Geochemistry and spectrometric prospection of younger granites and granitic pegmatites bearing uranium mineralization at G. Kab El Rakeb area, Central Eastern Desert, Egypt

Abstract

The present study deals with the detailed field geology, mineralogy, geochemistry, and spectrometric prospection of rare metals and radioactive minerals associated with granitic pegmatites in the Gabal Um Lassaf- Abu Dob- Um Atelia- Kadabora- Kab El Rakeb area (LDAKK), which are situated in the central Eastern Desert of Egypt. The study area is composed of granodiorites and monzogranites. The latter is dissected by granitic pegmatites with a discriminatory distribution of economically important mineralization (rare-metals and U–Th minerals). The granitic pegmatites display a zoning structure composed of feldspar-rich zones enveloping pockets of mica (mostly muscovite) and all zoning internal quartz core. Microscopically, the monzogranite and granitic pegmatites are composed of potash-feldspar, albite, and quartz with a small amount of biotite and muscovite. The mineralogical investigation of the highly radioactive zones in the granitic pegmatite shows enrichment in kasolite, uranothorite, thorite, xenotime, columbite, zircon, bismuth, and galena. Geochemically, the granitic pegmatites are enriched with high field strength elements (HFSE; Zr, Nb, Th, and U) and ion lithophilic elements (LILE; Rb, and Pb) and depleted in Ba, Sr, and Eu. They are strongly peralkaline to metalumainous except for two samples, which are peraluminous. They are formed by partial melting of metagreywackes at depth. The studied granitic pegmatites could belong to the NYF family (Niobium–Yttrium–Fluorine family) according to the geochemistry of the trace elements. The studied granitic pegmatites show deep negative Eu anomaly and display a strong M-type tetrad effect of rare earth elements. The field spectroscopy measurements showed the localization of the radiometric anomalous associated with the granitic pegmatites, which are intruded in the granitic host rocks. Their eU and eTh contents reached up to 316 and 1367 ppm, respectively. Uranium and thorium occurrences in the investigated granitic pegmatites are related to magmatic (syngenetic) origin with hydrothermal (epigenetic) input. The magmatic mineralization is evidenced by the occurrence of thorite and zircon, whilst the hydrothermal activity is represented by alteration of feldspars and formation of pyrite and iron oxides associated with the radioactive minerals. The high concentrations of uranium and rare metals mineralization in the investigated granitic pegmatites make them a target to exploration and to enlarge the potentiality of the highly mineralized zones.