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

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.