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 gmax = 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, provided 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.
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 gmax = 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 daughter isotopes. Moreover, notable decreases in the intensity of silicon-vacancy hole centers in the EPR spectra of quartz separates after partial dissolution with hydrofluoric acid, provided 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.
Abstract Regolith-hosted rare-earth-element (REE) deposits are the world’s primary source of heavy REEs (HREEs) critical to the global clean-energy transition. Previous studies suggested that REEs in regolith-hosted deposits are largely inherited from their parent granites. However, several HREE-dominated deposits occur in the weathering crusts of LREE-enriched granites, where the mechanisms of REE fractionation remain poorly understood. Also, the conventional mining method of regolith-hosted REE deposits has limited efficiencies in REE recovery while causing enormous environmental contaminations. Herein we have investigated the distribution and speciation of Y and REEs in three representative regolith-hosted REE deposits (i.e., Gucheng and Shangyou, HREE-dominated; and Renju, LREE-dominated) as well as Y-sorbed birnessite from batch experiments. Our results show that birnessite in all three deposits is a minor constituent but contains anomalously high REE concentrations, and contributes to 25.3%, 23.4%, and 26.5% of the HREE contents of mineralized saprolites. Measured Y K-edge X-ray absorption spectroscopic data suggest that Y3+ (representing HREE3+) is adsorbed on birnessite as YO8 complexes in all three deposits but via different linkages: i.e., the bidentate corner-sharing mode in the HREE-dominated deposits but a mixture of both bidentate corner-sharing and edge-sharing modes in the LREE-dominated deposit. These binding mechanisms are also observed in Y-sorbed birnessite prepared at different ionic strengths. Therefore, different binding mechanisms of Y and HREE sorption on birnessite together with its preferential adsorption of HREE not only are responsible for the formation of HREE-dominated deposits from LREE-enriched granites but have important implications for the sustainable development of regolith-hosted REE deposits.
Abstract. The occurrence of jadarite (LiNaSiB3O7OH) as a major ore mineral in the world-class lithium–boron deposit of the Miocene Jadar lacustrine basin (western Serbia) raises interesting questions about its formation conditions and potential associations for lithium mineralization in other sedimentary basins. This contribution reports on the first successful synthesis of jadarite in the Li2O–Na2O–B2O3–SiO2–NaCl–H2O system at temperatures from 180 to 230 ∘C and pH values from 6 to 12. Synthetic jadarite has been characterized by powder X-ray diffraction (PXRD), Fourier transform infrared (FTIR) spectroscopy, laser Raman spectroscopy, and synchrotron Li and B K-edge X-ray absorption near-edge structure (XANES). First-principles theoretical calculations reproduce the measured FTIR and Raman spectra and allow definitive assignments of vibration modes. Similarly, the measured Li and B K-edge XANES spectra are reasonably reproduced by first-principles theoretical calculations. Our synthesis results, together with its association with searlesite in the Jadar basin, suggest jadarite forms in deep sediments derived from Li-rich alkaline brines under high-temperature diagenetic conditions.
'/%3e%3cuse xlink:href='%23a' transform='rotate(23.036 .093 25.536)'/%3e%3cuse xlink:href='%23a' transform='rotate(45.87 1.273 16.18)'/%3e%3cuse xlink:href='%23a' transform='rotate(69.945 .996 12.078)'/%3e%3cuse xlink:href='%23a' transform='rotate(20.66 -19.689 31.932)'/%3e%3c/svg%3e)