Reviews in Economic Geology Volume 5
SEDIMENTARY AND DIAGENETIC MINERAL DEPOSITS: A BASIN ANALYSIS APPROACH TO EXPLORATION
CONTENTS PART I: INTRODUCTION Basin Analysis for the Mineral Industry J.J. Eidel Sedimentary Processes as Ore-Forming Processes E.R. Force PART II: BASIN ANALYSIS AND SEDIMENTARY PROCESSES Rationale for Modern Basin Analysis Applied to Ore Deposits G. deV Klein Basin-Forming Processes G. deV Klein Sedimentary Basin Classification G. deV Klein Basin Sedimentology and Stratigraphy--The Basin Fill G. deV Klein Diagenesis and Fluid Movement--Basin Maturation G. deV Klein Synthesis: Brief Examples of Basin Analysis G. deV Klein Part II: References PART III: MINERAL DEPOSITS AND THE SEDIMENTARY ENVIRONMENT Placer Deposits E.R. Force Iron: Syngenetic Deposition Controlled by the Evolving System Ocean-Atmosphere J.B. Maynard Manganese: Syngenetic Deposits on the Margins of Anoxic Basins E.R. Force and J.B. Maynard Evaporite Basin Analysis P. Sonnenfeld Metalliferous Black Shales: Accumulation of Carbon and Metal Cratonic Basins R.B. Schultzin Shale-Hosted Deposits of Pb, Zn, and Ba: Syngenetic Deposition from J.B. Maynard Exhaled Brines in Deep Marine Basins Uranium: Syngenetic to Diagenetic Deposits in Foreland Basins J.B. Maynard Copper: Product of Dagenesis in Rifted Basins J.B. Maynar
Editors E.R. Force, J.J. Eidel, and J.B. Maynard
SOCIETY OF ECONOMIC GEOLOGISTS, INC. Society of Economic Geologists, Inc.
Reviews in Economic Geology, Vol. 5 Sedimentary and Diagenetic Mineral Deposits: A Basin Analysis Approach to Exploration E.R. Force, J.J. Eidel, and J.B. Maynard, Editors J.M. Robertson, Series Editor
Additional copies of this publication can be obtained from
Society of Economic Geologists, Inc. 7811 Shaffer Parkway Littleton, CO 80127 www.segweb.org
ISBN: 978-1-629495-63-7 The Authors:
1. 1ames Eidel 1. Barry Maynard Illinois State Geological Survey Department of Geology 615 E. Peabody Drive University of Cincinnati Champaign, IL 61820 Cincinnati, OH 45221-0013
Eric R. Force Richard B. Schultz U.S. Geological Survey Department of Geology Gould-Simpson Building University of Cincinnati University of Arizona Cincinnati, OH 45221-0013 Tucson, AZ 85721 Peter Sonnenfeld
George de V. Klein University of Windsor Department of Geology Windsor, Ontario University of Illinois Canada N9B 3P4 Urbana, IL 61801-2999
ii FOREWORD
Volume 5 of Reviewsin Economic Geology-Sedimentary and professional assistance with the volume has made the Series Diagenetic Mineral Deposits: A Basin Analysis Approach to Editor's job much more manageable. Exploration-served as a text for an SEG short course held Last but by no means least, I acknowledge the continuing in Toronto, Ontario, in May, 1991. Unlike its predecessors, support, both moral and economic, of the New Mexico Volume 5 actually appeared, in final form, in time for the Bureau of Mines and Mineral Resources and its Director, short course it supported. This precedent-setting occur Frank Kottlowski. rence is due, in part, to a longer-than-usual lead time for the short course, but mainly to the persistence and dedication of the volume editors, Eric Force, Jim Eidel, and Barry James M. Robertson Maynard. Series Editor It has been a special pleasure to work with Mary Lou Motl Socorro, NM of Custom Editorial Productions, Inc., whose timely and February, 1991
PREFACE
The textbooks on economic geology list many types of to specific mineral deposit types and to the exploration mineral deposits, but for most of us the term "ore deposit" process are also emphasized. The volume covers both conjures up an image of a hydrothermal metal deposit. synsedimentary and diagenetic deposits, but excludes Economic geologists do about 60 percent of their work on hydrothermal sediment-hosted deposits such as the Missis such deposits, as measured by articles in Economic Geologyin sippi Valley type. However, basin analysis and sedimentary the last year. process techniques may be applied to any type of sediment Yet the term "economic geology" implies that the atten hosted deposit. tion and expertise of the fieldshould be partitioned among ACKNOWLEDGMENTS-The patience and tact of the Series deposit types by some measure of their economic value. My Editor, Jamie Robertson, and Mary Lou Motl of Custom rough calculations show that sedimentary mineral deposits Editorial Productions are invisible ingredients in this contribute over a third of total world income from produc volume. Phil Bethke of the SEG Short Course Committee tion of non-fuel minerals (excluding cement limestone and originally suggested this topic to the Volume Editors. The sand and gravel), with large credits from iron, gold, phos authors would like to thank all those who read drafts of phate, salts, gems, and many other commodities. In contrast, articles herein. I personally would like to thank USGS such deposits were addressed by only about 10 percent of reviewers, editors, and illustrators for their prompt Economic Geology articles in the last year. attention. The purpose of this volume, and of the short course that prompted it, is to provide economic geologists with up-to Eric R. Force date information on sedimentary process and basin analysis U.S. Geological Survey techniques, at a level these are being used by our colleagues Tucson, AZ in the petroleum industry. Applications of this information February, 1991
