Sediment-Hosted Mineral Deposits (IAS Special Publication 11)

SEDIMENT-HOSTED MINERAL DEPOSITS

Sediment-Hosted Mineral Deposits Proceedings of a symposium held in Republic of China, 30 July-4 August 1988

Beijing, People's

Edited by John Parnell, Ye

and

Lianjun

Chen Changming

Symposium sponsored by

the International Association of Sedimentologists, the National Natural Science Foundation of China, IGCP

project

219

(Comparative in Space

project

IGCP

SPECIAL

project

BY

to

254

palaeoenvironments), and

(Metalliferous Black Shales)

PUBLICATION

INTERNATIONAL

PUBLISHED

and Time),

226 (Correlation of Manganese

Sedimentation

I GCP

11

NUMBER

OF THE

ASSOCIATION OF SED I MENTOLOGISTS

BLACKWELL

OXFORD

Lacustrine Sedimentology

LONDON

MELBOURNE

SCIENTIFIC

EDINBURGH

PARIS

BERLIN

PUBLICATIONS

BOSTON

VIENNA

©

1990 The International A sociation of Sedimentologists and published for them by

Blackwell Scientific Publications Editorial o(iices:

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First published

1990

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British Library Cataloguing in Publication Data

Sediment-hosted mineral deposits. 1. Sedimentary rocks. Mineral de po sits I. Parnell, John II. Ye, Lianjun )[(. Chen, Changming IV. I ntern a t ional Association of Sedimentologists V. Series 553 ISBN 0-632-02881-5 Library of Congress Cataloguing-in-Publication

Data

mineral deposits: proceedings of a symposium held in Beijing, People's Republic of China, 30 July-4 August 1988/edited by John Parnell, Ye Lianjun, and Chen Changming; sponsored by the International Association of Sedimentologists ... ret a/.]. p. em. (Special publication number J 1 of the International Association of Sedimentologists) Includes bibliographical references and index. Sediment-hosted

-

ISB

0-632-02881-5

I. Ore deposits-Congresses. 2. Metallogeny­ Congresses. I. Parnell, John. 11. Yeh, LienchOn. TIL Chen, Changming. IV. International Association of Sedimcntologists. V. Series: Special pu bli ca tion ... of the International Association of Sedimentologists; no. ll. QE390.S43 1.990 553-dc20 90-674 CIP

Contents

vii

Preface

Manganese and Iron Deposits 3

Groote Eylandt manganese norm: a new application of m�neral normalization techniques on supergene alteration products B. Pracejus

17

Palaeogeographic setting of late Jurassic manganese mineralization in the Molango district, Mexico J.B. Maynard, P.M. Okita, E.D. May and A. Martinez-Vera

31

Manganese and iron facies in hydrolithic sediments G.A. Gross

39

Manganese deposits of the Proterozoic Datangpo Formation, South China: genesis and palaeogeography X. Xu, H. Huang and 8. Liu

51

Manganese enrichment in a Triassic aulacogen graben in the Lijiang Basin, Yunnan Province, China H.Liu

57

Processes of formation of iron-manganese oxyhydroxides in the Atlantis-ll and Thetis Deeps of the Red Sea G. Yu. Butuzova, V.A. Drits, A.A. Morozov and A. I. Gorschkov

73

Mineoka Umber: a submarine hydrothermal deposit on an Eocene arc volcanic ridge in central Japan

A. Iijima, Y. Watanabe, S. Ogihara and K. Yamazaki 89

Mineralogy, geochemistry and genesis of manganese-iron crusts on the Bezymiannaya Seamount 640, Cape Verde Plate, Atlantic l.M. Varentsov, V.A. Drits and A./. Gorschkov

109

Microbiota from middle and late Proterozoic iron and manganese ore deposits in China L. Yin v

vi 119

Co111e111s Metal precipitation related to Lower Ordovician oceanic changes: geochemical evidence from deep-water sedimentary sequences in western Newfoundland J. W. Borsford and D. F. Sangsrer

139

Origin of iron carbonate layers in Tertiary coastal sediments of Central Kalimantan Pro vi nee (Borneo), Indonesia G. R. Sieffermann

147

Mineral deposits in Miocene lacustrine and Devonian shallow-marine facies in Yugoslavia J. Obradovic and N. Vasic

Copper Deposits

159

Syngenetic and paleokarstic copper mineralization in the Palaeozoic platform sediments of West Central Sinai, Egypt M.A. £1 Sharkawi, M.M. £1 Aref and A. Abdel Motelib

173

Geochemical data for the Dongchuan- Yimen strata-bound copper deposits, China

C. Ran

Metal Enrichments Associated with Organic Matter

183

Metal enrichments in organic materials as a guide to ore mineralization J. Parnell

193

Relationships between organic matter and metalliferous deposits in Lower Palaeozoic carbonate formations in China R. Jia, D. Liu and.!. Fu

203

Comparative geochemistry of metals and rare earth ekments from the Cambrian alum shale and kolm of Sweden J. Leventhal

217

Uranium enrichment in the Permian organic-rich Walchia shale, Intra-Sudetic Depression, southwestern Poland

S. Wo/kowicz 225

Index

Preface

This special publication consists of papers delivered

of China (Xu er at.), the Triassic of China (Liu) and

at an International Symposium of the International

the Tertiary of Japan

Association of Sedimentologists, held in Beijing,

specialized aspect of the Proterozoic deposits in

People's Republic of China, from 30 July to 4 August

China, the evidence for a microbial role in manga­

L988. The theme of the symposium was Sedimen­

nese precipitation, is discussed by Leiming. Super­

tology Related to Mineral Deposits and incorpo­

gene manganese mineralization, and in particular

rated meetings of three International Geological

the use of a normalization technique to express it, is

(lijima

er at.). A more

Correlation Programme (IGCP) projects; IGCP 219

described by Pracejus. A review of manganese­

on Comparative Lacustrine Sedimentology in Space

bearing facies in iron formations is provided by

and Time, IGCP 226 on Correlation of Manganese

Gross, and the diversity of iron-bearing deposits is

Sedimentation to Palaeoenvironments, and IGCP

represented by papers on Tertiary siderite formation

254 on Metalliferous Black Shales. Each of these

in Indonesia (Sieffermann) and Devonian oolitic

projects has been very successful and enhanced our

ironstones in Yugoslavia (Obradovi6 & Yasic).

knowledge of economic resources in sedimentary

Two accounts of copper mineralization emphasize

rocks. The papers arc included for convenience

the role of organic matter in a Proterozoic deposit in

under the headings of

(2)

(1)

China (Chongying) and pedogenic

manganese and iron

(3)

processes in

metal enrich­

Palaeozoic deposits in Egypt (EI Sharkawi er at.).

ments associated with organic matter. However,

The significance of organic matter in metal con­

deposits,

copper deposits, and

there is considerable overlap between these themes,

centration is further discussed in accounts of the

and in particular several accounts of manganese

Cambrian alum shales in Sweden (Leventhal) and

deposits involve ores hosted in black shale. The

Permian shales in Poland (Wolkowicz). Character­

papers include five contributions

from Chinese

ization of the organic matter in some Palaeozoic­

workers. The interpretation of many of the exciting

hosted deposits in China is used to infer conditions

ore deposits in China is still at an early stage but we

of ore deposition (Jia et at.), and metal enrichments

have taken this opportunity to present what data are

in organic materials arc considered as an ore pro­

available for some of them.

specting guide (Parnell).

Accounts of manganese mineraljzation include

The Beijing symposium was equally successful in

two papers on Recent manganese and iron deposits

attracting workers who would not normally contri­

in the Red Sea (Butuzova et at.) and the Atlantic (Yarentsov et

at.)

bute to lAS activities, and in emphasizing to sedi­ mentologists

which emphasize the roles of

Auctuating redox conditions and hydrothermal ac­

the economic importance of their

subject. lt is to be hoped that the common ground

tivity respectively. The redox theme is taken up for

between Sedimentology and Metallogeny will be

ancient manganese enrichments in the Jurassic of

further explored.

Mexico (Maynard er at.) and the Ordovician of

JoHN PARNELL, DepartmenrofGeofogy,

Newfoundland (Botsford & Sangster), while fossil

The Queen's University of Bela f st,

hydrothermal activity is invoked in the Proterozoic

Belfast BT7 INN. UK

VII

Manganese and Iron Deposits

Spec. Pubis int. Ass. Sediment. (1990) 11, 3-16

Groote Eylandt manganese norm: a new application of mineral normalization techniques on supergene alteration products B . P R A C EJU S Department of Geology and Geophysics, University of Adelaide, Adelaide, PO Box 498, Australia 5001

ABSTRACT The method described assists in the quantification of oxidic manganese minerals and associated materials from the Groote Eylandt manganese deposits (Northern Territory, Australia) which have been influenced by supergene processes. These ores are commonly composed of very fine grained minerals, intergrown with lateritic components like kaolinitic clays and iron oxyhydroxides. Additionally, many manganese phases are poorly-ordered structures which are difficult to identify. Although Fourier transform infrared (FTIR) spectroscopy has produced dependable data for a limited range of processed ores, it failed with rocks that contained a mixture of ore minerals and various gangue phases, as was the case with other analytical techniques (microscopic studies, XRD, IR, etc.). The normalization is based on the same principles as other mineral norms (e.g. CIPW-Norm) and the norm minerals themselves were developed according to the mineralogical conditions in the supergene manganese deposits of Groote Eylandt in the Northern Territory of Australia. Nevertheless, the list of minerals can easily be extended and adjusted to slightly different environments (e.g. bauxites). The following minerals can be obtained from this normalization technique: romanechite, todorokite, cryptomelane, pyrolusite, anatase, quartz, kaolinite, gibbsite, goethite for hematite-free and hematite-containing samples, hematite, and excess water.

INTRODUCTION

manganese minerals can be found in a paper by Babenko et al. (1983), who quoted calculated min­ eral compositions (partly different from those of this discussion) of manganese ores from Nikopol. Unfor­ tunately, they do not specify the method for their calculations, nor do they state whether or not this is only an approximation. It is not intended here to replace sophisticated analytical techniques, such as FTIR (including com­ puterized infrared characterization of materials: CIRCOM) or differential thermal analysis (DTA), because this would go far beyond the capability of the proposed method. However, the norm provides a tool to process quickly large sample sets, once the calculation procedure has been established in a com­ puter program. The obtained data can then be cor­ related with results from other analyses. The necessary background information for the

Until recently, many researchers examining manga­ nese oxides have had to overcome a number of problems when a quantitative mineralogical analysis of their samples was required for scientific or techni­ cal application. Very commonly manganese ores are extremely fine grained and their manganese minerals possess low crystallinities and are intergrown with other minerals. The crystal structures are not well defined, or hybrid structures exist. This makes quantification and even identification very difficult, because traditional mineralogical techniques, such as ore microscopy, X-ray diffraction (XRD), and the more advanced Fourier transform infrared (FTIR) analysis fail, when confronted with such complex matter. Therefore, a method has been developed which approaches the problem from a theoretical viewpoint (Pracejus et al., 1988a). Indi­ cations for an attempted development of a norm for Sediment-Hosted Mineral Deposits Edited by John Parnell, Ye Lianjun and Chen Changming © 1990 The International Association of Sedimcntologists ISBN: 978-0-632-02881-8

3

4

B. Pracejus

normalization technique has been obtained from Ostwald (1980, 1988) and Pracejus et al. (1988b), who examined the mineralogy and geochemistry of supergene manganese ores from Groote Eylandt in the Northern Territory of Australia. The deposit shows an extensive supergene alteration of the pri­ mary sedimentary sequence, which is mainly com­ prised of oolitic and pisolitic manganese oxides. Because the secondary manganese minerals were precipitated in a number of host lithologies (e.g. manganese ores, sands and sandstones, clays and claystones, iron oxides and oxyhydroxides), they have created a large range of assemblages which obscure the 'real picture' of the quantitative relationships. The deposits of Groote Eylandt contain pyrolusite, cryptomelane, romanechite and todorokite as the main ore constituents. Manganite, vernadite, bir­ nessite, and a number of other manganese oxides can also be identified, but they appear in much smaller quantities (Ostwald, 1988) and are therefore neglected in this theoretical approach. The dominant gangue minerals are quartz, kaolinite, goethite (plus other iron oxyhydroxides) and hematite. These minerals set the frame for the norm model and sensu stricto can only be applied to conditions similar to those of Groote Eylandt (tropical/subtropical supergene alteration of manganiferous protores), but the setup of the norm can easily be adjusted to comparable geological environments (e.g. bauxites). At the moment it is difficult to assess how far this method can be used for manganese minerals of other origins (e.g. deep-sea nodules), but it may prove to be helpful for the understanding of other deposits.

METHODOLOGY

When the first mineral norm (CIPW; Cross et al., 1902) was developed, the complex structure of sili­ cates and many other minerals was not yet known. The chemical composition of minerals was generally described by molecules and the molecular weights of oxides. This idealized approach provides a relatively easy way for a theoretical assessment of mineral quantities in very fine grained rocks or even glass, but it has serious disadvantages when minerals occur in higher amounts in the natural sample which are not covered by the calculation. Nevertheless, de­ posits which are comparable to Groote Eylandt should present no problem for the normalization

procedure. Additional norm minerals such as rhodo­ chrosite (MnC03) or alabandite (MnS) can also be incorporated without difficulty, provided that the necessary carbonate and sulphide analyses are avail­ able. However, the latter compounds can only be found in trace element quantities in Groote Eylandt and thus they only serve as examples for possible extensions of the norm. Often it has not been possible to incorporate specific elements such as potassium, magnesium, aluminium, iron or barium in more than one norm mineral because of strong element variations in a number of host minerals (for instance barium in cryptomelane). The minerals also rely on at least one element for their calculation, and this element is subsequently 'consumed' for the formation of the respective norm mineral. Potassium for instance can be found in cryptomelane, romanechite, todorokite, and also kaolinite, but the normalization uses po­ tassium only for cryptomelane and kaolinite, and all other phases are calculated on a potassium-free basis. This means that relatively small errors are automati­ cally introduced for the remaining minerals which also accommodate potassium. For the same reasons, intergrowths of different manganese oxides had to be neglected (e.g. romanechite-todorokite or romanechite-hollandite; Turner & Buseck, 1979). In the following sections, the various minerals are discussed in the same order in which they should be calculated, because a number of phases depend on preceding minerals for their own calculations. The numbers in parenthesis next to the formulae cor­ respond to the steps shown in Figs 1(a)-(d). To simplify the understanding of the norm, two example calculations are shown in Table 1 (manganese ore) and Table 2 (iron ore). The norm calculation commences with the division of the weight percentage of the analysed elements by their molecular weight. The result will be called mol equivalent (ME). As the ME is represented by fairly small numbers, it is multiplied by 1000 (ME 1000). The latter step is not necessary, but it makes handling easier for separate calculations which are not done by the computer. The next step distributes the ME 1000 product to the various norm minerals. The consumption of the appropriate el­ ements must be calculated after each step. The addition of each oxide that is needed to produce one mineral is followed by a division of the sum of all ME 1000 products of the total of the analysis, and a multiplication by 100 to produce the final mineral percentages.

