INITIAL RESULTS OF THE INTEGRATED ISOTOPE-HYDROGEOCHEMICAL STUDIES OF THE NOVOBIBEEVO OCCURRENCE OF RADON-RICH WATERS
The relevance of the investigation is in obtaining the first isotope-geochemical data on natural waters and embedding rocks at the Novobibeevo occurrence of radon-rich waters.Goal: to study the features of the chemical composition of natural waters and water-bearing rocks and to obtain the first data on the activity of 222Rn and on the isotope composition: δD, δ18O, δ13С.Methods. Laboratory investigation of chemical composition by means of tritrimetry, ion chromatography, mass spectrometry with inductively coupled plasma was carried out in Basic Research Laboratory of Hydrogeochemistry at the School of Earth Sciences and Engineering of the Tomsk Polytechnic University. Determination of a set of characteristics - δD, δ18O, δ13СDIC waters and dissolved inorganic carbon (DIC) - was carried out in the Shared Equipment Center at the Institute of Geology and Mineralogy SB RAS using an Isotope Ratio Mass Spectrometer FinniganTM MAT 253, equipped with the attachments for sample preparation H/Device (to determined δD) and GasBench II (to determine δ18O and δ13СDIC). The concentration of 222Rn in water samples was measured with the Alfarad Plyus complex at the Laboratory of Hydrogeology of the Sedimentary Basins of Siberia of the IPGG SB RAS. Geophysical studies were carried out using the electrical exploration equipment Skala-48 with 48 electrodes and a 5 m step between them, according to the Schlumberger electrical exploration scheme. Data separation into uniform geochemical entities was performed using the coefficients Са/Na, Са/Mg, Ca/Si, Mg/Si,𝑖Na/Si. To reveal the degrees of chemical element concentration in natural waters, we calculated the concentrating coefficients = 𝑚𝑥,𝑛𝑥1and water migration coefficients (according to A.I. Perelman) = 𝑚𝑥∙100.𝑎∙𝑛𝑥Results. Integrated isotope-geochemical studies of radon-rich waters of the Novobibeevo occurrence have been carried out. Radon-rich waters (222Rn activity up to 429 Bq/dm3) are mainly characterized by HCO3 Mg-Ca composition with total mineralization (TDS) from 385 to 818 mg/dm3 and silicon content from 5,77 to 13,30 mg/dm3. The geochemical parameters of the environment vary from the reductive to oxidative setting with Eh from -81,2 to +212,7 mV; pH from 6,6 to 7,5, and O2dissolved from 1,62 to 7,89 mg/dm3. Goundwaters were divided into two geochemical groups: 1) fracture-vein waters of granitoids with the ratios Ca/Si 11,49; Mg/Si 248; Na/Si 1,25; Si/Na 0,87; Ca/Na 10,02; Ca/Mg 4,76; rNa/rCl 8,79, and SO4/Cl 4,35, and 2) waters of the zone of regional fracturing of granitoids under anthropogenic influence, with the ratios Ca/Si 16,3; Mg/Si 2,21; Na/Si 2,21; Si/Na 0,62; Ca/Na 9,84; Ca/Mg 9,95; rNa/rCl 0,89 and SO4/Cl 1,78. The composition of surface waters under the conditions of technogenic disturbance is SO4-HCO3 Na-Mg-Ca with TDS from 385 to 461 mg/dm3 and silicon content from 5,02 to 9,60 mg/dm3. The geochemical parameters of the environment correspond to the oxidative setting with Eh from+107,8 to +145,6 mV; pH from 7,8 to 8,6, and O2dissolved from 6,49 to 14,38 mg/dm3. Radon activity in the waters does not exceed 39 Bq/dm3. The surface waters of the Oyash river are characterized mainly by the HCO3 Na-Mg-Ca composition with TDS from 407 to 466 mg/dm3 and silicon content from 1,22 to 2,87 mg/dm3. The geochemical parameters of the environment correspond to the oxidative setting with Eh varying from +120,1 to +150,0 mV; pH from 8,4 to 8,5, and O2dissolved from 7,45 to 9,53 mg/dm3. Radon activity in the river water varies from 1 to 12 Bq/dm3. With an increase in total mineralization, the elements that are concentrated in radon-rich waters are Li, Cr, Zn, Br, Sr and U, which is accompanied by a decrease in the concentrations of B, V, As, Nb, Mo and Au. In the spectrum of element distribution, the highest content (mg/dm3) was consistently determined for Si up to 8,85, Mn up to 0,22, Fe up to 0,34, Sr up to 0,77, and Ba up to 0,13, because water-bearing rocks are represented by biotite granites, porphyry-like and olivine dolerites. The elements accumulated in waters to a higher extent are Br, I, Se, Te, Re and U. The stable isotope composition (δD values varying from -139,4 to -112,5 ‰ and δ18O values varying from -18,9 to -14,4 ‰) of waters and position of experimental points on the (δD vs δ18O)-plot indicating the meteoric origin of all the studied waters. The obtained δ13CDIC values vary from -14,2 to -10,0 ‰, with DIC content from 3,4 to 8,7 mmol/L. The main source of DIC is soil carbon dioxide of the mixed composition.