03 Aug The Deepest Gold Mine in the World: Mponeng Mine
- Location: Guateng, South Africa
- Depth: 2.5 miles below the surface
Popular culture has created a very specific preconception of what people imagine a mine to look like. Mines are often thought of as these crude, makeshift structures held up by rickety wooden beams and lit by gas lanterns. While not as pretty as a skyscraper, or as innovative as a zero-gravity living space, modern mine shafts are none the less comparably complex pieces of engineering that don’t get enough credit. The Mponeng gold mine stands out among others of its kind for being the deepest gold mine in the world and demonstrates the pinnacle of mining related engineering.
Transportation and Structural Integrity
The tricky thing about mine shafts is that the raw amount of overhead rock grows as depth increases. Even if a mine shaft isn’t very impressive to look at, the fact that it manages to support the weight around it, is what deserves consideration. The tunnel walls of Mponeng are standard concrete (more specifically, shotcrete) walls, supported with steel rebar. What stands out is the use of artificial diamonds which are used to create mesh netting that further supports tunnel integrity.
The Mponeng gold mine has a vertical depth of more than 2.5 miles, which is approximately half of the vertical distance by which Everest extends upwards. Transfers between multiple high-speed elevators are required to descend, with the lowest reaches of the mine requiring on foot hiking. A trip to the bottom takes more than an hour to complete.
To go back to the skyscraper comparison, mines do have one design consideration in common with the monolithic metropolitan towers- elevators. Speed, load yield, safety, all factors which must be taken into consideration in the design and maintenance of an elevator. Mponeng, and in fact most mines, differ in the size of the elevator. In order to sufficiently transport more than 4,000 miners, who work in the depths of Mponeng, the elevator cage is sufficiently large to accommodate larger groups of miners and their accompanying weight.
Solving the Temperature Problem
Think back to elementary school and one will recall that the earth is comprised of layers, much like a cake. There’s the crust, which comprises the solid land we live on, the mantle, which is a hyper compressed sea of magma, and the core, which is the incredibly dense, metallic focal point of our planet. The further down one traverses the crust, the closer they come to approaching the mantle. Go deep enough into the deepest gold mine in the world, and eventually one will experience drastic changes in temperature due to the increased proximity to the mantle.
The rock at the lowest levels of the mine can reach temperatures up to 150 degrees Fahrenheit. To put this into perspective, the minimum temperature required to cook an egg is 130 degrees Fahrenheit.
In order to sustain prolonged work, and not cook their miners alive, the mine requires some serious cooling. Because of this, a system was created which pumps ice down the length of the shaft. This, coupled with internal insulation, cools the tunnel air down to a surprisingly livable temperature of around 80 degrees Fahrenheit. Even with the cooling, working at the bottom of Mponeng is still a grueling experience as the miners excavate more than 5,400 tons of rock per day.
Why All The Trouble?
A writer for BBC News once reported that Warren Buffett estimates that all the gold in the world that has been mined so far would be able to fit in a square cube with walls 67 feet long.
While this statistic is highly controversial, gold is understood to be a rare resource, and many fail to realize just how rare. While a 67 ft cube might seem rather large if it was sitting right in front of you, think of that amount spread across the entire world and the rarity of gold becomes clear.
Despite all of this, the mine only needs to retrieve 0.35 ounces of gold, the equivalent of a handful of paperclips, per ton of rock excavated, in order to turn a profit. So, while it might seem like an unnecessarily extreme structure to create, it shows that humans are willing and able to create just about anything so long as there’s a good enough reason to justify it.