Geochemistry of uranium and REEs in Dalir phosphate deposit, Central Alborz zone

The Dalir phosphate deposit is located 57 km southwest of Chalus city in Mazandaran province, the Central Alborz zone. This deposit is hosted by Soltanieh Formation, one of Iran's important hosts of sedimentary phosphates. The results of X-ray diffraction (XRD) analysis and optical and electron microscopy studies on the phosphate samples indicate that the main minerals include apatite, calcite, quartz, and dolomite accompanied by montmorillonite, pyrite, and barite in minor amounts; siderite, rutile, illite, and goethite in trace amounts. The concentration of P2O5, U, and REEs in the studied samples ranged from 5 to 16.1%, 1.9 to 5.5, and 45.9 to 136.9 ppm, respectively. The studied samples have negative Ce anomaly, indicating an anoxic environment during the Dalir phosphate deposition. Based on the factors controlling uranium concentration in phosphorites, the phosphate horizon of Soltanieh Formation does not have uranium enrichment potential due to warm to semi-warm humid paleoclimate with neutral to acidic pH of the seawater during the Dalir phosphate deposition in lower Cambrian. Finally, considering the results of the chemical analysis of phosphate samples of the Dalir deposit (lack of uranium enrichment) and also the factors controlling uranium concentration in phosphorites, it can be predicted that the other phosphate deposits of Soltanieh Formation probably not be uranium enriched.