Estimation of Reminant Gold Resources of Old Underground Workings by Indicator Approach – A Case Study

The lack of geological control and old underground development at AngloGold Ashanti (Bibiani mine) in Ghana was a major setback for the conventional methods of resource estimation to produce accurate estimates of the deposit. Consequently, inverse distance weighting of indicator variables were used. This estimation approach, however, overestimated the boundaries of the old underground workings (voids) into inappropriate areas of the resource model and thereby caused significant underestimation of ore tonnage and overestimation of grade. This paper highlights the study that re-evaluated the Bibiani deposit using indicator kriging. The results of re-evaluated reserves compared well with actual production figures in terms of tonnes, grade and stoping volume