Revealing mistake: Axel's badge says deputy sheriff. He is THE sheriff. Not a deputy.
Factual error: As Sarah is being chased toward the mine by "Harry" she is unable to open a door and is trapped as Harry approaches. The shadow of Harry cast on the wall gets bigger as he gets closer to her. If Harry were walking in front of the light source casting his shadow, his shadow would get smaller as he walked further away from the light source and closer to Sarah. (01:40:00 - 01:41:30)
Continuity mistake: In the final mine scene when "Harry" is walking toward them and popping light bulbs with the pickax along the way, the second bulb he hits causes the wire to swing down and swing back and forth. In the next shot, the wire is back up on the shoring post. (01:32:20)