I really don't know what to make of this. It is definitely not...

I really don't know what to make of this. It is definitely not comparable to other groups testwork.
Hydrochloric acid is a much stronger acid than Sulphuric acid so it will always give a better dissolution concentrations. It will also dissolve all the other clay and gangue minerals which is what you don't want; isn't it? I would think any clay with REE would be able to get these levels using such a strong acid. I thought these things were dependent on pH. My feeling is this acid would create a pH well below 1.
It seems to me like the weak acid digestion method (which use HCl digestion) the industry uses for checking the leachable portion of the host rock.
Am I missing something here?
Any metallurgist or chemists that no more about this out there to give some more insight?