Life cycle of the Phosphoria Formation: from deposition to the post-mining environment

Handbook of Exploration and Environmental Geochemistry VOLUME 8 Life Cycle of the Phosphoria Formation: From Deposition...

Author: James R. Hein

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Handbook of Exploration and Environmental Geochemistry

VOLUME 8 Life Cycle of the Phosphoria Formation: From Deposition to the Post-Mining Environment



H A N D B O O K OF E X P L O R A T I O N A N D E N V I R O N M E N T A L GEOCHEMISTRY M. HALE (Editor) 1. 2. 3. 4. 5. 6. 7. 8.

ANALYTICAL METHODS IN GEOCHEMICAL PROSPECTING STASTISTICS AND DATA ANALYSIS IN GEOCHEMICAL PROSPECTING ROCK GEOCHEMISTRY IN MINERAL EXPLORATION REGOLITH EXPLORATION GEOCHEMISTRY IN TROPICAL AND SUB-TROPICAL TERRAINS REGOLITH EXPLORATION GEOCHEMISTRY IN ARCTIC AND TEMPERATE TERRAINS DRAINAGE GEOCHEMISTRY GEOCHEMICAL REMOTE SENSING OF THE SUB-SURFACE LIFE CYCLE OF THE PHOSPHORIA FORMATION: FROM DEPOSITION TO THE POST-MINING ENVIRONMENT



Edited by JAMES R. HEIN

US Geological Survey Menlo Park, CA, USA

2004 ELSEVIER Amsterdam 9B o s t o n 9H e i d e l b e r g Paris 9S a n D i e g o 9S a n F r a n c i s c o

9L o n d o n 9N e w Y o r k 9S i n g a p o r e 9S y d n e y

9O x f o r d 9T o k y o

E L S E V I E R B.V. S a r a B u r g e r h a r t s t r a a t 25 P.O. B o x 2 1 1 , 1000 A E A m s t e r d a m ,

92004 US Geological

The Netherlands

Survey. All rights reserved.

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V

PREFACE

US Geological Survey (USGS) scientists have studied the Phosphoria Formation in the Western United States Phosphate Field throughout much of the twentieth century (see Chapter 2). In response to a request by the US Bureau of Land Management (BLM), a new series of geologic, geoenvironmental, and resource studies was initiated in 1997. This program followed three earlier USGS field programs that took place in 1909-1916, 1941-1944, and 1947-1952. Follow-up work to each of those programs continued for many years after conclusion of the main phase of field work. This latest program (1997-2002) consisted of integrated, multiagency, multidisciplinary research with emphasis in four areas: (a) geological and geochemical baseline characterization of the Meade Peak Phosphatic Shale Member and related rocks of the Permian Phosphoria Formation, headed by R.I. Grauch; (b) delineation, assessment, and spatial analysis of phosphate resources and lands disturbed by mining, headed by P.R. Moyle; (c) contaminant residence, reaction pathways, and environmental fate associated with the occurrence, development, and use of phosphate rock, headed by J.R. Herring; and (d) depositional origin and evolution of the Phosphoria Formation and geoenvironmental and deposit modeling, headed by G.J. Orris. The overriding objective of this latest research program was science in support of land management. To carry out these studies, the USGS formed cooperative research relationships with the BLM and the US Forest Service (USFS), which are responsible for land management and resource conservation on public lands, and with five private companies currently leasing or developing phosphate resources in Southeast Idaho. Four operating phosphate mines exist in Southeast Idaho (Dry Valley, Smoky Canyon, Rasmussen Ridge, and Enoch Valley mines) and one in northern Utah (Vernal Mine; see Chapter 3). In addition, 12 inactive mines exist in Southeast Idaho and leases have been or are in the process of being developed for several new mines. The Western Phosphate Field encompasses an area of about 350,000 sq. km in adjacent parts of Idaho, Utah, Montana, Wyoming, Nevada, and Colorado in the northern Rocky Mountains. The thick, high-grade phosphate deposits in the Meade Peak Member of the Phosphoria Formation constitute an important economic resource providing about 12-14% of total United States production (see Chapter 3). The remaining phosphates in the Western Field constitute about 3% of the world reserves and 30% of United States reserves. Phosphorus is an essential nutrient for life and phosphate is essential for the production of many commodities used by modem societies. The principal use of phosphate is as fertilizer. However, products derived from phosphate are also used in other industrial applications,

Preface

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such as fire retardants, detergents and other cleaning supplies, pharmaceuticals, food and beverages, feed, herbicides, and water softeners (see Chapter 22). Many large sedimentary phosphate deposits are hosted by black shale. Black shales are well known to host a wide variety of trace elements, some of economic interest and some of environmental concern. Many of those trace elements may be environmentally sensitive and can be released during mining and weathering of waste rock. In the Western Phosphate Field, phosphate is mined from two high-grade zones in the Meade Peak Member. The ore zones enclose a middle waste zone about 25-30 m thick composed predominantly of low-grade phosphatic black shale. This waste rock is placed in waste piles along with unmineralized rock that is removed to expose phosphate-bearing strata rich enough to be mined. Leaching of the waste rock has released several potentially toxic elements into the environment. Selenium has been the most detrimental element released in terms of its affect on livestock and wildlife. Selenium is a nutrient in low concentrations and a toxicant in only slightly higher concentrations. An important part of our 1997-2002 study, and nine of the 22 chapters (11-19) in this book, concern the distributions of selenium in rocks, soils, plants, animals, and water and its effects on the environment. Other elements of potential environmental concern in the Western Phosphate Field include chromium, copper, molybdenum, vanadium, uranium, and zinc. In fact, the concentrations of vanadium and uranium are high enough that vanadium was recovered as a byproduct of phosphate mining from the early 1940s until 1999; geochemical exploration for uranium occurred during the 1947-1952 USGS field program. Our five-year program has tied together geology, geochemistry, water resources, and biology into an integrative approach to understand an important United States phosphate resource and the consequences of recovery of that phosphate. This type of approach and the knowledge gained are essential prerequisites required for the mining of ores that are essential to the functioning of modern society in an environmentally sound way.

ACKNOWLEDGEMENTS I would like to acknowledge and thank Brandie Mclntyre for invaluable help in processing and standardizing all the manuscripts that compose this 22-chapter book. We would like to thank the mining companies for access to the mines for sampling, especially Nu-West, Rasmussen ridge Mine, J.R. Simplot Co., Smoky Canyon Mine, and P4 Production LLC, Enoch Valley Mine, as well as Rhodia Inc. and Astaris Production LLC. The following scientists provided excellent and timely reviews of one or more chapters in this book: 9 9 9 9 9

Michael C. Amacher, USDA, Forest Service, Logan, UT; John A. Barron, USGS, Menlo Park, CA; Paul Belasky, Ohlone College, Fremont, CA; John M. Besser, USGS, Columbia, MO; Arthur A. Bookstrom, USGS, Spokane, WA;

Preface 9 9 9 9 9 9 9 9 9 9 9 9 9 9 9 9 9 9 9 9 9 9 9 9 9 9 9 9 9 9 9 9

VII

Steven E. Box, USGS, Spokane, WA; George N. Breit, USGS, Denver, CO; George A. Desborough, USGS, Denver, CO; Robert E. Garrison, University of California, Santa Cruz, CA; Richard I. Grauch, USGS, Denver, CO; Philip L. Hageman, USGS, Denver, CO; Steven J. Hamilton, USGS, Yankton, SD; Peter W. Harben, Industrial Minerals Consultants, Las Cruces, NM; James R. Hein, USGS, Menlo Park, CA; Stephen M. Jasinski, USGS, Reston, VA; Margaret A. Keller, USGS, Menlo Park, CA; Lisa B. Kirk, Maxim Technologies Inc., Bozeman, MT; Andrea Koschinsky, International University Bremen, Germany; Randolph A. Koski, USGS, Menlo Park, CA; Joel S. Leventhal, USGS, Denver, CO; Dean A. Martens, USDA, Tucson, AZ; Greg M611er, University of Idaho, Moscow, ID; Philip R. Moyle, USGS, Spokane, WA; Joyce A. Ober, USGS, Reston, VA; Peter Oberlindacher, USBLM, Boise, ID; John C. Mars, USGS, Reston, VA; Robert B. Perkins, Portland State University, Portland, OR; David Z. Piper, USGS, Menlo Park, CA; Theresa S. Presser, USGS, Menlo Park, CA; Robert Rosenbauer, USGS, Menlo Park, CA; Richard E Sanzolone, USGS, Denver, CO; Calvin H. Stevens, California State University, San Jose, CA; Peter W. Swarzenski, USGS, St. Petersburg, FL; Marc A. Sylvester, USGS, Menlo Park, CA; George E Vance, University of Wyoming, Laramie, WY; Florence L. Wong, USGS, Menlo Park, CA; Robert A. Zielinski, USGS, Denver, CO. JAMES R. HEIN, Menlo Park, CA February 2003

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LIST OF CONTRIBUTORS

Michael C. Amacher received a BSc in chemistry, a MSc in chemistry, and a PhD in soil

chemistry from Pennsylvania State University. He joined the USDA Forest Service in 1989. He works on soil analysis methods, trace element biogeochemistry in soils, reactivity, and transport of metals in soils, and the status and trend of forest soil quality indicators (USDA, Forest Service, Logan, UT). Kenneth J Bird joined the US Geological Survey in 1974. His research focused initially on

the petroleum potential of carbonate rocks in northern Alaska. With broadening interests, primarily in stratigraphy and sedimentology, he became extensively involved in research and petroleum resource assessment activities in Alaska and elsewhere in the United States. Currently he is the leader of a relatively large, multidisciplinary team conducting petroleum geologic research and new assessments of undiscovered oil and gas resources in Alaska (USGS, Menlo Park, CA). James R. Budahn received a BSc in chemistry from Southwest State University, Marshall,

Minnesota and a MSc in chemistry from Oregon State University, Corvallis, Oregon. He joined the US Geological Survey in 1979. From 1979, he has worked on INAA and gamma-ray spectrometry methodologies and applications (USGS, Denver, CO). Kevin J. Buhl received a BA in biology from St. Mary's College, Winona, Minnesota and

an MA in biology from the University of South Dakota, Vermillion. He joined the US Fish and Wildlife Service in 1979. He has conducted laboratory and field studies of environmental contaminant problems in a variety of aquatic ecosystem types. He has published 41 scientific papers and reports (USGS, Yankton, SD). Steven J. Detwiler did his doctoral research at the University of California Davis on sele-

nium toxicokinetics in avian eggs. His work focused upon detectable inter-specific differences to help elucidate Se ecotoxicology, and potential underlying toxicodynamic mechanisms. Steven worked as part of the Interagency San Joaquin Valley Drainage Program spawned by the discoveries at Kesterson in the 1980s, and currently works for the US Fish and Wildlife Service conducting primarily Se-related biomonitoring and risk assessment (USFWS, Sacramento, CA).

List of contributors

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James G. Evans received a BSc in geology in 1960 from the University of Massachusetts at Amherst and a PhD (structural geology and igneous and metamorphic petrology) in 1966 from the University of California (Los Angeles). His dissertation comprised the first structural analysis of a segment of the San Andreas fault zone. Since 1967, he has worked for the US Geological Survey on projects with a mineral resources focus. An early assignment included detailed mapping of the Lynn Window, site of the Carlin gold mine. Data gathered during that study was the basis of the first structural analysis of a segment of the Roberts Mountains thrust. Most of his work concentrated on resource assessments and commodity studies (especially Au, Cr, P). Data from these studies resulted in structural analyses of the widespread Josephine Peridotite in NW California and SW Oregon, Belt-age rocks in northeast Washington, and most recently of the Meade thrust plate in Southeast Idaho. He presently works on garnet deposits (abrasives) in northern Idaho and Great Basin studies in Nevada and southern Oregon (USGS, 904 W. Riverside Ave., Rm 202, Spokane, WA, 99201; [email protected]). Carlotta B. Chernoff received a BSc in geophysics and MA in geology from The University of Texas at Austin, and a PhD in geology from The University of Arizona. She studies the processes controlling the incorporation of metals into sedimentary rocks and the mechanisms of chemical exchange and mass transfer that occur during diagenesis and metamorphism of those rocks. Since completing her PhD in 2002, she has been working as an exploration geologist for Conoco Phillips in Houston, Texas (ConocoPhillps, Houston, TX). Andrea L. Foster received a BSc in geology from Indiana University (Bloomington) and a PhD in geochemistry from Stanford University (Stanford, CA). She joined the US Geological Survey in 1999. Her work has focused primarily on the application of synchrotron-based spectroscopic techniques to identify the forms of potentially toxic metals such as As, Cd, Cr, Se, and Hg in solid materials derived from recent and historical mining activities (USGS, Menlo Park, CA). Richard I. Grauch received an AB from Franklin and Marshall College and a PhD from the University of Pennsylvania. He was a postdoctoral researcher at SUNY, Binghamton, and a postdoctoral scholar at the University of California (Los Angeles) before consulting for the Ministerio de Minas e Hidrocarburos in Venezuela. He joined the US Geological Survey in 1974 where he has worn several different administrative hats, but prefers research which has focused on the genesis of a variety of ore deposits, mostly unconventional types. Recent work focuses on detailed petrologic and geochemical studies that include (a) natural and anthropogenic sources of environmental contaminants and (b) experimental work on element partitioning in the system shale-brine-vapor under diagenetic P - T conditions (USGS, DFC, MS 973, Box 25046, Denver, CO, 80225-0046; [email protected]). Mickey E. Gunter received a BSc (geology and mathematics) from Southern Illinois University, Carbondale, and a MSc and PhD (geological sciences) from Virginia Tech,

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Blacksburg, Virginia. He joined the Department of Geological Sciences, University of Idaho in 1989 and is currently a Professor of Mineralogy. Gunter's research involves crystal chemical and structural characterization of natural and cation-exchange zeolites, phosphates, and new minerals. He is also interested in studying the directional dependence of the physical properties of minerals and health affects of minerals, both positive and negative. He continues to pursue research and development of new methods in optical mineralogy (University of Idaho, Moscow, ID). Jeffery O. Hall received a BSc in agriculture economics and a DVM from Oklahoma State

University, and a PhD in toxicology from the University of Illinois and is a Diplomat American Board of Veterinary Toxicology. He joined the Utah Veterinary Diagnostic Laboratory/Utah State University in 1996. He works in diagnostic toxicology, with mineral toxicoses and interactions, and with poisonous plants (Utah State University, Logan, UT). Steven J. Hamilton received a BSc (Wildlife Management) from Humboldt State

University, Arcata, California, and MSc and PhD (Fisheries and Wildlife) from the University of Missouri, Columbia. He joined the US Fish and Wildlife Service in 1975. He works on various aspects of toxicology in aquatic ecosystems and since 1984 has focused primarily on selenium toxicology. He has published 102 scientific papers, reports, and book chapters (USGS, 31247 436th Ave., Yankton, SD, 57078-6364; steve_hamilton@ usgs.gov). Mark A. Hardy received a BSc (water science/limnology) from the University of

Wisconsin, Stevens Point, Wisconsin. He then joined the US Geological Survey in 1975. In addition to performing numerous assessments of water quality in streams, ground water, and wetlands across the United States, he has been extensively involved with the standardization of data-collection methods and the development of instrumentation for national water-quality programs. He currently evaluates data-quality needs, project designs, data-collection methods, and data interpretations for water-quality studies (USGS, Boise, ID). James R. Hein received a BSc (geology) from Oregon State University and a PhD (Earth

Sciences) from the University of California (Santa Cruz) before joining the US Geological Survey in 1974. Hein has spent much of his career studying marine mineral deposits in the modern ocean basins and analogs in the geologic record. Mineral deposit types studied include phosphorite, hydrogenetic ferromanganese crusts, diagenetic-hydrogenetic ferromanganese nodules, hydrothermal manganese deposits, barite, ironstones, and polymetallic sulfides. Hein is also applying geochemical and isotopic proxies in marine chemical sediments to the study of paleoceanography. Hein has edited or co-edited seven books, including this one (USGS, MS 999, 345 Middlefield Rd., Menlo Park, CA, 94025; [email protected]). James R. Herring received a PhD in Earth Science from Scripps Institution of

Oceanography, University of California, San Diego. He joined the US Geological Survey


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in 1978 and has conducted a variety of geochemical and mineral deposit studies (USGS, DFC, MS 973, Box 25046, Denver, CO, 80225-0046; [email protected]). Stephen M. Jasinsld received a BSc in geology from the University of Pittsburgh and worked for the US Bureau of Mines from 1987 until 1996 as a mineral commodity specialist in the nonferrous metals section. He joined the US Geological Survey in 1996 and has been the mineral commodity specialist for phosphate rock and peat since 1997 (USGS, 983 National Center, Reston, VA, 20192; [email protected]). E.A. Johnson received a PhD from Rice University and is a sedimentologist-stratigrapher with the US Geological Survey. He spent most of his career conducting research in support of regional framework studies of energy resource-bearing sedimentary systems by constructing depositional models as a component of basin analysis. His research has been both domestic (Colorado, Wyoming, Nevada) and foreign (China, Pakistan, Kyrgyzstan, Armenia, China). Currently, he is Acting Associate Team Scientist for the Central Energy Team, and participates in national resource assessments of oil and gas and coal (USGS, Denver, CO). Andrew C. Knudsen received a BA in geology from Hamilton College and a PhD in geology from the University of Idaho. He has worked as a Post-Doctoral Research Fellow in the Environmental Soil Chemistry lab at the University Idaho. His research has focused on environmental mineralogy and geochemistry in mining-impacted sites. He is now a professor in the Geology Department, Lawrence University, Appleton, WI, 54911 ([email protected]). Paul J. Lamothe received a BSc (chemistry) from the University of San Francisco, California and a PhD (chemistry), from Marquette University, Milwaukee, Wisconsin. He was a research chemist with the US Environmental Protection Agency prior to joining the US Geological Survey in 1976. He is editor of "The Geoanalyst" and he is a member of the council of the International Association of Geoanalysts. His research interests include atomic spectroscopy and trace-element geochemistry (USGS, DFC, MS 973, Box 25046, Denver, CO, 80225-0046; [email protected]). William H. Lee received a BA (geology) from the University of Colorado and pursued graduate studies at the Colorado School of Mines before joining the US Geological Survey in 1961. From 1961 to 1972, he worked on the safety of underground nuclear testing in the Special Projects Branch. From 1972 to 1982, he worked in economic geology and mineral resource management in the western United States. From 1982 to 1983, he worked for the Minerals Management Service in economic mineral resources and from 1983 to present he has worked for the Bureau of Land Management in Wyoming, Washington DC, and Idaho as a senior minerals specialist (USBLM, Boise, ID). Cheryl L. Mackowiak received a BSc (plant and soil science) and MSc (plant and soil science) from Southern Illinois University. She was a research horticulturist at NASA's

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Advanced Life Support program, Kennedy Space Center, Florida, before completing a PhD (plant nutrition and soil fertility) at Utah State University. She subsequently joined the USDA Forest Service as a postdoctoral soil scientist in 2002. She works on trace element biogeochemistry, transport, and plant bioavailability (USDA, Forest Service, 860 N. 1200 E., Logan, UT, 84321-5700; [email protected]). Brandie R. Mclntyre received a BSc (geology) from California State University, Fresno and joined the US Geological Survey in 2001. She is currently working on a graduate degree at San Jose State University and is doing research on marine mineral deposits and environmental geochemistry (USGS, Menlo Park, CA). Phillip R. Moyle received a BSc (geology) from the University of California at Davis and has worked in mineral resources, especially industrial minerals, for over 25 years. Most of his resource assessment and deposit investigations, including extensive underground work, were conducted from 1979 to 1996 while with the US Bureau of Mines. He also specialized in shallow geophysical methods while a member of the Bureau's mine waste site environmental characterization team and worked to develop real-time, multidisciplinary, siteinvestigation techniques. Since joining the US Geological Survey in 1997, he has studied phosphate, aggregate, diatomite, and garnet deposits in the western United States. He also teaches a mine safety course on "health risks associated with abandoned mine and mill sites" for the US Forest Service National Mineral Training Center (USGS, 904 W. Riverside Ave., Rm 202, Spokane, WA, 99201; [email protected]). Benita L. Murchey received a BA in biology from Rice University and a PhD in geology from University of California at Santa Cruz. She joined the US Geological Survey in 1978. Her work has focused on the stratigraphic and paleogeographic distribution of siliceous microfossils in Paleozoic and Mesozoic marine basins of western North America. The depositional and tectonic histories of basins receiving biosiliceous sediments have been a particular interest as well (USGS, MS 973,345 Middlefield Rd., Menlo Park, CA, 94025; [email protected]). Greta J. Orris received a BA and a MSc in geology and PhD in mineral economics. She has spent much of her career as a research geologist for the US Geological Survey. As an industrial minerals expert, much of her research has focused on the development of deposit models, numerical modeling of deposit distribution, economic modeling, and development of resource appraisal techniques. These skills have allowed her participation in a wide variety of domestic and international research efforts (USGS, 520 N. Park Ave., Tucson, AZ, 85719; [email protected]). Robert B. PerMns received a BSc (geology) from Morehead State University (Morehead, Kentucky) and a MSc (geology) from Eastern Kentucky University (Richmond). He then became an environmental consulting geologist prior to completing a PhD (environmental


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geology) at Portland State University, Oregon. The research presented in this volume was completed as part of a US Geological Survey Mendenhall Postdoctoral Fellowship. He is now a professor in the Department of Geology, Portland State University, P.O. Box 751, Portland, OR, 97207-0751 ([email protected]).

David Z. Piper received a BSc from the University of Kentucky, a MSc from Syracuse University, and PhD from Scripps Institute of Oceanography before joining the US Geological Survey in 1975. His research focused initially on the geochemistry of ferromanganese deposits in the Pacific Ocean. He then moved on land to examine phosphaticenriched black shales of Paleozoic to Holocene age. Currently, he is involved in the examination of the geochemistry of soils and stream sediments in the conterminous States, while still maintaining an interest in unraveling the depositional environments of black shales (USGS, Menlo Park, CA). Theresa Presser is a chemist with the US Geological Survey. She became involved in selenium issues in 1983 during the investigation of environmental damage at Kesterson National Wildlife Refuge, California. Her biogeochemical model describing the kesterson effect and the kesterson, a unit of measure of hazard to wildlife, has contributed to the overall understanding of selenium's origins, exposures, and risk. She authored, among other articles, chapters in Selenium in the Environment and Environmental Chemistry of Selenium. She recently collaborated on a selenium model for the San Francisco Bay-Delta Estuary to help resolve issues of water management and ecological effects (USGS, MS 435, 345 Middlefield Rd., Menlo Park, CA, 94025; [email protected]). Joseph P Skorupa has been conducting field research on the ecotoxicology of selenium since 1987 when he first joined the US Fish and Wildlife Service as an avian ecologist. His research has focused on California, but has also included research in Nevada, Wyoming, and southeast Idaho. From 1992-1998 he served as the US Fish and Wildlife Service's technical lead for the National Irrigation Water Quality Program's data synthesis project, a detailed examination of selenium ecological risk across the entire western United States. Currently, he is serving as the Clean Water Act biologist in one of the national offices (USFWS, Arlington, VA). Lisa L. Stillings received a BSc (geology) from Allegheny College, Pennsylvania, a MSc (hydrogeology) from Kent State University, Ohio, and a PhD (geochemistry) from Pennsylvania State University, University Park. She joined the US Geological Survey in 1998 and works on mineral weathering and metal cycling in mining-impacted environments (USGS, MS 176, University of Nevada, Reno, NV, 89557; [email protected]). Robert A. Zielinski received a BSc (chemistry) from Rutgers University, New Brunswick, New Jersey and PhD (geochemistry) from MIT, Cambridge, Massachusetts, before joining the US Geological Survey as a postdoctoral researcher in 1972. He was appointed as a

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research chemist in 1974. His work for the US Geological Survey utilizes chemical, isotopic, and instrumental measurements as well as laboratory-based selective extractions and process simulations. His primary area of interest is the study of natural processes that influence the mobility of trace elements and radionuclides of environmental and human health concern (USGS, DFC, MS 973, Box 25046, Denver, CO, 80225-0046; rzielinski@ usgs.gov).

XV

CONTENTS

Preface ........................................................................................................................................ V List o f Contributors ................................................................................................................ VIII PART I. I N T R O D U C T I O N

Chapter 1. The Permian Earth .................................................................................................... 3 J.R. Hein Introduction ................................................................................................................ 3 Geology, plate tectonics, paleogeography .................................................................. 3 Climate ...................................................................................................................... 6 Oceanography ............................................................................................................ 7 Western North American margin and the Phosphoria sea ...................................... 10 End o f Permian ........................................................................................................ 12

Chapter 2. Evolution of thought concerning the origin of the Phosphoria Formation, Western US Phosphate Field .................................................................................. 19 J.R. Hein, R.B. Perkins and B.R. Mclntyre Abstract .................................................................................................................... 19 Introduction .............................................................................................................. 20 Delineation o f western phosphate lands: Pre- 1940s ................................................ 21 Geochemical exploration, P, U, and V: The 1940s-1950s ...................................... 24 Depositional environments and transgressive-regressive cycles: The 1960s-1970s .................................................................................................... 27 Paleogeography, phosphogenesis, and sequence stratigraphy: 1980-2002 ............ 30 Paleogeography o f the Phosphoria basin ............................................................ 30 Phosphogenesis .................................................................................................... 32 Eustatic changes and sequence stratigraphy ........................................................ 34 Outstanding issues .................................................................................................. 36 PART II. R E G I O N A L S T U D I E S

Chapter 3. The history of production of the Western Phosphate Field .................................... 45 S.M. Jasinski, W.H. Lee and J.D. Causey Abstract .................................................................................................................... 45 Introduction .............................................................................................................. 45 Early scientific surveys ............................................................................................ 48

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Contents Laws associated with US phosphate exploration and mining ................................ Idaho ........................................................................................................................ Montana .................................................................................................................. Utah .......................................................................................................................... Wyoming .................................................................................................................. Mining in the Western Phosphate Field in the twenty-first century ........................

49 52 55 55 58 59

Chapter 4. The Meade Peak Member of the Phosphoria Formation." Temporal and spatial variations in sediment geochemistry ..........................................................73 R.B. Perkins and D.Z. Piper Abstract .................................................................................................................... 73 Introduction .............................................................................................................. 74 Oceanographic setting of the Phosphoria basin .................................................. 74 Origin of Meade Peak sediments ........................................................................ 76 Methods and data evaluation .................................................................................. 77 Element associations ................................................................................................ 80 Temporal variations in terrigenous elements .......................................................... 80 Major-element oxides .......................................................................................... 83 Minor and trace elements .................................................................................... 89 Spatial variations in terrigenous elements .............................................................. 90 Temporal variations in marine elements .................................................................. 90 Spatial variations in marine elements ...................................................................... 99 Conclusions ............................................................................................................ 103

Chapter 5. Regional analysis of spiculite faunas in the Permian Phosphoria basin: Implication for paleoceanography ........................................................................ 111 B.L. Murchey Abstract .................................................................................................................. Introduction ............................................................................................................ Background and previous studies .......................................................................... Methods .................................................................................................................. Identification of sponge spicule morphotypes .................................................. Quantitative comparison of sponge spicules to radiolarians ............................ Results .................................................................................................................... Eastern belt: Rhax-bearing, demosponge-dominated spiculite assemblages ........................................................................................................ Rex Chert of the Phosphoria Formation in southeastern Idaho, central basin (Table 5-II; Sample 1 - 3 ) .......................................................... Black chert, northeastern Nevada, southwestern margin of Phosphoria Basin and inferred Antler high (Table 5-II; Sample 4-7) .............................. Edna Mountain Formation of Nevada, overlap sequence deposited on the Antler high (Table 5-II; Samples 8-12) ........................................................ Spiculitic black chert, Havallah assemblage, Nevada eastern basin margin facies (Table 5-II; Samples 1 3 - 2 4 ) .................................................. Central belt mixed choristid demosponge-hexactinellid sponge assemblages associated with (ruzhencevispongacid) radiolarians ..........................................

111 112 114 117 117 118 119 119 119 122 122 123 124

Contents

XVII Western belt: Radiolarian-dominated assemblages with or without a minor component o f hexactinellid sponge spicules .................................................... N o r t h e m Basins ................................................................................................ N o r t h w i n d Ridges, Chukchi Sea ...................................................................... A n g a y u c h a m terrane and Northern Brooks Range ................................................ Discussion and conclusions ..................................................................................

125

125 125 126 126

Chapter 6. Strain distribution and structural evolution of the Meade plate, southeastern Idaho ................................................................................................ 137 J.G. Evans Abstract .................................................................................................................. Introduction ............................................................................................................ Depth o f burial ...................................................................................................... Thermal history ...................................................................................................... Petroleum generation and very low-grade m e t a m o r p h i s m ................................ Low-grade m e t a m o r p h i s m ................................................................................ Structure ................................................................................................................ Pretectonic structures ........................................................................................ Syntectonic structures ........................................................................................ Orogenic and structural terminology ................................................................ Timing o f thrusting in southeastern Idaho ........................................................ Shortening o f the Meade and other plates ........................................................ Direction o f tectonic transport .......................................................................... Thickness o f the Meade thrust plate and topology o f the Meade thrust .......... Style o f deformation o f the Meade thrust and plate .......................................... Shortening and extension implied by folding and faulting in the Meade plate Estimates o f shortening and compression directions from other data .............. Variable displacement ........................................................................................ Conclusions ............................................................................................................

137 137 140 141 141 142 143 143 144 144 145

146 147 147 151 152

157 158 161

PART III: G E O L O G I C A L A N D G E O C H E M I C A L STUDIES IN S O U T H E A S T I D A H O

Chapter 7. The effects of weathering on the mineralogy of the Phosphoria Formation, southeast Idaho .................................................................................................... 169 A.C. Knudsen and M.E. Gunter Abstract .................................................................................................................. Introduction ............................................................................................................ Carbonate fluorapatite ............................................................................................ Methods .................................................................................................................. Sampling and sample preparation ...................................................................... X R D analysis and Rietveld refinement ............................................................ CO 2- substitution in CFA .................................................................................. Statistical analyses ............................................................................................ Results .................................................................................................................... Bulk mineralogy ................................................................................................

169 169 171 172 172 172 173 173 174 174

Contents

XVIII

N o n d i f f r a c t i n g c o m p o n e n t ................................................................................ C a r b o n a t e substitution in fluorapatite ................................................................ D i s c u s s i o n .............................................................................................................. W e a t h e r i n g ........................................................................................................ C a r b o n a t e substitution in C F A ..........................................................................

177 180 180 180 182

C o n c l u s i o n s ............................................................................................................ 185

Chapter 8. Petrogenesis and mineralogic residence of selected elements in the Meade Peak Phosphatic Shale Member of the Permian Phosphoria Formation, southeast Idaho .................................................................................. 189 R.I. G r a u c h , G.A. D e s b o r o u g h , G.P. M e e k e r , A.L. Foster, R.G. Tysdal, J.R. H e r r i n g , H.A. L o w e r s , B.A. Ball, R.A. Z i e l i n s k i and E.A. J o h n s o n A b s t r a c t .................................................................................................................. I n t r o d u c t i o n ............................................................................................................ G e o l o g i c setting and h i s t o r y .................................................................................. A p p r o a c h and m e t h o d o l o g y .................................................................................. R e s u l t s and d i s c u s s i o n .......................................................................................... Detrital a s s e m b l a g e ............................................................................................ A u t h i g e n i c / d i a g e n e t i c a s s e m b l a g e ....................................................................

189 190 192 193 197 197 201

P h o s p h a t e ...................................................................................................... 201 Silicates and c a r b o n a t e s ................................................................................ 2 0 4 S u l f i d e s .......................................................................................................... O t h e r m i n e r a l s ................................................................................................ E p i g e n e t i c / s u p e r g e n e a s s e m b l a g e ...................................................................... Silicates .......................................................................................................... H a l i d e s .......................................................................................................... O t h e r M i n e r a l s ..............................................................................................

206 212 212 212 213 213

S e l e n i d e (CuxSey) .......................................................................................... 213 N a t i v e e l e m e n t s .............................................................................................. 213 O x i d e s ............................................................................................................ 217 P h o s p h a t e s ...................................................................................................... 217 Sulfates .......................................................................................................... 217 S u l f i d e s .......................................................................................................... 218 C o n c e p t u a l m o d e l .................................................................................................. 218

Chapter 9. Weathering of the Meade Peak Phosphatic Shale Member, Phosphoria Formation: Observations based on uranium and its decay products .................. 227 R.A. Zielinski, J.R. B u d a h n , R.I. G r a u c h , J.B. P ac e s and K.R. S i m m o n s A b s t r a c t .................................................................................................................. 227 I n t r o d u c t i o n ............................................................................................................ S a m p l e c o l l e c t i o n and d e s c r i p t i o n ........................................................................ A n a l y t i c a l m e t h o d s ................................................................................................ G a m m a - r a y s p e c t r o m e t r y .................................................................................. F i s s i o n - t r a c k r a d i o g r a p h y .................................................................................. Selective extraction e x p e r i m e n t s ........................................................................ M a s s s p e c t r o m e t r y ............................................................................................

227 228 230 230 232 232 232

O t h e r a n a l y s e s .................................................................................................... 233

Contents

XIX Results and Discussion .......................................................................................... 233 A m o u n t o f extractable uranium and comparison to other elements .................. 233 Microdistribution o f uranium in phosphorite .................................................... 234 Disequilibria in the 238U decay-series determined by g a m m a - r a y spectrometry ...................................................................................................... 240 Disequilibria in the 238Udecay-series determined by mass spectrometry ........ 243 Conclusions ............................................................................................................ 246

Chapter 10. Mineral affinities and distribution of selenium and other trace elements in black shale and phosphorite o f the Phosphoria Formation .............................. 251 R.B. Perkins and A.L. Foster Abstract ................................................................................................................ Introduction .......................................................................................................... Methods ................................................................................................................ Sample selection and preparation .................................................................... Solid characterization o f selected samples ...................................................... Sequential extractions ...................................................................................... Sequential-extraction techniques ................................................................ Analyses o f extracts .................................................................................... Initial and residual solids characterization .................................................. Results .................................................................................................................. Solid characterization ...................................................................................... Scanning electron microscopy .................................................................... Quantitative analyses using the electron microprobe .................................. X-ray absorption spectroscopy .................................................................... Sequential extractions ...................................................................................... Reference materials ...................................................................................... Samples ........................................................................................................ Discussion ............................................................................................................ Conclusions ..........................................................................................................

