Electron Microprobe U-Th-Pb Chemical Dating of Pitchblende and Its Geological Significance of Jinguanchong Uranium Deposit in the Mingyuefeng Area,Eastern Hunan
The Jinguanchong uranium deposit is located in Mingyuefeng area of east Hunan province,which be-longs to granite outer contact zone type uranium deposit,and the main types of uranium mineralisation are pitch-blende-calcite and pitchblende-microcrystalline quartz-fluorite.Detailed field geological investigations,petrogra-phy,electron microprobe chemical analyses,and U-Th-Pb chemical dating studies have been carried out to deter-mine the age and stage of uranium mineralisation in the Jinguanchong area.The results show that both types of pitchblende exhibit high UO2 contents and low PbO and SiO2 contents.There is no obvious correlation between w(CaO)and w(UO2+PbO),w(SiO2+CaO+FeO)and w(PbO)and the age of the pitchblendes,which indi-cate that the pitchblendes are relatively stable at the time of their formation and weakly affected by the later modi-fication effects.The weighted average age of pitchblende-calcalite type uranium mineralization in Jinguanchong u-ranium deposit is calculated as(90.7±3.2)Ma(MSWD=1.9,n=17)using U-Th-Pb chemical dating meth-od.For the pitchblende-quartz-fluorite type uranium mineralization,the weighted average age is determined as(70.1±2.4)Ma(MSWD=2.1,n=20).These results indicate at least two stages of secondary uranium miner-alization occurred primarily during late Cretaceous.Combined with the previous dating results,it can be conclu-ded that uranium mineralization in the Jinguanchong uranium deposit aligns with the lithospheric extension and thinning event in South China,which may be the result of the subduction of the Paleo-Pacific plate.
chronologyEPMA U-Th-Pb chemical datinggranite outer contact zone type uranium depositseast-ern HunanJinguanchong uranium deposit
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