Abstract

The Willyama Complex in western New South Wales, Australia, is characterized by the presence of both stratiform and vein-type lead-silver-zinc mineralization; these are known, respectively, as the Broken Hill type (of which the main Broken Hill Lode is the most important example) and the Thackaringa type. Isotopic similarity of the sulfur from the two types of deposits supports the hypothesis that the Thackaringa-type veins were derived from the Broken Hill-type mineralization, possibly during retrograde metamorphism of the Willyama Complex.Variations in sulfur isotope composition among individual Broken Hill-type deposits are consistent with a contribution of sulfur from more than one source, and a multi-basin model is proposed, with the variation being due primarily to differences in the relative proportion of biogenic sulfide contributed in each basin.Although delta 34 S sp-gn measurements show considerable variation, a temperature of metamorphism of the main Broken Hill Lode of the order of 700 degrees C is indicated.

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