251 252 252 252 256 257 257 259 260 260 260 260 264 268 270 270 273 287 291

P A R T IV. G E O E N V I R O N M E N T A L S T U D I E S

Chapter 11. The Phosphoria Formation: A Model for forecasting global selenium sources to the environment ................................................................................299 T.S. Presser, D.Z. Piper, K.J. Bird, J.P. Skorupa, S.J. Hamilton, S.J. Detwiler and M.A. H u e b n e r Abstract ................................................................................................................ 299 Introduction .......................................................................................................... 300 Methods and sources o f data .............................................................................. 300 Selenium guidelines ........................................................................................ 300 Western US (Colorado River watersheds and San Joaquin Valley and San Francisco Bay-Delta Estuary, California) ................................................ 301 Idaho ................................................................................................................ 301 Global distribution o f phosphate deposits and petroleum basins .................... 302 Conceptual model ................................................................................................ 302

XX

Contents S e l e n i u m b i o c h e m i s t r y a n d g u i d e l i n e s ............................................................ 303 S e l e n i u m o c e a n c h e m i s t r y .............................................................................. 305 F i e ld c a s e - s t u d i e s a n d e n v i r o n m e n t a l s e l e n i u m c o n c e n t r a t i o n s ...................... 305 I d a h o c a s e - s t u d y .................................................................................................. 308 P h o s p h a t e p r o d u c t i o n a n d shale e x p o s u r e s .................................................... 308 G e o c h e m i c a l m e c h a n i s m o f d i s p e r s a l a n d s e l e n i u m d i s c h a r g e s .................... 308 B i o l o g i c a l r e a c t i o n s a n d s e l e n i u m c o n c e n t r a t i o n s in b i o t a ............................ 310 Plants, invertebrates, a n d fish ...................................................................... 310 B i r d s a n d m a m m a l s .................................................................................... 311 G l o b a l o c c u r r e n c e o f p h o s p h o r i t e s a n d p e t r o l e u m .............................................. 313 P r e d i c t i o n o f s e l e n i u m s o u r c e s ........................................................................ 313 C o m m o d i t i e s a n d e x p l o r a t i o n .......................................................................... 315 C o n c l u s i o n s .......................................................................................................... 315

Chapter 12. Lithogeochemistry of the Meade Peak Phosphatic Shale Member of the Phosphoria Formation, southeast Idaho ............................................................ 321 J.R. H e r r i n g and R.I. G r a u c h A b s t r a c t ................................................................................................................ 321 I n t r o d u c t i o n .......................................................................................................... 322 P u r p o s e and b a c k g r o u n d .................................................................................. 322 M e a s u r e d sections ............................................................................................ M e t h o d s ................................................................................................................ S a m p l i n g .......................................................................................................... A n a l y s e s .......................................................................................................... R e s u l t s .................................................................................................................. C o m p o s i t i o n a l a v e r a g e s o f e l e m e n t s in the M e a d e Peak ................................

324 327 327 328 329 329

G e o m e t r i c m e a n s and d e v i a t i o n s .................................................................... L i t h o l o g i c c h a r a c t e r i z a t i o n .............................................................................. Trace e l e m e n t s ................................................................................................ I n d i v i d u a l rock s a m p l e s ..................................................................................

333 334 338 338

C l o s e - s p a c e d c h a n n e l s a m p l e s , S e c t i o n Z ...................................................... 340 C o m p o s i t i o n a l c h a n g e s due to w e a t h e r i n g , E n o c h Valley c h a n n e l s a m p l e s ............................................................................................................ 340 W e a t h e r i n g and other alteration .......................................................................... 343 T r a c e - e l e m e n t a s s o c i a t i o n s as a f u n c t i o n o f alteration .................................... 345 I n d i v i d u a l trace e l e m e n t s ................................................................................ 354 S e l e n i u m ...................................................................................................... U r a n i u m ...................................................................................................... V a n a d i u m .................................................................................................... O t h e r G e o e n v i r o n m e n t a l l y s i g n i f i c a n t trace e l e m e n t s ........................................ Silver ............................................................................................................ A r s e n i c ........................................................................................................ C a d m i u m ...................................................................................................... T h a l l i u m ...................................................................................................... A l t e r a t i o n m o d e l .................................................................................................. C o n c l u s i o n s ..........................................................................................................

356 356 358 358 358 358 358 359 359 363

Contents

XXI

Chapter 13. Rock leachate geochemistry of the Meade Peak Phosphatic Shale Member of the Phosphoria Formation, southeast Idaho ............................................................ 367 J.R. H e r r i n g A b s t r a c t ................................................................................................................

367

I n t r o d u c t i o n .......................................................................................................... 368 B a c k g r o u n d ...................................................................................................... 368 R e l e v a n c e o f l e a c h a t e e x p e r i m e n t s .................................................................. 368 R o c k s a m p l e s .................................................................................................. 369 M e t h o d s ................................................................................................................

370

S a m p l e p r e p a r a t i o n .......................................................................................... 3 7 0 A n a l y s e s .......................................................................................................... 371 R e s u l t s ..................................................................................................................

372

D i s c u s s i o n ............................................................................................................ 373 C o r r e l a t i o n a n a l y s i s ........................................................................................ 373 C o r r e l a t i o n s w i t h m a j o r c o m p o n e n t s .............................................................. 379 C o r r e l a t i o n w i t h m i n e r a l o g y ............................................................................ 379 F a c t o r a n a l y s i s .................................................................................................. 380 C o r r e l a t i o n w i t h b u l k c h e m i s t r y ...................................................................... 382 L e a c h a t e c o n d i t i o n v a r i a t i o n s .......................................................................... 383 Particle size .................................................................................................. 383 L e a c h a t e t i m e .............................................................................................. 383 H i g h l y a l t e r e d r o c k s .................................................................................... 392 L e s s - a l t e r e d r o c k s ........................................................................................ 393 L e a s t - a l t e r e d r o c k s ...................................................................................... 393 A n o x i c c o n d i t i o n s ........................................................................................ 394 F r e e z e - t h a w effects ...................................................................................... 395 M u l t i p l e l e a c h i n g ........................................................................................ 396 C o n c l u s i o n s .......................................................................................................... 396

Chapter 14. Rex Chert Member of the Permian Phosphoria Formation." Composition, with emphasis on elements of environmental concern .............................................. 399 J.R. Hein, B.R. M c l n t y r e , R.B. Perkins, D.Z. P i p e r a n d J.G. E v a n s A b s t r a c t ................................................................................................................ 399 I n t r o d u c t i o n .......................................................................................................... 4 0 0 P r e v i o u s studies .................................................................................................. 401 M e t h o d s ................................................................................................................ 402 Field s a m p l i n g .................................................................................................. 402 R o c k s a m p l e p r e p a r a t i o n ................................................................................ 405 G e o c h e m i c a l a n a l y s e s ...................................................................................... 405 Statistical a n a l y s e s .......................................................................................... 405 M i n e r a l o g i c a l a n a l y s i s .................................................................................... 4 0 6 R e s u l t s .................................................................................................................. 4 0 6 L i t h o s t r a t i g r a p h y .............................................................................................. 4 0 6 P e t r o g r a p h y ...................................................................................................... 4 1 0 M i n e r a l o g y ...................................................................................................... 411 C h e m i c a l c o m p o s i t i o n .................................................................................... 411

XXII

Contents S t r a t i g r a p h i c c h a n g e s in c h e m i c a l c o m p o s i t i o n .............................................. 4 1 9 P h a s e a s s o c i a t i o n s o f e l e m e n t s ........................................................................ 4 1 9 D i s c u s s i o n a n d c o n c l u s i o n s : E n v i r o n m e n t a l l y sensitive e l e m e n t s ...................... 4 2 4

Chapter 15. Gaseous selenium and other elements in near-surface atmospheric samples, southeast Idaho .................................................................................................. 4 2 7 P.J. L a m o t h e and J.R. H e r r i n g A b s t r a c t ................................................................................................................ I n t r o d u c t i o n .......................................................................................................... L o c a t i o n .............................................................................................................. S t u d y d e s i g n ........................................................................................................ S a m p l e c o l l e c t i o n a n d a n a l y s i s ............................................................................ R e s u l t s a n d d i s c u s s i o n ........................................................................................ C o n c l u s i o n s ..........................................................................................................

427 427 428 428 430 432 433

Chapter 16. Selenium loading through the Blackfoot River watershed." Linking sources to ecosystems ...................................................................................................... 437 T.S. Presser, M. Hardy, M . A . H u e b n e r a n d P.J. L a m o t h e A b s t r a c t ................................................................................................................ I n t r o d u c t i o n .......................................................................................................... Site location and d e s c r i p t i o n ................................................................................ M e t h o d s ................................................................................................................ F l o w ................................................................................................................ S a m p l e collection ............................................................................................ W a t e r ............................................................................................................ S e d i m e n t ...................................................................................................... A n a l y s i s ............................................................................................................ R e s ults .................................................................................................................. Q u a l i t y a s s u r a n c e and q u a l i t y control ............................................................ R e g i o n a l w a t e r - d i s c h a r g e and s e l e n i u m c o n c e n t r a t i o n , speciation,

437 438 441 444 444 444 444 445 446 446 446

and l o a d i n g ...................................................................................................... 4 4 8 H y d r o l o g i c c o n d i t i o n s .................................................................................. 448 S e l e n i u m c o n c e n t r a t i o n s .............................................................................. 453 S e l e n i u m s p e c i a t i o n - s u p p l e m e n t a l data ...................................................... 4 5 4 S u s p e n d e d s e d i m e n t - s u p p l e m e n t a l data .................................................. 455 D i s s o l v e d s e l e n i u m load c a l c u l a t i o n s .......................................................... 455 S e l e n i u m load forecasts for a v e r a g e and wet y e a r s - s u p p l e m e n t a l data .... 4 5 6 R e g i o n a l s e l e n i u m r e s e r v o i r ................................................................................ 457 G e o h y d r o l o g i c b a l a n c e .................................................................................... 4 5 7 S e l e n i u m sources and source d r a i n a g e ............................................................ 4 5 8 C o n c l u s i o n s .......................................................................................................... 461

Chapter 17. Selenium attenuation in a wetland formed from mine drainage in the Phosphoria Formation, southeast Idaho ................................................................................ 4 6 7 L.L. Stillings a n d M.C. A m a c h e r A b s t r a c t ................................................................................................................ 4 6 7 I n t r o d u c t i o n .......................................................................................................... 468

Contents

XXIII M e t h o d s ................................................................................................................ 469 Site .................................................................................................................. 469 C o l l e c t i o n and analytical m e t h o d s .................................................................. 469 Surface waters .............................................................................................. 469 S e d i m e n t s .................................................................................................... 472 Results .................................................................................................................. 473 Water samples .................................................................................................. 473 S e d i m e n t samples ............................................................................................ 473 D i s c u s s i o n ............................................................................................................ 474 C o n c l u s i o n s .......................................................................................................... 480

Chapter 18. Selenium and other trace elements in water, sediment, aquatic plants, aquatic invertebrates, and fish from streams in SE Idaho near phosphate mining ................................................................................................ 483 S.J. H a m i l t o n , K.J. Buhl and P.J. L a m o t h e A b s t r a c t ................................................................................................................ 483 I n t r o d u c t i o n .......................................................................................................... 483 M e t h o d s and materials ........................................................................................ 484 Collection site description .............................................................................. 484 Sample collection ............................................................................................ 487 Water quality analyses and flow m e a s u r e m e n t ................................................ 488 E l e m e n t analysis .............................................................................................. 489 Statistical analyses .......................................................................................... 489 Results and discussion ........................................................................................ 490 Quality assurance/quality control o f c h e m i c a l analyses .................................. 490 Water ................................................................................................................ 491 S e l e n i u m ...................................................................................................... 491 O t h e r e l e m e n t s ............................................................................................ 493 C o m p a r i s o n to other Idaho data .................................................................. 494 S e d i m e n t .......................................................................................................... 495 S e l e n i u m ...................................................................................................... 495 O t h e r e l e m e n t s ............................................................................................ 498 C o m p a r i s o n to other Idaho data .................................................................. 500 Aquatic plants .................................................................................................. 501 S e l e n i u m ...................................................................................................... 501 O t h e r e l e m e n t s ............................................................................................ 501 C o m p a r i s o n to other Idaho data .................................................................. 503 Aquatic invertebrates ...................................................................................... 504 S e l e n i u m ...................................................................................................... 504 O t h e r e l e m e n t s ............................................................................................ 505 C o m p a r i s o n to other Idaho data .................................................................. 506 Fish .................................................................................................................. 506 S e l e n i u m ...................................................................................................... 506 O t h e r elements ............................................................................................ 508 C o m p a r i s o n to other I d a h o data .................................................................. 513 O t h e r considerations .................................................................................... 515 H a z a r d a s s e s s m e n t .............................................................................................. 515

Contents

XXIV

Chapter 19. Uptake of selenium and other contaminant elements into plants and implications for grazing animals in southeast Idaho ........................................ 527 C.L. M a c k o w i a k , M . C . A m a c h e r , J.O. H a l l a n d J.R. H e r r i n g A b s t r a c t ................................................................................................................ 527 I n t r o d u c t i o n .......................................................................................................... 528 L o c a t i o n s a n d g e n e r a l g e o l o g y ........................................................................ 528 Se a n d o t h e r trace e l e m e n t s - e n v i r o n m e n t a l c o n c e r n s .................................. 528 Plants for a s s e s s i n g t r a c e - e l e m e n t m o b i l i t y .................................................... 529 M e t h o d s ................................................................................................................ 531 E x p e r i m e n t a l d e s i g n ........................................................................................ 531 P l a n t s a m p l i n g a n d p r e p a r a t i o n ...................................................................... 531 A n a l y s e s .......................................................................................................... Statistical a n a l y s e s .......................................................................................... R e s u l t s and d i s c u s s i o n ........................................................................................ S e l e n i u m in v e g e t a t i o n .................................................................................... G e o g r a p h i c effects ...................................................................................... G e o l o g i c effects .......................................................................................... R e d o x effects .............................................................................................. Ve g e t a t i o n effects ........................................................................................ O t h e r trace e l e m e n t s in v e g e t a t i o n ..................................................................

533 533 534 534 534 535 535 539 542

C a d m i u m ...................................................................................................... 542 C h r o m i u m .................................................................................................... 544 C o p p e r .......................................................................................................... M a n g a n e s e .................................................................................................. M o l y b d e n u m ................................................................................................ N i c k e l ..........................................................................................................

544 544 545 545

Z i n c .............................................................................................................. 545 L i v e s t o c k / w i l d l i f e r e s p o n s e to s e l e n i u m a n d other trace e l e m e n t s ................ 546 S e l e n i u m ...................................................................................................... 546 M o l y b d e n u m ................................................................................................ 548 O t h e r trace e l e m e n t s .................................................................................... L i v e s t o c k p r o t e c t i o n ........................................................................................ P h y s i c a l m a n i p u l a t i o n s ................................................................................ C h e m i c a l m a n i p u l a t i o n s ..............................................................................

549 549 549 550

Vegetation m a n i p u l a t i o n s ............................................................................ 550 C o n c l u s i o n s .......................................................................................................... 551 P A R T V. M O D E L I N G S T U D I E S

Chapter 20. Review of world sedimentary phosphate deposits and occurrences .................. 559 G.J. Orris and C.B. C h e r n o f f I n t r o d u c t i o n .......................................................................................................... 559 D a t a ...................................................................................................................... A c q u i s i t i o n ...................................................................................................... D e s c r i p t i o n ...................................................................................................... S e d i m e n t a r y p h o s p h a t e deposits ..........................................................................

559 559 561 562

Contents

XXV Marine sedimentary phosphate deposits .......................................................... Active margin basin and epicontinental sea deposits .................................. Shelf and platform deposits ........................................................................ Other marine deposits .................................................................................. Insular phosphate deposits .............................................................................. Weathering-related residual and infiltration deposits .................................. Guano and guano-related deposits .............................................................. Formation and distribution o f deposits ................................................................ Conclusions ..........................................................................................................

563 563 563 563 564 564 565 565 571

Chapter 21. Western Phosphate F i e l d - Depositional and economic deposit models .......... 575 P.R. Moyle and D.Z. Piper Abstract ................................................................................................................ 575 Introduction .......................................................................................................... 576 H y d r o g r a p h y o f the Phosphoria s e a - a depositional model .............................. 576 Non-marine sediment fraction ........................................................................ 578 Marine sediment fraction ................................................................................ 580 Character and controls o f phosphate r e s o u r c e s - an economic model .............. 586 Geological setting ............................................................................................ 586 Geological attributes related to mining .......................................................... 587 Mining characteristics and specifications ........................................................ 589 Weathering ...................................................................................................... 590 Resources and reserves .................................................................................... 592 Conclusions .......................................................................................................... 593

Chapter 22. Societal relevance, processing, and material flow o f western phosphate Refreshments, fertilizer, and weed killer ............................................................ 599 S.M. Jasinski Abstract ................................................................................................................ Introduction .......................................................................................................... Utilization and societal relevance o f phosphate .................................................. Mining methods .................................................................................................. Processed products .............................................................................................. Phosphoric acid production ............................................................................ Elemental phosphorus production .................................................................. End products ........................................................................................................ Fertilizer products ............................................................................................ Major non-fertilizer applications .................................................................... Material flow in the environment ........................................................................

599 599 600 602 604 604 604 607 607 607 608

Appendix CD: Table o f world sedimentary phosphate deposits (with appendices for chapters 12, 13, 18, and 19) .......................................................................... 611 G.J. Orris and C.B. Chernoff

Author Index ............................................................................................................................ Subject Index ..........................................................................................................................

613 621

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PART I.

INTRODUCTION


Life Cycle of the Phosphoria Formation: From Deposition to Post-Mining Environment Edited by James R. Hein Handbook of Exploration and Environmental Geochemistry, Vol. 8 (M. Hale, Series Editor) Published by Elsevier B.V.

Chapter 1

THE PERMIAN EARTH J.R. H E I N

INTRODUCTION The Permian (about 290-250 Ma) was a time of immense global change and unique paleogeographic configurations. Climate conditions evolved from a glacial icehouse Earth to a hothouse Earth. Land masses were assembled into one great continent of Pangea that extended from pole to pole and the mega-ocean Panthalassa dominated the Earth's surface. Ocean chemistry changed dramatically. For example, the ratio of the isotopes of strontium dissolved in ocean water plunged sharply, equivalent in magnitude (not absolute values) to the marked rise in that ratio during the Cenozoic. Climatic and oceanic conditions were favorable for the formation of vast quantities of energy resources and mineral deposits, such as petroleum, coal, phosphorite, and evaporites. During the Late Permian, central northern Pangea was rocked by the outpouring of voluminous volcanic eruptions that produced the Siberian traps. The Permian ended with the greatest mass extinction of biota recorded in Earth history. Because of these dramatic events that characterized the Permian, many books have been produced over the past decade describing this remarkable geologic Period (e.g. Erwin, 1993; Scholle et al., 1995a,b; Shi et al., 1998; Yin et al., 2000; Shi and Metcalfe, 2002). Here I provide but a very brief summary of the Permian to set the stage for later chapters in this book. The International Union of Geological Science's (IUGS) International Commission on Stratigraphy (ICS) has adopted a subdivision of the Permian that includes three Epochs that are divided into nine Stages, that is four Stages, three Stages, and two Stages for the Cisuralian, Guadalupian, and Lopingian Epochs, respectively (Fig. 1-1; http://www.micropress.org/stratigraphy). According to the IUGS-ICS, the Permian began about 292 Ma ago and ended about 251 __+3.6 Ma.

GEOLOGY, PLATE TECTONICS AND PALEOGEOGRAPHY Through movement of Earth's tectonic plates, the land masses had largely amalgamated into the supercontinent of Pangea by the Early Permian. Pangea during that time consisted of an arcuate western subduction margin with several huge embayments (Fig. 1-2). Gondwana, Laurasia, and Siberia were colliding at that time to form the western part of Pangea.

1 --

I

Harland e t a .

-

248_+10My

Marine Series and suws

(

SW North America

I

Ural Region Russia

1

NW Europe

1

Tethyan Asia SW

I

China

I

Age Ma

Tatarian

-

-?-

-

Kazanian

Ufimian

z - 258f12My 9

3w

Kungurian

a

-

263illMy

-

Artinskian

-

268t6My

-

Sakrnarian

---Asselian

- 286SMy

-

CARBONIFEROUS

Fig. 1-1. International Commission on Stratigraphy's (ICS) recommended Periods and Stages of the Permian, compared with that of Harland et al. (1990) and Stages used in various parts of the world as presented by Ross and Ross (1995). The bold ages for Stage boundaries are those approved by the ICS and the remainder of the ages were proposed by Wardlaw (1 999).

b

3

2

$.

I:: Summer~nlyupwelling

I (~2OOOm) IL a w h d (O-ZfMm) ~ Mountains Summer & winter upwelling I (1000-2000 m) l Shelf (-2OMm) Uplenda (20(t1000 m) I Deep Ocean (c-200m) Pre-accreted Terranes

Fig. 1-2. Paleogeographic continental reconstruction of the Roadian-Wordian Earth and location of the Phosphoria sea (base map from Ziegler et al. (1997); surface water currents, climatic provinces, and pre-accreted terranes from Mei and Henderson (2001); and upwelling zones from Parrish (1982).

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An irregular eastern margin of Pangea semi-enclosed the wide Paleotethys sea and was characterized by a complex array of continental fragments. Those continental fragments of Cimmeria were being tiffed from northern Gondwana to the north through the Paleotethys (Scotese and Langford, 1995). The Paleotethys covered what is now most of southern and central Europe. Subduction characterized much of the eastern margin of Pangea and the northern margin of the Paleotethys (Scotese and Langford, 1995). The Paleotethys contracted during the Permian and closed completely near the end of the Triassic. Shallow, salty inland seas (e.g. Zechstein sea) covered parts of what is now northern Europe and very large freshwater lakes formed in the southern hemisphere after the south polar ice cap melted. Pangea moved north during the Permian. Most of the southem hemisphere south of 60 ~ was covered by glacial ice during the early Permian, which had disappeared by late-early Permian (Ziegler et al., 1997). Mountain ranges bordered the southern, southwestern, and northeastern margins of Pangea, with the extensive northeast-southwest trending Central Pangean Mountains (Appalachian-Mauretanide-Variscan orogenic belts) dividing the continent (Fig. 1-2; Hatcher et al., 1989; Ziegler et al., 1997). An island arc bordered the northwest continental margin, which formed the western margin of the Phosphoria sea.

CLIMATE The formation of Pangea had profound effects on continental climates. Temperatures in continental interiors increased, thereby gradually increasing the size and aridity of deserts and decreasing the size of the south polar ice cap and extent of northern sea ice. Seasonal fluctuations in climate increased dramatically as did the number of great storms (e.g. Parrish et al., 1986; Crowley et al., 1989; Kutzbach and Gallimore, 1989; Barron and Fawcett, 1995; Parrish, 1995). The general increase in aridity and decrease in humidity are reflected in the expansion of eolian and evaporite deposits and decrease in coal formation through the Permian. Low latitudes in Pangea were characterized by a monsoonal climate in the Early Permian, which gave way to increased aridity in the Late Permian (Parrish, 1995). Global warming may have been caused by a nearly twofold increase in atmospheric carbon dioxide levels, from levels somewhat less than modem values to levels no more than twice that of present day (Berner, 1991). Kutzbach and Gallimore (1989) modeled a fourfold increase in carbon dioxide levels for the Permian, which resulted in minor to moderate changes in precipitation (8% increase) and mean surface temperature (3.5~ increase). More recent studies have indicated that the rise in carbon dioxide levels in the atmosphere through the Permian may have been much greater, with concomitant increases in temperatures (Berner, 1994; Ekart et al., 1999; Ghosh et al., 2001). Temperatures may have gotten hot enough near the end of the Permian to have caused stress to global ecosystems. Atmospheric oxygen contents plunged from the Phanerozoic high in the Carboniferous of about 40% 02 to about 20% 02 at the end of the Permian, essentially equivalent to the present-day 21% 02 (Berner et al., 2000). Siberia and continental fragments of Cimmeria in the Paleotethys may have been the only parts of Pangea with a positive moisture balance,

The Permian Earth

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with much of the remainder of interior Pangea within 45 ~ latitude of the equator being arid (Ziegler, 1990; Barron and Fawcett, 1995). Winter storm tracts may have occurred mostly between 40 ~ and 70 ~ south latitudes (June-August) and 30 ~ and 50 ~ north latitudes (December-February; Barron and Fawcett, 1995). The northern hemisphere storm track only impinged on the continent of Pangea in the northeast, otherwise was confined to Panthalassa. The southern hemisphere storm tract may have been accompanied by a small, secondary track in the northern hemisphere, offshore northeastern Pangea.

OCEANOGRAPHY Little is known about Panthalassa except along its margins with Pangea. General circulation modeling, however, indicates that surface-water currents were likely rather simple for this mega-ocean that spanned about 300 ~ of longitude at its greatest extent. Equatorial Panthalassa was likely characterized by a westward-flowing surface-current system, that entered the Paleotethys sea on encountering eastern Pangea (Belasky et al., 2002). After transiting the Paleotethys sea, the current bifurcated into coast-parallel northto-east and south-to-east currents (Kennett, 1982; Kutzbach et al., 1990). In the northern and southern hemispheres, Panthalassa may have been characterized by subpolar cyclonic and subtropical anticyclonic circulation cells (Kutzbach et al., 1990). High-latitude surface waters and deep waters were likely warmer than they are today, whereas the equator-to-pole thermal gradient was less or about the same as it is today (e.g. Ziegler et al., 1997; Ziegler, 1990; Belasky, 1994). Thermohaline circulation might have been driven by sinking of Panthalassa cool polar water by melting of seasonal sea ice, and secondarily from sinking of warm, saline Paleotethys water (Kutzbach et al., 1990; Beauchamp and Baud, 2002). Thermohaline circulation may have ceased during the Lopingian. Identification of zones of upwelling is important in terms of mapping potential regions of petroleum source beds and phosphorites (Parrish, 1982). Upwelling of deep cold marine waters to the surface redistributes nutrients and reflects specific conditions of atmospheric circulation. The Late Permian Earth displayed zones of upwelling distributed much as they are today, that is off the west coast of continents. Modeling of atmospheric circulation and pressure cells for the Late Permian indicate that upwelling occurred along most of the western margin of Pangea from about 35~ to 35~ latitudes (Parrish, 1982). In addition, local areas of upwelling may have occurred along the margin of the Paleotethys sea, especially along the northeast, west, and southeast margins (Fig. 1-2). One of the many controversies in Permian studies is whether Panthalassa was stratified and anoxic, and if so, at what water depths and when. An anoxic Panthalassa has been implicated in the great Permian-Triassic biotic extinctions (see below; Erwin, 1993). Based on analysis of redox sensitive elements in what are interpreted to be open-ocean deep-water cherts from Japan, Kato et al. (2002) determined that the deep-waters of Panthalassa were anoxic to suboxic for nearly l0 Ma prior to the Permian-Triassic boundary. Also based on the composition of cherts from Japan and British Columbia,

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The Permian Earth

9

Isozaki (1997) suggested that deep-water anoxia was maintained for 20 Ma and that the entire water column was anoxic for 10 Ma. Musashi et al. (2001) measured a significant drop in 813C values for what are interpreted to be open-ocean shallow-water carbonates and organic matter, similar to the ~il3c drop found in continental margin rocks of Late Permian age. This global drop in gl3c values indicates a significant input of 12C into the oceans and atmosphere in the Late Permian, perhaps by dissociation of huge quantities of gas hydrates. On the other hand, modeling of Panthalassa indicates that it would be difficult to sustain sulfate-reducing anoxic condition in the deep oceans for any significant length of time (Zhang et al., 2001). Hotinski et al. (2001) add that oceanic anoxia would markedly reduce upwelling and consequently productivity; yet the accumulation of carbon dioxide and hydrogen sulfide that may have promoted mass extinction would have required considerable increases in nutrient supply. The chemical composition of Panthalassa ocean water may have changed markedly through the Permian (Fig. 1-3). Ocean water had a relatively high Mg2+/Ca 2+ ratio (>2.1, maximum --5) and relatively high Na + concentration during the Permian, although that ratio fluctuated dramatically (Hardie, 1996; Lowenstein et al., 2001; Dickson, 2002; Horita et al., 2002). During the whole of the Permian, non-skeletal aragonite and high-Mg calcite precipitated from Panthalassa ocean water, rather than calcite, as determined by a Mg 2+ / Ca 2§ ratio of >2; evaporite basins produced predominantly mixed MgSOa-plus KCl-type potash deposits, rather than solely one type or the other (Hardie, 1996). The precipitation of aragonite from high Mg2+/Ca 2+ ocean water resulted in low ratios of Sr2+/Ca 2+ in Permian ocean water (Steuber and Veizer, 2002). These variations in ocean-water chemistry are thought to have resulted from variations in the production of ocean-floor basalt (and associated hydrothermal products) relative to the input of materials from rivers. The production rate of oceanic crust was among the lowest rates for the Phanerozoic, comparable to present-day rates (Gaffin, 1987). The isotopic compositions of Panthalassa ocean water changed markedly through the Permian, during which C, S, and Sr isotopes reached their most extreme Phanerozoic values (Scholle, 1995). Sulfur isotopes of ocean-water sulfate gradually decreased from about 30%0 ~34ScDT in the Cambrian to the lowest Phanerozoic value of 10%o in the Permian. ~34S then increased sharply near the Permian-Triassic boundary to about 30%0, dropped just as sharply in the Early Triassic to about 12%o and then slowly climbed to its present-day value of 21%0 (Scholle, 1995; Strauss, 1997). Global changes in the isotopic

Fig. 1-3. Geologic, oceanographic, and biotic changes that occurred during the Permian; shaded horizontal band marks time of deposition of the Phosphoria Formation. Magnetic data from Haag and Heller (1991); climate change based on conodonts from Mei et al. (2002); tectonic-volcanic events from Holser and Magaritz (1987), Lo et al. (2002), and Reichow et al. (2002); third-order eustatic curve from Ross and Ross (1995); ocean-crust production (on the scale of the Phanerozoic, the whole range of Permian production rates is low) from Gaffin (1987); number of extant genera from Holser and Magaritz (1987); ~13CpDB from Scholle (1995) and Kakuwa (1996); ~34S from Scholle (1995) and Strauss (1997); 87Sr/86Sr from Holser and Magaritz (1987) and Denison and Koepnick (1995); Mg/Ca molar ratio of ocean water from Hardie (1996).

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composition of ocean-water sulfate is generally considered to result from relative changes in the rates of formation of reduced and oxidized sulfur deposits, sulfides, and sulfates (e.g. Strauss, 1997). Because of changes in the amount of biomass, it would be expected that ~34Sof ocean-water sulfate should decrease during major extinction and increase during the subsequent radiation. The dating of Permian-Triassic sections where ocean-water sulfate isotopic values can be determined are not dated well enough to pinpoint where the spike in the curve occurs. Sulfur isotopes did decrease prior to the main extinction event(s) and increased sometime after the major spike near the Permian-Triassic boundary. During the Permian, C isotopes (813C) in carbonates and organic matter varied in tandem and decreased slightly, increased slightly, or remained constant in different regions up to the Late Permian. Then in all sections, 813C values plunged dramatically (negative excursion) near the Permian-Triassic boundary (e.g. Scholle, 1995; Musashi et al., 2001). This negative excursion has been recognized for many years and can be found at times of other mass extinctions in the geologic record. A variety of explanations have been put forth to explain the negative excursions, with early explanations involving changes in the rate of burial and storage of organic carbon. More recent explanations have included dramatic inputs of 12C-rich material into the ocean-atmosphere system, such as by dissociation of gas hydrates, volcanic eruptions, overturn of a stagnant ocean, etc. (see End of Permian section below). Likewise, Sr isotopes (87Sr/86Sr) show their lowest Phanerozoic ratio near the Permian-Triassic boundary. Sr isotopes show a steep decline from about 0.7083 at the beginning of the Permian to about 0.7067 in the Late Permian (Denison and Koepnick, 1995). This dramatic drop is equivalent in magnitude to the dramatic increase in the ratio during the Cenozoic. Changes in the Sr isotope ratio of ocean water is usually attributed to changes in the ratio of input of low-ratio Sr from mafic crustal sources relative to highratio Sr from old continental cratonic crust. Although production of oceanic crust was low during the Permian in general, and decreased during the first half of the Permian, it increased during the last half and, combined with extensive production of flood basalts, likely contributed to the decline in the oceanic Sr isotope ratio. Perhaps more important was the increasing aridity of Pangea through the Permian and the accompanying increase in internal drainage and sedimentation, which inhibited the input of old continental material to Panthalassa (Denison and Koepnick, 1995).

WESTERN NORTH AMERICAN MARGIN AND THE PHOSPHORIA SEA The Phosphoria Formation was deposited off the western margin of North America (northwest margin of Pangea) predominantly during the Roadian and Wordian Stages (Wardlaw et al., 1995). That margin consisted of islands to the west, a marginal sea with a wide, shallow-water eastern margin, and wide coastal plain on which sand dune fields and evaporite basins were common (Fig. 1-4). Terranes that would later be accreted to the northwest Pangean continental margin existed farther to the west (Belasky et al., 2002). The shallow marginal sea was the location of deposition of the Phosphoria Formation.

