Abstract

Study of the spatial and mineralogical distribution of gold and silver in the Rosebery north end orebody indicates that both silver and gold are concentrated in massive sphalerite-galena-pyrite ore and barite mineralization. Six styles of gold mineralization have been recognized: (1) in massive sphalerite-galena-pyrite ore (the dominant occurrence), (2) in massive barite mineralization, (3) in the upper parts of pyrite-chalcopyrite pods (in general, pyrite-chalcopyrite pods are gold poor), (4) in distal pyrite mineralization (at the edges of sphalerite-galena-pyrite mineralization and in the overlying host rocks), (5) in footwall mineralization (poorly sampled and understood), and (6) in remobilized quartz-carbonate veins.Mineralogically, gold occurs as electrum which is commonly associated with pyrite in sphalerite-galena-pyrite ore and distal pyrite mineralization. A lesser association of gold with tetrahedrite has been noted by Brathwaite (1969). The grain size of electrum has a lognormal distribution, with most grains having dimensions of less than 25 mu m.Silver occurs dominantly in tetrahedrite, and to a lesser extent, in galena (Henley and Steveson, 1978). Remobilized tetrahedrite is silver and antimony rich, whereas in tetrahedrite from both sphalerite-galena-pyrite ore and massive barite mineralization the silver contents increase with the antimony contents.

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