SOCIETY OF ECONOMIC GEOLOGISTS, INC.

ORE DEPOSITION ASSOcIATED wITH MAGMAS

CONTENTSPART I: MAFIC ROCKS

Introduction: Magmatic Deposits Associated with Mafic Rocks A.J. Naldrett

Sulfide Melts: Crystallization Temperatures, Solubilities in Silicate Melts, A.J. Naldrett and Fe, Ni, and Cu Partitioning Between Basaltic Magmas and Olivine

Vapor Associated with Mafic Magma and Controls on its Composition E.A. Mathez

Geochemistry of Platinum-Group Elements in Mafic and E.A. Mathez and C.L. Peach Ultramafic Rocks

Komatiite-Associated Nickel Sulfide Deposits C. M. Lesher

Ores Associated with Flood Basalts A.J. Naldrett

Contamination and the Origin of the Sudbury Structure and its Ores A.J. Naldrett

Stratiform PGE Deposits in Layered Intrusions A.J. Naldrett

Interactions Involving Fluids in the Stillwater and Bushveld Complexes: E.A. Mathez Observations from the Rocks

PART II: SILICIC ROCKSIntroduction: Ore Deposits Associated with Silicic Rocks J.A. Whitney

Origin and Evolution of Silicic Magmas J.A. Whitney

Magmatic Ore-Forming Fluids: Thermodynamic and Mass-Transfer P.A. Candela Calculations of Metal Concentrations

Felsic Magmas, Volatiles, and Metallogenesis P.A. Candela

Granitoid Textures, Compositions, and Volatile Fugacities J.D. Keith, W. van Middelaar, Associated with the Formation of Tungsten-Dominated A.H. Clark, and C.J. Hodgson Skarn Deposits

EditorsJ.A. Whitney and A.J. Naldrett

REvIEwS IN EcONOMIc GEOLOGY

volume 4

Society of Economic Geologists, Inc.

Reviews in Economic Geology, Vol. 4

Ore Deposition Associated with MagmasJ.A. Whitney and A.J. Naldrett, Editors

J.M. Robertson, Series Editor

Additional copies of this publication can be obtained from

Society of Economic Geologists, Inc.7811 Shaffer ParkwayLittleton, CO 80127

www.segweb.org

ISBN: 978-1-629495-62-0

The Authors:

Philip A. Candela Laboratory for Mineral Deposits Research Department of Geology University of Maryland College Park, MD 20742

Alan H. Clark Department of Geological Sciences Queen's University Kingston, ON Canada, K7L 3N6

C. Jay Hodgson Department of Geological Sciences Queen's University Kingston, ON Canada, K7L 3N6

Jeffrey D. Keith Department of Geology University of Georgia Athens, GA 30602

C. Mike Lesher Department of Geology University of Alabama Tuscaloosa, AL 35487-0338

Ed A. Mathez Department of Mineral Sciences American Museum of Natural History New York, NY 10024

Wim van Middelaar Department of Geology University of Georgia Athens, GA 30602

Anthony J. Naldrett Department of Geology University of Toronto Toronto, ON Canada, M5S IAI

Cheryl L. Peach Lamont-Doherty Geological Observatory Palisades, NY 10964

James A. Whitney Department of Geology University of Georgia Athens, GA 30602

CONTENTS

Part 1: Mafic Rocks

Chapter 1-INTRODUCfiON: MAGMATIC DEPOSITS ASSOCIATED WITH MAFIC ROCKS

REFERENCES .......................................... 1

Chapter 2-SULFIDE MELTS: CRYSTALLIZATION TEMPERATURES, SOLUBILITIES IN SILICATE MELTS, AND Fe, Ni, AND Cu PARTITIONING BETWEEN BASALTIC MAGMAS AND OLIVINE

INTRODUCTION . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5 PHASE RELATIONS IN THE SYSTEM Fe-S-0. . . . . . . . . 5

EFFECT OF OTHER COMPONENTS ON SOLIDUS

TEMPERATURES. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6 VARIATION IN fo2, fs2, AND aFeo . . . . . . . . . . . . . . . . . . . . . . . . 6 APPLICATION OF THE SYSTEM FE-S-0 :ro NATURAL

