Study On Geological Characteristics And Genesis Of Xiarlhamu Nickel Deposit, Qinghai Province

Eastern Kunlun orogenic belt is one of the important metallogenic belts of QinghaiProvince. Numerous deposits have been found, especially in2011, when a largecopper-nickel sulfide deposits-Xiarihamu nickel deposit was discovered. This was a majorbreakthrough in the area of geological prospecting.Xiarihamu nickel deposit is located in Eastern Kunlun middle uplifted basement andgranitic belt, and near the north Eastern Kunlun fault. The main strata exposed areJinshuikou Group and Quaternary. Faults developed in the mines, and mainly to EW faultsand NEE faults. NEE trending faults occur after the EW trending faults. MiddleSilurian-Early Devonian and Late Triassic magmatic rocks are widely distributed in themining aera, such as mafic-ultramafic intrusive complex and syenogranite.The NO. Ⅰo rebody is located in north-central part of the mining aera. The complexoutcrop is about0.7km2and elongated strip nearly EW whose southwest section is buriedbeneath Jinshuikou group. The northern part of the complex dips southward with dipangles between0°to30°while its southern part dip northward with dips angles between5°to30°. The orebody to the east of exploration line3occurs as a lopolith, and thewestern part seems like a plate, and it becomes smaller and thinner to the west and deep.The ultra-mafic and mafic rocks that are related to metallogeny has the obviouscharacter of zoning and composit complex, such as gabbro phase, pyroxenite phase andperidotite phase. The contact relationships among them are invasive transitional or constructor broken. Peridotite and pyroxenite phase are the main ore facies. Thegabbro-norite outcrops in the southern and northern of mining aera, and in the central ispyroxenite and olivine pyroxenite. Peridotite and pyroxenite phases are lenticular orbedded. A multi-stage, intrusive activity formed the mafic-ultramafic intrusive complex.Sulphide and silicate melt and separated from each other in the deep magma chamber andthen invade the crust from low-grade magma to high-grade one to form the complexwhich consists of gabbro norite, rhombic pyroxenite, olivine pyroxenite, plagioclaselherzolite and harzburgite and so on.All the olivine is peridot, and there are two kinds of pyroxenite such as stubborndiopside and bronzite. Si/(Si+Ti+Al) of pargasites are between0.691to0.718, whichindicates that they are mantle-derived. Plagioclase mainly outputs in the gabbro norite,and is Labradorite.M1is the main orebody which is strictly controlled by the complex. Its angle ofstrike is about70°and inclination is0~35°. On the east of exploration line7, the orebodyis mainly located in the upper part of the complex.The main metal sulphides contain pentlandite, chalcopyrite, pyrrhotite, cobaltite,violarite, dobschauite, and the secondary metal sulphides contain capillarychalmersite, limonite, and chalybite. The ores present disseminated, spotted, spongy,lumpish, brecciated construct,and present hypautomorphic, flame, ring, beamedspotted and teardrop-shaped structure.Geochemistry indicates that gabbro, pyroxenite and peridotite phases belong to theproduction of intrusion in the same magmatic activity era but different evolutive phase.The character of isotopes reflects that ore forming material mainly came from mantle.Magma is the product of the mantle-derived magmatism, and experienced olivine,orthopyroxene and plagioclase fractional crystallization, at the same time, subject to acertain degree of crustal contamination that leads to sulfur saturation of magma, and thenfractional crystallization occurred.According to the research of regional geological background, geological featuresof mafic-ultramafic rock and deposit, δ34S and tectonic setting, we can come to the conclusion that Xiarihamu nickel deposit is formed in the Early Devonian, and belong tothe deep segregation-pulse penetration model.