<p>The Gabo lithium deposit represents a newly discovered pegmatite-type lithium deposit within the Himalayan metallogenic belt. The tourmaline-muscovite granite, the largest leucogranite in the mining area, displays a close spatial correlation with the Li-pegmatite veins. This study aims to examine the genesis of tourmaline and evaluate the significance and potential of pegmatite lithium deposits. Tourmaline is extensively distributed in tourmaline-muscovite granite at Gabo deposit in Luozha county (Xizang). Investigation of the compositional and in situ boron isotopes of the tourmaline revealed that the tourmalines mainly belong to the schorl group and exhibit uniform elevated Li–Sn contents and <i>δ</i>¹¹B values (− 11.6 ‰ to − 10.5‰). This indicates that the tourmaline mainly crystallized from a boron-rich granitic magma undergoing enrichment in elemental lithium during the tourmaline crystallization process. Compared with the principal rare metal leucogranite-pegmatites in the Himalayan orogen, it is proposed that the elevated lithium (Li) content of tourmaline serves as an effective mineral indicator for the highly evolved pegmatite-type rare metal deposits.</p>