Evidence for a magmatic origin for Carlin-type gold deposits: isotopic composition of sulfur in the Betze-Post-Screamer Deposit, Nevada, USA |
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Authors: | Stephen E Kesler Lee C Riciputi Zaojun Ye |
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Institution: | (1) Department of Geological Sciences, University of Michigan, Ann Arbor, MI USA, 48109;(2) Oak Ridge National Laboratory MS6365, PO Box 2008, Oak Ridge, TN 37831, USA |
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Abstract: | We report here new sulfur isotope analyses from the Betze-Post-Screamer deposit, the largest Carlin-type gold deposit in the
world. Carlin-type deposits contain high concentrations of arsenic, antimony, mercury, tellurium and other elements of environmental
interest, and are surrounded by large volumes of crust in which these elements are also enriched. Uncertainty about the source
of sulfur and metals in and around Carlin-type deposits has hampered formulation of models for their origin, which are needed
for improved mineral exploration and environmental assessment. Previous studies have concluded that most Carlin-type deposits
formed from sulfide sulfur that is largely of sedimentary origin. Most of these studies are based on analyses of mineral separates
consisting of pre-ore diagenetic pyrite with thin overgrowths of ore-related arsenian pyrite rather than pure, ore-related
pyrite. Our SIMS spot analyses of ore-related pyrite overgrowths in the Screamer zone of the Betze-Post-Screamer deposit yield
δ34S values of about −1 to 4‰ with one value of about 7‰. Conventional analyses of realgar and orpiment separates from throughout
the deposit yield δ34S values of about 5–7‰ with one value of 10‰ in the Screamer zone. These results, along with results from an earlier SIMS
study in the Post zone of the deposit and phase equilibrium constraints, indicate that early arsenian pyrite were formed from
fluids of magmatic origin with variable contamination from sulfur in Paleozoic sedimentary rocks. Later arsenic sulfides were
formed from solutions to which sulfur of sedimentary origin had been added. The presence of Paleozoic sedimentary sulfur in
Carlin-type deposits does not require direct involvement of hydrothermal solutions of sedimentary origin. Instead, it could
have been added by magmatic assimilation of Paleozoic sedimentary rocks or by hydrothermal leaching of sulfur from wall rocks
to the deposit. Thus, the dominant process delivering sulfur, arsenic, gold and mineralizing fluids to Carlin-type systems
and their surrounding country rocks was probably separation of fluids from a magmatic source.
Editorial handling: G. Beaudoin |
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Keywords: | Sulfur isotope Carlin-type deposit Gold arsenian pyrite Nevada |
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