Geochemistry of unique fresh alkaline water basin of Chulym
The hydrogeological conditions of the unique mineral water "Omega" deposit are investigated in the article The uniqueness of this water consists in high alkalinity (pH between 8 and 10) and low salinity waters (up to 1 g/l). It is shown that the basin of the Chulym on the border of the West Siberian Basin and the Yenisei hydrogeological folded area in the sediments of the Cretaceous and Jurassic at depths ranging from 500-100 to 800-1500 m has favourable hydrogeological conditions for the formation of this type of water: flow of fresh fracture-vein waters of the Yenisei Ridge in the zone of deep faults in the basin, large capacity of sandstones with high values of porosity, no water confining stratum. It caused the storage of huge stocks of fresh water at big depths. The results of researches of ion-salt, gas and isotopic composition of the water confirmed that it is infiltrate and it circulates in the zone of active water exchange. The mineralogical structure of water containing deposits of the Ileksky suite was studied represented by sand, sandstones and silts. The chemical, gas and isotope composition of mineral water ''Omega'' was thoroughly examined, data on other waters of the basin of the Chulym were also provided. According to the received data the water is warm (in the mouth the temperature is 21...23°C), sub-saline with the total salinity level of 0.2...0.4 g/l, alkaline (рН 9.1.10.3) and with Eh -86 mV. By its chemical composition the water belongs to hydrocarbonate sodium (soda) type. The water contains such specific components as metasilicic acid (up to 35 mg/l) and dissolved organic substances (up to 10 mg/l by DOC. In gas structure nitrogen (76.77%) prevails, then oxygen (18.19%), methane numbers are low (0.5%). The isotope composition of water is investigated: SD and S <sup>18</sup>O, as well as isotope composition of carbon of the dissolved ion of HCO <sub>3</sub> <sup>-</sup> (S <sup>13</sup>CHC0 <sub>3</sub> <sup>-</sup>). The latter has a sharply facilitated value (-30.3 %%) that indicates biogenic genesis of CO <sub>2</sub> as a part of HCO <sub>3</sub> <sup>-</sup> formed by oxidation of the organic substance of soils and coals, and disseminated in rocks. The results of the calculation of equilibriums in the water-rock system are given. The water dissolves primary aluminosilicates of water-bearing rocks: feldspar (except albite), muscovite, biotite, pyroxene, hornblende, epidote, and many others. At the same time the solution plants secondary minerals: clay (hydromica and Ca-montmorillonite) and carbonates (calcite, dolomite, siderite). Of all the elements entering the solution by dissolving aluminum silicates, Na least of all links in the secondary deposits, therefore, continues to accumulate in the water. In addition, the lack of carbon dioxide in the water stimulates accumulation of the group of OH <sup>-</sup> formed by hydrolysis. Thus, fresh alkaline sodium bicarbonate water are formed.