ANOMALOUS SULFUR ISOTOPE COMPOSITIONS IN THE GOLDEN MILE, KALOGOORLIE.

A reconnaissance study of the Kalgoorlie gold deposit suggested that it had a sulfur isotope signature quite distinct from many smaller Archean gold deposits. A tentative explanation emphasized the large size of the Kalgoorlie hydrothermal system, with greater opportunity for fluid evolution and sulfate formation during wall-rock alteration. The light isotopic compositions of Golden Mile phyrites suggest more oxidizing local environments created by fluid-wall rock alteration in ductile shear zones in more differentiated wall rocks. The structural environment (long-lived shear zones) may have influenced the progress of fluid-wall rock interactions, and hence oxidizing conditions only in the Golden Mile. It appears that local wall-rock reactions have resulted in considerable proportions of oxidized sulfur species in solution at the time of deposition, and anhydrite should be expected. In terms of explanation, it is predicted that pyrites with significantly negative delta **3**4S values should indicate large deposits, particularly those within ductile shear zones in Fe oxide-bearing host rocks. Other equally large deposits may have normal delta **3**4S values if they have different mineralization styles and/or host rocks.