I am not 100% sure about this but... Heavy Rare Earth Elements, REE’s, are really not all that rare. What makes them difficult to produce is all of the difficult refining techniques and the radioactives that are usually associated with REE deposits.
As a disclosure I have some shares in a overseas company that is working on getting a REE mine and refinery complex going. If they manage to do it in a reasonable time there will be an alternative to China’s REE monopoly it currently holds.
Oh, horrors! I'm eating radioactive material for breakfast!
As we speak mines in the western USA and Australia are working on opening. Permitting I believe is done. The chinese screwed the pooch on this one, massive enviro damage, and now likely end game for their mines as enviro weenies make laws restricting importation of carelessly mined and refined rare earth elements. BTW Thorium is a REE and the best fuel for nuke reactors for power.