SkyTEM helicopter transient electromagnetic surveys of tailings dams

Abstract

The SkyTEM helicopter transient electromagnetic system has been used to map the environs of a number of tailings dams in Australia. Residues from mining and industrial processes typically have high conductivity and can be effectively mapped using airborne electromagnetic methods. Airborne surveys allow complete coverage of tailings sites otherwise inaccessible to surface geophysics. The SkyTEM system is capable of operating in a dual moment mode, in which measurements with low transmitter current, fast switch off and early-time sampling are interleaved with those performed using a high transmitter moment and measurements to late delay times. This provides high near-surface resolution and the capability to penetrate through thick accumulations of highly-conductive tailings. Surveys around tailings sites are characterised by significant surface infrastructure, which presents hazards to airborne operations and results in numerous cultural electromagnetic anomalies unrelated to the subsurface. These obstacles can be overcome with appropriate survey planning and careful editing of the airborne data prior to interpretation. A brief field example from a coal fly-ash dam in Australia illustrates the ability of the SkyTEM system to provide detailed hydrogeophysical information. Useful data were obtained even in close proximity to metallic infrastructure and high-voltage power lines. The SkyTEM survey was able to identify several zones of anomalous conductivity at points downstream of the embankment, which are a priority for future ground follow-up.