GEOLOGY AND RADIOACTIVITY OF ALKALINE GRANITES OF SOUTHWEST GABAL NUSAB EL BALGOUM AREA, SOUTH WESTERN DESERT, EGYPT

This paper is concerned with the geology and radioactivity of alkaline granites southwest Gabal Nusab
El Balgoum area, South Western Desert, Egypt. The alkaline granites are equigranular in texture, fine- to
medium-grained and dominated mainly by perthitic orthoclase and quartz, aegirine-augite, aegirine, and
plagioclase, while Bastnaesite, xenotime, calcite, monazite, zircon and apatite are accessory minerals.
Opaques represented by Hematite, ilmenite, goethite and little sulphides (chalcopyrite and pyrrhotite).
Applying alpha-track emission technique indicates that iron oxides and altered feldspar minerals contain
great amount of radio-elements (U and Th). Representing field radiometric contour maps for eU, eTh
(ppm) and K% indicate that U and Th concentrate in the main fault trend NE-SW, which suggest that the
enrichment of U is structurally controlled. A difference between field measurements (eU and eTh) with the
chemical analysis data (U and Th) can be explained due to recent U addition. The trace elements contents
show that Zr, Nb, Y (HFS elements) values increase with increasing U due to hydrothermal alteration
at later stages of magmatic activity. Chondrite normalized REE diagram shows that the alkaline granite
has enrichment of " REE and display progressive enrichment in LREE relative to HREE which shows
a slightly flat pattern with large negative Eu anomaly. The enrichment of REEs may be attributed to the
presence of bastnaesite and monazite as a source of LREE and xenotime as a source for HREE.