Mineral chemistry of garnet and its implication for the magmatic-hydrothermal transition in rare metal leucogranites in the Lalong dome, southern Tibet, China

In order to acquire a mineralogical indicator for the degree of leucogranite magmatic evolution and the mineralization of Be-Nb-Ta rare metals, the garnets of the Lalong dome, located at the eastern part of the North Himalayan Gneiss Domes (NHGD), was performed Electron probe analysis and in-suit LA-ICP-MS analysis. Major elements results in garnet show that MnO contents range from 12.42%~13.48% in muscovite granite to 16.83%~22.09% in albite granite. Almandite mainly occur in muscovite granite, while spessartite in albite granite, both types resulted from magmatic crystallization. Trace elements results show that garnets in muscovite granite and albite granite are characterized by the enrichment of heavy rare earth elements (HREE), high depletion in light rare earth elements (LREE), and the negative Eu anomalies. With the increasing degree of magma differentiation evolution from muscovite granite to albite granite, Zn, Be, Nb and Ta contents in garnet gradually increase with the degree of magma evolution, while Sc, Y and HREE contents decrease, which indicates that the magma evolution has changed from normal magma stage to the magmatic-hydrothermal transition stage. Spessartite in albite granite can be used as a mineralogical indicator for the mineralization of Be-Nb-Ta rare metals in Lalong Dome.