Sedimentological, Geochemical and Hydrogeochemical Studies of Alluvial Fans for Mineral and Environmental Purposes (Case Study of Southwestern Iran)

Abstract

The alluvial-fan sediments play a very important role in mineral reserves and underground water resources, though a comprehensive study on such sediments, especially from a geochemical point of view, is still lacking. In this research, a total of 22 particularly important alluvial fans across the Khuzestan Plain in the southwestern Iran were studied through field surveys, petrographic evaluations, and geochemical assessments. These investigations included particle size distribution studies, microscopic observation of 193 samples, subsurface study of 60 boreholes along 10 different sections, facies analysis on 46 different sections, and comprehensive geochemical studies through XRD, XRF, ICP Mass, and wet chemical analyses. Based on these studies, the sediments were found to be dominantly composed of gravel, muddy sand, silt, and clay. The sediments exhibited good roundness and good to fair sorting. The most abundant oxide in the study area being MgO followed by SiO2, Al2O3, and Fe2O3. According to the studies, most of the samples fell in the range of iron-bearing sandstones with rare cases of iron-bearing shales. Investigation of the geochemical indices showed the long sediment transport path from the source, humid climate, and moderate to extensive weathering of the deposit. The depositional setting was found to be dominantly an active continental margin and, to a lesser extent, a continental island arc. Investigating of the studied sediments provenance indicate a felsic to slightly basic source rock. The environmental studies were indicative of relatively low contamination of the region and abundance of rare earth elements including Y, Sc, Nd, La, and Ce, and the abundance of heavy elements including Cr, Zn, Pb, and Cd. Based on the mineralogical studies on the samples, the inter-grain cement in both gravel and conglomerate particles was found to be composed of calcite.