Three-Dimensional Inversion of AEM Data for Conductivity and Chargeability in the Mpatasie Area, Ghana

Interest in incorporating induced polarization (IP) effects into airborne electromagnetic (AEM) data interpretation has been steadily increasing. Until recently, however, the inversion of AEM data for both resistivity and conductivity has been predominately done using 1D models, where the subsurface is assumed to consist of horizontal layers at each transmitter-receiver location. This method shares the same drawbacks as conventional 1D conductivity inversion, including distorting 3D targets and the inability to use in the inline field component.

To address these limitations, we have developed a fast and robust 3D inversion technique for airborne EM data modeling and inversion that accounts for both electromagnetic induction and IP effects—capturing the full physical behavior of EM responses. Our modeling and inversion framework employs a hybrid approach that combines full 3D finite difference (FD) and integral equation (IE) methods.

In the presented case study, the conventional 1D inversion did not recover the chargeability anomaly associated with the known gold mineralization, while 3D inversion clearly identified this anomaly. Performing a full 3D inversion that incorporates both EM and IP effects enhances the value of airborne geophysical surveys in mineral exploration by delivering improved conductivity models and valuable additional information in the form of chargeability.