Abstract

The delta S 34 values for 261 sulfide concentrates from the "B" limestone replacement and Galena fissure deposits of the U. S. mine range from +3.8 to --8.0 permil; the mean is +0.56 permil. The data indicate that (1) sulfides of the "B" limestone ore deposits are depleted in S 34 by 0.4 to 0.7 permil relative to those of the Galena fissure ore deposits; (2) sulfides of both deposits exhibit a primary fractionation trend characterized by increasing S 34 depletion in the sequence pyrite, sphalerite, tetrahedrite, and galena; (3) delta values for coexisting sulfide pairs of the "B" limestone deposit increase with increasing altitude; (4) sulfides of both deposits are increasingly depleted in S 34 with increasing altitude; (5) the paragenetic order of sulfide deposition is accompanied by an apparent depletion of S 34 that is independent of mineral species; and (6) pyrite disseminated in wall rocks is depleted in S 34 relative to pyrite from adjacent ore deposits.The similarity of delta S 34 values and isotopic trends to those of the central porphyry-type deposit at Bingham (Field, 1966) suggests that the hydrothermal deposits of the district were formed by fluids that originated from a common source during one episode of sequential mineralization. Gross isotopic differences between the deposits, consistent differences between coexisting sulfides, and systematic variations of delta values are attributed to temperature effects imposed upon sulfide exchange equilibria; isotopic temperatures suggest a lateral gradient between the "B" limestone and adjacent Galena fissure deposits and a possible vertical gradient within the "B" limestone deposit. The vertical zonation of delta S 34 values and trends related to pyrite physical occurrence and sulfide paragenesis are provisionally attributed to a pH-Eh control. Although the apparent trends are imperfectly resolved because of textural complexities, the marked depletion of S 34 in pyrite disseminated in country rocks warrants additional study as a potential exploration method.

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