Mineral deposit models for resource assessment
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Porphyry copper deposit model: Chapter B in Mineral deposit models for resource assessment
.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
Robert A Ayuso Mark D Barton Richard J Blakely Robert J Bodnar John H Dilles Floyd Gray Frederick Turner Graybeal John Mars Darcy K McPhee Robert R Seal Ryan D Taylor Peter G Vikre
128040877
A deposit model for Mississippi Valley Type lead zinc ores: Chapter A in Mineral deposit models for resource assessment
David L Leach Ryan D Taylor David L Fey Sharon F Diehl Richard W Saltus
130206282
A deposit model for carbonatite and peralkaline intrusion related rare earth element deposits: Chapter J in Mineral deposit models for resource assessment
Philip L Verplanck Bradley S Van Gosen Robert R Seal A E Mccafferty
187293486
Descriptive Models for Epithermal Gold Silver Deposits: Chapter Q in Mineral deposit models for resource assessment
David A John Peter G Vikre Edward A du Bray Richard J Blakely David L Fey Barnaby W Rockwell Jeffrey L Mauk Eric D Anderson Frederick Turner Graybeal
229214926
Alkalic type epithermal gold deposit model; Chapter R in Mineral deposit models for resource assessment
This report summarizes the primary characteristics of alkalic type epithermal gold (Au) deposits and provides an updated descriptive model. These deposits, primarily of Mesozoic to Neogene age, are among the largest epithermal gold deposits in the world. Considered a subset of low sulfidation epithermal deposits, they are spatially and genetically linked to small stocks or clusters of intrusions containing high alkali element contents. Deposits occur as disseminations, breccia fillings, and veins and may be spatially and genetically related to skarns and low grade porphyry copper (Cu) or molybdenum (Mo) systems. Gold commonly occurs as native gold, precious metal tellurides, and as sub micron gold in arsenian pyrite. Quartz, carbonate, fluorite, adularia, and vanadian muscovite/roscoelite are the most common gangue minerals. Alkalic type gold deposits form in a variety of geological settings including continent arc collision zones and back arc or post subduction rifts that are invariably characterized by a transition from convergent to extensional or transpressive tectonics. The geochemical compositions of alkaline igneous rocks spatially linked with these deposits span the alkaline subalkaline transition. Their alkali enrichment may be masked by potassic alteration, but the unaltered or least altered rocks (1) have chondrite normalized patterns that are commonly light rare earth element (LREE) enriched, (2) are heavy rare earth element (HREE) depleted, and (3) have high large ion lithophile contents and variable enrichment of high field strength elements. Radiogenic isotopes suggest a mantle derivation for the alkalic magmas but allow crustal contamination. Oxygen and hydrogen isotope compositions show that the fluids responsible for deposit formation are dominantly magmatic, although meteoric or other external fluids (seawater, evolved groundwater) also contributed to the ore forming fluids responsible for these deposits. Carbon and sulfur isotope compositions in vein hosted carbonates and sulfide gangue minerals, respectively, coincide with magmatic values, although a sedimentary source of carbon and sulfur is evident in several deposits. Deep seated structures are critical for the upwelling of hydrous alkalic magmas and for focusing magmatic hydrothermal fluids to the site of precious metal deposition. The source of gold, silver (Ag) tellurium (Te) vanadium (V) and fluorine (F) was probably the alkalic igneous rocks themselves, and the coexistence of native gold, gold tellurides, and roscoelite in several deposits is primarily a function of similar physicochemical conditions during deposition (for example, overlapping pH and oxygen fugacity (fO2) Potential environmental impacts related to the mining and processing of alkalic type epithermal gold deposits include acid mine drainage with high levels of metals, especially zinc (Zn) copper, lead (Pb) and arsenic. However, because alkalic type gold deposits typically contain carbonates, which contribute calcium and magnesium ions that increase water hardness, aquatic life may be afforded some protection. Impacts vary widely as a function of host rocks, climate, topography, and mining methods. Geologic mapping to (1) highlight the distribution of potassic alteration; (2) define fault density and orientation of structures; (3) determine the distribution of alkaline rocks and hydrothermal breccias; and (4) identify uniquely colored gangue minerals, such as fluorite and roscoelite, will be critical to exploration and future discoveries. Geophysical techniques that identify potassium (K) anomalies (for example, radiometric and spectroscopic surveys) as well as magnetic, resistivity, aeromagnetic, and gravity surveys, may help locate zones of high permeability that control advecting hydrothermal fluids. Geochemical surveys that include analyses for Au, Ag, barium, Te, K, F, V, Mo, and mercury, which are key elements in these deposits, should be undertaken along with the measurement of other pathfinder elements such as arsenic, bismuth, Cu, iron, nickel, Pb, antimony, selenium, and Zn.
Karen D Kelley Paul G Spry Virginia McLemore David L Fey Eric D Anderson
129670985
Arc related porphyry molybdenum deposit model: Chapter D in Mineral deposit models for resource assessment
Ryan D Taylor Jane M Hammarstrom Nadine M Piatak Robert R Seal
128427093
Volcanogenic massive sulfide occurrence model: Chapter C in Mineral deposit models for resource assessment
W C Pat Shanks Randolph A Koski Dan L Mosier Klaus J Schulz Lisa A Morgan John F Slack William Ian Ridley Cynthia Dusel-Bacon Robert R Seal Nadine M Piatak
126581405
Nickel cobalt laterites: a deposit model: Chapter H in Mineral deposit models for resource assessment
Erin E Marsh Eric D Anderson Floyd Gray
128181720
Occurrence model for magmatic sulfide rich nickel copper (platinum group element) deposits related to mafic and ultramafic dike sill complexes: Chapter I in Mineral deposit models for resource assessment
Klaus J Schulz Laurel G Woodruff Suzanne W Nicholson Robert R Seal Nadine M Piatak Val W Chandler John Mars
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Stratiform chromite deposit model: Chapter E in Mineral deposit models for resource assessment
Ruth F Schulte Ryan D Taylor Nadine M Piatak Robert R Seal