million mt? Is that million megatons? And which rare earth elements are they?
It's mostly light rare earth elements. Over half of it is cerium and most of the rest is lanthanum. Most of the economic value is in the elements that are not cerium or lanthanum. It appears to have about the same proportion of neodymium and praseodymium (valuable light rare earth elements used in magnets) as the Mountain Pass, California mine, plus more terbium (more expensive heavy rare earth element also useful in magnets) than Mountain Pass.
Ore is by definition the "economically feasible/interesting" subsection of the rock covered by the claim.