Debswana Diamond Mines, Botswana

Debswana is the world's leading producer of gem diamonds, contributing about 30% of world output by value from four mines. Following detailed exploration by De Beers in the 1960s, the Orapa diamond mine, located about 240km west of Francistown, began production in 1971. Since then, Debswana Diamond Company Ltd has opened three more open pits: Letlhakane, which is 50km from Orapa, in 1977; Jwaneng, 120km west of the capital city, Gaborone, in 1981–2; and the P225 million Damtshaa, which is 20km east of Orapa and is managed from there, in 2003. In 1989–99 the P1.6 billion Orapa 2000 project doubled capacity there, while the engineering firm Bateman is currently studying the feasibility of doubling capacity at Damtshaa to 400t/d. The operations draw artesian water that is carefully recycled.

Debswana is a 50/50 partnership between the Botswana Government and Swiss-based De Beers Centenary, a 100% subsidiary of DB Investments/De Beers SA in Luxembourg. The Botswana Government has a 15% interest in DB Investments which it took over from Debswana. The company had an overall workforce of about 5,500: 180 at Damtshaa, 2,150 at Jwaneng, and a total of 3,137 at the Orapa and Letlhakane operations, as of 2003.

GEOLOGY AND RESERVES

The AK1 kimberlite at Orapa intruded Archaean and Karoo Supergroup strata some 93 million years ago. The kimberlite covers 118ha at surface, but comprises two individual intrusions that coalesce near the surface. Rocks from all three facies (crater, diatreme and hypabyssal) have been identified. Current mining levels are contained within the crater-facies units. At Letlhakane, three different distinct episodes of intrusion are currently recognised in the D/K1 kimberlite, resulting in the formation of two ore types. LM2 (Letlhakane Mine 2) has a basalt content ranging from 5% to 80% while LM1, found in the northern half of the pipe, has less than 10% basalt.

There are four pipes at Damtshaa. The 5.5ha B/K1, which was actually the first kimberlite to be discovered in the Orapa/Letlhakane province, partly comprises tuffisitic kimberlite breccia (TKB). B/K9 has a sub-outcrop area of 11.4ha, includes hypabyssal kimberlite and TKB, and contributes 88% of the new mine's output. The B/K12 pipe, 800m northwest of B/K9, has a sub-outcrop area of 3.2ha, and a maximum diameter of just over 200m with sedimentary crater facies infill to at least 90m depth. The B/K15 kimberlite can generally be described as a diatreme-facies TKB.

The kimberlite pipes at Jwaneng intruded shales of the Transvaal Supergroup about 250 million years ago, and are older than most kimberlites in southern Africa. They are filled with crater-facies material to a depth of 600m, the dominant infill being reworked volcaniclastic kimberlite, but each pipe exhibits a distinct geology and diamond grade signature. In 2004, mining revealed the existence of a fourth pipe.

The company does not publish information about its reserves.

MINING

Working a seven-day week, the open pits are medium- to very large-scale operations: Orapa extracts 20Mt/y of ore and 40Mt/y of waste. They use rotary drills and large shovels, either electric where grid power is available or diesel / hydraulic where it is not, dozers, wheeled loaders, and a variety of Caterpillar and Komatsu haul trucks ranging from 85st capacity to 240st capacity Caterpillar 793Cs used at Jwaneng. Truck dispatch is by computer-based systems, and Jwaneng has a Gemcom integrated mine production and management system.

PROCESSING

Debswana introduced in-pit crushing at Jwaneng in the mid-1990s. Following secondary crushing, dense-medium cyclones separate 99% of the waste from the diamonds. Tailings from this process are recrushed and recycled. Security is a key feature of plant design, especially the materials-handling systems. For example, pneumo-drier conveying systems simultaneously transport, dry and protect particulate materials.

The concentrate from Orapa, Letlhakane and Damtshaa goes to the multi-storey Completely Automated Recovery Plant (CARP) at Orapa, and that from Jwaneng to a similar facility on site. The Jwaneng CARP is part of the Aquarium project, which reached full capacity during 2003 and added the Fully Integrated Sort House to handle the diamonds recovered by both CARPs. The Aquarium project was De Beers' first fully hands-off recovery and sorting facility, utilising X-ray and laser technology. The Orapa process plant will be replaced by 2010, and that at Jwaneng in 2011, at which time a new tailings dump-treatment plant should start work at Letlhakane.

PRODUCTION

In 2005, Debswana recovered a third successive record amount of diamond, 31.89Mct compared with 31.12Mct in 2004 and 30.2Mct in 2003, despite a major slope failure and the loss of a loading shovel by fire at Orapa. Orapa, Letlhakane and Damtshaa contributed 16.3Mct and Jwaneng 15.6Mct.