RADIOACTIVITY, PETROGENESIS AND RARE EARTH ELEMENTS TETRAD EFFECT OF THE MINERALIZED GRANITE OF GABAL GATTAR, NORTH EASTERN DESERT, EGYPT

The batholith of Gabal Gattar is bounded by diorite and granodiorite from the northeastern corner
and Hammamat sediments from the northwestern corner. Wadi Belih extends between Hammamat
sediments and Gabal Gattar following a major fault trending N75°-80°E. Petrographically, the studied
Gattarian granites at GII occurrence composed mainly of potash feldspar, plagioclase and quartz
associated with substantial percentage of mica minerals. Modal composition revealed that this granite
is quartz-rich syenogranite. Microscopic examination clarifies the presence of two types of secondary
radioactive minerals; the first type is syngenetic comprising the minerals that derived from the primary
minerals (uraninite-coffinite) as uranophane and kasolite associating the metamict zircon and violet fluorite.
The second type of the secondary uranium minerals is epigenetic like uranophane which is the most common
secondary uranium mineral that formed by hydrothermal solutions using the silica ions that derived from
the silicate minerals. Radioactivity of the studied granite is very high where eU varies between 450 and
4600 ppm with an average 1889.7 ppm, eTh between 0.59 and 900 ppm with an average 80 ppm, Ra
between 418 and 2530 ppm with an average 1212 ppm and potassium between 0.01 and 2.40 % with an
average 1.05%. The binary relations between the radionuclides show that uranium mineralization in GII
occurrence are mainly connected to hydrothermal alteration processes during the late stages of magmatic
crystallizations. The ratios (La/Y and Y/Ho)and the anomalies (Ce-and Eu-), in addition to the recorded
pattern of REEs tetrad effect (M-type) for the studied granite indicate that this granite is highly evolved
and affected by late stage hydrothermal alteration. Mineralogical investigations clarified that U-minerals
comprise the primary minerals (uraninite and pitchblende) and the secondary minerals (uranophane and
kasolite).