Radiometric Studies of Magnetic Anomalies in the Middle Timan

The article presents the results of an express radon survey on the territory of the Timan Ridge. The study objects were kimberlite pipes and local anomalies of the Middle Timan similar to them in the magnetic field. In the course of the study, the maps of the magnetic field of different scales were used to identify and sort magnetic anomalies similar to those of pipe-like bodies. Magnetic anomalies were distinguished using such qualitative characteristics as location, shape, size, sign, intensity, and gradient. Magnetometric and radon surveys were carried out to study the explosion pipes and magnetic anomalies. The magnetometric observations were conducted along a profile network in order to detect and determine the contour of the anomaly. The method of radiometric studies consisted in crossing the magnetic anomaly with a profile passing through three observation points—center, edge, and beyond the contour. The radiometric measurements within the Umbinskaya, Srednenskaya, Vodorazdelnaya and the Verkhnemezenskaya series of explosion pipes revealed the elevated values of volumetric radon activity (VRA) above the pipes. Thus, radon survey can be used as an additional search criterion included in the complex of geophysical works. Based on morphological variations in the magnetic field, several sites were distinguished in different tectonic structures of Middle Timan, within which radiometric studies of 68 magnetic anomalies were carried out. Moreover, 23 of the considered anomalies were characterized by the elevated VRA values. These anomalies, in turn, were divided into two promising categories that are of interest for further study. The first category includes anomalies with VRA values more than 1000 Bq/m³, the second category includes anomalies with VRA values from 450 to 1000 Bq/m³. This scatter of VRA values is associated, first of all, with the geological and tectonic position of the structure. The identified promising anomalies are very close in morphology to the pipe type, and geologically they can be caused by small intrusive bodies or explosion pipes. However, not only explosion pipes can be characterized by high VRA values, but this is also typical of individual magnetic anomalies caused by dikes and sills of basic, ultrabasic, and alkaline composition, as well as rocks enriched in radioelements. When setting tasks for studying magnetic anomalies aimed at searching for explosion pipes, the first step is to sort out such anomalies according to their location in the studied tectonic structures, morphology, and intensity.