Study On Chronology, Rock Geochemistry, Uranium Bearing Mineral Of Ziyunshan Peraluminous Granite, Centre Jiangxi

The Ziyunshan granite is located in the east part of the combination between the cathaysian plate and the Yangtze plate, and it is a typical granite rich in tungsten and uranium. According to the different lithologic, the rock can be divided into three units facies belt, between each unit are present the pulsation contact. On the basis of previous studies, by means of detailed petrography, rock geochemistry, geochronology, isotope geochemistry research methods, to study petrogenesis, diagenetic environment, diagenetic age, occurrence state of uranium in three different units?s granite for Ziyunshan granite.The detailed petrographic and petrogeochemistry indicated that the Ziyunshan granite have high silicon, potassium, alkali, low phosphorus and low calcium, it is typical peraluminous S type granite.The Ziyunshan granite are rich lithophile element(Rb,Th,U,Ce) and high field strength elements(Zr,Hf,Nb,Y), the Ba,Sr,Ti have negative anomaly characteristi. The Ziyunshan granite have high content of U and Th, the U content is 9.92 to 25.30 ppm,the average value is 15.29 ppm, Th content is 8.82 to 90.00 ppm, the average value is 27.99 ppm, it may provide an important source of material for the enrichment of uranium.The Zircon U-Pb dating by LA-ICP-MS method is applied to determine the ages of Ziyunshan granite, the results showed that Jiaokeng(J3J) two samples ages are 153.1±2.5Ma and 151.2±2.1Ma, the Yaoli(J3Y) is 150.5±2.3Ma, the Miaoqian(J3M) two samples ages are 155.2±2.1Ma and 149.3±2.1Ma,the three showed the same age.The result shows that the rocks of the three units are the products of the same magmatic events.Try to using the Electron microprobe dating for uraninite, choose the uraninite to dating which crystal form are complete and the gray are uniform. Electron microprobe U-Th-Pb dating results in the Jiaokeng unit(J3J) the weighted average age is 161.8±2.4Ma, the Miaoqian unit(J3M) the weighted average age is 159.7±3.2Ma. Chemical ages of uraninite and Zircon U-Pb ages are consistent within the error range.We can think uraninite EMPA dating is a suitable method for U-fertile peraluminous granites.The Sm-Nd isotope analysis test showed that εNd(0) content are-13.7~-11.6, εNd(t) content are-17.0~-11.3, fSm/Nd are-0.23~-0.04, it showed that Ziyunshan granite is mainland crust granite.The analysis test showed that Nd model ages are 1858Ma-2020 Ma, consistent with the ages of basement rocks in southeastern China.The Electron microprobe Chemical composition analysis showed that biotite which in Ziyunshan granite are rich Fe and Ti, poor Mg and Al, it belong to Fe-biotite. These characteristics implicate that Ziyunshan granite belong to peraluminous granite.The formation depth are 9.56Km-12.18 Km.By means of mineralographic microscope, scanning electron microscope, Electron microprobe to detailed observation and composition determination of uranium bearing minerals which in Ziyunshan granite. It is showed that uranium-bearing minerals are are zircon, monazite, xenotime, uraninite, uranothorite and thorianite in Ziyunshan granite, majority uranium bearing minerals are hosted in biotite and majority biotite are occurrenced chloritization. The uraninite is recognized as the source of uranium minerals, if the zircon, monazite, xenotime, uranothorite and thorianite are rich uranium, when they crystal structure is destroyed, the uranium in the structure can be activated to become active uranium, which provides the source of uranium for the migration and enrichment of U, and becomes a potential source of uranium under the fluid action.