Late Triassic Mineralization in the Dupangling Area, Western Nanling Belt, China: Evidence From Cassiterite U–Pb Geochronology, Fluid Inclusions and H–O–S Isotopes of the Dawan Sn–Polymetallic Deposit

The Nanling metallogenic belt in South China is a world‐class W–Sn province characterized by polyphase mineralization during the Caledonian, Indosinian and Yanshanian orogenies. However, compared to the extensively studied Yanshanian events, the Late Triassic mineralization remains relatively poorly constrained. The Dawan Sn–polymetallic deposit, located in the northeastern Dupangling composite batholith, hosts orebodies in the exocontact zone of a highly fractionated biotite monzogranite. Based on the regional geological context, the Dawan deposit was selected to investigate its potential genetic link to Late Triassic mineralization. This study employs cassiterite U–Pb dating, trace element analysis, fluid inclusion microthermometry, laser Raman spectroscopy and H–O–S isotopic analysis to elucidate its ore‐forming processes. We obtained a cassiterite U–Pb age of 214.7 ± 3.2 Ma, confirming that the mineralization occurred during the Late Triassic. This timing is coeval with regional post‐collisional lithospheric extension and the emplacement of A‐type granites in the western Nanling Range. Fluid inclusion data reveal an initial medium–high temperature, moderate‐salinity H 2 O–NaCl–CO 2 ± CH 4 system. Hydrogen and oxygen isotopes (δD = −81.9‰ to −75.3‰; δ 18 O H2O = 3.7‰–5.1‰) indicate that the ore‐forming fluids were predominantly magmatic in origin and gradually mixed with limited amounts of meteoric water. Notably, Sulphur isotopic compositions and cassiterite trace element chemistry collectively indicate that the ore‐forming materials were derived from Indosinian highly fractionated granitic magmatic–hydrothermal fluids. We propose that fluid boiling initiated early cassiterite precipitation, while the continuous cooling and limited influx of meteoric water during the main stage triggered the oxidation of Sn 2+ –Sn 4+ , leading to large‐scale mineralization. The Dawan deposit represents a critical component of the Indosinian Sn system in the western Nanling Range, associated with A‐type granite emplacement during the tectonic transition from compression to lithospheric extension. These findings provide essential evidence for the ‘West‐strong and East‐weak’ extensional model and support the regional ‘West Sn–East W’ metallogenic zonation across the Nanling Range.