ABSTRACT
Application of the electromagnetic (EM) method in mineral exploration has been quite extensive and successful. In mineral exploration targets are mostly metallic ore bodies which are highly conductive, generally occurring in a very low conductivity (high resistivity) host rock. In hard rock groundwater exploration a major difference is in the range of conductivities of the targets and in conductivity contrasts with the host. The freshwater bearing weathered and fractured zone targets have much less conductivity as well as less contrast with the host medium. According to Kaikkonen (1979) for a good conductor, generally the ratio of conductivity of the conductor to that of the host medium should be more than 100. As such, fractured zones are not good conductors. The EM method is, however, in use for groundwater exploration in hard rock over several decades and has been successful in many areas. It has been used to delineate saturated weathered and fractured zones and select sites for water well drilling. The EMmethod is applied in frequency domain (FEM) as well as Time domain or Transient (TEM) with controlled source. It includes the very low frequency (VLF) method also which uses higher frequencies and a remote source. The FEM and VLF profiling are quite common for reconnaissance and to identify groundwater priority areas in hard rock. The applications of EM methods have been on the ground, in boreholes as well as airborne.
