The iron ore resources of the world are essentially all in Archean time.  This was related to cyanobacteria active in the ocean. One area of Archean rock in the US is the Central UP. The iron formations we will see are part of the Marquette Iron Range, a syncline of sedimentary layers squeezed between two blocks of Archean gniess and granite. The UP is a major producer of iron for the whole world.  Iron Mining started here in 1845 and is still quite active today.