A comprehensive account of ore-forming processes, revised and updated
The revised second edition of Introduction to Ore-Forming Processes offers a guide to the multiplicity of geological processes that result in the formation of mineral deposits. The second edition has been updated to reflect the most recent developments in the study of metallogeny and earth system science.
This second edition contains new information about global tectonic processes and crustal evolution that continues to influence the practice of economic geology and maintains the supply of natural resources in a responsible and sustainable way. The replenishment of depleted natural resources is becoming more difficult and environmentally challenging. There is also a change in the demand for mineral commodities and the concern around the non-sustainable supply of ‘critical metals’ is now an important consideration for planners of the future. The book puts the focus on the responsible custodianship of natural resources and the continuing need for all earth scientists to understand metallogeny and the resource cycle. This new edition:
- Provides an updated guide to the processes involved in the formation of mineral deposits
- Offers an overview of magmatic, hydrothermal and sedimentary ore-forming processes
- Covers the entire range of mineral deposit types, including the fossil fuels and supergene ores
- Relates metallogeny to global tectonics by examining the distribution of mineral deposits in space and time
- Contains examples of world famous ore deposits that help to provide context and relevance to the process-oriented descriptions of ore genesis
Written for students and professionals alike, Introduction to Ore-Forming Processes offers a revised second edition that puts the focus on the fact that mineral deposits are simply one of the many natural wonders of geological process and evolution.
Table of Contents
Preface to the 2nd Edition xiii
Preface to the 1st Edition xv
Introduction: Mineral Resources xvii
Part I Igneous Processes 1
1 Igneous Ore-Forming Processes 3
1.1 Introduction 4
1.2 Magmas and Metallogeny 4
1.2.1 Crustal Architecture and Mineral Wealth 4
1.2.2 Magma Types and Metal Contents 7
1.2.2.1 Basalt 7
1.2.2.2 Andesite 9
1.2.2.3 Rhyolite 10
1.2.2.4 Alkaline Magmas, Carbonatite and Kimberlite 12
1.3 Why Are Some Magmas More Fertile than Others? The “Inheritance Factor” 13
1.3.1 The “Late Veneer” Hypothesis of Siderophile Metal Concentration - An Extraterrestrial Origin for Au and Pt? 14
1.3.2 Diamonds and the Story They Tell 15
1.3.3 Metal Concentrations in Metasomatized Mantle and Their Transfer into the Crust 20
1.3.4 Metal Enrichment in Carbonatitic and Peralkaline Magmas 21
1.3.5 I- and S-Type Granite Magmas and Metal Specificity 27
1.4 Partial Melting and Crystal Fractionation as Ore-Forming Processes 30
1.4.1 Partial Melting 31
1.4.1.1 Trace Element Distribution During Partial Melting 32
1.4.2 Crystallization of Magma 34
1.4.2.1 The Form and Internal Zonation of Igneous Bodies 36
1.4.2.2 Trace Element Distribution During Fractional Crystallization 39
1.4.3 Fractional Crystallization and the Formation of Monomineralic Chromitite Layers 43
1.4.3.1 The Irvine Model 43
1.4.3.2 Other Mechanisms for the Formation of Chromitite Layers or Pods 47
1.4.4 Filter Pressing as a Process of Crystal Fractionation 48
1.4.4.1 Anorthosite Hosted Ti-Fe Deposits 48
1.5 Liquid Immiscibility as an Ore-Forming Process 49
1.5.1 Silicate-Oxide Immiscibility 49
1.5.2 Silicate-Sulfide Immiscibility 50
1.6 A More Detailed Consideration of Mineralization Processes in Mafic Magmas 52
