Ann: Gold Extraction Results from Ema and Tres Estados, page-209

I think sometimes it takes a bit more than a microscope and a few hundred dollars. I just googled 'gold silver sulphide compounds' and came up with one I've never heard of. Read this article about the gold silver sulphide uytenbogaardtite, (Ag₃AuS₂ )and how only last year they managed to understand its crystal structure. My point is, just because we don't fully understand where the gold is coming from, doesn't mean its not there. Its not alchemy, its chemistry. Who knows, maybe this is the mystery substance ? We are not experts, lets leave it to those that are qualified.

http://minmag.geoscienceworld.org/content/80/6/1031