The Immobility of Uranium (U) in Metamorphic Fluids Explained by the Predominance of Aqueous U(IV)

The solubility of uranium (U) in hydrothermal fluid is thought to be controlled by oxidation. In general, mainly transported as U(VI) oxidized fluid, but precipitated U(IV) reduced fluid. However, many geological observations indicate that metamorphic fluids, which are buffered rocks with protoliths such pelite or altered marine basalt, not enriched U. To explore the reason low U we simulated hydrous speciation and fluids equilibrium rocks. simulations were conducted at pressure–temperature (P-T) conditions greenschist amphibolite facies metamorphism. results show dissolved U(IV), instead U(VI), fluids. remains a level ~10−12 molal, significantly influenced temperature, pressure, salinity. This result consistent and, thus, can explain low-U nature natural simulation also shows high (1.3 × 10−7 molal) pelite-buffered temperature (<250 °C), fact mobilized low-temperature geofluids.