The iron in your inventory, and the resource iron that is being used on the overview map, aren't the same. You need to build a mine that produces iron. The system is not turn based anymore, the resource will be produced automatically in the background once you have the necessary building for it. Resources are automatically used as materials for the production of advanced resources, so the iron might not pile up in your stroage until all production that are being done with it are finished. In the next update, I'll add the option to pause productions, so that you can stop that from happening when you need the base resource.
