Mi-go Mine

subtitle:
An adventure set in R.E.H.’s mythic Hyboria

from the overview:
In attempting to track down the origins of a mysterious artifact, the PCs venture into a remote, mountainous region of Ophir known for its played-out (and long abandoned) mines. They soon discover a fresh trail leading up the side of an old volcanic cone--and an active mining operation going on inside, presided over by sinister mi-go, their alchemist quisling, and a band of slavers armed with alien weaponry!