Evidence for throttling as a control over localized late-stage Au/Ag mineralization in the Mineral Hill breccia pipe, Golden Sunlight mine, Jefferson County, Montana

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

OSTI ID:6875468

Coppinger, W W; Porter, E

A restricted zone of anomalous gold and silver mineralization, coupled with localized intense alteration and textural variations, documents the existence of a natural throttle which controlled Au/Ag emplacement during late-stage mineralization of the Mineral Hill breccia pipe. The zone is roughly funnel-shaped with a maximum width of 10m and a length of 30m. Mineralization and alteration are developed along the trend of a steep-dipping to vertical fracture zone and apparently pinch out at depth. Small displacement post-mineralization cross-faults offset contacts and influence grade distribution within the feature. Breccia texture, nature and intensity of alteration, and ore grade very systematically from the margin to the interior of the zone. The breccia becomes rubbly and friable, with frothy, cellular quartz comprising the matrix and as much as 50 percent of the rock in some locations. Au/Ag grades vary directly with the development of the cellular quartz and are highest in the interior, grading to local background levels in the wallrock. Barite and minor white opaline quartz occur in the matrix adjacent to contacts, diminishing in volume toward the interior. Minor primary hematite occurs in some clasts in the interior. Iron-oxides after sulfides are common throughout the zone. The feature is interpreted as late-stage localized zone of venting and pressure-release developed above a constriction in the Mineral Hill hydrothermal mineralizing system.

• Research Organization: Trinity Univ., San Antonio, TX (USA)
• OSTI ID: 6875468
• 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
GOLD ORES
GEOCHEMISTRY
MINERALIZATION
MINERALOGY
MONTANA
SILVER ORES
CHEMICAL COMPOSITION
GEOLOGIC FAULTS
GEOLOGIC FRACTURES
GEOLOGIC HISTORY
HEMATITE
HYDROTHERMAL ALTERATION
LITHOLOGY
QUARTZ
TEXTURE
CHALCOGENIDES
CHEMISTRY
FEDERAL REGION VIII
GEOLOGIC STRUCTURES
IRON COMPOUNDS
IRON ORES
IRON OXIDES
MINERALS
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ORES
OXIDE MINERALS
OXIDES
OXYGEN COMPOUNDS
SILICON COMPOUNDS
SILICON OXIDES
TRANSITION ELEMENT COMPOUNDS
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