UMS Prepares for Shaft Pre-sink at Karowe

United Mining Services (UMS) is gearing up for the pre-sinking of two shafts for the Karowe Underground Mine Expansion Project (UGP) in Botswana. Following the completion of the feasibility study for the Karowe UGP, UMS was appointed by Lucara Botswana Pty Ltd. and JDS Energy & Mining Inc. in October 2019 to engineer and design the sinking of an 8.5-meter (m)-diameter production shaft and a 6-m-dia. ventilation shaft, both reaching a depth of approximately 750 m below surface.

Lucara’s Karowe mine is one of the world’s leading producers of large, high-quality, Type IIA diamonds. Fully commissioned in 2012, Karowe (which means “precious stone” in the local language) is an open-pit mine with operations until 2026. The UGP will extend Karowe’s mine life to at least 2040. At the end of 2020, Karowe’s total probable mineral reserves were estimated at 53.9 million metric tons (mt) containing 7.4 million carats including stockpiles. Dr. Pieter Louw, group executive project services at UMS, said the company’s wealth of knowledge and expertise in shaft sinking played a key role in securing the contract, and the company is bringing in the heavyweights in the industry for the project.

Louw explained that the two shafts at Karowe will be blind sunk using conventional drill and blast techniques. The production and ventilation shafts will both have equipment installed to pre-sink to a shaft depth of 100 m if required to accommodate the main sink shaft equipment. The pre-sink phase also allows the sinking process to commence as soon as possible while the main sink infrastructure is being fabricated and installed. The new underground mine’s production shaft will have an A-frame type headgear, which will hoist 21-mt payload skips, and will have a single-drum auxiliary winder for people movement, and a man/ material winder with counterweight and a big cage to service the underground.

UMS has refurbished four winders that will be going to the mine for shaft sinking, including two stage winders and two Kibble winders. The company also purchased and refurbished Scotch derrick winder cranes which will be used for the pre-sink. UMS is in the process of mobilizing up to 170 people to site for the pre-sink, which was expected to commence at the end of August and take between eight and 12 months to achieve changeover ready for the start of the main sink. The main sink will take another two years after that, at which point it will be ready for mine development to commence in 2024, and full underground operations in 2026.

To make sinking safer, Louw said UMS adopted different sinking methodologies and equipment to be used at Karowe. “In the past, we used to sink with cactus grabs, which needed people in the bottom,” he said. “We are now using vertical shaft muckers and are buying state-of-the-art jumbo drill rigs to drill at the bottom. We’re doing inline work as opposed to concurrent work with people working at the bottom.”

As featured in Womp 2021 Vol 09 -