Print

“There’s not even Fool’s Gold in these here hills!”

In the Waterberg town of Vaalwater, that well-known rumour mill, stories keep circulating about possible mineral discoveries and mining operations in the Waterberg. It is time to put these rumours - and your concerns (or hopes) to rest.

The problem is that the word “Waterberg” means different things to different people: the Waterberg District Municipality, for example, includes in its area the important  mining towns of Lephalale (coal), Mokopane (platinum) and Thabazimbi (iron ore), as well as the old tin mines of Rooiberg (near Bela-Bela), Union (Mookgophong) and  Zaaiplaats (Mokopane); and the Buffalo fluorspar mine outside Mookgophong. And since these places effectively surround the plateau that is the heart of the Waterberg, it is not surprising that some assume that it too must be richly endowed in valuable minerals just waiting to be discovered and extracted. However, I hope I can persuade you that this is not so.

The Waterberg plateau consists of a mass of sandstone rocks that define an area bounded more or less by the following points, moving in a clockwise direction:  Marken  – Masebe  – Kloof Pass  – Entabeni  – Bokpoort Pass  –Heuningfontein – Rankin’s Pass – Bakker’s Pass – Matlabas – D’Nyala (on the new Lephalale road) – and back to Marken. This area includes the whole of the currently-defined  Waterberg Biosphere Reserve; all of  Welgevonden,  Lapalala and the Moepel Farms;  most of Marakele;  the entire catchments of the Lephalala, Melk, Dwars, Blocklands and Mokolo Rivers; Vaalwater, Twenty-Four Rivers, Bulge Rivier, Mokolo Dam, Melkrivier, Lindani, Emaweni, Tarentaalstraat, etc. The following discussion applies to the geology and mineral potential of this plateau.

The Waterberg sandstone rocks were laid down by a very long-lived river system that drained from a mountainous region to the north-east, more or less where Tzaneen is today, during the period 1900-1500 million years ago. In the course of their long journey, the sediments carried by these rivers became clean, wellsorted and almost entirely winnowed or leached of any useful minerals that they might have contained when they started their journey, apart from minor amounts of iron and ilmenite (an iron-titanium oxide). The result is that a huge pile of sandy material – with a few pebble bands but very few clay horizons - up to 2 km thick in places near Vaalwater, accumulated over a long period of time in a slowly subsiding basin that extended south-westwards towards the present-day Kalahari. It is essentially barren of any economic mineralisation. The Waterberg sediments were formed at a time when the only life on earth consisted of single-celled, carbon-monoxide/dioxide respiring organisms: there were no plants, and no animals – and so there are also no fossils present from which to have formed fossil fuels like coal, oil or gas.  There are, however, a few occurrences of minerals on the Waterberg plateau that have been explored or even mined briefly. The only one of any consequence was the Nooitgedacht  lead  mine, about 16 km  NNE of Vaalwater, which was mined for a couple of years in the 1940s and which also contained small amounts of zinc and copper. The mineralisation at Nooitgedacht was contained in a quartz vein, which in turn is associated with one of the many dolerite dykes and sills that have intruded into the Waterberg sandstones during the 1.5 billion years since they were deposited. Occurrences of localised copper mineralisation related to dolerite can also be found for example on Lapalala and near Dorset, none of them having any economic potential. Other minerals known to occur on the plateau,  albeit in very small quantities, include surface, or “placer” accumulations of heavy minerals like ilmenite and zircon, which have been eroded out of the sandstones (for example on Boschdraai); and alluvial tin and thorium, which occur towards Alma and are remnants of source rocks that used to exist further south.

Another mineral that  might occur on the plateau is diamond  – although none have been found yet, as far as I know. Diamonds occur in rocks called kimberlites, which are relatively young rocks that intruded volcanically through many different older formations. The location of individual kimberlite pipes or fissures was determined by a combination of deep-seated structural features of the earth’s crust. Among these features are the pronounced regional fractures that criss-cross the Waterberg plateau, which are easily seen on aerial photographs and satellite imagery and which are also important controls for underground water. Examples of economically mineralised kimberlites in the region include the Venetia mine near Alldays and the Klipspringer pipe east of Mokopane (Klipspringer, in its short life, was the richest diamond pipe ever mined anywhere on earth!). Several companies have prospected for kimberlites on the Waterberg plateau over the last 30 years, but there is no evidence that any were found – and anyway, only about 1 in 200 kimberlites contains any diamonds! So I don’t think much too sleep should be lost about this possibility.

OK, so the Waterberg plateau itself  doesn’t have any mineral wealth worth mining. But then, how can it be that it is encircled by mines? Well, the answer is that all these minerals occur in rock formations that are either older or younger than the Waterberg sandstones and have very different characteristics.

The oldest of them are the ironstones of the Thabazimbi area, which were deposited in a shallow marine environment about 2400 million years ago, in a series of linked basins that extended all the way from Sabie in the east to Prieska in the west. All the limestones that occur in the northern part of South Africa – at Sabie, Mokopane, in the Magaliesberg, around Kuruman and even at Potchefstroom - were laid down as chemical sediments in this huge basin (a sea), immediately beneath the iron (and manganese) formations that gave rise to the mineable deposits at Thabazimbi, Sishen and elsewhere. These were later overlain and buried by shales and sandstones that were deposited in the basin as it filled up.

It is not impossible that further, unknown deposits of iron ore occur beneath the southern Waterberg,  where they might be buried by the younger sediments of the Waterberg Group,  but they would be far too deep even to discover, let alone to mine, with current technology. It is important to bear in mind that iron, like coal, is a relatively low-value commodity; and that for it to be viable, it needs to be mined (and transported) in bulk, by which I mean in quantities of millions of tons per annum. Underground mining of iron ore would not make economic sense in prevailing market conditions.

