Soil air carbon dioxide (CO2) and oxygen (O2) measurements as a guide to oxidising sulphide have been assessed over areas of known mineralisation in a variety of geological and geographical settings. The rationale is that sulphide oxidation in the presence of water and oxygen will produce sulphuric acid which in turn will attack any carbonates present to produce CO2. Oxygen is consumed in the process. Both CO2 and O2 are easily measured to an acceptable accuracy in the field with portable equipment. Menninnie Dam prospect lies about 60 km north of Kimba, immediately south of the Gawler Ranges. High grade lead-zinc-silver mineralization occurs in steeply dipping metamorphosed carbonate and carbonate-bearing calc-silicate sequences of the Hutchison Group which are exposed in a window of Gawler Range Volcanics.