Mineral resource estimation at Ashanti Goldfields Company Limited: a comparative study

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Ashanti Goldfields Company Limited (AGC) has delineated four main granitic deposits within its Obuasi consolidated concession. Out of these four deposits the most prominent is the Anyankyerim deposit which strikes over 1 .6 km and has a total resource of 7.8 Mt at 2.2 g/t. The Anyankyerim deposit is currently being exploited by surface mining technology. However one of the major problems which have been of great concern during mining is the discrepancies between the estimated and the actual mined reserves. This problem may be attributed to inaccurate estimation method, poor mining practice and inefficient mineral processing. The Objective of this thesis is to look at the geological characteristics of the Anyankyerim deposit, investigate the applicability of geostatistics as an alternative method to the inverse distance squared method currently being used, and adopt a strategy that may minimise the differences between the estimated and the mined reserves. In this thesis, exploration information used included trench, Reverse Circulation drilling (RC), and Diamond Drilling (DD) data. In order to facilitate the work and eliminate human errors, DATAMINE software was used. The exploration data were validated and statistically analysed. Subsequently, the orebody model was built using wireframe and block model techniques in DATAMINE to obtain a 3-D deposit. Both inverse distance squared and cubed, and geostatistics (ordinary kriging) methods were applied. Further analysis of the estimated reserves and the mined reserves unveiled that the major factor contributing to the discrepancies is the tonnage factor being used by exploration during resource estimation and that used by the mining engineers. Recommendations to minimise these discrepancies have been provided.
A thesis submitted to the Board of Postgraduate Studies, Kwame Nkrumah University of Science and Technology, Kumasi, in partial fulfilment of the requirement for the award of the Degree of Master of Science in Mineral Exploration, 1999