Volatile evolution of ore fluids in Coeur D'Alene veins during metamorphism of the Belt Basin

Conference · Tue Jan 01 00:00:00 EST 1985 · Geol. Soc. Am., Abstr. Programs; (United States)

OSTI ID:6459467

Hofstra, A H; Landis, G P; Leach, D L

Two major vein types are recognized in the Coeur d'Alene district, Idaho and Montana. Early Zn-rich veins fill axial plane shears of WNW-trending folds in competent lithologies of Prichard Fm. and Ravalli Group metasediments. Later, Ag-rich veins occur predominantly in upper Revett Fm. quartzite in east- to northeast-trending fractures. Both vein types were deposited from fluids generated during regional greenschist grade metamorphism. Volatile composition of individual fluid inclusions in quartz and sphalerite from these veins were estimated using microthermometry and laser Raman spectroscopy. A high-sensitivity quadrupole mass spectrometer was used to obtain quantitative analyses of fluid extracted from whole crystals. Fluid inclusions from both vein types generally contain less than 10 mole % total gases and 5-10 eq. wt. % NaCl. However, fluid inclusion in Zn-rich veins contain greater concentrations of CH/sub 4/, short chain hydrocarbons, and N/sub 2/ compared to Ag-rich veins in which CO/sub 2/ is the dominant volatile component. The observed change in volatile compositions during metamorphism is consistent with a shift from relatively reducing to oxidizing conditions. The change from Zn- to Ag-rich veins may reflect the combined effects of a) volatile evolution of the metamorphic fluids through time, b) episodic development of large fractures with different orientations, and c) different lithologies contributing metamorphic fluids to these fractures.

• Research Organization: Geological Survey, Denver, CO (USA)
• OSTI ID: 6459467
• Report Number(s): CONF-8510489-
• Journal Information: Geol. Soc. Am., Abstr. Programs; (United States), Vol. 17; Conference: 98. annual meeting of the Geological Society of America, Orlando, FL, USA, 28 Oct 1985
• Country of Publication: United States
• Language: English

Related Subjects

58 GEOSCIENCES
IDAHO
SILVER ORES
ZINC ORES
INCLUSIONS
CHEMICAL COMPOSITION
VOLATILE MATTER
MONTANA
MINERALIZATION
GEOCHEMISTRY
GEOLOGIC FORMATIONS
GEOLOGIC FRACTURES
METAMORPHISM
QUANTITATIVE CHEMICAL ANALYSIS
QUARTZ
RAMAN SPECTROSCOPY
ROCK-FLUID INTERACTIONS
SCHISTS
SPHALERITE
THERMOGRAPHY
CHALCOGENIDES
CHEMICAL ANALYSIS
CHEMISTRY
FEDERAL REGION VIII
FEDERAL REGION X
GEOLOGIC STRUCTURES
LASER SPECTROSCOPY
MATTER
MEASURING METHODS
METAMORPHIC ROCKS
MINERALS
NORTH AMERICA
ORES
OXIDE MINERALS
OXIDES
OXYGEN COMPOUNDS
ROCKS
SILICON COMPOUNDS
SILICON OXIDES
SPECTROSCOPY
SULFIDE MINERALS
USA
580400* - Geochemistry- (-1989)
580300 - Mineralogy
Petrology
& Rock Mechanics- (-1989)