The Drybones Kimberlite: a case study of VTEM and ZTEM airborne EM results

Abstract

Two airborne EM surveys were conducted over the Drybones Kimberlite by Geotech Ltd. A VTEM helicopter time domain EM survey flown in 2005 is compared to a ZTEM helicopter tipper AFMAG EM survey flown in 2009. Both surveys detect anomalous responses over the pipe, however according to conductivity-depth transforms and skin-depth estimates, supported by 3D modeling, it seems unlikely that VTEM response is representative of the actual kimberlite, buried more than 100 meters underneath the conductive sediments. It appears that the consolidated kimberlite might be too resistive to be differentiated from granodiorites using conventional TEM methods. On the other hand the ZTEM response appears to be able to differentiate between the diatreme (consolidated kimberlite) and the host rock, lying below the conductive blanket.