Lime mines and fossil sites in South Africa

One of the well-known features of Plio-Pleistocene early hominid sites in South Africa is that they are all associated with historic lime mines – think of Taung, Sterkfontein, Makapansgat, and others. As mentioned in earlier posts, this association is one of the critical factors that we used to develop our method and implement this field project, and thus has great practical value to us in the field – find the old lime mines, and we might also find some nice fossils!

However, there is also a very interesting historical component to this association. Mining, primarily of gold and other precious metals, was a principal factor supporting the economic development of the early South African state in the late 19th Century. The lure of vast riches associated with mining attracted migrants from many parts of the Western world. Lime mining was important for many industrial uses, literally providing the mortar and cement for building new towns and factories, and it was also an important component in the extraction process for gold and other economically important metals.

Cemetery at Pilgrim’s Rest, Mpumulanga. The gravestone on the left (pointed pillar) is for a chap from East Dulwich, London.

Speaking of gold, there were several early ‘gold rush’ events in South Africa, including Pilgrim’s Rest (1873), Ottoshoop (1879), Barberton (1881), Kaapsche Hoop (1882), and finally the Reef goldfields on the Witwatersrand (1886) which led to the establishment of the city of Johannesburg – and to conflicts that contributed to the start of the second Anglo-Boer War (1899-1902). We have covered some of these geographic regions in our survey activities, and read a great deal of information about their history in our archive work.

Photo of a gold rig in the Ottoshoop area, from ‘Developments on the Malmani Goldfields’, The Mining and Industrial Magazine, Nov 8 1933.

The people we have met in all of these areas are very knowledgeable about their local history, and of the historical importance of these events, and we have also located additional documentation about mining history through our archive work at the Wits University Historical Papers Library, Council for Geosciences, and other sources.

One example is the lime kilns near Ngodwana in Mupumulanga Province. We located them through a reference in a geological textbook1, and later determined that there was an old lime mine nearby. Our local contacts informed us that the kiln site (see photos) had been an important distribution centre for lime extracted from many mines in the area prior to 1899, and after processing the lime was shipped out to other areas by railroad. With this information, we were able to locate six additional lime mines within a few kilometers of the kiln site, and there are likely to be even more! (While we did not find fossil deposits at any of these mines, we did find in situ clastic cave sediments, or ‘rock breccia’, and some very thick remnant speleothem deposits. Definitely worth some future sampling!).

The Ngodwana lime kilns, closed down around 1899, but used later as a citrus packing plant when lime mining was no longer lucrative in the region.

As it turns out, the geological formations in which the metallic ores occur – including gold, iron, and other mined resources – are closely related geographically to the dolomite formations of the Transvaal Supergroup. Thus, in the areas of our survey we have walked across other rock units in the Transvaal Supergroup such as quartzites and Banded Iron Formations (BIFS) [see previous posts], and encountered mines for resources such as gold, iron, and asbestos. In fact, some alluvial sources (i.e., those that have eroded out from original geological context and were redeposited elsewhere) actually occur in younger sedimentary context in dolomite regions. In both a geological sense, and historically, our observations in the field have led to a strong connection between the mines and our quest to locate new fossil localities in the dolomite formations. In learning more about mining history and practice in our study areas (focusing on lime mines, but requiring some understanding of more general issues), we believe that we will be able to refine our field methods to identify additional areas that hold strong potential to locate fossil sites. This is not a simple task, however, and will continue to be a focus of the research programme in the long term.

-KL Kuykendall

 

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We think we found a fossil site – now what?

When we locate a potential site locality, we begin a process of exploration and evaluation to determine whether there is potential for further research at that locality. Our basic tools are a handheld GPS, a rock hammer, and a panga (or machete).

Field crew, 2nd trip: Andy with the GPS, Morris with the rock hammer, Kevin with the machete: Did the timer go off? is the camera working? did anyone hear a ‘click’?

