Thanks - i'll take a better run at cleaning this and see if it can get it off. Its the fact that it looks like its oozing out from the colored part to the silver part that concerns me. It also seems like a gritty substance (as you can see on the driveway). Seems sandy.
Follow @raydog9379 advice and get the iron remover. I've used the product from Adams polishes, but Chemical Guys or other equivalent should be fine.