Genetic Mechanism of Uranium Concentration in Ferruginous Sandstone of the Wajid Group in Southern Saudi Arabia

Uranium anomalies were discovered in ferruginous sandstone in the Khusayyayn Formation of the Wajid Group in southern Saudi Arabia. Based on field surveys, ground radiometric surveys, and chemical analysis, this paper summarizes the characteristics of the lithology and lithofacies of the ferruginous sandstone and analyzes the genetic mechanism of uranium concentration in ferruginous sandstone. Ferric iron basically exists in the form of Fe2O3 in ferruginous sandstone, with an average content of 28.95 wt.%. The formation period of the ferruginous sandstone occurred during the early synsedimentary and later diagenesis stages from the Carboniferous to the Devonian. The uranium anomaly is hosted in thin-bedded and lenticular ferruginous sandstone, with a uranium content ranging from 50 to 766 ppm. The average U-Ra equilibrium coefficient of ferruginous sandstone was 1.00, indicating that the uranium was weakly reformed after the uranium concentration. Ferric ions are closely related to uranium mineralization. The initial concentration of the uranium occurred during the deposition of the ferruginous sandstone. Most of the uranium was adsorbed by a ferric colloidal solution, and part of it was reduced by Fe2+, organic carbon, and sulfur in the uranium preconcentrated stage during the deposition of ferruginous sandstone. The uranium ore was superimposed, transformed, and concentrated due to the change in the pH environment in the early Neogene.