Evaluation of a diagnostic leaching technique for gold in native gold and gold +/- silver tellurides

A detailed investigation of the stability in cyanide solutions of native go ld and gold +/- silver tellurides in a flotation concentrate from the Golde n Mile, Kalgoorlie, has been undertaken to assess whether leaching under di fferent conditions can be used to quantify the distribution of Au between n ative gold and gold +/- silver tellurides, as suggested by, for example, Ch ryssoulis and Cabri (1990). The leaching was carried out on +20 mum native gold and gold +/- silver tel lurides separated from a high-grade flotation concentrate and then diluted with barren quartz. The material leached assayed 270 ppm Au and 118 ppm Te. About 77% of the Au was present as native gold (largely liberated) and abo ut 23% was in gold +/- silver tellurides (predominantly calaverite with tra ce petzite and Au-bearing hessite, also largely liberated). The grainsize o f the gold-bearing minerals was mainly in the range 20 mum to 100 mum. The leach conditions used were: Stage 1: Leaching in dilute cyanide (0.1%) at pH 9.5 for 24 hours to dissol ve native gold but not gold +/- silver tellurides. Stage 2: Leaching the residue from Stage 1 in strong cyanide (2%) at pH 12. 5 for 96 hours to dissolve gold +/- silver tellurides. Extractions of native gold and gold +/- silver tellurides in the two stages of leaching were found to be as follows: [GRAPHICS] The results showed that the bulk of the native gold dissolved in the Stage 1 leach (weak cyanide, moderate pH), along with aborts half the hessite and petzite but hardly any of the calaverite. The estimate of Au in native gol d from the Stage 1 leach corresponded fairly closely to the native gold con tent as the hessite/petzite concentrations were low. However, although the Stage 2 leach (strong cyanide, high pH) dissolved almost all the remaining hessite/petzite, only a small proportion of the calaverite dissolved. The main conclusions of the investigation are that calaverite is very refra ctory to cyanidation, much more so than hessite/petzite, and that the diagn ostic leaching procedure studied did not provide a good estimate of Au in g old +/- silver tellurides. For the diagnostic leach procedure to be effecti ve, a treatment, such as chlorination, which breaks down calaverite prior t o the Stage 2 cyanidation is required. (C) 2000 Published by Elsevier Scien ce Ltd. All rights reserved.