I think you just go there at night with nothing but a hammer equiped and he askes you to
smash the wall you do it and it opens the door to the mine your welcome:)

You have to go to the mine in the morning then have the hammer equipped, speak to carter,
then go into the mine. This works for me so it should work on other games.

Midnight is the time. And yes carter is the one who is the one who tells you about the
tunnel and needs your help with opening it up.