The Xiaoliugou W-Mo (Cu) deposit is located in Jingtieshan-Zhulongguan rift valley in North Qilian Mountains with mineralization occurring in basic volcanics and carbonate rocks of Zhulongguan Group of Changcheng series. The Xiaoliugou deposit is a porphyry-skarn-quartz type deposit related to granitoids in which tungsten was mainly derived from skarn type mineralization and molybdenite came mainly from porphyry-type mineralization. Xiaoliugou granitoids are composed of monzogranite and granodiorite, with the monzogranite closely related to the Xiaoliugou deposit. Taking minerals in granitoids and garnet in skarn as the study objects and using electron microprobe technology,the authors investigated the mineralogical characteristics. Electron microprobe analyses show that the monzogranite and granodiorite were derived chiefly from the crust and its high oxygen fugacities provided suitable conditions for the formation of the W-Mo deposit. Garnets in the skarn are grossula-rite-andradite and the end member is dominated by grossular. The skarn in the Xiaoliugou deposit belongs to calc skarns and was generated in a reducing environment. Garnet of oscillatory zoning shows the concentration of Al decreased and Fe increased gradually during the evolution,indicating the gradually decreasing temperature of the ore-forming fluid together with the gradually increasing oxygen fugacity and pH value. The Mn/Fe ratio of garnet may be related to mineral metals. The sulfide isotope indicates that the sulfide was derived from magmatic hydrothermal solution. Based on this study combined with previous research results,the authors hold that the W was from the monzogranite and strata, whereas the Mo mainly came from the monzogranite.