Name:

Karowe Mine.

Location:

North-central Botswana; the mine is part of the Orapa/Letlhakane kimberlite district.

Mine Owner/s:

Lucara Diamonds subsidiary Lucara Botswana (formerly Boteti Mining).

Brief Description:

Karowe is one of world’s foremost producers of large, high-quality Type IIA diamonds.

Brief History:

De Beers discovered the AK6 kimberlite in 1969; however, the project was not pursued until 2000, when further drilling and geophysical surveys indicated that the pipe was larger than previously estimated. De Beers released the project to a joint venture in April 2004.

Following the completion of a feasibility study in October 2008, Lucara acquired a 70.27% interest in Boteti Exploration from De Beers, with Boteti the holder of the AK6 development project.

In 2010, Lucara acquired African Diamonds, thereby becoming the 100% owner of the AK6 project. It also updated the feasibility study and published the AK6 Kimberlite independent technical report in March 2010. In July 2010, Lucara decided to proceed with the construction of the mine. The AK6 diamond mine was renamed Karowe diamond mine in December 2011.

Commercial production started in 2012 and the first record recoveries – the 813 ct Constellation Diamond and 1 109 ct Lesedi La Rona – were made in 2015.

Primary Metals/Minerals:

Diamonds.

Secondary Metals/Minerals:

None.

Geology and Mineralisation:

The Karowe Mine is exploiting the AK6 kimberlite which is part of the Orapa Kimberlite Field in the Central District of Botswana.

The country rock at Karowe is sub-outcropping flood basalt of the Stormberg Lava Group (about 130 m thick), underlain by a condensed sequence of sedimentary rocks that form part of the Karoo Supergroup (about 345 m thick), below which is the granitic basement.

AK6 is a north‐south-trending elongate kimberlite body (with a surface expression) of about 3.3 ha and a maximum area of about 8 ha, about 120 m below surface. It comprises three geologically distinct, coalescing pipes – known as the North, Centre and South lobes – that taper at depth into discrete roots.

The South Lobe is the largest of the three lobes; it is also distinctly different from the North and Centre lobes, which are similar in terms of their geological characteristics.

The South Lobe is broadly massive and more homogeneous than the North and Centre lobes, which exhibit greater textural complexity, and more variable and higher proportions of internal country-rock dilution.

Reserves:

Lucara reports that, at December 25, 2021, Karowe’s openpit operation had a probable reserve of 9.7-million tonnes containing about 1.37-million carats.

Its underground prospect had a probable reserve of 37-million tonnes containing about 5.23-million carats.

The total mineral reserve, which also includes stockpiles, amounted to about 55.9-million tonnes containing 7.3-million carats.

Resources:

At December 25, 2021, Karowe had a total indicated resource of 46.43-million tonnes containing 7.2-million carats, with an inferred resource of 6.9-million tonnes containing 1.19-million carats.

Type of Mine:

The openpit operation will reach the end of its life in 2026, at which point the mine will transition to an underground operation, with a life-of-mine (LoM) to 2040.

Mining Method:

The openpit operation is mined using conventional drill-and-blast methods, with truck and shovel operations.

The underground operation will be a long-hole shrinkage operation. 

Major Infrastructure/Equipment:

Initially, material was processed through a diamond treatment plant comprising primary crushing, autogenous milling, dewatering and screening, dense-media separation (DMS), processed kimberlite disposal, X-ray machines and hand sorting.

The comminution and diamond liberation unit processes of primary crushing and autogenous milling produced material to be treated by the DMS. The DMS concentrates were further treated in a final recovery plant employing magnetic separation and  X-ray recovery technology.

Lucara, having implemented various diamond recovery projects after 2012, notes that it now has a mega diamond recovery circuit, which treats material of between 50 mm and 120 mm. The circuit – the commissioning of which was completed in 2017 – is located directly after the primary crusher and before of the process plant. This design maximizes the upfront recovery of “exceptional diamonds” prior to the comminution processes, where diamond damage may occur.

The plant also has a submiddles X-ray transmission (XRT) circuit that processes material of between 4 mm and 8 mm. The submiddles circuit, also commissioned in 2017, replaced the need for a DMS and five diamond recovery unit processes.

Prospects:

In November 2017, Lucara announced the positive results of its preliminary economic assessment for the development of an underground mine, intended to start production once Karowe’s openpit mine reached the end of its life.

The feasibility results were released in November 2019, with the company noting that the underground expansion was expected to double the mine life and generate significant revenue and cash flow to 2040, with an LoM production of 7.8-million carats.

The study also confirmed the long-hole shrinkage underground bulk mining method, owing to its enabling early access to higher-value ore and allowing for a short payback period.

Lucara, following the onset of the Covid-19 pandemic, decided to limit capital expenditures related to the underground expansion project. Consequently, in 2020, it focused on activities, such as detailed engineering and design work and early procurement initiatives, with a particular focus on long lead time critical-path items.

In May 2021, the company secured $220-million, in credit-approved senior debt facilities, to fund the project, with the Lucara board formally approving the expansion in September 2021.

By June 2022, pre-sink activities for the production and ventilation shafts were completed, including the placement and erection of headgear for the production shaft. Meanwhile, the main sinking of the ventilation shaft had started; the production shaft stage winder was installed and roped up, and the procurement of shaft station underground mobile equipment and the mine bulk air cooler was initiated.

However, the project has experienced sink-related delays, with the company releasing an updated schedule and budget for the project, in August this year.

The anticipated start of production from the underground expansion project has been moved from the second half of 2026 to the first half of 2028, with a revised forecast cost of completion of $683-million, compared to the initial estimate of $547-million.

Lucara CEO Eira Thomas explained when that the reviewed schedule and budget have increased costs by about 25%; however, sufficient surface stockpiles will ensure that the mill operates to capacity and the project remains economically robust.

Contact Details:

Lucara Diamonds
Tel +1 604 674 0272
Email info@lucaradiamond.com

Sources:

Lucara Diamonds. Website https://lucaradiamond.com

Lucara Diamonds. Operations. Karowe Mine.

Lucara Diamonds. Lucara Announces Completion of its Diamond Recovery Capital Projects (September 11, 2017).

Lucara Diamonds. Lucara Announces Positive Preliminary Economic Assessment for Karowe Underground (November 02, 2017).

Lucara Diamonds. Lucara Continues to De-Risk Potential for Karowe Underground - Feasibility Scheduled for Completion in H2 2019 (January 24, 2019).

Lucara Diamonds. Lucara Announces Positive Feasibility Study for Karowe Underground (November 04, 2019).

Lucara Diamonds. Karowe Mine Underground Feasibility Study Technical Report Botswana (December 17, 2019).

Lucara Diamonds. Lucara Announces Q2 2020 Results Delivering Strong Operating Performance and a Groundbreaking Supply Agreement for 2020 (August 10, 2020).

Lucara Diamonds. 2022 Mineral Resource Update.

Lucara Diamonds. Lucara Announces Strong Q2 2022 Financial and Operational Results as Underground Shaft Sinking Commences (August 10, 2022).

Mining Weekly. Website https://www.miningweekly.com

Mining Weekly. Lucara secures $220m for Botswana diamond mine expansion (May 6, 2021).

Mining Weekly. Lucara’s Botswana expansion formally approved (September 24, 2021).

Mining Weekly. Lucara posts higher output, recovers fourth diamond weighing more than 1 000 ct at Karowe (August 10, 2023).