Geology and geochemistry of regolith carbonate accumulations of the southwestern Curnamona Province, SA: Implications for mineral exploration

Abstract

Although regolith carbonate accumulations (RCAs) have been extensively used in mineral exploration programs in the regolith-dominated terrains of the Yilgarn and Gawler Cratons, their use has so far been limited within the Curnamona Province, SA. This study shows how the detailed characterisation of RCAs in the southwestern Curnamona Province enhances their use in mineral exploration programs at the regional to prospect scales. A regional RCA distribution map for the study area shows that RCAs are generally widespread, although certain RCA morphological facies are dominant in different parts of the landscape, and in some areas RCAs are absent or at best a very minor component of the regolith. A dataset of whole rock geochemical assays of RCAs provides the basis of graphical presentations and geochemical maps that highlight the chemical characteristics of RCAs proximal to areas of known Au mineralisation in contrast to more distal samples. Several Au pathfinder elements in RCA assays were found to include As, W, Bi, and Mo, and greatly assist in further anomaly definition when used in conjunction with Au assays. Major element composition (e.g. Ca, Mg, Fe) showed little relationship to local landform setting, however, landscape setting appears to be a more important control on Au assay results both at the regional and prospect scales. Gold distribution in the area was independent of the presence of major elements such as calcium and magnesium. Microprobe analysis showed that Au was rare and invisible at the resolution of the analysis and existed in the calcium carbonate matrix as well as in detrital material. The composition of the underlying rock lithologies was also compared to the whole rock chemistry of the RCAs and showed the possibilities of this technique to aid geological mapping in regolith-dominated terrains and to assist in locating mineralised systems.