Pensana's very successful Coola soil sampling results clearly show the RE-bearing carbonatite ring structure there.
Given that the volcanic ring structure with 3.2km perimeter and the dyke are largely intact at the surface, it seems that this RE-bearing material probably runs from the surface to any realistic depth that you care to go.
I can see the Saltend RE refinery/separation facility with nameplate production capacity of 4,500tpa NdPr oxides just being the first of multiple RE separation lines that Pensana builds!