Aeroradiospectrometry in the spatial formation characterization of Ogun State, south-western, Nigeria

Abstract

In this study, aeroradiospectrometric data sets of Ogun State, Latitudes (6.2° to 7.8° N) and Longitudes (3.0° to 5.0° E), Nigeria were analyzed for lithological characterization. The data used comprised of Total count (TC), Uranium (U), Potassium (K) and Thorium (Th). The major objectives of this study are to characterize and identify the anomalies associated with various Interpreted Radiometric Lithological (IRL) units with respect to the three radioelements as well as Total count. The lithologies of the study area were described by three formations (basement, weathered basement and sediment), from which forty- seven IRL units were deduced. The study made use of the geological map in conjunction with the petrographic map as a tool to examine the three formation groups. The Interpreted Radiometric Lithologic (IRL) units in each formation group were subjected to the inferential test to examine the homogeneity in the total count of various rock units by adopting T-test and F-test. Multivariate statistical analysis was also conducted on the radioactive data to ascertain the radioactive variable that was associated with the same bedrock source. The results obtained showed that the anomalous responses of radiometric parameters to bedrock units were observed to be more prevalent in the Basement (B) and Weathered Basement group (WB). Majority of the radioelements deposition of 67.5%, 48.6% and 48.5% for potassium, thorium, and uranium respectively; were found in sediment (S) formation. This may be attributed to geomorphic activity such as weathering, leaching, and intrusion. Inferential test results showed that up to 26 and 32 pairs in the basement while 3 and 5 pairs in weathered basement were found to be F-test and T-test statistically and aeroradiometrically homogeneous at 5% significant level. Of the 13 pairs identified for the two tests in sediment formation, only 5 pairs were found to be uniquely homogenous. The results also revealed that most of the formation groups have their uranium and thorium values above the world average. Multivariate analysis revealed thorium and uranium as the major constituent of the total count. This study has therefore successfully characterized and identified the formations associated with anomalous response in bedrock units of the study area.