TREATMENT OPTIONS FOR PROCESSING DOUBLE REFRACTORY MATERIAL FROM THE BARBERTON GREENSTONE BELT IN SOUTH AFRICA

摘要

South Africa is currently the 7th largest gold producer in the world and has two main gold resources, the Witwatersrand Basin and the Barberton Greenstone belt. The Barberton Greenstone deposit is very rich in gold and contains gold grades as high as 22 g/t. However, the gold particles are usually associated with arsenopyrite, pyrite and other secondary sulphides. The ore also contains carbonaceous material, which acts as an absorber of the gold-cyanide complex from solution; resulting in preg-robbing. Therefore, this ore is typified as being double refractory and has a history of poor metallurgical performance when using conventional processing methods for gold extraction.A number of technologies have been proposed for gold extraction from double refractory gold ores. However, each ore body has specific characteristics necessitating individual selection of the optimum treatment option. This paper presents results from testwork aimed at the development of an efficient process for gold extraction from the Barberton Greenstone belt. All work was conducted on a flotation concentrate generated from a Barberton Greenstone belt sample. The concentrate contained 58 g/t of gold, of which 12% was extractable via direct cyanidation. The minerals contained in the concentrate included 23% pyrrhotite, 46% pyrite and 13% organic carbon. The gold extractions varied from 13% by direct cyanidation up to 89% by POX. The process used in the past for this specific ore relied on bacterial leaching (long retention time) followed by cyanidation, which reportedly yielded 80% gold extraction. The increased gold extraction made possibly by POX marks a major milestone in the processing of the Barberton Greenstone deposit future and possibly the future of other double refractory ore deposits.