The nature of the mantle source and exploration implications of the Qixin intrusion , Beishan, Xinjiang: Insights from olivine compositions

Xinjiang Qixin Ni-Co mineralized intrusion is located in the south-central of the Beishan orogenic belt. It is one of the important new discoveries in nickel, cobalt other strategic minerals in Beishan orogenic belt in recent years. The intrusion is mainly composed of lherzolite, olivine pyroxenite, troctolite, norite gabbro, olivine-gabbro and gabbro, and mineral bodies are mainly hosted by peridotite and gabbronorite. In this study, we carried out the in-situ composition analysis of olivine major and trace elements in four small ultramafic intrusion of Qixin to identify the nature of mantle source and portray the processes of sulfide segregation. The results show that olivine of peridotite in each intrusion has Ni losses of varying degrees ( the Fo value and Ni concentration of olivine in the No. I and II intrusion are 84.0~87.5 and 134~2562 ppm, the No. III and IV intrusion are 82.3~86.1 and 581~2970 ppm). However, the olivine have high Mn/Zn ratio (>15) and 100*Mn/Fe ratio (1.4~1.7), and low 10000*Zn/Fe ratio (3.5~9.4), Ni/Co ratio (7.3~14.0), and Li concentration (1.8~9.8 ppm).The trace element characterization of olivine indicates that mantle origin of the Qixin intrusion is a peridotite mantle with water-rich component in the source origin and was no added the material from oceanic crust, but mixed by material from continental crust during magmatic evolution. The characteristics of olivine Fo value, Ni concentration and other components suggest that the sulfide segregation of the deep in the intrusion No. I and II are more significant, and there is potential to search for Ni-Co deposit in the deep. Therefore, ore prospecting and exploration need to focus appropriately on intrusion No. I and II, and need to pay attention to the deep and periphery of the intrusion No. I and II.