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DIAMONDS
32
MODERN MINING
November 2016
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
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).