Cullinan Diamond Mine, Gauteng, South Africa
Cullinan diamond mine is located in the Gauteng Province of South Africa. The site is situated about 40km east of Pretoria city in Cullinan. The diamond mine is also known as Premier mine.
The open-pit mining at Cullinan diamond mine began in 1903. It is one of the major sources of blue diamonds in the world.
Petra Diamonds purchased a 37% stake in the mine from De Beers in 2008. The company increased this to 74% in 2009 by purchasing Al Rajhi's shares.
Petra Diamonds has planned for the expansion of the Cullinan diamond mine to increase the mine's production from 920,000 carats to 2.6 million carats by 2019.
The mine has a life of more than 50 years. The current mining plan is for 16 years.
Geology of Cullinan mine
Cullinan diamond mine is located on a diamond-bearing kimberlite pipe. The carrot-shaped pipe, with a volcanic neck, is considered to be the largest kimberlite pipe of the region. It was first mined in 1871, the mining site is currently referred to as Kimberley's big hole.
The surface area of the mine is 32ha. The length of the big hole is 1,000m and breadth is 400m. At 500m level below the ground it narrows down to 21ha. The depth of the mine is 190m from the surface.
The Cullinan pipe has three types of kimberlite; brown, grey and black (hyperbyssal).
The diamond mine has a reserve base of 203.7 million carats (mcts). The reserve estimates are based on block cave depletion modelling and external waste. The planned expansion will increase the reserve estimate.
Production at Cullinan
The Cullinan Diamond mine is one of the world's well known producers of diamonds. The largest rough diamond gem of 3,106 carats was produced here.
The acquisition of the mine led Petra Diamonds to discover world-class diamonds, which includes a 39 carat blue diamond, a 26 carat blue diamond and a 507 carat white diamond.
The mine has produced more than 350mt of ore yielding nearly 120mcts of diamonds. It has reprocessed more than 75mt of coarse tailings material and yielded 20mcts of diamonds.
Petra Diamond's expansion plans
Petra Diamonds has planned for a major expansion of the diamond mine. The C-Cut expansion plan includes the deepening of Shafts 1 and 3, related infrastructure to the shaft and planned level development to the Cullinan ore body.
The 350m deep existing shaft 1 will be deepened to 920m. It will lift up the ore and waste from the new C-Cut phase 1 block once the process of deepening completes.
The 60m deep existing shaft 3 will be deepened to 904m. It will take workers and material to and from the new C-Cut phase block 1.
A new block cave will be opened in the C-Cut phase 1 of the Cullinan Kimberlite pipe. The C-Cut phase 1 area is located 200m below the existing operations. The new block will receive the C-Cut reserves.
Murray & Robert Cementation will be responsible for all engineering requirements. ABB will take the charge to upgrade the winder and ropes.
Mining and processing at Cullinan diamond mine
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 July 1971.
Petra Diamonds uses the block cave mining method to develop the underground resources. In this method, a drilling level is built-up through which the ore body is cut by drilling and blasting.
Once a large area is undercut, caving is started. Mining works are also done at the undercut level. The mining work includes long hole drilling, blasting, charging and tramming of required ore.
The production level is located 15m below the undercut level and tunnels are bored into the orebody at the level. Draw points are developed on these tunnels and raise-bored.
A draw bell is built-up to receive the caved ore. The caved ore then flows into the draw point. Load haul dump trucks load the ore and carrry it out of the orebody. Nearly 43% of rocks are extracted to carry out the mining operation.