ORE MAGMAS. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6 Controls on the S and 0 Content of Ore Magmas . 6 Crystallization of Sulfide Ores . . . . . . . . . . . . . . . . . . . . . 9

THE SOLUBILITY OF SULFUR IN SILICATE MELTS . . 9 EFFECT OF TEMPERATURE .............................. 11 EFFECT OF PRESSURE. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12 EXPERIMENTS WITH MELTS IN EQUILIBRIUM WITH

H-0--S AND H-C-0-S FLUIDS . . . . . . . . . . . . . . . . . . . . . . 12 VARIATION OF SOLUBILITY OF SULFIDE DURING

FRACTIONAL CRYSTALLIZATION OF A LAYERED

INTRUSION . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13 PARTITIONING OF CHALCOPHILE ELEMENTS

AMONG SULFIDES, SILICATE MELTS, AND SILICATE MINERALS ................................ 14 PARTITIONING OF NICKEL BETWEEN SULFIDE AND

SILICATE LIQUIDS . ... . . . . . . .. . . . . . . . . . . . . . . . . . . . . . . . . 14 PARTITIONING OF NICKEL AND IRON BETWEEN SULFIDE

LIQUID AND OLIVINE ................................ 16 GENERAL REMARKS OF pARTITIONING OF NICKEL

BETWEEN SULFIDE LIQUIDS AND SiLICATE-RiCH

PHASES ............................................. 18 REFERENCES .......................................... 19

Chapter 3-VAPOR ASSOCIATED WITH MAFIC MAGMA AND CONTROLS ON ITS COMPOSITION

INTRODUCTION ...................................... 21 IMPORTANCE OF OXIDATION STATE ................ 21

HISTORICAL BACKGROUND . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 21 INFLUENCE OF TEMPERATURE ON REDOX EQUILIBRIA .... 22 CONCEPT OF RELATIVE OXYGEN FUGACITY .............. 22 RELATIONSHIP BETWEEN OXIDATION STATE AND f02 OF

MAGMA ............................................ 22 OXYGEN FUGACITIES OF NATURAL SYSTEMS ............. 23

Subaerial Lavas . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 23 Submarine Basalts ................................. 23 Xenoliths and Megacrysts from Alkali Basalts

and Kimberlites . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 23 Layered Intrusions ................................. 24

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PROCESSES THAT PERTURB MAGMATIC OXIDATION

STATE .............................................. 24 Perfect Fractional Crystallization .. . . . . . .. . . . . . . . . . . 24 Degassing . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 24

IMPORTANCE OF f02 AND PREDICTIONS FOR

LAYERED INTRUSIONS ................................ 25 NATURE OF THE MAGMATIC VAPOR ................ 25

SOLUBILITY AND ABUNDANCE CONSTRAINTS .. . . . . ... . . . 25 Carbon and Hydrogen ............................. 25 Sulfur .............................................. 26 Chlorine . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 26 Other Elements .................................... 27

CHEMICAL EVOLUTION OF FLUID FROM STILLWATER AND BUSHVELD MAGMAS .......... 27 EVOLUTION OF A MODEL FLUID IN RESPONSE TO

GRAPHITE PRECIPITATION ............................ 27 SUMMARY ............................................. 29 REFERENCES . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 29

CHAPTER 4-GEOCHEMISTRY OF PLATINUM­GROUP ELEMENTS IN MAFIC AND ULTRAMAFIC ROCKS

INTRODUCTION ...................................... 33 DISTRIBUTION OF PGE BETWEEN SULFIDE AND

SILICATE MELTS .................................... 33 THE ISSUE IN LAYERED INTRUSIONS . . . . . . . . . . . . . . . . . . . . . 33 DATA FROM SUBMARINE BASALTS . . . . . . . . . .. . . . . . . . . . . . 34

PGE IN CHROMITE, OLIVINE, AND OTHER SILICATES . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 34 EFFECT OF FRACTIONATION ON Pd/Ir RATIOS . . . . . .. . . . . 34 IRIDIUM IN OLIVINE AND OTHER SILICATES .... . . . .... . . 35 IRIDIUM IN CHROMITE . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 35 EXPERIMENTAL DATA .................................. 35

