Gold extraction from low grade sulfide minerals in Chahkhatoon and Senjedeh mines by bioleaching technique (Muteh mine field, Isfahan State)

Abstract

Muteh goldfield is located in 295Km S-SW of Tehran and 70 km of Delijan city in central Iran, is<br />very important for Iran's annual gold production rate. There are 9 recognized gold deposits but, according to tonnage, Au grade, economic factors, geologic and engineering parameters, gold is extracted from only 2 deposits: Chahkhatoon and Senjedeh. There is a big problem because the gold reserves of Chahkhatoon and Senjedeh in oxide zones are nearly finished and gold extractions will be continue from sulfide zones. Based on mineralogy and geochemistry studies, sulfide ores are very resisting because the recovered gold of these sulfide resisting ores is less than 80%. In the sulfide resisting deposits of Muteh, very fine gold is surrounded by Pyrite and Arsenopyrite. The common methods for extraction are not economical, therefore these resisting ore deposits should settle in a primary treatment, but the suggested methods are very expensive and the environment is polluted at a high level. In this paper, according to bioleaching advantage, this method was used for gold extraction from sulfide minerals. Thiobacilus Ferrooxidans is a proper microorganism in this method because gold grades from samples of Chahkhatoon and Senjedeh are less than 3 ppm. So, a norm sample was provided from Senjedeh and Chahkhatoon mines. Next, it was used in Stirred tank process. Their search showed that after 20 days of bioleaching process, M8 species with pH=2.2 are very important for the elimination of sulfide (%96.30).