IMWA 2025 Advances in mine dewatering design and monitoring at Tharisa chrome mine Rustenburg South Africa (2025)
Mark Roebert, Nathi Mntungwa, Moses Msitsini², Pieter Holtzhausen², Kym L Morton²
Tharisa Minerals, Rustenburg, South Africa
2KLM Consulting Services Pty Ltd, 22 Central Road, Sunrella AH, 1748, South Africa
Abstract
Tharisa Minerals operates a large chrome and platinum group metals (PGM) open pit mine near Rustenburg, situated in the western limb of the Bushveld Complex, which holds over 70% of the world’s platinum and chrome resources. Tharisa mines and processes five MG chromite layers. Despite the region’s low rainfall, the mine must dewater its three pits and planned underground mine ahead of mining operations. The proximity to old underground mining voids in the eastern side wall of the East pit means the mine has to manage its water in advance of mining to ensure risk free ore extraction.
The dewatering strategy comprises: accurate stormwater control, the use of in-pit and pit-perimeter dewatering boreholes, and sump pumping. The locations of the dewatering boreholes were determined using geophysical surveys, achieving a 100% success rate. Conceptual and numerical models were developed to optimize borehole placement and estimate the water volumes that need to be removed to maintain targeted water levels. A detailed, automated monitoring network is used to manage the water and show the effect of pumping on water levels for specific sectors of the mine.
Main findings are the importance of early and well-maintained storm water controls coupled with early installation of in-pit and pit perimeter dewatering boreholes. The effect of the flooded neighbouring and underlying mine has to be managed in advance to ensure the ore can be accessed in all seasons. The utilisation of as much water as possible in the plant reduces the release of water to the environment and moves towards a zero-discharge strategy.
Tharisa mine is a good example of how a dewatering design can be implemented once mining has started and shows the cost effectiveness of a phased approach to mine dewatering design. This case study provides valuable insights to all surface and surface to underground transition mines.
Keywords: Chrome, Dewatering, Pit-Perimeter, Monitoring, In-Pit Pumping, PGMs
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