The study of Li-minerals in granitic pegmatites from Gyirong, Himalaya

Massive leucogranites and granitic pegmatites were exposed in the Gyirong region, the middle of Himalayan orogen. Recent studies reported that the Li minerals, such as zinnwaldite, lepidolite and spodumene, were found in the leucogranites and granitic pegmatites from the Yingxionggou and Tsalung district in Gyriong pluton. In this study, two-type lithium-rich pegmatites from the Tsalung district were identified by the detailed petrographic and mineralogical studies, including spodumene pegmatite and lepidolite-elbaite pegmatite (aplite included). The major Li-rich minerals in spodumene pegmatites are spodumene, lepidolite and petalite which is new-found in this study. Especially, sokolovaite ((Cs, K)Li2Al[Si4O10]F-2, Cs/(Cs + K) atomic ratio >0.5), Cs-analogue lepidolite, is firstly discovered in the Himalayan orogen, with the marginal occurrence adjacent to the lepidolite and Cs2O content up to 16.9%. It is suggested that sokolovaite is the product of lepidolite reacting with late Cs-rich fluids by the mineral texture. In the lepidolite-elbaite aplite, the main Li-rich minerals include lepidolite and elbaite. Lepidolite contains 0.9% similar to 6.7% Li2O content. Tourmaline contains Li2O content up to 2.4%, and low FeO, MgO, and CaO contents (< 1.1%, < 0.01% and 2.6%, respectively), close to the end-member of elbaite. Combined with abundant pollucite and microlite found in the Tsalung Li-mineralized pegmatites in Gyirong pluton, it is confirmed that the Tsalung pegmatite is typical LCT(Li-Cs-Ta)-type pegmatite, and the mineral constitution and their chemical compositions demonstrate that the pegmatite is extremely high-evolved.