This is a simple reaction mod to create iron bars from any type of metal ore. The mod creates a new task at the smelter, Make iron bars. The task requires metal ore and fuel, so hopefully it doesn't feel too much like cheating. I created this in response to the metal scarcity changes in the recent versions of DF.

Existing smelting reactions, including iron ores, are unaffected. You should be careful if you have platinum or aluminum (or any other metal ore you want to use normally) on your map; the new reaction will use them to create iron. The reaction will not deplete your cotton candy stockpile.

The mod works by adding a new reaction class, METAL_ORE, and a new reaction, IRON_FROM_ANY_ORE. The new reaction class is applied to metal ores in inorganic_stone_mineral.txt, and the reaction is defined in reaction_ironfromanyore.txt. entity_default.txt is modified to add the new reaction to the dwarf civilization.

Installation
Extract the archive into your df/raw/objects folder. This mod will require you to regenerate your world, as it adds a new reaction.

Workarounds

• Change the stones used in the reaction
  If you don't want to use certain ores in this reaction, remove [REACTION_CLASS:METAL_ORE] from its definition in inorganic_stone_mineral.txt. Likewise, if you want to use a stone which wasn't included, add the reaction class to that stone's definition.[/li]
  
• Use the reaction without regenerating the world
  I haven't tested this, but you should be able to replace an existing reaction and use this mod on an existing savegame. In your save folder's raws, replace inorganic_stone_mineral.txt with this version, then copy the contents of the new reaction over an existing reaction. Make sure you pick an alloy that you don't care about, because no one in the world will be able to make it any more! Any culture which can make the replaced alloy can now make iron from any metal ore, which may do interesting things to the game; remove the reaction from the other civilizations' permitted reactions if you don't want this to happen. Existing bars/items made from that alloy should remain unaffected, and you should still be able to make items from bars which already exist.
  
• Coexisting with other mods
  This mod should be fairly simple to integrate into other mods. reaction_ironfromanyore.txt is fine unless the file name clashes. entity_default.txt only needs one additional reaction permission which can easily be added by hand. inorganic_stone_mineral.txt needs the new reaction class added to 16 different stones; tedious but doable. Search for METAL_ORE and add [REACTION_CLASS:METAL_ORE] on the next line.