Has the City of Gold still got lustre?

Contrary to popular belief, great opportunities still exist for gold miners in South Africa. In fact, the country might be sitting on the world’s next great gold deposit. But we won’t know until the drill rigs are unleashed, writes Leon Louw.

For more than a century, the origin of the Witwatersrand gold in South Africa has been the subject of vociferous arguments and debates. Generations of geological researchers have burnt the midnight oil to explain the phenomenon that continues feeding a ravenous global demand for yellow metal. Despite these years of research, and knowledge gained by more than 120 years of non-stop mining, the origin of South Africa’s gold deposits remains uncertain. Today, the shallower portions of the Witwatersrand Basin, where most of the country’s gold is found, is a warren of tunnels and stopes. Nonetheless, they continue producing the goods.

More gold to be mined

Many believe that the Witwatersrand Basin is reaching the end of its productive life, and that it won’t be able to continue delivering the gold on which the foundations of South Africa’s most prosperous city, Johannesburg, and the country’s economy were built.

The mainstream narrative is that gold mining in South Africa is a sunset industry. Most geologists with a good knowledge of the Witwatersrand Basin, nonetheless, say that half of the in-situ gold has not been brought to surface yet. The problem is not so much the depth of the remaining reefs (which is true, especially on the West Rand) or the low grades of what is left (which is also true), but most importantly, the lack of drilling holes in areas previously not explored to the full.

According to an article authored by three legendary South African geologists — Morris Viljoen, Richard Viljoen, and Rodney Tucker — the Witwatersrand contains six times more gold than the world’s second-largest goldfield. In an article titled A review of the Witwatersrand Basin — the world’s greatest goldfield that appeared in the June 2016 issue of Episodes Journal of International Geoscience (Vol. 39 No. 2: The great mineral fields of Africa), they write that the Witwatersrand is a mature goldfield with declining production, but that there is still a significant amount of gold left to mine.

“Much of the remaining resource occurs at considerable depths. However, there are still opportunities for extracting lower-grade deposits at moderate to shallow depths. The Basin thus remains a major exploration target,” the article states.

Pursuing the low-hanging fruits

That there are shallow, low-hanging fruits in and around the traditional mining areas of the Witwatersrand Basin is a fact. One doesn’t need to look much further than the many artisanal workings that pockmark areas

previously deemed mined-out. The presence of companies like Mintails, West Wits Mining, Gold One, and White Rivers Exploration in the past and now Pan African Resources (PAR), DRDGOLD and Shallow Reef Gold, is proof that there is life in the reefs yet. Many potentially shallow, productive deposits were sterilised during the past 50 or so years, and West Wits has showcased what can be done if a mining company changes its mindset and pursues lower-grade deposits, which are easier to mine than deep and complex underground reefs. White Rivers, on the other hand, went after deeper, potentially higher-grade deposits in the Free State.

According to John Paul (JP) Hunt, senior exploration geologist at SRK Exploration Services, the challenge is that most of the remaining deposits are getting deeper, which makes them more difficult to access. “Furthermore, the grades become lower the further one moves away from the primary source areas into the more distal parts of the depositional fan,” he said when African Mining interviewed him a while back.

But apart from these deeper deposits, did historical gold mining companies not leave us with at least some pickings after their insatiable feasts? (Not referring only to their tailings, which DRDGOLD is competently taking care of.)

Mark Wanless, partner, and principal geologist at SRK Consulting (SA), said that there are indeed reefs that contain gold, and which nobody has really exploited before, mostly because of their low grades. To mine these lower-grade reefs would be expensive, and it would be a big ask to expect junior mining companies to carry the cost burden of developing the necessary infrastructure to get the gold out. Mining companies have historically mined through these lower-grade reefs to get to the high-grade areas without even reporting the lower-grade reefs. “So, I guess that although we can say there is still plenty of gold in the Witwatersrand Basin, we have to ask whether it would make economic sense to liberate the gold,” said Wanless.

Wits Basin has plenty to offer

Manie Swart and Rob Handley, geologists at consultancy firm Shango Solutions, agreed that many gold-bearing reefs of the Witwatersrand Basin are not yet depleted, as is often reported. Both men have worked extensively throughout the Witwatersrand Basin on different projects for many years and are convinced that there are reefs that still have plenty to offer. There is a false perception that the Witwatersrand Basin is now depleted, and that there is hardly any gold left. Improved technology, and better government legislation, will make the country more attractive for junior mining companies. “Unfortunately,” said Swart, “the regulatory uncertainty and political instability over the past decade or so have kept the exploration companies and drill-rigs at bay.”

“There could be just as much gold left in the ground in South Africa as what has already been mined in the country over the past 40-odd years,” said Handley. “Of course, the great producing reefs like the Main Reef and the Main Reef Leader have virtually been mined out, but there are a number of lower-grade narrow reefs out there that are ready for the taking,” he added.

The main concern is that, apart from the Modder East gold mine, close to Springs on the East Rand, and the Burnstone project, near the town of Balfour in Mpumalanga, on what is referred to as the South Rand Goldfield of the Witwatersrand Basin, not many new gold mines have come online since the early 1990s. Moreover, mining companies in South Africa have basically stopped investing in exploration, and that reinforces the belief that the gold has run out.

