LAURENCE ROBB is Visiting Professor in Economic Geology at the Department of Earth Sciences, University of Oxford. He continues to work on the metallogeny of the mineral districts of the African continent and also in SE Asia. He served a term as President of the Society of Economic Geologists in 2017.

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...