DEPOSITION AND TRANSPORT OF GOLD BY THIOSULPHATES, VEITSCH, AUSTRIA

Two types of gold can be distinguished in tetrahedrite from the Veitsc h magnesite deposit, Austria. Primary gold present in unfractured mass ive tetrahedrite, has a grain size up to 18 mum and contains, on avera ge, Cu 8.73, Ag 7.01, Au 78.63 and Hg 2.35 (wt.%). Secondary gold is p resent in fractures and is directly intergrown with digenite, covellit e, Cu-thiosulphate, cuprite and chrysocolla but not with malachite or azurite. The secondary gold is up to 200 mum in size with an average c omposition of Cu 3.06, Ag 6.82, Au 86.41 and Hg 3.51 (wt.%). It is usu ally closely intergrown with thiosulphates containing up to 0.21 wt.% Au. This, together with the presence of 'dirty' gold with cloudy thios ulphate inclusions, directly indicates the transport and deposition of Au by a thiosulphate ligand. We believe this is the first reported di rect evidence of gold transport and deposition by thiosulphate complex es in a natural environment.