Botswana’s Karowe mine has been covered in a number of articles in Modern Mining over the past several years. For a fresh look at the mine, and in particular its astonishing record of large stone production, we publish here an article by Michael (Mike) Brook, who is employed as a project manager by Debswana but who has also forged a name for himself as a writer of books on Botswana, including its diamond mining industry and its wildlife.
Karowe is located in northern Botswana, 22 km south-east of the Orapa mine, which was established in the early 1970s as the nation’s first diamond mine after the kimberlite on which it is based (A/K1) was discovered in 1967. Karowe is wholly owned by Lucara Diamond Corporation and has been a remarkable success story in its first five years of production.
The Karowe mine showing the processing plant area.
Between 1967 and 1976, De Beers discovered a grand total of 79 kimberlites, the host rock for diamonds, in Botswana, 75 of which were in the Orapa Kimberlite Field (OKF) and eight of which were diamondiferous. This was truly the heyday for De Beers’ exploration in Botswana with this period also seeing the discovery of the kimberlites which later led to the development of not only Orapa and Karowe but also the Letlhakane, Damtshaa and B/K11 mines.
Karowe mine (Karowe means a precious stone in the local Sesarwa language) ranks as one of the most valuable in the world. The developers have seen their initial investment increase over 10-fold and it has delivered some incredible, large exceptional stones, including the brilliant Lesedi La Rona in November 2015, the second largest rough stone recovered to date, and Botswana’s largest, thereby carving Karowe mine and Botswana firmly into the diamond history books. In February, 2016, Thembani Moitlhobogi won the national competition to name the massive 1 109-carat (ct) stone (a carat equals 0,2 grams in weight) Lesedi La Rona, meaning ‘Our Light’.
The largest rough gem diamond ever recorded, the Cullinan, weighing 3 106 ct, was mined from Premier mine in South Africa in 1905 and named after the mine’s chairman, Thomas Cullinan. It produced no fewer than 105 cut and polished diamonds, including the second largest to date, the Cullinan I at 530 ct. The Star of Africa, at 546 ct, is the largest cut and polished gem; it was cut from a 756-ct stone, also discovered at the Premier mine, in 1985. The Lesedi La Rona gem therefore offers a perfect opportunity to be cut into one of the world’s largest ever finished diamonds. It was bought by Graff Diamonds in 2017 for US$53 million and they are currently weighing up their options. According to Laurence Graff, their founder and Chairman, “this stone will give us a collection of diamonds like no other – they will be among the most valuable diamonds ever created.”
Ownership of Karowe has passed hands three times; De Beers discovered the kimberlite in 1970 but their early evaluation showed the A/K6 pipe to be sub-economic with poor mineral chemistry, a small resource (it has a surface area of just 3,4 ha compared to Orapa’s 118 ha) and a very low diamond grade. In 2009, De Beers sold their 70 % shareholding in the project to Lucara Diamond Corporation, based in Canada, for US$49 million.
A 2010 Feasibility Study, using new data and more advanced techniques of evaluation, concluded that A/K6 could be developed into a mine with the project delivering an NPV of US$189 million. The capital investment required was estimated at just US$165 million. This study also proved the pipe actually had an area of 4,2 ha at surface which expands to 7,0 ha at a depth of 120 m and also has a much higher diamond grade of 19 carats per hundred tons (cpht) with a price tag of US$183/ct (rough diamonds are valued based on their size, shape, quality and colour, otherwise commonly known as the 4Cs (carat, cut, clarity and colour), a grading system which was invented by the Gemological Institute of America back in 1953).
In the same year, Lucara bought African Diamonds’ 30 % shareholding in the A/K6 project for US$70 million in stock, thus making Lucara the sole owner through Boteti Mining. Lucara is now valued at almost US$1,0 billion – a remarkable figure since it paid only US$120 million for Karowe seven years ago.
The Karowe mine was commissioned in 2012 and consists of three lobes, South, Centre and North, of which the South Lobe makes up approximately 75 % of the kimberlite’s original resource potential. Construction of the mine required a capital investment of approximately US$120 million, which includes the process plant and all mine site and off-site infrastructure. Karowe now employs over 800 people, more than 98 % of them Botswana citizens.
