De Beers’ first new diamond mine to be built in South Africa since Venetia two decades ago, the R1.3 billion Voorspoed mine in the Free State, is expected to produce 800,000 carats a year when in full production.

The sod turning ceremony for the project took place in October 2006, the main construction of the Voorspoed mine by Murray & Roberts Cementation was completed by April 2008, and by August/September the commissioning of the operation was largely complete. When the mine held its official opening on the 4th of November 2008, operations manager Andy Taylor told Mining Review Africa the mine had already completed a 72 hour test run at its nameplate rating and was running at 60% of nameplate capacity on a round the clock basis. By January 2009, Voorspoed is expected to be operating at full capacity.

De Beers has owned Voorspoed, located about 30 kilometres north-east of Kroonstad, since 1912 when it purchased it from the Voorspoed Diamond Mining Company which had closed the mine after experiencing difficulty mining the hard and competent kimberlite. At the time the technology for crushing the ore did not exist to recover diamonds from the Voorspoed kimberlite pipe economically. In the old days the mined material was laid out for five to eight years to allow natural weathering to do the job of breaking it up. Taylor describes the mine as marginal, and while sampling took place in the 1960s and 70s, it was not developed until now. He says it will be the lowest cost producer in the De Beers stable.

The crushed ore stockpile

The crushed ore stockpile at
Voorspoed holds some 100,000
tonnes of material.

Taylor says that Voorspoed is different from previous De Beers mines in that it uses a single process stream entailing less redundancy than the group traditionally built into its operations. The use of a high pressure roll crusher (HPRC) is also a first for the company.

Voorspoed is an open pit mine, currently being mined to a depth of 47 metres and which will be mined to a depth of some 360 to 420 metres, using standard drill and blast methods. The mine will deliver some four million tonnes of kimberlitic material to the plant each year.

ANDY TAYLOR

Voorspoed operations
manager Andy Taylor.

The blasted material is loaded into haul trucks and transported to the primary crusher. This is a jaw crusher, situated underground for safety reasons and to ease tipping by the trucks, which reduces the material to -200 mm, before the material is transported to a secondary, cone, crusher which reduces it to -60 mm. This material is conveyed to the mine’s crushed ore stockpile, which holds some 100,000 tonnes.

Material from the crushed ore stockpile is then conveyed to the HPRC for tertiary comminution. “Combining the tertiary crushing and the recrush comminution is also new for De Beers and it saved us about R40 million. Another saving, of some R20 to R30 million, was due to using two dense media separators (DMS) instead of the originally planned for three,” Taylor says.

The processing plant is highly automated with only 14 people required per shift. The HPRC product is scrubbed and screened prior to the +1.5 mm and -25 mm material being sent to the DMS section for concentration. The sinks material from the DMS then reports for further concentration using De Beers’ X-ray technology prior to hand sorting.

The -6 mm to +0.5 mm coarse residue is stored on the resource tailings facility. The -0.5 mm residue slurry is thickened in two high rate thickeners and the paste underflow is pumped by centrifugal pumps to the ultra fines disposal facility. The mine is designed to use 0.6 m3 of water per tonne of ore mined.

The Voorspoed plant.

The Voorspoed plant.

Voorspoed is expected to be operational for the next 12 to 16 years and over its life of mine, it is expected to produce more than 10 million carats. The average stripping ratio of the mine over its life is 2.1:1 and its stripping requirements will peak at 6:1. The mining equipment is owned by Voorspoed, with the drill rigs having been supplied by Sandvik Mining and Construction and the load and haul fleet by Barloworld Equipment. AEL has the blasting contract.

The mine will produce some 18 to 20 carats per 100 tonnes and while it does not feature many large stones, the diamonds from Voorspoed include rare pinks and fine yellows. The total amount of diamonds recovered by the beginning of November at Voorspoed was 89,000 carats, with some 7.7 million tonnes of material having been moved and 847,000 tonnes treated. The diamonds recovered had an average value of US$120 a carat, above the South African average of US$100 a carat.

The Voorspoed open pit.

The Voorspoed open pit.

Gareth Penny, group managing director of De Beers at the opening ceremony, said that Voorspoed was the fourth major project De Beers has inaugurated in 2008, the others being the Snap Lake and Victor mines in Canada and the launch of the Peace in Africa diamond mining vessel that is operating off the shores of South Africa. Voorspoed will have some 350 permanent De Beers employees as well as 80 partner company employees. During the life of the mine, in excess of R1 billion will be generated in the Free State region. The mine is also promoting the women in mining initiative, and Taylor says that by 2011, 52% of the mine’s employees will be women.

Nicky Oppenheimer, the chairman of De Beers, said that through Voorspoed together with Peace in Africa, and upgrades at operations such as Finsch, De Beers has demonstrated its faith in South Africa by investing R3 billion in projects in the country.