Since the early sixties, there has been optimism that trucks in large open pit mines would be replaced by belt conveying systems, resulting in improvements in terms of economics and. more recently, carbon emissions. In the last five years, these developments have become more interesting due to the highest oil piice in history, and this lias led manufacturers to design a number of alternative systems. Consequently, there has been a “new focus on IPCC (in-pit crushing and conveying) systems” and this is one of the focal areas of tins congress.
Despite tins increased interest, in-pit crushing has had limited or no success in deep, hard rock open pit mines, and trucks have continued to find application as they get larger and pits deeper. While ore crushing has been used in specific conditions, few mines have successfully and economically implemented waste crushing.
The authors of this presentation come from two different directions: one from the planning of deep. hard rock open pit mines, winch are specifically targeted here, and the other from the design and application of continuous mining systems. The presentation revolves around these two counter-view points and will attempt to stimulate discussion on how the industry can plan conveying systems in deep, hard rock open pit mines while at the same time maintaining the primary objective of maximization of Net Present Value (NPV) and returns to the stakeholders.
Development of large open pit hard rock mines
To comprehend how more energy-efficient haulage systems can be applied in this type of mine, one needs to understand the way they are developed. NPV is the primary objective, and the economics of large open pit hard rock mines is driven by two key phrases – “mine the next best ore” and “delay waste as long as possible”.
On tins basis, most large open pit mines are developed as a series of phases or pushbacks (also called expansions), which initially develop the most economic material and then expand outwards as a series of phases showing incrementally lower economics. Each of these phases will generally have its own access system or will link to the access system of a previous phase. In addition, it will have adequate width and length to support the productive capacity of the phase. Tins is standard practice in large porphyry copper mines, gold operations and many others. If open pit operations were not developed in tins way. many would be uneconomic.
Large open pits may be developed in 10 to 20 phases. Some examples of typical phase mining are shown in figures 4 to 6. At any point in time, a mine’s production may come from three to five active pushbacks with typically one pushback well established in ore. a second in a mixture of ore or waste, and the others in different stages of phase development. This is illustrated in figure 4.
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