Reviews in Economic Geology, Vol. 2

Reviews in
Economic Geology
Volume 2
GEOLOGY AND
GEOCHEMISTRY OF
EPITHERMAL SYSTEMS
CONTENTS
The Geothermal Framework for Epithermal Deposits
R.W. Henley
A Practical Guide to the Thermodynamics of Geothermal
Fluids Hydrothermal Ore Deposits
R.W. Henley and K.L. Brown
The Behavior of Silica in Hydrothermal Solutions
R.O. Fournier
Carbonate Transport and Deposition in the Epithermal Environment
R.O. Fournier
Fluid Inclusion Systematics in Epithermal Systems
R.J. Bodnar, T.J. Reynolds, and C.A. Kuehn
Light Stable-Isotope Systematics in the Epithermal Environment
Geologic, Mineralogic, and Geochemical
Characteristics of Volcanic-Hosted Epithermal
Precious-Metal Deposits
C.W. Field and R.H. Fifarek
D.O. Hayba, P.M. Bethke, P. Heald, and N.K. Foley
Geologic Characteristics of Sediment-Hosted, Disseminated
Precious-Metal Deposits in the Western United States
W.C. Bagby and B.R. Berger
Relationship of Trace-Element Patterns to Alteration and
Morphology in Epithermal Precious-Metal Deposits
M.L. Silberman and B.R. Berger
Relationship of Trace-Element Patterns to Geology in
Hot-Spring Type Precious-Metal Deposits
B.R. Berger and M.L. Silberman
Boiling, Cooling, and Oxidation in Epithermal Systems:
A Numerical Modeling Approach
M.H. Reed and N. Spycher
Using Geological Information to Develop Exploration
Strategies for Epithermal Deposits
S.S. Adams
Editors
B.R. Berger and P.M. Bethke
SOCIETY OF ECONOMIC GEOLOGISTS, INC.
Society of Economic Geologists, Inc.
Reviews in Economic Geology, Vol. 2
Geology and Geochemistry of Epithermal Systems
B.R. Berger and P.M. Bethke, 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: 978-1-629495-60-6
The Authors:
Robert 0. Fournier
Samuel S. Adams
Branch of Igneous and Geothermal Processes
3030 Third Street
Boulder, CO 80302
U.S Geological Survey
MS 910
William C. Bagby
Branch of Western Mineral Resources
345 Middlefield Road
Menlo Park, CA 94025
U.S. Geological Survey
Daniel 0. Hayba
MS 901
345 Middlefield Road
Branch of Resource Analysis
Menlo Park, CA 94025
U.S. Geological Survey
MS 959, National Center
B. R. Berger
Branch of Exploration Geochemistry
Reston, VA 22092
U.S. Geological Survey
Pamela Heald
Branch of Resource Analysis
.
U.S. Geological Survey
MS 959, National Center
Reston, VA 22092
MS 973
Box 25046, Federal Center
Denver, CO 80225-0046
Philip M. Bethke
Branch of Resource Analysis
R. W. Henley
U.S. Geological Survey
Chemistry Divsion
MS 959, National Center
D.S.I.R., Private Bag
Taupo
Reston, VA 22092
New Zealand
R. J. Bodnar
Department of Geological Sciences
Virginia Polytechnic Institute and State University
C. A. Kuehn
Blacksburg, VA 20461
The Pennsylvania State University
Department of Geosciences
University Park, PA 16802
K. L. Brown
Chemistry Division
Mark H. Reed
D.S.I.R., Private Bag
Department of Geology
Taupo
University of Oregon
New Zealand
Eugene, OR 97403
Cyrus W. Field
T. J. Reynolds
FLUID, Inc.
Department of Geology
Oregon State University
P.O. Box 6873
Corvallis, OR 97331-5506
Denver, CO 80206
Richard H. Fifarek
M. L. Silberman
Department of Geology
Branch of Exploration Geochemistry
U.S. Geological Survey
MS 912
Southern Illinois University
Carbondale, IL 62901
Box 25046, Federal Center
Denver, CO 80225-0046
N. K. Foley
Branch of Resource Analysis
N. Spycher
U.S. Geological Survey
Department of Geology
MS 959, National Center
University of Oregon
Eugene, OR 97403
Reston, VA 22092
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GEOLOGY & GEOCHEMISTRY OF EPITHERMAL SYSTEMS
CONTENTS
FOREWORD
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PREFACE
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B I OGRAPHIES
CHAPTER 1
THE GEOTHERMAL FRAMEWORK OF EPITHERMAL DEPOSITS
R. W. Henley
INTRODUCT ION
HYDROTHERMAL SYSTEMS IN GENERAL
Co l l i s ion-Related Amagma t ic Hydro thermal S y s tems
Terre s trial Magma-Rel a t e d Hydro thermal Sys tems
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TERRESTRIAL MAGMATIC-HYDROTHERMAL SYSTEMS
Large Scale S t ructure
Na tura l D i s charge s
Hydrothermal Erup t i on Vents
He a t and Ma s s Fl ow in Geothermal Sys tems
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CHEMISTRY OF GEOTHERMAL D I S CHARGES
EPITHERMAL ORE-FORM ING SY STEMS
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Re quirememts for Ore Dep o s i t ion
Chemis try o f Sys tems Re s pons ible for Ore Fo rmation
Chemical and Phy s i ca l Proce s s e s in Ore Fo rmation
Ho s t-Ro ck Relat ions
SUMMARY
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EP ILOGUE
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ACKNOWLEDGMENTS
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REFERENCE S
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CHAPTER 2
A PRACTICAL GUIDE TO THE THERMODYNAMICS OF GEOTHERMAL FLUIDS AND
HYDROTHERMAL ORE DEPOSITS
R. w. Henley and K. L. fuoo'/Jn
INTRODUCTION
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GEOLOG I CAL CHARACTERI S T I C S OF THE BROADLANDS GEOTHERMAL SYSTEM
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FLU ID CHEMISTRY
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FLUID-MINERAL EQUILIBRIA :
ALTERATION MINERALOGY . . . . . . .
