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11/30/2012
1
Descriptive Mineralogy
Native Elements:Pure elements that occur
as minerals
Classification of the Minerals• Non-Silicates
– Native Elements– Halides– Sulfides– Oxides– Hydroxides– Carbonates– Sulfates– Phosphates
• Silicates– Orthosilicates– Sorosilicates– Cyclosilicates– Chain Silicates– Layer Silicates– Tektosilicates
Native ElementsNative Elements: Metals
• Fe, Co, Ni: Meteorites
• Platinum Group: (Ru, Rh, Pd, Os, Ir, Pt): Mafic Igneous Rocks
• Coinage metals: Cu, Ag, Au– Cu, Ag: Supergene Enrichments (Sulfide
Oxidation)
– Au: Low Temperature Hydrothermal, Placer
Native Iron: Meteorites Native Iron: MeteoritesWidmanstätten Pattern
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Iron-Nickel Phase Diagram
FCC
BCC
Platinum Group MetalsRu, Rh, Pd, Os, Ir, Pt
• Strongly siderophile elements• Enriched in Fe meteorites• Found in layered mafic intrusions
– Bushvelt Complex (South Africa)– Stillwater Complex (Montana)– Skaergaard Complex (Greenland)
Bushvelt: Layered Gabbroic Intrusion Bushvelt: Layered Gabbroic Intrusion
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Skaergaard: Layered Gabbroic Intrusion Skaergaard: Layered Gabbroic Intrusion
Skaergaard: Layered Gabbroic IntrusionNative Elements: Cu, Ag, Au• Cu and Ag: Supergene Enrichment
– Oxidation of Cu, Ag sulfides in unsaturated zone
– Precipitation of metal, oxides and carbonates at water table
• Ag and Au: hydrothermal– Native metals and tellurides
• Au: placer – oxidized hydrothermal
Supergene Copper Hydrothermal Silver
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Hydrothermal Gold Hydrothermal Gold
Gold Tellurides
• Calaverite (AuTe2)
• Krennerite (Au3AgTe8)
• Sylvanite (AuAgTe4)
• All weather to TeO2 + native gold
Native Elements: non metals
• Carbon: – Graphite: Metamorphic Rocks– Diamond: Kimberlites
• Sulfur (+Se): – Salt Domes (Sulfate reduction), – Volcanos (H2S oxidation)
• Tellurium (Te) Telluride oxidation
Native Elements: Carbon
• Graphite (Low Pressure)– Metamorphosed Organic-rich sediments
• Diamond (High Pressure >100km)– Kimberlites– Placers from kimberlites
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Native Elements: Diamond Native Elements: Diamond
Kimberley Mine 1875
Native Elements: Sulfur
• Fumaroles (Volcanic hydrothermal vents)– Oxidation of H2S
• Salt dome cap rocks– Sulfate reduction by petroleum
Fumarole Sulfur: Nysseros
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Fumarole Sulfur: Kilauea In the caps of salt domes, gypsum (CaSO4 2H2O) is reduced to native sulfur
Native Elements