The use of “light vs. heavy” ratios is very misleading and should not be the metric to rank or rate rare earth projects. Ratios do not reflect grade or value and is a flawed metric.
Not all light rare earth oxides (LREOs) are “bad” (i.e have low value and are in oversupply). There are 4 LREOs of which 2 are critical in the production of magnets – Neodymium (Nd) and Praseodymium (Pr).
The perception that all heavy rare earth oxides (HREOs) are “good” (i.e have higher value due to scarcity, hence in undersupply) is inaccurate. There are 11 HREOs of which 4 are critical in the production of magnets and 3 for phosphors. 5 have negligible value as they are produced and used in limited quantities (Ho, Er, Tm, Yb and Lu). 2 are non-critical and have relatively low values (Sm and Gd).
Due to the abovementioned factors, Critical Rare Earth Oxide (CREO) grade is a better metric to benchmark rare earth projects, than HREO / LREO ratio. The term was originally defined in the US Department of Energy “Critical Materials Strategy 2010”, and is similar to the “Critical REEs” terminology employed by Gareth Hatch and Jack Lifton, founders of Technology Metals Research.
There are 5 CREOs (neodymium, praseodymium, dysprosium, terbium and europium), with neodymium being the largest by value and volume. Criticality of CREOs is based on their importance to sustainable clean energy and the supply risk of such elements over the short (0 – 5 yrs) and medium term (5 – 15 yrs).