5

Groote Eylandt manganese norm 3

(a)

(4)

Print gb

1

Fig. l(a). Flow diagrams of mineral normalization, calculated from chemical analyses. For explanatioll of abbreviations see text.

Fig. l(b).

=

0%

no

(11)

5

Fig. l(c). Normalization flow (continued). As every chemical analysis contains an analytical error, the reliability on the final results may not exceed one decimal place or even less. Despite these limitations it is advisable to calculate the norm to two decimal places, as this improves the quality of diagrams which otherwise might be distorted. Errors that could develop from the necessary simplifications for some of the minerals are in most cases negligible, especially when ores of the same type are being compared, because the errors will also be compar-

able. The basis on which each mineral is calculated is printed in bold. The nomenclature of this norm has been chosen in such a way that mineral abbrevi­ ations of already existing norms are not duplicated where possible. Anatase (an): Ti02

(1)

The mineral anatase is used instead of rutile (also Ti02), because it is the main constituent in bauxitic and lateritic soils (Bardossy, 1982). At present,

7

Groote Eylandt manganese norm

no

Print: check for additional minerals and correct input

(

)

D /

Input, Output Decision

(1)

Calculation, Step

yes

7

Print

�

Flow Direction

J_

Joint

Fig. l(d). Normalization flow (continued) and legend for Fig. l(a to d).

Quartz (q): Si02 Ti02 is calculated as a separate phase. However, later developments of this normalization might lead to an incorporation of Ti02 into kaolinite, because it has an excellent correlation with the latter mineral.

(2)

A decision has to be made as to whether or not there is excessive quartz. This will also be the basis for the determination of kaolinite and gibbsite. In the system quartz (q) - kaolinite (ka) -gibbsite (gb) no more

00

Table l. Normalization procedure for manganese oxide orcs

Mn-Orc Mn02 Fc203 Si02 AI20, P20o KzO CaO SrO BaO Ti02 Na20 MgO LOI L

Wt'Y.,

At. wt

ME 1000

72-3 1·5 5-4 4·7 0·07 1·29 0·05 0·21 2-46 0·15 0·20 0·5 11·2

86·936 159·692 60·084 101·961 141·944 94·203 56·079 103·619 153·339 79·898 61·979 40·304 18·015

831·6 9·4 89·9 46·1 0-49 13·7 0·9 2·0 16·0 1·9 3·2 12-4 621·7

an

1·9

Norm Wt% Mn02 Fez03 Si02 Alz03 Pz Os K20 CaO SrO BaO Ti02 Na20 MgO LOI L

Norm

72-3 1·5 5-4 4·7 0·07 1·29 0·05 0·21 2-46 0·15 0·20 0·5 11·2 100·0

At. wt

ME 1000

86·936 159·692 60·084 101·961 141·944 94·203 56·079 103·619 153·339 79·898 61·979 40·304 18·015

831·6 9·4 89·9 46·1 0-49 13·7 0·9 2·0 16·0 1·9 3·2 12-4 621·7 1649·3

q

/"-,

ka

/"-,

0·0

89·9

4·2 89·9 44·9

5·2 0·0 1·2

0·4

13·3

89·9

531·8

/"-,

gb

1·2

0·0

3·5

530·2

/"-,

he

/"-,

gt (II)

5·2

0·0

0·0

0·0

0·0

5·2

525·1

gt (I)

0·0 0·0

10-4 0·6

4·6 0·3

229·3 13-9

em

/"-,

rm

/"-,

to

/"-,

pr

248·3

583·3

105·6

477-7

54·9

422·8

422·8

13·3

0·0

2·0

0·0

/"-,

bJ

P20s

16·0

32·0 153·6 9·3

0·9

0·0

3·2 12-4 49·5

0·0 0·0 443-6

/"-,

w

/"-,

L

;:: "'

0·0

0·0

493·1

120·9 7·3

211-4 634·2 38·5

'"i:l

;:; '"'

�

0·0

0·49

263-6 16·0

/"-,

0·0

1·9 0·1

1649·4

100·0

6

232·2

232·2 0·49 0·03

232·2 14·1

0·0

100·1

Table 2. Normalization procedure for iron oxyhydroxide ores

Fe-Ore Mn02 F�03 Si02 AI203 P20s K20 CaO SrO BaO Ti02 Na20 MgO LOI W Corr. L

Wt% 1-4 73·7 4·9 7·7 1·17 0·08 0·01 0·01 0·01 0·36 0·01 0·01 10·7

At. wt

ME 1000

86·936 159·692 60·084 101·961 141·944 94·203 56·079 103·619 153·339 79·898 61·979 40·304 18·015

16·1 461·5 81·6 75·5 8·2 0·8 0·2 0·1 0·1 4·5 0·2 0·2 593·9 593·9

100·0

L

Norm

4·5

6.

4·5 0·4

6.

ka

6.

0·0

81·6

3·5 81·6 40·8

458·0 0·0 34·7

0·3

0·5

gt (I)

6.

458.0 34·7

6. 0·0

he

6.

51·8

406·2

gt (II)

6.

406·2 0·0

0·0

0·0

C)

..., C) C)

0·0 0·0

Wt%

At. wt

ME 1000

em

6.

rm

1·4 73·7 7·7 1·17 0·08 0·01 0·01 0·01 0·01 0·01 10·7

86·936 159·692 101·961 141·944 94·203 56·079 103·619 153·339 61·979 40·304 18·015

16·1 461·5 75·5 8·2 0·8 0·2 0·1 0·1 0·2 0·2 593·9 593·9

15·3

0·8

0-4

1242·9

16·3 1·3

100·0

gb

q

81·6 81·6

1243·0

Norm

Mn02 F�03 Ah03 P20s K20 CaO SrO BaO Na20 MgO LOI W Corr.

an

0·8

0·0

0·1

0·0 0·1 0·2 0·2 0·7 0·1

512·4 512·4

207·7 16·7 6.

0·3

104·2 408.2 104·2 408.2

458·0

139·0 11·2

916·0

to

6.

pr

2·0

-1·6

0·0

0·2

0·0

0·2 0·2 1·8 1·8

0·0 0·0 -51·8 0·0

�

-49·8 406·2 2·0

6.

812·4 65·4

51·8 4·2

P20s

6.

8·2

0·0

w

6.

L

0·0

�

El ;:;

� 2l

1:> ;:; C1Q 1:> ;:; "' "' "' ;:; C) ...,

�

0·0 -50·0 1·8

4·3 0·3

0·0 0·0 0·0 0·0

-51·8 0·0

-51·8 0·0 8·2 0·7

0·0 0·0

0·0 100·2

'D

lO

B. Pracejus

than two minerals can be in equilibrium at one time (Kittrick, 1969). In aqueous systems kaolinite will form at the expense of either gb or q. This means that q � 0 when gb = 0 or q = 0 when gb � 0 in the present calculation. Under natural conditions this thermodynamic rule can be broken because of the slow reaction kinetics of the involved mineral species. Nevertheless, the final stage will lead to a two mineral configuration which will be accounted for in this calculation. The decision mentioned above depends on a preliminary calculation of kaolinite (only step 3a!). The result will indicate excess quartz (remaining Si02) or an overestimated consump­ tion which will lead to no quartz, but also to the calculation of gibbsite (4). Kaolinite (ka): AhSi205(0H)4 ::::} Al203 + 2Si0z + 2Hz0 ::::} Si02 + 1/2Al203 + H20

(3a) (3b)

Depending on the result of the previous decision, kaolinite will either be determined �rom (3a) or (3b). If there is excessive quartz, then kaolinite is calculated on the basis of the available alumina. In the case of a quartz deficiency, the mineral relies on the total silica content of the sample and there will be free alumina for the formation of gibbsite as an additional phase (4). Analyses of reasonably pure clay samples have shown that the kaolinite from Groote Eylandt contains �1·7% FeO and �0·17% K20. These values are incorporated in the final result of the kaolinite calculation. The latter two steps should be investigated for materials from other deposits and adjusted accordingly. Because these compounds are relatively low in their concentration, they could also be omitted from this part of the norm. Gibbsite (gb): 2Al(OH)3::::} Alz03 + 3H20

(4)

The conditions for the stability of gibbsite have already been discussed in context with quartz (2) and kaolinite (3). Although this mineral has been described as an accessory from the deposits on Groote Eylandt, it has to remain a theoretical phase under the present normalization program, because it is not known to what extent the excess alumina is incorporated in minerals like goethite or hematite. If excess quartz has been determined, then gibbsite does not exist. Cryptomelane (em): Ks1Mn801r, ::::} K20 + MnO + 15Mn02 Correlations with SrO strongly suggest that stron-

tium is incorporated in the lattice of the cryptome­ lane, and the size of its ionic radius (within a range of ± 15% ) implies that strontium can substitute for potassium. This is also in accordance with Post et a!. (1982), who discussed a cryptomelane with the fol­ lowing formula: (K0.9 Nao.zsSro.nBao.t) (Mn, Fe, 4 Al)8(0, OH)16. Because cryptomelane at Groote Eylandt varies in its barium content, and also because barium is needed for the calculation of romanechite, this element will not be used here. The same applies for sodium which is taken for the development of todorokite. The following oxide formula will be used: (K20 + SrO) + MnO + 15 Mn02

(5)

A small amount of potassium has been used in the kaolinite calculation. Therefore it may happen that manganese samples with a very low cryptomelane content will give a result of em = 0. Theoretically, such a sample could be calculated on the basis of the strontium content, if present, but the normalization procedure neglects cryptomelane if there is no po­ tassium. Separate strontium minerals such as celestite have not been detected in the deposit. MnO is calculated from the total Mn02 analysis, because it had not been determined for the Groote Eylandt 2 samples. However, if an analysis of Mn + is avail­ able, it should preferably be used. Romanechite (rm): Baz[Mnl+ Mn114+030]·4H20 ::::} BaO + Mn203 + 5·5Mn02 + 2H20 (6) The barium content of the sample is taken as the basis for the romanechite calculation (Burns & Burns, 1977; Giovanoli & Balmer, 1983; Burns et a!. 1985). Mn203 is calculated from the total Mn02 content, as is the case for the previous mineral for MnO. The strongly varying K20 contents of ro­ manechite in Groote Eylandt (Ba0/K20 ratios of 1·8-34·7; Ostwald, 1988) have been neglected in favour of cryptomelane, because no consistent values could be obtained. Todorokite (to) This mineral seems to be fairly complicated, having different compositions in different deposits. A num­ ber of formulae have been proposed by various authors: 2 2 (Ca, Na, K, Mn +)(Mn4+, Mn +, Mg0)r,01z·3Hz0 after Straczek et a!. (1960); 2 (Ca, Na, K, Ba, Mn +)Mn5012·3H20 after Burns & Burns (1977);

11

Groote Eylandt manganese norm

2 (Mn +, Zn, Mg, Ba, Sr, Ca, Na2, K2, Cu, PbhMn104+023·9H20 after Larson (1962). Calculations of analytical results from Groote Eylandt ores demonstrate that a high number of rock samples show a very limited interval of the ratio between calcium, sodium and magnesium (Ca + Na20)/Mg0 0·30-0·34. This indicates a strong structural association of these three elements, which most probably is due to a concentration in one single mineral. Although some samples contain ex­ cess MgO when compared with the ratio mentioned above, no correlation to any other mineral has been found for this element. Therefore calcium, sodium and all the magnesium will be taken as the basis for the todorokite calculation. The error is fairly small, which is introduced knowingly by the incorporation of all the magnesium into todorokite, and it saves the normalization from further complications. Fronde! et al. (1960) and Straczek et a!. (1960) reported significant amounts of magnesium in todorokites. The author favours the composition quoted by Larson (1962) because it contains all the elements that are believed to play an important role in the todorokite under investigation. This formula will be shortened and adjusted in the following way: =

(Mg, Ca, NazhMn104+0z3'9HzO =? (MgO, CaO, Na20) + 3·33Mn0z + 3Hz0 (7)

Pyrolusite (pr): Mn02 =? MnOz + xHzO (x = 0-0·5)

(8)

Pyrolusite, the last manganese phase, is calculated from the remaining manganese which has not been consumed by the previous minerals (em, rm, to). Correlation plots between pyrolusite and excess water also led to the additional incorporation of up to 50% water, although water does not take part in the structure of pyrolusite. However, this finding is in accordance with analytical results from Gryaznov & Danilov (1980) and Ostwald (1988). It is assumed that the pyrolusite lattice contains micro-inclusions of <XMnOOH or yMnOOH, which thus result in a larger loss on ignition (LOT) than expected. As indicated by x = 0-0·5 for the water portion of the norm mineral, the water content of pyrolusite can be variable. Normally the excess water of the sample will be larger than 50% of the remaining manganese (after the calculation of the previous manganese minerals) and therefore, the 'inclusion water' can easily be accommodated, where a small amount of water is left. In a few cases however, less water is available at this stage of the calculation, and

all remaining water is then added to the manganese component of the formula above. Goethite (gt) (1): 2FeOOH =? Fe203 + H20 (9) Goethite is calculated from the remaining iron (a small amount has been used for kaolinite) and its equivalent to water. As there are many samples which have undergone oxidation, it is necessary to adjust the goethite content in a later step (11). The decision for this correction is based on step (10). If an adjustment has to be made, then it will result in the production of hematite. XW

Structural water (xw): =? LOI - HzO[ka. gb, gt,

rm,

to]

(10)

The LOI and most of the previous water-containing phases are used for a first approximation of the remaining structural water in goethite. The only exception in this calculation is pyrolusite, because of its variable water content. If the value of the calculation becomes negative at this stage, it is an indication for the formation of hematite in iron-rich samples. Therefore this operation is essential for the adjustment of goethite in step (11) and for the establishment of hematite (12). The LOI of the Groote Eylandt ores relates entirely to water-bearing phases, because other compounds such as carbon­ ates are absent in the deposit or exist only as traces. Goethite (gt) (II): 2Fe00H =? Fe203 + HzO - 21 xw I

(11)

If hematite replaced goethite, then the amount of goethite must be corrected. This is done by a correc­ tion with the help of negative structural water. Hematite (he): Fe203 =? I

xw

I

(12)

In the case of oxidized goethitic rocks where hematite has formed, the amount of Fe203 is equivalent to overestimated structural water from step (10). Phosphorus: PzOs

(13)

All P205 is normalized only, and it is not put into a mineral. The most appropriate phosphate mineral which has been described from Groote Eylandt is vivianite (hydrated iron phosphate), but it is very rare and it will not be calculated as a separate phase. Further treatment will have to rely on correlations with other minerals where it may be incorporated. This phase is not essential for the normalization and can be omitted in most cases as long as the amount in the sample is negligible.

