relaxed, then the throughput in the system can be increased and a greater amount of the objective unit can be produced. There may be many constraints in a system but of these only a small number, or as few as one, are the primary constraints or bottlenecks. These control the overall throughput through the system. Common constraints in mining enterprises are plant capacity limits, plant concentration limits, mining tonnage limits, vertical rate of advance limits, stockpile or dump size limits, power and water supply limits, product specifications and pollutant limits. In an optimised system, the bottleneck should be the constraint that the system operator has the least ability to change . This is most commonly the most capital-intensive part of the operation (e.g. an expensive piece of equipment such as a ball mill); though in some cases it may also be an externally imposed constraint (e.g. a certain product specification, a regulatory constraint, or a resource supply limitation). If an Enterprise Optimisation finds that the bottleneck limiting the overall generation of cash by the system is relatively simple or inexpensive to alleviate, then that action should be taken. Cash generated by the operation will then increase until another constraint becomes the bottleneck. Activity Based Costing Any model is only as good as its inputs, as per the well-known ‘Garbage In, Garbage Out’ adage. In Enterprise Optimisation, it is essential that all resource consumption costs are assigned to the activity that consumes that resource. This is called Activity Based Costing (ABC). Furthermore, it is essential that all costs are split into variable (attributable) costs, incurred per unit of resource consumed, and period costs, incurred as a fixed cost to keep a process (e.g. item of equipment) operating over a period of time. Software A mining enterprise has many elements and relationships between these elements that specialised software is required to implement modelling and Optimisation. Whittle Consulting utilises Prober®, a proprietary optimisation algorithm that has been continually developed by Jeff Whittle for over two decades. Prober® is used to model the mining and processing operation from material inputs to market. This is then optimised for NPV, producing a schedule showing the path of all cash-flows and materials through the system over the life of the mine. Prober® receives material inputs with specified sequence rules (e.g. start-afters, minimum leads and lags). However, it is not practical to provide block models (which often contain millions of blocks) directly to Prober® without prior aggregation of alike material (rock type, grade/value range, processing options). In open-pit operations the mining shape selection (i.e. pits and phases) are sized using Geovia Whittle pit optimisation software. This utilises the Lerchs-Grossman algorithm to determine optimum pit size and shape. Whittle Consulting uses specific techniques to integrate Geovia Whittle with the Prober® schedule optimiser, including iteration between the two optimisers if necessary. Underground operations with alternate mining shapes or sequences (prepared by a mining engineer) can be evaluated using a similar approach. 1.3.5 1.3.6
ReCYN™ Case Study – Martabe Operations
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