Radiometric Survey as a Useful Tool in Geological Mapping of Western Nigeria

Gamma ray Spectrometer (DISA-300) and broadband gamma ray scintillometer (BGS-ISL) were used to evaluate the radiometric properties of rocks (Igneous, Sedimentary and Metamorphic) in parts of southwestern Nigeria. The study revealed that although the two instruments used recorded different gamma radiation value and the graphs generated by the instruments are quite similar. Based on the major peaks and troughs of the radioactivity graph, the different formations in the area were clearly delineated and these correspond approximately to the geological boundaries in the area. Lithologic characterization of the formations revealed that the concentration of radioactive elements in rock varies. Shale, clay and granites have the highest amount of gamma count (60-105) while amphibolites show the lowest gamma count (16-46). The gamma count is a function of the concentration of radioactive elements in the rock. The reading ranges from 65-85cps in the scintillometer while the spectrometer varies from 19.75-38.88cps. The difference in readings may be attributed to the higher sensitivity of the scintillometer to gamma radiation than the spectrometer. However, the two instruments display similar pattern of curves and good correlation.