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Fig. 1-4. Physiographic map of northwest Pangea during the early Guadalupian and location of the Phosphoria sea (map from the web site of R. Blakey, Northern Arizona University and used with his permission: http://jan.ucc.nau.edu/--rcb7/RCB.html). During the Late Permian, the Ancestral Rocky Mountains were subdued and the Front Range and Uncompahgre uplifts were the only important sediment sources (Burchfiel et al., 1992). Late-Permian and Triassic subduction-related mountain building is reflected in the Sonoma orogeny. Remnants of that arc can be traced from California into southern British Columbia (Burchfiel et al., 1992; Miller et al., 1992). Northwest Pangea was dominated by high pressure in both the summer and winter seasons and winter storm tracts were well to the north of the Phosphoria basin (Barron and Fawcett, 1995; Parrish, 1995). The entire area of the Phosphoria basin was a region of moderate to intense upwelling during both the summer and winter. Upwelling brought cold-nutrient-rich waters to the surface, which promoted productivity, leading to the accumulation of organic carbon-rich sediments on the seafloor. Organic matter was the source of the phosphorous for the phosphorites (see Moyle and Piper, Chapter 21). Upwelling was created by the equator-directed surface current that flowed along the continental margin (Fig. 1-2). This situation is comparable to that of the California margin today. Upwelling would have been promoted by westerly winds at temperate latitudes. A decline of upwelling related to a number of oceanographic and atmospheric changes during the Late Permian terminated the deposition of high-grade phosphorite. However, minor episodes of phosphogenesis producing low-grade or localized deposits occurred into the Triassic within the Phosphoria sea and elsewhere adjacent to Pangea during the

12

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Permian, especially around the margins of the Paleotethys sea (Herring, 1995). However, about 85% of Permian phosphorites formed in the Phosphoria sea. High-grade phosphorite, deposited within the Phosphoria sea during the Roadian (Meade Peak Member) and Wordian (Retort Member), formed under cool-water conditions during maximum transgression, in contrast to warm-water conditions that characterized deposition of carbonates below the Meade Peak Member of the Phosphoria Formation (Wardlaw et al., 1995; see also Murchey, Chapter 5). The Phosphoria sea was characterized by a low influx of terrigenous sediment, suboxic bottom-water conditions during phosphorite deposition, and moderate levels of primary productivity in the photic zone (Cook, 1968; Piper, 2001; see also Chapters 4, 5, and 21). Sedimentary structures indicate that bottom waters were relatively calm compared to those typically found in open-shelf environments. Estimates of the maximum water depth of the Phosphoria sea have varied widely, up to 1000 m (e.g. McKelvey et al., 1959), but likely had a maximum depth range of 300-500 m.

END OF PERMIAN The cause(s) of the end of Permian mass extinction is difficult to assess for many reasons, not the least of which is the poor preservation of Late Permian and Early Triassic strata resulting from marine regression and reflected by a global hiatus. Raup (1979) and Sepkoski (1989) suggested that up to 96% (90% commonly cited figure) of marine species became extinct during the latest Permian. A dominant change from Late Permian to Early Triassic was the replacement of marine sessile filter-feeding epifauna by mobile infauna (Erwin, 1993). Reef communities, plankton, and invertebrates with a planktonic larval stage were especially devastated. The amount of loss of land fauna and flora is less clear because of poor preservation of terrestrial strata, but up to 70% of vertebrate species may not have survived the Late Permian. Terrestrial organisms clearly declined, but correlation of those declines with those of marine organisms has generally not been established (Erwin, 1993), except in a section in Greenland (Twitchett et al., 2001). A whole range of causes or mitigating circumstances for the mass extinction has been put forward: (a) Extensive volcanism, especially the west Siberian Traps (e.g. Renne and Basu, 1991); (b) Bolide impact (e.g. Becker et al., 2001); (c) Tectonic events (Holser and Magaritz, 1987); (d) Magnetic reversal, end of the Kiaman reversed superchron (Fig. 1-3; Haag and Heller, 1991); (e) Profound marine regression (Erwin, 1993); (f) Severe environmental changes (e.g. climatic cooling; Stanley, 1988); (g) Dramatic decrease in atmospheric and soil oxygen content (Sheldon and Retallack, 2002); (h) Development of oceanic anoxia (e.g. Wignall and Hallam, 1992; Hotinski et al., 2001); (i) Development of extensive evaporite basins and brackish oceans (e.g. Fischer, 1964; Stevens, 1977); (j) Massive release of methane from gas hydrates (e.g. Erwin, 1993); and (k) Changes in marine hot-spot systems and spreading ridges (Fig. 1-3; Holser and Magaritz, 1987). The final answer for the cause(s) of this enormous mass extinction is still pending. It is likely that the end of Permian extinctions developed over a million years or so. Also, this relatively slow progression may have been finalized by a devastating blow from eruption

The Permian Earth

13

of the Siberian Traps (Bowring et al., 1998), overturn of an anoxic ocean causing carbon dioxide poisoning of shallow-water biota (Wignall and Twitchett, 1996; Knoll et al., 1996), and/or a bolide collision with the Earth at that time (Becker et al., 2001), which may in fact have initiated the Siberian Traps volcanism (Jones et al., 2002). It is likely that a host of events and processes conspired in this greatest mass extinction, including climate change due to the evolution of Pangea and major volcanic events; a disruption of nutrient supplies and loss of habitat caused by major oceanic regression, and decreased upwelling resulting from changes in ocean stratification. The potential for considerable climate change is supported by recent work that has demonstrated that the west Siberian flood basalts were twice as voluminous as had been previously thought for this largest of known Large Igneous Provinces (LIP) (Reichow et al., 2002). Its potential to have influenced climate change is compelling. In addition, the Emeishan flood basalts in south China were erupted at the same time or slightly before the Siberian Traps. Significantly, the Emeishan basalts were erupted through marine limestones that likely triggered massive releases of carbon dioxide and methane (Lo et al., 2002). These two huge volcanic events could have produced a severe but short-lived cooling event (caused by volcanic dust, aerosols, sulfur dioxide- with acid rain) followed immediately by global warming (caused by CO2, CH4; in part from dissociation of gas hydrates), which in concert may have orchestrated this unparalleled mass extinction.

ACKNOWLEDGEMENTS Brandie McIntyre provided technical support. Paul Belasky, Ohlone College, and Calvin Stevens, San Jose State University, provided very helpful reviews. I thank R. Blakey, Northern Arizona University, and A.M. Ziegler, University of Chicago, for allowing the use of their paleogeographic maps.

REFERENCES Barron, E.J. and Fawcett, P.J., 1995. The climate of Pangaea: A review of climate model simulations of the Permian. In: P.A. Scholle, T.M. Peryt and D.S. Ulmer-Scholle (eds.), The Permian of Northern Pangea l: Paleogeography, Paleoclimates, Stratigraphy. Springer-Verlag, Berlin, pp. 37-52. Beauchamp, B. and Baud, A., 2002. Growth and demise of Permian biogenic chert along northwest Pangea: evidence for end-Permian collapse of thermohaline circulation. Palaeogeogr. Palaeoclimatol. Palaeoecol., 184: 37-63. Becker, L., Poreda, R.J., Hunt, A.G., Bunch, T.E. and Rampino, M., 2001. Impact event at the Permian-Triassic boundary: evidence from Extraterrestrial noble gases in fullerenes. Science, 291: 1530-1533. Belasky, E, 1994. Biogeography of Permian corals and the determination of longitude in tectonic reconstructions of the paleoPacific region. Can. Soc. Pet. Geologists Memoir, 17; 621-646.

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Belasky, P., Stevens, C.H. and Hanger, R.A., 2002. Early Permian location of western North American terranes based on brachiopod, fusulinid, and coral biogeography. Palaeogeogr. Palaeoclimatol. Palaeoecol., 179: 245-266. Berner, R.A., 1991. A model for atmosphere CO2 over Phanerozoic time. Am. J. Sci., 291: 339-376. Berner, R.A., 1994. GEOCARB II: A revised model of atmospheric CO2 over Phanerozoic time. Am. J. Sci., 294: 56-91. Berner, R.A., Petsch, S.T., Lake, J.A., Beerling, D.J., Popp, B.N., Lane, R.S., Laws, E.A., Westley, M.B., Cassar, N., Woodward, El. and Quick, W.P., 2000. Isotope fractionation and atmospheric oxygen: implications for Phanerozoic 02 evolution. Science, 287:1630-1633. Bowring, S.A., Erwin, D.H., Jin, Y.G., Martin, M.W., Davidek, K. and Wang, W., 1998. U/Pb zircon geochronology and tempo of the end-Permian mass extinction. Science, 280:1039-1045. Burchfiel, B.C., Cowan, D.S. and Davis, G.A., 1992. Tectonic overview of the Cordilleran orogen in the western United States. In: B.C. Burchfiel, P.W. Lipman and M.L. Zoback (eds.), The Cordilleran Orogen: Conterminous US. Geology of North America vol. G-3, Geological Society of America, Boulder, CO, pp. 407-480. Cook, P.J., 1968. The petrology and geochemistry of the Meade Peak Member of the Phosphoria Formation. Unpublished Ph.D. thesis, University of Colorado, Boulder, CO, 204 pp. Crowley, T.J., Hyde, W.T. and Short, D.S., 1989. Seasonal cycle variations on the supercontinent of Pangea. Geology, 17: 457-460. Denison, R.E. and Koepnick, R.B., 1995. Variation in 87Sr/86Sr of Permian seawater: an overview. In: P.A. Scholle, T.M. Peryt and D.S. Ulmer-Scholle (eds.), The Permian of Northern Pangea 1: Paleogeography, Paleoclimates, Stratigraphy. Springer-Verlag, Berlin, pp. 124-132. Dickson, J.A.D., 2002. Fossil echinoderms as monitor of the Mg/Ca ratio of Phanerozoic oceans. Science, 298: 1222-1224. Ekart, D.D., Cerling, T.E., Montanez, I.P. and Tabor, N.J., 1999. A 400 million year carbon isotope record of pedogenic carbonate: implications for paleoatmospheric carbon dioxide. Am. J. Sci., 299: 805-827. Erwin, D.H., 1993. The Great Paleozoic Crisis: Life and Death in the Permian. Columbia University Press, New York, 327 pp. Fischer, A.G., 1964. Brackish oceans as the cause of the Permo-Triassic marine faunal crisis. In: A.E.M. Nairn (ed.), Problems in Palaeoclimatology. Interscience, London, pp. 566-574. Gaffin, S., 1987. Ridge volume dependence on seafloor generation rate and inversion using long term sealevel change. Am. J. Sci., 287:596-611. Ghosh, P., Ghosh, P. and Bhattacharya, S.K., 2001. CO2 levels in the Late Palaeozoic and Mesozoic atmosphere from soil carbonate and organic matter, Satpura basin, Central India. Palaeogeogr. Palaeoclimatol. Palaeoecol., 170:219-236. Haag, M. and Heller, E, 1991. Late Permian to Early Triassic magnetostratigraphy. Earth Planet. Sci. Lett., 107: 42-54. Hardie, L.A., 1996. Secular variation in seawater chemistry: an explanation for the coupled secular variation in the mineralogies of marine limestones and potash evaporites over the past 600 m.y. Geology, 24: 279-283. Harland, W.B., Armstrong, R.L., Cox, A.V., Craig, L.E., Smith, A.G. and Smith, D.G., 1990. A Geologic Time Scale 1989. Cambridge University Press, Cambridge, 263 pp. Hatcher, R.D. Jr., Thomas, W.A., Geiser, P.A., Snoke, A.W., Mosher, S. and Wiltschko, D.V., 1989. Alleghanian orogen. In: R.D. Hatcher Jr., W.A. Thomas and G.W. Viele (eds.), The

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Appalachian-Ouachita Orogen in the United States. Geology of North America vol. F-2, Geological Society of America, Boulder, CO, pp. 233-318. Herring, J.R., 1995. Permian phosphorites: A paradox of phosphogenesis. In: EA. Scholle, T.M. Peryt and D.S. Ulmer-Scholle (eds.), The Permian of Northern Pangea 2: Sedimentary Basins and Economic Resources. Springer-Verlag, Berlin, pp. 292-312. Holser, W.T. and Magaritz, M., 1987. Events near the Permian-Triassic boundary. Mod. Geol., 1 l: 155-180. Horita, J., Zimmermann, H. and Holland, H.D., 2002. Chemical evolution of seawater during the Phanerozoic: implications from the record of marine evaporites. Geochim. Cosmochim. Acta, 66: 3733-3756. Hotinski, R.M., Bice, K.L., Kump, L.R., Najjar, R.G. and Arthur, M.A., 2001. Ocean stagnation and end-Permian anoxia. Geology, 29: 7-10. Isozaki, Y., 1997. Permo-Triassic boundary superanoxia and stratified superocean: Records from lost deep sea. Science, 276: 235-238. Jones, A.P., Price, G.D., Price, N.J., DeCarli, P.S. and Clegg, R.A., 2002. Impact induced melting and the development of large igneous provinces. Earth Planet. Sci. Lett., 202:551-561. Kakuwa, Y., 1996. Permian-Triassic mass extinction event recorded in bedded chert sequence in southwest Japan. Palaeogeogr. Palaeoclimatol. Palaeoecol., 121: 35-51. Kato, Y., Nakao, K. and Isozaki, Y., 2002. Geochemistry of Late Permian to Early Triassic pelagic cherts from southwest Japan: implications for an oceanic redox change. Chem. Geol., 182: 15-34. Kennett, J., 1982. Marine Geology. Prentice-Hall, Englewood Cliffs, N J, 813 pp. Knoll, A.H., Bambach, R.K., Canfield, D.E. and Grotzinger, J.P., 1996. Comparative earth history and Late Permian mass extinction. Science, 273: 452-457. Kutzbach, J.E. and Gallimore, R.G., 1989. Pangean climates: megamonsoons of the megacontinent. J. Geophys. Res., 94: 3341-3357. Kutzbach, J.E., Guetter, EJ. and Washington, W.M., 1990. Simulated circulation of an idealized ocean for Pangaean time. Paleoceanography, 5: 299-317. Lo, C.-H., Chung, S.-L., Lee, T.-Y. and Wu, G., 2002. Age of the Emeishan flood magmatism and relations to Permian-Triassic boundary events. Earth Planet. Sci. Lett., 198: 449-458. Lowenstein, T.K., Timofeeff, M.N., Brennan, S.T., Hardie, L.A. and Demicco, R.V., 2001. Oscillations in Phanerozoic seawater chemistry: evidence from fluid inclusions. Science, 294: 1086-1088. McKelvey, V.E., Williams, J.S., Sheldon, R.P., Cressman, E.R., Cheney, T.M. and Swanson, R.W., 1959. The Phosphoria, Park City, and Shedhorn Formations in the western phosphate field. US Geological Survey Professional Paper 313-A, 47 pp. Mei, S. and Henderson, C.M., 2001. Evolution of Permian conodont provincialism and its significance in global correlation and paleoclimate implication. Palaeogeogr. Palaeoclimatol. Palaeoecol., 170: 237-260. Mei, S., Henderson, C.M. and Wardlaw, B.R., 2002. Evolution and distribution of the conodonts Sweetognathus and Iranognathus and related genera during the Permian, and their implication for climate change. Palaeogeogr. Palaeoclimatol. Palaeoecol., 180:57-91. Miller, E.L., Miller, M.M., Stevens, C.H., Wright, J.E. and Madrid, R., 1992. Late Paleozoic paleogeographic and tectonic evolution of the western U.S. Cordillera. In: B.C. Burchfiel, P.W. Lipman, and M.L. Zoback (eds.), The Cordilleran Orogen: Conterminous US. Geology of North America vol. G-3, Geological Society of America, Boulder, CO, pp. 57-106.

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Musashi, M., Isozaki, Y., Koike, T. and Kreulen, R., 2001. Stable carbon isotope signature in mid-Panthalassa shallow-water carbonates across the Permo-Triassic boundary: evidence for 13C-depleted superocean. Earth Planet. Sci. Lea., 191: 9-20. Parrish, J.T., 1982. Upwelling and petroleum source beds, with reference to Paleozoic. Am. Association of Petroleum Geologists Bulletin, 66: 750-774. Parrish, J.T., 1995. Geologic evidence of Permian climate. P.A. Scholle, T.M. Peryt and D.S. UlmerScholle (eds.), The Permian of Northern Pangea 1: Paleogeography, Paleoclimates, Stratigraphy. Springer-Verlag, Berlin, pp. 53-61. Parrish, J.M., Parrish, J.T. and Ziegler, A.M., 1986. Permian-Triassic paleogeography and paleoclimatology and implications for Therapsid distribution. In: N. Hotton III, P.D. MacLean, J.J. Roth and E.C. Roth (eds.), The Ecology and Biology of Mammal-like Reptiles. Smithsonian Institute Press, Washington DC, pp. 109-131. Piper, D.Z., 2001. Marine chemistry of the Permian Phosphoria Formation and basin, southeast Idaho. Econ. Geol., 96: 599-620. Raup, D.M., 1979. Size of the Permo-Triassic bottleneck and its evolutionary implications. Science, 206:217-218. Reichow, M.K., Saunders, A.D., White, R.V., Pringle, M.S., Al'Mukhamedov, A.I., Medvedev, A.I. and Kirda, N.P., 2002. 4~ dates from the west Siberian basin: Siberian flood basalt province doubled. Science, 296:1846-1849. Renne, P.R. and Basu, A.R., 1991. Rapid eruption of the Siberian Traps flood basalts at the PermoTriassic boundary. Science, 253:176-179. Ross, C.A. and Ross, J.R.P., 1995. Permian sequence stratigraphy. In: P.A. Scholle, T.M. Peryt and D.S. Ulmer-Scholle (eds.), The Permian of Northern Pangea 1: Paleogeography, Paleoclimates, Stratigraphy. Springer-Verlag, Berlin, pp. 98-123. Scholle, EA., 1995. Carbon and sulfur isotope stratigraphy of the Permian and adjacent intervals. In: P.A. Scholle, T.M. Peryt and D.S. Ulmer-Scholle (eds.), The Permian of Northern Pangea 1: Paleogeography, Paleoclimates, Stratigraphy. Springer-Verlag, Berlin, pp. 133-149. Scholle, P.A., Peryt, T.M. and Ulmer-Scholle, D.S. (eds.), 1995a. The Permian of Northern Pangea 1: Paleogeography, Paleoclimates, Stratigraphy. Springer-Verlag, Berlin, 261 pp. Scholle, P.A., Peryt, T.M. and Ulmer-Scholle, D.S. (eds.), 1995b. The Permian of Northern Pangea 2: Sedimentary Basins and Economic Resources. Springer-Verlag, Berlin, 319 pp. Scotese, C.R. and Langford, R.P., 1995. Pangea and the paleogeography of the Permian. In: P.A. Scholle, T.M. Peryt and D.S. Ulmer-Scholle (eds.), The Permian of Northern Pangea 1: Paleogeography, Paleoclimates, Stratigraphy. Springer-Verlag, Berlin, pp. 3-19. Sepkoski, J.J. Jr., 1989. Periodicity in extinction and the problem of catastrophism in the history of life. J. Geol. Soc. Lond., 146: 7-19. Sheldon, N.D. and Retallack, G.J., 2002. Low oxygen levels in earliest Triassic soils. Geology, 30: 919-922. Shi, G.R. and Metcalfe, I. (eds.), 2002. Permian of southeast Asia. Special Issue, J. Asian Earth Sci., 20: 549-774. Shi, G.R., Archbold, N.W. and Grover, M. (eds.), 1998. Permian of Eastern Tethys: Biostratigraphy, Palaeogeography and Resources. Proc. Royal Soc. Victoria, vol. 110(1/2), Melbourne, Australia, pp. 480 pp. Stanley, S.M., 1988. Paleozoic mass extinctions: shared patterns suggest global cooling as a common cause. American Journal of Science, 288: 334-352. Steuber, T. and Veizer, J., 2002. Phanerozoic record of plate tectonic control of seawater chemistry and carbonate sedimentation. Geology, 30:1123-1126.

The Permian Earth

17

Stevens, C.H., 1977. Was development of brackish oceans a factor in Permian extinctions? Geol. Soc. Am. Bull., 88, 133-138. Strauss, H., 1997. The isotopic composition of sedimentary sulfur through time. Palaeogeogr. Palaeoclimatol. Palaeoecol. 132:97-118. Twitchett, R.J., Looy, C.V., Morante, R., Visscher, H. and Wignall, P.B., 2001. Rapid and synchronous collapse of marine and terrestrial ecosystems during the end-Permian biotic crisis. Geology, 29:351-354. Wardlaw, B.R., 1999. Notes from the SPS chair. Permophiles issue #35: 1-4. Wardlaw, B.R., Snyder, W.S., Spinosa, C. and Gallegos, D.M., 1995. Permian of the western United States. In: P.A. Scholle, T.M. Peryt and D.S. Ulmer-Scholle (eds.), The Permian of Northern Pangea 2: Sedimentary Basins and Economic Resources. Springer-Verlag, Berlin, pp. 23-40. Wignall, EB. and Hallam, A., 1992. Anoxia as a cause of the Permian/Triassic mass extinction: Facies evidence from northern Italy and the westem United States. Palaeogeogr. Palaeoclimatol. Palaeoecol., 93:21-46. Wignall, P.B. and Twitchett, R.J., 1996. Oceanic anoxia and the end Permian mass extinction. Science, 272:1155-1158. Yin, H., Dickins, J.M., Shi, G.R. and Tong, J. (eds.), 2000. Permian-Triassic Evolution of Tethys and Western Circum-Pacific. Developments in Palaeontology and Stratigraphy 18, Elsevier, Amsterdam, 392 pp. Zhang, R., Follows, M.J., Grotzinger, J.P. and Marshall, J., 2001. Could the Late Permian deep ocean have been anoxic? Paleoceanography, 16:317-329. Ziegler, A.M., 1990. Phytogeographic patterns and continental configurations during the Permian Period. In: W.S. McKerrow and S.R. Scotese (eds.), Palaeozoic Palaeogeography and Biogeography. Geol. Soc. Lond. Memoir 12, pp. 363-379. Ziegler, A.M., Hulver, M.L. and Rowley, D.B., 1997. Permian world topography and climate. In: I.P. Martini (ed.), Late Glacial and Postglacial Environmental C h a n g e s - Quaternary, Carboniferous-Permian and Proterozoic. Oxford University Press, New York, pp. I I l-146.



19

Chapter 2

EVOLUTION OF T H O U G H T C O N C E R N I N G THE O R I G I N OF THE PHOSPHORIA FORMATION, WESTERN US PHOSPHATE FIELD J.R. HEIN, R.B. PERKINS and B.R. MclNTYRE

ABSTRACT The Phosphoria Formation has been the subject of intensive study for nearly 100 years. Most work during the first half of the twentieth century on the Phosphoria Formation fell under three US Geological Survey (USGS) programs. The first program, from 1909 to 1916, was concerned with mapping the extent of phosphate rock within the western United States, the so-called Western Phosphate Field. Many of the basic features concerning the distribution, structure, and composition of the Phosphoria were determined during that time. The work of Blackwelder was especially critical in delineating geochemical conditions of the depositional basin, the Phosphoria sea. An important process in the formation of the Phosphoria Formation, coastal upwelling, was not understood in those earlier works. A detailed understanding of the processes involved in coastal upwelling was first developed by Kazakov in the late 1930s and those processes were later applied to the Phosphoria Formation in the late 1940s by McKelvey and co-workers. The second USGS program began in 1941 and involved detailed sampling and analyses of Phosphoria rocks to delineate vanadium-rich zones, which were discovered during the earlier USGS program. This sampling and analysis program also identified zinc- and uranium-rich strata within the Phosphoria Formation. The discovery of uranium, along with an increasing demand for phosphate, led to the third large USGS program headed by McKelvey, which began in 1947. From 1947 to 1952, hundreds of stratigraphic sections were measured, described, and sampled from 200 locations in Montana, Wyoming, Idaho, and Utah. From this work, a comprehensive genetic model was developed for the sedimentary and oceanographic conditions that promoted phosphorite deposition. Delineation of regional facies changes, thickness changes, and chemical and petrologic changes also provided criteria for regional correlations of rock units. The cyclic nature of deposition of Phosphoria Formation strata was emphasized. Succeeding studies in the 1960s and 1970s established the characteristics of regional and local depositional environments and paleogeographic and paleoclimatic conditions of the Phosphoria sea and surrounding areas. The Phosphoria Formation was placed into a more restrictive Middle Permian time frame than had been used by previous workers. From the 1980s to the present, investigations focused on the details of phosphogenesis and the use of sequence stratigraphy to understand the role that sea level played in the evolution of the Phosphoria sea and in the cyclic deposition of the Phosphoria sequence.

20

J R . Hein et al.

INTRODUCTION The Middle Permian Phosphoria Formation comprises one of the largest resources of phosphate rock in the world and has been mined for nearly a century (Jasinski et al., Chapter 3). Phosphoria Formation strata are found throughout a region covering 350,000 k n l 2 in Idaho, Wyoming, Montana, Utah, and Nevada in the so-called Western US Phosphate Field (Fig. 2-1). This formation has been studied systematically by the US Geological Survey (USGS) during three major field mapping and sampling programs in 1909-1916, 1941-1944, and 1947-1952; and during follow-up work, which continues to the present day. USGS scientists have returned to the Phosphoria off-and-on for much of the past half century in an effort to better understand this remarkable accumulation of phosphate. The book that includes this paper is a product of the latest USGS effort (1997-2002) to study the geology and resources, in addition to environmental aspects concerned with mining of the deposit. The Phosphoria Formation was named by Richards and Mansfield (1912) for sections they studied in southeast Idaho. It is our primary purpose here to trace the evolution of thought concerning the origin of this world-class phosphate-ore deposit, especially with respect to the depositional environment, nature of the Phosphoria sea, and conditions that promoted accumulation of huge quantities of phosphate. Although many of the early studies were solely descriptive works, they set the background for work that came later and therefore are briefly discussed here.

na

Western

'

Phosphate Field

.~!

9

~L

.,,.

"

,..

\, ~,.~.,,

,.~

-

..

Nevada

.t;

% ,~.- ..-~

J

9, / U,a.

/

i/Colorado

.

1.,I

Fig. 2-1. Outline of the Western Phosphate Field, a 350,000 km2 area in the northern Rocky Mountains; exposures of the Phosphoria Formation are indicated in black.

Origin of the Phosphoria Formation, Western US Phosphate Field

21

DELINEATION OF WESTERN PHOSPHATE LANDS: PRE-1940s USGS geologists started mapping the Western Phosphate Field in 1909, shortly after the first mining of phosphate began in 1908. This initial USGS field program was conducted between 1909 and 1916 and involved geologic mapping and chemical and paleontological analyses of collected rocks. The objective was to identify phosphate and nonphosphate lands in the Western Phosphate Field as mandated by the 1908 land withdrawal order of the Secretary of the Interior (see Jasinski et al., Chapter 3). That survey not only identified rocks rich in phosphate, but also found rocks with high concentrations of vanadium, nickel, and molybdenum. The second large-scale USGS effort was initiated in 1941 because of the vanadium-rich rocks discovered during the 1909-1916 survey. The earliest works that resulted from that first project were published in 1910 (Blackwelder, 1910; Gale, 1910; Gale and Richards, 1910; Girty, 1910; Richards and Mansfield, 1910) and provided field, petrographic, and paleontological analyses of Phosphoria Formation rocks in Idaho, Wyoming, Montana, and Utah. At that time, the Phosphoria Formation was considered to be part of the Park City Formation of Carboniferous age. The definitive and comprehensive work derived from the 1909-1916 field program was by Mansfield (1927), which addressed the entire geologic history of southeast Idaho. Another outcome of this early work in the Western Phosphate Field was assignment of names to strata in Idaho, Utah, and Wyoming, specifically the Phosphoria Formation, the Rex Chert Member of the Phosphoria Formation, and the Wells Formation, which underlies the Phosphoria Formation in Idaho (Richards and Mansfield, 1912). Although this 1912 paper was the first to publish those names, Gale selected the name for the Rex Chert after Rex Peak studied during his field work in the Crawford Mountains in Utah. The Phosphoria Formation, named after Phosphoria Gulch near Georgetown, Idaho, was considered to be coeval with the upper part of the Park City Formation, and therefore of Pennsylvanian age. By 1914, the Phosphoria was provisionally assigned a Permian age (Richards and Mansfield, 1914) and the name Phosphoria Formation was applied to rocks in Montana by 1916 (Pardee, 1917). Most early researchers correctly considered the bedded phosphorites of the Phosphoria to be of primary sedimentary origin. They, however, were divided into two camps: (a) those who thought that organisms played a major role and (b) those who thought that inorganic chemical and physical processes were dominant. Richards and Mansfield (1910) considered that the phosphorites formed predominantly by chemical and physical processes rather than by organisms. They stated that the CO2 content of the atmosphere was greater than it is at present (1910), but did not provide evidence. They also calculated that the Western Phosphate Field is the largest accumulation of phosphorite in the world. For a contrasting view, Richards and Mansfield referenced a G.A. Koenig (unpublished) who hypothesized that the phosphate was secreted by extremely prolific protozoa that accumulated rapidly in great quantities. Along those same lines, Breger (1911) reasoned that the bitumen and phosphate in the phosphorites and black shales shared a common origin. Breger envisioned a submarine ooze composed of microorganisms living on the seafloor, most likely bacteria, that extracted phosphate and calcium from seawater and deposited

22

J R . Hein et al.

calcium phosphate. He thought that distillation of that ooze upon burial produced the petroleum associated with the Western Phosphate Field. Blackwelder (1916) developed a model for global phosphorus cycling that started with formation of igneous phosphorus, weathering of that phosphorus and its delivery to soils, plants, animals, rivers, and eventually to the oceans where it is used by marine biota. He correctly outlined many of the basic chemical and biochemical processes that likely occurred in the Phosphoria sea during accumulation of Phosphoria phosphorites. He understood that phosphorus accumulates in tissue, bone, teeth, and shells of marine organism, but dismissed earlier ideas that large phosphate deposits could form by accumulation of the hard parts of marine organisms supplied during one or more episodes of mass mortality. This is curious, however, because many papers produced during the next half century ascribed to Blackwelder that mass mortality of organisms was the source of phosphorus for marine phosphorites, an idea that he rejected. He also rejected fecal pellets as being the sole source of phosphorus for such deposits. From marine biota, the phosphorus is transferred via birds to form guano deposits, or via the death of the biota and their sinking to the seafloor where they provided the organic matter that would release the phosphorus needed to form primary sedimentary phosphorites (Blackwelder, 1916). Blackwelder understood that the Phosphoria seafloor was suboxic or anoxic (he emphasized anoxic conditions) and that phosphorus, hydrocarbons, nitrogen, ammonia, and hydrogen sulfide were released during bacterial degradation of organic matter on the seafloor. He concluded that oxygen deficiency was the key factor that allowed accumulation of organic matter on the seafloor. He surmised that bottom-water circulation was weak and that semi-closed basins prevented ventilation of the oxygen-deficient bottom waters. The phosphoric acid produced by bacterial decay reacted primarily with carbonates in the presence of ammonia to produce calcium phosphates. Calcium phosphate precipitated as cement in near seafloor sediment, replaced some sediment grains, and formed pellets and ooids in some places. He believed that the phosphorus for even the largest phosphorite deposits could be supplied by normal seawater during a relatively short period of time. Blackwelder's observations established a reasonably accurate scenario for the origin of Phosphoria phosphates. What he did not address was the oceanographic environment in which large quantities or organic matter were produced and accumulated. A succinct presentation of that aspect would not come for another 20 years (see below; Kazakov, 1937). Pardee (1917) added another dimension by bringing climate into the picture. He suggested that development of biogenic (coralline-type) carbonates and the precipitation of calcium carbonate were inhibited by cold oceanic waters produced by glaciation. He believed that the Phosphoria sea (called Carboniferous sea) was of moderate depth and high productivity, which produced the organic-rich sediments associated with the Phosphoria. Decay of organic matter on the seafloor produced CO2, which further inhibited the formation of carbonates, but not phosphates. The phosphates precipitated from seawater at an ordinary rate, but because of the lack of carbonate deposition, accumulated in relatively pure form.


23

Mansfield (1918) added several ideas to the growing list based on field evidence, petrographic observations, earlier twentieth century work on the formation of aragonite ooids, and the earlier proposed ideas about the Phosphoria. He suggested that the Phosphoria sea was closed to the east, west, and south, but open to the north and northwest. Further, he proposed that an important factor in the deposition of the phosphorite was the lack of detrital input, which resulted from the low relief of the continental margin east of the Phosphoria sea. A condensed section formed by slow precipitation unaffected by the input of much terrigenous debris. Less insightful was his proposal that the Phosphoria ooids formed originally as aragonite ooids under the influence of denitrifying bacteria in an environment similar to the modern Bahamas, that is, shallow, warm waters. Those ooids were then replaced by phosphates when seawater cooled by a change in currents, or perhaps by Pardee's glaciation. He envisioned that productivity increased and organic matter accumulated and decayed on the seafloor via Blackwelder's mechanism. The temperature change was considered necessary to cause the death of great numbers of organisms. Mansfield (1927) later abandoned the idea of replaced aragonite ooids and agreed that the phosphate ooids in the Phosphoria were original precipitates. In a still later paper, Mansfield (193 l) proposed that the vast quantity of fluorine, estimated to be 5.4 x 108 metric tons in the phosphorites, was derived from considerable volcanic activity in the vicinity of the Phosphoria sea, an incorrect idea (see discussion of McKelvey et al., 1953), that he continued to develop (Mansfield, 1940). Condit et al. (1928) went a different direction and proposed a shallow-water restricted basin for much of the Phosphoria. They proposed a beach origin for the lowermost bed composed of abundant shell fragments and other bio-debris (the so-called fish-scale bed); a mudflat (occasionally subaerially exposed) origin for phosphorite pebbles; and evaporative basin origin for phosphorite desiccation conglomerates. They suggested that the organic matter in the Phosphoria was terrestrial plant debris. Decay of that plant debris created toxic bottom waters where hydrogen sulfide combined with carbon dioxide to produce a solvent for phosphatic skeletal debris, which then precipitated as acid phosphate salts on the seafloor. Branson (1930), based on regional fossil assemblages, found that the Phosphoria sea extended into Nevada and that the sea was open to the north and northwest based on similarities of Phosphoria and Alaskan Artinskian fauna. Based on lithologic correlations, he proposed that phosphate rocks in Alberta were deposited in a connecting sea. Further, he suggested that rocks in what is now known as the Permian basin in the southwest US were coeval in part with the Phosphoria Formation, but the faunas were different enough to have been deposited in different arms of the Pennsylvanian-Permian sea. An important piece of the puzzle missing from these early scenarios was the mechanism by which primary productivity was maintained. That mechanism is upwelling and was first articulated by Kazakov in 1937 at the International Geological Congress in Leningrad, when many of the salient conditions that promote the formation of marine phosphorites were proposed. Though he did not discuss the Phosphoria Formation per se, his ideas, with minor modifications, were applied to the Phosphoria Formation by McKelvey (1946b) and McKelvey et al. (1953) and are still accepted in large part today (see below).

24

J R . Hein et al.

