The Mineralogical Feature Of Granite-pegmatite-type Uranium Deposit In Guangshigou

The Guangshigou uranium deposit in Danfeng area are the typical pegmatite type in China, this uranium deposit is located the caledonian fold belt in north qinling,which between Caichuan and Shangdan faulted structure. Based on the works of predecessors, the author analyzed the geologic feature and character of mineral geology in the Guangshigou pegmatite type uranium deposit, focusing on the microscopic inspection, scanning electron microscope and electron microprobe analyses of the uraninite and close associationzircon as well the biotite in this deposit.The systematic mineralogical studies are worked based on mineralogical feature and chemical composition analysis, then it analyzes the principle of migration and evolvement rules of the uranium in this area and uranium precipitating enrichment mechanism preliminary. After the microscopic observation and electron microprobe analyses for the uraninite, zircon and biotite in Guangshigou area, the following conclusion can be reached preliminary:(1)The uranium in Guangshigou deposit are mainly existed as uraninite form, parts of that exists in zircon and monazite in form of isomorphism, in shape are quadrilateral and irregular polygon, with large crystalline particles(about 200μm).Mainly distributed in the interior of Quartz, feldspar and biotite gangue or the intercrystalline, which gets a close associated relationship with biotite and zircon etc.Besides that, it’s common associated with chlorite, pyrite and hematite, the uraninite is mainly surrounded by the chlorite and pyrite, forms the chlorite and pyrite rimmed textures.(2)The main component of the uraninite is UO2 and Th O2, the UO2 content is81.62%~89.40% and the Th O2 content is 1.39%~3.72%, most of the samples contain avariable amount of Si O2、Y2O3、Pb O etc. The content of the UO2 pegnatite dike are higher than pegnatite dike in uraninite. However the content in Xiaohuacha ore body is relatively low.The research also found that the single transistor without the later stage hydrothermal activity occur in uraninite had the highest UO2 content, which is 86.75%~89.40%.(3)The biotite in ore-bearing pegmatite veins and Huichizi pluton from Guangshigou uranium deposit are characterized by iron,Ti-rich, the biotite in Huichizi biotite monzonitic granite is iron-rich mica, the biotite in ore-bearing pegmatite veins is siderophyllite; all of them gets the low oxygen fugacity.The crystallization temperature of the biotite in ore-bearing pegmatite veins is higher than biotite in Huichizi pluton biotite adamellite, it means that pegmatite is not the outcome from biotite adamellite by fractional crystallization;(4)The compositional variation of the zircon is small, parts of that zircon get the some obvious zonal struture.In conclusion,the ore-forming processes of the uranium mineral in Guangshigou pegmatite type uranium ores can be approximately divided into two-period. Magmatism period, and hydrothermal superimposition reformation period.The main metallogenic stage is magmatism period,The uranium mineral includes the uraninite, broeggerite, coffinite etc.After the squeezing action of the uraninite in the hydrothermal superimposition reformation period,the uraninite occurred crushing after the hydorthermal metasomatic replacement during the late magmatic stoping, to make parts of the uranium emigration,then the hydrothermal activity happened.The newly formed pyrite was filling within the fissures of the uraninite, or wrapped the uraninite(chlorite or hematite etc).Finally, because of the uranium mineral such as uraninite are in near-surface, the uranophane formed after the uranotile surface oxidation,And cleavage distributed along the rock presenting occurrence inveins. Therefore, the Guangshigou granite-pegmatite-type uranium deposit is formed by differentiation of the protomagma and superimposed mineralization of the late hydrothermal.