I don't do this any more, but a decade or so back you could actually buy unwashed ancient coin lots over the internet. You then clean them up and see what you have. It later became increasingly clear that these were coming out of parts of the world where treasure hunters can pillage archaeological sites, and also that these coin lots had been thoroughly sorted through prior to my getting them. But early on you would get some interesting things. Later, just endless numbers of low grade small change from the various squabbling late Roman Emperors.
But one time I actually found gold in a batch. Sort of.
This is a tremissis, a small gold coin of the Byzantine Emperor Justin I. Not very well done artistically, and the back is a total mess. The Wikipedia link btw probably shows a much nicer version of this very coin.
See the rust peeking out around the upper left edge and at central wear points? This is a counterfeit, nothing more than a base metal coin with a very, very thin gold wash. I wonder if anybody in ancient times fell for it?