The rationale of utilising soil air carbon dioxide and oxygen measurements as a guide to oxidising sulphide 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 can easily be measured to an acceptable accuracy in the field with portable equipment. The project aim is to test the technique over areas of known mineralisation in a variety of geological and geographical settings.