The geophysical signature of the Paleoproterozoic Menninnie Dam lead-zinc-silver prospect, South Australia

Abstract

The Menninnie Dam lead-zinc-silver prospect was discovered through follow-up of anomalies defined by an airborne magnetic survey flown as part of a programme to explore for Broken Hill type deposits in the Palaeoproterozoic rocks of the northern Eyre Peninsula, South Australia. Shallow reconnaissance drilling indicated the presence of base-metal mineralisation, and subsequent surface geophysical surveys, including moving- and fixed-loop TEM, gravity and ground magnetics, confirmed the presence of large magnetic and conductive sources. After drill testing, the magnetic sources were found to be banded iron formations, whilst the conductors were caused by a combination of clays and saline water, overlying deeply weathered massive sulphide zones. The regolith created major difficulties in data interpretation due to its highly conductive nature and the deep weathered profile across the mineralisation. Surface moving- and fixed-loop TEM surveys were used in an attempt to locate the source(s) of the strong conductivity anomaly, both in plan and in section. Neither method was clearly able to differentiate between the deeply weathered regolith and the underlying sulphide mineralisation.