Identifying structural complexity in aeromagnetic data: An image analysis approach to greenfields gold exploration

Abstract

Aeromagnetic data is important for the exploration of gold and other hydrothermal deposits because geologically favourable environments are associated with changes in rock magnetism. For example, Archean orogenic gold mineralisation is known to be present in areas of structural complexity near major shear-zones that form conduits for mineralising fluids. Potential fluid pathways such as shear zones and faults are often associated with magnetite destructive alteration resulting in linear negative anomalies in magnetic data. Here, we present a new image analysis method that identifies geological structural complexity using lineaments automatically mapped within magnetic data. This quantitative analysis is efficient and self consistent in dealing with large volumes of data, and is suitable as a first-pass ground selection tool for orogenic gold exploration in greenfield terrains.Using regional aeromagnetic data, our method firstly identifies lineaments as a reliable indicator of geological structures, exploiting a combination of texture analysis and contrast invariant ridge detection to find laterally continuous textural ridges. Using the detected lineaments, two scenarios of local structural complexity are explored: feature intersection density based on the number of faults intersections and splays; and feature orientation diversity representing deviations of strike of lower order faults and ductile shear zones. The local structural complexity is visualised using heat maps that highlight the regions of structural complexity.The method has been tested using aeromagnetic data from the Archean Eastern Goldfields Superterrane of the Yilgarn Craton in Western Australia and a region from the Archean Abitibi greenstone belt in the Superior Craton, Ontario, Canada. Both cratons are mature exploration areas where granite–greenstone terrains host numerous orogenic gold deposits. The regions selected by the proposed system as most structurally complex, and hence prospective, correlate with the known gold deposits in these areas.