Rare-metal enriched peraluminous granite: examples from south Eastern Desert, Egypt

Abstract

Gabal Hamret Mukbud and Gabal Homr Akarim granites represent promising examples for rare-metal enriched peraluminous granite hosting or acting as source for the uranium, rare-metal (Nb, Ta, Th, Be, Yb) mineralization and rare-earth (La, Ce, Lu, Y) contents in the south Eastern Desert of Egypt. They form two famous plutons crop out at wadi Khasab area. These granites show a strong enrichment in some rare-metal and rare-earth contents (Nb = 75.22, Y = 168.5, Th = 29.70, U = 15.58, Ta = 106.3, Be = 191.80, Yb = 33.01, Lu = 5.19, La = 139, Ce = 55.98 ppm). These granites are classified as peraluminous leucogranites (A/CNK = 1.38–2.01), P-poor (P2O5 < 0.001 wt%), and Na2O rich (<5.01 wt%). Field studies indicate that these granites are categorized into fine, medium, and coarse grained. Petrographic studies indicate that these granites are composed essentially of microcline-perthite, perthite, albite plagioclase, quartz, biotite, and muscovite. Zircon, fluorite, sphene, and apatite are the main accessory minerals in these granites. Also, these studies confirmed the presence of radioelements in the form of secondary radioactive minerals such as uranophane and their uranium-bearing minerals such as metamict zircon and violet fluorite, suggesting that the radioactivity of Gabal Hamret Mukbud and Gabal Homr Akarim granites is gained by the post-magmatic processes and hydrothermal solutions. Petrochemical studies and tectonic discrimination diagrams for these granites reveal that they are ranging in composition from granite to admelite, have peraluminous affinity and developed in post-orogenic granitoids. Albitization, silicification, and greisenization are the prevailing alteration processes in these granites. Field radiometric measurements for both Gabal Hamret Mukbud and Gabal Homr Akarim granite revealed that uranium and thorium as secondary minerals and also the in resistant accessory minerals represent by metamict zircon and fluorite mineral. Radioactivity level reached up to 12.5 ppm (eU) at Gabal Hamret Mukbud granite, while it reaches up to 21.8 ppm (eU) at Gabal Homr Akarim granite.