In the stope
of existing operations. The proclamation of the
Barberton Biodiversity Heritage Site might
have carved out portions of the Barberton
greenstone belt, but these areas were by and
large of lower mineral potential.
Are the existing mines in Barberton
still doing exploration work?
How long do you think these
mining companies will continue in
Barberton?
There might be external factors which can
have an influence – such as the gold price,
for example. Depth is also normally a big
constraint. Historically, mining beyond the
water table was often a major constraint, and
the introduction of technology that resolved
this increased the potential. So, unless a mine
develops some sort of remote mining method
that doesn’t put people at risk, the current
operation may then just become too dangerous
and expensive, resulting in mine closure.
At Lily, for example, Vantage Goldfields
changed the way they looked at the ore body
historically. They didn’t have wonderful 30g per
tonne payshoots, but they had enough low-
grade gold that they could extract it in a bulk
operation. They changed the mining method,
which unlocked the metal. As a result, this
became a significant gold resource in Barberton.
It won’t be possible to duplicate this
at every deposit, but if you look at
deposits differently in terms of economics
and mining methods, there is real potential
to increase their value. I think the next
big mine in Barberton is one we already
know about; it would have been mined
historically as either a high-grade shoot
which might have been blind at surface or
has a mineralised halo that nobody’s really
looked at.
Do the ore bodies at Barberton
extend much deeper than what is
currently mined?
Yes, certainly, many deposits have not been
fully delineated. The mines won’t be as deep as
in the Witwatersrand, but there will definitely
be opportunities to mine deeper.
What are the differences between
the Zimbabwean and Barberton
Greenstone Belts?
At the time when the gold in these two
systems were formed, there were two different
continents. In most current reconstruction
models, the gold mineralising events pre-date
their amalgamation.
They formed in very similar environments
and their volcano-sedimentary sequences
being preserved in very similar ways.
When the continents collided with each
other, the Archean successions were force
downwards; at the same time, granitic magma
forces its way upwards. The currently exposed
Greenstone Belts are preserved relics of
Yes, they are, and some of the best results are
coming from newly discovered extensions of
known deposits. For the size-frequency study
that I did, I had access to historic information
in which the production of each deposit during
the first 100 years was tabulated. I then added
the production from 1983 to 2013. Interestingly,
the mines continued exploration, not to make
a new discovery, but to just to keep their
operations going. These companies had actually
mined more gold than what was predictable in
1983. Furthermore, the expectation for more
gold has also increased in real terms, although
not in relative terms. This does mean that the
region is slowly becoming more mature. Its
residual potential has decreased; in 1983 it was
47%, while in 2013 the residual potential was
42%. Interestingly, therefore, the known gold
endowment of absolute metal had nearly trebled
from 1983 to 2013 even though the residual
potential is decreasing.
I approached a number of the mines to
determine why this is the case; I hoped they
had a new geophysical technique
or were doing something
different to unlock all this metal. The answer
was that they are actually drilling ahead of
the delineated part of the orebody – and this
makes sense. Once a company has delineated a
decent ore body that will keep it operating for
the next 20 years or so, exploration won’t be a
priority. The mining companies in Barberton
are fortunate in that the mineralised system
simply continues, and they are able to sustain
their operations incrementally.
[34] MINING MIRROR JULY 2019
www.miningmirror.co.za