MINERALOGY AND RADIOACTIVITY OF SOME PEGMATITE BODIES, SOUTHEASTERN SINAI, EGYPT

The area under consideration constitutes the extreme eastern part of the Kid metamorphic belt in Sinai
Peninsula. The Neoproterozoic rock units exposed there comprise gneisses, migmatites, old granitoids and
monzogranites. Most of the pegmatite bodies encountered in the monzogranite rocks occur as plug-like
bodies and veins of variable dimensions. These studied pegmatites are mainly of the simple unzoned type.
They are composed of intergrowths of smoky quartz and pink K-feldspar with some accumulations of micas
which host most of radioactive mineralizations. Radiomertrically, the concentration of eU ranges between
41 and 117ppm with an average of 73ppm, while eTh varies between 160 and 433ppm with an average
of 223ppm. The Ra content reaches up to 94ppm with an average of 62ppm. The radioelements variation
diagrams illustrate that the distribution of radioelements is due to both magmatic origin and hydrothermal
redistribution. The high level of radioactivity in the studied granitic pegmatites is mainly resulted from the
presence of ishikawaite, thorite, uranothorite, thorianite, zircon, betafite and fluorite. Most of the studied
radioactive minerals commonly occur in the metamict state. Other accessory minerals like anatase, hematite
and magnetite are also recorded. The study reports for the first time the presence of Ishikawaite-Th, where
Th prevails U. Ishikawaite-Th grains contain exsolution intergrowths of ishikawaite-U and thorianite.