PETROLOGY AND RADIOACTIVITY OF EL MAGAL GRANITOID ROCKS, QENA-SAFAGA ROAD, CENTRAL EASTERN DESERT, EGYPT

The present work deals with the granitoid rocksof GabalEl Magal (35km²) which located along Qena-Safaga road, central Eastern Desert of Egypt.
Petrographically, the studied granites are composed essentially of perthite, quartz, plagioclase and amphiboles. Sphene and opaques are accessory minerals. The granites could be considered as subsolvus granites due to the presence of both orthoclase perthite and plagioclase. The petrographical observations indicate a hydrothermal alteration episode (sericitised plagioclase).
Geochemically, the granites of Gabal El Magal area seem to have originated fromperaluminous calc-alkaline magma with many chemical features similar to I-type granites. The granitoids magma was originated in an island arc tectonic setting. The studied granitoids were generated at somewhat intermediate depths (20-30 km) equivalent to 3-6 kb, under temperature ranging from 760º to 840º with multi-processes of both assimilation and fractional crystallization. This is consistent with the high k/Rb ratios, and the low k/Ba ratios.
 The concentration of U and Th in the granitoid rocks were controlled by magmatic processes which are clear from the positive relation between U and Thin addition to weak negative relation between U and Th/U. They are also controlled by the presence of some accessory minerals e.g. zircon, sphene and iron oxides.  Iron oxides and hydroxides are known to absorb U from circulating fluids.