GEOCHEMICAL EXPLORATION, P, U, AND V: THE 1940s-1950s Publications and new ideas about the Phosphoria in the 1940s were few. Keller (1941) provided excellent petrographic descriptions of the Rex Chert, but incorrectly surmised that the silica was derived from precipitation of silica gel on the seafloor. A second important USGS Phosphoria program (1941-1944)was part of the Strategic Minerals Program and involved detailed sampling and chemical analyses of Phosphoria rocks. That program, headed by W.W. Ruby, was undertaken to delineate vanadium-rich zones in the Phosphoria Formation, originally identified in the 1909-1916 project. The vanadium data were included in McKelvey's (1946a) PhD dissertation. That early 1940s survey not only delineated vanadiferous zones, but also identified zinc- and uranium-rich strata. This discovery of uranium, along with an increasing demand for phosphate, led to the third USGS program headed by McKelvey in 1947 (see below). Other works in the 1940s included studies by Gardner (1944) of regional thickness variations of the Phosphoria and the contribution of thrust-plate structures to those thickness variations. He showed that in places the Phosphoria has been tectonically thickened up to fivefold. Deiss (1949) was the first to describe discrete ore zones in the Meade Peak Phosphatic Shale Member (called phosphatic shale member in the 1940s) in southeast Idaho. He described a lower phosphate ore, middle medium- to low-grade ore (now called middle waste zone, which is not mined), and upper ore, the subdivision of the Mead Peak Member used today. Deiss also proposed an origin for carbonate nodules in the phosphatic shale member that involved formation from ground waters after deposition of the sediment and uplift of the rocks. It is now known that the nodules are early diagenetic (pre-compaction) deposits. In the 1950s, considerable progress was made in understanding the nature of the Phosphoria sea and adjacent areas of northwest Pangea (see Hein, Chapter 1). McKelvey et al. (1952, 1953) determined the basic oceanographic and sedimentary conditions for deposition of phosphorite of the Phosphoria Formation. They based their conclusions on the theory developed by Kazakov (1937, 1938), the basic tenets of which follow. Marine phosphorites are a direct result of the process of coastal upwelling. The phosphorites generally form during transgressions and in areas of little input of terrigenous debris (very low sedimentation rates). The phosphorites form on the shelf with the adjacent offshore basin having an open connection to the ocean. The thickness of the phosphorites and the amount of P205 increase seaward. Phosphate was precipitated at the seafloor generally by inorganic processes at water depths of 50-200 m. The pH and temperature of upwelled water increased along its path thereby promoting the precipitation of phosphate. McKelvey and coworkers modified these ideas to fit field and analytical data that they had collected for the Phosphoria. They thought that the water depth was more likely between 200 and 1000 m, that the Phosphoria basin was at least partly closed to the open ocean, and that phosphorites were deposited on three sides of the basin, as opposed to one side as suggested by Kazakov. Significantly, McKelvey and coworkers suggested that the phosphorus for the phosphorites was derived from the bacterial decay of planktonic organic matter produced in the zone of upwelling, which is an additional source of phosphorus from the


25

dissolved phosphate in the cold, upwelled waters. In addition, McKelvey and coworkers calculated the mass balance for phosphorus and determined that the Phosphoria Formation contains more than five times the amount of phosphorus dissolved in the modern ocean. They also calculated that the amount of phosphorus in the Phosphoria Formation is not unusual in the context of ancient continental-margin upwelling systems where sedimentation rates were high and the phosphorus was dispersed through a thick stratigraphic section of siliciclastic rocks. Finally, McKelvey and coworkers surmised that the large amounts of fluorine, chromium, vanadium, rare-earth elements, selenium, and other elements in the Phosphoria were derived from seawater, either directly through precipitation or sorption, or indirectly through alteration of biogenic material, and these conclusions are supported by the recent work of Piper (2001). Most of these ideas are accepted today, although the water depth of the Phosphoria sea is still a matter of discussion. Two seminal papers on the regional characteristics of the Phosphoria Formation and other Permian rocks in the western United States (McKelvey et al., 1956, 1959) subdivided the Permian rocks into the classification used today. These papers were based on the measurement and description of hundreds of sections from 200 locations in Montana, Wyoming, Idaho, and Utah. Field work was carried out during 1947 through 1952 and data were published in a series of USGS Circulars (208-211,260, 262, 301-307, and 324-327) in 1953 and 1954. These circulars contain a representative stratigraphic section from each region and chemical data for rocks through each measured section. This extensive mapping effort provided an understanding of the regional facies changes, thickness changes, and chemical and petrologic changes sufficient enough to define the basic characteristics of the Phosphoria sea and provide criteria for the correlation of rock units regionally (Fig. 2-2 and Table 2-I). McKelvey et al. (1956, 1959) divided the Permian rocks into the Park City, Phosphoria, and Shedhorn Sandstone Formations. The Park City Formation was subdivided into the Grandeur, Franson, and Ervay Members. TABLE 2-! Permian stratigraphy as proposed by McKelvey et al. (1956, 1959) Formation

Member

Shedhorn Sandstone

Upper Lower

Phosphoria

Tosi Chert Retort Phosphatic Shale Cherty Shale Rex Chert Meade Peak Phosphatic Shale Lower Chert

Park City

Ervay Carbonate Rock Franson Grandeur

Southern Idaho

Western Wyomlng

'

$a 9 C

g

P

-0,a,

a C

8

Central Wyoming m 5 a,

gF $9

,-a. 2

wz

V)

5 $E b aE

c m

9

+

1

V)

E2

c

?a,

--=

Southeastern Wyomlng

a,

U E

m

u

22

.g '5 c

E

02 E V)

E'

LL

Explanation

Phosphorla Formation of PermIan age

Park City Format~onand its equ~valentsof PermIan age

Chugwater Formation and equivalant of Permian

Vertical scale greatly exagerated

0

I 0

50 km I

150 km

I 50 miles Horizontal scale

Fig. 2-2. Composite section across the Phosphoria basin, modified from McKelvey et al. (1956, 1959).

I

100 miles


27

The Phosphoria Formation was subdivided into six members: (a) Lower Chert, (b) Meade Peak Phosphatic Shale, (c) Rex Chert, (d) Cherty Shale, (e) Retort Phosphatic Shale, and (f) Tosi Chert (Table 2-I). In places, some Phosphoria members are lateral equivalents, such as the Tosi Chert and the upper Retort, the Retort and the Cherty Shale, and the Lower Chert and the Meade Peak. Where these members interfinger, they are called tongues rather than members. Only the Meade Peak, Rex Chert, and Cherty Shale Members are present to any significant extent in southeast Idaho, the focus of this volume. The Shedhorn Sandstone Formation was subdivided into Upper and Lower Members. Regional facies changes in northwestern Wyoming and petrographic analyses led Sheldon (1957) to propose cyclic deposition of Phosphoria rocks starting with carbonate then chert then phosphorite and back to chert followed by carbonate. In addition, subcycles within the chert and phosphorite cycles were proposed. He related these cycles to two transgressive-regressive sea-level cycles where phosphorite was associated with transgression and carbonate with regression. Sheldon proposed that changes of seawater pH and Eh were associated with these cycles and reflected the characteristics of the extant upwelling regime. Sheldon incorrectly associated the transgressive-regressive sea-level changes predominantly with local tectonism rather than eustatic sea-level changes. He correctly determined that the silica for bedded and nodular Phosphoria cherts was derived from dissolution of biogenic silica, mostly sponge spicules. He also determined that the phosphorites are diagenetic deposits, but incorrectly thought that phosphatization was post-compaction. He suggested that the deeper basin was characterized by subdued bottomcurrent activity, an idea initially proposed by Blackwelder (1916) and accepted today. One other important conclusion published in the 1950s was that the source of sand in the Phosphoria Formation had eastern, western, and possibly northern sources, whereas the silt and clay were derived only from western and northwestern sources (Cressman, 1955). Cressman also correctly determined that the Phosphoria chert was primarily a product of the diagenesis of siliceous sponge spicules. Each of the three major USGS Phosphoria programs had components of geochemical exploration for phosphate, the latter two for vanadium, and the last one for uranium. The first program identified vanadium-rich strata, which led to the 1940s vanadium program that supported the WWII effort. That program in turn identified zinc- and uranium-rich zones that led directly to the work begun in 1947 that was partly funded by the US Atomic Energy Commission because of their interest in uranium resources.

DEPOSITIONAL ENVIRONMENTS AND TRANSGRESSIVE-REGRESSIVE CYCLES: THE 1960s-1970s The 1960s and 1970s saw a broadening of investigations of the Phosphoria Formation with the completion of several PhD and MA dissertations regarding these rocks. In addition, the USGS efforts continued with follow-up work to the program that was started in 1947. Based on detailed study of drill core and outcrop facies and thickness changes and petrography, Campbell (1962) described the eastern margin of the Phosphoria sea in the

28

J R . Hein et al.

region of the Big Horn Basin, western Wyoming. Permian rocks in the Big Horn Basin reflect two transgressive-regressive cycles. He described a broad carbonate-producing shelf that did not attain depths greater than about 10 m for a distance of up to 110 km offshore. Marine evaporite basins occurred to the east and still farther east were mudflats. The elongate evaporite basins extended into the continental margin and had physical barriers during the first cycle and dynamic barriers during the second. Campbell proposed that the net flow of surface water was toward the coast due to evaporation in near-shore areas and that dense saline waters sank and flowed offshore, perhaps dolomitizing the carbonate sediments on the shelf in the process. The climate was thought to be semi-arid to arid and subtropical to tropical. The coastal plain was nearly flat with no more than about 60 m relief that become more subdued with time. Flash floods and ephemeral rivers produced localized sand bodies and deltas. Phosphorites formed farther to the west, outside his study area, where temperatures of cold upwelling waters were < 15~ By the time these waters reached the shoreline, they may have been more than 30~ Sheldon (1963) expanded his earlier work on cyclic sedimentation of Permian rocks, with the two transgressive-regressive cycles each represented by 11 lithologic units. Distribution and thickness maps showed that the Phosphoria facies of the second cycle extended farther north and east than it did during the first cycle, although the first cycle was much thicker in the southern part of the region. Sheldon detailed how transgressive overlap and regressive offlap sequences manifested in vertical sequences and areal distributions, and how those related to energy and mineral resources (Fig. 2-3). He also described how the distributions of minerals such as pyrite, anhydrite, glauconite, fluorite, and apatite, as well as organic matter were determined by the transgressive-regressive cycles. Kazakov's (1937) upwelling ideas were supported by inferring dominant south-flowing currents through the

East

West Southeast Idaho

Central Wyoming

9

source beds

i reservoir beds

D sealing beds

sea level

o0e,,,n0

-

~~r162 ~.~--'~

,,

,oO ~ ~ " ~ Cher ^ . . .

~

1l

~ I

~ ~

1

Limestone

"

... - ~

Dolomite

i Algal

edbed

S~~

Anhydrite

Dolomite

ark Phosphatic Shale, Phosphorite and Dolomite P

V, U, Cr

Fossiliferous Pelletal .

Foss~hferous

"

7,--

I I

Fig. 2-3. Schematic pattern of sedimentation, currents, petroleum generation, and metal accumulation in the Phosphoria sea (modified from Sheldon, 1963).


29

Phosphoria sea and westward-directed winds, both essential in supporting coastal upwelling. This latter inference was derived primarily from the fact that little volcanic debris is found in the Phosphoria Formation even though coeval volcanism occurred to the west. He also inferred upwelling of cold water from the fact that corals are rare in Permian rocks of the Western Phosphate Field. The vertical zoning of the cycles indicates that the transgressions were more rapid that the regressions. Sheldon persisted in the idea that the sea-level changes were dominantly the result of regional tectonism. From an extensive study of Permian rocks in southwest Montana, Cressman and Swanson (1964) came to much the same conclusions as Sheldon (1963). Cressman and Swanson thought that upwelling in Meade Peak and Retort times was promoted by the submergence of a ridge located along the present Montana-Idaho border, which allowed free access of a southward-flowing current to the Phosphoria basin. An analysis of 1509 fossil collections from the Shedhorn, Phosphoria, and Park City Formations led Yochelson (1968) to many of the same conclusions that Cressman, Sheldon, and coworkers had made based on paleogeography, lithology, and physical stratigraphy. Yochelson did differ with the estimate of the maximum water depth for the Phosphorita sea, which he suggested was about 90 m rather than the 200-1000 m postulated by McKelvey et al. (1953). He also emphasized the low diversity of fauna in these rocks, a characteristic that is generally associated with environments that are less than optimal for life. He suggested that the Phosphoria sea had generally normal salinity throughout most of its history, but may have been hypersaline in some near-shore environments. Near-shore environments generally had quiet bottom waters, intermediate-depth environments had somewhat more vigorous bottom waters, and deepest-water environments again had quiet bottom waters. Perhaps most importantly, Yochelson correctly indicated that these formations were more restricted in time than formerly thought. They were likely deposited only during the Middle Permian, during the late Leonardian through the late Wordian. Previous papers had suggested that these rocks were deposited during half of the Permian or even the entire Permian. Yochelson (1968) mentioned that carbonates in the Rex Chert might represent bank deposits, an idea that was more fully developed by Brittenham (1976). Brittenham based his results on field studies and on the fossil identifications provided by Yochelson. He suggested that the banks developed on the outer-shelf margin during transgression when open circulation was established on the shelf. Carbonate banks started with the build-up of ramose bryozoa, and brachiopods in areas of greatest circulation. Crinoids and rugose corals were also common components of the banks in places. These small mounds developed into larger banks up to several kilometers long that comprised a variety of biofacies and sedimentary structures. Shallow (125 ~ and

32

JR. Hein et al.

a prevailing northerly wind direction in the region of the Phosphoria basin during the Permian (see Hein, Chapter 1). Carroll et al. (1998) argued that terrigenous sediment in the Meade Peak Member was transported by northerly winds to the Phosphoria basin from present central Montana, citing as evidence well-sorted grain-size distributions, a scarcity of clay minerals, and the planar-parallel fabric of siltstone beds. These indications of a predominant northerly wind direction support oceanic upwelling via offshore Eckman transport of surface waters. Wardlaw (1980) and Wardlaw and Collinson (1984) suggested that upwelling water in the area of maximum phosphate deposition was relatively cold, based on the presence of presumed cold-water conodonts and brachiopods. Hiatt (1997) questioned that interpretation, citing a greater abundance of other species that have widespread occurrence in low-paleolatitude sections of western North American and the possibility that the initial associations of the specific fauna referenced by Wardlaw and Collinson with Arctic environments were based on inaccurate paleogeographic locations. Piper and Kolodny (1987) measured phosphate (PO 3 - ) 618OsMow values of between + 14.9 and + 17.5%0, from which they calculated water temperatures of 34-40~ similar to the summer surface-water temperatures for the Persian Gulf today. Hiatt and Budd (2001) reported an even larger range of phosphate 61SOsMow values, from 13.7 to 20.2%0, from which they calculated temperatures of 14-26~ for western sections, presumably representing temperate upwelling waters, and 34-42~ in eastern sections, representing warming of water across the shallow paleoshelf. Hiatt (1997) and Hiatt and Budd (2001) suggested that a drop in the oxygen-carrying capacity of impinging waters resulting from this warming helped maintain dysoxic conditions that promoted phosphogenesis in shallow-water environments.

Phosphogenesis

Several important papers, first presented at the 1978 International Congress on Sedimentology, were published by the Society of Economic Paleontologists and Mineralogists (SEPM) in 1980 in a collection entitled Marine Phosphorites- Geochemistry, Occurrence, Genesis. In this volume, Bentor (1980) attempted to discredit the hypothesis that phosphates were inorganically precipitated from bottom waters, arguing that direct precipitation was inconsistent with measurements of P concentrations in modern upwelling systems and carbonate fluorapatite (CFA) solubility. Bentor pointed out that plankton concentrate P from seawater about 250,000-fold, which can account for most of the phosphorus locked up in ancient phosphorites. He also suggested that phosphorite accumulation was largely dependent on the lack of dilution by other materials, especially carbonates, which are largely unstable in porewaters with a pH 1.2). The high ratios are due to the decreased TOC content (Fig. 4-12) as the average S content in these beds (1.2%) is significantly lower (at the 95% CI) than the average content in the underlying beds (3.7%; t-statistic = 5.4, df = 33). The high S/TOC ratios are, therefore, not likely indicative of euxinic bottom-water conditions, but rather increased retention of S over C within the sediment column. A greater amount of reactive iron (i.e. decoupled from terrigenous siliciclastics; Figs 3 and 6) would allow for metal sulfide formation within anoxic sediments. The upper Lakeridge section is also rich in apatite (up to 60%); as much as half of the average total S content of 1.2% may be incorporated in apatite, which may contain > 2 % S O 4 (Benmore et al., 1983; McArthur, 1985). An enrichment of HREE relative to LREE in seawater occurs from east to west across the basin, as suggested by the shift in the zero-intercept regressed slopes of La versus Yb from section to section (Fig. 4-14). Enrichment of HREE in seawater has been ascribed to preferential complexation of HREE and their resulting retention in solution

TABLE 4-IV General statistics for selected marine element concentrations (mg kg-') in five sections of the Meade Peak Member, Phosphoria Formation Element

Sectiona

Mean

Standard Error

Count

Minimum

Maximum

"MS: Mud Spring (Medrano and Piper, 1995); EV: Enoch Valley (Piper, 1999); HS: Hot Springs (Piper et al., 2000); FC: Fontanelle Creek (Medrano and Piper, 1995); Lakeridge core (Medrano and Piper, 1995).

102

R.B. Perkins and D.Z. Piper

Fig. 4-13. Plot of total S vs. TOC in the Mead Peak Member of the Phosphoria Formation showing position of samples from six sections in dysoxic, anoxic, and euxinic chemofacies fields defined by Hiatt (1997).

Fig. 4-14. La vs. Yb as surrogates for light and heavy REEs in five sections of the Meade Peak Member. The values listed in the legend are zero-intercept slopes and associated errors as calculated by least squares method.

(Sholkovitz et al., 1994). Assuming little biogenic uptake from surface waters, preferential sorption of LREE would be expected where reactive Fe oxyhydroxides are abundant. The high LREE/HREE ratios in eastern sections further suggest some degree of terrigenous sedimentation from the easterly Goose Egg basin, which was rich in Fe oxides, or sediment reworking and preferential retention of REE-rich phases.

The Meade Peak Member of the Phosphoria Formation

103

REE enrichment over terrigenous levels is indicated by the WSA-normalized patterns shown in Fig. 4-11. The flatter patterns represent beds rich in terrigenous debris, with normalized values near one. Interestingly, the basal Meade Peak is generally the most REE-rich bed in most sections. This may be the result of initial concentration of carrier phases (e.g. Fe oxides) under oxic to suboxic sediments prevalent during lowstand conditions and subsequent burial by organic-rich material that would have initiated reductive dissolution and incorporation of the REE in apatite.

CONCLUSIONS Our approach has been to investigate the geochemistry of the Meade Peak Member using ratios of elements associated with either the terrigenous or marine sediment fractions and a key element representing each fraction. Despite the simplicity of this approach and the underlying assumptions, the method is useful in highlighting geochemical changes that might otherwise be masked by lithologic variability and which may be important with respect to understanding the regional Middle Permian environment. The inter-element relationships in the terrigenous component appear useful for chemostratigraphic correlation. A sharp decrease in K20/A1203 ratios occurs in all but the northeasternmost section, where an offset occurs in average and minimum values. These offsets correspond closely to the lower Guadalupian Series boundary coincident with a change from major lowstand to transgressive conditions (Behnken et al., 1986; Ross and Ross, 1995; Hiatt, 1997). The decrease may be related to transgression of the Phosphoria sea on the Wyoming shelf. Assuming that the terrigenous fraction is mostly windtransported material, such a reduction in the K/A1 values may be related to changes in paleoatmospheric circulation, to inundation of particular source areas, or to increased transport distances. Three intervals displaying high Fe203/AI203, Ba/A1203 and Sc/AI203 ratios occur in the upper beds of the easternmost sections. These intervals occur within transgressive to highstand tracts that include the upper Meade Peak and inter-tonguing beds of Rex Chert. The location of these sections near the eastern margins of the basin and the lack of excess Fe, Ba, and Sc over their terrigenous contribution in other sections suggest that Fe-, Ba-, and Sc-rich sediments from southern or eastern sources (i.e. the Goose Egg basin) were either transported into the eastern margin of the Phosphoria basin by shoaling or surface-water transport during maximum-flooding conditions. Altematively, these intervals may reflect sediment reworking and preferential retention of heavy minerals hosting these elements. The westernmost section, presumably representing the deepest portions of the Phosphoria basin, has high Ba/AI203 ratios in the uppermost beds. We suggest that these intervals represent periods of low sediment accumulation during maximum flooding and highstand conditions. Such signals could be particularly useful in correlations of shale-rich basinal sections. Inter-element relationships in the marine fraction imply that bottom waters of the Phosphoria basin were dominantly denitrifying (dysoxic to anoxic), although temporary

104


sulfate-reducing (anoxic to euxinic) conditions may have occurred intermittently during deposition of the most phosphate-rich sections. Ratios of Cd and Mo to Zn and Cu closely approach those in modern plankton in most of the sections, implying a major biogenic source for these elements. Lower values for these ratios occur throughout the westernmost (distal) section, possibly due to different algal populations and relative nutrient uptakes. Large shifts in marine element ratios occur in the upper part of the northeasternmost (shoreward) section. These shifts are accompanied by decreases in organic carbon and an increase in REE concentrations and are coincident with the high Fe203, Ba, and Sc to alumina ratios. We interpret these changes as indicative of increasing redox potential in bottom waters, which nonetheless remained under denitrifying conditions as evidenced by relatively high Cr concentrations. The transition to more oxic conditions occurs at a horizon in the upper-middle part of the Meade Peak Member interpreted as the maximumflooding surface. Elevated oxic conditions persisted through the overlying and increasingly siliceous interval representing highstand conditions. The decrease in organic content could have been due to increased efficiency in oxidation of organic matter via increased water depths (Suess, 1980). However, the occurrence of apatite-rich zones, including pelletal packstones, suggests a relatively high organic input to the sediment column. Therefore, we attribute the noted offsets in the eastern sections to increased oxidation of the sediments resulting from increased mixing at the sediment interface. Removal of finer sediments by winnowing may also have concentrated apatite pellets. Deepening waters would likely have resulted in shoreward migration of the zone of intersection (less dampening) of wavebase turbulence along the gently sloping ramp margin, resulting in the higher energy bottom conditions. Some observations from this study may be of use in interpreting similar systems. 1. 2.

3.

Correlative offsets in terrestrial geochemical signatures in "sediment-starved basins" may be used as chemostratigraphic horizons. Distal areas may contain relatively thick phosphatic layers due to lack of terrigenous dilution. Lower concentrations of several important trace elements, however, may reflect deposition away from areas of peak primary production. Differing populations of primary producers with differing nutrient requirements may also have affected trace-element relationships in distal sections. Both mid-shelf (middle ramp) and marginal environments may have accumulated phosphate-rich layers and high concentrations of trace elements. However, sediments in marginal areas are likely to have the most varied geochemistry because they experienced the greatest variability in terrigenous sediment influx and because even moderate eustatic changes may have dramatic effects on facies, energy levels, sediment mixing, and the amount of organic detritus reaching the sediment surface.

ACKNOWLEDGEMENTS The authors are grateful for the reviews and suggestions of Greg M611er of the University of Idaho and George Desborough of the US Geological Survey, Denver. This


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work was funded by the US Geological Survey M e n d e n h a l l Postdoctoral Fellowship Program.

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Section of Society of Economic Paleontologists and Mineralologists, Los Angeles, CA, pp. 7-22. Ross, C.A. and Ross, J.R.P., 1995. Permian sequence stratigraphy. In: P. A. Scholle, T.M. Peryt and D.S. Ulmer-Scholle (eds.), The Permian of Northern Pangea; Volume I, Paleogeography, Paleoclimates, and Stratigraphy. Springer-Verlag, Berlin, pp. 98-123. Rossignol-Strick, M., Nesteroff, W., Olive, P. and Vergnaud-Grazzini, C., 1982. After the deluge: Mediterranean stagnation and sapropel formation. Nature, 295:105-110. Ryan, W.B.E and Cita, M.B., 1977. Ignorance concerning episodes of ocean-wide stagnation. Mar. Geol., 23:197-215. Sarnthein, M., Winn, K., Duplessy, J.C. and Fontugne, M.R., 1988. Global variations of surface ocean productivity in low and mid latitudes- influence on CO2 reservoirs on the deep ocean and atmosphere during the last 21,000 years. Paleoceanography, 3: 361-399. Schuffert, S.D., Jahnke, R.A., Kastner, M., Leather, J., Struz, A. and Wing, M.R., 1994. Rates of formation of modern phosphorite off western Mexico. Geochim. Cosmochim. Acta, 58: 5001-5010. Sheldon, R.P., 1963. Physical stratigraphy and mineral resources of Permian rocks in western Wyoming. US Geological Survey, Professional Paper, vol. 313-B, pp. 49-273. Sheldon, R.P., Cressman, E.R., Carswell, L.D. and Smart, R.A., 1954. Stratigraphic sections of the Phosphoria Formation in Wyoming. US Geological Survey, Circular, 325, 24 pp. Sheldon, R.P., Waring, R.G., Warner, M.A. and Smart, R.A., 1953. Stratigraphic sections of the Phosphoria Formation in Wyoming, 1949-1950. US Geological Survey, Circular, 307, 45 pp. Sholkovitz, E.R., Landing, W.M. and Lewis, B.L., 1994. Ocean particle chemistry: the fractionation of rare earth elements between suspended particles and seawater. Geochim. Cosmochim. Acta, 58: 1567-1579. Smart, R.A., Waring, R.G., Cheney, T.M. and Sheldon, R.P., 1954. Stratigraphic sections of the Phosphoria Formation in Idaho, 1950-1951. US Geological Survey, Circular, 327, 22 pp. Suess, E., 1980. Particulate organic carbon flux in the oceans; surface productivity and oxygen utilization. Nature, 288: 260-263. Taggart, J.E., Lindsey, J.R., Scott, B.A., Vivit, D.V., Bartel, A.J. and Stewart, K.C., 1987. Analysis of geologic materials by wavelength-dispersive X-ray fluorescence spectrometry. In: P. A. Baedecker (ed.), Methods for Geochemical Analysis. US Geological Survey, Bulletin, vol. 1770, pp. E I-E 19. Thunell, R.C., 1998. Particle fluxes in a coastal upwelling zone - sediment trap results from Santa Barbara Basin, California. Deep-Sea Res., II, 45: 1863-1884. Tisoncik, D.D., 1984. Regional lithostratigraphy of the Phosphoria Formation in the Overthrust Belt of Wyoming, Utah and Idaho. In: J. Woodward, EE Meissner and J.L. Clayton (eds.), Hydrocarbon source rocks of the Greater Rocky Mountain region. Rocky Mountain Association of Geologists, Denver, CO, pp. 295-320. Torres, M.E., Brumsack, H.J., Bohrmann, G. and Emeis, K.C., 1996. Barite fronts in continental margin sediments; a new look at barium remobilization in the zone of sulfate reduction and formation of heavy barites in diagenetic fronts. Chem. Geol., 127: 125-139. Tsoar, H. and Pye, K., 1987. Dust transport and the question of desert loess formation. Sedimentology, 34:139-153. Tsunogai, S. and Noriki, S.A., 1987. Organic matter fluxes and the sites of oxygen consumption in deep water. Deep-Sea Res., 34: 755-767. Turekian, K.K. and Wedepohl, K.H., 1961. Distribution of the elements in some major units of the Earth's crust. Geol. Soc. A. Bull., 72: 175-191.

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Wardlaw, B.R. and Collinson, J.W., 1986. Paleontology and deposition of the Phosphoria Formation. In: D.W Boyd and J.A. Lillegraven (eds.), Western Phosphate Deposits. University of Wyoming, Laramie, Contributions to Geology, pp. 107-142. Webster, R., 1973. Automatic soil-boundary location from transect data. J. Int. Assoc. Math. Geol., 5: 27-37. Wedepohl, K.H., 1969-1978. Handbook of Geochemistry. 4 Volumes, Springer-Verlag, Berlin. Whalen, M.T., 1996. Facies architecture of the Permian Park City Formation, Utah and Wyoming; implications for the paleogeography and oceanographic setting of western Pangea. In: M.W. Longman and M.D. Sonnenfeld (eds.), Paleozoic Systems of the Rocky Mountain Region. Society for Sedimentary Geology (SEPM), Denver, CO, pp. 355-378.

Li[e Cycle of the Phosphoria Formation." From Deposition to Post-Mining Environment Edited by James R. Hein Handbook o['Exploration and Environmental Geochemistry, Vol. 8 (M. Hale, Series Editor) Published by Elsevier B.V.

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Chapter 5

REGIONAL ANALYSIS OF SPICULITE FAUNAS IN THE PERMIAN PHOSPHORIA BASIN: IMPLICATIONS FOR PALEOCEANOGRAPHY B.L. MURCHEY

ABSTRACT The sponge spiculites of the Permian Phosphoria basin, Antler high, and eastern Havallah basin were the southernmost expression of one of the largest spiculite belts in the Earth's history. This spiculite belt extended from Nevada to the Barents Sea. In Idaho and Nevada, the spicule populations of this belt are dominated by demosponge spicules and are distinctive for their abundant rhax microscleres, large monaxons, and lithistid desmas. They form an Eastern Belt of spiculites that interfingers with spicule assemblages derived from choristid demosponges and hexactinellids that lived along the eastern margin of the deeper Havallah basin. The Havallah basin assemblages are similar to those in Permian arc terranes to the west, and together the sponge populations in this domain constitute a distinct Central Belt. Radiolarians are virtually absent in the siliceous microfossil populations of the Eastern Belt, abundant in the populations of the Central Belt, and dominant in the populations of a Western Belt confined to Mesozoic accretionary complexes in the Pacific Coast States. The scattered sponge spicules in the Western Belt radiolarites were derived from hexactinellids. During the Permian, the relative abundance and apparent diversity of siliceous sponges expanded over a wide range of depths in the basins from Nevada and Idaho to the open ocean. Radiolarian preservation and apparent diversity increased in the deeper Cordilleran basins as well. In the Arctic regions, significant sponge spiculites were deposited in epicratonic basins. At the same time that siliceous sponge populations expanded along the northwestern margin of Pangea, warm-water carbonate producers disappeared. Suppression of carbonate-producing organisms along the margin was critical to the accumulation and preservation of both the demosponge spiculites in the Eastern Belt and the spicule-rich argillites of the Central Belt. Vigorous thermohaline circulation was the major control on the paleobiogeography of the late Early, Middle, and early Late Permian along northwest Pangea. It was driven by cold, nutrient- and oxygen-rich northern waters and it produced a coastal current that swept down the margin of the supercontinent. The upwelling associated with deposition of world-class phosphorites in the Phosphoria basin was a part of this larger oceanographic system.

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INTRODUCTION Siliceous sponge spiculites in the Permian Phosphoria Formation of Idaho and adjacent States are remnants of an immense belt of spiculite deposits that rimmed the northwestern quadrant of Pangea. The belt stretched from central Nevada and Idaho (Fig. 5-1) through Alberta and British Columbia (not given in the figure) all the way to the seas off Norway and Arctic Canada (Fig. 5-2) (Murchey and Jones, 1992; Beauchamp and Baud, 2002). Even if the Pangean spiculite belt may have been locally discontinuous, its aggregate length eclipsed that of any older or younger spiculite accumulations along western and northern North America. The Permian spiculites are economically important because they form oil and gas reservoirs in the northern seas (Ehrenberg et al., 2001), alternate with the world-class phosphorite deposits in the Phosphoria basin (this volume), and host disseminated gold deposits in central Nevada (Murchey et al., 1995).

Fig. 5-1. Map showing present locations of Permian basins and terranes in Idaho, Nevada, California, Oregon, and Washington. Terrane names follow Silberling et al. (1987). Numbers correspond to samples listed in Table 5-II and mentioned in the text. The shaded area encompasses localities from which rhax-bearing, demosponge-dominated spiculites (Eastern Belt) are documented. The approximate locations of the Central and Western Belt assemblages discussed herein are illustrated as well.

Regional analysis of spiculite faunas in the Permian Phosphoria basin

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Fig. 5-2. Paleogeographic map of the Arctic region showing the distribution of Permian siliceous marine deposits, primarily spiculites, based on a figure in Beauchamp and Baud (2002). Numbers correspond to samples listed in Table 5-II and mentioned in the text.

Siliceous sponge spicules are the principal allochems of the Middle Permian Rex and Tosi Chert Members of the Phosphoria Formation and they are common sedimentary components of other members. For this reason, the total volume of siliceous sponges in the Phosphoria exceeds that of any other fossil group. Dissolved silica from dissolution of sponge spicules was the primary source of the silica in bedded and nodular Phosphoria chert (Sheldon, 1957). Despite the abundance of sponge spicules, the faunal compositions of the spiculites are less well-documented than the conodont and megafossil faunas of the Phosphoria (e.g. Yochelson, 1968; Wardlaw and Collinson, 1986) primarily because disaggregated spicules are not very useful for dating purposes or species identification. They have the potential, however, to provide new information regarding the environment of the Phosphoria basin and its relationship to basin systems along and across strike. This study will characterize siliceous microfossil assemblages in the southern part of the Permian spiculite belt from the Phosphoria basin in Idaho to the eastern Havallah basin and Antler high in central Nevada. In order to define and constrain the width of the spiculite belt, Permian siliceous microfossil assemblages will be compared across a broad east to west transect from Idaho and Nevada to California, Oregon, and Washington. The transect traverses paleogeographic settings from the epicontinental margin, across the deep Havallah basin, to island arc terranes and offshore oceanic basins. Siliceous sponge spicules and (or) radiolarians accumulated in many of these settings during the latter half of the Permian, an interval of especially widespread deposition of siliceous sediment in the global ocean (Murchey and Jones, 1992, 1994). In addition, a very preliminary comparison between the southern and northern siliceous spiculite belts will be made, based on the fossils from a few chert samples from the Chukchi Sea and northern Alaska.