1.6.1 A Closer Look at Sulfide Solubility 52
1.6.2 Sulfide-Silicate Partition Coefficients 53
1.6.3 The R Factor and Concentration of Low Abundance Trace Elements 54
1.6.4 Factors that Promote Sulfide Saturation 56
1.6.4.1 Addition of Externally Derived Sulfur 56
1.6.4.2 Fractional Crystallization 56
1.6.4.3 Injection of a New Magma and Magma Mixing 58
1.6.4.4 Magma Contamination 68
1.6.5 Other Models for Mineralization in Layered Mafic Intrusions 69
1.6.5.1 PGE Clusters 69
1.6.5.2 The Role of Chromite in PGE Concentration 71
1.6.5.3 Hiatus Models 72
1.6.5.4 Fluid-Related Infiltration of PGE 72
1.7 A Model for Mineralization in Layered Mafic Intrusions 72
1.8 Summary 75
Further Reading 75
2 Magmatic-Hydrothermal Ore-Forming Processes 77
2.1 Introduction 77
2.2 Some Physical and Chemical Properties of Water 78
2.3 Formation of a Magmatic Aqueous Phase 81
2.3.1 Magmatic Water - Where Does It Come from? 81
2.3.2 H2O Solubility in Silicate Magmas 83
2.3.3 The Burnham Model 85
2.3.3.1 A Note on the Mechanical Effects of Boiling 88
2.4 The Composition and Characteristics of Magmatic-Hydrothermal Solutions 88
2.4.1 Quartz Veins - What Do They Tell Us About Fluid Compositions? 88
2.4.2 Major Elements in Magmatic Aqueous Solutions 89
2.4.3 Other Important Components of Magmatic Aqueous Solutions 89
2.4.3.1 Magmatic Fluid Compositions from Fluid Inclusion Analysis 92
2.4.4 Carbon Dioxide in Magmatic Fluids 94
2.4.5 Other Important Features of Magmatic Fluids 95
2.5 A Note on Pegmatites and Their Significance to Granite-Related Ore-Forming Processes 97
2.5.1 Early Models of Pegmatite Genesis 98
2.5.2 More Recent Ideas on the Origin of Pegmatites 98
2.6 Fluid-Melt Trace Element Partitioning 100
2.6.1 Early Experiments on Metal Solubilities in Aqueous Solution 100
2.6.2 A More Detailed Look at Fluid-Melt Partitioning of Metals 102
2.6.2.1 Fluid-Melt Partitioning During “First Boiling” 103
2.6.2.2 Fluid-Melt Partitioning During “Second Boiling” 103
2.6.2.3 Partitioning of Metals into H2O-Vapor 104
2.6.3 Partitioning of Cu, Mo, and W Between Melt and H2O-Fluid 106
2.7 Water Content and Depth of Emplacement of Granites - Relationships to Ore-Forming Processes 107
2.8 Models for the Formation of Porphyry-Type Cu, Mo, and W Deposits 110
2.8.1 The Origin of Porphyry Cu-(Mo) and Porphyry Mo-(Cu) Type Deposits 110
2.8.2 The Origin of Porphyry W(±Sn) Type Deposits 114
2.8.3 The Role of Sulfur in the Formation of Porphyry Copper Deposits 115
2.8.3.1 The Role of Sulfur in Concentrating Metals in Porphyry Systems 115
2.8.3.2 The Role of Sulfur in Precipitating Ore Minerals in Porphyry Systems 116
2.9 Near-Surface Magmatic-Hydrothermal Processes - The “Epithermal” Family of Au-Ag-(Cu) Deposits 116
2.9.1 Gold Precipitation Mechanisms in Epithermal Deposits 119
2.10 Skarn Deposits 123
2.10.1 Prograde - Isochemical Contact Metamorphism 126
2.10.2 Prograde - Metasomatism and Replacement 126
2.10.3 Retrograde - Meteoric Fluid Influx and Main Metal Precipitation 127
2.11 Fluid Flow in and Around Granite Plutons 128
2.12 The Role of Hydrothermal Fluids in Mineralized Mafic Rocks 133
2.12.1 The Effects of a Magmatic-Hydrothermal Fluid on PGE Mineralization in the
Bushveld Complex 134
2.13 Summary 135
Further Reading 136
Part II Hydrothermal Processes 139
3 Hydrothermal Ore-Forming Processes 141
3.1 Introduction 142
3.2 Other Fluids in the Earth’s Crust and Their Origins 142
3.2.1 Sea Water 144
3.2.2 Meteoric Water 144
3.2.3 Basinal (or Connate)Water 145
3.2.4 Metamorphic Water 149
3.2.5 Waters of Mixed Origin 150
3.3 The Movement of Hydrothermal Fluids in the Earth’s Crust 152
