The Egyptian younger granites are characterized by the presence of more than 14 exposures of raremetal 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 K 2 O 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 Na 2 O 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)

The average apparent density of studied sediment is 1599kg/m 3 and its effective porosity is 0.22. The total heavy mineral contents in the black sands at Mastarouh area was found to vary from 10.56 % to 39.66% with an average of 26.60%. Its variation affects the activity concentrations of the four radio-nuclides, 238 U, 232 Th, 226 Ra, and 40 K, as well as the absorbed dose rate, radon flux and the total radioactivity. The mentioned variables display the same behavior like the total heavy minerals except 232 Th. The averages of the activity concentration, in Bq/kg, for the four profiles due to the four radio-nuclides are:

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