Beibei Xu

In recent years, a series of pegmatite-type rare metal deposits and occurrences—including Chakabeishan, Shaliuquan, Jinshuikou, Adatan, and Gaduo—have been reported in Qinghai, sparking a wave of rare metal exploration. The Southern Kunlun Convergence Zone is a key tectonic unit of the Eastern Kunlun Orogenic Belt; however, systematic geochronological and geochemical constraints on the granitic–pegmatitic rare metal mineralization system within this region have long been lacking. This study focuses on the newly discovered beryllium ore body at Wulugou in the Southern Kunlun Mountains. Samples from the ρ10 and ρ38 beryllium-bearing pegmatite veins were selected for petrological analysis, LA-ICP-MS zircon–monazite U-Pb geochronology, and whole-rock major and trace element analyses. Zircon Lu-Hf and monazite Sm-Nd isotope analyses were also conducted on the ρ10 and ρ38 beryllium-bearing pegmatite veins. This study precisely determined the diagenetic and mineralization ages of the pegmatites; systematically clarified the genesis and evolutionary relationships among the ore-bearing pegmatite, the surrounding granite, and the barren pegmatite; and elucidated the characteristics of the magma source region and the mechanisms of beryllium mineralization. LA-ICP-MS dating results for monazite and zircon in the pegmatites indicate that the ore-bearing pegmatite formed during the Early Devonian (404.9–408.3 Ma). Whole-rock geochemical analysis indicates that the albitized granites, barren pegmatite, and beryllium-bearing pegmatites in the study area constitute a continuous, homologous, highly differentiated evolutionary sequence, all of which are highly differentiated granites. As the degree of crystallization increases, the rock undergoes continuous enrichment in SiO₂, Na₂O, MnO, P₂O₅, and Be, while K₂O, Ca, and Sr are progressively depleted. The effects of the four rare earth groups, along with the Zr/Hf and K/Rb ratios, collectively indicate that saturation and dissolution of volatile fluids in the late stage are the key controlling factors in the precipitation of beryllium ore. For primary magmatic zircon, ε_Hf (t) = −2.69 to +1.95 (mean + 0.76); the two-stage Hf model age is 1.28 to 1.57 Ga; isolated ε_Nd (t) = −6.71 to −5.44; and the Nd two-stage model age is 1.57 to 1.68 Ga. The source-area discrimination diagrams all fall within the muddy clastic-melt zone, indicating that the parent magma originated from low-degree partial melting of the Middle Proterozoic Wanbaogou Group metamorphic basement, accompanied by contamination by mantle-derived magma. This study discovered Early Devonian Caledonian-period pegmatite-type beryllium deposits in the Southern Kunlun Mountains, providing a theoretical basis and practical reference for the exploration of granitic–pegmatite-type beryllium deposits in the Southern Kunlun Mountains.