Airborne EM for mine infrastructure planning

Abstract

Airborne electromagnetic (AEM) surveys with near-surface vertical resolution provide rapid and comprehensive coverage of a mine site ahead of infrastructure planning. In environments of sufficient electrical conductivity contrast, the data will map variations in the depth to bedrock, providing guidance for expected excavation depths for solid building foundations, or mine pre-strip volumes. Continuous coverage overcomes the severe areal limitation of relying only on drilling and test pits. An AEM survey in northern Finland illustrates the success of this approach for guiding the placement of a mine crusher and related infrastructure. The cost of the EM data collection and interpretation is insignificant in comparison to the US$300 million capital cost of the mine infrastructure. This environment of shallow glacial cover challenges the limits of AEM resolution, yet analysis of subsequently collected three-dimensional (3D) surface seismic data and actual pre-strip excavation depths reinforces the predictive, but qualitative, mapping capability of the AEM. It also highlights the need to tune the modelling via petrophysics for the specific goal of the investigation, and exposes the limitations of visual drill core logging.

In environments of suitable conductivity contrast, airborne electromagnetic surveys can map variations in the depth to bedrock for mine infrastructure planning. A survey in northern Finland illustrates the success of this approach for guiding the placement of a mine crusher and related infrastructure.

Key words::

• airborne electromagnetics, mine infrastructure, overburden mapping, seismic tomography.

Acknowledgements

Niels Bøie Christensen and SkyTEM developed and ran the statistical EM inversions that were essential for advancing the reliability of shallow mapping. Ari Tryggvason and Alireza Malehmir at Uppsala University supplied the seismic tomography modelling.