Study On Geological Characteristics And Genesis Of Xiwanggou Copper-Nickel Deposit In Eastern Kunlun,Qinghai

The East Kunlun Orogenic Belt is one of the important metallogenic belts in China.The East Kunlun orogenic belt is divided into three EW-trending tectonic units of the Northern East Kunlun Caledonian back-arc basin belt,the Middle East Kunlun basement uplift granitic belt,and the Southern East Kunlun composite accretion belt by the North Kunlun fault?the Middle Kunlun fault and the South Kunlun fault.The East Kunlun orogenic belt has great metallogenic conditions and rich mineral resources.It can be divided into five major mineralization periods: Indosinian,Caledonian,Hercynian,Yanshanian and Pre-Xingkai Period.The Caledonian and Indosinian periods are the most important mineralization age in East Kunlun.In the past,it was generally believed that there were no magmatic copper-nickel deposits in the East Kunlun area.Large scale magmatic copper-nickel sulfide deposits such as Xiarihamu,Akchuksai,Langmuri,Shitoukengde have been discovered since 2011 which providing references for prospecting East Kunlun copper-nickel sulfide deposits.The Xiwanggou copper-nickel sulfide deposit is located in the Dulan area of Qinghai Province and the geotectonic location is located in the eastern section of the East Kunlun orogenic belt and the eastern section of the Middle East Kunlun basement uplift granitic belt.The main strata exposing in the mining area are the early Proterozoic Baisahe formation gneiss,the Late Triassic Orashan Formation dacite and the Quaternary strata.The mining area mainly develops NW-trending fault structures.The magmatic activity in the mining area is strong,and the exposed intrusive rocks mainly include Late Ordovician granodiorite,Late Permian-Early Triassic olivine pyroxenite and gabbro,Triassic potash feldspar granite and monzonitic granite.19 mafic-ultramafic rock masses have been discovered in the Xiwanggou mining area.The lithology is mainly gabbro and olivine pyroxenite,and is dominated by gabbro.Gabbro(13)has poor mineralization and most of them have no obvious mineralization,while olivine pyroxenite(6)has good ore-bearing properties.10 nickel-cobalt ore bodies are delineated in olivine pyroxenite,and most of the ore bodies are stratiform-like.Metallic minerals are mainly nickel pyrite,pyrrhotite,chalcopyrite,etc.Transparent minerals are mainly pyroxene,plagioclase,olivine,etc.,and some self-metamorphic minerals such as epidote,serpentine,and tremolite.The ore mineral structure mainly includes euhedral-semi-automatic granular structure,its granular structure,unequal granular structure and inclusion structure,etc.The main ore structure are disseminated structure,block structure,star point structure and patchy structure.The U-Pb ages of olivine pyroxene and gabbro zircon in the mining area are252.7±2.2 Ma and 251.3±1 Ma,respectively,which belong to the product of early Indosinian magmatism..Combined with the regional geodynamic background,it is believed that the Xiwanggou copper-nickel sulfide was formed in the northward subduction structure of the Paleo-Tethys Ocean Plate.The olivine pyroxene and gabbro are analyzed for the earth elements in the rock geochemistry of the mining area.The results show that the rock mass is an island arc porphyry basalt in a subduction environment,and the magma source is a depleted mantle.The subduction fluid replaces the lithospheric mantle in a plate subduction environment.Combined with the analysis of S isotope and S/Se value,it is shown that there is separation and crystallization of olivine,orthopyroxene and plagioclase during the evolution of magma,and the assimilation and contamination of crustal materials during the ascending and emplacement process of magma with the addition of exogenous S.After melting,condensation,crystallization,and then mineralization occurs.The early Indosinian Paleo-Tethys ocean plate stretched after subducting into the Southern East Kunlun composite accretion belt,forming a large number of NW-oriented linear structures on both sides of the Kunzhong fault.The slab dehydrated and replaced the lithospheric mantle,resulting in decompression melting to form magnesium Iron-ultramafic magma.The magma penetrates into the mineralization along the structural fissures after multiple periods of ascending and emplacement.In summary,it is considered that the Xiwanggou copper-nickel sulfide deposit is a magma-melting-type copper-nickel sulfide deposit formed in the early Indochina.Due to the low degree of partial melting of the mantle source in the Indosinian period,which is not conducive to the formation of large mineralization.