Geostatistical mineral reserve estimation of a Diamondiferous deposit - a case study

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Ghana Consolidated Diamonds (GCD) Limited is located at Akwatia in Ghana and mines alluvial diamonds from the Birim River Basin by open-cast mining technology. GCD has faced and is still facing the problem of discrepancies between the estimated and actually recovered diamonds, with the latter, most often, being substantially lower than the former. These discrepancies had been suspected to be due to grade and volume overestimation and poor plant recovery. Renovation of the processing plant, recently, has resulted in the reduction of loss of diamonds at the plant. However, the discrepancies between the estimates and actual recoveries still exist which can now be attributed mainly to overestimation of grade and volume by the mine’s estimation method. This paper has reviewed the mineral reserves estimation method in use at GCD, and has investigated and demonstrated the applicability of geostatistics as an alternative method that would provide a more reliable grade and volume estimates of the reserve blocks. In this study two areas with different geological characteristics have been considered, namely, Sandy Creek Reserve Block 42/188/BV and Kusi Reserve Block 30/448/AV. Results from the study revealed that, in both cases, the grade and volume estimates using geostatistics were quite lower than the grade and volume estimates using the mine’s method. The implication is that, with the application of geostatistics to the estimation of mineral reserves at GCD, the disparity between the actual recoveries and the estimates will be reduced. It has been concluded that GCD can use geostatistics to estimate its mineral reserves in order to minimise the discrepancies between the estimated and actually recovered diamonds.
A thesis submitted to the Board of Postgraduate Studies, Kwame Nkrumah University of Science and Technology, Kumasi, in partial fulfilment of the requirements for the Post-Graduate Professional Diploma in Mining Engineering, 1995