLEANU, N., BITOANU,C., NICOLAE, Gh., POPESCU, A., TICLEANU,M., MUNTIU, O. & PROD,~,NESCU,I. 1992. P~trographie et propri6t6s physico-chimiques des charbons pliocenes du secteur Jiu-Danube. Romanian Journal Mineral Deposits, 75, 107-115.

Bulgarian low rank coals: geology and petrology GEORGE D. SISKOV Sofia University 'St. Kliment Ohridski', 15 Tsar Osvoboditel Blvd, 1504 Sofia, Bulgaria

Abstract: The largest coal-forming maximum in Bulgaria took place during the Neogene. Fifteen coal deposits are located in four coal-bearing provinces. The coal deposits south of the Balkan Mountains were formed in small grabens and depressions filled with molasse. Only the coals in Northern Bulgaria were formed in a small palaeodelta. The coal measures are of varying thickness and contain a few coal seams, with compact to complex structure and a range of thickness. Three groups are defined on the basis of maceral composition, allowing a reconstruction of the coal-forming ecosystems and the genesis of the genotypes during biochemical coalification. According to Alpern's classification the coals have middle to high ash content (ashy to coaly facies). They are of huminite type with low liptinite and inertinite content, and of low rank - lignite and mat brown coals.

Bulgaria contains more than 50 coal deposits but most of them are of no industrial value due to the complex conditions affecting their exploitation, the nonprospective character of the resource and the low quality of the coals (high ash and sulphur content). Their formation coincides with the world coal-forming maxima during Carboniferous, Early Jurassic, Late Cretaceous, Paleogene and Neogene. The geological potential of Bulgarian coal resources is about 8 x 109 tonnes, of which 85 % are low rank, 15 % middle rank, and < 1% high rank coals. According to the Bulgarian Standard they are divided into four g r o u p s lignites, brown coals (mat and bright), hard coals, and anthracites (Si~kov & Valceva 1983). Lignites are concentrated in the Neogene sediments and are one of the main energy resources in Bulgaria.

the beginning of the Late Oligocene (Si~kov et al. 1986). In that period typical marine sedimentation was gradually replaced by limnic sedimentation caused by progressive regression (Panov 1982). The coal formation occurred in highly peneplaned coastal areas covered with eutrophic swamps.

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Geology of the Neogene coal deposits On the basis of topographical, morphotectonic, lithologic and genetic characteristics the Neogene coal deposits are located in four coalbearing provinces, three of them being south of the Balkan Mountains (Fig. 1, Table 1). The coal formation process started in Middle Miocene and ended in Pliocene. It took place within the period of the Pyrenian and Styrian phases of the Late Alpine orogeny and was concentrated in local depressions and grabens filled with molasse (Ivanov 1983). Features representing continuous coal formation during the Paleogene maximum have been established in the region of the Thracian Valley. Here, after the Savic phase, a post-tectonic depression was formed (Ivanov 1983) in which there were favourable conditions for coal formation from

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5

6

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8

9

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Fig. 1. Location of the coal-bearing provinces, geolgical age and structure of the coal-bearing strata of the Neogene coal deposits in Bulgaria. A, Dacian coal, bearing province: (1) Lom; (2) Kozloduj; B, Thracian coal-bearing province: (3) Elhovo; (4) Mariza East; (5) Mariza West; C, Sofia coal-bearing province: (6) Sofia; (7) Beli Brjag; (8) Aldomirovzy; (9) Stanjanzy; (10) Kovachevzy; (11) Karlovo; (12) Chukurovo; D, Strimon-Mesta coal-bearing province: (13) Kjustendil; (14) Oranovo; (15) Razlog; (16) Goze Delchev.

From Gayer, R. & Pe~ek, J. (eds), 1997, European Coal Geology and Technology, Geological Society Special Publication No. 125, pp. 141-148.

142

G . D . SISKOV Table 1. Neogene coal deposits in Bulgaria Coal-forming maximum

Coal-bearing provinces

Neogene

Dacian

Coal deposits

Lom Kozloduj Thracian Elhovo Mariza East Mariza West Sofia Sofia Beli Brjag Aldomirovzy Stanjanzy Kovacevzy Karlovo Chukurovo Strimon-Mesta Kjustendil Oranovo Razlog Goze Delchev

Thracian coal-bearing province This province is situated in the area of the Thracian depression and is filled with sediments of the lower (Paleogene) and the upper coalbearing molasse (Neogene). The coal formation started in the Late Oligocene and continued through the Miocene and into the Pliocene. Gradual younging of the coal-bearing sediments occurred from west (Mariza West) to east (Elhovo). According to Kojumdgieva (1983) this is due to the gradual progression of the regression in this direction as well as to the formation of the Black Sea. Under these circumstances the plain had been raised relatively following the marine regression. The period of relatively compensated sedimentation led to the formation of thick peat deposits. The Second coal seam of the Mariza East deposit (maximum thickness of 25 m) is a good illustration of the long duration of the peat formation process. The coal-bearing strata consist of terrigenous sediments varying in thickness from 45 m (minimum at Mariza East) to 390m (maximum at Elhovo) where 3-4 coal seams form coal-bearing measures of varying thickness (up to a maximum of 25 m). Paleogeographical reconstruction shows that the water table in the eutrophic swamps was generally high, falling very low only during seasonal desiccations. An interesting phenomenon is the small coal deposit in the area of the Gulf of Sozopol, where a thin coal layer with preserved root systems

Number of coal seams

Geological age

3 2 3 3 4 3 1-5 1-3 1 1 3 16 1 4 8 14

Pliocene Pliocene Pliocene Early-Middle Miocene Early-Middle Miocene Pliocene-Late Miocene Pliocene-Late Miocene Pliocene-Late Miocene Pliocene-Late Miocene Pliocene-Late Miocene Pliocene-Late Miocene Middle Miocene Pliocene-Late Miocene Pliocene-Late Miocene Pliocene-Late Miocene Pliocene-Late Miocene

under the silicified 'Stone Forest' has been found. Geological and petrological studies have shown that the coal formation occurred in a swamp situated in the crater of an extinct volcano which was destroyed by a storm during which marine water influx produced a rapid change of geochemical conditions. The coal layer is covered with pyritized wood tissue with upright silicified Taxodium stumps mostly covered by recent sands (Si~kov et al. 1988).

Sofia coal-bearing province This province covers the area of Western Bulgaria between the Balkan and the Sredna Gora Mountains. The coal-bearing sediments fill subequatorial grabens and small depressions in which coal formation started in the Middle Miocene (Chukurovo) and lasted till the beginning of the Pliocene (Stanjanzy). In this highly active tectonic zone continental lakes were formed, later to be rapidly filled with terrigenous sediments. Gradually these lakes were transformed into eutrophic swamps with a high degree of mineralization and highly dynamic ground waters. The coal-bearing strata consist of clastic sediments - conglomerates, sands, clays. Their thickness varies from 25 to 100 m while in the outlying parts of the deposit it reaches 900 m (Sofia). The number of coal seams varies from 1 to 5, except at Chukurovo where 16 coal seams are present in the coal-bearing sequence. The thickness of the coal seams varies up to a maximum of 15-20 m.

BULGARIAN LOW RANK COALS

Strimon-Mesta coal-bearing province This province is located in the southwestern part of Bulgaria. Several small coal deposits are situated along the valleys of the Strimon and Mesta rivers in almost meridional orientation. The coal deposits were formed in restricted and small grabens filled with coarse clastic terrigenous sediments. The thickness of the coalbearing strata varies reaching a maximum of 800m (Goze Delchev). In the highly active tectonic zone favourable conditions for the formation of mezotrophic to oligotrophic swamps occurred resulting in a variable number of coal s e a m s - 1 (Kjustendil) to 14 (Goze Delchev). Laterally their thickness changes very rapidly. The coal seams very often wedge out and split into benches and lenses of coaly clay and clay.

Dacian coal-bearing province This province is located mostly in the northern areas of the Moesian Platform including the Lom and the Kozloduj deposits, the latter representing the southern fragments of the Oltenia basin in Romania. The coal formation is connected with the desiccation of the Pontian Basin during a prolonged regression in the Pliocene (Kojumdgieva 1983). The coal sediments are of Pliocene age - Dacian-Romanian, with the exception of

143

some small coal deposits which are older (Kojumdgieva & Popov 1988). In various parts of the Lom deposit the deltaic sedimentary complex differs in structure and thickness as illustrated by the irregular alternation of the lithological bodies, represented by coarser to finer clastic sediments. These sediments contain unevenly developed benches and lenses which vary in number; a typical feature of a subaeral delta. The finer pelitic sediments of the Lom area are typical of the lower-upper delta plain (Si~kov & Angelov 1984). In the Lom depression extensive but uneven peat accumulation occurred associated with a vast lower-upper delta plain in which lateral facies migration was developed by a northward shift of the deltaic front and contained fluvial channels. The coal formation in the zone of the Kozloduj deposit developed in a coastal plain environment. The swamp was large. In contrast to the Lom deposit the coals were found in interdeltaic environments with a high water table and associated with fine-grained clastic sediments. The coal seams are up to 4 m thick and cover an area of about 1 km 2 (Si~kov & Angelov, unpublished data).

Petrology of the Neogene coals Over 6200 coal samples were collected from opencast and underground mines, exploratory boreholes and outcrops.

Table 2. Maceral composition of the Bulgarian low rank coals No.

Coal deposits

Ash Maceral composition (%) A d (%) Total H

1. 2. 3. 4. 5. 6. 7. 8. 9. 10. 11. 12. 13. 14. 15. 16. 17.

Lom Kozloduj Elhovo Mariza East (briqueting) Mariza East (energetic) Mariza West Sofia Beli Brjag Aldomirovzy Stanjanzy Karlovo Kovachevzy Chukurovo Kjustendil Oranovo Razlog Goze Delchev

42.6 20.1 38.3 20.2 39.7 23.8 16.6 15.0 25.4 21.9 17.7 33.2 22.3 23.1 20.1 20.8 17.6

53 71 60 74 61 63 77 66 64 74 70 68 75 36 63 75 80

L

I

3 7 2

1 1 2

1

2

2 8 7 7 8 8 8 4 14 3 7 6 11

1 4 2 8 6 5 5 6 1 15 3 1 3

Org. matter

M

H

43 21 36 23 36 25 14 19 22 13 17 22 10 46 27 18 6

92 90 96 96 95 82 89 87 88 85 83 89 84 67 88 92 85

L 5 8 2

I 3 2 2

1

3

3 12 9 9 11 8 10 5 15 5 10 7 11

2 6 2 4 1 7 7 6 1 28 2 1 4

144

G . D . SISKOV

Petrological data show that the homogeneous genotypes gelide, peptide, liptide and fiside form the coal matter in various proportions, though gelide and peptide predominate. The heterogeneous genotypes gelofuside, fusoliptide, etc. are also represent. The wide genotype differentiation is caused by: (1) the different chemical, anatomical, species and plant ecosystem compositions of the coal-forming plants and their behaviour during peat formation; (2) the physico-chemical parameters (Eh, pH) of the ground water environment; (3) the type and rate of the chemical reactions and petrological processes depending on the oxygen supply; (4) the activation energy involved in the phytogenic matter transformation during microbial metabolic processes (Si~kov 1988). In the lithotype balance humoclarite is prevalent (up to 85%). A higher quantity of xylain and liptain(the latter is a specific lithotype formed by impregnated coniferous fragments with resins - Si~kov 1976) fragments of various size are found mainly in the coal deposits from the Thracian and the Sofia coal-bearing provinces. They are distributed chaotically. Semifusain and fusain are found in small amounts, and occasionally mark bedding in the coal seams of some deposits from the Thracian (Elhovo, Mariza East) and Strimon-Mesta provinces (Kjustendil, Goze Delchev). All mono-, bi- and trimacerites are represented in the microlithotype composition. Humoclarite prevails and, along with carbargilite represents partially to completely disintegrated plants, consisting of variously fragmented atrinite, and more rarely, of densinite. The average compositions of the maceral analyses are given in Table 2. The macerals of the three groups are in different proportions, with the huminite macerals predominating. They form the groundmass in which other fragmentary macerals of the huminite, liptinite and inertinite groups are chaotically dispersed. Atrinite and densinite are present in differing amounts. Liptinite macerals are represented mainly as resinite and more rarely as cutinite, sporinite and suberinite. The mineral components are represented by widely varying amounts of clays and pyrite. The clay minerals consist of kaolinite, illite and montmorilonite. The maceral amount recalculated per organic matter shows that the Neogene coals are relatively homogeneous in composition containing more than 80% of huminite, with the exception of the Kjustendil coals (Table 2, Fig. 2). The average petrological data show

H

RANK

80%

80%

A~-/. SHALES 75 SHALEY

W m o ,< u.

50 35

~A~

,~,1I 4

ASHY

1(

,I

1

I,'i5i 'r IIII

PURE Rr %

BRIGHT 16 17

15

MAT Z 0.3 < n"

LIGNITE

0.2

~Io I

10,S 862 -Tg 4 1~3[ 11 |

fILIal1

100% H TYPE

80% L

Fig. 2. Triangular diagram and petrological position by type, facies and rank of the Neogene coals in Bulgaria according to Alpern's classification: 1, Lom; 2, Kozloduj; 3, Elhovo; 4, 5, Mariza East; 6, Mariza West; 7, Sofia; 8, Beli Brjag; 9, Aldomirovzy; 10, Stanjanzy; 11, Karlovo; 12, Kovachevzy; 13, Chukurovo; 15, Oranovo; 16, Razlog; 17, Goze Delchev. that the Neogene coals in Bulgaria are of huminite type with a minimum content of liptinite and inertinite. The principal components are determined on the basis of a correlation matrix using the algorithm reported by Wehlstedt & Davis (1968). The Q-dendrograph was plotted by the method of McCammon&Wenninnger (1970) (Si~kov & Andreev 1987). The cluster analyses indicate that the Neogene coals are very distinctly differentiated into three groups (Fig. 3, Table 3).

BULGARIAN LOW RANK COALS

I 0.06

I B

I

[

J

0.04

I I

] A2

i

I B2

B~

0.02

2 7 16 8 17 15 9 40

13

6

11 10

12

50

1 4 5 3

60

1PC = 0.74 H - 0.08 L - 0.66 I (79%) 2PC = - 0.34 H - 0.81L - 0.48 I (21%)

HII

1Q ~3 \

/ ./

14

A

\

-20

- 30

Fig. 3. Q-dendrograph and grouping of the Neogene coal deposits by their maceral composition: 1, Lore; 2, Kozloduj; 3, Elhovo; 4, 5, Mariza East; 6, Mariza West; 7, Sofia; 8, Bell Brjag; 9, Aldomirovzy; 10, Stanjanzy; 11, Karlovo; 12, Kovachevzy; 13, Chukurovo; 14, Kjustendil; 15, Oranovo; 16, Razlog; 17, Goze Delchev.

Groups A and B are each subdivided into two subgroups. Coals, having huminite 82-92%, are referred to Group A. Coals, containing huminite above 92%, are assigned to Group B. A significant difference is observed in the Kjustendil deposit due to the higher content of inertinite (Group C). The grouping of the coals in accordance with the ratios (H/I) and (L/I, H) is illustrated in Fig. 3, where the H/I ratio has an average value of 79%. The statistical analysis of the maceral content provides a means of reconstructing the peatforming ecosystems in combination with the

tectonic position of the coal deposits, the physico-chemical environment in the peat bogs and the hydrodynamics of the groundwater table. Coals in which the coal-forming communities are equally divided between forest and herbaceous populations are referred to Group A. The petrological investigations show that the forest vegetation consists of angiosperm and coniferous species. The coniferous species in combination with herbaceous vegetation form Subgroup A~ where the amount of densinite groundmass considerably predominates. The amount of well preserved wood tissue producing textinite and textoulminite filled with resinite also increases. Coals from three deposits form Subgroup A2 (Table 3) in which herbaceous vegetation predominates while the number of angiosperm and coniferous species is equivalent. The amount of densinite is prevalent and the content of euulminite and gelinite increases. The coals from the Chukurovo deposit are distinct. They contain mainly species, Taxodiaceae being particularly typical. Due to the prevalence of coniferous vegetation the amount of resinite also increases markedly. Coals predominantly formed by herbaceous vegetation in peat-producing ecosystems with a lower participation of forest species are assigned to Group B. In this case huminite macerals are highly gelified and the groundmass consists of atrinite. Their division into two subgroups is based on the amount of inertinite. Another important petrological factor, related to the genesis of coal macerals is the nature of the peat swamps and their hydrodynamics. Where major tectonic activity and enhanced hydrodynamics and aeration of ground water occurs, possible seasonal desiccation would result in oxidation leading to a deviation from the general maceral balance. This is the reason

Table 3. Petrological groups of the Neogene coal deposits in Bulgaria Group Subgroup Maceral composition (%) Coal deposits H A

B

C

L

I

A1

85-92

7-11

1-4

A2

82-85

8-12

6-7

B1

> 92

B2

89 67

1-5 5 15

2-3 6 28

145

Kozloduj (2), Sofia (7), Beli Brjag (8), Aldomirovzy (9), Oranovo (15), Razlog (16), Goze Delchev (17) Mariza West (6), Stanjanzy (10), Karlovo (11), Chukurovo (13) Lom (1), Elhovo (3), Mariza East (4, 5) Kovachevzy (12) Kjustendil (14)

Table 4. Rank parameters of the Neogene coals in Bulgaria Coal deposits

Relectance Rr (%)

Bed moisture W r (%)

Carbon Volatile matter C daf (%) VM daf (%)

Calorific value Osdaf (kJ/kg)

Lom Kozloduj Elhovo Mariza East Mariza West Sofia Beli Brjag Aldomirovzy Stanjanzy Kovachevzy Karlovo Chukurovo Kjustendil Oranovo Razlog Goze Delchev

0.13 0.22 0.18 0.20 0.21 0.22 0.22 0.21 0.21 0.22 0.19 0.20 0.33 0.34 0.39 0.41

50.0 51.8 63.6 64.4 43.1 50.0 47.5 51.6 52.5 48.6 44.0 33.0 26.6 30.4 32.5 43.5

64.7 65.1 63.8 65.0 62.3 64.6 63.8 64.1 61.6 63.9 64.8 64.3 66.9 66.0 64.8 67.9

22.52 22.68 22.76 22.31 22.87 23.51 23.27 22.92 19.42 22.78 23.77 23.38 23.98 23.85 22.92 23.02

LOW RANK

67.7 64.1 53.0 55.8 58.8 52.0 53.4 52.6 61.0 67.3 58.8 57.0 51.0 48.3 55.4 49.1

I TRANSITIONzoNE ]

MEDIUMRANK .x

I -24 MJ/Ro

.--

Xx

,

[ ~

.

~

~

~ -

21.

Q = 21.569+ 6.316Rr - 3.183Rr2 r = 0.653, n = 27

19

.

.

0.4

0.6

l~ls~3~tl

L

0.8 ,

,,

1~0 ,

%RF

l,,

Stand. LIGNITE

ASH

HIGHVOL BITUMINOUS

SUB. ~ B I T ' ~ - ~

r xx xx x ~ ~

0.2 o~

6al x

x

x

~

0.4

~ ,,~mll-"~ 0.2

0.8

1.0

VM = 69.187

r = 0.836, n-26~7"15Rr + 26"885Rr2

x

x x

_x

0.2 o2

x

0.6

~ x

75 70

W = 76.602 - 159.664Rr + 101.913Rr 2 r = 0.862, n=27

x

0.4

2 )(~'

0.6

x

x x

x

x 0.4

0.8

1.0

xx r = 0.924, n=27

0.6

O.8

1.0

%Rr

Fig. 4. Rank classification of the Cenozoic coals in Bulgaria and the position of the Neogene coals according to Alpern's classification, Bulgarian Standard and ASTM as well as relationship of reflectance (Rr, %), bed moisture (W r, %), volatile matter (VM daf, %), carbon content (C daf, %) and calorific value (Qdaf, MJ/kg).

BULGARIAN LOW RANK COALS

The author would like to thank Dr A. Andreev (Geological Institute of the Bulgarian Academy of Sciences) for computation of the maceral data. The author is also indebted to Dr I. Todorov (Bulgarian Research & Services Group Ltd) for the preparation of the figures.

for the difference in the coals from the Kjustendil and Kovachevzy deposits. The results of the maceral analysis of our study appear to be in agreement with the published indices (Diessel 1986; Calder et al. 1991). The coal facies determined on the basis of the ash content and maceral composition are illustrated in Fig. 2, where the position of macerals is projected on the abscissa. The content of ash is between 17.6 wt % (Goze Delchev) and 42.6 wt % (Lore). Most of the coals belong to the ashy humic facies. Only coals from the Lom and Elhovo deposits as well as a part of the Mariza East deposit are coally humic facies. The average classification parameters - huminite (gelinite) reflectance (Rr, %), calorific value (Qsdaf, MJ/kg), bed moisture (W r, %), yield of volatile matter ( V M ~ %) and carbon content (C dav, %), are given in Table 4. The position of the Neogene coals is plotted in Fig. 4. There are good correlations between the huminite reflectance and the other classification parameters.

Conclusion The Neogene coals in Bulgaria belong to the low rank coals of Alpern's classification. On the ASTM scheme they are determined as lignites. According to the Bulgarian Standard the coals are divided into lignites (Class O1) and mat brown coals (Class O2), with the exception of the coals from the Goze Delchev deposit which are referred to the bright brown coals (Class 03). The low coalification of the coals from the Thracian, Sofia and Dacian coal-bearing provinces is a consequence of the relatively small thickness of the overburden sediments and the short geological time for the development of the coalification process. The coalification degree of the coals from the Strimon-Mesta province is higher and depends on: (1) the thickness of the overburden sediments (to 500m) which has caused the reorientation of the coal genotypes (lithotypes, microlithotypes, macerals) and the appearance of macro- and microbedding; and (2) an anomalous geothermal gradient. Velinov&Bojadgieva (1981) have stated that the temperature measured in the boreholes at 300 m depth is 37-38~ and at 500m depth, 66~ (3) the tectonic mobility - rapid tectonic movements occurring along faults, typical of the zone of the Kraishte lineament.

147

References ALPERN, B. 1981. Pour une classification syntetique universelle des combustibles. In: La geologie des charbons, des schistes bitumineux et des kerogenes, 271-290. CALDER, J. H., GIBBING,M. R. • MUKHOPADHYAY,P. K. 1991. Peat formation in a Westphalian B piendment setting, Cumberland Basin, Nova Scotia: implications for the maceral-based interpreparation of rheotrophic and raised paleomires. Bulletin de la Societe geologique de France, 162, 2, 283-298. DIESSEL, C. F. K. 1986. On the correlation between coal facies and depositional environments. In. Advances in the Study of the Sydney Basin. Proceedings of 20th Newcastle Symposium~ 19-22. |VANOV, Z. 1983. Apercu general sur l'evolution geologique et structurale des Balkanides. In: Guide de l'exeursion. University Press of Sofia, 3-26. KOJUMDGIEVA,E. 1983. Paleogeographic environment during the desiccation of the Black Sea. Palaeogeography, Palaeoclimatology, Palaeoecology, 43, 195-204. & PoPov, N. 1988 . Lithostratigraphy of the Neogene sediments in Bulgaria. Palaeontology, Stratigraphy, Lithology, 25, 3-26. MCCAMMON, R. I. t~ WENNINNGER, G. 1970. The dendrograph. Kansas Geological Survey Computer Control, 48. PANOV, G. 1982. Tertiary coal sedimentation in the Upperthracian depression. PhD thesis. SlgI~OV, G. 1976. Liptain- properties and genesis. Annuaire de l'Universite de Sofia, Faculte de Geoloque et Geographie, 67, 1, 151-169. 1988. Theoretical fundamentals of biochemical eoalification. Kliment Ohridski University Press, Sofia. - - & ANDREEV,A. 1987. A way to reconstruct coalforming peleoplant communities based on the micropetrographic composition of Bulgarian Neogene coals. Comptes rendus de l'Academie bulgar des sciences, 40, 4, 77-80. & ANGELOV, A. 1984. Delta-plain model of sedimentation of the Lom lignite basin. Comptes rendus de l'Academie bulgar des sciences, 37, 11, 1531-1533. - - & VALCEVA,S. 1983. Petrological nomenclature of lignites and brown coals. Comptes rendus de l'Academie bulgar des sciences, 36, 6, 799-801. SISKOV, G., STEFANOVA, U. t~ ZLATEV, I. 1986. Petrological characteristics of the coals from the Brod member in the West Mariza basin. Annuaire de l'Universite de Sofia, Faculte de Geologie et Geographie, 76, l, 40-53.

-

-

148

G.D.

SISKOV, G., VALCEVA, S. & PIMPIREV, H. 1988. Preconditions for the formation of the 'Stone forest' and coal deposits in the Gulf of Sozopol. Annuaire de l'Universite de Sofia, Faculte de Geologie et geographie, 77, 1, 190--200.

SISKOV VELINOV, T. & BOJADGIEVA, K. 1981. Geothermal investigations in Bulgaria. Technika, Sofia. WEHLSTEDT, W. C. & DAVIS, J. C. 1968. Fortran IV program for computation and display of principal components. Kansas Geological Survey Computer Control, 21.

Coal petrology and facies associations of the South Yakutian Coal Basin, Siberia I. E. S T U K A L O V A

Geological Institute of Russian Academy of Sciences, Pyzhevsky per., 7, Moscow, 109017, Russia Abstract: The South Yakutian Coal Basin consists of isolated depressions in the south of the Yakutian region of Eastern Siberia in Russia, which are filled with Jurassic and Cretaceous coal-bearing sediments. The basin contains considerable resources of highquality bituminous coals, with a caking index (y) of 6-21 mm. The coal-bearing formation contains coal seams of various thickness, from 0.5-2.5m up to 15.0m and above. Some of them are near the surface and can be mined by opencut methods. Genetic types and facies of the Mesozoic coal-bearing strata have been recognised as proluvial, alluvial, delta, lacustrine-swamp and peat bogs sediments. The petrographic composition of the sandstones identified four terrigenous-mineral associations, which are represented by true arkoses, greywacke arkoses, feldspar-quartz and quartz-feldspar greywackes. Humic coals consists of vitrinite (70-90%), inertinite (10-20%) and liptinite (0-10%) maceral groups. In the vitrinite maceral group there is a high percentage of telinite macerals, up to 60-65%. The basin is characterized by a high alteration of Mesozoic sediments and organic matter. Coals are of middle and high rank (0.65-2.15% R0). There are high concentrations of bitumen in chloroform extracts of organic matter from the coals, from 0.0938% to 3.6466%. The mineral matter of terrigenous rocks is altered to the catagenetic stage and the metagenetic stage. The South Yakutian coals are of high quality because of their rank and composition.

The South Yakutian Coal Basin is located in the south of the Yakutian region of Eastern Siberia in Russia, between 56~ ~ North and 120~ ~ East (Fig. 1). The basin extends from the Oliokma river in the west to the Uchur fiver in the east and covers an area of 25 100 square km. The towns of Aldan, Nerjungri and Chulman

-

126~

120 0

Q i

132.* E

75 150Km *

.

;OON

I

Fig. 1. Sketch map of the South Yakutian Coal Basin (revised after Bredihin 1973). 1, Mesozoic coal-bearing deposits; 2, Coal-bearing regions: (1) Usmun, (2) Aldano-Chulman, (3) Tokin.

are situated in the region. It is a very important coal basin in Russia, and contains considerable resources of high-quality bituminous coals. The coal-bearing formation contains coal seams varying in thickness from 0.5-2.5m to greater than 15.0 m. Some of the seams are near the surface and can be mined by opencut methods. The South Yakutian Coal Basin includes three main coal-bearing regions, namely: Usmun, A l d a n o - C h u l m a n and Tokin regions (Fig. 1). The Nerjungri coalfield in the A l d a n o - C h u l m a n region contains caking coals which are now opencut mined, producing about 9 Mt per year. The Nerjungri coalfield is situated near the rail station at Chulman town and the coals are exported to the Far East region of Russia and to Japan. The Elga coalfield in the Tokin region also contains caking coals, but the coalfield is situated far from the rail system and it will be opencut mined in the future. The stratigraphy and coal-bearing potential of the sediments in the South Yakutian Coal Basin have been investigated by many authors (Prosviryakova 1961; Mokrinsky 1961; Waltz 1961; Fatkulin et al. 1970; Bredihin 1973; Prilutsky 1979; Zhelinsky 1980; Markovich 1981; Vlasov 1981; Nazarov & Stukalova 1991) and are now well known; but many problems have yet to be solved. At present there is no information about reasons for the high degree of metamorphism of the South Yakutian coals.

From Gayer, R. & Pe~ek, J. (eds), 1997, European Coal Geologyand Technology, Geological Society Special Publication No. 125, pp. 149-160.

150

I. E. STUKALOVA

There is no concensus about the tectonic position of the South Yakutian Coal Basin. Some investigators consider that the basin formed in intermontain depressions (Bredihin 1973; Terentyev 1979; Vlasov 1981); others that the depressions are paleorifts (Nazarov & Stukalova 1991).

Geological setting and stratigraphy The South Yakutian Coal Basin consists of isolated depressions in the south of the Siberian platform, which are filled with Jurassic and Cretaceous coal-bearing sediments (Fig. 2). The Mesozoic aulacogens are related to major region faults. The Mesozoic sediments are deposited on Archean-Proterozoic igneous and high-grade metamorphic basement. Precambrian granites and gneisses are widespread in the region and metamorphosed. Lower Cambrian carbonate

rocks also occur. Mesozoic rocks are more than 3500m thick and are represented by various members of terrigenous strata, ranging from Early Jurassic to Early Cretaceous in age. Lower Cretaceous terrigenous sediments without coals of the Nagornaya Member are developed in the south of the region as are Cretaceous volcanic sediments of the Karaulov Member. Jurassic-Cretaceous alkaline intrusive rocks also occur (Fig. 2). Coal-bearing strata are developed in the Usmun and Aldano-Chulman regions, where Early Jurassic deposits of the Juhta Member consist of conglomerates and coarse and medium sandstones of proluvial origin (Fig. 3). Middle Jurassic sediments of the Duraji Member are represented by coarse, medium and fine ground alluvial sandstones with many coal seams between 0.5-2.0m thickness. Upper Jurassic sediments comprise three Members: Kabakta, Berkakit and Nerjungra. The Kabakta

Fig. 2. Geological map of the South Yakutian Coal Basin, Siberia (revised after Zhelinsky, 1980). 1-4, Mesozoic coal-bearing deposits: (1) Lower Jurassic, Juhta Member (J1); (2) Middle Jurassic, Duraji Member (J2); (3) Upper Jurassic, Kabakta, Berkakit and Nerjungra Members 03); (4) Lower Cretaceous, Holodnican Member (Crl); (5) Lower Cretaceous terrigenous sediments of Nagornaya Member; (6) Cretaceous volcanic sediments of Karaulov Member; (7) Jurassic-Cretaceous alkaline intrusive rocks; (8) Lower Cambrian carbonate metamorphic rocks; (9) Precambrian igneous and metamorphic rocks; (10) faults; (11) Coal-bearing regions: 1, Usmun, 2, Aldano-Chulman, 3, Tokin; (12) profiles with boreholes in regions: (AB) Usmun region, (CD) Aldano-Chulman region, (EF) Tokin region.

SOUTH YAKUTIAN COAL BASIN

/./sare/t re eian

,4,~#erzoClqu[azo'/t /'e.Cte/t

151

@~i~ r e j i ~#

.

~9":'. .."~

~K. , , ~~:% ~ m ~

~.

~9 .

.... '7

o~

- ~..

~

.~--~

Fig. 3. Stratigraphy, lithology and coal rank in coal-bearing strata in three regions of the South Yakutian Coal Basin.

and Berkakit Members consist of nearshore medium and fine grained sandstones and coarse and fine grained siltstones and mudstones with paralic coal seams 1.0-2.5 m in thickness. The Nerjungra Member is formed of alluvial and deltaic coarse, medium and fine-grained sandstones and coarse and fine-grained siltstones with coal seams of great thickness up to 25.030.0m in the Aldano-Chulman region. The high-quality caking coals of the Nerjungry coalfield in the Aldano-Chulman region are mined by opencut methods. In the Usmun region the Nerjungry Member is missing. In the Tokin region the Nerjungra Member is represented by proluvial and alluvial coarse and medium grained sandstones with thin coal seams. Early Cretaceous sediments of the

Holodnican Member contain, in the Tokin region, alluvial conglomerates, coarse, medium and fine-grained santstones and coarse and finegrained siltstones with thick coal seams (5.0-10.0 m). In the Aldano-Chulman region the Early Cretaceous sediments consist of alluvial conglomerates and sandstones without coals, and in the Usmun region Early Cretaceous sediments are absent (Fig. 3). The strata are cyclic and contain a complex of floral fragments and palinology (Mokrinsky 1961; Bredihin 1973). The age of coal-bearing strata has been determined by the flora and other fossils. The Jurassic sequence is characterized by the flora Annulariopsis microphylla Vassil., Neocalamites sp., Phlebopteris cf. polypodiodes Brougn., Czekanowskia Setacea Heer,

152

I. E. S T U K A L O V A

SOUTH YAKUTIAN COAL BASIN Raphaelia diamensis Sew, Cladophlebis serrulata Sam and others (Prosviryakova 1961; Bredihin 1973; Markovich 1981). The cretaceous rocks contain the flora Equisetites asiaticus Pryn., Ctenis yokoyamai Kr. et Pryn., cf. burejensis Pryn., Coniopteris nymphrum Heer, Czekanowskia rigida Heer, Pityophyllum nordenskioldii (Heer) Nath., and others (Prosviryakova 1961; Markovich 1981). The palaeoenvironment and facies of the Mesozoic coal-bearing strata have been determined as proluvial, alluvial, delta, lacustrineswamp and peat bogs (Nazarov & Stukalova 1991).

153

too"/.

s

too%

F

1s

Petrographic composition of coals One of the aims of the study of the South Yakutian coals was to explain the high caking characteristics of the coals. We investigated coals in the Usmun, A l d a n o - C h u l m a n and Tokin regions of the South Yakutian Coal Basin. The method was to define the maceral composition, and the technological and chemical properties of the very thick coals, such as the Upper Jurassic coal seams in the A l d a n o Chulman region and the Lower Cretaceous coal seams in the Tokin region. The coals were analyzed microscopically, and by chemical and organic geochemical methods. We investigated the maceral composition of the coals using transmitted light with thin sections and incident light with polished sections with magnifications of 20-600x. Humic coals consist of vitrinite (70-90%), inertinite (10-20%) and liptinite (0-10%) maceral groups. The vitrinite maceral group contains a high percentage of telinite macerals, up to 60-65% (Fig. 4). For example, bituminous coals with high volatile matter content in the Elga coalfield of the Tokin region, using an oil immersion objective, was shown to contain: inertinite components (I) representing transformed wood fragments (sample 375.0/128 and sample 410.0/128, Fig. 4, photo 1,2); a high percentage, up to 70-80%, of vitrinite components (Vt) represented by telinite (Vtl) and collinite (Vt2) (sample 505.0/128 and sample 320.0/131, Fig. 4, photo 3,4); and liptinite

Fig. 5. Terrigenous-mineral associations of sandstones in the coal-bearing strata of the South Yakutian Coal Basin (revised after Nazarov & Stukalova, 1991). Diagram by Shutov 1972. Explanation: Q, quartz; F, feldspar; R, rock fragments; (1) true arkoses and feldspar~luartz sandstones with a low content of quartzite, granite and gneiss fragments; typical of the Lower Jurassic association in the Aldano~hulman and the Usmun regions; (2) feldspar~luartz greywackes and greywacke arkoses with a high content of quartzite, granite and gneiss fragments; typical of the Middle and Upper Jurassic association in the three regions; (3)'greywacke arkoses, feldspar-quartz greywackes and quartz-feldspar greywackes with high content of quartz porphyry, felsitic porphyry, andesite, granite and trachyte fragments; typical of the Upper Jurassic and Lower Cretaceous association in the Aldano-Chulman region; (4) greywacke arkoses and quartz-feldspar greywackes with a high content of rhyolite, felsitic porphyry, trachyte and their tuff fragments; typical of the Lower Cretaceous association in the Tokin region. components (L) represented by cutinite and resinite (sample 225.0/131 and sample 325.0/ 131, Fig. 4, photo 5,6).

Proximate analyses and vitrinite reflectance values Chemical analyses of the South Yakutian coals gave moisture contents (W daf) from 0.20% to

Fig. 4. Petrographic composition of bituninous coals with high volatile matter in the Tokin region (Elga coalfield) of the South Yakutian Coal Basin, Lower Cretaceous, Holodnikan Member, incident light, oil immersion, magnification x300. Indices: Vtl, telinite; Vt2, collinite; I, inertinite; L, liptinite. Photo 1. Sample 375.0/128. Inertinite components, borehole 128, depth 375.0 m. Photo 2. Sample 410.0/128. Inertinite components, borehole 128, depth 410.0 m. Photo 3. Sample 505.0/128. Vitrinite components (collinite), borehole 128, depth 505.0 m. Photo 4. Sample 320.0/131. Vitrinite components (telinite), borehole 131, depth 320.0m. Photo 5. Sample 225.10/131. Liptinite components (cutinite and resinite), borehole 131, depth 225.0 m. Photo 6. Sample 325.0/131. Liptinite components (cutinite) and vitrinite components (telinite), borehole 131, depth 325.0 m.

154

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Fig. 6. Lithology and terrigenous-mineral associations of the coal-bearing strata in the Aldano Chulman region of the South Yakutian Coal Basin, Siberia. Expiation for figures 6-8: 1, conglomerates; 2, sandstones; 3, siltstones and mudstones; 4, coal seams; 5, true arkoses and feldspar-quartz sandstones with a low content of quartzite, granite and gneiss fragments; typical of the Lower Jurassic association in the Aldano Chulman and the Usmun regions; 6, feldspar-quartz greywackes and greywacke arkoses with a high content of quartzite, granite and gneiss fragments; typical of the Middle and Upper Jurassic association in the three regions; 7, greywacke arkoses, feldspar-quartz greywackes and quartz-feldspar greywackes with a high content of quartz porphyry, felsitic porphyry, andesite, granite and trachyte fragments; typical of the Upper Jurassic and Lower Cretaceous association in the Aldano-Chulman region; 8, greywacke arkoses and quartz-feldspar greywackes with a high content of rhyolite, felsitic porphyry, trachyte and their tuff fragments; typical of the Lower Cretaceous association in the Tokin region; 9, isoreflectance lines; 10, boreholes. 2.80%, volatile matter contents (V daf) ranging from 17.0% to 40.0%, ash content (A daf) varying from 1.57% to 25.92%, caking index (y) of 6-21 ram. Vitrinite reflectance was measured according to ICCP standards (Stach 1982) on polished sections of the coals using a microscope-photometer 'MRE-Leitz', with a magnification of 600x. Jurassic and Cretaceous coals in the South Yakutian Coal Basin have middle and high rank, with vitrinite reflectance values (R0)

of 0.65-2.15%. In all the boreholes investigated (more than 50 boreholes with more than 500 samples) the vitrinite reflectance values increase with depth. In the Usmun region the vitrinite reflectance (Ro) of organic matter varies from 0.55% to 1.00%. On the profile A - B of the Usmun region (Fig. 6) the isoreflectance lines of 0.55% R0 and 0.85% R0 are indicated. These are high volatile bituminous coals (Fig. 3). In the A l d a n o - C h u l m a n region the vitrinite reflectance varies from 1.15% to 2.15%. The profile C - D of

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Fig. 7. Lithology and terrigenous-mineral associations of the coal-bearing strata in the Aldano-Chulman region of the South Yakutian Coal Basin, Siberia. the Aldano-Chulman region (Fig. 7) shows isoreflectance lines of 1.55% R0 and 2.00% Ro. These are low volatile bituminous coals (Fig. 3). In the Tokin region of the South Yakutian Coal Basin vitrinite reflectance ranges from 0.65% to 1.15%. On the profile E-F of the Tokin region (Fig. 8) isoreflectance lines of 0.75%Ro, 0.85% R0 and 1.00% R0 are shown. These are high volatile bituminous coals (Fig. 3).

Bitumen

analyses

In order to better understand the effects of metamorphism on the technological and chemical properties of the coals (Teichmuller 1974,

1990; Puttmann et al. 1985) bitumen analyses and column chromatography were carried out. Samples from different coalfields in the South Yakutian Basin were investigated. In the Usmun region we investigated high volatile coals from three boreholes, No 50, 165 and 203 in the Syllach coalfield. The vitrinite reflectance (R0) is 0.75%, the volatile matter is about 33-40% and the caking index is 6-21 ram. In the Tokin region high volatile coals were investigated with a vitrinite reflectance of about 1.0%, volatile matter of about 27-40% and a caking index is 6-21 mm. The coals are from boreholes No 13, 108, 110, 146, 158 and 160 in the Elga coalfield. In the Aldano-Chulman region low volatile coals were investigated with 1.5%R0 and

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Fig. 8. Lithology and terrigenous-mineral associations of the coal-bearing strata in the Tokin region of the South Yakutian Coal Basin, Siberia. 17-22% volatile matter. The caking index is up to 6-21 mm. The samples were from borehole No 3455 in Nerungri coalfield. According bitumen analyses, the fifteen investigated samples contain water (H20) from 0.08% to 2.71%. The contents of ash varies from 9.20% to 40.75% and CO2 from 0.80% to 10.00%. Insoluble organic matter varies between 77.88%-95.05%. No humic acids were detected due to the high alteration of sediments. Extracts of organic matter in chloroform from the coals

in the basin yielded high levels of bitumen. Concentrations of chloroformic bitumen vary from 0.0938% to 3.6466%, of alcohol-benzolic bitumen (A) from 0.0345% to 3.7266% and of alcohol-benzolic bitumen (C) from 0.0322% to 1.886%. Concentrations of total bitumen range from 0.1635% to 7.9838%. Chloroform extracts were separated into different fractions by column chromatography. The concentrations of methano-naphthene oils are from 6.25% to 26.21%, and of polyaromatic

Fig. 9. Petrographic composition of sandstones in coal-bearing strata in the Aldano-Chulman region of the South Yakutian Coal Basin, transmitted light, crossed polars, magnification • Indices: Q, quartz; P1, plagioclases; F, feldspars; R, rock fragments. Photo 1. Sample 27.5/1868. Lower Cretaceous, Holodnican Member, borehole 1868, depth 27.5 m. Greywacke sandstone with high content of quartz and felsitic porphyry, quartzites and granites, sericitization of feldspar. Photo 2. Sample 74.5/1868. Lower Cretaceous, Holodnican Member, borehole 1868, depth 74.5 m. Greywacke sandstone with high content of quartz and felsitic porphyry, quartzites and granites, chloritic and laumontite cement, sericitization of feldspar. Photo 3. Sample 560.1/2777. Middle Jurassic, Duraji Member, borehole 2777, depth 560.1 m. Quartz-feldspar greywacke with high content of felsitic and quartz porphyry, granites, gneisses and rare trachytes, hydromica and laumontite cement. Photo 4. Sample 590.4/2777. Middle Jurassic, Duraji Member, borehole 2777, depth 590.4 m. Feldspar-quartz greywacke with high content of granites and gneisses, hydromica and quartz cement. Photo 5. Sample 837.9/2777. Lower Jurassic, Juhta Member, borehole 2777, depth 837.9 m. Feldspar-quartz sandstone with few quartzite, granite and rarely dolomite fragments, hydromica and laumontite cement. Photo 6. Sample 847.9/2777. Lower Jurassic, Juhta Member, borehole 2777, depth 847.9 m. Feldspar-quartz sandstone with few quartzite and granite fragments.

SOUTH YAKUTIAN COAL BASIN

157

158

I. E. STUKALOVA

oils from 4.92% to 15.95%. The total content of methano-naphthene, aromatic and polyaromatic oils is from 12.50% to 34.13%, with a maximum of 43.51%, representing a high concentration of hydrocarbons. The extracts contain 7.38-21.90% of benzolic resins 0.41% to 1.88% of alcohol resins and 0.49-1.15% of alcohol-benzolic resins present in three samples. The concentration of high molecular weight resins and combinations are from 4.92% to 21.39%. The contents of all resins varies from 13.30% to 49.90%. The extracts also contain asphaltenes ranging from 20.34% to 69.95%. The high concentration of bitumen in the chloroform extracts of organic matter of the South Yakutian coals, is probably responsible for the high caking properties of the coals.

Petrographic composition of sandstones The petrographic composition of the sandstones in coal-bearing strata of the South Yakutian Coal Basin identified four terrigenous-mineral associations, according to the scheme proposed by Shutov (1972). The first is represented by true arkoses and feldspar-quartz sandstones with a low content of quartzite, granite and gneiss fragments (Fig. 5). It is a typical Lower Jurassic association in the Usmun and AldanoChulman regions (Figs 6 & 7). For example, sample 837.9/2777 from a depth of 837.9m in borehole 2777 in the Aldano-Chulman region, is a feldspar-quartz coarse sandstone containing 60% of quartz (Q), 20% of feldspar (F) and 20% of rock fragments (R), represented by quartzite, granite and dolomite fragments. These sandstones contain a hydromica and laumontite pore cement (Fig. 9, photo 5). Another example, sample 847.9/2777 from a depth of 847.9m in the same borehole 2777, is a feldspar-quartz medium sandstone containing 55% of quartz (Q), 20% of feldspar (F) and 25% of rock fragments (R), represented by quartzite and granite fragments. Feldspar is represented by plagioclases (P1). These sandstones contain a hydromica pore cement (Fig. 9, photo 6). The second association features greywacke arkoses, feldspar-quartz and quartz-feldspar greywackes with a high content of felsitic and quartz porphyries, granites, gneisses and rare trachytes (Fig. 5). It is characteristic of the greater part of the Middle and Upper Jurassic coal-bearing strata in three regions (Figs 6, 7, 8). For example, the Duraji Member in the Aldano-Chulman region is represented by feldspar-quartz greywackes (Fig. 9, photo 3,4).

Quartz-feldspar greywacke of sample 560.1/ 2777 from 560.1m in borehole 2777 contains 20% of quartz (Q), 40% of feldspar (F) and 40% of rock fragments (R), represented by felsitic and quartz porphyries, granites, gneisses and trachytes. These sandstones contain a hydromica and laumontite pore cement (Fig. 9, photo 3). Another example, sample 590.4/2777, is represented by feldspar-quartz greywacke from 590.4m in borehole 2777. It contains 30% of quartz (Q), 35% of feldspar (F) and 35% of rock fragments (R), represented by granites and gneisses. These sandstones contain a hydromica and quartz pore cement (Fig. 9, photo 4). The third association of true arkoses, greywackes with high content of quartz and felsitic porphyries, quartzites and granites (Fig. 4), is typical of the Upper Jurassic and Lower Cretaceous deposits in the Aldano-Chulman region (Fig. 7). For example, the greywacke medium sandstone of sample 27.5/1868 from 27.5m in borehole 1868 contains 20% of quartz (Q), 30% of feldspar (F) and 50% of rock fragments (R), represented by quartz and felsitic porphyries, quartzites and granites. The sericitization of feldspar is widespread (Fig. 9, photo 1). Another example, sample 74.5/1868 is represented by greywacke medium sandstone from 74.5m in borehole 1868 in the Aldano-Chulman region from the Lower Cretaceous, Holodnican Member. It contains 25% of quartz (Q), 25% of feldspar (F) and 50% of rock fragments (R), represented with high content of quartz and felsitic porhpyries, quartzites and granites. These sandstones contain a chloritic and laumontite pore cement. The sericitization of feldspar is widespread (Fig. 9, photo 2). The fourth association of feldpathic greywackes and greywacke with a high content of rhyolites, felsitic porphyries, trachites and their tufts (Fig. 4), is mostly encountered in the Lower Cretaceous deposits of the Tokin region (Fig. 8).

Mineral alteration Mineral alterations were investigated both by light microscopy and by X-ray diffraction analyses of clay minerals. The mineral matter within the terrigenous rocks of the South Yakutian Coal Basin has been altered within the catagenetic and metagenetic stages. The terminology of the stages and periods of lithogenesis are those proposed by Vassoevich (1962). The metagenetic stage is seen in highly altered Lower Jurassic deposits in the basin (Figs 5 & 7). In this stage of lithogenesis the blastic structures

SOUTH YAKUTIAN COAL BASIN and welded joints are widely spaced. X-ray diffraction analyses of clay minerals show that kaolinite, dickite, and mica of the 1 Md polytype are present. The catagenetic stage affects Middle and Upper Jurassic and Lower Cretaceous deposits in the basin. This stage of lithogenesis is characterized by alteration of allogenic minerals and formation of new structures. The catagenetic stage includes two subzones: the smectite-mica subzone and the laumontite subzone. X-ray diffraction analyses of clay minerals show that the rocks from the smectite-mica subzone contain up to 5-15% mixed-layer phase smectite-mica and chlorite. X-ray diffraction analyses of the clay nminerals show that in the laumontite subzone laumontite, chlorite and mixed-layer phase smectite-mica with packages up to 10-15% are present. Laumontite forms mainly in the central parts of pores or substitutes for other minerals such as plagioclase, hornblende, biotite and pyroxene (Fig. 9). Other authigenic minerals typical of the laumontite subzone are epidote, sphene and quartz. The characteristics of the three regions of the South Yakutian Coal Basin were compared. Different parts of the basin demonstrate different alteration of organic and mineral matter. Lower Jurassic deposits in the basin are in the metagenetic stage. In the Usmun region high volatile bituminous coals occur and in the Aldano-Chulman region there are low volatile bituminous coals. The middle-Upper Jurassic and Lower Cretaceous deposits of the basin are in the catagenetic stage. The coals in the A l d a n o - C h u l m a n region are low volatile bituminous rank and in the Tokin region they are high volatile bituminous coals.

Conclusions Investigation of the coals in the Usmun, Aldano-Chulman and Tokin regions of the South Yakutian Coal Basin demonstrate that humic coals consist of vitrinite (70-90%), inertinite (10-20%) and liptinite (0-10%) maceral groups. There is a high percentage of telinite macerals, up to 60-65%, in the vitrinite maceral group. According to chemical analyses the coals contain moisture (W daf) from 0.20% to 2.80%, volatile matter (V daf) ranging from 17.0% to 40.0%, ash content (A daf) between 1.57% to 25.92%, caking index (y) is 6-21 ram. Coals are of middle to high rank, with vitrinite reflactance values (R0) of 0.65-2.15%.

159

The South Yakutian coals are of high quality because of their rank and composition. The secondary bitumen macerals are probably responsible for the high caking index of the coals and their coking properties, as compared with coals of the same rank from others coalfields and basins. Sandstones in the coal-bearing formation are represented by true arkoses, greywacke arkoses, feldspar-quartz and quartz-feldspar greywackes. The mineral matter of terrigenous rocks are altered to the catagenetic stage and the metagenetic stage. Vitrinite reflectance and mineralogical parameters were used to evaluate the stages of alteration of sediments.

References BREDIHIN, I. S. 1973. South Yakutian (Aldan) Coal Basin. Geology of coalfields and shales of the USSR., Vol. 9, Nedra Publishing, Moscow, 5-117 (in Russian). FATKULIN, I. Ya., GEBLER, I. I. & RESHETKO,A. N. 1970. Statistic correlation between vitribite reflectance and quality of the coals in the AldanoChulman region. Chemistry of fuels, Vol. 3, 141-143 (in Russian). MARKOVICH, E. M. 1981. Palaeobotanic considerations of stratigraphy and correlation. South Yakutian coal-bearing formation, Leningrad, Nauka Publishing, 33-43 (in Russian). MOKR1NSKY,V. V. 1961. Metamorphism of coals in the South Yakutia. South Yakutian Coal Basin, Leningrad, Publishing of Academy of Sciences of the USSR, 382-420 (in Russian). NAZAROV,V. I. & STUKALOVA,I. E. 1991. Catagenetic alterations of the Jurassic and Lower Cretaceous deposits in South Yakutia. Geology of the coalfields, Ekaterinburg, 100-112 (in Russian). PRILUTSKY, A. M. 1979. Petrographic composition and quality of coals in the South Yakutian Coal Basin. Stratigraphy, paleoenvironment and lithology of the South Yakutian Coal Basin. Transections, VSEGEI, Vol. 306, Leningrad, Nauka Publishing, 78 82 (in Russian). PROSVIRYAKOVA,Z. P. 1961. Palaeobotanic characteristics of the coal deposits in the South Yakutia. South Yakutian coal-bearing formation, Publishing of USSR Academy of Sciences, Vol. XI, pp. 122 175 (in Russian). PUTTMANN, W., WOLF, M. & WOLFF-FISCHER, E. 1985. Chemical characteristics of liptinite macerals in humic and sapropelic coals'. Advances in Organic Geochemistry, Vol. 10, 625-632. STACH, E., MACKOWSKY,M. Th., TEICHMULLER,M., TAYLOR, G. H., CHANDRA, D. & TEICHMULLER, R. 1982. Stach's Textbook of Coal Petrology'. 3rd edn. Gebruder Borntraeger, Berlin. SHUTOV, V. D. 1972. Classification of the terrigenous rocks and greywackes. Greywackes, Nauka Publishing, Moscow, 9-29 (in Russian).