The main objective of our project is to locate historic mining sites, and to evaluate whether they contain deposits and other features that are useful to us as palaeoanthropologists. We are looking for a variety of in situ (i.e., undisturbed) deposits including:

  • speleothem or cave formations, which can be sampled to obtain geological dates, and for stable isotopes which tell us about past climatic and environmental conditions;
  • cave infill sediments (derived from soil and other debris from both outside and inside the cave), which can tell us how the cave filled in, and also may contain evidence of the outside environment such as pollen;
  • fossil bone, including those of reptiles, birds, and rodents, as well as of larger animals including bovids, carnivores, primates, and of course, our own ancestors (hominids).

For some sites, the presence of such evidence can be quite obvious, especially if there are dense fossil deposits just waiting to be excavated. However, at other sites, it can take considerable effort to determine whether this evidence is present. Some sites are small and the deposits easily located, and others – especially when the mining activity was extensive – can be complex and more difficult to define.

One of the underlying objectives of this project is to consider what evidence at such sites can be used to answer questions of interest to palaeoanthropologists even in the absence of fossils. After all, when we find fossils (and especially those of hominids), we then use a battery of sampling techniques such as those above to obtain information about the temporal, environmental, and depositional context of that fossil. But since fossils are relatively rare in the geological record, we may be missing out on valuable information about past environmental conditions by passing over deposits in which hominid or other fossils are rare or even absent. This information could help us to refine our models about environmental and adaptive change during hominid evolution.

So, after that extensive preamble, what do we do when we think we have located a site? There are three basic tasks to complete: defining the limits and features of the site; mapping the locality; and evaluating the site’s potential for future research.

Defining the limits of the site involves exploration of the site’s geographical and geological features. We walk up and down hills, climb rock outcrops, and (carefully!) climb into mine shafts and trenches, looking for speleothem deposits, breccia and cave infill sediments, and fossils.

A miner’s trench exposing a lot of geological formation: Can anyone see any breccia up there?

One of the challenges in this work is being able to see the ground clearly in order to find features, breccias blocks, and of course, fossils. This is where the panga comes in handy!

Like most arid regions, many of the plants here have thorns. This site is overgrown with acacia trees and brambles. Keep repeating to self: ‘This is better than being stuck behind my desk at the universiity!’ (There is actually a nice cave infill deposit in this view… just to the right of the machete!)

The miner’s dumps are a great source of information about the deposits on the site. We comb the hills of rock, searching for fossils and other evidence of the nature of the underground deposits. Depending on what we find, we then have to search the mine trenches and chambers to determine where the blocks in the dump came from.

Fossils can be difficult to ID in the field. Observe the fossil braincase (below the knife to the right), and a vertebra (to the right on the edge of the block) of un-named mammals in this breccia block.

Finally, all of the features of the site are mapped using the handheld GPS, which locates each data point taken to within approximately 5 meters. For our initial fieldwork survey, this is good enough, but if we were to return for sampling or excavation we would use total station survey equipment and map the site with more accuracy.

Andy enters data points on the Trimble GPS at a small locality near Gondolin, North West Province.

The initial survey and exploration of a new locality can take several days, and also includes extensive photographic and written documentation; we also record information about the site on databases on the handheld GPS and a table PC. The final task is to sit in the shade and discuss what we have observed on site, and evaluate the potential for further work in the form of sampling or excavation.

Once we have completed this process of site survey and evaluation, we go back to the maps, head out to a new area, and begin the process again. All in a day’s work!

– KL Kuykendall

Malmani Dolomites

To a large degree, our project is a field survey of the geological formation known as the Malmani Dolomite Subgroup, of the Chuniespoort Group of the Transvaal Supergroup. The Transvaal Supergroup is an extensive geological sedimentary rock sequence extending across much of the northern part of South Africa and into Botswana (Ericksson & Altermann, 1998). The Malmani Dolomites are just one rock formation in this sequence, and they are of interest to us because it is in the dolomites that we find the historic lime mines, and thus palaeocave fossil deposits. On the map below, the Transvaal Supergroup, including the Malmani dolomites, is indicated by the light blue-shaded areas in the north & central regions of South Africa. Geological dates for these rocks indicate that they were formed between 2.6-2.5 billion years ago, making them one of the oldest dolomite formations known.

