Isotope-hydrogeochemical features of the Belokurikha field radon waters

Abstract

The purpose of the work is to carry out integrated isotope-geochemical studies of the mineral waters of the Belokurikha deposit. The methods of titrimetry, ion chromatography, inductively coupled plasma mass spectrometry (ICPMS) have been used in the laboratory investigation of the chemical composition of waters. The isotope composition of oxygen, hydrogen and carbon in dissolved carbon dioxide has been studied with the help of the Isotope Ratio Mass Spectrometer FinniganTM MAT 253 equipped with the attachments for sample preparation H/Device (to analyze the δD ratio) and GasBench II (to analyze δ18O and δ13СDIC ratios). There are two aquifers at the deposit. The first nonartesian aquifer comprises loose sediments of the Quaternary age. The second artesian aquifer includes the granites of the upper Paleozoic age with the different fracture degree: from monolith to loosened. Three groups of waters are distinguished on the basis of geochemical coefficients: fracture-vein waters bedded in weathered granites; groundwaters of the zone of rare earth mineralization and background composition; surface waters of the Belokurikha river. The isotope data on oxygen and hydrogen provide evidence that the production aquifers of the Belokurikha field are fed through the infiltration of meteoric waters, with the feeding shift to winter precipitation. The paper provides the first data of the integrated isotope-hydrogeochemical studies of nitric-siliceous low-radon thermal waters of the Belokurikha deposit. The composition of these waters is HCO3-SO4 Na and SO4-HCO3 Na with the total dissolved salts value ranging from 198 to 257 mg/dm3. The waters are characterized by alkaline pH of 8.6–9.6, silicon content ranging from 19.8 to 24.6 mg/dm3, and they are referred to the fracture-vein waters of the Upper Paleozoic granites. 222Rn activity is up to 359 Bq/dm3. The ratios of δD (from -126.9 to -102.7 ‰) and δ18O (from -17.5 to -14.2 ‰) in the studied waters indicate their atmospheric origin. The values of δ13СDIC vary from -9.7 to -25.6 ‰ and point to the biogenic origin of carbon.