You're making me remember a day when it was very hot in Sudbury. On the upper levels the mines are quite cool even in summer and almost all of the miners wear long winter underwear underground. So on this very hot day my father went into work bragging to everybody how he was going to work in a nice cool mine. Unfortunatly for him there was a brush fire on surface that day that was threatening the powder magazine. All available men had to spend the day on surface fighting the fire including father in his suit of long winter underwear. He looked a little beat when he got home.

The deepest I ever worked in a mine was 4000 feet. The air was stale and warmish at that depth, maybe 80 to 85 degrees. I didn't much care for it.

In South Africa in the deeper mines I understand that they have freezers underground that freeze water in vests. The men wear these vests of frozen water and when one thaws out they go back to the freezer to get another frozen one enabling them to work in some very hot places at depth.

The better the ventilation the lower the underground temperature will be. In Sudbury I was pretty happy with ventilation in the Inco mines I was in but never really worked too far down.

In some places I have read that they break out rock around the ventilation shafts. In the winter ice forms in the broken out rock and then in the summer they pump ventilation air through this broken out rock and ice to help cool the air.

Anyway the ore at NOT is easily rich enough that they will go down after it.

Just some thoughts.