Mineralogical, geochemical and radioactivity of Gabal Nasb Hebili, Arabian Nubian Shield, Egypt: Implication for rare metals mineralization

Abstract

Field geology, geochemical studies and spectrometric prospecting were used to detect rare metals and uranium mineralization in Neoproterozoic garnetiferous muscovite granites from Gabal Nasb Hebili area in the South Eastern Desert of the Egypt from the Arabian-Nubian Shield (ANS). They intrude the surrounding metaultramafic rocks, metagabbros, mélange matrix, older granitoids, younger granitoids (garnetiferous muscovite granites) and post-granitic dykes. The present study will focus on the garnetiferous muscovite granites, which occur as stocks of domal shape and composed of quartz, plagioclase, potash feldspars, muscovite and garnet. These garnetiferous muscovite granites were affected by sericitization, silicification and fluoritization processes. These alteration products are associated with visible uranium mineralization. Mineralogical study of the mineralized zones in the garnetiferous muscovite granites reveals the uranium minerals (zippeite, uranophane, kasolite and autunite) and rare earth-bearing minerals (monazite, allanite, bastnäsite, coronadite and garnet). The presence of these different paragenetic minerals with the various alterations in the studied granites, indicate that these rocks were subjected to the effect of mineralizing acidic and alkaline solutions in post magmatic stage. Geochemically, the garnetiferous muscovite granites are peraluminous (A/CNK= > 1.1) and showing of S-type granites which formed in a syn-collision tectonic regime. The Gabal Nasb Hebili granites exhibit positive slopes of LREEs (Ce/Sm)n (3.2) with negative HREE slopes [(Gd/Lu)n from 4.6). The negative Eu anomaly in the granite is very strong, suggesting serious addition of Eu during the alteration. The increase in the LREE, and other light isovalents, can be supported by the petrographic observations where monazite and allanite appear to be important refractory minerals in the sheared granite. Gabal Nasb Hebili is markedly enriched in eU, where its content varies between 4.3 and 199.2 ppm (averaging 34.4 ppm) with eU/eTh ratio (0.9–7.1), while eTh content varies between 2.2 and 95.3 ppm (averaging 13.8 ppm).