Distribution, mineralogy, and geochemistry of gold and silver in the North End Orebody, Rosebery, Tasmania

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.