3D inversion of SPECTREM and ZTEM data from the Pebble Cu-Au-Mo porphyry deposit, Alaska

Abstract

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.