Feng He and 4 co-authors reported mid-2022 that 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, the authurs summaried the characteristics of the lithology and lithofacies of the ferruginous sandstone and evaluated the possible 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.
The authors concluded that:
1. The ferruginous sandstone is mainly found in the Khusayyayn Formation of the Wajid Group, mainly distributed along the bottom or bedding of the sandstone, thin-bedded and lenticular, mainly cemented by hematite and limonite. The ferric iron basically exists in the form of Fe2O3 in the ferruginous sandstone, and a small amount of reducing substances remains, such as FeO, organic carbon, and sulfur.
2. All of the uranium anomalies were hosted in ferruginous sandstone in the Khusayyayn Formation of the Wajid Group. It indicates that the uranium was weakly reformed after the uranium concentration in an alkaline oxidation environment.
3. It is concluded that there was poor potential for uranium mineralization in the ferruginous sandstone in the work area, and its radioactivity has little impact on the environment. The primary reason is that the uranium mineralization in the ferruginous sandstone was small in size and unfavorable for in situ leaching mining.
4. The formation of the ferruginous sandstone in the study area occurred during the early synsedimentary and later diagenesis stages. The initial concentration of the uranium occurred during the deposition of the ferruginous sandstone.
5. Ferric ions are closely related to uranium mineralization. Most of the uranium was likrly adsorbed by ferric colloidal solutions, and part of it was reduced by Fe2+, organic carbon, and sulfur in the uranium preconcentrated stage during the ferruginous sandstone deposit. The uranium ore was superimposed, transformed, and concentrated due to the change in the pH environment in the early Neogene.
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