Abstract
Environmental responsibility and the sustainable development of mineral resources are a topic of critical importance to the mining industry and at the same time relate to operational and rehabilitation costs to be considered in technical studies. Open pit mining operations impact their local environment in terms of their modification of the landscape and local ecosystems. Many of these impacts are the result of the transportation of large volumes of materials mined and shifted from and to different locations. External stockpiles and waste dumps occupy considerable space as well as involve substantial transportation costs to move materials from open pits to stockpiles and then move them back to the pit for rehabilitation after the end of exploitation. Depending on the shape of the deposit and the intended design of the pit, a desirable option may be to place it directly in the free spaces within the pit, instead of storing all waste and tailings materials in stockpiles and/or waste/tailings dumps. This paper presents a new mathematical formulation integrating to life-of-mine planning and the maximization of net present value, with the related waste and tailings disposal kept within the mined-out parts of a pit, using a stochastic integer program that manages geological uncertainty including metal grades, material types and related chemical compositions. In addition to the traditional variables related to the materials being extracted from the ground in the form of mining blocks, strips of ground following the dip of a pit are considered within the pit as decision variables, and the optimization process aims to optimally define both the sequence of extraction of mining blocks and the reservation of strips needed to store waste materials. An application at an iron ore mine demonstrates the feasibility, applied aspects and advantages of the proposed method.
Highlights
Life-of-mine (LOM) planning is a core element of production forecasting, financial valuation and environmentally responsible development of open pit mining projects and operations
The OMPSIP-ITD model contains 64,680 binary variables, 680 continuous ones and around 413,000 constraints, from which the in-pit storage only represent 1140 binary variables, 380 continuous ones and around 33,000 constraints. This model is too complex to be solved by the solver Cplex; a sliding time window heuristic (STWH), adapted from the method used in Dimitrakopoulos and Ramazan (2008) and Cullenbine et al (2011), is used here instead
A bar diagram shows which strips are free and which ones are available for storage for all the periods
Summary
Life-of-mine (LOM) planning is a core element of production forecasting, financial valuation and environmentally responsible development of open pit mining projects and operations. It is critical to simultaneously optimize the extraction sequence of materials represented by mining blocks and the in-pit waste disposal to optimally define the mining production policy The literature on this topic is limited, and some related work is found in Zuckerberg et al (2007), who present an extended version of BHP's mine planning software Blazor, named Blasor-InPitDumping (BlasorIPD). In terms of waste management, a smoothed representation of the grade distribution of a deposit tends to minimize the waste tonnage forecasts and results in unexpected additional material sent to the waste dump To avoid this and address inevitable uncertainty, a set of stochastic simulated realizations of the mineral deposit may be used. The novelty of the proposed approach explicitly considers in-pit storage considerations and simultaneously accounts for geological uncertainty within the stochastic optimization framework, a topic relevant in terms of waste production forecasts and management.
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