Summary of trials of an integrated gold exploration system at Chakari, Zimbabwe

An integrated system of exploration for gold-sulphide mineralisation in shear zones was tested in the Chakari area of Zimbabwe. This integrated system was developed in Ghana and uses the shear zone as the exploration target. This is located by interpretation of aerial photography of geological settings favourable for gold mineralisation. The shear zone is located on the ground by vapour geochemistry traverses across its strike and sulphide-rich portions are determined from detection of high CO2 values. These sites are tested for gold m inera lisa tion by process ing the over 1 y ing res idua 1 so Us us ing a so i 1 loam ing technique, improved by the use of large soil samples for sieving and panning, the concentrate obtained being passed over a spiral concentrator to extract the gold. The gold particles are counted on a gridded pan. The shear zones at Chakari have no topographic expression but are readily identified on aerial photographs as they form distinct lineaments. In an orientation study high CO2 values were obtained over the Arlandzer shear zone and a small footwall shear zone. These high CO2 values are associated with high gold particle counts, which form a zone of elevated values extending for about 60m on either side of the peak gold particle counts directly over the mineralised shear zone. The footwall shear zone is associated with high radon and thoron values, probably indicating the presence of water in it. High CO2 values near the old Bonzo 2 shaft are related to sulphides only, the gold particle counts being low. In a gold exploration exercise over a ploughed field at Chadshunt farm, a shear zone -was traced in a south south-westerly direction beneath the field by following its CO2 signature until it died away. The presence of gold m inera lisa t ion was es tab I ished by so 11 loam ing. Th is exp lora t ion exerc ise was - performed with minimal interruption to -farm work. The integrated exploration system was shown to work in the semi-arid conditions at Chakari. The uses of aerial photographic interpretation and vapour geochemistry will be of more interest to exploration companies than the soil loaming since they can afford to use the geochemical laboratories in Zimbabwe. The soil loaming will be of more interest to the prospectors and small-scale miners in the exploration of their claims. Prospectors and small-scale miners form an important grouping in the rural economy in Zimbabwe and improvements in their expertise will also benefit the exploration companies who often develop mineral occurrences flrst found by prospectors.