The negotiation “add on”. After you get them to say yes, it is easy to get more.
Art of the Deal.
The only problem is that Russia will own the minerals, not Ukraine.
Once they have a revenue stream from selling the rare earths, they might want to settle with Russia in order to keep their fortune. Now that Russia knows about the value of the rare earths they might decide to destroy Ukraine just to get the rare earths...upshot...Ukraine’s sues for peace...keeps its rare earths...just sayin’....if so, quite brilliant way to end a war. Also, Dr. Z takes the loot, snitches on Biden crime family and disappears...win...win...win...