New horizons for Wonderstone
Ottosdal is a small town in the North West province that Mining
Weekly passes through on the way to places such as Black Mountain
or Beeshoek, or the mines of Namibia.
What is little known is that ten minutes’ drive to the north
of this dusty hamlet is a remarkable mining and processing
The market capitalisation of this company is some R100-million
– not a large operation, when compared to the gold-mines
However, the Wonderstone operation could be a model for its larger
cousins in the minerals industry.
While Minerals and Energy Minister Phumzile Mlambo-Ngcuka calls on
the mines to add value to their ores or metals, Wonderstone, with a
healthy dash of home-grown ingenuity, has been turning a low-value
mineral into high-value products for many years now.
Recently, the mine has undergone a transformation, moving from
being a natural stone quarry to being a high-tech producer of
The rock that is mined at Wonderstone is correctly termed
pyrophyllite, a name derived from the Greek words for
‘fire’ and ‘leaves’, as the rock exfoliates
readily when exposed to flames.
The slatey rock has a slightly slippery feel, and is, basically,
aluminium silicate in the form of ametamorphosed clay originally
derived fromvolcanic ash.
On surface, where weathering has taken place, the stone is light
grey; however, as one goes deeper in the deposit, the grey colour
This is due to a higher carbon content, but this does not seem to
alter the commercially-exploitable qualities of the material.
The ash was laid down in layers, something which led to its
Early farmers in the area came across the outcrop on the farm
Gestoptefontein and found it was a simple matter to lever off
uniform slabs of the rock for use as gravestones.
As the stone was soft (1 on the Mohs scale), it was easy to carve
the names of the deceased in the yielding material.
Interestingly, though the stone is soft, it does not weather
easily, explains Desmond Sacco, chairpersonof Assore.
The deposit occurs in the form of a low hill some 4,6 km long.
Geological action has tilted the deposit so that the laminations in
the body dip at about 80˚.
In terms of life-of-mine, the deposit has been drilled to a depth
of 192 m to give a reserve of some 80-million tons.
At present, the mine moves about 40 000 t a month.
stone, about 2% of the deposit is usable.
Early miners used wire-rope saws, which they stretched over the
crown of the hill, to saw out slabs, a painfully slow procedure. At
one stage, a mobile circular stone saw was brought in to cut large
one-metre cubes from the face.
Although the blocks looked flawless, all too often, when they
reached the factory, an undetected hairline crack rendered the
Today, the mine uses a mounted hydraulic hammer to lever slabs
loose. This more vigorous separation method defines which chunks of
rock are usable at source.
The mine is neatly maintained, with excavation being from
100-m-long 8-m-high benches. A Komatsu shovel loads the slabs of
rock into either a Bell or a Caterpillar dump-truck, to be hauled
An eye for an opportunity
Guido Sacco (father of the current Assore chair-person, Desmond
Sacco) the founder of the Assore group of companies, apparently saw
the tombstone quarry and realised the value in this
Though pyrophyllite is not a geological rarity, the Gestoptefontein
deposit is of a particularly high purity and volcanic in origin,
and is the only A grade deposit in South Africa.
In 1937, Wonderstone was incorporated as a company.
The rock has good thermal insulation qualities. It can also
tolerate high degrees of thermal shock and has a low coefficient of
thermal expansion. It is also very fine-grained and is a poor
conductor of electricity.
In industrial-diamond manufacture, the ingredients for a diamond
have to be placed in a crucible and subjected to high pressure and
Wonderstone is ideal, as it is sufficiently inexpensive to allow
for the once-off use of the crucibles.
What is important is that wonderstone has a consistent density and
hardness so that the quality of the crucibles remains
Any fault in a crucible can result in tremendous energy releases,
which can easily damage the costly anvils that apply the required
pressure. Supply of crucibles to the synthetic-diamondindustry was
the foundation of Wonderstone’s early financial growth.
About three years ago, Wonderstone started to make inroads into the
It was realised that wonderstone was a good natural ceramic with
some excellent inherent qualities.
One of the products that was looked at was using powdered
pyrophyllite with a binder as an alternative to formed basalt,
which is used as a low-cost wear-resistant medium.
