The late Keith "Ben" Bentham did quite a lot of ferreting about and digging in the Winnats over the years. I'm pretty sure he kept extensive records of his activities; there might be useful material in the Eldon library?
There is a blocked shaft, high up on the north side, about 50m NW of the Old Tor entrance, and higher still, near the prominent outcropping rib of rock - me and Scud had a look at it in the summer one evening. It wouldn't go into Old Tor, and from the remains left on surface it looked like it could be natural rather than mined - couldn't see any shotholes. That's the only one I know of that isn't logged. Apart from one I can't put in. The editor's decision is final