WITHDRAWN: Rare metal mineralization and geochemical characterization of El Mansouri Ring Complex, Northern Arabian Nubian Shield: Implications for petrogenesis and tectonic setting

Abstract

The geographic distribution of alkaline-carbonatitic complexes in the Egyptian Eastern Desert is restricted, leading to ongoing arguments on their geotectonic settings and petrogenesis. The petrogenesis of the El Mansouri Ring Complex has been investigated through the evaluation of the mineral chemistry and whole-rock geochemical data of alkaline and carbonatite rocks associated with this complex. The El Mansouri Ring Complex consists of trachyte, alkali feldspar syenite, and quartz syenites, along with carbonatites. Three types of carbonatites have been formed: a) calcite-carbonatite (søvites), b) dolomite-calcite carbonatite, and c) dolomite-carbonatite (beforsite). The alkaline rocks mostly include K-feldspar, plagioclase, sodic pyroxene (aegirine-augite), and alkali amphiboles (riebeckite and arfvedsonite), along with zircon, apatite, allanite, fluorite, and opaques. The El Mansouri intrusive rocks exhibit alkaline to peralkaline geochemical properties, characterized by low amounts of CaO, MgO, and Sr and significant concentrations of total alkalis (Na2O + K2O), Nb, Rb, Y, and REEs. These characteristics bear a resemblance to the properties seen in A-type granites that are formed from mantle-derived magma in an anorogenic setting. Their composition contains abundant rare earth elements (REEs) and incompatible elements, exhibiting negative anomalies in K, Sr, Ti, Ba, and P and positive anomalies in Zr and Rb. The carbonatites exhibit significant concentrations of high-field strength elements (HFSE), such as U, Th, Zr, Nb, and Y, as well as large ion lithophile elements (LILE), including Rb, Pb, and Sr. Additionally, they have negative anomalies of K, P, and Ti with regards to REEs. The El Mansouri alkaline rocks are plotted in the field of the within-plate granites and exhibit characteristics of the A1 subtype of the A-type granite. Additionally, the associated carbonatites are classified as calcio-carbonatites. The studied El Mansouri Ring Complex is proposed to have been formed by the fractional crystallization of a mafic magma comparable to oceanic island basalt (OIB). While the carbonatites originated from the crystal fractionation of a parental carbonated-syenitic magma. In the highly radioactive zone, the main minerals are kasolite, uranothorite, columbite, ishikawaite, xenotime, zircon, monazite, and fluorite. The carbonatites have the greatest U and Th. The radioactivity level in these carbonatites may reach up to 395 ppm eU, whereas the alkali feldspar syenite has 173 ppm eU and, and the quartz syenite contains 125 ppm eU.