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BACKGROUND AND PREVIOUS STUDIES The Phosphoria basin of Idaho and parts of Montana, Wyoming, Utah, and Nevada was a large marine embayment that formed above the autochthonous craton margin of western Pangea (Fig. 5-1). The largest Permian phosphorite deposits in the world accumulated in the Phosphoria basin during the latest Early and Middle Permian. Those deposits cyclically alternate with spiculite accumulations as eustatic sea levels rose and fell (Hein et al., Chapter 2). The eastern and southern margins of the basin were flat ramps across which the Phosphoria Formation intertongued with the Park City Group (Wardlaw and Collinson, 1986; Hiatt, 1997; Hein et al., Chapter 2). The southern margin of the Phosphoria basin trended due west across the Utah panhandle into the northeastern corner of Nevada where it was truncated by the Antler orogenic belt (Stevens, 1991). The western side of the basin is hidden by the Idaho batholith, which leaves key information regarding the basin topography in the realm of speculation. If the Antler high extended northward from Nevada, it would have formed a ridge, island chain, or sill along the western side of the Phosphoria basin. From the southwestern corner of the Phosphoria basin, the Antler high tracks southwest and then south to central Nevada (Stevens, 1991) (Fig. 5-1). This welt of Lower Paleozoic marine strata, also known as the Roberts Mountain allochthon, was thrust over the continental margin along the Roberts Mountain thrust fault in the Middle Paleozoic (Roberts, 1964). Stevens (1991) illustrated the Antler high as an emergent ridge during the Middle Permian, as very little marine strata of that age had been identified along the belt. However, as the result of gold exploration along the Golconda thrust fault, the Wordian Edna Mountain Formation has been recognized on the western side of the trend in a number of new localities (Murchey et al., 1995). In its type area, the Edna Mountain includes marine sandstone, siltstone, and minor conglomerate. Abundant siliceous sponge spicules and phosphatic coated grains are distinguishing characteristics of the fine-grained sandstone and brown siltstone intervals in the Edna Mountain (Murchey et al., 1995). The remapped Edna Mountain and its equivalents are used herein to help define the known southern limits of the Pangean spiculite belt (Fig. 5-1). Moore and Murchey (1998) also documented latest Early and Middle Permian radiolarian- and sponge-bearing argillite within the overlap sequence deposited on the Antler high in the Shoshone Range of central Nevada. The expansion of the number of known Middle Permian marine deposits along the Antler high suggests that it may have formed a chain of islands during Phosphoria time. Throughout the Late Paleozoic, the Antler high marked the boundary between western marine basins in which radiolarians were common rock-formers and eastern marine basins where radiolarians were only episodically present and were volumetrically insignificant. The Antler high formed the autochthonous eastern margin of the Late Paleozoic Havallah basin, which herein includes the Schoonover basin of northeastern Nevada (Fig. 5-1). The deeper reaches of the Late Devonian through Permian basin were characterized by pillow basalt, radiolarian chert, and turbiditic sandstone derived from the Antler high (Murchey, 1990; Whiteford, 1990). In central Nevada near Battle Mountain, basin and slope facies of the Havallah basin were thrust eastward over the Edna Mountain Formation no earlier than


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the late Wordian (Roberts, 1964). The Golconda thrust fault marks the eastern edge of the allochthon (Fig. 5-1). The absence of a Triassic overlap sequence across the fault and the pervasiveness of the Mesozoic tectonic overprint on the history of Nevada have created controversy about the age of the Golconda thrust fault. Not all regional geologists believe that the present position of the allochthon's leading edge predates the Jurassic (Ketner, 1998). Nevertheless, the closure of part of the Havallah basin was well underway when the Triassic Koipato sequence of the Tobin Range was deposited unconformably on imbricated stacks of uppermost Devonian and Mississippian through Lower Permian deep-marine strata (Stewart et al., 1986). I suggest that the more westward location of deep-marine Triassic depocenters and the absence of Triassic strata within the deformed assemblage indicate that the Havallah basin had substantially closed by the end of the Permian. In the Middle Permian, therefore, the Havallah basin was more likely a relatively narrow trough than a wide and expansive marginal sea. In some paleogeographic models for the Phosphoria Formation, the Havallah basin is projected northward into western Idaho beneath the Idaho batholith and west of the Phosphoria basin (e.g. Hiatt, 1997). Permian radiolarian- and spicule-bearing argillaceous slope facies of the eastern Havallah basin have been documented both above and below the Golconda thrust fault. Murchey (1990) described them in the Havallah tectonic assemblage immediately overlying the Golconda thrust near Antler Peak. In this area, argillite and siliceous argillite interleave with packages of black spiculitic chert that represent turbidite deposits (Murchey, 1990). The Permian spiculitic chert had previously been correlated with older radiolarian chert (Roberts, 1964). In the Shoshone Range to the south, Permian radiolarian- and spicule-bearing argillaceous strata form part of the autochthonous Antler overlap sequence, as previously mentioned, and Permian black spiculitic chert occurs in allochthonous strata above the Golconda thrust fault (Moore and Murchey, 1998). The latter is the basis for extending the southern limit of the Permian sponge spiculite belt at least as far south as the Shoshone Range (Fig. 5-1). One or more Permian island arc systems were likely located to the west of the Phosphoria and Havallah basins. In southern Nevada, the structurally highest tectonic units in the Havallah tectonic assemblage tie the basin to an active Permian arc by virtue of redeposited volcanic and plutonic material (Whiteford, 1990). Permian arc remnants are preserved in a discontinuous belt of accreted terranes from California and northwestern Nevada to northeastern Oregon. The Permian arc remnants included in this study follow the terminology of Silberling et al. (1987): the Northern Sierra terrane of California, Black Rock terrane of northwestern Nevada, Eastern Klamath terrane of California, and the Grindstone terrane of northern Oregon (Fig. 5-1). With the possible exception of the Northern Sierra terrane, these arc fragments share a number of characteristics including a similar association of Early and Middle Permian fusulinids and megafossils, commonly called the McCloud fauna (Stevens et al., 1990). Although the arc remnants are the most obvious candidates for a volcanic archipelago off the western margin of the greater Havallah basin (Harwood and Murchey, 1990), there is no universal agreement that the McCloud faunal province was located near the Cordilleran margin (Stevens et al., 1990).

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West and north of the Permian arc terranes, Early Mesozoic accretionary complexes contain sequences of Permian chert and siliceous mudstone. Samples from the North Fork and Hayfork terranes of California, the Baker terrane of Oregon, and the Hozameen and San Juan terranes of Washington were included in the regional comparisons of this study (Fig. 5-1). These rocks are associated with basalt and their pelagic protoliths were probably deposited on oceanic crust (Murchey and Jones, 1994). This interpretation is supported by the presence in these terranes of Permian limestone blocks with fusulinids of Tethyan affinity. The blocks are exotic to North America and may have formed on fartravelled seamounts (Stevens, 1991). In summary, the Phosphoria embayment was the easternmost marine basin in a series between the interior coastline and the open ocean. During the Permian, siliceous marine sediments were deposited in all the basins (Murchey and Jones, 1992). The distribution patterns of the two main fossil groups in these strata, radiolarians and siliceous sponge spicules, can help to define provinces within the expansive tract of siliceous deposits. In a previous study, Murchey and Jones (1994) compared Permian siliceous microfossil faunas from the allochthonous and parautochthonous terranes west of the Golconda thrust

Fig. 5-3. Modified X-Y diagram showing the ratio of ruzhencevispongacid radiolarians to albaillellacids (horizontal axis) vs. percentage of sponge spicules in total microfossil population (vertical axis) for Permian fauna from l0 tectonostratigraphic terranes in the western United States (Murchey and Jones, 1994) as well as from the Phosphoria basin and Antler high (Fig. 5-1). The shaded area is based on population counts illustrated as point data in Murchey and Jones (1994). The black-filled circle corresponds to new results from spiculites in the Phosphoria basin, eastern Havallah basin, and the Antler high. The three belts of sponge spicule assemblages distinguished in this study fall in different regions of the diagram.


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fault (Fig. 5-1). On the basis of population counts of radiolarians and siliceous sponge spicules, two major paleogeographic domains could be distinguished based on their quantitatively different faunal characteristics. The domains were defined by the ratio of two major radiolarian groups to one another and the ratio of radiolarians to sponge spicules. A domain characterized by assemblages containing both abundant radiolarians and sponge spicules encompasses the Permian volcanic arc terranes and the allochthonous part of the Havallah basin. The radiolarian populations in these assemblages were notable for their high concentrations of ruzhencevispongacid radiolarians relative to albaillellacids (Murchey and Jones, 1994) (Fig. 5-3). A western domain, characterized by abundant radiolarians but few or no sponge spicules, is defined by the assemblages in the oceanic terranes (Fig. 5-1). The radiolarian populations are notable for their very low ratios of ruzhencevispongacid radiolarians relative to albaillellacids. Whereas Murchey and Jones (1994) focused primarily on the characterization of radiolarian populations in terranes west of the Golconda fault, this study focuses on the characterization of siliceous microfossil faunas deposited east of the Golconda thrust in the Phosphoria basin and along the Antler high, as well as the sponge spicule assemblages in the more western basins. One goal is the expansion of the criteria that can be used for characterization of geographically distinct faunal assemblages.

METHODS Hundreds of rock samples from Paleozoic marine deposits of the western States were processed for siliceous microfossils. First, sponge spicules and radiolarians were etched from the rock matrix using diluted hydrofluoric acid (10% o f - - 5 0 % concentrate) (Dumitrica, 1970; Pessagno and Newport, 1972). Then, the fossils were washed off the rock surface and collected on Tyler-equivalent 250-mesh (63 Ixm openings) and 80-mesh (180 Ixm openings) screens. The fossils were examined with a binocular microscope. Of the processed samples with reasonably well-preserved siliceous microfossil faunas, 99 were determined to be Permian based on their contained fossils or on the fossil ages of surrounding strata.

Identification of sponge spicule morphotypes Ten sponge spicule morphotypes accounted for an estimated 99% of the sponge populations (Table 5-I). Their presence or absence in each sample is recorded in Table 5-II. More than 500 sponge spicules were commonly examined when sufficient quantities were extracted. In Table 5-II, X signifies that three or more specimens of a particular morphotype were observed, while R (rare) signifies that only one or two specimens were observed.

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TABLE 5-I List and brief description of the most common siliceous sponge spicules in Permian rocks of the western Cordillera: Idaho, Nevada, California, Oregon, and Washington. Their distribution in individual fossil assemblages is recorded in Table 5-II Spicule type

Comments

Monaxon

Class Demospongiae and Hexactinellida; broken single(?) axons and single axons with pointed ends (oxea monaxons) are the most abundant spicules in almost all samples; large monaxon spicules are present only in samples with few or no radiolarians - they are probably demosponges Class Demospongiae; small kidney-bean-shaped spicule, a microsclere; probably a demosponge selenaster Class Demospongiae, likely lithistids: polyaxon, polyactine; Tricranoclones are distinct forms that may prove to have paleogeographic significance Class Demospongiae, Hexactinellida(?); barbell-shaped monaxons Class Demospongiae, possible choristid; 4-axon, 4-actine; three actines curve away from fourth Class Demospongiae, possible choristid; 4-axon, 4-actine of approximately equal length, tetragonal symmetry Class Demospongiae, possible choristid; 4-axon, 4-actine; three actines curve downward toward fourth Class Hexactinellida; anchor-shaped spicules, some associated with root tuft Class Hexactinellida; modern forms restricted to the deep-water Amphidiscophora; morphotypes include paraclavules (ring of recurved spines at one end of straight shaft), hemidiscs (ring of recurved spines and one end of straight shaft, tiny ring of recurved spines at other end), and amphidiscs (equant rings of recurved spines at each end of shaft) Class Hexactinellida; 3-axon, 6-actine [5-, 4-actine]; more than 99% of the morphotypes observed in this study have pointed non-bifurcating terminations (oxyhexactine); variations of hexactines, such as pentactines and stauractines, are included in this category because they are difficult to distinguish from broken hexactines, and they occur with hexactines.

Rhax Desma Strongyle Protriaene Calthrops Anatriaene Anadiaene Birotule

Hexactine

Quantitative comparison of sponge spicules to radiolarians The 250-mesh screen residue (size fraction 63-180 txm) was used for relative comparisons of abundance. This size fraction commonly has the greatest abundance and diversity o f both sponge spicules and radiolarians. A ratio of sponge spicules to the total microfossil population (radiolarians plus spicules) was obtained by strewing the 250-mesh residue on a picking tray and counting 50-100 specimens lying on a line. The ratio is represented as a percentage (%S250 = (sponge/sponge + radiolarians)25o x 100%). The %S25o value for each sample is given in Table 5-II, which includes the data from Murchey and Jones (1994) for terranes lying west of the Golconda thrust fault. .


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RESULTS An eastem belt of rhax-bearing, demosponge-dominated spiculites can be distinguished from the two faunal domains previously defined by Murchey and Jones (1994). The differences are based on quantitative as well as qualitative observations. This belt can be traced from the Phosphoria basin in Idaho to the southwest and south along the Antler high (Fig. 5-1). Redeposited spicules from the Antler high can be recognized in the structurally lowest faultbounded strata above the Golconda thrust fault. The eastern spiculite belt appears to have characteristics similar to at least some of the spiculite deposits in the Arctic.

Eastern Belt: rhax-bearing, demosponge-dominated spiculite assemblages Twenty-four samples from chert or siltstone in Idaho and Nevada are characterized by demosponge spicules (Table 5-II; Samples 1-24). Large monaxons coupled with the presence of rhaxes, strongyles, and spheroidal microscleres distinguish these spiculites from all other Permian samples from the conterminous western States. The monaxon spicules of probable demosponge (Class Demospongiae) origin are abundant in all samples. Their axial canals are commonly filled with dark material, including collophane or a related phosphate mineral. Desmas from lithistid demosponges are generally more common than protriaene, anatriaene, or calthrop spicules of probable choristid demosponges. Oxyhexactine hexactinellid spicules (Class Hexactinellida) are present in many samples, but are a small component, a few percent at most, of the total spicule population. Radiolarians are absent in all but two samples which contain less than 1% radiolarians with no albaillellacid forms (Fig. 5-2).

Rex Chert of the Phosphoria Formation in southeastern Idaho, central basin (Table 5-11; Samples 1-3) Three samples from the Rex Chert Member of the Phosphoria Formation in southeastern Idaho yielded abundant sponge spicules but no radiolarians. Two composite samples (Samples 1 and 2, Table 5-I) were collected from an outcrop of the Rex Chert Member at Trail Canyon (locality 1206 in McKelvey et al., 1953a). At this outcrop, the Rex Chert consists of 7 m of black chert with beds 2.5-30 cm thick overlain by about 9 m of pale-gray chert with beds 16-61 cm thick. The black chert beds in the lower part of the outcrop contain no shale partings. Laterally, several beds commonly fuse into a single bed. The acidetched surfaces of individual beds reveal fine sedimentary laminae. The sponge spicules in this unit (Sample 2) are small, densely packed, and fairly diverse. In decreasing order of abundance, the spicules include broken monaxons (abundant), rhaxes (common), spheroidal microscleres (common), anatriaenes (rare), desmas (rare), hexactines (rare), calthrops (rare), and monaxon strongyles (rare). The pale-gray chert beds in the upper part of the outcrop have undulating bedding surfaces. The beds are densely packed with large,

B.L. Murchey

120 T A B L E 5-II

Sponge spicule data for individual samples. X indicates the presence of spicule morphotypes

in

r e s i d u e c o l l e c t e d o n a 2 5 0 - m e s h s c r e e n (at l e a s t t h r e e o b s e r v e d ) . R i n d i c a t e s o n l y o n e o r t w o s p e c i m e n s o b s e r v e d . L a n d S i n d i c a t e l a r g e or s m a l l m o n a x o n

spicules SPONGE SPICULE MORPHOTYPES

en

~

~

SE IDAHO,

O ~

1

My 700

100

L

~

2 3 4

My699 Lico 2 13681A

100 100 99+

L L L

"-

5 6

13681B 13679 13686B 91 ~ r r

99+ 100 !00 !00

L

L L L

X X X

X X

100 100 100 100 100 100 100 100 100 100 100 100

L L L L L L L L L L L L

X X X X X X X

X X

100

L

100 100 100 100 1oo 100 100

L L L L L L L

92-P34 (292-332) 100

L

..~

Rex Chert Member of the Phosphoria Formation L~ N.EAST NEVADA Mt. lchabodarea Unnamed black chert

~ ~~ r ~..~

7

N.CENTRAL NEVADA

8

~ ~ Edna Mountain Formation ~ ~ phosphatic siltstone: ~ L~ ~ ~ m CENfRAL NEVADA ~ Havallah assemblage: ~ ~ Black spiculitic chert, 8 ~

silty--turbidites

~ ~

13-22: North Central NV Battle Mt.,Antler Peak

L; L~ ~

23_24:

O

~

m

co~

ShoshoneRange CHUKCHI SEA, NORTHWIND RIDGE ~ Chert clasts derived from a~ < Van Hauen Fm. equivalent(?)

9 10 11 12 13 14 15

911"I"046 91"II"064 91"I/'065 9 ITI'~6 82MYI6D 82MY19 82MY22 1716 82MY21 MYI64 ..~ IS MY165 "~ 19 MYI69 ~: 20 MYI73 21 MYi84 22 MY317 23 13 24 19 25 93-PI6#1 r 26 #14 #17-1 28 #17-2 29

X X

X

X

R R R

R X X

X

X X

~,R X

R X R

R

X

X

X

R

X X R R

X X X X X X X

X X

X X

X

X

X

R

X X X

X X x

X x

X

Continued


121

TABLE 5-II Continued SPONGE SPICULE MORPHOTYPES m

oo

N. CENTRAL NEVADA Havallah Assemblage:

NORTHWEST NEVADA

30 31 32 33 34 35 36 37 38 39 40 41

82MYI6X 82MY 18 82MY20 82MY24 82MY23 83MY167 83MY171 84MY325 84MY330 84MY342 82MY352 5

60 52 95 40 20 51 23 80 50 40 60 I

S S S S S S S S S S S S

BLACKROCKTERRANE .~ "~ Chert overyling carbonate. 1A ~ is base of deepening upward sequence. ~

42 43 44 45

4 3 2 IB

465 !0 - - " ~k(,,.,~ ~ "~ ~" ,L~

Bear~ Lake Co~lnty

~o

ooo. \o~ _

i

0 I

10km I

Fig. 6-2. Index map of 7.5' quadrangles; quadrangles studied for phosphate resources during this and previous investigations are shown by larger letters; x, approximate location of historic open-pit mine; X, approximate location of active and recently active open-pit mines; B, Ballard; CH, Champ; CO, Conda; E, Enoch Valley; F, FMC Corp.; G, Georgetown Canyon; H, Henry; MC, Maybe Canyon; MF, Mountain Fuel; R, Rasmussen; S, Smoky Canyon. hosts the phosphate ore, is a deformed rock unit occupying a stratigraphic position between thick, relatively competent Paleozoic formations below it and thick, relatively competent Mesozoic strata above it. Pioneering studies of the Meade thrust plate and adjacent structures were made by Mansfield (1927, 1929, 1952) who mapped the geology of much of southeast Idaho and

140

J. G. E v a n s

adjacent southwest Wyoming at the scale of 1:62,500, including compilations at the scales of 1:250,000 and 1 : 125,000. Most of the more detailed geologic mapping in southeastern Idaho, done at a variety of scales over many years by many geologists, was compiled by Oriel and Platt (1980) into a geologic map of the Preston 1~ by 2 ~ quadrangle at the scale of 1:250,000. The structure of the Phosphoria Formation in the Meade plate was studied at macroscopic to microscopic scales to obtain a model of three-dimensional strain in the rocks in which the phosphate deposits are located and determine whether strain history and strain distribution correlate with mining characteristics, ore volume, or ore grade. A burial and thermal history of the Meade plate is included because it has a bearing on some of the physical conditions during thrusting and macroscopic structural development. The name Putnam-Paris thrust is used here for the pre-Meade and earliest thrust in the Sevier orogenic belt because the two thrusts that supply the name are apparently of similar age and may be the same structure. The Phosphoria Formation in the Meade plate, the focus of this study, includes three members: (a) Meade Peak Phosphatic Shale, which contains the phosphate resources, and the overlying (b) Rex Chert, and (c) Cherty Shale (McKelvey et al., 1956, 1959, 1967). The Rex Chert and Cherty Shale Members may interfinger in the central part of the plate and have been confused on some maps; the confusion in part reflects the generally poor exposures of the Phosphoria and the similar appearance of float composed of chert and cherty shale. In some places, the thicknesses of the Rex Chert and Cherty Shale vary so abruptly that faulting, including thrusting, and (or) folding within the upper Phosphoria is likely. The Triassic Dinwoody Formation, a secondary focus of this study, overlies the Phosphoria Formation and consists of thin-bedded limestone and interbedded silty and shaly limestone, and carbonate-cemented siltstone. In places where the contact with the Phosphoria is relatively well exposed, the Dinwoody is usually a pale-brown, brown, and greenish-brown weathered siltstone or shale and rarely sandstone. The contact between Phosphoria and Dinwoody usually corresponds to a topographic swale.

DEPTH OF BURIAL Claypool et al. (1978) and Herring (1995) noted that post-Permian strata were thinner on the continental shelf and thicker toward the west, farther from the paleoshore. The hinge across which the Mesozoic strata thicken is located just west of the present-day Idaho-Wyoming State line. Claypool et al. (1978) estimated that the depth of burial of Permian strata in eastern Idaho by the end of the Cretaceous was 5.5-8.3 km. The lower estimate is from the Gay mine on the Fort Hall Indian Reservation (western Chesterfield Reservoir quadrangle (Fig. 6-2) and west and north of the quadrangle). The greater estimate of thickness is from the Georgetown Canyon-Snowdrift Mountain area (Cressman, 1964) close to the Meade thrust. Edman and Surdam (1984b) estimated the depth of burial of the Phosphoria in the vicinity of Wooley Valley (Meade plate, Lower Valley quadrangle,

Strain distribution and structural evolution of the Meade plate

141

Fig. 6-2) at 4.15 km. An additional 9-12 km of tectonic overburden may have been added by emplacement of the Putnam-Paris plate (DeCelles et al., 1993).

THERMAL HISTORY

Petroleum generation and very low grade metamorphism Angevine and Turcotte (1983) developed a model of thermal evolution leading to oil generation in overthrust belts. They suggested that oil is generated in the rocks of a lower plate soon after emplacement of a thrust sheet. The thrust plate insulates the underlying rocks, causing their temperature to rise. Depending on the thickness of the thrust plate, oil may be destroyed through cracking in less than 5 Ma or last as many as 100 Ma in footwall rocks. This model applied to the Meade plate suggests that temperatures due to emplacement of the Putnam-Paris thrust graded from relatively low in the east to relatively high in the west, varying with the thickness of the Putnam-Paris plate. This relatively simple model is broadly consistent with evidence (see below) bearing on the thermal evolution of the Meade plate. Thermal models of thrusting also attribute a rise in temperature in a lower plate to formation of a reverse thermal gradient as the result of emplacement of a warm upper plate, in which relatively high temperatures are derived from the pre-emplacement geothermal gradient in the source region of the upper plate (Brewer, 1981). Several studies of hydrocarbons in the Meade Peak Member have presented a mixed picture of temperatures in the Meade Peak. Claypool et al. (1978) found the Meade Peak in the Meade plate to have been "overcooked" during burial to depths of as much as 8.5 km so that fluid hydrocarbons were destroyed by cracking. Subsequent studies including the Gay mine area on the Fort Hall Indian Reservation suggested: (a) that the samples of Claypool et al. were oxidized, weathered, and (or) biologically degraded, and therefore appeared to have been subjected to temperatures above the oil generation window (Desborough et al., 1988); (b) that conodont alteration indexes (CAI = 2-3) for Permian strata in the Gay mine area indicate that the rocks there were heated above the window for oil generation (Harris et al., 1980); and (c) that three samples from the Meade Peak Member (Rock-Eval) and one from the Wells Formation (CAI) below the Putnam-Paris thrust at the Gay mine had not been heated beyond the oil generation window (Desborough et al., 1988). Another study by Edman and Surdam (1984b) found a discrepancy in a single sample from Wooley Valley that showed temperature-related attributes characteristic of temperatures within and outside the oil generation window. This discrepancy was explained by a heat pulse from Tertiary plutons that influenced pyrolysis temperature, but not reflectance temperature. An estimate of depth of burial of the Wooley Valley segment of the Meade Peak Member of 4.15 km (Edman and Surdam, 1984b) suggests a temperature at the base of the Meade plate of nearly 250~ assuming a 32.8~ km -I geothermal gradient. In Early Cretaceous, the Meade plate was also covered by an estimated 12 km thick Putnam-Paris plate (DeCelles et al., 1993), which would have raised the temperature (assuming 32.8~ km -l)

142

J G. Evans

to about 400~ at the level of the Phosphoria and 640~ at the base of the Meade plate, given enough time. If the Phosphoria was exposed to 400~ it would most likely show more mineralogical indications of greenschist-facies metamorphism (range 300-550~ Turner and Verhoogen, 1960) than it does and possibly more abundant syntectonic mesoscopic structures that commonly accompany widespread greenschist-facies metamorphism (cleavage, foliation). The general lack of mineralogical and structural indications of incipient metamorphism in the Phosphoria may be indicative of a short duration of tectonic burial of rocks that would become the Meade plate, and later rapid activation of the Meade thrust, and uplift and erosion of the Meade plate.

Low-grade metamorphism Fractured quartz in Rex Chert in which biotite fills the cracks suggests that parts of the Meade plate experienced temperatures of low-grade metamorphism (_>300~ Turner and Verhoogen, 1960) at least briefly. However, occurrences of diagnostic metamorphic minerals are uncommon in the Phosphoria and absent in older formations of the Meade plate. This may be due to lack of the necessary chemical components required for neomineralization of diagnostic metamorphic minerals in chert, limestone, and dolostone, or the rocks may have lacked necessary fluids and permeability. Early diagenesis would have eliminated most of the permeability in the Phosphoria (Edman and Surdam, 1984a) and other parts of the section so that carbonate- or silica-rich, nearly monomineralic sedimentary rocks, isolated from pore fluids, could remain stable at and above 300~ Very finely grained silty limestone in the Dinwoody Formation of the Meade plate contains chlorite, biotite, amphibole, plagioclase, minerals of the epidote group, and garnet. The most abundant of these minerals are from the epidote group and are so abundant in places that the rock is green in outcrop. The metamorphic minerals are estimated to comprise as much as 30% of the rock in Dinwoody samples. Much of this green rock was found as far east as the Georgetown syncline in the Georgetown Canyon area. A suite of low-grade metamorphic minerals (garnet, chlorite, biotite, zoisite, and amphibole) was also found in samples of middle Paleozoic rocks from just above the Putnam-Paris thrust in southern Hatch quadrangle (Fig. 6-2). This distribution of low-grade metamorphic minerals in the upper Meade plate and the lower Putnam-Paris plate suggests that the upper strata of the Meade plate were subjected to a reverse geothermal gradient that could have coincided with emplacement of a warm Putnam-Paris plate. The thermal model ofYonkee et al. (1989) shows a P-T path for their Willard-Meade plate consistent with initial thermal gradients between 30 and 35~ km -l. Fluid pressures were less than lithostatic pressure in the hanging wall. Temperatures under 300~ in the footwall, consisting of the Crawford and Absaroka plates in this model, are also consistent with the findings of Yonkee (1983), Mitra and Yonkee (1985), and Mitra et al. (1988). The temperature of the rocks of the hanging wall (Willard-Meade plate) resulted from the pretectonic geothermal gradient in the region from which the upper plate rocks came. A reverse geothermal gradient was established after these relatively warm hanging-wall


143

rocks were thrust over the rocks that would eventually constitute the Crawford plate. According to this model, the base of the Meade plate should show at least low-grade metamorphism, but the metamorphic grade higher in the section should decrease (prehnite-pumpelleyite or zeolite facies?). The reverse appears to be true. If the Willard thrust model is applied to the Putnam-Paris thrust (Fig. 6-1), then the data from Yonkee et al. (1989) would indicate that metamorphism at the base of the Willard plate translates to a warm Putnam-Paris plate above the rocks that later became part of the Meade plate. Based on the presently perceived distribution of the epidote-bearing rocks in the Dinwoody Formation, the warm thrust plate model would require that the Putnam-Paris thrust system have extended much farther east than it does at present. It may have extended close to the present position of the Meade thrust or farther east, for a minimum amount of tectonic transport of about 40 km (compare with 48 km, Mitra and Yonkee, 1985; Allmendinger, 1992). There must be additional factors influencing the variations of paleogeothermal gradients because part of the Meade Peak Member and Dinwoody Formation near the Putnam-Paris thrust was not subjected to low greenschist-facies temperatures (Harris et al., 1980; Paul et al., 1985; Desborough et al., 1988), contrary to the warm thrust-plate model. Lacking additional information about distribution of low-grade metamorphic minerals, explanation of the presently inferred pattern of metamorphic rock and sedimentary rock capable of generating fluid hydrocarbon includes the possibility that postmetamorphic tectonism may have shuffled the strata of the upper Meade plate and disturbed Early Cretaceous metamorphic isograds. Some of this rearrangement may be due to concealed backthrusting, remobilization of the Putnam-Paris thrust in the Late Cretaceous or Early Cenozoic and emplacement of large tectonic lenses (duplexes) of unmetamorphosed Permian and Triassic rocks, Tertiary backsliding of unmetamorphosed rocks along former reverse faults or intraplate thrusts, or detachment faulting. The discussion above suggests a Cretaceous temperature profile of the Meade plate of >_300~ near the Putnam-Paris thrust(s) gradually decreasing to perhaps 250~ at the base of the Meade plate. The threshold of greenschist-facies temperature (300~ may have been reached at the stratigraphic level of the Phosphoria, possibly near the contact of the Meade Peak Member and Rex Chert, in which biotite was identified.

STRUCTURE P r e t e c t o n i c structures

The model of pretectonic changes in the Phosphoria Formation suggests that the stress affecting the rocks at that time would have been largely due to the lithostatic pressure of overlying Mesozoic sediments during compaction and following initial lithification. Boudinage, pinch-and-swell structure, and isoclinal folds can be produced in sedimentary rocks of varying lithification in the section and could have led to local anisotropic strain as the result of different yield strengths of the strata. Stylolites subparallel to bedding

144

J. G. Evans

suggest formation during Mesozoic compaction. The locally close relation of quartz and carbonate veins perpendicular to bedding and attached to stylolites suggests that the fractures that host the veins provided paths for silica- or carbonate-rich solutions that left behind laminae of insoluble residues, for example, hematite and clay minerals.

Syntectonic structures As a result of emplacement of the Putnam-Paris thrust system, most of the rocks that would eventually constitute the Meade plate were subjected to additional flattening from the overburden of the Putnam-Paris plate. Many of the same kinds of structures listed above as pretectonic may also have been produced during this phase of flattening. Allmendinger (1979) provided evidence that the rocks in the Meade plate closest to the Putnam-Paris thrust were deformed prior to emplacement of the thrust, so that the tectonic overburden in places may have been emplaced at an angle to bedding. One strategy for sorting structures into stages is to assign bedding-parallel strain features to the Sevier orogeny. Syntectonic structures can resemble structures developed during compaction (fractures, veins, stylolites, boudinage), but would theoretically be oriented as much as 90 ~ from similar pretectonic structures, assuming horizontal generally east-west compression and near-horizontal bedding. In places where bedding was rotated to steep dips on the limbs of macroscopic folds, regional northeast-southwest-trending to east-westtrending horizontal compression (see below) further flattened the rock along bedding. As a result, flattening parallel to bedding should comprise a large component of the total strain and it may have accumulated in as many as three stages: (a) during initial compaction by sedimentary overburden; (b) during emplacement of the Putnam-Paris plate; and (c) during continuing near-horizontal compression at large angles to bedding in steeply tilted strata. Some of the minor structures, like stylolites and quartz veins, that can be assigned to a younger layer-parallel compressive event according to the criteria mentioned above appear to be poorly developed in contrast to similar structures associated with compaction and later emplacement of tectonic overburden of the Putnam-Paris plate. These observations suggest that the rocks were relatively strain-hardened after early compaction events. In addition, the conditions during deformation (pressure, temperature, pore fluid volume, porosity, permeability, and a lack of appropriately oriented pre-existing planes of weakness, e.g. bedding) may have changed and been unfavorable for further development of certain kinds of minor structures by layer-parallel compression. The short duration of horizontal compressive stress would also have affected intensity of development of minor structures.

Orogenic and structural terminology Here, the name Sevier orogeny is used for thrusting episodes that took place from Early Cretaceous to Eocene (from Late Jurassic according to Armstrong, 1968; Heller et al., 1986) in the southeastern Idaho part of the fold-and-thrust belt. The Putnam-Paris thrust,


145

considered the oldest thrust in this part of the Sevier orogenic belt, was formerly included in the "Bannock overthrust" of Richards and Mansfield (1912) and Mansfield (1927), and the "Bannock thrust zone" of Armstrong and Cressman (1963) and Armstrong and Oriel (1965). Armstrong and Cressman (1963) showed that the Paris and Meade thrusts are separate imbricate thrust faults of the thrust belt. Northwest of Soda Springs, the Putnam thrust (Fig. 6-1) was recognized and named by Mansfield (1920, 1929). Kellogg (1992), Kellogg et al. (1999), and Rodgers and Janecke (1992) suggested that the Putnam thrust is connected to the Paris thrust by a thrust-transfer system, which further suggests that the Putnam thrust is partly coeval with the Paris thrust (Early Cretaceous). During recent field mapping, an attempt to map the northwestern extent of the Paris thrust as far as Chesterfield Reservoir was unsuccessful, as the critical area was covered by Cretaceous and (or) early Tertiary to Quaternary gravel and alluvium. The lower to middle Paleozoic limestone mapped in the southern part of the Hatch 7.5' quadrangle (Mansfield, 1929; Fig. 6-2) is in the Paris plate and suggests a continuous thrust trajectory between the mapped Putnam and Paris thrusts. The Meade plate, or duplex of Armstrong and Cressman (1963), has been assigned various relations with adjacent thrust plates. Here, the Crawford plate is considered to be in the footwall of the southern part of the Meade thrust. The footwall of the northern part of the Meade thrust is the Absaroka plate, as the Crawford thrust is not mapped north of 42 ~30' latitude (Dixon, 1982; Yonkee, 1983). The lower boundary of the Meade plate as used here is in part the one originally mapped by Mansfield (1927) as the Bannock overthrust, but is closer to the Meade thrust of Armstrong and Cressman (1963).

