Just chipping in with my thoughts. It's definitely portraying a
byzantine emperor so I'd guess 5th-9th century cause of the diademed
bust and how it looks familiar to examples on coins. So it's copying something that excists and that would naturally lead us to the ostrogoths, however the
style reminds me of
celtic coins or ostrogothic issues. Could be a harness mount of mercenaries perhaps or just a mount for a chest .. etc.
Very interesting piece, wonder if somebody will know more