I can't say specifically about your mast, but often, they are not anodized. As js says, the surface oxidation becomes a self-protecting barrier layer that prevents further oxidation.
I have built garden structures out of copper pipe, sand them to a bright smooth finish and painted them in varnish and they have remained bright and copper colored for years in all kinds of weather where unpainted copper turns green in months. But that green also protects the copper.
Just something to think about.
-Will (Dragonfly)