A novel mechanism of uranium mineralization: The role of zircon adsorption at the Qigequan deposit, Qaidam Basin, NW China

Uranium mineralization in sandstone-hosted deposits is influenced by the adsorption capacity of minerals, especially in basin fluids with sub-saturation uranium concentrations. This study investigates the Qigequan sandstone-type uranium deposit in the Qaidam Basin, focusing on uranium distribution and adsorption behavior in zircon. Samples were analyzed using TIMA, BSE, CL imaging, EDS, and EPMA. Results show zircon is abundant in both matrix and clastic components, with uranium occurring in three forms: U1 (in growth zones or inclusions), U2 (in fractures), and U3 (on grain rims). U1 is a magmatic or early hydrothermal product with low U/Th, while U2 and U3 are associated with surface adsorption by mineralizing fluids and have high U/Th. By contrast, uranium minerals unrelated to zircon (i.e., Other-U) have different Th and U characteristics. EPMA mapping reveals that absorbed uranium around rims correlates with elements like Th, Y, Mg, and Ti. Zircon demonstrates a stronger and more selective uranium adsorption capacity than other accessory minerals, despite their higher abundance. We suggest that uranium is absorbed by zircon through a physical-chemical adsorption mechanism, primarily controlled by pH changes caused by the mixing of mildly alkaline oil-gas-related fluids and supergene oxidized fluids. These findings highlight the significant role of zircon as a uranium adsorbent in sandstone-hosted uranium deposits and suggest that surface adsorption, in addition to classical precipitation due to fluid supersaturation, is an important pathway for uranium enrichment. This mechanism offers new insights into uranium mineralization and may refine genetic models of sandstone-type uranium deposits.