Engineering News and Mining Weekly
Diamond miner progresses Botswana shaft sinking
Diamond explorer and miner Lucara Diamond Corporation made significant shaft sinking progress in 2023 at its Karowe Underground Project (UGP), in Botswana, where the miner invested $101.3-million for the year, focusing on development of the underground portion of the project.
Development efforts in the fourth quarter of 2023 comprised mainly shaft sinking, lateral development and grouting programmes in both the ventilation and production shafts of the Karowe UGP.
As a result, at the end of 2023, the production and ventilation shafts were both at 348 m below collar, or 666 m above sea level, and the process of establishing the first shaft stations and lateral connection between the two shafts on 670 level, had started.
The miner is expanding the Karowe mine, the existing openpit of which is expected to be depleted in 2026, with plans underway to develop the underground orebody, thereby extending the life-of-mine to at least 2040.
The Karowe UGP is designed to access the highest value portion of the Karowe orebody, with initial underground carat production predominantly from the highest value eastern kimberlite unit.
During the fourth quarter of 2023, the ventilation shaft was sunk to 76 m, the 718 slinging cubby was completed and the 670-level station catwalk was established, while the lateral station development was started.
Total lateral development of the ventilation shaft in this period was 97 m, and development equipment – including a Kubota machine, a Sandvik DD321 boom jumbo drill and a Caterpillar R1300G 7 t load-haul-dump unit – was mobilised at the 670-level for lateral development mining.
During the period, a total of 30 m of lateral development for the production shaft was completed, with activities in this shaft including the shaft sinking of 114 m and the establishment of the 670-level station catwalk.
Additionally, Lucara also completed the commissioning of the temporary bulk air coolers at each shaft, while construction at the permanent bulk air coolers at the production shaft continued.
Both shafts have completed sinking through the water-bearing Ntane and Mosolotane sandstones. Sinking and lateral development during the fourth quarter took place in the Thalbala mudstone in dry conditions.
The mid-2023 appointed president and CEO William Lamb noted that this UGP progress was part of Lucara’s effort to focus on the UGP and, with the attendant resource deployment, presented an “exciting and valuable future for Lucara”.
Meanwhile, Lucara also signed a contract for fabrication of the permanent personnel and materials winder during the fourth quarter of 2023, representing the last major component for the permanent winders of the production shaft.
Mining engineering advanced with a focus on supporting shaft sinking, underground infrastructure engineering and finalising level plans, Lucara reports.
UGP Scheduling
Lucara updated the Karowe UGP schedule and budget during July 2023 in response to slower-than-planned ramp-up to expected sinking rates in 2022, and, to account for time incurred to complete grouting programmes while mining through the water-bearing geological zones.
The ventilation shaft is currently 61 m, or about 26 days, ahead of the July 2023 schedule update; while the production shaft is 11 m, or about 24 days, behind the July 2023 schedule update, mainly owing to an unscheduled grouting event.
These chemical grouting programmes took longer than anticipated as a result of a combination of high-water volumes in the sandstone lithologies between the depths of 144 m to 262 m below the shaft collar, as well as owing to technical challenges associated with the transition to main sinking.
The updated schedule incorporates a 28% increase in the duration of construction, extending the anticipated start of production from the underground from the second half of 2026 to the first half of 2028.
The revised forecast of costs at completion is $683-million (including contingency) – a 25% increase to the May 2022 estimated capital cost of $547-million.
The forecasted increase of $136-million in estimated capital to reach project completion is predominantly related to increased schedule duration and related labour costs, which make up about 56% of the total increase; grouting costs, which account for about 20% of the total increase; while the balance is attributable to owner's costs, procurement and indirect project costs.