Petrogenesis Of Shitoukengde Mafic-ultramafic Intrusion And Analysis Of Its Metallogenic Potential,East Kunlun

The Shitoukengde mafic-ultramafic intrusion is located in the middle part of the eastern Kunlun orogenic belt. The teotonic position of Shitoukengde intrusion is very similar with a series of magmatic copper-nickel sulphide deposits or ore occurrences, like Xiarihamu,Bingounan and Kaimuqi and so on. Based on the characteristics of geology, petrology,mineralogy, chronology, and geochemistry, this paper will reveal its petrogenesis, constraint the process of magma evolution, proved sulfide segregation and its influence factors, explore the information of mineralization, analysis of the potential metallogenic and provide more data and basis for nickel mine exploration in eastern Kunlun orogenic belt. The main results of this paper can be drawn as follows:(1) The Shitoukengde intrusion is a sill, with an outcrop area of about 4.0km2, the contact relationship between it and its surrounding rocks is intrusive. The intrusion is mainly composed of all kinds of rock type belonging to gabbro facies, pyroxenite facies and peridotite facies, which shows that the magma is well differentiated. The intrusion is a composite body and the sequence of each rock facies is gabbro faciesâ†' pyroxenite faciesâ†'peridotite facies.(2) The olivines in this intrusion are chrysolite with Fo ranging from 81 to 86;orthorhombic pyroxenes are bronzite; clinopyroxenes are diopside mainly, and others are endiopside and augite; most plagioclases are labradorite, and others are bytownite; most hornblendes are pargasite. The crystallization sequence of minerals is spinel/olivineâ†'orthopyroxeneâ†'clinopyroxeneâ†'plagioclaseâ†'hornblende. And the crystallization temperature of them is between 835℃ to 1307℃.(3) This intrusion is a ferruginous basic-ultrabasic intrusion with m/f values ranging from 3.61 to 5.55 and its rock are belonging to tholeiite. All rocks show LREE enriched appreciably pattern, and even flat pattern between LREE and HREE in chondirite-normalized REE diagram. They are also enriched in large ion lithophile element(LILE), but depleted in Nb, Ta, Ti, which indicates arc related information.(4) The magma of Shitoukengde intrusion undergoes fractional crystallization of olivine,orthorhombic pyroxene, clinopyroxene and plagioclase. The characteristics of geological in field and geochemistry both show that the magma has experienced significantly assimilation and contamination partially.(5) The magma source of this intrusion is lithospheric mantle, and originates from 11.2%to 14.2% partial melting of mantle. Partial melting occurrences in the stable domain of spinel.The primary magma of Shitoukengde intrusion belongs to high magnesium tholeiite magma which containing about 10.5%MgO, and nickel in this magma is 325.6×10-6.(6)The platinum-group elements shows IPGE-deplet-stype, which is related with low mantle partial melting.(7) The gabbro ziron U-Pb age of Shitoukengde intrusion is 423.5Ma, belonging to late of middle Silurian. Combined with regional tectonic evolution, the Shitoukengde intrusion formed in extensional environment of post-collision. And the arc information of trace elements from all rocks should be hysteresis effect of island-arc magma.(8) The study on the rock assemblage, differentiation situation of magma, rock body type,primary magma, structural sign, direct mineralized markers and mineral assemblage,Ni-content and Fo of olivine, R factor, show that the Shitoukengde intrusion has favorable conditions for the formation of copper-nickel deposit, and has great potential of metallogenic.Crust sulfur adding, contamination from surrounding rocks and the fractional crystallization of olivine, pyroxene play important roles in sulfur saturated and sulfide segregation.(9) Combined with Xiarihamu, Bingounan, Kaimuqi magmatic copper-nickel sulphide deposits or ore occurrences in this zone, this paper holds that the eastern Kunlun orogenic belt can be important nickel prospective region.