An Overview of the ZTEM and AirMt Airborne Electromagnetic Systems: A Case Study from the Nebo-Babel Ni-Cu-PGE Deposit, West Musgrave, Western Australia

Abstract

To improve mineral exploration success, there is an industry-wide consensus on the need to increase the 'discovery space' by exploring under cover and to greater depths. Over the last decade, airborne electromagnetic (AEM) systems have evolved with ever higher moments, and sensor calibration and post-acquisition processing technologies have improved data quality signifi cantly. As an alternative to conventional AEM, the Z-axis Tipper Electromagnetic (ZTEM) and Airborne Magnetic Tensor (AirMt) systems were developed to measure the transfer functions of audio-frequency natural electromagnetic sources from airborne platforms. The ZTEM system measures tipper transfer functions, and the AirMt system measures the rotational invariant of the transfer functions. Ancillary data measured by both systems include radar altimeter, receiver altitude, GPS elevation, and total magnetic intensity. For both ZTEM and AirMt, data are typically measured from 30 Hz to 720 Hz, giving detection depths to 1 km or more, depending on the terrain conductivity. This makes it a practical method for mapping large-scale geological structures. This paper discusses technical specifi cations of both the ZTEM and AirMt systems, including data processing and interpretation. Both ZTEM and AirMt capitalise on Geotech's logistical and technical experience from its helicopter-borne Versatile Time-domain ElectroMagnetic (VTEM) system, which has been in commercial operation since 2002 with subsequent generational improvements. The fi rst commercial surveys for ZTEM were commissioned in 2006, and the fi rst commercial surveys for AirMt were commissioned in 2009. Presently, eight ZTEM systems and one AirMt system are in functional operation around the world. ZTEM and AirMt surveys have been fl own in Australia, North America, South America, Africa and the Middle East for Sedex, VMS, IOCG, Ni-Cu-PGE, porphyry, uranium and precious metal mineralisation systems for numerous major and junior exploration companies. In this paper, we present a case study for the 3D interpretation ZTEM and AirMt surveys fl own over the Nebo-Babel Ni-Cu-PGE deposit in Western Australia.