Constraints on sulfide saturation by crustal contamination in the Shitoukengde Cu-Ni deposit, East Kunlun orogenic belt, northern Qinghai-Tibet Plateau, China

The Shitoukengde Cu-Ni deposit is located in the eastern part of the East Kunlun Orogenic Belt (EKOB). The overall complex underwent emplacement into the surrounding rock, including the gneiss and marble. The ore-bodies exist in complex I, which is composed of peridotite, pyroxenite, and gabbro. The petrogeochemical characteristics of the rocks show that the m/f values range from 1.93 to 5.97, and the Fe3+/ΣFe ratios of the spinel are < 0.3, indicating that the Shitoukengde complexes have the potential to form a Cu-Ni ore deposit. Based on the evidence of marble and gneiss xenoliths, there are higher CaO and Al2O3 contents in the peridotite and pyroxene, there are Nb and Ta depletions, in the Shitoukengde; these results indicate that the ore-forming parental magma has been obviously contaminated by crustal material during the evolution process and that the materials responsible for the contamination mainly originated from the middle-upper crust. The mafic-ultramafic complex, which is closed to marble, has higher CaO and Al2O3 contents; higher (87Sr/86Sr)i values and lower Ni contents; thus, it is reasonable to infer that the Shitoukengde mafic-ultramafic rocks assimilated some marble, and the contamination of marble without sulfide suppresses the sulfide saturation. The pyroxenite with better mineralization is mainly orthopyroxene, and the increase in the sulfur isotope values in the pyroxenite and peridotite is accompanied by an increase in the Ni content; these results suggest that the SiO2 and S of biotite-plagioclase gneisses, especially the S addition, were important for the Shitoukengde intrusion to reach sulfide saturation. The whole-rock Ni content in the peridotite shows a positive relationship with the FeO content of spinel, indicating that the crystallization of spinel has little effect on sulfide saturation. The capable of crystallizing olivine with Fo content as high as 89.3 mol% and olivine Fo value exhibits a positive relationship with the olivine NiO content, indicating that olivine fractional crystallization did not play a significant role in sulfide saturation. The δ34SV-CDT value of the giant Xiarihamu deposit is much higher than that of Shitoukengde. The degree of crustal S contamination is probably responsible for the difference in the scale and ore grade of the Cu-Ni sulfide deposits in the East Kunlun area. The above indicators could guide the exploration and evaluation of similar deposits in the EKOB.