Genesis of the Heima zinnwaldite deposit in the Gongshan region, Southeast Tibetan plateau

Abstract

The middle-scale Heima zinnwaldite deposit is situated in the southeastern Tibetan Plateau, SW China. The NNW- to NS-trending orebodies are hosted in the Gaoligongshan metamorphic zone. To clarify the zinnwaldite genesis at Heima, this study presents an integrated investigation of the Heima pegmatites, combining precise geochronology, isotopic tracing, and detailed mineral chemistry to constrain its formation age, petrogenetic origin, and mineralization processes. Our robust geochronological framework, employing magmatic zircon (56.93 ± 0.53 Ma) and cassiterite (57.0 ± 4.2 Ma), establishes the pegmatite emplacement during the Late Paleocene to Early Eocene, representing the maximum age of lithium mineralization. Hf isotopic compositions (εHf_(t) =  −14.3 to −12.4) demonstrate that the Heima pegmatite originated from remelting of ancient sediments, distinguishing it from contemporaneous Eocene Gangdese–Tengchong granites (εHf_(t) =  −12.7 to +11.0) that show mantle contributions. This crustal signature aligns with the evolutionary trend of Hf isotopes in regional gneissic granites (600−420 Ma), supporting an anatectic origin from ancient continental crust rather than being derivatives of nearby Eocene granitic plutons. Detailed geochemical analysis of Li-micas reveals two distinct generations with contrasting formation mechanisms. The primary mica-Ia (53.45 ± 0.86 Ma, Rb–Sr age) exhibits extreme incompatible element enrichment (Li, Be, Rb, Cs) and remarkably low K/Rb ratios (3.98–4.37), characteristic of crystallization from highly fractionated granitic melts. In contrast, secondary mica-Ib and mica-II (17.9–16.0 Ma, Rb–Sr age) show significant Nb–Ta–W enrichment, reflecting precipitation from F–P-rich hydrothermal fluids during Miocene metamorphic–hydrothermal events. Principal component analysis (PCA) confirms the compositional disparity between these mica generations, with the later phases attributed to fluid-induced alteration and reworking. Regional correlation identifies two distinct lithium mineralization episodes in the Gongshan area, southeast Tibetan Plateau. The Eocene phase (~ 55 Ma) is zinnwaldite-dominant (e.g., Heima, Puladi), associated with crustal melting following Neo-Tethyan closure. The Miocene phase (~ 17 Ma) is spodumene-dominant (e.g., Danzhu, Peili), linked to Himalayan leucogranites formed as the rapid exhumation, denudation, and decompression partial melting of Himalayan Crystalline Complex.