I'm guessing plated brass, but you do need an acid test to make sure it's not a low karat gold.
You can't make metallurgical determination from a detector response. The size, shape and mass has as much or more influence than the metal its made of.
I find "rings" like that a lot. I resorted that they are usually the ring on a pen, that separate the 2 plastic screw together pieces. They're never marked, lol. (I don't have a 3030, just an Excal, so I don't know their numbers).
They're fun to find, but irritating, too, lol!
I think it's a pen part.