Study On The Mafic-ultramafic Rocks Of Xiarihamu Nickel Mining Area In East Kunlun

Xiarihamu nickel deposit is the first mantle-derived magmatic nickel deposit found recently in Eastern Kunlun Orogenic Belt. There are four mafic-ultramafic instrusions occurring in the ore district. Combining with metallogenic theory of magmatic Ni-Cu sulfide deposit and research development of mafic-ultramafic rocks, with modern testing technology as support, this paperanalses geologic feature, petrology, petrography, mineralogy, geochronology, metallogeny, geochemistry and regional geology. The main achievements of this study are summarized as follows:(1) No.â… and No. â…¡ intrusions which emplaced in Jinshuikou group Baishahe formation metamorphic rocks of paleoproterozoic, associated with copper-nickel deposit.(2) No.â…  intrusion consists of peridotite facies(dunire, harzburgite, lherzolite), pyroxenite facies(olivine orthopyroxenite, plagioclase-bearing pyroxenite) and noritic-gabbro(melagabbronorite, olivine gabbro, gabbro, leucogabbro).The sequence of emplacement is peridotite faciesâ†'pyroxenite faciesâ†'gabbro facies. No. â…¡ intrusion consists of gabbro facies(gabbro, melagabbro) and pyroxenite facies(plagioclase-bearing clinopyroxenite).(3)No. â…¢, No. â…£ and No.â…¤ magnesium peridotite rocks are part of the ophiolite suite, consisting of serpentinite, mylonitized gabbro, garnet amphibolites and eclogite. Tectonic emplacement of ophiolite into Jinshuikou group Baishahe formation.(4)The major fractional crystallization/cumulate minerals of No. â…  are olive and orthopyroxene. The crystallization temperature of olivine is 1303~1315℃, 1311℃ average; The crystallization temperature of clinopyroxene is 1101~1161℃, 1132.6℃ average. The major fractional crystallization/cumulate minerals of No. â…¡ are clinopyroxene and plagioclase, The crystallization temperature of clinopyroxene is 1120~1144℃, 1132.3℃ average.(5) All rock types show the enrichment of large ion lithophile elements(Rb, Sr), and depletion of high field-strength element(Zr, Hf, Ta, Nb, Ti).(6)The main ore bodies of Xiarihamu mining area were produced in the No. â… intrusion, the morphology of ore body mainly are stratoid, lenticular and irregular. Structural type mainly are submassive-massive, sideronitic and disseminated sulfide ores, which divided into segregation type, injection-type and hydrothermal type.(7)The East Kunlun orogenic belt belongs to trench-arc-basin structural framework during early Cambrian to early Silurian.Xiarihamu nickel-copper deposit formed in the tension island arc environment, it is the production of none-ore magma, ore-baring magma and ore magma impulse instrument. Magma source is subduction-related lithospheric mantle,the primary magma is magnesium basaltic magma. The sulphur of metallogenetic materials is innate in crust and mantle mixed source, but the major is the crust sulphur. Fractional crystallization and assimilation are the main mechanisms of sulfide segregation.(8) Xiarihamu ophiolite belongs to SSZ type of island arc and it is controlled by Heishan-Nalinggele lithospheric fault. The basalt of Xiarihamu ophiolite changed into eclogite during the process of ocean-basin subduction. But it was metamorphismed to garnet amphibolites in the process of retracement along Heishan-Nalinggele fault. And then, Xiarihamu ophiolite emplaced into Baishahe Formation.