Chetdin Radon Anomaly (Komi Republic): Localization and Study

When studying the fault tectonics of the Vychegodskii trough, we detected an area of high concentrations of soil radon, confined to the zone of the Vychegda–Lokchim fault. To localize the radon anomaly, we carried measurements of the volumetric radon activity out over a network of observation points. Air sampling at each point was performed from the wellhead with a depth of 0.5 m and a diameter of 0.1 m. Based on the data obtained, an intense radon anomaly was contoured. At different times, the anomaly changed in the size, shape, and intensity, but its center always remained fixed. According to areal observations, in the central part of the 2 × 2-km anomaly, the radon concentration reached 3800–4800 Bq/m³. The results of continuous daily monitoring in the center of the anomaly showed that the of radon concentration is subject to daily dynamics, which directly depends on meteorological parameters, namely on temperature and humidity. At night, with a decrease in temperature and an increase in air humidity, the level of radon increased to 6000–8000 Bq/m³ on average, in rare cases up to 10 000–12 000 Bq/m³. In the daytime, with an increase in temperature, a decrease in the volumetric radon activity was noted. In addition to the daily dynamics, seasonal variability of the radon field was observed. In autumn, the radon concentration is lower than in summer, which is associated with short-term precipitation and, as a result, the filling of the pore space with water. The Archean–Early Proterozoic basement composed of gneisses, amphibolites, quartzites, and migmatites at a depth of 2 km is considered as the main source of radon. Due to the fact that the anomaly is located in the zone controlled by the Vychegda–Lokchim fault, the latter is considered the main pathway for fluid transport to the surface.