FACIES AND DEPOSITIONAL ENVIRONMENT OF THE PHOSPHATE DEPOSITS AT EL-RASHDA, EL-MAWHOOB AREA, DAKHLA OASIS, WESTERN DESERT, EGYPT.

This work which is based on the field and laboratory investigations represents to throw light on the geological, mineralogical, geochemical and environmental deposition of the phosphorite deposits at El-Rashda, El-Mawhoob area, Dakhla, Western Desert, Egypt.
fifty stratigraphic sections, 19 borholes representing the study area, are measured, sampled and studied.
The laboratory work comprises 69 samples for studying physical properties, 11 samples for XRD analyses, 27 thin sections and 133 samples for chemical analyses using XRF method to detect the major oxides, as well as trace element.
The studies revealed that flour apatite, carbonate flourapatite, carbonatehydroxylapat, flourellestadite, ankerite, dolomite, are the main constituents of the studied phosphorite deposits. While the associated minerals are, halite, quartz, anhydrite, montmorillonite, calcite. (table.1).
Chemically; the average contents of Al2O3, SiO2 are comparatively low in the study area, while the average content of MgO, Fe2O3 and SO3 are relatively high.
The low contents of Al2O3, SiO2 may be attributed to locate them outside the apatite lattic. While the high content of MgO may be due to derivation of MgO from dolomite by the oxidation processes, or resulted from the negative relationship of MgO, CaO where Ca2+ substitute by Mg2+ (McConnell 1980).
The iron content in phosphorites deposits is valueless for any postdepositional indications, as iron may enter the site of deposition at any stage, whether syngenetic or epigenetic.
Field observations and petrographic, mineralogical, chemical studies revealed that the origin of the phosphorite deposits at the study area points to shallow marine environment and controlled by various physico-chemical conditions.