Wanderer,

The temperature underground stays pretty moderate and gets a bit warmer with depth. There is a lot of ventilation pumped in so the temp is not as affected by the warmth of the ground as you might expect. On the other hand, I have been to quite a quite warm area at the 6300 foot level where ventilation wasn't as good, but it is not hot.

In the hot summer, it is actually kind of cool down there.

In hard rock mining, 600m and 1000m are really that deep.

Cheers,

Bluenoser