Integrated Geophysical Survey of Lower Benue Trough, Nigeria, Using Airborne Radiometric and Gravity Data

The airborne radiometric and gravity data sheets of Agana, Gboko, Oturkpo, and Makurdiareas were interpreted to address the following objectives: estimating the depth to the basement (sedimentary thickness), determining the density contrast and the type of mineralization prevalent in the area, determining the radiometric mineralization content of potassium, uranium, and thorium (K, U, and Th) and delineating areas of radiometric anomalies. The data were grided and minimum curvature was applied to produce radiometric maps of potassium, uranium, thorium, radiometric ratio maps, and ternary maps. The three radioelements vary in concentrations systematically with one another, thus maintaining average constant ratios among them in all rock types. The analysis of radiometric data revealed that the thorium abundance compared with the standard radiometric table are related to the presence of sedimentary rocks such as limestone and clay mostly in the Makurdi area, and sandstone in the Gboko area. In contrast, the Oturkpo area with high concentrations of Thorium abundance (above 17.5 ppm) is possibly sedimentary rocks. The low concentration of K abundance is dominant in the northern part of the Agana area with the presence of igneous rocks while the high concentration of K abundance is dominant in the Makurdi area which are likely sedimentary rocks. The source parameter imaging depthranges from -392.7 to -5159.5 m indicating the depth of potential field sources or estimated depth to the basement (sedimentary thickness) while the Euler deconvolution ranges from 929.1 to -4442.1 m indicating the nature and corresponding depths of the geologic sources. The forward and inverse modeling employed the trialand-error method for the modeled profiles P1, P2, P3, and P4, with respective depths of -1706, -3702, -2451, and -1146m. The density values were 2.51, 2.19, 2.62 and 2.53g/cmᵌ. The result from the forward and inverse modeling analysis indicated the presence of rock-bearing minerals like granite, limestone, shale, clay, and sandstone.Therefore, the research area has identified rock-bearing mineral deposits that could be utilized as raw material(s) by numerous companies and industries in Nigeria. The maximum sedimentary thickness of 4907.9m obtained indicates the possibility of hydrocarbon accumulation and exploration in the area.