Mineralogical Characteristics Of Uskol Lake Sediments (Republic Of Khakassia)

This is a detailed study of mineralogical and geochemical characteristics of Uskol Lake sediments and waters. Uskol Lake exists in semiarid conditions and belongs to South-Minusinsk salt lakes group, Southern Siberia of Russia. It consists of three reservoirs, two of which are intermittent.Using X-ray diffraction analysis allowed determination of mineral species, among which are oxides (quartz), aluminosilicates (illite, Na- and Ca-Mg-montmorillonite, analcime, albite and sanidine), carbonates (calcite, dolomite), sulfates (gypsum, thenardite) and halides (halite). According to their origin, the minerals can be divided into two associations: terrigenous and hydrogenous. Terrigenous association includes non-soluble minerals and corresponds well to the bed rocks composition. Hydrogenous association includes minerals, which form due to evaporation processes.While studying the regularities of vertical and lateral distribution of mineral species it was stated that mostly they are evenly distributed. However, there is a tendency of gypsum and halite accumulation in the upper parts of cross sections; also it was noted that at the depths of 30-100 cm there is illite and Ca-Mg montmorillonite contents increase in relation to Na-montmorillonite content. Carbonate (calcite, mostly) contents increase at about 200 m from lake shore. The order of hydrogenous minerals sedimentation from chloride-sulfate waters of the Lake Uskol was determined. In general, minerals are precipitating as following: CO32- -> HCO3- -> SO42- -> Cl- for anions, Ca2+ -> Mg2+ -> Na2+ for cations.Obtained results are confirmed and enhances by physicochemical calculations, which show balance between lake waters and oxides, aluminosilicates, carbonates and sulfates. It is stated that evaporation processes as well as rocks weathering greatly influence the mineral formation.