Banded iron formations are some of the most primordial rock formations on Earth and usually have ages in the billions of years. we are in an Archean Greenstone belt with KXL in the Canadian Shield so their prescence is not a surprise. I posted earlier that BIF's can host gold although visible gold is rare. Very fine particles sandwiched in the chemical sedimentary layers that compose BIF's. In general they are not an economic source of iron. Cheers!