Instead of using conventional scrubbers and crushers to disaggregate the kimberlite ore in order to liberate the diamonds, this mine uses an autogenous (AG) mill. The AG mill acts as a tumbling mill where the ore is reduced in size by the interaction between the pieces of ore through tumbling. This non-crushing process, along with more sophisticated sensor-based bulk sorting using X-Ray Transmission (XRT) technology supplied by the Tomra Group, has resulted in less diamond breakage and the ability to recover the exceptional over-size stones for which Karowe is now famous.
Between July 2012 and December 2017, over 2,0 million carats (Mct) were mined and sold, generating in excess of US$1,2 billion in revenue.
Diamonds greater than 10,8 ct in weight, the lower threshold for exceptional size stones, represent approximately 5 % by weight of all diamond production over the life of mine to date. Life of mine average stone size for the +10,8-ct production is 27,8 ct/stone. Lucara sells its production in Botswana through regular and exceptional stone tenders. The largest stones are sold through the exceptional stone tenders, where buyers submit sealed bids over a number of days. There are about four to five regular and one to two exceptional stone tenders each year.
By the end of 2017, Lucara had sold 156 exceptional diamonds for more than US$1 million each, generating US$598 million.
In 2015, with the commissioning of the XRT circuits, Karowe ‘rocked’ the diamond world with the recovery of seven +300-ct diamonds. Three of these incredible exceptional stones were recovered in the same week in November: the Lesedi La Rona at 1 109 ct, The Constellation at 813 ct and the smallest gem, an unnamed 374 ct. Earlier in the year Karowe had recovered the 342-ct Queen of the Kalahari. The combined weight of 2 638 ct sold, via tender and solo sale, for a stunning US$154 million, more than the cost of developing the mine. Stones cut from the Queen of the Kalahari have adorned Charlize Theron on the red carpet at the Oscars.
In April 2018, Lucara again made the headlines by recovering a 472-ct light brown diamond, the third largest ever for Karowe.
Significant stone recoveries and sales from Karowe mine to date are: 156 individual diamonds sold for more than US$1,0 million each; six diamonds of more than 300 ct as single diamonds; 77 gem quality diamonds of more than 100 ct sold as individual diamonds; and 54 diamonds between 100 ct and 199 ct.
The mine’s estimated resource down to a depth of 700 m is over 14 Mct with a 2018 production of between 270 000 to 290 000 ct worth between US$170 and US$200 million. Open-pit mining is scheduled until the year 2026, after which underground mining will be a possible option.
Up until the incredible 2015 discoveries at Karowe, the largest diamond discovered in Botswana was that at Jwaneng mine in March 1993, weighing 446 ct. In January 2016, a beautiful 425-ct gem was also discovered at Jwaneng.
The superb gem quality stones from Jwaneng, owned by Debswana, are used in some of the finest jewellery in the world, proudly worn by film stars and dignitaries. In 2013, a pear-shaped colourless diamond, mined from Jwaneng and weighing 101,73 ct, was sold for US$26,7 million at Christie’s International jewellery auction in Geneva, Switzerland. It had taken almost two years to cut and polish. It was bought by the Harry Winston Corporation and has subsequently been named the Winston Legacy.
With future improvement in diamond XRT recovery technology, and with more Botswana mines now wanting to adopt such technology, specifically to safeguard against accidental diamond breakage, the chances of another Lesedi La Rona being recovered are very high.
At the time of independence from the UK in 1966, Botswana was a very poor country with a GDP per capita of only US$70. The discovery of the Orapa kimberlite in 1967 was about to change all of that.
Today Botswana is a modern African state, a middle income country with a GDP per capita of about US$7 450, more than 100 times that of 50 years ago. In 2017, revenue from diamond mining accounted for almost 30 % of government revenue, 76 % of foreign exchange and 16 % of GDP.
‘Botswana’s Diamonds – Prospecting to Jewellery’ and also ‘Botswana Diamond Jewellery’, both authored by Mike Brook, are available on Amazon.com