A supergene exploration model for Cobar style deposits

Knowledge of the geochemical “signature” of particular mineralisation is a prerequisite for exploration in the supergene environment. Particular elements may be widely dispersed compared to others and it is necessary to have some understanding of the chemical controls that govern this dispersion. With this in mind, it has been adventitious that the oxidised zone of the New Cobar orebody near Cobar, New South Wales, has been recently exposed. Primary mineralisation at New Cobar is of the typical “Cobar” type (Rayner, 1969; Stegman, 2000; Stegman & Pocock, 1996) and consists of arsenopyrite, (FeAsS), pyrite, (FeS2) marcasite, (FeS2), chalcopyrite (CuFeS2), galena, (PbS), sphalerite, ZnS, pyrrhotite, (Fe1-xS), and magnetite (Fe3O4). Cassiterite, (SnO2), native bismuth, bismuthinite, (Bi2S3), and rarer tungsten, molybdenum and selenium minerals are accessories, in common with a number of other deposits in the region. Quartz is the most common gangue mineral and very little primary carbonate mineralisation is present