Contents

Abstract...........................................................................................................................................................1
Summary of Porphyry Copper Deposit Model ..........................................................................................1
　Associated Commodities and Deposit Types ...................................................................................1
　Regional Environment ..........................................................................................................................1
　Physical Description of Deposits........................................................................................................2
　Geophysical Characteristics................................................................................................................3
　Hypogene Ore Characteristics............................................................................................................3
　Supergene Ore Characteristics...........................................................................................................4
　Hypogene and Supergene Gangue Characteristics........................................................................4
　Hydrothermal Alteration......................................................................................................................5
　Geochemical Characteristics..............................................................................................................6
　Petrology of Associated Igneous Rocks............................................................................................7
　Theory of Ore Deposit Genesis............................................................................................................8
　　Sources of Fluids .........................................................................................................................8
　　Controls on Permeability and Fluid Flow...................................................................................8
　　Chemical Transport and Transfer Processes...........................................................................9
　　Heat-Transfer Processes.............................................................................................................9
　　Pressure Gradients......................................................................................................................9
　　Wall-Rock Reaction and Ore-Mineral Deposition Processes...............................................9
　　Relation between Alteration, Gangue, and Veins..................................................................10
　Geoenvironmental Features...............................................................................................................10
　Porphyry Copper Deposit Exploration and Resource Assessment Objectives and Guides...10
　Broader Implications, Societal Relevance, and Knowledge Gaps of Porphyry Copper Deposits...10
A. Introduction............................................................................................................................................11
B. Deposit Type and Associated Commodities.......................................................................................11
　Name ..................................................................................................................................................11
　Synonyms.............................................................................................................................................11
　Brief Description.................................................................................................................................13
　Associated and Transitional Deposit Types....................................................................................14
　Primary Commodities .........................................................................................................................14
　By-Product Commodities ...................................................................................................................14
　Trace Constituents..............................................................................................................................14
　Example Deposits...............................................................................................................................14
C. History of Porphyry Copper Deposits..................................................................................................14
D. Regional Environment ...........................................................................................................................15
　Geotectonic Environment ..................................................................................................................15
　Temporal (Secular) Relations.............................................................................................................18
　　Variations Through Geologic Time...........................................................................................18
　　Variation Within Magmatic Cycles..........................................................................................18
　Duration of Magmatic-Hydrothermal Systems that Form Porphyry Copper Deposits ............18
　Relations to Structures ......................................................................................................................21
　　Structural Setting(s) and Controls...........................................................................................21
　　Tectonic Setting.........................................................................................................................21
　　Structural Control of Magma Emplacement...........................................................................21
　　Origin of Veins............................................................................................................................21
　　Preservation and Dismemberment of Porphyries.................................................................23
　Relations to Igneous Rocks................................................................................................................24
　Relations to Sedimentary Rocks ......................................................................................................24
　Relations to Metamorphic Rocks......................................................................................................24
E. Physical Description of Deposits..........................................................................................................24
　Dimensions in Plan View....................................................................................................................25
　Vertical Extent ....................................................................................................................................25
　Form/Shape .........................................................................................................................................25
　Size of Hydrothermal Systems Relative to Extent of Economically Mineralized Rock...25
　Host Rocks ..........................................................................................................................................28
　Structural Setting(s) and Controls....................................................................................................28
F. Geophysical Characteristics .................................................................................................................28
　Introduction ........................................................................................................................................28
　Regional-Scale Geophysics ..............................................................................................................31
　Deposit-Scale Geophysics ................................................................................................................32
　　Magnetic Anomalies..................................................................................................................32
　　Electrical and Electromagnetic Methods...............................................................................33
　　　Electrical Methods............................................................................................................35
　　　Electromagnetic Methods................................................................................................36
　　　Examples of Electrical and Electromagnetic Surveys in Porphyry Copper Exploration...37
　　Other Geophysical Methods.....................................................................................................37
　　　Self (Spontaneous) Potential ..........................................................................................37
　　　Gravity ................................................................................................................................37
　　　Seismic Reflection.............................................................................................................38
　Limitations ...........................................................................................................................................38
　VINR-SWIR and TIR Remote Sensing of Porphyry Copper Deposits..........................................38
　　Introduction................................................................................................................................38
　　Porphyry Copper Deposits and Spectral Characteristics....................................................38
　　Hyperspectral and Multispectral Imaging Systems and Previous Studies Mapping Porphyry Copper Deposits...39
　　Case Study.Mapping Altered Rocks in the Sar Cheshmeh Region of Iran using ASTER Data...43
　　　Introduction, Geology, and Mapped Alteration............................................................43
　　　Data and Calibration.Mapping Methods.ASTER False Color Composite Image...45
　　　Description and Interpretation of ASTER468 Image and ASTER Alteration Minerals Map...46
　　Conclusions................................................................................................................................50
G. Hypogene Ore Characteristics.............................................................................................................50
　Grade ..................................................................................................................................................50
　Mineralogy...........................................................................................................................................50
　Mineral Assemblages........................................................................................................................51
　Paragenesis and Zoning.....................................................................................................................51
　Forms and Textures............................................................................................................................51
H and K. Hypogene and Supergene Gangue Characteristics..............................................................55
　Mineralogy...........................................................................................................................................55
　Mineral Assemblages and Paragenesis..........................................................................................55
