Uranium mineralization in the Thrace Basin, NW Türkiye: Evidence from radiation-induced defects in detrital quartz and synchrotron XRF/XANES analysis

The Paleogene-Neogene Thrace Basin in northwestern Türkiye has long been known to host economic gas and oil resources and has recently been reported to potentially host sandstone-type uranium deposits in the Oligocene Süloğlu Formation. The latter discovery raises questions about the source and deposition mechanism of uranium mineralization in the basin. This contribution reports on the results of a detailed electron paramagnetic resonance (EPR) spectroscopic study of detrital quartz from four sandstone and one mudstone samples in the Süloğlu Formation and documents the distribution and speciation of uranium using combined microbeam synchrotron X-ray fluorescence maps (μsXRF) and microbeam X-ray near edge structure spectroscopy (μsXANES). The EPR spectra of quartz separates are characterized by the presence of diagnostic radiation-induced defects (i.e., silicon-vacancy hole centers H′₃, H′₄, and H′₇ with g_max = 2.049, 2.034, and 2.018, respectively, and the oxygen-vacancy electron center E′₁), formed by the bombardment of alpha particles emitted from uranium, thorium, and their unstable progenies. Moreover, notable decreases in the intensity of silicon-vacancy hole centers in the EPR spectra of quartz separates after partial dissolution with hydrofluoric acid, provide compelling evidence for the circulation of uranium-bearing fluids in the Thrace Basin. The μsXRF and μsXANES data reveal the occurrences of mixed U⁶⁺ and U⁴⁺ species in hematite partially replacing pyrite aggregates but dominantly U⁴⁺ in disseminated pyrite and illite in sandstones of the Süloğlu Formation. These results provide new insights into uranium transport, reduction, and deposition mechanisms, with important implications for better understanding sandstone-type uranium deposits in general and further exploration in the Thrace Basin.