iii BIOGRAPHIES
J. JAMES EIDEL is Principal Geologist and Branch Chief of authored more than 200 papers, books, technical reports, Mineral Resources and Engineering at the Illinois State abstracts, and reviews. Geological Survey and an Adjunct Professor at the Univer sity of Illinois. He received his B.S. in Geological Engineering J. BARRY MAYNARD received his undergraduate training from the University of Arizona and M.S. in Geology from at Duke University and graduate training at Harvard. Since UCLA. He was a Mine Geologist and Engineer and Explora 1972, he has been on the faculty at the University of Cincin tion Geologist for Duval Corporation prior to 19 years in nati, serving as department head from 1985 to 1990. His metal and hydrocarbon exploration management for the research focuses on the chemistry of sedimentary rocks as Hanna Mining Company (Coastal Mining Company) in the applied to ore deposits and has resulted in a number of United States, Canada, Australia, New Guinea, and New papers and two books: Geochemistry of Sedimentary Ore Zealand, and other countries. He joined the Illinois State Deposits and, as a co-author, Sedimentology of Shale. He is also Geological Survey in 1985 to manage, coordinate, and a co-editor of the book, Chemical Cycles in the History of the promote research on coal, oil and gas, and industrial and Earth. In addition to North American ore deposits, he has metal deposits in an interior cratonic basin. worked in Pakistan, Venezuela, South Africa, and China.
ERIC R. FORCE has served the U.S. Geological Survey as RICHARD B. SCHULTZ attended Illinois State University titanium resource specialist for 19 years, and studied in Bloomington-Normal, Illinois, where he received his B.S. sedimentary manganese deposits from19 80 to 1988. His in geology in 1985. He studied the stratigraphic relations of training, at Occidental College, Lehigh University, and the an Upper Pennsylvanian clastic unit at Wichita State University of Otago, centered on sedimentary petrology, University where he received his M.S. in geology in 1988. He and his interests in economic geology are primarily in is currently studying the geochemistry, metal constituents, syngenetic deposits of both sedimentary and igneous and depositional setting of Pennsylvanian black shales in origin. He isan author of 16 papers on placer deposits and 10 midcontinent North America at the University of Cincinnati on manganese deposits, among many others. He has done as part of his Ph.D. in geochemistry. extensive geologic fieldwork in 13 countries and 14 states. PETER SONNENFELD graduated in 1947 from Comenius GEORGE deV. KLEIN is Professor of Geology at the Univer University in Bratislava, Czechoslovakia, and received in sity of Illinois at Urbana-Champaign where his research and 1949 the Dr. rer. nat. from Charles University in Prague, teaching expertise are in basin analysis and in clastic Czechoslovakia. His experience includes field work from sedimentology. He earned a B.A. fromWesleyan University, 1949 to 1951 for a consultant in Toronto, from19 51 to 1952 for an M.A. fromthe University of Kansas, and a Ph.D. fromYale a mining company in Newfoundland, and exploration and University; all degrees are in geology. Prior to joining the production geology for major oil companies in western faculty at Illinois, he worked as a research sedimentologist Canada from 1952 to 1963. He started geology in a newly with Sinclair Research, and taught at the University of established department of Geography and Geology at Texas Pittsburgh and the University of Pennsylvania. Klein's A&I University, Kingsville, Texas, from19 63 to 1966; started research has dealt with fluvial sedimentology, tidal sedi geology and geological engineering and established the mentology, deep-water marine sedimentology, sandstone department at the University of Windsor, Windsor, Ontario, petrology and diagenesis, cratonic basins, rift basins, Canada, from 1966 to 1988; and became Professor Emeritus foreland basins, and backarc basins. He has authored or co- in 1989.
