The mines of Mercury were a location in Tom Paris' holodeck program The Adventures of Captain Proton, worked by slaves of Doctor Chaotica. As a nod to the practice of re-using sets in the 1930s serials Captain Proton was emulating, Planet X looked almost identical to the later featured Planet X, though unlike planet X it had an erupting volcano. (VOY: "Bride of Chaotica!")
When Chaotica was about to conquer the Earth in the final chapter, he threatened to send all earthlings that did not cooperate to the mines. VOY: "Night")