The present study focuses on the distribution of natural radionuclides and the determination of radioelement favorability in the Nugrus mylonite rock. The radionuclide contents were measured with a NaI(Tl) detector. The concentrations of U, Th, Ra (in terms of eU), and K in the mylonite studied range from 27 to 247 ppm, from 96 to 377 ppm, from 11 to 166 ppm, and from 1.14 to 3.12%, with the averages of 100 ppm, 201 ppm, 55 ppm, and 2.1%, respectively. The interelement relationships indicate that the radioelement distribution is not only magmatic but also hydrothermal. Variations of migration parameters for uranium indicate fluctuations in physicochemical conditions that lead to U accumulation and leaching processes, which are confirmed by increments and decrements in uranium concentrations. The examined samples demonstrate disequilibrium, with eU/Ra (eU) ranging from 1.32 to 3.26, with an average of 1.95, which suggests uranium addition. Uranium, thorium, and potassium favorability indices of the investigated mylonite rocks indicate moderate favorability of these rocks for uranium and thorium and high favorability for potassium. The F-parameter illustrates the presence of different stages of alterations. Mineralogical investigation indicates the presence of such radioactive minerals as thorite and Uranothorite, of Nb–Ta minerals (columbite and ishikawite), and of zircon and xenotime.