Thanks for the reply. That's very interesting. I was wondering if someone had attempted some kind of destructive assaying but what you suggest makes more sense. The guy I brought it from seems to be a scrap jewelery dealer so it's quite probable that it's from a ring.
Do you happen to know what the accepted weight variance is for gold Krugerrands? If what this is is far out then I'll complain as it was advertised as an 1/10th of an ounce coin.