12

B. Pracejus 1.2

�·

1.0

�

0.8

� .s

0.6

"' " ...:

..

Excess water: w :::} LOI - HzO [ka, gb, gt, rm, to, prJ (14)

..

' �. .. · \, .. .

'· .

The final determination of excess (free ) water is based on the LOI and all water-containing phases.

.

.

·

0.4 I..

0.2 0.0 0

. •.

.

t,"

,-y· 20

. : ... : � · ·' . . · ·

40

...

. . . . .

Final sum: L :::} L (norm minerals)

,

60

80

Normally it is not necessary to calculate the sum of the normalized minerals, because the result should be very near to 100% , if existing and normative minerals coincide. Deviations of more than ±2% are considered to be indicative of analytical mistakes, erroneous input, or additional minerals that contain elements which have not been accounted for in the normalization (e.g. organic remains) . The latter case might be camouflaged by a larger LOI and could

100

Kaolinite[%] Fig. 2. Correlation between norm minerals kaolinite and

anatase (n

=

20

364).

40

ka [%]

4

8

gb [%]

20

40

gt[%]

60

1

3

2

(15)

4

0.4

P205 [%]

he [%1

0.8

Fig. 3. Vertical geological cross­

10

20

em[%]

1

2

rm[%]

1

2

to[%]

3

25

50

pr [%]

75

10

20

w[%]

30

section from Groote Eylandt showing the distribution of normalized gangue and ore minerals.

13

Groote Eylandt manganese norm

probably go undetected. Nevertheless, it is a quick way of checking the correctness of the norm result (statistics of a large batch of samples: n = 364, 0 99·82, max = 102·24, min 98·7, SD 0·529). Rhodochrosite and alabandite are examples of additional manganese minerals which could easily be incorporated into the previous calculation flow before pyrolusite (step 8). These minerals do not exist in Groote Eylandt, but are mentioned as examples for the development of additional norma­ tive phases. Such minerals may be required for the examination of other deposits. Other more complex manganese phases require an exact knowledge about the element(s) that can be taken as the calculation basis. =

=

=

Rhodochrosite (rh): MnC03 =? MnO + C02 (7b) Alabandite (ad): MnS =? Mn + S

(7c)

EXAMPLES

The previous sections have demonstrated the nor­ malization procedures in detail. A few possible ap­ plications are shown below. The first one is a simple correlation plot between kaolinite and anatase (Fig. 2). A similar plot can be obtained by correlating

Ti02 (not normalized) with Al203, but silica, which is also part of the kaolinite, will produce ambiguous results (both a positive and a negative trend) when correlated with Ti02. The normalization however is able to split the silica in the calculation and produce free quartz which can later be related to other minerals, for instance to heavy minerals in the sand fraction. The quartz content may also be used to detect and estimate trace element contaminations that derive from grinding procedures (e.g. tungsten from a tungsten-carbide mill). Other analysed el­ ements, such as trace elements and rare earths, allow a detailed insight into the relationships be­ tween the various minerals and elements. The next example shows a vertical geological profile and the distribution of norm minerals (Fig. 3). The samples were taken from a section on Groote Eylandt and they represent a sandwich-like structure of manganese ores that are replaced by iron on top and at the bottom of the unit. Easily detectable is a separation of minerals and a preferential develop­ ment of specific phases at different horizons. Dia­ grams like this can provide genetic information, for instance for overprinting supergene processes. A third way of using the norm is its application on ternary diagrams (Fig. 4). Here the ore or gangue minerals can be plotted for rock types, and fields for

2.5

rm

Fig. 4. Ternary plot of manganese oxide norm minerals for some manganese ore types from Groote Eylandt.

pr

em+

to

14

B. Pracejus 30 .-------� • 12th week o 17th week

s

Q,

•

20

•

..:::

:::;

••

• •

+ N c

•

•

0

10

•

Fig. o +-----�----�--4 0

10

20

Norm Mineral [%] individual rocks can be produced. Such diagrams can also provide valuable ideas about formation conditions for minerals. In the last example the norm was used to monitor the successive time-related breakdown of manganese phases during microbiological leaching tests (Fig. 5; after Pracejus et al., 1989). It can be observed that the thermodynamically least stable manganese oxides are also the first to become unstable during the leaching procedure, that time gaps exist between the breakdown of the individual minerals, and that pyrolusite (not plotted here), the most stable phase of the examined system, seems to resist the microbial reduction.

DISCUSSION

Above, the development of a number of normative manganese phases and associated gangue minerals has been discussed using the example of supergene manganese oxide ores from Groote Eylandt. The method has been applied with success to over 600 partially very complex ore/rock samples ( =20 differ­ ent types), and the results of this normalization procedure are promising. However only further work on materials from other deposits can test the wider applicability of this technique. The examples that were given above demonstrate the practical use of the method, but it must be added that a mineral norm should only be an aid in cases where other methods of quantification have failed, are very diffi­ cult to obtain or are too expensive. Such a theoretical technique must always go hand in hand with studies

30

5. Time-related breakdown of two manganese oxides (norm minerals) from Groote Eylandt, exposed by dissolved manganese during microbiological leaching tests. (After Pracejus et al., 1990.)

of the relevant deposits and should come as close as possible to the natural conditions of the rocks/ores, otherwise the results are superficial and of no use.

ACKNOWLEDGEMENTS

This paper is a contribution to IGCP project 226. The Australian UNESCO Committee has provided financial assistance through Grant-in-aid 1988, which is gratefully acknowledged. I am thinkful to Dr R. Burns (Massachusetts Institute of Technology) and to Dr A. Kleyensttiber (Mintek, South Africa) for their helpful comments on the manuscript. REFERENCES L.M. & SEREBRYANAYA, M.Z. (1983) Characteristics of the bacterial breakdown of primarily oxidized manganese ores from the Nikopol deposit. Mikrobiologiya, 5215, 851-856. BARDOSSY, G. (1982) Karst Bauxites: Bauxite Deposits on Carbonate Rocks, p. 441. Akademiai Kiad6, Budapest. BURNS, R.G. & BURNS, V.M. (1977) Mineralogy of manga­ nese nodules. In: Marine Manganese Deposits (Ed. by G.P. Glasby), pp. 185-248. Elsevier, Amsterdam. BURNS, R.G., BURNS, V.M. & STOCKMAN, H.W. (1985) Tl.e todorokite-buserite problem: Further consider­ ations. Am. Mineralogist 70, 205-208. CROSS, W., IDDINGS, P.J., PIRSSON, L.V. & WASHINGTON, H.S. (1902) Quantitative Classification of Igneous Rocks, pp. 286. Chicago University Press, Chicago. FRONDEL, C., MARVIN, U .B. & ITo, J. (1960) New occur­ rences of todorokite. Am. Mineralogist 45, 1167-1173. GIOVANOLI, R. & BALMER, B. (1983) Darstellung und Reaktionen von Psilomelan (Romanechit). Chimia 37(11), 424-442. BABENKO, Y.S., DOLGIKH,

Groote Eylandt manganese norm V.I. & DANI LOV , I.S. (1980) Oxidized manga­ nese ores of the Nikopol manganese deposit, Ukranian SSSR. In: Geology and Geochemistry of Manganese (Ed. by l.M. Varentsov & G. Grassely), Vol. 2, pp. 403-416. E. Schweizerbartsche Verlagsbuchhand­ lung (Nagele & Obermiller), Stuttgart. KITTRICK, J .A. (1969) Soil minerals in the Al203- Si02H20 system and a theory of their formation. Clay and Clay Minerals 17, 157-160. LARSON, L.T. (1962) Zinc-bearing todorokite from Philips­ burg, Montana. Am. Mineralogist 47, 59-66. OsTWALD, J. (1980) Aspects of the mineralogy, petrology and genesis of the Groote Eylandt manganese ores. In: Geology and Geochemistry of Manganese (Ed. by I.M. Varentsov & G. Grassely), Vol. 2, pp. 149-58. E. Schweizerbartsche Verlagsbuchhandlung (Nagele & Obermiller), Stuttgart. OSTWALD, J. (1988) Mineralogy of the Groote Eylandt manganese oxides: A review. Ore Geol. Rev. 4, 3-45. PosT, J.E., VoN DREELE, R.B. & BusEcK, P.R. (1982) Symmetry and cation displacements in hollandites: Struc­ ture refinements of hollandite, cryptomelane and pride-

GRYAZNOV,

15

rite. Acta crystallog. 38, 1056-1065. & FRAKES, L . A. (1988a) Mineral normalization for supergene Mn-oxides and associated rocks on ores from Groote Eylandt, NT, Australia. !AS Symposium on Sedimentology Related to Mineral Deposits 1988 (Abstract), p. 202. Beijing, China. PRACEJUS, B., BOLTON, B.R. & FRAKES, L.A. (1988b) Nature and development of supergene manganese de­ posits, Groote Eylandt, Northern Territory, Australia. Ore Geol. Rev. 4, 71-98. PRACEJUS, B., VARGA, R.A., MADGWICK, J.L., FRAKES, L . A. & BoLTON, B.R. (1990) Effects of mineral com­ position on microbiological reductive leaching of man­ ganese oxides. Chern. Geol (under review). STRACZECK, J.A., HOREN, A., Ross, M. & WARSAW, C.M. (1960) Studies of the manganese oxides- IV, Todorokite. Am. Mineralogist 45, 1174-1184. TuRNER, S. & BuSECK, P.R. (1979) Manganese oxide tunnel structures and their intergrowths. Science 203, 256-458.

PRACEJUS, B., BOLTON, B.R.

Spec. Pubis inr. Ass. Sediment.

( 1990)

11, 17 -30

Palaeogeographic setting of late Jurassic manganese mineralization in the Molango district, Mexico J . B . M A YNA R D*, P . M. O K I T A*, E . D . MA yt and A. MA R T I N EZ- V E RA * *"�"Department of Geology, University ofCincinnati 13, Cincinnati, OH 45221, USA; *Cia. Minera Aut/an, S.A. de C. V., Mariano Escobedo 456, Mexico, DF 11590

ABSTRACT

A large sedimentary deposit of manganese carbonate formed during the late Jurassic in eastern Mexico. Throughout the Mesozoic, deposition in this area was in fault-bounded basins with considerable relief. Both clastic and carbonate sediment was derived from adjacent highs. The manganese ores were deposited in the slope facies of a shelf-basin transition in water deeper than storm wave base. Rocks below the ore were deposited in a euxinic basin; rocks above the ore in a more oxidizing, but still suboxic basin. Manganese was mobilized in deeper, low-oxygen water, then precipitated as manganese oxide on contact with shallower , oxygen-rich water. Manganese carbonate formed diagenetically from the manganese oxide via reduction by organic matter and iron sulphide. Because organic matter was in excess, no primary manganese oxide survived early diagenesis.

INTRODUCTION

The predominance of carbonate ore in the Molango di strict i s in contra st to better-known giant mangane se depo sit s such a s Chiatura and Groote Eylandt where mo st production i s from primary oxide s (Force & Cannon, 1988). Recent model s for the gene si s of the se large depo sit s have empha sized the importance of geometry and degree of oxygen­ ation of the ba sin for concentrating large volume s of mangane se (Cannon & Force, 1983; Frake s & Bolton, 1984; Bolton & Frake s, 1985; Force & Cannon, 1988). Becau se mangane se i s soluble a s 2 Mn + under reducing condition s but in soluble a s a solid such a s Mn02 under oxidizing condition s ( Maynard, 1983), a euxinic marine ba sin such a s the Black Sea can accumulate large amount s of mangane se in solution in deep water, mangane se that i s available for precipitation at the interface between oxygen-bearing surface water and H2S­ bearing deep water. Wherever thi s anoxic-oxic boundary inter sect s the edge of the ba sin, there i s a potential for mangane se enrichment in the sediment s. In thi s paper we will examine the stratigraphic and

Upper Jura s sic rock s of ea st-central Mexico are ho st to several sedimentary mangane se ore depo sit s that compri se the Molango di strict. Centred on the town of Molango, the di strict produce s mangane se car­ bonate ore from one mine at the village of Tetzintla and supergene oxide ore from several smaller oper­ ation s. The di strict cover s an area of about 25 x 50 km (Fig. 1) and ha s been in production since 1968, with Compania Minera Autlan the major operator. DeYoung et a/. (1984) e stimated the total re source to be 1·5 billion metric ton s of mangane se. In 1982, 183 000 ton s were mined, making Mexico the world's eighth large st producer of mangane se. Carbonate ore s make up the bulk of the production, 700 000 ton s of ore compared with 34 000 ton s of oxide s in 1987 ( Jone s, 1986), but the supergene oxide s are a much more valuable product becau se of their suitability for u se in dry-cell batterie s. * Present address: MS 954, National Center, US Geo­ logical Survey, Reston, VA 22092, USA. t Present address: Chevron USA, PO Box 6056, New Orleans, LA 70174, USA.

Sediment-Hosted Mineral Deposits Edited by John Parnell, Ye Lianjun and Chen Changming © 1990 The International Association of Sedimcntologists ISBN: 978-0-632-02881-8

17

J. B. Maynard et a!.

18 'g

.'g

r:2:.2-=00 .::c --"-0· --- · C iudad

·o 0

.......

0 "' Ol

0 Ol Ol

�

�

(

•

T ampico

�·�--------1-----,�-��

Valles

,�I

;...

