Through systematic microscope identification and scanning electron microscope observation, pyrites were divided into 6 types (i.e., cuboidal, framboidal, finegrained, coarsegrained, zoned and linelike pyrite) according to their topographic characteristics in the Nibao gold deposit, Pu'an, southwestern Guizhou. Electron microprobe analysis (EMPA) results for pyrites showed that goldbearing minerals were mainly arsenian pyrite (zoned pyrite and finegraned pyrite) and arsenopyrite. The core and zone of zoned pyrite were formed in different diagenetic and metallogenic stages, respectively. The core, formed in the diagenetic stage (partially formed in early hydrothermal stage), is poor in Au and As and is rich in Fe and S. The zone, formed in the main metallogenic stage, is rich in Au and As and is poor in Fe and S. There is a positive corresponding relationship between Au and As in the zone of zoned pyrite, and they have a positive correlation in a certain wedgeshaped space; the high Au content generally corresponds to the intermediate As content (2%~6%). In contrast, there is clearly a negative correlation between As and S, thus indicating that the Asrich zone was generated because As replaced S to enter into the lattice of the pyrite. Finegrained pyrite has high Au and As contents and low Fe and S contents, and its characteristics are similar to those of the zone of zoned pyrite. As a result, it is inferred that the Asrich zone and the finegrained pyrite are both formed in the main metallogenic stage. Arsenopyrite frequently interpenetrates or distributes along the rim of arsenian pyrite, which suggests that it was formed later than the arsenian pyrite in the hydrothermal stage. Therefore, the crystallization order of goldbearing minerals in the Nibao gold deposit is roughly as follows: Aspoor sedimentogenic pyrite (core)zone of Asrich pyrite and finegrained pyrite arsenopyrite. Point analysis by EMPA and the scanning of the surface wave spectrum showed that the distribution of Au in goldbearing minerals (i.e., arsenian pyrite and arsenopyrite) is not uniform. According to the solubility limit of Au (Au/As 002) and the lgw(As)—lgw(Au) diagram, this paper inferred that Au mainly occurs in arsenian pyrite and arsenopyrite as an “invisible” solid solution (Au+1) and probably also as small amounts of nanoparticles native gold (Au0).