Petrogenesis of the Bingzhou rare metal pegmatites, West Kunlun: Implications for regional exploration

• The mineralization age of the Bingzhou rare metal pegmatites is ca. 207 Ma. • The Bingzhou rare metal pegmatites are genetically related to the two-mica granite. • The Bayanharshan Group metapelites are the potential source rocks of two-mica granites in Bingzhou deposit. • The southern Dahongliutan-Bailongshan orefield has broad exploration potential. Understanding the petrogenesis and evolution of lithium-rich pegmatites is crucial for regional exploration. The world-class Dahongliutan–Bailongshan orefield hosts seven large to super-large lithium deposits distributed around the Bailongshan granite complex. However, its petrogenesis remains controversial, and most previous studies have focused on the northern deposits (e.g., Dahongliutan, Bailongshan, Xuefengling), with limited attention to the southern deposits. These limitations collectively hinder regional exploration efforts. This study addresses this gap by focusing on the Bingzhou lithium deposit, located on the southern side of the Bailongshan granite complex. Geochronology, REE geochemistry, and in-situ Nd isotopic analyses of monazite, along with the geochronology of columbite–tantalite group minerals, were conducted to constrain the emplacement ages, material sources, and genetic relationships between the granites and pegmatites. This study aims to utilize these findings to guide regional exploration. U–(Th)–Pb dating of monazite and columbite-tantalite group minerals constrains the emplacement ages to ca. 212.7 Ma for the two-mica granites, ca. 206.1–205.4 Ma for the spodumene-absent pegmatites, and ca. 207.2–206.7 Ma for the spodumene-bearing pegmatites. The close temporal relationship between the two-mica granites and pegmatites, as well as their spatial proximity observed in the field, suggests a genetic link between the two-mica granites and pegmatites. The εNd(t) values of monazite from the two-mica granite, spodumene-absent pegmatite, and spodumene-bearing pegmatite are similar (–10.0 to –8.0) and are consistent with the whole-rock εNd(t) values of Triassic Bayanharshan Group metapelites (–11.5 to –7.1). These characteristics indicate that metapelites are the source rocks of the two-mica granites, while the pegmatites represent the products of fractional crystallization of the two-mica granitic magma. The systematic variations in the Sm/Nd ratio and Eu anomaly coefficient in monazite, along with their strong positive correlation with lithium content, further suggest that fractional crystallization is the key process in the formation of rare metal pegmatites. The Bingzhou deposit shares similar metallogenic ages, material sources, and petrogenetic characteristics with its northern counterparts, reinforcing the exploration potential of the southern orefield.