FLUID-MINERAL EQUILIBRIA :
TRACE-METAL CONTENTS
Lead
Gol d
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Copper, Sil ver, and Ars e nic
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MINERAL DEPO S I T ION
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Silica
caiCfte
Met a l S u l f id e s and Gold
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ACKNOWLEDGMENTS
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REV IEW QUE S TIONS
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REFERENCE S
APPENDI X
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CHAPTER 3
TBR BEHAVIOR OF SILICA IN HYDROTHERMAL SOLUTIONS
R. 0. Fournie1'
INTRODUCTION
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SOLUBILITIES OF S IL I CA MINERALS
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THE BEHAV IOR OF D I S SOLVED S IL I CA IN HOT- SPRING SYSTEMS . . . . . . . . . . . . . . .
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ALKALINE WATERS
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ACID WATERS
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REACTION WITH GLA S S
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AMORPHOUS S I L I C A- CHALCEDONY RELATIONS
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SPECULATIONS REGARDING SOME TEXTURES OF QUARTZ
Ja speroid and Mas s ive Replacement of Lime s t one by Sil ica
quart z Solub i l i t y a t High Tempera tures
C ONCLU S IONS
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ACKNOWLEDGMENTS
REFERENCE S
APPENDIX
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CHAPTER 4
CARBONATE TRANSPORT AND DEPOSITION IN THE EPITHERMAL ENVIRONMENT
R. 0. Four>nie1'
INTRODUCTION
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DI S SOLVED IN AQUEOU S SOLUTIONS
THE SOLUBILITY OF CALCITE IN AQUEOU S SOLUTIONS
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SUMMARY
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REFERENCE S
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CHAPTER 5
FLUID-INCLUSION SYSTEMATICS IN EPITHERMAL SYSTEMS
R. J. Bodna1', T. J. ReynoLds, and C. A. Kuehn
INTRODUCTION
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INFORMATION AVAILABLE FROM FLUID-INCLU SION PETROG RAPHY
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IDENTIFICATION OF FLUID INCLU SIONS TRAPPED FROM BOILING SOLUTIONS
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IDENTIFICATION OF GAS E S IN FLUID INCLU SIONS FROM THE EPITHERMAL
ENVIRONMENT
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INTERPRETATION OF FLUID INCLU SIONS FROM THE EPITHERMAL ENVIRONMENT
APPLICATION OF FLUID INCLU SIONS IN EXPLORATION FOR EPITHERMAL
PRECIOU S-METAL DEPOSITS
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SUGGESTIONS FOR FUTURE FLUID-INCLU SION RE SEARCH
REFERENCE S
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CHAPTER 6
LIGHT STABLE-ISOTOPE SYSTEMATICS IN THE EPITHERMAL ENVIRONMENT
C. W. FieLd and R. H. Fifa1'ek
INTRODUCTION
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CONVENTIONS , SYSTEMATI C S , AND RATIONALE
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Fra c t iona t i on
Equ i l ibrium Rea c t ion
App l icat ions
GEOLOGIC DI STRIBUTIONS
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Hydrogen and Oxygen
Carbon
Sul fur
EPITHERMAL DEPOSITS
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Hyd rogen and Oxyg en
SUMMARY
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RE FERENCE S
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CHAPTER 7
GEOLOGIC, MINERALOGIC, AND GEOCHEMICAL CHARACTERISTICS OF
VOLCANIQ-HOSTED EPITHERMAL PRECIOUs-METAL DEPOSITS
D. 0. Hayba, P. M. Bethke, P. Heatd, and N. K. Fotey
INTRODU CTION
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SUMMARY OF THE CHARACTERISTI C S OF VOLCANI C-HOSTED EPITHERMAL ORE DEPOSITS
Charac t e r i s t i c s o f Adu laria- Se r i c i t e-Typ e Dep o s i t s
Chara c t e r i s t i c s o f Ac i d-Sul fate-Type Depo s i t s
Summary o f Cha rac t e r i s t ics
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GEOTHERMAL INTERPRETATION OF VOLCANI C-HO STED EPITHERMAL nEPOSITS
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THE ADULARIA- S ERICITE ENVIRONMENT :
CREEDE AS AN EXAMPLE
Creede as an Exemp lar
Summ a ry o f Importan t Stud i e s
Geolog i c and Mineralogic Charac t e r i s t i c s
Geochemical Env i ronment
Hydrologic Env i ronment
Boil ing and Mixing in the Ore Zone
Summary o f Creede Mineral i z a t i on
THE ACID- SULFATE ENVIRONMENT :
SUMMITVILLE AS AN EXAMPLE
Geolog ic and Mine ralogic Charac t e r i s t i c s
Geochemical Env i ronment
Summ a ry of Summi tville Minera l i z a t i on
Adu laria- Se r i c i t e Depo s i t s
Ac id-Su l f a t e Dep o s i t s
ME CHANISMS O F ACID- SULFATE ALTERATION
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ACKNOWLEDGMENTS
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REFERENCE S
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CHAPTER 8
GEOLOGIC CHARACTERISTICS OF SEDIMENT-HOSTED,
DISSEMINATED
PRECIOUs-METAL DEPOSITS IN THE WESTERN UNITED STATES
W. C. Bagby and B. R. Berger
INTRODUCTION
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CLAS SIFICATION
REGIONAL GEOLOGI C CHARACTERISTI C S OF DEPOSITS IN MINERAL TRENDS
AND ISOLATED DEPO SITS
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The Getche l l Trend
The Carlin Trend
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The Co r t e z Trend
Is o l a t e d Depos i t s
GEOLOGIC CHARACTERI STIC S O F THREE END-MEMBER , SEDIMENT-HOSTED ,
DI SSEMINATED PRECIOU S-METAL DEPOSITS
