Physical property measurements as an aid to magnetic interpretation in basement terrains

Abstract

lnterpretation of magnetic anomalies from the southwest Arunta, and Cloncurry, Precambrian basement complexes has been possible only with information on the geochemistry and magnetic properties of the outcropping rocks. The lithological descriptions provided by regional geological maps are not adequate for the purpose of interpretation, owing to the paucity of Precambrian outcrop and also because the magnetic properties of rocks generally are not related to the factors used to classify rock types. Analyses of rock samples from the southwest Arunta Block indicate that the magnetic properties depend in part on rock composition, but also on the degree of metamorphism and other geological processes which are not always reflected in lithological descriptions. Modelling of aeromagnetic data using the measured magnetic properties as a primary control has yielded a new solid geology interpretation of the region. Magnetic susceptibilities and densities measured on samples from the eastern edge of the Cloncurry Complex have been used to interpret aeromagnetic and gravity data over a part of the complex where geological mapping of the basement is precluded by a thin veneer of younger rocks and alluvium. Both lithology and structure of the buried rocks have been interpreted in this way.