Mineralogical characteristics of the leucogranite-pegmatite in the Yardoi Gneiss Dome, Himalaya, Tibet: Implication to the rare -metal mineralization.

In recent years, it has been proposed that the model of the Himalayan highly -differentiated Cenozoic leucogranite makes this belt gradually become a highly -potential strategic prospective area for the rare -metal mineralization in China. At present, the type of metal assemblages in the northern Tethys Himalayan belt is dominated by beryllium -niobium -tantalum ( tin -tungsten) assemblage, while the southern Higher Himalayan belt is dominated by lithium -beryllium -niobium -tantalum assemblage. The present study has newly discovered the beryl -bearing pegmatites in the Yardoi Gneiss Dome, and the detailed field observation, internal structures of pegmatites and mineralogical compositions have been analyzed by in -situ microanalysis of EPMA and LA-ICPMS on the feldspar, mica, tourmaline and beryl from the leucogranite-pegmatite. Finally, all the results comprehensively shape the degree of magmatic differentiation of the Yalaxiangbo leucogranite-pegmatite and its rare metal mineralization potential. Based on the detailed field observation and in -situ microanalysis of minerals, the following concluding remarks were obtained: 1) rare -metal minerals in the Yalaxiangbo leucogranite and pegmatite rocks are mainly beryl hosted in the microline-albite pegmatite; 2) compositions of the mica minerals, feldspars, tourmalines and beryl were controlled by the magmatic differentiation, and the elemental substitution includes Ale DR'', and Al4Si_3 rectangle (_1) for muscovite, MgFe_1 and (x)rectangle, Al( Na, R2+) _1 in schorl, and Na( Fe2+, Mg) rectangle(_1),A1 (_1) in beryl; 3) according to feldspar Cs content and K -feldspar K/Rb ratio, muscovite Li -B -Cs content and K/Rb ratio, schorl Ge-Pb content, and beryl Li -Cs content and Cs/Na ratio, we suggest the Yalaxiangbo leucogranite-pegmatite evolution is similar to that of typical Be-Nb-Ta mineralized pegmatites and Be mineralized zones in complex pegmatites.