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

Abstract

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.