Diamond Mining
Perhaps the event that sparked a rush to begin mining diamonds in South Africa occurred in 1868 when a young African boy, now referred to as Swartboy, picked up a shiny rock near the Orange River. In hopes of bartering with his newfound acquisition, he took it to a local man named Schalk van Niekerk who was known for collecting fancy-looking rocks. This particular rock, which turned out to be a diamond, wasn't the first to be discovered, but at 83.50 carats, it was the largest one found so far. Van Niekerk offered Swartboy much more than food and lodging in place of the rough diamond; he traded all of his livestock for the stone.
These days, it's sheer luck and chance timing that a person would be fortunate enough to find a large diamond out in the open. For this reason, many techniques have been developed to increase the chances of finding diamond deposits. The most widely used method is the South African method where prospectors search for mineral deposits which are commonly known to contain diamonds. Since material surrounding diamonds are generally more abundant than the diamonds themselves, it's easier to find diamonds this way. Coastal and marine prospection involve searching for diamonds along coasts and underwater. In alluvial prospection, diamonds are directly sought out in alluvial deposits, although it's more difficult to do this because of the absence of the dry season.
There are two basic types of diamond deposits: primary and secondary sources. Primary deposits are kimberlite and lamproite pipes produced by volcanic activity while secondary deposits consist of deposits found as a result of erosion and oceanic movements. When mining in primary deposits, two types of mining are employed: open-cast mining and underground mining. Open-cast mining is widely used, and one of the most famous diamond mines, the Big Hole in Kimberley, South Africa, is an open-cast mine. Explosives are used to break down the rock and the rubble is placed into trucks to be processed. Open-cast mines are enlarged until the diamond reserves are exhausted. Underground mining is more costly than an open-cast mine because it requires better technology to excavate diamonds. These mines can also reach to depths of 1,000 meters and requires additional safety precautions for workers.
With secondary deposits, diamonds are mined near rivers and along coasts and are retrieved from the sediments that conceal them. Industrial mining in secondary deposits utilizes large machines such as hydraulic shovels to reach diamond deposits. In marine littoral deposits, which fall under the category of secondary deposits, diamonds are mined along beaches and underwater. Oftentimes, it is necessary to go down 20 or so meters below sea level before reaching diamond deposits. Underwater mining is especially difficult, but DeBeers leads the way in this line of work.
The methods in which diamonds are separated from the rocks they are found in follow the same general pattern. Ore processing includes crushing (care must be taken to avoid crushing any diamonds contained within the ore), screening (to separate the larger elements from the smaller pieces), washing (to clean off any mud), concentrating (separating the different densities from each other), and collecting (enlisting the use of x-ray separators).
When it comes to sorting diamonds, the process is usually done by hand with people sorting the diamond rough into different categories. Gem quality stones are set aside from diamonds for industrial use or for boart. Only about 20% of diamonds mined are of gem quality, while the rest will be used for industrial purposes. The diamond rough set aside for industrial applications will be used as drill bits and for other machinery while boart will be crushed and used as diamond dust for polishing stones.
Sorting of stones from the rest of the rubble is done by an x-ray or by eye via a grease table. Diamonds have a natural affinity to grease and oils, so the grease table is an essential tool in separating diamonds from rocks. As the diamonds and other materials pass, water is sprayed on the table, removing any rocks and other debris. The diamonds are trapped in the grease and are later heated to melt the grease, revealing the diamonds. The x-ray machine is more high-tech than this method, employing a photomultiplier that generates a stream of air, knocking the diamond into a separate bin.
Once diamonds are separated from other materials, they will be sorted and distributed among sightholders.