Aeromagnetics as an aid to geological mapping—a case history from the Arunta Inlier, Northern Territory

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Abstract
Correlation of aeromagnetic and available geological information has allowed extrapolation of geological mapping between isolated basement outcrops in the Jervois Range area of the eastern Arunta Inlier. The superior resolution of computed vertical gradient, in comparison with total field data, aided the delineation of magnetic lithostratigraphic marker horizons, and the subsequent development of a detailed structural model through determination of basement structure and lithology. Rock types in the area include a multiply deformed sequence of metasediments and metavolcanics intruded by basic and acid igneous bodies. Economic concentrations of silver and base metals occur along intense linear magnetic highs associated with magnetite‐chlorite‐garnet host rocks, and the delineation of these host rocks was a primary objective of aeromagnetic interpretation. In situ and laboratory determinations of magnetic susceptibility and natural remanent magnetization (NRM) helped to constrain magnetic interpretation. Results indicate many rock types possess distinct magnetic properties, giving rise to characteristic magnetic signatures. The anomalous magnetic low associated with one intrusive, the Attutra Metagabbro, is due to remanence. This is the only rock type in the study area considered to have a well‐defined stable NRM. Magnetite and hematite are the dominant iron oxides within metasediments, whilst ilmenite and magnetite with minor hematite are associated with intrusive rocks. Detailed qualitative and quantitative aeromagnetic interpretation supports conclusions from geological mapping, indicating that the area has undergone three separate phases of deformation. The oldest (D1) produced a layer or bedding‐parallel schistosity, possibly a result of thrusting. Subsequent deformations resulted in isoclinal folding of the Jervois metamorphic sequence (D2), followed by gentle regional warping of these structures (D3). The magnetic method, as well as aiding the delineation of potentially ore‐bearing magnetite‐rich host rocks, may be capable of indirectly detecting ore bodies, as their size and shape are controlled by structures of the host rock which give rise to atypical, intense, elongate magnetic highs.