Transition from open-pit to underground mining
In general, shallow deposits are mined by open-pit methods. When deposits reach a substantial depth, it is possible to combine open-pit and underground mining methods. In this case, mine planning and optimisation play an important role in the decision-making process. The transition from open pit to underground mining is one of the major challenges in mining engineering. Mines that are likely to transition from open-pit to underground mining will reach a transition point where a decision must be made whether to expand the pit or go underground. Determining the optimum transition point is the transition problem. In the current traditional approach to combined mining, the ultimate pit boundary is determined and the pit design is carried out as a first step. At this stage, the ultimate pit limit can be optimally determined using algorithms such as the Lerchs-Grossman algorithm. Optimisation and design of the underground mine will begin after the standard ultimate pit limit. However, if the economic potential associated with underground resources is taken into account, the final pit can be significantly reduced. It is therefore essential to consider both the open pit and underground potential simultaneously, in order to maximise the profitability of the project. 🔄The schematic section illustrates three critical elements to be considered in mining transitions: 1️⃣ Ultimate Pit Boundary: The limit of economically viable open pit mining. Determines the optimum time to switch to underground mining. 2️⃣ Optimal Transition Point: The point at which the marginal costs of deepening the mine exceed those of going underground. Must take into account: geology, metal prices and operating costs. 3️⃣ Crown Pillar: Buffer zone between the two operations. Thickness calculated for : ✓ Preserve shaft stability ✓ Maximise ore recovery.
