Work on the underground expansion project (UGP) at the Karowe diamond mine, in Botswana, has made significant strides in the past year, achieving a number of important milestones.

All presinking activities have been completed on schedule and within budget, a main shaft sinking contract has been executed and main shaft sinking activities are continuing to ramp up.

However, Karowe owner Lucara Diamond Corp reports that equipment and operational challenges are negatively impacting on planned cycle times. Cycle time is the period it takes to complete a series of activities within the sinking process to achieve the next planned vertical advance.

Lucara states that it has made equipment and personnel changes, as well as shift and rotation schedule optimisations, along with the roll-out of a behavioural-based safety training programme to resolve these issues.

“The impact of delays and a slower-than-anticipated ramp-up in shaft sinking cycle times, together with experience gained from our first grouting programme, will be incorporated into a refreshed schedule and budget which is expected to be completed in the second quarter of 2023,” president and CEO Eira Thomas has said.

Lucara has completed the first phase of grouting in the production shaft between December and February, confirming the planned approach and methodology to keep water inflows from the stand stones at bay.

During 2022, Lucara invested $106-million in the Karowe UGP, with a total investment to date of $226.1-million. The company is currently working on a capital cost estimate of $547-million for the UGP, which will extend Karowe’s mine life to at least 2040.

The current schedule puts mine ramp-up in 2026, with full production from the UPG in the second half of that year.

Meanwhile, the Karowe mine delivered 335 769 ct at a grade of 12.12 carats per hundred tonnes of direct milled ore.

The mine yielded 795 diamonds greater than 10.8 ct, representing 7.2% weight percentage of the total carats recovered. Another 34 diamonds were greater than 100 ct, including nine diamonds greater than 200 ct.

Lucara reported lower revenue of $212.9-million (2021: $230.1-million) in the year and its net income increased to $40.4-million (2021: $23.8-million).

“The Karowe diamond mine completed its tenth year of continuous operations and successfully delivered on all of its financial and operating metrics, including safety, production, processing, sales and revenues, with costs trending below guidance and continued access to sufficient liquidity in support of our growth plans,” said Thomas.

Commenting on the diamond market, she said that the market remained healthy and stable, although price softening was observed in the latter half of 2022, which impacted on revenues year-on-year.