Geochemistry and mineralogy of Qaroun Lake and relevant drain sediments, El-Fayoum, Egypt

Abstract

Qaroun Lake (El-Fayoum, Egypt) is a saline endorheic basin within the northern arid zone of El-Fayoum, Egypt. Mineralogical and geochemical investigations were conducted on 32 samples from the Holocene sediments of the lake and relevant drains to get information on the sediment type and maturity, source rocks, weathering, environments of deposition, and tectonic settings. The lithology of sediment samples consists of pelites and sandstones with low compositional maturity degree characterizing first cycle deposits. The sediments are mainly composed of quartz and calcite, with minor phases including feldspar, dolomite, saponite, kaolinite, hematite, goethite, gypsum, and halite minerals. The lake's sediments are enriched in Cr, Mo, Hf, Pr, and Nd and depleted in Ni, Zn, As, Rb, Y, Sn, Sb, Ba, and La, while the drain's ones are enriched in V, Sr, Zr, Cr, Mo, Hf, Pr and Nd and depleted in Co, Zn, As, Rb, Y, Sn, Sb, Ba, Pb, and La, compared to the earth's crust shale. These sediments are mainly sourced from intermediate and felsic igneous rocks, as well as, calcareous and sandstone materials incorporated in the nearby geologic formations and soils. The high SiO2 and the low Fe2O3 and MgO concentrations reflects the acidic nature of rocks in the source area. The SiO2 and (Al2O3+K2O+Na2O) binary plot indicates the prevailing semiarid to arid climatic conditions during the sedimentation. High values of CIA and PIA and low values of ICV as well as the relationship between K2O/Na2O and K2O+Na2O contents reveal relatively moderate to a high degree of chemical weathering in the source area. The elemental ratios and geochemical discrimination diagrams show that the sedimentary environments are fluviatile-deltaic environments that experienced oxic to dysoxic conditions. The geochemical characteristics of the lake sediment samples point to a transitional tectonic setting from oceanic island arc to active continental and passive continental margins, while those of the drains samples indicate an active continental tectonic setting. The obtained data can be meaningful for the development of Qaroun lake environment.