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REVIEWS IN ECONOMIC GEOLOGY
(ISSN 0741-0123) Volume 2
GEOLOGY AND GEOCHEMISTRY OF
EPITHERMAL SYSTEMS ISBN 0-9613074-1-2
Volume Editors:
B. R. BERGER P. M . BETHKE Branch of Exploraton Geochemistry Branch of Resource Analysis
U.S. Geological Survey U.S. Geological Survey MS 973 MS 959, National Center
Box 25046, Federal Center Reston, VA 22092 Denver, CO 80225-0046
Series Editor: JAMES M . ROBERTSON New Mexico Bureau of Mines & Mineral Resources Campus Station Socorro, NM 87801
SOCIETY OF ECONOMIC GEOLOGISTS
GEOLOGY & GEOCHEMISTRY OF EPITHERMAL SYSTEMS
CONTENTS
FOREWORD z
PREFACE xi
BIOGRAPHIES xvi
CHAPTER 1
THE GEOTHERMAL FRAMEWORK OF EPITHERMAL DEPOSITS
R. W. Henley
INTRODUCTION 1
HYDROTHERMAL SYSTEMS IN GENERAL 1
Collision-Related Amagmatlc Hydrothermal Systems Te r r e s t r i a l Magma-Related Hydrotheraal Systems
TERRESTRIAL MAGMATIC-HYDROTHERMAL SYSTEMS 4
Large Scale Structure Natural Discharges Hydrothermal Eruption Vents Heat and Mass Flow In Geothermal Systems
CHEMISTRY OF GEOTHERMAL DISCHARGES 11
EPITHERMAL ORE-FORMING SYSTEMS 12
Requlrememts for Ore Deposition Chemistry of Systems Responsible for Ore Formation Chemical and Physical Processes In Ore Formation Host-Rock Relations
SUMMARY 19
EPILOGUE 21
ACKNOWLEDGMENTS 21
REFERENCES 21
CHAPTER 2
A PRACTICAL GUIDE TO THE THERMODYNAMICS OF GEOTHERMAL FLUIDS AND HYDROTHERMAL ORE DEPOSITS
R. W. Henley and K. L. Brown
nmoDucTioN 25
'T":~CICAL CHARACTERISTICS OF THE BROADLANDS GEOTHERMAL SYSTEM 25
CHEMISTRY 26
iii
FLUID-MINERAL EQUILIBRIA: ALTERATION MINERALOGY 28
FLUID-MINERAL EQUILIBRIA: TRACE-METAL CONTENTS 32
Lead Gold Other Metals: Copper, S l i v e r , and Arsenic
MINERAL DEPOSITION 36
S i l i c a Calclte Metal Sulfides and Gold
ACKNOWLEDGMENTS 41
REVIEW QUESTIONS 41
REFERENCES 41
APPENDIX 43
CHAPTER 3
THE BEHAVIOR OF SILICA IN HYDROTHERMAL SOLUTIONS R. 0. Foumier
INTRODUCTION 45
SOLUBILITIES OF SILICA MINERALS 45
THE BEHAVIOR OF DISSOLVED SILICA IN HOT-SPRING SYSTEMS 46
ALKALINE WATERS 48
ACID WATERS 60
REACTION WITH GLASS 51
AMORPHOUS SILICA-CHALCEDONY RELATIONS 51
SPECULATIONS REGARDING SOME TEXTURES OF QUARTZ 51
Jasperold and Massive Replacement of Limestone by S i l i c a Quartz Solubility at High Temperatures
CONCLUSIONS 55
ACKNOWLEDGMENTS 56
REFERENCES 56
APPENDIX 60
iv
CHAPTER 4
CARBONATE TRANSPORT AND DEPOSITION IN THE EPITHERMAL ENVIRONMENT
ff. 0. Foumier
INTRODUCTION 63
CO2 DISSOLVED IN AQUEOUS SOLUTIONS 63
THE SOLUBILITY OF CALCITE IN AQUEOUS SOLUTIONS 67
SUMMARY 71
REFERENCES 71
CHAPTER 5
FLUID-INCLUSION SYSTEMATICS IN EPITHERMAL SYSTEMS R, J . Bodnar, T. J . Reynolds, and C. A. Kuehn
INTRODUCTION 73
INFORMATION AVAILABLE FROM FLUID-INCLUSION PETROGRAPHY 73
