Application of Very Low Frequency- Electromagnetic (VLF-EM) Method to Map Fractures/Conductive Zones in Auchi South western Nigeria.

Geophysical survey involving very low frequency electromagnetic technique was applied to investigate possible geologic features like fractured / conductive zones in Auchi and its environs in Edo state, Southwestern Nigeria. The study area is located within latitudes 7o05’ N.to 7o10’N. and longitudes 6o11’E to 6o22’E The geologic Formations outcroping in the area are mainly Ajali and Nsukka. Three profiles were taken along the roads from Auchi to Igara, Auchi to Fugar and Auchi to Uloke using Abem Wadi Terrameter. Plots of the profiles were carried out using computer software (Excel) and contouring using Surfer 10 to delineate the fractured/conductive zones. The values range from 0.3 to 22.5 Siemens. Areas of low conductivity values indicate highly massive resistive rocks while Areas of high conductivity indicates the sedimentary terrain/ host rock or mineralized zones. The area is sparsely (few) fractured. Along profile A, two fractured zones were identified with conductivity values of 7.6 to16.8 Siemens between 100m(7.146oN,6.195oE) to 400m (7.150oN, 6.200oE) and 420m to 460m with conductivity value range of 11.0 to 22.5 Siemens. For profile B, one fractured zone was identified and a stretch of massive intrusive from 7.099oN and 7.102oN and 6.357oE to 6.364oE, with conductivity range of 0.9 – 5.2 Siemens at points 400m and 520m – 1000m. Profile C has identifiable fractured zones at 900m – 1100m with conductivity of (35 – 50) Siemens. The intrusive/ host rock conductivity values of (0.3 – 8.7) Siemens located at 380m to 880m 7.156oN and 6.308oE, 1100m to 2000m, 7.148oN and 6.3295oE. A total of five conductive zones were observed.