　Zoning ..................................................................................................................................................55
　Textures and Grain Sizes of Hypogene Gangue ............................................................................56
　Textures and Grain Sizes of Supergene Gangue ...........................................................................56
　Significance of Gangue......................................................................................................................57
I. Hydrothermal Alteration.........................................................................................................................57
　Mineralogy...........................................................................................................................................57
　Mineralogy of Assemblages and Associated Veins......................................................................57
　Lateral and Vertical Dimensions ......................................................................................................60
　Selvages...............................................................................................................................................60
　Rock Matrix Alteration.......................................................................................................................62
　Intensity................................................................................................................................................62
　Textures................................................................................................................................................62
　Zoning Patterns...................................................................................................................................62
J. Supergene Ore Characteristics ...........................................................................................................64
　Dimensions, Tonnages, and Grades ................................................................................................65
　Formation and Distribution ................................................................................................................65
　Mineralogy...........................................................................................................................................66
　Mineral Associations and Assemblages.........................................................................................66
　Textures and Grain Size .....................................................................................................................66
L. Weathering/Supergene Processes .....................................................................................................66
　Introduction.........................................................................................................................................66
　Mineralogy...........................................................................................................................................68
　Rates ..................................................................................................................................................68
　Effects of Micro and Macro Climates..............................................................................................68
　Effects of Hydrologic Setting.............................................................................................................68
M. Geochemical Characteristics..............................................................................................................70
　Lithochemistry ....................................................................................................................................70
　Minor Element Zoning Patterns ........................................................................................................70
　Mineral Compositions ........................................................................................................................73
　Fluid-Inclusion Thermometry and Geochemistry ..........................................................................80
　Chemical Compositions of Fluids .....................................................................................................83
　Stable Isotope Compositions of Fluids ............................................................................................87
　Nontraditional Stable Isotopes.Copper and Molybdenum .......................................................88
N. Petrology of Associated Igneous Rocks ............................................................................................89
　Rock Names.........................................................................................................................................89
　Forms of Igneous Rocks and Rock Associations ..........................................................................89
　Mineralogy ..........................................................................................................................................89
　Textures and Structures.....................................................................................................................89
　Grain Size.............................................................................................................................................91
　Petrochemistry....................................................................................................................................91
　Trace-Element Geochemistry............................................................................................................97
　Isotope Geochemistry......................................................................................................................100
　Radiogenic Isotopes of Ore .............................................................................................................106
　Depth of Emplacement.....................................................................................................................107
O. Petrology of Associated Sedimentary Rocks .................................................................................107
P. Petrology of Associated Metamorphic Rocks ................................................................................107
Q. Theory of Ore Deposit Formation ......................................................................................................108
　Ore Deposit System Affiliations ......................................................................................................108
　Controls on Permeability and Fluid Flow........................................................................................109
　Sources of Fluids and Metals..........................................................................................................109
　Chemical Transport and Transfer Processes................................................................................112
　Heat Transport and Transfer Processes........................................................................................113
　　Time Scale.................................................................................................................................113
　Pressure Gradients During Porphyry Copper System Formation..............................................114
　Wall-Rock Reaction and Ore-Mineral Deposition Processes ...................................................114
　Relation Between Alteration, Gangue and Vein Mineralization................................................115
R. Porphyry Copper Exploration and Resource Assessment Guides ...............................................116
　Hypogene Characteristics of PCDs and Gradients within PCD Systems.................................116
　　Mapping of Rock Types, Structure, Hydrothermal Minerals, and Zoning.......................116
　　Fluid Inclusion Zoning and Thermal Gradients ...................................................................117
　　Mineral Properties....................................................................................................................117
　　Vein Abundance, Mineralogy, and Paragenesis.................................................................117
　　Distribution of Sulfide Minerals..............................................................................................117
　　Minor-Element Geochemistry.................................................................................................117
　　Spectral Imagery......................................................................................................................120
　Supergene-Enriched and Oxidized PCDs......................................................................................120
　　Supergene Enrichment and Leached Capping Characteristics........................................120
　　Copper-Oxide Minerals ...........................................................................................................120
　Recognition of Permissive Terrain for Porphyry Copper Exploration and Assessment.........121
　　Postmineralization Cover and Proximity to Porphyry Copper Deposits...........................121
　　Regional Structure and Intrusion Emplacement.................................................................121
　　Continental-Scale Permissive Terrains ................................................................................121
　　Depth Limitations.....................................................................................................................121
S. Geoenvironmental Features ...............................................................................................................122
　Weathering Processes.....................................................................................................................122
　Pre-Mining Baseline Signatures in Soil, Sediment, and Water ................................................123
　Past and Future Mining Methods and Ore Treatment ................................................................124
　Volume of Mine Waste and Tailings ..............................................................................................124
　Mine Waste Characteristics ...........................................................................................................124
　Acid/Base Accounting .....................................................................................................................124
　Metal Mobility Related to Mining in Groundwater and Surface Water ...................................124
　Pit Lakes ............................................................................................................................................124
　Ecosystem Issues .............................................................................................................................125
　Human Health Issues .......................................................................................................................125
　Climate Effects on Geoenvironmental Signatures ......................................................................125
T. Knowledge Gaps and Future Research Directions .........................................................................125
U. Broader Implications and Societal Relevance of Porphyry Copper Systems............................126
References Cited.......................................................................................................................................131