Simplified Geology of South Africa: The Malmani Dolomites in blue in the north and central parts of the country – unfortunately, NOT at the coast!

Dolomite is a type of limestone rock that forms in warm, shallow seas from the slow accumulation of the remains of marine microorganisms and fine-grained sediment. It differs from other limestone rocks in having a higher magnesium content, and these dolomites are also characterised by fossils of algae formations that are known as stromatolites (see picture below). These materials contain high levels of calcium carbonate, and thus such rock formations are often referred to as carbonates.

Photo of stromatolite fossils (the clusters of concentric structures) in the roof of Sudwala Cave, Mpumalanga. These represent ancient algae formations in the sea at the time that the dolomite rock sediments were accumulating, roughly 2.6 billion years ago. 

One important quality of dolomite is that, over long periods of time, this rock is water soluble – ground water is a weak acid that will erode away the calcium carbonate matrix as it percolates through cracks and fissures within dolomite rock layers. This process eventually results in the occurrence of underground solution cavities, and when these break through to the surface due to erosion or collapse they form caves and sinkholes (see schematic below). Further percolation of groundwater through these solution cavities results in the precipitation of calcium carbonate to form various kinds of speleothem – the beautiful cave formations known as stalactites, stalagmites, and other structures. In addition, once the cave or sinkhole is open to the surface, it will begin to fill in with sediment, and if occupied by carnivores the infill will include animal bone. In South Africa, the ancient caves of this kind were open to the surface, and filling in with sediment and bone, between roughly 3-1 million years ago.

Idealised model of cave formation in dolomites (Martini, et al. 2003). The brick-like symbol indicates dolomite, and the differently-stippled symbols represent separate infill deposits over time.

Thus, over a period of millions of years solution cavities will form in the dolomites, break through to the surface as caves and sinkholes, and then fill in again with sediment and bone. The constant percolation of groundwater through the deposits will cement everything together in a calcium-carbonate matrix, and fossilise the bones. Finally, lime miners in the early 20th century blasted and excavated into the dolomite formations to retrieve the extensive cave formations (calcium carbonate, or ‘lime’), and in so doing often exposed the infill deposits containing fossilised bone. This attracted the attention of palaeoanthropologists who were interested in the fossil record of human ancestors and other mammals.

And that is why we are in South Africa surveying the Malmani Dolomite formation, looking for ancient cave deposits!

– KL Kuykendall

Map accuracy: are we there yet?

The project is focused on the relocation of historic lime mines sites across South Africa. Information we have gathered includes high resolution scans of two maps showing the location of every mine in South Africa open at the time of printing. It is from these maps, along with other documentary sources, that we have selected the areas to visit. As you can see below, the location of the mines is clearly marked with a point and a two letter code relating to the mineral being mined with Ls indicating lime (on a side note I have been keeping a beady eye out for those marked as Diamond and Gold, you never know what they might have left behind!).

© Department of Mines, Republic of South Africa 1959

Given that the maps are of a relatively large size it was not feasible to bring them into the field, which even if we did would prove difficult to glean any particularly useful location data from anyway. The solution to this is to make a digital version of the map from the high-resolution scans. Unfortunately the handheld computers we are using do not have a particularly large processing capacity so loading an A0 map scanned at 300dpi and then trying to use it, isn’t efficient or effective. So, what we have to do is to store the data as a much smaller file so it can be used on the handheld computers. This transformation is quite common when using maps like these in an archaeological context, digitising vector data (lines and dots) from raster data (pictures and photos etc.). Vector data files are much smaller than raster data files and they can hold text information about them which is very helpful in the field and saves a lot of time flicking through notebooks.

By using a GIS (Geographical Information System) package it is possible to create a file displaying the locations of the mines as dots, which we can then load onto our handheld computers and use its GPS function to guide us to them. Oh so simple I hear you say, alas no such luck I’m afraid.

