Sediment-hosted disseminated gold deposits as a product of mixing of deeply circulating meteoric waters in compressional tectonic environments

Conference · Thu Apr 01 00:00:00 EST 1993 · Geological Society of America, Abstracts with Programs; (United States)

OSTI ID:5437435

Arehart, G B ^[1]

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1. Argonne National Lab., IL (United States)

Until recently, most models for sediment-hosted disseminated gold (SHDG) deposits were predicted on a shallow environment of formation, akin to hot springs-type deposits. More recent data suggests formation at depth and from deeply circulating meteoric water. Fluid inclusion salinities are typically low (<5 wt.% NaCl eq.), and appear to decrease as mineralization progresses. Pressures are estimated to be in the range of 800 [+-] 400 bars, requiring multiple kilometer depths (> 2.5 km. lithostatic). Temperatures of formation are near 225 C. Stable isotope data on alteration phases (quartz, kaolinite) and from fluid inclusions associated with mineralization are most consistent with evolved meteoric water as the major ore fluid. Ore-stage sulfides have high [delta][sup 34]S values, consistent with an original sulfate source. No stable isotopic evidence for magmatic fluid involvement is observed. The author believes that most SHDG deposits in the western US are Cretaceous (85--125 Ma), although some evidence exists for younger ages for a few minor deposits. During this time, western North America was in a compressional tectonic environment with crustal thickening in the Great Basin. Deep-seated structures (likely Precambrian in origin) may have acted as major conduits for fluid upwelling, and may explain, in part, the roughly linear arrangement of some groups of deposits ( trends''). Geochemical modeling and field observations suggest that gold was deposited primarily as a result of mixing of an ascending, isotopically-evolved, gas-rich, reduced, Au- and As-rich fluid with a less-evolved, gas-poor, and slightly more oxiding water (also meteoric ) perhaps in regional aquifers. Such a model best explains the observed alteration, mineralization, and geochemical features of SHDG deposits.

• OSTI ID: 5437435
• Report Number(s): CONF-9305259-; CODEN: GAAPBC
• Journal Information: Geological Society of America, Abstracts with Programs; (United States), Vol. 25:5; Conference: 89. annual meeting of the Cordilleran Section and the 46th annual meeting of the Rocky Mountain Section of the Geological Society of America (GSA), Reno, NV (United States), 19-21 May 1993; ISSN 0016-7592
• Country of Publication: United States
• Language: English

Related Subjects

58 GEOSCIENCES
GOLD ORES
INCLUSIONS
MINERALIZATION
GREAT BASIN
PLACERS
CHEMICAL COMPOSITION
GEOLOGY
GEOBAROMETRY
GEOCHEMISTRY
GEOLOGIC HISTORY
GEOLOGIC MODELS
ISOTOPE RATIO
METEORIC WATER
SALINITY
CHEMISTRY
DEVELOPED COUNTRIES
GEOLOGIC DEPOSITS
GROUND WATER
HYDROGEN COMPOUNDS
NORTH AMERICA
ORES
OXYGEN COMPOUNDS
USA
WATER
580000* - Geosciences