Petrological and mineralogical characteristics of the Xiangshanzhong maficultramafic intrusion in eastern Tianshan Mountains: Constrains on rockforming and ore-forming processes

Mafic-ultramafic rocks in Xiangshan are located in Huangshan-Jingerquan mafic-ultramafic rock zone in east Tianshan Mountains, Xinjiang. The main rock types are iherzolite, (containing feldspar) clinopyroxene peridotite, olivine pyroxenite and hornblende gabbro. According to the mineralogical characteristics, the rock mineral crystallization sequence is in order of chrome spinel, olivine, orthopyroxene, clinopyroxene, plagioclase, and angle amphibole. In the same period, the transition of the lithofacies in each stage of the invasion period has a good transition. The content of olivine in the drilling section and the composition of the particles and the composition of the particles in the drilling section vary with depth. The evolution of Cr→Fe³⁺, Ti in picotite is good. According to these features, the formation of the rock mass is mainly controlled by the crystallization differentiation. Abrupt change of olivine and the composition of the olivine in the (feldspar-bearing) clinopyroxene show the existence of crustal mixture in the process of magma crystallization. The simulation results show that the crystallization of olivine was accompanied by the melting of the sulfide. At the depths of 295-325 m in ZK3693 borehole, abrupt change of the composition of (feldspar-bearing) clinopyroxene in the olivine, plagioclase, single grain clino-feldspar and the Al→Cr evolution of the Cr spinel indicates that there is a higher basic level of magma injection in the interval. The Cu and Ni grades of the ore in this area are obviously higher than those of the same rock mass which is not in the interval. That injection of fresh magma is an important cause of the sulfide enrichment in Xiangshan.