Study On Petrogenesis And Metallogenic Conditions Of The Gaxiuyapingdong Mafic-ultramafic Intrusion,North Margin Of Qaidam

There are a series of mafic-ultramafic intrusions in the Qaidam Block, Qinghai Nuclear Geology found Niubiziliang deposit in2008. Then, looking for nickel ore in this area have aroused general concern. The project team discovered Gaxiuyapingdong intrusion which bears Cu-Ni mineralizion, So Gaxiuyapingdong intrusion has been chosen as an object of study. This thesis will discuss the magma source, primary magma, assimilation and fractional crystallization, tectonic condition, mineralization by doing researches on petrography, mineragraphy, mineralogy and geochemistry. The achievements obtained as follows:(1)Gaxiuyapingdong intrusion is lacated in the Olongbuluke micro-continent, which is in the northern margin of Qaidam Block, Qinghai Provence. It is a mafic-ultramafic intrusion which covers an area of about3km2and is irregular shaped with east-west extension.(2) There are abundant types of rocks, and the rocks are peridotite, wehrlite olivine pyroxenite, pyroxenite, gabbro, leucogabbro and anorthosite.(3) The SiO2values of all rocks range from37.44to49.57, they are belong to basic-ultrabasic rocks. The m/f values of all samples have a large range between2.92and7.25, and its Mg#range from0.74～0.88. It is from2.33×10-6to22.18×10-6that the concentration of rare earth elements and trace elements ranges, The rocks show LREE weakly depleted pattern in chondirite-normalized REE diagram and primary mantle-normalized trace elements diagram with LILE abundance, HFSE depletion. Element geochemical characteristics show that the intrusion has strongly assimilated and contaminated with country rocks, as a result, magma property changed from tholeiitic basalt series to calc-alkali basalt series(4) Based on geochronology and regional geologic characters, we discussed the intrusion formed in the intracontinental extending or rifting environment.(5) The element geochemical and Nd、Sr isotope composition characteristics indicate the primary magma could be asthenosphere mantle.(6)The∑PGE values of all rocks range from8.82×10-9to84.80×10-9, and the average is50.23×10-9. In the process of evolution intrusion experienced weakly sulfide liquation.