Geochemistry of the trace and rare earth elements mineralisations in the lower member of Um Bogma Formation in the area east of Wadi Baba, southwestern Sinai, Egypt

Abstract

ABSTRACT The exposures of the lower member of Um Bogma Formation (Early Carboniferous) in a vast area east of Wadi Baba were studied in six localities. The member is dominated by argillaceous rocks in the western and southwestern occurrences, carbonates in the central sector of the area and sandstones at the east.These rock types, especially the carbonates in Allouga locality, consist of large assemblages of non-radioactive, radioactive and REEs- and base metals- bearing minerals of a mixed allogenic-authigenic and primary-secondary origin. Most of the allogenic minerals were inherited from unaltered and altered precursors in felsic igneous rocks. The results of extensive geochemical studies confirmed varying enrichment of the studied rocks in many trace and rare earth elements as well as base metals. The rocks in Allouga locality and, to a lesser extent, those in Talet Seliem and Abu Zarab have the highest potential as possible resources of these elements. Sequential extraction of Mn, Cu, Fe, Pb, U, Th, Y, La and Dy from five fractions revealed that these elements are exchangeable, bound to carbonates, iron and manganese oxides and organic matter and/or residual. The distributions of trace elements and REEs among the different rock types show variation based on their affinities to specific lithologies. The REEs generally show enriched patterns and negative Eu anomalies. U enrichment in rocks of this member is correlated with the occurrence of several types of uranyl silicate minerals. The co-existence of these minerals reflects variations in the activities of Ca, Mg, Cu and Pb. The hydrothermal activities related to the Red Sea extension were responsible for the oxidation of sulphides, alteration of primary minerals and genesis of Mn oxides, surficial uranyl and REEs mineralisations. Based on the obtained data, certain localities are recommended for future prospecting plans.