Exploration under regolith cover, and the problem of remanent magnetism: an example from the Tanami Au province

Abstract

Evidence of remanent magnetism was observed in aeromagnetic images fromThe Granites/Tanami Inlier in the Northern Territory. An investigation was undertaken to verify whether remanent magnetism existed, and if so, what mineral and/or system caused it. Alternating field demagnetisation and Curie Temperature analyses was employed to calculate the magnetic properties of whole rocks. Optical petrology and electron microscopy were then used to determine the minerals present and their chemical compositions. The two dominant magnetic minerals in this region are multidomain magnetite and monoclinic pyrrhotite, confirmed by petrological analysis. Chemical analysis determined the magnetite and pyrrhotite were pure with no substitution of elements. Alternating field demagnetisation and Curie Temperature analyses show monoclinic pyrrhotite holds the remanent magnetism, but has a low magnetic susceptibility. The study indicates there is remanent magnetism in the Tanami region. If there is inadequate understanding of magnetic data, misinterpretation of magnetic anomalies could occur.