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Gold Paragenesis in Intrusion-Marginal Sediment-Hosted Gold Mineralization at Eureka, Nevada

By
Jacob Margolis
Jacob Margolis
Senior Geologist Homestake Mining Company
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Published:
January 01, 1997

Abstract

The Archimedes gold deposit, discovered in 1992 by Homestake Mining Company, is about 1 mile northwest of Eureka, Nevada in the northern part of the Eureka minin district (Nolan, 1962). The deposit, described in further detail by Dilles et al. (1996), is a largely stratiform body of silicification within non-carbonaceous, cherty Ordovician limestones of the Pogonip Group. This zone, West Archimedes, is approximately 2600 feet long at N60°W, and averages 260 feet inwidth and 75 feet in height; the zone plunges gently east. Gold mineralization has low concentrations of Ag-Pb-Zn-Cu and correlates strongly with silicification, which is generally surrounded by decalcified but unsilici:fied limestone containing lower grade. Published reserves for the western zone are 7.62 million short tons grading 0.099 ounces per ton (opt) Au; the mineralization is oxidized. Values above 0.25 opt Au are common in the central part of the zone. This stratiform silicification is concealed by as much as 500 feet of alluvium and locally intersects the bedrock surface. No intrusive rocks or calc-silicate alteration are present within the West Archimedes deposit, although an altered sill lies more than 1000 feet below. This gold-bearing silicification is herein referred to as Type A. North-northeast and west-northwest trending normal faults are thought to have provided ingress for hydrothermal fluids in the deposit area (Dilles et al., 1996); however, the lack of bedrock exposure at the deposit has precluded thorough analysis of the structures.

More strongly brecciated gold-bearing silicification (Type A) on the east side of West Archimedes is underlain

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Contents

Society of Economic Geologists Guidebook Series

Carlin-Type Gold Deposits Field Conference

Peter Vikre
Peter Vikre
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Tommy B. Thompson
Tommy B. Thompson
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Keith Bettles
Keith Bettles
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Odin Christensen
Odin Christensen
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Ron Parratt
Ron Parratt
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Society of Economic Geologists
Volume
28
ISBN electronic:
9781934969816
Publication date:
January 01, 1997

GeoRef

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