Abstract
Block caving is an underground mining technique which extracts ore from the base, rather than from the top, of typically massive deposits. Mining infrastructure is developed below the deposit before extraction commences. A network of tunnels provides access to a collection of drawpoints from which ore is hauled. With large deposits, not all drawpoints are developed simultaneously and the opening of drawpoints is sequenced to facilitate orderly extraction of ore columns above drawpoints. Sequencing fixes the initiation point for the entire block cave, or a part of it, as well as identifying the direction of cave advancement. The drawpoint opening sequence exerts influence on the block cave mine economics. This paper discusses the optimisation of sequencing based on the net present value associated with extraction over the life-of-mine. It is shown that the maximum attainable net present value is obtained by a sequence in which ore columns are ranked in descending order of value. If significant variation of grade is present inside columns, an iterative procedure is given which corrects the sequence which yields the maximum net present value. The sequence with maximum net present value may not be practical or attractive from a caving perspective. Systematic design of sequences which permit orderly development of a block cave is discussed. To provide context, the net present value obtained from these feasible sequences is compared with the maximum attainable net present value. It is shown that the best feasible sequences are preferentially initiated in zones with columns of high-grade ore.
Highlights
As global demand for metals is continually rising, the number of large open pit mines is more or less stable in recent years
This paper addresses the question how to define an optimal drawpoint opening sequence during mine planning and discusses a novel approach to provide a practical solution
A brute force approach to identifying a sequence which is optimal, i.e. generates a maximum Net Present Value (NPV), is to calculate and compare the NPV of every feasible sequence. This approach soon becomes computationally onerous because a footprint may contain hundreds of drawpoints which can be arranged in the factorial of N sequences, where N is the number of drawpoints
Summary
As global demand for metals is continually rising, the number of large open pit mines is more or less stable in recent years This could be due to scarcity of large, nearsurface deposits, which may herald a shift towards development of deep underground orebodies. While the operational unit cost of extracting ore with block caving is attractive by underground mining standards, the method requires significant upfront capital expenditure prior to the start of mining. This is primarily related to the development of underground infrastructure which, for example, includes the sinking of shafts to depth and creating an intricate network of tunnels below the deposit. This paper addresses the question how to define an optimal drawpoint opening sequence during mine planning and discusses a novel approach to provide a practical solution
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