3D imaging of the caldera-collapse system: implications for uranium mineralization in the Xiangshan volcanic basin, South China

The Xiangshan volcanic basin in South China hosts the world’s third-largest volcanic-type uranium deposit. However, the deep structural framework of the caldera-collapse system and its coupling with mineralization remain poorly constrained. We perform resistivity-model–constrained 3D joint inversion of gravity and magnetic data and apply derivative-based edge detection to enhance imaging of shallow structural boundaries. The recovered density and magnetic-susceptibility models reveal two steep, deeply rooted collapse columns that coincide with volcanic conduits, with a dominant eastern column and a smaller western one. Collapse-related low-density zones extend to depths exceeding 2 km, indicating that magma withdrawal caused depressurization and roof instability that drove multi-center, piecemeal subsidence. Segments of the ring-fault belt closely coincide with belt-like granitic-porphyry emplacement, suggesting that the collapse framework remained permeable after collapse and was repeatedly exploited by subvolcanic magma and hydrothermal fluids. In the northern basin, tight conduit–ring-fault coupling aligns with intense alteration and uranium occurrences, implying more efficient ascent and local focusing of mineralizing fluids, whereas weak shallow alteration above large southern intrusions suggests that prospective targets in the south may lie deeper, within granitic-porphyry bodies, along deeper ring-fault continuations, and at intersections with basement faults.

This work was funded by the National Natural Science Foundation of China (42130811, 42304090, and 42374097), the Autonomous Deployment Project of the National Key Laboratory of Uranium Resources Exploration-Mining and Nuclear Remote Sensing (2025QZ-YZZ-03 and 2024QZ-TD-15), and the Science and Technology Project of Jiangxi Province (20242BAB20143).