Authigenic Iron Minerals in River Sediments of the Eastern Donbass

Abstract

Relevance. Eastern Donbass is a territory in the western part of the Rostov region, where all environmental components , but especially river systems were subjected to heavy technogenic impact for many decades in the process of developing coal deposits and the subsequent liquidation of unprofitable mines. As it is known, the most important component of the river systems river sediments, which carry information about the pollution degree of the aquatic environment, the ecological state of entire catchment areas, the sedimentation conditions, the nature and direction of post-sedimentation processes, primarily diagenetic ones. Aim. Investigation of authigenic iron minerals in river sediments of the Eastern Donbass, assessment of the technogenic factor effect on diagenetic mineral formation. Methods. The study of the authigenic iron minerals assemblage have carried out using electron probe methods on a scanning electron microscope VEGA II LMU with an energy dispersive microanalysis system. Results. Authigenic iron minerals are represented in river sediments by iron hydroxides (ferrihydrite) and oxides (magnetite), and, less frequently, sulfides (pyrite) and carbonates (siderite). They are formed in essentially pelitic silts enriched in organic matter of modern origin, and these minerals are members of the same mineralogical series. The observed authigenic iron minerals assemblage is produced under the combined influence of natural and anthropogenic factors. Among the latter technogenic mine waters play an important role as the main source of iron, sulfates and other components in river sediments. The formation of authigenic iron minerals occurs under unstable physicochemical conditions, which is typical for the early stage of diagenesis. This is evidenced by the presence of authigenic minerals (iron oxides and hydroxides along with sulfides and ferruginous carbonates) in mineral assemblage, X-ray amorphous state of mineral masses, the presence of pseudomorphs, the absence of a clearly defined crystal structure indicating the incompleteness of mineral formation processes in river sediments. It is emphasized that the magnetitite formation from iron hydroxides is most preferable from the energetic point of view at the early stage of diagenesis of the river sediments studied. It is the “magnetite reaction” that starts earlier, proceeds faster and requires less organic matter than the “siderite” and even more so “pyrite” reaction.