PGE PATTERNS OF ROCKS ............................ 37 PGE TRANSPORT BY FLUIDS ......................... 37 CONCLUSION ......................................... 39 REFERENCES .......................................... 39 APPENDIX I. ........................................... 41 APPENDIX II ........................................... 41

CHAPTER 5-KOMATIITE-ASSOCIATED NICKEL SULFIDE DEPOSITS

INTRODUCTION ...................................... 45 NOMENCLATURE AND CLASSIFICATION . . . . . .. . ... 45 AGE AND DISTRIBUTION ............................. 45 TECTONIC SETTING .................................. 46 STRATIGRAPHIC SETTING ............................ 50

REGIONAL STRATIGRAPHY . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 50 LOCAL STRATIGRAPHY ................................. 50 KOMATIITIC PERIDOTITES AND DUNITES . . . . . . . . . . . . . . . . . 50 FooTWALL RocKS ..................................... 53 INTERFLOW SEDIMENTS . . . . . . . . . . . . . . . . . .. . . . . . . . . . . . . . . 54 FOOTWALL EMBAYMENTS .............................. 57

HOST UNITS ........................................... 58 INTERNAL STRUCTURE AND COMPOSITION . . .. . . . . . . . . . . . 59

MINERALOGY .......................................... 59 Olivine ............................................. 59 Chromite ........................................... 60

WHOLE-ROCK GEOCHEMISTRY . . .. .. . ..... ..... . . . .... . . 61 Aphyric and Spinifex-Textured Rocks .............. 63 Cumulates ......................................... 65 Lower/Lateral Chilled Margins ..................... 65 Chalcophile Element Depletion .................... 65

MINERALIZATION .................................... 74 DISTRIBUTION . . . . . .. .. . . . . ... .... . ... ..... . .... . ..... . 74 ORE MINERALOGY . . ........ . . . . . ..... . . .... . . ... . . .... 75 DEFORMATION . . . . . .. . . . . . ..... . . ... ... . ...... . . . ..... . 75 METAMORPHISM ....................................... 75 ORE CHEMISTRY ....................................... 77 SULFUR ISOTOPES AND S/Se RATIOS .................... 78

PHYSICAL VOLCANOLOGY OF HOST KOMATIITES . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 78 MAGMA GENERATION ................................. 78 ASCENT AND ERUPTION ................................ 79 FRACTIONAL CRYSTALLIZATION ......................... 79 LAY A EMPLACEMENT .................................. 79 OLIVINE ENRICHMENT ................................. 79 CRYSTALLIZATION ..................................... 81 SEDIMENT DISTRIBUTION ............................... 81 FooTWALL EMBAYMENTS .............................. 82

Syn-Volcanic Faulting . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 82 Post-Volcanic Deformation . . . . . . . . . . . . . . . . . . . . . . . . . 83 Thermal Erosion . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 83 Volcanic Topography . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 84

VOLCANIC SETTING .................................... 86 ORE GENESIS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 86

TIMING OF SULFIDE SEPARATION ....................... 88 Strata-Bound Deposits . . . .... . . . .. . . ....... . .. ..... 88 Stratiform Deposits .. . . . .. . . ...... .. . . ........ . . ... 88

SULFUR SOURCE ... . ...... . . . ..... . .. ...... . . . ... ...... 90 Mantle Sulfur . ....... . ... . ...... ........ . .... . . .... 90 Crustal Sulfur .... . . . . . . .............. .... ........ . . 91

ORE TENOR VARIATIONS ............................... 92 Magma Composition ... . . . ............. . . .. ........ 92 Variations in f02 • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • 93 Magma:Sulfide Ratio ..... ...... . . ............... . . . 93

DISTAL VOLCANIC-ASSIMILATION MODEL . . .. . . ... 93 EXPLORATION GUIDES . ....... . .... . ..... . . . . . . . .... . 94 REFERENCES .......................................... 96

