Geochemistry and radioactive potentiality of Um Naggat apogranite, centraleastern Desert, Egypt

The northern part of Um Naggat granite massif (UNGM) has suffered extensive post-magmatic metasomatic reworking which results into the development of (Zr, Hf, Nb, Ta, U, Th, F)- and albite-enriched and greisenized apogranite body (UNAP) of 600 m thick, and more than 3 km in the strike length. Albitization produced an enrichment in Zr (av. 2384 ppm), Hf (61), Nb (419) , and U (43). The Th/U ratio ranges between 1.33 and 1.90. Extreme albitiza tion (i.e. the albitite rock) is characterized by sharp decrease in the rar e metals contents. However, extreme greisenization (i.e. endogreisen bodies ) is characterized by a considerable enrichment in Zr (av. 5464 ppm), Hf (1 43), Nb (2329), Ta (152), U (66) and Th (178). The Th/U ratio ranges betwee n 1.57 and 3.60. In contrast to extreme greisenization, it seems that extre me albitization does not apparently change the fluid pH and therefore poor amounts of rare metals are localized in the albitites. It is suggested that the presence of Na+, H+ and F- in the ore fluids was e ssential to stablize complexes of Zr, Hf, Nb, Ta, U, Th, and HREE during ex traction and transportation. In contrast, contemporaneous decrease of tempe rature and increasing pH due to decreasing pressure are considered the esse ntial factors for localization of disseminated mineralization of Zr and Nb in the apical parts of the UNAP. The enhanced uranium content in the altera tion facies of UNAP coupled with the absence of significant uranium mineral ization may indicate the metalliferous rather than mineralized nature for t he UNAP. The high uranium contents are stabilized in refractory accessory m inerals. However, with repect to Zr and Nb, the UNAP especially the albitiz ed and greisen facies, can be categorized as a mineralized productive grani te.