O.M. ALLIE

This study was carried out to investigate the occurrence and structural effects of bitumen in Agbabu community using integrated geophysical methods (aeromagnetic, aero-radiometric and electrical resistivity tomography (ERT). Two forms of datasets (Secondary and Primary) were used. These datasets provided useful information on the lithology and geological structures within the area. The geophysics data processing approach employed concentrated on enhancing the geophysical data quality and this aided in tracing accurate positioning of geological boundaries, the responses related to bituminous zone and geological structures that may be of vital economic importance The digitized geological map covering the study area was obtained for lithological information. The secondary datasets consist of an aeromagnetic and aero-radiometric basically for the reconnaissance study. Aeromagnetic and aero-radiometric map was obtained from the Nigerian Geological Survey Agency (NGSA) and processed using Oasis Montaj software to depict main lithology and structural features present in the Agbabu area. The primary data was acquired within the area suspected to have high potential for bitumen deposit using the wenner-schlumberger configuration. The potential difference produced was measured with the aid of PASI 16 GL-N Earth resistivity meter. The apparent resistivity
values obtained was processed using RES2DINV software which helped to automatically obtain the 2D inversion model of the subsurface. The results of aeromagnetic study show low TMI amplitude (-201.5 – 16.8nT) and high AS amplitude (0.053 – 0.172nT) at suspected bitumen deposit regions. The low TDR amplitude (- 1.4 to - 0.4nT) confirms a concealed basement depression hosting bitumen deposit. The 3D-Euler deconvolution helps to locate the sources of magnetic anomalies, it is deeper within the sedimentary terrain (841 – 1703m) and shallower (185 – 841m) within the basement. The interpretations of radiometric datasets revealed the spatial variation of potassium (K), thorium (Th) and uranium (U) radioelement concentrations as high as (0.6 – 2.5%), (7.9 – 28.0 ppm) and (1.9 – 5.1 ppm) respectively within the basement complex, but also low as (0.0 – 0.6%), (1.8 – 9.2ppm) and (0.3 – 1.9ppm) respectively within the sedimentary terrain. The ternary image shows very 16 low radiometric intensity that contained the bitumen structures, moderately high around lithological boundaries and concealed linear features reveal. This research has shown that the occurrence of bitumen was found between the depth of 13.4m and 9.93m for Traverses 1,2,3 and Traverses 4,5 respectively in 2- Dimensional electrical resistivity images which corroborated by boreholes with a depth of about 18m. The
results of this research indicated that bitumen has an average thickness of 11.67 m. The answers aid the exploitation of bitumen and made available for government and other relevant bodies in formulating policies for minerals development in the country. From the result of the coordinates of the airborne surveys, agreed perfectly with the values of Geophysical (ERT) traverses indicating the reliability of this type of joint geophysical investigation