African Mining | Page 31

OPERATIONS •

deepened to a depth of 904m below surface . The upgraded Shaft 3 will transport workers and material to and from the new C-Cut phase block 1 .

After being tipped by the skip on surface , the ore is either fed onto the surface stockpile , or directly into the plant . The stockpile is indicated to have a capacity of 60 000t . The ore is fed into the plant at an average rate of 550t / h . The ore is washed and screened at the entrance to the plant . The oversized rocks are crushed and , together with the screened product , pass through an X-ray sorter where any large diamonds are extracted . Interparticle crushers and a re-crush section reduce the ore feed to less than six millimetres in size . The ore is then passed through a dense media separation process at various stages . The concentrate is sent to the recovery section where grease belts and X-ray machines are used to recover liberated diamonds before final sorting .

© Sharyn Macnamara , African Mining

Headgear of the No 1 vertical shaft .

Mining Method The Cullinan mine employs a standard block cave mining method to develop underground resources . This method is suited to a massive orebody , and has the advantage of lower unit costs , since it is not necessary to drill and blast every ton . This is done by establishing a drilling level built-up through which the ore body is cut by drilling and blasting . Once a large area is undercut , caving is initiated . Mining works are also performed at the undercut level . The mining work includes long-hole drilling , charging , blasting , and tramming of required ore . The operational production level is located 15m below the undercut level and tunnels are bored into the orebody at the level that is in production . Draw points are developed on these tunnels and raise-bored . A draw bell is built-up to receive the caved ore , from where it flows into the draw point . Rocks which are still too big to be loaded by the six-ton capacity production machines must be reduced in size . This part of the process is called secondary blasting . The big rocks are drilled and blasted until they are reduced to a manageable size . Load haul dump trucks load the ore and carry it out of the orebody . Currently up to 43 % of kimberlite ore is extracted to carry out the mining operation .

The extension of life for the Cullinan diamond mine is referred to as the C-Cut expansion plan . The main elements include the deepening of Shafts 1 and 3 , along with the related infrastructure to the shaft and planned level development to the Cullinan ore body . 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 350m-deep existing shaft 1 will be deepened to a depth of 920m below surface . It will hoist the ore and waste from the new C-Cut phase 1 block after the process of deepening the shaft project has been completed . The 60m-deep existing shaft 3 will be

© Dr Nicolaas Steenkamp

Per Petra , Cullinan contains a world-class gross resource of 149.82 Mcts as at 30 June 2021 , which suggests its mine life could be significantly longer than the current mine plan to 2030 .

Sources : Sharyn Macnamara Sources : 1 . Petra Diamonds Limited press release , 22 February 2022 : Interim results for the Six Months ended 31 December 2021 , Investor update on strategy and operational guidance 2 . www . petradiamonds . com 3 . Cullinan Mine Tours

Dr Nicolaas Steenkamp Sources : 1 . Cullinan Diamond Mine , South Africa . [ https :// m . miningweekly . com / article / cullinan-diamond-mine-2003-11-14 ] 2 . Premier Mine , South Africa . [ https :// m . miningweekly . com / article / premiermine-x2013-gauteng-1999-09-10 ]

Silos

Cullinan is known the world over as a source of some of the largest , high-quality gem diamonds , including Type II stones , as well as being the world ’ s most important source of blue diamonds .’