Modern Mining November 2016

DIAMONDS

undercut level on 824 level (824 m below surface), the new production/extraction level on 839 level and ground handling on 895 m level. The undercut tunnels have been sized to 4 m wide and 4 m high and the extraction level development to 4,2 mwide by 4,2 m high. The production level has a tunnel spacing of 32 m and a drawpoint spac- ing of 18 m. The project also includes the simplification of the ground-handling system, as the deepening of the shafts will allow material to be han- dled only four times by the time it is fed into the hoist-

ing system, compared to the 11 times currently. This is expected to have a positive effect on the operating costs at Cullinan. The upgrade to the ground-handling infra- structure includes not only the new north and south declines (developed from 763 level to the ground-handling level at 895 m below sur- face) and two 1 200 mm strike conveyors (each with a capacity of 850 t/h) but also four large, heavy-duty, high-volume (450 t/h) jaw crushers for both the north and south ramp areas, posi- tioned below the production level, as well as two large storage silos. While several contractors have been involved in the implementation of the C-Cut project, the biggest single portion of the work – roughly a third by value – has been under- taken by Murray & Roberts Cementation, which was awarded the contract to extend the vertical shafts in August 2012. “We’ve extended the No 3 men-and-material shaft from 805 level to 885 level and the No 1 rock-hoisting shaft from 580 level to 934 level,” says Robbie Duyts, Project Executive, Murray & Roberts Cementation. “In both cases, we used the raise-bore and slipe method, which allowed us to deliver excellent development rates as we were able to undertake equipping and sinking simultaneously.” Sinking of the 9,6 m x 2,3 m lined No 1 Shaft was completed in December 2015 while sink- ing of the 7 m diameter x 6 m lined No 3 Shaft has been completed more recently, with com- missioning currently in progress. In addition to the shaft sinking contract, Murray & Roberts Cementation is responsible for the ‘slipe and line’ of the two 13 m x 36 m storage silos, one of which is complete with the second at an

Above: Seen here underground at the C-Cut are (from left): Louis Steyn, Engineer; Daniel Grobler, Managing Director; Robbie Duyts, Project Executive; Gerrie Pieters, Financial Director; Patricia Vergeet, Risk Officer; and Allan Widlake, New Business Director – all fromMurray & Roberts Cementation (photo: Arthur Tassell). Right: Petra’s Andre Cloete (left), Project Manager for the C-Cut, with Michel van Heerden, Project Engineer (photo: Arthur Tassell).

produced since mining first started at the site in 1902. Petra acquired its initial 37 % interest in Cullinan in 2008 (this was increased to 74 % the following year) and wasted no time in pur- suing the C-Cut project, starting on the two declines to access the C-Cut mining block in 2009. In all, the project entails establishing new surface and underground infrastructure to extract the next mining block below the depleted BA5 mining block using block caving with an advance undercut at a production rate of approximately 3,7 Mt/a. The existing vertical shafts (nos 1 and 3 shafts) have been extended to provide access, services and rock hoisting on the C-Cut horizon and this work has included two new shaft bot- toms, a loading level, pumping infrastructure, underground stores and workshops. In addi- tion, the No 1 shaft winder has been upgraded to increase the hoisting capacity to 4 Mt/a from 934 m below surface. The new C-Cut block is 194 m high, with the

32  MODERN MINING  November 2016