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TEICHMULLER, M. T. 1974. Generation of petroleum like substances in coal seams as seen under the microscope. In: TISSOT, B. & BIENNER, F. (eds) Advances in Organic Geochemistry, Paris, 321-348. - - 1 9 9 0 . The genesis of coal from the viewpoint of coal geology. International Journal of Coal Geology, 16, 121-124. TERENTYEV, E. V. 1978. Tectonics of the coalfields of the USSR. Geology of coalfields and shales of the USSR, 12, Nedra Publishing, Moscow, 94-162 (in Russian). VASSEOVICH, N. B. 1962. About terminology for the stages and periods of lithogenesis. Transactions, VNIGRI, 190, Leningrad, 220-230 (in Russian).

VLASSOV, V. M. 1981. Usmun, Tokin and Gonam reg(ons in the South Yakutian Coal Basin. South Yakutian Coal Formation, Leningrad, Nedra Publishing, 24-32 (in Russian). WALTZ, I. I. 1961. Petrographic composition and structure of coal seams in South Yakutia. South Yakutian Coal Basin, Leningrad, Publishing of Academy of Sciences of the USSR, 176-277 (in Russian). ZHELINSKY, V. M. 1980. Mesozoic coal-bearing formation of South Yakutia. Novosibirsk, Nauka Publishing (in Russian).

Coal rank variations with depth related to major thrust detachments in the South Wales coalfield: implications for fluid flow and mineralization ROD

GAYER,

RICHARD

FOWLER

& GARETH

DAVIES

Department of Earth Sciences, University of Wales Cardiff, PO Box 914, Cardiff, CF1 3YE, UK Abstract: Coal maturity data in the form of volatile matter (daf and dmmf) and random vitrinite reflectance have been analysed for the South Wales coalfield. They show that in general coals increase in rank with depth, obeying Hilt's law, and increase in rank laterally from high volatile bituminous coals in the south and east of the coalfield to anthracite in the northwest of the coalfield. The lateral increase in rank does not coincide with the basin depocentre which was located to the southwest of the coal basin during Westphalian times. The rank pattern with depth in the Westphalian A-Lower Westphalian C Coal Measures of the eastern half of the coalfield suggests a palaeogeothermal gradient of approx. 310~ -1, equivalent to a basal heatflow of 295mWm -2. Investigation of vitrinite reflectance in a coal sequence repeated by intense Variscan thrusting indicates that coal rank was acquired both pre- and syn-thrusting. Detailed analysis of the volatile matter data reveals the presence of excursions from Hilt's law present in one or more coal seams close to the boundary between Westphalian A & B. Of the 154 data sets analysed from the coalfield, 94 (61%) show one or more excursion. It is shown that the excursions correlate with thrust detachments within the coal seams, and it is argued that the excursions represent an increase in maturity temperature caused by fluids carrying heat into the coal seam along the seismically active thrusts. The fluids may also have been responsible for the carbonate, oxide and sulphide mineralization of the coalfield. Preliminary comparisons with the Ruhr coal basin in Germany suggest that future studies involving computer generated thermal models are required to understand the thermal evolution of both basins. The South Wales coalfield represents a major Late Carboniferous coal basin developed on the Variscan foreland. Mining in the coalfield has long recognised the presence of coals ranging in rank from high volatile bituminous coals in the south and east of the coalfield, through intermediate ranks, into anthracite in the northwest of the coalfield. Attempts to explain this rapid rank variation, laterally over c. 50km, have ranged from those invoking differences in the original coal-forming plant communities or depositional environments (Strahan & Pollard 1915; MacKenzie-Taylor 1926; Fuchs 1946), through those resulting from differential burial (Jones 1949; Wellman 1950; White 1991) to those associated with differing heat flows brought about by magmatic heating (Firth 1971), frictional heating along thrusts (Trotter 1948, 1950, 1954), differing basement regimes (Gill et al. 1979), and effects of hot fluids (Davies & Bloxam 1974; Gayer et al. 1991; Austin & Burnett 1994). Most of these have been discussed in detail by White (1991) and by Austin & Burnett (1994), but no convincing proof of the process producing the rank variation has been forthcoming. This paper presents some additional data on the age of rank development relative to Variscan thrusting and the presence of variations in

maturity with depth in the coalfield. By converting maturity indices to temperature, using the formula devised by Barker & Goldstein (1990), values of palaeo-geothermal gradients both for specific stratigraphic intervals within the Coal Measures succession and for different localities within the coalfield are derived. It is argued that the magnitudes and variations of these geothermal gradients are difficult to reconcile with a burial model alone and that the presence of excursions in maturity values coincident with thrust detachments in the coals suggests a causal link, possibly associated with the flow of hot mineralizing fluids guided by thrusts.

Regional geology of the South Wales coalfield Stratigraphy The sediments of the South Wales coal basin are preserved in a structurally complex E - W trending Variscan synclinorium extending from SW Dyfed to the western flank of the Usk antiform (Fig. 1). The coal basin overlies a southward thickening (0-1 km) Lower Carboniferous platform carbonate sequence (Wilson et al. 1987)

From Gayer, R. & Pe~ek, J. (eds), 1997, European Coal Geology and Technology, Geological Society Special Publication No. 125, pp. 161-178.

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Synform

Fig. 1. Map of South Wales coalfield, showing major structures and generalized stratigraphy. BTS, Betws-Tonyrefail Synform; CCA, Cardiff-Cowbridge Antiform; CCD, Careg-Cennen Disturbance; GS, Gelligaer Synform; LCS, Llantwit-Caerphilly Synform; LLD, Llanon Disturbance; MA, Maesteg Antiform; MGF, Moel Gilau Fault; ND, Neath Disturbance; PA, Pontypridd Antiform; SVD, Swansea Valley Disturbance; TD, Trimsaran Disturbance; UA, Usk Antiform; 1, Ffos Las OCCS; 2, Treforgan No. 2 borehole; 3, Treforgan No. 3 borehole; 4, Park Slip OCCS; 5, Ffaldau Colliery; 6, Park Colliery; 7, Ffyndaff OCCS; 8, Maerdy Colliery; 9, Llanharan Colliery; 10, Coedely Colliery; 11, Lewis Merthyr Colliery; 12, Cwm No. 4 shaft; 13, Lady Windsor Colliery; 14, Merthyr Vale Colliery; 15, Windsor Colliery; 16, Nantgarw Colliery; 17, Penalta Colliery, 18, Brittania Colliery; 19, Bedwas Colliery; 20, Oakdale Colliery; 21, Nine Mile Point Colliery; 22, Celynen North Colliery; 23, Celynen South Colliery; 24, Blaenserchan No. 2 shaft and Underground Borehole. that passes conformably downwards into a thick (3 km) Old Red Sandstone unit and a shallow marine Lower Palaeozoic succession. Crystalline basement underlies the coal basin at depths ranging from 3.5km in the northwest of the main coalfield to over 6 km in the east (Hillier 1989). The Coal Measures sequence is up to 3.5 km thick in the centre of the basin and ranges in age from basal Namurian to early Stephanian, covering a time span of some 21 Ma (according the timescale of Lippolt et al. (1984)). The basin was initiated during the early Namurian, following a regional compressional event that resulted in the breakup of the Dinantian carbonate platform, relocation of the basin depocentre and the influx of clastic detritus (Hartley & Warr 1990). The basin has been interpreted as a Late Carboniferous foreland basin at the northern margin of the Variscan orogenic belt (Kelling 1988; Gayer & Jones 1989) thought to have been formed by lithospheric downflexure as a

response to a Variscan tectonic load to the south in SW England. The basin was filled by sediment derived both from the north but mainly from the erosion of the tectonic load to the south (Kelling 1988, Jones 1989a, Hartley & Warr 1990). Throughout Silesian sedimentation the basin depocentre was oriented approximately E-W (varying from NE-SW to NW-SE) and centred on the Swansea-Gower area (Fig. 2). Stratigraphical thicknesses decrease markedly away from the depocentre, particularly to the east but more gradually to the north and west (Hartley 1993). The basin-fill sequence coarsens and shallows upwards from marine mudstones and sandstones (Namurian A-lower Westphalian A), through coastal plain coalbearing mudstones and sandstones (upper Westphalian A-lower Westphalian C) to coarse grained sandstones and conglomerates deposited in an alluvial braidplain (upper Westphalian CStephanian) (Fig. 3, Jones 1989b, Hartley 1993).

COALIFICATION EXCURSIONS AND T H R U S T - G U I D E D FLUIDS

2,5

a. Shale Gp., Namurian R2-G1

I

75

b. Upper Westphalian A

~

-- _

_

~

..~.~

~

~

10

dlf 120 11

c. Lower Westphalian B

~ ~ _

~

:30

~,,,f~-

=1oo

d. Brithdir Beds, Upper Westphalian C Fig. 2. Isopach maps for four time slices to show

depocentrc in south of the coalfield.

Contours in metres.

163

164

E T AL.

R. GAYER

NN

< Z

< -r

Mynyddis lyn

114

~.-_-.-_-.-.-.-,

Swansea

U.I

Three F e e t

m

Hughes

m

if?

----.-~ ~

-.-.-.-.-.,

Z

Brithdir




+::I



@

9 0

~m

(tu) 'I 6 ure~ ~OlOq 41d~G

4

~o

4

(m) 'I6 u*~s ,~opq 41d~(l

COALIFICATION EXCURSIONS AND THRUST-GUIDED FLUIDS Seam Records of the National Coal Board. Data sets were collected from 154 collieries, shafts and boreholes in which Vm values from five or more seams were available. For these localities Vm values were plotted against depth. In general a regular decrease in Vm occurs with increasing depth, indicating an increase in rank with depth and that Hilt's law is obeyed. However, 94 data sets show an excursion from Hilt's law. Figure 9 shows 12 plots of variations of Vm (dmmf) with depth (after White 1992), representing the range of data available from locations across the coalfield. Three main types of pattern can be seen: (i) Vm decreases regularly with depth throughout, with no excursion (e.g. Treforgan No. ! borehole & Lady Windsor colliery); (ii) a single excursion occurs to lower Vm content, shown by one or more seams (e.g. Cwm colliery); and (iii) two or more excursions to lower Vm content occur (e.g. Coedely colliery). The excursion in Vm is mirrored by similar excursions in the volatile elements Sulphur and Phosphorous (Fig. 10). Where an excursion occurs the regular pattern of decreasing Vm with depth is perturbed, with an increase in Vm occurring with depth above the excursion (e.g. Nantgarw colliery). The geothermal gradient, calculated by converting %Vm to %Rm, using the graphs in Stach et al. (1982), and thence to temperature, using the Barker & Goldstein (1990) equation, is also highly variable with values ranging from 8-15~ -~ at Nantgarw colliery to 133-193~ k m -1 at nearby Cwm colliery (Fig. 9). The excursions from Hilt's law most commonly occur centred on seam 37 (48% of excursions) but ranges from seam 80 (< 1%) to seam 13 (2%). The excursion is thus not seam specific and hence is unlikely to be related to the original coal composition. There does, however, appear to be a strong correlation between the stratigraphical level of the excursion and the presence of thrusting within the seam. Although it is difficult to obtain information on the presence of in-seam thrusting from the abandoned mine records, they can be directly observed in the working opencast coal mines. Here thrust detachments in coal seams commonly produce a pervasive, oblique, sigmoidally shaped fabric that has been described as a cleavage duplex (Frodsham et al. 1993; Gayer !993). The detachments also develop true duplexes with roof thrusts immediately above the seam roof and floor thrusts in the seat earth below the seam. The duplexes interleave seat earth and carbonaceous roof rock into the seam and can be recognised in boreholes and shafts as 'rashings', a miners' term for this type of

171

structure (Woodland & Evans 1964). Thrust detachments commonly occur in seams 30-43, with the greatest incidence in the Nine Feet group (seams 30-34) and the Six Feet group (seams 36-39) in the east of the coalfield and in seam 40 in the west of the coalfield. At Llanharan colliery, in the hangingwall of the major Llanharan thrust (Woodland & Evans 1964), two excursions from Hilt's law are recorded in the Vm (daf) data at the level of seams 37 and 27. These are both associated with in-seam thrust detachments revealed by rashings, which also occur within or adjacent to coals 40, 36, 32, 30 and 13 (Fig. lla). In the New Shaft at Park colliery, rashings occur associated with coals between seams 31 and 36 with a Vm (dmmf) excursion present at seam 36. The Cockshot Rock, a persistent fluvial sandstone, lies 45m beneath the excursion at seam 36 (Fig. 11b) In this latter case, the absence of Vm values for the seams between 31 & 36, in which the rashings are present and immediately beneath which the permeable Cockshot rock occurs, means that the precise location and extent of the excursion cannot be determined precisely.

Discussion

Palaeogeothermal gradients and heat flow in the South Wales coalfield One of the outstanding problems of the South Wales coal basin is the explanation for the major lateral rank variation, with seams at the base of the Coal Measures varying from a Rm of 1.0% in the southeast of the coalfield to 4.0% in the northwest of the coalfield (White 1991). This represents a variation of maximum maturity temperature from approx. 150~ in the southeast to 325~ in the northwest. It is difficult to explain this variation by burial depths alone, since the depocentre for the preserved Coal Measures succession lies to the south of the area of highest rank (compare Figs 2 & 5). It would require a considerable thickness of younger sediments deposited before the onset of Variscan deformation to develop the required burial temperatures (e.g. White 1992). Any such sediments have since been completely eroded. Calculation of the required burial depth to produce the maximum maturity temperatures in the northwest of the coalfield is not simple as it depends on a number of undefined variables that include the magnitude of the palaeo-heat flow during the Late Carboniferous, and the thermal conductivity of the now-eroded sedimentary

(a) -250

Manly 4237~40

Nhte MilePeat

-150 ,,~ -200 ~ 91

36 ~ 3 1

~-~ -300

~ "250 t 4 ~ _ - 3 0 0 -350 1-

-351)

f

9

10

-400

I

11 12 Volatile% dmmf

Lady WhMsor

-450

~

I

-5oo[

40

~

13.1/~/ 26 --

-650

I

28

28.5

13

14 15 Volatile% dmmf

I

I

I

29 29.5 30 Volatile% dmmf

-150

30.5

37

-200 -250

26~,,,,,/30 , 17 19 21 Volatile% dmmf

13~

16

Merthyr Vale

23

Lewis Merthyr

-400 -420t 37~

-300 ~ 3 0

-460 -480

I

Ffaidaa

-300 12

"-e-A"2

--13#r26

!

-100

~

-550 -600

31

40----"-'-'-~"~31

-350 t 306 ~

26

13

-500

-450

I

12

12.5 13 Volatile% dmmf

13.5

I

16

I

16.5

I

t

I

17 17.5 18 Volatile% dmmf

19

18.5

(b) Treforl~m2

~

"~-25o

40

3 / _ _ ~ 6

~-300

-310 -330

-350 9 4

t

t

4.5

t

6.5

7

~

-600"550 I -650 -700 26

C-

t

26

26.5

]"

31 i

t

i

27 27.5 28 Volatile% dmmf

D

-800

28

29

..-..----"~31 W" t

30 31 Volatile% dmmf

t

I

6.2

-700

37 t

23

36 t

25

P

27 Volatile% dmmf

29

Coedely

-300i -

30

-650 -250

65

37 ,

29

I

5.9 6 6.1 Volatile% dmmf

Cwm 4

-850

28.5

Naatgarw

-700

~

2 37

-750 13

~

5.8

-550 91~4

t

32

42

37

~ 31

-350 5.7

-

t

5 5.5 6 Volatile% dmmf ][~dwm

400

Treforf,~ 1

-200

-250 -230 t 3 6 ~ "~ -270

-511t)

-650 20

3 3 7 ~ t

31 I

25 30 Volatile% dmmf

6.3

COALIFICATION EXCURSIONS AND THRUST-GUIDED FLUIDS cover. Whatever values might finally be reached for these variables and the thickness of the cover, it would be necessary for the palaeogeothermal gradient imposed by the model to match the palaeogeothermal gradients measured in the various preserved stratigraphical successions. The geothermal gradient indicated in this study of 310~ -1 for the preserved Lower and Middle Coal Measures in the eastern half of the South Wales coalfield, and the assumed even higher gradient in the anthracite zone to the northwest imply high levels of heat flow, as indicated by the following calculation: heat flow (m Wm -2) = geothermal gradient (~ km-1) x thermal conductivity (Wm -1 ~ -l) Thus, with an average thermal conductivity of Coal Measures of 0.9Wm -l ~ -l, a palaeogeothermal gradient of 310~ km -a implies that the South Wales Late Carboniferous heat flow was 295 m Wm -2. This level of heat flow is comparable with values associated with oceanic spreading ridges (Sclater et al. 1980) and is completely unrealistic for continental foreland basins. Preliminary attempts to model the situation in the South Wales coalfield using the commercial basin maturity computer software package BasinMod (Platte Rivers Associates 1996) suggest that such gradients are unlikely to have been generated by burial alone, and it seems likely that the normal continental foreland basal heatflow was enhanced by heat carried into the basin by transient hydrothermal fluid flow.

Role of fluids in the South Wales coalfield The recognition of excursions from Hilt's law in the Lower and Middle Coal Measures of the South Wales coalfield provides strong evidence for localised increase in temperature at specific stratigraphical levels. This is precisely the form of thermal depth profile to be expected where heat has been transferred laterally into the basin along a permeable conduit (Duddy et al. 1994). The temperature would have been raised to

173

produce higher than normal values immediately along and above the conduit, and higher than normal thermal gradients in the overlying sequence. Below the conduit temperatures would have reverted to values associated with the normal heat flow in a normal thermal gradient. Conodont CAI values for the Dinantian limestones beneath the foreland basin show broadly equivalent thermal conditions as for the overlying Coal Measures, but with one major exception. This is in the southwest of the basin in the Swansea and Gower Peninsular area, where very high values of CAI have been recorded (Austin & Burnett 1994) in an area where the overlying Coal Measures show their lowest values of maturity. It is also broadly the site of the foreland basin depocentre (cf. Fig. 2). The origin of this relationship is unclear, but it seems unlikely to have developed from normal burial maturation and may imply the passage of fluids through the Dinantian limestones. The correlation of excursions with in-seam thrust detachments suggests that the thrusts were fluid pathways. Evidence from the Caribbean accretionary prism indicates that fluids are expelled along the basal thrust detachment of the accretionary wedge (Bangs et al. 1990). Similarly, thrust detachments associated with the destructive continental margin west of Vancouver Island channel fluids and produce abnormal heat flows (Westbrook et al. 1993). In recent years there has been a growing recognition that thrusts are able to guide fluids into sedimentary basins (Lawrence & Cornford 1995), and indeed the seismic action of the thrusts may well have increased the rate of fluid flow by seismic pumping (Sibson 1994). In the case of the thrusts within the South Wales coalfield it is clear that the strains associated with thrust deformation has produced extensional and contractional fracture systems that have allowed the volume surrounding the thrust to become permeable and thus to allow fluid ingress (Hathaway & Gayer 1996).

Mineralization in the South Wales coalfield The fracture systems in the coals of the South Wales coalfield are extensively mineralized and more than 50 different mineral species have so far

Fig. 9. Plots ofVm% (dmmf) against depth for 12 sites in the South Wales coalfield, located in Fig. 1 to show the three main types of variation. See text for explanation. Calculated palaeogeothermal gradients between specific seams are shown for seven data sets as follows: Coedely, 117-140~ -l (seams 91-13); Cwm 4, 133193~ km -l (seams 42-13); Nantgarw, 008-016~ km -1 (seams 91-31); Bedwas, 035-053~ km -1 (seams 91-13); Mardy, 056-079~ km -1 (seams 42-13); Lady Windsor, 056~ km-1 (seams 40-13); Faldau, t33-164~ -1 (seams 42-13).

174

R. GAYER E T A L . a)Volatile M a t t e r

-200 -250

91

-300 8O

-350

-400

65

4

6O

-450 -500 .

36

_

-550 -600 -650 20

22

26

24

28

I

t

30

32

34

Volatile % d m m f

b)Phosphorous and Sulphur

-200

-250

91

___...--4

-300

-350

-400 J

-450

-500

42

4o

37

-550

9

-600

26

9

!

-650 0

0.5

1

1.5

2

2.5

--

,,, I 3

3.5

4

% Element

Fig. 10. Vm, sulphur and phosphorous variations with depth at Coedely colliery (located in Fig. 1). (a) Vm% (dmmf), lines represent +1 standard deviation from the mean, and show two excursions from Hilt's Law. (b) Variations in S (squares) and P (circles) showing similar excursions to those in (a). been identified (Gayer & Rickard 1994). These include an early carbonate and oxide phase consisting of Ca, Mg, Fe and Mn carbonates, Ba and Ca sulphates, clays (kaolinite, various illites and mixed layer clays), and quartz, followed by a base metal sulphide and selenide phase consisting of Fe, Co, Ni, Cu, Zn, Mo, Cd and lead sulphides and clausthalite. Gold has

also been discovered in the coal cleat system in some coals, associated with the late stage of the earlier mineral paragenesis (Gayer & Rickard 1994). It has been argued by Gayer et al. 1991 that this mineralization was a result of fluid movements along thrusts carrying exotic ions into the basin and leaching elements from the compacting sediments.

(a)

Lianharan Colliery

-50 -100 Oe

-150

repeat

37

Llanharan Thrust

,.-.,

g

-200

-250 42 -300

37

-

4~_0

it

A36 3 1 G ~

-350

O/~

Red

30

A Amman

~

Yard.

26

-400

13

-450 32

=

~.

!

t

,

I

i

:

33

34

35

36

37

38

Volatile % daf

(b)

Park

42 -300 4O 37

-400

26

-50C 12

t 13

t 14

I 15

16

Volatile % dmmf Fig. 11. Plot of Vm against depth to show relationship between excursions from Hilt's law and in-seam thrust detachments revealed by rashings bands, and the C o c k s h o t Rock sandstone; (a) L l a n h a r a n colliery, lines represent +1 standard deviation from the mean; (b) Park colliery (located in Fig. 1).

176

R. GAYER ET AL.

Comparison with the Ruhr coal basin It is interesting to compare the situation in the South Wales coal basin with that in the Ruhr coal basin, another coal-bearing foreland basin along the northern Variscan margin (Gayer et al. 1993). Computer generated thermal models for 11 localities in the Ruhr coal basin of Germany have suggested that the Ruhr Coal Measures were buried beneath an additional 2.2-3.5 km of younger Carboniferous sediments that were completely eroded before the deposition of the Mesozoic cover (Littke et al. 1994). In order to achieve a match between calculated and observed geothermal gradients the Late Carboniferous heat flow was calculated to have been between 64 and 83 m Wm -2, very high values for downflexed continental crust in an orogenic foreland which in modern situations have low heat flow values with average geothermal gradients of 22~ km -1 to 24~ -l (Allen & Allen 1990). In the Ruhr coal basin the modelled average palaeogeothermal gradient was between 36-47~ -~ but the observed gradient in the preserved Coal Measures succession is 63-65~ km -1, reflecting the lower thermal conductivity of the Coal Measures (and the assumed higher thermal conductivity of the now eroded cover). The above suggests that the Ruhr basin experienced high Carboniferous values of heat flow and a thick Late Carboniferous cover, subsequently eroded. This is in contrast to the South Wales basin where locally high heat flow values appear to be related to fluid inflow along thrusts. In the Ruhr basin there is little evidence for in-seam thrust detachments; the thrusts are commonly ramps and are intimately associated with the folds (Kunz & Wrede 1985). However, as in South Wales, the coal rank was developed at the time of deformation. Excursions from Hilt's law have also been observed in the volatile matter data, although it is unclear how these have been interpreted Ouch 1991). It seems at least possible that fluid inflow has had some role in the development of the Ruhr basin. Computer generated thermal modelling involving possible transport of heat into the basins by fluids is required to understand the thermal evolution of both basins.

Conclusions 1. Coals in the South Wales coal basin show an increase in rank not only with stratigraphical depth, obeying Hilt's law, but also laterally towards the northwest of the coalfield. 2. Vitrinite reflectance (Rm) studies in a thrust repeated succession indicate that rank was developed both before and during thrusting.

3. The geothermal gradient within the Lower and Middle Coal Measures of the eastern part of the coalfield is 310~ -1 and is presumed to be higher in the northwest of the coalfield. Preliminary thermal modelling of the basin suggests that burial alone cannot be responsible for this gradient which would require Late Carboniferous basal heat flow values of 295 m Wm -2. 4. Excursions from Hilt's law occur in locally developed zones associated with one or more coal seams, and most commonly with seam 37 near the base of the Middle Coal Measures. These excursions are observed in plots of volatile matter variations with depth and are interpreted as localised zones of higher temperature. Thermal gradients associated with the excursions vary from 8~ -1 to 193~ -I 5. The excursions are correlated with in-seam thrust detachments, seen as cleavage duplexes and thrust duplexes in working opencast coal mines and as rashings in the colliery records. 6. It is argued that fluids, associated with seismic activity along the thrusts, have carried heat into the coal seams, causing a local increase in the heat flow and a resultant perturbation of the thermal gradient. The fluids have also introduced minerals into the coals. 7. Comparisons with the Ruhr coal basin imply possible similarities as well as differences between the two basins. It is suggested that thermal modelling of both basins may provide the solution to an understanding of the thermal histories of the Variscan foreland basins. The maturity data collated for this study were made available by the former British Coal Corporation. We are extremely grateful to British Coal Opencast and to Celtic Energy for allowing access to opencast coal mines in South Wales and for providing plans and sections from which the thrust structure within the South Wales coalfield has been deduced. The final version of the manuscript has been greatly improved by suggestions made by Ron Austin and Chris Cornford.

References ALDERTON, D. H. M. & BEV1NS, R. E. 1996. P-T conditions during formation of quartz in the South Wales coalfield: evidence from coexisting hydrocarbon and aqueous fluid inclusions. Journal of the Geological Society, London, 153, 265~75. ALLEN, P. A. & ALLEN, J. R. 1990. Basin Analysis." Principles and Applications. Blackwell, Oxford. AUSTIN, R. L. & BURNETT, R. D. 1994. Preliminary Carboniferous conodont CAI data South Wales, the Mendips and adjacent areas, United Kingdom. M~moires Institut Gdologique de l'Universit~ Catholique de Louvain, 35, 137-153.

COALIFICATION EXCURSIONS AND THRUST-GUIDED BANGS, N. B., WESTBROOK, G. K., LADD, J. W. & BUHL, P. 1990. Seismic velocities from the Barbados Ridge Complex: indicators of high pore fluid pressures in an accretionary Complex. Journal of Geophysical Research, 95, 8767 8782. BARKER, C. E. & GOLDSTEIN, R. H. 1990. Fluid inclusion technique for determining maximum temperature in calcite and its comparison to the vitrinite reflectance geothermometer. Geology, 18, 1003-1006. BARTENSTEIN, H. & TEICHMULLER, R. 1974. Inkohlungsuntersuchungen, ein Schlfissel zur Prospektierung yon Palfiozoischen KohlenwasserstoffLagertsfitten? Fortschritte in der Geologie von Rheinland und Westfalen, 24, 129-160. BEVINS, U. E., WHITE, S. C. & ROBINSON, D. 1996. The South Wales Coalfield: low grade metamorphism in a foreland basin setting? Geological Magazine, 133, ?39-749. BROOKS, M., MILIORIZOS, M. & H1ELIER, B. V. 1994. Deep structure of the Vale of Glamorgan, South Wales, UK. Journal of the Geological Society, London, 151,909 917. COLE, J. E., MILIORIZOS, M., FRODSHAM, K., GAYER, R. A., GILLESPIE,P. A., HARTLEY,A. J. & WHITE, S. C. 1991. Variscan structures in the opencast coal sites of the South Wales Coalfield. Proceedings of the Ussher Society, 7, 375-379. DAVIES, M. M. & BLOXAM, T. W. 1974. The geochemistry of some South Wales coals. In: OWEN, T. R. (ed.) The Upper Palaeozoic and PostPalaeozoic Rocks of Wales. University of Wales Press, Cardiff, 225-261. DUDDY, I. R., GREEN, P. F., BRAY, R. J. & HEGARTY, K.A. 1994. Recognition of the thermal effects of fluid flow in sedimentary basins. In: PARNELL, J. Geofluids: Origin, Migration and Evolution q[ Fluids in Sedimentary Basins. Geological Society, London, Special Publication, 78, 325-335. FIRTH, J. N. M. 1971. The Mineralogy of the South Wales Coalfield. PhD thesis, University of Bristol. FRODSHAM, K., GAYER, R. A., JAMES, J. E. PRYCE, R. 1993. Variscan thrust deformation in the South Wales Coalfield- a case study from Ffos-Las Opencast Coal Site. In: GAYER, R. A., GREILING, R. O. & VOGEL, A. (eds) The Rhenohercynian and Subvariscan Fold Belts. Earth Evolution Science Series, Vieweg, Braunschweig., 316-348. FUCHS, W. 1946. Origin of coal and change in rank in coalfields. Fuel in Science and Practice, 25, 132. GAYER, R. A. 1993. The effect of fluid over-pressuring on deformation, mineralisation and gas migration in coal-bearing strata. In: PARNELL, J., RUFFELL, A. H. & MOLES, N. R. (eds) Contributions to an International Conference on fluid evolution, migration and interaction in rocks. Geofluids '93 Extended Abstracts, Torquay, 186-189. --, COLE, J., FRODSHAM, K., HARTLEY, A. J., HILLIER, B. MILIORIZOS, M. & WHITE, S. 1991. The role of fluids in the evolution of the South Wales Coalfield foreland basin. Proceedings of the Ussher Society, 7, 380-384. - - , GREILING, R. O., HECHT, C. & JONES, J. A. 1993. Comparative evolution of coal bearing

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foreland basins along the Variscan northern margin in Europe. In: GAYER, R. A., GREILING, R. O. & VOGEL, A. (eds) The Rhenohercynian and Subvariscan Fold Belts. Earth Evolution Science Series, Vieweg, Braunschweig, 47-82. - - , HATHAWAY,T. M. & DAVIS, J. 1995. Structural geological factors in open pit coal mine design, with special reference to thrusting: case study from the Ffyndaff sites in the South Wales Coalfield. In: WHATELEY, M. K. G. & SPEARS, D. A. (eds) European Coal Geology. Geological Society, London, Special Publication, 82, 233-249. & JONES, J. 1989. The Variscan foreland in South Wales. Proceedings of the Ussher Society, 7, 177 179. -& RICKARD, D. 1994. Colloform gold in coals from southern Wales. Geology, 22, 35-38. GILL, W. D., KHALAE, F. I. & MASSOUD, M. S. 1979. Organic matter as indicator of the degree of metamorphism of the Carboniferous rocks on the South Wales Coalfields. Journal of Petroleum Geology, 1, 39-62. HATHAWAY, T. M. & GAYER, R. A. 1994. Variations in the style of thrust faulting in the South Wales Coalfield and mechanisms of thrust development. Proceedings of the Ussher Society, 8, 279 284. & ----1996. Thrust-related permeability in the South Wales coalfield. In. GAYER, R. A. & HARRIS, I. H. (eds) Coalbed Methane and Coal Geology. Geological Society, London, Special Publication. 109, 121-132. HARTLEY, A. J. 1993. A depositional model for the Mid-Westphalian A to late Westphatian B Coal Measures of South Wales. Journal of the Geological Society, London, 150, 1121-1136. & WARR, L. M. 1990. Upper Carboniferous basin evolution in SW Britain. Proceedings o[" the Ussher Society, 7, 21-216. JONES, J. A. 1989a. The influence of contemporaneous tectonic activity on Westphalian sedimentation in the South Wales coalfield. In: ARTHURTON, R. S., GUTTERIDGE, P. & NOLAN, S. C. (eds) The Role of Tectonics in Devonian and Carbonferous Sedimentation in the British Isles. Special Publication of the Yorkshire Geological Society, Wigley, 243-253. 1989b. Sedimentation and Tectonics in the Eastern Part of the South Wales Coalfield. PhD thesis, University of Wales, Cardiff. 1991. A mountain front model for the Variscan deformation of the South Wales coalfield. Journal of the Geological Society, London, 148, 881-891. JONES, O. T. 1949. Hilt's Law and the volatile content of coal seams. Geological Magazine, 86, 303-364. JUCH, D. 1991. Das Inkohlungsbild des RuhrkarbonsErgebnisse einer Ubersichtsauswertung. Glrickauf Forschungshefte, 52, 37 47. KEELING, G. 1988. Silesian sedimentation and tectonics in the South Wales basin: a brief review. In: BESLY, B. & KEELING, G. (eds) Sedimentation in a Synorogenic Basin Complex, the Upper Carboniferous of Northwest Europe. Blackie, London, 38 42. -

-

-

-

-

-

178

R. G A Y E R E T AL.

KUNZ, E. & WREDE, V. 1985. Exploration und Aufschluss des Nordfeldes der Zeche Haus Aden aus geologischer Sicht. Fortschritte in der Geologie yon Rheinland und Westfalen, 33, 11-32. LAWRENCE, S. R. 8r CORNFORD, C. 1995. Basin geofluids. Basin Research, 7, 1-7. LITTKE, R., BUKER, C., LI3CKGE, A., SACHSENHOFER, R. F. & WELTE, D. H. 1994. A new evaluation of palaeo-heat flows and eroded thicknesses for the Carboniferous Ruhr basin, western Germany. International Journal of Coal Geology, 26, 155-183. LIPPOLT, H. J., HESS, J. C. & BURGER, K. 1984. Isotopische Alter yon pyroklastischen Sanidinen aus Kaolin-Kohlentonsteinen als Korrelationsmarken fiir dan mitteleuropfiische Oberkarbon. Fortschritte in der Geologie yon Rheinland und Westfalen, 32, 119-150. MACKENZIE-TAYLOR, E. 1926. Base exchange and its bearing on the origin of coal. Fuel in Science and Practice, 5, 195. MCCARTNEY, J. T. & TEICHMULLER, M. 1972. Classification of coals according to degree of coalification by reflectance of the vitrinite component. Fuel, 51, 64-68. SCLATER, J. G., JAUPART, C. ~; GALSON, D. 1980. The heat flow through oceanic and continental crust and the heat loss of the Earth. Reviews in Geophysics and Space Physics, 18, 269-311. SmSON, R. H. 1994. Crustal stress, faulting and fluid flow. In" PARNELL, J. (ed.) Geofluids: Origin, Migration and Evolution of Fluids in Sedimentary Basins. Geological Society, London, Special Publication, 78, 69-84. STACH, E., MACKOWSKY, M-Th., TEICHMI]LLER, M., TAYLOR, G. H., CHANDRA,D. & TEICHMI3LLER,R. 1982. Stach's Textbook of Coal Petrology. Gebruder Borntraeger, Berlin.

STRAHAN, A. & POLLARD,W. 1915. The coals of South Wales, with special reference to the origin of anthracite. Memoir of the Geological Survey of Great Britain. TEICHMULLER, M. • TEICHMULLER, R. 1982. The geological basis for coal formation. In: STACH, E., MACKOWSKY, M. Th., TEICHMOLLER, M., TAYLOR, G. H., CHANDRA, D. d~ TEICHMULLER, R. (eds) Stach's Textbook of Coal Geology (3rd edition). Gebriider Borntraeger, Berlin, 5-86. TROTTER, F. M. 1948. The devolatilization of coal seams in South Wales. Quarterly Journal of the Geological Society, London, 104, 387-437. 1950. The devolatilization equation for South Wales coals. Geological Magazine, 87, 196-208. --1954. The genesis of the high rank coals. Proceedings of the Yorkshire Geological Society, 29, 267-303. WELLMAN, H. W. 1950. Depth of burial of South Wales coals. Geological Magazine, 87, 305-323. WESTBROOK, G., CARSON, R., MUSGRAVE, R. & Shipboard Scientific Party. 1993. Fluid flow within a convergent continental m a r g i n - results from ODP Leg 146, Cascadia margin. Geofluids '93 Extended Abstracts, Torquay, 178-180. WHITE, S. 1991. Palaeo-geothermal profiling across the South Wales Coalfield. Proceedings of the Ussher Society, 7, 368-374. WHITE, S. C. 1992. The Tectono-Thermal Evolution of the South Wales Coalfield. PhD Thesis, University of Wales Cardiff. WOODLAND, A. W. & EVANS,W. B. 1964. The Geology of the South Wales Coalfield (Part IV). The Country around Pontypridd and Maesteg (3rd edition). Memoir of the Geological Survey of Great Britain.

Deep borehole evidence for a southward extension of the Early Namurian deposits near N6m~i~ky, S. Moravia, Czech Republic: implication for rapid coalification J. D V O I ~ A K l, J. H O N I ~ K 2, J. P E S E K 3 & P. V A L T E R O V A 4

1 Czech Geological Survey, Leitnerova 22, 658 69 Brno, Czech Republic 2 Hongk Co. Ltd, Opavsk[t 4150/9, 70800 Ostrava 4-Pustkovec, Czech Republic 3 Faculty of Science, Charles University, Albertov 6, 12843 Praha 2, Czech Republic 4 Geofond, Kostelni 26, 170 O0 Praha 7, Czech Republic Abstract: Unexpected Early Namurian (Namurian A) sediments were identified in several

boreholes in the vicinity of N6m6i~ky (the N6m6i~ky basin), south Moravia. Coal fragments were recovered from the boreholes N6m 1, 2, 5 and 6. These fragments come partly from in situ coal seams, partly from eroded coal seams and partly from coalified logs. Although these fragments were recovered from depths of 2690.9 m (N~m 5) to 4803 m (N~m 1), their mean reflectance (R0) is 0.57% up to 0.9% which corresponds to subbituminous to high volatile bituminous coal. The very low rank of the coal at these depths argues for very fast coalification of the coal fragments most likely during the Carboniferous. The rank of the coal is believed not to have been affected by later burial beneath Jurassic sediments or by tectonic burial under Carpathian nappes. The presence of Early Namurian (Namurian A) sediments has been proved below the Carpathian Flysch nappes at relatively great depths in several boreholes drilled by Moravsk6 naftov~ doly Co. during exploration for oil and

natural gas in the vicinity of N6m~i6ky, SE of Brno (Fig. 1). In addition to rocks, some of which strongly resemble sediments of the Czech part of the Upper Silesian coal basin, fragments of isochronous coal were also identified. The

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Fig. 1. Schematic geological map of Moravia-Silesian Devonian and Carboniferous. 1, unfolded rocks on the platform; 2, volcano-sedimentary formations on the surface; 3, basinal formations below the flysch; 4, carbonate formations on the surface or below the flysch and molasse; 5, Upper Silesian basin; 6, borehole Jablfinka 1.

From Gayer, R. & Pe~ek, J. (eds), 1997, European Coal Geologyand Technology, Geological Society Special Publication No. 125, pp. 179-193.

180

J. DVOI~.AK E T A L . A

Age

Formation

Westphalian A

Member Doubrava Such~i

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Karvinfi Saddle

Namurian

Poruba

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Jaklovec

Barbora group of marine bands

Ostrava

Enna group of marine bands Hrugov Frantigka group of marine bands Pet~kovice

Main whetstone horizon

1)hiatus Fig. 2. Lithostratigraphical scheme of the Upper Silesian basin (A) and proved age of sediment filling of the N6m6i6ky basin (B).

first record of fragments of Carboniferous coal found in drilling mud was that of the N6m 1 borehole (Reh/tk 1975). However, no systematic coring of the boreholes was undertaken because the programme was aimed at testing the oil and gas potential in the area. The discovery of coal bearing Carboniferous strata was completely unexpected at such depths. The samples obtained from the drilling mud were subjected to technological tests and petrological investigation despite some uncertainty about the true number of coal seams penetrated during the drilling. It is also possible that some fragments have come from eroded and redeposited coal seams or from

coalified logs. The total length of the analyzed borehole section was from 4250 m up to 4535 m. Palynological studies suggest a Carboniferous age of the examined coal (Knobl-Jachowicz in I~eh~k et al. 1973). Another Carboniferous coal was found in the N6m 2 borehole. A bituminous coal seam, 1700mm thick, was penetrated by the borehole at a depth of 3374.30 to 3376m. Numerous coal fragments were also found in drilling mud in addition to the above mentioned coal seam. The great thickness of the coal seam was the main reason for detailed investigation of both the coal and adjacent sediments which were found

EARLY NAMURIAN COAL-BEARING DEPOSITS, CZECH REPUBLIC in the N~m 1 and 2 boreholes (Hon~k et al. 1978, Hon~k-Vrbovfi 1980, Hon6k et al. 1980, Polick)-Fialovfi 1980) and in other boreholes (see below). Phytopalaeontological studies proved the Late Carboniferous age of these sediments (Early Namurian) which appear to be the same age as the Ostrava Formation in the Upper Silesian basin. Specifically they appear isochronous with the upper part of the Ostrava Formation, commencing with the Enna marine horizon and including the Jaklovec and Poruba members (Purkyfiovfi 1978a, b). Palynological studies by Valterovfi (1978, 1982) also proved the Carboniferous age of the unit (Fig. 2). Later finds of coal fragments from the N6m 5 and 6 boreholes were studied to a lesser extent. No gamma-gamma logging was undertaken in the boreholes for technical reasons. Consequently, the true number of coal seams penetrated during the drilling remains unclear. The source of some coal fragments is also questionable. Despite this uncertainty, the results indicate the extension of the Upper Silesian coal basin into the area beneath the Carpathian Flysch nappes and have important implications for the timing and process of coalification.

Geology of the N~m~i~ky area The region under consideration belongs to the M~nin block (cf. Dvof'fik 1993) which is the southernmost part of the Paleozoic Drahanskfi Vrchovina Plateau, located south of the city of Brno. The basement beneath its sediments consists of the Precambrian Brno-granitoid massif. Two sub-blocks (Fig. 3) were distinguished in the area: the western sub-block consists of the Basal Clastic Formation of Old Red facies resting on the granodiorites. This formation is more than 1400m thick and likely Early Devonian in age. It is overlain by relatively thin (400m) reef limestones (Middle Devonian and Frasnian). The eastern sub-block has suffered greater subsidence. The sedimentation also starts with terrestrial red-purple arkoses of the Old Red facies, with unknown thickness. These were deposited on weathered granitoids of the Precambrian Brno massif. The boundary between the sub-blocks is formed by a N-S trending fault which was penetrated by the N~m 5 borehole (see Figs 3 & 4). The marine transgression recorded in the eastern sub-block reached this area at approximately the boundary between the Eifelian and Givetian. The transgression was followed by

181

deposition of dark, partly dolomitic, limestones of the La~finky Limestones which grade into light grey very pure Vil6movice Limestones. Both types of limestones belong to the Macocha Formation which is of Givetian-lowermost Fammenian age (Fig. 5). This formation is characterized by reef-building coral- and stromatoporoid faunas. The thickness of this formation is about 800 m in the west, gradually thinning to 480 m in the east. A major regression occurred at about the Middle Fammenian, following which the Vil6movice Limestones were karstified. Dark biodetrital Hfidy-l~i~ka Limestones, locally with corals and brachiopods (Gigantoproductus) were deposited after a second marine trans-gression which occurred in the Late Vis6an. These limestones are about 120 to 130 m thick in the west (N~m 2 and 5 boreholes) but thin out to the east. The Hfidy-l~i6ka Limestones are transitional toward the top into dark, locally calcareous silty shales, which represent here the Myslejovice Formation. The shales which were penetrated by N6m 5, N6m 2 and N6m 1 boreholes were 23, 47 and 38 m thick respectively. The onset of coarse-grained sedimentation which outpaced the basin subsidence occurred at the boundary between the Early and Late Carboniferous. A large body of coarse-grained petromict (polymict) conglomerates about 500 m thick was deposited along the western margin of the rapidly subsiding eastern sub-block which is only 150 thick in the N6m 2 borehole. These conglomerates are completely missing in the N6m 1 borehole. The Early Namurian is represented by a cyclic series in which grey to black-grey sandstones, locally with numerous fragments of fossil flora, are the dominant sediments. The N~m 1 borehole penetrated the following rock sequence from the bottom to the top: greywacke sandstone about 80m thick; pink arkoses about 160m thick, and finally feldspathic sandstones more than 250 m thick which represent the last member of the whole sequence terminating the sedimentation. Intercalations of black-grey siltstones and shales and also coal seams, confined to the upper part of the sequence, are much less abundant. Intercalations consisting of tuffites, often mixed in sandstones, represent a typical constituent of this sequence. The N~m 5 borehole revealed also a layer of coarse-grained conglomerates about 200m thick which must thin out towards the N6m 1 borehole. The preserved thickness of the whole sequence reaches 1100 m thick in the west. It is reduced to 600 m toward the N~m 1 borehole some 5 km

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Values V daf are derived from relationship R0 - Vaar, established by Weiss (1976) for the Czech part of the Upper Silesian basin. ESE (Fig. 4) and this has no effect on the coal rank in the underlying Carboniferous (c.f Fig. 4 and Table 3). By analogy with the coalification process in the Upper Silesian basin it is likely that the rank was developed during the late Carboniferous.

Conclusions

The discovery of previously unknown Early Namurian (Namurian A) sediments has been proved palaeontologically in the N~m6i6ky 1, 2, 5, 6 boreholes, drilled in the search for oil and natural gas in SE Moravia (Purkyfiovfi 1978a, b; Valterovfi 1978, 1982). However, neither systematic coring, because the program was aimed at testing the oil and gas potential of the area, nor logging of the boreholes for technical reasons was undertaken. (1)

The partially cored N6m 2 borehole penetrated part of a coal seam at a depth of 3374.3-3376.0m. This borehole and some

(2)

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other boreholes (e.g. N6m 1, 5 and 6) provided the majority of coal fragments found in drilling mud. Some of them likely represent redeposited coalified logs and coal clasts eroded from coal seams. With the exception of the coal seam identified in the drill core from a specific depth in the N~m 2 borehole the remaining coal fragments brought up in drilling mud may not have originated from the indicated depths. Lithological similarities between sediments from the boreholes and those occurring in the Upper Silesian basin indicate that Early Namurian occurrences in the N~m6icky basin were linked with the Upper Silesian foredeep. Purkyfiovfi (1978a, b) considered that these sediments are isochronous with the Jaklovec and/or Poruba Members of the Ostrava Formation of the Upper Silesian basin, suggesting an Early Namurian (Namurian A) age. Palynological studies of coal and sediments also support a similar age (Valterovfi 1978, 1982).

192 (4)

(5)

(6) (7)

J. DVOI~,h,K E T AL. Coal samples from the N6m 2 borehole show the following composition (data in parenthese show the composition of coal fragments from the N6m 1 borehole): vitrinite 77.6-91.9% (78-84%), liptinite 5.3-12.4% (10-16%), inertinite 2.8-12% (5-13 %). A few samples of drill cuttings analysed as bulk samples from the N6m 2 borehole (unknown depth) show an increased content of inertinite, which in one fragment exceeds 50%. Their composition corresponds to that of coal coming from the overlying Karvin~ Formation of the Upper Silesian basin. Basic technological parameters of the coal fragments from the N6m 1, 2, 5 and 6 boreholes are as follows: A a 5.8-37.9%, V daf 37.1-41.5% Qoaf S 31.1434.81MJkg -1, S d 0.37-5.35, SI 0.5-2.0. The mean reflectance (R0) measured on Namurian coal fragments is 0.57-0.81%. Mean values of Rmax obtained from all layers of the Late Carboniferous penetrated by the N6m 1 borehole (total 11 samples) are equal to 0.7%. The calculated gradient of all boreholes is 0.03% Rmax.

Coal fragments identified in the drilling mud from these boreholes and samples of a coal seam penetrated by the N~m 2 borehole at a depth of 3374.3-3376.0 m show that their reflectance (R0) corresponds to that of high volatile bituminous, and occasionally to subbituminous coal. The very low rank of coal found in these boreholes argues for very fast coalification of peat which is in agreement with coal clasts found both in the Ostrava Formation of the Upper Silesian basin which come from eroded Early Namurian coal seams and the Westphalian C and D units of the South Wales basin (Gayer-Pe~ek 1992, Gayer et al. 1996). The rank of coal from N~m6i~ky was not affected by the deposition of overlying Jurassic sediments and a flysch cover nor by its burial under Carpathian flysch nappes. Very fast coalification provides evidence that the temperature gradient in the Variscan foredeep varied between 70 and 90~ -1 (Dvo~'~tk 1990).

References BUNTEBARTH, G., KOPPEL, J. & TEICHMOLLER, M. 1982. Palaeogeothermic in the Ruhr Basin. In: (~ERM~.K, V. & HAENEL, R. (eds) Geothermics and Geothermal Energy, 45-55. DrolL&K, J. 1980. Geotectonic condition of the forming and the extinction of the reef complex, notably in the Devonian of Moravia. Vdstnik Usoredniho fistavu geologick~ho, 55, 203-208.

1989. Anchimetamorf6za ve varisk6m tektog6nu st~edni Evropy -jeji vztah k tektogenezi. Vdstnik (/st(edniho ftstavu geologick~ho, 64, 17-20. 1990. Geology of Palaeozoic sediments of the deep borehole Jablfinka 1 (Beskydy Mts, NE Moravia)- comparison with the deep borehole Mfinsterland- 1. Sbornlk geologick~eh vdd, 45, 65-90. - - 1 9 9 3 . Moravsk~ paleozoikum. Geologie Moravy a Slezska. Sbornik pfisp6vkfi k 90. v~,ro~i narozeni prof. dr. K. Zapletala, 41-58. 1994. Varisk~ flydovf~ v~voj v NizkOm Jesenlku. Czech Geological Survey, Special Papers 3. 1995. Moravo-Silesian Zone. Stratigraphy. In: DALLAMEYER, R. D., FRANKE, W. & WEBER, K. (eds) Pre-Permian Geology of Central and Eastern Europe. Springer, Berlin, 447-489. ELIAg, M. 1974. Mikrofaci~lni v~,zkum karbonfit6 naftonad6jn~,ch oblasti na p[iklad6 autochtonni jury jihov~,chodnich svahfi Cesk6ho masivu. Zemni plyn a nafta, 19, 359-374. GAYER, R. & PEgEK, J. 1992. Cannibalisation of Coal Measures in the South Wales Coalfield- significance for foreland basin evolution. Proceedings of the Ussher Society, 7, 380-384. - - , S~'KOROV,k,I. & VALTEROVA,P. 1996. Coal clasts in the Upper Westphalian sequence of the South Wales coal basin: implications for the timing of maturation and fracture permeability. In: GAYER, R. & HARRIS, I. (eds) Coalbed Methane and Coal Geology. Geological Society, London, Special Publication, 109, 103-120. HON~K, J. & VRBOVA, V. 1980. Chemicko-technologick6 a uheln~-petrografick6 vyhodnoceni karbonsk6ho uhli z vrtfi N6m~i6ky 1 a N~m6i6ky 2. Sbornlk GeologickOho prdzkumu Ostrava, 21, 51-77. et al. 1978. Zhodnoceni vrtnf~ch jader paleozoic~ch hornin z vrtu Ndmdidky 2. MS Geofond, Praha. --, POLICK?, J. & WEISS, G. 1980. Diageneze karbonsk~ch hornin z vrtfi N6m6i6ky 1 a N6m8i6ky 2. Sbornik Geologickkho pr~tzkumu Ostrava, 21, 77-79. PATTEISKY, K. & TEICHMOLLER,M. 1960. InkohlungsVerlauf, Inkohlung-Masstabe und klassifikation der Kohlen auf Grund von Vitrit-Analysen. Brennstoff-Chemie, 41, 79-84, 97-104, 133-137. POLICKY, J. & FIALOVA, V. 1980. Petrografick~, a litologick~ charakter karbonu ve vrtech N6m6i6ky 1 a N6m6i6ky 2. Sbornik Geologickgho pr~zkumu Ostrava, 21, 49-51. PURKY]qOVA, E. 1978a. F16ra svrchniho karbonu (namuru A) v paleozoiku jv. svahfi (~esk6ho masivu u N6m6i6ky na ji~ni Morav6. Casopis SlezskOho Muzea Opava, A27, 77-86. 1978b. Makrofloristick~i korelace sedimentfi karbonu ve vrtech Zaro~ice - 1, Uhfice - 1 a 2 a N~m6i6ky 1 a 2. Zemnf~ plyn a nafta, 23, 555-566. I~EHAK, J. 1975. Carboniferous coal from M~m6i6ky 1 deep borehole near Hodonin in southern Moravia. Vdstnik (/st(edniho ~stavu geologick~ho. 50, 179-182.

