Shaft pre-sinking at Canadian-headquartered diamond mining company Lucara’s Karowe mine, in Botswana, was completed at the end of February.

“Each shaft is about 52 m below collar. The final depth for the ventilation shaft is 730 m below surface, and 767 m below surface for the production shaft,” says Lucara VP technical services Dr John Armstrong.

Shaft sinking for Karowe is scheduled to be complete in 2024 and the ramp-up to production from the underground operation is scheduled for the second half of 2026.

Armstrong adds that the underground development will add an additional 13 years to the life-of-mine, while delivering about $4-billion worth of net revenue from the production of approximately five-million carats from the South Lobe of the AK06 kimberlite.

“The Karowe mine is one of the world’s leading producers of high-value Type IIa diamonds and has produced three +1 000 ct diamonds since 2015, the only mine in recorded history to produce three +1 000 ct diamonds,” he says.

The EM/PK(S) geological unit of the South Lobe is the source of the largest diamond recoveries from the Karowe mine and is expected to provide more than 90% of the mill feed during the first three years of underground production. The EM/PK(S) unit currently provides about 35% of the mill feed from the openpit’s production.

The capital cost of the underground project is $534-million and sinking contractor United Mining Services Botswana is using conventional drill-and-blast sinking techniques.

Meanwhile, Lucara’s shaft sinking projects at the Karowe mine have been delayed, owing to the Covid-19 pandemic.

During the lockdown period, Lucara secured project financing and focused on detailed engineering and design works, as well as the procurement of long-lead time items required for shaft sinking activities, notes Armstrong.

“The project had a one-year delay from the original feasibility schedule. However, during the pre-sink, and as the project is transitioning to the main sink, no significant challenges have been encountered thus far.”

Armstrong was responsible for the Lucara oversight of the feasibility study which was authored by JDS Energy and Mining Inc. of Vancouver, Canada. JDS is currently providing engineering, procurement and construction management to Lucara for the project. Armstrong has also been responsible for the development of diamond size and value distribution models and forecasts for the Karowe mine since 2013.

Long-term shaft maintenance requirements at the Karowe mine are still in the planning phase.