I revisited the Copper Mill in order to try and do the tomb to the far north of the area. I climbed all the way to the top, where I found that that the area you fight the 'boss' in (those flamer chaps) is blocked by burning debris.
So I cannot progress past this to reach the other side.
Going back down, I need to back eject (jump back off a wall) in order to land on a balance beam, which I can't figure out either.
So am I really stuck, or is there a way through the Copper Mill, once completed, or a secret way back down to the camp in order to fast travel?