E A R L Y N A M U R I A N C O A L - B E A R I N G DEPOSITS, C Z E C H R E P U B L I C et al. 1973. Zhodnocenl uhli z hlubokf:ch vrt~ v okoli Velk~ch Pavlovic. MS Geofond, Praha. STgAKO~, Z. & REHAK, J. 1975. Diskuse k vfskytu uhli karbonsk~ho st6?i na ji~ni Moravd. Sbornik II. uheln6 geologick+ konference Pfirodov~deck+ fakulty UK, 137-141. VALTEROVA, P. 1978. Palynologick~ v2~zkum ve vrtu N6m6i6ky 2. Zemnf: plyn a nafta, 23, 597-618.

--

193

1982. Zji~tdni karbonsk~ch miospor v hlubok~ch vrtech jv. svah~ Cesk~ho maslvu na jiYni Moravd. Sbornik IV. uheln6 geologick6 konference P~irodov6deck~ fakulty UK, 151-154. WEiss, G. 1976. K prfib6hu zm6n stupn6 prouheln~ni s hloubkou v 6s. 6~isti hornoslezsk6 p~inve. Sbornik Geologick~ho pr~zkumu Ostrava, 11, 9-34.

M6ssbauer spectroscopic investigation of low rank coal lithotypes IRENA

K O S T O V A l, K A L I N K A

MARKOVA 2 & KRASIMIR

KUNTCHEV

1

l Institute of Applied Mineralogy', Bulgarian Academy of Sciences, 92, Rakovska Str., 1000, Sofia, Bulgaria 2 St Kliment Ohridski University of Sofia, Tzar Osvoboditel Blvd 15, Sofia, 1000, Bulgaria Abstract: Low rank coal lithotypes- xylain, humovitrain, semifusain, fusain and liptain sampled from the Maritsa Iztok coal basin (Bulgaria) have been examined by M6ssbauer spectroscopy with no pre-concentration procedures. The results are used to identify three iron species in coal lithotypes and show that covalent iron (Fe n) related to pyrite, is the main iron species in xylain, while in humovitrain ferric iron is dominant. The total quantity of iron species in semifusain, fusain and liptain is about the same, but their distribution is different. Ferric iron dominates in all the three lithotypes. Ferrous iron, although present in smaller quantities, has a higher content in fusain than in semifusain. Our results illustrate the type of oxidation processes which formed the coal lithotypes. A transformation of Fez+ to Fe 3+ has occurred out as a result of differing oxidation processes. The intensity of that transformation increases during the destructive microbial oxidation and decreases during thermal oxidation and direct oxidation processes. The opposite transformation of ferric to ferrous iron has been achieved during both thermaloxidation and direct oxidation processes.

Detailed study of the mineral matter in coal is very important for the preservation of the environment since mineral matter may cause air, water and soil pollution as a result of the combustion of coal. There are various techniques which have been used for the analysis of mineral matter in coal. X-ray diffraction, infrared spectroscopy, thermal and microscopic analysis are the most commonly used techniques, but in some cases, due to their low sensitivity, pre-concentration procedures are required. The high sensitivity and noninterference characteristics of the M6ssbauer effect allows it to be used for the determination of several iron species without any pre-concentration procedure. Bituminous and subbituminous coal and their lithotypes have been examined in detail using M6ssbauer spectroscopy (Smith et al. 1978; Melchior et al. 1982; Martinez-Alonso et al. 1987). We have used this method for the investigation of iron species in low rank coal lithotypes which had not previously been attempted. The main iron-bearing minerals found in the Maritsa Iztok coal basin are illite, pyrite, siderite and dolomite. Some pyrite in coal is very unstable and is converted into iron sulphates with different number of hydrous water molecules.

Experimental method

Coal samples The subject of the present study is coal lithotypes of low rank: xylain, humovitrain,

semifusain, fusain and liptain sampled from the Troianovo mine No. 1 in the Bulgarian Maritsa Iztok coal basin (Fig. 1) Their characteristics are presented in Table 1. The investigated lithotypes belong to three genetic series. The first genetic series is primary plant m a t t e r x y l a i n - humovitrain; the second genetic series is primary plant m a t t e r - s e m i f u s a i n - fusain; and the third genetic series is primary plant matter - liptain. The coal lithotypes have been sampled because of their more homogeneous nature than the trivial coal molecular structure. This is the reason these petrographic ingredients have been selected to develop a model in our study.

M6~sbauerspectroscopy M6ssbauer spectra of the samples were obtained using a purpose-made spectrometer with constant acceleration and a resolution of about 0.1 mm/s per channel. The radiation source used was 57Co in a palladium matrix, while the isomer shifts were measured with respect to the center of the spectrum of a reference sample of c~-Fe. Owing to the low content of iron in the samples the spectra were accumulated to reach a signal of 10 6 counts per channel. To determine the line parameters the spectra were processed by the computer program 'M6sspec' for iterative approximation of the experimental points through a sum of Lorentzian profiles using the least-square method.

From Gayer, R. & Pe~ek, J. (eds), 1997, European Coal Geology and Technology, Geological Society Special Publication No. 125, pp. 195-199.

196

I. KOSTOVA E T AL.

> k~

BULGARIA

(

- - -

GREECE ~'~

Varna et'/"J" ~

.

.

.

.

..J

.

45km

MaritsaIztokCoal Basin

Fig. 1. Location of Maritsa Iztok coal basin in Bulgaria.

Table 1. Characteristics of lithotypes Lithotypes

Xylain Humovitrain Semifusain Fusain Liptain

Proximate analysis (wt%)

Elemental analysis (%)

Moisture

Volatile matter V daf

Carbon

Hydrogen Nitrogen

Sulphur

Oxygen

Wa

Ash content Ad

cdaf

H daf

N daf

sdaf

odaf

7.2 10.0 9.4 8.8 4.0

2.6 5.9 9.2 4.4 2.4

61.1 56.4 35.1 17.0 70.9

68.7 66.9 71.1 87.2 70.8

6.8 5.2 4.3 3.1 7.0

0.7 1.2 0.8 0.8 0.8

4.7 3.2 3.3 1.9 3.7

19.1 23.5 20.5 7.0 17.7

a, analytical; d, for dry basis; daf, for combustible basis.

Results The results obtained from the M6ssbauer study of low rank coal lithotypes are presented in Fig. 2 and Table 2. Ferric (Fe 3+) and ferrous (Fe z+) iron, including covalent iron (FeII) were established in different quantities in the five examined lithotypes - xylain, humovitrain, semifusain, fusain and liptain. With Fe u we identify the covalent iron, connected with pyrite in contrast to the other ferrous iron, which may be related to other mineral phases such as siderite and dolomite, which have been detected with X R D analysis, or organic compounds. The ferric iron is connected mainly with the clay mineral illite. The observed iron species can be subdivided in

two groups (a) and (b) with similar M6ssbauer parameters. These groups have centre shifts (6 mm/s) and quadrupole splittings (A mm/s) as follows: group (a) 0.32-0.42 and 0.62-0.85 group (b) 1.05-1.33 and 2.11-2.99 Ferric or ferrous covalent iron, or a combination of both, belong to group (a). It is not possible to determine separately ferric and covalent iron due to a covalent deposition of iron in pyrite on the one hand and the close M6ssbauer parameters (centre shifts of 0.32-0.35 and quadrupole splitting of 0.60-0.65mm/s) of both iron species on the other hand. An additional real

LOW RANK COAL LITHOTYPES

197

(1)

(2)

(3) ..,~_ (-'1

.> .1-,, m

(4)

fl) n"

(5)

9

-a

t

I

-2

1

I

I ,,,

1

2

o

1

r

~

[

I

(;

J

I

+3

l

I

I0

Velocity (mm/s)

Fig. 2. M6ssbauer spectra of (l) xylain; (2) humovitrain; (3) semifusain; (4) fusain and (5) liptain. Velocity axis is with respect to ~Fe. difficulty is the insignificant content of iron in these samples. Ferrous iron belongs to group (b). It may be related to the carbonate minerals, siderite and dolomite, in coal. Iron from group (a) has been established in xylain and humovitrain in the first genetic series (Table 2). With the help of other parallel studies (XRD, SEM and TEM), and according to unpublished data it can be demonstrated that in xylain iron is connected mostly with pyrite, i.e. covalent iron (FeII) dominates. The expected presence of Fe 3+ is in a subordinate quantity, about 8 to 10%. With the second representative of the genetic series, humovitrain, because of the higher value of quadrupole splitting, the iron present is Fe 3+ (Fig. 2).

In the members of the second genetic series, semifusain-fusain, iron of both group (a) and group (b) has been established. Fe 3+ and Fe 2+ can be clearly distinguished in semifusain (Fig. 2). A very small quantity of covalent iron can be masked by Fe 3+. Ferrous iron is present in considerably smaller amounts (11.4%), and ferric iron predominates. It is very likely that Fe 2+ is connected with carbonates, siderite and dolomite, which have been established in this type of coal under X-ray diffraction and SEM analysis. With the second representative of the genetic series, fusain, the iron forms observed coincide with those established in the semifusain, but their quantities are different (Table 2). The amount of Fe z+ is greater (group b), and the

198

I. KOSTOVA E T AL. Table 2. M6ssbauer parameters a for lithoO'pes low rank

Sample

Group b

Centre shift c

Quadrupole splitting

Line widthd

Xylain

a

0.32 4- 0.05

0.62 4- 0.05

0.56 4- 0.08

100+8

Humovitrain

a

0.35 4- 0.015

0.66 4- 0.1015

0.41 4- 0.025

100 4-4

Semifusain

a b

0.334-0.15 1.124-0.03

0.694-0.015 2.11 4-0.03

0.564-0.03 0.26+0.07

88.64-2 11.44-4

Fusain

a b

0.424-0.01 1.334-0.01

0.854-0.01 2.994-0.01

0.554-0.02 0.424-0.02

67.6 4- 3 32.4 4- 3

Liptain

a b

0.36 4- 0.06 1.054-0.10

0.65 4- 0.06 2.73+0.1

0.30 4- 0.08 0.384-0.06

80.04- 10 20.0 4- 10

a All parameters are in mm/s. b a is assigned as pyrite (FeII) or Fe 3* or combination of both. b is Fe 2+. c The centre shifts are reported relative to c~Fe. d Width at half maximum of the peak.

amount of the iron of group (a) less (Fe 3+ or/ and Fe n) in comparison with semifusain, as can be demonstrated by the high quadrupole splitting of the first peak (Fig. 2). The basic iron present (67%), is Fe 3+. If there is any admixture of covalent iron, its amount will a be minimal, (about 5 to 7%). One third of the iron established in fusain is bivalent. In semifusain, and especially in fusain, an increased content of macropores is observed (Markova et al., 1992) with 98.4% in semifusain and 99% in fusain. A large proportion of the clay minerals and pyrite is found in these pores. The porous structure of these lithotypes is related to the high ash content (Table 1). It is likely that a great part of the Fe 3+ and Fe z+ is connected with mineral matter. In liptain, from the third genetic series, iron of both (a) and (b) groups has also been established, Fe 3+ (80%) being predominant (Table 2).

Discussion

Ferrous iron was found to be present in the low rank lithotypes of the first genetic series: x y l a i n - humovitrain formed as a result of gelefication under microbial oxidation destruction conditions (Sigkov 1988). However, in xylain covalent iron (Fe n) is dominant indicating pyrite. Pyritic iron in humovitrain is probably present at rather low concentration, in the range 10-15 wt%. Salts of metals with variable valency have been identified in peat bogs (Garrels & Maskenty 1974). It is suggested that these salts have acted catalitically during the

decomposition of the peroxides and hydroperoxides to free radicals: R O O H + Fe 2+ ~ RO" + Fe 3+ + OH"

(1)

These peroxides and hydroperoxides have been produced by the oxidation of organic matter. The resultant free radicals RO" and OH" are very active and are the reason for the polimerization process (Kucher et al. 1980). The formation of lithotype maceral of the first genetic series represents a continuation of the destruction by microbial oxidation (Si~kov 1988). Therefore, the probable reason for the high Fe 3§ content in the final product of this genetic series, humovitrain, is the continuous oxidation process represented by mechanism (1). According to Sigkov (1977) this lithotype appears to be a huminic polymer. The lithotypes of the second genetic series: semifusain - fusain contain both Fe 3§ and Fe 2§ These lithotypes are a product of fusanization which has taken place as a result of thermal processes in a strongly acidic medium with high oxygen fugacity (Sigkov 1988). It can be assumed that due to this intensive oxidation process the peroxide and hydroperoxide groups have disintegrated under the action of the salts of the transition metals by a combination of reaction (1) and mechanism (2) (Ivanov 1970): R O O H + Fe 3+ ---+ROO" + Fe 2+ + H +

(2)

However, our results indicate that the processes of formation of ferrous iron {mechanism (1)} are dominant not only xylain and humovitrain but also in semifusain and fusain. With the

LOW RANK COAL LITHOTYPES progressive increase in the fusanization process, from semifusain to fusain, the intensity of reaction (1) decreases, while the intensity of a mechanism (2) increases (i.e. the ferric iron content increases). The lithotype of the third genetic s e r i e s liptain, which was formed under the direct action of oxygen, contains both iron species - Fe 3+ and Fe 2+ but the ferrous iron predominates. Consequently, it can be concluded that the peroxides and hydroperoxides produced by oxidation have been decomposed by the action of metals with variable valency according to the two mechanisms as discussed above. The results illustrate the processes of oxidation associated with the formation of the coal lithotypes.

Concusions Low rank coal lithotypes contain three iron species which can be identified using M6ssbauer spectroscopy without pre-concentration procedures. Covalent iron (Fe n ) related to pyrite is the main iron species in xylain. However, in humovitrain ferric ison is dominant. Almost 100% ferric and ferrous iron in different quantities has been determined in the three lithotypes - semifusain, fusain and liptain. Ferric iron dominates in all three. Ferrous iron is present in smaller quantity but it increases in fusain. Our study demonstrates that a transformation of Fe 2+ to Fe 3+ has been carried out as a result of different oxidation processes. The intensity of that transformation increases during microbial oxidation destruction and decreases during

199

thermal oxidation and direct oxidation processes. The opposite transformation of ferric to ferrous iron occurs during both thermal oxidation and also direct oxidation processes.

References GARRELS, P. & MACKENZY, F. 1974. Evolusia osadachnix porod. Ser. Earth Sciences, Vol. 58, Mir, Moskwa. IVANOV, S. 1970. Verishni radicalovi reactsii. Nauka I izkustvo, Sofia. KUCHER, R.V., KOMPANETS,V. A. & BUTUZOVA,L. F. 1980. Structura iskopaemix uglei i ix osobenost k okisleniu. Naukova dumka, Kiev. MARKOVA, K., RADEV, G. & KOSTOVA, N. 1992. Razpredelenie por v ugolnix litotipax niskogo ranga. Ximia tv topliva, 3, 20-22. MARTINEZ-ALONSO, A., GRACIA, M., GANCEDO, R., GONZALEZ-FLIPE, A. R. & TASCON, J. M. D. 1987. The roles of organic and mineral matter in aerial oxidation of brown coal. In: MOULUN,J. A. et al. (eds) International Conference on Coal Science 1987.

MELCHIOR, D. C., WILDEMAN, T. R. • WILLIAMSON, D. L., 1982. Mrssbauer investigation of the transformations of the iron minerals in oil shale during retorting. Fuel, 61, 516-522. SIgKOV, G. D. 1988. Teoretichni osnovi na biohimichnata vaglefikatsiya. Univ. Izd. St. Kliment Ohridski. SMITH, G. V., Liu, J. H. & SAPOROSCHENKO,M. 1978. Mrssbauer spectroscopic investigation of iron species in coal. Fuel, 57, 41-45. VOITKEVICH, G. V., KIZILTSTEIN,L. I. & HALODKOV, J. I. 1983. Rol organicheskogo vechtestva v konsentrasii metalov v zemnoi kore. Nedra, Moskva.

Comparison of solid state 13C NMR of algal coals/anthracite and charcoal-like fusinites: further evidence for graphitic domains P. I. P R E M O V I ( ~ , R. S. N I K O L I ( ~ & M. P. P R E M O V I ( ~

Laboratory for Geochemistry and Cosmochemistry, Department of Chemistry, University of NiY, P.O. Box 91, 18000 NiY, FR Yugoslavia 13C NMR crosspolarization (CP)/magic angle spinning (MAS) spectrometry. We examined two charcoallike fusinites from Serbia: the Jerma (Jerma mine) and Miro~ (mine 'Aliksar') seams. This examination revealed that atomic H/C ratios calculated (on the basis of the CP/MAS parameters) for fusinites studied are higher by 68% (Jerma) and by 64% (Miro6) than the H/C values which are determined by elemental analysis. Calculated H/C values infer that either more carbon or less hydrogen is required for the fusinite structures than is contained in the samples. We conclude that the differences in the estimation of H/C for bituminous charcoal-like fusinites between solid state 13C NMR and elemental analysis can be explained by graphitic domains within the maceral 'invisible' in the CP/MAS experiment. Abstract: Carbon distribution in coals and coal macerals was studied by

Coals have been subjected to many magnetic resonance studies, and many parameters have been measured to obtain information about coal molecular structure. During the last decade researchers have focused their attention on solid state 13C N M R spectroscopy with CP/ MAS because in principle this technique provides a non-destructive way to measure the aromatic/alkenic carbon fraction of coals fa (the ratio of aromatic/alkenic carbon Car to total carbon C), one of the key parameters which characterize the coal structure (Wilson & Vasallo 1985). Usually in 13C N M R spectra of most coals two broad lines can be distinguished belonging to the aromatic/alkenic and aliphatic carbon atoms respectively: fa of coal is defined as the ratio of the integrated line intensity for aromatic/alkenic carbon atoms to the total integrated line intensity (Speight 1994). In addition to aromaticity fa, dipolar dephasing (DD) experiments provide estimates of other structural parameters of coals including the aliphatic (s) and the aromatic/alkenic (p) fraction which are protonated (Wilson & Vasallo 1985). Yet major problems exist concerning the use of solid state 13C N M R spectrometry in coal research. One such problem is that the 13C N M R experiment gives inadequate quantitative estimation of carbon distribution in coal which strongly contradicts other geochemical data (Premovi6 et al. 1992). This contributes to the difficulty in the unequivocal interpretation of the N M R data. The purpose of this report is to show that the estimation of H/C for fusinite (maceral.of the inertinite group) with solid state 13C N M R is not in agreement with elemental data. For the sake of clarity, we will consider only two fusinite materials from two Serbian

seams: Jerma (the Jerma mine) and Miro6 (the Aliksar mine) with high maceral purity (>90%). For comparison, two fresh-water algal coals (torbanites) (Scotland and S. Africa) and, marine algal coal tasmanite (Australia) and the Vrgka Cuka anthracite (Serbia) were also examined. The earliest spectroscopic work of which we are aware which discusses chemical structure of algal coal-torbanites is that of Millais & Murchison (1969). These authors investigated five torbanite samples from: S. Africa, France and Scotland. Their petrographic examination indicates that these freshwater coals contain alginite (maceral of the exinite group) in excess of 90% by volume. Cane & Albion (1971) have proposed that alginite is an oxidative polymer of straight-chain alkadiens of molecular formula: CH2 = CH(CH2),,CH = CH(CH2)4CH3 (n = 15, 17 and 19). Allan et al. (1979) analyzed three torbanites (S. Africa, Australia and Scotland) using various geochemical and optical techniques. They concluded that the torbanites are composed of polymeric materials which contain relatively high proportion of aliphatic structures. According to Allan et al. (1979) the evidence for aromaticity is conflicting but the total Car is suggested to be small on the basis of the elemental analysis and infrared (IR) spectra. For a number of years, this laboratory has been engaged in the structural elucidation of coals and kerogens. Premovi6 et al. (1987) studied two torbanites from Scotland and S. Africa by both 13C N M R CP/MAS technique combined with DD experiments and 1H N M R MAS technique. This examination has shown that these coals have predominantly both aliphatic carbon and protons ( > 9 5 % of total

From Gayer, R. & Pe~ek, J. (eds), 1997, European Coal Geology and Technology, Geological Society Special Publication No. 125, pp. 201-205.

202

P. I. PREMOVI(~ E T AL.

organic carbon and hydrogen) incorporated into polymethylene (-CH2-) skeleton structures.

Experimental procedure The isolation procedure was similar to that used by Premovi6 (1984) and Premovi6 et al. (1986). Powdered rock (50g) was extracted with benzene methanol (3:lv/v) for 96h in a Soxlet apparatus. The residue remaining in the Soxlet thimble was treated with boiling hydrochloric acid (HC1, 4 M) to remove most of the carbonates. Carbonate removal was checked by IR analysis. The insoluble residue was further demineralized by repeated treatment with boiling hydrofluoric/hydrochloric acids (HF/HC1, 22 M and 0.25 M, respectively). This acid mixture removes silicates and the removal was checked by IR analysis. The final residue is the coal sample. It contained only small traces of inorganic minerals, including pyrite, as confirmed by the electron microprobe analysis. Algal coals (Table 1) are of Permian age (about 250 Ma). The Vrgka (~uka antracite and the maceral concentrates from Serbian seams (Table lb) are of Jurassic age (about 200 Ma). All 13C N M R spectra of the coal samples were recorded at 25.15 MHz on a Bruker CXP-100 as previously described (Premovi6 et al. 1986). The

1 K FIDS, acquired with a 3 ms contact time, 0.35 second recycle time and a rotor frequency of c. 4 kHz, were zero filled to 8 K before Fourier transformation. The pulse sequence employed for obtaining the dipolar dephasing (DD) spectra is described elsewhere (Premovi6 et al. 1987). Proton N M R spectrum of tasmanite was taken at 270MHz with MAS and BR-24 at room temperature on an N M R pulse spectrometer constructed in the laboratories of the Friedrich Schiller University, Jena (Germany) (Premovi6 et al. 1987). For F T I R analysis, the sample was mixed with anhydrous potassium bromide and pressed into the disc (2.5 mg/150 mg KBr) with a load of 200 MPa. The spectra were recorded at room temperature on a Bruker ISF l13V F T I R spectrometer.

Results and discussions In addition to torbanites, we have studied by 13C CP MAS marine algal coal: tasmanite containing more than 90% by volume sporinite (maceral of the exinite group). Figure 1 shows typical 13C and 1H N M R spectrum of tasmanite which indicate a presence of a strong aliphatic carbon (Fig. l a) and proton (Fig. l b) bands

Table 1. Geochemical data on the coals." (a) algal coals," (b) bituminous coal macerals (Serbian seams) b (a) Location

Maceral

C

H

(O,N) a

)ca

s

H C

H C

0.09 0.12 0.10

0.89 0.92 0.90

1.66* 1.57" 1.53"

1.61t 1.62t 1.62t

fa

S

p

H C

H C

1.00 0.90 0.80

0.00 0.80 0.80

0.25 0.55 0.65

0.25* 0.40* 0.50*

0.25~ 0.66~ 0.85~

(mol/kg) South Africa Scotland Tasmanite

alginite alginite sporinite

67 69 60

111 108 92

5 4 1

(b) Location

Maceralc

C

H

(O,N) a

(mol/kg) Vr~ka6uka Jerma Miro~

vitrinite inertinite inertinite

76 78 76

19 32 38

0.7 2 3

* Experimental. t Calculated using expression 2. Calculated using expression 1. a Dry, ash-free corrected maceral data. b Separated by sink-and-float procedures by heavy liquids starting with hand-picked lithotypes that were rich in the desired maceral. Predominant maceral (>95%) component.

SOLID STATE 13C NMR

203

--CH 2--

a

~i = I

.

9

l

160

,

I

140

~

l

120

i

I

,

1

~

!

1

,

100 80 60 40 CHEMICAL SHIFT (Plan)

1

20

9

1

0

~

1

-20

Aliphatlc

b

A

1

10

~

1

5

0

CHEMICAL SHIFT

L

(ppcn)

Fig. l. 13C (a) and 1H NMR (b) spectra of the powdered sample of the Vrgka Cuka anthracite. inferring that more than 95% of both organic carbons and protons are aliphatic. Thus these results suggest that the tasmanite is an aliphatic material which also contains a relatively high proportion of polymethylene chains and rather low amount of aromatic/alkenic groups in the structures. It is likely that the best estimated fa value for these materials is close to 0.10 (Premovid et al. 1987). If total coal carbon is apportioned to both aliphatic (Ca0 and aromatic/alkenic carbons C~r, then C = C a l + C a r assuming an overall H/C

value of: 2 for aliphatic portion and 1 for aromatic/alkenic part, we may write H = 2SCal +pCar were H is the total hydrogen of coal. Combining these two equations we obtain H ~ - = 2s(1 - f ~ ) +Pfa-

(1)

As N M R study indicates that fa values for the algal coals in question is small (c. 0.1) and that

204

P. I. PREMOVI(~ E T AL.

most of aromatic/alkenic carbons are nonprotonated (Premovi6 et al. 1987) then the product Pfa is small and can be neglected. In this case, formula (1) is simplified into the form: H

~ - = 2s(1 -fa).

in elemental data tend to imply) there is a good correspondence between experimental (obtained by elemental analysis) and calculated (through NMR data) H/C ratios for algal coals considered here. We have also studied the Vrgka Cuka anthracite using both the 13C N M R CP/MAS (Fig. 2a), 1H N M R MAS (Fig. 2b). The results show that this coal has predominantly polyaromatic structures withfa = 1.0 and consists chiefly of the vitrinite maceral (>90%). It has been suggested that all X3C atoms in these structures

(2)

The H/C values (calculated using the expression 2) of algal coals studied are listed in Table la. Unless the calculations are more seriously in error (than the stated uncertainly

Aromatic

a

I

160

,

I

140

,

I

1

120

100

,

1

80

,

l

,

60

I

,

40

1

20

CHEMICAL SHIFT (ppm)

Aromatic

b

-*:

1

I

lo o CHEMICAL SHIFT (OOm)

,

Fig. 2. 13C (a) and ]H NMR (b) spectra of the powdered sample of tasmanite.

~

1

0

,

i

- 20

SOLID STATE 13C NMR are not equally cross polarized with IH nuclear spins. Most researchers of the subject now agree, however, that the number of ~3C atoms in these coal structures that are not observed by 13C N M R is small (Speight 1994). Since the anthracite is wholly polyaromatic, the total carbon can be expressed as C = C a r . If this is correct then the total hydrogen is given by H = pCar = pC. Hence p = H/C. The calculated value of H/C(= p) shown in Table 1b is in excellent agreement with the experiment. Table 1b lists atomic H/C ratios of Serbian (Jerma and Miro~) fusinite samples computed using expression (1). An examination of this table reveals that calculated H/C values for the fusinite samples are higher by 68% (Jerma) and by 64% (Miro6) than those experimentally determined values. Thus, the H/C values calculated on the basis of the CP/MAS parameters suggest that either more carbon or less hydrogen is required for the fusinite structures than it is contained in the sample. If this notion is valid then there are only two reasonable explanations for the contradiction (between experimental and calculated H/C value given in Table lb): (1) the fusinite carbons are extensively substituted e.g. by O or N for which there is, however, no persuasive geochemical evidence; and, (2) in the fusinite structures there are carbon atoms which do not show their resonancies in the 13C N M R CP/MAS spectrum. In general, the CP/MAS experiment relies on the presence of organic structures abundant in protons in order to observe the 13C N M R resonancies. Consequently, the 13C N M R spectra do not show signals from carbon atoms in structural domains within coal lacking protons, such as graphite. On the other hand, physical, chemical and other studies indicate that the coal fusinites are similar to natural charcoals which is consistent with the view that these macerals had been exposed to elevated temperatures and charred before incorporation in the sediment (Panti6 and Nikoli6 1973). If this concept is true then fusinites as natural charcoal materials would undoubtedly contain a high amount of graphitic components which are inactive for the CP/MAS approach. Thus, we suggest that the differences in the estimation of H/C for charcoal-like fusinites (Serbian seams) between solid state 13C N M R

205

and elemental analysis can be explained by graphitic domains* within these macerals invisible in the CP/MAS N M R experiment. This work is supported by a grant to PIP from Ministry of Science (Serbia), Project 0206. Special thanks to: the late D. Urogevi6 who supplied the fusinite samples (Serbia), the Vrgka Cuka mine (Serbia) for providing the anthracite sample, and Buerau of Mineral Resources, Geology & Geophysics (Australia) for supplying the tasmanite sample.

References ALLAN, J., BJOROY, M. & DOUGLAS, A. G. 1979. A

geochemical study of the exinite group maceral alginite, selected from three Permo-Carboniferous torbanites. In: DOUGLAS, A. G. & MAXWELL, J. R. (eds) Advances in Organic Geochemistry 1979. Technip, Paris, 599-618. CANE, R. F. & ALBION,P. R. 1971. The phytochemical history of torbanites. Journal of the Proceedings of the Royal Society New South Wales, 104, 31-37. MILLAIS, R. & MURCHISON,D. G. 1969. Properties of coal macerals: infrared spectra of alginites. Fuel, 48, 247-258. PANTIE, N. & NIKOLIC,P. 1973. Ugalj. Nau6na knjiga, Belgrade. PREMOVlC, P. I. 1984. Vanadyl ions in ancient marine carbonaceous sediments. Geochimica et Cosmochimica Acta, 43, 873-877. --, PAVLOVIC, M. S. & PAVLOVIC, N. Z. 1986. Vanadium in ancient sedimentary rocks of marine origin. Geochimica et Cosmochimica Acta, 50, 1923-1931. , STOJKOVIC, S. R., PUGMIRE, R. J., WOOLFENDEN, W. R., ROSENBEREG, H. & SCHELER, G.

1987. Spectroscopic evidence for the chemical structure of algal kerogens. In: RODRIGUEZCLEMENTE, R. R. & TARDY, Y. (eds) Proceedings of the International Meeting 'Geochemistry of the Earth Surface and Process of Mineral Formation '. C.S.I.C., Madrid, 421-430. , JOVANOVIC, Lj. S., & MICHEL, D. 1992. SolidState 13C and 1H NMR in kerogen research: Uncertainty of aromacity estimation. Applied Spectroscopy, 46, 16-18. SPEIGHT, J. R. 1994. Application of spectroscopic techniques to the structural analysis of coal. Applied Spectroscopy Review, 29(2), 117-169. WILSON, M. A. & VASALLO, A. M. 1985. Developments in high resolution solid state 13C NMR spectroscopy of coals. Organic Geochemistry, 8, 299-312. * Consists chiefly of amorphous charcoal.

Composition and properties of North Bohemian coals IVANA HELENA

SYKOROV,~

PAVLiKOV,~

l, J A R O S L A V

3 & ZUZANA

( ~ E R N ' ~ 2,

WEISHAUPTOV,~

1

l Institute of Rock Structure and Mechanics, Czech Academy of Sciences, V HoleYovidk(tch 41, 182 09 Prague, Czech Republic 2 Department of Petroleum Technology and Petrochemistry, Institute of Chemical Technology, Technickdt 5 166 28 Prague, Czech Republic 3 N M R Laboratory, Institute of Macromolecular Chemistry, Czech Academy of Sciences, Heyrovskdho ndtm. 2, 162 06 Prague, Czech Republic Abstract: This work presents the mean chemical, micropetrographic, surface and other characteristics of coal seams from western, central, and eastern parts of the North Bohemian brown coal basin. Attention was especially paid to the elemental composition, ash content, content and forms of sulphur, occurrence of syngenetic and epigenetic sulphides, maceral composition, and degree of gelification and decomposition of components in the huminite maceral group. Some other coal characteristics were also assessed, such as pore texture, extractability and solvent swelling of the coals. The coals examined were huminitic with a variable xylite and detrite content. Huminite reflectance varied between 0.33 and 0.39%. Substantial differences in pore texture of the coals were found in the range of meso- and macropores. These differences largely affected the extractability of the North Bohemian coals. The coals also exhibited extremely high swelling ratios in basic solvents, such as pyridine.

The N o r t h B o h e m i a n basin is the most important b r o w n coal basin in the Czech Republic. It is situated south of the Kru~n6 H o r y m o u n t a i n s and has an area of approximately 1400 k m 2.

The main coal seam belongs to the M i o c e n e Most F o r m a t i o n . The only mineable seam in the N o r t h Bohemia coal basin is the m a i n coal seam with an average thickness of 30 m a n d m a x i m u m

i

,_.r-'/% L

S' '73.75"bs7

@~

.....

.+f'

~"'"'"

_

=_-_.

~

== >_.

>

~=

,-4 E

232

S. SYABRYAJ

Table 1. Comparison of the composition of mega- and microfloral remains from the Upper Pliocene of the

Transcarpathians Pollen and spores

Megaflora

Taxa

Number of palynomorphs

Taxa

Number of megafloral remains

1

2

3

4

Ilnitsa, mine N 1 Polypodiaceae Osmunda Pinus Pinus cf. sylvestris P. tertiaria P. cf. strobus P. cf. Baileyana Picea Picea media

2 1 49 1 1 1 5 6 1

Taxodiaceae Glyptostrobus

4

Sciadopitys Poaceae

1 2

Liliaceae Juglandaceae Juglans J. cf. cinerea Carya C. cf. aquatica Alnus Carpinuas Zeilkova Ulmus Celtis Liquidambar Tilia cordata

Cornaceae Rosaceae Oleaceae (Fraxinus) Ericaceae Gentianaceae Veliky Rakovaets Pinus Picea Abies Tsuga

2 2 3 1 3 2 21 2

Equisetum parlatorii Dryopteris denticulata D. linneaneiformis Osmunda heeri Pinus (wood)

Cupressinoxylon Taxodium dubium Glyptostrobus europaeus Sequoia langsdorfii Phragmites oeningensis Cyperacites zollikoferi

1 7 1 5

4 29 12 4

1

Betula Quercus pontica miocenica

10

Acer Cercediphyllum crenatum Alangium tiliaefolium

21 2 16

Fraxinus paviifolia

18

1

1 6 2 1 2

1 3 1 1 2

Loranthus

1

Taxodium dubium

1

Arundo anomale Phragmites oeningensis

1 6

Cyperus Phyllites cf. Myrica

1 1

35 10 6 2

Sciadopitys

2

Poaceae (cf. Phragmites) Potamogeton Sparganium

2 1 3

P A L Y N O L O G I C A L STUDIES OF T H E T R A N S C A R P A T H I A N S Table 1.

233

(continued)

Pollen and spores Taxa

Number of palynomorphs 2

1

Veliky Rakovats

Megaflora Taxa 3

Number of megafloral remains 4

(continued) Salix rozmarinifolius S. varians

Juglans cf. regia Juglans Carya C. cf. elegans Pterocarya Betula Alnus Corylus Fagus Quercus cf. Castanea Celtis Ulmus Moraceae Liquidambar Elaeagnus Tilia cf. cordata Tilia

1

5 15 3 5 3 22 2 17 3 4 9 9 2 3 2 2

Carpolites cf. Carya Pterocarya paradisiaca

Aesculus hippocastanea

34

1

Acer integerrimum A. subcampestre A. trilobatum A. campestre Cedrella sarmatica Alangium tiliaefolium Fraxinus paviifolia

4 27 17 3 2 234 53

Rosaceae Nymphaeaceae Labiatae Ranunculaceae Urticaceae Lythraceae Franceniaceae Primulaceae Rubiaceae Solanaceae Berezinka Polypodiaceae Polypodium Cyatheaceae Pinus Picea Larix Tsuga Taxodiaceae Taxodium Poaceae

Salix

4 1

2 44 3 1

2 4 2 1

Glyptostrobus europaeus Phragmites oeningensis Typha latissima Cyperus reticulata Arundo goepperti Salix varians S. subaurita Salix Populus rhamnifolia

5 1

2 4 25 6 5 2

234 Table 1.

S. SYABRYAJ

(continued)

Pollen and spores Taxa

Megaflora

1

Number of palynomorphs 2

Berezinka (continued) Juglans Carya Alnus Corylus Betula Quereus Fagus Castanea Ulmus Moraceae Nymphaeaceae Liquidambar

1 2 4 2 4 2 13 3 5 3 1 1

Nyssa Rhus

Oleaceae Fraxinus cf. ornus Rosaceae Legominiosae Ranunculaceae Valerianaceae Thymeliaceae

Taxa 3

Number of megafloral remains 4

Quercus pontica-miocenica

6

Castanea atavia Ulmus longifolia

3 3

Nelumbo protospeciosa Liquidambar europea Platanus aceroides

8 3 16

Acer aegopodifolium A. hungaricum A. sancta-crucis A. trilobatum Acer cf. sinense cf. A. pseudoplatanus Trapa transcarpatica Alangium tiliaefolium

2 2 6 10 2 8 13 6

1 1

2 1 2 1 2 1 1

contains a lesser quantity of thermophile plants and more abundant hydrophile angiosperms, as well as dark coniferous elements and more numerous herbaceous taxa. It is necessary to concentrate on the third coal seam, which is poorer than the lower and upper ones. It does not contain thermophile elements, including light-dependent ones like Celtis and it shows fewer sporomorphs of angiosperm pollen whilst Taxodium and Osmunda are abundant (Fig. 2). The third seam may be regarded as the boundary between the lower and upper horizons, but its palynological composition is more akin to that of the upper horizon. The spectra of the first, second and third coal seams are to be considered togather. The spectrum from the coal seam of Gorbki, the upper seam of Uzhgorod, and several small seams from Rocosovo are identical to the second palynocomplex. The composition of taxa and their numerical content is an argument in favour

of correlating these coal seams with the upper horizon. The presence of Luzatisporis punctatus and L.perinatus in the Gorbki coal bed allows its correlation with the second seam of Ilnitsa. The palynological contents of the Ilnitsa Suit can be compared with megafloral remains from the Berezinca, Ilnitsa, and Veliky Racovets localities. This comparison between the palynological and megafloral composition highlights similarities on the generic level. However, the palynological contents are more diverse (Table 1). The general picture of vegetation throughout the coal bearing formation shows generally a rather monotonous warm-temperate deciduous forest cover with some subtropical elements. However, coniferous forests existed in the Trancarpathians as well as in marshy conditions as is shown by the presence of Taxodium, Nyssa, Alnus and Osmunda which were found to be widespread in some of the wetter areas. Sphagnales were important in the swamps, especially during the

PALYNOLOGICAL STUDIES OF THE TRANSCARPATHIANS accumulation of the fourth coal seam. Some species of pine also inhabited swampy grounds, as can be seen in the contemporary Mshana swamp in the Transcarpathians. Brush swamps with Myrica and Salix invaded the outer parts of marshes. Wet forests with Carya, Liquidambar, Pterocarya, Alnus, Acer, and Ulmus occured in the vicinity. Mixed and deciduous forests with Pinus, Abies, Cedrus, Tsuga, Betula, Fagus, Quercus and Castanea developed in the drier habitats on higher areas. The climate was warm-temperate, rather humid. Only when the third coal seam accumulated did the broad-leaved forests become more impoverished. The third coal seam overlies a thick volcanic ash band and the coal contains much tuffaceous material. Volcanic activity taking place immediately before the third coal bed accumulated, evidently influenced the floral composition. Some thermophile and lightdependent elements (such as Celtis) vanished from the plant cover. However the volcanicity also had a positive influence. The broad-leaved forests on the Vigorlat-Gutin mountain ridge probably expanded due to the volcanic products accumulating at the foot of the volcanoes (Syabryaj 1991). Such processes can be observed today in areas of modern volcanic activity, e.g. Kamchatka and Indonesia. The enrichment of plant communities is observed during the period of formation of the second and first coal seams, when volcanism diminished. Taxa such as Castanea, Platycarya, Engelhardtia, Magnoliaceae and the lightdependent Celtis reappeared in the deciduous forests, and the area of Quercus communities increased. Modern beech forests are of importance in separate regions of Carpathians and on the Vigorlat-Gutin mountain ridge, where the rich original beech forests are preserved today as forest reservations. Only the marsh forests remained unchanged during the period of Upper coal-bearing formation. At the end of the Pliocene the flora became poorer, but there were no fundamental changes in plant cover and its structure. The Late Pliocene flora of the Transcarpathians was warm-temperate, essentialy wet, with predominantly thermophile deciduous forest elements, producing swamp forests. Coniferous and mixed forests occurred in the mountain areas.

Conclusions With regard to the floral composition, the entire period of coal formation of the lower and upper

235

horizons shows marked similarities. The entire interval is referred to the Romanian. The climate was warm-temperate, rather humid with a tendency to become cooler prior to the Gunz glaciation. The flora from the coaly sediments of the Ilnitsa suite formed different communities similar to the ones of the same age in neighbouring areas. Thanks are due to Dr. I. Iljinskaja for kindly providing the samples of the Ilnitsa Suite with megafloral remains from the Berezinka, Ilnitsa and Veliky

Rakovets localities. I am grateful to the anonymous reviewers for suggesting several corrections.

References CHMARSKY, N. Z. 1954. Some data about fossil flora of the Tertiary of the Transcarpathians. In: Scientific notes of Dnepropetrovsk Institute. Collected works of geol.-geogr, faculty and Institute of Geol., 39, 127-132 (in Russian). ILJINSKAJA, I. A. 1968. The Neogene flora of the Transcarpathian region of the UkrSSR. Publ. house 'Nauka', Leningrad (in Russian). RYBAKOVA, N. O. 1964. The new data about the Upper Neogene flora of the Transcarpathian region of UkrSSR (by palynological study). Bull. Moscow Society of test of nature, Geol. Series, 64, 241-245 (in Russian). - - 1 9 7 5 . Palynological description of the Miocene and Pliocene deposits in the Transcarpathians (UkrSSR). Paleontol. collect., 1-2, N 12, 142-147 (in Russian). SCHEKINA, N. O. 1960. History of the Neogene flora of the Ukrainian Carpathians and Precarpathians. Flora and fauna of the Carpathians. Publ. house AS USSR, 58-74 (in Russian). SYABRYAJ,V. T., LEVITSKY,B. P., SYABRYAJ,S. V. & EMETS, T. P. 1969. Substantial and palynological composition of coal-bearing formation of the geosinclinal part of UkrSSR. Publ.house 'Naukova dumka', Kiev (in Russian). SYABRYAJ,S. V. 1975. Description of the Levantinian

flora and vegetation of the Transcarpathians. In: Flora. Taxonomy and Phylogeny of plants, 279-288 (in Russian). - - 1 9 8 6 . Evolution of the Neogenian flora and vegetation of the Carpathians. Doct. hab.thesis (in Russian). - - 1 9 9 1 . Vegetation and volcanism in the Neogene of the Transcarpathians. Palaeovegetational development of Europe and region relevant to its palaeofloristic evolution. Proc. PEPC. Vienna, 231-234. VODOP'JAN,N. S. 1979. The diatoms in the Pliocenian deposits of the Transcarpathians. Ukr. Botan.journ. 35, 141-146 (in Ukrainian).

The distribution of sulphur in the Palaeocene coals of the Sindh Province of Pakistan S. R. H. B A Q R I

Pakistan M u s e u m o f Natural History, Garden Avenue, Shakarpyran, lslamabad, Pakistan

Abstract: 46 samples of coals were collected, representing eastern and western coalfields of the Sindh Province of Pakistan to investigate any systematic quantitative changes in total sulphur. The coal is Palaeocene in age and the number and thickness of coal seams decreases from east to west. The sulphur content was determined as total sulphur on an elemental analyser Carlo Erba model EA 1108 on a dry basis. The sulphur content displays systematic variations and increases gradually from east to west. It is about 1.44% in the eastern coalfields at Tharparkar, 2.55% in the central coalfields at Badin and 4.95% in the western coalfields at Lakhra. The Palaeocene coalfields of the Sindh Province were deposited in shallow continental lagoonal areas towards Tharparkar in the east and comparatively down dip deeper areas with brackish waters (deltas, estuaries) towards the Lakhra in the west. The distribution of sulphur displays a good theoretical example in the change of depositional environment from fresh water to brackish waters environments. It is concluded that the coalfields with low sulphur occur in the east as compared to the coalfields with high sulphur in the west.

The Palaeocene coals of the Sindh Province of Pakistan occur in the Bara Formation and have been discovered from east to west at Tharparkar, Badin and Lakhra (Fig. 1). Stratigraphically, coal bearing Palaeocene sediments in the Sindh area have been studied by several authors (Shah 1977). Frederiksen et al. (198990: in Shah et al. 1992) named the Palaeocene rocks, from base to top the Khadro Formation, the Bara Formation, the Lakhra Formation and the Sonahri Formation (Fig. 2). The coal bearing Bara Formation consists of shales, sandstones, marls and coal bends in the western side at Lakhra, while it consists of clays and sandstones of probably fresh water origin in the east at Tharparkar. The presence of marls and lenticular argillaceous limestone bands at Lakhra in the west (Fig. 2) reflect comparatively more saline and deeper water conditions as compared to the east at Tharparkar. There are about 11 coal seams in the Tharparker coalfield that range in thickness from 1.42 to 27 m. In addition, there are numerous thin coal partings intercalated with the shales. There are three workable coal seams in the Badin area and the thickness varies from 0.55 to 3.1m (Khan et al. 1992). Three coal seams have been reported from the Lakhra Coalfield which range in thickness from 0.3 to 3.00m. The number and total thickness of coal seams generally decrease from east to west, indicating

a source of the coal vegetation towards east where the Precambrian granitic basement rocks are also exposed at Nagarparkar. The Bara Formation is unconformably overlain by Pleistocene conglomerates and sandstones of probable fresh water origin in the eastern coalfields (Tharparkar and Badin coalfields) and conformably overlain by Eocene marls and clays of probable bracklish water to marine origin in the western coalfields, located in the Lakhra area. Figure 2 gives a generalized section of the Palaeocene rocks in the Lakhra Coalfield of the Sindh Province. The depths of the respective samples are provided in Table 1 and the details about the locations drilling cores lithology etc are provided by Shah et al. (1992). 46 coal samples were collected to investigate the total distribution of sulphur and to understand the palaeo-environments of the depositional basin. The sulphur content was determined as total sulphur in an elemental analyser carlo Erba model EA 1108 on dry basis.

Distribution of sulphur Figures 3 and 4 and Table 1 give the distribution of total sulphur in two boreholes (TP-3, TP-4) in the Tharparkar area and in some coals from the Badin and the Lakhra coalfields. The sulphur in most of the samples is less than 1%

From Gayer, R. & Pegek, J. (eds), 1997, European Coal Geology and Technology, Geological Society Special Publication No. 125, pp. 237-243.

238

S. R. H. BAQRI

' 72"

I

6,~"

L

U.S.S. R

/

AFGHANISTAN

NW R#, - ~ ::)NTIE~ ~ ~'\'~:~3) ~,--~

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JAMMU a KASHMIR

/ ,~'.~s ,6 ,7 ( PAN JAB

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/

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(SINDH. /

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4 /~ 4 ~ ' / 4 /r ,-e~-.4

0 } 0

200 krn I.,

TP4

~

J~

1

e.~. 200mi I

Fig. 1. The location map of the coalfields of Pakistan. The circles display the locations of the samples collected for the present work: 1, Indus East Badin; 4, Lakhra; 26, Tharparkar.

with the exception of eight samples and indicates the lowest concentration of sulphur in Pakistani coals. The average concentration of sulphur in 40 samples of the two boreholes in the Tharparkar coalfield is about 1.44% and is the lowest of all coalfields of Pakistan (Baqri 1993). Figure 4 and Table 1 show that the sulphur in most of the samples (with the exception of one sample) from borehole TP-3 remains even less than 1% and

indicates a good prospect for an area of low sulphur coal. The distribution of sulphur with depth in bore hole TP-3 does not show any systematic variation and probably reflects the uniformity of the processes of deposition or diagenesis. The distribution of sulphur in bore hole TP-4 is interesting and is not uniform. It does not show any systematic variation with depth but appears as a random distribution and

S U L P H U R IN P A L A E O C E N E COALS, P A K I S T A N

MEMBER

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EXPLANATION

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9

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Shale and ctay stone ;:.~:: Sandy shale .. ; ... _.:.-, Siltstonr and sift Shaly sandstont Sandstone sctr~d~ Coat Undorctay

100

Meting Shale

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Meting Limr

TM'sohnaricoat zone

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Laki Limestone

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239

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,

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SCALE IN NETERS

Fig. 2. The stratigraphic section of the Palaeocene/Eocene rocks from the Lakhra Coalfield in Sindh Province

240

S. R. H. BAQRI

Table 1. The weight percentage of sulphur (wt%) in Palaeocene coal samples with respective borehole numbers and depths in metres. Tharparkar (TP4, TP3) Badin (BN1) and Lakhra (LS4, SOs)

Sample

Sample No and depth in metres

Sulphur (wt%)

1. 2. 4. 5. 6. 7. 8. 9. 10. 11. 12. 13. 14. 15. 16. 17. 18. 19. 20. 21. 22. 23. 24 25. 26. 27. 28. 29. 30. 31. 32. 33. 34. 35. 36. 37. 38. 39. 40. 41. 42. 43. 44. 45. 46.

LS4, 156.97-157.64 LS4, 190.98-191.28 BN1, 0.36m Bara Fm. BN1, 101.7 BN1, 122.85-123.31 TP4, 180.91-181.25 TP4, 181.25-181.6 TP4, 181.6-181.93 TP4, 192.05-193.02 TP4, 193.2-193.58 TP4, 193.58-194.31 TP4, 194.51-195.16 TP4, 200.68-201.12 TP4, 203.45-203.75 TP4, 205.73-206.08 TP4, 223.78-224.66 TP4, 229.01-229.71 TP4, 229.71-230.18 TP4, 230.18-230.73 TP3, 148.6 TP3, 153.92-154.22 TP3, 154.22 TP3, 155.7-156.72 TP3, 156.72-156.97 TP3, 157.64-158.24 TP3, 158.34-158.94 TP3, 158.52-160.02 TP3, 158.94-160.02 TP3, 161.52-162.42 TP3, 162.42-163.07 TP3, 163.07-162.42 TP3, 164.30-164.75 TP3, 164.75-165.52 TP3, 165.52-166.11 TP3, 166.11-167.66 TP3, 167.66-168.21 TP3, 168.21-169.21 TP3, 169.21-169.90 TP3, 169.90-170.72 TP3, 170.73-171.83 TP3, 171.38-172.26 TP3, 172.26-172.83 TP3, 172.93-173.83 TP3, 173.83-175.23 TP3, 197.25-198.35

0.92 6.27 1.65 5.29 0.73 3.53 7.81 16.94 0.43 0.43 0.37 0.42 2.97 2.93 0.56 0.3 0.44 1.36 2.88 0.82 0.71 1.36 0.85 0.71 0.84 0.69 0.72 0.57 0.62 0.69 0.49 0.66 0.59 0.54 0.1 0.51 0.59 0.45 0.2 0.69 0.71 0.38 0.58 0.7 0.76

therefore reflects probably variations during the depositional and diagenetic history. Seven samples contain less than 1% sulphur, five samples display sulphur between 1-4% and only two samples display more than 7% sulphur (Table 1).

Table 2 provides the average distribution of sulphur in the Badin and Lakhra coalfields of the Sindh Province. The sulphur in the Badin coalfield is lower (2.55%) than the Lakhra (4.95%). The low sulphur in the Badin coalfield is due to leaching of the sulphate ions through meteoric waters, poor in sulphate ions, most likely fresh/brackish waters as the Bara Formation with intercalating coal seams is overlain by conglomerates and sandstones of Pleistocene age.

Discussion

Querol et al. (1991) studied the total sulphur in coals of Teruel District, Spain and concluded that the distribution of sulphur in the coals is influenced by the depositional and diagenetic environments. Querol et al. (1989) carried out detailed investigations on the iron sulphide precipitation sequence in Albian coals from the Maestrazgo basin, southeastern Iberian Range, northeastern Spain. They proposed five stages of iron sulphide precipitation which were controlled by the coalification evolution. The lowest concentration of sulphur in the coalfields is generally due to either their deposition in the proximal part of the depositional basin (fresh water ponds, Fig. 5) or due to the leaching of the sulphate ions during early or late diagenetic stage through the waters poor in sulphate ions. It is most likely that the eastern coalfields of the Sindh Province experienced both processes. The eastern coalfields were likely deposited in the proximal part (fresh water, Fig. 4) of the Palaeocene depositional basin, shallower in the east and comparatively deeper towards the west (representing brackish to delta front environments). The basement rocks are still exposed further east at Nagarparkar in Tharparkar district. The second cause for the low sulphur concentration in the eastern coalfields (Tharparkar area and Badin area) is due to the leaching of the sulphate ions by meteoric waters from the overlying Pleistocene conglomerates and sandstones of probably fresh/brackish water origin as compared to the western coalfields at Lakhra where the Palaeocene rocks are conformably overlain by Eocene marls, clays and limestones of marine origin. Figures 3 and 4 display the increasing distribution of sulphur from east to west and indicate a basin with its proximal end towards the east (Tharparkar) and the distal end towards the west where more sulphate rich waters acted during the deposition of the Palaeocene coal field at Lakhra.

