If you want lots of information, I suggest you get a copy of "the copper mines of the manifold valley" by Lindsey Porter and John Robey (Mike Moore will probably have a copy for sale - look in the links section)
As for accessibility, not generally at the moment is the simple answer. The trust who now have ownership
(http://www.ectonmine.org/) do intend it to be used for educational purposes but they're still working on the facilities and aren't yet fully operational. PDMHS do occasional trips in, but these are members-only and usually heavily oversubscribed as party size is limited to 8. I'm currently trying to negotiate a visit for ANHMS but I can't guarantee this will come off, and if it does, party size will be limited.
Follow the horses, Johnny my laddie, follow the horses canny lad-oh!