iv CONTENTS
Part I: Introduction CLASSIFICATION USED IN THIS CHAPTER ••....•45 CRITERIA • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • 45 BASIN TYPES Chapter 1-BASIN ANALYSIS FOR THE MINERAL •••••••••••••••••••••••••••••46
INDUSTRY ....•••.•••.•.•.•••.••.••••••1 TECTONIC VERSUS GEOCHEMICAL BASIN
THE ROLE OF BASIN ANALYSIS IN EXPLORATION CLASSIFICATION •••••••••••.•••••.•••••.47
FOR SEDIMENT-HOSTED ORE DEPOSITS ••...•..1 WORLD-CLASS ORE DEPOSITS, BASIN TYPE AND Chapter 6-BASIN SEDIMENTOLOGY AND
HISTORY .••••••••••••.•••.•••.••.•.•.••5 STRATIGRAPHY-THE BASIN FILL ••••••.•.••51
VARIATION IN ORE DEPOSITS AND BASINS PALEOGEOGRAPHY ••••••••.•.••••••••..•.51 MODERN pALEOGEOGRAPHIC PRINCIPLES THROUGH GEOLOGIC TIME •.•••.••..•••.•.8 •••••••••••51 PALEO-UPWELLING ORE MINERAL OCCURRENCES AND DEPTH OF •••••••••••••••••••••••••52 pALEO-DiSTRIBUTION OF CARBONATE ROCKS MINERALIZATION ••••••.••..•••.••.•.•..•8 •••••••••52
DATA SOURCES FOR BASIN ANALYSIS ••.••••••••8 BASIN CLASTIC SEDIMENTOLOGY AND FACIES ••.54 INTRODUCTION ADVANCES IN GEOLOGY, GEOCHEMISTRY, AND •••••••••••••••••••••••••••54 GEOPHYSICS THAT APPLY TO EXPLORATION FOR ALLUVIAL FANS •••••••••••••••••••••••••••56 SEDIMENT-HOSTED ORE DEPOSITS 10 BRAIDED STREAMS •••••••••• •••••••••••••••••••••••••57 CRUSTAL PROCESSES ANASTOMOSING STREAMS • • • • • • • • • • • • • • • • • • • • • • • • 10 •••••••••••••••••••••58 LABORATORY TECHNIQUES MEANDERING STREAMS ••••••••••••••••••••11 ••••••••••••••••••••••58 COMPUTER TECHNIQUES oLIANSAND Booms •••••••••••••••••••••11 E •••••••••••••••••••••••58 CoASTAL BARRIER IsLAND SYSTEMS REFERENCES .•••••••••••.••...••.••.••.•11 •••••••••••••••58 INTERTIDAL FLATS APPENDIX ••••••••.•••..••.•••..•..•..••13 •••••••••••••••••••••••••58 DELTAS ••••••••••••••••••••••••••••••••59 CoNTINENTAL SHELVES Chapter 2-SEDIMENTARY PROCESSES AS ORE ••••••••••••••••••••••59 SUBMARINE FANS FORMING PROCESSES ••.••••••.•.••.•••.17 ••••••••••••••••••••••••••59 SEQUENTIAL EVOLUTION OF SYNSEDIMENTARY SUMMARY OF SANDSTONE VERTICAL SEQUENCES •••••••61 AND DIAGENETIC ORE DEPOSITS 17 BLACK SHALES •••••••••••• •••••••••••••••••••••••••••62 SOLUTION INTERFACES AS LOCI OF MASSIVE BASIN STRATIGRAPHY •••.•••••..•••••...••64 PRECIPITATION 17 INTRODUCTION ••••.•..•.•••.•••.••••••• •••••••••••••••••••••••••••64 THE STRATIGRAPHIC COLUMN AS SUCCESSIVE CRATONIC SEQUENCES •••••••••••••••••••••••64 EQUILIBRIA 18 SEA LEVEL, SEQUENCE AND SEISMIC STRATIGRAPHY .•.••••••••..•..•••.•••••••• •••••66 SYNSEDIMENTARY DEPOSITS AND BASIN SEA-LEVEL EvoLUTION ••••••••••••••••••••••68 CRITI UE OF SEA-LEVEL CuRvEs BY VAIL ET AL. (1977A) AND ANALYSIS ••.•••••••••••••.••••.••.••..19 Q PALEOCLIMATE 20 HAQ ET AL. (1987, 1988) .••.••••.••.••••••••••.••• ••••••••••••••••••••••73 IMPACT OF SEA-LEVEL ANALYSIS ON STRATIGRAPHIC REFERENCES ••..•••.•••••.•••••••.••.•••20 CONCEPTS ••••••••••••••••••••••••••••78 TRANSGRESSIVE-REGRESSIVE SEQUENCES ••••••••••••79