A selection of digitised mine locations as displayed in vector format overlaid on a 1:50000 topographical map in raster format.

The main issue with the maps is their accuracy, and furthermore the accuracy of the points we take from the maps. Firstly it is difficult to say how accurately the cartographer plotted the locations. Secondly the scale of the map is so large that the effective accuracy of any point will only be within 1.5 kilometres, in any direction, of the actual location of the mine.  So, even when we are standing right on top of the point stored on the handheld, the mine could be anywhere in a 9 square kilometre area. That’s where we depart from our GPS system to locate the mines and use our eyes, and feet, to find them (always being careful to avoid falling into sinkholes and the occasional thorny bush).

This was only the first step in our preparation for fieldwork, the next will be covered in a subsequent blog post and will deal with how we use and prepare geological maps for the project.

-AR Reid

Taung Heritage Site: 17 June 2012

The early hominid fossil site of Taung is one of the ‘Big Five’ Plio-Pleistocene sites in South Africa, and is historically the first australopithecine site to be recognized. The discovery and recognition of the Taung skull fossil is a fascinating story, and is detailed in Raymond Dart’s Adventures with the Missing Link (Dart and Craig, 1959). In December 1924, a crate of breccias blocks (rocks containing fossils) from the lime mine at Taung was delivered to Raymond Dart at the University of Witswatersrand in Johannesburg. In it, he discovered a small skull of a juvenile hominin, which became nicknamed “the Taung child”. The fossil preserved much of the facial skeleton, mandible, and endocast (an impression of the brain on the inner surface of the skull). Dart quickly published a report on his find in February 1925 and proposed that it represented a new hominin species, Australopithecus africanus – or ”the Southern ape from Africa” (see photo of the Taung skull). More recent research has determined that the fossil is more than 2 million years old.

In his report, Dart stated “the specimen is of importance because it exhibits an extinct race of apes intermediate between living anthropoids [apes] and man [emphasis original]” (1925, p. 125). At the time, many scientists would not accept that humans evolved from an ape-like ancestor and the skull’s significance was largely ignored for several decades. But it was this challenge to Dart’s interpretation of the Taung fossil that led other researchers such as Robert Broom to explore other South African lime mines for further fossil traces of human ancestry.

One of the original published (1925) photos of the Taung Skull in lateral view, showing the facial skeleton to the right, and the brain endocast to the left.

We visited the Taung limeworks near the town of Buxton in the North West province. The site, which was designated a National Heritage Site in 2002 (see plaque photo), is quite large and was an active mine during the 1920s. It was later systematically excavated by paleoanthropologists from the University of California in the 1940s, and from the University of Witswatersrand between 1988 and 1992. Both the mining and excavations resulted in extensive dumps that surround the area of the site from which the skull is thought to derive. However, the exact location at which the skull was found can only be approximately reconstructed from mine records and historical documents – after all, it was only recognized after it arrived in Johannesburg in a wooden crate!

The Taung site is both a National, and World Heritage Site. This plaque provides the essential information about the site, and the Taung Skull fossil.

The Dart and Hrdlička pinnacles, and the monument marking the possible location of the Taung Skull.

How the Taung juvenile died, and became deposited in the fossil record is not certain. One hypothesis is based on taphonomic evidence from the fossil and associated specimens in the deposit, including possible raptor claw marks on the skull. This model suggests that a large bird of prey snatched the child from the air, and the skull was subsequently left below the raptor roost (e.g., Berger and McGraw, 2007). Cases demonstrating this hunting technique by large raptors are documented for other primate species.

Another hypothesis is palaeoenvironmental in nature and is based on deposits of tufa present at the site. Tufa is a calcium-carbonate rock produced when organic matter settles in still or slow-moving water with algal blooms, and builds up into massive deposits over time. Animals may be incorporated into such deposits if they die in or near the water source – thus, it may be that the Taung child died of natural or unknown causes, fell into the stagnant water, settled, and fossilized (McKee, 1993). If the exact location of the deposit from which the Taung fossil was derived were known, these different hypotheses could be tested more rigorously, and a firmer conclusion might be possible.

