Mponeng is a mine of extremes. 4km of depth means immense pressures (just think maximum depth people can dive, static pressure increases lineraly with depth as the rock above needs to be supported (and rock bursts). The amount of engineering and resources poured in to support the tunnels and openings gets crazy.
Not only that, but heat is a problem. Here in Québec the mine Laronde is famous for its air problem. The typical pattern of ventilating mines is to bring air down these tall vertical passages (raises) to just about the bottom of the mine then let it pass to the surface through workings. Cold air in the winter at high speeds means ice build up on the raise wall, which risks decreasing airflow in winter (smaller passage) or flooding/falling ice in summer. So the mine Burns propane in the stream of incoming air. However, the mine is more than 3km deep, so the ambient temperature of the rock grows as that same air continues down, and at some point you reach greater than safe working temperatures, so that exact same air is AC'd further down on a massive scale so the humans and machines can work safely at the bottom. What a headache.
I don't know many specifics about Mponeng but I did was a doc on Youtube about it a couple years ago which miners following very narrow gold seams, reinforcing the opening with blocks of wood, which even they felt weren't safe (wood would only last a short bit of time). Travel time also becomes a big consideration. Workers in most mines travel from the surface to their workplace and back during work hours. If you have 3 or more hoists (elevators) to take, many KMs to get to your workplace after, before/after shift meetings, time to change, etc. you don't get many productive hours from your people. I think Mponeng has at least experimented with having guys sleep underground close to the face for short periods (kinda like on-off rotations in remote mines) to get more effort out of them.
I’ve packed those wooden jenga blocks during a visit to Kusasalethu mine, which is similar to Mponeng. You can see the older blocks slowly collapsing under the persistent pressure of the hanging rock. Took about 20 minutes working with two miners, squatting in the 120cm high cut of rock leading up to the seam face. By the end of it I was soaked and exhausted.
Even more crazy when you learn that the average age on a South African hard rock mine is approaching 50. I don’t know how the drillers keep at it for a full 4 hour shift (2 hour shaft-underground train-3km hike commute to and from the main shaft entrance).
The entrance is at about 1560m altitude, so the mine goes way below sea level. It's nowhere near as deep as the Kola Superdeep Borehole though [1], which has been on HN a number of times [2], and is only a narrow bore that people can't go down. The temperature at the bottom of that one got to 180°C, preventing further drilling.
This contains some graphs (the 2nd graph is most relevant) that show how the temperature changes as a function of depth. It increases much faster than I thought.
This story was posted on HN a couple months ago, there is a push right now for use of a somewhat novel technique to drill extremely deep holes, producing geothermal power anywhere on the planet, with several commercial ventures in their early phases:
Assuming that air can equalise and the bottom of the mine is 2.5km below sea level, from air pressure calculations air pressure would be about ⅓ more, 1⅓ atm.
I had an idea to see if plants would grow faster in a denser atmosphere. I’ve found one small study, I think the air pressure was thought to be denser when dinosaurs were about.
One of the reasons why I never studied Geology and instead did Computer Science.
I collected rocks - had books on rocks - orientation day at the Geology Dept and the dude told me I am not going to be driving a Landrover but will be working in a mine.
I looked up the deepest mine in the world - recalled a childhood memory of spelunking in the Cango Caves.
Hard rock mining is pretty insane when you look at the history. In california the Empire mine hit ~3.3km deep in the 1950s before closing due to costs. That's about 2.4km below sea level.
Not only that, but heat is a problem. Here in Québec the mine Laronde is famous for its air problem. The typical pattern of ventilating mines is to bring air down these tall vertical passages (raises) to just about the bottom of the mine then let it pass to the surface through workings. Cold air in the winter at high speeds means ice build up on the raise wall, which risks decreasing airflow in winter (smaller passage) or flooding/falling ice in summer. So the mine Burns propane in the stream of incoming air. However, the mine is more than 3km deep, so the ambient temperature of the rock grows as that same air continues down, and at some point you reach greater than safe working temperatures, so that exact same air is AC'd further down on a massive scale so the humans and machines can work safely at the bottom. What a headache.
I don't know many specifics about Mponeng but I did was a doc on Youtube about it a couple years ago which miners following very narrow gold seams, reinforcing the opening with blocks of wood, which even they felt weren't safe (wood would only last a short bit of time). Travel time also becomes a big consideration. Workers in most mines travel from the surface to their workplace and back during work hours. If you have 3 or more hoists (elevators) to take, many KMs to get to your workplace after, before/after shift meetings, time to change, etc. you don't get many productive hours from your people. I think Mponeng has at least experimented with having guys sleep underground close to the face for short periods (kinda like on-off rotations in remote mines) to get more effort out of them.