CHAPTER 6-0RES ASSOCIATED WITH FLOOD BASALTS

INTRODUCTION .... . . . . ... . . . .... .... .. .. . ... . ....... 103 NORIL'SK-TALNAKH ............... ...... . ........... 103

TECTONIC AND GEOLOGIC SETTING . . . . . . ... . . ....... . .. 103 HOST INTRUSIONS . ......... . ..... ... . . .. ... . ... . ... . .. 105 MINERALIZATION .. . ... . ....... . ..... .... . . . ........... 107

Ore Types . ...... .... . ............... . .. .... .. . . . . .. 107 Mineralogy and Mineral Zoning ................... 109 Sulfur Isotopes ........... ....... . ..... . .... . . ...... 110 Genesis of Mineralization . . . ....... . . . . . ...... . .. . . 111

MINERALIZATION OF THE DULUTH COMPLEX .. . . 112 GEOLOGICAL SETTING . . .... . ..... . .. . ..... . . ...... . ... 112 MINERALIZATION . . . . . . . . . .. . . . . . . . . . . . . . . . . . . . . . . . . . . 113

REFERENCES ..... . .... . .... . ... . .. . .... . . . ...... . . . . . 117

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CHAPTER 7-CONTAMINATION AND THE ORIGIN OF THE SUDBURY STRUCTURE AND ITS ORES

INTRODUCTION . ...... . .. .. . .. . .. ......... . ... . .... . . 119 GEOLOGICAL SETTING ...... . . . . . . . . ... . . . . ... . .. . . . . 119 PETROLOGY OF THE SUDBURY IGNEOUS

COMPLEX .. . . . . . ............. . ......... . .. .... . .... . 121 MAIN MASS ........................................... 121 SUBLA YER . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 121

MAJOR AND TRACE-ELEMENT GEOCHEMISTRY .... 122 MAJOR ELEMENTS ..................................... 122 TRACE ELEMENTS ...................................... 123 DISCUSSION OF MAJOR AND TRACE-ELEMENT DATA ..... 123 SUMMARY OF CONCLUSIONS FROM MAJOR AND TRACE-

ELEMENT DATA ..................................... 126 ISOTOPE GEOCHEMISTRY .... . ... . . . ... . . .. . ....... . . 129 RELATIONSHIP OF ORE DEPOSITS TO ROCKS OF

THE COMPLEX . . . ... . . . . . . . . . . ..... . . ...... . ... . . . .. 129 RELATIONSHIPS AMONG INCLUSIONS, SUBLAYER, AND

MAIN MASS OF THE SIC . ..... ...... . ... . ... . ... .. . .. 130 SEGREGATION OF SULFIDES .. . . . . . . .... . .... . ....... . . .. 130

A MODEL FOR THE FORMATION OF THE SUDBURY IGNEOUS COMPLEX . . .... . ........... . . 131

REFERENCES . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 133

CHAPTER 8-STRATIFORM PGE DEPOSITS IN LAYERED INTRUSIONS

INTRODUCTION . . ..... . ....... . ...... . ............... 135 STRATIGRAPHY OF THE BUSHVELD AND

STILLWATER COMPLEXES ... ............. . ... . . . . . . 135 BUSHVELD COMPLEX ................................... 135 STILLWATER COMPLEX ................................. 135 COMPARISON OF BUSHVELD AND STILLWATER ........... 137

SETTING OF THE MINERALIZATION ................. 137 BusHvELD CoMPLEX ................................... 137 STILLWATER COMPLEX ................................. 141

The J-M Reef ...... . . ............... . ........... . .. 141 MINERALIZATION ...... . . ..... . .. . ................... 142

BusHVELD COMPLEX: THE MERENSKY REEF ..... ....... . 142 Origin of Merensky Pegmatoid .................... 143 Potholes and Dimpling . . . . .. .. . .. . ....... . . ...... . . 145 Composition of the Sulfides .... . ........ . . . .. . .. . . 145

STILLWATER COMPLEX: THE J-M REEF .................. 147 DISCUSSION . ..... . ... . . ..... .......... . ............... 149

CONSTRAINTS OF GENETIC MODELS .................... 149 Merensky Reef . . .. . . . ... . . .. ....................... 149 J-M Reef . . ..... . . . ....... . . ........ . .. . . ....... .... 150

