On the scope and limitations of the electromagnetic method in groundwater prospecting in a Precambrian basement terrain - a Nigerian case study

Abstract

A pre-drilling, geophysical investigation for groundwater development in the Proterozoic basement of the northern central part of Kaduna State, Nigeria, involved the electromagnetic (EM) method. The amplitude of the EM conductivity measurements correlates more with the weathered layer conductivity than with the overburden thickness. The anomaly amplitude is a poor index of the overburden thickness. The prediction of groundwater yield from the EM conductivity amplitude is also not feasible as no dearly defined relationship is established between these parameters. Although shallow, water-bearing, unconfined fractures are easily delineated by the EM method, the method is not amenable to the mapping of confined fractures that are concealed beneath fresh and infinitely resistive basement rocks.