I have iron in my star-menu, but I can't use it

[Jugi]

I have couple of iron-rewards from some previous quests in my star-menu, but I can't use it. When I open my star-menu, and click on the iron, I cannot add it to the mayors house.

[Nukar]

Those are ment to be used on an iron deposit/mine

[Jugi]

Why haven't I tried it before?! Thanks for the advice!