A new set of magnetic field derivatives for mapping mineral prospects

Abstract

A powerful new set of magnetic derivatives is reported, based on the Tilt derivative and its Total Horizontal derivative, They can be used to map geological structures, magnetic fabric, lineaments and depths more effectively than other commonly used derivatives. The methods described are similar to the local phase and local wavenumber but are formulated differently to make them easier to use in profile- and grid-based methods. This contribution reveals new insights into why the Tilt derivative is better suited to mapping structure, due to its ability to (a) act as an effective AGC (Automatic Gain Control) filter, (b) out-perform the vertical derivative in mapping the spatial extent of bodies; and (c) map edges of bodies when applied to Reduced to the Pole (RTP) or Equator (RTE) magnetic fields by using the anomaly zero crossings. The Total Horizontal derivative of the Tilt derivative is independent of inclination of the geomagnetic field and generates maximum values over the edges of bodies. Its negative reciprocal provides depth estimates which can be used to estimate depth to sources over large areas, thus allowing a rapid estimation of whether or not mineralised structures are recoverable. These derivative methods have been applied to re-evaluating the Erindi gold prospect in Namibia using the recently acquired national high-resolution aeromagnetic data. All map images used in this paper have been generated using GETgridTM.