I've never seen such a big cash coin - but that doesn't mean it's not real. Maybe some kind of medal or token? I don't know.
Ask @manymore To me it looks modern, they often bake these in an oven to get this bright green color.
That's what I was scared of, I know patina means nothing and can easily faked. I sent a PM asking about the coin to @manymore.
i don't think it's a coin, i'm pretty sure it isn't northern song...but not 100%. my guess would be token or charm...as to how old...i don't know.