"'J p, "'q:/, .,� 3i -4. 21° 30' \--t--- ----' (/)

6

..

4

to

to

2 0

Chipoco ..

�

.. to

0

�

;;$�!... 1

to

2

•

PALAEOGEOGRAPHY ·

to

8 7 6 5 3 4 Organic carbon wt. %

• Black shale

"'Rhodochrosite

9

10

to Limestone

Fig. 3. Relationship of sulphide sulphur to organic carbon in ore and host rocks. The positive intercept on the sulphur axis for samples from the 'Santiago' Formation implies deposition under euxinic conditions; the lower sulphur concentrations and intercept of the sulphur/carbon correlation line near the origin for Chipoco facies samples implies less reducing, probably suboxic conditions. . Redrawn from Liu ( 1990).

The sedimentological and geochemical data summar­ ized above suggest a depositional model for the Molango ore (Fig. 4) in which the ore was deposited on the slope in a shelf-basin transition. The San Andres Member is representative of the shallow shelf, the Chipoco facies represents the slope, and the Taman Formation at the town of Taman is representative of the deepest part of the basin in the Kimmeridgian. The rapid facies transitions and abundance of clastic material suggest a rimmed shelf rather than a carbonate ramp, following the classi fi­ cation scheme of Read (1985). The ideal facies sequence for this setting is tidal flat/lagoon-rim

Manganese mineralization, Mexico

25

0

Sections studied 1. Nonoalco 2. Te tz:i ntl a 3. Acoxcatlan

4. Totonicapa 5. Taman

6. Huitepec

Fig. 4. Depositional model for the Molango area. Ore deposition occurred on the slope on the west side of a chain of islands. The other slope facies shown on the diagram are not exposed and are only inferred from the shelf facies at Amixco reported by Aguayo-C. (1977).

with blanket shoal-escarpment-talus-mud gullies-proximal turbidites-distal turbidites­ pelagics. The San Andres Member contains lith­ ologies typical of the first two facies, the Chipoco facies represents the mud blanket environment with packages of proximal turbidites, and the rocks at the town of Taman are the distal turbidites. The base­ of-scarp talus is conspicuously lacking, but it is a

dominant feature in similar deposits of the Alps ( Eberli, 198 7). The Alpine sequence seems to have formed in a similar tectonic setting to that of eastern Mexico, is of early Jurassic age, and contains manganese enrichments ( Germann, 19 73; Jenkyns 1988). The southern part of the Gulf of Mexico seems to have lacked biohermal accumulations in shallow-water facies in the Jurassic, unlike the Alpine

J. B. Maynard et a!.

26

sequences ( Wilson, 1975; Crevello & Harris, 1984). This absence of frame builders perhaps accounts for the absence of base-of-escarpment talus in the Molango district. Deeper-water sponge reefs are common in the Jurassic, and may have been the upslope source of the prominent spiculite horizons seen at the Tetzintla mine. Changes in lithology with time in the Molango district can be attributed to a nearly continuous rise in sea level. Worldwide, sea level was rising throughout the middle and late Jurassic (Vail et at., 1984, fig. 2; Hallam, 1989, fig. 10). The total rise over this time interval was about 50-100 m. Super­ imposed on this trend of rising sea level are several shorter regressive episodes. Hallam (1989)identi fied a regression at the end of the Callovian and two in the Oxfordian, with a pronounced transgressive event in the middle Oxfordian. The Vail et al. (1984) curve only identifies a late Callovian unconformity, followed by a smooth rise of sea level into the late

Kimmeridgian (see Hallam & Maynard, 1987, for a further discussion of the differences in these two sea-level curves for the mid to late Jurassic). In the Molango district, the Tepexic Formation is the shallowest marine facies, and indicates the onset of the Callovian transgression. The Tepexic Formation passes upwards gradually into the deeper-water sediments of the 'Santiago' Formation, but the change from dominantly carbonate to dominantly clastic sediments suggests that there was tectonic movement, accentuating the relief between adjacent highs and lows,and that the highs provided abundant fine clastics. Most of the 'Santiago' deposition in the study area occurred during the Callovian. A brief regressive episode, correlative with one of Hallam's (1989) Oxfordian regressions, may have occurred at the top of the 'Santiago', where grain size becomes coarser, a shelly fauna appears, and wood fragments are common. This event may correspond to the Buckner red bed-anhydrite sequence intercalated in

--s- Tithonian Sea Level

Kimmeridgian Sea Level

50

0 Km

PRE-JURASSIC BASEMENT

Fig. 5. Generalized palaeogeographic model for eastern Mexico during the late Jurassic showing progressive flooding. Ore deposition began abruptly at the beginning of the Kimmeridgian, perhaps reflecting access of the basin to an external supply of manganese such as the spreading centre in the newly opened Gulf of Mexico. (Based on Padilla y Sanchez, 1982, fig. V7, and Aguilera-H, 1972, fig. 1.)

Manganese mineralization, Mexico the underlying Smackover ( Oxfordian) and overlying Haynesville ( Oxfordian- Kimmeridgian) Lime­ stones of the northern Gulf region (Faucette &Ahr, 1984, fig. 3). The return to carbonate deposition in the Taman-Chipoco-San Andres interval can be attributed to sea level rising to the point that most highs were covered by seawater and began exporting carbonate debris to deeper water, in the same way as the Bahamas do today. As reconstructed by Boardman & Neumann (1984) and by Boardman et al. (1986), the Bahama Banks act as a carbonate factory when bank tops are flooded during high stands of sea level, exporting fine carbonate mud, largely aragonite, to the deep water between the banks. During low stands, the bank tops are subject to karstic erosion, little material is washed over the rim into deep water, and only a pelagic calcite component is seen in the sediments adjacent to the banks. For eastern Mexico, the low stand time would have seen abundant clastics produced by weathering of the exposed basement and pre-Jurassic clastic deposits, a supply that was mostly shut off in the Kimmeridgian. The Pimienta Formation reflects the continuation of this process to maximum flooding of the bank tops (Fig. 5).

IMPLICATIONS FOR METALLOGENESIS

Manganese mineralization in the Molango district is con fined to the slope facies of a shelf-basin tran­ sition. Neither the shelf nor the basin facies show manganese enrichment, and the mineralization is continuous along the exposed trend of the slope facies. Vertically, manganese appears abruptly at the transition from a euxinic black shale to a suboxic shale-limestone sequence at a time of rising sea level. These patterns are consistent with the strati fied basin model of manganese deposition described by Force & Cannon (1988): manganese was soluble in deep water, precipitated at the oxic-anoxic boundary, and settled back through the water column as manganese oxide particles. Over most of the basin, these particles redissolved, but in shal­ lower water on the basin slope they reached the bottom sediment, de fining a manganese oxide com­ pensation depth. In a refinement of the Force & Cannon model, Okita et at. (1988) proposed that reaction with organic matter during early diagenesis converted the manganese oxides to manganese carbonates.

27

At Molango, in contrast with other large deposits, all the manganese oxide was converted to carbonate. Perhaps the proximal oxide facies has been lost by subsequent erosion, but one would expect some remnant over such a large district. The balance between manganese oxide and manganese carbonate in a deposit is most likely controlled by the rate of supply of Mn02compared with the rate of supply of organic matter at the time of deposition. If available carbon exceeds one-half the (molar) amount of manganese, then all oxide will be converted to carbonate. Mineralization at Molango appears to have occurred on a steeper palaeoslope in deeper water than in the deposits at either Chiatura or Groote Eylandt (Force & Cannon, 1988). Molango was entirely below normal wave base, whereas other deposits show abundant evidence of wave activity (Bolton et at., 1988). Consequently, organic matter preservation should have been better at Molango than at the other deposits, an idea supported by residual Corg values between 0·5 and 1·0% (Liu, 1990). The sudden appearance of manganese and its gradual disappearance also needs explanation. If the progressive flooding model presented above is correct,the basin should have experienced increasing communication with adjacent basins through time in the late Jurassic. The vertical sequence suggests that at the beginning of the Kimmeridgian, the depth of water in the basin exceeded a sill depth that allowed communication with an external source of manga­ nese. One possible source would be a spreading centre in the Gulf of Mexico ( Pindell, 1985). In­ creasing water depth then led to a gradual improve­ ment in the ventilation of deep water in the basins and a consequent decrease in the amount of manganese in solution.

ACKNOWLEDGEMENTS

Special thanks are due to E. Force, who first sugges­ ted this project to us, and to R. Alexandri, who made the field work possible. R. Imlay identified an early collection of bivalves, and we are grateful for being able to bene fit from his years of experience with the Jurassic of Mexico. J. Calloman was kind enough to identify our collection of ammonites, and T. Hallam joined us in the field to help with fossil identi fications and with environmental re­ constructions. We are particularly appreciative of his sharing his insights into Jurassic palaeogeography

1. B. Maynard et al.

28

a nd of t he oppo rtu nity to compa re our respective expe rie nces w hile i n t he field, co nf ro nted by t he dif ficult e i s of t he actual rocks. T he staff of Cia. Mi ne ra Autla n have bee n u nsti nti ng i n t heir suppo rt of t his p roject , a nd we have be ne fitted f rom t heir yea rs of effort i n u nde rsta ndi ng t he local geology. We could not have p roceeded wit hout t he suppo rt of A. Medi na.

REFERENCES

J . E. ( 1 977) Sedimentacion y diagenesis de Ia formacion 'Chipoco' (Jurasico Superior) en aflora­ mientos; estados de Hidalgo y San Luis Potosi. Rev. lnst. Mex. Petroleo 9 , 1 1 -37. AGUILERA- H . , E. ( 1 972) Ambientes de deposito del J urasico Superior en Ia region Tampico-Tuxpan. Sol. Asoc. Mex. Geologos Petroleras 24, 129- 163. ALEXANDRI- R . , R., FORCE, E.R. , CANO N , W . F., SPIKER, E. C. & ZANTOP, H. ( 1 985) The sedimentary manganese carbonate deposits of the Molango District , Mexico . Ceo!. Soc. A m . , Program with Abstracts, 17, 5 1 1 . ALEXANDRI- R . , R . & MARTINEZ-V . , A. ( 1988) Geologia del distrito manganesifero de Molango, Hgo. In: Geologia Economica de Mexico (Ed. by G. P . Salas) , pp. 40 1 -408. Fondo de Cultura Economica, Mexico. A LLER, R.C. & Ru DE, P . O. ( 1988) Complete oxidation of solid phase sulfides by manganese and bacteria in anoxic marine sediments. Geochim. cosmochim. Acta 52, 75 1 -765. BOARDMAN, M. R . & N E U MAN N , A.C. ( 1984) Sources of periplatfonn carbonates: northwest Providence Channel, Bahamas. J. sedim. Petrol. 54, 1 1 10 - 1 123. BOARDMAN , M . R . , NEUMANN , A . C . , BAKER, P. A . , D U L I N , L. A . , KENTER, R.J. , H U NTER, G.E. & KIEFER, K.B. ( 1 986) Banktop responses to Quaternary fluctuations in sea level recorded in periplatfonn sediments. Geology 14, 28-31 . BoLTO N , B . R . & fRAKES, L.A. ( 1 985) Geology and genesis of manganese oolite, Chiatura, Georgia, USS R . Geol. Soc. Am. Bull. 96, 87- 102. BoLTON , B . R . , fRAKES, L . A . & CooK, J. N . ( 1988) Petro­ graphy and origin of inversely graded manganese pisolite from Groote Eylandt, Australia. Ore Geology Reviews 4, 47-69. CANNON , W. F. & Fo RCE , E . R . ( 1983) Potential for high­ grade shallow-marine manganese deposits in North America . I n : Unconventional Mineral Deposits (Ed. by W.C. Shanks), pp. 1 75 -1 90 . AlMME, New York. CANTU-C. , A. ( 1 971 ) La Serie H uasteca (Jurasico Media­ Superior) del centro este de Mexico. Rev. lnst. Mex. Petroleo 3, 17-40. CARRILLO- B . , J. ( 1 965) Estudio geologico de una parte del anticlinoria de Huayacocotla. Sol. Asoc. Mex. Geologos Petroleras 17, 73-96. CREVELLO, P. O . & HARRIS, P.M. ( 1984) Depositional models for Jurassic reefal buildups. l n : The Jurassic of the Gulf Rim (Ed . by P.S. Ventress, D.G. Bebout, R. F. Perkins & C. H. Moore), pp. 57- 102. Gulf Coast

AGUAYO-C . ,

Section, Society of Economic Paleontologists and Mineralogists, Austin, Texas . DEYOU N G , J . H . , SUTPHIN , O.M. & CAN N O N , W. F . ( 1984) International strategic minerals inventory summary report-manganese. US Geol. Survey Circular 930-A , 22pp. D u FF, K.L. ( 1 978) Bivalvia from the English lower Oxford Clay (Middle Jurassic) . Palaeontographical Society Monographs, London, 137pp . EBERLI, G . P. ( 1987) Carbonate turbidite sequences deposited in rift-basins of the Jurassic Tethys Ocean (eastern Alps, Switzerland). Sedimentology 34, 363-388. ENos , P. ( 1983) Late Mesozoic paleogeography of Mexico. ln: Mesozoic Paleogeography of West-central United States (Ed. by M.W. Reynolds & E.D. Dolly) , pp. 133- 141 . Rocky Mountain Section , Soc. Econ. Paleont. Miner. FoRCE, E.R. & CAN N O N , W . F. ( 1 988) Depositional model for shallow-marine manganese deposits around black­ shale basins. Econ. Ceo!. 83, 93- 1 17. FoRcE, E. R . , CAN NON, W . F . , KoSKI, R.A. , PASSMORE, K.T. & DoE, B . R . ( 1983) I nfluences of ocean anoxic events on manganese deposition and ophiolite-hosted sulfide preservation. US Ceo!. Survey Circular 822, 26-29. fRAKES, L.A. & B O LTON B . R . (1984) Origin of manganese giants : Sea level change and anoxic -oxic history . Geology 1 2 , 83-86. fRIES, C. & RINCON-0 . , C. ( 1965) Nuevas aportaciones geocronologicas y tectonicas empleadas en el laboratorio de geocronometria. Sol. Jnstituto de Geologia de Universidad Nacional A u tonoma de Mexico 73, 57 - 133. FROELICH, P. N. , KLINKHAMMER , G. P. , B E N DER, M. L. , LUEDTKE, N . A., HEATH, G. R., C U L L E N , 0 . , D A U PHI N, P . , HAM MOND, D. , HARTMAN , B. & MAYNARD, V. ( 1979) Early oxidation of organic matter in pelagic sediments of the eastern equatorial Atlantic: Suboxic diagenesis. Geochim. cosmochim. A cta 43, 1075- 1091. GERMA N N , K. ( 1973) Deposition of manganese and iron carbonates and silicates in Liassic marls of the northern Limestone Alps ( Kalkalpen). In: Ores in Sediments (Ed. by G.C. Amstutz & A.J. Bernard), pp. 129- 138. Springer, Berlin. GooDFELLOW, W.O. & JONASSO N , I . R. ( 1984) Ocean stagnation and ventilation defined by dei34S secular trends in pyrite and barite, Selwyn Basin, Yukon. Geology 1 2 , 583-586. HALLAM, A. ( 1987) Mesozoic marine organic-rich shales. In: Marine Petroleum Source Rocks (Ed. by J. Brooks & A .J. Fleet), pp . 25 1 -261. Spec. Pub!. Geol . Soc. 26. HALLAM, A. (1 989) A re-evaluation of Jurassic eustacy in the light of new data and the revised Exxon curve. In: Sea Level Changes - A n Integrated Approach (Ed. by C. K. Wilgus). Spec. Pub!. Soc. econ. Paleont. Miner. 42. HALLAM, A. & MAYNARD, J.B. ( 1987) The iron ores and associated sediments of the Chichali formation (Oxfordian to Valanginian) of the Trans-Indus Salt Range, Pakistan. J. geol. Soc. 144, 107 - 11 4 . HERMOSO D E LA TORRE, C. & MARTINEZ-P . , J . ( 1 972) Medicion detallada de formaciones del Jurasico Superior en el frente de Ia Sierra Madre Oriental. Bot. Asoc. Mex. Geologos Petroleras 24, 45-63.

