The underground expansion project of Karowe Mine (KDM) in Botswana will help in extending the operational life of the property and continue diamond production.
The mine is fully owned by Lucara Diamond, a Canadian diamond mining company.
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As per an updated Feasibility Study (FS) reported in March 2024, the underground portion will be completely constructed in 2027.
The Life of Mine (LOM) capital for the project is estimated to be $752.3m. Underground operations are expected to run for a total of 15 years from 2028 to 2042.
Karowe Diamond Mine Background
Karowe Mine is located in Central Botswana. It is known for producing large, gem quality, Type IIa diamonds.
The project, comprising an existing open pit (OP) mine and processing facility, commenced commercial operations in July 2012.
It feeds around 2.7 million tonnes per annum (Mt/a) of feed to the processing plant.
KDM has processed more than 28 million tonnes (Mt) of ore and sold around 3.9 million carats (Mct) since operations began, according to the updated FS.
In 2015, the plant was upgraded with XRT machines. The refurbishment included the commissioning of a new secondary gyratory crusher, a tertiary crusher, and upgrades to the existing recovery building, XRT sizing, and XRT diamond recovery circuits.
In 2017, a Mega Diamond Recovery Project was completed which included the installation of XRT sorting technology ahead of the AG mill. This will sterilise the diamond feed above 50mm.
The underground expansion project received approval from Lucara board of directors in September 2021. The project was approved following financial close and other conditions were met.
In February 2024, Lucara signed a 10-year New Diamond Sales Agreement (NDSA) with HB Antwerp, a diamond cutting and technology company.
The in-situ open-pit reserve may be depleted by 2025. As per the updated FS, the open pit has approximately two years of stockpiled kimberlite ore, which will be used to meet the production gap between the closure of the OP and the start of underground production.
Karowe Project Reserves
According to the 2023 Mineral Resource Statement, Karowe includes 41.92Mt containing 6.60 million carats (Mcts) of diamond at a grading of 15.8cpht and 2.90 tonnes per metre cube (t/m3) density in the indicated category.
The inferred mineral resource of the mine is 5.42Mt containing 1.01Mcts of diamond at a grading of 18.6cpht and 2.97t/m3 density.
Total probable reserves at Karowe were estimated to be 52.2Mt containing 6.834 Mcts at a grading of 13.1cpht.
Karowe Underground Expansion Details
The open-pit operation at KDM involves a conventional drill-and-blast mining approach, using diesel-powered excavators and trucks. Mining at the open pit is expected to conclude at an elevation of approximately 713 metres above sea level (masl).
The resources that remain below the economic limits of the open pit will be extracted using underground (UG) mining methods.
A 7,400-tonne-per-day (t/d) shaft operation, employing long-hole shrinkage (LHS) mining—a fully assisted caving method—is currently under construction. This underground development, following an eight-year construction phase, is expected to extend KDM’s mine life by an additional 13 years.
The KDM resource is contained within three coalescing kimberlite pipes- North, Centre, and South Lobe. These vertically dipping pipes were originally sub-cropping and differ in size and depth.
The South Lobe is the most significant in terms of volume, with Indicated Resources extending approximately 760 metres below the surface (mbs), from 1,010 masl to 250 masl. The North and Centre Lobes have been excluded from the underground mine plan as their deeper sections remain classified as Inferred Resources.
Within the South Lobe, four distinct domains have been identified, each with unique mineralogical characteristics.
The underground mining operation will employ LHS stoping to systematically drill and blast the entire lobe in a vertical retreat sequence. In this method, blasted material is left in place during stoping to help stabilise the surrounding rock, with only the swell volume being extracted during the blasting phase. Ore mucking will take place from drawpoints located at the 310 Level (310 masl).
As blasting progresses, the ore expands beyond its in-situ volume, and this excess material is removed from the drawpoints to maintain a void for continued blasting. Once blasting is complete, the South Lobe will be fully emptied by mucking from the drawpoints.
Access to the underground mine will be via a 767m deep production/service shaft (P/S) with an 8.5m diameter, extending from the surface to 245 masl.
The shaft will be equipped with two 21-tonne skips for ore hoisting, a service cage for personnel and materials transport, and an auxiliary cage for shaft inspections and worker movement.
Infrastructure
The underground operations at Karowe will include leveraging existing and new infrastructure to support a 2.7 Mt/a UG mine operation.
This includes 220/132kV substation and 132kV switchyard at 400/220kV Letlhakane substation of Botswana Power Corporation, and a 132/11kV substation with switchyard at mine site.
A 29km long 132kV overhead powerline will connect the Letlhakane substation to the mine substation of Botswana Power.
It will also include UGP pad surface substation and power distribution; 8MW of diesel generator back-up power; reverse-osmosis plant water supply plant; sewage treatment plant upgrades; shaft sinking infrastructure and other building and facilities.
Contractors Involved
The updated FS for Karowe Diamond Mine was prepared by JDS Energy and Mining.
JDS was supported by DRA Botswana on mineral processing; Itasca Denver on Hydrogeological modelling; K-Met Consultants on metallurgical testing; Knight Piésold Botswana on waste material management; and PRIZMA on environment, permitting and social considerations.
SRK Consulting Canada offered support with geology, mineral resource estimation and UG material flow simulation, while SRK South Africa conducted geotechnical analysis.
