Interpretation and field investigation of some aeromagnetic anomalies from the Abminga Area, South Australia

Abstract

Aeromagnetic surveying carried out in the Abminga area by Mines and Energy South Australia (MESA) and published in 1993 identified several groups of isolated magnetic anomalies which have a strong prima facie resemblance to kimberlite or lamproite diatreme fields. Aeromagnetic anomalies produced by diatremes are characterised as being generally of low amplitude, isolated, compact, di-polar, of short strike length and indicative of a shallow source. This paper compares data flown for diamond explorer Caldera Resources NL at 100 metre line spacing with the published 400 metre line spaced data. Modelling of several of the anomalies using an inversion algorithm gives very good fits to shallow pipe-like bodies with appreciable depth extent. Conventional field exploration techniques such as loaming have not been successful but floaters of ultramafic rocks collected at 3 anomaly sites have been petrographically identified as extremely weathered kimberlites. Chromite grains recovered from these carry up to 59% Cr2O3. Diamonds have not yet been recovered but active exploration is in progress. It is concluded that while most of the magnetic anomalies were successfully identified from the 400 metre line spaced data, useful modelling can only be done using more detailed data. Although positive identification of the source of these magnetic anomalies is still awaited they constitute some very intriguing exploration targets.