Once built using many materials.
You drop/sell ore to the base.
It then processes each unit of ore into a unit of it's refined product.
Or possibly a ratio of 2 ore = 1 refined unit or vice versa.
For this to be "profitable" or worthwhile the price of refined ore's would have to be greater than the value of the unrefined Ore.
Gold would sell for 12,000 per unit or something, while Gold Ore would easily be sold for 3000 per unit at refineries closer to the Mining sites.