Part II: Basin Analysis and Sedimentary Processes GLOBAL SEDIMENTARY CYCLES •.•••••••.•...80 Two PHANEROZOIC SuPERCYCLES •••••••••••••••83 MILANKOVITCH CYCLES Chapter 3-RATIONALE FOR MODERN BASIN ••••••••••••••••••••••87
ANALYSIS APPLIED TO ORE DEPOSITS •••••••21
BRIEF HISTORY OF BASIN ANALYSIS ••.•••.••••21 Chapter 7-DIAGENESIS AND FLUID MOVEMENT-
HEAT FLUX AND FLUID FLOW .••••••••••...••22 BASIN MATURATION ••••.•••••..•...•••.91
A NEW VIEW OF THE STRATIGRAPHIC RECORD •••22 INTRODUCTION •.••..•.••••.•.••.••••.•.•91
THE FUTURE OF SEDIMENTARY GEOLOGY •.••••.23 SANDSTONE DIAGENESIS •..•••••.••••.•••••91 SIMPLIFIED OVERVIEW OF ORGANIC CHEMISTRY 95
Chapter 4-BASIN-FORMING PROCESSES •••.•••25 BASIN HYDROGEOLOGY •••••••••••••••••.••97
ISOSTASY •..•••••.••.•••••••••..•••.••••25 Chapter 8-SYNTHESIS: BRIE F EXAMPLES OF THERMAL SUBSIDENCE ••••••.•••••••..••••.27
FLEXURAL SUBSIDENCE •••••••••••.•••..•.•31 BASIN ANALYSIS ••.••.••.••.•••.••••...103
INTRAPLATE STRESS •••••.••••••.•••.••••••34 INTRODUCTION •••••••••••.••••••••••.•.103
TECTONIC SUBSIDENCE AND GEOHISTORY BASIN ANALYSIS OF THE NORTH SEA ••••.•••.103 ARKOMA BASIN 110 ANALYSIS •.•..•••.•••••••••••.•••....•36 .•••.•..••••.•••••.•••.••
PACIFIC OCEAN BACKARC BASINS ••..•.•.••••113
Chapter 5-SEDIMENTARY BASIN ILLINOIS BASIN ••.••...•••.••..•••.••.•..115 ORIGIN OF CRATONIC BASINS 118 CLASSIFICATION •••.••.••.••••..•••••••43 •.••••....•••••
INTRODUCTION •••••••••••.••••••••.•••••43
PLATE TECTONIC BASIN CLASSIFICATIONS .•••••43 Part II: References • • • • • • • • • . • • • • • . . • • • • . • . • 121
v Part III: Mineral Deposits and the Sedimentary INITIAL MARINE PRECIPITATION •••••••••••••160 ARAGONITE PRECIPITATION Environment •••••••••••••••••••160 BIOTA IN AN EVAPORITE BASIN •••••••••••••••••160 GYPSUM PRECIPITATION Chapter 9-PLACER DEPOSITS •••••••••••••••131 •••••••••••••••••••••160 CLASTICS MECHANISM OF PLACER FORMATION •••••••••131 • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • 162 TYPES OF HYDRAULIC EQUIVALENCE ••••••••••••••131 The Clay Fraction ••••••••••••••••••••••162 MARINE CHLORIDE DEPOSITS Settling Equivalence ••••••••••••••••••••131 ••••••••••••••••••162
Entrainment Equivalence •••••••••••••••••131 The Precipitation Sequence • • • • • • • • • • • • • • • • 162
Transport Equivalence •••••••••••••••••••132 Site of Potash Deposits • • • • • • • • • • • • • • • • • • • 163 PLACER ENRICHMENT SETTLING EQUIVALENCE Red and White Carnallites 163 BY ••••••132 •••••••••••••••• PLACER ENRICHMENT BY THE SEQUENTIAL OPERATION OF Tachyhydrite •••••••••••••••••••••••••163 DIFFERENT EQUIVALENCE LAws •••••••••••••••132 Evolution of Evaporites ••••••••••••••••••164 BASIN CoNFIGURATION AND FACIES DisTRIBUTION ENVIRONMENTS OF PLACER FORMATION ••••••133 •••••164 DEPOSITION ••••••••••••••••••••••••••••133 Significance of Precipitation Rates • • • • • • • • • • • 164 PRESERVATION •••••••••••••••••••••••••••134 Synsedimentary Subsidence •••••••••••••••164
