Source of ore-forming materials for the Redamen deposit: Constraints from geochronology and mica geochemistry

• The Redamen deposit is a distinctive pegmatite-type Li deposit hosted primarily within granitic rocks. • The Taiyanghe pluton, southwest of Ke’eryin, shows markedly lower evolutionary degrees and distinct mineral geochemical differences. • The Ke’eryin granites are potential parent rocks of Redamen pegmatite, while Taiyanghe pluton contributes minimally to mineralization. • The formation of the Redamen deposit is predominantly controlled by magmatic fractional crystallization processes. The Redamen lithium deposit is mainly hosted in the Taiyanghe pluton in the southwestern part of the Ke’eryin composite pluton, though the parental rock remains unclear. To investigate the source of ore-forming materials in the Redamen deposit, this study focuses on the biotite monzogranite from the Taiyanghe pluton and the Redamen pegmatites. Integrating existing research findings from the orefield, we conducted comprehensive analyses including U-Pb geochronology of columbite-tantalite group mineral (CGM), mica petrography, and mineral geochemistry. CGM U-Pb dating yielded an emplacement age of 207.1 ± 1.1 Ma (n = 30, MSWD = 0.54) for the Redamen albite-spodumene pegmatite. This age is consistent within error with the ages of other lithium deposits in the Ke’eryin ore field and overlaps significantly with the age of the Ke’eryin pluton, indicating a genetic link. Mica geochemistry and mineralogical analyses reveal that the Taiyanghe and Ke’eryin plutons underwent distinct magmatic evolutionary processes. The biotite monzogranite of the Taiyanghe pluton exhibits high K/Rb ratios (>300), indicating limited fractional crystallization, with rare metal contents significantly differing from those of the Ke’eryin pluton and associated pegmatites. In contrast, the Ke’eryin composite pluton and Redamen pegmatites display a progressive differentiation sequence (biotite K-feldspar granite → two-mica monzogranite → muscovite granite → pegmatite), characterized by decreasing K/Rb ratios (144 → 5) and systematic enrichment of Li, Rb, and Ta. This trend demonstrates continuous differentiation evolution from the Ke’eryin granite to the pegmatites. Rayleigh fractional crystallization modeling demonstrates that the pegmatites of the Redamen deposit are more likely generated through extreme fractional crystallization of the Ke’eryin composite pluton. Both the two-mica monzogranite and muscovite granite within the Ke’eryin pluton could potentially supply ore-forming materials for the Redamen deposit, while the contribution of the Taiyanghe biotite monzogranite to regional mineralization remains limited. In conclusion, we propose that the Redamen deposit shares a similar genesis with deposits such as Dangba and Lijiagou. All were dominantly controlled by magmatic differentiation crystallization processes. Multi-stage magmatic activity and tectonic activity collectively gave rise to the distinctive Redamen pegmatites.