Timing o f thrusting in southeastern Idaho The oldest Mesozoic thrust in the region may be the Middle Jurassic Manning Canyon detachment of Allmendinger and Jordan (1981) and Allmendinger et al. (1984), about 70km west of the westernmost exposures of the Meade thrust plate. Movement on the Manning Canyon detachment was assigned to the Nevadan orogeny. Movement on the Putnam-Paris thrust, formerly thought to be Late Jurassic to Early Cretaceous in age (Armstrong and Cressman, 1963), was later found to be Early Cretaceous, based on fossil evidence indicating that the age of the syntectonic Ephraim Conglomerate is Aptian to Cenomanian (Heller et al., 1986). Principal movement on the Meade thrust occurred in Early to Late Cretaceous (Coniacian, about 88 Ma, Armstrong and Oriel, 1965; Albian to Turonian, about 105-90 Ma, Allmendinger, 1992). Based on provenance of clasts in the Bechler Conglomerate at Red Mountain, Idaho, about 1.5 km east of the present trace of the Meade thrust, DeCelles et al. (1993) proposed that the Meade thrust initially developed in Aptian (-118-113 Ma; Early Cretaceous). Deposition of conglomerate continued during Albian to Cenomanian time, during which the Meade thrust overrode the Bechler Conglomerate and other rocks in the footwall. Movement on the Meade thrust was probably completed by Cenomanian or Turonian time (-95-90 Ma).

146

J. G. Evans

Subsequent movements on Crawford, Absaroka, Darby, Prospect, and Hogsback thrusts range through the Late Cretaceous and Paleocene. These thrusts and their upper plates are important for understanding the structural evolution of the Meade plate because deformation in those plates may have affected the Meade plate. Geologic relations in the western part of the Meade thrust plate in the Chesterfield Reservoir quadrangle, southeast Idaho, strongly suggest that the Putnam-Paris plate to the west was uplifted after deformation of the Meade plate was complete. Evidence for this sequence of events is Cretaceous and (or) Tertiary gravel up to 400 m thick that contains conspicuous white blocks of early Paleozoic or Late Proterozoic quartzite as much as 5 m across and less conspicuous boulders of early Paleozoic limestones as much as 1 m across (Mansfield, 1927; Evans, unpub, mapping, 2000, Chesterfield Reservoir quadrangle). The uplift of resistant rocks in the Putnam-Paris plate could have accompanied movement on thrusts younger than the Meade thrust, such as the Absaroka or Darby thrusts, possibly as the Putnam-Paris plate was passively elevated above one or more thrust ramps (Schm'itt and Steidtman, 1990; DeCelles, 1994). Ramp-related uplift of the Putnam-Paris plate, however, is not obvious because geologic interpretations of seismic data (Dixon, 1982) suggest that the present extent of the Putnam plate does not overlie a younger ramp (see below). In addition, one or more of several Mesozoic or Cenozoic tectonic processes may have disrupted Cretaceous isograds and other geologic relations, so that the present relative locations of all parts of thrust plates may be different from their Cretaceous to Early Cenozoic arrangement. Also, the Putnam-Paris plate of today is a remnant of a more extensive plate, the leading edge of which may have originally been at least 40 km farther east.

Shortening of the Meade and other plates Leeman et al. (1992) suggested that the Sevier thrusting in the northwest Montananorthern Idaho area moved the upper plate of the Sevier system as much as 150 km northeast and was crustal in scale. Estimates of cumulative shortening for the Sevier foldand-thrust belt range from 43 to 54% (Rubey and Hubbert, 1959; Monley, 1971; Royse et al., 1975) and 100-150 km (Rubey and Hubbert, 1959; Royse et al., 1975; Claypool et al., 1978; Allmendinger, 1992; Craddock, 1992). Estimates have been made of more than 10-44 km of tectonic transport along the Putnam-Paris thrust (Wiltschko and Dorr, 1983; Allmendinger, 1992; Coogan, 1992; Cradddock, 1992; this chapter). Estimates of 23-48 km of tectonic transport of the Meade plate have been reported (Royse et al., 1975; Wiltschko and Dorr, 1983; Mitra and Yonkee, 1985; Allmendinger, 1992; Coogan, 1992; Craddock, 1992; DeCelles et al., 1993). According to models of Sevier thrusting, once movement along the Meade thrust ceased, the plate was passively carried an additional 60-75 km farther east on younger thrusts (Wiltschko and Dorr, 1983; Allmendinger, 1992). The Sevier orogeny was followed by Middle and Late Cenozoic Basin-and-Range regional extension, which needs to be considered in estimating Sevier-age shortening. Levy and Christie-Blick (1989) restored Basin-and-Range extension of ~250 km, most of which was west of the Meade plate. This restoration moved the leading edge of the Sevier

Strain distribution and structural evolution of the Meadeplate

147

fold-and-thrust belt 130 km west of the Idaho-Wyoming State line. This reconstruction of the entire Sevier orogenic belt is too broad in scope to assist in assessing Tertiary extension within the Meade plate in detail, but it suggests that extension in places may be about the same order of magnitude as the earlier shortening, similar to conclusions from crosssections (see below). Late Tertiary extension of the Meade plate probably concentrated in north-trending grabens that contain thick Tertiary sediment and volcanic rocks, such as Gem Valley, Blackfoot lava field, Willow Creek lava field, Grays Lake, and Bear Lake Valley. Slip on relatively minor reverse and intraplate thrusts may also have been reversed.

Direction o f tectonic transport Eastward tectonic transport of thrust plates during the Sevier orogeny is based on the assumption that movements on the thrusts are predominantly up-dip, resulting in older rocks on top of younger ones (Armstrong and Oriel, 1965; Armstrong, 1968; Royse et al., 1975) and overturning of eastern limbs of folds to the east. Other estimates are based on structural analyses. Crosby (1968, 1969, 1970) studied minor structures at 22 localities across the Idaho-Wyoming-Utah fold-and-thrust belt, and concluded that the transport directions varied across an arc of about 80 ~, from northeast to east-southeast. These transport directions are approximately perpendicular to major fold axes in the Meade plate (Fig. 6-3). Other estimates of direction of transport based on macro-, meso-, and microscopic fabric are generally about east-west (Allmendinger, 1981, 1982; Craddock, 1992).

Thickness o f the Meade thrust plate and topology o f the Meade thrust In contrast to the 2.4 km maximum thickness of the Meade plate suggested by Mansfield (1927, 1929, 1952), more recent work has inferred that the thickness is much greater, 5.8 km (Edman and Surdam, 1984b). Royse et al. (1975) showed variable thickness (2.4-5.5 km) of the Meade plate, with general thickening to the west and merging with the Putnam-Paris thrust at the regional Mississippian detachment under Gem Valley, about 5 km east of Soda Springs. Dixon (1982) interpreted proprietary seismic data from southeastern Idaho using several assumptions, some of which have not been substantiated. Nevertheless, his work is one of the most important in the region because it provides interpretations of deep structure. Dixon interpreted seismic profiles across the Meade plate to indicate a vertical thickness of the plate of as much as 3-4 km in the east and from 9.5 to 14 km in the west. Structure contours on the Meade thrust were derived from Dixon's cross-sections (Fig. 6-4). Maximum thickness perpendicular to the principal (first) ramp is about 12 km. Dixon's cross-sections 25-47 were not used because this study concentrates on the northern and broader segment of the Meade plate. Cross-sections showing the greatest depth of the thrust are numbers 1 through 9; towards the Bear Lake area (Fig. 6-1) to the south, the depth of the Meade thrust decreases to about 9.5 km.

148

J. G. Evans 111 ~ 30 r

43 ~ 15'

111 ~

I

Willow~ Creek

~)

~

Lava Field

0! " " '~-~

.... '. . . .

~

""-,

Absaroka Plate

10km I

Anticline Syncline

43 ~

\ \ \

\

Blackfoot Lava ~, Field

_

\ \ \

%, \

i 42 ~ 30'

Fig. 6-3. Central part of Meade plate showing large fold axes (after Mansfield, 1927, Plate I). Axes of most large folds trend from north-northeast in the south to northwest in the north. Figure does not show Rasmussen fault of Pratt and Oriel (1981) and Oberlindacher et al. (unpublished mapping, Lower Valley Quadrangle). The steeply dipping or vertical Rasmussen fault is about 5 km north of the Blackfoot fault, strikes east, and shows left-lateral offset of formations and structure. SA, Snowdrift anticline; GS, Georgetown syncline; LGA, Little Gray anticline.

149


112 ~

43 ~30'

Eastern L_Snake River Plain _.., . \

\\

01A t

I

~

-,0,000 -20,000

,,.,

-30,000 -40,000

111 ~

Meade plate Meade thrust Absaroka-Crawford plates Absaroka Plate

43 ~

/ Approximate location of Putnam-Paris thrust(s) 60

Putnam-Paris Plate(s) 95 ~

43 ~30'

107'

j

Crosssection

2o..___.A.~'

Crawford Plate

~' o r o00

0

10km

I

J

Fig. 6-4. Structure contours on northern part of Meade thrust; elevation data from Dixon (1982); contour interval 5000 ft (1525 m); thick lines show axes of folds in Meade thrust; north-trending faults are Cenozoic in age; scale, latitude, and longitude are approximate. Cross-section A-A' (inset) approximately parallels general strike of this part of the thrust and is drawn with no vertical exaggeration; top of cross-section is 0 ft, mean sea level.

150

J. G. E v a n s

The structure contours on the Meade thrust (Fig. 6-4) are drawn as far to the west as can reasonably be inferred from Dixon's (1982)cross-sections. A contour interval of 5000 ft (1525 m) was used and the normal faults associated with the Bear Lake fault zone show substantial offsets that were taken into account when drawing the contours in the southern part of the study area. Feet are used in Fig. 6-4 to facilitate direct reference to Dixon's cross-sections. The Meade thrust is characterized by ramp and "fiat" geometry (Fig. 6-4), which is considered typical of thrust faults (Boyer and Elliott, 1982). Below-35,000 fl (below sea level; - 1 0 , 6 7 5 m), the Meade thrust appears to flatten (trailing branch), presumably before merging with the underlying regional Mississippian d6collement from which the Putnam-Paris thrust system originated (Royse et al., 1975). The largest part of the Meade thrust is a lower ramp most of which is between -10,000 ft ( - 3 0 5 0 m) and -35,000 ft (-10,675 m). The ramp, varying from 18-20 km wide horizontally, extends from the northwest end of the plate southeast of the Snake River Plain to what appears to be a broad, central, strongly folded zone. From there, it continues southward just west of the Bear Lake fault and associated faults (north-striking normal faults in the southeastern corner of Fig. 6-4). Dip of the lower ramp varies from as much as 47 ~ southwest at the northwestern end to as little as 36 ~ west-southwest at the latitude of Dixon's (1982) cross-section 17 (42 ~ 10'-15'N latitude). About 3 km east of the leading edge of the Putnam-Paris thrust, a northwest-trending cross-section, drawn to cut the deepest part of the Meade thrust, shows the thrust as a line. Its curved path suggests shortening of about 9% parallel to the orogen, assuming the thrust originated as a planar structure. Two relatively flat segments of the Meade thrust above the first ramp are located between 42 ~30'-45'N latitude and at depths between -10,000 ft ( - 3 0 5 0 m) and near sea level, and between 43 ~0 ' - 2 0 ' N latitude and at depths between - 10,000 ft ( - 3 0 5 0 m) and - 5 0 0 0 ft ( - 1525 m). The dip of the upper "fiat" is as much as 22.5 ~ southwest in the north to 15~ west-southwest at the latitude of Dixon's cross-section 17. Although this part of the thrust is not actually "fiat" (0 ~ dip), the dip angle of the thrust changes relatively abruptly by about 50~ from the lower ramp to the second "fiat." The broad extent of this "fiat" may result from the Meade thrust following a zone of weakness in the Jurassic Twin Creek Formation (Evans and Craddock, 1985) and (or) a zone of salt in the Preuss Formation (Coogan and Yonkee, 1985). Alternatively, the shape and extent of the southern "fiat" may reflect variable displacement along the Meade thrust (see below). The variable displacement, however, may be controlled by competency of the strata encountered. The uppermost 5000 ft (1525 m)-8000 ft (2440 m) parts of the thrust above sea level in the south and the uppermost 10,000 ft (3050 m) in the north appear to steepen, suggesting that these parts of the thrust comprise the lower part of an upper ramp. Most of the characteristics of the Meade thrust are duplicated in the younger thrusts of the Sevier belt. Dixon (1982) drew structure contours on the Absaroka, Prospect, and Hogsback thrusts, and Mitra and Yonkee (1985) drew structure contours on the Crawford thrust using Dixon's data. These thrusts have lower ramps and middle "fiats," like the second "fiat" of the Meade thrust, that are defined by abrupt decreases in dip. The thrust faults steepen abruptly into upper ramps before they are truncated by the erosion surface.


151

The structure contours on these thrusts appear to show folds that trend at large angles to the strike of the thrusts like the folds in the Meade thrust (Fig. 6-3). In addition, Dixon (1982; Fig. 16) interpreted structure contours in the central part of the Darby thrust as folds with hinges subparallel to the trend of the orogen. Dixon attributed the flattening in the thrusts younger than the Meade to interaction of the thrusts with Cretaceous foredeep shales or basement blocks.

Style o f deformation o f the Meade thrust and plate Axes of apparent macroscopic folds in the Meade thrust trend from 50 to 110 ~ and are most prominent in the central part of the study area (Fig. 6-4). Trends of macroscopic to subregional folds defined by stratigraphy at the surface, however, are mostly at right angles to trends of folds in the Meade thrust (Fig. 6-3), although a few subordinate macroscopic northeast-trending folds cross the dominant set at the surface. The northeast-trending folds of the Meade thrust suggest the possibility that the rocks below the second "fiat" (below -10,000 fl; - 3 0 5 0 m) may have different structural components or components that are different in style, orientation, and (or) development from the structures in exposures. The axes of folds in the Meade thrust parallel directions of tectonic transport inferred by Crosby (1968, 1969, 1970) from mesoscopic structural data. The large north-northeast- to northwest-trending folds and the northeast-trending folds may be components of a B perpendicular to B' tectonite (Hills, 1963), suggesting that the folds formed penecontemporaneously. Northeast-trending folds may be dominant at depth, and subordinate at the surface. Above sea level, the northeast- to east-trending folds of the Meade thrust that are so obvious along the lower "fiat" and ramp are not noticeable above what can be seen of the top of the upper "fiat" (Fig. 6-4). Both observations suggest a layering of deformation styles in the plate. Concentric folds were considered the typical fold type in the Sevier fold-and-thrust belt (Mansfield, 1927, 1929, 1952; Royse et al., 1975; Dixon, 1982) despite evidence to the contrary. Others challenged the assumption of parallel flexural-slip folds in the Cordilleran thrust zones and instead described the kink-band and box fold geometry (narrow hinges and long, planar limbs; Allmendinger, 1981, 1982; Boyer, 1986; Coogan, 1992). The biggest and most easily seen box fold in the Meade plate is near the south end of the Georgetown syncline near the former site of the Georgetown Canyon mine offices and plant (in the process of dismantling and reclamation in 2001; Mansfield, 1927; Cressman, 1964). The ramp-fiat model of thrusting postulates that folds in the overriding plate form as the result of ascending a ramp, which forms a syncline at the base of the ramp and an anticline at the top as the strata are constrained to flex in one direction, unfold, and then flex in another direction (Rich, 1934; Davis et al., 1983; Suppe, 1983). While this model of strain may seem reasonable for folds near the Meade thrust, other large folds in the plate occur several kilometers above the Meade thrust and involve formations of varying competence. The relevance of ramp-related folding for these structures is not clear. Some large folds like the Rock Creek Syncline (Chesterfield Reservoir quadrangle, Mansfield, 1929)

152

J. G. Evans

are relatively close to the Putnam-Paris thrust and may have been generated in strata modified by displacements along the Putnam-Paris thrust before, during, or even after movement along the Meade thrust. Dixon's cross-sections, work by Lageson and Schmitt (1994), and suggestions from more detailed local analyses (Allmendinger, 1979, 1981, 1982) suggest that the rocks near the Meade thrust deformed differently from those higher in the plate. If so, then the rampflat model of folding may not be appropriate for the entire Meade plate, especially at depths below -10,000 ft ( - 3 0 5 0 m). Surficial structure in the Meade plate is dominated by nearly plate-long, mostly upright folds (e.g. the 75-km-long Snowdrift anticline) that trend northwest near the eastern Snake River Plain, and north to north-northeast east of Soda Springs (Fig. 6-3). Some of the synclines in the western part of the plate have western limbs overturned to the east.

Shortening and extension implied by folding and faulting in the Meade plate Numerous published cross sections drawn across the Meade thrust approximate the amount and locations of macroscopic strains that the Meade plate has undergone (Table 6-I). The age of shortening is generally not apparent in a complex orogenic zone like the Sevier orogenic belt. Some of the deformation within a thrust plate, including folding and faulting, may be associated with significant movement of an older or younger thrust. Wojtal and Mitra (1986) suggested that much of the internal shortening in a thrust plate develops concomitantly with the underlying thrust zone itself, but that internal strain may have an upper limit depending on local PTx conditions, beyond which strain tends to be concentrated in a basal strain-softened, cataclastic zone. In addition, as deformation progresses, there may develop a basal zone where the rocks are flattened and extended while rocks higher in the plate are compressed, thickened, and shortened (Allmendinger, 1979; Wojtal, 1986). As suggested above, the Meade plate may contain this layering of deformational styles. Consequently, inferences about shortening derived from surficial geology may apply only to the uppermost 10,000 to 18,000 vertical-feet (3050-5490 m) of the Meade plate. Several assumptions are used here in determining a minimum amount of shortening from cross-sections (Table 6-I): (a) the trends of the cross-sections approximate the profiles of the folds, and parallel the principal direction of shortening; (b) an insignificant amount of material moved across the plane of section; and (c) mesoscopic and microscopic strain were insignificant additions to total shortening. As mentioned above and below, assumption (b) may be untenable. There is evidence of relatively minor (joints, faults, folds, veins) extension parallel to major fold axes and, therefore, through the planes of cross-sections; the amount, however, may be less than 10%. Assumption (c) mostly points to the inability to correlate relations among macroscopic, mesoscopic, and microscopic strain components. Also, macroscopic strain may be the result of distributed smaller-scale processes and may give an estimate of total strain within the plate, irrespective of when it occurred. Measurements of the length of the upper contact of the Meade Peak Member of the Phosphoria Formation are used here as a proxy for estimating shortening because of the


15 3

TABLE 6-I Macroscopic shortening and extension within Meade plate

Cross-

Reference

section

% shortening

% shortening

% total

% extension

% cross-

Length o f

by folding

by faulting

shortening

(faulting)

section used

crosssection used (km)

1. D - D ' , plate l l

Mansfield

18

-

18

19

60

2.3 4.5

(1927) 2. F - F ' , plate 11

Same

21

-

21

-

90

3. G - G ' plate 11

Same

24

-

24

8

99

8.2

4. I - I ' plate 11

Same

16

5.7

21.7

0.3

75

16.5

5.4

18.8

5. K - K ' , plate 11

Same

16

21.4

1.1

80

6. L - L ' , plate 11

Same

7

-

7

1.8

60

9.8

7. M - M ' , plate I1

Same

12

4

16

3.2

100

19.3

plate 11

Same

7.4

-

7.4

-

50

9.4

9. O - O ' , plate 12

Same

6

0.3

6.3

1.6

90

29.4

1.3

! 7.3

0.7

75

26

-

74

7

6O

2.3

8. N - N '

10. S - S ' , plate 12

Same

!6

11. V - V ' , plate 12

Same

6

-

6

12. A-B, plate 2

Mansfield

23

-

23

2.8

--

33

1.8

(1929) 13. C - E , plate 2

Same

33

95

16.8

! 4. F- (;, plate 2

Same

33

33

1oo

9.8

15. tt-I, platc 2 16. A A' (cast)

Samc Rioux ct al.

18

18

80

6.6

15

15

2.7

57

6.5

!.3

(1975) 17. B B'

Same

20

3.3

! 3.3

18. A A'

('ressman

i3

!.8

14.8

19.5 -

11

68

8.2

100

8.3

-

86

4.7

5.5

82

9.6

-

63

5.1

and Gulbrandsen (1955) 19. B - B '

Same

19.5

20. C - C '

Same

I1

2 !. D - D '

Same

8

22. E - E '

Same

17.3

18.2

35.5

4.2

56

2.4

23. A - A '

Cressman, (1964)

36.4

1.7

38.1

-

97

8.7

8

Snowdrift Mtn. 24. B - B '

Same

31

1.2

32.2

2.9

78

8.3

25. C - C '

Same

19.5

-

19.5

-

86

4.7

26. D - D '

Same

22.5

0.6

23. I

1.1

71

7.6

27. E - E '

Same

26.2

0.9

27.1

-

68

7.2

28. F - F '

Same

26.8

-

26.8

-

60

6.3

29. A - A '

Cressman ( ! 964)

32.4

3

35.4

! 4.1

83

17.3

(Meade Peak)

Continued

154

J. G. Evans

TABLE 6-I Continued Cross-

Reference

section

% shortening

% shortening

% total

% extension

% cross-

Length of

by folding

by faulting

shortening

(faulting)

section

cross-

used

section used (km)

30. C - C ' 31. A - A '

Same Gulbrandsen

18.7 6.6

4.6 -

23.3

60

12.6

6.6

11.7

-

98

10.62

8.8

10.4

97

9.3

14.6

3.9

89

4.9

et al. (1956) 32. B - B '

Same

8.2

33. C - C '

Same

14.6

34. D - D '

Same

3.5

0.6

4.1

7.3

100

4.3

35. A - A '

Montgomery

8.5

-

8 . 5

-

100

4.7

0.6 -

and Cheney (1967) 36. B - B '

Same

9.6

9.6

-

100

10.7

37. C - C '

Same

12.8

12.8

-

100

10.7

38. D - D '

Same

16.2

16.2

-

96

9.9

39. E - E '

Same

21.3

21.3

-

97

! 0.1

principal interest in this unit. Strains are likely to be different at other stratigraphic levels owing to changes in magnitude and intensity of the strain resulting from differences in depth, temperature, proximity to bounding thrusts, history of deformation, and responses to strain of the rocks under the physical conditions at those levels. Here, the cumulative lengths of the upper contact of the Meade Peak Member are compared with the lengths of each segment of the cross-sections that show significant amounts of Meade Peak. Lengths of segments of cross-sections used initially ranged from 20 to 100% of published sections. Parts of cross-sections were ignored because of focus on the Phosphoria Formation and, therefore, only parts of cross-sections were used in which the Phosphoria could be reasonably projected above or below the erosion surface. In addition, interpretations of many structures were not well constrained in the field beyond the Phosphoria Formation with its diagnostic lithologies. Extrapolation and interpretation of fold profiles to depths below Mansfield's Meade thrust (his Bannock overthrust) is realistic because Dixon (1982) determined the thrust plate to be at least twice as thick as Mansfield's estimates. Dixon also showed that folds exposed at the surface extend down nearly to the Meade thrust in the eastern, thinner part of the plate. Some unknown factors that could be important in framing the context of the internal deformation of the Meade plate include the original eastward extent of the Meade thrust and original thickness of this missing part of the Meade plate. In addition, there is no clear way to separate deformation seen in most cross-sections listed in Table 6-I into clear stages. Allmendinger (1979, 198 I), however, showed that broad open folds in the Meade plate were truncated by the Putnam-Paris thrust. Some of the deformation in what is now the Meade plate, therefore, dates from or preceded emplacement of the Putnam-Paris thrust. Slip may have occurred on the Putnam-Paris thrust during eastward translation of


155

the Meade plate on the Meade or younger thrusts (Fig. 6-1). To complicate matters further, Mansfield showed some normal-slip arrows on faults that otherwise show shortening of the section. One interpretation of this apparent anomaly is that Cretaceous shortening was larger than Tertiary extension along these faults although not much greater. However, the reason Mansfield reached this interpretation is not clear. Detachment faults with this kind of displacement history are proposed for the Sevier orogenic belt in west-central Utah (Allmendinger et al., 1983). The effect of this extension is to reduce the apparent amount of shortening by faulting at least in the upper levels of the plate. Macroscopic extension by faulting in some cross-sections of the Meade plate is of the same order of magnitude as macroscopic shortening (Table 6-1). The most reliable estimates of shortening within and across the Meade plate are probably along the longest segments of the longest cross-sections. For purposes of this study that focuses on the northern part of the Meade plate, segments of cross-sections that are less than 50% of the original cross-sections are excluded as potentially unrepresentative of macroscopic shortening. Using this criterion, 20 cross-sections of Armstrong (1969), Allmendinger (1979), and Kellogg et al. (1989, 1999) are excluded. These short segments have a higher average shortening than the longer segments (29.7 vs. 18.8%), are considered atypical for estimating shortening in the Meade plate, and are not included in Table 6-I. However, some of these cross-sections may more accurately portray the amount of shortening in narrow domains adjacent to the floor and roof thrusts. Shortening and extension of 39 cross-sections meet the criterion of reliability. Within the Meade plate, shortening from folding varies from 3.5 to 36.4% with a median between 15 and 20% and a sub-maximum between 5 and 10%. The median and average (18.8%) are close. In general, estimates of orogen-normal shortening by folding are consistent where cross-sections from separate studies overlap or are near one another. Shortening by folding is 14-36% near the Meade thrust. In the northwestern and upper part of the Meade plate, from the Lower Valley quadrangle to Paradise Valley quadrangle (Fig. 6-2), orogennormal shortening is 18-33%. A north-northeast-trending cross-section in the Snowdrift Mountain quadrangle (Cressman, 1964) shows 6% shortening by folding parallel to the axis of the Snowdrift anticline (Snowdrift Mountain quadrangle; Figs 6-2 and 6-3). This cross-section contradicts the assumption that material was not moved parallel to the trend of the orogen. The amount of orogen-parallel shortening by folding is of the same order of magnitude as the estimated strike-parallel shortening of 9% mentioned above for the Meade thrust (Fig. 6-4, upper right). The amount of shortening related to reverse or within-plate thrust faulting is as much as 18.2%, assuming largely dip slip, but most sections portray shortening by faulting of less than 50, and many of these less than 2%. Shortening by faulting is absent in most of the sections (discussed later), but occurs in a north-trending zone that lies north of the large normal faults that strike north from the Bear Valley graben (Fig. 6-4). The southern part of this zone of faulting is truncated by the Meade thrust. Total surficial orogen-normal shortening (by folding and faulting) near the Meade thrust ranges from 17.3 to 38.1% in the Harrington Peak and Snowdrift Mountain quadrangles and between 18 and 33% north and west of Blackfoot Reservoir. Between these two areas, total

156

J. G. Evans

shortening varies from 4.1 to 35.5%; however, all the cross-sections with total shortening of 11% or less are in an east-west-trending middle zone in parts of the Johnson Creek, Dry Valley, Diamond Flat, and Stewart flat quadrangles (Figs 6-2 and 6-5). Location of the zone of shortening by faulting above the upper margin of the lower ramp in the Meade plate suggests that this faulting is related to the change in dip during emplacement when these rocks were refolded at the ramp-flat hinge as they approached the surface and responded to further stress by brittle failure rather than by more ductile processes. Ramp-related deformation may be important in the central part of the plate about 8 km horizontally from the Putnam-Paris thrust and as much as 14 km horizontally from the easternmost part of the Meade thrust (Fig. 6-5). Extension by faulting was found in 21 cross-sections. Fourteen of the cross-sections showed extension of less than 5%. Five of the cross-sections showed extension ranging from 7.3 to 19%. Twelve cross-sections that showed extension also showed shortening by faulting. Part of this association may be a result of creation of fault zones of the right orientation for extension (parallel to the lower ramp), or possibly portions of the plate that experienced early brittle compressive deformation were strain-softened by fracturing, and slip reversal had the lowest energy requirements of available deformational processes. Orogen-normal extension by normal faulting is 1.8-8% in the southwestern part of the study area, 1.1-14.1% in the Harrington Peak and Snowdrift Mountain quadrangles,

1 1 2 0.02 mm) with sphalerite and large (~0.1 mm) masses of microcrystals) N = 11 Average element total = 92.6% 2 Average: 34.2 Maximum: 34.9 % Detects: 100

0.026 0.149 64

720 1,260 100

< 130 150 45

6,700 7,520 100

48.8% 49.3% 100

NA -

650 1,250 91

4,460 5,350 100

82,300 90,600 100

o~

e5

~See footnotes, Table 10-III. 2See text for explanations of low totals.

tO

268

R.B. Perkins and A.L. Foster

pyrite in sample HS-565 appears to be the only Fe sulfide with a V concentration (0.15%) significantly greater than that measured in the bulk-rock (0.04%). Cu-V sulfides, typically in association with sphalerite, were observed in several samples from the lower Lakeridge section. Analyses of subhedral Cu-V sulfide crystals (~10 Ixm across) in LR-M21 indicate average S, Cu, and V contents of 34.4, 48.8, and 8.2%, respectively. The S average closely matches that of stoichiometrically ideal sulvanite (Cu3VS4; 34.7% S) while the Cu and V averages are lower than that of ideal sulvanite (51.6% Cu and 13.8% V). However, sulvanite forms a series with arsenosulvanite (Cu3(As,V)S4).Although As was not measured, such a phase containing 8.2% V (Xv = 0.61) would contain 7.7% As, very close to the average residual of 7.4%. The difference between the measured and ideal S content (< 0.6%) is within the likely analytical error. The deficiency in Cu (< 1.5%) could be due to substitution of other transition metals, including Ag, which was not measured. The chemistry of this phase thus closely matches that of an As-bearing sulvanite, that is enriched in both Cr and Se (average of 6700 and 4500 ppm, respectively) and, to a lesser degree, in Ni and Zn (< 1000 ppm).

X-ray absorption spectroscopy

X-ray absorption near edge spectra (XANES) are useful in determining bulk oxidation state because the position of the absorption edge (i.e. primary inflection point) of Se K-edge XANES spectra shifts as a function of Se valence (Pickering et al., 1995). In this study, XANES spectra of reduced (sulfide associated or native) Se model materials had measured absorption-edge energies between 12,656.5 and 12,658.5 eV, spectra of Se(IV) model materials had edge energies between 12,662.0-12,663.0 eV, and Se(VI) model compounds had edge energies between 12,666.0 and 12,667.0 eV (Fig. 10-4). The measured absorption-edge position of Lakeridge sample spectra averaged 12,658.8 ___0.08 eV, consistent with Se in a reduced form. In contrast, the edge positions of Enoch Valley spectra averaged 12,662 ___0.10 eV, consistent with those of Se(IV) reference materials. Selenium K-edge XANES spectra are also sensitive to chemical speciation. Such spectra of model materials have previously been used as "fingerprints" to identify and quantify bulk Se species in soils, fungi, and aqueous solutions by linear, least-squares fitting (Pickering et al., 1995). In this study, least-squares fits indicate that the XANES spectral lineshape of upper Lakeridge samples (LR) M37a, M36-40, and M41a are well matched by the XANES spectrum of the same seleniferous pyrite/marcasite material used in REF03 (fits not shown, but compare spectra in Fig. 10-4A). Least-squares fits to XANES spectra of Lower Lakeridge samples (LR) M14 and M16-18 indicate that seleniferous pyrite and Cu-sulfides or Cu-selenides are the primary hosts for Se, although it should be noted that the fits to these samples are poorer than the fits to the upper Lakeridge samples. XANES spectra of Enoch Valley samples EV-76 and EV-195 are best fitted by the XANES spectrum of Se(IV) adsorbed on synthetic vernadite (MnO2), whereas the spectrum of EV-185 is best fitted by the spectrum of Se(IV) adsorbed on synthetic manganite (MnOOH; fits not shown, but compare spectra in Fig. 10-4B). This result is somewhat

Se(0)-red, amorphous Se(0) black, amorphous

"--'-~..~

Se(IV)-MnO2 (vernadite)

Seleniferous pyrite/marcasite

Se(IV)-MnO OH (manganite) ~....

,,_._...._ Se(IV)-Fe oxyhydroxide

~

Se(IV)-kaolinite

LR-M41A LR-M37-40 LR-M37A

1

"""-"-

r~

EV-P195

Selenocysteine EV-P186 LR-M14 c~ -.-------- EV-P76

LR-M16-18 Cu(I)Se

/ i , t l l l l l l a , , l l , l l l l l l l l

12.65 12.66 12.67 12.68 12.69 12.70 Enerav (KeV~

~.,.~,~.~._Aqueous Se(Vl) l

I l

II

11

II

II

ll

II

II

,

I

II

II

I.

12.65 12.66 12.67 12.68 12.69 12.70 Enerav (KEY)

Fig. 10-4. Comparison of X-ray absorption spectra from selected samples and relevant reference materials; note the higher (0.3-0.4 KeV) K-edge energies for Se(IV) reference materials and Enoch Valley samples in right-hand plot.

270

R.B. Perla'ns and A.L. Foster

problematic as both bulk chemical and extraction results indicate these samples are not particularly enriched in Mn. Furthermore, these samples contain ample Fe oxyhydroxides, which have been shown to scavenge Se(IV) more effectively than MnO2 (Balistrieri and Chao, 1990). For this reason, we believe that the results of the least-squares fingerprinting analysis may be in error in this case. One possible reason for the error could be that the model XANES spectrum used to represent Se(IV) sorbed to amorphous Fe oxyhydroxides is not representative. Evidence for this argument comes from the XANES spectra of Se(IV) sorbed to the Mn oxyhydroxides in Fig. 10-4B; the Mn oxyhydroxides are structurally and compositionally distinct and Se(IV) adopts different sorption geometries on the two substrates, producing distinctly different XANES spectra. An analogous situation might hold for the Se(IV)-Fe oxyhydroxide system, but further work is needed to determine if this is true. Regardless of this result, XANES analysis and extended X-ray absorption fine structure (EXAFS) analysis (not discussed here) clearly indicate that Se(IV) in the Enoch Valley samples is associated with metal oxyhydroxides.

