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This paper examines the case of a large open pit that is being planned at the site of an existing underground mine. Strategic planning work is undertaken to investigate the project value associated with an expansion of underground operations in conjunction with the proposed pit. Previous analysis by mine planners has determined that any depletion of the available open pit resource that changes the optimum pushback sequence will have a significant negative impact on overall project value. As a result, the main objective of this case study is to determine a strategic plan capable of yielding the optimum economic value for a combined undergroundopen pit operation. To investigate the viability of an underground expansion, a system to identify the stope resource that would add value to a combined operation if mined ahead of the pit is required. The main solution to this problem is the use of a resource model variable that defines the blocks which have greater discounted value if mined by stoping rather than by the open pit. From this potential underground resource, a series of mineable stope shells are generated at various cut-offs. This stope reserve data formed the input to an optimisation process used to optimise the underground mining plan, at a conceptual level, for various project configurations. Then, a dynamic programming mathematical program is used to evaluate the optimum value of a combined open pit and underground operation. The results generated in the case study presented herein provide a clear focus and direction for the next level of detailed mine design and planning.

Mine planning for oil sands involves the integration of waste management into the long term production planning process. This ensures that while ore is provided for the processing plant, sufficient in-pit tailings containment areas are made available as dedicated disposal areas for backfilling. This enables the creation of a trafficable landscape at the earliest opportunity to facilitate progressive reclamation. Apart from being a regulatory requirement, this integration impacts directly on the profitability and sustainability of oil sands mining operations. This paper introduces a mixed integer linear programming mine planning framework that seeks to simultaneously determine the production schedule, dyke construction schedule and the backfilling schedule. Different waste management strategies were also investigated. The model generated a practical, smooth and uniform schedule for ore, dyke material and backfilling activities. The results show that for the case studies considered, increasing the number of in-pit tailings cells reduces the net present value of the mine as a result of a reduced operational flexibility. However, this strategy makes in-pit tailings storage areas available earlier in the mine life, and ensures an efficient use of in-pit storage areas required for sustainable operations.

Strategic mine planning is the process of determining the configuration that will optimise project objectives. Current methods for ensuring that objectives are optimised, for a given project configuration, contain a number of limitations. In particular, the strategic mine planning process for a given configuration is often completed by the sequential optimisation of key decisions. This approach does not allow for relationships between decisions to be measured accurately. As such, suboptimal mine plans are often produced. The ability to model and optimise key decisions simultaneously, so as to achieve greater value, is investigated in this paper. Some of the areas in which significant advances are made include time cost modelling, cutoff grade and stockpile optimisation for open pit operations. A case study was used to benchmark the proposed model against a marginal cutoff grade scheduling method, resulting in significant net present value increases.