The wear properties of wonderstone are equivalent, while its cost
is considerably less.
Wonderstone had the opportunity to buy out a ceramics company,
Ceramox, of the East Rand, which allowed the new owners to tap into
a sound source of expertise.
At Wonderstone, in the meantime, ultrahigh-pressure presses were
installed to begin the manufacture of alumina wear tiles.
The rapid growth in this market surprised even the people at
Wonderstone, explains John Connelly, Wonderstone’s director
The French connection
The most recent development in the life of Wonderstone is the
signing of an agreement with the French corporate, Saint-Gobain, a
world leader in glass and wear-resistant technologies.
While the agreement was signed in Johannesburg, Wonderstone had
been in discussion with the French for nine months
The benefit that Saint-Gobain brings to Wonderstone is twofold.
“From our side, this gives us access to their technical
expertise, such as their computer-aided design facility and
high-powered research and developmentfacility,” says
The group has a multimillion-dollar investment in test and lab
Connelly and his team are now tapping into this department to try
and find new applications and markets for wonderstone.
The results on the first batch of wonderstone that was sent to the
US for testing have recently been returned to the Ottosdal
The tests included baseline characterisation to investigate broader
uses of the material.
The wonderstone was subjected to rigorousacid-testing, which gave
promising results. Finally, the Americans carried out a wear
comparison with wear-resistant material made from basalt.
When it is used in pipes carrying abrasive slurries, the alumina
material would be used on the bends and the basalt material on the
However, initial indications are that a Wonderstone alumina could
be cheaper to produce, whiledelivering a product that will match
basalt in wear applications. “In terms of capital items, we
have installed and commissioned a new 500-t uniaxial press which is
predominantly used in the manufacture of alumina wear-resistant
tiles,” explains Connelly.
This freed up the original 500-t press, which is also used to carry
out more specialised orders. The factory has also bought and
commissioned an extruder, which is being used for the production of
The long-term view is that the extruder will be used for
manufacturing a product that will be in either tile or tubular
The prospects for a wear-resistant pipe-lining that will ultimately
replace the basalt product look promising.
Wonderstone has also boughtanother furnace, which is installed and
All of the three Wonderstone kilns at the moment are ‘top
hat’-type units, where the heating elements are housed in a
box-like structure, which is raised and lowered over the packed
This limits the factory to batch-processing only. Indications are
that, with increased production, a continuous-firing kiln will be
With the new kiln, if another similar unit is placed in line,
firing can then be carried out continuously.
The factory is also spending ‘severalmillion rands’ on
the purchase of a spray dryer and two ball mills.
“The spray dryer will be used for alumina wear-resistant tile
production, but we also see a large benefit in employing that
equipment to manufacture spray-dried wonderstone powder,”
The largest short-term demand for reconstituted wonderstone is in
the making of the crucibles that are, in turn, used in
polycrystalline-diamond manufacture. At the moment, the 300 000
crucible components that are produced every month are 75%
manufactured from the natural stone. However, Wonderstone is keen
to introducecustomers to crucibles made from reconstituted
wonderstone – pyrophyllite powder which has been combined
with a binder, pressed and fired.
Wonderstone is working closely with its customers abroad to perfect
the powder-formed crucibles.
“Where the ball-mills play an important role is when we take
material from our fines stockpile and run this into the ball-mill,
a very controlled dosage of binder can be achieved,”
From Wonderstone’s experience of its 36-hour cycle in the
ball mill, it is possible to control the moisture levels and binder
The feed from the ball mills will be pumped into the spray dryer,
which then gives a closely-defined particulate size, where each
particle is uniformly coated withbinder.
The mix is consequently homoge-neous.
Previously, although the factory had an efficient high-energy
mechanical mixer, the binder tended to concentrate in certain areas
of the mix.
The product from the ball-mill is an easy-flowing material, so one
gets a much better fill in the dyes and bags used in the isostatic
There is also a saving to be made on thealumina.
“At the moment, we buy-in ready-to-press alumina powder;
however, in the future we will be able to buy a calcined
powder,” says Connelly.
The calcined material will be milled and combined with wonderstone,
with the final product being spray-dried.
