Considering the state of copper theft, the large number of videos on facebook and youtube describing how to melt metals into bar stock, and the low cost of the tools I dont know why this would be considered specialist knowledge.
Maybe if they needed aqua regia or something.
There's a pretty lively market in gold on ebay. Often forged into bars or coins by end users.
I have personally dealt with retail gold buyers who legally clear gold of all sorts with little question. They pay based on purity and likely have a price for whatever purity the horde gold is smelted at.
There's also that Singapore Gold Port at the Singapore Airport. Even if they wont touch you directly, there are IIRC, in person trades in the airport which can then be deposited straight into storage.
There's always people going, "psh, this won't make weed any more accessible, it's already so easy to get, anybody can do it!"
And yet, nevertheless, inevitably there are people who try it only because it's now legal and openly sold in stores. A lot of people simply don't want to do things they consider shady, no matter how easy it is. Maybe it being legalized doesn't make it any more accessible to you, but you aren't everyone.
What I am saying is that the process is already legal and available, so the process isn't a barrier to melting and selling the gold. I don't take a position on whether someone would simply not do it because its illegal.
The process of growing and selling weed was illegal, and thus also a barrier to accessing weed.
If anything your line of reasoning makes me want to legalise and protect melting gold you find and selling it.
It's a bit like internet piracy, make it easy and convenient to follow the law and most people will do it.