Abstract:

Due to the controversy over the diagenesis and mineralization of the newly discovered Xiarihamu super-large magmatic copper-nickel-cobalt sulfide deposit, it started a new round of discussion on the metallogeny of the magmatic copper-nickel-cobalt sulfide deposit. The copper-nickel-cobalt sulfide deposits in the orogenic belt in China have a distinctive distribution feature. In the 1980s, with the discovery of a series of magmatic copper-nickel-cobalt sulfide deposits in the mafic-ultramafic rocks in eastern Tianshan, it was proposed that these mafic-ultramafic rocks are ophiolites. Then, a mainstream viewpoint was formed that the copper-nickel-cobalt deposits in eastern Tianshan were formed in the continental crust rifting trough environment after the subduction of the oceanic crust and the closure of the continental collision. The discovery of the Early Permian Tarim Large Igneous Province in the 21st century suggested that the magmatic copper-nickel-cobalt sulfide deposits in eastern Tianshan and the Beishan in Xinjiang are related to the formation of the Tarim mantle plume. However, based on the geochemistry of mafic-ultramafic whole-rock with typical island arc characteristics, some researchers maintained that some magmatic copper-nickel-cobalt deposit could be associated with subduction-reduction plates. We believe that the trace elements of whole-rocks that show island arc information are a geochemical shielding effect caused by the subduction and crustal contamination. The composition of the chrome spinel and the oxygen fugacity environment indicated that these deposits were formed in an extension environment, rather than the island arc. The three-period magmatic copper-nickel-cobalt sulfide deposits around the Tarim block represent the three most critical nickel-forming events in China, which reflect the vital convergent events between the Tarim block and the supercontinent. First, the Neoproterozoic giant Jinchuan Cu-Ni-Co-PGE deposit represents the Rodinia supercontinent break-up event, which led to the formation of the Paleo-Asian Ocean among the Tarim Block, Yangtze Block, and Western Australian Block. Second, the large Xiarihamu nickel-cobalt deposit in the Early Paleozoic was the product of the break-up event in the southern Gondwana land, leading to the formation of the Paleo-Tethys in the Paleozoic. Third, the Early Permian Poyi copper-nickel deposit should be a plutonic facies composed of mantle plumes and large igneous rocks grown in the Pangea supercontinent. This article systematically summarizes and compares the metallogenic characteristics of the three deposits. Although Poyi has the highest MgO content of parent magma among the three deposits, it shows a lower degree of crustal contamination, especially crustal sulfur contamination, compared with Xiarihamu and Jinchuan. This is probably the main reason why the Poyi intrusion has the lowest Cu-Ni mineralization among the three deposits. Furthermore, the Poyi intrusion has some contamination of calcium, which can hinder sulfide saturation.

Key words: magmatic Cu-Ni-Co-PGE sulfide deposits, orogenic belts, island arc, mantle plume, crustal contamination, Tarim