An integrated simulation-based method for deep-level mine dewatering planning
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The South African gold mining industry has declined rapidly over the last decades. The main contributors are rising operational costs and fluctuating gold prices. Due to increased electricity costs and increased mining depths, operational costs have increased steadily as shallow ore reserves are being depleted. Further aggravating the situation is the reducing ore grade at these deeper depths, which reduces the profitability per tonne ore mined. A change in commodity prices can either extend a mine’s LOM or shorten it. For example, multiple mining operations extended their life expectancy throughout 2020 due to an increase in mineral prices, making it more profitable to mine lower-grade ore. The rise in mineral prices was caused by the Covid-19 pandemic scoring the mining sector. Capital is re-invested into a mine to ensure it remains profitable and operational. These capital investments include implementing planning projects to ensure that the mine has the required infrastructure for further expansion and development. It further entails avoiding unnecessary expenditures of capital on infrastructure that will not be utilised accordingly. In addition, energy-saving projects are included in these capital investments to reduce the power consumption and energy wastage of mining operations. Various studies have shown the success of using a simulation model to replicate mining dewatering systems. After a simulation model has been verified according to the parameters and conditions of the existing system, it can be used to simulate configuration changes without physically installing pipes or pumps. However, previous studies have not considered using these models to assist with LOM planning. The simulation can be applied during the planning of future configurations to evaluate the feasibility of the recommended changes. This will ensure that suitable reconfigurations are implemented to reduce the risk of unnecessary expenditure. The objective of this study was to develop a simulation-based method to assist in mine dewatering planning to prevent these over-expenditures. The method was applied to a case study to investigate the pre-feasibility of a large capital project. To reduce the cost over the LOM, Mining Company A considered closing one of their care and maintenance shafts used for pumping. The deep-level gold mine had multiple integrated shafts. The case study focused on investigating the pre-feasibility of closing the pump shaft and diverting the water to a neighbouring shaft. The pumping shaft removed approximately ±40 megalitres (ML) of groundwater each day. A simulation model was created to simulate the neighbouring shaft’s dewatering capacity. After the simulation model was verified against the measured values, the model was expanded to include the diverted groundwater from the pump shaft. The model was used to identify the necessary infrastructure required on the neighbouring shaft to handle the additional capacity. The results of the pre-feasibility study validated the recommendations of this study. The results indicated that it would be feasible to close the pumping shaft. It is important to note that the LOM is dependent on the stability of the gold price. Fluctuations in the gold price could reduce or extend the LOM, thus influencing the period over which the cost savings have been estimated. For the project to be feasible, the LOM should be at least six years. The payback period of this project is in Year six. The overall LOM-estimated cost savings that could be achieved over the 16-year LOM would exceed R1 300 million. Therefore, the study’s objective of developing a simulation-based method to assist with mine dewatering planning and investigating the pre-feasibility of this project was met.
- Engineering