I had this same problem until they changed the global market prices recently. I was building mines and depots like crazy. My new city now only has 1 coal mine and 1 ore mine and I was able to upgrade to the smelting factory.
OK am I missing a step here or something? I plopped an oil refinery and some fuel containers at my trade depot but I am not refining any oil. I read somewhere that there are upgrades for the refinery but when I go to edit the refinery there are no options to add anything. Am I missing a step here? Do I have to upgrade my HQ again?
My Origin name is "kreichs"
Just started a city in North American East 2, join me if you like, just search my name.
My city so far is going oil crazy, going to start mining for ore soon as well.
Thanks