I think the Franklin mint usually put the metal details on the edge of their medals. I presume you used a search engine and looked for Franklin Mint 1987 Christmas coins or medals?
If you search the bay for "1987 Franklin Mint SANTA'S WORKSHOP Season's Greetings Card w/ Bronze Medal COIN" you may find one similar to yours, but it says it's bronze. It's not unusual for the Franklin Mint to have made both bronze and Sterling Silver of the same design.