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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On field survey methods using handheld GPS

The previous post dealt with the various software packages we use for desktop mapping, ArcView, ArcCatalog etc. In this post we will look at the software we use to complete mapping tasks in the field.

ArcPad is a mobile version of ArcView and can perform many of the same functions as its desktop counterpart, but is designed for handheld devices used in the field. The main benefit in using ArcPad is the ability to combine map data with a GPS receiver on the mobile device. The GPS receiver, through various conversions, communicates with ArcPad to plot the location of the Trimble (and thus the person holding it) on the screen, relating it to the relevant map data.

After a few minutes to allow the GPS receiver to pick up a sufficient number of satellites, a crosshair appears on the screen indicating our location. As we work, the receiver will track our movements in real time and ArcPad will update our geographic position on the screen map, including point locations and shape files we have added. Thus, we can use the combination of the GPS position and the locations of the historic lime mines (stored in the handheld’s memory in Vector format) to guide us to the location of a specific mine, within an error range of a kilometre or so.


Image of ArcPad using GPS to plot a current position (crosshairs) on the Trimble Handheld. The points represent either historic mines or sites added to our database, depending on what colour they are.

Not only can we use existing files in the field, ArcPad also allows us to edit blank shapefiles and add data for new locations in the field, along with text-based attributes to describe relevant features of each location. This is another great advantage to mobile GIS. As explained in the previous post we use ArcCatalog to create blank shapefiles. Once these are loaded onto the handheld and opened in ArcPad we can use the GPS receiver to record our location and store it within the shapefile. This is how we add new locations to our database and record a more accurate location for any historic lime mines we find.

A major downside to using handheld platforms is that they do not have particularly quick processors. As such, using large raster data sets, like topographical maps, is tricky. It is possible to convert raster data to a size that ArcPad can handle, but this has limitations on the amount of data it can convert. Consequently only a very small section of a topographical map can be converted for use on the handheld. For survey work over large regions, this is not really useful.

Given the large scale of the project it has not been feasible, or deemed necessary, to perform this conversion over and over again for each of the regions we have visited. Rather we have mainly focused on using the digitised vector data to represent point locations and geological units extracted from the mining and geological maps for use on the handheld. This takes quite a bit of time to prepare but has provided invaluable information to us in the field. Once we have finished surveying for the day we download the shapefiles with the new location data on them onto our tablet PC and add them as new layers to ArcView. We can now view the points along with the topographical map, enabling us to view the new information in a wider context.

To summarise, ArcPad allows us to:

  • Know our exact location through the GPS receiver
  • View pre-existing Vector shapefiles like our historic mine location database and geological formations
  • Add new data blank Vector shapefiles with points or polygons captured using the GPS receiver
  • Upload the new information to our tablet PC viewing it in a wider context and with other relevant data like topographic maps

Without ArcPad and the GPS function of our handhelds relocating historic lime mines and plotting the accurate location of new sites for our database would be incredibly difficult. Using ArcPad and ArcGIS for mapping also has the added advantage of being able to connect directly to our project database in Microsoft Access and update our field data on daily basis. The next post on our survey procedures will deal with the database software and how we use both desktop and handheld-based software to record the sites we visit, and how all the components work together.

– A Reid