Geochemistry, mineralogy, and radioactivity of Upper Cretaceous Abu Khruq Ring Complex, South Eastern Desert, Egypt

The upper Cretaceous Abu Khruq ring complex (ARC) is located in the South Eastern Desert between latitudes 24A degrees 00'10'' and 24A degrees 03'15'' N, and longitudes 33A degrees 54'50'' and 33A degrees 58' E and has a roughly circular shape with a diameter of 7 km. ARC is built up by major extrusion of alkaline volcanic rocks comprising mainly rhyolite porphyry and alkaline trachyte rocks at the center of the ring complex followed by successive intrusions of alkaline gabbro and syenitic rocks comprising quartz syenite (oversaturated), syenite (saturated), and nepheline syenite (undersaturated). Petrographical and geochemical studies were carried out for the rocks of the forming ARC. For mineralogical and radioactive investigations, samples were collected from the most promising locations representing the hematitized nepheline syenite, nepheline syenite pegmatites, and quartz syenite. The most important minerals comprise: phosphuranylite, zircon, monazite, xenotime, plumbopyrochlore, pyrite, huttonite, apatite, REE mineral, rutile, and atacamite. The hematitized nepheline syenite is the most U- and Th-rich rocks, where eU content in this rock ranges from 375 to 788 ppm with an average 502 ppm and the average eTh content is 2,345 ppm ranging from 1,918 to 3,067 ppm. The pegmatite syenite and quartz syenite contain relatively low concentrations of U and Th, where the average eU content are 11 and 16 ppm and average eTh contents are 27 and 327 ppm, respectively.