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Carlin
Taylor
Preble
GENERAL ASPECTS OF TRACE ELEMENT AND STABLE-I SOTOPE GEOCHEMISTRY
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SUMMARY OF GEOLOGIC CHARACTERI S TIC S
Re g ional and D i s t r i c t Sc ale
Depos i t Sc ale
ENVIRONMENT OF FORMATION
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EXPLORATION APPLICATION
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INFLUENCE OF GEOLOGIC CHARACTERI STIC S ON MINING
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Grade and Tonnage
Mine ab i l i ty
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CHAPTER 9
:RELATIONSHIP OF TRACE-ELEMENT PATTERNS TO ALTERATION AND MORPHOLOGY
IN EPITHERMAL PRECIOUs-METAL DEPOSITS
M. L. Silberman and B. R. Berger
INTRODUCTION
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GEOTHERMAL SY STEMS
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Morphology and Charac t e r i s t i cs
Al t e ra t i on Pa t t e rns
Geo chemical Zone s
EPITHERMAL ORE DEPOSITS
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Morphology and Charac t e r i s t ic s
Al terat ion Pat t e rns
NATURE OF FLUID S INVOLVED IN GEOTHERMAL SYSTEMS AND EPITHERMAL
ORE DEPOSITS
TIMING
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GEOCHEMICAL ZONING IN EPITHERMAL DEP O SITS
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BODIE MINING DISTRICT
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Large- scale Vertical Zoning at Bod i e Bluf f--The Big Pic ture
De t a i le d Lat e ra l Zoning
PARAMOUNT MINING DISTRICT- -VERTICAL ZONING
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SUMMARY
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A CKNOWLEDGMENTS
REFERENCES
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CHAPTER 10
RELATIONSHIPS OF TRACE-ELEMENT PATTERNS TO GEOLOGY
IN HOT-SPRING-TYPE PRECIOUs-METAL DEPOSITS
B. R. Berger and M. L. Silberman
INTRODU CTION
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CONTROL S ON TRACE-ELEMENT PATTERNS
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TRACE-ELEMENT PATTERN S IN STUDIED DEPOSITS
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Ha sbrouck Mount ain , Ne vada
Round Mount ain , Ne vada
DI S CU S SION
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REFERENCES
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CHAPTER 1 1
BOILING,
COOLING, AND OXIDATION IN EPITHERMAL SYSTEMS:
A NUMERICAL MODELING APPROACH
M. H. Reed and N. F. Spyaher
INTRODUCTION
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BOILING
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BOILING RESULTS
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DISCU S SION OF BOILING AND COOLING
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Sul f i de and Carbona t e M inera l Precipi t a t ion
Pre c i p i t a t i on o f S i l icates
Bo i l i ng Wi thout Frac t i onat i on and Cool ing Onl y
SUPER- AND SU B-I SOENTHALPIC BOILING
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BOILING AND GOLD PRE CIPITATION
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THE HOT-SPRING ENVIRONMENT
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Conden s a t ion of the Bo iled Gas
Oxida t i on o f Ga s e s t o Produce Ac i d- S u l f a t e Wat e r s
Re act ion o f Ga s e s with Me teoric G r ound Wat e r
G o l d P r e c i p i t a t ion f rom M ixing o f Ac id- Su l f a t e Wa t e r
w i t h Bo i l e d Aqueous Phas e
Go ld P r e c i p i t a t ion f rom Mixing of Oxyg enated Ground
Wa t e r wi th Bo iled Aqueous Phas e
SUMMARY
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ACKNOWLEDGMENTS
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REFERENCES
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viii
OIDW�Rl2
USING GEOLOGICAL INFORMATION TO DEVELOP EXPLORATION STRA�GIES
FOR EPITHERMAL DEPOSITS
S. S. Adams
INTRODUCTION
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S OME CONSIDERATIONS IN THE USE OF GEOLOGICAL INFORMATION
IN EXPLORATION
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STRATEGIC FACTORS
Organ i z a t i onal Obje c t ives
Commod i ty Prices
Financ ial Re s ourc e s
Explora t ion Organi zat ion
Regu l a t i ons and Land Avai l abi l i t y
Compet i t o r Act ivity
Previous Exp lorat ion
Geolog i c Inf o rma t ion
Explora t i on Me thod s
Opportun i t i e s
Ri sk
HUMAN FACTORS
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Personal Objec t ives
Educat i on and Training
Problem Solv ing
Intu i t ion and Crea t i v i t y
Uncertainty
Avers ion t o Lo s s
DEVELOPMENT OF MINERAL-DEPO SIT MODELS
Organ i z a t ion of Geologic Informat i on
Model Te rminology
Level o f Mod e l Developmen t
DATA- P RO CE S&- C RITERIA MODEL
De f in i t ion of a Mine ra l-Depo s it Type
Comp i l a t i on of Analog Depo s i t s
Se l e c t ion o f G e o l o g i c Dat a
Dat a-Proce s s Linking
Ident i f i c a t ion o f Format ion Proce s s e s
Evaluat ion o f Dat a-Proc e s s Links
Se l e c t ion of Diagno s t ic Cri t e r i a
Evalua t i on o f Data-Proc e s s - Cr i t eria Mode l
App l ica t i on o f Data-Proce s s-Criteria Model t o Explorat i on
Summary of Da t a-Proc e s s-Gr i t e r i a Model
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CONCLU SIONS
REFERENCE S
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TABLE OF CONVERSION FACTORS
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In s i de Back Cover
FOREWORD
Exploration Geochem istry, U.S. G eological Survey,
Denver, Colorado. These ladies, M arilyn A. Billone,
Candace A. Vassalluzzo, and especially Pamela S.
