1�� No�� 5 Geological and Mineral Survey Institute of Qinghai Province��Xining 810000��China; 2�� No�� 3 Geological and Mineral Survey Institute of Qinghai Province��Xining 810029��China; 3�� College of Earth Sciences��Jilin University��Changchun 130061��China

Based on X- ray diffraction��optical microscopy and scanning electron microscopy analysis of the Dachang gold ore��it is showed that the sulfide of ore is the main carrier minerals of gold�� A majority of gold is embedded in pyrite and tetrahedrite as the form of inclusion and a small amount intergrowth with pyrite and gangue mineral�� occasionally the presence is in form of monomer natural gold�� The main factors which influence the recovery rate are sulfide mineral particle size��and the fine grained sulfide is beneficial for the dissociation and flotation of gold bearing minerals�� The monomer dissociation degree of gold bearing minerals can reach 91. 3%��when the grinding fineness is less than 0�� 074 mm and grain level accounts as 80%�� It is not condu- cive to the flotation of sulfide if the grinding fineness is low or high�� It is difficult to completely dissociate the monomer if there is a small amount of pyrite and arsenopyrite in the ore�� Therefore��before leaching the gold�� it must conduct pretreatment to reach the ideal recovery rate of the gold��like roasting oxidation��pressure oxida- tion and biological oxidation�� The fine microscopic gold has little influence on the gold recovery rate��