During the last few decades, open pit mines have been deepened to the remote depths of the ground such that removing great volumes of waste rocks may jeopardize their profitability. In such circumstances, an early transition from open pit to underground mining may prove more profitable. This is the case in many large-scale open pit mines, where considerable amount of mineral reserve remains beneath the pit bottom. This paper develops a set of classified integer programming models for determining an optimum transition depth (OTD) between open pit and various underground mining methods. The models lie within the scope of long-term production scheduling because the OTD is revealed through scheduling of all mineral reserve. To provide a quantitative analysis, two optimization models with distinct solution strategies are executed on a three-dimensional sector of a real orebody. The results indicate that the integrated models increase the total NPV of the mining operations by up to 8.62%. However, the scenario-based models enhance the primitive solution (the base scenario) by up to 3.42%. It is also shown that the integrated models present solutions that are practically more realistic.

中文翻译：

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一组用于从露天矿到地下采矿方法的最佳过渡的分类整数编程（IP）模型

在过去的几十年中，露天矿已深化到地面的较深深度，因此清除大量废石可能会危害其盈利能力。在这种情况下，从露天开采到地下采矿的早期过渡可能会证明更有利可图。许多大型露天矿就是这种情况，在矿山底部下方仍保留着大量的矿藏。本文开发了一套分类的整数规划模型，用于确定露天矿和各种地下采矿方法之间的最佳过渡深度（OTD）。这些模型属于长期生产调度的范围，因为OTD是通过调度所有矿产储量揭示的。为了提供定量分析，具有不同解决方案策略的两个优化模型在真实矿体的三维区域上执行。结果表明，综合模型使采矿作业的总净现值提高了8.62％。但是，基于方案的模型将原始解决方案（基本方案）提高了3.42％。还表明，集成模型提供了实际上更现实的解决方案。