Studies of disseminated gold deposits near Carlin, Nevada: Evidence for a deep geologic setting of ore formation
The Carlin gold deposit occurs in the upper 175 meters of the Siluro-Devonian Roberts Mountains Formation in Eureka County, Nevada. Pre-, syn- and post-gold episodes are distinguished by (1) hydrocarbon maturation, (2) gold mineralization and alteration and (3) subsequent oxidation. Mineralization post-dates Early Cretaceous dikes which cut zones of thermally mature petroleum residue. Preore P-T conditions of 155 {+-} 20 C and 0.6 to 1.4 kb are defined by coexisting saline aqueous and methane-rich fluid inclusions. Main Gold Ore Stage (MGOS) alteration of pyrite-bearing unaltered calcareous carbonaceous argillaceous siltstones progresses from K-feldspar silt and calcite destruction, then dolomite dissolution, and finally illite conversion to dickite/kaolinite in intensely altered silicified zones near hydrothermal conduits. MGOS fluids are acid from elevated CO{sub 2} contents (5-10 mole percent), and also contain appreciable H{sub 2}S, 3 {+-} 1 wt% NaCl and {delta}{sup 18}O{sub H2O} values +5{per thousand} to {gt} +9{per thousand}. CO{sub 2}-exsolution occurs at 215 {+-} 30{degree}C and 800 {+-} 400 bars during portions of MGOS time and constrains ore formation to minimum depths of 4.4 {+-} 2.2 km. Late Gold Ore Stage (LGOS) fluids are non-boiling and gas-poor with {lt}1.5 wt% NaCl and {delta}{sup 18}O{sub H2O} values {le}-4{per thousand} to -3{per thousand}. As LGOS fluids flood the system, calcite {delta}{sup 18}O values shift from near whole-rocks at +12 {+-} 3{per thousand} to 0 {+-} 1{per thousand} in veinlets containing unoxidized As {+-} Sb-phases. Gas-rich MGOS fluids may result from buried intrusions, contact aueroles, or deeper low-grade metamorphism. Deposition may occur in throttling zones where conditions change abruptly from lithostatic to hydrostatic.
- Research Organization:
- Pennsylvania State Univ., Middletown, PA (USA)
- OSTI ID:
- 6091462
- Resource Relation:
- Other Information: Thesis (Ph. D.)
- Country of Publication:
- United States
- Language:
- English
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Related Subjects
03 NATURAL GAS
GOLD ORES
MINERALIZATION
NATURAL GAS DEPOSITS
GEOCHEMISTRY
NEVADA
PETROLEUM DEPOSITS
ALUMINIUM
CALCITE
CALCIUM
CARBON DIOXIDE
CARBONATE ROCKS
DEPOSITION
DEVONIAN PERIOD
DIKES
DOLOMITE
ENRICHMENT
GEOLOGIC FORMATIONS
GEOLOGIC HISTORY
GEOLOGY
HYDROGEN SULFIDES
HYDROTHERMAL ALTERATION
ILLITE
INCLUSIONS
IRON
KAOLINITE
MAGNESIUM
MATURATION
METEORIC WATER
OXYGEN 18
PH VALUE
PLUTONIC ROCKS
POTASSIUM
RESERVOIR FLUIDS
RESERVOIR PRESSURE
RESERVOIR TEMPERATURE
SILICON OXIDES
SILTSTONES
SILURIAN PERIOD
SODIUM CHLORIDES
TITANIUM
ALKALI METAL COMPOUNDS
ALKALI METALS
ALKALINE EARTH METAL COMPOUNDS
ALKALINE EARTH METALS
ALUMINIUM COMPOUNDS
ALUMINIUM SILICATES
CALCIUM CARBONATES
CALCIUM COMPOUNDS
CARBON COMPOUNDS
CARBON OXIDES
CARBONATE MINERALS
CARBONATES
CHALCOGENIDES
CHEMISTRY
CHLORIDES
CHLORINE COMPOUNDS
CLAYS
ELEMENTS
EVEN-EVEN NUCLEI
FEDERAL REGION IX
FLUIDS
GEOLOGIC AGES
GEOLOGIC DEPOSITS
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HALIDES
HALOGEN COMPOUNDS
HYDROGEN COMPOUNDS
IGNEOUS ROCKS
ISOTOPES
LIGHT NUCLEI
MAGNESIUM CARBONATES
MAGNESIUM COMPOUNDS
METALS
MINERAL RESOURCES
MINERALS
NORTH AMERICA
NUCLEI
ORES
OXIDES
OXYGEN COMPOUNDS
OXYGEN ISOTOPES
PALEOZOIC ERA
RESOURCES
ROCKS
SEDIMENTARY ROCKS
SILICATE MINERALS
SILICATES
SILICON COMPOUNDS
SODIUM COMPOUNDS
STABLE ISOTOPES
SULFIDES
SULFUR COMPOUNDS
TRANSITION ELEMENTS
USA
WATER
020200* - Petroleum- Reserves
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& Exploration
030200 - Natural Gas- Reserves
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& Exploration