Bob, something's all mixed up with your facts/posts.
a) is this your own personal property, or isn't it ? From post #1 & #4 context, it appears that this is your land.
b) In #7, it's "been found". In post #10, it's been "validated". I'll take that from the context to mean that "found" and "validated" are the same thing, right?
c) If so, I will ask if by "found" you meant ACTUALLY FOUND. Ie.: NOT just "... are certain that it's at such such point/place", etc... But rather: Truly excavated, looked at, held physically, etc... RIGHT ? (lest how else can you say it was "found" ??)
d) and if so, then if you label that guy as "partner", (who did the actual finding) , appears, as you say, to have no interest in it. Re: #11 post. Right ?
e) and the entire context of your post (the mere fact that you post with concern about the matter) seems to indicate that no prior agreements , between you and this fellow, had been entered into, right? (lest why else would you be posting such a question , if all those details had been ironed out ahead of time).
f) Thus, if he doesn't care (as per [d] above), then I'm having trouble figuring out what the heck your worried about. If it's your land [a], then we're in a country (the USA) that deems valuables under-the-ground (oil, gold, etc...) as belonging to the land-owner. Then I fail to see what you're worried about.
Am I missing something ?