113-16 Lithium mineralization processes in the Chakabeishan pegmatites, Northeastern Tibetan Plateau: insights from in situ elemental and boron-isotope variations in tourmaline and muscovite

Session: Mineralogical Characterization of Economic Resources: From Critical Minerals to Gemstones (Posters)

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The mechanism of lithium (Li) mineralization in regionally zoned pegmatites remains incompletely understood. In this study, we present detailed textural observations, in situ elemental data, and in situ boron (B) isotopic compositions of tourmaline and muscovite from regionally zoned pegmatites in the Chakabeishan (CKBS) pegmatite deposit, northeastern Tibetan Plateau. These pegmatites comprise three sequentially developed lithological zones: garnet–tourmaline (GT), beryl–muscovite (BM), and beryl–spodumene (BS) zones, corresponding respectively to barren, Be-mineralized, and Li-mineralized pegmatite veins. Both tourmaline and muscovite are present in all three zones. Seven tourmaline compositional subtypes across three types (Tur I, Tur II, and Tur III) were identified: (1) core, (2) mantle, and (3) rim of Type-I (Tur I) from the GT zone; (4) Type-II (Tur II) from the BM zone; and (5) Type-IIIA (Tur IIIA), along with (6) core and (7) rim of Type-IIIB (Tur IIIB) from the BS zone.

Specifically, Tur I core, Tur II, and Tur IIIA exhibit similar δ¹¹B values, suggesting a shared origin. In the GT zone, Tur I shows a compositional transition from schorl to elbaite across its core, mantle, and rim. The rim of Tur I is enriched in Li, Rb, Sr, Ga, and Pb, but depleted in Sc, V, Zn, and Ti relative to its core and mantle, indicating crystallization from a more evolved melt. In the BS zone, the core of Tur IIIB belongs to the schorl–dravite series and exhibits discontinuous contents of Li, Sc, V, and Sr compared to Tur IIIA. This reflects its crystallization from a fluid-enriched melt with progressive accumulation of fluids. In contrast, the rim of Tur IIIB, belonging to the schorl–elbaite series, is characterized by higher Li, but lower V and Ti contents, indicative of hydrothermal crystallization.

Across all zones, muscovite exhibits increasing Li contents and decreasing K/Rb ratios from the GT zone through the BM zone to the BS zone, with Li contents reaching up to 833 ppm. These trends suggest that the three zones record multiple magmatic pulses. Compared with magmatic processes in a melt-dominated system, Li enrichment and redistribution via hydrothermal processes may play a more critical role in Li mineralization in pegmatitic systems.

Geological Society of America Abstracts with Program. Vol. 57, No. 6, 2025

doi: 10.1130/abs/2025AM-9695

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