Compositions Study of Auxiliary Minerals in Altered Granitic Rocks of the Mianhuakeng Uranium Deposit in Northern Guangdong

The Mianhuakeng uranium deposit is one of the most important uranium bases with complex mineralization conditions.In the paper,the characteristics of auxiliary minerals,especially U-bearing minerals,have been systematically studied using the electron-microprobe in altered rock of the deposit.Auxiliary minerals include pitchblende,zircon,parisite,coffinite-thorianite,aapatite,xenotime,and allanite.The main U-rich minerals are coffinite-thorianite,xenotime and monazite.Our study shows that hydrothermal activity can have great impact on crystal structure and composition of auxiliary minerals,even giving a rise to new minerals.Meanwhile,U-rich auxiliary minerals can release a large amount of uranium into hydrothermal fluid,altering xenotime to apatite,coffinite-thorianite to plumbothorite,and monazite to parasite.Apatite,zircon and allanite are relatively stable in crystalline structures and emit less uranium during the alteration process due to the fact that they contain less amount of uranium.But part of altered zircons behaves opposite,rising in uranium content.The study also suggests that the stronger hydrothermal activity the U-rich minerals undergo,i.e.more close to the center of hydrothermal activity,more distinct the decreasing of U content.This provides abundant source for the formation of uranium deposit.