Long-Term Production Scheduling Optimization for A Polymetallic Open Pit Mine

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2022-2
Kaydım, Hatice Esin
Open-pit production plannings are commonly performed as short-term and long-term production planning. Short-term production planning is generally conducted at the operational level on a weekly and daily basis, while long-term planning determines the production limits on an annual basis that can be divided into semiannual or quarter periods. Therefore, long-term plans set a boundary for short-term plans and require the inclusion of multiple parameters that should be evaluated attentively. The main intention of production planning in open pit mines is to determine ore and waste extraction sequences that satisfy geotechnical, processing, and other operational constraints so that the overall benefit of the block selections in different periods should be maximized. On this basis, production plans commonly aim to maximize the total amount of the final product or maximize net present value (NPV). Maximizing the final product is generally aimed in cases where market pressure or other commitments are available. The majority of long-term production plannings are carried out to maximize NPV. Production in open-pit mining areas generally advances mainly in horizontal and vertical directions with the sequential excavation of multiple pit geometry called phases (pushbacks) from the inside out and is completed with reaching the ultimate pit geometry. Therefore, geotechnical, processing, and other operational constraints should be satisfied within the limits of each production phase and the ultimate pit. Decisions on the block and its excavation period can be more challenging if the blending of materials in multiple blocks is also required to keep the plant efficiency above target levels. At this point, this study intends to present an integer programming model to optimize the long-term production scheduling of open-pit mines by maximizing the NPV value. The model was constructed in such a way that any constant pit slope value can be integrated into the model, and decisions on ore blocks are taken considering the periodic requirements of the plant and feeding material ranges that may entail blending of different blocks before the feeding stage. The model was computed in AMPL CPLEX Solver using NEOS Server for a real dataset acquired from an open-pit mine having Zn and Cu deposit, and that will produce ore for an eight-year mine life with three production phases. Besides, 30º overall pit slope was maintained in the model, and a Zn/Cu feeding requirement between one and six was considered. The integer model optimized the long-term production scheduling of the mine by maximizing the NPV to $11,489,800. Moreover, the sensitivity of the optimized production plans to the variations in operational cost, sales prices, and discount values was also evaluated. It was observed that the sales price is the most influential factor in NPV, while the changes in the discount rate and the operational cost values were detected to modify the block extraction sequence more when re-optimizing the production schedule.

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Citation Formats
H. E. Kaydım, “Long-Term Production Scheduling Optimization for A Polymetallic Open Pit Mine,” M.S. - Master of Science, Middle East Technical University, 2022.