Mine excursion
the high life — to the detriment of the
company. West Wits now mostly uses
South African geologists and recently
completed a drilling project close to the
Circular Shaft, which proved positive.
Ripping the reefs
West Wits has also completed some
trenching, which is done at right angles
to the reef to locate the outcrop and
define the stratigraphy. Over billions
of years, the Witwatersrand system has
faulted and shifted, so the reef is not
always uniform, which makes trenching
important. “Our trenches are about two
metres deep and probably about 40–50m
long,” says Swart.
West Wits will mostly mine the
Kimberley Reef and the Bird Reef, but
also some of the Main Reef and the
South Reef, north-east of Main Reef
Road. The Main and South Reefs were,
of course, targeted mostly by mining
companies throughout the years, and
formed the backbone of the South
African gold mining industry for more
than 120 years. So, although there are
pockets of the Main Reef left, it won’t
be the number one target.
The total area covers about 6 000ha
and the surface footprint of mining
will only cover less than 2%. In the
[18] MINING MIRROR OCTOBER 2018
first phase, West Wits will be using
opencast methods to mine. “The pits
will not be there for more than six to
eight months, before we backfill and
rehabilitate them again,” says Quinert.
In total, there will be about eight
open pits. After four to five years,
the operation will refurbish the old
Circular Shaft, and work will continue
underground. The plan is to have two
entry and two exit shafts, and each
shaft will cover an area of about 20m.
According to Milne, there is no need
to build a processing plant on site, as
there are many plants in the vicinity
that are not running at full capacity.
Currently, West Wits is recovering
about 900–1 000 ounces per month
from what they call the Sol Plaatjie
site, and that ore is sent to Sibanye
Gold’s Ezulwini plant, about 40km
west of the operation.
“The four Spanish Xcentric
Rippers enables us to mine the reef
at surface without blasting. We have
been operating at Sol Plaatjie for
over 12 months without blasting
at all,” says Milne. The reefs at this
site are very shallow and the deepest
the machines have mined is about
30m below surface. “The rippers are
running at close to an 80% efficiency,
which is what you would expect from
a traditional load and haul operation.
Although the life expectancy of an
excavator is longer (up to 15 000
hours), the ripper comes in a discount
of almost R7-million,” says Milne.
The rippers, of which there are two
50-tonners and two 80-tonners on site,
open up about 200m² of the surface per
hour. Drilling and blasting costs about
R20 per square metre, in comparison to
the R8 a square metre achieved with the
technology. “Since we started mining the
Kimberley Reef with these four rippers, we
have mined more than 1.5 million tonnes
of material, which we separate into waste
stockpiles and reef stockpiles,” says Milne.
The mining contractor, ALS Group, uses
40-tonne and 50-tonne excavators and a
fleet of Bell B30 ADTs to load and haul
the material. The 40-tonne excavators are
used for the reef, while the 50-tonners
are employed to load the waste. There are
three ADTs for each excavator.
Icy winds of change
Quinert says that West Wits would
eventually produce about 30 000–35 000
ounces of gold per year from the
opencast operations in the first three
to four years, while it hopes production
will peak at close to 80 000 ounces per