Hydrogeological conditions and hydrogeochemistry of the Kamenskoye hydro-radon occurrence, Novosibirsk, Russia

Abstract

Hydrogeological and hydrogeochemical conditions, the concentrations of major and some minor ions and ²²²Rn were determined in the Kamenskoye hydro-radon occurrence in the Southern part of West Siberia. Two different aquifer systems were revealed in the hydrogeological section: the Quaternary sediments with pore waters and the Upper Paleozoic granites including the waters of regional fracturing zone and fracture-vein waters. They are located in a common mixing area and are affected by flooding and anthropogenic pollution. Mineral radon fracture-vein waters in granites, not affected by anthropogenic impact, have been revealed in two boreholes. These waters are cool, fresh (TDS 613.4 to 689.9 mg/L) and Si⁴⁺ content within a range from 10.3 to 13.6 mg/L_. The pH of these waters is neutral to weakly alkaline (6.9–7.8), the gases dissolved in the waters are oxygen and nitrogen. The determined activity of ²²²Rn varies within the range from 1101 to 1570 Bq/L; ²³⁸U concentration varies between 5.6·10⁻³–6.5·10⁻³ mg/L, while ²²⁶Ra ranges from 2.7·10⁻⁹ to 1.8·10⁻⁸ mg/L. The relative fractions of cations (Mg²⁺, Ca²⁺, Na⁺, Sr²⁺, Ba²⁺) decrease with an increase in TDS value due to the formation of poorly soluble carbonate and sulphate compounds. The forms of Fe(II) are represented by Fe²⁺, FeHCO₃⁺, FeCO₃⁰, and Fe(III) migrates in the forms of hydroxo complexes Fe(OH)₂⁺ and neutral species Fe(OH)₃⁰. Manganese migrates mainly as a cation, while other forms (MnHCO₃⁺, MnCO₃⁰) are less abundant, and MnSO₄⁰, MnCl⁺, MnOH⁺ are minor. The chemical forms of nickel and copper migration are free cations, as well as hydrocarbonate and carbonate complexes. Copper, as well as beryllium, also migrate as hydroxo complexes. The forms in which chemical elements migrate and their migration coefficients provide evidence that the equilibrium minerals become more complicated when passing from surface waters (greenalite, siderite, and ferrihydrite and greenalite) to the fracture-vein waters in the Upper Paleozoic granites saturated with dolomite, calcite, talc, magnesite and rhodochrosite.