Spodumene pegmatites from the Pusila pluton in the higher Himalaya, South Tibet: Lithium mineralization in a highly fractionated leucogranite batholith

Abstract

The Himalayan leucogranite belt is evaluated as a prospect for rare-metal mineralization. The Pusila pluton is located 44 km northwest of Mount Everest, and consists of two-mica granite, muscovite granite, albite granite, and pegmatites. Numerous pegmatite dikes have intruded the Higher Himalayan crystalline sequence and the granites. Oligocene pegmatites in the Chomogu and Cuore areas, which we constrain to have formed at ca. 25–23 Ma, were investigated in this study, because they are strongly enriched in Li (up to 8460 ppm) and contain abundant spodumene±petalite. Lithium was progressively enriched from the two-mica granite to the muscovite granite, and finally Li mineralization occurred in the highly fractionated pegmatites. The Chomogu No. 1 pegmatite is a well-zoned dike that hosts beryl, columbite, cassiterite, and Li minerals, which are concentrated in the inner parts of the dike. Scanning electron microscopy and cathodoluminescence images reveal two stages of Li mineralization. Primary spodumene (Spd-1) crystallized in the magmatic stage, whereas secondary spodumene (Spd-2) and petalite formed later in the hydrothermal stage. The Pusila pluton is thus an important site of Li mineralization in the Himalayan leucogranite belt.