You'd probably be better off asking the question here:
https://ukcaving.com/board/index.php?board=7.0It's a caving board but I would think some posters would have knowledge of mines as well.
If your interest extends to caving there are maps showing the locations of most caves and potential caves in South Wales at
http://www.ogof.org.uk/Bare in mind that most major systems in South Wales are subject to access restricrtions and getting keys without club membership isn't always easy.