S U L P H U R IN P A L A E O C E N E COALS, P A K I S T A N

Distribution

241

of SuLphur

5

;"4

~3 m

2

0 WEST

LAKHRA

BADIN

T H A R P A R K A R EAST

Fig. 3. The average distribution of sulphur in the Sindh coals from east to west (Table 2).

Distribution of sulphur in Sindh coots I sulphur% ) 17 16-

1513 12 I1 tO 8 8

7 G 5 /,.

3 2 1 0

12 3 4 5 6 7 8 9 101112131/,1516171M92021ZZ?..~/,2r WEST

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Seriol no of somples(Tobte | ) . Fig. 4. The distribution of sulphur in the individual samples of coals from the coalfield of the Sindh Province.

242

S. R. H. BAQRI

Table 2. The distribution of sulphur in the Palaeocene coals of the Sindh Province Name of coalfield

Average sulphur (wt%)

SD

SE

No of samples

Lakhra Badin Tharparkar

4.95 2.55 1.44

3.55 2.41 2.85

2.05 1.39 0.45

3 3 40

3. The sulphur in the eastern coalfields or the Sindh Privince is low and therefore the eastern coalfields are the g o o d prospects for low sulphur coals and m a y be exploited for industrial purposes. I am grateful to the EEC for providing a financial grant as a post-doctorate Marie Curie Senior Research Fellowship for the carrying out of these studies. I wish to thank Professor Dr N. Hamilton, University of Southampton, for allowing me to conduct these studies in the Department of Geology, I am also grateful to Dr Bashir Ahmad Sheikh, Chairman of the Pakistan Science Foundation, Islamabad, for his encouragement and granting permission for me to carry out these studies in the UK. I am thankful to Dr Shahzad A. Mufti, Director General, Pakistan Museum of Natural History, who encouraged the publication of this work. I am grateful to Mr. Sher Akbari for his help in the laboratory. Finally, I pay my regards to Dr John Marshall for his keen interest, supervision and encouragement of these studies, and to Mr Abbas Ali Shah, Director, Geological Survey of Pakistan for providing the borehole samples for these studies.

SD, Standard deviation; SE, Standard Error.

Summaryand conclusions 1. The sulphur content in Palaeocene coals of the Sindh Province increases from east to west. It is 1 . 4 4 w t % at T h a r p a r a k a r , 2 . 5 5 w t % at Badin and 4.95 w t % at L a k h r a . 2. The Palaeocene coals were deposited in fresh water p o n d s towards the east and in comparatively m o r e saline brackish water conditions towards the west.

17 3

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Tidal flat= klangrovr swarr~Fre~ , and . _..and water Delta Front_ _ cnannets lid61- channel swam p

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Serial no of sarnples

( T a b l e 1)

Fig. 5. The palaeoenvironments of depositional basin and the distribution of sulphur in the Palaeocene coals of the Sindh Province of Pakistan.

S U L P H U R IN P A L A E O C E N E COALS, P A K I S T A N

References BAQRI, S. R. H. 1993. Research progress report for Marie Curie Bursary, No. B/Cl1"-923195, University of Southampton, UK. KHAN, S. A., KHAN, I. A., ABBAS, S. G. & KHAN, A. L. 1992. Coal Resources Potential of Pakistan. Information Release 533, Geological Survey of Pakistan. QUEROL, X., CHIUCHONS,S. • LOPEZSOLER,A. 1989. Iron Sulphide precipitation sequence in Albian coals from the Maestrazgo basin, Southeastern Iberian Range, northeastern Spain. International Journal of Coal Geology, 11, 171-189.

243

, FERUANDEZ-TURIEL J. L., LOPEZ-SOLER, A., HAGEMANN, H. W., DEHMER, J., JUAN, R. & Ruiz, C. 1991. Distribution of Sulphur in coals of the Termel mining district, Spain. International Journal of Coal Geology, 18, 327-346. SHAH, A. A., KHAN, S. A., TAGER,M. A., CHANDIO, A. H. & LASHARI, G. S. 1992. Drilling and Coal Resources Assessment in Southern Sindh, Pakistan. Information Release 537, Geological Survey of Pakistan. SHAH, S. M. I. (ed.) 1977. Stratigraphy of Pakistan, Memoir Geology Survey of Pakistan, 12, 138.

Sulphur distribution in a multi-bed seam PAUL

F. C A V E N D E R

& D. A L A N

SPEARS

Department of Earth Sciences, University of Sheffield, Sheffield $3 7HF, UK Abstract: The Parkgate Seam (Langsettian) is an important seam for the coal industry in the UK. It extends over a considerable part of the East Pennine Coalfield and a large database of information on the seam has been complied by (the former) British Coal for the Nottinghamshire area from many sampling locations. The seam has been subdivided into a series of mappable units termed plies. This paper demonstrates how sulphur concentrations may vary considerably on a vertical scale and that spatial distributions within individual plies may be markedly different to other plies within the seam. Often seam sulphur maps for industrial use are produced for a composite of the whole thickness of the seam, typically as the whole seam-less-dirt. The neglect of the vertical variation in seam sulphur content may lead to the production of maps which are of limited industrial use. Variations in sulphur distributions also has implications for the origin of the sulphur in the coal. Distribution maps have allowed the controls on sulphur in the Parkgate Seam to be investigated, and these are dominated by complex depositional processes.

Mapping of geochemical variables (sulphur and chlorine contents), ash content, seam splitting and, perhaps most importantly, seam thickness has been carried out throughout the history of the coal mining industry. This has been achieved by interpretation of data collected over the period of exploration, development and mining of seams, resulting in an in depth knowledge of the seam both vertically and spatially. Data are usually accumulated by seam sampling from borehole cores or pillar sections; see Ward (1984) for discussion of sampling techniques. Since economically viable seams are commonly in excess of 1 metre in thickness, several samples are usually collected and analysed. These analyses have allowed the accurate subdivision of seams, which are usually formed from a number of distinctive, laterally persistent units, termed plies. Historically data were manipulated by hand and profiles and isolines were then plotted by eye, rather than by a sophisticated technique. However, this work is now done as routine by computer, creating the opportunity of accessing and manipulating an extensive database in a way not previously feasible. Access to the British Coal database (British Coal 1992a) has allowed much investigation of the coal. The database includes extensive information (on 3569 samples) resulting from the exploitation, observation and analysis of seams for many locations. The Parkgate Seam, from the Langsettian (Westphalian A) of the Nottinghamshire Coalfield, UK, has been studied in detail and forms the basis for the work presented here. The seam is also the subject of other work on the prediction of sulphur in coal (Cavender & Spears 1995a) and an alternative analytical technique for the determination of forms of sulphur and

trace elements in coal, based on the use of ICPAES (Cavender & Spears 1995b). The present paper describes and discusses the mapping of sulphur in coal and investigates the use of ply-by-ply mapping in contrast to the mapping of the whole seam, taking into account also the vertical distribution of the sulphur content. It then goes on to discuss the controls on sulphur in the Parkgate Seam.

The Parkgate Seam The Parkgate Seam has been worked in the East Pennine Coalfield, UK, and substantial reserves remain at the present day. The seam was regarded by (the former) British Coal as one with an important future well into the next century. A considerable amount of data are available on the characteristics of the seam within the seam database (British Coal 1992a). Figure 1 shows the stratigraphical position of the seam within the Westphalian, together with the subdivision of the seam as used in this work. Seam plies are referred to by ply codes in the text of this work and the reader is referred to Fig. 1 for their intra-seam positions. The seam lies in the upper part of the Langsettian and is a considerable stratigraphical interval from any marine sediments in the sequence, a common prerequisite for high sulphur coals (Williams & Keith 1963). Several workers have discussed the depositional environments of the coal-bearing deposits of the East Pennine Coalfield, the most notable recent publications being by Guion & Fielding (1988), Guion et al. (1995) and Flint et al. (1995).

From Gayer, R. & Pe~ek, J. (eds), 1997, European Coal Geology and Technology, Geological Society Special Publication No. 125, pp. 245-260.

246

P. F. CAVENDER & D. A. SPEARS

Westphatian

Parkgate Seam

L a n g s e t t i a n ( W e s t p h a t i a n A) m- m-~

Clay Cross Marine Band

i (Vanderbeckei)

t s

]right coal

t

C

t

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,'

,

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,

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ledium sulphur

t

/ i

t

/

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I /

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t

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! SILKSTONE (YARD / BLACKSHALE)

i i z

I

/

'

~ KILBURN

bright and dull

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A

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Langsettian

...............

/

ash content very high sulphur )yrite common

m . m -~ ( G a s t r i o c e r a s s u b c r e n a t u m )

Fig. 1. Stratigraphical position of the Parkgate Seam within the Westphalian of Nottinghamshire and the

simplified subdivisions of the Parkgate Seam (redrawn from Cavender & Spears 1995a).

Correlation of the Parkgate Seam Before considering the sulphur distribution in the seam, the correlation of the seam is outlined, both from a historical perspective and for the purpose of this work. The Parkgate Seam extends over a considerable area, and is present throughout the East Pennine Coalfield. Figure 2 shows the extent of the seam and also the areas in which the intraseam correlation has been considered. It also shows the main area of the study of this work, which lies in the northern part of the Nottinghamshire Coalfield. Many workers have suggested subdivisions for the Parkgate Seam over the whole East Pennine Coalfield, and a summary of these subdivisions is given in Table 1 together with references. It should be noted that the most important and easily identifiable ply of the seam is the l st/2nd Piper split (X2P), this subdivides the seam into the 1st Piper (1P) and the 2nd Piper (2P). Originally the 'Pipers' of Derbyshire were not considered to be the same seam as the Parkgate of Yorkshire. This was noted by Edwards (1951), who introduced the term 'Dukeries' coal which represented a composite of the Deep Hard and 1st Piper Seams. This term was subsequently dropped by Edwards

(1967) when the Parkgate Seam (of Yorkshire) and the 1st and 2nd Piper Seams (of Nottinghamshire and Derbyshire) where proved to be continuous. The seam is termed the Parkgate Seam in this paper. The most up-to-date and relevant correlations of the Parkgate Seam in Nottinghamshire have been made by British Coal (1992a, b). These correlations show differing terminologies with the British Coal (1992a) division being used in this work. This subdivision of the Parkgate Seam has been made using a number of variables. Historically, a number of samples have been collected by British Coal at each sampling location. The boundaries between the samples are selected by either changes in the character of the coal, the presence of partings, or by a maximum sample thickness (usually around 200 mm). This means that several samples may be collected from a single ply of the seam. The following information is recorded for each sample collected: the thickness; the coal lithology and characteristics; the ash content and the total sulphur content. These variables, together with the presence of seam splits are used to define the individual plies of the seam and all of these data have been included in the seam database by British Coal (1992a). The seam subdivision is shown on Fig. 1, together

S U L P H U R D I S T R I B U T I O N IN A M U L T I - B E D SEAM

1320

[340.^.

,= . . . . . .

o~sea_m......

T ~-

247

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,."':'"-':

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,, i

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O' ', "" ; Thoresby Colliery ;, ~'-'

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S U L P H U R D I S T R I B U T I O N IN A M U L T I - B E D SEAM with a brief description of the characteristics of each ply. The 1PUB and 1PM plies are difficult to distinguish where seam splitting is absent and therefore are considered together in this work. The 2nd Piper is c o m m o n l y split, but the splits tend to be laterally impersistent and therefore the ply has not been subdivided. In addition to the plies m e n t i o n e d above a r o o f and a floor coal are sometimes present (Table 1), separated from the m a i n b o d y of the seam by splits.

Generation of seam sulphur maps M a p s showing the distribution of seam sulphur content have been p r e p a r e d using i n f o r m a t i o n from the British Coal seam database (British Coal 1992a). Table 2 shows an example of the seam data for one sampling location within the database. F r o m the database, for a ply or g r o u p

249

of plies (specified by the ply code, Table 2), data were extracted for a given variable, in this case the sulphur content. These r a n d o m l y spaced data were then gridded using the kriging technique (see Swan & Sandilands 1995) and then s m o o t h e d sulphur isolines were constructed. All m a t h e m a t i c a l procedures a n d plotting were carried out using a personal computer. If, as in m a n y cases, m o r e t h a n one sample had been analysed for an individual ply, then a m e a n value for this ply was calculated using a weighing related to the thickness of the individual samples.

Sulphur distribution in the Parkgate Seam The only sulphur data available in the seam database are for total sulphur contents and therefore distribution maps are for total sulphur

Table 2. Format of British Coal seam database

1

2

3

FLASH LANE

468 644

364 663

693.48 693.49 693.59 693.78 693.79 693.80 693.94 694.14 694.25 694.26 694.41 694.44 694.65 694.68 694.76 694.81 694.83 695.04 695.14 695.22 695.34 695.40 695.53 695.57 695.70

10 1 10 19 1 1 14 20 11 1 15 3 20 3 8 5 2 21 10 8 12 6 13 4 13

BRIT DULL BRIT BRIT DIRT DBRT BRIT BRIT BRIT DBRT BRIT DULL BRIT DULL BRIT DULL DBRT DIRT BRIT DIRT DBRT DBRT BRIT DIRT BRIT

1PUT 1PUT 1PUT 1PUT 1PUXB 1PUB 1PUB 1PUB 1PM 1PM 1PM 1PH 1PH 1PH 1PH IPH 1PH X2P 2PU 2PXL 2PL 2PL 2PL XFC2P FC2P

3.4 3.4 3.4 3.2 55.6 20.8 3.3 4.1 7.1 28.4 3.7 8.1 3.3 3.7 4.9 10.1 15.6 79.5 14.0 84.0 16.1 25.0 10.9 53.0 14.2

1.20 1.20 1.20 1.69 0.80 1.52 1.84 1.79 2.07 1.00 2.01 0.91 1.04 0.87 1.00 1.04 1.30 0.62 3.39 0.66 8.70 16.40 3.02 1.09 2.53

4

5

6

7

8

9

Table indicates data for one location. 1 - name of location, 2 - grid reference (eastings), 3 - grid reference (northings), 4 - depth to the base of unit from borehole origin, 5 - thickness of unit (cm), 6 - coal lithology code (BRIT Bright Coal, DULL - Dull Coal, DBRT - Dirty Bright Coal, DIRT - Dirt Band), 7 - ply-code (see Fig. 1), 8 - ash content (%), 9 - total sulphur content (%).

250

P. F. CAVENDER & D. A. SPEARS

distribution only. However, a number of samples have been collected for this study and 80 samples analysed, from all plies of the seam, in order to determine the forms of sulphur in the coal. Samples from seven complete seam sections were collected from the northern part of the Nottinghamshire Coalfield (see Fig. 2). Analysis of the samples for forms of sulphur was made using an alternative technique, based on the British Standard method, but using ICP-AES to determine sulphur in the digestion solutions prepared (see Cavender & Spears 1995b for details). Total sulphur was also analysed, using the British Standard high-temperature method (British Standards Institution 1977). The analyses have allowed the vertical distribution of the forms of sulphur within the seam to be studied. In addition the vertical distribution of total sulphur for a wider area has been studied using information in the seam database.

Forms of sulphur in the Parkgate Seam From the analyses carried out for this work, it has been demonstrated that the variation in total sulphur in the Parkgate Seam is almost entirely due to the differing concentration of pyrite (Cavender & Spears 1995a). This relationship can be seen clearly when total and pyritic sulphur are plotted against each other (Fig. 3a), and also in individual seam profiles (Fig. 4). Table 3 shows the general distribution of the forms of sulphur in the seam. Pyrite shows a considerable variation (1.17• in the seam with very high percentages in some samples being due to the presence of pyrite nodules. Organic sulphur is relatively constant with only a small variation

(a)

(1.09 + 0.36%). It has been suggested that organic sulphur increases with pyritic sulphur but to a lesser degree (Wandless 1959). This relationship is shown in Fig. 3b, but in this case the relationship between the forms of sulphur is unclear.

Vertical variation of total sulphur and forms of sulphur." analysed seam sections Figure 4 shows the vertical distribution of the forms of sulphur in the seam at the selected sampling locations (see Fig. 2). In all cases the 2P has the maximum total sulphur concentration, although in the Ollerton 18's (Fig. 4b), Ollerton 19's B and Thoresby sections, the total sulphur is not as high as in the other sections. Both the Welbeck (Fig. 4c) and Ollerton 3's (Fig. 4d) sections show very high concentrations of total sulphur in the 2P, with a maximum at the base of this ply (the base of the seam). In addition to the 2P, the 1PUB/1PM ply also has high total sulphur but this is much less prominent than in the 2P. The 1PH ply shows a low in the total sulphur profile. This ply is mainly composed of banded bright and dull coal, the latter often being consistent with a low sulphur content (Wandless 1959).

Vertical variation of total sulphur." seam database The vertical variation of total sulphur in the seam is summarized in Figure 5. The results have been calculated as the mean of all the mean total sulphur contents at each location for individual plies. The results are similar to those obtained

(b)

10

10 r2=0.09

9

~

8 7 ~

6

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0 ,r>,

-5

5

.tO

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9 ~o

9

9" ~ " i

tr22 = 0.9596 i

i

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L'~.,_

1 0 0 1 2 3 4 5 6 7 8 9 10 11 12 total sulphur % organic sulphur % Fig. 3. (a) Pyritic sulphur plotted against total sulphur for coal samples analysed (redrawn from Cavender & Spears 1995a). (b) Pyritic sulphur plotted against organic sulphur for coal samples analysed.

SULPHUR

DISTRIBUTION

IN

A

MULTI-BED

SEAM

251

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. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . ......................................................................

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252

P. F. CAVENDER & D. A. SPEARS

T a b l e 3. Forms of sulphur in the Parkgate Seam (data from Cavender & Spears 1995a)

Mean S.D. Min. Max.

total

pyritic

sulphate

organic

2.34 1.83 0.84 11.05

1.! 7 1.79 0.00 9.61

0.08 0.11 0.00 0.58

1.09 0.36 0.12 1.71

greater number of samples ( n = 192 except; 1PM, n = 179; 2P, n = 1 5 9 ) in the database. The maximum sulphur content is at the base of the seam (2P). Many ply descriptions from British Coal records indicated that pyrite nodules are commonly present in this ply, emphasising the importance of pyritic sulphur in this seam. The lowest concentration of sulphur is seen the 1PH ply, with the 1PUT ply also low in sulphur, and the 1PUT/1PM ply with a mean of just over 3%. From the analyses done for this work and also the information in the seam database it is clear that the vertical variation in the total sulphur is considerable.

n=75 from the seven analysed seam sections (above), although results from the latter are in all cases lower than the corresponding result from the seam database. It is likely that this is due to the

80

mean: 1.84 s.d: 0.55

60

1PUT

40 20 0

SOT

~ 1mean:3.15

40

.:

1PUB

.

20 10 0

~

50

mean: 3.25 s.d: 1.50

40

1PM

30 20

on IIINnn o .

10 0

i

90 ] ~ - ~ m e a n :

1.51

1PH

25

mean: 4.19

20

2P

15 10 5 0

,

,

0

,

,

,

1

IIl!lOOnnnOn

n 2

3

4

5

6

7

8

9

10

total sulphur %

Fig. 5. Vertical distribution of total sulphur in the Parkgate Seam (data from British Coal 1992a).

SULPHUR DISTRIBUTION IN A MULTI-BED SEAM

Ash-sulphur relationships in the Parkgate Seam Although the data on the forms of sulphur within the Parkgate Seam are restricted to analyses done in this work, a vast number of total sulphur analyses exist for the samples in the seam database. These samples also have been analysed for ash content. This ash content, determined by the high temperature ignition of coal, is a reflection of the mineral matter present in the coal in situ. The ash content is therefore controlled by various mineral fractions. By X-ray diffraction analysis, the main components of the mineral matter in the Parkgate Seam have been identified as quartz, illite, kaolinite and pyrite. Pyrite is transformed to iron oxide during the ashing process, and the reaction may be described as follows: 4FeS2 + 1102 - - + 2Fe203 + 8SO2

(1)

This reaction means that there is a minimum possible amount of iron oxide within the resulting ash for a given amount of pyrite within a coal sample. This amount can be calculated and a theoretical relationship between ash and pyritic sulphur determined. This relationship is: 0.8032 x ash

Spy =

(2)

253

where Spy is the percentage of pyritic sulphur in the coal sample and 'ash' is the percentage of ash in the coal sample. Since only total sulphur data are available in the seam database the theoretical relationship between total sulphur and ash is: St =

(0.8032 x ash) + So + Ss

(3)

where S t is the percentage of total sulphur in the coal sample, So is the percentage of organic sulphur in the coal sample and Ss is the percentage of sulphate sulphur in the coal sample. Since the values of organic and sulphate sulphur have been determined and they are both relatively constant in the Parkgate Seam (Table 2) they can be included in the theoretical equation: St = (0.8032 • ash)+ 1.18.

(4)

Figure 6 includes this line (4) on a graph of ash plotted against total sulphur, for all samples present within the seam database. Of note are the very small number of samples which lie outside this theoretical line (that is with high sulphur contents and low ash contents), indicating that equation (4) applies to the samples in the seam database. The outlying samples may be due to abnormally high percentages of organic sulphur or analytical errors. The plot also indicates another trend in the data. The minimum amount of sulphur present

35 t h e o r e t i c a l line of m i n i m u m ash a g a i n s t sulphur:

30

.

y = O . 8 0 3 2 x + 1.09

25

o~ z,..

= 20 (.-

C~

O)

O 9

9

10 9

5

L

]

,

9

/ .d~JSg~'~

0 /

9

9 o

, 9 ."

8

*O* ,4

~

o 9

..

**

.

.e.

,

. 9

" .........

. . . . 9

9

, .........

9

9149

' " ;;~" . . . . .

,

"-" " ""

/

0 /20 p r o g r e s s i v e 'dilution' of s u l p h u r by detrital fraction of coal ash

40

60 ash %

Fig. 6. Total sulphur plotted against ash for data within the seam database.

80

100

254

P. F. CAVENDER & D. A. SPEARS

decreases with increasing ash content, in contrast to the relationship already noted. In this case it is clear that the increase in ash content is not due to pyrite, although pyrite may still be present in small amounts in these samples, but silicate minerals such as detrital clays and quartz. The decrease in minimum sulphur content is caused by the relative decrease in the amount of carbonaceous material in the samples which are either dirty coals or from seam splits. Some samples on Fig. 6 show very high percentages of total sulphur. These samples are likely to include pyrite nodules and therefore abnormally high values of are obtained (>25%).

Spatial variation of total sulphur Sulphur distribution maps have been produced for the main plies of the seam. A composite map of the whole seam-less-dirt sulphur (Fig. 7) is shown in addition to the total sulphur in the 1PUT (Fig. 8), 1PUB/1PM (Fig. 9), 1PH (Fig. 10) and 2P (Fig. 11) plies. These figures show data other than sulphur distributions and are referred to in the discussion of controls on sulphur in the seam. The Parkgate Seam composite map (Fig. 7) shows a variation of sulphur contents from < 1 to >3%, with most of the seam being between

Fig. 7. The distribution of total sulphur in the Parkgate Seam (whole seam-less-dirt), showing fault trends.

Fig. 8. The distribution of total sulphur in the IPUT ply of the Parkgate Seam and the sandstone units above the seam.

Fig. 9. The distribution of total sulphur in the 1PUB/1PM plies of the Parkgate Seam.

Fig. 10. The distribution of total sulphur in the 1PH ply of the Parkgate Seam and the relationship to seam splitting (redrawn from Cavender & Spears i995a)

Fig. 11. The distribution of total sulphur in the 2P ply of the Parkgate Seam and the relationship to seam splitting (redrawn from Cavender & Spears 1995a).

SULPHUR DISTRIBUTION IN A MULTI-BED SEAM 2 and 3%. The spatial variation is considerable with, for example, Ollerton Colliery showing a generally lower sulphur content than Bevercotes Colliery. However, this map does not accurately represent the whole-seam sulphur as it would be mined since, it excludes the seam splits (dirt bands). Maps of the main plies of the seam show that the location of the area of maximum concentration of sulphur for each ply does not correspond. This is important since most maps used in the coal industry are usually composites, indicating whole seam-less-dirt (e.g. Fig. 7). Therefore these maps do not show the considerable vertical variation which may exist in seams and hence, are of limited industrial use in multibed seams of this type. Successful ply-by-ply mapping has been achieved in most of the area studied due to the high density of data points, however in some places (e.g. the easternmost extent of the 2P ply) data density is low and the distribution is interpolated over several kilometres.

Controls

o n s u l p h u r c o n t e n t d i s t r i b u t i o n in

the Parkgate

Seam

The fundamental controls on sulphur in coal have been outlined by a number of authors (Altshuler et al. 1983; Berner 1984; Casagrande, 1987; Chou 1990; Calkins 1994). These are essentially the availability of sulphate, iron and organic matter. Sulphate is found naturally in sea water, and to a much lesser degree in freshwater, therefore water salinity is an important factor affecting the sulphur content in peat and subsequently coal. Iron is required for the fixation of sulphur in the form of pyrite, which as already indicated is an important fraction of the total sulphur in the Parkgate Seam. The presence of organic matter, especially in a reactive form, is necessary to control the bacterial reduction of sulphate, which converts the sulphate to a form in which it may be fixed in the sediment. Both depositional and post-depositional controis may effect the sulphur content within a coal seam. The presence of pyrite nodules, which are of depositional origin, and pyrite in coal cleat, of clear post-depositional origin demonstrates this. As indicated above little relationship is seen between the sulphur contents of adjacent plies in the Parkgate Seam (Fig. 12). This may be used to demonstrate the structural control on sulphur in the seam is probably negligible. The two plies plotted are adjacent to each other in the seam succession but are commonly divided by the X2P split. The lack of any linear trend in these data indicates that the factors controlling the

257

12 10 i

~ 8 ,~ 6 -~ -~ 4 2

9

9 9

S~" oo 0

* 9

-

:.. ~ ~': :+ u

4 _"~.~ 1'.

s.-. 9 .,,

+7,.. 9 ,..'.--

0 1 2 3 total sulphur (1PH) % Fig. 12. Total sulphur in the 2P ply plotted against total sulphur in the 1PH ply of the Parkgate Seam (from Cavender & Spears 1995a).

sulphur distribution in these plies are operating differently, and therefore cannot relate to a geological structure which is geographically specific (Cavender & Spears 1995a). Plots of other adjacent plies in the seam also show a similar relationship. Lack of control by faulting may be shown by comparing the sulphur distribution with the actual pattern of faulting. Figure 7 shows the faulting and the whole seam-less-dirt sulphur content. Two sets of faults are observed, trending WNW-ESE and NE-SW with varying throws of up to 60 m. Although fault planes may provide pathways for pore waters within sediments (Goodarzi et al. 1993), even the area with the most concentrated faulting shows no relationship to the pattern of sulphur distribution. The seam is not a horizontal unit varying from about 350 to 850m below O.D. over the area studied. Prominent within the area is the crest of the Eakring Anticline (shown in Fig. 11) which trends from the central southern part of the area to the NNW. If percolation of groundwater by structural processes occurs, it will encounter either the roof or the floor of the seam first, and most likely the floor due to dewatering of sediments lower in the succession. Figure 11 shows a sulphur high in the area of Bilsthorpe Colliery in the 2P ply of the seam. This is near to the crest of the Eakring Anticline indicating a possible control. However other plies of the seam do not show a corresponding sulphur high in this area indicating that this control is unlikely. Movement of porewater in sediments after burial may be a potential source of sulphate to a

258

P. F. CAVENDER & D. A. SPEARS

coal seam (Spears 1991). A comparison of the presence of permeable beds, such as sandstones, near or adjacent to the base of the seam and the sulphur distribution in the floor of the seam may give some indication whether this process has been in operation. Although not discussed in detail here a study of sub-seam sandstone units indicates that there is no apparent relationship between their occurrence and the sulphur content in the 2P ply. In most documented cases, depositional controls are the most important on the sulphur distribution in the resulting seam. Although the depositional environment of the Parkgate Seam succession has not been discussed here, it has already been noted that previous publications indicate that there is apparently little marine influence. The major seams in the Langsettian/ Duckmantian succession of the coalfield have mean total sulphur contents of between 1.3 and 3.0% (Allen 1995). The identification of depositional controls is complicated by the multi-ply division of the seam, and especially by the sulphur variations from ply-to-ply. The base of the seam (2P) may be expected to be influenced by the mire environment and geochemistry during peat accumulation, flooding events during and after the cessation of peat deposition, and various later diagenetic processes. The sulphur content in the 2P shows a great variation in sulphur content from 9%. The presence of pyritic nodules, as noted earlier, would tend to suggest that pyrite is of a depositional stage origin, and is therefore related to processes operating in the mire. The occurrence of high sulphur contents at the base of seams, as shown for the 2P ply has been noted by several other workers. Wandless (1959) indicates that sulphur is often high at the roof and floor of a seam, as well as adjacent to dirt bands or seam splitting. This may be due to the less than optimum geochemical conditions for peat accumulation and organic preservation in these circumstances (Renton & Bird 1991). The flood events which caused seam splitting may have been possible mechanisms for the incorporation of sulphate into the mire during deposition, which may subsequently be fixed as sulphur in the resulting seam. The presence of seam splitting may therefore be a variable which can be used to demonstrate the occurrence of high sulphur coal. A broad relationship is seen at the southern part of Fig. 11, with a greater sulphur concentration where seam splitting (X2P) has developed. However in the northern part of the map where the split is in the form of a 'channel' feature, no such relationship is

seen. The 1PH (Fig. 10) ply also shows isolated sulphur highs, where seam splitting occurs below it. These examples do not show a clear positive relationship between sulphur content and seam splitting, although some indication of the role of flooding events in controlling sulphur contents is observed. Sandstone units above the seam may indicate the presence of post-depositional channels which developed after the cessation of peat accumulation. These channels may have been a source of sulphate allowing sulphur incorporation into the resulting seam. Figure 8 shows the sulphur concentration in the uppermost ply of the seam (1PUT), together with the sandstone channels and units above the seam (as mapped by British Coal 1992b). However little relationship between the sulphur content and the channels is seen. This is probably due to the fresh water nature of these channels which were thus an unlikely source of sulphate. Figure 8 also shows the trend of a swilley in the 1st Piper which also appears to have no influence on the sulphur characteristics of the seam, this swilley is likely to represent the course of a palaeochannel which was later abandoned with the re-establishment of the mire (Elliot 1965). The above discussion has excluded all postdepositional and a number of depositional controls as likely influences on the sulphur distribution in the Parkgate Seam. However although mappable depositional controls have not been identified complex controls which operated in the mire are likely to have caused the sulphur variations observed in the seam. At the beginning of this discussion, sulphate availability was emphasised as a fundamental prerequisite for sulphur incorporation into a seam. Flooding of the coal-forming mire with sulphate bearing waters therefore appears to be a likely control. Evidence for flood events is seen by the presence of seam splits within the seam and Fig. 1 and Table 1 show that a number of these exist within the Parkgate Seam. However the flood events which cause seam splitting may extend beyond the mappable boundary of the split and therefore their extent is difficult to map. These flooding events may also be the source of Fe 2+ in detrital form, another important input for the retention of sulphur in coal as pyrite. This does not necessarily mean that coal with a high pyrite content will be high in ash. The Fe 2+ is likely to be sourced from other external sources such as porewaters, providing the right geochemical conditions persist (Spears 1991). The swamp waters during this stratigraphical interval have commonly been suggested as being of fresh-water fluvial type, with deposition in an

SULPHUR DISTRIBUTION IN A MULTI-BED SEAM upper delta plain environment (Guion & Fielding 1988; Guion et al. 1995). However due to the lowlying nature of this type of environment and nearness to base level there is a possibility of a minor brackish influence, by mixing of saline and fresh water inland from the base level itself. This may be investigated further by using elements other than sulphur which are indicators of palaeosalinity. One such element is boron. In the Parkgate Seam it has been demonstrated that boron and sulphur show a high positive correlation (Cavender & Spears 1995b). In addition boron tends to be higher at the base of the seam and sometimes the roof. Although boron is commonly in concentrations of < 5 0 p p m in the seam, representing fresh water influenced environments (Banerjee & Goodarzi 1990) some samples have boron contents >100ppm and rarely >150ppm, indicating a brackish influenced environment. Therefore a rise in base level may have caused the increased availability of sulphate to the mire, from more brackish conditions, and resulted in plies with high sulphur contents within the seam. The spatial variation within individual plies is more complex, since for example although the 2nd Piper ply is generally high in sulphur content, there is a two to three-fold variation in the area studied. Intra-ply variations are likely to be controlled by more subtle controls which are unlikely to be preserved in the geological record as mappable features, such as palaeotopography and localized variations in iron availability and swamp salinity/sulphate availability.

Conclusions The initial part of this work demonstrates that seams may be subdivided using different variables into a number of plies and also that the distribution of sulphur in a seam plies may be mapped given sufficient data points. This ply-byply mapping is of value since this study indicates there is a considerable vertical and spatial variation of total and forms of sulphur in the Parkgate Seam. Therefore mapping on a ply-byply basis will provide more in-depth information than a composite map of the whole seam, which is commonly used in the coal industry. It has been demonstrated that the sulphur distribution in the Parkgate Seam is controlled mainly by depositional processes, although some late stage incorporation of sulphur does occur. These processes are highly complex and no specific mappable controls have been identified. However these depositional processes are likely to be dominated by flooding events.

259

The authors wish to thank a number of people who have aided this research, especially John Rippon. Also acknowledged are Mike Cooke, Allan Goode and John Raine. Acknowledgement is made to the British Coal Utilization Research Association Ltd. and the UK Department of Trade and Industry for a grant in aid of this research, but the views expressed are those of the authors and not necessarily those of BCURA of the DTI.

References ALLEN, M. J. 1995. Exploration and exploitation of the East Pennine Coalfield. In: WHATELEY,M. K. G. • SPEARS, D. A. (eds) European Coal Geology, Geological Society, London, Special Publication, 82, 207-214. ALTSHCULER,Z. S., SCHNEPEE,M. M., SILBER,C. C. & SIMON, F. O. 1983. Sulphur diagenesis in Everglades peat and origin of pyrite in coal. Science, 221, 221-227. BANERJEE, I. & GOODARZI, F. 1990. Palaeoenvironment and sulfur-boron contents of Mannville (Lower Cretaceous) coals of southern Alberta, Canada. Sedimentary Geology, 97, 297-310. BERNER, R. A. 1984. Sedimentary pyrite formation: an update. Geochimica et Cosmochimica dcta, 48, 605-615. BRITISHCOAL, 1992a. Parkgate Seam database. British Coal internal document. - - 1 9 9 2 b . Piper/Parkgate Seam, summary of geology. British Coal internal document (map). BRITISH STANDARDS INSTITUTION, 1977. Methods for Analysis and Testing of Coal and Coke, part 6. Total sulphur in coal. BS1016: Part 6: 1977. CALKINS, W. H. 1994. The chemical forms of sulphur in coal: a review. Fuel, 73, 475-484. CASAGRANDE,D. J. 1987. Sulphur in peat and coal. In: SCOTT, A. C. (ed.) Coal and Coal-bearing Strata." Recent Advances. Geological Society, London, Special Publication, 32, 87-105. CAVENDER,P. F. & SPEARS,D. A. 1995a. Assessing the geological controls on sulphur in coal seams: progress towards predictive mapping. In: Desulphurisation, IChemE Symposium Series No. 138, 197-205. -& 1995b. Analysis of forms of sulphur in coal, and minor and trace element associations with pyrite by ICP analysis of extraction solutions. In: PAJARES,J. A. & TASCON,J. M. D. (eds) Coal Science, 1653-1656. CHOU, C. L., 1990. Geochemistry of sulphur in coal. In: ORR, W. L. & WHITE, C. M. (eds) Geochemistry of Sulphur in Fossil Fuels. American Chemical Society Symposium Series No. 429, 30-52. EDEN,R. A., STEVENSON, I. P. & EDWARDS, W. N. 1957. Geology of the country around Sheffield. Memoirs of the Geological Survey (England and Wales). 3rd Edition. EDWARDS, W. N. 1951. The Concealed Coal)qeM of Yorkshire and Nottinghamshire. Memoirs of the Geological Survey (England and Wales). 3rd Edition.

260

P. F. C A V E N D E R & D. A. SPEARS

- - 1 9 6 7 . Geology of the Country' around Ollerton. Memoirs of the Geological Survey (England and Wales). 2nd Edition. ELLIOT, R. E. 1965. Swilleys in the Coal Measures of Nottinghamshire interpreted as palaeo-river courses. Mercian Geologist, 1, 133-142. FLINT, S., AITKEN, J. & HAMPSON, G. 1995. Application of sequence stratigraphy to coal-bearing coastal plain successions: implications for UK Coal Measures. In: WHATELEY, M. K. G. & SPEARS, D. A. (eds) European Coal Geology. Geological Society, London, Special Publication, 82, 1-16. FROST, D. V. & SMART, J. G. O. 1979. Geology of the Country' around Derby. Memoirs of the Geological Survey (England and Wales). GOODARZI, F., VAN DER FLIER-KELLER, E., BEATON, A. P. & CALDER, J. 1993. Influence of groundwater on the geochemistry of Canadian coals. In: MICHAELIAN K. H. (ed.) Proceedings of the 7th International Conference on Coal Science, Alberta, Canada, 1, 156-159. GUION, P. D. & FIELDING, C. R. 1988. Westphalian A and B sedimentation in the Pennine Basin, UK. In: BESLY, B. M. & KEELING, G. (eds) Sedimentation in a Synorogenic Basin Complex: the Upper Carboniferous of NW Europe. 153-177. - - , FULTON,I. M. & JONES, N. S. 1995. Sedimentary facies of the coal-bearing Westphalian A and B strata north of the Wales-Brabant High. In: WHATELEY, M. K. G. & SPEARS, D. A. (eds)

European Coal Geology, Geological Society, London, Special Publication, 82, 79-97. MITCHELL,G. H., STEPHENS,J. V., BLOMEHEAD,C. E. N. WRAY, D. A. 1947. Geology of the Country around Barnsley. Memoirs of the Geological Survey (England and Wales). NATIONAL COAL BOARD, 1957. Yorkshire Coalfield Seam Maps, Parkgate Seam Folio. Coal Survey Laboratory. SMITH, E. G., RHYS, G. H. & EDEN, R. A. 1967. Geology of the Country around Chesterfield, Matlock and Mansfield. Memoirs of the Geological Survey (England and Wales). & GOSSENS, R. F. 1967. Geology of the Country around East Retford, Worksop and Gainsborough. Memoirs of the Geological Survey (England and Wales). SWAN, A. R. H. & SANDILANDS,M. 1995. Introduction to Geological Data Analysis. Blackwell, Oxford. SPEARS, D. A. 1991. Pyrite in some U.K. coals. In: DUGAN, P. R., QUIGLEY, D. R. & ATRIA, Y. A. (eds), Processing and Utilisation of High Sulphur Coals IV 85-93. WANDLESS, A. M. 1959. The occurrence of sulphur in British Coals. Journal of the Institute of Fuel, 32, 258-266. WARD, C. R. (ed.) 1984. Coal Geology and Coal Technology. Blackwell, Oxford. WILLIAMS, E. G. & KEITH, M. L. 1963. Relationship between sulfur in coal and the occurrence of marine roof beds. Economic Geology, 58, 720-729.

262

V. BOUSKA E T AL.

Table 1. Content of sulphur in the lignites of the North NO. 4460

}

I

=2.006 =1.608

=1.578 ~O =1,927

min =0.030 __ normal. max -19.930 - - Iognorm.

Bohemian Basin

Sample

4014 I 3568 [ 3122 I

Ad

Sd

(%)

(wt%) (wt%) (wt%) (wt%)

Sdo,

Sd

Sd

Western part

2676 I 2230 I

7s4 I 1338 I 892 I 446 I

Merkur 3-333/94 1-332/94 232/94 16-328/94 65/211

17.59 5.99 8.18 1.68 8.60 1.81 80.49 0.58 27.80 2.99

2.11 0.09 0.49 0.01 1.33

2.26 0.09 0.21 0.03 0.98

1.62 1.50 1.11 0.54 0.68

Liboug 2-342/94 66/211 67/211 233/93

13.30 25.50 34.09 32.93

2.87 3.64 2.93 0.92

1.22 1.38 1.52 0.24

0.32 0.81 1.25 0.35

1.33 1.45 0.16 0.33

CSA 46/211 47/211 48/211 234/63

10.93 20.85 29.52 4.69

5.19 0.82 8.67 0.73

1.51 0.32 2.35 0.01

3.13 0.16 4.45 0.05

0.55 0.34 1.87 0.67

Bilina 10-338/94 12/340-94 8-339/94 51/211 53/94 28-343/94 52/211

16.61 8.33 4.94 3.89 3.37 14.56 40.94

0.52 1.26 0.71 1.24 1.35 3.60 0.88

0.01 0.13 0.02 0.37 0.02 0.69 0.24

0.02 0.50 0.07 0.62 0.69 1.84 0.43

0.49 0.63 0.62 0.25 0.64 1.07 0.21

Hlubina (1.M6j mine) 53/211 5.07 1.12 54/211 4.94 1.24 55/211 10.84 0.76 57/94 4.13 1.45 59/211 4.63 0.92 60/211 3.71 1.01 61/211 27.29 0.87 58/94 8.59 1.45 56/211 14.99 0.51 57/211 7.50 1.23 58/211 2.83 1.39

0.27 0.33 0.23 0.04 0.24 0.27 0.25 0.04 0.21 0.39 0.40

0.52 0.68 0.17 0.52 0.35 0.54 0.50 0.52 0.19 0.72 0.69

0.33 0.26 0.36 0.89 0.33 0.20 0.12 0.89 0.11 0.12 0.30

Eastern part 43-363/94 44-364/94 62/211 54/94 45-365/94

0 0 0.21 0 0

0 0 0.11 0 0

0 0 0.04 0 0

^

A NO.

I

~

-1.728

s -0.934 GD =1.774

2090 t 18.2 CM "1"4"85

1672 [

11' /11

,,631 1254

I

I II

N =11477 rain =0.O30 - - normal. max -19.930 - - Iognorm.

\

Central part

1045 [ 836 I 627 I

418 I

9

B Fig. 1. Histograms of sulphur constructed for total number of samples n = 14993 (A) and for the most frequently occurring values (B). Sulphur values correspond to wt%. to occur within the whole basin but the lowest contents are confined to the eastern and southeastern margin of the NBB (i.e. contents not exceeding 1 wt% S in coal). Contents between 1 and 1.5 wt% S in coal are most frequent in the southern segment of the central part of the NBB. Lower contents were also identified in the area of the Zatec delta and its northern extension. In contrast, high contents of sulphur (exceeding 1.5 wt%) occur along the northern margin of the basin at the foot of the Kru~nhory Mts and in the westernmost part of the NBB. The content of the organic sulphur is rather low (0.65-1.0 wt%; Hokr 1975) but an unusually high content was reported from the Hrabfik mine (2.95wt%, Bou~ka 1981). Concentrations of sulphate sulphur range mostly between hundredths to tenths of a per cent, with a maximum of 0.2wt%. Higher contents of sulphate sulphur indicate local oxidation processes have occurred (Hubfi6ek 1964; Bou~ka

4.67 14.60 5.66 3.65 45.78

0 0.24 0.36 0.30 0.38

1981). Elemental sulphur was found only in burnt-out parts of the coal seam. Its origin is derived from reduction of iron disulphides at high temperatures at the centre of the fire. The largest component of sulphur in coal of the NBB is pyrite (aggregates of microscopic dimensions) with a significant proportion of marcasite (Zelenka et al. 1970). The content of sulphide

~345 OF IRON DISULPHIDES sulphur varies considerably. Some local enrichment with disulphides of iron has been observed particularly in the lower part of the lower bench of the coal seam. Another local enrichment occurs in the upper bench in the central part of the basin, along its northern margin. Higher values of St~ were reported from the western part of the basin whereas in the eastern part, in the vicinity of Chabafovice, the lowest concentrations of St~ = 0.2-0.8 wt% occur (Zelenka 1993). Our data support this pattern (see Table 1).

Geological setting

numerous volcanic bodies and pyroclasticsclose to the basin (Doupovsk~ hory Mts, Cesk6 stfedohofi Mts). Volcanic activity preceded and also followed the formation of lignite.

Iron disulphides confined to the coal seam of the NBB Iron disulphides, the most abundant of which are pyrite and marcasite, occur in the coal seam and are represented by three major genetic types (Bougka 1981, Dubansk~ & Gottstein 1990): (i)

The North Bohemian Basin (NBB) represents the most important lignite basin in the Czech Republic (Fig. 2). It is filled with Eocene to Miocene, exclusively continental, mostly fluvial and lacustrine sediments which were deposited in a subsiding rift zone on the Variscan consolidated basement. A large peat bog developed in the North Bohemian Basin in the Early Miocene. A high to low volatile lignite seam, 30 to 40, locally even 60 to 70 m thick, was formed. Its formation was accompanied by extensive mostly basic volcanism which gave rise to

263

Synsedimentary type. The origin of disulphides of this type is isochronous with the origin of coal. They originated during the biochemical and partly also geochemical stage of coalification (Bou~ka 1981, Dopita et al. 1985). These disulphides are therefore of syngenetic or early diagenetic origin. Amorphous monosulphides were precipitated during this stage in the form of FeS.H20 or melnikovite, greigite, mackinawite or even pyrite and marcasite. It is known that the bacterium Desulfovibrio desulphuricans preferentially reduces

.r

9

f c ~ . , . t .''~

_

\

~

,,

,, ~\\\\ , ~ \ ~

~.~

"

..~,~

'~'~,-~,>~J-"

"kl\

'-'"~

0

50km

Fig. 2. Geological sketch map of the North Bohemian Basin and its vicinity: 1-4 Tertiary formations: 1, sediments of the Sokolov and Cheb Basins; 2, sediments of the North Bohemian basin; 3, effusive rocks and pyroclastics of the Doupovsk6 hory Mts; 4, effusive rocks and pyroclastics of the (~esk6 stfedohofi Mts.

264

V. BOUSKA ET AL.

the lighter ion 32802- than the heavier ion 34802-. Consequently, the hydrogen monosulphide which forms at the beginning of coalification is richer in the lighter isotope of sulphur whereas the heavier isotope concentrates in the residual sulphate solution. Pyrite, in particular, represents the characteristic synsedimentary variety of disulphide. The mineral was identified by X-ray diffraction. It forms finely dispersed microscopic framboids and tiny veinlets arranged mostly parallel with the bedding of coal and also layers of pyrite-bearing sandstone which occur at the base of the coal seam in the western part of the NBB. (ii) Diagenetic type. This disulphide formed together with the coal seam, during its burial. Tiny veinlets of iron disulphides usually filled desiccation cleats. (iii) Epigenetic type. This type is developed in already formed coal seams in which the iron disulphides were concentrated along faults in form of marcasite twins and clusters of crystals or as crystalline aggregates which filled cleats and fractures. Dubansk2~ & Gottstein (1990) anticipated the existence of iron disulphides of hydrothermal origin whose source was in the basement of the coal seam. However, this type of iron disulphides has not yet been found in the coal seam of the NBB even though low-temperature solutions could have occurred in the coal seam where some exothermal reactions might have taken place during the process of coalification (Bougka 1981). Volcanic activity could have also played some role in accumulation of this type of disulphide (Dubansk~, 1984).

Analytical methods Separated samples of iron disulphides were oxidized under vacuum using CuO at a temperature of 790~ The sulphur isotopic composition of the generated SO2 gas was measured using a Finnigan MAT251mass spectrometer. Overall analytical error is +0.15%.

Values of 6345 in lignite of the North Bohemian Basin Hokr et al. (1972) provided the first data on isotopic composition of sulphur in coal of the NBB. They gave 634S values from - 1 to 0%0 with

accuracy -4-1.0% for total sulphur in lignite. Values of 634S of-0.6%0 correspond to pyrite and 634S of +3.2%o correspond to sulphate sulphur. The amount of organic sulphur (0.852.9wt%) in lignite of the NBB is almost negligible, and therefore the isotope 6348 value equal to +1.2%o is of little importance for the general assessment of isotopic composition of local sulphur. Dubansk~, & Gottstein (1990) indicated that 634S values of synsedimentary and diagenetic types of iron disulphides in the NBB are similar to each other. These authors believe that the majority of disulphides in the NBB could have originated through thiobacterial reduction of sulphates. As the parent solution consisted of sulphates, then the disulphides showing negative 634S values are considered to be relatively younger than those exhibiting positive 634S, thus higher values. However, these authors do not provide an unambiguous explanation for markedly negative 634S values found in epigenetic disulphides among which marcasite is most abundant. They assume that a sublimation process could have been involved. Rainswell (1982) considered that pyrite from Jet Rock, which showed values -40%0 up to -43%0, formed through a reduction of sulphates in an open marine environment with an unlimited supply of sulphate ions. During the kinetic bacterial fractionation of sulphur isotopes the residual sulphates became isotopically heavier (the 634Svalues of the residual sulphate and later sulphides increase). The kinetic fractionation in a relatively fast low-temperature process of bacterial reduction of sulphates causes pyrite originated through such a process to be depleted in the heavier isotope of sulphur. The shift in isotopic composition of sulphur between the source sulphate and the final sulphides which originated through bacterial reduction may vary considerably depending on specific conditions; if the system for sulphate is closed or open, if there is enough nutrition for bacteria, if the originating H2S is immediately fixed in sulphides or remains free, etc. In general, the major shifts in isotopic composition of sulphur between sulphate and sulphide are characteristic of an open environment for sulphate or where there is unlimited supply of sulphate ions (seas) which the bacteria drain to form sulphides. In contrast to that, a minimum shift, sometimes almost non-existant, can be observed in the environment where the supply of sulphate is limited, i.e. when all incoming sulphate is continually reduced. There is, of course, a wide spectrum of various environments between these two extremes.

~34S OF IRON DISULPHIDES

265

Table 2. Variation in the sulphur isotopic composition o f the Krugnk hory Mts sulphides and sulphates and disulphides of the North Bohemian Basin (NBB)

Samples

(~348 range

References

of values Sulphides of the crystalline rocks of the Krugn6 hory Mts, Smr6iny and Slavkovsk~, les Mrs

-1 to +5%0

Smejkal et al. (1978)

Sulphates of the Miocene lake, thenardite (NazSO4) and gypsum as well as the sulfates of the Western Bohemian Spa mineral waters

+2 to +6%0

Smejkal et al. (1978)

Estimated value for the sulphate supplying the Basin

+ 5%o

Smejkal et al. (1978)

Volcanic sulphur from Cesk~ sffedohofi and Doupovsk6 hory Mts (estimate)

,-~0%o

Smejkal et al. (1978)

St for the coal of the NBB Pyrite from the coal of the NBB Sulfate sulphur from the NBB Organic sulphur in the coal of the NBB

-1 to 0%o -0.6%o +3.2%o +1.2%o

Hokr Hokr Hokr Hokr

Synsedimentary (early diagenetic) pyrite (sample No. 23) in claystone from the upper part of the coal seam, Doly Bilina open-cast mine Synsedimentary (early diagenetic) pyrite (sample No. 34) in claystone from the upper part of the coal seam, Doly Bilina open-cast mine Framboids of synsedimentary pyrite (sample No. 65/291) in coal, lower seam, Merkur open-cast mine Very fine radially divergent aggregates of early diagenetic pyrite (sample No. 37b) on the base of a big sandy lens, Doly Bilina open-cast mine Small crystals of synsedimentary pyrite (sample No. 37a) on the base of a big sandy lens, Doly Bilina open-cast mine

-0.8%o

this work

+0.8%o

this work

-0.5%o

this work

+0.5~

this work

0.0%o

et et et et

al. al. al. al.

