RADIOACTIVITY AND GENETIC RELATION BETWEEN THE MONZOGRANITES AND THE ENCLOSED PEGMATITES IN DAHAB AREA, SOUTHEASTERN SINAI, EGYPT

The study area lies at the southeastern part of Sinai Peninsula along the western bank of Gulf of Aqaba
occupying the extreme southern part of the Arabian- Nubian Shield. Dahab area is mainly covered by
volcanic rocks, younger gabbros, younger granites and pegmatites. The pegmatite bodies of the study area
are abundant, hosted in monzogranites and distinguished into zoned and unzoned types. They are found
as lenticular pocket and vein-like bodies. Some of these pegmatite bodies have abnormal radioactivity.
Radionuclide measurements of younger granites show that their equivalent uranium content (eU) ranges
between 6 ppm and 11 ppm, while their equivalent thorium (eTh) varies from 13 ppm to 26 ppm. The
average contents of U and Th of the anomalous pegmatites are 88.6 ppm and 107.9 ppm, respectively
indicating their uraniferous nature.
Geochemically, Both monzogranites and pegmatites have high K-calc alkaline characters, metaluminous
and peralkaline natures, intruded in withinplate condition, derived from magma of crustal materials source
of moderate fractionation.
The Mineralogical investigations of anomalous pegmatites revealed the presence of secondary uranium
mineral (autunite), in addition to thorite, uranothorite, zircon, monazite and columbite. Primary and
secondary radioactive mineralizations indicating that the mineralization is not only magmatic, but also
post-magmatic.