Audio-magnetotellurics (AMT) for steeply-dipping mineral targets: Importance of multicomponent measurements at each site

Steeply-dipping mineralized bodies present a particular problem for audio-magnetotelluric (AMT) exploration. Such targets have little observable effect on currents flowing perpendicular to their dominant strike, thus TM-mode AMT data are not useful for target detection or delineation. The TE-mode and vertical-field transfer function data do detect such targets, and appropriately-designed surveys can define their geometries. The anomalous responses due to such targets are greater in the magnetic fields than in the electric fields. Conducting overburden suppresses the high frequency response, moving the anomaly maxima to lower and lower frequency with increasing overburden conductance. For optimal resolution of target geometries, all five AMT components must be measured at each and every site.