Huh?? Why would you mention eBay?
Also, I just clicked on the pic for the first time (trying to save on data usage, you know). First off, the pic is quite fuzzy. Second, you said, "It unfolded into a sheet", though I see no fold marks. That's not saying much, as the image is out of focus. But you mention how you found this on the surface, even though gold is one of the heaviest metals to exist - it LIKES to work its way under lighter materials.
Finally, after enlarging the pic, that piece looks really thin - like maybe some type of foil. Could that be? Could it be gold-colored foil? Could it be crystalline or leaf gold? I haven't a clue.(!!) The color looks to be about right - but then I'm no expert!!
It's really interesting at this point, and I, for one, would love (DEARLY!!) to see some better pics and know the weight/dimensions. But it baffles the hell out of me that you would bring up eBay. I'm hoping very much that it was just a poor choice of words.