Contrasting siliceous replacement mineralization, east-central Nevada

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

OSTI ID:5318562

Barton, M D; Ilchik, R P ^[1]; Seedorff, C E ^[2]

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1. Univ. of Arizona, Tucson, AZ (United States). Dept. of Geosciences
2. Magma Copper Co., Ely, NV (United States)

Fine-grained siliceous replacement of carbonate-bearing rocks (jasperoid) occurs in most mineral districts in east-central Nevada. In most of these occurrences, jasperoid contains Au and(or) Ag and little or no base metals, although concentrations and ratios vary significantly. Broadly, two end-members are distinguished: (1) silicification as an intermediate- to late-stage part of complex alteration associated with igneous centers, and (2) jasperoids lacking other associated alteration and having few or no associated igneous rocks. Within this region, siliceous replacements are found with all metallic ([+-] magmatic) suites. No single factor in these occurrences relates the distribution, metal contents, fluid geochemistry, igneous rocks and associated alteration. Summarizing these characteristics: geochemical and fluid inclusion evidence shows that fluids in igneous-related jasperoids can be high-salinity magmatic (Ely), low-salinity magmatic (McCullough Butte), or metoric (Ward). Fluids in igneous-poor systems are low-salinity, exchanged meteoric waters from which a minor magmatic component can not be excluded. At this level of detail, the best predictor of Ag:Au are the district-scale alteration characteristics. Siliceous replacement takes place in many kinds systems and probably requires no more than a cooling, mildly acidic hydrothermal fluid. Metal suites, other fluid characteristics, and geological environment all need to be considered in evaluating the significance of any jasperoid.

• OSTI ID: 5318562
• 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

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15 GEOTHERMAL ENERGY
58 GEOSCIENCES
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MINERALIZATION
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HYDROTHERMAL SYNTHESIS
NEVADA
SILVER
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CHEMICAL COMPOSITION
GEOCHEMISTRY
GEOTHERMAL FLUIDS
GOLD ORES
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INCLUSIONS
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CHEMISTRY
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