3.3.1 Factors Affecting Fluid Flow at a Crustal Scale 152
3.3.2 A Note on Hydrostatic Versus Lithostatic Pressure Gradients 154
3.3.3 Deformation and Hydrothermal Fluid Flow 155
3.3.4 Other Factors Affecting Fluid Flow and Mineral Precipitation 158
3.3.4.1 How DoWe Know that a Fluid Has Passed Through a Rock? 159
3.4 Additional Factors Affecting Metal Solubility 160
3.4.1 The Important Metal-Ligand Complexes in Hydrothermal Solutions 162
3.4.1.1 Hard Metals 162
3.4.1.2 Borderline Metals 163
3.4.1.3 Soft Metals 165
3.4.2 More on Metal Solubilities in the Aqueous Vapor Phase 167
3.4.3 A Brief Note on Metal-Organic Complexes 167
3.5 Precipitation Mechanisms for Metals in Solution 169
3.5.1 Physico-Chemical Factors Affecting Metal Precipitation 170
3.5.1.1 Temperature 171
3.5.1.2 Pressure 171
3.5.1.3 Phase Separation (Boiling and Effervescence) 172
3.5.1.4 Fluid Mixing/Dilution 173
3.5.1.5 Fluid/Rock Reactions (pH and Eh Controls) 176
3.5.2 Adsorption 176
3.5.3 Biologically Mediated Processes of Metal Precipitation 179
3.5.3.1 Biomineralization 180
3.6 Fluid-Rock Interaction - Introduction to Hydrothermal Alteration 183
3.6.1 Types of Alteration and Their Ore Associations 187
3.6.1.1 Potassic Alteration 187
3.6.1.2 Phyllic (or Sericitic) Alteration 190
3.6.1.3 Propylitic Alteration 190
3.6.1.4 Argillic Alteration 190
3.6.1.5 Silication 190
3.6.1.6 Silicification 190
3.6.1.7 Carbonatization 191
3.6.1.8 Greisenization 191
3.6.1.9 Hematitization 191
3.7 Metal Zoning and Paragenetic Sequence 191
3.7.1 Replacement Processes 194
3.8 Modern Analogues of Ore-Forming Processes - The VMS-SEDEX Continuum 195
3.8.1 “Black Smokers” - A Modern Analogue for VMS Deposit Formation 196
3.8.2 The Salton Sea and Red Sea Geothermal Systems - Modern Analogues for SEDEX Mineralization Processes 204
3.8.2.1 Salton Sea Geothermal System 204
3.8.2.2 The Red Sea and the VMS-SEDEX Continuum 206
3.9 Mineral Deposits Associated with Aqueo-Carbonic Metamorphic Fluids 209
3.9.1 Orogenic Gold Deposits 210
3.9.1.1 Archean 210
3.9.1.2 Proterozoic 211
3.9.1.3 Phanerozoic 211
3.9.2 Carlin-Type Gold Deposits 211
3.9.3 Quartz Pebble Conglomerate Hosted Gold Deposits 214
3.10 Ore Deposits Associated with Basinal Fluids 217
3.10.1 Stratiform Sediment-Hosted Copper (SSC) Deposits 218
3.10.2 Mississippi Valley Type (MVT) Pb-Zn Deposits 222
3.11 Ore Deposits Associated with Near Surface Meteoric Fluids (Groundwater) 230
3.11.1 A Brief Note on the Aqueous Transport and Deposition of Uranium 230
3.11.2 Sandstone-Hosted Uranium Deposits 231
3.11.2.1 Colorado Plateau (Tabular) Uranium-Vanadium Type 231
3.11.2.2 Roll-Front Type 233
3.12 Summary 235
Further Reading 237
Part III Sedimentary/Surficial Processes 239
4 Surficial and Supergene Ore-Forming Processes 241
4.1 Introduction 241
4.2 Principles of Chemical Weathering 242
4.2.1 Dissolution and Hydration 243
4.2.2 Hydrolysis and Acid Hydrolysis 244
4.2.3 Oxidation 244
4.2.4 Cation Exchange 245
4.3 Lateritic Deposits 245
4.3.1 Laterite Formation 245
4.3.2 Bauxite Ore Formation 246
4.3.3 Nickel Laterites 251
4.3.4 Gold in Laterites 253
4.3.5 A Note on Platinum Group Element (PGE) Enrichment in Laterites 257
4.4 Clay Deposits 258
4.4.1 The Kaolinite (China Clay) Deposits of Cornwall 259
4.4.2 “Ion-Adsorption” Rare Earth Element (REE) Deposits in Clays 261
4.5 Calcrete-Hosted Deposits 265
4.5.1 Calcrete-Hosted or Surficial Uranium Deposits 265
4.6 Supergene Enrichment of Cu and Other Metals in the Near Surface Environment 267
4.6.1 Supergene Oxidation of Copper Deposits 267
4.6.1.1 A Note on Supergene Enrichment of Other Metals 272
4.7 Summary 275
Further Reading 276
