Mineralogical, geochemical characteristics and origin of Late Cretaceous phosphorite in Duwi Formation (Geble Duwi Mine), Red Sea region, Egypt

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The Late Cretaceous Duwi Formation in Egypt overlies non-marine, varicolored shale of the middle Campanian Quseir Formation. It is conformably overlain by gray, laminated, foraminiferal-rich marine shale of the middle Maastrichtian Dakhla Formation. Detailed mineralogical and geochemical studies were carried out on the phosphate rocks of the Duwi Formation in Quseir-Safaga province (Geble Duwi Mine) to infer their source rocks, paleo-weathering and provenance of the sources. The importance of the effect of phosphate rock depends on the chemical form of phosphorus in which this element is combined. This information is important in the assessment of possible radiological hazards to human health; due to the presence of uranium in the apatite structure. The phosphatic rock materials may be used as building stones or as phosphatic fertilizers and animal feed ingredients. Mineralogically, they are composed mainly of apatite (fluor-apatite), calcite and quartz with minor amounts of pyrite. The studied Duwi phosphates are authigenic in origin, comparable to those of phosphatic nodules of Peru and Chile margins. They are most probably derived from pre-existing authigenic phosphorites. Provenance, they originate from reworked older sedimentary phosphorites and biogenic sources. The geochemical data, CIA values suggested that the Duwi Formation phosphates were subjected to low chemical weathering.Generally, the enrichment of the trace elements, REEs and uranium may have occurred during diagenesis. The studied phosphate samples were compared to the average of the Average World Phosphorite (AWP) and the Average Shale Composition (ASC). The major, trace and rare earth elements contents are compared with those in Egypt, North African, Asian and other localities. The ratios V/Cr, V/(V+Ni) and Mo/Al and the high concentrations of the redox sensitive elements revealed that the studied phosphates were deposited under anoxic reducing marine environments coupled with hydrothermal solutions, which is comparable to the environmental condition of the associated black shales. The concentration of the trace and toxic elements in the studied samples are considered to be below the limits for most field-grown crops.