Detra and Dorothy B. Wesson, accom plished the long,
arduous, and often frustrating j ob of assem bling,
editing, and form attin g the book with a uniformly high
level of professionalism and good che er. Their efforts
are gratefully acknowledged. Carol Hjellming of the
New Mexico Bureau of Mines and Mineral Resources
(NMBM MR) editing staff checke d, balanced, and
helped interpret the chemical equations; Lynne McNeil
(N MBMMR) form at ted the cutlines. Lastly, I wish to
express my continuing appreciation to the New Mexico
Bureau of Mines and Min eral Resources and its
Director, Frank Kot tlowski, who provide the Series
Editor with time, space, and encouragement.
Geology and Geochem istry of Epithermal
Systems--Volume 2 of Reviews in Economic
Geology--was created to accompany a Society of
E conomic Geologist s (SE G) short course of the same
nam e that was given in October, 1 9 85, prior to the
annual m eetings of the Geological Society of Am erica
and Associate d Societies in Orlando, Florida. As was
the case with Volum e 1, the final published version of
Volum e 2 unfo rtunately postdates the short course by
som e m onths.
Geology and Geochemistry of Epithermal
Systems presents a synthesis of the current under­
standing of the processes responsible for the
concentration of m etals (especially gold and silver) in
near-surface environments, provides an overview of
the system atics of the m ost important appr oaches to
the study of epithermal ores and processes, and
summ arizes the geology of both sediment-hoste d and
volcanic-hoste d epitherm al precious-metal deposits.
After the volum e edi tors, the m ost signifi cant
contributors to the production of this volum e were the
mem bers of the Editorial Suppo rt Group, Branch of
James M. Robertson
Series Editor
Socorro, N M
M arch, 1 986
X
PREFACE
In a speech on May 1 0, 1 9 1 1 , before the
Geological Society of Washington, Waldemar Lindgren
described his system atic classification of all types of
mineral deposits.
One of his categories included
deposits related to intrusive and eruptive igneous rocks
that form veins at shallow depths that contain open­
cavity filling textures and that have been a primary
source of "bonanza" grades of gold and silver--the
epitherm al deposits. Historically, most of the ores in
epithermal systems have been mined from quartz
veins, breccias, or disseminations that are as.sociated
with non-marine volcanic rocks. Open-space filling
textures and structures are common--com b structure,
crustification, symm etrical banding, and crystal-lined
vugs. Ore minerals include native gold, native silver,
electr um , argentite, sulfosalts, tellurides, and
selenides and often the com mon sulfides sphalerite,
galena, and chalcopyrite. Common gangue minerals
are quartz, adularia, calcite, barite, rhodochrosite, and
fluorite. Alteration is commonly widespread in epi­
thermal systems, particularly in the upper portions of
the vein systems; among the alteration phases are
quartz, adularia, illite, chlorite, alunite, and kaolinite.
Lindgren ( 1 928) recognized the dif ficulty of
developing a rigid subsidiary classification scheme for
epithermal deposits; he separated them into six
categories:
1.
2.
3.
4.
5.
6.
Gold deposits
Argentite-gold deposits
Argentite deposits
Gold selenide deposits
Gold telluride deposits
Gold telluride deposits with alunite
Nolan ( 1 933) and Fer guson ( 1 929) felt that few of
these six characteristics were restricted enough to be
diagnostic and proposed only two classes of epithermal
systems based on the weight ratio of gold to silver,
silver-gold, and gold-silver. Based on his experience
with deposits in Nevada, Ferguson ( 1 929) found that
there is a bim odal distribution of gold-silver ratios,
and Nolan ( 1 933) felt that the bim odality was due to
genetic processes.
For the silver-gold deposits, Nolan ( 1 9 33) noticed
that through-going fault fissures control the ore and
felt that this implies a deep origin for the source of
the m etals. Nolan ( 1 933) also n oted that the precious­
metal ores are ver y com monly sharply limited above
and below by approxim ately parallel surfaces refer red
to as the ore "horizon." He suggested that these limits
are related to tem perature. Base metals tend to
increase at and below the base of the lower surface of
the precious-metal ore. Figure 1 is a longitudinal,
vertical proj ection of the Last Chance-Confidence
silver-gold vein in the Mogollon mining district, New
C o nfi d e n c e
La s t C h a n c e
70o-FT LEVEL
500
0
I 000 FEET
900-FT LEVEL
Figure P.l. Vertical, lorigitudinal projection of the Confidence-last Chance vein in the Mogollon
m1n1ng district, New Mexico (Ferguson, 19 2 7). Banded quartz vein is continuous along strike
with ore grade material occurring in specific masses {stippled areas ) in the vein. The tops
and bottoms of the silver-ridh ore bodies describe near parallel surfaces referred to as the
"ore hor i zon."
xi
I
Mexico (Ferguson, 1 927) il lustrating the ore horizons,
the shape of ore bodies, and the typical distribution of
ore grades within a continuous banded quartz-adularia­
sericite vein.
Burbank ( 1 9 3 3) reported that base
m etals appear to be m ore abundant in silver-gold
deposits in regions of sedimentary rocks with overlying
volcanic rocks and in thick, volcanic sequences with a
long history of volcanic activity. In contrast to the
silver-gold deposits, Nolan ( 1 933) noted that gold­
silver deposits are com monly within or close to small,
shallow intrusive bodies and that the ore-controlling
fracture systems are frequently more discontinuous
than those associated with silver-gold deposits. The
gold-silver ores are also m ore irregular in distribution
than the silver-gold ores.
