Fair enough but understand the presence of REOs in sapprolitic...

Fair enough but understand the presence of REOs in sapprolitic clays is only the first page of the long story. there are three main categories REEs can be present in ion absorption clays:

colloidal phase: REEs deposited as insoluble oxides or hydroxides or as part of coal polymeric ornanometallic compounds. which can only be recovered by acid leach

exchangeable phase : REEs occur as soluble free cations/hydrated cations out part of positively charged complexes in solution absorbed species of clays. these represent 60-90% of of total content of rare earths in ores and can be recovered by ion exchange leaching with monovalent salts - this is what you want

mineral phase: REEs as part of solid fine particles with same mineral matrix of host rocks - REE partitioned as part of the crystal lattice. these can only be recovered by aggressive conditions - alkaline bake and acid leach

I'm certainly no expert but notice that the presence of REs is only one condition. Mek needs to have an extensive study done on the on how the REs present themselves but they don't have the expertise and it's not their current focus.