It's interesting, because it seems to be just copper bombarded with Argon. But Argon is a noble gas: https://sciencenotes.org/wp-content/uploads/2013/06/PeriodicTable-NoBackground2.png

So I'm surprised it bonds to anything. In the article it says they ionize the argon before, so I guess that's how it works. I wonder what percent of the atoms in the final alloy are copper vs argon. It almost sounds like there's no argon in the final product, and just the act of interacting with the fast-moving ionized argon creates ionized copper that acts more like gold.

Interesting article, thanks for sharing.