Interpretation of Magnetics Using Magnetic Property Data—Case Histories from Australia

Although magnetics is the most widely used geophysical method in hard rock mineral exploration, interpretation of the data suffers from inherent non-uniqueness. Ignorance of the magnetic properties of magnetic rock units may lead to faulty interpretation, with expensive consequences. Several examples of interpretations which have been assisted by magnetic property measurements will be presented. Applications include siting drill holes in order to maximise the probability of intersecting the target and testing whether intersected material explains the anomaly. Factors which may have to be considered include the remanence direction and Koenigsberger ratio (particularly for volcanics, basic plutonic rocks and pyrrhotite-bearing rocks), the age of remanence relative to folding, and susceptibility anisotropy (particularly for banded-iron formations and certain orebodies). Palaeomagnetic cleaning and data analysis techniques are essential for extracting maximum information from samples.