I think that the government has “first dibs” on antiquities but must pay a fair market value for them. This seems to be subject to abuse but I haven’t read of complaints.
It’s because a great deal of the value of these sorts of finds comes from their provenance, not from their melt.
The Government essentially provides the provenance for free by bringing in experts to validate the coins.
So it works out well for the finder and the land owner, who typically split the proceeds.
I love treasure hunting. Here are the complaints leveled at the “hobbyist” in that part of the world, They are technically only allowed to get “targets” from disturbed soil and not allowed to dig into undisturbed soil. This raises many stories, speculations, and accusations.
So take this scenario. I get a signal and dig down 18” (which I think is a logical plow depth) but I do not locate the target. At this point I notice undisturbed soil, what do I do? The machine is giving me a sweet high silver signal. Well crap, I am so excited that I continue and thereby ruin some information that can be gleaned from the area. They are technically supposed to call the museum to continue into the undisturbed soil. I imagine that if you do that they are not super responsive. I imagine it may take several days just to go back and find out that you have a cache of horseshoes that were fooling your machine.
This is all happening on private property by the way. They have been operating under this treasure trove law since sometime in the 90’s I believe. There are vacation tours you can go on that take people to these fields.