CONTRIBUTION TO THE GEOLOGY AND RADIOACTIVITY OF THE OLDER GRANITOIDS AND YOUNGER GRANITED OF GABAL EL-URF-GABAL ABU SHIHAT AREA, EASTERN DESERT, EGYPT

The younger granites form an elongated belt following NNE-SSW direction. They intrude the older granitoids with sharp intrusive contacts and carry them as roof pendants. Two varieties of the younger granites are identified. They were intruded in successive pulses. Starting with greyish pink varieties (syenogranites of Gabal El-Urf) which are intruded by the red varieties (alkali-feldspar granites of Gabal Abu Shihat). The contact between them is usually inferred, but several small offshoots of red granites invade the greyish pink variety of Gabal El-Urf.
The pegmatites could be subdivided into zoned and unzoned pockets. Zoned pockets dominate in G. El-Urf as relatively small size subrounded pockets. The unzoned pockets dominate along the southwestern corner of G. Abu Shihat alkali-feldspar granites as relatively large size elongated pockets, which possess dissemination of metallic black and waxy yellow minerals (samarskite, oxinite, fergusonite, betafite and uranophane). It is worth to mention that, the unzoned pegmatites show more than twice the radioactivity level of the enclosing younger granites, while the zoned pegmatites pockets usually show radioactivity level less than the younger granited themselves, suggesting that pegmatite pockets in the studied area represent two successive phases.
The field, petrographic and radioactivity studies revealed that the alkali-feldspar granited of Gabal Abu Shihat originated from uranium-rich magma. Moreover, the secondary processes leached the labile uranium from country rocks and redeposited it in the fractures of the alkali-feldspar granites. Especially along hematized zones. Also, the U-rich hydrothermal solutions, which introduced unzoned pegmatites in the southwestern corner of Gabal Abu Shihat, have supplied additional amounts of uranium to the hosting alkali-feldspar granites. Thus, Gabal Abu Shihat younger granites may represent a good environment for uranium resources.