Great geology presents opportunity

Hennie Theart, corporate consultant, partner, and geologist at SRK Consulting (SA), said in a previous interview, that geologically speaking, there is still huge opportunity in South Africa, but warns that the political risks have increased and that the operational challenges are greater. “There is definitely potential for small-scale shallow gold operations if the regulations allow. Unfortunately, companies shy away from investing money in exploration because of concerns that have nothing to do with mining. The South African government needs to encourage exploration more than ever before to ensure the future of the gold mining sector in South Africa,” said Theart.

Exploration, of course, would have to include drilling, not only at current mining operations, but ideally in new areas not previously considered, which is an expensive exercise. But there are areas where more drilling could lead to unexpected results. Over the past 100 years or so, geologists have been able to delineate what they refer to as ‘goldfields’ in and around the Witwatersrand Basin. Today, these goldfields are well established. However, there are what Theart called ‘gaps’ between these existing gold provinces that need closer scrutiny.

“The Potchefstroom Gap and the Bothaville Gap, for example, might have potential. Furthermore, there is definitely mineralisation in some of these gaps to the north and north-east of the Free State Goldfield. This is where Harmony Gold has developed the Target Mine, one of the later additions to gold mining in that region. Immediately north of Target is a zone of gold enrichment that could possibly be described as a new ‘fan’, the Paradise Fan, where some initial drilling has been undertaken,” Theart explained.

As far as African Mining could establish, Anglovaal (later AVGold) explored this area in the past and discovered the Target and Paradise Fan. Similarly, there are known lower-grade gold deposits on the south-eastern and eastern side of the Basin, north-east of the Free State Goldfield.

According to Wanless there are several challenges in the Bothaville Gap. “For one, the cover is much thicker here. So those reefs would be deeper than for example at Harmony’s Target Mine, and the company’s Loraine Mine to the south of Target,” said Wanless.

Both Target and Loraine initially mined the Basal Reef and the B-Reef, which are the bottom economic reefs in the Free State Goldfields. Today, Target is also mining the Elsburg Reef, a set of stacked reefs that require massive mining methods, like what Goldfields has to deal with, at times, at its beleaguered South Deep Mine on the Far West Rand Goldfield of the Witwatersrand Basin.

The Basal and B-Reefs are very deep, and although the Elsburg Reef occurs near the top of the sequence, they are extremely challenging to explore and to find the areas that contain the high-grade mineralisation.

Adding more goldfields

 Up to now, geologists have identified eight established goldfields, namely the South Rand Goldfield; Evander Goldfield; East Rand Goldfield; Central Rand Goldfield; West Rand Goldfield; Carletonville Goldfield; Klerksdorp Goldfield; and the Free State Goldfield. To the north-east of the Free State Goldfield possibly lies another goldfield, which could be referred to as the Ventersburg Goldfield.

The potential Ventersburg Goldfield to the east of the Free State Goldfield was explored extensively by AngloGold Ashanti and much more recently by Gold One. Unfortunately, the excitement seems to have waned, again possibly because of the increased risk of committing to a long-term exploration and mining development project.

Are we looking in the right places?

According to Professor Terence McCarthy, emeritus professor of geology at Wits University and principal geologist at Shango Solutions, we are probably still not looking in the right places. Although the Witwatersrand Basin is punted to be the area where the next big gold discovery will be made, there are other regions in South Africa that could be prospective. These include the Barberton Greenstone Belt in Mpumalanga, which is the oldest gold region in the country and offers, according to Hunt, potential for shorter-term shallow operations.

“We have done several studies and looked at the complete distribution of the Witwatersrand-type rocks, and it turns out that they are much more extensive than originally thought,” said McCarthy. He added that there are potentially two new areas containing Witwatersrand rocks. “We’ve mapped out the full distribution of upper and lower Witwatersrand rocks using information available in the public domain. They stretch from Johannesburg all the way to Colesberg in the Karoo and eastwards to Bethlehem, where there are possibly other gold-bearing basins,” he said.

A few holes were drilled in and around the Bethlehem area in the early 1990s, when the mining industry decided there was no longer a future for deep-level mining, and no exploration work has been done since. Moreover, no work has been undertaken in the Colesberg Basin. According to Theart, there is another sub-basin in the Koster area of the North West Province that is worth mentioning. The Koster sub-basin has been explored by Goldfields and other exploration companies.

McCarthy is at the forefront of a movement that challenges traditional thinking about the Witwatersrand Basin and has proposed in the past that South Africa’s gold was transported into the Witwatersrand Basin by glaciers, during a previous ice age, and that therefore, the gold could have been carried much further south than was originally thought. Traditional theory postulates that water and hydrothermal events, or a combination of the two, were the principal transportation agents of the abundant gold deposit in the Witwatersrand Basin.

According to McCarthy, there are three gold basins in South Africa: the well-known Witwatersrand Basin, the Bethlehem Sub-Basin, and the Colesberg Sub-Basin. “Research indicates that the distribution of the Witwatersrand-type rocks is much wider than what was previously thought,” said McCarthy. “There are definitely Witwatersrand-type rocks outside of the Witwatersrand Basin in the Bethlehem and Colesberg areas,” said McCarthy.

To revitalise the interest in gold mining and exploration in South Africa, it is imperative that we start to critically re-examine existing theories on the formation of the Witwatersrand gold deposits (like McCarthy and others have done). We need to re-assess the geological record contained in the rocks, and then develop new theories that might lead us to virgin ground that has never been on the map. And that will require out-of-the-box thinking.

“The problem is not so much the depth of the remaining reefs or the low grades of what is left, but most importantly, the lack of drilling holes in areas previously not explored to the full.”