Nolan felt that this
irregularity may be related to the com plex thermal
regimes in these types of systems due to the shallow
intrusive activity. Figure 2a shows a series of plan
views of the January mine, Goldfield mining distrct,
Nevada and a cross section through the January shaft
( Ransom e, 1 909) showing the relationships of ore to
quartz-alunite-kaolinite replaced wallrock ("ledge
m atter" ) and the host rocks. Figure 2b shows two
cross sections from Ransome ( 1 909, p. 1 54) of the
Com bination m ine in Goldfield illustrating the
irregular vertical distribution of bonanza-grade ore
masses within the "ledge matter." Also, the ore bodies
were not persistent along strike.
Although Waldemar Lindgren ( 1 928) recognized
the correlation between epithermal systems and active
geothermal systems, it was Donald E. White ( 1 955,
1 98 1 ) who cham pioned the detailed study of active
systems and the application of the results and concepts
derived from these studies to epither mal ore deposits.
The im pact of White's leadership in the study of
hydrothermal systems, in general, and epithermal
systems, in particular, was recognized by the Society
of Economic Geologists when it held a sym posium in
w
Ore
a
JANUARY
SHAFT
I 09-FT LEVEL
I 09-FT LEVEL
51-FT LEVEL
81-FT LEVEL
232-FT LEVEL
CROSS SECTION
0
I 60-FT LEVEL
232-FT LEVEL
50
I 00
1 50 FEET
283-FT LEVEL
Figure P. 2 . a ) . Plan views of the January m ine
at selected mining levels and a cross sec­
tion through the January shaft Goldfield
mining d i s t r i ct , Nevada ( Ransome, 1 909) .
Bonanza-grade gold ores occur in replaced
dacite referred to as "ledge matter." The
ore bodies are not persistent either down­
dip or along strike, and occur both on the
hang ing wal l s ide of the ledge and on the
foot wall s ide. b ) . Two cross sections
from Ransome (1909, p. 154) of the Combina­
t ion m ine in the Gold field distr i ct. Bo­
nanza-grade gold ores occur in i rregular ,
discontinuous masses within the ledge. The
ledge fol lows a l i thologic contact and
flattens with depth.
8Q-Ft Lev•l
I 30-Ft Level
I 8Q-Ft Level
23Q-Ft Level
28o-Ft Level
xii
his hon or in February, 1 9 84 entitled: Geothermal
Syste rns and Ore Deposi ts. It clearly em phasized the
val ue of using active ge othermal areas as models of
fossil , ore-forming hydrothermal systems.
Thus, the evolution of understanding of the
geology and genesis of epithermal precious-metal
deposits has fol lowe d a pathway from the early, vividly
descriptive studies of mining districts such as the
Com stock Lode, Nevada (Becker, 1 882), Cripple Creek,
Colorado (Lindgren and Ransome, 1 906), and Waihi,
New Zealand (Bell and Fraser, 1 9 1 2) to the later,
topical studies on st ructure (Wisser , 1 960), alteration
(Hemley and Jones, 1 964), stable isotopes (Taylor,
197 3), and fluid chemistry (Barton et al., 1 977). The
most recent research on epithermal deposits has built
on these past studies and has em phasized the thermal
and com positional roles of volcanic rock terranes; the
genesis, significance , and pattern of alteration miner­
alogies; the sources of the geothermal fluids and the
paleohydrology of the systems; and, the chemical con­
ditions surrounding the deposition of the ore minerals.
The present volume is an attem pt to provide a
synthesis of the current state of geological and
geochemical knowledge of epithermal precious-metal
systems.
It follows on, and should be used in
conj unction with, the first volume in this series:
Mineral-Fluid Equilibria in H ydrothermal Systems by
Henley et al. ( 1 984). In the present volume we have
attempted to provide a framework for understanding
the system atics of controls on fluid com positions and
of metal and gangue transpor t and deposition. The
structure, dynamics, and transport properties of active
geothermal systems are use d as a starting point. With
active systems as a reference, the evolution of fluid
com positions and the constraints on m etal and gangue
transport and deposition in the epithermal environment
are explored. The systematics of fluid inclusion and
light stable-isotope applications is developed because
these two approaches have been so useful in the
development of our understanding of epitherm al
processes. The im portance of boiling, cooling, and
oxidation in transport properties of epitherm al systems
is evaluated through a numerical m odelling approach.
With the foregoing as background, the observational
base and its inter pretation for epitherm al ore deposits
in continental volcanic and sedimentary ter ranes is
explore d through sum m aries of the geologic, mineral­
ogical, and geochemical characteristis of, and trace­
element distributions in, some well-studied epithermal
ore deposits. The final chapter is devoted to the use
of our understanding of epithermal systems in the
development of exploration strategies.
This volume does not attem pt to be the final
word on epitherm al ore deposits, nor does it claim
comprehensive treatment. The absence of a chapter
on the hydrology of epithermal systems documents the
fact that our current understanding of this aspect is
woefully inadequate. It does not reflect a lack of
recognition of the im portance of hydrologic controls.
Sim ilarly, this volum e focuses on volcanic- and
sediment-hosted epithermal deposits in the cordil lera
of western North Am erica, particularly the United
States. It does not treat aspects of alkaline- or
basaltic-rock related deposits such as Cripple Creek,
Colorado, and Vatacoula, Fiji, nor does it treat the
relationship of epithermal systems to deeper hydro­
thermal systems responsible for the formation of
porphyry-type deposits. A gain our reason is the lack
of an adequate observational base.
Our primary
purpose in organizing this volume and the related Sho rt
Course has been to stim ulate critical studies to
improve our cur rent understanding of epit hermal
deposits and processes rather than to document it.
Perhaps our omissions will serve this purpose equally
as well as o ur inclusions.
REFERENCES
Barton, P . B., Jr., Bethke, P. M., Roedder , E., 1977,
Environm ent of ore deposition in the Creede
mining district, San J uan Mountains, Colorado:
III.
