The Tulargen Cu-Ni sulfide deposit, whose discovery means a great breakthrough in Cu-Ni exploration in Xinjiang in the past ten years, is located in the eastern section of the Huangshan-Jingerquan ore belt. The Tulargen Cu-Ni deposit is a magmatic differentiation deposit related to mafic-ultramafic complex, which comprises three intrusions, namely complex Ⅰ, Ⅱ, Ⅲ, respectively. The hornblende pyroxene peridotite of complex Ⅰ is associated with abundant mafic enclaves, which include ore-bearing gabbro enclaves and plagioclasite enclaves without mineralization. Mafic enclaves and the host display different characteristics in such aspects as mineral species, types and intensities of alteration, con tacts between minerals and forming sequence. There exists a distinct boundary, composed of squamiform chlorite, between the mafic enclaves and the host. The Harker diagram of major elements and figures of La, Nd, Zr, and Yb versus SiO₂ have shown that samples of the Tulargen complex display a good correlation, whereas the mafic enclaves don't show such characteristics, which indicates that magmatic contamination played a significant role in the formation of the mafic enclaves. Nb/U and Ce/Pb ratios imply that, after crustal contamination, some elements of the mafic enclaves was mobilized and migrated by the late magmatic hydrous fluids.