I have a few ideas, hope they're not stupid...
Mines can have different yields, say frags or gold or, even rarely reserve stam, maybe even bonus prizes like those useless ruby rings, or a loyalty class potion if held till fruition successfully...
Mines have a decay rate, making them last a finite time when occupied, and can be plundered for a piece of the yield, or possibly even stolen outright, and maybe should be guarded similar to a relic. Once occupancy time is expired, total yield is sent to your item mailbox in a box. Hold times similar to global chests, maybe....
If a mine isn't discovered and occupied after a specific time, it will vanish and respawn elsewhere, to a random location.. Like chests, spawns could be anywhere, you just gotta trip over it....
Edited by BadPenny, 11 September 2017 - 01:38.