LAUSR

Microscopical and mineralogical studies reveal first recorded spherulitic dahllite (3Ca 3 (PO4)2 Ca CO3) in the phosphorite rocks associated with carbonate rocks of Hamadat Mines (Duwi Formation) at Qusier area, Central Eastern Desert, Egypt. Mineralogically, the phosphatic rocks of Hamadat Mines are mainly consisting of fluor-apatite, dahllite, dolomite, calcite, quartz and pyrite. Petrographically, the studied dahllite in Hamadat Mines are authigenic in origin. Genetically, spherulitic dahllite at Hamadat Mines (Duwi Formation) in Qusier area is resulting from diagenesis processes; dolomitization and the re-crystallization process. Geochemical analysis of trace, rare earth elements and the petrogaphical is indicated that the phosphatic rocks are deposited under oxic to anoxic condition. Dolomitization process plays an important role in the concentration of trace and rare earth elements in the phosphatic rocks at Hamadat Mine. Dahllite layer has a relatively higher content in most of rare earth and some of the trace elements than those in the phosphate layer, which reveal that dahllite structure may be having the ability to scavenging them than the phosphatic construction. The chemical index of alteration (CIA), trace elements and La/Ce ratios pointed out that these phosphatic rocks were of hydrogenous origin deposited in cold and dry climate during low weathering. Finally, the hydroxial-apatite can be prepared to be used as a natural row material in the biological industry according to the chemical composition.