The Taung site is where the modern field of palaeoanthropology began, because it produced the first early hominid fossils from Africa, a discovery which eventually transformed the field, and our view of our own evolutionary history. For us, it is also significant that the site was located at an old lime mine – and this is one of the reasons that we are currently in the field, attempting to locate other such lime mines in new areas. Who knows what future discoveries these sites might reveal?

REFERENCES

Berger, LR and McGraw, WS. 2007. Further evidence for eagle predation of, and feeding damage on, the Taung child. South African Journal of Science 103:496-498.

Dart, RA. 1925. Australopithecus africanus: the man-ape of South Africa. Nature 115:195-199.

Dart, RA and Craig, D. 1959. Adventures with the Missing Link. New York: Harper & Brothers.

McKee, JK. 1993. Formation and geomorphology of caves in calcareous tufas and implications for the study of the Taung fossil deposits. Transactions of the Royal Society of South Africa 48(2):307-322.

-KL Lewton and KL Kuykendall

Kuruman: 10 June 2012

Though located in the middle of the Kalahari on the Ghaap Plateau, Kuruman is a thriving mining community in the Northern Cape Province, and was an important missionary post in the early 1800’s. The Scottish missionary Robert Moffat lived here from 1820-1870, and printed the first bible in Africa. Today the mines in the region produce manganese, iron ore, tiger’s eye, and asbestos, and signs of the importance of the mining industry are everywhere.

Wow! we want one of THOSE for next year’s field season!

We drove an approximately 275-km route via Kuruman – Danielskuil – Postmasburg – Kathu and back to Kuruman intending to locate some of the historic lime mines in our database. Frustratingly, we encountered fenced-off fields, locked farm gates and roads-to-nowhere.

The road to nowhere…

Geologically, the hills in this area are predominated by banded iron formations (or BIFs) which is the source of the iron ore in the region – and we saw many iron mines on our drive – but almost no dolomite, and no lime mines at all! The BIF overlays the carbonate platform (our dolomites!), and we did encounter massive slabs of bedrock dolomite along some of the dirt roads in lower-lying areas.

BIFs in the distance; dolomite in the valley floor

We also visited Wonderwerk Cave, which is an archaeological site occupying a massive solution cave in the dolomites – so all hope is not lost. Our next step is to visit the municipal lands office in Kuruman for contact information about the farms on which the historic lime mines are located.

-KL Kuykendall

Project introduction

Since the 1920s, palaeoanthropological fieldwork in South Africa has focused on a handful of fossil-bearing cave sites mostly located in what is now known as the Cradle of Humankind. Our objective is to survey and inventory over 200 other historic mines located in the Malmani Dolomite system throughout the northern region of South Africa. We are using GPS and GIS systems to record the location of these sites and the presence or absence of fossiliferous sediments and other palaeontologically interesting features. Our ultimate goal is to discover new hominin fossil sites to further our understanding of Plio-Pleistocene human evolution.

Our first site visit of this field season was to Gondolin, a 1.7-1.8 Ma palaeocave located in the Northwest Province of South Africa that has previously yielded Paranthropus teeth and various fossilized fauna, including bovids (antelope), equids (horses), and one lagomorph (rabbit) (Adams et al., 2007). The good news is that our field test of our GPS equipment was successful! Part of the site documentation process includes photographic recordings of the site and its features. Here is a photo that demonstrates just how dense the fossils in bone breccias can be:

For more information about our field crew and project partners, please click on the “About” tab.

References
Adams JW, Herries AIR, Kuykendall KL, Conroy GC. 2007. Taphonomy of a South African cave: geological and hydrological influences on the GD 1 fossil assemblage at Gondolin, a Plio-Pleistocene paleocave system in the Northwest Province, South Africa. Quaternary Science Reviews 26:2526-2543.