In the stope
these sequences, squashed between the later
magmatic granites.
The Komatiitic volcanic rocks that are
found in both Barberton and Zimbabwe also
show differences. Komatiite is a magnesium-
rich variety of basaltic lava. Petrologically,
they’re distinct as they form at much higher
temperatures. At present day temperatures, the
earth’s crust is too cool for the formation of
komatiites. The early earth had much higher
temperatures. The komatiites of Zimbabwe are
associated with nickel sulphide deposits that are
not as evident in Barberton. There are also two
distinct ages of komatiite in Zimbabwe, one
older, one younger, whereas all the komatiite in
the Barberton Greenstone Belt belongs to the
older group.
How expansive are the Zimbabwe
greenstone belts?
Coincidentally, the limits of the Zimbabwe
craton nearly match the limits of the country.
The areas in the northwest and the southeast
of the country are off the craton. The
greenstones are present as various fragments
within this craton but have an aerial extent
three times greater than that of Barberton.
An interesting exercise might be to compare
the various Zimbabwe craton greenstone
belts with each other to assess their relative
endowments.
In a nutshell, what are the main
opportunities in Barberton?
The main opportunities are re-looking at
historical mineralisation. Of course, getting
good geochemistry results when undertaking
an exploration project does not automatically
mean one will be able to develop a top-class
mine. There are a lot of factors to consider
when building a mine, including the continuity
of mineralisation, the ‘mineability’ and recovery.
For example, some deposits have metallurgical
challenges that will have to be overcome. All
these factors combined will determine the
eventual economic viability of a deposit.
Are there a lot of historical mines
around?
There are many small historical prospects
and mines. Looking at re-opening old mines,
however, is a challenge and hugely costly, when
these workings have flooded or collapsed.
What are the challenges of operating
mines in the Barberton area?
Underground mining in Barberton can be
challenging. It is steep. Wits reefs are generally
shallow-dipping, on average dipping around 25
degrees (although ranging 5-35 degrees), but
the Barberton mines are significantly steeper.
Mineralisation is also less continuous. Other
challenges may include geotechnical issues.
Can new technology improve the
way we mine gold in the Barberton
area?
There is a Barberton reef system known
www.miningmirror.co.za
as the Barbrook Line which has a slightly
different geology and mineralogy to the
active mines in the area. The Barbrook Line
was discovered very early in the prospecting
history. It is easily traced by its prominent
siliceous outcrops. Along the ridge there are
numerous little adits and pits where miners
have prospected in the past. The problem is
that the gold is “double refractory”, which
means it is embedded in the lattice of the
pyrite and processing this material is a more
costly exercise. So, the mineralisation is
there but it has been left for metallurgical
reasons. New beneficiation technologies
may increase the extraction of gold on the
Barbrook Line. There are several people
doing research on how to get the gold out in
an economical way.
Is it a big area?
It is a relatively narrow system, which I would
say is about 10m wide? However, it runs
the full length of the Barberton Mountain
land – probably in the region of 20‒30km; I
don’t know how much of that is economically
mineralised.
Has any drilling been done there?
I expect there has been some drilling, but in
general if exploration companies perceive it
as uneconomical, it will be a lower priority
target. It’s simply too expensive to get the
gold out.
Will it be mined in the future?
What’s been shown in the past is that we’re
quite good at coming up with solutions to
problems given the right economic incentive.
JULY 2019 MINING MIRROR [35]