COMPARATIVE STUDY ON THE GEOLOGICAL AND GEOCHEMICAL CHARACTERISTICS OF SOME RARE-METAL GRANITES, SOUTHEASTERN DESERT, EGYPT

Abstract

The Egyptian younger granites are characterized by the presence of more than 14 exposures of rare-metal granites. The studied granites are included into three geological modes of occurrence. The firstincludes Igla and Abu Dabbab plutons, which occur as small stocks of circular, ovoid, or apophyses andleucocratic outcrops. The second comprises the plugs and dyke-like bodies intruded peralkaline granitesof Bir Um Hibal. The third includes Homrit Waggat and Muweilha plutons. They cover small areas andexhibit obvious pervasive post magmatic alterations.The petrographic and mineralogical studies are confirmed by the geochemical investigations indicatingthat the concerned rare-metal granites being broadly distinguished into magmatic and metasomaticassociations. The magmatic granite associations are further subdivided into two subgroups; i) peraluminousgranites (Li-mica rich) including Igla and Abu Dabbab plutons and ii) peralkaline granites including UmHibal pluton. The studied peraluminous granites are generally enriched in Nb, Rb, Ta, Li, F, Y, Zr, Uand Th elements. The peralkaline granites are enriched in K2O oxide as well as Zr, Nb, F, U, Th and Taelements. On the other hand, the metasomatic granite associations are represented by Homrit Waggat andMuweilha plutons. They are characterized by high contents of Na2O oxide as well as Nb, Ta, U, Th andRb elements.Igla pluton has highest average U & Th contents (42 ppm & 58 ppm respectively), while Um Hibalpluton has lowest average U & Th contents (14 ppm & 26 ppm respectively)