The Maodeng Sn-Cu deposit is a medium-sized deposit in the southern segment of the Great Xing'an Range located in Xinlinhot City of Inner Mongolia. Whole rock geochemistry, LA-ICP-MS zircon and cassiterite U-Pb ages, and Sr-Nd-Pb isotopic compositions of the granite porphyry and Sn-Cu ores in the Maodeng deposit have been studied in detail and are reported in this contribution. The zircon from the ore-related granite porphyry has a weighted mean U-Pb age of 138±0.6 Ma, while the cassiterite from cassiterite-sulphide-quartz vein-type ore has a Tera-Wasserburg concordant U-Pb age of 139±3.2 Ma. These two ages are consistent within error, which indicates that the emplacement of granite porphyry and Sn-polymetallic mineralization in Maodeng took place during the Early Cretaceous. Geoche¬mically, the granite porphyry is characterized by high SiO2 (73.18% to 77.3%), (Na2O+K2O) (8.00% to 8.69%), and K2O (4.80% to 5.22%), with low CaO (0.49% to 0.95%), Al2O3 (11.67% to 12.83%), MgO (0.12% to 0.46%), and relatively high FeOT/(MgO+FeOT) (0.74 to 0.91), and 10000×Ga/Al (3.64 to 4.28) ratios. The rock is enriched in Rb, Th, K, Hf, and depleted in Ba, Sr, P and Ti. The REE distribution patterns of the granite porphyry are of typical gull-wing shape with obviously negative Eu anomalies (δEu=0.05 to 0.2). Zircon saturation temperatures of the granite porphyry vary from 817 to 861 ℃. All these show that the granite porphyry exhibits geochemical characteristics typical for A-type granite. The granite porphyry has relatively low (87Sr/86Sr)i values (0.702907 to 0.704506), high εNd(t) values (+0.8 to +4.4) and young two-stage Nd model ages (tDM2=572 to 863 Ma), suggesting that the rock was dominantly derived from partial melting of a juvenile lower crust, followed by strong fractional crystallization during magma ascent. The Pb isotope compositions of the granite porphyry and ores are similar, indicating that the Pb of the ores could be sourced from the granite porphyry. According to the trace element characteristics, chemical subdivision diagrams and tectonic environment discrimination diagrams, the granite porphyry in the Maodeng belongs to A2-type granite, which formed in an extensional setting. Based on previous studies and combining geological characteristics, ages of the ores and granite porphyry, and Pb istope characteristics, it is believed that the intensely fractionated granite porphyry at the Maodeng deposit is spatially and temporally, and possibly genetically related to the Sn-Cu mineralization. It is proposed that the size of the Sn deposit is constrained by the degree of fractional crystallization of the magma. © 2021, Science Press. All right reserved.
