The influence of bench height and equipment selection on effective mineral resource utilization

Abstract

The mine planning process converts resources into economically mineable reserves, focusing on value addition and risk reduction. Equipment selection is traditionally addressed late in the process and addresses production capacity, equipment matching and equipment allocation. The primary focus being to reduce the operating cost per unit of material handled. Mineral resource management is an integration of the key functions in the mining process. A focus on resource utilisation plays a key role in the management process and leads to the question whether lower operating costs always add value in the long term. It was determined that traditional equipment selection methods are not effective for all mineral deposits and might even be short sighted, destroying value over the long term. The mine planning process was adapted to allow for an early investigation into the potential for increased recovery. The effect of selectivity in the loading action is simulated in a 3D environment over a range of bench heights. The results are analysed with a grade tonnage curve and the saleable product at each bench height is calculated, taking account of the required product qualities. The concept of financial materiality is applied to classify the resource as either a massive or selective deposit. A massive deposit support the traditional drive for bigger equipment and will benefit from lower operating costs. A selective deposit requires less focus on production capacity, equipment matching and allocation and more on resource recovery. In order to take advantage of the potential indicated in the evaluation, it is necessary to modify the traditional equipment selection techniques. A thorough understanding of the capabilities of the loading equipment is required in an attempt to match these abilities with the geometry of the ore deposit. The objective is to identify the equipment that will ensure the highest mining recovery at the lowest cost. This will be achieved when the loading equipment can attain a mining recovery smaller than the bench height it is mining or if the equipment can be applied economically on small bench heights. The most suitable equipment can only be determined at the hand of a total value chain costing analyses. This means that the production cost i.e. the cost to produce the final product must be evaluated and not the operating cost i.e. the cost to move a unit of material, as is often the case. The proposed mine planning approach and equipment selection technique was used on the Thabazimbi iron ore mine deposits. The results indicated that the NPV of the project could be increased dramatically. It was concluded that the ability to load selectively cannot be calculated mathematically. It is a judgment made on a thorough evaluation of the design and operating features of the shovel in conjunction with the ore body geometric parameters and the loading face conditions. The efficiency of the selected shovel can be manipulated through the application of different bench heights, and the optimum combination can only be determined through a total value chain costing analyses.