Известия Томского политехнического университета: Инжиниринг георесурсов (Mar 2021)
ISOTOPE GEOCHEMICAL FEATURES OF OCCURRENCE OF LOW-RADON WATERS «INSKIE SPRINGS» (SOUTH-WESTERN SIBERIA)
Abstract
The relevance of the research lies in obtaining the first isotope-geochemical data on natural waters and host rocks of the «Inskie springs» occurrence of low-radon waters. The aim of the research is to study the peculiarities of chemical composition of natural waters and water-bearing rocks and obtain the first information on the total ά- and β-activity of natural waters, the activity of 222Rn and the isotopic composition of δD, δ18O, δ13С, 234U, 238U, 226Ra and 228Ra. Methods. Sampling was carried out in accordance with generally accepted techniques. Laboratory study of the chemical composition by titrimetry, ion chromatography, inductively coupled plasma mass spectrometry was carried out at the Problem Research Laboratory of Hydrogeochemistry of the TPU School of Natural Resources. The analysis of the complex of isotopic ratios δD, δ18O, δ13СDIC of waters and dissolved inorganic carbon was carried out at the Center for Collective Use of the IGM SB RAS using the Isotope Ratio Mass Spectrometer FinniganTM MAT 253. Data on the total ά- and β-activity of natural waters, as well as the activities of 234U, 238U, 226Ra и 228Ra were obtained using gamma and alpha spectrometry (after preliminary radiochemical sample preparation). Results. In 2019, 35 km from Novosibirsk, far from the known granite massifs, the «Inskie springs» occurrence of low-radon waters was discovered, referring to the waters of the regional fracture zone. The work presents the first results of their geochemical studies. The waters are moderately fresh HCO3 Mg-Ca with a total mineralization from 389 to 536 mg/dm3 with a silicon content of 4,14–8,61 mg/dm3. They are characterized by pH from neutral to slightly alkaline (7,1 – 8,4), oxidative geochemical environment with Eh +205,3 –+231,8 mV and O2dissolved content of 6,24–12,26 mg/dm3. The activity of 222Rn varies in the range of 7–149 Bq/dm3; contents: 238U from 2,83∙10–3 to 4,13∙10–3 mg/dm3 and 232Th from 2,39∙10–6 to 1,16∙10–5 mg/dm3. According to the isotopic composition, the origin of water is infiltration. The range of δ18O values in waters varies from –17,1 to –16,7 ‰ with δD values from –128,4 to –126,2 ‰ and δ13C variation is in the range of –13,1 to –10,3 ‰. The host rocks are dark gray (to black) shales, sometimes gray, with a small admixture of silty and sandy-silty material. The isotopic composition of calcite in the host rocks is characterized by similar values: δ13C varies from –3,1 to –2,7 ‰, δ18O – from 17,2 to 18,4 ‰. Weathered clay shales are characterized by lower contents of δ13C (up to –11,0 ‰) and δ18O (up to 13,9 ‰). Also, according to the results of geochemical studies, these samples are characterized by a significant decrease in the content of all trace elements (except for U), which indicates an active interaction of waters with the host rocks.
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