Examination of an aeromagnetic anomaly over the Talisker Mine area on the southern Fleurieu Peninsula, South Australia

Abstract

A N-E striking elongate aeromagnetic anomaly is observed over the Talisker Mine area, on the southern Fleurieu Peninsula, which has character and amplitude similar to an anomaly observed at Delamere (several kilometres to the north) found to be caused by magnetic Brachina Formation. Geological and geophysical techniques have been used to determine if the rock type at Talisker is also magnetic Brachina Formation, why there is a gap between the two anomalies, and why the anomaly at Talisker ends near the south coast.

Geological mapping, microscopy and petrologic studies have been used in conjunction with local ground magnetic surveys and modelling procedures, to reveal magnetic Brachina Formation as the cause of the anomaly at Talisker. Mapping has shown the anomaly to be the result of a sliver of magnetic Brachina Formation caught up within a local zone of intense deformation that extends for at least 1500m across strike, and which outcrops on the coast. The Brachina Formation is sheared out against Cambrian Backstairs Passage Formation to the south, forming the southern end to the anomaly. To the north, the Brachina Formation suffered deeper erosion during Permian times, and is covered by a greater thickness of non-magnetic cover which causes the apparent gap in the aeromagnetic anomaly.