The cost advantage here will be in the region of 25%.
A further capital item could be another large calciner, which will
be dedicated to making the wonderstone powder, as this is seen as a
With the investment that Wonderstone has made in the drying ovens,
the factory is now able to limit the amount of warping that happens
during kiln firing.
From train brakes to aerospace
Although Connelly believes that there will always be demand for the
pyrophyllite in its natural state, the rock in itspowder form is
where the future for the company lies.
The company has some two-million tons of wonderstone already mined
and lying in stockpiles.
The Ottosdal operation has a powder plant, which consists of a
feeder-breaker or hammer crusher, which feeds two jaw crushers
which, in turn, feed two hammer mills.
The plant, though it is on Wonder-stone’s property, was
originally owned by De Beers, which used the powder in
industrial-diamond manufacture. Subsequently, Wonderstone bought
the plant and has diversified its customer base.
An illustration of the versatility of wonderstone powder was seen
in a corner of a factory, where a technician was making a range of
acid-resistant lab ceramics using the ancient method of
The powder is mixed with an alumina slurry and then poured into
slip-cast moulds and, once the mouldings are dry, they are fired to
make a hard ceramic product.
“We have recently developed quite a healthy local market for
calcined wonderstone powder, which is finally used in train brake
pads, a side of the business that is set to expand significantly
with good export potential” When the Saint-Gobain delegation
carried out the site visit to Ottosdal, discussions were held on
using the company as a conduit for exports of calcined wonderstone
to North America.
The other potential – and here Wonderstone is only starting
to scratch the surface – is in the use of wonderstone in
mould coats in the foundry industry.
Saint-Gobain itself is a major user of mould coats with its
involvement in the glass and high-tech materials industry.
Another application which caught the attention of the Saint-Gobain
delegation was the Wonderstone chromic-acid purification pot.
The purification pot is required to regenerate chromic acid, which
is used in the chrome-plating industry.
Chrome-plating plants have the problem that, with successive
platings, the acid used in the process becomes impregnated with
impurities such as copper and iron. The plating time increases,
while the quality of the chrome-plating deteriorates.
The acid-purification pot is an electrolytic container in which the
contamination of thechromic acid can be reversed.
This has the advantage, apart from the cost saving that is
involved, of solving a serious environmentalproblem.
Saint-Gobain has already made contact with several potential
customers for this Wonderstone innovation.
“While we have some local customers that are delighted with
the performance of the pots, in the next six months we will be into
North America with some trial samples,” says Connelly.
The original powder plant will continue with its current customer
base, while the new powder plant, which will be sited next to the
new factory, will be used to service the new product ranges.
The growth at Wonderstone has been in both the natural and the
reconstituted product. “Both the machine shop, with its
computer numeric control turning and milling centres, and the
Ceramox side have shown phenomenal growth,” expounds
“It is a good sign when you start growing out of your
buildings,” he adds.
“None of us in the Wonderstone team believe that we have even
scratched the surface when it comes to the applications for the
material.” The application for Wonderstone is almost as broad
as the imagination.
However, Wonderstone is staying away from consumer-type products,
concentrating on high-tech applications.
There are many markets where Wonderstone can replace existing
materials in longevity and costs.
“I am excited about the relationship with Saint-Gobain and
the potential it has for both com-panies,” says
The rapid growth of Wonderstone is illustrated by the fact that, in
2003, the company spent R10,5-million oncapital items.
Some R21-million is being spent in the next year on capital
The capitalisation of Wonderstonehas grown exponentially over the
last couple of years, explains Connelly, to a point where the
company has a capitalisation near R100-million.
A characteristic of the operation is the levels of ingenuity that
The isolation and the singular nature of the operation have
compelled it to rely on its own resources.
“We cannot go out and see what our competitors are doing
because, in South Africa, there is no one to compare
against,” explains Connelly.
Today, Wonderstone can boast a workforce that is dedicated and a
staff turnover that is also very low.
The operation has a labour force of 160, which has grown from about
90 people just more than a year ago.
Currently, the operation makes some 200 components; however,
Connelly sees no reason why this should not expand by leaps and
bounds in the future.