Primary gold ore from Bangi, Guizhou, belongs to a clastic-type, finely disseminated, refractory particles. It is difficult to extract gold from the ore by cyanide infusing. So a pretreat-ment should be performed on the primary ore before cyanide infusing. By means of chemical, X-ray powder diffraction, infrared spectroscopic and scanning electron microscopic analyses the relationship between the change of the mineral structure and the quantity of Au cyanide infused from the ore samples after roasting in air at different temperatures has been studied. This paper explores the microstructure of these samples and its application in the pretreatment. The result obtained may be useful for the study on the genesis and structural control of the ore.