Ann: Magnetic separation increases TREE grade by 126% at La Paz, page-41

Amigo, the short answer is that the value for TREO is higher than the value for TREE. As far as I can explain, the mass (ie weight) of TREO is greater than TREE because in the calculation, the rare earths are reckoned to be combined with oxygen. The oxide gives a high percent increase of about 50% for the lightest rare earth (eg scandium) and a low percent increase of about 15% for a heavy rare earth (eg dysprosium). So, the difference between the grade of TREE and TREO will depend on the various types of rare earths in the deposit. That's the best I can do, someone else can add or improve.