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Sulfur isotope analyses have been performed on 64 monomineralic concentrates from 37 samples that are representative of mineralization in time and space at E1 Salvador.The hypogene sulfates (mean +10.75o; range +7.3 to +17.05o) are enriched in s4S relative to supergene sulfates (--0.75ø; --4.6 to +3.67oo) and to hypogene sulfides (--3.05ø; --10.1 to --0.37oo). Coexisting hypogene sulfides are increasingly depleted in a4S in the order molybdenite, pyrite, chalcopyrite, and bornite. The isotopic data suggest that sulfur in the supergene sulfates was largely derived from the oxidation of hypogene sulfides and that supergene "chalcocite" probably replaced hypogene chalcopyrite or bornite, but not pyrite. Isotopic temperature estimates from sulfate-sulfide fractionation pairs range from 400 ø to 570øC and are only in crude agreement with temperatures (<300 ø to >600øC) indicated by other geologic evidence. Those estimated from pyrite-chalcopyrite fractionation pairs (95 ø to 185øC) are nmch too low. Fractionation between 13 coexisting hypogene sulfate-sulfide assemblages (21 mineral pairs) defines a rather narrow band in /o•-pH-T space and suggests that [o• and pHacted as internally controlled variables throughout mineralization. Mass balance estimates of •s4Szs indicate a value of about +6 per mil for the sulfate zone and a value probably significantly heavier than 0 per mil for the entire deposit as presently exposed. The •s4S per mil values of coexisting hypogene sulfate and sulfide pairs approximate linear trends when plotted against their respective delta (/x) values. These trends suggest that Early anhydrite-chalcopyrite-bornite assemblages were formed from a sulfur reservoir having $a4Szs of approximately +1.6 per mil whereas Late anhydrite-pyritechalcopyrite assemblages formed from a reservoir +6.8 per mil $a%.s. Speculative interpretation suggests that Late sulfur was derived either from remobilization of Early assemblages below the deepest levels of exposure or from volcanic wall rocks surrounding the deposit, rather than from continued emanations from the underlying magma chamber that was the source of Early mineralization. However, at least one totally different interpretation of these data is possible. Recent experimental work by Ohmoto and Rye (1975, written and oral commun.) indicates that our $a4S per rail values for pyrite may require a correction factor, which would reduce both Early and Late sulfate-.sulfide assemblages to approximately single linear trends. This would imply that the underlying magma chamber continued to be the predominant source of sulfur ($s•Szs • +2%•) throughout the entire sequence of alteration-mineralization. The isotopic data do not show any consistent trends of s4S depletion with either paragenesis or zoning that would suggest a restricted reservoir of sulfur in the hydrothermal system. More questions than answers are provided by these data. Andesite; peripheral, 2,400 m; sericite-chlorite Andesite; peripheral, 2,400 m; sericite-chlorite "L" porphyry; central, 2,400 m; "D" v...

Typical porphyry-type Cu-Mo mineralization occupies two connected domal centers, the eastern Pittsmont and western Anaconda domes, that predate and largely underlie the well-known, throughgoing, Main Stage polymetallic veins of Butte. Among the sulfur-bearing minerals recovered from deep drill core of this early pre-Main Stage hydrothermal assemblage are anhydrite, chalcopyrite, pyrite, and molybdenite in veinlets bordered by K-silicate alteration, and pyrite from slightly younger quartz-pyrite veinlets with dgray-sericiticT alteration selvages. The ranges of d 34 S values for minerals of the K-silicate assemblage are 9.8-18.2x for anhydrite (n=23 samples), 3.0x to 4.7x for molybdenite (n=6), 0.4x to 3.4x for pyrite (n=19), and À0.1x to 3.0x for chalcopyrite (n=13). Sulfate-sulfide mineral fractionation is consistent with an approach to isotopic equilibrium, and calculated temperatures for mostly coexisting anhydrite-sulfide pairs (anhydrite-molybdenite, n=6, 545 to 630 8C; anhydrite-pyrite, n=13, 360 to 640 8C; and anhydrite-chalcopyrite, n=8, 480 to 575 8C) are broadly consistent with petrological, alteration, and fluid-inclusion temperature estimates. The d 34 S values for pyrite (n=25) in veinlets of the dgray-sericiticT assemblage range from 1.7x to 4.3x. The d 34 S values for sulfides of the pre-Main Stage K-silicate and dgray-sericiticT assemblages are similar to those of most Main Stage sulfides, for which 281 analyses by other investigators range from À3.7x to 4.8x. Sulfide-sulfide mineral pairs provide variable (À175 to 950 8C) and less reliable temperature estimates that hint of isotopic disequilibria. The sulfide data, alone, suggest a conventionally bmagmaticQ value of about 1x or 2x for Butte sulfur. However, the high modal mineral ratios of sulfate/sulfide, and the isotopic systematics of the early K-silicate assemblage, suggest that pre-Main Stage fluids may have been sulfate-rich (X SO 4 2Àc0.75) and that total sulfur was isotopically heavy (d 34 S AS c10x), which would have required an evaporitic crustal component to the relatively oxidized granitic parental magma that was the source of the hydrothermal fluids and sulfur. Modeling of brine-vapor unmixing of a 10x fluid, reduction of sulfate, and vapor loss suggest that these processes may have formed the isotopically heavier (14x to 18x) anhydrite of the western and shallower Anaconda Dome, contrasting with the lighter and more numerous values (9.8x to 12.9x) for anhydrite of the eastern and

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Sulfur isotope analyses of 10 epigenetic occurrences of pyrite in ocean-floor basalts yield an unexpectedly large range of á 34 S values (from -24.2 to +23.O°/oo) for sulfides that are inferred to be of hydrothermal origin. The existing geologic, mineralogical, and isotopic data do not permit an unambiguous interpretation of the chemical and thermal characteristics of these hydrothermal systems. They fit either of two hypothetical models that assume isotopic equilibration between varying proportions of oxidized and reduced species of sulfur, but with pyrite deposition either (1) at 150°C and less from an infinite reservoir of heavy (+21°/oo) seawater sulfur, or (2) at 300°C and less from a finite reservoir of deep-seated (O°/oo) "magmatic" sulfur. Further detail and elaboration of these or alternative models must await additional mineralogical and isotopic studies, particularly of coexisting hydrothermal assemblages.