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

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 first
includes Igla and Abu Dabbab plutons, which occur as small stocks of circular, ovoid, or apophyses and
leucocratic outcrops. The second comprises the plugs and dyke-like bodies intruded peralkaline granites
of Bir Um Hibal. The third includes Homrit Waggat and Muweilha plutons. They cover small areas and
exhibit obvious pervasive post magmatic alterations.
The petrographic and mineralogical studies are confirmed by the geochemical investigations indicating
that the concerned rare-metal granites being broadly distinguished into magmatic and metasomatic
associations. The magmatic granite associations are further subdivided into two subgroups; i) peraluminous
granites (Li-mica rich) including Igla and Abu Dabbab plutons and ii) peralkaline granites including Um
Hibal pluton. The studied peraluminous granites are generally enriched in Nb, Rb, Ta, Li, F, Y, Zr, U
and Th elements. The peralkaline granites are enriched in K2O oxide as well as Zr, Nb, F, U, Th and Ta
elements. On the other hand, the metasomatic granite associations are represented by Homrit Waggat and
Muweilha plutons. They are characterized by high contents of Na2O oxide as well as Nb, Ta, U, Th and
Rb elements.
Igla pluton has highest average U & Th contents (42 ppm & 58 ppm respectively), while Um Hibal
pluton has lowest average U & Th contents (14 ppm & 26 ppm respectively)