Antique Button Mystery

I found a unique button and would love to know more about it. It is very light, looks to be cast out of metal and has evidence of gilt left on the side. It measures about an inch across. The shank has a mold seam. It is not magnetic. I have not found any buttons like it and would appreciate any thoughts on age or where it came from. It seems very old and very different from the buttons I typically find. I collect vintage buttons mainly for repurpose on vintage clothing or just to keep for their beauty, this button was in a small bunch of mostly antique buttons purchased in a box at a flea market. Thanks for any responses!