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 Eastern
Desert of Egypt. They comprise Gabal El Resha fine-grained granite, Gabal Homret El Sawrhiya mediumgrained
granite and Wadi El Misdar coarse-grained granite. They have nearly similar mineralogical
compositions and could be classified as alkali feldspar granites. However, the presence and proportions of
the accessory minerals show some variations among the three granitic bodies, causing observed changes in
their trace element compositions. Geochemically, these granites exhibit pronounced A-type affinity and
belong to the alkaline series. They have high concentrations of SiO2 and total alkalis, low abundances of
CaO, MgO and TiO2 and enrichment in some HFSE (Zr, Y and U). The granitic bodies show similar REE
patterns 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 is
suggested that they were formed from single parent magma through its differentiation in post-orogenic
environment. The radiometric investigation indicates that Gabal Homret Al Sawrhiya granite and its
associated pegmatites have the highest levels of gamma-ray measurements in the study area. This granite
shows similar mineralogical and geochemical features with U-bearing granite in Egypt. It is enriched in
radioactive inclusions along with higher contents of zircon and fluorite, suggesting parallel enrichment of F
and HFSE, which extending toward the associated highly evolved pegmatites. Additionally, it displays
various forms of post-magmatic hydrothermal alterations, especially along faults and shear zones. One
radioactive anomaly was recorded in a pegmatite body in Gabal Homret El Sawrhiya granite. The
pegmatite hosts U-Th, Zr and REE showings along the contact between the host granite and the pegmatite.