MINE EXCURSION
the team explains that the top part of the structure which has
remained above the water level, has deteriorated more rapidly
as a result of being exposed to oxygen.
According to Shamu, closer inspection of the steel members
(above the water), has revealed that the main structural steel
members are still 9mm thick, despite the wear and tear, which
is still above the specs for a framework of this size and strength.
The original steel installed by Anglovaal was 10mm in diameter.
“A shaft of this size needs beams of only 7mm for the duties we
plan for. Besides, we are not intending to overwork the shaft. In
the Anglovaal days the mine was hauling out 250 000 tonnes of
ore per month (tpm); we will only be carrying 200 000tpm with
two skips, each weighing 22 tonnes, so we will be well below the
maximum capacity,” says Shamu. He adds that Orion has made
provision for 30% of the shaft’s steel to be removed and replaced.
Access to a world-class VMS deposit
Errol Smart, managing director and CEO of Orion says that
initially they felt the water would be too murky to get a clear
view all the way to the bottom of the shaft. “But at the moment
(at the time of writing in early February 2020) we are at 758m
below the water surface with the camera and we have visual
confirmation that there are no skips or cages in the shaft, which
was our other initial concern, says Smart.
So, is there a plan B in case the steel structure and headgear are
found to be unsafe and cannot be used? Shamu explains that it
will obviously result in a drop in margins, but that it would have
to be almost a complete collapse to render the shaft unusable.
“In the worst-case scenario, we still have the decline, which
means we won’t be working optimally, but the project will still
be viable,” says Shamu.
Below 1025 level, underneath the bottom level of the historic
mine workings, Orion intends accessing what Van Schalkwyk
regards as “world class VMS copper and zinc deposit of 30.49
million tonnes (Mt) at 1.2% copper and 3.7% zinc.”
The ore body dips steeply and remains open to strike but
flattens out considerably at depth, which is why Anglovaal
packed up and left. They needed to recapitalise to go deeper
and just couldn’t do it, exactly why Orion needs to raise an
additional USD400-million in funding before work can continue.
The portal decline access at Prieska is still in immaculate condition.
The bulk of Orion’s new footprint will start below the 957m
level. That is where they will construct new declines. Anglovaal
made a start in the eighties and blasted an initial trail starting
at 1025m below surface. They used small trucks and Load Haul
Dumpers (LHDs), which wasn’t very efficient, and they just
couldn’t keep up with development. “We will use more efficient
methods of lateral development which will allow us to extract
more ore and build an excellent business case of mining the
rich, deeper deposit, “says Shamu.
Mining the ore
To get the ore out, Anglovaal utilised extremely intensive mining
methods. They used 3.4m by 3.4m drives, 2.4km long. At that
time, they obviously didn’t use remotely-operated equipment
and used crosscuts instead of open stopes, in the process
leaving fantastically sound hanging and footwalls. Thereafter
they put in long holes and had three levels to work from and
dropped the ore down ore passes to a rail system at the bottom
level. At the peak of mining, Anglovaal deployed up to 42 LHD’s
at any one time in the mine.
When Anglovaal left in 1991, they left all the tunnels and shafts intact.
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Thus, the mining method then was extremely development-
intensive. Orion, on the other hand, will automate as much of
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African Mining April 2020
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