(1972) (1972) (1972) (1972)

this work

Synsedimentary pyrite, Velkolom (2SA open-cast mine Synsedimentary marcasites, Velkolom CSA open-cast mine Diagenetic marcasites, Velkolom CSA open-cast mine Diagenetic marcasites, M. Gorkij I, Brafiany, today Doly Bilina open-cast mine Diagenetic marcasite, 1. M~ij mine, H~ije at Duchov, NBB

-4.2%o +3.5%0 +2.8%o 3.1%o -3.3%o -3.3& -4.8%o -3.5%0

Dubansk~ & Gottstein (1990) Dubansk~ & Gottstein (1990) Dubansk~ & Gottstein (1990) Dubansk~ & Gottstein (1990) Dubansk~ & Gottstein (1990) Dubansk9 & Gottstein (1990) Dubansk~,& Gottstein (1990) & Gottstein (1990) DubanskSI

Epigenetic layer of marcasite from the base of the sandy clay layer (sample No. 39), Doly Bilina open-cast mine Epigenetic pyrite concretion, the base of the 3 seam (sample No. 42), Doly Nfistup Tu~imice, Libou~ open-cast mine, NBB Crystals of marcasite (size up to 6 cm), Bilina tectonic fault (sample No. 46), Doly Bilina open-cast mine Radially divergent aggregate of epigenetic pyrite (cubes of 2-3 mm, sample No. 33), Bilina tectonic fault, Doly Bilina open-cast mine Crystals of marcasite, near the Bilina tectonic fault (sample No. 35a), Doly Bilina open-cast mine Crystals of marcasite on the fine grained aggregate of pyrite (sample No. 36), base of the coal seam, Doly Bilina open-cast mine

+4.2%o

this work

+5.8%o

this work

+4.9~

this work

+11.5%o

this work

+12.0%o

this work

+ 12.6%0

this work

Sulphate aerosols + flying ash from the power plant Chvaletice Sulphate aerosols + flying ash from the power plant Chvaletice

+0.1%o -0.8%0 -0.7%o

~ern~, (1982) Cern~, (1982) Buzek & Sr~imek (1985)

-

266

V. BOUSKA E T AL.

The isotopic composition of sulphur was studied on disulphides from the NBB, particularly on pyrite and marcasite representing various genetic types which were examined by petrographic and geochemical methods prior to isotopic studies (Bou~ka & Pegek 1995). The results obtained, together with other data are summarized in Table 2 and Fig. 3. The dissolved sulphate which supplied the NBB during the Miocene is believed to have been derived from weathered sulphides of the Krugn6 hory crystalline complex, Smr6iny unit and Slavkovsk~, les region (Smejkal et al. 1974). Consequently, based upon the knowledge of isotopic composition of sulphides of these units (-1 up to +5%o) and the fact that during syngeneous oxidation of sulphides no significant shift in isotopic composition occurs, the sulphate supplying the NBB should exhibit similar slightly positive 634S values. Volcanogenic sulphur is considered to be less important. Its isotopic composition should be close to 0%o. The TeplfiBarrandian region, located to the south of the NBB is characterized by accumulations of sulphides with low ~534Svalues averaging below 0% (Smejkal et al. 1974). Obtained sulphur isotopic compositions of sulphides from the NBB indicate that this unit was not the dominant supply of sulphur into the basin. Shifts in the isotopic composition of sulphur in the studied samples compared with anticipated values in source sulphates are rather small. In general, the sulphides showing lower values (around 0%0) were formed in larger reservoir of sulphates, and are believed to be of earlier origin and synsedimentary. Sulphides exhibiting higher values were formed during later stages of bacterial reduction when the isotopic composition of sulphates had already shifted towards higher ~348 values due to the previous drain of sulphur isotopes into earlier sulphides. Consequently, the sulphides with high ~348 values are

thought to have been formed during later stages of the whole process, i.e. during the diagenesis or as epigenetic sulphides. Smejkal (1978) estimated the ~534S values in sulphates of a Miocene lake at the onset of sedimentation of the Cypris Formation in the Cheb Basin to be +2 up to +5%o. Rather positive ~534S values in biogenetic pyrite of the Cheb Basin, in comparison with those of the original sulphates, indicate that pyrite was formed during an advanced stage of sulphate reduction in a closed basin, most likely in an undrained lake. Pyrites of the Cypris Formation showed (see Smejkal et al. 1974) 634S values varying between +7 and +45%0, the mean value being +16%o. In contrast to that, thenardite efflorescence and gypsum showed values exhibiting a conspicuous peak between +5 and +6%0. These values are close to those of sulphates which occur in the majority of mineral waters of western Bohemia which argues for their similar origin or source. Similar values were obtained in our samples no. 39, 42 and 46 (see Table 2). Some epigenetic sulphide types show higher ~534S values in the range from +4.2 to +12.6%. The formation of these sulphides is probably related to bacterial (or organic-matter related) reduction of the sulphate content of basinal porewaters. These pore-waters represent a residual sulphate reservoir already shifted to higher ~34S values by previous stages of sulphate reduction. Synsedimentary disulphides, mostly pyrites, which form microframboids or veinlets parallel with bedding, show values close to 0%o (our samples no. 23, 34, 37a, 37b and 65/291- see Table 2). These mostly control the overall isotope composition of sulphur in common lignite samples. The synsedimentary disulphides, showing various relative proportions, are distributed through the whole section of the coal seam, except in the eastern part of the NBB where they are less abundant. Sulfide.s of the crys'(alline rocks (Kru~,n~ h.ory M~s] Volcanic sulfur {Cesk~ st~edohoH, Doupovsk~ hory M'(s)

I

Organic sulfur Sulfate sulfur Synsedimentary ( 'early diagene'(ic) disulfides Epigene'dc disulfides Aerosols * flying ash, ChvaLe~ice

I

I

J

I

t

910~

Fig. 3. Diagram of plotted data from Table 2.

~" S

~34S OF IRON DISULPHIDES The mean 6348 values established in the coal of the NBB when compared with those of atmospheric SO2 and sulphate ions in water, suggest that some fractionation and a certain shift towards heavier values took place in the atmosphere and water environments (Cern~, 1982). Nevertheless, the combustion products (ash and sulphate aerosols) of the Chvaletice power plant which burns lignite of the NBB showed /534S values equal to +0.1 and -0.8 (Cern~ 1982). Several measurements at the same power plant (Buzek & Srfimek 1985) showed a mean value of ~534S corresponding to -0.7%o which is close to the mean value of coal and pyrite from the NBB. A certain but not too considerable shift may be caused by organic sulphur in the coal of the NBB. However, the concentrations are small and its isotope composition is known from only one measurement (Hokr et al. 1972).

Conclusions Among the genetically different types (synsedimentary, diagenetic and epigenetic) of iron disulphides (pyrite, marcasite) which occur in lignite of the North Bohemian Basin, the synsedimentary disulphides appear to be most abundant. They form fine dispersed microscopic framboids or veinlets mostly parallel with bedding. These disulphides show c534S values fluctuating around 0%0. These values when compared with those of sulphur dioxide in gases of the Chvaletice power plant, which burns lignite of the North Bohemian Basin, indicate that they correspond to mean values of synsedimentary disulphides. This also

267

suggests that no considerable shifts in isotopic composition of sulphur take place during thermal oxidation process in power plants.

References BOUgKA,V. 1981. Geochemistry of Coal. Elsevier, New York. - - & PEgEK,J. 1995. Mineralizace uhelnf~eh slojL MS Faculty of Science, Charles University, Prague. BUZEK, F & SRAMEK,J. 1985. Sulphur isotopes in the studies of stone monument conservation. Studies in Conservations, London, 171-176. (~ERN'I', J. 1982. Sledovdni pomdru stabilnlch izotopft slry ve srd~kdch v Praze. MS Faculty of Science, Charles University, Prague. DOPITA, M., HAVLENAV. & PE~EK, J. 1985. Lo~iska fosilnich paliv. SNTL, Prague. DUBANSKY, A. 1984. Sulfidick~ mineralizace v uhli severo6esk+ hn6douheln~ p~nve. Uhli-Rudy, 32, 223-231. -& GOTTSTEIN, O. 1990. Izotopick6 slo2eni siry Fe-sulfidh z SHR. Uhli, 38, 301-305. GOTrSTE1N, O. 1985. Vliv antropogenni (innosti na geochemii izotop~ siry. MS Institute of Applied Geology, Czechoslovac Academy of Sciences. Report No II-6-2/03.102. HOKR, Z., KOHOUT, J., HLADiKOVA,J. 1972. ~34S v hnJd~ch uhllch severo(esk~ho baz~nu. MS Geofond, Prague. RAINSWELL,R. 1982. Pyrite texture, isotopic composition and the availability of iron. American Journal of Science, Washington, 282, 1244-1263. SME~KAL,V. 1978. Isotopic geochemistry of the Cypris Formation in the Cheb basin. VJstnik Ust(ednlho flstavu geologick~ho, Praha, 53, 3-18. , HAUR, A., HLADiKOVA,J. & VAVIS.IN,I. 1974. ISOtOpic composition of sulphur of some sedimentary and endogenous sulphides in the Bohemian Massif. Casopis pro Mineralogii a Geologii, Praha, 19, 225-237.

Determination of different forms of sulphur in Yugoslav soft brown coals G. J A N K E S 1, O. C V E T K O V I ( ~ 2 & T. G L U M I ( ~ I C 2

1Faculty of Mechanical Engineering, University of Belgrade, 27.marta 80, 11000 Belgrade, FR Yugloslavia 2 IChTM, Center of Chemistry, Njegogeva 12, 11000 Belgrade, FR Yugoslavia Abstract: This paper presents the results of determination of different forms of sulphur in

two Yugoslav soft brown coals, Kolubara (KOL) and Kostolac (KOST). The forms of sulphur were determined as sulphate, monosulphide, pyrite and organic sulphur containing compounds by step-wise oxidation with perchloric acid. The tests were carried out in an inert atmosphere in Bethge's apparatus. KOL and Kost were quite different in sulphur content, KOL containing 0.71wt% of sulphur and KOST 3.11wt%, as well as in the distribution of each type of sulphur compound. Pyrite was dominant in KOST (1.89 wt%) and organic sulphur in KOL (0.47wt%). The analytical method applied was simple and good reproductivity of results was shown. It was important that all types of sulphur were determined in a single and small sample, using the same oxidizing agent. The Kolubara (KOL) and Kostolac (KOST) deposits of soft brown coal are of utmost importance for electricity production in Yugoslavia. They are located in northern and northeastern Serbia respectively (Fig. 1), over an area of several hundred square kilometres. Geological research has shown that the carbonaceous layer in Kolubara was formed sometime between the upper and lower Pontian, on the edges of the Panonian sea, created from various types of marshland vegetation. The carbonaceous rocks of Kostolac consist of two geological units, one of them dating from the boundary between the Panonian and Pontian, while the other formed during the Pontian and early Pliocene. According to their chemical, mineralogical and petrographic features, both are typical soft brown coals with a low degree of carbonation and a variable petrographic composition (Petkovi6 & Novkovi6 1975). There are six power plants located close to the Kolubara and Kostolac open cast coal mines near Belgrade, in the middle of an agricultural and densely populated area. The total output of these plants is 4860 MW and average emission of SO2 is 308 000 tonnes/year (Antic et al. 1992). This means that the use of coal in electricity production in the future will require limiting SO2 emissions. There are no emmision standards in Yugoslavia. At present emission standards for SO2, NO~, particulates, CO etc. are at a proposed stage, but their adoption has been postponed due to the existing economic situation. Currently, average SO2 emissions from Kolubara and Kostolac coals exeeds the limits determined by EEC environmental regulations (Federal Hydrometeorological Institute 1994).

A number of techniques are available for SO2 control: (a) coal cleaning, (b) gasification (or pyrolysis) with combustion and gas cleaning prior to combustion, (c) flue gas desulphurization, (d) combination of these techniques. Numerous commercial processes exist for each of these tehniques. The price of electricity under the emission limit in force determines the possibility of applying these processes. Proper choice depends on sound knowledge of the quality and forms of sulphur in coal and possible ways of their transformation in different prosess conditions. There was a serious lack of information about this matter for domestic coals in Yugoslavia. Sulphur compounds in coals are inorganic compounds, mainly sulphates, monosulphides and pyrite, and organic compounds such as thiophenes, aryl-, cyclic-, aliphatic-sulphides, as well as disulphides, which are minor components (Atar 1978). Because of the diversity of sulphur forms, estimation of various types of sulphur compounds in coal has always been an interesting, important and difficult analytical problem. Several analytical methods for the determination of inorganic forms of sulphur have been proposed (ASTM 1982; Tuttle et al. 1986). According to analytical procedures most often used, the monosulphide-type of sulphur was not determined (its content was usually small). On the other hand, organic sulphur was always determined indirectly, as the difference between total sulphur and the sum of inorganic forms of sulphur. In the determination of sulphur forms for small samples of KOL and KOST coals step-wise

From Gayer, R. & Pe~ek, J. (eds), 1997, European Coal Geology and Technology, Geological Society Special Publication No. 125, pp. 269-272.

270

G. JANKES E T AL.

i

i

L.~ ' ~

0 i

50km

'~ 9 % 'I. ".,,. .....

i

r.-.i

gOST

~'~

KOL

~,,r

"~" ~,,

(

'

-,%.

\

5 .7

"~"% % 9

p-

Cv i 9 9 ".-

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9s " . . . .

k g ) ? i9 .~./

Fig. 1. Map of Serbia showing the location of Kolubara and Kostolac coal fields. oxidation with perchloric acid was used (McGovan & Markuzevski 1988) 9 The results are presented in this paper.

Experimental procedure The samples used in the experiment were obtained from Kolubara and Kostolac coal mines and from coal seams which have been for the past few years in exploitation. The samples were obtained by a standard sampling method (ISO 5069-1), from the power plant conveyer belt. By means of a standard method of sample preparation (ISO 5069-2), 200 kg of coal yielded 0.5 kg of sample each, with grain

size - 125 + 90 m. The characteristics of these samples are given in Table 1 and the major constituents of the ash are presented in Table 2 (standard procedure according to the ISO 1171 was used for the ash analysis). The same samples were prepared for wire-mesh devolatilization experiments where only 0.01 g of coal was used for each test. Therefore, it was important to determine the proportion of various forms of sulphur (sulphate, monosulphide, pyrite and organic sulphur-containing compounds) in a very small sample 9This was done by successive treatment of the sample (300-500rag) with perchloric acid solutions of different concentrations, i.e. of different boiling points, as selective oxidizing agents 9The tests were carried out in an inert atmosphere (N2) in a somewhat modified

FORMS OF SULPHUR IN YUGOSLAV BROWN COALS Table 1. Characteristics of KOL and KOST coal samples

Parameters

Samples KOL

KOST

Ash (wt%, dry basis) Sulphur, total (wt% dry basis)

35.12 0.72

37.12 3.06

Ultimate analysis (wt% dry ash free) Carbon Hydrogen Nitrogen Sulphur + oxygen (by differences)

54.81 5.47 0.80 38.92

52.70 4.82 0.79 41.69

Heating value (kJ/kg-1) HHV LHV

15880 14585 15030 13625

Bethge's apparatus (McGovan & Markuzevski 1988). To determine the monosulphide and sulphate forms of sulphur the samples were treated with 40% HC104 at 115~ for 40min. The hydrogen sulphide originating from monosulphides, was introduced into 30% H202, where it oxidized and was determined as sulphate. Sulphate sulphur was determined from a filtrate obtained by filtering and rinsing the sample at the end of the reaction. Pyritic sulphur was determined in the sample residue. The oxidation was carried out by 55% HC104 at 145~ for 90min. The sulphur-containing gases were introduced into 30% H20 2. After the termination of the reaction the sample was filtered, rinsed and dried. The filtrate was added to the H2Oz-solution and the sulphate content was determined in the combined liquid mixture. Finally, the organic sulphur was determined by oxidation of the residual sample with a mixture of 75% HCIO4 and concentrated H3PO4 (9: 1) at 200~ for

271

60 min. At the end of the reaction the content of the flask was filtered and the filtrate was added to the 30% solution of hydrogen peroxide. In all cases the concentration of sulphate was determined turbidimetrically and calculated as the content of sulphur in the dry sample. Using this method, all the types of sulphur compounds present were determined in a single sample with the same oxidizing agent.

Results and conclusions

The results of direct determination of sulphur compounds in coal samples KOL and KOST are presented in Table 3. They were compared with the results of ultimate analyses of the same samples presented in Table 1. The sum of all sulphur forms determined by step-wise oxidation (Table 3) is assumed to be the total sulphur. This value for total sulphur ranged within the limits of microanalitical experimental errors. Moreover, the results were found to be reproducible (McGovan & Markuzevski 1988; Cvetkovi6 et al. 1995). It is shown that KOL and KOST are quite different in sulphur content, as well as in distribution of each type of sulphur compound. For example, KOL contains 0.71 wt% of sulphur while KOST has 3.11 wt% (Table 1). The samples do not show significant differences in ash content, but they are quite different in their content of pyrite, and organic sulphur (Table 3). The difference in total sulphur, as well as pyrite sulphur content (KOL 25%, KOST 61% of total sulphur), in the samples analyzed may point to difference in precursory matter and to different conditions in the depositional environment. A considerably higher content of pyrite sulphur (Table 3) and approximately identical

Table 2. Major constituents of ash (wt% ) Sample

KOL KOST

Constituents SiO2

A1203 Fe203 CaO

MgO

K20

Na20

SO3

Total

55.8 45.9

22.4 20.9

2.0 2.8

0.4 0.4

0.5 0.3

2.9 4.1

100.0 100.0

11.3 16.4

4.7 9.2

Table 3. Sulphur forms in Yugoslav soft brown coals (wt%, d.b.)

Sample

Monosulphide

Sulphate

Pyritic

Organic

Total

KOL KOST

0.01 0.06

0.06 0.76

0.18 1.89

0.47 0.40

0.71 3.11

272

G. J A N K E S E T AL.

amounts of organic matter in both samples (Table 1) indicate that KOST coal was formed in a more pronounced reducing environment than KOL coal. Regardless of the amount of Fe in the samples under consideration, which differs significantly (Table 2), in the KOL sample most of the sulphur (66% of total suphur) is bound to organic matter, because the reducing environment was not as pronounced. The results of organo-geochemical analysis of aliphatic hydrocarbons isolated from the soluble part of the organic matter of the above coals have also shown up difference in the character of the depositional environment. Reducing conditions in the depositional environment are charactered by a predominance of phytane as opposed to pristane, i.e. (Pr/Ph < 1 (Didyk et al. 1978)). The ratio of Pr/Ph,.

-----'Carbondale'

-KY9

Q,,, ..I

z < n ft. i if)

Fig. 1. KY 9 within the Pennsylvanian system. comm.). The elemental analysis of the coal is shown in Table 1. The coal is rich in vitrinite (around 80%). Vitrinite maximum reflectance measurement (%Ro, max=0.60) indicates that the coal under study belongs to hvCb rank.

Fig. 2. The W. KY and Illinois (Saline and Gallatin counties) coalfields (approximate (shaded) outline of the lateral distribution of coal samples rich in V). KY: U(nion), W(ebster), H(opkins), D(avies), He(nderson), Mc(lean), M(uhlenberg) and O(hio) counties; Illinois: G(allatin) and S(aline) counties.

ORIGIN OF V A N A D I UM IN COALS Throughout this paper the top 15cm part of the W. KY No. 9 coal (enriched with both V and VO 2+) will be referred to as K Y 9 unless otherwise specified.

E S R of VO 2+ and V-XAFS study Figure 3 shows the ESR spectrum of VO 2+ incorporated into the KY 9 matrix. One sees five of the weak parallel components of the spectrum at the extremites, two at low field and three at high field. The remaining ones are masked by the much stronger perpendicular components in the centre of the spectrum. There are two obvious points. First, all of the coal VO 2+non-P sites have the same magnetic parameters since there is only one set of lines in the spectrum. Second, the absence of any small splittings of the perpendicular components of

277

the spectrum implies that the VO2+-non-P sites have axial symmetry, aside from any possible rhombic distortions much smaller than the linewidth of 1 mT. In this case all the spinHamiltonian parameters can be derived from this ESR spectrum using the axially symmetric spin-Hamiltonian

=/3o[gflHzSz + g•

+ HySy)]

+ Syly)

+ AII(S.Iz) + A•

where gll, g• AIjand A l are the parallel (z) and perpendicular (x,y) components of g and 51V hyperfine coupling tensors, respectively. Hi, Si and L represent the vector components of the magnetic field, electron spin, and 51V nuclear spin along the i(= x, y, z) axes. Experimental ESR spin-Hamiltonian parameters for the VO 2+ compounds in KY 9 (given in Fig. 3), however, differed significantly from

]S,v

~20 mT

I

..I

,

51~11

1

Fig. 3. First derivative, room temperature, X-band spectrum of VO 2§ within the insoluble organic fraction of KY 9. ESR parameters: All = 17.6 4- 0.2 mT, A• = 5.7 • 0.4 mT; gLL= 1.951 + 0.003, and g• = 1.985 :t=0.010 (for VO2+-P, Premovi6 1984); All --- 19.2 + 0.3 mT and A• = 6.9 + 0.5 mT; gll --- 1.937 • 0.005, and .

.

~111_-11~931m~0a~d (Af~176

-

.

;

~

.

~

~

.

~93ur~Tc Aa~d in7 t5hmT(f~

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McBa~eel9~8~b);

AII = 19.9roT and A• = 7.5mT (for the VO2+-fulvic acid in the deep peat, Abdul-Halim el al. 1981); and All -- 19.2 mT, A• = 6.8* mT (for the VO2+-phthalate/salicylate mixture, Templeton & Chasteen 1980). * Calculated as mean value of hyperfine couplings (A:,x and Ayy) derived from a non-axial spin-Hamiltonian.

278

P. I. PREMOVIC ET AL.

those of VO2+-P (Fig. 3). It has been shown that these parameters are particularly sensitive to direct ligand substitution in VO 2+ complexes (Holyk 1979). Thus, the differences in ESR parameters, especially All (which is the most sensitive parameter to the bonding) can represent the differences in the bonding ligands around VO 2+ in a VO 2+ complex. Model compound studies have shown this to be valid (Holyk 1979). For this reason, a comparison of the spin-Hamiltonian parameters for VO 2+ in KY9 and voZ+-P of various bituminous sedimentary rocks (Fig. 3) implies that VO 2+ compounds in the coal are of non-P type. Our ESR signal intensity indicates that the concentration of VO2+-non-P incorporated into KY9 is around 600ppm of VO 2+, that most of the metal (60%) resides in an organic-insoluble phase and that 80% of this V is in the VO 2+ form (Table 1). The high value for All (19.2mT, Fig. 3) indicates that the VO 2+ ion incorporated into KY9 coal is probably complexed with oxygenated functional groups such as carboxylic/ phenolic. The All and A l of voZ+-non-P are very similar to those reported VO 2+ ions incorporated into the structure of soil humic acid (McBride 1978) and fulvic acid isolated from either a podzol soil (Templeton & Chasteen 1980) or an organic-rich deep peat (90% organic matter, Abdul-Halim et al. 1981) (Fig. 3). It is suggested by these authors that these ions are bound to (carboxylic/phenolic) oxygen ligand donor atoms in the humic/fulvic acid structures. It is interesting to note that most of V is concentrated in the fulvic fraction of modern peat (Cheshire et al. 1977). In an effort to model the binding environment, ESR spectra of many fulvic acid solutions containing a variety of ligand mixtures were studied by Templeton & Chasteen (1980). Particular emphasis was placed on the salicylate/phthalate mixture because, it is generally thought that carboxylic/phenolic structures are the probable functional groups present in fulvic acid. In addition, as these authors pointed out the fulvic acid used in their investigation are characterized by a preponderance of such groups. For this reason the ESR (All and A• hyperfine parameters for this model salicylate/ phthalate complex are given in Fig. 3. The similarity in the (AlL and A• values (Fig. 3) suggests that the ligand fields about VO 2+ are comparable for VO2+-non-P and for the fulvic acid complexes on the model (salicylic/phthalate) compound. The ESR data, of course, alone do not constitute proof that carboxylic/phenolic groups make up the first coordination sphere of

VO 2+ in VO2+-non-P. However, they are certainly consistent with this interpretation. Further support for this notion comes from XAFS investigation of V in KY 9 by Maylotte et al. (1981). This study shows that there is no evidence of V in the N environment (such as voZ+-P). The limit of detection using the V XAFS method was about 50 ppm for VO 2+. Therefore, one may safely conclude that VO 2+non-P are located within the KY9 organic structure and that they are coordinated with the oxygen ligand donor atoms. These atoms are arranged in a nearly octahedral system with a strong tetragonal compression along the V-O bond of VO 2*. It is probable that coordination is primarily by carboxylate/phenolate groups with their four oxygen ligand donor atoms in the equatorial plane of VO2+-non-P, which concurs with the known chelating functional groups of unoxidized/oxidized coals. In the free axial position, perhaps, there is one water molecule/ hydroxyl ion (OH-).

Pyrite ( F e S e ) and other S compounds

EDX analysis shows that the KY9 sample contains relatively high Fe (_>2% of total sample weight); SEM and chemical analysis indicates that most of this Fe is in an unoxidized form. M6ssbauer spectroscopy reveals that 96% of total Fe present in KY 9 is pyritic Fe and only 4% appears as jarosite (the iron sulphate mineral). This mineral is usually present in weathered coals; presumably weathering product of FeS2 (Huggins & Huffman 1979). According to Smith & Batts (1974) the Fe sulphates (as weathering products of FeS2) in the coals are only of significance in relationship to very recent secondary processes. Very recently, we have initiated in situ XAFS measurements of KY 9 part. Analysis of the data are still under way and only a few preliminary results will be discussed here. The S K-edge XAFS spectrum of KY 9 (Fig. 4) can be resolved in terms of two major general form components, unoxidized and oxidized. One of the unoxidized forms is the inorganic sulphide derived principally from FeS2 (associated with the organic insoluble part). The SEM and EDX analyses indicate that all macerals of KY9 contain substantial FeS2, especially inertinite in which FeS2 is the dominant S form. The other unoxidized forms are aliphatic sulphides and aromatic thiophenes. Oxidized forms include sulphate which can conceivably be derived from both inorganic and organic S compounds. The fact that sulphate is present in KY9 (Fig. 4)

ORIGIN OF VANADIUM IN COALS

279

Origin o f VO2+-non-P

t-

Py T

si4

L ul

O

,Q ,
102 J) epicentres located during 1992. Mine takes and tectonic blocks are demarcated by thick and thin lines, respectively. In the upper right corner the energy scale is given. adjacent longwall panels in the 7th tectonic block at the CSA Mine. Mining panel no. 17331 induced a very low level of seismic activity and was completed without any occurrence of a large seismic event. In contrast, extraction of the adjacent panel, no. 17332, induced a high level of seismic activity, manifested by a steep slope on the graph of cumulative strain release, exceeding the value of S l i m = 15 J1/2/day in the graph of diurnal increment (Fig. 4) whose definition will be given below. During coal extraction by longwall face no. 17332, only a single strong rockburst ( E = 107j) occurred, in January 1992. Almost a month later, this longwall face was stopped and the release of seismic energy rapidly decreased. This example is in good agreement with general geomechanical considerations, for the operation of the first longwall in the appropriate tectonic block usually proceeds without any problems. A higher degree of seismic hazard may be expected subsequently when mining neighbourhood longwall panels, especially the third or fourth panels in an area when a substantial part of the coal seam in the investigated tectonic block has been extracted and the area affected has been enlarged.

Another example of the process of seismic energy release during longwall operation comes from face no. 13933 at the CSA Mine (Fig. 5). Without respect to the fact that this longwall panel was the first one, mined in the seam no.39 in the 3rd tectonic block, the situation from the viewpoint of geomechanics was here very hazardeous, all preventative measures are intensified. It is worthwhile to mention that this area was affected by the strongest rockburst (E=101~ which occurred in the whole Ostrava-Karvinfi Coalfield in 1983. Further details concerning this longwall panel operation and results of seismological observations have been given by Kalenda et al. (1992).

Frequency-energy distribution This distribution can be described by a formula given by Gutenberg and Richter (1954), which for our purposes can be written as log N - - a b l o s E where N is the cumulative number of events with energy within the prescribed energetic window, E is the amount of seismic energy released in a single event, and a and b are numerical constants. This formula

SEISMIC MONITORING FOR ROCKBURST PREVENTION

325

Fig. 4. (a) Benioff graph and (b) its diurnal increment during mining operations for longwall faces nos. 17331 and 17332 in the 7th tectonic block at the CSA Mine. The period of working for each panel is shown in (a) by lines parallel to the time axis. represents a straight line, whose slope b characterizes the number of weak seismic events relative to the number of strong ones. For fitting real data sets, two different approaches to b-value determination were applied. The first method is based on the calculation of slope b of the straight line using least-squares regression, while the other known as the maximum likelihood method, was suggested by Aki (1965) and Utsu (1965) for analysing earthquakes. The advantage of the latter method is that single strong seismic events (induced events and/or earthquakes) have less influence on the estimated slope b of the regression straight line. The software in use at the operational centre enables the b-values for different regions (the whole coal mine district, mine, or tectonic block) to be calculated. In our computations, all data sets are strictly limited to events having a minimum energy value of 102j. Due to different approaches in the b-value calculation, only slight differences in the resulting values appear to have occurred (Slavlk et al. 1992; Holub 1996).

A typical example of the time-space variation of b-values was the effect of mining operations on seismic activity when the single longwall panel no. 13933 was mined in the 3rd tectonic block at the (~SA Mine in 1990-1991 (Fig. 6). An examination of the b-value variations has revealed that the higher b-values were found in 1989 before starting the mining operations ( b l - 0 . 7 4 - 0 . 8 0 and b 2 = 0 . 6 7 - 0 . 8 0 ) . After coal winning started during 1990-1991, lower values were established (b~--0.38- 0.55 and b 2 = 0 . 2 9 - 0.41). The b~-values were computed by using least squares regression, and the b2-values by means of the maximum likelihood method.

Utilization of long-term seismological observations in geomechanical practice In the Ostrava-Karvinfi coal mines, all seams and mine workings are classified in one of three categories of the rockburst hazard according to the prevailing geological (e.g. type of

326

K. HOLUB

Fig. 5. (a) Benioff graph and (b) its diurnal increment for the 3rd tectonic block at the (~SA Mine before and during mining of longwall panel no. 13933. The period of working is shown in (a) by a line parallel to the time axis. sedimentary rocks, tectonics, depth of the coal seam) and geomechanical (e.g. mechanicalphysical properties of sediments, mined out area and edges of unmined seams in the roof, occurrence of the rockbursts in the past) conditions: 9 (1) Rockburst occurrence is not expected during mining operations even if no preventative measures are applied 9 (2) Rockburst occurrence cannot be excluded during mining operations unless preventative measures are applied 9 (3) Rockburst occurrence is to be expected unless preventative measures are applied. This category includes mine workings where rockbursts have already occurred For mine workings in the third category, extensive active preventative measures are obligatory, e.g. destressing blasting in the seam, drilling tests, camouflet shotfiring of a large amount of explosives in the roof above a longwall face, water infusion, and others. In contrast to active preventative measures, the passive ones, are aimed at specific activities (e.g. mine design, mine field development,

choice of mining equipment and others) which could prevent rockbursts occurrence and/or mitigate their consequences. The criteria for assigning areas to third category are not always in agreement with the real rockburst hazard, resulting in an overestimate of the number of regions in this category. Therefore it was recommended that mine workings should be classified for rockburst hazard using the results of long-term seismological observations. At present, applications of the seismic observations are directed towards the determination of seismically active regions, monitoring the development of seismic activity to assess rockbursts hazard, and checking the efficiency of the measures applied to prevent rockbursts. The objectives of these efforts are: 9 to determine regions where active and passive preventative measures would have to be applied 9 to check the effectiveness of the active preventative measures applied 9 to reclassify mine workings according to the degree of rockburst hazard

SEISMIC M O N I T O R I N G FOR ROCKBURST PREVENTION

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On the negative side, all efforts aimed at predicting the times of rockbursts with greater precision are very questionable, in common with the general experience for earthquake prediction. The analysis of long-term observations has shown that for any region of the coalfield a value Sli m c a n be defined. This value represents the maximum diurnal increment in strain release (in units of J1/2/day) for which the probability of rockburst occurrence is negligible. It can generally be stated from our investigations of the Ostrava-Karvin~i coal mines, that the value of Sli m is 15 j1/2/day, i.e. this is considered to be a safe value for continued mining provided that it has not been exceeded during the two preceding months. Once the value S=15j1/2/day is exceeded, the occurrence of a rockburst cannot

be excluded and all active preventative measures must be taken. Values of diurnal increment greater than 15j1/2/day were found in all areas where a rockburst had previously occurred (Holub et al. 1991). As an example of this approach, the reclassification of individual mine workings into lower categories of rockburst hazard has been proposed and in several cases this has been done. However, the diurnal increments in strain release are not the only parameter to be considered. When making such a decision, one take into account many factors, such as the level of the seismic activity, location plots, geological and tectonical situation, and the effects of old workings in adjacent areas. Destressing blasting and camouflet shotfiring of a large amount of explosives are the principal

328

K. HOLUB

preventative measures employed to reduce rockburst hazard. Their effectiveness can be checked by using seismic methods. Whereas we have primarily investigated the effectiveness of the latter method, the investigations in Polish mines are aimed at checking the effectiveness of destressing blasting with charges of up to 300 kg, as reported by Filipek et al. (1992) and Dubinski & Syrek (1994). For our work with camouflet shotfiring in the Ostrava-Karvinfi coal mines, an empirical formula is used for estimating the efficiency of the large explosions (up to 3000kg): ~7 = E s / 2 . 6 Q

where Es is the seismic energy in joules determined by using interpreted data from seismograms and Q is the amount of explosives in kg. It is considered that if V > 3, then the blasting has been effective in releasing accumulated strain energy. The application of b-value estimates to rockburst prediction in the Ostrava-Karvinfi coal mines is still under evaluation at the present time. Preliminary results have confirmed the general validity of the b-value criterion, which hypothesizes lower values in regions of higher rockburst hazard. At this stage of investigation, only qualitative changes in time dependent b-values have been established, as reported, for example, by Gibowicz (1979) and Holub (1996).

Concluding remarks The advantages of long-term continuous seismological observations for assessing rockburst hazard in the Ostrava-Karvinfi coal mines are as follows. Routine application of rockburst prevention measures is based on reliable predictions of hazardeous conditions within the rock mass for those mines where the rockburst hazard exists. All possible measures are taken to increase the safety levels in mine workings where rockbursts represent a serious threat. Efficient application of preventative measures at appropriate times minimizes stoppages in coal production, and represents substantial reductions in costs which have been confirmed by several individual mines. This work was carried out as part of research project No.105/93/2409, which was financially supported by the Grant Agency of the Czech Republic. This manuscript benefited from critical and thoughtful review by N. R. Goulty. The technical assistance of J. Rugajovfi in the preparation of the manuscript is also appreciated.

References AKI, K. 1965. Maximum likelihood estimate of b in formula log N = a bM and its confidence limits. Bulletin of the Earthquake Research Institute, Tokyo University, 43, 237-239.

DOPITA, M. & KUMPERA, O. 1993. Geology of the Ostrava-Karvinfi Coalfield, Upper Silesian Basin, Czech Republic, and its influence on mining. International Journal of Coal Geology, 23, 291-321. DUBINSKI, J. & SYREK, B. 1994. The effectiveness of destressing blasts performed in the Wujek Coal Mine. In: RAKOWSKk Z. (ed.) Geomechanics 93. Balkema, Rotterdam, 59-62. FILIPEK, M., MITREGA, P. & SYREK, B. 1992. An attempt to assess the efficiency of destressing blasting performed in longwalls with caving under high rockburst hazard conditions. Publications of the Institute of Geophysics of the Polish Academy of Sciences, M-16 (245), 319-332 (in Polish). GmowIcz, S. J. 1979. Space and time variations of the frequency magnitude relation for mining tremors in the Szombierki Coal Mine in the Upper Silesia, Poland. Acta Geophysica Polonica, XXVII, No. 1 39-49. GUTENBERG, B. & RICHTER, C. F. 1954. Seismicity of the Earth and Associated Phenomena. 2nd edn, Princeton University Press. HOLUB, K. 1996. Space-time variations of the frequency-energy relation for mining-induced seismicity in the Ostrava-Karvinfi Mining District. Pure and Applied Geophysics, 146, 265-280. - - , VAJTER, Z., KNOTEK, S. t~ TRAVNICEK,L. 1991. Application of results of seismologic monitoring during the operation of mine workings in the Ostrava-Karvinfi Coal Basin. Publications of the Institute of Geophysics of the Polish Academy of Sciences, M-15 (235), 219-228. - - , SLAViK,J. & KALENDA,P. 1995. Monitoring and analysis of seismicity in the Ostrava-Karvin~t Coal Mine District. Acta Geophysica Polonica, XLIII, No. l, 11-31. KALENDA, P., SLAVIK, J., HOLUB, K. ~r VAJTER, Z. 1992. Statistical analysis of induced seismicity parameters in the Ostrava-Karvinfi Coal Basin with regard to the 3rd tectonic block of the CSA colliery. Acta Montana, 84, 85-96. KARNiK, V., MICHAL, E. & MOLNAR, A. 1958. Erdbebenkatalog der Tschechoslowakei bis zum Jahre 1956. Travaux Gdophysiques, 69, N(~SAV, Praha, 411-598. PROCHAZKOVA, D. 1994. Earthquakes in the Jeseniky Mts. in 1986. Travaux Gdophysiques, XXXVI (1988-1992), Geophys. Inst. of CAS, Praha, 28-38. SLAViK, J., KALENDA,P. & HOLUB, K. 1992. Statistical analysis of seismic events induced by the underground mining. Acta Montana, Series A, No. 2 (88), 133-144. UTSU, T. 1965. A method for determining the value of b in formula log N = a - bM showing the magnitude-frequency relation for earthquakes. Geophysical Bulletin, Hokkaido University, 13, 99-103.

An analysis of mining induced seismicity and its relationship to fault zones ZDENl~K

KAL,~B

Institute of Geonics, Academy of Sciences of the Czech Republic, Studentskd 1768, Ostrava-Poruba, 70800, Czech Republic Intense induced seismicity has resulted from long-standing mining activity in the Karvin/t part of the Ostrava-Karvin~ Coal District, Upper Silesian coal basin. Interpretation of mining induced seismic events in combination with other knowledge (geological, tectonic, geomechanical, technological) aids the understanding of failure processes in the rock mass. Seismological observations over a three-year period were analysed. Four sets of mining-induced seismic events have been tested to evaluate the seismicity of important fault zones. It follows from the analysis that the seismic activity on important fault zones occurs only as a consequence of mining activities. Accumulations of mining induced seismic events occur on stress concentrators, which may be geological and/ or anthropogenic structures. Abstract:

The geological and tectonic structure of the rock mass of a deposit is an important factor that influences the origin of seismic events induced by mining activities (henceforth referred to as seismic events). This influence is present in the Czech part of the Upper Silesian basin, where the Ostrava-Karvinfi Coal District (OKR) is located (Fig. 1). The underground mining of black coal has taken place for more than 100 years and during this period, a complicated network of worked-out and caved mine spaces has been created. As a result, a complex induced stress field, variable with time, has been formed.

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mechanism of the failure process and, significantly, the relation between seismic events and current geological and mining conditions. Subsequently, this leads to the possibility of specifying the probability of rockburst occurrences. The aim of this paper is to observe the connection of seismic activity with important fault zones in the area most affected by induced seismicity, i.e. the Karvinfi part of the OKR.

Tectonic and geomechanical situation The Czech part of the Upper Silesian basin is formed by Carboniferous sediments (a detailed description of the geological structure is given in Dopita & Kumpera 1993). The Karvinfi part of the OKR has the character of a basin with principal fault systems trending both in N-S and E-W directions. It is possible to model the region as a partial block structure consisting of beds of medium-thick psephito-psammitic layers that have a typically subhorizontal orientation. The thickness of individual beds ranges from metres up to 10-20m. Laterally, the dimensions of partial geological blocks vary from hundreds to several thousands of metres. The boundaries of the blocks are usually formed by fracture dislocations, largely filled with plastified materials. Intrablock tectonics is not very marked, but it exists and can divide the layers within the block into smaller partial blocks. Areas of varying intensity of tectonic dislocation differ in mininginduced seismic activity (Rakowski 1989). A geological analysis of important tectonic structures in the Karvin/l part of the OKR has been made. From a geomechanical point of view, the analysis has given the following results: 9 the thickness of faults (fault zones) ranges from several metres to some tens of metres 9 throws vary from metres to several tens of metres 9 the majority of faults (especially those with greater thickness), contain a filling consisting of plastified cataclastic materials 9 faults are commonly, although not always, wet The detailed evaluation of both tectonic structure and palaeostress conditions has proved the existence of dominant structuro-dynamic conditions favouring rockbursts. Critical sites were identified in the massif (e.g. the most important fault zones, hanging corner structures, sections with a small frequency of faults and others) where rockbursts could occur given the existence of disadvantageous, especially mechanical conditions (Kumpera et al. 1991). From a

geomechanical point of view, an analysis of the intensity of tectonic dislocations has resulted in the following relationships (Rakowski 1989): 9 rockburst areas are situated usually in places little affected by intrablock fault tectonics 9 in areas with sudden changes in the intensity of tectonic dislocations, a greater intensity of rockburst events can be expected 9 in areas with a smaller intensity of intrablock tectonic dislocation, the existence of tectonic discontinuous concentrators of stress and residual tension cannot be excluded

Seismicity and mining situation An analysis of mining induced seismic events, in relation to mining activities, has proved the existence of two important groups. The first is closely connected in space and time with the advance of mine openings, whereas, in the second group a more or less random relationship exists between seismic events and mining activities. These seismic events are induced at greater distances and are likely to be the effects of several workings. Moreover, shifts in time between mining activities and the initiation of events can also occur (Gibowicz & Kijko 1994; Rudajev 1989). An example where the development of seismic activity in a given area is influenced by the driving of mine workings is presented by Kone6n~, (1994). An empirical relationship between the process of massif failure in a limited area and the probability of the origin of anomalous rockbursts can be established. This is based on the relation between the number of mining-induced seismic events, the amounts of emitted seismic energy and the intensity of coal fracturing. The relationship is not simple because, in addition to the effects of mining operations, it is necessary to take into account 'natural' factors. The behaviour of all the factors given below must be studied to understand the development of seismic activity (Kone~n2~ 1989): 9 the primary stress field and geological structure (factors unaffected by human activity) 9 the geomechanical structure of the massif (given by natural factors, but partly influenced by active interference) 9 the secondary stress field and changes in it (impacts of mining activity) From the above, it follows that for mining purposes, it is desirable to study the development of induced seismicity under the geological

AN ANALYSIS OF SEISMICITY and geomechanical circumstances of the primary stress field by monitoring the stress changes that occur as a result of mining activities.

Seismological monitoring Induced seismicity results from anthropogenic activities causing changes in the rock massif that lead to its failure. Failure is accompanied by the generation of seismic waves that can be monitored by seismic stations. Events due to blasting operations have a special signifcance. If the intensity of an event corresponds to the size of the charge, the seismicity simply recording the blasting operation. However, if an event with an

331

energy greater than that corresponding to the charge is recorded, the blasting operation must have initiated failure of the massif in an area where stress conditions were close to critical. To monitor the seismic activity in the OKR, three levels of seismic networks are used. Local seismic networks of individual collieries represent a basic level of monitoring. The second level is ensured by a regional network named Seismic Polygon of the Ostrava-Karvinfi Collieries. The station Ostrava-Kr~isn6 Pole, which is a part of both the state and world seismological networks, is also situated in the Ostrava region. The development of seismological monitoring in the O K R as well as its utilization in the fight against rockbursts is described by Kalfib et al. (1994).

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Modern methods of interpreting digital seismic data also test for tectonic effects. Seismic events recorded only in the focal area are represented by data from the experimental seismic network of a modular system in the Lazy Colliery with the possibility of connecting with up to eight surface or underground stations. The network monitors a seismically active part of the mine, covering an area of about 3 km 2 (Knejzlik et al. 1992). The layout of the stations of the Seismic Polygon of the OKD corresponds with its position as a regional network. Seven surface stations surround the Ostrava-Karvinfi District. The remaining three stations are located in underground workings. The network covers an area of 200km 2, using Lennartz Electronic GmbH equipment. The Fren~tfit Seismic Polygon is an autonomous unit situated about 30 km southwest of the Karvinfi part in an area of the Fren~t~it colliery under projection. It contains five surface stations that are telemetrically connected with the central recording station (Knejzlik & Zamazal 1992).

Data sets To evaluate the seismicity of significant tectonic zones in the Karvinfi area, four sets of mining induced seismic events have been identified: 9 9 9 9

all recorded mining induced seismic events intense rockbursts mining shocks intense seismic events induced by blasting operations

The sets cover seismic events that occurred from 1989 to 1991. Altogether, the localizations of about 14000 mining induced seismic events with an energy E > 100J (according to the energy scale in the OKD) were used in the first set, but due to limited data, the focal depths were not defined. The second set contained rockbursts with an energy E > 105 J. There were 94 events within the three year period. The set of mining shocks (weak surface shocks) comprises 183 records. This set is spatially inhomogeneous because it is based upon weak seismic events that can be observed on the surface and reported by the public to the processing centre. The last set consists of seismic events induced by blasting operations when 'shooting a charge'. The energy of these seismic events was higher than that stated because of the correlation between the charge weight and the energy of the induced

event. The correlation ratio was determined on the basis of a 100kg charge for all blasting operations. The bulletins 'Seismologickfi aktivita OKR' (Seismological Activity in the OKR) processed at the seismological centre in the CSA Colliery served as the basic information. A tectonic schematic map of the Karvinfi part of the OKR was used to create a visual analysis of the seismicity associated with tectonic zones. The map was processed in the DPB Paskov company (Mine Exploration and Safety) by plotting the distribution of tectonic elements at a depth of 500m. This depth corresponds roughly to the supposed z-coordinates of the foci of seismic events. With regard to the fact that the tectonic structure of the OKR is very complex, only the most important fault zones were taken into account. Nevertheless, it is not possible to determine unambiguously, whether a given seismic event originated or did not originate on an existing tectonic plane. To obtain unambiguous results, it would be necessary to establish data sets, in which the focal depth is also known to test whether the dislocation plane contains the focus. This will soon be possible using data recorded by seismic networks which provide three-component digital records of the wave patterns of seismic events. For the purpose of assessing the extent of mine activities, synthetic maps of mining intensity for the observed and previous periods were produced. The intensity of exploitation was evaluated by means of the Ik index (Kone6n~, 1989), which represents the thickness of the seam that could be extracted provided that exploitation is realized across the whole area under evaluation (in accordance with the mine network, a square 250 • 250 m network is used, see Fig. 2). Worked-out areas are determined from the mine maps within individual time intervals.

Discussion of results and conclusions As a consequence of potential inaccuracies, (e.g. in the localization of faults, the determination of their dip and the focal depth of the seismic event) a non-quantitative method was used to assess the seismic activity of significant fault zones in the Karvinfi part of the OKR. A visual comparison of the horizontal position of the focus with the fault at a depth of 500 m was used as a basis. In contrast to research in areas without mining-induced seismicity (Prochfizkovfi 1985) in this area, it is necessary to consider induced stresses that are variable in time. These arise as a result of mining activities.

AN ANALYSIS OF SEISMICITY Data from individual sets were, with half-year intervals, compared with the tectonic sketch plan and the intensity of mining in the area under study (e.g. see Figs 3 & 4). The data can be interpreted as follows: 9 No seismic event of natural origin (e.g. tectonic earthquake) has been identified in the data under analysis. No mining-induced seismic event has been recorded which was located within an area of a significant fault zone, where no mining activity had occurred. 9 The induction of seismic events is wholly dependent upon the space-time distribution of mine workings, especially of active faces.

333

This is valid also for the set of intense rockbursts that are not connected directly with mining activities. If an important fault zone occurs in the vicinity of the face, seismic events do not originate preferentially on it or in its surroundings. This result contradicts the results of Spi~fik & Zimovfi (1988) which suggested an increased seismicity along some fault zones. However, the authors warned that actual mining activities and the distribution of worked-out spaces were not considered. Significant concentrations of seismic events are observed in areas, where mining operations took place under extremely complicated

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geological, geomechanical and technological conditions. These concentrations are connected with the existence of important stress concentrators, on which seismic events are induced. 9 The connection between mining shocks and tectonics has been studied previously (Mtiller 1989; Veseki 1993). The results are not unambiguous, there is no demonstrable significance in the concentration of foci of these shock. It is possible to produce similar results as for previous studies. 9 Seismic events induced by blasting operations in workings are usually localized in the rocks overlying the working, in which the

blasting operation was undertaken (release of stress in the roof). In only a very small number of seismic events has a shift of foci towards fault zones been demonstrated. It is often not possible to distinguish a seismic manifestation of the blasting operation from an induced seismic event. Analysis of the data recorded within the threeyear period from 1989 to 1991 by the stations of mine network showed: 9 No incidence of the generation of seismic events on important fault zones or in their close vicinities has been proved in areas where no mining operations have occurred.

AN ANALYSIS OF SEISMICITY

9 Significant sources of induced seismicity are generated in zones of stress concentration where the spatial distributions of both geological and anthropogenic structures is critical. 9 The influence of the characteristics of the massif on the generation of mining-induced seismic events, can be determined by interpreting the digitally recorded data, with particular emphasis on assessing the depth of the focus and parameters of the plane of dislocation, or other physical parameters of the focus (see e.g. Swanson 1992; Tepper et al. 1992). The author acknowledges financial support from the Grant Agency of Czech Republic (reg. No. 105/93/ 2904 and 105/95/0474) and from the Czech-American Scientific and Technical Program (reg. No. 930 65).

References DOPITA, M. & KUMPERA, O. 1993. Geology of the Ostrava-Karvin~ coalfield, Upper Silesian Basin, Czech Republic, and its influence on mining. International Journal of Coal Geology, 23, 291-321. GIBOWlCZ, S. J. & KIJKO, A. 1994. An Introduction to Mining Seismology. Academic, San Diego. KAL,~B, Z., KNEJZL]K, J. & M~LLER, K. 1994. Seismological monitoring in Ostrava area. Exploration Geophysics, Remote Sensing and Environment, 1, 26-33. KNEJZLiK, J., GRUNTORAD,B. & ZAMAZAL,R. 1992. Experimental local seismic network in the A. Z~tpotock~, Mine of the Ostrava-Karvin~ Coal Field. Acta Montana, 84, 97-104. -& ZAMAZAL, R. 1992. Local seismic network in southern part of the Ostrava-Karvin~ Coalfield. Acta Montana, 88, 211-220. KONE~N~, P. 1989. Mining-induced seismicity (rock bursts) in the Ostrava-Karvin6 Coal Basin, Czechoslovakia. Gerlands Beitr. Geophysik, Leipzig, 986, 525-547.

335

1994. Mining induced seismicity in the Czech part of Upper Silesian Coal Basin depending on mining conditions. In: RAKOWS~I, Z. (ed.) Geomechanics 93 Proceedings. Balkema, Rotterdam, 63-68. KUMPERA, O., GRYGAR, R., KALENDOV,~,J., ADAMUSOV~,,M. & VONDRAKOVA,J. 1991. The evaluation method of structure and tectonic setting and palaeostress conditions in relation to rockbursts prognosis. MS Report, Technical University, Ostrava (in Czech). MI2LLER, K. 1989. Location of mining shock in Karvinh part of OKB. In: Seismology in engineering and mining practice. Proceedings, Technical University, Ostrava, 33-36 (in Czech). PROCHAZKOVA, D. 1985. Space-and-time pattern of seismicity. Proceedings of symposium, Geophysical Institute of CAS, Prague, 46-53. RAKOWSKI, Z. 1989. The conception of a physical model of rockburst prone areas in OstravaKarvin~ Coal Basin. Proceedings of symposium, ECE of the United Nations, Ostrava, Czechoslovakia, A21. RUDAJEV, V. 1989. Major causes of rockbursts and the role of seismology in their research. Proceedings of symposium, ECE of the United Nations, Ostrava, Czechoslovakia, A23. SWANSON, P. L. 1992. Mining-induced seismicity in faulted geologic structures: An analysis of seismicity-induced slip potential. PAGEOPH, 139, No. 3/4, 657-676. SPIC,~K, A. & ZIMOV,/k, R. 1988. Seismic activity in Karvin6 part of OKB and its reasons. MS Report, Geophysical Institute of CAS, Prague (in Czech). TEPER, L., IDZIAK,A., SAGAN,G. & ZUBEREK,W. M. 1992. New approach to the studies of the relations between tectonics and mining tremors occurrence on example of the Upper Silesian Coal Basin (Poland). Acta Montana, Ser. A, 88, 161-178. VESEL,~, V. 1993. An elementary analysis of mining shock. In: KALAB, Z. (ed.) Seismology and the Environment. Proceedings, Institute of Geonics, CAS, Ostrava, 146-152 (in Czech).

