Cassiterite U–Pb Geochronology of the Dahongliutandong Li Pegmatites, West Kunlun, NW China

The West Kunlun represents one of the largest and most economically significant rare metal metallogenic belts in NW China. The newly discovered Dahongliutandong Li deposit is the first Li deposit identified within the Permian Huangyangling Group in this region, and its discovery has important implications for regional lithium exploration. In this study, whole-rock major and trace-element geochemistry and cassiterite U–Pb isotope data from both Li-poor and Li-rich pegmatites of the Dahongliutandong deposit were analyzed to constrain the mineralization age and tectonic setting. Geochemically, the pegmatites are characterized by high SiO2 (70.57–78.50 wt%), low TiO2, MnO, and MgO (<0.2 wt%), and strongly peraluminous signatures (A/CNK = 1.45–1.95). They exhibit coherent chondrite-normalized REE patterns with LREE enrichment and negative Eu anomalies (Eu/Eu* = 0.03–0.77), along with consistent enrichment in LILEs (e.g., Rb, U, K) and depletion in HFSEs (e.g., Nb, Ti) on primitive mantle-normalized spider diagrams, suggesting a common magmatic source or evolutionary path. Cassiterite U–Pb dating yielded consistent lower-intercept ages of 208 ± 11 Ma (MSWD = 0.86) for Li-poor pegmatites and 206 ± 5 Ma (MSWD = 1.7) for Li-rich pegmatites, both indicating Late Triassic mineralization. Combined with regional geology, these data suggest that Li mineralization was likely related to post-collisional extension following the closure of the Paleo-Tethys Ocean. This study provides new insights into regional rare metal mineralization in the West Kunlun orogenic belt.