Progress toward interpretation of the
chemistry of the ore-forming fluid for the OH
vein: Economic Geology, v. 72, p. 1-25.
Becker, G . F., 1 882, Geology of the Com stock lode and
the W ashoe district:
U.S. Geological Survey
Monograph 3, 4 42 p.
Bell, J. M . , and Fraser, C., 1 9 1 2, The great Waihi gold
mine: New Zealand Geological Survey, B ulletin
1 5.
Burbank, W . S., 1 9 33, Epithermal base-metal deposits
in Ore deposits of the Western States: Am erican
Institute of M ining Metallurgical Engineers, New
York, Part VI, p. 64 1 -652.
Ferguson, H. G., 1 927, Geology and ore deposits of the
Mogollon mining district, New Mexico:
U.S.
Geological Survey Bul letin 787, 100 p.
Ferguson, H . G., 1 929, The mining districts of
Nevada: Economic Geology, v. 24, p. 1 3 1 - 1 4 1 .
Hemley, J. J . , and Jones, W. R . , 1 964, Chemical
aspects of hydrothermal alteration with em phasis
on hydrogen m etasom atism : Economic Geology,
v. 59, p. 538-569.
Henley, R. W., Truesdell, A. H., and Barton, P. B., Jr.,
1 9 84, Fluid-mineral equilibria in hydrothermal
systems: Society of Economic Geologists , Review
in Economic Geology, v. 1, p. 267.
Lindgren, W ., 1 928, M ineral Deposits: Third Edition,
M cGraw Hill, New York, 1 049 p.
Lindgren, W ., and Ransome, F. L., 1 906, Geology and
gold deposits of the Cripple Creek district,
Colorado: U.S. Geological Survey, Professional
Paper 54, 5 1 6 p.
Nolan, T. B., 1 9 33, Epithermal precious-m etal deposits
in Ore deposits of the Western States: A m erican
Institute of M ining Metal lurgical Engineers, New
York, Part VI, p. 623-640.
Ransome, F. L., 1 909, The geology and ore deposits of
Goldfield, Nevada:
U.S. Geological Survey
Professional Paper 66, 258 p.
Taylor, H . P . , Jr., 1 973, 1 8 /o 1 6/ 0 evidence for
meteoric-hydrothermal
alteration
and
ore
deposition in the Tonopah, Com stock Lode, and
Goldfield mining districts , Nevada:
Economic
Geology, v. 68, p. 747-7 64.
xiii
Wisser, E., 1 960, Rei a tion of ore deposition to doming
in the North American Cordil lera:. Geological
Society of Am erica, Memoir 77.
White, D. E., 1 95 5, Thermal springs and epithermal ore
deposit s: Economic Geology, Fiftieth Anniversary
Volume, p. 99- 1 54.
White, D . E., 1 98 1 , Active geothermal systems and
hydrothermal o re deposits: Economic Geology,
Sevent y-fifth A nniversary Volume, p. 392-42 3.
xiv
ACKNOWLEDGMENTS
As is tr ue for any effort of the scope of this vol­
ume, m any people in addition to the editors played key
roles along the r oad to final publication. T he time and
effort expended by each author is greatly appreciated
as are the co ntributions of the large cadre of
individual reviewers who have of fered insights and
alternative perspectives to the authors. Technical
support to the e ditors including manuscript pre paration
and revision, final format ting for publication, and
badgering of both editors and authors was provided by
the Editorial Support Group, Branch of E xploration
Geochemistr y, U .S. Geological Survey. Within this
group we would especially like to thank Pamela Detra,
Dorothy Wesson, Marilyn Billone, and Candy
Vassalluzzo. An e arlier version of this text was
assembled for use at the Society of Economic
Geologists Short Course by the B ranch of Exploration
Geochem istry Cler ical Support Group. Finally, we
would like to express appreciation for the patience of
Jamie Robertson, Series Editor, Reviews in Econom ic
Geology, and the support of the Society of Economic
Geologists.
Byron R. Ber ger
Philip M. Bethke
XV
BIOGRAPHIES
B YR ON R. BERGER received a B.A. degree in
EconomicSTGeology from Occidental College in 1 966
and a M .S. in Geology from the University of
California, Los Angeles in 1 97 5. He worked as a
petroleum exploration geologist for Standard Oil
Company of California from 1 968- 1 9 70 and a minerals
exploration geologist and research scientist for
Continental Oil Compan y from 1 9 7 1 - 1 977. He j oined
the U.S. Geological S urvey in 1 977, and has been
involved in research on epitherm al precious-m etal
deposits and the relationship of m agma genesis to ore
genesis. He is currently the Chief of the Branch of
Exploration Geochemistr y. He is an adj unct assistant
professor of geology in the Department of Geologi cal
Sciences at the University of Colorado, Boulder, where
he has taught courses on the geology and geochem istry
of epithermal ore deposits and exploration geo­
chem istr y. He is a mem ber of several professional
societies including the G eological Society of America
and the Am erican Geophysical Union.
government agencies in the areas of mineral deposits,
exploration, and resource assessm ent. His principal
research interest is the representation of data and
concepts for all types of m ineral deposits in coherent
and predictive m odels for exploration and resource
studies. He is currently a Councillor of the Society of
Economic Geologists and the Geological Society of
America.
WILLIA M� BABGY received a Ph.D. degree in Earth
Science from the University of California, Santa Cruz,
in 1 979 based on petrogenetic resear ch of Tertiar y
volcanic rocks in the Sier ra Madre Occidental,
Mexico. His industry experience includes geologic
eval uation of volcanic-hosted uranium in the
McDermitt caldera com plex, Nevada, and the bulk
mineability potential of the am ythest silver vein
system at Creede, Colorado.
Industry research
included development of an occur rence model for hot
spring-related gold deposition based on the McLaughlin
gold deposit in California. Present research interests
are focused on the genetic aspects of sediment-hosted
precious-m etal deposits.