LAYERED MAGMA CHAMBERS .......................... 150 MoDELS FOR THE ORIGIN OF PGE-RicH REEFs .......... 151 A MODEL FOR THE MERENSKY REEF .. .. .. .. .. .. .. .. .. .. 152

Magma: Sulfide Ratio ...... . ......... . ....... . ...... 152 Details of the Model .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. . 153 Application of the Model to the J-M Reef ... . ...... 155

ASSOCIATION OF PGE WITH CHROMITITE IN LAYERED INTRUSIONS ............................. 156 COMPOSITIONAL DIFFERENCES BETWEEN CHROMITITES

FROM OPHIOLITES AND THOSE FROM LAYERED

INTRUSIONS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 156 INTERACTION BETWEEN SULFIDE AND CHROMITE

DuRING CooLING. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. 158 PGE CONCENTRATIONS IN CHROMITES FROM LAYERED

INTRUSIONS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 158

MIXING OF A FRESH INPUT OF MAGMA WITH THAT

RESIDENT IN A CHAMBER . . . . . . . . . . . . . . . . . . . . . . . . . . . 158 MAGMA MIXING AND THE SEGREGATION OF SULFIDE

AND CHROMITE . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 159 CONCLUSIONS AND APPLICATIONS TO EXPLORATION ... 162

REFERENCES ......................................... 162

CHAPTER 9-INTERACTIONS INVOLVING FLUIDS IN THE STILLWATER AND BUSHVELD COMPLEXES: OBSERVATIONS FROM THE ROCKS

INTRODUCTION ...................................... 167 REPLACEMENT BODIES IN THE STILLWATER

COMPLEX ........................................... 167 DISCORDANT DUNITES ................................. 167 AMEBOIDAL TROCTOLITE HORIZONS .................... 168

THE BUSHVELD DISCORDANT PEGMATOIDS AND PIPES ................................................ 169 PLATINIFEROUS DUNITE PIPES ......................... 169 IRON-RICH PEGMATITES ................................ 170 VLAKFONTEIN NICKEL PIPES ........................... 170 HIGH-TEMPERATURE VEINS ............................. 171 PROBLEMS CONCERNING PETROGENESIS ................. 171

CHROMITITES, FLUIDS, AND PGE ................... 172 PGE IN THE CHROMITITE HORIZONS . ; ................. 172 PECULIARITIES OF THE UG-2 ........................... 172 THE CHROMITITE-MAFIC PEGMATITE ASSOCIATION ...... 173 EVIDENCE FOR INFLUENCE OF FLUID ON PGE ........... 173

PGE Mineral Variations in the UG-2 and Merensky ........................................ 173

The Stillwater Picket Pin Horizon .................. 174 VOLATILE-RICH PHASES ............................. 174

HALOGEN-BEARING PHASES ............................ 174 APATITE ............................................... 174 PHLOGOPITE ........................................... 174 GRAPHITE ............................................. 174 FLUID INCLUSIONS ..................................... 176

CONCLUSION ......................................... 176 REFERENCES .......................................... 177

Part II: Silicic Rocks

CHAPTER tO-INTRODUCTION: ORE DEPOSITS ASSOCIATED WITH SILICIC ROCKS ............ 181

CHAPTER 11-0RIGIN AND EVOLUTION OF SILICIC MAGMAS

INTRODUCTION ...................................... 183 VOLCANIC ANALOGS OF GRANITIC

BATHOLITHS ........................................ 183 EXPERIMENTAL STUDIES OF SILICIC SYSTEMS ..... 184 SOURCES OF WATER FOR THE GENERATION OF

GRANITIC MELTS ................................... 188 DEHYDRATION REACTIONS ............................. 189 VOLATILES FROM SUBDUCTED OCEANIC CRUST AND

MANTLE ............................................ 192 FRACTIONAL CRYSTALLIZATION AND

ASSIMILATION ...................................... 195 SEPARATION OF A VOLATILE PHASE .............. . 195 MAGMATIC ORE DEPOSITION ...................... 197

