VLF anomalies at contacts between Precambrian rocks in southwestern Nigeria

Abstract

Four examples of very low frequency (VLF) electromagnetic (VLF-EM) anomalies within the Basement Complex in the Igbeti district, southwestern Nigeria, revealed that the method can be successfully used to map non-conductive mineral bodies like marble and quartzite as well as geological boundaries and faults. Rocks of extremely low conductivity were marked by very distinct VLF anomalies with varying magnitudes. The VLF anomalies are believed to be due to faults and water bearing fracture zones, possibly at moderate depth, at the contact of the rocks. A poorly known N-S trending fault traversing the western margin of the Igbeti marble was mapped and confirmed by the VLF survey. The results obtained over the marble indicate that the technique is cost-effective and particularly suitable for mapping such lithologies, especially where the geology is relatively simple.