CHEN You-wei^1,2,BI Xian-wu¹,HU Rui-zhong¹,ZHU Wei-guang¹,XU Lei-luo^1,2,DONG Shao-hua^1,2

1.State Key Laboratory of Ore Deposit Geochemistry,Institute of Geochemistry,Chinese Academy of Sciences,Guiyang 550002,China;
2.Graduate University of Chinese Academy of Sciences,Beijing 100049,China

Abstract:　　The Luxi granite and the Xiazhuang granite are important parts of the Gui-dong composite pluton in the northern Guangdong provice.They have the same tectonic setting,similar spatial association and similar age.However,many uranium depostites are formed in Xiazhuang granite while none is found in the Luxi granite.A detail study on this difference is significant for understanding the metallogenic mechanism of granite-type uranium deposit.Biotite contains a lot of geochemical information about the magmatic crystallization.The results of the electrion microprobe,Mssbauer spectroscopy and ICP-MS analyses of biotites collected from Luxi and Xiazhuang granites indicated that these biotites have similar major element contents,rich in Fe but poor in volatile consitutents,and have similar trace element contents,strong negative Eu anomalies.The biotites of Xiazhuang granite are distinguished from those of the Luxi granite by higher evolution degree,more F content,lower temperature and lower oxygen fugacity.The evolution degree and F content increase and the temperature and oxygen fugacity decrease from Luxi granite to Xiazhuang granite may cause that the uranium content increases and that the existing state of uranium changes from isomorphism to uraninite,a mineralization unfavorable condition to a mineralization favorable condition.It is the main reason for that there are many uranium depostites in Xiazhuang granite while none is in the Luxi granite.

Key words:　 biotite； mineral chemistry； uranium content； existing state of uranium

*Corresponding Author, E-Mail: chenyouwei1983@163.com

Bulletin of Mineralogy, Petrology and Geochemistry Vol. 29, No.4, 2010, page 355-363

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