Manganese mineralization, Mexico J. ( 1980) Stable lsowpe Geochemistry, 2nd edn. Springer, Heidelberg, 208pp. I M LAY, R.W. ( 1980) Jurassic paleobiogeography of the conterminous United States in its continental setting. U S Geol. Survey, Prof. Paper 1062, 134pp . J E N KYNS, H .C . ( 1988) The early Toarcian (Jurassic) anoxic event: stratigraphic, sedimentary, and geochemical evi­ dence. A m . J. Sci. 288, 101- 151. JONES, T.S. ( 1 986) Manganese. US Bureau of Mines, Minerals Yearbook 1 986 I, m 1 -ml3. LEVENTHAL, J.S. ( 1983) An interpretation of carbon and sulfur relationships in Black Sea sediments as indicators of environments of deposition. Geochim. cosmochim. Acta 47, 133-138. L w , T-B. ( 1990) CIS relationships in shales hosting manganese ores from Mexico , China , and Newfoundland : I mplications for depositional environ­ ment and for mineralization. In : Manganese Metallogenesis (Ed. by B. Bolton) . Elsevier, Amsterdam . LONGORIA, J.F. ( 1 984) Mesozoic tectostratigraphic domains in east-central Mexico. In: Jurassic- Cretaceous HOEFS,

Biochronology and Paleogeography of North A merica

(Ed . by G. E . G . Westermann) , pp. 65-76. Geol. Assoc. Canada Spec. Paper 27. LOPEZ-I. , M. ( 1986) Estudio petrogenetico de las rocas igneas en las formaciones Huizachal y Nazas. Sol. Soc. Geol. Mex. 67, 1 - 18. MAYNARD, J.B. ( 1983) Geochemistry of Sedimentary Ore Deposits, Springer, New York, 305pp. OKITA, P.M. ( 1987) Geochemistry and mineralogy of the Molango manganese orebody, Hidalgo State, Mexico.

PhD Dissertation , University of Cincinnati , 362pp. P. M. , MAYNARD, J.B. & MARTINEZ-V . , A. ( 1986) Molango: a giant sedimentary manganese deposit in Mexico. A m . Ass. Petrol. Geol. Bull. 70 , 627. 0KITA, P. M. , MAYNARD, J.B. , SPIKER, E.C. & FO RCE , E . R. (1988) Isotopic evidence for organic matter oxidation by manganese reduction in the formation of stratiform manganese carbonate ore. Geochim. cosmochim. A cta 52, 2679-2685. 0KJTA, P.M. & SHANKS, W .C. ( 1987) Stable isotope study of the Molango Deposit, Hidalgo State , Mexico. Geol. Soc. A m . (Abstracts with Programs) 1 9 , 793. OKITA, P . M. & SHANKS, W.C. ( 1988) Del-13 C and del-34 S trends in sedimentary manganese deposits, Molango (Mexico) and Taojiang (China): evidence for mineraliz­ ation in a closed system. Int. Assoc. Sedim. Proc. , pp. 188- 189. Beijing, China. PADILlA Y SANCHEZ, R. J. ( 1982) Geologic evolution of 0 KITA,

29

the Sierra Madre Oriental between Linares, Concepcion

Unpubl. PhD Thesis, Univ. Texas at Austin, 2 16pp. PEDRAZZINI, C. & BASANEZ, M.A. ( 1978) Sedimen­ tacion del Jurasico Medio-superior en el anticlinoria de Huayacocotla, Cuenca de Chicontepec, Estados de Hidalgo y Veracruz, Mexico. Rev. Inst. Mex. Petrol. 1 0 , 6- 19. PINDELL, J . L . ( 1 985) Alleghenian reconstruction and sub­ sequent evolution of the Gulf of Mexico , Bahamas, and proto-Caribbean. Tecwnics 4, 1-39. P01TER, P . E. , MAYNARD, J.B. & PRYOR, W.A. ( 1980) Sedimentology of Shale. Springer, Berlin, 306pp . RAISWELL, R . & B ERNER, R. A . (1985) Pyrite formation in euxinic and semi-euxinic sediments. A m . J. Sci. 258, 7 10-724. READ, J .F. ( 1985) Carbonate platform facies models. Bull. A m . Ass. Petrol. Geol. 69 , 1 - 2 1. RU I Z , J . , PATCHETT, P.J. & ORTEGA-G . , F. ( 1988) Proterozoic and Phanerozoic basement terranes of Mexico from Nd isotopic studies. Geol. Soc. Am. Bull. 100, 274 -281. SALVADOR, A . ( 1987) Late Triassic-Jurassic paleo­ geography and origin of Gulf of Mexico Basin. A m . Ass. Petrol. Geol. Bull. 7 1 , 49 1 -55 1. SCHMIDT-EFFING, R. ( 1980) The Huayacocotla aulacogen in Mexico (Lower Jurassic) and the origin of the Gulf of Mexico. In: The Origin of the Gulf of Mexico and the Early Opening of the Central North A tlantic Ocean (Ed. by R.H. Pilger) , pp. 79-86. Louisiana State University Press , Baton Rouge. SHANKS, W.C. , WOODRUFF, L . G . , JiLSON , G.A. , JENNINGS, D.S . , MoDE N E , J . S. & RYAN , B . D . ( 1987) Sulfur and lead isotope studies of stratiform Zn-Pb-Ag deposits , Anvil Range, Yukon: Basinal brine exhalation and anoxic bottom-water mixing. Econ. Geol. 82, 600-634. STANLEY, S. M. ( 1972) Functional morphology and evolution of bysally attached bivalve mollusks . J. Paleo. 46, 165-2 12. VAIL, P. R. , HARDENBOL, J. & TODD, R.G . ( 1984) Jurassic unconformities, chronostratigraphy and sea­ level changes from seismic stratigraphy and biostrati­ graphy. A m . Ass. Petrol. Geol. Mem. 36, 129- 144. WiLSON , J.L. ( 1975) Carbonate Facies in Geologic History . Splinger , Heidelberg, 471 pp. WiNKER, C.D. & BuFFLER, R . T . ( 1988) Paleogeographic evolution of early deep-water Gulf of Mexico and margins , Jurassic to Middle Cretaceous (Comanchean). Bull. Am. Ass. Petrol. Geol. 72, 318-346. del Oro, Saltillo, and Monterrey, Mexico .

Spec. Pubis int. Ass. Sediment.

( 1990) 1 1, 31-38

Manganese and iron facies in hydrolithic sediments

G.A. G R O S S Geological Survey of Canada*, 601 Booth St., Ottawa, Canada, Kl A 0£8

ABSTRACT

Manganese-rich facies in Algoma, Lake Superior and Rapitan types of iron formation are an important part of the stratafer group of siliceous metalliferous sediments. Manganese oxide and carbonate facies associated with iron formation, chert, carbonate, shale, turbidites, tuff and lava are up to 30 m thick and have iron to manganese ratios ranging from 0·2 to 2. The major and minor element contents of stratafer manganese sediments are compared to typical oxide facies of iron formation and to modern protolithic facies on the seafloor that formed by hydrothermal effusive and hydrogenous processes. Cherty manganiferous facies and their gondite metamorphic equivalents occur throughout the geological record, provide major resources of manganese, and are the most common protore for high-grade manganese deposits that formed by secondary enrichment processes.

RELATED

Many manganese and iron ore deposits have been studied separately in the past without recognizing spatial and genetic relationships of the associated manganese- and iron-rich facies of protore. The cherty iron-, manganese- and sulphide-rich facies are the most common and abundant members of the stratafer group of hydrolithic metalliferous sedi­ ments. Typical relationships between manganese­ and iron-bearing facies are outlined in this paper to give a better understanding of the metallogeny of stratafer sediments and its application in exploration and development of the extensive mineral resources hosted in them. The term stratafer has been adopted ( Gross & McLeod, 1987) to include the great variety of litho­ logical facies that are genetically a part of or related to cherty iron formations, including the associated manganese, polymetallic sulphide and various other facies formed by chemical, biogenic and hydro­ thermal effusive or exhalative processes (Gross, 1988). They are commonly composed of banded chert and quartz interbedded with oxide, sulphide, carbonate, and silicate minerals containing ferrous, nonferrous, and/or precious metals. '

Manganese facies and their equivalent meta­ morphosed strata, known as gondite, host important syngenetic ore deposits and are protore for many large manganese deposits formed by oxidation, leaching and secondary enrichment processes (Roy, 1981). The world's largest syngenetic deposits of copper, zinc, lead and gold are hosted in sulphide facies of iron formations, and large deposits of rare earth elements, tin, tungsten and barite occur in oxide and other facies (Gross, 1986). Many banded chert and siliceous metalliferous facies containing less than 15% iron that developed separately or within iron-formation units are important host rocks for gold. Lithological facies from one or more of the three main groups of stratafer sediments are frequently interbedded or traced laterally through transitions from facies to facies, and a common origin or direct genetic relationship between them is evident. Gen­ etic models developed for both ancient and Recent stratafer sediments indicate that they formed by volcanogenic or hydrothermal effusive processes (Gross & McLeod, 1987). Their composition, distri­ bution, facies development and depositional en­ vironment appear to have been controlled mainly by the tectonic setting and physical, chemical and bio­ logical factors in the depositional basins (Gross,

Geological Survey of Canada Contribution No. 4 1888.

Sediment-Hosted Mineral Deposits Edited by John Parnell, Ye Lianjun and Chen Changming © 1990 The International Association of Sedimcntologists ISBN: 978-0-632-02881-8

FACIES

31

G. Gross

32

l983a). Stratafer sediments occur on all continents from early Precambrian to Recent (Gross, 1986) and the deposition of the great variety of lithological facies developed within them does not appear to coincide with events or environmental factors that were peculiar or unique to a particular period in the Earth's history. Much attention has been given to the extensive thick sequences of Lake Superior type iron formation which developed on the shelves and tectonically active marginal parts of Proterozoic platforms or cratons (Gross, 1965, 1968; James & Sims, 1973). Iron formations of this type and age appear to represent the largest and most extensive stratigraphic units of hydrolithic sediment. There are also many Archaean iron formations such as the Hamersley in Australia or Kudremuk in India, or late Proterozoic and younger iron formations of the Rapitan type, that are of a similar order of magnitude as the Lake Superior type formations. Some of the sedimentary manganese deposits such as Nikopol and Chiatura in the USSR have been considered to have formed by non-volcanogenic or hydrothermal processes. The manganese and iron in these and other deposits of a similar type could have been derived from a continental source by erosion pro­ cesses, by the reworking and redeposition of manganese from submarine volcanogenic sediments, crusts or nodules, or by hydrothermal processes. Probably geochemical data and the presence of banded chert in sequences of stratafer sediments provide the best criteria for identifying volcanogenic or hydrothermal primary sources of the metals.

