Black stains from brush??

I just looked at my carboy after 2 weeks in primary and the small marks that you can sometimes see after using a brush in the carboy right at the neck from the metal on the brush are a lot blacker than usual, could this be black mold? Iron oxide? Would this be harmfull to drink if it was iron oxide?. Have not seen this before, anyone else had this happen to them? Hope this doesnt wreck this batch.....

I would have pictures but do not have my camera, it does not look furry like mold but definetly something different than usual..

Do you use idophor?

nope, starsan, and i clean and sanitize like its my job.. usually after using the brush you can see faint lines in the glass from the steel rubbing on it but this was different after a few weeks