Superparamagnetic effects discrimination in VTEM™ data of Greenland using multiple criteria and predictive approaches

Superparamagnetic (SPM) effects caused by the viscous magnetic properties of single-domain nanoscale particles (magnetite) have been observed in VTEM™ data acquired over the Maniitsoq project area located in southwestern Greenland. These SPM effects, which constitute a major geological noise, manifest themselves as slowly decaying EM responses at late times yielding elevated time constant values that can be misinterpreted to be caused by strong conductors such as Ni-sulphide mineralized bodies. Therefore, their identification and discrimination from conductive sources response is crucial before any follow-up actions. In this paper, we describe the effectiveness of an innovative dual EM receiver for attenuating SPM effects, the use of a robust multi-criteria discrimination approach and an enhanced predictive technique for identifying and discriminating the SPM effects from the conductive sources response observed in VTEM™ data of Greenland. The proposed approach applied to the airborne EM data collected between 2012 and 2015 has allowed classifying approximately 50% of anomalies as SPM effects, thus aiding in a more reliable prioritization of non-SPM related EM anomalies beginning in 2015.