Insights on the felsic magma reservoirs beneath the Xiangshan volcanic basin, southeast China: Revealed by integrated magnetotelluric and petrological data

Abstract The Xiangshan volcanic basin in Jiangxi Province hosts China’s largest volcanic-related uranium deposit. The intermediate to felsic volcanic-intrusive complexes in the basin are the primary ore-bearing units and are central to studies of uranium mineralization. However, their formation mechanisms remain controversial. To address this, we integrate thermodynamic modeling with geochemical analyses of volcanic-intrusive complex samples to establish relationships between melt fraction, magma composition and bulk resistivity obtained from the electromagnetic imaging of the magma reservoir beneath Xiangshan basin. Our results demonstrate that the conductive feature of this magma chamber can be explained by saturated partial melt (~9 vol%) containing a volatile phase (~3 vol%) at 677°C. It suggested that the magma chamber is not a simple two-phase medium, as previous estimates, but rather a complex three-phase system comprising intermingled melt, crystals, and volatiles. Meanwhile, the volatile components are primarily attributed to mantle-derived CO₂ and F introduced during the evolution of the magmatic system, which indicate that the formation of Xiangshan felsic magma reservoirs likely involved contributions from mantle-derived materials. The identified volatiles in the magma system likely provide the direct carriers for the upward migration of uranium elements. Overall, this study provides novel geophysical constraints and petrogenetic evidence that help us understand the genesis of uranium-enriched volcanic-intrusive complexes and the trans-crustal migration of uranium elements in the Xiangshan uranium deposit.