Sequential 3D inversion strategy of airborne geophysical survey data for exploration of ore mineral deposits overlapped by layers with heterogeneous conductivity and magnetic susceptibility

We present a sequential 3D inversion strategy for airborne electromagnetic and magnetic survey data when searching for areas characterized by high values of conductivity and magnetic susceptibility, in a situation where these are overlapped by layers with heterogeneous conductivity and magnetic susceptibility. We explore the possibility of obtaining equivalent models for magnetic survey data (i.e. models that are quite different from each other but give the same data responses). It is shown that for relatively deep bodies overlapped by heterogeneous (in magnetic properties) layers, only an upper estimate of their magnetic susceptibility is possible. A sequential 3D inversion strategy of electromagnetic (EM) and magnetic data is proposed. An important component of this strategy is a two-stage 3D EM data inversion, which allows the high-precision reconstruction of the geometry and depth of local conductive bodies underlying heterogeneous conductivity layers. The final stage of the strategy is to determine whether the discovered local bodies may have enhanced magnetic properties. To test the proposed approach, we use data from an airborne geophysical survey performed in the Creighton area (Canada) in search for polymetallic ores. The sequential 3D inversion is carried out for an airborne electromagnetic survey dataset and two magnetic survey datasets at different flying height levels. Comparison with drilling data indicates that the proposed sequential 3D inversion strategy allows not only identification of prospective areas, but also improves planning of well drilling trajectories.