MANGANESE-IRON DEPOSITS

Descriptive data from a survey by Gross (1983b) of facies rich in manganese and iron in many parts of the world that are associated with iron formations are summarized in Table 1. The following generalizations are based on these data. 1 Manganese carbonate and oxide facies are the most common and abundant manganese ores, or protore for enriched deposits. 2 Manganese-rich facies are commonly associated with oxide and carbonate facies of iron formations. 3 Chert and siliceous facies are associated in varying amounts with nearly all of the deposits studied. 4 The associated sediments and their metamor­ phosed equivalents vary from mature sandstone, quartzite and dolomite deposited in shelf and mar­ ginal basins, to turbidites, greywacke and shale from

deeper-water environments in graben basins, island arc and spreading-ridge tectonic systems. Banded siliceous manganiferous facies are as­ sociated with cherty iron formations in most of the iron ranges of the world, except in North America where they are not well developed. They are com­ monly interbedded with oxide and carbonate facies but they may occur in all kinds of mineralogical facies of iron formation and stratafer sediments. Fine-grained clastic facies at the margins of depo­ sitional basins evidently mark transitions from chemical to clastic deposition. Highly metamorphosed manganese-rich facies form gondite (Roy, 1980), which is a common type of protore for enriched manganese deposits. Sedimentary features and evidence of the primary nature of many gondite rocks have been destroyed by recrystallization and migration of elements during later stages of metamorphism. Review of the litera­ ture indicates that manganese facies occur more frequently, but are generally thinner or less abundant, in Algoma than in Lake Superior type iron formations. They appear to be more common in Phanerozoic and Mesozoic than in Precambrian basins. Manganese facies related to iron formations occur as three types. 1 Those within stratigraphic units of iron formation that contain sufficient manganese, usually from 1-5%, to provide manganiferous iron ore and protore. Examples are found in the Cayuna Range in the Lake Superior Region, at Wabush Mines in Labrador, McLeod Mine at Wawa, Ontario, in Minas Gerais in Brazil and in many other iron formations. 2 Manganese facies interbedded in or transitional to cherty iron formations, with manganese : iron ratios greater than one. This type is widespread throughout the world and is protore for most of the large manganese ore deposits. Important examples are: the Postmasburg and Kuruman deposits in Lake Superior type iron formations in the Transvaal of South Africa; Morro do Urucum in Brazil; Karadzhal in Kazakhstan; Jalisco in Mexico; manganese facies in the Kitakama, Ashio and Tambo belts in Japan; Marra Mamba iron formation and others in the Pilbara Goldfields, Phillips River and Yilgarn Goldfields in Australia; in the Guyana shield in Brazil and Guyana; in the Spanish-Portuguese pyrite belt; Maliy Khingan in the USSR; in the Orissa, Karnataka and Andhra Pradesh regions of India; Moanda in Gabon; at Woodstock, New

Manganese and iron facies

Brunswick; and on the Nastapoka Islands in Canada. Shale-hosted manganese facies, commonly manganese oxide and/or carbonate associated with muds and fine-grained clastic sediment which may be transitional to or isolated from iron-rich facies and chert beds. Occurrences of this type commonly form thin facies of limited extent and are widely distributed. Nikopol in the Ukraine and Chiatura in Georgia, USSR, are outstanding examples, and other examples are the Tangganshan and Taojiang deposits near Changsa in Hunan Province, and Wafangzi in Liaoning Province in China, and numerous other deposits on all continents. 3

Karadzhal and San Francisco manganese-iron

33

manganese deposit at Jalisco, Mexico (Zantop, 1978, 1981). Banded cherty iron and manganese oxide facies of iron formation are developed in a Tertiary lacustrine basin in association with tuff, andesite flows, red mudstones and siltstones, conglomerates tuffs and shales. The iron formation forms a stratified lens up to 3 m thick and 1·6 by l km in extent. Iron : manganese ratios range from 40 : 1 in the iron oxide­ rich facies at one side of the lens to 1 :50 in the manganese-rich part with an overall ratio of 2: 1. Zantop (1981) concluded that the higher concen­ trations of arsenic, barium, copper, molybdenum, lead, tin, zinc and vanadium in the manganese and iron oxide facies were evidence of a hydrothermal volcanogenic contribution to their formation.

deposits

Research on two deposits has been very instructive m understanding the genetic relationships of manganese- and iron-rich facies of stratafer sediments. The Karadzhal iron-manganese deposits in the Dzhail'min syncline in central Kazakhstan occur in a succession of quartz-magnetite-hematite and carbonate facies of iron formation in a thick sequence of Devonian sandstones, conglomerate, reddish-grey limestones, cherty calcareous shales and volcanic rocks. The iron formation is closely associated with reddish limestone and ranges in thickness from 1 to 24 m over a distance of 15-20 km. Manganese and carbonate beds are intermixed with jasper and chert-carbonate facies of the iron formation. The jasper facies are associated with spilitic rocks in the northwest part of the syncline where they achieve their greatest thickness, and contain up to 60% iron and probably average over 30%. In the eastern part of the area the iron-formation beds are 1-5 m thick and contain up to 40% manganese and 6-10% iron. The iron : manganese ratios in the iron formation change from 10: 1 to 7: 1 in the west to 1: 1 and 1 : 1·5 in the east (Sapozhnikov, 1963; Kalinin, 1965). Probably the siliceous iron formations in the western part of the area were deposited closer to the effusive hydrothermal source of the metals while deposition of the thinner manganese-rich facies may have been distal from the metal source. Manganese facies in iron formations similar to those described at Karadzhal occur in other Algoma type iron formations in Kazakhstan and the southern Ural Mountains. A transition from iron oxide to manganese oxide facies in iron formation is found in the San Francisco

MANGANESE FACIES IN IRON FORMATIONS IN CANADA AND THE UNITED STATES

The banded cherty manganiferous Algoma type iron formation near Woodstock, New Brunswick, Canada forms part of a succession of thinly bedded grey, grey-green and red slate, sandstone, greywacke and limestone of Silurian age. The manganiferous jasper-hematite facies of the iron-manganese­ formation are up to 30 m thick and have an iron content ranging from 11 to 30%, a manganese con­ tent from 12 to 25% and an overall iron: manganese ratio of about 1: 5. Several hundred million tons of potential manganiferous resource material have been outlined in the Woodstock area, and manganiferous facies are present in this group of rocks where they extend westward into the state of Maine (Gross, 1967; Anderson, 1986). Manganese facies in the extensive Lake Superior type iron formations in North America are thin and of limited lateral extent. Beds rich in manganese in carbonate facies iron formation have been traced for several kilometres on Belanger and Flint Islands of the Nastapoka Chain on the east side of Hudson Bay ( Bell, 1879; Chandler, 1982). A bed of rhodonite up to 20 em thick was observed in the Mount Reed iron formation in northern Quebec and some beds in magnetite-hematite facies of iron formation near Wabush Lake in southwest Labrador, Newfound­ land contain up to 2% manganese (Gross, 1968). Manganiferous facies in the Cayuna Range in Minnesota have been investigated as a source of manganese.

Table 1. Manganese-iron facies associated with iron formation

Country

Australia

. Africa

Region

Deposit rock group

Pilbara Phillips Rv Yilgarn

Age

FeO

Zaire

Katanga

Kisenge

Precambrian

Transvaal

Kuruman

Proterozoic

Botswana

Kalahari

Palapye

Proterozoic

Moanda

Proterozoic

Um Bogma

Mesozoic

Bandarra

Precambrian Proterozoic Proterozoic Precambrian

Mato Grosso Canada

Appalachian Nastapoka Is

Serrade Navio Morrodu Urucum Woodstock

Facies FeO, FeC, FeSi, FeS

MnO, MnC, MnSi

Precambrian

Bahia Minas Gerais Para Amapa

Facies MnO, MnC, MnSi

FeO Fe FeO

South Africa

Brazil

Range

MnO MnO MnO

Mokta, Nsuta, Tambao

Sinai

Fe: Mn Average

Proterozoic Archaean Archaean

West

Gabon

Manganese content (%)

UTI, (d) 4 !J.ITI.

The structural order of the mineral increases with greater depth. 2 Hematite is also present in two morphologically different forms, i.e. as dense finely flaked aggregates with goethite crystals (Fig. lc) and as flat 0·02-0·04 mm hexahedrons 2-4 f.tm thick (Fig. ld). We have also found hematite in the sediments in the south­ western part of the Atlantis-II Deep in the immediate

vicinity of hydrothermal vents where hematite forms lens-like patches and clearly delineated interlayers. 3 Ferrihydrite in iron-manganese ore deposits occurs as mineral aggregates with bacterial form (Fig. 2a). 4 Lepidocrocite occurs as elongated plates of less than 1 �lm size, which develop from a spherical jelly-like matrix (Fig. 2b). Individual samples of

60

G. Yu. But uzova et a/.

Fig. 2. Morphology of particles and microdiffraction

pattern of ferrihydrite and lepidocrocite (Atlantis-I I Deep). (a) Aggregate o f particles o f bacterial ferrihydrite; (b) globular aggregates of spicular crystals of lepidocrocite; (c) aggregate of particles of bacterial lepidocrocite. Each scale bar 0·5 �-tm.

lepidocrocite, like ferrihydrite, have bacterial forms of aggregates of mineral particles (Fig. 2c). This lepidocrocite variety has a lower structural ordering and is normally found together with ferrihydrite.

Manganese and iron-manganese oxyhydrox ides Three major components are distinguished in the manganese-rich interlayers: the basic finely dispersed mass, solid kidney-shaped micronodules and various concretions of complicated morpho­ logical type. The three components differ not only in texture and morphology, but their mineral compo­ sition is essentially different; they also have differ­ ently crystallized minerals and some geochemical peculiarities.

1

The major mass of ore material is composed of 2-6 �m globules shaped like rosette lepispheres with characteristic elongate crystals up to 2-4 �m long at the edges (Figs 3a, b). Electron micrographs show platey crystals sometimes forming twinned crystals (Fig. 3c). The mineralogy of the major mass is represented mainly by todorokite whose presence is characterized on diffractograms by reflections with d spacings of 9·58, 4·78, 2 4 0 and 2·20 A. We emphasize here that the same set of reflections characterizes at least four other mineral varieties of manganese hydroxides which are structurally dif­ ferent from todorokite (Chukhrov et a/., 1987). Therefore a reliable diagnosis of todorokite was carried out by combining the X-ray and micro­ diffraction methods. The analysis of electron diffrac·

,

Iron-manganese oxyhydroxides, the Red Sea

..

...

I

I

61

+

j '

' 1

' I

I '

I

'

I

..

t '

8

Fig. 3. Electron micrographs and electron diffraction

pattern of todorokite from the major mass of manganese ore horizon (Atlantis- II Deep, site 1905(5), horizon 48305000 mm). (a), {b) Globular todorokite particle; (c) triple cluster of todorokite; {d) electron diffraction pattern of the triple cluster of todorokite with a = 9·75 A; (e) electron diffraction pattern of todorokite with a = 24-4 A. Scale bars (a) 10 f.lm, {b) 2 f.tm, (c) 0·5 [lm .

62

G. Yu. But uzova et a/.

tion patterns, obtained from the studied samples, has shown that manganese ore horizons contain three todorokite modifications with parameter a of 9·75 (Fig. 3d), 19·5 and 24·4 A (Fig. 3e). This is associated with the different size of channels in the tunnel structure of microcrystals of minerals. The most common is todorokite with parameter a of 9 ·75 A. Short columnar microcrystals 0 ·1-0·15 �lm in size were revealed in the mass in association with todorokite. Their electron diffraction patterns cor­ respond to the characteristics of goethite (cx­ FeOOH) and groutite (cx-MnOOH) which are isostructural. The particles contain comparable amounts of manganese and iron. These data seemed to indicate the presence of isomorphic substitutions of Mn3+ and Fe3+ in the structure of the compounds or the growth of goethite and groutite at the sub­ microscopic level. H owever, a subsequent detailed X-ray absorption spectroscopic study has shown that this phase consists of Fe3+ and Mn4+ domains co­ existing within a uniform hexagonal packing. The cation distribution in Fe3+ domains is similar to that in goethite, while the Mn4+ cations in manganese domains are distributed layerwise as in phyllo­ manganates. This phase is to be called manganese goethite (Manceau et a!., 19 9 0). Individual samples of the basic mass of ore ma­ terial, besides todorokite and manganese goethite, have traces of buserite-II, a laminated 10 A man­ ganese oxide, the Mn4+ octahedron layers of which have chains of vacant octahedrons: below and above these octahedrons are located Mn3 + , Mn2+ , Ca2+ and other cations coordinated by H 20 molecules (Chukhrov et a/., 1984). A study of 10 samples by microprobe revealed considerable chemical inhomogeneity of the finely dispersed material. The manganese content varies from 55 to 93%, with an irregularly distributed admixture of iron (0·14-11·6% ), silicon (0 ·36% ), calcium (0·3-1·7%) and magnesium ( 1-1·16% ). Among trace elements the most com­ mon are zinc (0·02-1·5%) and lead (0·05 -0·5% ). The silicon, magnesium, calcium and some iron in the major ore mass are probably associated with insignificant and irregularly distributed admixtures of the host sediment, with small amounts of au­ thigenic smectites and the presence of cations in the adsorbed complex of manganese hydroxides. An essential admixture of iron is found in manganese goethite, lepidocrocite and ferrihydrite. 2 Kidney-shaped microconcretions are black and

shiny, 0 ·2-0·5 mm in size, seldom up to 1 mm. They are quite varied morphologically, occurring in rounded, oval, and dumb-bell forms, commonly with pancake 'growths' attached to the principal surface (Fig. 4a). The inner parts of microcon­ cretions are composed of randomly oriented crystals (2-5 �lm) of elongate platey shape (Fig. 4b). The microconcretions are composed of well-crystallized manganite. No other cations other than manganese are present in the manganite particles. 3 Morphologically complex concretions and crusts are normally dark-grey, dull, friable and slaggy. Their size does not exceed 1 mm, the shape is extremely variable (branched, dendritic, angular: Fig. 4c), and their surface is rough and bumpy. Their mineral and chemical composition is inter­ mediate between the first two types. The dominant minerals are todorokite and manganite. Some of the samples show small admixtures of manganese goethite. The set of associated microelements is the same as in the basic mass, but their content is generally less.

General descr iption of the phys ico-chemical env ironment The Atlantis-II Deep is the best-studied part of the Red Sea rift area. A number of papers describe the major structural features, the general mineralogical-geochemical characteristics of the sediments and physico-chemical parameters of brines filling the Atlantis-11 Deep (Degens & Ross, 19 69; Backer & Richter, 197 3; H ackett & Bischoff, 197 3; Butuzova, 1984a,b). The area of the Atlantis-II Deep is 7 0 km2; it is filled with dense, highly mineralized thermal brines about 17 0 m thick with distinct vertical stratification. The lower and thickest layer has a temperature of 62 -65°C, salinity up to 320 %o, is completely devoid of oxygen, and pH values in it reach 5·5-5 ·6. Above this layer, a change in all parameters of the water mass occurs at a definite boundary, i.e. the tempera­ ture falls to 51 °C, salinity is reduced to 153 %o, the pH value is 5·9, and oxygen is present in small amounts (0·05-0·06 mg/1). This layer is about 30 m thick, and above an intermediate horizon of about the same thickness is a layer of normal seawater (Degens & Ross, 1969). Data available in the literature on the structure of the brine layers and their physico-chemical charac­ teristics were used to work out a scheme for the formation of a complex of mineral phases (Fig. 5). A

Iron-manganese oxyhydroxides, the Red Sea

63

Fig. 4. Morphology of solid aggregates in the major mass

of manganese ore material and diffraction pattern of manganite (the Atlantis-II Deep, site 1905(5), horizon 4830-5000 mm). (a) Microconcretion of mangani te; (b) platey crystals of manganite composing the microconcretions; (c) aggregate of polycomponent composition ( todorokite, manganite, manganese goethite). Scale bars (a) 400 �-tm, (b) 1 �-tm, (c) 200 �tm.

rather informative addition to the scheme is a set of data on iron and manganese distribution throughout the brine layers, from the contact with bottom sediments to the boundary with seawater (from Brewer & Spencer, 1969) (Fig. 6). The mechanism of formation of iron oxyhydroxides

Figure 6 clearly shows that a sharp change in iron content in the brine layer occurs at the boundary between the lower layer (A) and the overlying hor­ izon (B). This change in properties is caused by an overall transition of the dissolved iron into solid' phases in the zone where oxygen appears. A direct confirmation of the formation of a major mass of iron hydroxides at the boundary between two layers in the brines is a perceptible rise in the amount of

rusty-brown suspended material in this area which is completely amorphous (Hartmann, 1979). Holm et a!. (1982), however, have established the presence of the mineral phase �-FeOOH (akaganeite) in the suspended material. Most workers believe that the presence of chlorine (or fluorine) anions in solution is a necessary condition for the formation of the phase �-FeOOH, in addition to an acid or neutral environment, as realized in the Atlantis-ll Deep. Akaganeite is as yet the only crystallized phase of 3 Fe +, found in small amounts in suspension in the brines of the Atlantis-II Deep. However, neither previous research nor our studies have found this mineral in the sediments. Taking into account the metastable character of the phase FeOOH, we as­ sume a rapid transformation of akaganeite into more stable crystalline phases (goethite, hematite).

