Distribution of chemical elements in the water–rock system (based on the example of a Zheleznodorozhny spring in the valley of the Inya river)

Relevance. The necessity to identify the characteristics of the distribution of chemical elements in the water–rock system using the example of the Zheleznodorozhny spring within the Ob-Zaisan folded region, actively used by the population for decentralized drinking water supply. Aim. To identify the features of the chemical and isotopic (238U, 234U, 226Ra, 228Ra) composition of spring waters and assess the nature of the equilibrium in the water–rock system. Methods. Laboratory studies of the chemical composition by means of titration, ion chromatography, mass spectrometry with inductively coupled plasma were carried out at the Research Laboratory of Hydrogeochemistry at the School of Earth Sciences and Engineering of the Tomsk Polytechnic University. The data on the total β-activity of waters, as well as on the activities of 234U, 238U, 226Ra and 228Ra, were obtained at the Center for Collective Use of Scientific Equipment for Multi-Element and Isotope Research Institute of Geology and Mineralogy SB RAS. Water-bearing rocks were studied using polarization microscopy at the Institute of Institute of Oil and Gas Geology and Geophysics of the Siberian Branch of the Russian Academy of Sciences, Novosibirsk, and inductively coupled plasma mass spectrometry at the Plasma Chemical Analytical Center, Tomsk. Results. The study area is mainly dominated by thin-platy dark gray to black clayey shales, enriched to varying degrees with silty and carbonaceous material. Values of the ratio (La/Yb)N>8 and (Gd/Yb)N>1.5 indicate the predominance of acidic igneous rocks in the sources. To determine climatic conditions, the parameter ∑Ce/∑Y was used, which established a humid climate during the formation of rocks. The Zheleznodorozhny spring has a HCO3 Mg-Ca composition with a total mineralization value of 593 mg/dm3, the geochemical parameters of the environment correspond to an oxidizing environment with Eh +202.7 mV, pH 7.7 and a dissolved oxygen content of 5.20 mg/dm3. Comparing the chemical composition of the described spring waters with the host rocks composition, it can be assumed that the waters inherit their composition, which is expressed in repeating extremes. In comparison with the previously studied springs of the Inya River valley, the waters of the Zheleznodorozhny spring are enriched with uranium up to 4,76∙10–3 mg/dm3, which exceeds the level of the Insky springs (2,83∙10–3–4,16∙10–3 mg/dm3), but is lower than the studied objects in the village of Novolugovoe (3,08∙10–2–4,56∙10–2 mg/dm3). The uranium isotope ratio (γ) does not exceed 1.95. According to the results of thermodynamic calculations, the waters of the Zheleznodorozhny spring are in equilibrium with calcite and dolomite, as well as with kaolinite, which allows them to be classified as an aluminum-siliceous geochemical type.