I recently unlocked the Deep Deep and I was so disappointed. Especially with the added gems, the amount of stuff you can find in each location is simply too much with the size limit of the cart and the fact that you have to drag unsmelted ores back and forth (constantly using up those precious few slots in the cart) if you don't get the right amount. This really needs to change. Why am I still finding silver ore in the Deep Deep (the highest level area), when you can already find silver ore in the second area?!
There is no need to be able to find silver ore in 4 of the 5 areas. There is no need to find iron ore in 4 of the 5 areas. Remove them from the higher level areas. AND (possible an 'or', but ideally an 'and') let is drop off unsmelted ore at the furnace (not as in discarding them, but dropping them off to be smelted later), so that even when you don't get the right amount now, the limited slots in the cart aren't constantly wasted by dragging the same stuff back and forth.