Comparison of structures derived from mine workings and those interpreted in seismic profiles: an example from the Ka~ice deposit, Kladno Mine, Bohemia STANISLAV OPLUSTIL, JIl~I PESEK & JIl~i SKOPF,C Faculty of Science, Charles University, Albertov 6, 128 43 Prague 2, Czech Republic

Abstract: Five seismic profiles across the Ka6ice coal deposit were reinterpreted and compared with observations in mine galleries. The comparison shows that approximately 80% of normal faults with displacement exceeding 5 m detected on the seismic profiles really exist. In contrast, in only two cases have mine workings shown faults (vertical displacement 10-15m) that have not been identified by seismic measurements. Discrepancies may be mostly explained by: (i) misinterpretation of the fault with slope of the presedimentary palaeorelief accompanied by differential compaction; (ii) virgation of faults and misinterpretation of a fault zone composed of several small faults individually below the detection limit but whose aggregate displacement is detected, giving the appearance of a single fault; (iii) faults which die away toward the overburden indicating synsedimentary movements in the deposit. Reflection seismic has become a common and useful method of exploration of coal-bearing deposits in the central Bohemia, especially in the coalfields of the Kladno Basin (Kadle6ik et al. 1979, 1985, 1986). However, almost none of these coalfields has been mined until now. Exploitation of the Ka~ice deposit is the only exception which enables comparison between seismically derived tectonic interpretation and reality.

Moreover, at the end of 1970s and the begining of 1980s, reflection seismics was carried out in the central and northern parts of the deposit. Advanced exploitation allows us to compare observations in the galleries with the results of seismic interpretation.

Stratigraphy of the Kladno Basin and Kadice deposit

History of the deposit For more than 150 years, thick coal seams of the Radnice Member have been exploited in the Kladno coalfield located along the southern margin of the Kladno Basin. Later, in the mid1950s the Ka6ice deposit was discovered NW of Kladno coalfield, beyond an area of postsedimentary erosion of the coal seams (Fig. 1). Exploratory drilling of the deposit during the 1960s (Salava 1960; Richter 1964, 1966, 1969) allowed its opening in 1969 through a gallery from the Kladno Mine. Consequently, coal exploitation followed from 1975. The annual coal production from the deposit has varied between 400 and 450 x 103 tons during 1980s, however, in 1994 it was only 311 • 103 tons. From 1986 to 1992, refractory claystone was mined, but its exploitation was abandoned due to economic reasons. During the last 20 years of exploration and exploitation of the Ka6ice deposit a large amount of new data has been collected, the concentration of which is greater than for any other part of the Kladno Coalfield (results until 1980 are summarized in Spudil et al. 1980).

The Kladno Basin with the Kladno Coalfield including the Ka6ice deposit in central Bohemia is only a small part of a WSW-ESE elongated complex of Upper Carboniferous continental and partly coal-bearing sediments, which extends from western through central to eastern Bohemia with a length exceeding 250kin (Fig. 1). In western and central Bohemia, the Carboniferous sediments are divided into four lithostratigraphic formations. From the bottom these are: Kladno, T~,nec, Slan~, and Lin6 Fins based on alternation of red and grey sediments. Deposition began in mid-Westphalian and, including several hiatuses, lasted at least to the end Carboniferous. The coal reserves of the Kladno Basin are concentrated mainly within the Radnice Member at the base of the Carboniferous infill. It contains up to five mineable coal seams grouped into the Radnice (with Lower and Upper Radnice seams) and younger Lubnfi (with Lower, Middle and Upper Lubnfi seams) group of seams. Most of them have been mined in the study area. There are no other workable seams in overlying units. In the area of the Ka~ice deposit only the Kladno and T~nec Fins are fully present, whilst

From Gayer, R. & Pe~ek, J. (eds), 1997, European Coal Geology and Technology, Geological Society Special Publication No. 125, pp. 337-347.

338

S. OPLUSTIL E T AL.

~>i'ONIcE

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only the basal part of the Slan2~ Formation has been recognized. The preserved thickness of the Upper Carboniferous deposits varies from 450 m to 650 m depending on palaeotopography, erosion and tectonics. These deposits are underlain by Upper Proterozoic basement composed mainly of a monotonous complex of folded shales and uncommon volcanic rocks and cherts. Deep erosion of the basement created a significant palaeotopography with differences in elevation between the paleohighs and paleovalleys of up to 150 m in the study area and its close vicinity (Oplu~til-Vizdal 1995). The axes of the main elevations and depressions are in a good agreement with structural elements (foliation, fold axes, cherts and volcanic belts) of the basement and both follow a predominantly WSW-ENE direction which is the trend of the Kladno Coalfield itself. Workable coal seams are developed in palaeovalleys. The Ka6ice depression is the northern protrusion of larger Kladno depression. It is surrounded by two significant palaeohighs from which protrude minor ridges

with variable directions into the Ka6ice Deposit itself. The slope of the elevations commonly reaches 10-20 ~ locally even more. In the Ka6ice Depression the coal-bearing Radnice Member is dominated by siltstones and mudstones with four mineable coal seams (Fig, 2). Near the base, mudstones commonly interfinger with breccia derived from weathered basement surrounding the depression. In the upper part of the Radnice Member sandstone bodies also occur, the number and thickness of these increasing significantly to the south. The thickness of coals decreases upward; while the Upper Radnice and Lower Lubn~i coals commonly exceeds 3m (max. 7m) the remaining coals (Middle and Upper Lubnfi) rarely reach 2m. The thickness of the Radnice Member is only erosional and varies greatly from 0 to 185 m (average thickness around 90 m) within the study area and its close proximity. The overlying unit, the N~,~any Member, was deposited after a hiatus and reaches an average thickness of 350m with only slight variations.

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The fluviatile sediments of the N)~any Member are arranged into cycles, the thickness of which varies between 1 and 10m. The lower parts of the cycles dominate with medium-to-coarsegrained sandstones occasionally with conglomerates. These cycles are grouped into six 40 to 60m thick mesocycles which exhibit finingupward trends with a thin coal seam in the highest cycle of each mesocycle (Spudil 1982). The following unit, the T2)nec Formation, shows a very similar lithology and sedimentary architecture to the previous unit, making it rather difficult to distinguish. It is composed of three mesocycles with predominantly red coloured sediments without coal seams. The T)nec Formation passes gradually into the Slan) Formation. The Slan~, Formation is preserved only in the northern part of the Ka6ice Deposit with an erosional thickness of 30-40 m. Apart from the

predominantly grey coloured mudstones it is very similar to the underlying T~Tnec Fro. and N~7~any Member. Within the study area, the Carboniferous sediments are covered by Upper Cretaceous deposits, the thickness of which varies in relationship to the pre-Cretaceous relief and intensity of post-Cretaceous denudation. Usually, the Cretaceous deposits are less than a few tens of meters thick. They are composed of continental fluviolacustrine sediments (conglomerates, sandstones and mudstones, occasionally with a thin seam of dirty coal) at the base grading upward into marine sandstones and siltstone. They are overlain by marl.

Coalfield The concentration of data in the area of the Ka~ice deposit is greater than that of the other

340

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coalfields in the Kladno Basin. Since its discovery in the 1950s there have been more than 50 deep boreholes drilled from the surface to the basement and over 500 mining boreholes, penetrating usually only a part of coal-bearing succession of the Radnice Member. In addition, there are 47 kilometres of galleries, which have been the most useful for the construction of the tectonic map of the deposit. An independently created tectonic map has been derived from seismics. All the galleries and mining boreholes are located in the approximatly 100 m thick basal coal-bearing complex. The remaining 350-500m of overburden is known only from deep boreholes.

Reflection seismics The commonly used borehole spacing is insufficient to determine the fault tectonics of the Kladno basin. The CMP (common-midpoint) method of reflection seismics can be used to aid the fault analysis. The important advantage of the CMP method is its ability to detect separate horizonts even at a depth of several kilometres. The results of the CMP method are commonly presented either as time or depth sections, where continuous reflecting horizons are often clearly visible. The irregularities that exist in the course of these horizons can be interpreted as evidence of faults. The rocks filling a continental sedimentary basin may be developed as a cyclic sedimentatary sequence consisting of many sandy and clay layers. The lithological interfaces between neighbouring sedimentary layers create reflecting boundaries for seismic waves generated at the Earths surface. The parameter describing the reflectivity of a medium is called the reflection coefficient, which can be defined as the amplitude ratio of the incident and reflected waves. In practice the reflection coefficient is expressed as a simple function of the densities and longitudinal wave velocities in the overlying and underlying media. In the case of a cyclic sequence, the time differences between separate reflections are so small that many of these reflections arrive within the time interval corresponding to the wavelet of an individual reflection. Under such conditions, instead of separated true reflections, rather random interference patterns of numerous reflections coming from the individual boundaries may be expected. The amplitudes of these reflections are usually small, as are those from the summary reflections. The total amplitude of the reflections depends not only on the reflection coefficient, but also on the number of reflections

affecting the signal, on the thickness and lithological stability of separate layers, etc. Since these factors are more or less variable, the extent of such reflections is usually limited and the whole wave field can be characterized as rather irregular. The amplitude of a reflected wave depends on the difference in physical properties on both sides of a given interface. In coal-bearing sedimentary basins, coal seams appear as layers of an anomalous physical behaviour because of their low values of density and seismic velocity, which affects the reflection coefficient positively. Therefore, a group of beds containing coal seams is usually characterized by strong reflections that make it possible to determine fault positions where reflection horizons have been displaced. This shift can vary from several hundred seconds to a few milliseconds and may not be observed at all if the throw is too small. Seismic measurements in the Kladno Basin were carried out in 1979 and 1983 by Geofyzika Brno. The Vibroseis measurements with 12-fold coverage in the neighbourhood of Ka~ice village were processed by using standard procedures including wave migration. Strong reflections in the coal-bearing basal Radnice Member have allowed the detection of faults which can be compared with the results of later geological mapping. Within the overlying sediments, the fault structures affect the wave field less evidently, causing local and disconnected shifts of rather weak reflections. As an example of traceable faults causing time shifts in the coal-bearing Radnice Member, the part of seismic line 69/83 is presented in Fig. 3a. A number of normal faults with vertical throws of several tens of metres is obvious in the middle part of the seismic depth section. In Fig. 3b, a part of seismic line 70/83 is shown, where the sedimentary beds are only a little faulted by few minor normal faults. The time shifts are negligible, but correspond to faults located in the coal mine adits. On both figures, the different wave field can be observed for overlying Carboniferous sediments and underlying shales of Proterozoic age, while within the Carboniferous beds the part containing the coal seams is quite different from the overlying cyclic sediments without coal layers.

Structure derived from mine The deposit is affected by post-sedimentary normal faults with a general N W - S E strike. Faults with other strike directions are rare.

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STRUCTURES IN MINEWORKINGS AND SEISMIC PROFILES Moreover, they have only small vertical displacement with a maximum of a few metres. The majority of these faults dip SW. Reverse faults with throws exceeding several tens of centimetres have not been observed in the galleries. In the early 1960s, palaeo-ridges with a NW-SE direction were misinterpreted in seismic profiles as normal faults, because until that time only those ridges running NE-SW had been known. The throw of the normal faults varies greatly from several centimentres to over a hundred metres. Approximately 80% of all documented faults have throws less than 2m and only 10% exceed 5 m; thus they are around or above the detection limit of reflection seismics. Larger faults with more than 40m downthrow occur at a spacing of about 1.5km in the Kladno Coalfield (Fig. 4). They dip at approximately 75 ~ (Spudil 1982) and extend to the Proterozoic basement but are truncated by the pre-Cretaceous surface. Smaller faults (10-20m) are traceable for a distance of several hundred metres up to one kilometre and their dip is usually 55-75 ~. They also continue into basement but it is uncertain whether they reach the top of Carboniferous sequence. They are typically sinuous. The faults often virgate. They commonly occur as systems of antithetic faults, creating grabens several tens up to one hundred metres wide (near the base of the Carboniferous) running across the coalfield (Fig. 4). Small faults (throw less than 10 m) usually do not disturb the whole section of the Radnice Member and diminish as they approach basement. The most distinct reflection corresponds with the boundary between subhorizontally layered undeformed Upper Carboniferous sediments of various lithologies and the folded lithologically monotonous complex composed mainly of Proterozoic shales. The general dip of the basement surface is 5-8 ~ to NNE. Therefore the shallowest occurrence of this boundary is in SW part of the deposit (borehole K6 11, -38.8m); whilst the average altitude of the surface reaches 430 m. To the NE it falls to a depth below -280 m (borehole So 8, -287.7m surface 400m). In detail (Fig. 5), however, the general dip is superimposed on the slopes angles of the pre-Carboniferous ridges. Therefore the final angle may exceed 15~. The study area is affected by three significant normal fault systems. The largest one runs along the eastern margin of the deposit where it continues from the Kladno Coalfield to the south. The vertical displacement reaches 100 m in the SE corner of the Ka6ice Deposit. Further north the fault gradually diminishes and virgates

343

into several smaller faults, the downthrow of which varies between 10 and 20m. They are traceable over a distance of 1 to 2 km in seismic profiles and exceptionally in galleries. Another significant fault zone composed of two major antithetic faults limits the western part of the Ka~ice Deposit. In the SW it creates a 70 m wide graben at the level of the Upper Radnice Seam (about 50 m above the Carboniferous basement). It has a throw of 6-10m. Northward its vertical displacement increases up to 80 m (eastern fault, cross cut 243) in NW edge of the deposit. A vertical displacement of about 60 m on the western fault is estimated from the discrepancy in basement altitude between two boreholes located in the upthrown and downthrown blocks. A similar graben is known from the southwestern margin of the deposit, where it continues from the Kladno Coalfield. In the Ka6ice Deposit, however, only its eastern normal fault was proved in the gallery.

Comparison of structures observed in the mine and those interpreted in seismic profiles Five reinterpreted seismic profiles are compared with the structural map derived from mine. These profiles run mainly from WSW to ENE being more or less perpendicular to prevailing direction of the faults. The location of all seismic fault indications in Fig. 6 if not stated, corresponds with the base of the Carboniferous. Seismic profile 1C/78 runs from SW to NE through the study area (Fig. 6). Two normal faults have been inferred in the area of mining activity (vertical movement 20 and 5 m) and, just behind the eastern end of the galleries, a 200 m wide tectonic zone has been located. Within this zone two principal normal faults have been recognized. A larger one (80 m) on its western margin and a smaller one in its eastern margin. Both dip to the SW. These indications are in good agreement both in size and dip with a significant normal fault proved in a cross-cut at the SE margin of the deposit as a non-branched fault. Seismic measurement supports the idea of their virgation and gradual diminution to the NNW. The remaining two indications correspond only partly to observations in the mine. While the smaller one (5m) has been known from several galleries north of the profile, the larger one (c. 20m) dipping NE probably has no equivalent in the mine. However, the distance between the detection site and the closest gallery

344

S. O P L U S T I L E T AL.

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S T R U C T U R E S IN M I N E W O R K I N G S

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346

S. OPLUSTIL ET AL.

in the direction of the fault is 500 m and it has been observed that a 5m fault may terminate over a distance of 100m. Nevertheless, larger faults are usually more persistent. Detection of the fault in seismic profile through the whole Carboniferous sequence excludes misinterpretation due to the vicinity of a pre-sedimentary ridge or sudden facies changes within the Radnice Member. Seismic profile 69/83 crosses the middle part of the deposit in a WSW-ENE direction. The two westernmost indications lie outside the area proved by the galleries. They are interpreted as antithetic normal faults with vertical displacement of about 20-30 m. They match well with the hypothetical continuation of the graben proved in the mine l k m to SE. Its eastern limit, which is well known from several galleries, has been detected 240 m further east. 250 m further east on the profile a large fault (up to 100 m at the base of the Radnice Member, c. 30-50 m about 90 m higher) dipping eastward has been detected. This normal fault has no equivalent proved in the surrounding galleries (distance 100m). It is believed, that this discrepancy is induced by close proximity of a pre-sedimentary ridge protruding into the deposit from the west. The inclination of its slope probably exceeds 20 ~ (locally 30 ~ or more) as it results from palaeo-relief reconstruction. Moreover, misinterpretation could be affected also by rapid facies and thickness changes within the Radnice Member near the ridge and also by compaction. It is supported by a decreasing value of the throw to the top of the Radnice Member. There are seven other indications with sizes varying from 5 to about 15(20)m. Only two of them (throw 5-10m) remain unproven in the mine. They probably correspond to a narrow fault zone composed of small normal faults under the detection limit, the aggregate throw of which could affect the seismic reflections. Seismic profile 70A/83 runs SW-NE c. 300500m north of profile 69/83. There are seven indications of normal faults with vertical displacements between 5 and 15 m. Only two of them probably do not correspond to the fault system proved in the mine. The westernmost indication dips westward with an estimated throw of about 10(15)m. Its parameters are comparable with the normal faults observed in the mine, but, c. 80-100 m eastward at the level of the Lower Lubnfi Coal, i.e. 50m above the basement. It is believed that this discrepancy could be due to different stratigraphic levels. Otherwise the faults proved in the mine lack any indication on the seismic profile.

The second indication without a proved equivalent is an east-dipping normal fault with an estimated displacement of c. 5-10m (Fig. 6). It is situated in a zone with an increased number of small normal faults whose aggregate displacement may resemble a single fault in seismic profile. Seismic profile 70/83 crosses the northern part of the deposit from WSW to ENE. Five indications of normal faults have been recognized within the seismic profile. Their throw varies from 5 to 25 m. Four of them are situated in the mining area and have been observed in galleries. The fifth indication is located behind the eastern margin of the galleries in the proximity of borehole Le 3. It is interpreted as an east-dipping normal fault with estimated throw of 25m. Probably on the same fault, gallery 1008 terminated at the NE margin of the deposit. The second indication from the east has been detected only at the base of the Carboniferous (throw c. 10 m); it seems to be absent higher but is indicated again around the boundary of the Kladno and the T~nec Fms approximately 400 m higher. Seismic profile 71/83 runs NNW-SSE along the eastern margin of the deposit, just behind the eastern end of the galleries. It is nearly parallel with the main faults of the study area. Therefore all of the indications belong to the main fault (fault zone) of the Kladno Mine. They dip either to the W or to the E due to undulations of a fault with a low angle of dip, 30-40 ~. Their throw decreases gradually northward from 20 to 10m.

Conclusion Comparison of structures interpreted in seismic profiles with those observed in mines show good agreement. Approximatly 75% of seismic indications correspond with the observations in mine galleries in both dip and throw. The seismic data have indicated nearly all of the observed normal faults above the detection limit, which in the central and western Bohemian Carboniferous is between 5 and 10m. The number of normal fault indications in seismic l:rofiles slightly exceeds the number of observed faults. Most of them are around the detection limit. However, in one case a large fault with a throw of several tens of metres has been interpreted with no equivalent in the mine. The possible explanations for most of the discrepancies between seismic data and observations in mine are as follows:

STRUCTURES IN MINEWORKINGS AND SEISMIC PROFILES 9 misinterpretation of the slope of a presedimentary ridge, which could exceed 150m elevation accompanied by sudden facies change. The influence of presedimentary palaeotopography and different compaction could persist up to the level of the T~nec Fm. (Spudil et aL 1980) 9 several smaller faults under the detection limit whose aggregate throw is interpreted as a single fault. The apparent discontinuous character of some faults in seismic sections can be induced by the coincidence of the throw of the normal faults with the thickness of the cycles. The resulting reflections appear to be uninterrupted. It could be a common phenomenon in the N ~ a n y Member and the T2?nec Formation where the average cycle thickness varies between 7 and 10m. In one case a normal fault dying out towards overlying beds indicates an occurrence of synsedimentary movements in the deposit. Despite the above mentioned discrepancies, reflection seismics has been proved to be a useful method for exploration of new coalfields in the Upper Carboniferous coal basins of western and central Bohemia. It indicates that a proper density of seismic profiles allows the construction of a reliable structural plans where even faults with small vertical displacements can be indicated by the geophysical method.

347

References KADLE~iK, J., SKAROV,~, M. & JIHLAVEC, F. 1979. Geofyzik6lnY - geologick6 zhodnoceni reflexnYseismickfwh pracl S R B technologii VIBROSEIS na ~kolu Peruc-Slapanice. Written final report. --

Archives Geofond, Brno. et aL 1985. Seismickf: prdzkum na lo~isku Slanj~ v r. 1983-1985. Written final report. Archives Geofond, Brno. et al. 1986. Z6vJre(nd zprdva o reflexnJseismick6m prdzkumu SRB v oblasti PerucKokovice v r. 1983. Written final report. Archives

Geofond, Brno. OPLUSTIL, S. & VIZDAL, P. 1995. Pre-sedimentary palaeo-relief and compaction: controls on peat deposition and clastic sedimentation in the Radnice Member, Kladno Basin, Bohemia. In: WHATELEY, M. K. G. & SPEARS, D. A. (eds), European Coal Geology. Geological Society, London, Special Publication, 82, 267-283. RICHTER, V. 1964. Kadice. Zdvdrednd zprdva pJredb~n6 etapy prdzkumu. Written final report. Archives Geofond, Praha. - - 1 9 6 6 . Dopln~k zdv#rednd zprdvy Kadice. Written final report. Archives Geofond, Praha. 1969. Dopln~k zdvgredn~ zprdvy Ka~ice sever. Written final report. Archives Geofond, Praha. SALAVA,J. 1960. Z6vYre?n6 zprdva Ka?ice. Vyhleddvaci etapa. Written final report. Archives Geofond, Praha. SPUDIL, J. 1982. Strukturn6 geologickfi charakteristika lo2iska Ka6ice. In: HAVLENA,,V.,~ PESEK,J. (eds) Sbornik IV, uhelng geologickd konference pFidovYdeck~ fakulty, Praha, 133-142. et al. 1980. Z6v~re?n6 zpr6va ~kolu Ka{ice.

Written final report. Archives Geofond, Praha.

Improvements in direct coal liquefaction using beneficiated coal fractions J. B A R R A Z A ,

M. C L O K E

& A. B E L G H A Z I

Coal Technology Research Group, Chemical Engineering Department, University o f Nottingham, Nottingham NG7 2RD, UK.

Abstract: Beneficiated coal fractions from Point of Ayr coal (North Wales) were liquefied in order to determine their effect on conversion, product and metal distribution in coal extract solutions. The coal fractions were obtained in a dense medium cyclone separation unit, using aqueous solutions of Ca(NO3)2, as medium, of relative density 1.26. The original coal and the coal fractions were liquefied in an autoclave with hydrogenated anthracene oil (HAO) as solvent. Liquefaction results show an improvement in conversion for the overflow fractions over the feed coal, together with a shift in the net product distribution toward higher oils content and lower asphaltenes and preasphaltenes material in the liquid products. A marked decrease in the proportion of A1, Mg, Mn and Si was found in the extracts using overflow coal. However, Ti and Ca, which are deactivating elements of the hydrocracking catalyst used to upgrade the coal liquids, increased their proportion.

During the last decade, work has been carried out in order to separate and concentrate macerals for use in liquefaction processes (Dyrack & Horwitz 1982; Cronauer & Swanson 1991). Investigators seem to agree that the coal characteristics, particularly petrographic and mineral compositions are important parameters in the coal liquefaction process, affecting overall conversions, product and metal distribution in the coal liquids. It has been established (King et al. 1984; Steller 1987) under a wide range of liquefaction conditions that the more reactive maceral is liptinite followed, in decreasing order, by vitrinite and inertinite. Also, some studies (Keogh & Poe 1987; Oner et al. 1994) have shown that the presence of mineral matter in coal has a catalytic effect towards oils production in liquefaction carried out in the presence of hydrogen and at conditions of high severity. One of the liquefaction techniques which could process coals of a wide range of maceral and mineral compositions is the British Coal two-stage coal liquefaction. In the first stage, the coal is digested in a hydrogen-donating solvent in the absence of hydrogen, at a low pressure (20-30 barg), and the resulting mixture is filtered to produce a low-ash extract solution. In the second stage the extract solution is catalytically hydrocracked in the presence of hydrogen to upgrade the products. Catalytic deactivation, during the hydrocracking stage was found (Robatt & Finseth 1984; Kovach et al. 1978) due to the deposition of metals such as titanium, calcium and magnesium. Because of this, attempts have been made to reduce these undesired elements in the extract

before the hydrocracking process. Cloke (1986), reported that an increase in the digestion pressure produced a significant reduction in the extract ash levels. Also, the addition of toluene before the filtration process, precipitates heavy organics producing extracts of low concentration in mineral matter (Cloke et al. 1993). However, very little work has been reported in order to attempt to decrease the metal content in coal extracts using beneficiated coal fractions, which are simply clean coal fractions with high concentration of organic matter and low concentration of mineral matter. The purpose of this study was to ascertain the effect of liquefying beneficiated coal fractions, obtained by a dense medium cyclone unit, on conversion, product distribution and element content in the extract solutions.

Experimental Materials A bituminous coal from Point of Ayr (North Wales) was used in the study. Coal samples, runof-mine and uncrushed, were supplied by British Coal. The dense medium used for the separation was an aqueous solution of Calcium Nitrate Tetrahydrate, obtained from Berk Ltd, UK. Advantages of this medium include that: it can produce solutions of a wide range of densities; it has low toxicity; and it is moderately inexpensive (Rhodes et al. 1993). The solvent used for the liquefaction was a process-derived Hydrogenated Anthracene Oil (HAO), supplied by the

From Gayer, R. & Pe~ek, J. (eds), 1997, European Coal Geology and Technology, Geological Society Special Publication No. 125, pp. 349-356.

350

J. BARRAZA ET AL. overflow and the under flow fractions. The product of the digestion was filtered to produce a filter cake and a coal extract solution. Details of the liquefaction procedure has been previously reported in the work of Cloke et al. (1987).

British Coal Liquefaction Project. Standards and controls used to determine the metal element concentration were made from B.D.H. 'Spectrosol' solutions.

Procedures

The fresh coal was crushed, wet screened, filtered and air-dried at room temperature to obtain coal samples of particle size -250 + 63 #m. Coal samples were processed in a dense medium cyclone unit, which is a closed circuit sumppump-cyclone. A diagram of the process is shown in Fig. 1. Water and Calcium Nitrate (powder) were added to the feed sump and the density determined and adjusted. A relative density of 1.26 was used in the experiment, which was obtained by increasing the medium concentration or diluting it with tap water. The coal was added to the media, producing a slurry, which was agitated with a stirrer driven by air. The slurry was pumped (2 barg) to the cyclone and samples of overflow and underflow were collected. The recovered samples were filtered and air-dried in the laboratory at room temperature ready to liquefy. Liquefaction runs were made in a 2 litre autoclave with HAO as solvent in a ratio HAO/Coal: 2/1, w/w. Approximately 350g of coal (as received) was fed to the autoclave. The liquefaction was carried out for 1 hour and a temperature of 420~ Digestion pressures of 10barg and 40barg were used for the original coal, while a pressure of 40 barg was used for the

Analysis

Analysis for moisture and ash were carried out using the Standard BS1016 methods, while maceral analysis was performed by the procedure described elsewhere (Cloke et al. 1994). The coal extract solution was analyzed for hexane, toluene and tetrahydrofuran (THF) insoluble, in order to determine the product distribution. In the present study, the product distribution is defined as: oils, (100-hexane insolubles); asphaltenes, (hexane insolubles- toluene insolubles); preasphaltenes, (toluene insolubles - THF insolubles) and heavy organics, (THF insolubles). The coal conversion (on a dry mineral matter free, dmmf, basis) is defined in terms of coal ash, filter cake ash and quinoline insoluble. The extract solution and filter cake were analyzed for ash content at a temperature of 815~ in platinum crucibles. Nine elements (A1, Ca, Fe, K Mg, Mn, Na, Si and Ti) concentrations were determined in the original coal, overflow, underflow, coal extract liquid and HAO, using a Perkin-Elmer model 2380 Atomic Absorption Spectrophotometer. The metal concentrations were determined on the basis of the work of Hamilton (1986).

Overflow

Air Coal+ medium

IJ

T---~ (~ d---~~ ] - - - Cycloneunit

Underflow

I

i~

/ Cleaj,

! Stirrer

'\,,, \,

SumpTank J

Gaugepressure

//

ReceptorMedium Tank

/'

~/// Feedp u ~

|

Recirculation pump

9

Fig. 1. Diagram of the dense medium cyclone process.

DIRECT COAL LIQUEFACTION

Results and discussion Dense medium cyclone separation Mass yields, ash, macerals and element analysis of the original coal and coal fractions obtained in the separation are shown in Table 1. Results show that the overflow fraction gives a lower vitrinite concentration than the original coal, however, it has the lowest ash content and the highest concentration of liptinite. By contrast, the underflow fraction shows the lowest vitrinite and the highest inertinite content. Clearly, the findings indicate that the cyclone separation had

Ash, maceral and major element analysis of coal samples

Table 1.

Coal samples as received Original

Overflow Underflow

Relative Density Yield mass (% w/w) Ash (%, db) 14.5

1.26 43.0 1.2

1.26 57.0 24.0

Maceral analysis, mmf (% v/v) Vitrinite Liptinite Inertinite

77.0 15.7 7.3

73.6 7.7 18.7

7.85 8.40 9.00 1.22 1.65 0.02 0.85 18.74 1.35

9.07 3.10 9.10 2.61 1.89 0.16 0.23 29.38 0.67

80.9 10.1 9.0

Element analysis in ash (% w/w) A1 9.31 Ca 2.94 Fe 8.70 Mg 2.46 Mn 1.69 K 0.13 Na 0.34 Si 30.16 Ti 0.69

351

a positive effect to concentrate the organic matter and to decrease the mineral matter in the overflow fraction. The higher concentration of liptinite in the overflow fraction would be of benefit to the liquefaction process, while the higher concentration of non-reactive macerals in the underflow would be detrimental. Results of concentration of the elements in ashes of coal samples show that in general, the elements with the highest concentration are Si, Fe, A1, Ca and K. In order to analyze changes in the concentration of the elements in the overflow fractions relative to the original coal fed to the cyclone, the concentrations are expressed in terms of proportions. Figure 2 shows the proportion values. In the overflow, it was found that Ca has the highest increase followed by Na and Ti, while Fe and Mg show the same proportions, and the rest of the elements show a decrease. The above results suggest that Ca, Na and Ti have a tendency to be associated with the organic matter, and A1, Si, K and Mn with the mineral matter. In agreement with our results, a previous study (Barraza et al. 1994) has shown that Ca shows organic affinity using float-sink separations. The above changes in the concentration proportion suggest that some elements have been removed more than others. In order to examine this trend, the results are evaluated in terms of the masses of the elements present in the original coal, overflow and underflow. Results of the elemental masses obtained in Table 2 show that the biggest decrease of all the elements occurs in the overflow fractions, however some elements show greater reductions than others. In order to compare the removal of the elements, the masses were transformed into proportions, relative to the original coal feed. Figure 3 gives the mass proportion of elements for the overflow coal fraction. Ca, Na and Ti have the highest proportion, which in terms of

3.00 1 2.50 -' 2.00 1.50 1.00 0.50

-[ 1-

0.00

AI

Ca

Fe

K

r , Mg

Mn

Na

Si

Ti

Element

Fig. 2. Concentration proportion of elements is ashes of overflow relative to original coal.

J. BARRAZA E T AL.

352

Table 2. Global and major element mass in original feed

and the coal fractions. The overflow fraction produced the highest conversion, while the underflow fraction gave the lowest conversion. The highest conversion from the overflow fraction would be associated with its high concentration of reactive macerals (liptinite+ vitrinite) as well as to its low mineral matter content, and the lowest conversion in underflow may be due to the high inertinite level. These results are consistent with those reported for Parkash et al. 1985; Joseph et al. 1991. Performing the digestion at higher pressure appears to produce a slight increase in conversion in the original coal. Higher content of light compounds, which were not released from the autoclave, may explain this increase in conversion. Despite the high conversion values obtained from the overflow fraction, it gave lower oils content and higher heavy organics material in the coal extract liquid compared to the original coal and the underflow fraction. The digestion pressure appears to affect the oils level in the original coal. Oils concentrations are higher at 10barg than 40barg, however the latter pressure, appears to reduce the concentration of asphaltenes and preasphaltenes in the product from the overflow fraction. Low heavy organics content in the underflow compared with the overflow fraction also was achieved. The product distribution obtained above includes the oils from the HAO and the oils produced from coal. HAO represents a large amount of the oils in the final product and it would have affected the distribution obtained. Therefore, an analysis is carried out on the basis of products formed from the coal alone. In order to evaluate the net product distribution, a mass balance is performed taking as basis 100kg of coal, which was separated into an overflow

cyclone, overflow and underflow coal fractions Coal samples Original Mass (g) Ash (g)

Overflow

Underflow

Global mass (g) 100.00 132.56 1.20 31.81

232.56 33.72

Element mass (g) Element AI Ca Fe K Mg Mn Na Si Ti

3.14 0.99 2.93 0.83 0.57 0.04 0.11 10.17 0.23

0.09 0.10 0.11 0.01 0.02 0.00 0.01 0.22 0.02

2.89 0.96 2.39 0.73 0.55 0.04 0.09 9.47 0.20

Basis: 100.00g of overflow as received. removal means that they were partially removed, while A1, K Mn and Si show a significant degree of removal. Again, the notable proportion of Ca and Ti in the overflow is observed. These variations in the mass of the elements suggest that they may show different behaviour during liquefaction.

Liquefaction o f original coal and coal fractions Results of conversion and product distribution in the coal extract liquids are shown in Fig. 4. Note that the oils figure includes the original HAO solvent. Differences were observed in liquefaction conversion from the original coal

0.12 - 0.10 ~-

0.08 0.06 0.04 0.02

0.00

I A1

I Ca

i [ Fe

] K

t

,

Mg

r--1

Mn

1[

I

Na

Element

Fig. 3. Mass proportion of elements of overflow fraction relative to original coal.

Si

Ti

DIRECT COAL LIQUEFACTION

353

100 90 u

80

m !

70

60 50

ji

!

40 30

~'

20 10

i

N

0o

Feed lO

0

Feed-dO

OF-I 26 40

DciOn.ois ...

I

nll Asphaltens

L

mHeavy Organics

UF-I26-40

Feed to autoclave

Fig. 4. Conversion and product distribution.

fraction and then liquefied in the autoclave. For this mass balance, it was assumed that the amount of gas produced is 2% of the coal converted and all the HAO during the liquefaction finish as oils. Results of the net product distribution are presented in Fig. 5. These findings show that, in general, the overflow fraction produced the highest net percentage of oils, with small reductions in the asphaltenes and preasphalteues. However, the heavy organics content is the highest. The underflow produced

the lowest oils percentage value. These results show that the overflow fraction has a beneficial effect towards production of oils. With regard to the element distribution during the digestion process, results of the concentration of the elements and ash content of the coal extracts are shown in Table 3. The concentration of the element and ash of the HAO are also reported in the same table. These findings show that for digestion at higher pressure, a reduction in the ash content for the

50.0 45.0 r'loils mAsphaltenes mPreasphaltenes

40.0

mHeavy Organ es

35.0 ,5

30.0

g~ 25.0 ~'

2

1. Original coal, 10 bar 2. Original coal, 40 bar 3. Overflow, 40 bar 4. Underflow, 40 bar

20.0 15.0 10.0 5.0 0.0 !

2

3 Feed to auloclave

Fig. 5. Net products distribution oi] a basis of 100kg as received.

354

J. BARRAZA E T AL. Table 3. Major element analysis in ashes of coal extract liquids and HAO Feed to autoclave

Original

Digestion Pressure, bar Extract ash value, % w/w

10 0.045

Concentration of element in ash (% wt) A1 Ca Fe K Mg Mn Na Si Ti

2.96 17.26 5.9 0.04 4.6 0.52 0.42 1.21 1.37

Overflow

Underflow HAO

40 0.023

40 0.048

40 0.041

1.76 17.53 9.9 0.05 0.62 1.9 0.35 2.92 1.09

0.37 22.24 9.4 0.03 0.22 0.18 0.19 1.21 1.37

0.55 20.83 10.5 0.03 0.65 1.17 0.22 0.59 0.68

0.003

8.11 1.65 10.9 1.07 0.67 0.16 1.85 15.2 N/D

N/D: Not detected.

extract solution from the original coal is achieved. These findings are in agreement with the results obtained by Cloke (1986). Thus, a digestion pressure of 40 barg was used with the overflow coal fractions, since it was expected that this would give a low ash content in the coal extracts. However, the results of ash content in the extracts from the coal fractions show that the beneficiated overflow did not produced a coal extract with ash content lower than the coal extract from the original coal. This may be due to the differences in heavy organics material content in the coal fraction as is shown in Fig. 5. Differences in the proportion of elements found in the extracts, defined as the concentration of the element in the ash of the extract divided by the concentration of the element in the ash of the feed to the autoclave, are shown in Fig. 6. Ca and Mn show the highest increase in all the coal extract liquids, however, Ca gives the lowest proportion in the extract solution from the overflow fraction, while Mn has the lowest

~9

t~

s

proportion in extract solution from the original coal digested at 10 barg. With regard to Na and Mg, both show a high proportion in the extract liquid from the original coal and a low proportion in the extract from the overflow. Ti and Fe do not show variations, while A1, K and Si give a great reduction in the majority of extract solutions. Kovach et al. (1978), have shown that the alkali metals, Ca and Na, and the acidic metals, Ti and Si, are greater deactivators of the hydrocracking catalysts used in a two-stage liquefaction process. In the present study, a reduction in the concentration of these elements using overflow fractions has been achieved, which would be beneficial in prolonging the hydrocracking catalyst life. The above results show that there are changes in the major element proportions between the extracts produced using different types of feed to the autoclave. In order to examine this trend the results are recalculated in terms of the masses of the elements in each extract and coal samples fed

16.00 14.00

ii

12.oo 10.00

~

o

s.oo

6.00 4.00 2.00 0.00

[] Original10 I~1Original40 IlllOF 1.2640 [] UF 1.26 40

_ _ _

AI

Ca

Fe

K

Mg

Mn

Na

Si

Element

Fig. 6. Concentration proportions of elements in coal extracts relative to feed autoclave.

Ti

355

DIRECT COAL LIQUEFACTION Table 4. Mass of major element in coal extract solutions

Feed to autoclave

Overflow

Original coal

Digestion Pressure, bar

10

40

Mass of coal converted, dmmf (g) 65.90 Mass of extract (g) 260.58

Underflow 40

40

71.60 266.16

88.63 282.86

62.98 257.72

Mass of element in extracts (mg) Element A1 Ca Fe K Mg Mn Na Si Ti

3.47 20.24 6.92 0.05 5.39 0.61 0.49 1.42 1.61

to the autoclave. For this, a basis of 100g of coal fed to the autoclave was used and the material vented was estimated 2% of the coal converted. The results for each type of coal fed to the autoclave are shown in Table 4. Differences were observed in both the amount of coal converted and the mass of the elements in the extracts. The highest mass of coal converted was obtained with the overflow fraction, which is due to the high conversion achieved. Also, it was found that the majority of masses of the elements show a decrease in the extracts from the original coal as the pressure is increased. However at 40 barg, the masses of some elements in the extract from the overflow were not reduced compared to the masses of the same elements in the extract from the original coal. Therefore, in order to analyse which elements give a reduction in the extracts from overflow relative to the original coal, the masses of the elements are transformed into the proportions shown in Fig. 7. Results show a decrease in the proportion for A1, Mg, Mn and

1.08 10.73 6.06 0.03 0.38 1.16 0.21 1.79 0.67

0.50 30.20 12.76 0.04 0.30 0.24 0.26 1.64 1.86

0.58 22.01 11.09 0.03 0.69 1.24 0.23 0.62 0.72

Si. However, Ti, Ca and Fe have the highest increase and K and Na show approximately the same proportions. It indicates that the elements Ca, Ti and Na, which are considered to be the deactivating elements of the hydrocracking catalyst, were not reduced in the extracts using the overflow fraction compared to the original coal. These findings again may suggest the association of Ca and Ti with the organic matter, such as has been shown in other studies (Robatt et al. 1984; Cloke 1986)

Conclusions

1. The dense medium cyclone unit produced an overflow coal fraction of high concentration in organic matter and low concentration in mineral matter. 2. In general, liquefaction results show an improvement in conversion for the overflow

J

2.5

1.5 ~-

1

0.5 +--F , [---] ~

0 AI

Ca

Fe

K

Mg

Mn

Na

Si

Ti

Element

Fig. 7. Mass proportion of element in extract from overflow relative to extract from original coal.

356

J. BARRAZA E T AL.

fractions over the original coal. By contrast, the underflow fraction gave the lowest conversion. Given the high mineral matter content to remove in the filtration process, the underflow fraction is not a material desired for liquefaction purposes. 3. A shift in the net product distribution towards higher oils and lower asphaltenes and preasphaltenes were obtained in the liquid product using the overflow fraction. However, it gave the highest heavy organics content, which would be detrimental for the hydrocracking stage. 4. The beneficiation did not reduce the ash content in the filtered coal extract solution compared to the ash content in the extracts from the original coal. However, the quantity of mineral matter to be removed at the filtration stage was reduced. 5. Reduction in the proportion of masses of A1, Mg, Mn and Si, in the extracts from the overflow relative to the original coal were obtained. However, some of the strongest deactivating elements such as Ti and Ca show a large increase in proportion. The authors gratefully acknowledge the award of a grant in aid of research from the European Coal and Steel Community (ECSC), the Colombian Institute of Science and Technology (COLCIENCIAS), the British Coal Utilization Research Association and the United Kingdom Department of Trade and Industry. The assistance of British Coal Liquefaction for provision of samples is acknowledged. The views expressed are those of the authors and not necessarily those of the funding bodies.

References BARRAZA, J., GILFILLAN,A., CLOKE, M. & CLIFT, D. 1994 International Coal Conference on Coal Bed Methane, Cardiff, Wales, September. CLOKE, M. 1986. Fuel, 65, 417. - - 1987. PhD. Thesis, University of Nottingham - - , BELGHAZI,A., MARTIN, S., KELLY, B., SNAPE, C. E., MCQUEEN, P. & STEEDMAN, W. 1993. International Conference on Coal Science, Banff, Canada, - - , CLIFT, D., GILFILLAN,A., MILES, N. & RHODES, D. 1994. Fuel Processing Technology, 38, 153. CRONAUER, D. & SWANSON, A. 1991. 201 ACS National Meeting, Atlanta, Georgia, 14. DYRKACK, G. R. & HORWlTZ, E. P. 1982. Fuel, 61, 3. HAMILTON, S. 1986. Thesis M. Phil, University of Nottingham. JOSEPH, J. T., FISHER, R. B., MASIN, C. A., DYRKACZ, G. R. & BLOOMQUIST, C. A. 1991. Energy and Fuels, 5, 724. KEOGH, R. A. & POE, S. H. 1987. International Conference on Coal Science, The Netherlands, 289-294. KING, H. H., DYRKACKZ, G. R. & WlNANAS, R. E. 1984. Fuel, 63, 341. KOVACH, S. M., CASTLE, L. J. & BENNETT,J. V. 1978. Industrial and Engineering Chemistry; Production, Research and Development, 17, 1 62-67. ONER, M., ONER, G., BOLAT, E., YATIN, G., KAVLAK, C. & DINCER, S. 1994. Fuel, 73, 10. PARKASH, S., LALI, K., HOLUSZKO,M. & DU PLESSIS, M. P. 1985. Liquid Fuel Technology, 3, 3. ROBBATT,A., Jr., FINSETH, D. H. & LETT, R. G. 1984. Fuel, 63, 1710-1714. RHODES, D., HALL, S. T. & MILES, N. J. 1993. XVIII International Mineral Processing Congress, 23-28. STEELER, M. 1987. International Conference on Coal Science, The Netherlands, 115-118.

Conversion of low rank coal into liquid fuels by direct hydrogenation B. R. A L E K S I ( ~ ~, M. D. E R C E G O V A C ,

O. G. C V E T K O V I ( ~ 3,

B. Z. M A R K O V I ( ~ ~, Y. L. G L U M I ( ~ I ( ~ 3, B. D. A L E K S I ( ~ ~ & D. K. V I T O R O V I ( ~ 3

'IChTM, Center of Catalysis and Chemical Engineering, NjegoYeva 12, 11000 Belgrade, FR Yugoslavia 2 Faculty of Mines and Geology, University of Belgrade, DjuYina 7, 11000 Belgrade, FR Yugoslavia 3 IChTM, Center of Chemistry, Njegogeva 12, 11000 Belgrade, FR Yugoslavia Abstract: A study of low-rank coal conversion into liquid products by direct catalytic hydrogenation was undertaken. A soft brown coal from the 'Tamnava' field of the Kolubara mines characterized by a huminite reflectance of 0.27+0.03%RR, ash content of 10.4wt%(db), carbon content of 64.0wt% (daf), and volatiles ca. 50wt%(db), was submitted to liquefaction in a batch reactor. The effect of reaction parameters on both the yield and nature of liquefaction products was studied for temperatures ranging from 365 to 440~ and pressure from 13.5 to 16.5 MPa, with process duration from 1 to 8 hours. The total coal conversion was high at all applied reaction conditions (84-93%, daf coal basis), pointing to a high reactivity of this coal. The yield of particular liquid products varied markedly depending on temperature and residence time. The yield of light-oil (n-heptane soluble products) increased and that of asphaltenes decreased by increasing the temperature and prolonging the residence time. Changes in petrographic composition of the coal were examined by microscopic analysis. At more severe reaction conditions the content of semicoke and coke increased. With the increase of temperature at mild conditions, the proportions of both the reacted coal and granular residue increased, while the cenospheres and mineral matter decreased.The nature of the changes observed in the organic and mineral components of the coal grains was used to correlate the degree of coal conversion with the experimental conditions.

Contrary to the previous conception that only bituminous and subbituminous coals might be used for liquefaction, much research effort has recently been directed toward determining the susceptibility of low-rank coals to liquefaction. It has been reported (Derbyshire & Stansberry 1987; Mondragon et al. 1988) that certain soft brown coals liquefy more readily than high-rank coals. There is a number of research papers dealing with the correlation between liquefaction behaviour and various properties of coals, especially coal petrography (Artemova et al. 1989; Given et al. 1980; Hower et al. 1991; Parkash et al. 1984), but there is a lack of generally valuable correlations. One of the reasons is the chemical and petrographic heterogeneity of coals within the same rank. The other reason might be the complex interaction of coal mineral components with the organic part of coal during liquefaction. Therefore, data obtained under certain experimental conditions of a particular coal liquefaction cannot be considered reliable for other types of coals or even for the same coal treated by a different liquefaction procedure (Tischer & Utz 1983).

The work presented here was aimed at obtaining information on the behaviour of soft brown coal from the 'Tamnava' field of the Kolubara mines (Serbia) during liquefaction by direct catalytic hydrogenation. The effect of the reaction parameters on the changes in the coal petrographic composition was examined and correlated with the changes observed in the degree of coal conversion and in the liquefaction product yields.

Experimental method Liquefaction of pulverized coal (< 160 #m) slurry in tetralin in the presence of a granulated cobaltmolybdenum hydrodesulphurization catalyst was performed by a stream of hydrogen in a batch reactor. The reaction parameters were varied in the following ranges: temperature, from 365 to 440~ pressure, from 13.5 to 16.5 MPa; residence time in the reaction conditions, 1 to 8 hours. The choice of particular parameters was based on preliminary experi-

From Gayer, R. & Pe~ek, J. (eds), 1997, European Coal Geology and Technology, Geological Society Special Publication No. 125, pp. 357-363.

358

B. R. ALEKSIC E T A L .

mental work. After cooling, the liquefaction products were separated according to a previously established procedure (Vitorovi6 et al. 1991). After filtration the solid residue and the catalyst were rinsed several times with the filtrate itself, then the catalyst was separated by sieving and dried to constant weight at 300~ The liquid liquefaction products were separated from tetralin by distillation. The light oil was dissolved in n-heptane, the undissolved part consisting of asphaltenes. The liquid products were characterized by ultimate analysis and gas chromatography (30m Supelco capillary SPB-1 column). The solid residues were characterized by ultimate and micropetrographic analyses. The methods have been described in more detail elsewhere (Vitorovi6 et al. 1991, 1994). The degree of coal conversion (X) was calculated on the basis of the dry, ash free solid residue (R) according to: X = lO0(mo-R)/mc, where mc denotes the initial mass of the coal (dry, ash free). Microscopic examination of the solid residues and the initial coal sample was carried out on two polished blocks prepared from each sample, involving 1000 measurements according to ICCP standards (1963, 1971).

Results and discussion The characteristics of the initial coal sample are given in Table 1. The coal substance of the 'Tamnava' coal sample is in a relatively low stage of humification and gelification (0.73). The proportion of the non-gelified macerals is 42.0vo1%, and that of gelified (homogenous) macerals 31.0vo1%. According to huminite

reflectance, 0.27 + 0.03% RR, and volatiles, 49.5 (wt%, dry basis), the average coal sample belongs to soft brown coals, designated as M2 coals (Ercegovac 1986) with a xylite content of 42.0 wt%. The liquefaction yields representative of different reaction conditions (temperature, T; pressure, p; residence time, rr) are shown in

Table 1. Characteristics of Tamnava coal sample Equilibrium moisture (wt%) 12.3 Ash (wt%, dry basis) 10.4 Sulphur, total (wt%, dry basis) 1.0 Fixed carbon (wt%, dry basis) 26.1 Volatiles (wt%, dry basis) 49.5 Ultimate analysis (wt%, dry basis, ash free) Carbon 64.0 Hydrogen 5.7 Nitrogen 1.3 Oxygen (by difference) 29.0 Heating value (kJ kg-1) HHV 19 327.3 LHV 18 425.5 Macerals and minerals (vol%) Huminite 67.0 Textinite 25.0 Ulminite 21.0 Atrinite 11.0 Densinite 4.0 Gelinite 6.0 Liptinite 3.5 Inertinite 6.0 Minerals 23.5 Clay 20.0 Pyrite 2.5 Carbonates 1.0 Gelification index 0.73 Huminite reflectance, RR (%) 0.27 Xylite (wt%) 42.0

Table 2. Liquefaction yields (wt% daf coal) and coal conversion (%) Test No 1 2 3 4 5 6 7 8 9 10 11 12

Conversion

Reaction conditions

Products

T (~

p (MPa) rr (h)

Oil

Asphaltenes

Solid residue

365 365 365 365 365 400 400 420 440 440 440 440

13.5 13.5 13.5 13.5 16.5 13.5 16.5 15.0 13.5 13.5 15.0 15.0

22.6 21.8 16.8 16.5 22.2 26.6 25.5 52.5 68.2 74.4 65.4 73.0

25.5 26.3 17.0 15.7 27.0 27.8 23.5 7.2 7.8 5.1 6.2 3.3

15.7 11.5 14.5 6.7 10.3 13.8 15.3 9.2 11.5 11.3 10.8 13.6

1 4 6 8 4 4 4 4 4 8 4 8

84.3 88.5 85.5 93.3 89.7 86.2 84.7 90.8 88.5 88.9 89.2 86.4

C O N V E R S I O N OF LOW R A N K COAL INTO L I Q U I D FUELS

359

Table 3. Petrographic composition and optical characteristics of liquefaction residues of Kolubara coal ("Tamnava')

Categories of grains (vol%) No. 1 2 3 4 5 6 7 8 9 10 11 12

Unreacted and partly reacted coal Reacted coal Isotropic humoplasts Asphaltenes (pitch-like material) Cenospheres (Iso.) Semi-coke (Iso.) Coke (Aniso.) Isotropic grains (porous, A-type) Homogenous isotropic grains (high % RR) Granular residue (partly porous structure) Fragments (84%) of the soft brown coal 'Tamnava' was observed during liquefaction by direct catalytic hydrogenation. Varying the reaction conditions (the temperature, pressure and residence time), high yields of liquid products were obtained. The high reactivity of the coal was confirmed by petrographic analysis which showed that there was no unreacted coal in the solid residues with most of the liquefaction runs. The petrographic composition of the residues depended on the reaction conditions, but a more reliable correlation requires additional investigations. Nevertheless, petrographic analyses produced valuable data concerning the changes in the 'Tamnava' soft brown coal during liquefaction. This work was supported in part by the Research Fund of Serbia (Project No 0816). The authors are grateful to the Kolubara Mine for providing the coal 'Tamnava' samples.

