This paper presents the results of complex hydro-geochemical studies of the natural waters of the Kastropol tract. It was found that the studied waters are characterized mainly by HCO3 Ca and HCO3 Mg-Ca composition with a total mineralization value varying in the range from 220 to 2306 mg/dm3 and a silicon content from 0.78 to 6.08 mg/dm3 . It was revealed that the geochemical parameters of the medium vary from reducing to oxidizing with Eh -146.6 – +275.9 mV, pH 7.4 – 8.5 and O2 content of 1.80 – 7.73 mg/dm3 . It is determined that B, Br, I, Re and Au accumulate in the waters. In solution, Li, B, Sr, Re and Au have a very strong migration ability. The state of equilibrium of the studied waters with respect to carbonate (calcite and dolomite) and alumine silicate minerals (gibbsite and kaolinite) was revealed. It is established that the studied waters belong to the aluminum-siliceous type and characterize the monosiallite geochemical type of weathering. The controlling factors for achieving equilibrium with respect to kaolinite are the contents of aluminum, silicon and the pH of the medium in the solution.