PREDEPOSITIONAL FACTORS IN PLACER Area of Water Surface • • • • • • • • • • • • • • • • • • • • 164
FORMATION ••••••••••••••••••••••••••134 Depth Estimates • • • • • • • • • • • • • • • • • • • • • • • 165 CYCLICITY OF DEPOSITION BASIN CONTEXT •••••••••••••••••••••••••135 •••••••••••••••••••165 EPIGENETIC ALTERATIONS EXAMPLES •••••••••••••••••••••••••••••136 ••••••••••••••••••••165 WITWATERSRAND •••••••••••••••••••••••••136 Porosity and Permeability •••••••••••••••••165 uATERNARY SHORELINE DEPOSITS OF THE EASTERN Q Anhydritization •••••••••••••••••••••••165 AusTRALIA CoAST •••••••••••••••••••••••137 Sulfatization ••••••••••••••••••••••••••166 SALT DoMES EXPLORATION ••••••••••••••••••••••••••138 ••••••••••••••••••••••••••••166 EFFLUENTS REFERENCES ••••••••••••••••••••••••••••139 • • • • • • • • • • • • • • • • • • • • • • • • • • • • • 167
Seepage •••••••••••••••••••••••••••••167
Chapter 10-IRON: SYNGENETIC DEPOSITION Removal of Silica •••••••••••••••••••••••167
CONTROLLED BY THE EVOLVING OCEAN Disposal of the Magnesium Surplus ••••••••••167
ATMOSPHERE SYSTEM ••••••••••••••••••141 Fluid Inclusions • • • • • • • • • • • • • • • • • • • • • • • 167
VERTICAL SEQUENCE •••••••••••••••••••••141 Fate of Organic Matter •••••••••••••••••••167 ALGOMA TYPE •••••••••••••••••••••••••••141 Repositories of Organic Matter •••••••••••••168 AKE SuPERIOR PE 168 L TY •••••••••••••••••••••••142 Release of Base Metals • • • • • • • • • • • • • • • • • • • KAPITAN PE 168 TY •••••••••••••••••••••••••••142 SUMMARY ••••••••••••· •••••••••••••• ••• CLINTON PE 168 TY •••••••••••••••••••••••••••142 REFERENCES ••••••••••••••••••••••••••••
TECTONIC SETTING ••••••••••••••••••••••143 ALGOMA PE TY •••••••••••••••••••••••••••143 AKE SUPERIOR TYPE L •••••••••••••••••••••••143 Chapter 13-METALLIFEROUS BLACK SHALES: KAPITAN PE TY •••••••••••••••••••••••••••143 ACCUMULATION OF CARBON AND METALS CLINTON PE TY •••••••••••••••••••••••••••144 IN CRATONIC BASINS •••••••••••••••••••171
EXPLORATION ••••••••••••••••••••••••••144 CHEMICAL PROPERTIES OF BLACK SHALES •••••171
REFERENCES ••••••••••••••••••••••••••••145 FOUR CASE STUDIES ••••••••••••••••••••••172 ALUM SHALE ••••••••••••••••••••••••••••172 EW ALBANY SHALE Chapter 11-MANGANESE: SYNGENETIC DEPOSITS N •••••••••••••••••••••••173 CHINESE BLACK SHALES ON THE MARGINS OF ANOXIC BASINS ••••••147 •••••••••••••••••••••173 PENNSYLVANIAN BLACK SHALES OF MIDCONTINENT TYPES OF MANGANESE DEPOSITS ••••••••••••147 NORTH AMERICA SEDIMENTARY GEOCHEMISTRY OF MANGANESE 147 ••••••••••••••••••••••••174
BASIN CONTEXT-DEPOSITIONAL BASIN •••••••147 SUMMARY •••••••••••••••••••••••••••••175
BASIN CONTEXT -STRUCTURAL BASIN ••••••••150 REFERENCES ••••••••••••••••••••••••••••175 GROOTE EYLANDT DEPOSIT -AN EXAMPLE OF