IDENTIFICATION OF FLUID INCLUSIONS TRAPPED FROM BOILING SOLUTIONS 79
IDENTIFICATION OF GASES IN FLUID INCLUSIONS FROM THE EPITHERMAL
ENVIRONMENT 83
INTERPRETATION OF FLUID INCLUSIONS FROM THE EPITHERMAL ENVIRONMENT 93
APPLICATION OF FLUID INCLUSIONS IN EXPLORATION FOR EPITHERMAL
PRECIOUS-METAL DEPOSITS 94
SUGGESTIONS FOR FUTURE FLUID-INCLUSION RESEARCH 95
REFERENCES 96
CHAPTER 6
LIGHT STABLE-ISOTOPE SYSTEMATICS IN THE EPITHERMAL ENVIRONMENT
C. W. Field and R. H. Fifarek
INTRODUCTION 99
CONVENTIONS, SYSTEMATICS, AND RATIONALE 99
Fractionation Equilibrium Reaction Applications
GEOLOGIC DISTRIBUTIONS 110
Hydrogen and Oxygen Carbon Sulfur
EPITHERMAL DEPOSITS 113
Carbon Sulfur
V
Hydrogen and Oxygen
SUMMARY
REFERENCES
124
125
CHAPTER 7
GEOLOGIC, MINERALOGIC, AND GEOCHEMICAL CHARACTERISTICS OF VOLCANIC-HOSTED EPITHERMAL PRECIOUS-METAL DEPOSITS
D. 0. Hayha, P. M. Bethke, P. Heald, and N. K. Foley
INTRODUCTION 129
SUMMARY OF THE CHARACTERISTICS OF VOLCANIC-HOSTED EPITHERMAL ORE DEPOSITS 129
Characteristics of Adularia-Serlclte-Type Deposits Characteristics of Acld-Sulfate-Type Deposits Summary of Characteristics
THE ADULARIA-SERICITE ENVIRONMENT: CREEDE AS AN EXAMPLE 136
Creede as an Exemplar Summary of Important Studies Geologic and Mlneraloglc Characteristics Geochemlcal Environment Hydrologlc Environment Boiling and Mixing In the Ore Zone Summary of Creede Mineralization
THE ACID-SULFATE ENVIRONMENT: SUMMITVILLE AS AN EXAMPLE 151
Geologic and Mlneraloglc Characteristics Geochemlcal Environment Summary of Summltvllle Mineralization
GEOTHERMAL INTERPRETATION OF VOLCANIC-HOSTED EPITHERMAL DEPOSITS 158
Adularla-Serlclte Deposits Acld-Sulfate Deposits
MECHANISMS OF ACID-SULFATE ALTERATION 159
ACKNOWLEDGMENTS 162
REFERENCES 162
CHAPTER 8
GEOLOGIC CHARACTERISTICS OF SEDIMENT-HOSTED, DISSEMINATED PRECIOUS-METAL DEPOSITS IN THE WESTERN UNITED STATES
W. C. Bagby and B. R. Berger
INTRODUCTION 169
CLASSIFICATION 169
REGIONAL GEOLOGIC CHARACTERISTICS OF DEPOSITS IN MINERAL TRENDS
AND ISOLATED DEPOSITS 172
The Getchell Trend The CarlIn Trend
vi
The Cortez Trend Isolated Deposits
GEOLOGIC CHARACTERISTICS OF THREE END-MEMBER, SEDIMENT-HOSTED, DISSEMINATED PRECIOUS-METAL DEPOSITS 183
Carlln Taylor Preble
GENERAL ASPECTS OF TRACE ELEMENT AND STABLE-ISOTOPE GEOCHEMISTRY 189
SUMMARY OF GEOLOGIC CHARACTERISTICS 192
Regional and D i s t r i c t Scale Deposit Scale
ENVIRONMENT OF FORMATION .195
EXPLORATION APPLICATION 195
INFLUENCE OF GEOLOGIC CHARACTERISTICS ON MINING 196
Grade and Tonnage Mlneablllty
REFERENCES 199
CHAPTER 9
RELATIONSHIP OF TRACE-ELEMENT PATTERNS TO ALTERATION AND MORPHOLOGY IN EPITHERMAL PRECIOUS-METAL DEPOSITS M. L. Silherman and B. R. Berger
INTRODUCTION 203
GEOTHERMAL SYSTEMS 204
Morphology and Characteristics Alteration Patterns Geochemlcal Zones
