GEOLOGY AND GEOCHEMISTRY OF THE PERALUMINOUS GRANITES AT WADI UM ADDEBAA AREA, SOUTHEASTERN DESERT, EGYPT

Wadi Um Addebaa area is located about 70 km Southwest of Marsa Alam City. The rocks
exposed in this area include: ophiolitic metagabbro, ophiolitic mélange, peraluminous granite and post
granite dykes and veins. The most common feature in the studied peraluminous granite is the presence of
spessartine garnet aligned in monomineralic bands within its periphery (1m thick) along the contact with
the surrounding ophiolitic schists.
Petrographically, the peraluminous granite is mainly composed of sodic plagioclase (An 5-15),
K- feldspar, quartz, muscovite and biotite. Sericite and chlorite are secondary minerals. Tourmaline,
spessartine, zircon, allanite and opaques are accessory minerals.
Geochemical characteristics of the studied peraluminous granite indicate that this granite crystallized
from relatively soda rich magma having peraluminous character, I–type, Syn-collision setting and has
calc-alkaline affinity. It is emplaced at relatively shallower depth (water pressure 3-2 kb) in the crust and
crystallized at temperature ranges from 800 to 760Cº. It possesses high content of LILE (Rb, Y & Zr) and
has a moderate to high content of HFSE (Cu, Zn, Pb, As, Bi & W). It constitutes an average 6.7 ppm of
Be content. Accordingly, it is believed that this granite is the source of beryl mineralization in Wadi El
Gemal area.
Microprobe study of garnet revealed spessartine composition with core rich in CaO, MgO, TiO2
and Y2O3, while the rim is enriched in FeO, Al2O3 and SiO2. MnO shows variable enrichments. The
composition differs due to the variation in the ratio of Fe and Mn. Whereas the Mn increases in the core
more than the rim whereas Fe vice versa.
Radiometric study shows that, the peraluminous granite shows uranium and thorium contents with
averages of 19 ppm and 4.5 respectively, suggesting that it is fertile granite.