Quote Originally Posted by Wakizashi
Iron is not a mineable resource. It is used for Armour and Weapons upgrades on your troops. Each Level of Armoury adds +1 to your units Armour and Each Level of Swords Guild adds +1 to your units Weapons, making them FAR more effective in Battle.

Actually, iron just means you can build a Metalsmith in that province, which gives all units trained there an attack bonus (dependent on what level of Metalsmith you've built). Iron isn't needed to upgrade armour, just an Armourers Guild (and the like).