This is a Authorized Replica of the 1854 O $20 gold coin recovered from the SS Republic shipwreck. It is 24K gold layered and assume it is metal underneath as there is no description in the COA of what the base metal is and it is certified by NGC and has a certificate of authenticity from Odyssey which is the company that discovered the shipwreck. It is clearly stamped COPY on the reverse so note this and it is gold plated and the certificate states it weighs 1 ounce but does not say what the base metal is. Still a super cool piece and interesting to add to your shipwreck collection.