Magmatic-hydrothermal evolution and rare metal mineralization in the Chamuhan W-Mo-Sn-Be deposit in the southern Great Xing’an Range, Northeastern China

Understanding the processes involved in the formation of vein-type deposits associated with granites is crucial for comprehending the magmatic-hydrothermal evolution and enrichment processes of rare metals in granitic-hydrothermal systems. The primary focus of this study is to elucidate the mechanism controlling rare metal mineralization and the evolution of ore-forming fluids. We present zircon-monazite-cassiterite-wolframite U-Pb ages, whole-rock compositions, monazite Nd isotopic data, as well as mineralogical and chemical data for mica, beryl, and tourmaline from granites and quartz veins in the Chamuhan deposit in the southern Great Xing’an Range (SGXR), northeastern (NE) China. Our objectives are to investigate the temporal and genetic relationships between magmatism and mineralization, assess the factors influencing the rare metal mineralization, and elucidate the properties and evolution of the ore-forming fluids. The U-Pb dating results for the Chamuhan monzogranite (144 ∼ 139 Ma) closely coincide with the mineralization period (142 ∼ 132 Ma), which, along with other Late Jurassic-Early Cretaceous deposits, indicate a peak in rare metal mineralization in the SGXR. During this epoch, an extensional environment provided sufficient time for magma evolution and facilitated the formation of these rare metal deposits. The ore fluids likely separated from the underlying fine-grained monzogranites (G3), which exhibited the highest degree of evolution and strongest melt-fluid interaction, ultimately precipitating towards the top of the altered intrusion represented by the altered biotite monzogranites (G2), thereby forming the W-Be-Sn mineralization. The chemical data for hydrothermal mica, beryl, and tourmaline elucidate the evolution processes of the ore fluids. These fluids transition from high concentrations of Si, F, and rare metals, accompanied by low oxygen fugacities and Mg-Fe contents, to conditions characterized by high oxygen fugacities and B contents with low rare metals and low to medium salinities. Isotope geochemistry indicates that system self-cooling rather than addition of external fluids, led to the precipitation of ore minerals. Detailed comparisons of whole-rock geochemical and monazite Nd isotopic data among the coeval Chamuhan, Maodeng, and Weilasituo rare metal granites reveal that the source regions offer limited concentrations of rare metals. The abnormal enrichment of rare metals in the Chamuhan deposit is probably the result of a combination of high degrees of crystallization differentiation, fluid-melt interactions, and changes in melt structures. Overall, our study not only provides new insights into the refined magmatic-hydrothermal evolution of the Chamuhan deposit, but also demonstrates that mica, beryl, and tourmaline can serve as valuable indicators for mineral prospecting, where elevated concentrations of rare metals and F suggest an increased likelihood of mineralization.