Some legends, like that of Atlantis and Lemuria say that there were 2 advanced "ethnicities" on Earth, unknown species. One group wanted to teach humans things, and the other thought they should just watch them, and not mess with them us. There was a war, and one was destroyed. This story is sort of echoed in Sumerian Enlil and Gilgamesh, if I remember right. Also, in the Book of Enoch, from the "Book of the Courses of the Heavenly Luminaries". I don't know where the Gold part came from.... but, I have heard that for a long time too, so probably from some legend.