In Wajrakarur Kimberlite Field in Dharwar Craton, south India, there are more than 100 Proterozoic kimberlite pipes and some of the world famous diamonds like Kohinoor, Nizam, Orloff, etc. were won from this field. The top regions of many of these kimberlites are weathered and altered and have the presence of clayey minerals, thus providing good targets for electrical and EM exploration. As kimberlites outcrop in a limited area, the weathered top material acts as a localized 3D conductor with confined spatial distribution. Highly resistive Archaean granitic gneiss host the kimberlites and the geological setting is ideal for the application of various electrical and EM methods. Depending on the availability of equipment, different electrical and EM surveys were carried out over a long period stretching more than a decade to study some of these kimberlites. Here a comparison of the performance of the following methods is presented: electrical resistivity tomography (ERT), frequency or time-domain electromagnetic (FEM or TEM) surveys, VLF or Radio MT surveys, etc. Suitability of a particular method in delineating such 3-D conductors critically depends on factors like scale and cost of the survey, available time-frame, required details on the subsurface, availability of survey space and logistic constraints, topography, habitation, vegetation, ambient electromagnetic noise, interpretational rigor, etc. Choice of the most appropriate method thus becomes important in efficiently procuring the desired information optimally. The results are expected to be useful in optimizing survey strategy not only for kimberlites but for a variety of mining and urban problems requiring mapping of 3-D conductors.


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