>How would law abiding citizen Joe Random from Nowhere even know where to offload that on the black market?

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.

Can't say I've tried, but I think it's pretty easy to find buyers for gold.

Melting it removes the legal risk.

You'd be surprised of how easy it is for "Joe Random from Nowhere" to sell their illegaly sourced priceless artefacts. See: https://en.wikipedia.org/wiki/Lava_Treasure

Crime and theft happen in Denmark as in other countries. But finders get compensated for the metal value so unless they are collectors or have contacts to private collectors, there is not a lot to gain.

I know a guy who found a gold treasure on a field and he was contacted by a private collector after appearing in local news (he turned them down). So who knows how often it happens? But I don’t think finds are common enough that detecting and selling can be a lucrative business. It is usually enthusiasts with an interst in history.

It's enthusiasts - hobbyists willing to invest in metal detection gear, spending their free time doing this. If their aim was to get wealthy, they would be doing basically anything else.

Digging for gold artifacts and treasure is not a great strategy to become rich - these people are obviously much more interested in the history, and maybe the recognition. Of course they will turn it in.

>could be that 10kg was kept for all we know!

Doubtful. Finding such a hoard and reporting it to the authorities for formal examination by default means showing where you found it so the site itself can be examined by archaeologists. They'd likely be able to tell if you'd found more than you reported in the cache site. It's like forensics, but for ancient artefacts and ruins, pretty sophisticated at times.

It isn't, but it's impossible to know what will be useful for research again in the future, so historical researchers make an effort to preserve what they can and avoid excavating if possible.

What else should be done with the artifacts? And also why not? It's like storing your data. If you can keep it relatively inexpensive, why not keep it around just in case some future need or curiosity makes it worthwhile?

You can probably do a detailed 3d scan and retain 95% of the scientific value.

Understood. But it's also true that you get what you pay for.