53 doesn't sound like that much. I guess it's average between the sucky ones where you get ~20 and the ones with 100+. I looted 8 crypts in a swamp in my current game and I filled up 2 chests, so 600 iron for an average of 75 iron per crypt. (I actually didn't finish the last one but decided to stop after 2 full chests for now)