Geological mapping with power line fields measured with MEGATEM data

As an experiment, we extracted the intensity of the EM fields at the power-line frequency from raw MEGATEM survey data. This was done to determine if additional geological information could be extracted from EM secondary fields due to power-lines. We selected a survey near Chibougamau, Quebec where there are many strong powerlines and some conductive features in an otherwise resistive environment. The estimated half-space apparent conductivity mapped the strong conductors, but gave poor information in the resistive areas. Better geological information was obtained in the resistive areas by imaging the powerline field amplitudes after removal of the long wavelength features. Correlations with known geology show that power line fields can help in geological interpretation.