The activity concentrations of potassium, uranium and thorium in minerals and soil samples from a mining site in Ibadan, Southwestern Nigeria were measured using gamma ray spectroscopy method. Effective dose per annum has been calculated from the activity concentrations of dominant gamma-emitting natural radionuclides, potassium, uranium and thorium. Samples collected include minerals (beryl, quartz and feldspar), soil samples from the mining pits, heaps and undisturbed land around the mining site. The activity concentrations of 40K, 238U and 232Th, respectively in Bq kg-1 in the mineral samples were as follows: 1985 ± 16, 4.8 ± 0.9 and 11.8 ± 5.8 for beryl sample, 115.1 ± 27.9, 5.0 ± 1.3 and 6.3 ± 5.0 for feldspar samples and 1421 ± 122, <4.8 and 20.1 ± 3.5 for quartz samples. For the soil samples, the mean activity concentrations of 40K, 238U and 232Th, respectively, were 314.2 ± 5.7, 27.7 ± 2.6 and 11.5 ± 5.9 Bq kg-1 for soil samples from the pits and 278.1 ± 5.4, 21.1 ± 2.0 and 15.3 ± 7.5 Bq kg-1 for soil samples from heaps. The mean activity concentrations of soil samples from the undisturbed land around the mining site were 194.3 ± 25.2, 14.5 ± 5.1 and 13.3 ± 5.9 Bq kg-1 for 40K, 238U and 232Th, respectively. The effective dose to which the miners are exposed according to exposure scenarios were calculated as 89.9 µSv y-1 for digging and handling of soil and mineral samples in the pit and 63.6 µSv y-1 for handling of soil and mineral samples at the heaps.