PETROGRAPHY, GEOCHEMISTRY AND RADIOACTIVITY OF ALKALINE A-TYPE GRANITES AND ASSOCIATED PEGMATITES FROM GABAL UM GURUF REGION, NORTH EASTERN DESERT, EGYPT

The present study focuses on three granitic bodies from Gabal Um Guruf region in the North EasternDesert of Egypt. They comprise Gabal El Resha fine-grained granite, Gabal Homret El Sawrhiya mediumgrainedgranite and Wadi El Misdar coarse-grained granite. They have nearly similar mineralogicalcompositions and could be classified as alkali feldspar granites. However, the presence and proportions ofthe accessory minerals show some variations among the three granitic bodies, causing observed changes intheir trace element compositions. Geochemically, these granites exhibit pronounced A-type affinity andbelong to the alkaline series. They have high concentrations of SiO2 and total alkalis, low abundances ofCaO, MgO and TiO2 and enrichment in some HFSE (Zr, Y and U). The granitic bodies show similar REEpatterns and spider diagrams with striking depletions in Ba, Sr, P, Eu, and Ti. The obtained geological,petrographical, and geochemical data of the studied granites suggest close genetic relationships and it issuggested that they were formed from single parent magma through its differentiation in post-orogenicenvironment. The radiometric investigation indicates that Gabal Homret Al Sawrhiya granite and itsassociated pegmatites have the highest levels of gamma-ray measurements in the study area. This graniteshows similar mineralogical and geochemical features with U-bearing granite in Egypt. It is enriched inradioactive inclusions along with higher contents of zircon and fluorite, suggesting parallel enrichment of Fand HFSE, which extending toward the associated highly evolved pegmatites. Additionally, it displaysvarious forms of post-magmatic hydrothermal alterations, especially along faults and shear zones. Oneradioactive anomaly was recorded in a pegmatite body in Gabal Homret El Sawrhiya granite. Thepegmatite hosts U-Th, Zr and REE showings along the contact between the host granite and the pegmatite.