S e q u e n t i a l extractions Reference materials

Although recoveries from reference samples provide some measure of the effectiveness of the technique (Tables 10-Va and 10-Vb), they may not accurately reflect recoveries from natural samples in which other secondary reactions (sorption and precipitation) may occur. For sequential-extraction Scheme A, the total recovered Se for each material was within acceptable weighing and analytical measurement errors of the total expected Se (< 20% difference). However, full recovery from the specific target extract was not achieved in three of the four reference materials. Extraction of the NazSeO3-spiked material (REF-01) resulted in measurable Se concentrations in all five extracts although 71% was recovered in the initial target extraction ("P-buffer") and 94% was recovered in the first two extractions (P-buffer; K2S2Os). The "bleed-over" may have been due, in part, to inadequate rinsing of the first extract. The complete lack of recovery of Se in the target extraction step for the Scheme B reference material suggests either analytical error or that precipitation or sorption of selenite may occur despite acidification and refrigeration of extracts. This process may be strongly time dependent as the time between extraction and analyses of Scheme B reference samples (~ 7 weeks) was considerably longer than for the Scheme A reference samples (< 2 weeks). The percentage of elemental Se recovered from REF-02 during the target (Na2SO3) extraction was 74 and 94%, respectively, for Schemes A and B. The recovery of 10.3% of the total Se in REF-02 during step 2 of Scheme A suggests greater oxidation of elemental Se by the K2S208 extract than was measured by Martens and Suarez (< 1.6%; 1997b). Extraction of elemental Se as a second step, as in Scheme B, is therefore suggested for future studies. In both Schemes A and B, significant amounts of the measured Se (15.4 and 7.6%, respectively) were recovered subsequent to the target step. This may indicate remobilization or could result from other forms of Se in the reagent; the manufacturer

TABLE 10-V

t~

Selenium concentrations (mg kg-1 of solid and % of total) in various fractions from quality assurance reference materials using (a) Scheme "A" sequential partial-extraction method and (b) Scheme "B" sequential partial-extraction method

Reference 2

Scheme A Fractions I

Total Selenium

1

2

3

4

5

Fraction sum

Calculated

%Difference 3

(a) BLK-01-A

< 0.41

< 0.40

< 0.40

< 0.40

< 0.41

< 2

0

0

REF-01-A Na2SeO3 REF-02-A E1 Se REF-03-A

63 _ 3 (71.0%) < 0.41 < 0.41

20 ___2 (23.0%) 37.1 ___0.9 (10.3%) < 0.41

0.8 -4- 0.05 (0.9%) 268 +__2 (74.3%) < 0.41

0.6 (0.7%) 4.9 +_ 0.4 (1.4%) < 0.41

3.8 +__0.1 (4.4%) 51 ___4 (14.0%) 2.7 +__0.2

88 +_ 5

Se-pyrite REF-05-A CuSe

1.4 + 1.3 (0.23%)

28 + 12 (5%)

110 + 30 (19%)

_

0.7 + 0.1 (0.12%)

361 +_ 7 2.7 -+- 0.2

(100%)

440 + 30 (76%)

580 + 80

Scheme B Fractions ~

(b) BLK-01-B

REF-01-B Na2SeO3 REF-02-B

670 14 (w/in measurement error) Total Selenium

1 (same as #1 in Scheme A)


3

Fraction sum

< 0.40

< 0.40

5.3 _+ 0.0

5.3 _+ 0.4

< 0.41

15.3 +__0.09 (17.2%) 340 4- 18

11.7 +__0.05 (13.4%) 27 ___3

27 -Z-_0.1 (30.5%) 367 +__21

< 0.40

100 12 (w/in measurement error) 440 18 (w/in weighing error) Unknown -

Calculated

t~ t~ t~ t~

% Difference 3

(no measurable Se in scheme A) 100 73 420

13 Ix.)

Continued

..

tO tO

TABLE 10-V Continued Reference 2

E1 Se REF-05-B fuSe

Scheme B Fractions 4

Total Selenium



3

Fraction sum

< 0.41

(94%) 29 __+4 (5.0%)

(7.6%) 297 ___11 (51%)

(102%) 326 ___11 (56%)

Calculated

% Difference 3

(w/in weighing error) 670 51

1Fraction 1, "Soluble + Exchangeable"; 2, "Organic"; 3, "Elemental"; 4, "Oxide + Carbonates + Apatite + Acid-volatile sulfides"; 5, "Crystalline sulfides". Errors are standard deviations based on analyses of duplicate samples; no errors listed if no measurable difference in duplicates. 2BLK-01" Blank consisting of 4.00 g iron-poor silica sand + 0.50 g activated charcoal; REF-01" Blank + 0.1 ml of 0.057 M NaSeO3 solution; REF-02: Blank + ~2 mg elemental (red) Se (Pfaltz & Bauer); REF-03" Blank + ~7 mg Se-rich marcasite (unknown Se concentration or purity); REF-05: Blank + ~5 mg Cu (II) selenide (Alfa-Aesar, 99.5%). 3percent difference = Calculated (expected) Total - Fraction Sum/Calculated Total. 4Fraction 1 -"Soluble + Exchangeable", same method as #1 in scheme A; 2 -"Elemental", same method as #3 in scheme A; 3 -"Organic", alternate method; errors are standard deviations based on analyses of duplicate samples; no errors listed if no measurable difference in duplicates; % of totals based on totals as measured in "full" extraction scheme A; organic (3rd) fraction concentrations in reference materials corrected for Se detected in blank.

b~ r~

Mineral affinities and distribution of selenium and other trace elements

273

(Pfaltz and Bauer) did not certify purity. Amorphous red Se prepared by reduction of NaSeO3 by ascorbic acid (only one of many methods for the preparation of this material) can contain small amounts of Se(IV), as indicated by a positive 1-2 eV shift in absorption edge position of this material relative to monoclinic or hexagonal forms of native Se (Fig 4A). Se(IV) present in red, amorphous Se(0) may exist as an adsorbed species or it may be occluded in the Se(0) matrix. Our previous work indicates that repeated washings with purified water do not remove it. All measurable Se in REF-03 was obtained from the final extract (~16 M HNO3, 90~ as expected for Se in pyrite. Recovery efficiency for REF-03 could not be calculated as the actual Se concentration and overall sample homogeneity of the pyrite/marcasite is unknown. Given the low total recovery (2.7 ppm), significant amounts of Se may have been solubilized in previous steps but still not detected. However, a prior study by Shannon and White (1991) found that 92% of the Fe added as FeS2 was recovered in their sulfide-targeted extraction, suggesting that the measurable Se in our extracts reflects the majority of the Se present in the reference material. The measured Se recoveries from REF-05 (CuSe) demonstrate potential difficulties in targeting monoselenides or monosulfides. Significant amounts of Se were extracted in both schemes during steps designed to target only elemental or organic-bound Se. Extraction with NaOC1 in Scheme B resulted in the liberation of nearly half (46%) the total recovered Se. Shannon and White (1991) also found that monosulfides (up to 25% of spiked FeS) could be extracted prematurely using MgCI2 and NaOAc extractants. In general, analyses of the reference materials reveal that the sequential-extraction methods used result in less than 100% recovery of target phases and may dissolve some portion of non-target phases. Nonetheless, Scheme A appears to result in reasonable total Se recoveries (> 80%) and specificity (71-100% of recoverable Se liberated in target extraction) and the results of the sample analyses should be useful for determining the overall significance of specific phases in hosting trace elements and in providing estimates of trace-element distributions. Samples

As with the reference materials, there are some discrepancies between Schemes A and B with respect to the amount of Se liberated in the initial ("P-buffer") extraction (Tables 10-Via and b). However, in neither scheme does the percentage of total recoverable Se extracted during the initial step exceed 5% and only in HS-565-B and LR-M 16-18-B does the percentage of total recoverable Se liberated in the first step exceed 2%. Precipitation or sorption of Se from the extract is unlikely to account for the low totals obtained from the P-buffer extract as many of the Scheme A samples were submitted and analyzed along with the reference materials for which 71% of the spiked selenite was recovered. Elemental Se appears to be a minor phase by either scheme, accounting for less than 5% of the total recoverable Se in all but one of the Scheme A samples (EV-P 186, 8%). Two Scheme B samples, EV-P186 and LR-M36-40, have average elemental Se contents of 11 and 16%, respectively. However, LR-M36-40 also has the greatest duplicate variability so that the percent of total Se occurring as elemental Se is uncertain. No elemental Se was

tO --..I 4~

TABLE 10-VI(a) Selenium concentrations (mg kg-1 of solid and % of total) in various fractions of rock samples

Scheme A Fractions I Sample 1

EV-P60 EV-P76 EV-P186 HS-521-77 HS-565-77 HS-218-74 LR-M14-15 LR-M16-18 LR-M36-40 LR-M51

Total Selenium

1

2

3

4

5

0.50 (0.2%) 0.4 _+ 0.04 (0.5%) 0.19 _+ 0.26 (0 - 1.0%) 2.7 _+ 0.09 (2%) < 0.40

1.0 (0.4%) 6.1 _+ 0.05 (7%) 3.9 _+ 0.4

0.00 (0.0%) < 0.40 3.2 _+ 0.2

30 _+ 5 (11.5%) 20 _+ 14 (22%) 14.0 _+ 0.7

229 _+ 4 (88%) 61 _+ 1 (71%) 17.6 _+ 0.6

(10%)

(8%)

(36%)

(46%)

11.3 (8.2%) 1.50

4.56 (3.3%) < 0.40

34.5 _+ 0.2 (25%) 5.3

86.1 _+ 0.1 (63%) 4.0 _+ 0.08

-

(14%)

-

(49%)

(37%)

1.98 (2%) 4.1 -+ 0.04 (2%) 0.6 (0.2%) 0.5 (0.8%) 0.25 _+ 0.35

11.3 -+ 0.4 (11%o) 12.3 -+ 0.1 (6%) 21.7 _+ 0.8 (7%) 2.76 (4%) 5 _+ 1

2.6 _+ 0.3 (2.6%) < 0.40 13.6 _+ 0.2 (4%) 2.0 _+ 1.9 (3%) 2.8 -+ 0.04

18 -+ 1 (18%) 42.9 _+ 0.7 (21%) 62 _+ 6 (20 _+ 2%) 5.60 (9%) 5.3 _+ 0.07

67.5 _+ 0.4 (67%) 142 _+ 1 (71%) 218 _+ 8 (69%) 52.6 _+ 0.4 (83%) 35 -+ 5

(10%)

(4%)

(11%)

(75%)

(0.0-1.2~

Fraction Sum

261 ___9

Analyzed in Bulk Rock

% Difference

287

9.1

87 _+ 14

124

30

39___2

73

47

137 ___4

120

-14

10.8 ___0.1

11.7"

7.7

101 _+2

111"

9.0

202 _+ 2

209

3.3

316 _+ 10

287

-10

63 _+ 2

55

- 15

47 _+ 6

32.1

-46

t~ ~t

TABLE 10-VI(b) t~

Comparison of selenium concentrations (mg kg-1 of solid) in various rock fractions determined by two different sequential extraction methods on select rock samples t.,~. t,,~.

Fractions 3 t~

EV-P186 Scheme A

(1) Soluble/ Sorbed

Scheme A (2) Organic

0.19 (0.50%) < 0.40

3.9 (10%)

Scheme B HS-521-77 Scheme A

2.7 (2%) < 0.40

Scheme B LR-M14-15 Scheme A Scheme B

--o-

Interval 59

Interval 59, first altered rock transect .--e-- Interval 59, second altered rock transect

>

80-

.0

0

Interval 75

--o-

0 OrJ

:

60-

t~ L_

40E oI = 20O-

,

,

,

10

|

,

|

I||

100

i l|,,l

!

1000

10000

Se (ppm) 120

Interval 75

m~oo

"-

"6

80>

0

::===-o

--o-

Interval 59

--o--

Interval 59, first altered rock transect Interval 59, second altered rock transect

=

6O

0t}

40

E c 20-

o~

|

0

I

20

=

40

60

U (ppm)

Fig. 12-7. Variations of Se (top) and U (bottom) concentrations with stratigraphic position for the detailed sampling in intervals 59 and 75 of Section Z (concentrations at 2 ppm are < 2 ppm).

sections to the pre-mined ground surface. Zone average concentrations of elements for these three sections (Fig. 12-8) reveal the importance of their removal through alteration and the variability of concentrations from zone to zone. Elements enriched at the base of Section J include T1, Mo, and Zn (Fig. 12-8). The weighted average of 22 ppm for T1 is the highest of any section interval. Also, carbonate, organic C, and total S are greatly enriched in Section J compared to the other two sections. Some elements show the opposite behavior and have higher concentrations in Section A. For example, A1, Fe, Cr, and Zr generally exhibit considerable enrichment in Section A, and Hg, Sb, Ti, Ba, and silica show lesser enrichments. Phosphate and elements associated with it are also enriched in Section A,

342

JR. Herring and R.I. Grauch

Chert p

I

Up. Waste

I

I

I

Up. Ore !1

r Mid. Waste

L. Ore t t

L. Waste I I

\

\

/

/

Idll

Grandeur 0 5 10 15 Carbonate C (%)

/

/

/

5 10 0 10 20 30 0 50 100 0 100 200 Org. C (%) Ag (ppm) As (ppm) Cd (ppm)

0

/

100 200 Me (ppm)

9 SectionB

Chert []

\

SectionJ 9

SectionA

Up. Waste ~ =

II

Up. Ore

tI

ib

,\'

Vlid. Waste

I~

L. Ore

L. Waste

/

l

Grandeur / 0

500 1000 Ni (ppm)

0

200 400 Se (ppm)

0

/ 100 200 U (ppm)

0

,/ 1000 2000 0 2500 5000 V (ppm) Zn (ppm)

Fig. 12-8. Comparison of weighted average concentrations of trace elements and carbon for Meade Peak zones based on Section A, B, and J channel samples.

Lithogeochemistry of the Meade Peak Phosphatic Shale Member

343

although U, curiously, is not. This enrichment in the weathered Section A reflects the removal of carbonate and organic C and consequent relative enrichment of phosphorite and detrital components. Other trace elements also exhibit significant concentration changes with alteration. For example, the enrichment of V at the top of the middle-waste-rock zone and just into the upper-ore zone, the "Vanadiferous Zone" discussed by McKelvey et al. (1986), is clearly evident in Section J. Cadmium, Mo, Ni, and Zn also are enriched in this zone. A second, apparently thicker, vanadiferous zone straddles the top of the lower-waste zone and extends into the lower-ore zone. To better compare element concentrations in zones of different thicknesses, concentrations were recalculated as average concentrations, weighted by interval length of each zone of Sections A, B, and J. These weighted average concentrations for the lower-waste rock, lower ore, middle-waste-rock, upper ore, and upper-waste-rock zones are shown on Fig. 12-8. This approach clearly shows a lower vanadiferous zone and a suppressed signature of the upper, previously defined, Vanadiferous Zone.

WEATHERING AND OTHER ALTERATION Alteration of Meade Peak rocks from water-rock interaction principally by surficial weathering profoundly changed their composition. The major effects were partial oxidation of organic matter, partial to complete leaching of carbonate, and a consequent enrichment of the phosphorite and detrital components. Minor component changes involved partial oxidation of pyrite and minor solution of some phosphorite. With oxidation of pyrite, limonite and sulfuric acid were produced. The acid reacted with phosphorite producing gypsum and phosphorus in solution. In turn, this may have resulted in intergranular phosphatic cement. In addition, F in the CFA would have been released and likely produced the fluorite found in these rocks (Grauch et al., Chapter 8). Alteration also changes rock color from black to dark or pale brown, which is predominantly due to the presence of carbonaceous matter. Variably colored coatings form on joint surfaces and the rocks change from hard to soft. Initially, the extent of alteration of the Meade Peak seems to be a function of depth below ground surface. However, alteration varies over regional to local scales and in places is extreme throughout much of a single mine, including the deeper strata mined. Besides changing composition, solution alteration may significantly reduce the thickness of the Meade Peak principally through loss of carbonate and organic carbon. For example, at several locations on the mine wall at Section G, indurated, silty carbonate layers about 1 m thick were reduced to a layer of claystone about 20 cm thick where fractures allowed water to dissolve the carbonate. Pure carbonate can be completely lost by solution alteration, whereas silty carbonate reduces to the thickness of the consolidated silt after removal of the carbonate. Loss of the relatively less-dense organic matter greatly reduces the thickness of the residual shale in an increasing amount proportional to the original organic-carbon content. For purpose of visualization, assume that the mass of organic matter is 1.4 times the

344


mass of organic carbon (Isaacs, 1980) and that it has a density of 1.9 g c m - 3 (the measured value for the carbon seam of Section A), and that the density of typical Meade Peak shale without carbonaceous matter is 2.6 g cm -3 (Gulbrandsen and Krier, 1980). The oxidation and removal of 1 or 30 wt.% organic C from a vertical section would reduce the thickness of a column of rock containing those amounts of carbonaceous material to 98 or 50% of the original thickness, respectively. In this J core section, the Meade Peak contains 6.7% organic C, equivalent to 12% of the section thickness, and 2.6% carbonate C, equivalent to 19% of the section thickness (assuming stoichiometric dolomite). In Section J, complete loss of organic C and carbonate, assuming the carbonate converts to 20% of its original thickness as silty clay, would result in a thickness reduction of 6.8 and 10.9 m, respectively. Therefore, complete solution alteration of these two lithic components of Section J would reduce the thickness of the Meade Peak from 57.3 to 39.5 m, 69% of original thickness. This hypothetically reduced thickness is near the lower range of thickness for the Meade Peak in southeast Idaho, 43-77 m (McKelvey et al., 1959). In our measured sections we note that the least-altered Section J is thicker than all others, except Section C (Table 12-I). This certainly suggests that thickness reduction in highly altered sections is likely. The alteration of the Meade Peak is predominantly an interaction with water, even though the rocks have relatively low porosity and permeability. The porosity in the unweathered mudstone is around 4% (Gulbrandsen and Krier, 1980) and the rocks are relatively impermeable compared to, for example, the overlying weathered Dinwoody siltstone. However, it is possible for water to move along bedding-plane surfaces and along the abundant fracture and fault surfaces. Movement of water along bedding planes, fractures, or faults can be observed directly in the pit walls of the phosphate mines. Even in the least-weathered Section J, there are localized effects of substantial solution alteration. For example, at more than 150 m below the ground surface in this section, the uppermost few tens of centimeters of Grandeur dolostone directly below the fish-scale bed are altered to brown claystone from the penetration of water along the unconformity surface at the top of the Grandeur. In addition, the Meade Peak in southeast Idaho experienced a regional alteration imprint through hydrocarbon generation (oil window) (Claypool et al., 1978), and possibly hydrothermal fluids. Based on field criteria for degree of alteration, highly altered samples have carbonate C o f -< 1% and organic C of 99.99% confidence level.

Trace-element associations as a function o f alteration Pearson correlation coefficients (Tables 12-III-12-V) and factor analysis were used to examine element relations. Two sample sets were used: (a) all analyzed samples of the Meade Peak and (b) the same set, but separated into degrees of alteration- highly altered, intermediate-altered, and least-altered. Carbonate C shows a strong positive correlation only with Mg, indicating the dolomite phase, but also has weaker positive correlations with Ca and Mn. Organic C has strong positive correlations with total S and Se and weaker positive correlations with Cr, Cu, Hg, Mo, and Ni, suggesting at least partial association with organic phases for some proportion of these elements. The detrital component is interpreted to consist of A1, Fe, K, Si, Ti, Ba, Th, As, and Zr. Arsenic correlates strongly only with Fe and has weaker correlations with all major elements in the detrital component for even highly weathered samples. P205 has strong positive correlations with Sr and U and weaker positive correlations with Cd, Cr, Cu, Hg, and V. Silver strongly correlates with Cr, Cu, Hg, and Sb and has weaker correlations with Ba, Sr, U, and V. Cadmium has significant correlations with TI, U, and V. Copper has significant correlations with Ag, Cr, and Hg, and weaker correlations with Sb and U. The host phase of Hg is unknown but possibly is an organic phase as it is for these other biologically active elements. Molybdenum has no strong correlations, but weakly correlates with Ni, which, in turn, strongly correlates with Zn. All three elements may be associated with organic matter; their correlations with organic C are weak to moderate and range from 0.3 to 0.5 for the set of all samples. Selenium only correlates strongly with organic C and total S, and therefore, likely occurs in part in organic compounds and sulfides. Its association with sulfur also could be due to coexistance with sulfur in organic compounds. Thallium has strong correlations with Cd and V and a negative correlation with organic C. Vanadium has a strong correlation with Cd and TI and a weaker correlation with P, suggesting that it is partly associated with CFA. For the least altered set of rocks (Table 12-IV), most correlations are similar to the set of all rocks. Organic C increases its number of significant correlations, adding Cr, Cu, and Hg to the previous set. Silver has a strong correlation with V. Copper strengthens its correlations with Ni and Sb, Hg with Sb, and Mo with Ni. Many of the significant trace-element correlations noted for the least altered Meade Peak rocks do not hold for the most-altered rocks. Alteration removes many elements from the rocks, particularly the organic-affiliated trace elements. Only Cr retains a significant correlation with organic carbon. Alteration has only a minor effect on the detrital component. Arsenic must be partially removed from that phase, but retains a significant correlation with an Fe-rich phase. Carbonate C in the altered rocks has a strong correlation only with Ca, which may indicate the presence of secondary calcite. Carbonate C also retains a

TABLE 12-III Correlation coefficients for all channel samples from the Meade Peak

Org. C Total S AI Ca Fe K Mg Na P Si Ti Ag As Ba Cd Co Cr Cu Hg Mn Mo Ni Pb Sb Se Sr Th T1 U V Zn Zr

Carb. C

Org. C

Total S

A!

Ca

Fe

K

Mg

Na

P

Si

Ti

Ag

As

Ba

Cd

Co

Cr

Cu

0.01 0.15 -0.40 0.53 -0.38 -0.30 0.75 -0.04 -0.13 -0.46 -0.45 -0.25 -0.05 -0.59 -0.13 0.02 -0.33 -0.31 -0.44 0.34 -0.04 -0.09 -0.24 -0.22 0.00 0.12 -0.56 -0.34 -0.22 -0.22 -0.07 -0.52

0.83 0.20 0.02 0.20 0.25 0.00 0.13 0.18 0.05 0.09 0.34 0.26 0.13 -0.07 0.01 0.62 0.53 0.52 -0.24 0.51 0.51 0.19 0.23 0.75 0.24 0.02 -0.08 0.10 0.02 0.28 0.03

0.07 0.06 0.10 0.13 0.07 0.24 0.12 -0.03 -0.04 0.07 0.22 0.02 -0.21 0.20 0.37 0.29 0.31 -0.08 0.47 0.39 0.21 0.04 0.67 0.20 -0.06 -0.14 0.05 -0.14 0.20 -0.02

-0.71 0.92 0.96 0.02 0.46 -0.40 0.89 0.96 0.07 0.53 0.73 -0.27 0.39 0.34 0.23 0.42 0.10 0.26 0.46 0.06 0.37 0.30 -0.41 0.78 0.04 -0.43 -0.13 0.14 0.80

-0.66 -0.63 0.05 -0.35 0.66 -0.79 -0.69 0.28 -0.33 -0.56 0.33 -0.38 0.04 0.13 -0.05 -0.17 -0.13 -0.29 0.02 -0.07 -0.16 0.73 -0.69 -0.05 0.55 0.19 -0.02 -0.67

0.87 -0.03 0.47 -0.34 0.83 0.89 0.08 0.67 0.73 -0.29 0.40 0.35 0.21 0.43 0.16 0.35 0.48 0.11 0.39 0.31 -0.32 0.77 0.04 -0.38 -0.11 0.16 0.78

0.08 0.47 -0.36 0.82 0.91 0.13 0.56 0.66 -0.22 0.38 0.35 0.29 0.44 0.08 0.32 0.50 0.10 0.45 0.35 -0.36 0.71 0.06 -0.39 -0.06 0.20 0.76

0.01 -0.54 -0.06 -0.06 -0.35 0.08 -0.37 -0.29 0.12 -0.33 -0.34 -0.41 0.40 0.02 0.03 -0.32 -0.18 0.09 -0.35 -0.21 -0.33 -0.55 -0.30 -0.11 -0.19

-0.23 0.45 0.52 -0. !6 0.44 0.35 -0.31 0.39 -0.07 -0.10 0.08 0.20 0.18 0.22 0.02 0.04 0.26 -0.18 0.42 -0.08 -0.36 -0.24 0.04 0.54

-0.45 -0.37 0.63 -0.16 -0.03 0.52 -0.32 0.44 0.51 0.42 -0.42 0.08 -0.04 0.33 0.21 -0.02 0.78 -0.28 0.32 0.89 0.44 0.22 -0.25

0.88 -0.09 0.40 0.74 -0.32 0.39 0.15 0.04 0.21 0.12 0.16 0.33 0.02 0.17 0.18 -0.52 0.76 0.03 -0.46 -0.22 0.02 0.77

0.07 0.50 0.73 -0.23 0.35 0.29 0.19 0.38 0.07 0.18 0.35 0.05 0.34 0.21 -0.41 0.78 0.07 -0.39 -0.09 0.07 0.86

0.21 0.22 0.63 -0.23 0.68 0.78 0.69 -0.39 0.32 0.31 0.35 0.66 0.16 0.48 0.03 0.44 0.61 0.63 0.42 0.09

0.44 -0.10 0.41 0.27 0.21 0.33 0.31 0.57 0.57 0.11 0.52 0.38 -0.08 0.40 0.12 -0.22 0.08 0.37 0.49

-0.02 0.30 0.42 0.31 0.47 0.04 0.26 0.41 0.28 0.36 0.17 -0.15 0.70 0.31 -0.04 0.06 0.20 0.72

-0.21 0.19 0.42 0.20 -0.23 0.14 0.11 0.41 0.40 -0.14 0.26 -0.16 0.66 0.67 0.80 0.49 -0.08

-0.15 -0.17 -0.03 0.57 0.23 0.46 0.12 0.02 0.05 -0.29 0.33 0.05 -0.34 -0.19 0.33 0.37

0.89 0.84 -0.38 0.39 0.42 0.29 0.55 0.41 0.41 0.21 0.12 0.41 0.29 0.27 0.19

0.85 -0.39 0.41 0.43 0.41 0.65 0.32 0.44 0.15 0.31 0.53 0.48 0.38 0.14

Hg Mn Mo Ni Pb Sb Se Sr Th TI U V Zn Zr

-0.36 0.39 0.43 0.3 i 0.62 0.38 0.38 0.35 0.21 0.37 0.32 0.3 ! 0.33

Mn

0.10 0.20 -0.09 -0.12 -0.09 -0.32 0.07 -0.07 -0.43 -0.22 0.10 0.08

Mo

Ni

0.62 0.27 0.49 0.52 0.05 0.14 0.23 0.09 0.24 0.54 0.24

0.30 0.51 0.45 -0.08 0.32 0.25 -0.04 0.17 0.79 0.32

Pb

Sb

0.35 0.14 0.09 0.18 0.55 0.49 0.50 0.44 0.19

0.25 O. 18 0.26 0.43 0.23 0.59 0.53 0.29

Se

Sr

Th

0.05 0.17 - 0.04 -0.08 0.01 0.23 0.19

-0.38 0.01 0.62 0.18 0.06 -0.40

0.16 -0.26 -0.07 0.11 0.75

Notes: Based on log concentrations. Values o f t - > 0.65 or 99.5% confidence.

T1

0.49 0.67 0.51 0.25

U

V

0.64 0.28 -0.22

0.51 0.07

Zn

0.16

TABLE 12-IV Correlation coefficients for least altered samples from the Meade Peak Carb. C Organic C Total S AI Ca Fe K Mg Na P Si Ti Ag As Ba Cd Co Cr Cu Hg Mn Mo Ni Pb Sb Se Sr Th TI U V Zn Zr

-0.21 - 0. i 7 -0.33 0.49 -0.33 -0.24 0.79 -0.23 -0.24 -0.43 -0.38 -0.20 -0.04 -0.56 -0.11 -0.13 -0.32 -0.28 -0.42 0.46 -0.14 -0.21 -0.40 -0.07 -0.13 0.08 -0.52 -0.34 -0.32 -0.19 - 0.20 -0.50

Org. C

0.78 0.39 - 0. i 0 0.41 0.42 -0.18 0.12 0.26 0.22 0.26 0.52 0.39 0.36 0.03 0.04 0.77 0.73 0.73 -0.26 0.60 0.56 0.25 0.54 0.74 0.31 0.19 0.04 0. ! 8 0.16 0.35 0.22

Total S

0.36 - 0.18 0.41 0.39 -0.12 0.27 0.14 0.22 0.23 0.21 0.42 0.33 -0.18 0.33 0.52 0.47 0.56 -0.05 0.55 0.44 0.26 0.33 0.66 0.22 0.21 -0.01 0.06 -0.08 0.23 0.26

AI

- 0.70 0.92 0.96 0.00 0.64 -0.34 0.90 0.95 0.09 0.53 0.72 -0.29 0.49 0.39 0.26 0.45 0.10 0.34 0.49 0.06 0.37 0.38 -0.40 0.77 -0.06 -0.40 -0.18 0. ! 2 0.80

Ca

-0.65 -0.62 0.05 -0.46 0.59 -0.79 -0.68 0.26 -0.23 -0.53 0.34 -0.44 0.01 0.13 -0.07 -0.11 -0.14 -0.23 -0.03 0.00 -0.13 0.76 -0.68 0.02 0.49 0.26 0.05 -0.69

Fe

0.86 -0.06 0.64 -0.26 0.84 0.88 0.10 0.66 0.73 -0.32 0.49 0.42 0.25 0.46 0.15 0.43 0.50 0.11 0.38 0.41 -0.29 0.74 -0.05 -0.34 -0.17 0.13 0.78

K

0.07 0.65 -0.30 0.84 0.91 0.15 0.55 0.66 -0.23 0.48 0.39 0.31 0.46 0.09 0.38 0.51 0.07 0.46 0.40 -0.34 0.70 -0.03 -0.38 -0.11 0.16 0.75

Mg

-0.13 -0.57 -0.08 -0.08 -0.34 -0.01 -0.43 -0.27 -0.02 -0.37 -0.37 -0.45 0.48 -0.10 -0.15 -0.50 -0.12 -0.07 -0.36 -0.24 -0.38 -0.60 -0.31 - 0.26 -0.22

Na

-0.14 0.60 0.71 0.02 0.52 0.56 -0.25 0.45 0.12 0.07 0.29 0.14 0.20 0.21 0.11 0.25 0.20 -0.18 0.60 0.02 -0.28 -0.16 0.01 0.71

P

-0.37 -0.32 0.64 0.02 0.10 0.51 -0.24 0.46 0.54 0.46 -0.45 0.19 0.16 0.43 0.28 0.15 0.81 -0.20 0.41 0.89 0.51 0.39 -0.18

Si

0.90 -0.06 0.38 0.72 -0.30 0.46 0.22 0.07 0.27 0.09 0.22 0.36 0.04 0.17 0.23 -0.52 0.75 -0.04 -0.40 -0.23 0.03 0.81

Ti

0.07 0.50 0.71 -0.25 0.46 0.34 0.20 0.40 0.06 0.25 0.37 0.04 0.33 0.28 -0.41 0.77 -0.02 -0.37 -0.13 0.05 0.85

Ag

0.36 0.26 0.62 -0.12 0.70 0.81 0.70 -0.38 0.46 0.52 0.40 0.72 0.37 0.51 0.01 0.45 0.58 0.65 0.60 0.10

As

0.49 -0.01 0.40 0.41 0.34 0.45 0.23 0.59 0.54 0.13 0.61 0.40 0.05 0.33 0.14 -0.09 0.10 0.36 0.49

Ba

0.00 0.44 0.49 0.37 0.54 0.05 0.37 0.58 0.39 0.40 0.31 -0.11 0.69 0.29 0.05 0.07 0.34 0.74

Cd

-0.15 0.17 0.41 0.18 -0.29 0.24 0.26 0.45 0.38 -0.01 0.27 -0.17 0.68 0.66 0.83 0.63 -0.08

Co

Cr

0.00 -0.02 0.14 0.43 0.22 0.38 0.19 0.09 0.02 -0.29 0.44 0.02 -0.28 -0.18 0.23 0.50

0.89 0.85 -0.33 0.49 0.61 0.29 0.64 0.54 0.45 0.24 0.12 0.38 0.29 0.40 0.23

Cu

0.85 -0.37 0.52 0.65 0.41 0.72 0.47 0.50 0.15 0.33 0.52 0.50 0.55 0.15

Hg Mn Mo Ni Pb Sb Se Sr Th TI U V Zn Zr

-0.35 0.50 0.60 0.36 0.67 0.55 0.42 0.36 0.23 0.37 0.31 0.43 0.33

Mn

Mo

Ni

Pb

0.00 0.07 -0.14 -0.13 -0.18 - 0.29 0.02 -0.17 -0.49 - 0.35 - 0.08 0.01

0.67 0.31 0.62 0.55 0.15 0.17 0.33 0.18 0.28 0.59 0.32

0.37 0.65 0.40 0.08 0.36 0.32 0.15 0.26 0.79 0.37

0.33 0.20 0.19 0.21 0.59 0.56 0.50 0.5 I 0.24

Sb

Se

Sr

Th

TI

-0.37 O. 10 0.63 0.27 0.20 -0.41

0.08 -0.20 -0.10 0.13 0.75

0.59 0.71 0.60 0.22

U

V

Zn

0.49 0.26

O. 19

0.19 0.40 0.24 0.52 0.60 0.28

0.26 0.08 O. 10 0.16 0.24 0.27

Notes: Based on log concentrations. Values of r_> 0.65 of < - 0 . 6 5 in bold. Values of r _>0.65 or < - 0.65 significantly differ from 0 with >99.5% confidence.

