Mineralogical and geochemical studies of copper mineralization in the Paleozoic sedimentary section in southwestern Sinai, Egypt

Abstract

The present study provides new insights into the distribution and characteristics of copper-bearing Paleozoic clastic-carbonate units, Araba and Um Bogma formations in southwestern Sinai, Egypt. Malachite, azurite, atacamite, chrysocolla, and cuprite occur as disseminations or stratiform, layer-parallel streaks, and lenticular bodies that are intercalated with vanadiferous sandstones in the middle unit of the Araba Formation. The vanadiferous sandstones are rich in mottramite, mimetite, duftite, beudantite, descloizite and vanadinite. The Um Bogma Formation is characterized by uncommon chalcanthite, antlerite, malachite, chrysocolla, covellite, and chalcocite in addition to traces of pyrite and barite. These ore minerals occur as acicular, fibrous, fracture-filling, disseminated, and pore-filling patches and are associated with Mn-minerals. Copper minerals form also thin laminae in the manganiferous and black organic-rich shales of the Um Bogma Formation.Copper and vanadium minerals are disseminated in the arkose, subarkose, sublitharenite, graywacke, shale, siltstone and dolostone members of the host formations. Elevated copper concentrations (up to 5.04 wt%) and vanadium (≤362.3 ppm) are associated with high CaO and MgO contents in the intergranular patches and discontinuous laminae. In the Um Bogma Formation, the mineralized layers show high contents of MnO (up to 84.27 wt%) and Fe2O3 (up to 72.1 wt%), Ba (0.03–2.86 wt%), S (up to 0.452 wt%) and Ni (0.012–0.041 wt%).Mineralogical and textural characteristics of the studied rocks indicate that copper and vanadium minerals in the Araba Formation are related to supergene processes and telodiagenesis after oxidation of sulfides and dissolution of feldspar grains and carbonate cement in the clastic rocks most probably during the Upper Devonian-Lower Carboniferous Hercynian event. In the Um Bogma Formation, copper mineralization is a supergene alteration of hydrothermal Fe-Mn minerals and associated primary Cu-Zn sulfides. Hydrothermal fluids likely mobilized several metals, i.e., Fe, Mn, and Cu, within dissolved and karstified carbonates in the Um Bogma Formation.