I don't know if bashing reduces your weapons durability (i.e., winds up costing you a tiny bit of coin in the long run), but you can also have a party member attack it by using the attack-target command, which is Z by default. Really fun to let them do the dangerous/dirty work, especially if it winds up being trapped ;)

Bump on this thread. I also have the same problem.

in the thread is everithing described

Hit them and use your companions to attack them to, some doors have a lot of hp and when you think that you are not dealing any damage you are, I think the ones you cant break you cant also hit them either (they only can be opened with keys)
Be careful because most of the time chests or doors have traps and will kill you in a second, so hit them a few times and then shot them with a bow from far away

The "Rusty Mine Key" is meant for the second closed door in Iron Mines - Level 1a behind which Horathius is waiting.