-- J

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Fig. 5. The scheme of iron-manganese mineral formation in the Atlantis-IT Deep. A, B, C- layers of brines (A- lower,

B- upper, C - transitional to seawater); I- upper zone of active oxidation; II - lower zone of slower oxidation. ( 1) Amorphous phase of suspension; (2) mineral phases; (3) sedimentation and mineral formation (coagulation, dehydration, crystallization); (4) migration in brine; (5) transformation of solid phases of the suspension and sediment; (6) area of manganese ore deposits.

Another possible cause of the absence of akaganeite in the sediments might be its destruction due to loss of chlorine from the sediment in the process of elutriation of samples by water to remove easily soluble salts. Disintegration of akaganeite after chlorine removal has been confirmed experimentally (Chukhrov et al., 1975a). The ore layer of the Atlantis-ll Deep has two major mineral associations of iron oxyhydroxides: the goethite-hematite association, typical of iron ore deposits of all lithological-facies zones, and the ferrihydrite-lepidocrocite association, confined to manganese-rich interlayers. Small amounts of ferrihydrite were also found in the iron ore sedi­ ments, mostly in the upper horizons of the sections. Since the major mass of oxidized iron appears at the boundary between two layers (Figs 5, 6, A and B), the amorphous hydroxides formed at this place

may be the origin for the bulk of the goethite and hematite in the ore material. 1 Goethite is formed over a wide range of con­ ditions, but experiments to synthesize ferrous phases show that high concentrations of Fe2+ in the brine at low oxygen content and rather low pH values stimu­ late goethite formation (Chukhrov et al., 1975b). The environment in the region of formation of the major mass of iron hydroxides fully complies with these conditions. The regular increase in the struc­ tural ordering of goethite from top to bottom of the ore section confirms the formation of its larger part by crystallization of the amorphous phase. Another means of goethite formation is related to a trans­ formation from lepidocrocite; the absence of lepido­ crocite in ferrous ore deposits could be due to its transition into goethite at higher temperatures. 2 Hematite, in contrast to goethite, is formed as a

Iron-manganese oxyhydrox ides, the Red Sea

depth

�

30 50

70

90 100

ma

m

ho

65 20

�0

60

ao

100

:J;

1920

1960

2000

2040

2080

Fig. 6. Distribution of iron and

manganese in the layer of brines in the Atlantis-II Deep ( after Brewer & Spencer, 1969). (A) Lower layer of brines; ( B ) upper layer of brines; (C) layer transitional to seawater; (D) seawater.

2120

2160 2180

result of the crystallization of amorphous hydroxides at higher temperatures. Accordingly, the maximum amounts of well-crystallized hematite, in the form of hexahedrons, are confined to regions in the immedi­ ate vicinity of hydrothermal vents. In the studied sections the total hematite content is notably higher in sediments at site 1905(5), which is nearer to the vents, than in the core from site 1905(4). The presence of finely flaked aggregates, which form another morphological variety of hematite in the sediments of both sections, is probably caused by the transformation of ferrihydrite into hematite. It is important to note that ferrihydrite in ferrous ore deposits remains only in the upper parts of the sections, which may imply that the major part of the mineral was transformed into hematite in the course of aging of the sediment. 3 Ferrihydrite is found both in ferrous ore deposits and in manganese-rich interlayers. It contains par­ ticles with bacterial form which may testify to the active role of microbiological processes in the for­ mation of this mineral. The C layer of the brines, which is transitional to seawater, is the most favour­ able environment for active microbiological oxida­ tion-reduction reworking of the ferruginous suspension. This layer is the gradient zone with a perceptible change in density and an increase m oxygen content (Fig. 5). Consequently, the conditions of formation of

Fe

Mn

amorphous iron hydroxides, which are transformed on the one hand into goethite and hematite, and on the other hand into ferrihydrite, are spatially separ­ ated. The sources of iron are also different: in the first case amorphous hydroxides are produced by 2 oxidation of Fe + which is supplied by hydrothermal waters; while in the second case they are a result of the transformation of ferruginous suspension from seawater (Fig. 5). 4 Lepidocrocite includes particles with bacterial form which develop from a biogenic matrix by the same processes and under the same conditions as ferrihydrite. The abiogenic lepidocrocite is probably 2 formed as a result of Fe + oxidation in the boundary zone of brines between layers A and B. The extensive production of hydrated forms of Mn02 and the presence of amorphous Si02 in manganese ore interlayers apparently stimulate the preservation in the sediment of metastable hydroxide phases of iron, i.e. ferrihydrite and lepidocrocite. Mechanism of formation of manganese oxyhydroxides

The behaviour of hydrothermal manganese in the brine layer of the Atlantis-11 Deep is essentially different from that of iron. Due to the higher oxi­ dation potential of manganese the transition of 2 hydrothermal Mn + from solution to the solid phase

66

G. Yu. But uzova et a/.

2 Mn + takes place in the brine layer into which the seawater oxygen penetrates. The process of massive manganese oxidation is shown in Fig. 6 as a sharp change in manganese content in the C zone tran­ sitional to the normal seawater. According to the data of Hartmann ( 1979), it is in this zone that a notable amount of brown suspended material appears composed of amorphous manganese hydroxides. The particles of hydrated manganese dioxide, sinking into the brine layer and reaching the lower A layer completely devoid of oxygen, are reduced by 2 the dissolved Fe +, and manganese again passes into solution. This process obstructs precipitation of ox­ ide forms of manganese in brines and provides high concentrations of the element in the solution (80-90 mg/1), which is about 20 000 times as great as the average manganese content in seawater. The natural consequence of these processes is the almost complete absence of manganese oxyhydroxides in the sediments in extensive areas of the Atlantis-11 Deep. The local presence in the sedimentary layer of manganese ore interlayers, confined by sharp lithological contacts with the surrounding muds, is evidence of the change of physico-chemical conditions in the near-bottom water. This change occurs against the background of a quiescent hydrological setting with intensive mixing of water masses. The most probable cause for the change of con­ ditions in the near-bottom water would have been the lowering of the level of brines which in turn was connected with a lower or temporarily discontinued hydrothermal activity during the period of forma­ tion of manganese ore horizons. A number of lithological-geochemical peculiarities of deposits in the CO zone testify to this possibility, including an appreciable admixture of the biogenic-terrigenous component to the ore material, and a low content of sulphides including diagenetic sulphides. Confine­ ment of manganese ore horizons to the relatively high parts of the sea floor is also evidence because these parts are in the upper layer B when the level of brines is lowered (Fig. 5). It is in this region that conditions are created to allow the possibility of massive precipitation and preservation of manganese hydroxide compounds in sediments, these con­ ditions being an increase in the oxygen content, a 2 sudden fall in Fe + concentration and temperature, and a rise in pH. In discussing the possible mechanisms of the for­ mation of manganese hydroxide compounds, it is 2 important to consider the nature of Mn + oxidation

processes and certain properties of the compounds formed during these processes. 2 The act of Mn + oxidation by oxygen in solution results in the appearance of Mn4+ in the form of a hydrated dioxide according to the reaction: 2 Mn + + 1/202 + 20H- __,. Mn02·HzO At a molecular level the hydrolized products of 2 the initial Mn + oxidation are coordinated hydrated polymeric aggregates. Their coagulation produces hydrated microstructures with adsorptive activity capable of dehydration and intraphase oxidation­ reduction transformations by the scheme: 2 Mn + + Mn4+ � 2Mn3+ The development and direction of certain trans­ formations of the amorphous phase and the formation of individual compounds are determined 2 mostly by the conditions of Mn + interaction with 2 dissolved oxygen and by the ratios of Mn + : 02 concentration, pH value, and adsorptive and cata­ lytical activity of the newly formed surface of hy­ drated Mn02. In the environment of the Atlantis-11 Deep, the stratification of the water layer provides differen­ tiation in the physico-chemical conditions of the medium where mineral formation takes place; these conditions control the polymineral composition of ore material. Formation of todorokite and manganese goethite of the major mass

2 Figure 5 shows two Mn + oxidation zones with a number of essentially different parameters. Zone I of active oxidation generally coincides with layer C of the brines, which is transitional to seawater and has a high content of dissolved oxygen, an alkaline environment, and relatively low tem­ peratures ( 100°C). The amorphous aggregates of colloidal calcic manganese oxides of the Mineoka Umber suggest rapid precipitation when the manganese­ enriched hot solution mixed with the cold seawater. The rate of sedimentation for the Mineoka Umber and the overlying chocolate-brown shale was prob-

ably much greater than the 18 mm/ 103 a for the hemipelagic biogenic sediments from the Shirataki Formation, because planktonic organisms such as radiolarian skeletons are rarely found, even in the shale. The pyrolusite of the steel-grey, metallic-lustred bands appears to have crystallized from the spherular aggregates of the amorphous manganese oxides, because a transitional morphology between the spherular aggregates and the microcrystalline pyro­ lusite was observed under the SEM (Fig. 8b). Pyrolusite generally forms under more oxidizing conditions when compared with the amorphous aggregates of calcic manganese oxides, which still contain variable amounts of MnO. The MnO: Mn02 ratio in the strata-bound metalliferous umber de­ creases from 0 77 to 1·94 at locality 3, where the pipe-filling umber exists, to 0·05-0·15 at locality 2, where small amounts of pyrolusite occur. Pyrolusite dominates at locality 1 (Tasaki et al., 1980), which is most distant from locality 3. It is therefore concluded that the conditions became more oxidizing with in­ creasing distance from the conduit at locality 3. The ratios between manganese and iron oxides in the metalliferous umber are comparable in the different localities: 0·24-0·33 at locality 2 and 0·19-0·35 at locality 3. Consequently, a separation of manganese and iron during precipitation has not been identified. ·

Site of d eposition

The Mineoka Umber was deposited on a submarine volcanic ridge during the Eocene. The ridge ex­ tended from the southern Boso Peninsula to central Shizuoka in the Mineoka- Kobotoke-Setogawa Tectonic Belt (Fig. 1). At Setodani, in the Setogawa terrain, a small lenticular body of ferruginous umber of 500 x 200 mm size occurs in a radiolarian black shale of the Takisawa Formation, about 10m above a basaltic pillow lava (Table 2). The Setogawa Umber consists of microcrystalline aggregates of hematite, chlorite and limited quartz, which suggest a diagenetic modification. The Setogawa Umber has also been interpreted to have formed by submarine hydrothermal activity following the basaltic volcanism (lijima et a/., 1981). There are two different theories for the ongm of submarine pillow basalts of the Mineoka­ Kobotoke-Setogawa Tectonic Belt: 1 accretion of the oceanic crust (Ogawa & Taniguchi, 1988); and

Mineoka Umber, Japan 2 an arc volcanic ridge. The following points favour the arc volcanic ridge theory: (a) the bulk chemical composition of the pillow basalt from the Kamogawa Formation matches that of the island arc tholeiites (Arai & Uchida, 1 978); (b) the distribution patterns of minor and trace elements in the tholeiite of the Kamogawa Formation and in the alkali basalt of the Setogawa terrain coincide with those of island arc basalts (Watanabe, 1989); (c) a dacitic tuff, >60 m thick, is closely associated with basalts of the Kamogawa Formation in the Mineoka Hills. On Kuroshima Isle at the base of the pier of the Kamogawa fishing port and in the north of Wada, it changes to a lapilli tuff/tuff breccia, suggesting that it erupted on the basaltic volcanic ridge ; (d) two tectonic blocks composed of crystalline schists and amphibolite crop out at the Kamogawa fishing port. The pelitic to psammitic biotite schist consists of biotite, quartz, microcline and plagioclase (Kanehira et al. , 1968), and its K/ Ar age is 38 Ma (Yoshida, 1974). Moreover, a large float of mylonitized and albitized biotite granite has recently been found on Kainagisa Beach in the south of the Kamogawa fishing port. The biotite schist and mylonitized granite are considered to have formed the basement of the arc volcanic ridge and to have been uplifted together with ultramafic rock masses. We therefore conclude that the Mineoka Umber accumulated on the arc volcanic ridge in the suprasubduction zone off the Japanese continental arc during the Eocene, when the Sea of Japan was not yet open, except for a late Oligocene embayment in the south (Iijima et al., 1988). A very similar setting is now postulated for the Troodos, Oman and Baer-Bassit settings. However they are primitive arcs built up before the genesis of major calc-alkaline edifices (Robertson & Fleet, 1986).

CONCLUSION

The Mineoka Umber, which is mainly composed of manganese oxides and hydrated ferric oxides, formed during submarine hydrothermal activity that followed basaltic volcanism. It was deposited at the foot of an arc volcanic ridge in the suprasubduction zone off the Japanese continental arc during the Eocene, when the Sea of Japan was not yet open. The temperature of the metal-carrying solution was probably much higher than the 55-68°C of the metal-free water from which calcite precipitated in pores and cracks of the conduit-filling umber.

87 ACKNOWLEDGEM ENTS

This study was partly supported by a Grant-in-aid for Cooperative Research (A) from the Ministry of Education, Science and Culture (Project No. 60303010). We are indebted to the Chiba-Kenzai I ndustrial Company for permission to collect the umber samples. We are grateful to S. Roy, B.R. Bolton and J.R. Hein for their invaluable dis­ cussion and comments at the lAS ISOSRMD Beijing meeting. Our thanks are due to J. Parnell, A.H. F. Robertson and B. Pracejus for critical reading of the typescript, H. Haramura for wet chemical analysis, H. Matsuda for isotopic analysis, R. Matsumoto for advice on interpretation of the isotopic compositions, and T. Fukuhara for preparing the typescript.

