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. / Dissertation (MEng (Mining Engineering))--University of Pretoria, 2005. / Mining Engineering / unrestricted

Faculty of Engineering and Built Enviroment School of Mining Engineering 0315711f musakale@egoli.min.wits.ac.za / Rockfalls are a significant risk in open pit mines. Once movement of a rock perched on the top of a slope (bench) has been initiated, the most important factor controlling its fall trajectory is the geometry of the slope (bench). The best possible knowledge of rockfall trajectories and energies is important in order to determine accurate risk zoning and for the design and construction of adequate defence systems near the threatened areas. This study attempts to determine the influence of bench geometries, and the coefficient of restitution of rock, on rockfall behaviour. A study of literature was carried out to review previous studies and other relevant information on rockfalls and their analysis. The literature may be divided into two categories: experimental methods involving physical modelling, and computer models involving rockfall analyses using computers analysis methods. Rockfall computer simulation is considered to be applicable, quick to carry out and reproducible. The accuracy of the results depends on the knowledge of site conditions and slope geometry. The use of the Modified Ritchie criterion for the design of catch benches in open pit mines was also investigated. The assessment of bounce height, maximum run-out distance and kinetic energy achieved during the fall of rocks on the catch bench were the bases of the evaluation of the results obtained in this project. The computer program, Rocfall Version 4, was used for the purposes of the research. The following parameter variables were considered in the analyses: three types of rock; slopes with three stack configurations; four bench heights; and four bench face angles. The results show that, for all stack configurations and rock types, the maximum runout distance and maximum bounce height increase as functions of bench height at a specific bench face angle. A single bench configuration provides a maximum run-out distance of falling rocks larger than the value determined using the Modified Ritchie criterion for all rock types and bench face angles. Multiple bench stack configurations provide maximum run-out distances less than the value determined using the Modified Ritchie criterion only for the 90o bench face angle in all rock types; those with 60o, 70o and 80o bench face angle provide a larger maximum run-out distance. Therefore, the validity of the Modified Ritchie criterion for the design of catch bench widths in open pit mines with inclined benches must be questioned. According to Ritchie’s study (1963), rocks that fall in trajectory (free fall) seldom give high bounces after impact on a catch bench. This project shows that this finding is valid for rocks with low coefficients of normal restitution. Rocks with lower coefficients of normal restitution provide larger run-out distances with flatter bench face angles compared with rocks with higher coefficients. In contrast, rocks with higher coefficients provide larger run-out distances than those with lower coefficients for steeper angles. The consideration of the influence of geometry (shape) of falling rocks on rockfall behaviour showed that, for a flatter slope, as could logically be expected, the maximum run-out distance is greatest for rounder rocks and smallest for flatter slabby iv rocks. This is due to the fact that on a flatter slope, the mode of falling of rounder rocks is rolling down the slope. This mode provides essentially no resistance to motion, resulting in largest maximum run-out distance. In contrast, for long flat slabs, the mode of movement will be sliding, which results in a smaller maximum run-out distance. The maximum run-out distance as function of rock shape reduces as the normal coefficient of restitution increases. For all rock types, the maximum bounce height reduces as a function of the friction angle for flatter slopes. This is due to the fact that rocks are in contact with the slope during the rockfall. As the coefficient of normal restitution increases, an increase in the maximum bounce height results.