I would like to visit some of the opal mines in Australia (Coober Pedy, Lightning Ridge, etc.).
Are tours available to the general public at any of the mines? Do any of them offer for-fee collecting?
The Umoona Opal Mine in Coober Pedy tour seems to be one of the more popular ones. You can also stay in underground bunkhouse-style rooms there, for average hostel prices.
There's another good tour at the Old Timer's Mine in Coober Pedy. It's won some state tourism awards, if that's anything to go by.
There's also the Chamber of the Black Hand tour in Lightning Ridge which includes the stone carvings of some eccentric guy as well as a mine tour.
This another mine tour in Lightning Ridge that is easy-access.