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Isotopic Composition of Sulfur in Carlin-type Gold Deposits: Implications for Genetic Models

By
Albert H. Hofstra
Albert H. Hofstra
U.S. Geological SurveyMS-973, Box 25046, Denver, CO 80225
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Published:
January 01, 1997

Abstract

The goal of this report is to consider new and existing sulfur isotope data from Carlin-type gold deposits within the context of a modem understanding of the geology of the region and processes of ore formation. Increased understanding of the source(s) of sulfur and mechanisms of H2S generation may help to discriminate between the various models proposed for the deposits. The source of reduced sulfur is very important because available evidence indicates the deposits formed from H2S-rich (SO4-poor) fluids that transported gold as a bisulfide complex. High H2S-concentrations in ore fluids are indicated by (1) the common occurrence of high sulfidation state minerals such as orpiment and realgar, (2) mass transfer studies which show that sulfur was one of the most abundant elements introduced by the hydrothermal fluids, (3) gas analyses of fluid inclusions which show the fluids contained 10-1 to 10-2m H2S, (4) petrographic and geochemical evidence which indicates that sulfidation of host rock iron was an important (but not the only) gold depositional mechanism in most of the deposits, and (5) chemical reaction path modeling which shows that sulfidation can produce the gold grades observed in the deposits (Hofstra et al., 1991; Hofstra, 1994). The predominance of H2S over sulfate is important because the isotopic composition of H2S is then representative of the bulk composition of sulfur in the ore fluids. Given that gold was transported as a bisulfide complex, knowledge of the sites of H2S production and migration pathways will also likely provide information on the source

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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

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