The application of multifrequency airborne electromagnetics to iron ore exploration

Abstract

Using helicopter-borne frequency domain electromagnetic (HEM) data to map magnetite has advantages over the magnetic method. It is independent of the earth's locally asymmetric inducing magnetic field, remanent magnetism, and magnetic anisotropy. It is also restricted to the notional "depth of exploration" of the HEM system, limiting detection to that which may be economically mined. A significant complication arises when interference between the magnetite polarisation and conductivity responses reduces the apparent magnetic content. This interference is significant over the conductive, magnetically polarisable ground common to the Hamersley Basin. The current procedures for magnetite mapping with HEM are reviewed. Both problems and successes of the method are highlighted using a case study as an example. Replacing the data transformation by an inversion increases the sensitivity of the method, but at the cost of enhancing noise.