Abstract

Sulfide minerals from five vein stages in and near Mineral Park have a shared delta 34 S range of 0 to 5 per mil (47 values). Anhydrites from anhydrite-molybdenite and anhydrite-chalcopyrite vein stages have nearly identical delta 34 S ranges of 12.6 to 22.7 per mil. No spatial isotopic zonation is evident. In the anhydrite-molybdenite vein stage, a delta 34 S versus delta 34 S plot for anhydrite-pyrite pairs suggests an H 2 S-dominated fluid and a bulk fluid delta 34 S value near 1 per mil, but general isotopic disequilibrium is suspected. In the anhydrite-chalcopyrite vein stage, mineral relationships indicate a sulfate-dominated hydrothermal fluid. Isotopic temperatures from anhydrite-pyrite pairs of this stage generally match fluid inclusion data in veins from felsic hosts but are more dispersed in veins from mafic hosts. This may reflect local isotopic disequilibrium resulting from reduction of sulfate by ferrous silicates in the mafic hosts. Use of the delta 34 S versus delta 34 S plot, which indicated different values for the sulfate/sulfide ratio and bulk fluid delta 34 S for mafic- and felsic-hosted data subsets, is thus compromised. The fluid that deposited late polymetallic quartz veins appears to have been H 2 S dominated, with a bulk fluid delta 34 S value of 2 to 4 per mil. The isotopic data are not sufficient to discriminate among potential sources for the hydrothermal sulfur.Oxygen isotope data on anhydrites indicate that two distinct generations were deposited. The data are compatible with a mixed magmatic-meteoric origin for waters (calculated delta 18 O water range, 6.5-9.2ppm) that deposited anhydrite-molybdenite veins, and with either a magmatic or an evaporitic origin for the waters (calculated delta 18 O water range, 11.8-17.1ppm) that deposited anhydrite-chalcopyrite veins. Magmatic sources for the fluids that deposited anhydrite are the most compatible with geologic and fluid inclusion data.

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