Grade and tonnage reconciliation of Afc1 Reef at Kottraverchy Pit, Goldfields Ghana Limited, Tarkwa Mine.

Abstract

Reconciliation is a vital aspect of checking and measuring variation or discrepancies between variables in the mining industry since it evaluates performance in mining ore. It is therefore necessary to have a good estimation method that can predict tonnages and grades with minimal errors as much as possible. The Afc1 reef at Kottraverchy pit has seen discrepancies in the grade and tonnage values of the ore deposit. Tonnage is underestimated and grades overestimated. This could be attributed to the method of estimation. Goldfields Ghana Limited Tarkwa Mine uses Ordinary Kriging a linear interpolation method as their method of estimation. Though it had proved well with the Tarkwaian deposit, estimation of Afc1 reef which has highly skewed distribution produces poor reconciliation results. Multiple Indicator Kriging is one of the few non-linear estimation techniques that can cope with highly skewed or difficult distributions and addresses some of the deficiencies of the linear estimation techniques. This research estimated the Afc1 reef using OK and MIK and compared their estimated values with the actuals. Figures obtained from OK estimate of Afc1 for 2013 was 235,771.75t with an average grade of 0.75g/t. MIK estimates was 272,855.79t with an average grade of 0.69g/t. And Afc1 ore mined for 2013 was 276,482.73t with an average grade of 0.70g/t. MIK was recommended as a better method for estimating Afc1 reef since its estimates compared better with the actuals.