Biogeochemical expression of the 'Tomahawk' Au-in-calcrete anomaly, Tunkillia, Gawler Craton, South Australia

Abstract

The Tunkillia gold prospect hosts the world's largest (spatially) Au-in-calcrete anomaly, although its association with underlying mineralisation has been enigmatic. The Tunkillia gold prospect provides a difficult setting for mineral exploration. The area is dominated by dunefields which makes surficial exploration very complicated. Biogeochemical sampling is effective in almost all areas, is efficient and the costs involved are very low compared to other sampling mediums. Within the Tunkillia area are zones of higher Au-in-calcrete content, such as the 'Tomahawk' Au-in-calcrete anomaly zone. At 'Tomahawk', exploration drilling has failed to identify significant, underlying mineralisation within the anomaly. Biogeochemical samples were collected along seven transects in the Tunkillia gold prospect. Samples were also taken directly over the top of the ‘Tomahawk’ anomaly. These results were found to be largely independent of the contemporary landscape setting. There is a palaeodrainage system flowing through the area broadly running from the south to the west of the target area. Therefore there may be a palaeolandscape control on the results as there are clusters in the northwest to southeast of the transect area. However, there is only a weak response from the ‘Tomahawk’ anomaly which corresponds to the confluence of the two palaeodrainage valleys. This suggests that the ‘Tomahawk’ anomaly is a transported (palaeodrainage) Au-in-calcrete anomaly and the plants are extracting a deeper response. Four high priority target areas have been defined in this study as areas of interest for mineral exploration to continue. This study has identified two plants (C. pauper and E. concinna) that appear to be effective for determining possible mineralisation in the underlying substrate. This research has supported the use of biogeochemistry as an effective sampling medium for mineral exploration.