0.68 0.46 -0.19

0.60 0.05

0.19

TABLE 12-V Correlation coefficients for most altered samples from the Meade Peak

Org. C Total S AI Ca Fe K Mg Na P Si Ti Ag As Ba Cd Co Cr Cu Hg Mn Mo Ni Pb Sb Se Sr Th TI U V Zn Zr

Carb. C

Org. C

Total S

AI

-0.07 0.18 -0.54 0.76 -0.45 -0.45 0.28 -0.08 0.57 -0.57 -0.51 0.22 -0.22 -0.52 0.41 0.01 -0.17 -0.11 -0.18 0.08 -0.11 -0.14 0.18 -0.09 -0.36 0.42 -0.51 0.06 0.46 0.13 0.20 -0.45

0.81 0.15 0. i 0 0.07 0.17 0.20 -0.13 0.12 -0. i I 0.10 0.46 0.04 -0.02 -0.01 -0.33 0.69 0.54 0.56 -0.44 0.08 0.27 0.06 0.11 0.60 0.14 -0.08 -0.19 0.07 0.02 -0.03 -0.06

-0.21 0.40 -0.22 -0.15 0.08 -0.19 0.40 -0.45 -0.25 0.47 -0.17 -0.32 0.17 -0.45 0.58 0.44 0.42 -0.43 0.05 0.03 0.11 0.05 0.39 0.31 -0.35 -0.28 0.35 0.10 -0.06 -0.33

- 0.70 0.92 0.96 0.35 0.36 -0.65 0.81 0.97 -0.01 0.64 0.72 -0.44 0.34 0.22 0.20 0.41 0.13 0.28 0.60 0.02 0.35 0.52 -0.39 0.80 0.16 -0.63 -0.13 0.24 0.82

Ca

-0.64 -0.60 -0. i ! -0.31 0.95 -0.79 -0.69 0.49 -0.47 -0.67 0.54 -0.34 0.16 0.16 0.05 -0.27 -0.22 -0.43 0.14 -0.1 i -0.35 0.69 -0.70 -0.11 0.81 0.18 -0.09 -0.61

Fe

K

Mg

Na

P

Si

0.90 0.34 0.36 -0.61 0.74 0.91 -0.01 0.79 0.68 -0.41 0.34 0.19 0.15 0.39 0.23 0.38 0.63 0.12 0.42 0.46 -0.37 0.82 0.18 -0.61 -0.08 0.30 0.80

0.37 0.34 -0.58 0.76 0.95 0.10 0.64 0.64 -0.31 0.26 0.25 0.27 0.44 0.07 0.34 0.60 0.16 0.46 0.54 -0.37 0.75 0.21 -0.53 -0.01 0.30 0.80

-0.01 -0.30 0.20 0.33 0.15 0.27 0.25 0.02 0.27 0.15 0.15 0.12 0.20 0.23 0.44 0.28 0.12 0.17 -0.36 0.22 0.29 -0.19 0.09 0.34 0.23

-0.31 0.38 0.46 -0.33 0.34 0.22 -0.37 0.17 -0.30 -0.25 -0.06 0.23 0.09 0.12 -0.15 -0.04 0.18 -0.16 0.40 -0.12 -0.44 -0.24 0.04 0.51

-0.75 -0.64 0.51 -0.49 -0.63 0.48 -0.40 0.24 0.22 0.13 -0.34 -0.25 -0.50 0.06 -0.10 -0.31 0.76 -0.65 -0.16 0.85 0.15 -0.20 -0.57

0.82 -0.33 0.50 0.78 -0.58 0.37 -0.09 -0.05 0.01 0.23 0.17 0.39 -0.10 0.10 0.35 -0.52 0.79 0.11 -0.77 -0.33 0.02 0.68

Ti

-0.05 0.64 0.72 -0.45 0.32 0.15 0.14 0.35 0.15 0.27 0.52 0.05 0.29 0.48 -0.42 0.81 0.16 -0.63 -0.15 0.19 0.89

Ag

0.02 -0.22 0.49 -0.26 0.63 0.64 0.59 -0.35 0.16 0.11 0.31 0.47 0.16 0.42 -0.21 0.19 0.53 0.44 0.15 -0.11

As

0.48 -0.29 0.38 0.08 0.07 0.27 0.41 0.60 0.65 0.16 0.55 0.37 -0.29 0.63 0.21 -0.46 0.12 0.41 0.63

Ba

-0.49 0.30 0. I1 0.00 0.10 0.15 0.16 0.30 -0.03 0.06 0.27 -0.36 0.67 0.11 -0.58 -0.21 -0.04 0.64

Cd

-0.17 0.10 0.27 0.01 -0.09 0.02 -0.05 0.40 0.32 -0.23 0.21 -0.50 0.46 0.72 0.72 0.39 -0.34

Co

-0.40 -0.35 -0.19 0.75 0.17 0.52 -0.04 0.08 -0.17 -0.26 0.32 0.35 -0.40 -0.09 0.50 0.33

Cr

0.87 0.80 -0.46 0.22 0.09 0.27 0.32 0.46 0.31 0.04 -0.10 0.30 0.21 -0.10 0.03

Cu

0.80 -0.41 0.28 0.10 0.44 0.46 0.35 0.25 0.07 0.05 0.36 0.36 0.02 0.04

Hg

-0.33 0.31 0.27 0.23 0.48 0.43 0.30 0.21 -0.07 0.13 0.20 0.11 0.24

Mo Ni Pb Sb Se Sr Th TI U V Zn Zr

Mn

Mo

Ni

Pb

Sb

Se

Sr

Th

TI

U

V

Zn

0.32 0.41 0.01 0.04 -0.12 -0.34 0.23 0.33 -0.32 0.05 0.47 0.24

0.46 0.21 0.54 0.32 -0.27 0.26 0.14 -0.11 0.38 0.38 0.34

0.18 0.55 0.39 -0.37 0.43 0.36 -0.42 0.17 0.76 0.42

0.53 0.06 -0.12 0.09 0.43 0.31 0.59 0.33 0.09

0.28 -0.02 0.24 0.40 0.09 0.67 0.60 0.29

-0.21 0.34 -0.07 -0.33 0.05 0.09 0.38

-0.44 -0.30 0.58 -0.04 -0.17 -0.41

0.16 -0.61 -0.21 0.12 0.71

0.05 0.48 0.49 0.20

0.48 -0.06 -0.50

0.47 -0.02

0.22

Note: Based on log concentrations. Values of r _> 0.65 or 99.5% confidence.

352


weak association with P, which in part could be carbonate that occurs in CFA. P20 5 retains correlations with Sr and U and Cd retains its strong correlations with U and V. Cobalt, which had no strong correlation in the least-altered samples, has a strong correlation with Mn perhaps as grain coatings. Chromium, Cu, and Hg still correlate with organic C, but not as strongly as in the data for the least-altered samples. Nickel and Zn strongly correlate, but neither correlate with organic C. Factor analysis provides a linear grouping of co-associating trace elements. Piper (2001) used an orthogonal transformation solution to group rocks sampled from the Enoch Valley mine into five factors: CFA; detrital; a trace element factor (hydrogenous) with largest loadings of Cd, V, and Zn; carbonate; and organic carbon. For the same trace elements as those considered here, he reported the following associations: CFA (Cr, Cu, Sr); detrital (As, Ba, Ni, Pb,); carbonate-none; and organic carbon (S, Ag, Cr, Cu, Mo, Se). For our analysis we computed solutions with different numbers of factors using an oblique transformation solution (Table 12-VI). The difference between the two solution types is generally small, with the oblique solution tending to generate slightly lower loadings onto factors. However, the oblique solution has an advantage in that orthogonal factor scores show zero intercorrelations and assume that all factors are independent, whereas oblique scores allow intercorrelations among factors. While these coefficients are not particularly high, they nonetheless indicate intercorrelations among factors, particularly between the carbonate and organic-C factors and between the trace-element and CFA factors (Table 12-VI). Similar to the results noted by Piper (2001), a five-factor result identifies components that, based on their association with major elements, are: (factor 1) detrital, with AI, Fe, K, Si, Ti, Ba, Th, and Zr; (factor 2) a partial loading for CFA with Cd, Pb, Sb, V, and Zn; (factor 3) organic carbon with Mo, Ni, and Se; (factor 4) a smaller loading for organic carbon, a larger loading for CFA with Ag, Cr, Cu, Hg; and (factor 5) carbonate (Table 12-VII). Factor 1 is a detrital component that corresponds to the terrigenous factor of Piper, but differs from Piper's factor in having considerably reduced loadings of Na, Ni, and especially Pb, but, in turn, shows major loadings of Th and Zr. Factor 2, with large loadings of Cd, Pb, Sb, T1 V, and Zn, corresponds approximately with the hydrogenous factor of Piper (2001). It is possible to extract nearly all of the above information with only four factors. Usually, it is an advantage in factor analysis to use the fewest number of factors that TABLE 12-VI Correlations of five factors from oblique solution factor analysis For an oblique solution Factor 2 Factor 3 Factor 4 Factor 5

Factor 1

Factor 2

Factor 3

0.10 0.15 -0.02 -0.01

0.09 0.28 -0.18

0.16

0.23

Factor 4

-0.29


3 53

TABLE 12-VII Factor analysis of all samples using a five-factor oblique solution

Detrital, factor 1 Carbonate C Organic C Total S A1 Ca Fe K Mg Na P Si Ti Ag As Ba Cd Co Cr Cu Hg Mn Mo Ni Pb Sb Se Sr Th TI U V Zn Zr

-0.56 -0.03 -0.16 0.95 -0.83 0.90 0.89 -0.10 0.45 -0.47 0.94 0.97 -0.01 0.48 0.77 -0.28 0.33 0.21 0.11 0.32 0.09 0.12 0.30 0.00 0.31 0.12 -0.52 0.86 0.07 -0.46 -0.13 0.00 0.87

Note: Values >0.50 are in bold.

Partial CFA plus trace elements, factor 2

Organic carbon, factor 3

Partial CFA plus trace elements, factor 4

Carbonate, factor 5

-0.04 -0.12 -0.17 -0.07 0.10 -0.02 0.00 -0.11 -0.13 0.27 -0.13 -0.07 0.48 0.30 0.13 0.79 0.24 0.06 0.29 0.13 0.23 0.42 0.49 0.58 0.59 -0.10 0.02 0.00 0.82 0.45 0.81 0.82 0.11

0.15 0.86 0.99 0.06 0.04 0.14 0.11 -0.01 0.37 0.17 -0.02 -0.05 0.02 0.33 0.09 -0.25 0.37 0.34 0.25 0.30 0.07 0.59 0.55 0.29 0.01 0.75 0.25 -0.02 -0.12 0.05 -0.19 0.35 0.00

-0.17 0.28 -0.07 0.13 0.28 0.09 0.17 -0.16 -0.33 0.41 -0.06 0.13 0.68 -0.04 0.05 0.18 -0.69 0.75 0.71 0.67 -0.67 -0.03 -0.12 -0.17 0.47 0.12 0.50 -0.03 -0.13 0.32 0.23 -0.20 -0.08

0.61 -0.08 -0.24 0.15 0.09 0.11 0.24 0.80 -0.17 -0.42 -0.03 0.09 0.10 0.31 -0.28 0.00 -0.09 -0.02 0.01 -0.09 0.29 0.14 0.16 -0.43 0.37 0.00 -0.17 -0.18 -0.22 -0.44 0.04 0.06 -0.14

354


explain the most variance. With the set of all channel sample data, a four-factor model explains 73% of the variance as opposed to the five-factor model, which only increases the explained variance to 78%. The only loss of information is the elimination of the carbonate factor, which only has a loading for Mg. The four-factor model produces a betterdefined single high loading for P along with associated Cr, Cu, Hg, Sr, and U. For the least-altered samples (Table 12-VIII) of the Meade Peak, a three-factor model explains 69% of the variance. A four-factor model only improves this to 76%, but it does offer a slight improvement over the three-factor model in defining the loading of Mg and Mn onto the carbonate phase. Alternatively, the three-factor model better shows the loadings of a group of trace elements onto a factor that includes P205, whereas many of the same trace elements in the four-factor model are loaded onto a factor that has no major component. For the three-factor model, factor 1 is a siliciclastic component, comprised of A1, Fe, Ka, Si, Ti, Ba, Co, Th, and Zr. Factor 2 is the CFA factor with P, Cd, Pb, T1, U, V, Zn, Ag, and Cu. Organic C and total S are the major components loaded onto factor 3, with Ag, As, Cr, Cu, Hg, Mo, Ni, Sb, Se, and Sr. For the most altered samples (Table 12-VIII), factor 1 is the detrital factor with A1, Fe, K, Si, Ti, As, Ba, Se, Th, and Zr. Factor 2 comprises organic C and total S, Ag, Cr, Cu, Hg, and Se. Note the appearance of Se on factors 1 and 2, indicating that Se, which had primarily been with organic C factor in the least-weathered rocks, now has partial affiliation with the detrital component. Factor 3 is a trace-element component with no particular association with a major-element phase: Cd, Mo, Ni, Pb, Sb, TI, V, and Zn. In summary, principal component analysis of Meade Peak rocks is relatively unsuccessful for identifying a set of factors unique to a grouping of trace elements with its highly variable degrees of alteration. Principal component analysis works better for identifying these components when restricted to end-member compositions of the least and most-altered rocks.

I n d i v i d u a l trace e l e m e n t s

Three trace elements have been selected for special consideration. Selenium is emphasized because of its potential damaging effect on the environment and U and V have been studied in the past because of their economic potential in these rocks. All three elements have been mentioned in previous studies as being associated with organic matter and the phosphate phase (Sheldon, 1959; McKelvey and Carswell, 1967; McKelvey et al., 1986; Zielinski et al., Chapter 9). Consequently, the relationships for Se, U, and V with phosphate and organic C was examined. For Se, there is a distinct relationship with organic C, which has increasing scatter at lower relative concentrations of phosphate. There is no discernable trend with alteration, although a large scatter exists between Se and organic C for highly altered samples at lowest concentrations of phosphate. Uranium is predominantly associated with phosphate and alteration seems to have had no great effect on that association. At low concentrations of organic C, there is a relationship between V and organic C that ranges over nearly the entire range of phosphate. At higher concentrations of organic C,


355

Table 12-VIII Factor analysis for highly altered and least altered data sets using a three-factor oblique solution Highly altered (106 samples)

Carbonate C Organic C Total S A1 Ca Fe K Mg Na P Si Ti Ag As Ba Cd Co Cr Cu Hg Mn Mo Ni Pb Sb Se Sr Th T1 U V Zn Zr

Least altered (231 samples)

Factor 1

Factor 2

Factor 3

Factor 1

-0.76 0.19 -0.19 0.93 -0.88 0.86 0.84 0.15 0.48 -0.79 0.93 0.93 -0.32 0.56 0.82 -0.82 0.18 0.15 0.04 0.27 0.02 0.18 0.38 -0.25 0.01 0.59 -0.46 0.86 -0.19 -0.86 -0.50 -0.16 0.78

-0.22 0.82 0.72 0.22 0.17 0.15 0.26 0.00 -0.17 0.29 -0.08 0.17 0.62 -0.01 0.04 -0.04 -0.62 0.94 0.82 0.83 -0.72 0.09 -0.03 0.11 0.22 0.58 0.38 0.02 -0.34 0.24 0.04 -0.29 0.02

0.34 -0.14 -0.10 0.08 0.11 0.20 0.20 0.42 -0.15 -0.01 -0.14 0.06 0.40 0.42 -0.12 0.68 0.44 0.00 0.21 0.12 0.49 0.52 0.61 0.67 0.77 -0.06 -0.17 0.03 0.78 0.26 0.83 0.90 0.15

-0.67 -0.06 0.03 0.83 -0.92 0.77 0.74 -0.30 0.70 -0.39 0.94 0.89 -0.16 0.30 0.79 -0.18 0.58 0.00 -0.09 0.14 0.09 0.09 0.26 0.24 0.05 0.01 -0.68 0.90 0.21 -0.32 -0.11 0.08 0.94

Note: Values >0.5, < - 0 . 5 in bold.

Factor 2

Factor 3

-0.81 -0.19 -0.30 -0.13 -0.05 -0.15 -0.18 -0.88 0.00 0.60 0.02 -0.01 0.43 -0.18 0.39 0.78 -0.04 0.09 0.27 0.21 -0.52 0.00 0.13 0.75 0.13 -0.21 0.09 0.24 0.89 0.82 0.77 0.52 0.30

0.35 0.96 0.82 0.31 0.25 0.38 0.41 0.24 0.09 0.24 0.00 0.14 0.59 0.64 0.13 -0.09 0.03 0.83 0.77 0.73 0.02 0.72 0.63 -0.04 0.74 0.81 0.56 -0.08 -0.22 0.02 0.02 0.33 -0.06

356


the association shifts to V and phosphate. As with U, there seems to be no association with the degree of alteration of the samples.

Selenium

In Section J, there are enrichments of Se up to 7000 ppm in a phosphorite layer that directly underlies the Rex Chert. We postulate that this results from Se oxidation and subsequent transport from overlying parts of the steeply dipping Meade Peak. The Se was carried by water into zones where conditions of sufficient organic matter and lack of oxygen reduced the Se to elemental form (see Grauch et al., Chapter 8). Minor Se also occurs in pyrite, organic matter, pyrite-vaesite solid solution, sulvanite, and sphalerite (Grauch et al., Chapter 8; Perkins and Foster, Chapter 10).

Uranium

Uranium is enriched in the Meade Peak rocks: 16% of the samples exceed 103 ppm (upper limit of central range) and 2.5% of samples exceed 279 ppm (upper limit of expected range) based on the geometric mean and deviation of the concentrations, respectively (Table 12-11). WSC and NASC have U concentrations of about 3 ppm and a Th/U ratio of about 4, whereas the Meade Peak has 58 ppm U on average and Th/U of 0.07 based on analysis of the channel samples. Uranium, which is mainly associated with phosphate minerals, does not show the same enrichment as phosphate in highly altered rocks. For example, altered rocks of Section A have a weighted average P2Os/U of 0.27, while the weighted average for all Meade Peak samples is 0.23 and that for least-weathered Section J is 0.25. However, this relationship is not uniform. The highly altered Section F weighted average of the ratio is 0.20. Nonetheless, others (e.g. Sheldon, 1959) determined that the weathered Meade Peak has a slightly increased P2Os/U ratio relative to less-weathered rocks. This suggests that additional processes may affect and remove U in the altered rocks relative to the host CFA. One likely mechanism involves leaching of carbonate. Oxidizing waters would become enriched in bicarbonate ions from carbonate dissolution, and the strong tendency to form a bicarbonate-U complex would compete for and in part remove some U in the rocks. Most if not all U in the phosphate occurs as U 4§ substituting for Ca in the CFA lattice (Altschuler et al., 1958; Sheldon, 1959). The exposure of the U to oxidizing groundwater laden with Ca would also tend to remove U from the CFA lattice by oxidizing U to the more soluble +6 state in the presence of abundant dissolved Ca that could replace it. A scatter plot indicates that there might be two superimposed linear relationships between U and phosphate (Fig. 12-9a). One occurs at lower concentrations of phosphate ( 100 ~zg L-1 between day 12 and day 43 is unexplained. As in the previous sample and for the least-altered rocks in general, Se and Mo gradually increased with time.

394

J.R. Herring

Sample J186 is a CFA- and quartz-rich rock with very few minerals detected by XRD that could be reactants in water except for gypsum - which does not alter pH when it dissolves. Besides CFA, there are no other acid-neutralizing minerals. Dissolution of the relatively abundant CFA, which is marked by concentrations of dissolved P that range from 2 to about 4 mg L-~, is insufficient to neutralize the acidity in this sample. The initial pH of about 5.2 resulted in relatively high Fe, AI, Zn, and Ni concentrations in the range of 2-7 mg L -~. However, it appears that oxidation and associated precipitation of Fe as Fe-oxide and later Fe-oxyhydroxide resulted in a lowering of final pH to about 4.3. This lowered pH allowed A1, Zn, and Ni concentrations to increase modestly. Modest changes in sulfate and conductivity are consistent with these interpretations. Selenium gradually increased to a final concentration of just over 1 mg L -~. This amount of Se represents about 5% of the Se that was originally present in the rock.

Anoxic conditions

It is not known whether an anoxic environment exists in waste piles of Meade Peak rocks. However, reduced chemical species have been found in water draining from waste rock disposal piles that suggest the presence of anaerobic conditions inside the piles (Stillings and Amacher, Chapter 17). Anoxic conditions were examined by using an Ar atmosphere to enclose a subset of samples during leaching. Prior to mixing with the ground rock, the deionized leachate water was degassed with bubbling Ar. Mixing of the water and rock was done in a glove bag inflated with Ar and the samples were maintained in the bag with a positive pressure of flowing Ar during the 6-day duration of the leachate experiment. One of the highly altered samples, A080, increased the leachate concentrations of Fe in the absence of oxidizing conditions (Table 13-1V), but the other highly altered sample, F 121, did not. There was little difference in conductivity or pH between the 6-day leachate under oxidizing or reducing conditions for these two samples. In sample A080, Fe, Zn, and As were elevated in leachate concentration in the reducing compared to the oxidizing environment. Selenium was slightly elevated, by 21%, in the reducing leachate, while Cd and Th decreased in concentration. The sample from highly altered Section F showed little difference in concentrations of most elements between reducing and oxidizing environment leachates. Presumably, the intense alteration to which Section F had been exposed had removed most of the soluble fractions of many of the trace elements. In the comparatively less-altered sample B134, conductivity, sulfate, Si, and P increased in the reducing leachate. However, most of the trace elements in the reducing leachate, with the exception of V, either showed no increase or had a slight decrease in concentration. In the least altered samples, Section J samples J084, J125, and J186, there was little change in pH or conductivity between the reducing and oxidizing environment. Sulfate showed slight to nearly two-fold increases in the reducing leachate solutions. The dissolution of all major elements was enhanced in the reducing leachate. Sample J084 showed little change in the concentration of Fe, reflecting its relatively low abundance in

Rock Leachate geochemistry of the Meade Peak Phosphatic Shale Member

395

the bulk rock, but the other two samples showed dramatic increases in Fe in the anoxic leachates. In the time-series study, sample J125 had initial Fe concentrations in the leachate around 40,000 Ixg L -l at 1 and 2 h reaction time. This decreased to around 1500 txg L-l by 6 days and to below the LDL, 50 txg L-1 by 12 days. However, the 6-day leachate sample kept in Ar maintained concentrations near 40,000 txg L-1. Sample J 186 had a concentration of Fe in the 6-day leachate sample kept in Ar that was nearly double that of the high concentration for the oxidizing leachate samples. Clearly, the lack of oxidizing conditions allowed the Fe and trace elements that are associated with it (Co, Ni, and Zn) to remain in solution for longer times. Selenium, As, Mo, Cd, and Sb showed little change in concentration between reducing and oxidizing leachates. Thorium and U concentrations decreased in the anoxic leachate.

Freeze-thaw effects

The area of phosphate mining in southeast Idaho has cold winters with freezing conditions. Consequently, the effect of freeze-thaw conditions during leaching were studied by quickly freezing the leachate and ground-rock samples in a bath of dry ice and acetone. These rock samples were splits of four of the 1 and 2 day leachate samples and were processed exactly the same up until freezing. The samples were kept in the bath until frozen, about 20 rain, then allowed to defrost at room temperature. The freeze cycle was repeated twice each day. In general, this process produced little effect on pH or conductivity of the highly altered samples A080 and A I31 (Table 13-1V). For sample A080, Zn is the only trace element that showed an increase after the freeze-thaw process in both the 1- and 2-day leachate samples. Curiously, sample A I31 has a higher Zn content in the original bulk rock by nearly a factor of four but produces a leachate Zn concentration of only about 1-2% of that of sample A080. One explanation for this is the relative difference in organic-carbon content of the original bulk rock. Samples A080 and A I31 have 8 and 1.7% organic carbon, respectively. Sample A131 has more Zn, but it must be in mineral phases that are resistant to dissolution. The bulk-rock Zn content in A080 is less than that of A 131, but much of it must occur in the high organic-carbon fraction and it is this phase that was more easily leached and mechanically disrupted by the freeze-thaw process to accelerate dissolution. In the two less-altered samples, J084 and J186, the freeze-thaw process produced slightly enhanced dissolution as indicated by increased conductivity. Sulfate generally increased in the freeze-thaw samples compared to the same leachate samples that were not frozen. Chromium and Mn concentrations increased in the freeze-thaw leachates of both samples, but Fe remained below its LDL in one sample and significantly decreased in the other. Molybdenum, Ni, Se, and Zn increased in the freeze-thaw leachates of both samples. Molybdenum increased in the freeze-thaw leachate of sample J084, but decreased in the other sample. This was the sample of the pair with much greater content of organic carbon in the bulk rock. Molybdenum is partially associated with organic matter in rocks of the Meade Peak.

396

J.R. Herring

Multiple leaching The effect of resuspension of a previously leached rock sample was studied in samples F 121, J084, and J 186 (Table 13-IV). The sediment from the 1-day leachate was resupended at a water/rock ratio of 20 with deionized water and allowed to react for an additional 6 days. As expected, easily leached elements were greatly reduced because of the initial leaching. Sulfate and conductivity in the two resuspended samples of day 6 from Section J were reduced to about 25% of that in the initial leachate of day 6. Conductivity in the sample from Section F was little reduced in the resuspended sample, but all leachate samples from this highly altered section had very low conductivities, typically less than 25 IxS cm -l. Nonetheless, multiple leachates of the same rock sample, especially if minerals such as pyrite are present, can continue to release trace elements for many cycles of leaching (Desborough et al., 1999).

CONCLUSIONS These leachate experiments show that Meade Peak rocks are highly reactive with water and that they can release significant quantities of several trace elements in periods as short as 1 h. Furthermore, the initial release of potential contaminant trace elements into solution is dominated by those rocks of the Meade Peak that are least altered and rich in organic matter.

ACKNOWLEDGMENTS I thank the phosphate mining companies for providing access for rock sampling. I appreciate help in sample preparation by M. Fallin, K. Long, and C. Santos. P.L. Hageman, G.A. Desborough, J.R. Hein, and L.B. Kirk provided comments on the manuscript.

REFERENCES d'Angelo, W.M. and Ficklin, W.H., 1996. Fluoride, chloride, nitrate, and sulfate in aqueous solution by chemically suppressed ion chromatography. In: B.F. Arbogast (ed.), Analytical methods manual for the Mineral Resource Surveys Program, US Geological Survey. US Geological Survey, Open-File Report, 96-525, 248 pp. Desborough, G.A., Leinz, R., Smith, K., Hageman, P.L., Briggs, P.H., Fey, D. and Nash, T., 1999. Acid generation and metal mobility of some metal-mining related wastes in Colorado. US Geological Survey, Open File Report, 99-332, 18 pp. Hageman, P.L., Briggs, P.H., Desborough, G.A., Lamothe, P.J. and Theodorakos, P.J., 2000a. Update and revisions for Open-File Report 98-624, Synthetic precipitation leaching procedure (SPLP) leachate chemistry data for solid mine-waste composite samples from the Silverton and Leadville Districts in Colorado. US Geological Survey, Open File Report, 00-150, 16 pp.

Rock Leachate geochemistry of the Meade Peak Phosphatic Shale Member

397

Hageman, EL., Desborough, G.A., Lamothe, EJ. and Theodorakos, P.J. 2000b. Synthetic precipitation leaching procedure (SPLP) leachate chemistry data for solid mine-waste composite samples from southwestern New Mexico, and Leadville, Colorado. US Geological Survey, Open File Report, 00-033, 18 pp. Hageman, EL. and Briggs, P.H., 2000. A simple field leach test for rapid screening and qualitative characterization of mine waste dump material on abandoned mine lands, in ICARD 2000: Proceedings from the Fifth International Conference on Acid Rock Drainage, Denver, Colorado, May 21-24, 2000. Society for Mining, Metallurgy, and Exploration, Inc., pp. 1463-1475. Herring, J.R., Desborough, G.A., Wilson, S.A., Tysdal, R.G., Grauch, R.I. and Gunter, M.E., 1999. Chemical composition of weathered and unweathered strata of the Meade Peak Phosphatic Shale Member of the Permian Phosphoria Formation - A. Measured sections A and B, central part of Rasmussen Ridge, Caribou County, Idaho. US Geological Survey, Open File Report, 99-147-A, 24 pp. Herring, J.R., Wilson, S.A., Stillings, L.A., Knudsen, A.C., Gunter, M.E., Tysdal, R.G., Grauch, R.I., Desborough, G.A. and Zielinski, R.A., 2000a. Chemical composition of weathered and less weathered strata of the Meade Phosphatic Shale Member of the Permian Phosphoria FormationB. Measured sections C and D, Dry Valley, Caribou County, Idaho. US Geological Survey, Open File Report, 99-147-B, 34 pp. Herring, J.R., Grauch, R.I., Desborough, G.A., Wilson, S.A. and Tysdal, R.G., 2000b. Chemical composition of weathered and less weathered strata of the Meade Peak Phosphatic Shale Member of the Permian Phosphoria Formation - C. Measured sections E and E Rasmussen Ridge, Caribou County, Idaho. US Geological Survey, Open File Report, 99-147-C, 35 pp. Herring, J.R., Grauch, R.I., Tysdal, R.G., Wilson, S.A. and Desborough, G.A., 2000c. Chemical composition of weathered and less weathered strata of the Meade Peak Phosphatic Shale Member of the Permian Phosphoria Formation- D. Measured sections G and H, Sage Creek area of the Webster Range, Caribou County, Idaho. US Geological Survey, Open File Report, 99-147-D, 38 pp. Herring, J.R., Grauch, R.I., Siems, D.E, Tysdal, R.G., Johnson, E.A., Zielinski, R.A., Desborough, G.A., Knudsen, A. and Gunter, M.E., 2001. Chemical composition of strata of the Meade Peak Phosphatic Shale Member of the Permian Phosphoria Formation. Channel-composited and individual rock samples of Measured Section J and their relationship to Measured Sections A and B, Central Part of Rasmussen Ridge, Caribou County, Idaho, US Geological Survey, Open File Report, 01-195, 72 pp. Lamothe, P.J., Meier, A.L. and Wilson, S., 1999. The determination of forty four elements in aqueous samples by inductively coupled plasma-mass spectrometry. US Geological Survey, Open File Report, 99-151, 14 pp. Smith, K.S., Walton-Day, K. and Ranville, J.E, 2000. Evaluating the Effects of Fluvial Tailings Deposits on Water Quality in the Upper Arkansas River Basin, Colorado: Observational Scale Considerations, in ICARD 2000: Proceedings from the Fifth International Conference on Acid Rock Drainage, Denver, CO, May 21-24, 2000. Society for Mining, Metallurgy, and Exploration, Inc., pp. 1415-1424. US Environmental Protection Agency, 1994. Test method for evaluating solid waste, physical/chemical methods (SW-846), 3rd edn., update 2B. Environmental Protection Agency, National Center for Environmental Publications, Cincinnati, OH 45268, order #EPASW-846.3.2B. Accessible at URL: http://www.epa.gov/epaoswer/hazwaste/test/sw846.htm.



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Chapter 14

REX CHERT M E M B E R OF THE PERMIAN P H O S P H O R I A FORMATION: COMPOSITION, WITH EMPHASIS ON E L E M E N T S OF ENVIRONMENTAL CONCERN

J.R. HEIN, B.R. MclNTYRE, R.B. PERKINS, D.Z. PIPER and J.G. EVANS

ABSTRACT We present bulk chemical and mineralogical compositions, as well as petrographic and outcrop descriptions, of rocks collected from three measured outcrop sections of the Rex Chert Member of the Phosphoria Formation in southeast Idaho. The three measured sections were chosen from l0 outcrops of Rex Chert that were described in the field. The Rex Chert overlies the Meade Peak Phosphatic Shale Member of the Phosphoria Formation, the source of phosphate ore in the region. Rex Chert removed as overburden constitutes part of the material transferred to waste-rock piles during phosphate mining. It is also used to surface roads in the mining district. It has been proposed that the chert be used to cap and isolate waste piles, thereby inhibiting the leaching of potentially toxic elements into the environment. The rock samples studied here are from individual chert beds representative of each stratigraphic section sampled. The Cherty Shale Member of the Phosphoria Formation that overlies the Rex Chert in measured section 1 and the upper Meade Peak and the transition zone to the Rex Chert in section 7 were also described and sampled. The cherts are predominantly spiculite composed of granular and mosaic quartz, and sponge spicules, with various but minor amounts of other fossils and detrital grains. The Cherty Shale Member and transition rocks between the Meade Peak and Rex Chert are siliceous siltstones and argillaceous cherts with ghosts of sponge spicules and somewhat more detrital grains than the chert. The dominant mineral is quartz. Carbonate beds are rare in each section and are composed predominantly of calcite and dolomite in addition to quartz. Feldspar, mica, clay minerals, calcite, dolomite, and carbonate fluorapatite are minor to trace minerals in the chert. The concentration of SiO2 in the chert averages 94.6 wt.%. Organic-carbon content is generally very low, but can be as much as 1.8% in Cherty Shale Member samples and as much as 3.3% in samples from the transition between the Meade Peak and Rex Chert. Likewise, phosphate (P205) is generally low in the chert, but can be as much as 3.1% in individual chert beds. Selenium concentrations in Rex Chert and Cherty Shale Member samples vary from 0.90.

Mineralogical analysis Mineral compositions were determined by X-ray diffraction using a Philips diffractometer with a graphite monochromator and Cu ket radiation. Samples were run from 4-70 ~ 2~) at 40 kV, 45 mA, and 10 counts per second. Semiquantitative mineral contents were determined and are grouped in Table 14-11 under the classifications of major (>25%), moderate (5-25%), and minor (

Life cycle of the Phosphoria Formation: from deposition to the post-mining environment

Nutrition Through the Life Cycle

Attachment Across the Life Cycle

The Project Management Life Cycle

The Environment: From Surplus to Scarcity

The formation of stars

Formation Of The Union

The Liberation of Life: From the Cell to the Community

The Formation of Stars

Essentials of Life Cycle Nutrition

Life-Cycle Assessment of Semiconductors

The Origins of Life: From the Birth of Life to the Origin of Language

From Suns to Life

Cycle of the Werewolf

Cycle Of The Werewolf

Cycle of the Werewolf

Cycle of the Werewolf

Cycle of the Werewolf

Cycle of the Werewolf

Cycle of the Werewolf

Cycle of the Werewolf

Life Cycle Reliability Engineering

Cycle of the Werewolf

Cycle of the Werewolf

Cycle of the Werewolf

Cycle of the Werewolf

Cycle of the Werewolf

Cycle of the Werewolf

Cycle of the Werewolf

Cycle of the Werewolf

Cycle of the Werewolf

Life cycle of the Phosphoria Formation: from deposition to the post-mining environment

Nutrition Through the Life Cycle

Attachment Across the Life Cycle

The Project Management Life Cycle

The Environment: From Surplus to Scarcity

The formation of stars

Formation Of The Union

The Liberation of Life: From the Cell to the Community

The Formation of Stars

Essentials of Life Cycle Nutrition

Life-Cycle Assessment of Semiconductors

The Origins of Life: From the Birth of Life to the Origin of Language

From Suns to Life

Cycle of the Werewolf

Cycle Of The Werewolf

Cycle of the Werewolf

Cycle of the Werewolf

Cycle of the Werewolf

Cycle of the Werewolf

Cycle of the Werewolf

Cycle of the Werewolf

Life Cycle Reliability Engineering

Cycle of the Werewolf

Cycle of the Werewolf

Cycle of the Werewolf

Cycle of the Werewolf

Cycle of the Werewolf

Cycle of the Werewolf

Cycle of the Werewolf

Cycle of the Werewolf

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