Review: The object of this research is the groundwaters and surface waters of the Sentsa River Basin. The area of explorations is situated in the Eastern Sayan hydrogeological folded region. Cold and thermal waters occur in the PR and PZ metamorphic and igneous rock. These waters are discharged through the spring series in the river valleys laid along fault zones. The main type of fieldwork was hydrogeological sampling. The analysis of the macrocomponent composition of waters was conducted in the «Geodynamics and Geochronology Center» (Institute of the Earth’s Crust SB RAS, Irkutsk), the trace element composition was determined by ICP MS on an Element-2, Finnigan MAT (Germany) at the Vinogradov Institute of Geochemistry SB RAS (Irkutsk). The scientific novelty consists in the fact that this article provides not only the characteristics of chemical composition of cold and thermal waters, but also the primary data on the distribution of microelements in the ground and surface waters of the Sentsa River Basin. Groundwater (thermal and cold) are revealed to have a bicarbonate Ca-Na composition, withal river and lake waters are generally bicarbonate Ca. Thermal waters (in the Khoyto-Gol River Basin) are largely enriched in Li, Be, B, Si, Mn, Ge, As, Br, Rb, Sr, Cs, Ba, W and depleted in Al, P, Cu, Zn, Ag relative to surface and rainwater. The REE distribution profile in groundwater and surface waters have peculiarities that are characterized by a positive europium anomaly and the prevalence of light REE over heavy ones.

Keywords: Khoyto-Gol spring, rare earth elements, trace elements, chemical composition, surface waters, thermal ground waters, cold ground waters, Manzaragshi spring, Sentsa River, Oka Plateau