Gabal Humr ar-Raha area, about 150 km2 of crystalline basement rocks, is delineated by Lat. 27o 18'
and 27o 26' N and Long. 32o 42' and 32o 48' E. It is covered by Dokhan volcanics (oldest), younger granites
(syenogranite) and post granitic dykes (youngest).
Dokhan volcanics are represented by a thick sequence of stratified lava flows of intermediate (andesites)
and acidic (rhyolites) composition. The main rock type of Gabal Humr ar-Raha granitoid rocks are classified
as syenogranites; their emplacement were structurally controlled by pre-existing fractures trending NNESSW
and NE-SW.
The acidic Dokhan volcanics and younger granites show the highest equivalent uranium and equivalent
thorium contents in the study area. The younger granites can be considered as uraniferous granites as
revealed from their radiometric studies. They are originated from highly fractionated U-rich magma that
trapping high concentrations of uranium in the accessory minerals. These granites host an interesting
radioactive anomalies which are essentially exhibited by a strongly altered granites occupying at the
intersection zone of two major strike-slip faults striking NNW-SSE and NE-SW. The sheared granites show
dark brown spots of iron oxides at this zone. Thus the enrichment of uranium in the study area is controlled
by structural elements.