Genesis and evolution of Late Oligocene to Late Miocene syn-rift Pb-Zn deposits along the Red Sea coast, Egypt: Inference from a petrographic and geochemical investigation

Abstract

Lead‑zinc deposits on the Egyptian Red Sea coast are hosted within a syn-rift system's carbonate platform; however, their origin is still under discussion. This study has used an integrated geological, petrographic, and geochemical analysis of these deposits along seven localities to investigate the record of the main processes that controlled their onset and evolution. Two main zones of mineralization are distinguished: an exposed upper zone composed essentially of smithsonite, hydrozincite, hemimorphite, goethite, and hematite with relics of galena, and a lower zone composed mainly of galena, sphalerite, and pyrite with minor amounts of marcasite. Geochemically, these deposits are depleted in Na, K, Al, Ti, and Nb but are enriched in Mo, Cd, and As. The chondrite-normalized patterns of Pb-Zn-bearing samples show pronounced negative Ce and Eu anomalies, whereas the pattern of the host rocks shows a distinctive pattern with pronounced negative Ce and positive Eu anomalies. The isotope geochemistry analysis of the present lead‑zinc-host rocks shows negative values of δ¹⁸O and δ¹³C in the saddle dolomite-II, dolomite-III, and Zn-dolomite, all of which reflect the effects of dolomitization by hydrothermal fluids. Based on mode of occurrence, texture, mineralogy, and geochemistry, the studied lead‑zinc deposits were formed in two stages: an early stage marked by the participation of primary sulfide ores from hydrothermal solutions, and a late stage involving the replacement of the precursor primary sulfides by means of surface water. These Pb-Zn ore deposits hosted in carbonate rocks are genetically considered to be of Mississippi Valley-type and could constitute important clues, taking into account their wide distribution, for the exploration of new targets of lead‑zinc in addition to a better understanding of the origin of lead‑zinc deposits in the Middle East area and provides important information to improve future mining in the area.