Determination of optimal production rate under price uncertainty—Sari Gunay gold mine, Iran

Abstract

Due to the long life, most mining projects face the risk of the parameters such as mineral price, grade, and cost. Uncertainty can lead to unfavorable results of the decisions made by managers and mining investors. Therefore, this paper aims to determine the Sari Gunay gold mine’s production planning, considering the certainty and uncertainty over the mineral price. Finally, the proposed planning will lead to the allocation of fixed or variable production rates throughout the mine life. These findings were assessed by Taylor and Zwiagin methods with 22 different scenarios in all conditions, including (a) price certainty and uncertainty such as daily price, 3- and 5-year average, Monte Carlo simulation, and binomial tree; (b) decreasing, increasing, and fixed production rates; and (c) mine life conditions. The scenarios evaluated under the price certainty conditions (scenarios 1 to 12) have lower NPV values than those under the price uncertainty conditions. This is because the price is fixed throughout the mine life. Due to historical price data and high fluctuations of estimated prices, this method’s NPV values fluctuate more than other scenarios evaluated by the Monte Carlo simulation. The binomial tree method scenarios have the lowest NPV value’s fluctuation because the fluctuation of the estimated prices is controlled, and the highest NPV values are related to this method. Out of the 22 scenarios, scenario 17 has the highest NPV value ($512,642,774). According to this scenario, the mine plan is determined, and the annual production rate is reduced to 3,241,977 tons in the first year and 270,165 tons in the last year with the Taylor life of 12 years.