Multi-stage Sn-polymetallic mineralization in Shuicheng Region, Western Yunnan, China: Cassiterite geochronology and geochemistry constraints

As a key metallogenic region in China, Tengchong in western Yunnan is situated in the southern section of the Sanjiang Metallogenic Belt. The area's polymetallic mineralization is characterized by multiple periods and stages. However, existing research lacks sufficient reliable chronological evidence to accurately define the tin polymetallic mineralization in this region. This study focuses on the Shuicheng tin-polymetallic deposit within the central north Tengchong block. Using the cassiterite U-Pb dating method, we identified two mineralization ages within the same deposit: the Dadongshan (DDS) tin metallogenic epoch at 75.12±0.87 Ma (MSWD= 0.82), which aligns with the early Cretaceous granite (76~72 Ma) in the ore district, and the Xiangchunyuan (XCY) tin metallogenic epoch at 52.23±0.80 Ma (MSWD= 1.09), which corresponds to the Paleogene granite (52 Ma) in the vicinity. Through observation of the ore body and identification of ore specimens, we believe that both periods of mineralization in the Shuicheng Tin polymetallic deposit are associated with magmatic activity. Based on the tectonic setting, large-scale magmatism and related tin mineralization events occurred in the central Tengchong block during the Late Cretaceous and Paleogene periods. Trace element analysis of cassiterite indicates that the DDS cassiterite has higher Fe, Mn, U, and Sb content, whereas the XCY cassiterite has higher Nb, Ta, Zr, Hf, and W. This indicates that XCY has a higher mineralization temperature than DDS and a more reduced mineralization environment. Based on the tectonic background of the region, we suggest that DDS formed during hydrothermal mineralization under conditions of oceanic plate subduction, while XCY was a magmatic hydrothermal mineralization formed under plate rollback under continental collision orogeny conditions. Our study, for the first time, identifies two distinct tin mineralization events in the same deposit within the central Tengchong block, offering new insights into the three north-south-oriented mineralization zones within the Tengchong block and providing new constraints on the magmatic mineralization processes in the Tengchong area.