Mining in focus
L
ocated in Pretoria, Cullinan
Diamond Mine is well known
for its rare blue diamonds and is
considered the world’s largest diamond
resource. The mine was acquired by
Petra Diamonds in 2008, which has
operations in Botswana and Tanzania.
In 2017, the mine managed to produce
diamonds that made up two-million
mega carats in total.
The mine uses two methods: sublevel
caving (SLC) and block cave mining.
In the old block cave areas, pillar
mining (retreat mining) was used.
“Similar to more conventional mines
that mine multiple narrow reefs on
different elevations simultaneously,
Cullinan Diamond Mine also exploit
different mining blocks within the
subvertical kimberlite pipe intrusion
on different horizons across the pipe.
Mining blocks are remote and demand
effort and time to travel between them,
making any localised blast system
complex to manage, time consuming,
and more prone to blast failures and
safety breaches,” explains Johan du
Plooy, drill and blast engineer at
Cullinan Diamond Mine.
The mine is over a hundred years old,
having been established in 1903. The
mine has two vertical shafts: one shaft
for transporting material and people,
and the other for bringing out the rock
from the mine.
On average, it produces four million
tonnes of diamonds a year, averaging
16 000 tonnes each month, and
operates on a five-day work week,
which works out to 250 shifts a year.
There are 210 vehicles, including a fleet
of LHDs (six and nine tonnes), utility
vehicles, and dozers.
Expansion and new plant
The Centenary Cut (C-Cut) project is
expected to ramp up production and
is close to full production. The C-Cut,
supplemented by primarily the CC1
East block, will deliver the run-of-mine
(ROM) production.
The C-Cut Phase 1 expansion project
is currently in production at Cullinan.
For this project, a new block cave
being was established on the western
side of the ore body; therefore, block
cave mining methods are being used
for the expansion project. The CC1
East block uses SLC mining methods.
The C-Cut ore body is average grade,
whereas the CC1 East has a higher
grade. The C-Cut project is expected to
[20] MINING MIRROR NOVEMBER 2018
add an additional 1.7Mtpa of diamond
production and is expected to reach
around 4Mtpa from the 2019 financial
year. The CC1 East and the integration
of the C-Cut project will extend
Cullinan’s life of mine to 2028 and
beyond. Cullinan still has a significant
source of diamond reserves, with a total
of 192.74 million carats at a depth of
1 073m.
The current ROM is 34 carats per
100 tonnes; however, with the mine’s
expansion plans, ROM is expected to
increase to 42 carats per 100 tonnes.
By 2020, the project is expected to
reach full production, where 81% of the
tonnages will come from the C-Cut
expansion project.
In 2017, a new plant was built and
completed for Cullinan. The plant
was implemented in May 2017 and
started operating in June 2017. The
old plant had a capacity of 2.8Mtpa
and produces 2.5Mtpa tailings. The
new plant’s capacity will be ramped up
to 6Mtpa ROM, with an initial feed
of 4Mtpa ROM. The tailings will be
between 2.3 and 2.5Mtpa.
There have been significant changes
with the equipment of the new plant,
one of which is the reduction of the
conveyor belts from 151 to 22. As a
result, the total kilometres covered
by the conveyor belts decreased from
15km to just 3km. The new plant also
has 22 screens and seven pumps — a
reduction from the previous plant’s
88 and 121, respectively. Due to these
and other changes, the new plant
will reduce the processing footprint
at Cullinan from 26 hectares to five
hectares.
The old Cullinan plant was originally
commissioned in 1947 and has been
revamped over the years since its
initial construction. The plant’s age
and operational complexity make it
expensive to maintain and costly to
operate — especially given the large
size of its footprint.
Construction and maintenance of the
new plant are much lower compared
to the old one. This plant uses less
power and water. In addition, the new
plant has been designed for a higher
extraction percentage, targeting a 97%
extraction factor. The latest processing
technology implemented at the new
plant makes achieving the targeted
extraction percentage possible. The
technology includes autogenous
milling, Bourevestnik X-ray machines,
and high-pressure grinding rolls. The
new plant is expected to optimise
recoveries and improve mining costs.
Benefits of CBS
Neil Alberts, BME’s product manager,
explains that the CBS was designed
to improve efficiencies and production
from a safety and operational point
of view. Petra Diamonds became
a design and development partner
for the CBS. Due to the nature of
underground blasting and the risks
involved in trialling such a system in a
real production environment, finding
a mine that would be receptive to the
idea was not be easy.
Discussions between BME and Petra
about the CBS started around 2016. “In
2017, early March, we started around
the design of the system,” says Alberts.
The CBS was installed at Petra’s
Cullinan Diamond Mine in December
2017, with the first blast taken live on
14 March 2018. Cullinan continues to
use the system.
Alberts believes that one of the
unique offerings of the underground
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