EQUILIBRIUM-NONEQUILIBRIUM STATE OF NATURAL WATERS IN THE AREA OF TOREY LAKES (EASTERN TRANSBAIKALIA) WITH LEADING MINERALS OF HOST ROCKS

Abstract

The relevance of the work is related to the issues of the groundwater’s chemical composition formation in environmental conditions, the solution of which, within the framework of the considered hypothesis of the interaction of water with rocks, is impossible without understanding the stage of water’s equilibrium with minerals of host rocks. This problem is particularly specific due to the wide distribution of fissured volcanogenic structures and salt lakes in the territory, as well as the dry climate. At the same time, existing hypotheses single out evaporation processes as the key factor leading to water salinization, ignoring all others. Meanwhile, this is not obvious for groundwater. The general theory of interaction in the water–rock system can reveal the mechanism of water’s different composition formation, distinguish different stages of salt accumulation, including the soda stage, which cannot be explained only by evaporation processes. To do this, it is necessary to calculate the degree of water saturation relative to the minerals of the host rocks. The aim of the research is to assess the equilibrium-nonequilibrium state of the natural waters in the territory with minerals of host rocks at different stages of evolutionary development, to determine the possible set of secondary minerals at each stage and to identify necessary hydrogeochemical parameters for their formation. In the future, the results will be used to study the mechanisms of groundwater formation. Objects. During chemical composition formation, groundwater goes through several stages of its development, among them: atmospheric (atmospheric waters as a source of nutrition), lithogenic (when interacting with host rocks) and evaporative (when interacting with lake waters that undergo evaporation). In order to trace the entire evolution of the composition, in addition to the directly groundwater of the upper dynamic zone (springs, wells and boreholes up to 70 m deep, 69 samples in total), atmospheric (6 samples), river (9 samples) and lake (10 samples) waters were also studied. Methods. Water’s macrocomponent composition was determined by modern standard methods: titrimetric, potentiometric, photometric, atomic absorption spectrometry with flame atomization and flame atomic emission spectrometry at the INREC SB RAS (Chita), microcomponent – by the ICP-MS method at TPU (Tomsk). Petrographic and mineralogical studies of host rocks were carried out using scanning electron microscopy at TSU (Tomsk). Physico-chemical modeling of equilibria in the water–rock system was calculated using the HydroGeo software package. Then the calculation results were compared with natural observations. Results. Thermodynamic calculations in the water–rock system showed that all natural waters of the Torey Lakes area from atmospheric precipitation to salt lakes are nonequilibrium with respect to primary aluminosilicates (especially basalts, which are found in the north of the study area), which they continuously dissolve throughout this interaction, and are in equilibrium with respect to secondary minerals they form (gibbsite, kaolinite, montmorillonites, various carbonates, chlorites, albite, microcline, muscovite, etc.). The paper introduces the main physicochemical parameters (chemical composition, pH and salinity of water) obtained by the authors in the calculations, which control the formation of a certain secondary mineral.

Keywords

• surface and underground waters of the upper dynamic zone
• water–rock system
• secondary mineral formation
• formation of chemical composition
• torey lakes
• eastern transbaikalia