Geophysical exploration for heavy-mineral sands near Mindarie, South Australia

Abstract

An airborne magnetic and radiometric survey, conducted in the Mindarie district of South Australia, detected a large number of very weak linear magnetic features disguised by magnetic noise caused by iron oxides in surface sands and cultural features. Enhancement of the aeromagnetic data, to emphasise linear features striking parallel to known heavy-mineral strandlines, has led to the discovery of several new occurrences, notably, the Halidon deposit. Many linear magnetic features are still to be drill tested. In addition, airborne radiometric measurements were successful in detecting outcropping thorium-rich heavy-mineral deposits. In the Mindarie district, whilst some strandlines have weak magnetic signatures, this is not always the case. Rutile-, zircon- and monazite-rich placers having minor concentrations of ilmenite usually do not produce an observable magnetic response. Highly oxidised ilmenite-rich placers can also be non-magnetic. In such cases, strandlines of magnetic iron oxides can be used to target adjacent heavy-mineral deposits.