Geological And Geochemical Characteristics Of Xiankou Granite Pluton And Its Uranium Fertility

Xiankou grantic pluton, located in the north of Dawangshan-Yushan uranium polymetallic metallogenic belt（related to the granite）, can be found in the area of Xiankou village-Dingyuan reservoir in Le’an county, Jiangxi province.There are 15 km between the north of the Xiankou grantic pluton and the super-huge Xianshan uranium polymetallic metallogenic belt（related to the volcano- volcanic rocks）,situated in the southwest of the Ganhang uranium polymetallic metallogenic belt. Many radioactive anomalies spot were found in Xian Kou pluton, Luoshan uranium deposit is in the peripheral area of the pluton. Therefore, this paper chose Xiankou pluton as the main research object, study its formation age, genesis,tectonic setting and relationship with uranium deposit around through research its geological features, petrology, geochemistry, zircon geochronology and uranium fertility..Xian Kou granite pluton cover area about 24 km2, and it includes Dianyuan unit,Henggang unit, Shangdianyuan unit and Paiqian unit, which lithologies are respectively medium-coarse giant phenocryst biotite adamellite, medium-coarse less phyenocrysts biotite adamellite, medium-fine grained porphyraceous biotite adamellite and fine particles alkali feldspar granite. There are dark enclaves in Dianyuan units. The LA-ICP-MS U-Pb zircon ages of each unit is respectively:231.3±2.6Ma, 234.8±2.8Ma, 234.8±2.5Ma and 234.5±2.9Ma, it indicates that the Pluton is Indosinian granites formed in the Middle Triassic. Xian Kou granite pluton which is characterized by high Si O2, rich Alkalis, rich K, belongs to peraluminous-strongly peraluminous granites, and the enclaves are characterized by the dilution of Si and the richment of mafic. There is similar REE and trace elementsdistribution plots in the other three units except Paiqian unit. The trace elements distribution plot shows enrichment of the incompatible elements U、Rb、Th、K、Nd、Hf etc. and depletion of Ba、Sr、P、Ti、Nb, and the REE spider diagram is rightincline seagull pattern.Due to the enrichment of fluid, the REE and trace elements distribution plots show abnormity in the Paiqian unit. By the study of the Sr-Nd-Pb isotope in the rocks, we find that the value of εNd（t） is（-7.07）^-8.10 and the T2 DM is1585¹669Ma. On the Pb isotopic diagram,all the samples locate between the crust and mantle evolution curves, and this phenomenon indicates that rock-forming substances mainly came from the Proterozoic crust and little from the mantle. Based on the rock association, Structure, mineralogical, lithogeochemical characteristics,this reached the conclusion that Xiankou granitoid pluton is Belong to straddling between S-type and aluminous A-type. The genesis of Xiankou pluton is that lower crust partial melting as temperature rise and pressure decrease caused by lithospheric delamination of the Triassic in South China triggered after orogeny, and crustal stretching, thinning of lithosphere, hot asthenosphere surge basaltic magma underplating mantle source heating fluid injected into the Earth’s crust and mantle.Xiankou granite pluton is U-riched granite, the average of uranium content of the pluton is 15.46×10-6, the uranium content is higher than uranium content of the granite of other ages and other stratas.The coefficient of variation of U、Th is:Cv（U）=47%,Cv（Th）=36%. The correlation coefficient of U、Th and Th/U of each unit is respectively: Dianyuan units r（Th、U）=0.65,Th/U=3.10;Henggang units r（Th、U）=0.26,Th/U=2.82;Shangdianyuan units Th/U=1.29;Paiqian units r（Th、U）=0.29,Th/U=1.68.Through the comparison the Xian Kou granite pluton between the other indo-chinese epoch uranium productive granitic massif of South China in the lithology, mineral assemblages, Geochemical Characteristics and the alteration situation,we found they are samilar.Luoshan uranium deposit has been discovered at contact zone of the Xiankou and Lean granite pluton, and the uranium source may come from the Xiankou granite pluton which should produce uranium. And we can speculate that in the deep of the Xiangshan uranium deposits, there may be a rich uranium Indosinian granite basement.