363

References

ARTEMOVA, N. J. KASATOCHKINA, L. J. CHIZHEVSKAYA, V. R. & SHULAKOVSKAYA,L. V. 1989. The effect of the petrographic composition of coals on their hydrogenation. Khim. Tverd. Topl. (Chem. Solid Fuels), 4, 75-79 (in Russian). DERBYSHIRE, F. & STANSBERRY,P. 1987. Comments on the reactivity of low-rank coals in liquefaction. Fuel, 66, 1741-1742. ERCEGOVAC, M. 1986. Brown and black coal hydrogenation in comparative studies of their petrographic composition and solid residue. An. Gdol. de la P~nins. Balkanique, 50, 419-441 (in Serbian). GIVEN, P. H., SPACKMAN,W., DAVIS, A. & JENKINS, R. G. 1980. Some proved and unproved effects of coal geochemistry on liquefaction behaviour with emphasis on U.S. coals. In: WHITEHURST, D. D. (ed.) Coal Liquefaction Fundamentals. American Chemical Society Symposium Series, 139, 3-34. GUYOT, R. E. & DIESSEL,C. F. K. 1981. Petrographic studies on insoluble residues of hydrogenated coals. International Journal of Coal Geology, 1, 197-207. HOWER, J. C., KEOGH, R. A. & TAULBEE,D. N. 1991. Petrology of liquefaction residues: maceral concentrates from a Pond Creek durain, eastern Kentucky. Organic Geochemistry, 17, 431-438. ICCP - Internationales Lexikon ffir Kohlenpetrologie 2. Ausgabe, Paris, Centre National du Recherche Scientifique, 1963. und Erg~inzungen Band zur 2. Ausgabe, 1971, Paris. MONDRAGON, F., QUINTERO, G., ACOSTA, R. & JARAMILLO, A. 1988. Liquefaction characteristics of some Columbian coals: 1. Reactivity in catalytic hydrogenation. Fuel, 67, 1709-1711. PARKASH, S., DU PLESSIS, M. P., CAMERON,A. R. & KALKREUTH, W. O. 1984. Petrography of low rank coals with reference to liquefaction potential. International Journal of Coal Geology, 4, 209-234. SHINN, J. H. 1984. From coal to single-stage and twostage products: a reactive model of coal structure. Fuel, 63, 1187-1196. TISCHER, R. E. & UTZ, B. R. 1983. Comparison of normal and rapid heat-up modes in a batch screening test for coal liquefaction catalysts. Industrial and Engineering Chemistry, Product Research and Development, 22, 229-233. VITOROVI(~, D., ALEKSIC, B. R., KONTOROVIC, S. I., ALEKSIC, B. D., ERCEGOVAC, M., MARKOV1C, B. Z., BOGDANOV,S. S. & CVETKOVlC,O. G. 1991. Liquefaction of brown coal prepared by grinding under different conditions. Fuel, 70, 849-855. VITOROVIt~, D. K., ALEKSIt~, B. R., ERCEGOVAC, M. D., ALEKSI{~, B. D., KONTOROVIC, S. I., MARKOVlC, B. Z., CVETKOVI~, O. G. & MITROVSKI, S. M. 1994. Liquefaction behaviour of Kolubara soft brown coal. Fuel, 73, 1757-1765.

Desulphurization of low-rank coals by low-temperature carbonization R. A S M A T U L U , N. A C A R K A N ,

G. O N A L & M. S. C E L I K

Istanbul Technical University, Mining Engineering Department, Coal and Minerals Processing Section, Ayazaga, 80626 Istanbul, Turkey Abstract: A lignite sample from the Istanbul region with 14.18% inherent moisture, 11.01%

ash, 1.86% total sulphur, 47.24% volatile matter, 41.75% fixed carbon and 5590kcal kg-1 calorific value as dried basis has been subjected to a set of systematic low-temperature carbonization tests. The tests have been carried out as a function of particle size, temperature and heating time. A semicoke product containing 15.22% volatile matter, 16.67% ash, 68.04% fixed carbon contents with 63% desulphurization on the basis of total sulphur has been obtained under the optimum conditions of 650~ temperature and 50 minutes of heating time. The product has a calorific value of 6403 kcal kg-1 but does not have enough strength for use as a fuel and thus needs to be improved by briquetting.

Istanbul, one of the major populated cities in the world, is currently encountering a severe air pollution problem in the winter season, partly caused by the burning of low-rank coals. The better quality coals extracted from coal mines in the vicinity of Istanbul are generally not upgraded by coal preparation processes. These coals are produced about 200-400mm in size with 30-40% moisture, 35-40% volatile matter, 1-3% total sulphur contents and calorific values of 2400-3800 kcal kg -1 as received basis. Coal used for household heating makes up about 60% of the total heating requirement in Istanbul. Lignites produced from the Istanbul region constitute about 80% of this total consumption. The high moisture, volatile matter and sulphur contents are the major causes of coal-based air pollution in Istanbul. High moisture not only leads to low combustion efficiencies but also the discharge of unburned fines into the atmosphere. In addition, since domestic boilers and stoves are not specifically designed for burning low-rank coals, the volatile matter is emitted into the air before it is fully burned. This problem results in hydrocarbon and particulate matter emission. All these problems mentioned above led to the development of new technologies for the minimization of air pollution originating from coal. Since sulphur is a major pollutant endangering the human life, various desulphurization techniques, i.e. desulphurization prior to combustion, desulphurization during combustion and, postcombustion desulphurization processes need to be systematicaly tested (Celik & Somasundaran 1994). One of these processes involving low temperature carbonization at temperatures in the range of 400-700~ aims to reduce the sulphur content of coal (Gazanfer 1983; Lowry 1945; Von 1982; Onal et al. 1995; Sciazko et al.

1993). Low-temperature drying processes have been employed since 1920s and the first patents by Fleissner appeared a few years later (Fleissner 1927 and 1928). In this process hot air or gas is sent to accomplish drying of either surface or inherent moisture of coal. Since the inherent moisture in low-rank coals is distributed in the form of very fine capillaries, high temperatures are necessary. This leads to fragmentation and consequently production of fines. Also, the dried coal is sensitive to spontaneous combustion. Work done in this area in the last two decades (Koppelman 1977; Cole & Ness 1977; Verschuur et al. 1976; Wash 1977; Evans & Sieman 1979) have focused on steam or hot water drying. The use of hot water or steam drying has advantages of (i) production of low moisture coal, (ii) reduction in the tendency of coal to reabsorb moisture, and most importantly, (iii) reduction in fragmentation and spontaneous ignition. A pilot plant erected in Wyoming in 1992 and Ceska Palivova commercial plant built now in the Czech Republic working under 80 atmosphere pressure and 400~ represents the most up to date technology in this area (Gentile 1995). It is the objective of this study to conduct lowtemperature carbonization tests on a typical Istanbul region lignite with the aim of reducing the sulfur levels in the coal. Table 1.

Analysis of the lignite sample on dry basis

% Moisture % Ash % Total sulphur % Combustible sulphur % Volatile matter % Fixed carbon Upper calorific value, Kcal kg-1

From Gayer, R. & Pe~ek, J. (eds), 1997, European Coal Geology and Technology, Geological Society Special Publication No. 125, pp. 365-369.

32.50 11.01 1.86 1.05 47.24 41.75 5590

366

R. ASMATULU E T AL.

Experimental procedure Materials

Low-temperature carbonization tests were carfled out on representative samples taken from Istanbul-Yenikoy region lignites. The complete analysis of the lignite sample on dry basis is presented in Table 1. The original sample of minus 100mm in size was crushed below 50ram and then classified into three size fractions. The analyses of these size fractons are shown in Table 2. Methods

The carbonization tests were performed in a 10 cm diameter cylindrical retort with an interior

volume of 1500 cm 3. The discharged gases were transferred to a cooling system via a screwed gate. The interior volume of the retort limited the upper size of the coal sample to 50 mm. The tests were conducted with 500 g samples brought to an inherent moisture of 14%. The furnace was preheated to desired temperature and the sample placed for a certain period. After the sample was taken out and cooled, the weight loss, volatile matter and total sulphur contents, size analysis, and drum strength measurements were performed (Table 2). The experiments were performed as a function of particle size ( 1 9 x 5 0 , 10x 19, and 1 x 10mm), temperature (400-700~ and heating period (20-120min). The physical and chemical properties of the semicoke product were also determined.

Table 2. The analysis of coal sample on dry basis as a function of particle size Size fraction (mm)

% by weight

% volatile % fixed matter carbon

% total sulphur

% ash content

calorific value (kcal/kg)

19 x 50 10 x 19 1 x 10

69.8 16.2 14.0

47.82 46.47 45.60

1.80 1.84 2.10

10.30 11.68 12.96

5598 5470 5270

41.88 41.85 41.44

Table 3. Total sulphur contents in semicoke products under different conditions Temperature ( ~

Heating time (min)

Size (mm) 19x50

10x 19

1 x 10

400

20 40 60 80 100 120

1.84 1.76 1.61 1.57 1.51 1.44

1.91 1.83 1.76 1.64 1.51 1.42

2.29 2.22 2.10 2.03 1.98 1.85

500

20 40 60 80 100 120

1.77 1.56 1.42 1.36 1.31 1.25

1.83 1.67 1.53 1.38 1.31 1.28

2.17 2.07 1.92 1.89 1.80 1.68

600

20 40 60 80 100 120

1.70 1.61 1.39 1.32 1.27 1.2

1.74 1.59 1.45 1.39 1.28 1.21

2.11 1.98 1.85 1.65 1.52 1.46

700

20 40 60 80 100 120

1.44 1.31 1.28 1.21 1.14 1.06

1.60 1.50 1.42 1.31 1.18 1.10

2.06 1.94 1.80 1.58 1.41 1.35

DESULPHURIZATION OF LOW-RANK COALS Results and discussion The total sulphur contents obtained upon low temperature carbonization of Yenikoy lignite at three different size fractions (19 x 50, 10 x 19, and 1 x 10mm) are presented in Table 3. The percent sulphur removal for each size fraction is respectively illustrated in Figs 1 through 3 as a function of heating time. The most important factor in the carbonization and also in the desulphurization process appears to be the level of temperature. For instance, while a 60% desulphurization is achieved on the semicoke product at 700~ after 40 rain and this accounts for about 90% of the total desulphurization, at 100

.... -50+19

9O

> 0

15 9 V.M.

mm

80

o 400 ~ o 5 0 0 *C zx 6 0 0 *C

l J ]

1 O0

120

70

i,i r~ 60 rY

A

u_ _J

5O

~o pZ

40

0 nL~ IX.

3O

2O I0

20

40

60

CARBONIZATION

80 TIME,

rain.

Fig. 1. The percent sulphur removal of coal as a function of heating time for 19 • 50 mm size fraction. 100 rnm

1oo F

15 ~ V . l d . /

90 iI .< > 0 "~ i,i

400~ even after 120 min only about 50% of the desulphurization is attained. The slope of the curves in Figs 1-3 also shows this trend, i.e. the slope increases with increasing the temperature. The results reveal that at low temperatures and initial heating periods only the removal of moisture is achieved. Only above 400~ does the volatile matter and sulphur begin to separate from the solid. The sulphur removal at 700~ and 120 min of heating attains its peak value of about 69.4%. Carbonization of coal is generally found to exhibit a parallel behaviour to that of desulphurization. For instance, the fixed carbon level of 41% has been raised to 66-70% with calorific values in the range of 63006500 kcal/kg upon carbonization. At this level of carbonization about 70% of sulphur removal is achieved. All the three size fractions exhibit a similar trend in that at 400~ and in the beginning of heating the sulphur removal remains at low levels and increases with increasing temperature. The lower sulphur removal levels from the finer particle sizes can stem from two contributing effects. First, as the coal bed used is fixed, the diffusion of heat through the particle takes some time and in such cases, coarser particles are more advantageous. Second, the systematic increase in the fixed carbon content as a function of size and temperature indicates that with increasing the temperature coal becomes more amenable to sudden shocks which in turn lead to higher carbonization levels. This difference is minimized as the temperature decreases (Asmatulu et al. 1995). The net affect appears to govern the results presented in Figs 1-3.

/

-19+10

o D "0

80

mm o a ~, O

I

70 _

,~ >

80

o

7o

400 ~ 500 ~ 600 ~c 700 ~

r 6O

50

2

5o

40

(/3

40

~

30

._J

~: 3o

U ~

. . . . 15 % V.M. -i0+1

I 90

400 500 600 700

60 u_ _J

367

0

C)

u

20

20 n

10

10

0-

0 0

20

40

60

80

IO0

CARBONIZATION TIME, rn[n.

Fig. 2. The percent sulphur removal of coal as a function of heating time for -19 + 10mm size

120

0

20

40

60

80

1O0

CARBONIZATION TIME, rain.

Fig. 3. The percent sulphur removal of coal as a function of heating time for -19 + 10ram size

120

368

R. ASMATULU E T AL.

Table 4. Physical and chemical properties of the semicoke product obtained at 650~ Size fraction (mm)

Moisture Ash CombustibleTotal Volatile Fixed Calorific Drum test Oversize Ignition (%) content sulphur sulphur matter carbon v a l u e oversize (%) temp. (%) (%) (%) (%) (%) (kcal/kg) (%) (~

-50 + 19 3.87 -19 + 10 3.94 -10 + 1 4.02

19.95 17.20 19.59

0.37 0.34 0.62

1.39 1.41 1.79

Coal undergoes fragmentation upon carbonization due to the removal of moisture and volatile matter from coal. This is strongly dependent upon the particle size and temperature. For example, the 19 • 50 mm size fraction treated at 400~ for 20min resulted in fragmentation producing only 13% below 19 mm, whereas at 700~ 45.6% of the coal passed below 19mm after 20 min heating. The fragmentation of coal also reduces the strength of coal. Low temperature coking on non-coking Mckinley and Crown lignites has been tested at 600-700~ and found to increase the fixed carbon content from 45 to 66%. These tests were performed in the size range of -75 + 20 mm. 20% of the coal was found to pass below 20 mm. Similar results have been also obtained on German and Turkish lignites (Lowry 1945; Von 1982; Onal et al. 1995; Asmatulu et al. 1995). Low temperature coking of Polish bituminous coals is now exploited on commercial scale (Sciazko et al. 1993). Low-temperature carbonization increases the calorific value of coal from 5200 kcal kg-I to 6000-6600kcalkg -1, depending upon the temperature and residence time of the process. The results reveal that 650~ and 50 rain are respectively the optimum conditions for Istanbul Region lignites. The physical and chemical properties of the semicoke product obtained under optimum conditions and for different particle sizes are given in Table 4. Coals with high moisture and volatile matter contents such as Istanbul Region coals usually cause air pollution when burned in simple combustion systems. Combustion of such coals must be done in specially designed systems in order to minimize air pollution or else lignite should be converted to a semicoke product by low-temperature coking. The optimum conditions established in this study is only valid for fixed bed coking furnaces. The mode of coking and the dimensions of the furnace certainly affect the time and temperature of the carbonization process. An important consideration from the viewpoint of air pollution is the removal of tar in

15.01 15.99 15.37

69.04 6459 66.33 6324 65.04 6221

11.28 40.91 90.55

52.41 65.41 90.63

320 300 290

lignite. The experiments showed that if semicoking is continued until 15% volatile matter remains, the tar in Istanbul Region lignites is fully removed. Another important advantage of carbonization is that in addition to upgrading of coal in terms of moisture and volatile matter, a significant portion of the combustible sulphur is also removed. Under optimum conditions 63% of desulphurization is achieved. The released gases can be purified for further use as a utility gas or portion of it can be recycled as an energy source for the process itself. A disadvantage of the low-temperature carbonization process is the fragile nature of the semicoke product. It is possible to use the plus 10 mm fraction for household heating while the finer fractions can be utilized in cement and ceramic industries. However, if feasible, the fine product can be briquetted both to improve its strength as well as its utilization. Conclusions Low-temperature carbonization studies conducted on the desulphurization of the Istanbul region lignite sample can be summarized as follows. 1. The Istanbul region lignite is amenable to low-temperature carbonization tests. Tests conducted as a function of temperature and heating time revealed the optimum conditions to be 650~ and 50 min of heating time. 2. A semicoke product containing 15.22% volatile matter with 6403kcalkg -1 has been obtained. 3. The sulphur removal increases with increasing the temperature and reaches a value of 63% at 650~ 4. Coal undergoes fragmentation upon carbonization process due to the removal of moisture and volatile matter from coal. This is strongly dependent on the particle size. As the particle size increases the tendency for particles to fragment increases and this in turn reduces the strength of coal. The strength can be improved by briquetting of coal.

D E S U L P H U R I Z A T I O N OF L O W - R A N K COALS

References ASMATULU, R., ACARKAN, N., ONAL, G. & CELIK, M. S. 1995. Upgrading of low-rank coals by lowtemperature carbonization. Proceedings of Technologies for Mineral Processing, Baia Mare, Romania, 29-35. CELIK, M. S. • SOMASUNDARAN,P. 1994. Desulfurization of coal. In Kural, O. ed., Coal: Resources, Properties, Utilization and Pollution, Kurtis Press, Istanbul, 253-269. COLE, E. L. & NESS, H. V. 1977. Treatment of Solid Fuels. U.S. Patent 4,018,571, April 19, 1977 and U.S. Patent 4,052,169, October 4, 1977 (Texaco). EKINCI, E. 1982. Production Methods of Metallurgical Coke and Smokeless Fuel and its Application to Turkish Coals (In Turkish). Proceedings of International Coal Technology Seminar, 127-137. EVANS, D. G. & SIEMAN, S. R. 1979. Separation of Water from Solid Organic Materials. U.S. Patent 3,552,031, January 5, 1979. FLEISSNER, H. 1927-1928. Drying of Coal. U.S. Patent 1,632,829,1927 and U.S. Patent 1,679,078, July 31, 1928. GAZANEER, S. 1983. Smokeless Fuel Experience of Seyitomer Lignites. International Coal Utilization Conference, Sept. 6-10, Istanbul.

369

GENTILE, R. H. 1995. Clean Fuel Technology: The Contribution of K-Fuel. Proceedings of 3rd Coal Technology and Utilization Seminar, Cayirhan, Turkey. KOPPELMAN, E. 1977. Process for Upgrading Lignitetype Coal as a Fuel. U.S. Patent 4.052,168, October 4, 1977. LOWRY, H. H. 1945. Low-Temperature Carbonization Chemistry of Coal Utilization. Wiley, New York. ONAL, G., MUSTAFAEV,I., ASMATULU,R., YILDIRIM,I., ACARKAN,N. 8s CELIK, M. S. 1995. Desulphurization of Turkish Lignites by Low temperature Coking, ECOS'95, July 11-14, Istanbul, 640-645. SCIAZKO, M., KUBICA, C. & RZEPA, S. 1993. The Smokeless Fuel-Properties and Testing Methodology. Fuel Processing Technology, 36, 123-128. VERSCHUUR, E. et al. 1976. Thermal Dewatering of Brown Coal, U.S. Patent 3,992,784, November 23, 1976 (Shell). VON, H. H. 1982. Thermich Veredelung Der Kohel mit Ausnahme von Kokereien Technische Mitteilunge 75. Jahrgang, Heft 2/3, p. 117-128. WASH, E. J. 1977. Upgrading Subbituminous Western Coal. Canadian Patent 1,020,477, November 8, 1977. ZIELINSKI, H., KACZMARZYK, G., SCIAZKO, M. & SECULA, M. 1992.2nd Int. Cokemaking Congress, London, 28-30 Sept. 1992, Inst. Mater., London, 551-554.

Amelioration of high organic sulphur coal for combustion in domestic stoves M I C H A E L K. G. W H A T E L E Y 1, Z A F E R G E N C E R 2 & E R T E M T U N C A L I 2

1Geology Department, University of Leicester, Leicester LE1 7RH, UK 2 Directorate of Mineral Research and Exploration (MTA), Ankara, Turkey Abstract" Despite the proximity to Ankara, raw coal mined in the Beypazari basin cannot be used as a domestic fuel in Ankara because the high combustible sulphur content would add to the already severe pollution problems in that city. This study investigated a method of reducing the SO2 emissions by adding lime (CaO) to the coal prior to combustion. Sorbent, as lime, was added to the combustion chamber (a domestic stove), by pretreating the coal by mixing crushed coal with lime and molasses and turning the coal into briquettes. Lime was added to lump coal for comparative purposes. The ratio of Cafree : S was varied for a series of combustion tests, and the heating efficiency and the amount of sulphur fixed in the ash were determined. The results of the tests show that optimum sulphur retention and heating efficiency were obtained when the Cafree :S molar ratio was between 0.95 and 1.15 for the briquettes and between 1.00 and 1.25 for the lump coal. For lump coal, 50% of the total sulphur could be fixed in the ash and at least 75% of the heating efficiency retained. During combustion of the briquettes, at least 57.5% of the sulphur could be fixed in the ash and at least 85% of the heating efficiency could be achieved. This suggests that the addition of lime to briquettes may be a feasible way of reducing the SO2 emissions for domestic stoves.

Ankara, the capital of Turkey, has a population of around 3.25 • l06 people, most of whom rely upon coal as a domestic fuel supply for cooking and heating. The climate is such that in winter temperature inversion on the high level plateau (elevation 1500m) often traps the sulphurous

and nitrous emissions from these stoves creating an e n v i r o n m e n t a l hazard ( D u r m a z et al. 1993). As m u c h as 0.8 M t of coal is b r o u g h t into A n k a r a from s u r r o u n d i n g areas a n d from outside T u r k e y to supply the domestic market. As far as is possible, low sulphur coals are used, but

{ ~

,t:t Jit:t:t:t t~~:t:[:t:l%, ::

:

v

v

-

Neogene

v v

v

v

Palaeocene{ ~

I

~

,

i :

9

V

9

V

Late Jurassic F ret : Taceous :TTIc

l ~ "~ "~ ~ " ~ ' ' "" "" "~ \ "~)liKg~ unfa~'l~l-] % "" ,~, "~

0

(~aylrhan lignite field// +

~ + \

PalaeozoicI ~

I++

Miocene sedimentaryunits Teke volcanics Kizil~zayGroup

Ophiolites Nardin Formation (flysch) So'uk~ am

limestone Granite

[ [-~'-] Mh;at;:~ics

lOkm

Fig. 1. Location of the Beypazari basin showing the position of the (~ayirhan lignite field and the main rock units in the region (from Whateley & Tuncali 1995b, modified after Yagmurlu et al. 1988). From Gayer, R. & Pe~ek, J. (eds), 1997, European Coal Geology and Technology, Geological Society Special Publication No. 125, pp. 371-377.

372

M. K. G. WHATELEY E T A L . desulphurization (FGD) plant, which effectively removes 99% of the SO2 from the flue-gas. FGD is economic at this scale, but would probably be inefficient and not cost effective on domestic stoves. This study was designed to determine whether the Beypazari lignite could be beneficiated with the addition of lime to the coal in order to reduce the SO2 emissions from domestic stoves to acceptable levels.

most of Turkey's cheaply mined lignites have a high sulphur content. To alleviate this problem, low-sulphur coal is imported into Turkey from USA, South Africa, Italy, Colombia and Australia, some of which is transported to Ankara. Importation and transportation costs result in raised prices of domestic fuel. One potential source of lignite for the Ankara market lies in the Beypazari basin (Fig. 1), only 100 km NW of Ankara. Coal, of Miocene age, is known in two areas of the basin, namely the ~ayirhan and the Koyunagili lignite fields (Fig. 1). Coal from the (~ayirhan field only was used in this study. The (~ayirhan field contains some 400 Mt of coal, which is currently mined to supply a 300 MW thermal power station (TPS). Unfortunately, this lignite is characterized by high sulphur content (maximum 8.2% on an air dried basis), up to 75% of which has been shown to be combustible sulphur (Whateley & Tuncali 1995a). The TPS is fitted with a flue-gas

Lignite characteristicas There are two separate lignite seams in the (~ayirhan lignite field (Fig. 1). The lower lignite seam was deposited in the lower part of the ~oraklar Formation (Fig. 2). It has variable thickness, is laterally impersistent and is of very poor quality. It was not used in this study. The thicker, economically important,

LITHOLOGY

FORMATIONS

AGE J

__

Z

__

~

- -

- -

claystone,

9

Kirmk-rgormaation~

mudstone & gypsum limestone conglomerate, sandstone

claystone, mudstone, fine-grained sandstone

-

Upper Miocene .......

=i i --

_

HirkaFormation

'

~

....

.... _.,--/

Upper ligniteseam . . . . (~oraklar Formation

~'~

--b

~

~ Vv "E

~(~

9

0

o Lowerlignites e a m ~ "~

PreNeogene f ~ ~

"~

+

+

K-~-7~/

~

+ ~

> v

+\ ,

%

%

~

'-,..,,

"'-' ".-, ",-, ,-,,_,

Basementrock )

~

silicified claystone & limestone, chert shale, bituminous shale, trona & tuff cross-bedded conglomerate, sandstone & mudstone Metamorphics, ophiolites, granites, limestones & clastic sediments

Fig. 2. Schematic stratigraphic section of the ~ayirhan basin (from Whateley & Tuncali 1995b, modified after Yagmurlu et al. 1988 and Inci 1991).

AMELIORATION OF HIGH ORGANIC SULPHUR COAL upper lignite seam was deposited at the top of the formation. It is laterally persistent and has a reasonably uniform thickness of about 3.0 m. A one metre thick, tuffaceous, siltstone parting, with cherty nodules, splits the upper seam into two lignite beds, referred to as the first (Tv) and second (Tb) seams (Whateley & Tuncali 1995a) Detailed descriptions of these two seams are given by Whateley & Tuncali (1995a), who examined proximate and ultimate analyses, calorific value, combustible sulphur and pyritic sulphur contents, palynological descriptions, petrographic analysis, reflectance values and ash oxide analyses derived from coal samples collected from boreholes and underground mine faces. Reflectance measurements (Rmax [%]) varied from 0.34 to 0.38, putting the coal into the lignite rank category. The first and second seams are mined and mixed together for combustion in the TPS and Table 1 gives the average quality of both seams.

373

Mineral matter chacteristics The inorganic fraction of the raw coal, the mineral matter, was examined using XRD and SEM EDX analytical techniques. The major minerals present are the zeolites, analcime and clinoptilolite, and pyrite, with variable amounts of minor minerals such as gypsum, albite/ anorthite, marcasite, quartz, illite, dolomite and apatite. Vertical variation between the top and bottom seams is recognized because of the almost exclusive presence of clinoptilolite in the first seam, with minor amounts of analcime and almost exclusively analcime in the second seam, with minor amounts of clinoptilolite. Most Turkish lignites contain quartz, kaolinite, illite, smectite and pyrite as the main minerals with varying minor amounts minerals which include calcite, dolomite, hydromuscovite, feldspar, barite, celestite and marcasite. No other Turkish lignite is known to contain the abundance of zeolites found in this coal.

Table 1. Average values of the proximate, ultimate, sulphur, calorific value and ash oxide analyses from the upper seam in the Beypazari basin, Turkey

As received Air dried results results Proximate analyses Moisture content (%) Ash content (%) Volatile matter (%) Fixed carbon (%)

23.38 23.27 28.74 24.61

9.00 35.88 29.12 26.00

2.52 0.84 3.38

3.81 0.77 4.58

Ultimate analyses Carbon (%) Hydrogen (%) Nitrogen (%) Oxygen (%) Total sulphur (%)

31.12 2.39 7.32 55.73 3.44

40.37 2.98 9.12 43.26 4.27

Calorific value Calorific value (kcal kg- 1)

2318

3391

Grindability index

64.21

Ash melting point (~

1250

Ash analyses SiO2 (%) A1203 + TiO2 (%) Fe203 (%) CaO (%) MgO (%) Na20 (%) K20 (%) SO3 (%)

41.99 16.32 11.96 8.71 4.19 4.95 1.17 9.30

Sulphur analyses Combustible sulphur (%) Sulphur in ash (%) Total sulphur (%)

Ash characteristics When coal is burnt the inorganic residue is referred to as the ash and is measured as a percentage of the original mass of the raw coal, either on an as received or air dried basis. The as received ash content changes vertically both in and between the first (Tv) and second (Tb) seams at Beypazari (Whateley & Tuncali 1995b). The average ash content of the second seam is 27.4%, compared to the first seam which averages only 19.2%. The ashes were analysed by ICP-AES after sample digestion. The oxide analyses were tabulated and correlation coefficients presented by Whateley & Tuncali (1995a, Table 5). They found that there was a strong positive correlations between CaO and SO3, of 0.84 and 0.87 in the first and second seams respectively. This was due to the anhydrite in the ash which developed during the combustion of the coal. The pyritic and organic sulphur forms were oxidized and the the SO2 combined with Ca found mainly in the clinoptilolite, but also in the organic matter, to form the anhydrite. Whateley & Tuncali (1995a) showed that an average of 28% of the total sulphur in the raw coal reported in the ash in the first seam and 25% of the sulphur reported in the ash of the second seam. The remainder of the sulphur was reported as combustible sulphur, and was lost to the atmosphere as SO2. Recent work has shown that the Beypazari coal consists of the following forms of sulphur

374

M. K. G. WHATELEY E T AL.

(British Standard 1977), namely sulphate sulphur, 0.23%, pyritic sulphur, 2.34%, and organic sulphur 2.03%. The organic sulphur is contributing some 45% towards the total sulphur. As more than 75% of the sulphur is lost as combustible sulphur, this suggests that the pyritic sulphur is contributing to the combustible sulphur as well. The ASTM and British Standard tests for measuring the ash content expect the coal to be ashed at between 750 and 850~ At these temperatures pyritic sulphur as well as the organic sulphur will oxidize, resulting in the release of SO2. It is apparent that the high sulphur coals in Turkey that are used as domestic fuels, contribute to the SO2 emissions that are a major factor in urban air pollution (Durmaz et al. 1993). This project intended to establish whether a practical solution could be found whereby the addition of Ca to the coal in forms other than that found in zeolites and organic matter would lead to a lowering of the SO2 emission from the Beypazari coals.

Results of sorbent addition

and molasses. The Cafree:S molar ratio was varied for a series of combustion tests (Table 2). The free Ca contained in the coal was not included in these ratios. A fixed mass of coal (7kg) was burnt in each experiment and the central grate and the flue gas temperatures were monitored continually (Fig. 3) and graphs of these variations with combustion time were drawn (Figs 5 and 6). For clarity only the raw coal (L1 and B1) and the penultimate experiment (L5 and B5) are shown. The raw coal, both as lump coal and as briquettes, burnt fiercely and within 25 minutes produced central grate temperatures as high as 1300~ The lump coal produced the highest central grate temperatures, but the stove lost heat rapidly. The briquettes retained their heat longer (Fig. 4). In general there was not a great difference in the combustion time between the lump coal and the briquettes in each experiment. As the Cafree :S molar ratio increased, so the time taken for both the lump coal and briquettes to reach their maximum temperature increased, e.g. 90 and 70minutes respectively in experiment 5 (Fig. 4). The combustion time increased in the stove as the Carree:S ratios increased,

One of the most freely available forms of Ca is in lime (CaO). Experimentation has shown (Gencer 1988) that in a domestic stove the coal burns at an average temperature of about 780~ although the maximum may reach as high as 1300~ At these temperatures, sulphur is released from oxidized pyrite and organic material. The CaO reacts with the pyritic S during combustion in the following way, 2FeS2 + 4CaO + 702 ~ 4CASO4 + 2FeO resulting in capture of some of the sulphur as anhydrite in the ash. Sorbent, as lime, was added to the combustion chamber (a domestic stove), firstly in briquettes and secondly with the lump coal. The briquettes were produced by mixing crushed coal with lime

Table 2. Cafree'S molar ratio used in the combustion tests when lime was added to lump coal and briquettes of Beypazari coal, Turkey

Briquettes

Lump coal

Cafree:S molar ratio

B1 B2 B3 B4 B5 B6

L1 L2 L3 L4 L5 L6

0 (no lime added) 0.50 0.75 1.00 1.50 2.00

Fig. 3. Photograph showing the domestic stove used in the experiment.

AMELIORATION OF HIGH ORGANIC SULPHUR COAL

i

1400

350

1200

300

1000

o~

250

800

~

200

600

~ E

150

375

"

'

Ls B5

E

L5

400t/t

~ 100

200

50

0

, 0

25

',"

,

, L1,

,

0

, 0

50 75 100 125 150 175 Time (minutes)

,

25

,

,

,

50 75 100 125 150 175 Time (minutes)

Fig. 4. Variations in the central grate temperature with combustion time in a domestic stove burning coal from the Beypazari basin, Turkey. The graph shows raw coal (L1 and BI) and coal mixed at a Cafree: S molar ratio of 1.5 : 1.

Fig. 5. Variations in the flue gas temperature with combustion time in a domestic stove burning coal from the Beypazari basin, Turkey. The graph shows raw coal (L1 and B 1) and coal mixed at a Cafree: S molar ratio of 1.5:1.

e.g. up to 175 minutes in experiment 6 (Table 3). The average central grate temperatures ranged from 924 to 506~ for the lump coal and between 856 and 702~ for the briquettes. There is no clear pattern to be seen in the grate temperatures to compare the different fuel types, except that in general, the average central grate temperatures decreased as the Cafree:S ratios increased (Table 3). The flue gas temperatures increased rapidly to maxima of around 310~ when raw coal was burnt both as lump coal and as briquettes (Fig. 5).

The flue gas temperatures decreased rapidly past the maxima. As the Cafree:S molar ratio increased, so the time taken for the lump coal to reach its maximum temperature increased, e.g. to 125 minutes in experiment 5 (Fig. 5). The flue gas temperatures were raised rapidly when the briquettes were burnt in experiment 5 (Cafree :S ratio of 1.5:1), but the temperature dropped more slowly past the maximum. In general, there was very little change in the average flue gas temperatures as the Cafree:S ratio increased (Table 3). The average flue gas temperatures

Table 3. Results of combustion tests in a domestic stove for a series of Beypazari lignite (L) and briquette (B) samples burnt with various amounts of lime (see Table 2) Average temps Heat losses (%) Sample Combustion time Stove No. (mins) grate

Flue gases

Heat loss Heat loss Heat loss Thermal Sulphur by flue due to in grate efficienty fixation gas CO in (%) (%) flue gas

L1 L2 L3 L4 L5 L6

105 120 130 150 170 175

790 894 798 924 793 506

200 215 215 210 215 214

21.76 27.00 30.29 30.30 35.25 38.00

7.69 10.25 4.27 7.12 3.42 11.00

4.94 4.87 6.94 7.82 21.00 12.00

65.6 57.9 58.5 54.7 40.3 39.0

20.7 36.5 40.8 50.3 59.1 60.6

B1 B2 B3 B4 B5 B6

145 135 140 150 160 175

856 827 833 724 736 702

205 217 224 220 225 227

25.50 26.90 29.80 30.50 33.60 36.50

5.78 7.35 5.30 2.60 6.00 11.30

0.63 2.90 4.20 6.60 3.20 5.60

69.1 62.8 60.7 60.3 57.2 46.6

20.9 43.7 52.5 53.6 63.7 69.3

376

M. K. G. WHATELEY E T AL. 70

70

./,,~~,,~

y=22.699x + 25.078

60 r = 0 . 9 4 7 8 ~ _ _

-

50-

~ 55" 50- y=-14.442x + 66.507 " ~ . I--'c:45" ~ r-'-0"9843 ~ ~ =

40

~ '

r=0.9629

_

~ 30" -3 f~ 20-

[] Lump coal samples 9 Briquette samples

03

10

35 3O

y=20.44 + 2s.078 40-

0 0.25 015 0.:75 i

1.25 1~5 1.75 2

Cafree :total S molar ratio

o o.;,s ols o. ,s

i

1.i,s lls 1.?s 2

Cafree:total S molar ratio

Fig. 6. Variations in the thermal efficiency of a domestic stove burning coal from the Beypazari basin, Turkey, with respect to the Carree : S molar ratios of the various feeds.

Fig. 7. Variations in the sulphur retention in the ash plotted as a percentage of the total sulphur content of the raw coal from the Beypazari basin, Turkey, with respect to the Carree : S molar ratios of the various feeds.

measured when the briquettes were burnt were, on average, some 5 to 10~ higher than those measured when lump coal was burnt. By measuring the temperatures in the grate and flue gases it was possible to calculate the heating efficiency of the central stove during each experiment (Table 3 and Fig. 6). With the addition of lime to the stove fuel, the heating efficiency dropped markedly at the low Cafree : S molar ratio of 0.5:1 (Fig. 6). The lump coal dropped from 66% efficiency with raw coal to 58% and briquettes dropped from 69% to 63% efficiency. Thereafter the rate of change slowed between ratios 0.5 : 1 and 1:1. At these ratios, the variation in efficiency was between 58 and 55% for lump coal and between 63 and 60% for the briquettes. As more lime was added with the lump coal (1.5:1 ratio) the heating efficiency dropped rapidly to 40%. A similar effect was seen with the briquettes, although the drop in heating efficiency was less noticeable at the 1.5:1 ratio (57%). The final heating efficiency recorded was 47%. The ash was analysed for total sulphur content and this was reported as a percentage of the total sulphur in the raw coal (Table 3 and Fig. 7). This figure reflects the amount of sulphur retained in the ash. Graphs of sulphur retention plotted against Carr~ :S molar ratios (Fig. 7) show a rapid increase in the amount of sulphur retained in the ash immediately lime was

added both to the lump coal (from 21% to 37%) and briquette fuel (from 21% to 44%). In both fuel types the rate of sulphur retention in the ash slows beyond the 1.5:1 Carrel: S ratio. In all cases the amount of sulphur retained in the ash was greater when the lime was mixed with the coal as briquettes.

Discussionof results The time taken to reach the maximum temperature in the grate and in the flue gases increased as the Carree :S molar ratio increased (Figs 4 & 5). The maximum temperature reached is lower as the ratio increases. The high sulphur content of the coal meant that lime had to be added in large proportions. This resulted in reduced operating temperatures (Fig. 4) and a reduced heating efficiency (Fig. 6). There is an immediate loss of heating efficiency as soon as lime is added to the coal, but between the 0.5:1 and 1 : 1 ratio of Cafree : S there is no significant change in loss of heating efficiency. This suggests that there is no additional benefit to be gained by increasing the ratio of Carrie : S to more than 1:1 as far as heating efficiency is concerned. Sulphur retention increased from a base level of 21% when no lime was added to over 60% when the Carrer : S molar ratio was 2:1 (Fig. 7). The retention of sulphur in the ash when raw

AMELIORATION OF HIGH ORGANIC SULPHUR COAL coal is burnt and no lime is added is a function of the presence of the clinoptilolite/heulandite zeolites. The effect of the addition of lime was an immediate increase in the amount of sulphur retained in the ash. The rate of retention remained high between a 1: 1 and 1.5 : 1 ratio, thereafter the retention rate slowed. This suggests that there is no particular gain in sulphur retention beyond the 1.5 : 1 ratio of Carree : S. From Figs 6 and 7 it can be concluded that the optimum sulphur retention and heating efficiency were obtained when the Cafree: S molar ratio was between 1.00 and 1.25 for the lump coal and between 0.95 and 1.15 for the briquettes. At these ratios for lump coal, 50% of the total sulphur could be retained in the ash and at least 75% of the heating efficiency achieved. During combustion of the briquettes, at least 57.5% of the sulphur could be retained in the ash and at least 85% of the heating efficiency could be achieved. The added advantage of the reduced operating temperatures of the stove once lime was added with the coal is that the anhydrite in the ash would be more likely to be retained in the ash and not broken down. Chinch6n et al. (1991) have shown that anhydrite is stable up to temperatures of 1060• 10~ beyond which anhydrite decomposes into CaO and SO2. This study showed that significant reduction of the SO2 emissions could be obtained with the addition of lime to the raw coal which, during combustion, would convert some of the SO2 derived from oxidation of pyritic and organic sulphur in the coal into anhydrite in the ash. At the optimum Cafree : S molar ratios there was no significant reduction of the heating efficiency of the coal. The briquettes proved to be slightly more thermally efficient and retained a greater proportion of the sulphur in the ash than the lump coal and lime mixture. This suggests that by pretreating the Beypazari coal by crushing and mixing the coal with lime and molasses to form briquettes for use as a domestic fuel, the SO2 emissions can be reduced without significantly reducing the heating efficiency of the fuel.

377

The authors wish to acknowledge their colleagues and the Director at MTA, Ankara and their colleagues in the Geology Department, University of Leicester who provided technical and scientific support during the project. They would also like to thank the Director of TKI, Ankara who gave permission for access to the coal site and the management and staff at the (~ayirhan mine for their assistance during the collection of the samples. Considerable help was given by Professor A. Spears and Dr X. Querol, who read and commented on earlier versions of this manuscript. Their help is very much appreciated.

References BRITISH STANDARD1997. Analysis and testing of coal and coke, Part I1, Forms of sulphur in coal, BS1016, part 11. CHINCHON, J. S., QUEROL, X., FERNANDEZ-TURIEL. J. L. & LOPEZ-SOLER, A. 1991. Environmental impact of mineral transformations undergone during coal combustion. Environmental Geology and Water Science, 18, 11-15. DURMAZ, A., DOGU, G., ERCAN, Y. & SIVRIOGLU,M. 1993. Investigation of the Causes of Air Pollution in Ankara and Measures for its Reduction. NATO Science for Stability Program. GENCER, Z. 1988. An Investigation of Methods for Fixation with Lime of Sulfur Dioxide Formed by the Combustion of Ankara-Beypazari Lignites. MSc thesis, Gazi University. INCI, U. 1991. Miocene alluvial fan-alkaline playa lignite-trona bearing deposits from an inverted basin in Anatolia: sedimentology and tectonic controls on deposition. Sedimentary Geology, 71, 73-97. WHATELEY, M. K. G. & TUNCALI, E. 1995a. The origin and distribution of sulphur in the Neogene Beypazari lignite basin, Central Anatolia, Turkey. In: WHATELEY,M. K. G. & SPEARS, A. (eds) European Coal Geology. Geological Society, London, Special Publication, 82, 307-323. & - - 1 9 9 5 b . Quality variations in the highsulphur lignite of the Neogene Beypazari Basin, Central Anatolia, Turkey. International Journal of Coal Geology, 27, 131-151. YAGMURLU, F., HELVACI, C. & INCI, U. 1988. Depositional setting and geometric structure of the Beypazari lignite deposits, Central Anatolia. International Journal of Coal Geology, 10, 337-360.

The use of pulverized lignite/natural gas mixed fuels in the high-temperature process of a cement rotary kiln M. bIANOJEVIC', (5. JANKES', M. K U B U R O V I C ' , M . S T A N O J E V I C 2 & P. B L A G O J E V I ( ~ 2

1Faculty of Mechanical Engineering, University o f Belgrade, 27 marta 80, 11000 Belgrade, Yugoslavia 2 Beodin Cement Factory. Beodin, Yugoslavia Abstract: This paper presents the results of industrial tests of low grade lignite combustion in the 500t/day wet-process rotary cement kiln. For the use of pulverized lignite, the following process characteristics are determined: combustion process parameters, flue gas properties, and the influence of coal ash properties on clinker quality. Industrial tests have shown that it is possible to substitute 50-80% of the natural gas with pulverized low-grade lignite, while the output of the kiln, specific heat consumption, and the quality of cement clinker remain unchanged.

The cement industry faced an increase in the prices of liquid and gaseous fuels used for clinker production after the energy crisis of 1973. This was the reason for the increasing introduction of coal as a fuel, which is the dominant fuel in the West European cement industry today. Anthracites and other highquality coals are commonly in use. The introduction of precalcination in new cement production technologies has enabled the use of low-grade fuels, such as soft brown coal. Soft brown coals (lignites) are the main energy resource in Yugoslavia, and it was of great importance to determine the conditions for their use in cement rotary kilns. The investigation focused on determining all the necessary process parameters and technical limitations for the use of 'Kolubara' lignite. This paper presents the experimental results of mixed lignite/natural gas fuel combustion for cement production, in a wet-process rotary kiln (in the 'Beo6in' cement factory).

Process and experimental details

The coal usually used in the cement industry should comply with the following requirements (Duda 1976): LHV: rain. 21 (MJ/kg) Ash content: 12-15 (wt%) Volatile matter: 18-22 (wt%) Moisture content: up to 12 (wt%) as delivered. The high moisture content of Yugoslav lignites (up to 50%) requires two-step drying. The first

step is performed in drying plants (near the open coal fields) and the second in the factory's drying-grinding plant. The coal ash remains as part of the clinker material, thereby reducing the amount of raw material. The chemical composition and ash content of coal determine the necessary corrections in the raw material used for the required cement clinker quality to be achieved.

Table 1. Production process parameters for cement

rotary kiln in Beodin cementfactory Nominal kiln output Range of output Specific kiln output Kiln dimensions: length (L) shell diameter length-to-diameter ratio (L/D) Inner volume Inclination Speed of the kiln Internal heat exchangers (chain curtain): length surface Clinker grate cooler (Follax) Fuel Specific heat consumption Secondary air temperature Flue gas temperature Outlet clinker temperature Flue gas dust content (% of raw material consumption)

From Gayer, R. & Pe~ek, J. (eds), 1997, European Coal Geology and Technology, Geological Society Special Publication No. 125, pp. 379-383.

t/day t/day kg/m 3h

500 450-520 15-17.2

m m

135 3.6-4.0 35

-

m3 % rpm m m2 m

1260 4 max. 1.2

20 1400 2.6 x 14.9 natural gas/ pulverized coal kJ/kg el. 6000-6700 ~ 550-600 ~ 150 ~ 50 % 1.5

380

M. STANOJEVI(~

Experiments were performed in the wetprocess rotary kiln in the 'Beo6in' cement factory. Technical data and process parameters of this plant are shown in Table 1. The scheme of the clinker production plant used for industrial tests is shown in Fig. 1. The plant consists of the following parts: wet-process rotary kiln with combined fuel burner (for pulverized coal and natural gas), a clinker grate cooler, and a tube ball mill with a direct coal-drying system. The plant was originally designed for use with high quality coal. The material balance scheme for this kiln is shown in Fig. 2. The mathematical model of the

material balance includes the following process parameters: consumption of natural gas, pulverized lignite, and raw material slurry; natural gas composition; flue gas composition; raw material, dust, and cement clinker composition; original and pulverized coal composition; dust concentration in flue gas; flow of hot air for the tube ball mill; primary air flow; moisture flow separated from coal. Four industrial tests were carried out. The aim was to determine the influence of the coal/ natural gas ratio on the clinker production process. The quality and grain size of 'Kolubara' dried lignite were different in each test. The

? 6

,-~

po21

to2ii~:o21k.~_

~01

l~

Fig. 1. The scheme of clinker production plant and the locations of measuring points. 1, rotary kiln; 2, grate cooler; 3, flue gas chamber; 4, flue gas fan; 5, chimney; 6, burner; 7, chain curtain

VVA'IERVAI=,~ 8EPARA'TEI:> I=ROMr I~.

DU6T IN FLLE~

A

MILL

l

~

ROTARY KILN

I r'~

CLINKER COOLER

~-

AIR Fig. 2. The material balance scheme of the wet process rotary kiln.

r

r

-

-

J

X=-

P U L V E R I Z E D L I G N I T E IN C E M E N T R O T A R Y K I L N m e a s u r e m e n t of characteristic parameters in each test was carried out in steady-state condition, which lasted a m i n i m u m of 6 to 8 hours. Seeing that the material remains in the kiln for a b o u t 2.4 hours the m e a s u r e m e n t periods were long e n o u g h to provide reliable data on the kiln operation.

Results The quality of the coal used in the experiment is presented in Table 2. F o r each test, the table gives data a b o u t the proximate and ultimate analyses of coal as it enters the mill and of pulverized coal as it enters the b u r n e r of the kiln.

The table shows that the moisture content of the original coal varied from 28.5 to 30.5 w t % while L H V varied between 13.7 and 15.7 MJ/kg. The ash c o n t e n t in tests a b, a n d c where coal with particle size of - 15 + 0 m m a n d - 15 + 5 m m was used, turned out to be 9.8 to 13.8wt%; in test d, using coal with a particle size o f - 5 + 0 m m the figure was 1 8 . 4 w t % . The moisture content o f the pulverized coal in tests a b, and c r a n g e d from 12.1 to 1 2 . 4 w t % . In test d the o u t p u t of the coal mill was reduced due to the use of lower-quality coal, which resulted in a moisture content of 9.8 w t % . The L H V of the pulverized coal was r o u g h l y the same in the samples p r o d u c e d by tests a and d i.e. 18.2MJ/ kg, for test b it was 19.3 MJ/kg, and for test c it had the highest value - 19.85 MJ/kg.

Table 2. Coal properties Industrial test in roatry kiln: Coal size distribution (tube ball mill inlet) Carbon Hydrogen Oxygen Nitrogen S. comb.

C H O N S

Moisture Ash S. total S. in ash S. comb. Coke C~ Volatile Combustible Low heat value Carbon Hydrogen Oxygen Nitrogen S. comb Moisture Ash S. total Coke Cfax Volatile Combustible Low heat value

C H O N S

a - 15 + 5 mm

b -15+0mm

c -15+5mm

d -5+0mm

wt% wt% wt% wt% wt%

Ultimate analysis of coal: 38.61 40.14 3.18 3.31 13.91 14.51 0.54 0.35 0.31 0.36

41.92 3.55 15.47 0.54 0.22

36.84 2.92 11.83 0.44 0.32

wt% wt% wt% wt% wt% wt% wt% wt% wt% kJ/kg

Proximate analysis of coal: 30.45 29.54 13.00 11.79 0.90 0.89 0.59 0.54 0.31 0.35 38.09 38.16 25.10 26.37 31.46 32.30 56.56 58.66 14 342 14954

28.50 9.80 0.73 0.51 0.22 37.01 27.20 34.49 61.70 15 717

29.27 18.38 0.96 0.64 0.32 44.14 25.77 26.59 52.36 13 698

wt% wt% wt% wt% wt% wt% wt% wt% wt% wt% wt% wt% kJ/kg

Ultimate analysis of pulverized coal: 48.64 50.10 51.41 4.01 4.13 4.35 17.52 18.11 18.97 0.68 0.44 0.67 0.39 0.43 0.27 Proximate analysis 12.39 16.37 1.13 47.98 31.62 39.63 71.24 18 171

381

of pulverized coal: 12.07 12.31 14.72 12.02 1.11 0.89 47.62 45.39 32.90 33.37 40.31 42.30 73.21 75.67 19284 19845

47.10 3.73 15.12 0.56 0.41 9.59 23.49 1.23 56.42 32.94 33.99 66.93 18209

382

M. S T A N O J E V I C

Table 3. Rotary kiln process parameters Industrial test in rotary kiln: Coal size distribution (tuble ball mill inlet)

a -15+5mm

b -15+0mm

c -15+5mm

d -5+0mm

Pulverized coal Low heat value

kJ/kg

18 171

19 284

19845

18209

Natural gas Low heat value (at ~

kJ/m 3

Raw material slurry Moisture content Specific consumption Consumption

% kg/kg cl. t/h

43.32 2.7850 58.82

44.62 2.8546 58.63

44.70 2.8678 57.36

44.00 2.8234 60.00

Dry raw material Ignition loss Specific consumption

% kg/kg cl.

34.01 1.5785

34.11 1.5809

34.32 1.5859

34.12 1.5811

Clinker Production

t/h

21.12

20.54

20.00

21.25

Fuel consumption Natural gas

35466

ma/h m 3/kg cl. kg/h kg/kg cl.

1741 0.0824 3390 0.1605

Specific energy consumption In natural gas In pulverized lignite Total

kg/kg cl. kg/kg cl. kg/kg cl.

2922 3004 5926

Natural gas/pulverized lignite ratio Natural gas Pulverized lignite

% %

49 51

Pulverized lignite

1323 0.0644 3918 0.1907

714 0.0357 4768 0.2384

1396 0.0657 4245 0.1998

2 284 3 678 5962

1266 4731 5997

2330 3637 5967

38 62

21 79

39 61

Table 4. Cement clinker properties Industrial test in rotary kiln: Natural gas/pulverized lignite ratio

referent 100/0

a 49/51

b 38/62

C

21/79

d 39/61

Mineralogical composition: 3CaO.SiO2 2CaO.SiO2 3CaO.A1203 4CaO.A12OyFezO3

wt% wt% wt% wt%

66.66 15.26 3.76 11.02

51.23 32.76 2.93 9.05

66.11 15.90 5.99 9.50

50.35 29.88 5.18 11.29

67.28 16.82 3.50 10.98

Oxides content: ignition loss SiO2 A1203 Fe203 CaO MgO free CaO

wt% wt% wt% wt% wt% wt% wt%

0.6 20.77 5.67 3.45 66.36 2.13 0.54

0.4 21.05 5.67 3.45 65.80 2.13 0.84

0.52 21.10 5.93 3.45 65.66 2.13 0.69

0.33 21.15 5.80 3.45 65.65 2.13 1.08

0.34 21.25 5.80 3.45 66.22 2.13 0.72

Characteristic modules: hydraulic module (HM) aluminate module (AM) silicate module (SM)

-

2.22 1.64 2.28

2.18 1.64 2.30

2.15 1.72 2.25

2.16 1.68 2.28

2.17 1.68 2.29

Bulk density

kg/m 3 1428

1383

1398

1388

1502

PULVERIZED LIGNITE IN CEMENT ROTARY KILN Rotary kiln process parameters determined in industrial tests are given in Table 3. It is shown that the energy from coal in total energy consumption for all industrial tests was 50 to 80%. The factors limiting the substitution of gas by coal were: a decrease in temperature in the kiln sintering zone, and the output of the coal mill. In order for the required clinker quality to be maintained, it is necessary to have a temperature of 1550~ to 1650~ When only natural gas was used, the mean temperature was around 1600~ dropping to 1540 to 1590~ in tests with coal, i.e. the maximum temperature drop was 60~ In tests a b, and d the degree of substitution of natural gas by pulverized coal was determined by this maximum drop in temperature. In test c the quality of pulverized coal was such that the degree of substitution reached (79%) was not accompanied by a drop in temperature below the above limits. However, a higher degree of substitution was impossible to attain due to limitations in the mill's output. Specific energy consumption and the rotary kiln output shown in Table 3 were roughly the same in all tests. They were similar to mean values attained when only natural gas is used. Table 4 shows clinker quality (as defined by mineralogical composition, bulk density, free CaO, characteristic modules) for all coal tests and the test which used only natural gas. All parameters indicate that clinker quality in coal test remained unchanged compared to the natural-gas test.

