An outline is given of the small lakes on two neighboring territories: Transbaikalia (RF), and Northeastern Mongolia, which are combined into five systems: Barguzinskaya, Eravninsko-Gusinoozerskaya, Ingodinskaya, Onon-Borzinskaya, and Eastern-Mongolian. Within these systems, the lakes are divided into compact groups characterized largely by common features of chemical composition, and by the type of geochemical evolution. Also, a characteristic of subterraneous and surface waters feeding the lakes is given. Based on studying the trace element composition of lacustrine (about 200 lakes) and subterranean (more than 100 springs, wells and boreholes) waters, it was possible to identify the elements concentrating in the evaporation process of lacustrine waters. We examine the prospects for using small lakes as “liquid ore” for commercial extraction of some metals (Li, U, REE, and others).Keywords: system of small lakes, Transbaikalia, Mongolia, water mineralization, ore-generating potential.