MINERAL CHEMISTRY OF BIOTITE AND ITS IMPLICATIONS FOR URANIUM MINERALIZATION IN GUANGSHIGOU PEGMATITE-TYPE URANIUM DEPOSIT,SOUTH SHAANXI PROVINCE

Biotite is one of the important minerals in the pegmatite-type uranium deposits.It not only exists in the pegmatites and granites which have close relationship with uranium mineralization,but also is closely related with the main uranium mineral in the deposit.Biotite in the granites,alaskites and pegmatites closely related with the Guangshigou pegmatite-type uranium deposit is selected as the research subject.Based on the mineral chemistry of biotite analyzed by EMPA,it is showed that all the biotites are characterized by rich in Mg and Mn,deplete in Ca and the volatile constituents F and Cl.The biotite in U-bearing biotite pegmatites is characterized by higher content in Mg,Mn and lower in Al,ACNK and oxygen fugacity,compared to other biotite pegmatite.The results show that the alaskites and pgematites are not from the fractional crystallization of the Huichizhi monzonite granite.It is also evidenced that the assimilation between the pegmatites and wall rock not only control the special structure and composition of biotite in Ubearing pegmatites,but also the key factor in forming of pegmatite-type uranium deposit.