Mineralogy and temperature of magma generation for A-type granitoids in Boziguoer,Baicheng County,Xinjiang

The Boziguoer A-type granitoids in Baicheng County of Xinjiang are ore-bearing rocks with abundant useful elements such as Nb,Ta and Zr.The petrological and mineralogical characteristics of the A-type granitoids were investigated on the basis of observation under polarized microscope,chemical analysis and detailed BSE images using EPMA,followed by the discussion on the p-T conditions of A-type magma generation and the tectonic setting.The results indicate that these A-type granitoids could be divided into three types,namely aegirine arfvedsonite quartz alkali feldspar syenite,aegirine arfvedsonite alkali feldspar granite and biotite alkali feldspar syenite.The major rock-forming minerals are quartz,albite,K-feldspar,aegirine,arfvedsonite and siderophyllite,whereas the accessory minerals include mainly zircon,pyrochlore,thorite,fluorite,monazite,bastnaesite and xenotime.The average temperatures of the magma are 832～839℃.A-type granitoids might have been formed in an anorogenic intraplate tectonic setting by which they generally show such features as hightemperature,anhydrous nature and low fugacity.