About 2050 million years ago, a most remarkable event occurred: a huge volume of molten material from deep within the earth’s crust, called magma, intruded, probably in several discrete pulses, into the thick sediments of the Transvaal Supergroup, as the package described above is known; as it cooled, the magma separated into layers of differing composition, to form the Bushveld Layered Complex. This is the largest formation of its kind in the world and one of the planet’s richest depositories of valuable metals: most of the global resources of platinum group metals, chrome and vanadium, as well as a significant amount of nickel occur here. The precise geometry of the Bushveld Complex is still to be understood, but it occurs  in at least three distinct ‘lobes’:  one in the west  between Brits, Rustenburg and Northam; a second in the east, from Dullstroom to Burgersfort; and a third, from just north of Nylsvlei, past Mokopane  almost up to Bochum. All three lobes are being intensively mined for the minerals mentioned.

Of interest here is that there is a fourth lobe too: poorly exposed and not significantly mineralised, but definitely comprised of similar rocks, the socalled Villa Nora lobe of the Bushveld Complex occurs immediately west of Marken, on the road to Lephalale. Its presence certainly introduces the possibility that extensions of the platinum-bearing rocks could occur beneath the younger Waterberg plateau. Platinum and its related minerals, unlike iron ore, are extremely high-value commodities, so they can support expensive, deep underground mining operations. However, the deepest deposits currently being evaluated (not yet mined) for extraction anywhere are around 2000m below surface – and any that might lie beneath the Waterberg plateau are almost certainly at least 3000m below surface.

The tin deposits mined historically at Rooiberg, Union and Zaaiplaats, as well as the numerous fluorspar occurrences around Mookgophong and west of Bela-Bela, while occurring in different hosts, had a similar origin at a similar time. The heat caused by the intrusion of the molten magma of the Bushveld Complex caused hot solutions enriched in elements like tin, molybdenum and fluorine – even platinum - to migrate into fractures in surrounding rocks, most of which were granites or Transvaal Supergroup sediments. Some of these were undoubtedly later buried by the early sandstones of the Waterberg Group – but would be very difficult to locate today. Finally, in the area between Lephalale and the Limpopo River, lies South Africa’s richest remaining coalfield, from which Eskom hopes enough coal can be extracted to fuel the country’s electricity demand for the rest of this century. Already home to one of the world’s biggest collieries (Grootegeluk) and one of the largest power stations – Matimba, with an even larger station, Medupi, now under construction - the Waterberg coalfield is expected, within the next decade, to support a quadrupling of its current electricity output, as well as the country’s first coal liquefaction plant. The westward extension of the field into Botswana is also under intensive evaluation for coal and methane gas mining. As we have heard at Conservancy meetings, these developments will have several environmental consequences, including pollution from the proliferation of transmission lines and water pipelines.

Now, this coalfield occurs in shales of the Karoo Supergroup, laid down a mere 260 million years ago in a series of vast basins that covered most of sub-equatorial Africa, as well as parts of India, South America, Madagascar, Antarctica and Australia - all these pieces of the earth being at that time, part of a single continent, Gondwana. These youngish sediments (more than a billion years younger than the Waterberg sandstones!) contained a high concentration of plant material (which formed the coal) and  could only have been deposited on top of, or next to, the Waterberg sequence, much of which had eroded away during the intervening eons.

Ha! you will be saying, in that case, there should be some coal potential on the Waterberg plateau, not so? Not so! If ever there were Karoo-age sediments on our plateau, they’ve long been removed by erosion too, for there’s no trace of them today.

But, then, what about Lephalale, which is about 700 metres lower than the plateau? Why are the coal beds preserved there? Well,  there’s a simple explanation for this too: along the northern boundary of the Waterberg escarpment is a very large regional fault, called the Melinda Fault, which with its extensions,  can be traced from eastern Botswana in a north-easterly direction all the way to Crook’s Corner at the top of the Kruger Park. The hot springs at Tshipise owe their existence to it.

The effect of the fault was to displace all the rocks to the north of it downwards relative to the rocks to the south of it – by several kilometres. The result has been that young Karoo rocks, including the coal beds, are preserved to the north of the fault, but not to the south. The line of the fault crosses the main road from Vaalwater to Lephalale (the R33), just about where that road goes over the Mokolo River outside Lephalale. See if you can feel the bump in the road.

A similar, parallel  group of faults forms the southern boundary of the Waterberg escarpment too, this time with the downthrow to the south – which is why you‟ll find Karoo-age sediments  from the outskirts of Modimolle to Pienaarsrivier (where there‟s also coal, and uranium), but none to the north.

This fault zone, called the Thabazimbi-Murchison Lineament, is marked by a series of hot springs that include Die Oog, Loubad, and the old Rondalia resort outside Mookgophong.

So, the net effect is that the Waterberg plateau stands like an island in a sea of younger rocks to the north and south; and older rocks to its east and west. Its thick pile of barren sandstones  may be underlain, at great depth (too great to detect, let alone mine) by formations that could host platinum, iron and tin mineralisation, but it is not covered with coal-bearing Karoo rocks – and no kimberlites have been reported from it.  Recent prospecting rights applications over properties on the Waterberg plateau for minerals as diverse as iron, manganese, vanadium, andalusite, platinum group metals and chrome may have been motivated by ignorance, deceit or fantasy; but not by geological facts.  

Prospectors and miners should expend their energies elsewhere; and conservationists can relax!

Richard Wadley,

July 2011