Seignorage has always pretty much been around, even when coins were gold and silver. In fact historians claim that this was the impetus for official state coinage to start with, back to ancient times! As found in nature in streambeds and such gold is often found alloyed with silver, called Electrum. I think it averages around 18kt, say. Well the very first coins minted were officially valued at the going “natural” 18kt lump-of-electrum exchange but were far less pure.
Silver prices and gold prices fluctuated at various times and really put commerce through problems because one or the other would become overvalued relative to the other. It became profitable at times to export the coinage for the scrap value, and so they would disappear. Arbitrage, sorta. In those days the way the mints operated, you would bring your bullion to the mint and they would give you back finished coins, minus nominal fabrication costs. Rinse, lather repeat.
Yes, I know, but in those days there was just a slight markup to cover the actual cost of minting. When the clad coins came out though, they still followed the old practice and pocketed the difference - making money out of money, if you will..