It seems like back on the mountain we found a bit of a problem with how he was planning to gather it anyway. Even his sword had trouble cutting the spider dude. I'm not sure how well those little throwing knife/vial things are going to work on the big deal demon bodies. Best case scenario, maybe they lose all that extra durability while they're breaking down? Otherwise, maybe they'll need to use some of that special ore to strengthen them or at the least he'll need to be in a state where he can use his strength properly instead of severely injured and/or disoriented. His sword supposedly broke in that fight only because he lacked the skills to pay the bills at the time.