CHARACTERIZATION AND CYANIDATION OF RIO-TINTO GOSSAN ORES

The mineralogical composition of Rio Tinto gossan was investigated wit h the aim of explaining the low silver recoveries obtained by conventi onal cyanidation. The ore basically consists of goethite, hematite and solid solutions of beudantite-plumbojarosite-potassium jarosite. Silv er occurs as halide, sulfide, mercury/silver sulfo-halide and as dilut e solid solution of argentojarosite in jarosite-beudantite phases. A s cheme to determine the amounts of the different silver carriers was de signed based on their chemical reactivity. The silver extraction by co nventional cyanidation corresponds to halide, sulfide and mercury/silv er sulfo-halide. The rates of extraction as well as the consumption of reagents were determined. The solid solutions of beudantite-plumbojar osite-potassium jarosite are not decomposed during conventional cyanid ation.