Appendix 1. Grade and tonnage models................................................................................................158
Appendix 2. Characteristics of Representative Porphyry Copper Deposits ...................................158

Abstract

This report contains a revised descriptive model of porphyry copper deposits (PCDs), the world’s largest source (about 60 percent) and resource (about 65 percent) of copper and a major source of molybdenum, gold and silver. Despite relatively low grades (average 0.44 percent copper in 2008), PCDs have significant economic and societal impacts due to their large size (commonly hundreds of millions to billions of metric tons), long mine lives (decades), and high production rates (billions of kilograms of copper per year). The revised model describes the geotectonic setting of PCDs, and provides extensive regional- to deposit-scale descriptions and illustrations of geological, geochemical, geophysical, and geoenvironmental characteristics. Current genetic theories are reviewed and evaluated, knowledge gaps are identified, and a variety of exploration and assessment guides are presented. A summary is included for users seeking overviews of specific topics.

Figure A1. Phanerozoic porphyry belts, porphyry deposits, and representative porphyry copper deposits summarized in Appendix 2 (red labels). Modified from Seedorff and others (2005, their Fig. 1). Figure B1. General setting of porphyry copper and associated deposit types (modified from Sillitoe and Bonham, 1990). Figure D1. Plate tectonic setting of porphyry copper deposits. (A) Typical continental margin arc above subduction zone. Porphyry copper generation as a product of normal arc magmatism; continental arc is shown, but similar processes can occur in mature island arcs. MASH.melting, assimilation, storage, and homogenization. SCLM.subcontinental lithospheric mantle. (B-D) Remelting of subduction-metasomatized SCLM or lower crustal hydrous cumulate zones (black layer) leading to potential porphyry copper-gold and epithermal gold deposit formation. (B) Collisional lithospheric thickening. (C) Postcollisional lithospheric mantle delamination. (D) Postsubduction lithospheric extension. High strontium/yttrium and lanthanum/ytterbium magmas may be generated in all cases by residual or fractionating hornblende (±garnet, titanite) in the lower crust. Reproduced from Richards (2009, his Fig. 1). Figure D2. Porphyry copper belts and major porphyry copper deposits in the Andes. From Sillitoe and Perello (2005, their Fig. 2). Figure D3. Optimum conditions for development of giant porphyry copper deposits. From Sillitoe and Perello (2005, their Fig.15). Figure D4. Southeast Asia and the west Pacific showing major Cenozoic arcs and copper ± gold and gold deposits. Porphyry copper deposits summarized in Appendix 2 are shown in red. From Garwin and others (2005, their Fig. 2). Figure D5. Ages of known porphyry copper deposits. Labeled deposits summarized in Appendix 2. Age data from Singer and others (2008). Figure F5. Illustrated deposit model of a porphyry copper deposit (modified from Lowell and Guilbert, 1970). (A) Schematic cross section of hydrothermal alteration minerals and types, which include propylitic, sericitic, advanced argillic, and potassic alteration. (B) Schematic cross section of ores associated with each alteration type. (C) Scale showing level of interpreted exposure for Iranian alteration sites based on ASTER mapped alteration units. Figure U1. Estimates of the annual flux of elements (diamond symbols) mined (in tons/year ore and waste) during the production of porphyry deposits (porphyry copper flux) as compared to annual global consumption of the same elements (tons/year). Elements that plot above the diagonal line have annual consumption greater than the masses of these elements contained in rock mined in porphyry copper deposits (for example, Cu, S, Au, Ag, Re), whereas elements below this line have masses in rock moved in porphyry copper deposits greater than their annual consumption (for example, Al, Ti, Zr, total REE). Note that many elements in porphyry copper deposits are in gangue or waste rock and are not recovered during ore processing. Also shown are estimates (thick colored orthogonal lines) for the masses of ore and total rock moved (ore + strip) during annual mining of porphyry copper deposits and for the annual masses of arc volcanism and total arc magmatism (volcanism and plutonism). The total mass of rock moved annually by global porphyry copper deposit mining is approximately equal to the annual mass of arc volcanism. John,D.A.(ed.)(2010)による『Porphyry Copper Deposit Model』から