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．