PHILIP M. BET HKE received a B.A. degree in Geology
from Am herst College in 1 952 and a Ph.D. in Geology
{specialization in Mineralogy and Ore Deposits) from
Colum bia University in 1 957.
He was Assistant
Professor of Geology at the Missouri School of Mines
and Metallurgy {now the University of Missouri-Rolla)
from 1 95 5 to 1 959. He joined the U.S. Geological
Survey as a W AE research geologist in 1 957 and
transfer red to full time in 1 959. His research has
com bined field and laboratory approaches to the study
of hydrother mal ore deposits, particularly to
epithermal vein systems.
He has held several
adm inistrative positions with the U.S.G.S., most
recently, Chief of the Branch of Experimental
Geochemistr y and Mineralogy. He is a mem ber of
several professional societies and is cur rently a
Councillor of the Society of Economic Geologists. He
has been active in the establishment of the SEG Short
Course Series, and is currently Chairman of the Short
Course Com m ittee.
ROBERT 2:. BODNAR received an M.S. degree from
the University of Arizona and a Ph.D. degree from The
Pennsylvania State University and has been involved in
various aspects of fluid-inclusion research for the past
10 years.
He worked for 1 year as a resear ch
geochem ist in the Ore Deposits Group of Chevron Oil
Field Research Com pany and is currently an assistant
professor in the Department of Geological Sciences at
Virginia Polytechnic Institute and State University.
KEVIN BROWN received an M.S. degree in Chem istry
in 1 969 and a Ph.D. degree in Chemical
Crystallography in 1 9 72 from the University of
Auckland, New Zealand.
Except for a two-year
soj ourn at the E.T.H. in Zurich, he has worked at the
Departm ent of Scientifi c and Indust rial Resear ch, New
Zealand. Initial ly in Wellington, his research interest
centered around the crystal str uctures of organic
reaction intermediates, but he gradual ly cam e down to
earth with the crystal str uctures of some new
epithermal minerals.
In 1 98 1 , he shifted to the
Geothermal Section at Wairakei, where his present
research is concerned with experimental studies of
mineral deposition from geotherm al fl uids.
SA MUEL S. ADAMS received B.A. and M.A. degrees
from Dar t mouth College in 1 959 and 1 96 1 , and a Ph.D.
degree from Harvard University in 1 967. From 1 964 to
1 977 he served as mine geologist, exploration
geologist, exploration manager, and exploration vice
president, em ployed by International Minerals and
Chemical Corporation and then the Anaconda
Company. During this period, his work em phasized
sedim ent-hosted mineral deposits, particularly potash
and uranium. Since 1977 he has served as a lecturer
and consultant to industry, research o rganizations, and
C YRUS W. FIEL D received a B.A. degree in Geology
from Dartmouth College in 1 95 6 and M.S. and Ph.D.
degrees in Economic Geology, Geochem istry, and
Petrology from Yale University in 1 957 and 1 96 1 ,
xvi
respectively. He worked as an exploration geologist
during the sum m ers of 1 955, 1 956, and 1957 for the
Oliver Iron Mining Company and Quebec Cartier
Mining Com pany subsidiaries of the U.S. Steel
Corporation, and served as a research geologist from
1 960 to 1 963 with the Bear Creek Mining Com pany
division of Kennecott Copper Corporation. In 1 963, he
j oined the faculty of Oregon State University where he
is cur rently Professor of Geology.
His research
interests are largely concerned with the geology and
geochemistry of hydr othermal mineral deposits;
particularly the application of stable isotope and
maj or-minor-trace element investigations to their
genesis. He is a mem ber of several professional
societies and was Vice President of the Society of
Economic Geologists in 1 9 8 1 .
sili ca species in water and saline solutions. He has
also been a leader in the development of several
chemical geothermom eters and mixing models that are
now widely used in the exploration for geothermal
resources. His present research focuses mainly on
internally consistent chemical, isotopic, and hydrologic
m odels of presently active hydrothermal systems. He
has served on NATO com mittees to review geothermal
energy development programs in Iceland, France,
Greece, Port ugal, and Turkey, and other com m ittees
to review geothermal exploration programs in
Argentina and Thailand. He was Chairman of the
Organizing Committee for the 1975 United Nations
International Symposium on Geothermal Energy, and
Chairman of the Technical Program Com mittee for
the 1 9 85 GRC International Symposium on Geothermal
Energy.
He now serves on panels to oversee
geothermal developments in Costa Rica and Panam a,
and several U.S. Col'ltinental Scientific Drilling
Committees. He is a member of several societies and
has served on the Board of Directors of the
Geochemical Society and the Geothermal Resources
Council.
RICHARD H . FIFAREK received a B.S. degree in
Geology from the University of Washington in 1 974,
and M.S. and Ph.D. degrees in Geology (specialization
in Economic Geology) from Oregon State University in
1982 and 1985, respectively. From 1 9 7 4 to 1 9 84, he
worked periodically as an exploration geologist (4 yrs.)
for several mir.ing com panies, as a research assistant/
scientist (1 yr.) at the facilities of the Branch of
Isotope Geology (Denver), U.S. Geological Survey, and
as an instr ucto r for Oregon State University.
Presently, he is an assistant professor in the
Department of Geology at Southern Illinois University
where he teaches and conducts research in economic
geology and isotope geochemistry.
His research
interests include integrated geologic (field) and
geochemical investigation of massive sulfide and
epithermal Au-Ag deposits, and m odeling the isotopic
evolution of fluids and rocks in hydrothermal systems.
