Well I think the mines inspector would have quite a lot to say about just how close they get to those old shafts when they are full of water. Its difficult to tell what the formations are even in a granite based mountain. There are always shale stringers and these can let loose a good distance under that water pressure and with seepage over the years. I really don't think the mine inspector will allow them to raise from the sinker unless those shafts are drained first.JMO
The repeated mention of 'timber' and 'timbering'(?) makes me think of every mention of the mine being in granite. And, as such, did not require reinforcement timber.