5 Sedimentary Ore-Forming Processes 277
5.1 Introduction 277
5.2 Clastic Sedimentation and Heavy Mineral Concentration - Placer Deposits 278
5.2.1 Basic Principles 279
5.2.2 Hydraulic Sorting Mechanisms Relevant to Placer Formation 281
5.2.2.1 Settling 281
5.2.2.2 Entrainment 283
5.2.2.3 Shear Sorting 285
5.2.2.4 Transport Sorting 285
5.2.3 Application of Sorting Principles to Placer Deposits 288
5.2.3.1 Small Scale 288
5.2.3.2 Intermediate Scale 288
5.2.3.3 Large Scale 288
5.2.4 A Note Concerning Sediment Sorting in Beach and Eolian Environments 290
5.2.4.1 Beaches 293
5.2.4.2 Wind-Borne Sediment Transport 295
5.2.5 Numerical Simulation of Placer Processes 296
5.3 Chemical Sedimentation - Iron-Formations, Phosphorites, and Evaporites 298
5.3.1 Iron-Formations and Ironstones 298
5.3.1.1 Bog Iron Ores 299
5.3.1.2 Phanerozoic Ooidal Ironstone (POI) Deposits 300
5.3.1.3 Banded and Granular Iron-Formation - An Enigmatic Rock Type 302
5.3.1.4 Mechanisms by Which BIFs Are Deposited 304
5.3.1.5 The Periodicity of Iron-Formation Deposition 308
5.3.1.6 Transformation of BIFs into Viable Iron Ore Deposits 309
5.3.2 Bedded Manganese Deposits 313
5.3.3 A Note on Ocean Floor Manganese Nodules 314
5.3.4 Phosphorites 316
5.3.4.1 A Model for Phosphogenesis Based on Present Day Deposition 319
5.3.5 Black Shales 322
5.3.6 Evaporites 323
5.4 Fossil Fuels - Oil/Gas Formation and Coalification 330
5.4.1 Basic Principles 330
5.4.2 Oil and Gas Formation (Conventional) 331
5.4.2.1 Source Rock Considerations and Organic Maturation 335
5.4.2.2 Petroleum Migration and Reservoir Considerations 337
5.4.2.3 Entrapment of Oil and Gas 340
5.4.3 Coalification Processes 345
5.4.3.1 Coal Characteristics 349
5.4.3.2 A Note Concerning Formation of Economically Viable Coals 352
5.4.4 Unconventional Hydrocarbons - Shale Gas, Oil Shales, and Tar Sands 354
5.4.4.1 Shale Gas and Oil Shales 354
5.4.4.2 Tar Sands (or Oil Sands) 354
5.4.5 Gas Hydrates 356
5.5 Summary 359
Further Reading 359
Sedimentology and Placer Processes 360
Chemical Sedimentation and Ore Formation 360
Fossil Fuels 360
Part IV Global Tectonics and Metallogeny 361
6 Ore Deposits in a Global Tectonic Context 363
6.1 Introduction 363
6.2 Patterns in the Distribution of Mineral Deposits 364
6.3 Continental Growth and the Supercontinent Cycle 366
6.3.1 Estimations of Continental Growth Rates 366
6.3.2 Supercontinent Cycles 369
6.3.2.1 Kenorland 370
6.3.2.2 Nuna (also referred to as Columbia) 370
6.3.2.3 Rodinia 370
6.3.2.4 Pangea 372
6.4 Geological Processes and Metallogenesis 375
6.4.1 Evolution of the Hydrosphere and Atmosphere 375
6.4.2 Secular Decrease in Global Heat Production and Mantle Temperature 376
6.4.3 Long-Term Global Tectonic Trends and Mantle Convection 377
6.4.4 Eustatic Sea Level Changes and “Continental Freeboard” 379
6.5 Metallogeny Through Time 380
6.5.1 The Archean Eon 380
6.5.1.1 The Hadean (>4000 Ma) and Eoarchean (>3600 Ma) stages 381
6.5.1.2 The Paleo-, Meso-, and Neoarchean stages (3600-2500 Ma) 381
6.5.1.3 Shield formation (pre-3100 Ma) 382
6.5.1.4 Cratonization (c. 3100-2500 Ma) 382
6.5.2 The Proterozoic Eon 384
6.5.2.1 The Paleoproterozoic Era (2500-1600 Ma) 385
6.5.2.2 The Mesoproterozoic Era (1600-1000 Ma) 386
6.5.2.3 The Neoproterozoic Era (1000-541 Ma) 386
6.5.3 The Phanerozoic Eon 388
6.5.3.1 Phanerozoic Tectonic Cycles and Metallogeny 392
6.5.3.2 Time-Bound and Regional Aspects of Phanerozoic Metallogeny 393
6.6 Plate Tectonic Settings and Ore Deposits - A Summary 396
6.6.1 Extensional Settings 396
6.6.2 Compressional Settings 396
6.7 Summary 399
Further Reading 400
References 401
Index 439
