in the same way as other buildings each is a improved version of the last only the first one being a 2x2 building and the others being 1 simple square of size allowing for practical mineral retrieval. also each version drags in more ore than the other.
the days like back in the old ford rouge plant or ford had their own barges of sand and liquid rubber and iron ore coming in one end and cars made of glass rubber and steel coming off the other
you will come to an area with two pods which contain [203 fol] and [iron ore x2]. return to the beginning of the caves and take the north path. hug the wall while you walk up this path; there is a hole in the wall that you can examine for [blueberries x2].
you'll have small settlements for gold & gems as well as maybe iron ore or bricks but those are low maintenance settlements that need the bare minimum of building materials and attention. there are a couple other efficient island choices but they're not as common as the ones i listed above nor as good in my opinion.
iron ore is the material used to make pig iron which is one of the main materials to make steel—98% of the mined iron ore is used to make steel. indeed it has been argued that iron ore is "more integral to the global economy than any other commodity except perhaps oil".