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The AAPG/Datapages Combined Publications Database

Montana Geological Society

Abstract

MTGS-AAPG

Billings Geological Society: Guidebook: Fourth Annual Field Conference, 1953
September 10, 11, 12, 1953

Pages 164 - 169

RUBY GULCH GOLD MINING DISTRICT, LITTLE ROCKY MOUNTAINS, MONTANA

J. L. DYSON

ABSTRACT

In the Little Rocky Mountains, porphyry intrudes Pre-Cambrian metamorphic rocks and overlying sedimentary rocks, with large roof pendants of Pre-Cambrian rocks projecting downward into the porphyry mass. A series of very high-angle faults radiate from the central part of the uplift. Hydrothermal solutions rising along these faults have deposited gold and other minerals, giving rise to epithermal deposits.

The ore deposits, which are worked primarily for gold, are mostly of low grade. In the ore zones, quartz is the most abundant mineral although pyrite, the only sulphide noted, is common. Fluorite is locally common close to the faults. Some relatively high grade ore consists of a mixture of quartz, pyrite, fluorite, gold and sylvanite.

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