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This case study compares 3D inversion results from Spectrem Air?s SPECTREM 2000 fixed-wing timedomain airborne electromagnetic (AEM) system, and Geotech?s Z-axis Tipper Electromagnetic (ZTEM) airborne audio-frequency magnetics (AFMAG) system flown over the Pebble Cu-Au-Mo deposit in Alaska. Within the commonality of their physics, 3D inversions of both SPECTREM and ZTEM recover conductivity models consistent with each other and with the known geology. Both 3D inversions recover conductors coincident with alteration associated with both Pebble East and Pebble West. The 3D interpretation of both surveys has yielded improved the understanding of the geology, alteration and mineralization of the Pebble system. There are distinct practical advantages to the use of both SPECTREM and ZTEM, so we draw no recommendation on one system over the other. We do conclude however, that 3D inversions of AEM and ZTEM surveys add significant value to exploration.

To improve mineral exploration success, there is an accepted need to increase the ?discovery space? by exploring under cover and to greater depths using 3D geological modelling supported by multiple 3D geophysical inversions. To facilitate this approach, multi-sensor airborne platforms capable of simultaneously measuring electromagnetic, gravity, and magnetic data are now being deployed. The availability of data from such systems poses a significant challenge to the exploration geophysicist: How do you generate a shared earth model that satisfies all data? We address this with a case study from the Reid-Mahaffy test site in Ontario, demonstrating how multiple 3D inversions of MEGATEM time-domain electromagnetic, FALCON gravity gradiometry and TMI data can be analysed by the self-organizing maps (SOM) data mining approach to produce 3D pseudo-lithological models. The results of our analyses are shown to be in agreement with the known geology of the Reid-Mahaffy test site.