DANIEL 0. HAYBA received a B.A. degree in Geology
from the College of Wooster in 1976 and an M.S.
degree in Geochemistry and Mineralogy from the
Pennsylvania State University in 1979 following a
study of the Salton Sea geothermal system. From 1 978
to 1 9 80, he worked for Exxon Production Research
Com pany on com puter m odeling of ore deposits. Since
that time, he has been a research geologist with the
U.S. Geological Survey where his research has been
directed towards understanding the ore-forming
processes in epithermal systems.
NORA .!S..:. FOLE Y received a B.S. degree in Geology
and Min eralogy from the University of Michigan in
1 978 and an M.S. degree in Geological Sciences from
Virginia Polytechnic Institute and State University in
1 980. She is cur rently working towards a doctoral
degree in Geology through Virginia Polytechnic
Institute and State University. Since 1 980, she has
been a research geologist at the U.S. Geological
Survey in Reston, Virginia. Her research has included
fluid-inclusion and isotopic studies of different types
of ore deposits, including Ag- and base-metal-bearing,
epithermal deposits, sediment-hosted, stratabound,
Pb-Zn deposits, and K uroko-type massive sulfides.
PA MELA HEALD received a B.A. degree in Geology in
1971 from Vassar Col lege and an M.S. degree in
Geology from George Washington University in 1 977.
She has been a research geologist at the U.S.
Geological Survey since 1 9 72.
Her research has
included spectral reflectance and structural studies in
Nevada, with a focus on ore deposits, and
mineralogical and geochemical studies to evaluate ore­
forming processes in epithermal precious- and base­
metal deposits.
RICHARD W. HENLEY received a B.S. degree in
Geology in 1 968 from the University of London and a
Ph.D. degree in Geochemistry from The University of
Manchester in 1 9 7 1 following experimental studies of
gold transport in hydrothermal solutions and the
genesis of som e Precambrian gold deposits. He was
Lecturer in Economic Geology Memorial University of
Otago, New Zealand, from 1 9 7 1 to 1 975, and at
Memorial University, Newfoundland, until 1 9 77.
Research interests have focused on the mode of origin
of a number of dif ferent types of ore deposits
including post-metamorphic gold-tungsten veins,
porphyry copper, massive sulfide, and placer gold
deposits.
He is cur rently with the Geothermal
Chemistry Section of the Departm ent of Scientific and
Industrial Research at Wairakei, New Zealand, and a
visiting lecturer at the Auckland Geother mal
ROBERT 0. FOURNIER received an A.B. degree in
Geology in 1 9 5 4 from Harvard College and a Ph.D. in
Geology (specializing in Economic Geology, in general,
and the Ely porphyry copper deposit, in particular)
from the University of California at Berkeley in
1 958. Since then, he has been a research geologist
with the U.S. Geological Survey.
His research
interests have ranged from laborato ry studies of
mineral-water interactions at hydrothermal conditions
appropriate for shallow levels in the crust, to field
studies of presently active hydrothermal systems,
including Yellowstone National Park, Coso and Long
Valley,
California,
and
Zuni!,
G uatemala.
Experimental studies have em phasized solubilities of
xvii
Institute. Through 1 9 8 3-84, he was a Fulbright Fellow
and G uest Investigato r at the U.S. Geological Survey
and during that tim e pr oduced Volume 1 of this Review
series. His present research includes a number of
isotope and chemical studies relating to the
exploration and development of geothermal systems
and geothermal im plications for the origin of ore
deposits.
C. A. KUEHN received an M.S. degree from the
Pennsylvania State University and has 7 years of
experience in exploration for sedim ent-hosted gold
deposits. He is cur rently an NSF Resea�ch Assistant
and Ph.D. candidate at the Pennsylvania State
University and part-time employee of the U.S.
Geo ! ogical S urvey working on the Carlin gold deposit.
MARK H. REED received a B.A. degree in Chemistry
and in Geology from Carleton College in 197 1 and
M.A. and Ph.D. degrees in Geology at the University of
California, Berkeley, in 1 977. His Ph.D. research was
on the geology and geochem istry of the m assive sulfide
deposits of the West Shasta District, California. From
1 9 7 7 through 1979, he worked for the Anaconda
Minerals Company at Butte, Montana. Since that
time, he has taught and conducted research at the
University of Oregon, where he is currently Associate
Professor of Geology. His research has focuse d on
alteration and metal zoning in the porphyry copper and
large vein deposits at Butte and the geochem istry of
hydrothermal alteration, metal transport, and ore
deposition in massive sulfide and epithermal systems.
T. J. REYNOLDS received an M.S. degree from the
Uni versity of Arizona and has been an exploration
xviii
geologist specializing in the application of fluid
inclusions to mineral e xploration for the past 5 years.
MILES b. SILBER MAN received a B.S. degree from the
City University of New York and M .S . and Ph.D.
degrees from the University of Rochester, New York.
He is a m ember of the B ranch of Exploration Geo­
chem istr y of the U.S. Geological Survey, with current
assignments to the Redding, California (CUS MAP)
project, and to the study of the geochemistry of
volcanic and metamorphic-hosted gold deposits in the
western U.S. and northern Mexico. Previous work for
the U.S;G.S. included geochronological, geochemical,
and regional geological studies of precious- and base­
m etal deposits in the Great Basin and Alaska, and
tectonic syntheses with particular focus on the
relationships of hydr othermal precious-metal deposits
to magmatic and metamorphic evolution. Between
tours at the U.S.G.S., he designed and supervised
exploration programs for precious-metal deposits in
the Great Basin for the Anaconda Minerals Company.
NICOLAS F. SPYCHER received a B.S. degree in Earth
Sciences in 1 979 and a Dip!. es Sc. in Exploration
Geophysics in 1 980 from the University of Geneva,
Switzerland. He is now a Ph.D. candidate and research
assistant at the University of Oregon. His present
research includes studies of the transport of arsenic
and antimony in hydrotherm al solutions, the m ixing
properties of geothermal gases, and the geochemical
modeling of hot spring syste ms.