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Detailed geological knowledge is often a major unknown factor in open pit mining and design, and therefore poses a significant risk in the mining venture. As the knowledge of the geology improves so the risk of unforeseen conditions reduces and therefore safety and productivity can be increased. Historically, geotechnical methods and information have predominantly been used exclusively for pit slope optimisation. This research documents the procedures and developments undertaken to compile a comprehensive geotechnical database, and the application of the geotechnical data to open pit mining, beneficiation and planning. The utilisation of the geotechnical information has been enhanced through the novel development and application of a computerised, 3D geotechnical model. Sandsloot open pit was developed to extract the Platreef pyroxenite orebody, which is hosted within the Northern Limb of the Bushveld Complex. Sandsloot is currently the world's largest open pit exploiting Platinum Group Metals. Interaction of the basic magma with the footwall sediments of the Transvaal Supergroup and varying degrees of assimilation has resulted in a unique suite of hybrid rock types. These various rock types provide significant engineering geological challenges. Geology and the detailed understanding of its properties are fundamental to the optimal design and successful operation of any mine. Extensive fieldwork was conducted to collect geotechnical information, both from exploration boreholes and in-pit mining faces. Over a 5-year period, geotechnical data were collected from 29,213 m of exploration core and 6,873 m of exposed mining faces. Extensive field and laboratory testing was undertaken in order to define the complete set of geotechnical properties for each rock type in the Sandsloot mining area. The geotechnical information relating to each borehole and facemap was stored in the Datamine® software package. The information was collected in the form of rock mass rating (RMR), uniaxial compressive strength (DCS), fracture frequency (FF/m) and rock quality designation (RQD). The architecture of the database was developed along the principals used for generating an ore reserve model. One of the novel applications was the development of a computerized 3D, geotechnical model in Datamine®. The geotechnical parameters, namely RMR, DCS, FF/m and RQD, were modelled for each rock type, using geostatistics, to generate a 3D model. The data were interpolated between exploration boreholes and exposed mining faces and the modelling was constrained using wireframes separated by rock type. The result is a 3D model containing 15 m3 model blocks populated with interpolated geotechnical information. The dimensions of the model blocks are linked to the mining bench height of 15 m. The model can be queried to give predictions on rock mass conditions for any planned mining area, as is the case with the ore reserve model, which provides predictions on platinum grades. The crux of the innovative research is the practical application of the 3D geotechnical model. This was achieved through the development of both a fragmentation and a slope design model, which read the interpolated geotechnical information. These models provided an engineering tool to optimise mining and milling perfonnance. Rather than viewing the drill and blast department as an isolated cost centre and focussing on minimising drill and blast costs, the application of the model concentrated on the fragmentation requirements of the milling and mining business areas. Two hundred and thirty-eight blasts were assessed to detennine the optimum fragmentation requirements for ore and waste. Based on the study a mean fragmentation target of 150 mm was set for delivery to the crushing circuit and a mean fragmentation of 230 mm was set for waste loading from the pit. The mine operates autogenous mills, which are sensitive to the fragmentation profile delivered. The harder zones occurring in the ore zone have a major impact on the plant's perfonnance. The geotechnical parameters in the model were related to Lilly's Blastability Index, and in turn to required explosive volumes and the associated drill and blast costs. Having defmed the fragmentation targets, the Kuz-Ram equation was used in the fragmentation model to predict the explosive volumes required to ensure consistent mining and milling perfonnance. The geotechnical model is used to predict changes in geotechnical conditions and therefore the blasting parameters can be adjusted in advance to ensure the milling and mining fragmentation requirements are met. Through the application of the fragmentation model over an eighteen-month period the loading and milling efficiencies improved by 8.5% and 8.8% respectively, resulting in additional revenue ofR29 million for PPL. Based on the mining rock mass rating (MRMR) values within the geotechnical model a stable slope design model was created in order to calculate optimum inter-ramp angles. From a slope design perspective the model was used to target data-deficient zones and highlight potentially weak rock mass areas. As this can be viewed in 3D, the open pit slopes were designed to accommodate the poor quality areas before they are excavated. It also follows that competent geotechnical zones can be readily identified and the slope optimised accordingly. Due to the detailed geotechnical infonnation being available in three dimensions, the open pit slopes were designed based on a risk versus reward profile. As a significant geotechnical database was available, more accurate and reliable designs were generated resulting in the overall slope angle increasing by 3 degrees. This optimisation process will result in a revenue gain of R900 million over the life of the mine. The revenue and safety benefits associated with this design methodology are substantial and have potential application to all open pit mining operations. The research has enabled detailed geotechnical infonnation to be available in three dimensions. This information can be readily accessed and interpreted, thus providing a powerful planning and financial tool from which production optimisations, feasibility studies and planning initiatives can be implemented. The development and application of a 3D geotechnical model has added a new dimension to the constant strive for business improvement and reflects a novel and successful approach towards the application of engineering geology at the Sandsloot mining operation. / Thesis (Ph.D.)-University of Natal, Durban, 2003.

A number of algorithms have been developed in order to determine the optimal final limits of an open pit mine. Due to the complex nature of this problem, however, very few of them can offer a reliable and complete answer. The case of an actual lignite deposit was used in this study, which enabled an investigation into the capabilities of one of the most established optimizers (Whittle Three-D™). A three-dimensional block model of the deposit was first developed, based on the available drillhole data, with the use of the Digital Underground™, an integrated geostatistical modeling package. The largest possible utilization of the original geologic information was intended, and the modeling results were correlated with existing reserves calculations and past geologic observations on quality characteristics. A flexible methodology was then followed to transform the geologic reserves block model into an economic one, where each block is assigned a net value. Two alternative objective criteria formulations where introduced to facilitate this scope. A series of parametric regular 3-D fixed economic block models were constructed by varying the block size and also some basic mining and economic parameters. A number of case studies were then conducted, to form an extended sensitivity analysis of the various parameters that affect the total value, tonnage, and waste volume of the final optimal pit. The conclusions drawn can develop useful guidelines for the decision making of the mine operator. The optimization also provides a detailed ultimate open pit layout, that can enable a comprehensive mine planning and design. / Master of Science

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In the increasingly competitive coal market, it is becoming more important for coal operators to develop mathematical models for surface mining which can estimate mining costs before the actual mining begins. The problem becomes even more acute with the new reclamation laws, as they affect surface coal mining methods, productivity, and costs. This study presents a computer simulator for a mountaintop removal type of surface mining operation. It will permit users to compare the costs associated with different overburden handling and reclamation plans. It may be used to minimize productivity losses, and, perhaps, to increase productivity and consequently to reduce operating costs through design and implementation of modified mountain top removal methods. / M.S.