MANGANESE OXIDE DEPOSITION •••••••••••151 MOLANGO DEPOSIT-AN EXAMPLE OF Chapter 14-SHALE-HOSTED DEPOSITS OF PB, ZN,
MANGANESE CARBONATE DEPOSITION ••••••153 AND BA: SYNGENETIC DEPOSITION FROM
AN ADDENDUM FOR PRECAMBRIAN DEPOSITS •••154 EXHALED BRINES IN DEEP MARINE BA SINS •••177
EXPLORATION ••••••••••••••••••••••••••155 VERTICAL SEQUENCE •••••••••••••••••••••177 ARKANSAS REFERENCES ••••••••••••••••••••••••••••156 •••••••••••••••••••••••••••••177 NEVADA •••••••••••••••••••••••••••••••177 MEGGEN Chapter 12-EVAPORITE BA SIN ANALYSIS ••••••159 ••••••••••••••••••••••••••••••178 SELWYN BASIN INTRODUCTION •••••••••••••••••••••••••159 •••••••••••••••••••••••••••178 CLIMATIC CoNSTRAINTS •••••••••••••••••••••159 TECTONIC SETTING ••••••••••••••••••••••178 INTRACONTINENTAL BASINS ARKANSAS • • • • • • • • • • • • • • • • • • • 159 •••••••••••••••••••••••••••••179 MARINE BASINS NEVADA ••••••••••••••••••••••••••159 •••••••••••••••••••••••••••••••179 MEGGEN The Interface Between Inflow and Outflow •••••159 ••••••••••••••••••••••••••••••179 SELWYN BASIN Heat Effects • • • • • • • • • • • • • • • • • • • • • • • • • • 160 •••••••••••••••••••••••••••180
vi GEOCHEMISTRY •••••••••••••••••••••••••180 PHANEROZOIC DEPOSITS: COLORADO PLATEAU WHOLE-ROCK CHEMISTRY ••••••••••••••••••••180 TYPE ••••••••••••••••••••••••••••••••191 SuLFUR IsoTOPES THE BASIN AND THE BASIN FILL •••••••••••••••••••••••••181 ••••••••••••••••192 DIAGENETIC SEQUENCE EXPLORATION ••••••••••••••••••••••••••183 •••••••••••••••••••••192 EXPLORATION CONCLUSIONS ••••••••••••••••••••••••••183 •••••••••••••••••••••••••••192
REFERENCES ••••••••••••••••••••••••••••183 PHANEROZOIC DEPOSITS: ROLL-FRONT TYPE •••193 HE BASIN AND THE BASIN FILL T ••••••••••••••••194 DIAGENESIS AND MINERALIZATION ••••••••••••••194 EXPLORATION Chapter 15-URANIUM: SYNGENETIC TO •••••••••••••••••••••••••••195
DIAGENETIC DEPOSITS IN SURFICIAL DEPOSITS: CALCRETE •••••••••••••195
FORELAND BASINS •••••••••••••••••••••187 REFERENCES ••••••••••••••••••••••••••••195 PALEOPLACERS AND THE NATURE OF THE EARLY
ATMOSPHERE •••••••••••••••••••••••••187 Chapter 16-COPPER: PRODUCT OF DIAGENESIS DETRITAL NATURE OF MINERALIZATION •••••••••••187 IN RIFTED BASINS ••••••••••••••••••••••199 MoDERN VERsus ANciENT OccuRRENCES ••••••••••187 THE KUPFERSCHIEFER ••••••••••••••••••••199 EXPLORATION •••••••••••••••••••••••••••189 WHITE PINE ••••••••••••••••••••••••••••201 203 PROTEROZOIC DEPOSITS; OKLO TYPE •••••••••190 AFRICAN COPPERBELT •••••••••••••••••••• VERTICAL SEQUENCE •••••••••••••••••••••••190 COMPARISON •••••••••••••••••••••••••••204 DIAGENETIC HISTORY • • • • • • • • • • • • • • • • • • • • • • 190 EXPLORATION ••••••••••••••••••••••••••204 EXPLORATION •••••••••••••••••••••••••••191 REFERENCES ••••••••••••••••••••••••••••205
INDEX ••••••••••••••••••••••••••••••••208
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