Geology and mineralogy of the radioactive Quaternary sediments of the North Fayium depression, Western Desert, Egypt

Abstract

Quaternary sediments of the North Fayium depression, are mainly represented by residual soil and calcrete, and have been found to be anomalously radioactive. These sediments are deposited on the irregular surface of the carbonaceous shale of the middle member of the Oligocene Qatrani Formation in the northern part of the Fayium depression. A mineralogical investigation involving a preliminary microscopic examination and detailed Environmental Scanning Electron Microscope (ESEM) has revealed the presence of several heavy accessory minerals. These include zircon, apatite, ilmenite, rutile and garnet as persistent detrital minerals. In addition, a highly suspected secondary uranium mineral has been identified between some mica flakes.

While uranium in the bed rock does not exceed 3.7 ppm, its assay in the residual soil varies from 20 to 200 ppm with an average of 94 ppm, whereas the analyzed two samples of calcrete assay 85 and 122 ppm. Trace element analysis in the studied rock types indicates enrichment in Zn, Zr, Y, Sr and V.