The Geochemistry Characteristics And Mineralization Of Jiang Ligou Granite In Tongren, Qinghai Province

The Jiang ligou granite rock in Tongren County,Qinghai Province is located inthe western part of West Qinling orogenic belt，in the convergent transition zone ofNorth China plate and Yangtze plate，which is one of the important polymetallicmetallogenic belt of China. By the research on petrography, petrogeochemistry andchronology of monzonite granite and geology, fluid geochemistry,isotope geochemistry of the deposit, this paper discusses the petrogenesis and therelationship between magmatism and mineralization, showing theoretical andpractical significance for guiding the regional geological prospecting work. The mainwork and achievement of this dissertation are listed as follows:The Jiang ligou monzonite granite has the characteristics of high silicon, lowmagnesium, and belongs to high-K calc-alkaline granites. The rock is enriched inlarge ion lithophile elements (LILE) such as Rb, Th, U, K and Pb, comparativelydepleted in high field strength elements (HFSE) such as （Nb，Ta，Y，Yb），Sr，P，Ti show obviously negative abnormality. The REE distribution curces are of rightinclination indicating they are relative enrichment of LREE. Jiang ligou intrusivecomplex belongs to S-type granite, which is derived from partial melting ofcontinental crust consisting of arenite and part of argillaceous rock. That the zirconSHRIMP U-Pb age is214±4Ma suggests the granite was formed in late period of theTriassic, which are the product of the crust thickening environment following thecontinental collision North China plate and Yangtze plate.Jiang ligou deposit is a Skarn type deposit related to granite. The skarn and theJiang ligou monzonite granite have similar REE distribution curves. The contents ofREE fall in the area between magmatic rocks and marble. The sulfer isotopiccompositions define a narrow range of1‰～-4‰, reflecting the charaeteristics of thesulfur from magma source. Hydrogen and oxygen isotopic datas show that theore-forming fluid is dominated by magmatic water in the early stage, but in the latestage, it could be produced by mixing magmatic and meteoric water. There are twodominant types of fluid inclusions as evidenced by petrography characteristic; theyare liquid-rich inclusions and gas-rich inclusions. The fluid of early stage was hightemperature magmatic fluid which has the feature of low salinity. Along with theevolution, homogeneous temperature and salinity of fluid inclusions showeddecreasing trend. The gas compositions of ore-forming fluids are major in H2O, with a small amount of CO2.Jiangligou granites have fine metallogenic potential of W、Cu、Mo as the granitesare featured by weak reduction-weak oxidation， high degree of fractionalcrystallization as long as high silicon，slight acid and peraluminous. The genesis ofdeposit has a close relationship with the granite body.