| The East Kunlun metallogenic belt is one of the most famous metallogenic belts in China and the most important metallogenic belt in Qinghai Province.According to statistics,there are 264 mineral areas in the East Kunlun area,which is called "gold belt".The area contains abundant mineral resources such as iron polymetallic deposits,copper polymetallic deposits,gold deposits and so on,and it is an important mineral accumulated belt.Since 2011,several large magmatic copper-nickel sulfide deposits have been discovered in the west of East Kunlun,including the Xiarihamu,Akchuksai,and Longmuri copper-nickel deposits in the east of East Kunlun,which were discovered in 2016.It has become another major breakthrough in the search for this type of deposit in this area.The Longmuri copper-nickel deposit is located in the west of the central orogenic belt of the Chinese continent,and on the granite belt of the central Kunzhong basement of northern Kunzhong fault in the east of the eastern Kunlun orogenic belt of Qinghai Province.The large strata are exposed in the mining area,and the main strata are the early Proterozoic Baisahe formation,and a small amount of Quaternary is exposed.Nine fault structures(F1-F9)of different sizes have been developed,in which F3 and F6-F9 are regional large-scale faults,showing NE-NE trending,with tensional and torsional faults in general and varying in scale,they are generally Tensional-torsional faults with different scales,mainly showing uneven tectonic stress,non-uniform mineralization and alteration;The secondary structures of NE-NEE trending faults are also developed.The magmatic activities in this area are frequent and intense,including the late Caledonian mafic-ultramafic rocks,the Varissian granodiorite,the early Indosinian monzogranite and the Yanshanian granites.Seventeen mafic-ultramafic rocks have been discovered in Longmui mining area.Among them,?2,?3,?4 have better nickel-cobalt orebodies,?2 rock exposed with only about 100 m long and 80 m wide,it is elliptical and nearly EW-trending,hidden in gneiss of Baishahe formation,the deep thickness of rock is 150 m,southward dip,the dip angle is between 45°and 50°.Its surface is peridotite facies,with medium grain structure and large rock grains.The crystalline differentiation of rocks is good.?3 rock mass is covered by thick soil on the surface,only a little exposed,hidden in the gneiss of Baishahe formation.the depth of thickness is 200 m,it is pyroxene facies,the middle part of the rock body is peridotite facies,showing medium-grained structure,there are many hydrothermal breccias in the surrounding rock,it can be seen that pyrrhotite with sponge meteorite structure appears in large quantities,and the content of the local sulfide is about 40%.?4 rock has a large surface area,about 850 m in length and 30~100m in width,and it is generally NW trending.The trench reveals that there is a copper-nickel mineralization zone in the rock mass,and Ni and Cu grade is high overall.From shallow to deep,the mineralization of the rock is intense,it is nickel pyritization and pyrrhotite,annabergite can be seen locally,and the shallow part is peridotite facies,the deep part is pyroxene facies.The ore body extends westward stably and has good ore-bearing property.There are obvious lithofacies zoning in the rock mass of Langmuri mining area,which is peridotite-pyroxene-gabbro facies.Pyroxene facies and peridotite facies are the main ore-hosting facies.It indicates that the original magma has undergone sulfide melting in deep underground,and emplaced upward along Deep and large fault or fissures,and condensed and crystallized to form deposits.The mainly ore minerals in this mining area are nickel pyrite,pyrrhotite,chalcopyrite and magnetite.The gangue minerals are pyroxene,olivine,tremolite,serpentine,sphene,phlogopite and a small amount of biotite.The ore structure includes granular structure,unequal granular structure,metasomatic structure,sponge meteorite structure and so on.The main structures are disseminated structure,massive structure,patchy structure and stellated structure.Geochemical characteristics S isotope and S/Se values of the rocks show that the original magma originated from the mantle,and experienced the separation and crystallization of olivine,orthopyroxene,clinopyroxene and a small amount of plagioclase,and was assimilated and contaminated with the crust in the process of ascension.The addition of exogenous S promoted the saturation of S in the magma and the melting crystallization and mineralization.The LA-ICP-MS zircon U-Pb dating of olivine pyroxenite and gabbro of Langmuri mining area shows that its crystallization age is 438.8±2.6Ma,439.5±2.0Ma,which is the early Silurian period,The age of formation of large-super large copper-nickel deposits in East Kunlun is similar to that of Xiarihamu and Akchuksai.Based on the comprehensive analysis of regional geological characteristics,mining geological characteristics,deposit geological characteristics,mafic-ultramafic rock characteristics,S/Se value,magmatic source area,metallogenic epoch and dynamic background of Langmuri mining area,it is considered that the Langmuri copper-nickel deposit was formed in the early Silurian magmatic melting type copper-nickel sulfide deposit.Its tectonic background is that the downward subduction,stretching and breaking of the oceanic crust,resulting in the formation of "plate windows",which resulted in the upwelling of asthenospheric materials,assimilation and contamination with surrounding rocks,separation and crystallization,S saturation,melting and multi-stage ascending emplacement,condensation and crystallization,finally forming the Langmuri copper-nickel sulfide deposit. |
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