EPITHERMAL ORE DEPOSITS 208
Morphology and Characteristics Alteration Patterns
NATURE OF FLUIDS INVOLVED IN GEOTHERMAL SYSTEMS AND EPITHERMAL
ORE DEPOSITS 213
TIMING 214
GEOCHEMICAL ZONING IN EPITHERMAL DEPOSITS 214
BODIE MINING DISTRICT 215
Large-scale Vertical Zoning at Bodle Bluff—The Big Picture Detailed Lateral Zoning
PARAMOUNT MINING DISTRICT—VERTICAL ZONING 224
SUMMARY 227
vii
ACKNOWLEDGMENTS 228
REFERENCES 230
CHAPTER 10
RELATIONSHIPS OF TRACE-ELEMENT PATTERNS TO GEOLOGY IN HOT-SPiaNG-TYPE PRECIOHS-METAL DEPOSITS
S. R. Berger and M. L. Silberman
INTRODUCTION 233
CONTROLS ON TRACE-ELEMENT PATTERNS 233
TRACE-ELEMENT PATTERNS IN STUDIED DEPOSITS 235
Hasbrouck Mountain, Nevada Round Mountain, Nevada
DISCUSSION 245
REFERENCES 246
CHAPTER 11
BOILING, COOLING, AND OXIDATION IN EPITHERMAL SYSTEMS: A NDMERICAL MODELING APPROACH M. H. Reed and R. F. Spyoher
INTRODUCTION 249
BOILING 249
BOILING RESULTS 252
DISCUSSION OF BOILING AND COOLING 252
Sulfide and Carbonate Mineral Precipitation Precipitation of S i l i c a t e s Boiling Without Fractionation and Cooling Only
SUPER- AND SUB-ISOENTHALPIC BOILING 258
BOILING AND GOLD PRECIPITATION 261
THE HOT-SPRING ENVIRONMENT 262
Condensation of the Boiled Gas Oxidation of Gases to Produce Acld-Sulfate Waters Reaction of Gases with Meteoric Ground Water Gold Precipitation from Mixing of Acld-Sulfate Water
with Boiled Aqueous Phase Gold Precipitation from Mixing of Oxygenated Ground Water with Boiled Aqueous Phase
SUMMARY 269
ACKNOWLEDGMENTS 270
REFERENCES 270
viii
CHAPTER 12
USING GEOLOGICAL INFORMATION TO DEVELOP EXPLORATION STRATEGIES FOR EPITHERMAL DEPOSITS
S. S. Mams
INTRODUCTION 273
SOME CONSIDERATIONS IN THE USE OF GEOLOGICAL INFORMATION
IN EXPLORATION 273
STRATEGIC FACTORS 274
Organizational Objectives
Commodity Prices Financial Resources Exploration Organization Regulations and Land Av a i l a b i l i t y Competitor Activity Previous Exploration Geologic Information Exploration Methods Opportunities Risk
HUMAN FACTORS 279
Personal Objectives Education and Training Problem Solving Intuition and Creativity Uncertainty Aversion to Loss
DEVELOPMENT OF MINERAL-DEPOSIT MODELS 282
Organization of Geologic Information Model Terminology Level of Model Development
DATA-PROCESS-CRITERIA MODEL 286
Definition of a Mineral-Deposit Type Compilation of Analog Deposits Selection of Geologic Data Data-Process Linking Identification of Formation Processes Evaluation of Data-Process Links Selection of Diagnostic C r i t e r i a Evaluation of Data-Process-Crlterla Model Application of Data-Process-Crlterla Model to Exploration Summary of Data-Process-Crlterla Model
CONCLUSIONS 296
REFERENCES 297
TABLE OF CONVERSION FACTORS Inside Back Cover
ix