MINERALOGY OF THE RADIOACTIVE OCCURRENCE AT THE NORTHERN PERIPHERY OF GABAL GATTAR GRANITES, NORTH EASTERN DESERT, EGYPT

The northern periphery of G. Gattar granites is mineralogically studied. The study area exhibits
significant potential for radioactive occurrences especially in the strongly altered granites at the intersection
between the basic dykes striking N300E and a sinestral strike-slip fault trending N-S. These occurrences are
mostly of epigenetic origin. They are closely associated with the hydrothermal alterations; hematitization,
kaolinitization and episyenitization causing marked enrichment of some elements notably, Zr, Y, Zn, Ba and
REEs. The uranium occurrences vary considerably in their contents from 68 ppm to 4800 ppm, whereas the
thorium contents reach up to 600 ppm especially in the desilicified granites.
These radioactive occurrences may be due to the existence of some primary and secondary radioactive
minerals. The primary minerals comprising uraninite and thorianite whereas the secondary ones including
altered aggregated fragments of coffinite, becquerelite and gummite which were probably formed in the
early stages due to uraninite dissolution. Furthermore, uranophane, kasolite, weeksite and autunite are
the most conspicuous supergene uranium minerals which are mostly formed as a result of the extensive
alterations of the pre-existing primary ones. The latter four minerals display mutual genetic association,
hence, it is suggested that the heterogeneous hydrothermal solutions may play a crucial role in formation of
the observed secondary U- minerals association in the northern part of Gattar granites pluton.