GRANITES OF GABAL EL-DOB AREA AND ASSOCIATED PEGMATITES, CENTRAL EASTERN DESERT, EGYPT: GEOCHEMISTRY AND SPECTROMETRY

Abstract

The late Pan-African El-Dob granites in the Egyptian Central Eastern Desert are small and circularbodies from older and younger granites. The older granitoids are represented by granodiorites and tonalitesand they are intruded by the younger gabbros and younger granites with sharp contacts. The youngergranites are represented by alkali feldspar granites cropping out in the central part of the studied areaforming Gable El-Dob. The older and younger granites are cut by pegmatite and quartz veins. El-Dobgranites are peraluminous and I-type granites. The older granites belong to volcanic arc granites (VAG),while the younger granites belong to within plate granites (WPG). Pegmatite veins possess high contentsof important elements as Zn, Y and Cu. The El-Dob granites have relatively high uranium and thoriumcontents. The average equivalent uranium is 19.2 ppm for the older granites and 32.5 ppm for the youngergranites, the average eTh is 55.4 ppm with the average eTh/ eU = 3.1 for the older granites and the averageeTh is 86 ppm with the average eTh/ eU = 2.8 for the younger granites. These radiometric measurementsare higher than the Clark values, i. e uraniferous granites. In pegmatites, the average eU content is 32.5ppm and the average of eTh content is 86 ppm. Most of the radioactive anomalies are associated with thepegmatites.