R E F E RENCES

ARAI, S. & UcHIDA, T. (1978) Highly magnesian dunite from the Mineoka Belt, central Japan. J. Japan. Ass. Min. Petrol. Econ. Geol. 73, 176-179 . ELDERFIELD, H . , GASS, I . G . , HAMMOND, A. & BEAR, L . M . (1972) The origin o f ferromanganese sediments associ­ ated with the Troodos Massif of Cyprus. Sedimentology 19, 1 -19. HASKIN , L.A. & HASKIN, M.A. (1966) Rare earths in European shale: a redetermination. Science 145, 507-509. lmMA, A. (1986) Occurrence of natural zeolites. Clay Sci. 26, 90-103. IuiMA, A. , MATSUMOTO, R. & IGUCHI, T. (1981) Occurrence and properties of the Setogawa 'Umber'. Abstracts Paper, Geol. Soc. Japan, 235. liHMA, A. , TADA, R. & WATANABE, Y. (1988) Devel­ opments of Neogene sedimentary basins in the North­ eastern Honshu Arc with emphasis on Miocene siliceous deposits. J. Fac. Sci. Univ. Tokyo , Section II , 2 1 , 417- 446. lUIMA, A., WATANABE, Y . & MATSUMOTO, R. (1984) Geo­ logic age of the Setogawa-Mineoka Tectonic Belt. In: Biostratigraphy and International Correlation of the Paleogene System in Japan (Ed. by T. Saito & H. Okade), pp. 69-74. Yamagata Univ., Yamagata. IlZASA, K. (1988) Metasomatism in manganese nodules. Bull. Sci. Univ. Tokyo 7, 21-24. KANEHIRA, K. , OKJ, Y . , SANADA s . , YAKOU, K. & ISHIKAWA, F. (1968) Tectonic blocks of metamorphic rocks at Kamogawa, southern Boso Peninsula. J. Geol. Soc. Japan, 74, 529 - 534. KARPOFF, A.M., WALTER, A.V. & PFLUMIO, C. (1988) Metalliferous sediments within lava sequences of the Sumail Ophiolite (Oman) : Mineralogical and geo­ chemical characterization, origin and evolution. Tec­ tonophysics , 1 5 1 , 223-245. MATSUMOTO, R . , MINAI, Y. & IIHMA, A. (1985) Manganese content, cerium anomaly, and rate of sedimentation as aids in the characterization and classification of deep-sea

88

A. Iijima et al.

sediments. I n : Formation of Active Ocean Margins (Ed. by N. Nasu). pp. 913-939. Terrapub, Tokyo. OGAWA, Y. & TANIGUCHI, H. (1988) Geology and tectonics of the Miura - Boso Peninsulas and the adj acent area. Mod. Ceo!. 12, 147-168. PIPER, D.Z. ( 1974) Rare earth elements in the sedimentary cycle: a summary. Chemical Ceo!. 14, 285-304. RoBERTSON, A.H.F. ( 1975) Cyprus Umbers: basalt­ sediment relationships on a Mesozoic oceanic ridge. J. Ceo/. Soc. Land. 131, 51 1-531. ROBERTSON, A.H.F. & BoY LE, ] .F. ( 1983) Tectonic setting and origin of metalliferous sediments in the Mesozoic Tethys. I n : Hydrothermal Processes at Seafloor Spreading Centres (Ed. by P.A. Rona) , pp. 595-663. NATO. Conf. Ser. , Plenum Press, New York. RoBERTSON , A.H.F. & FLEET, A.J. ( 1976) The origins of rare earths in metalliferous sediments of the Troodos Massif, Cyprus. Earth Planet. Sci. Letts 28, 385-394. ROBERTSON , A.H.F. & FLEET, A.J. ( 1986) Geochemistry and palaeo-oceanography of metalliferous and pelagic sediments from the Late Cretaceous Oman Ophiolite. Marine Petrol. Ceol. 3, 315-338.

ROBERTSON , A.H.F. & HuDSON , J.D. ( 1973) Cyprus umbers: chemical precipitates on a Tethyan ocean ridge. Earth Planet. Sci. Letts, 18, 93-101. SAVIN, S . M. & YEH , H . W . ( 1981) Stable istopes in ocean sediments. I n : The Sea. The Oceanic Lithosphere , Vol. 7 (Ed . by C. Emiliani) , pp. 1521- 1554. Wiley­ lnterscience, New York. SuzuKI, Y . , KoNDO, K. & SAITO, H. ( 1984) Latest Eocene planktonic foraminifers from the Mineoka Group, Boso Peninsula. J. geol. Soc. Japan 90, 497-499. TASAKI, K . , INOMATA, M. & TASAKI, K. ( 1980) Umbers in pillow lava from the Mineoka Tectonic Belt, Boso Peninsula (Short notes). J. geol. Soc. Japan 86, 413-416. WATANABE, Y . (1989) Evolution of the forearc basin of the Setogawa- Kobotoke - Mineoka Tectonic Belt, central Japan. Unpubl. PhD Thesis, Geological I nstitute, Univ. Tokyo. YosHIDA, Y. (1974) Discovery of foraminifers from the Mineoka Hills, Chiba. Chishitsu News, Ceol. Survey Japan , 233, 30-36.

Spec. Pubis int. Ass. Sediment. ( 1990) 1 1 , 89-108

Mineralogy, geochemistry and genesis of manganese-iron crusts on the Bezymiannaya Seamount 640, Cape Verde Plate, Atlantic l. M . V A R E N T S O V*, V . A . D R I T S*,

and

A .I. G O R S CH K O Vj

1 *Geological Institute of the USSR Academy of Sciences, 7 Pyzhevsky per. , 109017 Moscow, USSR; "1nstitut e of Ore Geology and Mineralogy of the USSR Academy of Sciences, 35 Staromonetny per. , 109017 Moscow, USSR

ABSTRACT

Manganese-iron oxyhydroxide encrustations overgrow and impregnate hydrothermally phosphatized Middle Eoce;1e limestones, which blanket the Bezymiannaya Seamount 640 (the Rocett Seamount) on the Cape Verde plate. In chemical composition, the manganese-iron crusts are transitional between hydrothermal and hydrogenetic types . The major minerals are iron vernadite and manganese feroxyhyte. The presence of goethite, mixed-layered asbolane-buserite, magnesium asbolane, and birnessite in the crusts is interpreted as a result of postdepositional transformations of the initial manganese-iron oxyhydroxide material.

INTRODUCTION

the Rocett Seamount) is situated about 750 km west- southwest of the rise of the Cape Verde Islands, a large volcanic structure of the Cape Verde plate composed of oceanic crust of early Cenozoic (Palaeogene) age. The base of the Bezymiannaya Seamount 640 lies at depths of 4500- 5000 m, and the top of the seamount is at 640 m. This rise is a submeridionally oriented block of oceanic crust about 74 km long. According to subsea photography and sample collection , the seamount surface is covered with moderately lithified limestones of lower Middle Eocene age. Moreover, the lime­ stones exhibit an increasingly shallow-water character towards the top of the seamount. The hydrothermal alteration of limestones irregularly increases in the same direction (recrystallizatio n , silicification, phosphatization, etc) . The intensity of formation of the manganese- iron oxyhydroxide crusts increases from the middle part of the slopes towards the top (Fig. 1 ) .

Manganese- iron oxyhydroxide crusts occur on the surface of seamounts, guyots, ridges and various rises on the ocean floor. There is a definite distinction between the manganese - iron oxyhydroxide crusts of hydrothermal origin and hydrogenetic origin , which is evident i n the geological settings o f the deposits and their structure, mineralogy and geo­ chemical characteristics (Crorian, 1976; Toth , 1980; Cronan et a/ . , 1 982; Varentsov et a/ . , 1983 ; Aplin & Cronan, 1985; Thompson et a/., 1 985; Lalou et a/., 1986; Carlo et a/ . , 1 987). The most common, how­ ever, are the manganese-iron encrustations formed as a combined accumulation of components of dif­ ferent genesis. An important problem in the miner­ alogy and geochemistry of oceanic manganese-iron ore formation is the objective and substantiated esti­ mation of the contribution of hydrothermal and hydrogenetic sources. The studies described here were based on materials collected during the first cruise of RV 'Akademik Nikolai Strakhov' and on the data of geological - geophysical studies on the Bezymiannaya Seamount 640. The samples were collected by a dredge and a shovel sampler. The Bezymiannaya Seamount 640 (on some maps: Sediment-Hosted Mineral Deposits Edited by John Parnell, Ye Lianjun and Chen Changming © 1990 The International Association of Sedimcntologists ISBN: 978-0-632-02881-8

METHODOLOGY

The samples were studied in thin section under the microscope, and by X-ray diffraction and other 89

90

I. M. Varentsov, V . A . Drits and A./. Gorschkov

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Fig. 1. Sublatitudinal lithological profile across the central part of the Bezymiannaya Seamount 640. Arrows show stations of sample collection (dredge). (1) Biogenic limestone: (2) biogenic limestone with relatively weak alteration; (3) altered limestone; (4) altered limestone, rudaceous; (5) altered limestone with manganese-iron oxyhydroxide crusts on bedding planes; (6) manganese-iron oxyhydroxide crusts; (7) modern coral structures; (8) foraminiferal sand; (9) silty mud; and (10) basalt.

physical methods of analysis (Varentsov et al., 1989). The study of mineral composition was much more effective using electron microdiffraction, in combi­ nation with microprobe energy dispersive X-ray (EDX) analysis. The chemical composition of samples was deter­ mined by classical wet chemical analysis combined with the plasma spectroscopy of small masses (about 0· 1 g) . Heavy metals and trace elements were de­ termined by emission spectroscopy. High concen­ trations of cobalt, antimony and silver were deter­ mined by instrumental neutron activation analysis.

GEOLOGICAL SETTING,

STRUCTURE,

AND MINERAL COMPOSITION

Three stations (34, 38 and 39) were selected for the study of m ineralogy and geochemistry of manganese - iron oxyhydroxide crusts and of changes in the substrate rocks (Fig. 1 ) . The description of samples, hauled at these stations, and their mineral compositions are given in the captions to Figs 2a,b and 3a,b. Moreover, the structural and crystallo­ chemical characteristics of the manganese- iron oxy-

hydroxide minerals discussed below are given in a previous paper (Varentsov et al., 1989 ) . 1 Station 34 was set up on the eastern slope of the Bezymiannaya Seamount 640 with coordinates 1 5°51-0'N, 36°07 ·0'W 1 5°50·0'N , 36°08·0'W; the depth interval was 2 100- 1400 m. Blocks of altered phosphatized limestone were torn off the parent deposit and collected; they are covered with a crust 50- 100 mm thick and intensively impregnated by manganese - iron oxyhydroxides. Samples 1 -34-D-11 1 5-(A) (Fig. 2a) and 1-35-D-1 1 5-(2) (Fig. 3a) were selected for detailed study of mineralogy and geochemistry as characteristic manganese -iron crusts and typical substrate rocks. 2 Station 38 (Fig. 1) is located at the top western part of the Bezymiannaya Seamount 640 with coor­ dinates 1 5°51-s'N and 36°09·7'W. Blocks of deeply altered bioclastic limestones were torn from the parent rock; they are up to 400 mm in size with an uneven lumpy surface covered with crust growths of manganese- iron oxyhydroxides. 3 Station 39 (Fig. 1) is at the top of the Bezymian­ naya Seamount 640. A plate-like block (200 x 700 mm) was broken off the parent deposit by a dredge; the block is composed of manganese - iron

Manganese- iron crusts, Bezymiannaya Seamount 640

(a)

91

1-34-D-1-115-A

Fig. 2. (a) Structure of manganese-iron oxyhydroxide crust on altered substrate, a recrystallized, phosphatized limestone.

Sample 1-34-D-1-115-(A), the Bezymiannaya Seamount 640. a, the upper finely botryoidal crust (40 mm), black manganese-iron oxyhydroxides with ochre (iron oxyhydroxides) and white cavities filled mainly with relict material residual after limestone dissolution . The material is mostly represented by manganese feroxyhyte, iron vernadite and subordinate quantities of goethite. b, relics of substrate represented by white recrystallized phosphatized limestone. c, black, dull, sooty manganese-iron oxyhydroxides impregnating substrate (40-80 mm) . They are represented mostly by iron vernadite, manganese feroxyhyte and subordinate amounts of goethite. The presence of relict patchy areas of the substrate is characteristic (see b ) . d, patches and lens-like areas of ochrous material which is a rather early product of substitution (b ) embedded in the mass of manganese-iron oxyhydroxides (c). They are represented by goethite, manganese feroxyhyte, an almost isotropic iron X-phase, probably vernadite, calcite, with admixtures of kaolinite, traces of chlorite, francolite and hydroxyl apatite. (b) Structure of crust of manganese-iron oxyhydroxides on altered substrate, a hydrothermally reworked (intensively phosphatized) limestone. Sample 1-39-D-126, the Bezymiannaya Seamount 640. a, the upper crust of manganese-iron oxyhydroxides with rough botryoidal surface (20 mm). The material contains mostly iron vernadite and manganese feroxyhyte with an admixture of goethite. b, a part of manganese-iron oxyhydroxide crust with microlayered structure (10-15 mm). Iron vernadite dominates with a somewhat subordinate amount of manganese feroxyhyte and admixture of goethite. c, a shiny, massive, dense, rather homogeneous material of manganese-iron oxyhydroxides (10-20 mm) composed predominantly of iron vernadite with lesser amounts of manganese feroxyhyte, admixture of goethite, and rather small quantities of mixed-layered asbolane-buserite. d, intensively reworked material of initial limestone almost entirely composed of phosphates; it is locally intensively impregnated and substituted by manganese-iron oxyhydroxides (20 mm). d-1, phosphate (hydroxyl apatite and francolite) interlayer intensively impregnated by manganese-iron oxyhydroxides (10 mm). e, the lower crust composed of loose sooty manganese-iron oxyhydroxides (20 mm). Iron vernadite and manganese feroxyhyte dominate with admixture of goethite and very small amounts of mixed-layered asbolane-buserite.

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