PGE metallogenesis related to mafic-ultramafic complex in North Xinjiang
Wang Yuwang1,2, Wang Jingbin1,2, Wang Lijuan1,2, Long Lingli1, Liao Zhen1,Zhang Huiqiong1, Tang Pingzhi11.Beijing Institute of Geology for Mineral Resources,Beijing 100012,China2.Key Laboratory of Mineral Resources,Institute of Geology and Geophysics,Chinese Academy of Sciences,Beijing 100029,China
Platinum group elements (PGE) mineralization is mostly related to mafic-ultramafic complex with dominant ore-forming type of magmatic deposit. The formation of this type of PGE deposit mainly relies on two conditions:abundant PGE contents in magma,and advantageous mechanism of PGE enrichment and separation out of magma in which sulfur reached saturation during the magmatic evolution. Mafic-ultramafic complex is widely developed in North Xinjiang,which produces four large-scale copper-nickel deposits like Kalatongke,Huangshan,Huangshan East and Tulargen and numerous small to medium-sized copper-nickel deposits such as Xiangshan,Tudun,Hulu,Baishiquan and others,as well as Xiangshan West and Weiya medium-sized V-Ti magnetite deposits,but rarely forms PGE deposit. Based on the ore-forming mechanism of PGE deposits and the characteristics of the magma source of mafic-ultramafic complex,we have discussed some questions about PGE metallogenesis in North Xinjiang in this paper. The rock types of the post-collisional mafic-ultramafic complex in North Xinjiang is ferrous rock series by fractional crystallization,a favorable rock type for PGE-hosted. For the Cu-Ni sulfide deposit,the participation of crustal material causes the sulfide liquation during the process of magmatic evolution and mineralization,which is evidenced by the characteristics of Sr,Nd,Pb,O,Os and S isotopes and lithogeochemistry,indicating the existence of ore-forming mechanism for magmatic PGE deposit. The weak PGE mineralization in North Xinjiang may principally ascribe to widely-developed depletion-type mantle source (with positive values of εNd) that possibly derived from partial melting of water-rich oceanic crust,which is associated with post-collisional orogen setting and development on the "oceanic crust" or "immature continental crust" basement. It is the PGE-poor original magma source,disadvantageous to PGE mineralization.