Conclusion The industrial tests of drying and grinding of lignite were performed in the factory's existing tube ball mill, and the pulverized lignite, together with natural gas, was used in the 500 t/day wet-process rotary kiln.

383

During the experiment the natural gas substitution ratio was 50-79% of total energy without affecting clinker production. The use of pulverized lignite did not affect specific energy consumption in the clinker production process. This could lead to the conclusion that the main process features, such combustion quality, heat transfer, and kiln output remained within the limits which did not influence the overall kiln production process. Higher substitution of natural gas with pulverized lignite was not possible during the industrial experiments. The main reason was the insufficient output of the tube mill and the pneumatic transport system which had been constructed for the use of high-quality coal. The results of the described experiment have shown that high-quality coal is not the only solid fuel utilisable in clinker production, and that there is a future for carefully pretreated lowgrade lignite as the main fuel for the Yugoslav cement industry. The same is possible for other coals of similar quality.

References DUDA, W. 1976. Cement Data Book. Bauverlag GmbH, Wiesbaden and Berlin, 279-283. PERKOVlC, B., STANOJEVIC, M., DOKI~, S. 1994. Industrial Tests of Substitutions of Anthracites with Dry Pulverized Lignite 'Kolubara' in Cement Factory Beo(in, Final Report. Mining Institute, Beograd, Faculty of Mechanical Engineering, Beograd. STANOJEVI(~, M. & KARAN, M. 1994. The Use of Yugoslav Solid Fuels (Lignites) in Rotary Kilns in Cement Industry. International Conference 'Energy for industry '94', Beograd, Proceedings, 218-223. , PETROV,A. & KUBUROVId:,M. 1993. Influence of lignite 'Kolubara' properties on the production of pulverized lignite. Termotehnika, Beograd, XIX, 1-2, 55-64. VULETII~,g. 8r STANOJEVIC,M. 1987. Possibilities and conditions for the use of lignite 'Kolubara'. Mining Journal, Beograd, 1, 64-67.

The possibility of underground gasification of Bulgarian Dobrudja's coal DOUCHKO

DOUCHANOV

& VENECIA

MINKOVA

Institute of Organic Chemistry, Bulgarian Academy of Sciences, Acad.G.Bonchev str., bl.9, 1113 Sofia, Bulgaria Abstract: The gasification of coal within underground coal seams and using the combustible

gas as a fuel is an idea that has attracted scientists for many years. Some success in gasifying thick coal seams near the surface has been demonstrated in recent experiments in the USA. Tests on underground coal gasification in Belgium and France have been carried out supported by the Energy Commission of the European Communities since 1978. The latest tests at Thullin, Belgium carried out by a joint Belgium and German team are thought to be promising. The depth of the seams has been selected as representative of Southern European and some Mid-European coals as an essential first attempt before moving to a further stage, at around 900-1000 metres depth. Work on this programme is at an early stage and its progress will be watched with much interest. For Bulgaria it is of vital importance to develop underground coal gasification on Dobrudja's coal (1.5 109 t ) - as an important energetic strategy and the possibility of environmental utilization of this resource.

The first tests on underground coal gasification (UCG) were performed in 1912. They were followed by a number of tests in the former USSR and France. However, these attempts on U C G were discontinued due to the low calorific value of the gas produced and the difficult control on the combustion processes and the chemical reactions in the underground gas generator. After the experiment carried out in Gorlovka (1932), the former USSR re-commenced the U C G tests. Following the completion of the test period, at the end of the 1950s, a series of U C G stations was built in: Tula (130kin south of Moscow), Yushno-Abinsk (Kuznets mine basin, Siberia), Shatsky (80 km southeast of Tula) and Angren (120kin southeast of Tashkent). These stations were designed to use lignite coals. The U C G installations at Lisichansk (Donets basin) and Kamenskaya (130 km from Rostov) operated in bituminous and anthracite coals. The gas station at Tula operated in lignite coals in horizontal seams between 0.3 and 5 m thick, lying at a depth of 50m. In 1958 a total of 400 x 106m 3 of low calorific gas (750-850 kcal/m 3) was produced. Its composition is as follows: CO, 5.5%; H2, 13.5%; CO2, 17%; CH4, 1.6%; CnHm, 0.2%; O2, 0.5%; HzS , 1.0%; N2, 60.7%. The seams developed in Yushno-Abinsc were 8-22 m thick at a depth of 250 m and with a dip of about 45-70 ~ (Antonova et al. 1967). In this installation a total of 100 x 106 m3/year gas at a calorific value of 1000 kcal/m 3 was produced and it is known that about 700 engineers and 3000 technicians were involved in its production in 1957. The gas produced is characterized by the

following composition: CO, 13.4%; He, 13%; CO2, 11.8%; CH4, 3.6%; CnHm, 0.1%; 02, 0.2%; H2S, 0.01%; N2, 57.9%. The U C G station at Shatsky, built in 1959 (lignite seams of 2.9 m thickness, lying at a depth of 40m), has produced 200 x 106 m 3 gas/year at a calorific value of 800 kcal/m 3. Initially this gas was used mainly for local plants after which it was employed to drive two 1 2 M W turboalternators in an electricity power station. The station at Angren is situated on lignite coal seams that are 20m thick, at a depth of l 1 0 - 1 5 0 m and dipping at 30 ~ The area of the coal deposit is 150 km 2 and the coal ash is 11%. The station has produced 600-800 x 106 m 3 gas at a calorific value of 700-800 kcal/m 3. The gas, whose composition was: CO, 5.6%; H2, 15.2%; C02, 19%; CH4, 2.5%; CnHm, 0.2%; O2, 0.5%; H2S, 0.4%; N2, 56.1.% (Lavrov et al. 1971) was used mainly for electricity generation in a 200 M W power-steam station. The station at Kamensky(Rostov) has operated in coal seams dipping at an angle of 40-50 ~ with a gas production rate of 2 x 106 m3/day at a calorific value 900kcal/m 3 and that at Lisichansk has operated in coal seams which are 0.5-1 m thick, with a dip of 30-40 ~ and a gas production rate of 100-120 x 106m3/year at a calorific value of 850 kcal/m 3 (Skafa 1960). The stations at Yushno-Abinsk and Angren were the only ones remaining in operation after 1980. Parallel to the experiments on U C G in the former USSR in 1945-1965, tests in USA, England, Belgium, Poland, Czechoslovakia (Prasek & Koranda 1989), in the Tatabanya

From Gayer, R. & Pe~ek, J. (eds), 1997, European Coal Geologyand Technology, Geological Society Special Publication No. 125, pp. 385-390.

386

D. DOUCHANOV & V. MINKOVA

mine in Hungary during 1979-1980 (Szechy et al. 1988), Italy, Japan and Morocco (Djerada, 1947-1950) were carried out. The tests performed in England (Newman Spinney 1949) and in USA-Gorgas, Alabama (1946-1958) gave the most promising results. In USA the development of underground coal gasification is considered as a prospective trend. Taking into account the fact that the coal reserves of USA amount to 87% of the mineral resources, the eventual realization of UCG could increase almost threefold the exploitation of the coal reserves. The oil crisis in the 1970s has initiated again experiments on UCG in USA. The Energy Center of USA undertook gasification experiments in Hanna, Wyoming to test the possibility of underground gasification of 10m thick subbituminous coal seams, lying at a depth of 120 m. The coal permeability in the seams was enhanced by hydrofracturing. In 1973 a total of 0.24 x 10 6 m 3 gas/day was produced using air as a gasification agent. A team at the Energy Center-Laramie has carried out UCG tests in Hanna for 55 days. The gas composition in vol% is as follows: H2, 17.3; CO, 14.7; C02, 12.4; CH4, 3.3; C2H4, 0.6; 02, 0.5; HzS, 0.1; N2, 51.0; At, 0.6. The Lawrence Livermore Laboratory at Wyoming has performed a number of tests on UCG in seams that are 15 m thick, at a depth of 150-900 m by applying a steam-oxygen mixture feeding. The gas production rate was 5 x 104 m3/day at a calorific value of 2350 kcal/m 3. The Morgantown Energy Technology Center (METC) has carried out underground gasification on 2m thick bituminous coals, at a d e p t of 275 m, in West Virginia (Strickland 1977). The gas production rate was 0.1 x 10 6 m 3 at a calorific value of 1100 kcal/m 3. It should be noted that this experiment has a dual importance. On the one hand, the reserves of bituminous coals amount to 817 gigatonnes and on the other, about 30% of these reserves are found at a great depth. In addition the majority of these reserves are highballast and their exploitation by deep mining would result in serious environmental problems (Clean Act, USA, 1970). These experiments on U C G in the United States should be supplemented by three additional tests. Firstly, he results obtained by the Los Alamos Scientific Laboratory (LASL) in the Fruitland mines (New Mexico) on the separate runs of the two processes accompanying UCG, i.e. pyrolysis and semicoke gasification in different areas of the mine, aimed at reaching an optimal control on the processes. Secondly, the UCG performed by the Basic Resources Inc. in Fairfield (Texas), following a Soviet pattern, in order to build two 20MW

steam-powered stations, and thirdly the UCG tests carried out in the Reno Junction, Wyoming by the Atlantic Richfield Company (ARCO).

The present UCG situation in Europe In Northern Belgium, between the Campine Basin and the border with Holland the hypothetical coal reserves amount to 15-20 gigatonnes which is equal to the total amount of coals produced in Belgium for the last 150 years. The German geologists consider that coal reserves in the Ruhr lying at a depth of 1200 m and those at a depth up to 5000m are 10 and 1000 gigatonnes, respectively. Holland possesses 1500 gigatonnes coal resources, with the majority of them lying at a depth of 1500-3000 m. On the basis of preliminary studies of the National Mine Institute (NMI)-Belgium and those of Professor Wenzel from AIX University in Germany a joint project between Belgium and Germany was agreed in 1986. In Thullin (Belgium) UCG tests were carried out at depths of 860 m. Air was used as a gasification agent in the underground gas generator and a low calorific generator gas was produced. The utilization of oxygen-steam mixture at a pressure of 10-20 MPa yielded a product with mean C H 4 content (32.6% without N2). This content is two times higher than that obtained in the pilot installation 'Ruhr-100' of the Lurgi Company, Germany. Thus after CO removal the calorific value of the gas has attained a value similar to that of natural gas. Figure 1 shows the principal scheme of operation of this installation. The air supplied by compressor 2 enters the basic seam layer through the pressure hole 3; the low calorific gas produced by UCG, is released through the outlet hole 4. The latter is cooled to protect it from excessive increases in temperature and a water steam is produced simultaneously as a result of the heat of the removed gas. The low calorific gas reaches the surface at high pressure with a temperature of about 250-300~ after which it is washed in scrubber 5 before its inlet into the combustion chamber of the steam generator 6. The gasification of the base coal layer yields a high calorific gas (grison) which is contained in the upper layers. In the programme described above the following partners participate: from BelgiumThe Geological Department at Brussels, the Department of Chemical Engineering at the University of Liege, the Mining Department at Mons Polytechnic, Distrigaz, Brussels; from

REVIEW OF HISTORY OF UNDERGROUND COAL GASIFICATION

Ai~

E

x h~

387

~,~////////////////" '/.--6 5; :-_ -

-

E O

,--

.z

"///t~//////-///z///~'~ O ,r-

i

g:

Fig. 1. Scheme of UCG carried out in Thullen, Belgium: 1, motor; 2, compressor; 3, injection hole; 4, gas removal hole; 5, scrubber for low calorific gas purification; 6, steam boiler with combustion chamber; 7, alternator; 8, turbine; 9, heat-exchanger; 10, condensation vessel; 11, pump; 12, grison outlet; 13, scrubber for high calorific gas purification: 14, coal seams. Germany - Rheinisch-Westfalische Technische Hochschule (AIX), Saarberg-Interplan (Saarbrucken), Bergbau-Forschung GmbH (EssenKray), Messerschmitt (Munchen). England and the former USSR were among the first to show great interest in development of UCG. Thus after a 30 years interruption the National Coal Board undertook in Newman Spinney (1949) the production of gas by UCG for electricity generation in a 100-200MW steam-power station. In France, a research group for underground coal gasification, i.e. Groupe d'Etude de la Gaz~ification Souterraine (GEGS) including Charbonnage de France, Gas de France and Institut Fran~ais du P~trole was founded in 1976. Its goal was the development of coal reserves amounting to 2 x 109 tonnes at a depth of more than 800m. In the 1980s about 22 million dollars were ensured for the realization of this project. For the first stage which was carried out in Bruay-en-Artois (Nord-Pas-deCalais) about 4.3 million dollars were spent (Ferreti 1982). The first stage of the test began from a derelict mine tunnel at a depth of 1000 m and with two boreholes (injection and gas

Fig. 2. Scheme of UCG carried out in Pas-de-Calais, France: 1, existing mine gallery at a depth of 1000m; 2, injection hole; 3, internal hole diameter (60 ram); 4, external hole diameter (110ram); 5, closing valve; 6, gas removal hole; 7, coal seam; 8, metal grid; 9, intrusion of water under 800 bars pressure. removal) at a depth of 170m, separated by 65m drilled in a 1.2m thick coal seam. The experiment proceeded in the following stages: first, water injection (hydrofracturing) at a pressure of 100-300 bars, followed by air feeding for expansion of the hole, in the third stage electrocombustion is carried out and in the last stage oxygen is supplied to produce a substitute of the natural gas (SNG) (Fig. 2). The very first objective of the Belgium and French projects was to produce a low calorific gas for electricity generation. Further it was aimed to produce a gas at a calorific value of 2600kcal/m 3 which after concentration could substitute for the imported natural gas (SNG) with a calorific value of 9500 kcal/m 3. In Bulgaria, since the discovery of the Dobrudja's coal basin, intensive geological investigations on the origins and petrographic composition of the coal have been carried out. Detailed study of the coalification of this coal has revealed the presence of a thick series of bituminous coals. Ultimate and proximate analyses of the coals show that according to the degree of coalification they are all volatile coals (V daf =35-40%; C d a f = 80-83% and swelling i n d e x - 1 ) . On average coals are characterized by a low sulphur content-0.6-1.5% and a low content of mineral matter-Ad = 6-12%. Individual seam samples have a higher content of mineral matter-A d = 13-31%, sulphur = 0.8-4.2% and volatile matter yield V daf = 3 7 - 4 5 % . The increased content of volatiles (up to 45%) and

388

D. DOUCHANOV & V. MINKOVA

2.1

l

~-a b " ~ d '

e

r

r

3

I Gas

Fig. 4. Countercurrent combustion in UCG: 1, injection hole; 2, gas removal hole; 3, compressor; 4, coal seam; 5, combustion flow direction.

Fig. 3. Electrolinking method: 1, electrodes; 2, injection and removal holes; 3, insulation: ab,de-highly conducting channel sections, c-unheated coal seam region. of cdaf-76-80% shows that some of the samples can be referred to high volatile bituminous coals (Minkova et al. 1983). In the 1970s it was considered that these volatile coals could be used in a mixture (up to 55%) for coking in the Kremikovtsi Metallurgical Plant (Trayanov, 1979). However, it turned out that the coal deposits are situated at a depth of 1500 m which requires large investments for mining. The gasification of coal seams at shallow and intermediate depths can be undertaken by directional drilling whereby the interaction between neighbouring holes (for injection and gas removal) is a result of the natural coal permeability. Often the latter is enhanced by: water feeding (hydrofracturing); air injection under pressure (electrolinking) (Fig. 3); blasting (Klimentov, 1964), or by using derelict mine tunnels from which holes of up to 200m are drilled, etc. The most complicated problems in this respect are: the realization of the linking along the coal seam whereby the countercurrent combustion ensuring sufficient gas flow between the holes is most often employed for its stabilization (Fig. 4); the pack compression of the rocks disturbing hermeticity facilitates the water penetration from the water-carrier layers; the control of the gasification front flow from the injection to the gas removal hole, etc. Some

environmental problems such as the air pollution caused by various chemical derivatives evolved during U C G should be also considered. In Table 1 are shown data from the studies on the pollution during U C G testing in Hoe Creek, Wyoming, USA (Mead et al. 1977). During U C G at greater depths, as will be required for the Bulgarian coal, similar pollution has not been registered: the clays, for example, take part in the neutralization of H2S and NH3. It should be noted that the coal seams in Europe are characterised by great depths and small thickness. Under these conditions the successful performance of U C G requires that a number of technical difficulties are overcome such as: the effective linking in the coal seam; the impeded control of the gasification front; and the control of the multistage gasification process as a whole. The reaction agents and the basic products used in UCG, as in all gasification processes of coal, besides coal are: oxygen, water, hydrogen, carbon oxides, methane, hydrogen sulphide, etc. (Douchanov & Angelova 1982). The composition of the gas produced is influenced by catalytic reactions which occur on the surface of the coal matrix and the inorganic salts which are found in abundance around the underground gas generator. The coal characteristics, the geometry of the coal seams (depth, dip, etc.), the amount, type and the quality of the gasification agent, its pressure and temperature, the geometry of the holes are some of the basic

Table 1. Study of the pollution by UCG during the Hoe Greek test Permissible concentration limit (mg/1)

Pollution Pregasification Inside burn zone species value (mg/l) Concentration increase (mg/1)

Outside burn zone Concentration (mg/1)

increase

Phenols CNNH~Pb 2+ SO~-

500 300 70 0.04 1000

5 • 105 0.001 3 K 10 4 0.20 100• 0.5 40 K 0.05 5K 250

0.001 0.01 0.5 0.001 200

0.1 0.4 20 0.001 2000

100K 40K 40x 10•

REVIEW OF HISTORY OF UNDERGROUND COAL GASIFICATION

389

to a 'new edition' of the interest towards this huge resource. This project includes the following participants: the Mine Geological Technological Institute in Madrid, the ENDESA and OCICARBON Companies, the English Nuclear Energy Board and the Belgium Council for UCG research. The main area of coal mined in Bulgaria belongs to the lignites from the M a r i t s a - East field. They are the main feed stock of the thermal power plants. It is envisaged that during the next 5-10 year the Elhovo lignite field (500 x 106 tonnes) will be set into operation (Douchanov & Angelova 1982). The characteristics of the coal from the aforementioned deposits are as follows: Marits-East (W, 5060%; A d, 30-60%; S d, 4.0-5.0%; C daf, 64%; H daf, 6.8%; Combustion heat of working fuel, 6.6 MJ/Kg) and Elhovo (W, 55-55%; A d, 30-37%; S d, 7.0-8.0%; C dar, 62%; Combustion heat of working fuel -6.3 MJ/Kg). During recent years, stand-tests were performed for coal gasification in a fluidized bed, at pressures of 1-2 MPa, both with steam-air and steam-oxygen mixes (Lazarov 1986). Besides the advantages, these experiments have certain shortcoming. For example, during gasification of high-ash coal, agglomeration of the particles and disturbance of the normal fluidized bed in the gas generator might occur. Such phenomena have been observed with steam-air gasification

parameters that determine the effectiveness of the UCG process. All these complex interactions indicate the necessity for various models and mathematical modelling (Gunn & Whitman 1976) to optimise conditions prior the realization of the underground experiments. The financial aspects of the problem are also of essential importance. The cost of a hole in the 1980s was two million French francs. The greater distance between the two holes (injection and gas removal) is decisive for the optimal amount of the burned coals utilized by them. This distance, imposed by the experiment, has a basic meaning for evaluating the economical efficiency of the process. French scientists (Pottier & Chaumet 1978) have derived the so called 'integral coefficient t(L)' (Fig. 5) which reveals the relationship between the following parameters: Q, E, L, S. As seen from Fig. 5, these are: the amount of the coal utilised by a pair of holes (injection and gas removal) Q = 6000 tons, coal seam thickness E of 2 m burned coal seam area S = 2 5 0 0 m 2 and the distance between the pair of holes L = 60 m the integral coefficient t(L), is 0.7. The fact that in 1991 (Furfari 1992) the Energy Council of the European Communities decided to invest 18 million ECU in a large-scale Spanish-English-Belgium test on UCG in the Alcorisa region of Spain with a depth of the holes of 600 and 900 m, points unambiguously

"d':O,~ ~-0,6 7"=0J3 "U=I,0

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90

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5

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,'

7 9 11 13 15 f

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|

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.-1

27 10~ 5 E t~E 3

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Fig. 5. Curves for calculation of the integral coefficient t(L): Q, quantity of the coal matrix utilized by a pair holes (injection and gas removal); E, thickness of the coal seam; L, distance between the holes.

390

D. DOUCHANOV & V. MINKOVA

of the Elhovo coal in a quasi boiling layer, under pressure, at gasification temperatures of 920930~ (Lazarov & Douchanov 1988). Due to the lower reactionability, compared to the MaritsaEast coal the gasification of the Elhovo coal does not run at a satisfactory speed when the temperature is below 950~ To clarify the possibility of overcoming the particle agglomeration during gasification of Elhovo coal, the following studies were performed: (i) on the cause of particle agglomeration (Douchanov et al. 1993) and (ii) on the impact of some catalysts. The results from study (i) on the Elhovo coal during gasification in the fluidized bed with a steam-air blow, under pressure, confirm the necessity of running the process at a lower temperature and at conditions avoiding local overheating, i.e. at intensive quasi-boiling layer. The effect of some catalysts on increasing the speed of gasification of the Elhovo coal was tested at temperatures below 900~ The results obtained, indicated that the carbonates of the alkaline metals are active catalysts during gasification of the Elhovo coal at 750-800~ (Angelova & Douchanov 1983; Douchanov & Lutskanov, 1996). Since proposals for mining the Dobrudja's coal basin have been abandoned, underground coal gasification remains an important strategy for utilizing this resource. During the past decade and particularly in the last few years a revitalization in the interest in U C G has occurred both in the United States and in other countries. Considering the large reserves of the Dobrudja's coal basin amounting to about 1.5 x 109t and the insufficient resources of petrol and natural gas in Bulgaria, we conclude that ways should be investigated including cooperation with other countries with experience in this field, to carry out research, mathematical modelling and pilot experiments on U C G in the Dobrudja's basin.

DOUCHANOV, D. & ANGELOVA,G. 1982. Issledvane vazmozchnostite za intenzifikatsiya na gazifikatsiyata na vuglischtata, Izvestiya na BAN, 15, 393-399. DOUCHANOV,D., LUTSKANOV,L., MARINOV,S. P., MINKOVA, V. & YOSSIEOVA,M. 1997. Catalytic effect of ZnC12 in the pyrolysis of lignites, Fuel, in press. DOUCHANOV, D., MINKOVA, V., MARTINEZ-ALONSO, A., PALAClOS, J. M. & TASCON, J. 1993. Low temperature ashing of Bulgarian lignites, Erdol und Kohle, 12, 461-467. GUNN, R. & WHITMAN, D. 1976. Packed-bed models for the in situ gasifier, Laramie Energy Research Center, Reprint No LERC/RI-762. FERRETI, M. 1982. La valorisation du charbon, Paris, 219-237. FURFARI, S. 1992. Gasification and 1GCC within the European Communites, Erdol und Kohle, 45, 292-293. KLIMENTOV, P. P. 1964. Gidravlicheskii razriv dlya podzemnoi gazifikatsii zalezchei uglei, Izvestiya

visshikh uchebnikh zavedenii-geologicheskaya razvedka, Moskva, 1097-105. LAVROV, N. B., KULAKOVA,M. A., KAZACHKOVA, S. T., ZHIRENYI,A. E., ANTONOVA,R. I. & VOLK, A. F. 1971. O podzemnoi gazifikatsii angrenskogo burougolnogo mestorozchdeniya, Khirniya tverdogo topliva, Moskva, 1, 73-76. LAZAROV, Y. 1986. Habilitazionen trud, MINPROEKT, Sofia. LAZAROV, L., DOUCHANOV, D., MARINOV, S. P. & STEFANOVA, M. 1988. Agglomeration of Elhovo's coal in the pressurised fluidized bed gasifier, Symposium 'Physico-technical problems of energetics', Moscow, Reprint 12. MEAD, S., CAMPBELL,J. H. & NTEPHENS,D. R. 1977. Environmental tests in Hoe Greek UCG. Proc. of 3rd Annual Underground Coal Conversion Symposium, Lawrence Livermore Laboratory, Reprint 770652, 475-489. MINKOVA, V., ANGELOVA, G., GORANOVA, M. & RAZVIGOROVA, M. 1983. Varhu khimicheskiya sastav na vaglischtata na Dobrudjanskiya basein, Khimiya i industriya, Sofia, 5, 207-210. POTTIER, M. & CHAUMET, P. 1976. Gaz6ification souterraine profonde du charbon; problemes et perspectives, L'Industrie du P~trole, 498, Septembre, 53-57. PRASEK, K. & KORANDA, J. 1989. Stav vyzkumu pdzemniho zplynovani uhli, PLYN, Praga, 69/5, 141-145. References SKAFA, P. V. 1960. Podzemnaya gazifikatsiya, Gosgortehizdat, Moskva, 110-115. ANGELOVA,G., DOUCHANOV,D. & RAZVIGOROVA,M. & LAZAROV, L. 1983. The role of catalysts in STRCLAND,L. 1977. In situ gasification of West Virginia coal by 'long wall generator', Proc. of intensifying the process of gasification of lignite to 3-rd Annual Underground Coal Conversion Symproduce synthesis gas, Seminar on Chemical from posium, Lawrence Livermore Laboratory, Reprint Synthesis Gas, Economic Commission for Europe, Geneva, Chem/Sem. 12, R. 17. No 770652, 81-85. ANTONOVA, R. I., GARKUSHA, I. S., GERSHEIV1CH, SZECHY, G., KISS, J. & AZENBEGI, J. 1988. UnderE. G., KREININ, E. V., LAVROV,N. V., SEMENKO, ground Gasification of Coal, MagyarKemikusok Lapja, Budapest, 8, 289-295. D. K. & FEDOROV,N. A. et al. 1967. Issledovanie TRAYANOV B. 1979. Kam Voprosa za Termichnata nekotorikh zakonomernostei protsessa podzemPodgotovka na Vuglischtata za Koksuvane, PhD noi gazifikatsii uglei. Khimiya tverdogo topliva, thesis, Sofia. Moskva, 1, 86-90.

Coalbed methane migration in and around fault zones E. L. B O A R D M A N

& J. H. R I P P O N

International M&ing Consultants Limited, PO Box 18, Common Road, Huthwaite, Sutton-in-Ashfield, Nottinghamshire, NG17 2NS, UK Abstract: One of the characteristics of all operating coalbed methane fields is the considerable variation in producibility success within these fields and even between adjacent wells, suggesting that very site-specific controls are operating. The most likely control in many coalfields is geological structure, particularly faults, which can divide the ground into fluid migration pathways and zones with bypassed, retained gas. Apart from the faulted zone itself adjacent ground will have been subject to dilational or contractional strain, and the strain profiles on either side of the fault will have their own individual permeability characteristics which may be further modified by subsequent burial history. Although any one well will be site-specific, this introductory paper seeks to describe the general ways in which modern understanding of faults and their associated strained ground can contribute to better well spacing and detailed siting and therefore a greater proportion of successful completions.

Methane from coal seams (coalbed methane) is potentially an important source of natural gas worldwide given the large volumes of gas contained in the coals and associated rocks in the world's coal basins. To date successful economic production of coalbed methane from virgin seams is limited to a few areas in the USA. More recently attention has turned to other coalfields, particularly in the United Kingdom, eastern and western continental Europe, China, South Africa, France, Spain and Australia. A common feature of coalbed methane production has been the co-existence of both low and high production wells in the same field and often in close proximity to one another. Current activity in the USA is addressing the problems of poorly producing wells, in particular focusing attention on why certain wells are not producing at their perceived potential even though many are located near to high productivity wells. For example, a well in the Cedar Grove Field of the Black Warrior Basin, which has been in production since March 1990 and currently averages 100 000 cuft/day (CFD) has offset wells in the same area producing between 200000 and 225 000 CFD (Kuuskraa et al. 1994). Surveys in the wells have provided evidence that some of the perforated horizons have taken little or no sand during hydraulic fracture treatment and some perforations are blocked by coal fines. The extent to which these factors are controlled by variation in the coal and strata properties or whether these are purely mechanical/treatment problems is not known. However, in other areas, increased gas production is attributed to the proximity of wells to tectonic structures. Additional fracturing and enhanced permeability have been attributed to the proximity of wells to the Crystal Creek

anticline in the Grand Valley Field in the central part of the Piceance Basin, Colorado (Stevens 1993). The detailed geology and hydrology of this reservoir are still not well understood and it is clear that a better understanding of cleat geometry and the structural controls on natural fracturing will help to improve characterization of the coals in terms of gas producibility. Coal seams constitute unconventional natural gas reservoirs. They not only store gas but they are also a source of gas. They are a more complex form of reservoir than a 'conventional' natural gas reservoir both in terms of their geology and in the mechanisms involved in gas production. Gas producibility from coal seams is generally controlled by the interplay between the following factors: coal distribution, rank, gas content, permeability, hydrogeology, depositional and structural setting. Local variations in the geology and reservoir characteristics must be expected to influence the feasibility of producing methane from them. One of the key local conditions will be permeability. It is aspects of local variation that are addressed by this paper, in particular the way in which faults and their associated strain zones may impose variations in the permeabilities and connectivities of the coals and their surrounding rocks. The paper is based largely on mining experience in the United Kingdom Carboniferous coalfields but is considered to be generally relevant. No single paper can adequately address all productivity settings with respect to faults. This contribution is seen as a general introduction, and discusses general concepts that can then be considered for site-specific use. These concepts are based on the most up-to-date geological models wherever appropriate. While compatible

From Gayer, R. & Pe~ek, J. (eds), 1997, European Coal Geology and Technology, Geological Society Special Publication No. 125, pp. 391-408.

392

E. L. BOARDMAN & J. H. RIPPON

TECHNICAL CONTROLS

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Fig. 1. Controls on coalbed methane producibility. Apart from 'external' controls, eg financial regime and marketing, a CBM prospecrs success will depend on the geology, and on the techniques involved in its interpretation and engineering. Geological interpretation is tabulated separately to emphasise the importance of detailed understanding where the geology itself is very variable. with these, it is the further intention of the paper to minimize descriptions and terminologies that are too detailed for an introductory paper.

Geological controls on coalbed methane producibility The ultimate producibility of any individual well will reflect both the site's geology and the design and technology of the investigative and extractive processes (Fig. 1). Individual well design is beyond the scope of this paper. Many geological controls may be considered significant for the ultimate producibility and these are reviewed in the literature. A resum6, with particular reference to two North American Cretaceous formations is

provided by Kaiser et al. (1994). A British contribution is provided by Baily et al. (1995). Figure 2 lists these controls in terms of geological history, from original depositional setting, through the varied phases of burial history, to the present stress setting. In any individual prospect, producibility will frequently reflect several of these controls and their interactions. The depositional setting will determine the thickness, lateral extents, degrees of connectivity, and vertical frequencies of the coals themselves, and also important inter-coal sediments particularly sandstones, which can form associated conventional hydrocarbon reservoirs. Also, ultimate coal strength and fracture permeability may be influenced by the nature and setting of the

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Fig. 3. Types of faulting in British Carboniferous Coal Measures. A large generic range is found, and each type will have geometries and linkage characteristics which reflect the very different modes of origin. precursor vegetation itself. Most identified geological controls relate to the long burial history that characterizes many hard coals, especially Carboniferous coals. As Fig. 2 illustrates, several of these factors interact to give the coal rank, and also the basic permeability of the deposit. The present stress setting provides a final control, with the principal horizontal stress vector in particular influencing the directional permeability of the inherited structure. Because of the many interacting geological processes, it is very unlikely that all relevant factors presented by the geology of a particular prospect will be sufficiently known and understood for complete analysis. Figure 1 therefore includes both inherent geology and its investigation and interpretation, as separate controls; in other words, the suitability of investigative techniques, and the applicability of the interpretation, will be critical in maximizing producibility. Of all the geological controls, the most site-specific, and currently the least understood in terms of coalbed methane producibility is considered to be faults and their associated structures (Figs 3 & 4).

Fluid migration through unfaulted ground Before considering the effects of fluid migrations in faulted ground, it is suitable to refer briefly to

the broad aspects of migration through unfaulted ground, specifically coal-bearing sequences. These are laid down in many depositional settings and characteristically comprise very varied rock types, usually reflecting river system migrations. The proportions and geometries of these rock types are also very variable. In most hard coal deposits, the sandstones can be significantly permeable via their well developed joint systems, with the claystones acting as aquicludes. (However, in some high rank coalfields, claystones may themselves be upranked sufficiently to allow passage of groundwaters at depth). Coal can form another permeable rock type, for example, in the near-surface where destressed, and in the tensile strain zones caused by mineworkings; in general, in situ coals in the UK can only rarely be considered permeable at any practical scale, particularly for water, but also for methane. The sandstones can form reservoirs for conventional hydrocarbons, and significant water inflows to mine workings usually involve sandstones as either source or migration pathway. As the sandstones are also the most intricate in geometry, fluid migration pathways cannot successfully be modelled without good borehole data control. A key factor in fluid migration through coal is the jointing; this includes 'cleat' and 'slip' in the British coalfields. Pervasive cleating usually lies roughly normal to the coal bedding, with fracture densities

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sometimes several tens/m; cleat densities vary according to structural setting, and also with coal lithotype and rank. The high rank coalfields of southern England and South Wales have greater cleat densities than those to the north. In general terms, the cleat orientations tend to reflect Variscan compressional trends, with deviations from the regional on the approach to individual faults. The degree of mineralization reflects the geological history of each coalfield, and in the U K can vary from the well mineralized cleats (carbonates and sulphides) of the eastern Pennine Basin to the poorly mineralized coal of South Wales. Many detailed cleat studies of British coals were undertaken in the 1950s and 1960s as part of studies on the introduction of plough coal cutters; these commonly recorded all cleats in terms of density, orientation, and relationship to coal lithotypes for a variety of seams and geological settings. However, there has been little published on cleat in British coals, and for an overall geological appreciation of cleating, and jointing in general, reference may be made to the wider geological literature, e.g. Rawnsley et al. (1992). Further comment on cleat is provided later, with respect to Longannet mine in Scotland. Regarding slip, this is typically a fracture system lying at around 45 ~ to the coal bedding and characteristic of the southern British coalfields of Kent and South Wales. These fractures are usually unmineralized, and form conjugate sets with fracture strike tending to parallel the local 'cross faults' - i.e. those of overall normal fault mode which intersect the Variscan compressional trends of these coalfields at a high angle; however, variations from this parallelism are known. Although often polished, there is only rarely minor displacement of the seams at

these fractures, the density of which is typically much less than cleating, perhaps 1/m being characteristic. Similar slip has been recorded locally in other British coalfields, mainly adjacent to large faults. Fluid migrations through coal-bearing sequences will also depend upon bedding dip, hydraulic gradients, and any mining extractions that have modified the sequence through voids and associated strains.

Faults and fault zones There is a very extensive geological literature on faults and fault zones, both general and also highly technical. The intention of the present paper is to discuss those aspects which relate to fluid migration and/or retention, specifically coalbed methane. Figure 4 tabulates the faultrelated factors. Faults may originate in various ways, some relating to the depositional processes of the host formation but the majority being tectonic and post-depositional. These are invariably categorized as normal, reverse/thrust or strike-slip depending on the dominant slip direction with respect to the fault plane. However, this is very much a simplification, especially when discussing zones of faults. For example a strike-slip fault zone may include many apparently normal and reverse faults. Individual faults may well show both dip-slip and strike-slip characteristics giving oblique slip with extension or contraction. Normal, reverse and strike slip faults and their variants grow in response to changes in the magnitude and ratios of the principal stresses. These may themselves alter throughout the geological history of a fault, from it initiation to its final extent, producing

COALBED METHANE AND FAULT ZONES variations in fault plane dip and curvature. Events in subsequent geological history may reactivate a fault, quite possibly under a different stress regime. The fracture or fracture zone itself will reflect these formative and subsequent stresses together with the physical characteristics of the host rocks and any lubricating clays and fluids. A wide 'damage zone' may result, with a hierarchy of interlinked faults with rotated or crushed pieces of host rock; alternatively a single neat fracture with minimal damage zone width may result. In particular contexts, there may be a relationship between fault throw and the width of the damage zone (e.g. Robertson 1983; Knott 1994). In this paper the term 'damage zone' refers to the immediate faulted volume across which there is measureable displacement and which includes the gouge and the normal drag. For a simple fault, the variation in throw (in normal faults, throw is the vertical component of the displacement) is known to be systematic, with the greatest throw - ideally corresponding to the point of initiation - located centrally on a fault plane that has essentially ellipsoidal limits when viewed in strike projection (e.g. Rippon 1985; Barnett et al. 1987; Walsh & Watterson 1990). Figure 5 illustrates the general principle, showing contours of displacement, the fault limit (tip line) being zero displacement. Following from Fig. 5 it should be noted that a fault cannot be viewed as a fracture independent of the adjacent ground. The variation in throw across the fault necessitates a related strain in the rock volume; in the simplest case of an isolated normal fault, the upper hangingwall and lower footwall of an ideal normal fault will be dilated above regional stratigraphic thickness with a corresponding compression in the lower hangingwall and upper footwall. Such strain zones will approximate to ellipsoidal volumes, and for large faults (hundreds of metres) may show very significant volumetric differences between adjacent hangingwalls and footwalls. Within these strains, the rock fabric will also vary and the most obvious variable is likely to be joint densities. Again, using the idealized simple fault (Fig. 5) the upper hangingwall and lower footwall may be expected to have much better developed joints; this may or may not translate into enhanced fracture permeability depending on geological history.

Fault modification of fluid migration From the above introductory account of faults and their associated damage and strain zones,

395

the following features are seen to affect the permeability of the fractured and strained ground.

Fault plane and damage zone Apart from the simple juxtaposing of permeable and impermeable formations, structural traps in conventional hydrocarbon reservoirs frequently depend on the sealing characteristics of a fault damage zone; oil and gas may be retained by a clay-rock dominated 'gouge', or may have migrated by leakage through 'windows' provided by, e.g. the fault juxtaposing sandstones, with minimal clay-rocks in the gouge (see e.g. Lindsay et al. 1993). Sandstone-to-sandstone situations may, however, still have reduced communication across the fault because of grain size reduction/recrystallization. Such considerations apply to water migrations as well as conventional hydrocarbons. The sealing characteristics will, however, be very site-specific and will depend on the following main factors: the lithologies actually present within the faulted sequence; the number of faulting events and their style; the diagenesis of the faulted rocks; and the displacement relative to the thickness of the bed in question. Potential migration along the fault zone itself will depend on similar considerations. However, there will be differences in the special case presented by coalbed methane, where the reservoir rock is coal, the permeability of which may be very low by comparison with sandstones, and in which producibility commonly requires direct stimulation. In this case, the fault plane and damage zone will aid methane depletion over geological time if the actual fracture pattern extends laterally into the coal seams for a significant distance, i.e. tens of metres.

The adjacent strained volume The general nature of the strained volume (Fig. 5) was discussed above, with the potential for extra joint permeability identified for the upper hangingwalls and lower footwalls of idealised normal faults. Although many examples of these strained volumes are known, actual field observations of the necessary rock fabric changes are rare. At Longannet mine in Scotland, a number of large (tens to hundreds of metres throw) faults are intersected by the mineworkings, and proved/ imaged by boreholes and high-resolution reflection seismic. Integration of all these data has allowed the mapping of the practical limits of the

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fault-adjacent strained volume, at mined horizons. Overall, this is expressed as prominent dilation/contraction of the hangingwall and footwall as appropriate, together with some extra minor faulting, mainly in the footwalls; gradient change at the mined horizon is the most

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COALBED METHANE AND FAULT ZONES frequency, are difficult to assess visually apart from very local swings in the main cleat; however, there are signifcant character changes noted from in-seam seismic transmission and reflection surveys, and reduced integrity of surface seismic reflectors is also prominent across these zones. The example in Figure 6 is drawn at a coal horizon, but it should be noted that the dilations/ contractions adjacent to these larger faults may actually relate more to the prominent sandstones and claystones that characterise the Longannet sequence, as, in bulk terms, these present the greater opportunity for modifications. In most British coalfields, an increase in coal cleat density is sometimes recorded in the immediate approach to a significant fault. This is not always the case at Longannet. The regional cleat trend there (Fig. 7) subparallels the main fault trend, and is prominently mineralised with carbonates, the secondary cleat generally being subordinate in density and less mineralized. The situation at Longannet is locally complicated by marked reduction in cleat density in areas subject to mild thermal metamorphism, and by intense fracturing adjacent to minor intrusions; however, the general picture shows only local increases in cleat density on the approach to faults. Much more noticeable is that the main cleat orientation can swing towards both smaller and larger faults, sometimes lying normal to the fault within a few metres of it; this recalls the noding of faultadjacent joints reported by Rawnsley et al. (1992). The Longannet descriptions are included here only to illustrate the potential geological relationships; there is no specific coalbed methane content. Given this background, it is assumed that for coalbed methane, fracture permeability will be enhanced in the dilated volumes in the coals, as well as the sandstones, but that the emphasized fracture systems in the coals will be more subtle. This probably represents the best conditions for producibility, with good retention and a latent fracture system that can be stimulated to encourage methane release. Those zones adjacent to the fault which have suffered compressional strain should, by contrast, have a much less pervasive fracture system. Field measurements of the bulk strength of in-place coals are notoriously difficult to standardise, mainly because of fracture systems; however, in such compressed settings, overall

399

stronger and 'tighter' coals are to be expected, probably with very good seismic propagation and reflection characteristics. Unless modified by later geological history, coals in these zones may be expected to have significant retained methane, but also poor producibility because of reduced fracture permeability. The fracture aperture effects of these strains are currently unknown, and will be difficult to detect directly in mined exposures, where disturbance is inevitable. In general it must be assumed that apertures will be greater where the fracture lies parallel to the local principal stress; open jointing will be prone to mineralizations through later geological history.

Fault linkages and populations The degree of connectivity of a fault fracture system will influence the potential for any fluid migration. Fault linkages may be considered in the following categories: (i)

(ii)

kinetically-related linkages, in which all the fractures result from a common geological deformation phase; other linkages, in which faults from various geological deformation phases interact and intersect to give a more complex situation.

As with the fault-adjacent strained volumes described above, there will be a fine balance between migration loss through fractures, a n d ultimate producibility through stimulation of latent fractures. In these circumstances, it is proposed that particularly beneficial coalbed methane producibility may be found in those zones where faults overlap. Fault overlaps (Peacock & Sanderson 1994; Childs et al. 1995) occur where the overall deformation associated with an individual fault - including its adjacent strained volume - interacts with that of another. Again, this particular form of 'linkage' may be kinematically consistent, or not, with differing detailed geologies as a result. Within these overlaps, ground strain may be considerable, with changes in horizon dip, and fabric change including extra faulting and jointing. Such zones may therefore provide the required permeability for producibility, without the overall fracture system depleting the methane over geological

Fig. 7. The Abbey Craig East Fault: coal cleat and present stress. This structure lies in the Scottish Midland Valley, some 40 km northwest of Edinburgh: it is essentially an isolated fault allowing easy study of its displacement and strain patterns. Fault displacement in metres. (a) The regional mineralised cleat shows general parallelism with the gross fault trend except immediately adjacent to faults. See text for discussion. (b) The present principal horizontal stress trend. See text for discussion; variations close to larger faults are known and on-going work is seeking to define these.

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time because the fracture pattern is not fully linked. Figure 10 illustrates an overlap/relay zone for a strike slip fault system. The concept of fault populations, well known in coal mining for many decades, has recently been developed for the assessment of fracture patterns in conventional hydrocarbon reservoirs. A fault population is a system of faults of all sizes in which there is some numerical relationship between the size categories (e.g. Walsh & Watterson 1992). For tectonic faults, power law size distributions are sometimes applicable. However, in the authors' experience there are significant gaps in fault size distributions in many British coalfields and power law size distributions may not be universally applicable. Ideally a fault population should be based on one geological deformation phase, but at least some published sets appear to include faults of several phases. The potential for describing conventional hydrocarbon prospectivity using fault population studies- in which fracture numbers below seismic resolution are assessed from those revealed by seismic- is very dependent on choice of the most suitable mathematical model, and is beyond the scope of this paper. For coalbed methane, it is considered that fault population studies will rarely have applicability, as they are essentially regionally-based whereas coalbed methane producibility requires much more site precision. Those aspects of fault population studies that may have coalbed methane application are as follows: (i)

(ii)

fault damage zone: specific fault hierarchies and linkages making up the broken ground itself; preferred faulted horizons: faults initiated preferentially at a particular depth, and propagating largely within a particular depth interval. For example, Rippon & Raine (1986) implied that fault populations lay at differing preferred horizons (Westphalian A/Westphalian B) at two adjacent collieries in Derbyshire, England. It is thought likely that such horizon preferences are common in many coalfields, with each 'cell' having its own fracture characteristics (orientations, size relationships, preferred nucleation depths) on a scale of 25 km2-100 km 2.

From this listing of fault-related features, it will be seen that fluid migration and retention characteristics are likely to vary significantly along, and adjacent to faults. However, any idealized pattern may well be modified by subsequent geological history.

Fault zone burial history In UK coalfields, the main deformation and faulting phase is generally considered to be later Carboniferous/early Permian, with some later reactivations. In certain coalfields, the later movements have both complicated the existing faults and initiated new faults. By contrast in other coalfields, existing faults have been reused, with renewed but essentially uncomplicated growth. These differences must partly reflect the orientation of the existing faults to the new stress pattern. In addition to reactivation, fault zones will be modified with respect to their permeability attributes by burial/uplift history; and by regional fluid migrations and mineralizations resulting from igneous replacements, or driven by tectonic uplift (e.g. Daniels et al. 1990) or from other geochemical redistribution mechanisms. It should be expected that such fluid migrations in the geological past will themselves have taken advantage of any structurally controlled permeability patterns presented by a fault zone, to the extent that a key fracture system, e.g. the main coal cleat, may be largely sealed by mineralization effected by these fluids. The burial history of a fault zone should also include consideration of the recent/continuing present stress field. It is known from British coalfields that stress magnitudes and ratios can vary over an area as small as one mine lease, and also vary through lithology and stratigraphy. For example, at Asfordby mine southeast of Nottingham (Whitworth et al. 1994), the variations indicated some response to ground heterogeneities produced at least partly by inherited, or 'fossil' fault structures. Current work by the authors is investigating the response of the present principal horizontal stress to the fossil strain zones adjacent to the Abbey Craig East Fault at Longannet mine (Fig. 6). As described previously the strain zones have been investigated and mapped for the mined horizon, and the volumetric differences between the lower footwall and hangingwall strains assessed using their fabric differences, which are thought to be largely joint orientations and frequencies. Ongoing mapping aims to define any refractions of the stress vectors, both fossil and present, within the strain zones. The modifications produced by 'fossil' heterogeneities on the present stress field are not currently well understood, and again are likely to be highly site-specific. However, the orientation of the principal horizontal stress with respect to that of the inherited fracture pattern will have considerable influence on well design and producibility for coalbed methane.

COALBED METHANE AND FAULT ZONES

Models for coalbed methane retention and migration One of the principles behind the present paper is that coalbed methane producibility is very sitespecific and will be strongly affected by fault zones. However, it is appropriate to the understanding of individual prospects and well sites that the general principles be understood. This can be attempted by combining the following: 9 idealization of normal, thrust, and strike slip fault geometries; 9 assessing the physical changes imposed on the adjacent rock ('fabric changes') with special reference to fracture permeability; 9 assessing any burial history particulars; 9 assessing the interaction between the 'fossil' fault structures and the present stress fields, drawing upon mining experience.

401

progressively greater subsidence towards the fault plane, directly influencing net coal thickness on a very local scale. It should be noted that in some circumstances, the greater coal thickness might alternatively form in the footwall. For example, the hangingwall may be subsiding too fast for peat generation or retention, with the footwall offering a better water-table balance within an overall basin subsidence setting. The fault plane in Fig. 8.4 is shown as concave to the hangingwall, or listric, only to illustrate another possible shape for normal faults. The listric shape is not essential for the 'growth' aspectactive during deposition - illustrated here. Also, the increasing inter-horizon thicknesses towards the fault should be recognised as potentially including both depositional increases and dilational effects from subsequent fault growth.

Thrust faults and zones Normal faults Figure 8 illustrates some of the interactive factors which will influence ultimate coalbed methane producibility. Given the very varied geology of faults and fault zones already described, only a few interactive factors can be dealt with in such simplified drawings, which are chosen more to illustrate general principles than provide immediately usable templates. Figure 8.1 illustrates an idealized normal fault. The stylized bedding is shown at a wider spacing across the faulted interval merely for clarity. In this simple case, the fault is seen as essentially unmodified by later geological events; it did not intersect the original free surface, and it is not exposed by the present erosion level. The idealized distribution of permeability characteristics, with respect to coalbed methane migration, retention and producibility are described above. In Fig. 8.2 the upper part of the idealized fault has been eroded, with likely coalbed methane depletion in the upper hangingwall. It is thought that widespread unconformities result in wholesale degassing over significant vertical ranges (Creedy 1988). However, subsequent reburial by later basin development may allow secondary gas generation (Fig. 8.3). The potential for retention of this methane will depend on many burial history aspects, including depth ranges, and the nature of the unconformity and overlying formations. Figure 8.4 shows a fault that was growing during deposition of the coal-bearing sequence. Here, coals are thickening into the fault on the hangingwall side, where vegetation growth and preservation were able to keep pace with the

Reverse f a u l t s - taken here to have fault plane dips characteristically greater than 45 ~ to bedd i n g - are considered by the authors to be relatively rare except in strike slip fault zones (see e.g. Fig. 10). They only rarely form in isolation, and very rarely form in regionally integrated systems; some will be reactivations of originally normal faults. These are, therefore, not considered in any detail in this paper. Thrust faults (Fig. 9) in the southern British coalfields, with Variscan deformation, typically have low fault plane dips,

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plus the amount of methane captured by degassing systems (E0) of each coal mine (only reliable measurements) by the coal mine output (Q): Ew+E0 Wek - - - -

Q

(7)

According to the assumption (3) of the work, the sum given in the numerator of equation (7) is the amount of methane that is released from coal

and surrounding rocks dynamically and so, taking into account the equations (3) and (4), it is proportional to G. On this basis, many variants of regression between the average methane content (GK) and the specific emissions (Wek) were analysed, and finally the best regression equations were chosen (Fig. 5) - those characterized by the least error of ventilation emission estimation (5-15%). Estimated values of the specific emission were

ESTIMATION METHOD FOR METHANE EMISSIONS

431

2e

G

10

0"

0

20

40

60

80

100

120

140

160

180

200

Ap, Fig. 4. Distribution of rate of desorption (AP2, 1 • 10-3 m of H20) versus methane content (O, m3/Mg) in one of the Upper Silesia coal mines.

assumed to be the release factors from underground (mining) processes (We). The resulting regression equation has the form: We = aa Gg~ + a2G~

(8)

where: 9 for coal mines 10m3/Mg: al = 9 for coal mines 10m3/Mg: al =

of specific emission 14%k< 3.776 and a2 = -0.605; of specific emission Wek _> 21.452 and a2 = -3.346.

In further work the established equations were extrapolated to all coal mines, with an additional assumption that for coal mines of average methane content lower than the residual methane content of the region, the final release factor is twice as low as the one calculated by equation (8). Release factors from post-mining processes and from waste heaps were not estimated. It is

assumed that all residual methane is released from coal before its final use, so the release factors from post-mining activities are equal to: 9 residual mines in is higher 9 methane mines.

methane c o n t e n t - in those coal which the average methane content than the residual methane content; c o n t e n t - in the remaining coal

However the above assumption is not accurate, since there are no data to identity the volume of methane burned during the final use of the coal. The release factors for waste heaps were established taking additionally into account, that the calculated average content of dispersed coal material in waste rock is equal to 15% (comp. Bolewski & Gruszczyk 1989; PIG 1988). Release factors from degassing systems were also not estimated, as the amounts released to the atmosphere can be precisely measured in coal mines.

432

I. GRZYBEK E T A L .

a) t Wek

[m3/Mgl 5O !

9

4 0 84 Wt"

21.542 G - 3.346 G :

30

~ _ 1,-----,"__'A" _-----"--2"-7-:-'