GEOCHEMISTRY OF THE WATER-ROCK SYSTEM OF WEAK HYDRO-RADON OCCURRENCE «INSKIYE SPRINGS» (SOUTH OF WESTERN SIBERIA)

: Week hydro-radon occurrence «Inskiye springs» was discovered in 2019, 35 km from Novosibirsk, in area where are no granite massifs, and relates to the groundwaters of the regional fracturing zone. The first results of their geochemical studies are represented. It is established that groundwaters are moderately fresh with TDS from 389 to 536 mg/dm 3 , with Mg-Ca HCO 3 composition. Silicon content vary between 4.14-8.61 mg/dm 3 . They are characterized by pH from neutral to slightly alkaline (7.1 - 8.4), oxidative geochemical conditions with Eh +205.3 - +231.8 mV and the content of solved O 2 between 6.24 - 12.26 mg/dm 3 . The concentrations of 222 Rn range from 7 to 149 Bq/dm 3 , 238 U from 2.83∙10 -3 to 4.13∙10 -3 mg/dm 3 and 232 Th from 2.39∙10 -6 to 1.16∙10 -5 mg/dm 3 . Using the isotopic composition it was established an infiltration origin of groundwaters. The δ 18 O content in waters varies from -17.1 to -16.7 ‰, the δD content from -128.4 to -126.2 ‰ and δ 13 C from -13.1 to -10.3 ‰. The host rocks are clay shales of dark gray (to black), sometimes gray, with a small admixture of silt, sand and silt material. In the host rocks, the isotopic composition of the calcite is characterized by close values: δ 13 C varies from -3.1 to -2.7 ‰ and δ 18 O - from 17.2 to 18.4 ‰. The content of δ 13 C and δ 18 O in weathered shales decreases to -11.0 ‰ and 13.9, respectively. According to the results of geochemical studies, these samples are characterized by a significant decrease (several times) in the content of all impurity elements (except for uranium). This indicates the active manifestation of processes in the water - rock system.