Gold mobility within dune systems on the Barns property, Wudinna, South Australia: a partial extraction approach

Abstract

Regolith carbonate is an established sampling medium in Au exploration. It has a demonstrated correlation with Au content in south western Australia and was the prime indicator in the discovery of the Barns Au prospect Eyre Peninsula, South Australia. Whole rock ICP-MS, AAS and XRF analyses on samples from regolith drill cores and a trench cut into an aeolian sand dune on the Barns prospect established a correlation of Au content (≤17 ppb) with Ca, K, Al and Mg. XRD whole rock and mineral-separate analyses identified calcite, smectite and ankerite/dolomite as the main authigenic mineral phases present in the dune sand. The range of Sr isotope ratios of regolith carbonate (87Sr/86Sr = 0.716234±16) and bedrock (87Sr/86Sr = 0.731205±15) samples and their systematic variation imply that the Sr (and Ca) in the authigenic minerals was derived from a combination of surface (87Sr/86SrSMOW = 0.709) and bedrock sources (87Sr/86Sr = 0.731205±15). Sequential extraction designed to determine gold fractionation between the authigenic mineral phases showed that Au is most prominently extracted from a Fe-Mn oxide phase while dissolution of carbonate does not necessarily mobilise the Au.