Multi-stage superimposed mineralization leading to exceptional Sn-W enrichment: Insights from cassiterite and wolframite U-Pb geochronology of the Cuonadong Deposit, Himalaya

Multi-stage superimposed mineralization is a critical yet poorly constrained process in giant Sn-W deposit formation. The Cuonadong deposit in southern Tibet, the sole large-scale Sn-W-Be metallogenic system, provides an exceptional opportunity to decipher its temporal and geochemical evolution. This study combines in-situ U-Pb geochronology and major/trace element analyses of cassiterite and, for the first time at Cuonadong, wolframite to reconstruct the multi-stage metallogenic process. Geochemical contrasts reveal distinct fluid pulses: early cassiterite (Cst-I) exhibits high Nb/Ta, Zr/Hf, and Ti/Zr ratios with negative W-Sb correlations, indicative of a high-temperature, reduced fluid with limited differentiation. Conversely, later Cst-II and Cst-III display lower ratios and positive W-Sb trends, reflecting oxidized, evolved fluids. Notably, Ti discrepancies between Cst-II and Cst-III preclude a simple cooling trend, implying separate hydrothermal sub-stages. New U-Pb dating defines three cassiterite generations: Cst-I at 17.29 ±0.30 Ma, Cst-II at 12.79-12.36 Ma, Cst-III at 12.18-11.48 Ma, and wolframite at 12.29 ±0.47 Ma. This establishes a prolonged 18-11 Myr history comprising early Sn (18-17 Ma), main Sn-W (15-14 Ma), and late Sn-W (12-11 Ma) stages. Mineralization was driven by two magmatic-hydrothermal phases: an early (18-17 Ma) poorly differentiated, reduced fluid precipitating greisen-type Sn, and a later (12-11 Ma) highly differentiated, oxidized acidic fluid controlling Sn-W polymetallic veins. The late stage (Cst-II and Cst-III) records two discrete hydrothermal episodes along structural channels. The multi-stage and diverse nature of mineralization in the Cuonadong deposit, when compared with typical tin deposits worldwide, reinforces multi-stage superposition is a fundamental mechanism for the formation of super-large tin-polymetallic deposits.