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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