As I noted in the other post, the Big Hole in South Africa was dug to a depth of 240 meters
by hand.
Coal mines of that depth nothing special, even with 19th Century steam technology.
https://en.wikipedia.org/wiki/History_of_coal_mining
"By 1856, the average depth in the Borinage was 361 meters (1,184 ft), and in 1866, 437 meters (1,434 ft) and some pits had reached down 700 to 900 meters (2,300 to 3,000 ft); one was 1,065 meters (3,494 ft) deep, probably the deepest coal mine in Europe at this time."