PORPHYRY COPPER SYSTEMS .......................... 197

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PORPHYRY MOLYBDENUM DEPOSITS ................... 197 SKARN SYSTEMS ...................................... 198 VOLCANIC EPITHERMAL DEPOSITS ..................... 198 EXHALATIVE MASSIVE SULFIDE DEPOSITS ............... 198

CONCLUSIONS ...................... . ................ 198 REFERENCES ......................................... 199

CHAPTER 12-MAGMATIC ORE-FORMING FLUIDS: THERMODYNAMIC AND MASS-TRANSFER CALCULATIONS OF METAL CONCENTRATIONS

INTRODUCTION ..................................... 203 THE FORMATION OF PARTITION COEFFICIENTS:

STOICHIOMETRIC ANALYSIS ...................... 203 SUMMARY OF THE MODELS OF CANDELA (1986a) 206

PARTITIONING OF ELEMENTS WITH CONSTANT PARTITim COEFFICIENTS DURING FIRST BOILING ............... 206

PARTITIONING OF CHLORIDE-COMPLEXED ELEMENTS

DuRING FIRST BoiLING ............................. 208 SECOND BOILING .................................... 210

PARTITIONING OF ELEMENTS WITH CONSTANT PARTITim

COEFFICIENTS DURING SECOND BOILING ............ 211 pARTITIONING OF CHLORIDE-COMPLEXED ELEMENTS

DURING SECOND BOILING .......................... 211 THE EFFICIENCY INTEGRAL ............................ 212 STATUS OF IRON IN THE MAGMATIC AQUEOUS PHASE .. 213

MODEL CONCENTRATIONS OF METALS AND CHLORINE IN MAGMATIC-HYDROTHERMAL FLUIDS ............................................. 213

REFERENCES ......................................... 217 APPENDIX I ...................................... 218 APPENDIX II ..................................... 220

CHAPTER 13-FELSIC MAGMAS, VOLATILES, AND METALLOGENESIS

INTRODUCTION ..................................... 223 THE EFFECTS OF INITIAL MAGMATIC WATER AND

FLUORINE CONCENTRATIONS AND THE DEPTH OF VAPOR EVOLUTION ON THE FORMATION OF MAGMATIC-HYDROTHERMAL ORE DEPOSITS ... 223 THE WORKING MODEL. ............................... 223 ORE-METAL SEQUESTERING IN CRYSTALLIZING PHASES:

THE ROLE OF VOLATILES IN ORE-METAL DISPERSAL . 223 CAVEAT EMPTOR . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 226 SUMMARY . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 226

THE EFFECT OF fa, ON THE EFFICIENCY OF REMOVAL OF METALS FROM MAGMAS ........ 226 THE AGUE-BRIMHALL MODEL, AND THE f02 OF INTRUSIVE

SYSTEMS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 227 EXPERIMENTAL AND FIELD DATA BEARING ON THE

ROLE OF fa, IN ORE-METAL SEQUESTRATION ......... 228 SUMMARY . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 230

DISCUSSION: SOURCE ROCKS, VOLATILES, AND METALLOGENIC PROVINCES ..................... 230

REFERENCES ......................................... 232 APPENDIX . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 233

CHAPTER 14-GRANITOID TEXTURES, COMPOSITIONS, AND VOLATILE FUGACITIES ASSOCIATED WITH THE FORMATION OF TUNGSTEN-DOMINATED SKARN DEPOSITS

INTRODUCTION ...................................... 235

FIELD RELATIONS OF PLUTONS . . . . . . . . . . . . . . . . . . . . . 235 RELATIVE VOLATILE FUGACITIES . . . . . . . . . . . . . . . . . . 244 GRANITOID COMPOSITIONS . . . . . . . . . . . . . . . . . . . . . . . . . 239 INFERRED OXYGEN FUGACITY . . . . . . . . . . . . . . . . . . . . . 247 LITHOPHILE METAL CONTENT OF GRANITOIDS . . . 239 CONCLUSIONS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 248 SUBSOLIDUS REEQUILIBRATION AND REFERENCES . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 248

HYDROTHERMAL ALTERATION . . . . . . . . . . . . . . . . . . . 241

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