Don't throw it way yet. Have it tested first.
I've seen some fake vintage buckles that were actually made from solid gold.
One guy used to sell these by the dozen on eBay years ago. If you wanted a vintage-looking precious metal buckle, it was just about your only alternative.
If it doesn't pass the acid test, then I would keep it, just because it looks nice. Just be sure to tell any future potential buyer that it's a fake buckle.
Just my 2c worth.
gatorcpa