Genesis of Water and Dissolved Matter in Soda Lakes of Nizhnii Kuitun of the Barguzin Depression

We examine the formation conditions for the resources and chemical composition of mineral lakes located in the vicinities to the unique natural site of the Barguzin intermontane depression, Nizhnii Kuitun. Presented are the results from studying the surface structure of this sand massif. It is shown that its formation is associated with peculiar features in the tectonic development of the Barguzin depression. It is pointed out that the block of rocks forming Nizhnii Kuitun is broken up by tectonic faults into several smaller parts, and this had a determining impact on its modern appearance. The lakes under study are situated in the northern part of Nizhnii Kuitun, in the Nukhe-Nur urochishche, in the topographically clearly pronounced drainless depression. The formation of this depression occurred during the uplifting stage of the block of rocks when intensively fragmented rocks, located at the interface of the faults, lagged behind in vertical movement. The depression receives the runoff of surface and underground waters which drain sedimentary deposits of Nizhnii Kuitun. Data are provided to demonstrate that the lakes are situated in the ablation funnels of sand-clay sediments. On the basis of a quantitative determination of the chemical composition of water and gases, it is proved that seepage waters of sandy sediments of Nizhnii Kuitun and nitrogenous fissure-vein waters play the main role in the formation of resources and chemical composition of the lake water in the area of the Nukhe-Nur urotshistshe. The hydrological-hydrogeological model of the formation of the lakes under study is suggested. In a dry period when the amount of water infiltrating through the sand deposits of Nizhnii Kuitun decreases, the proportion of deep fissure-vein waters increases; therefore, water mineralization increases in the lakes as well as fluorine, sodium, tungsten and molybdenum contents. In wet years, the contribution of drainage waters to the formation of the lake’s resources increases, and the concentration of these elements decreases.