Geochronology and geochemistry of the Huanglongling lithium deposit, Altyn Tagh orogenic belt: Insights into lithium mineralization

• The mineralization age of the Huanglongling lithium deposit is constrained to the Late Ordovician. • The Li-mineralized pegmatites are likely derived from the medium-fine-grained biotite monzogranite. • Mantle-derived thermal fluxes during post-collisional extension were instrumental for mineralization. The newly discovered Huanglongling pegmatite-type Li deposit in the Altyn Tagh Orogenic Belt hosts significant resource potential; however, the timing of mineralization and its genetic relationship with regional granites remain poorly constrained. Integrating field observations with bulk-rock geochemistry and U-Pb geochronology of zircon and CGMs, we reconstruct a multi-stage magmatic history. Zircon U-Pb dating yields crystallization ages of 461.1 ± 1.7 Ma for the medium-coarse-grained and 443.2 ± 2.1 Ma for the medium-fine-grained biotite monzogranite. CGMs U-Pb dating further reveals that Li-mineralized pegmatites were emplaced between 442.8 and 438.5 Ma, coeval with the younger granite, whereas barren pegmatites formed distinctly later at 401.4 ± 2.7 Ma. Both granites are peraluminous and classified as S-type, suggesting an ancient psammite-dominated crustal source. However, the more radiogenic zircon Hf isotopes of the medium-fine-grained monzogranite (ε Hf (t) = -3.7 to −1.4) compared to the medium-coarse-grained phase (ε Hf (t) = -10.5 to −9.0) indicate signficant input of mantle-derived components in the younger magma. The Li-mineralized pegmatites exhibit similar REE patterns but have significantly lower REE contents and extremely low Nb/Ta and Zr/Hf ratios compared to the granites. These features preclude a direct origin by low-degree crustal melting but are diagnostic of extreme fractional crystallization from the coeval monzogranitic magma. In contrast, distinct bulk-rock and CGMs compositions confirm that the barren pegmatites represent an independent magmatic phase. Within the regional tectonic framework, we conclude that the medium-coarse-grained biotite monzogranite formed in a syn -collisional compressional setting, whereas the medium-fine-grained biotite monzogranite and its related Li-mineralized pegmatites were generated during post-collisional extension. Lithospheric delamination and asthenospheric upwelling in this extensional regime provided the sustained high thermal flux, which was critical for large-scale crustal melting, efficient lithium release, and subsequent magmatic enrichment.