Radiometric and mineralogical dataset of microgranite dykes and stream sediments of Ras Abda area, north Eastern Desert, Egypt

Abstract

Ras Abda Area is located in the north part of the Eastern desert, and is characterized by a rugged topography and high relief. The main exposed rock units in the area comprise older granites, younger gabbros and granites as well as several types of post granite dykes (rhyolite, basic and microgranite dykes). Radiometric measurements indicated that the microgranite samples are characterized by anomalous concentrations of the radioelements which mean that the rocks originated from radioelements-bearing magma and may be subjected to epigenetic processes of leachability and migration of uranium. The stream sediments samples show low levels of radioactivity where eU ranges from 4.0 to 7.0 ppm with an average of 5.3 ppm, and eTh ranges from 6.0 to 18.0 ppm with an average of 10.65 ppm. The eTh/eU ratio ranges from 1.2 to 3.6 where the samples distal from the microgranite dykes are characterized by the highest eTh/eU ratio (3.6) while those close to the dykes have the lower eTh/eU ratios. Generally, the average eTh/eU ratio (∼2.08) is lower than the world ratio (3.5) implying that uranium probably enriched from an adjacent source may be the microgranite dykes. The calculated factors of equilibrium (P and D) indicated disequilibrium state for both rocks types (microgranite and stream sediments) and referred to incomplete U-decay series. Mineralogical studies revealed that the heavy minerals could be classified into: a) radioactive minerals comprising uranophane, kasolite, sklodowskite, thorite and uranothorite, and b) radioelements-bearing minerals comprising columbite, fergusonite, samarskite, pyrochlore, allanite, monazite, zircon and fluorite. The heavy minerals are mostly concentrated upstream rather than downstream; meandering portions of the stream may act as natural traps for the heavy minerals. Keywords: Ras abda, North eastern desert, Egypt, Microgranite dyke, Radioactivity, Mineralogy