To my knowledge and findings there is no such thing sorry. So it was either plated (which you can tell because the details will be blurry and you could scratch it) or someone "turned" it gold. I can tell you how to "turn" one gold, which this is what this sounds like. We did this in high school. You have to do it right but you make a sodium hydroxide and zinc mixture and boil it at the right temp, put the penny in, and I think you heat it up on a Bunsen burner after I don't remember. Anyway you can google how to do it. Ancient alchemists used this to rip people off.