Mineralogic and geochemical characteristics of Duwi Formation black shale, Safaga District, Central Eastern Desert, Egypt

The varicoloured compacted black shale of the Duwi Formation at Mohamed Rabah, Wasief, and Umm El-Huwitat mines is part of the huge black shale belt extending from the Egyptian western desert to the Red Sea coast in the east. Egypt’s black shale has been the focus of multiple studies to investigate its potential as a future energy resource due to its organic content. However, in the this study, the focus has been on the mineralogy and geochemistry of the inorganic content of these bearing shale mines, investigated to determine their chemical characteristics. These shales mainly comprise clay minerals, calcite, quartz, orthoclase, gypsum, and anhydrite. The studied clay fraction reveals that the clay minerals are represented by montmorillonite, kaolinite, and illite. Analysed black shales are recognized by their total organic carbon (TOC) content (0.14–2.52 wt%) and are rich in SiO₂ (50.83 wt%), followed by Al₂O₃ (14.7 wt%) and CaO (2.04 wt%). The chemical composition of these shales shows general enrichment of immobile elements and is associated with terrigenous influx, such as SiO₂, Al₂O₃, and TiO₂. Due to the oxidation and weathering of the organic matter, the geochemical composition shows that the studied black shales have high concentrations of V (1400 ppm), Sr (389.8 ppm), Zn (325.8 ppm), and Zr (258.3 ppm). The geochemical classification revealed that the studied black shale samples were related to siliceous and aluminous rocks due to the high SiO₂ and Al₂O₃ contents and were deposited in marine environment. The studied black shale is enriched in V, Sr, Zn, and Zr and is an important source of these elements. U at Wasief exists in high concentrations due to the richness of its black shale in organic matter. These black shales were deposited in a marine environment, derived from felsic igneous as source rocks, and affected by intense chemical weathering.