I had a chat with the owner of Tywarnhaile (Porthtowan) at the weekend.  The current situation with this (formerly) popular mine is that there is no access and the landowner will prosecute anyone seen anywhere near it.  This is due to a break-in at the bunkhouse where a lot of damage was caused a while ago.  Technically it's still a working mine so the penalties for gaining unauthorised access could be serious.