The name REE is a historical misnomer that confuses people as to why these metals are hard to come by. In truth, they are not rare at all but rarely found in pure form. Analytical chemists had a very difficult time separating the 17 lanthanide group metals using early methods which led them to believe they would be scarce in nature. However, we now know that lanthanides, such as cerium, are even more abundant than copper in the Earth’s crust. Neodymium even outranks gold by orders of magnitude.
And yet the world faces a supply crisis. The main issue is not scarcity but discoverability, extractability, and economic viability. As the global need for energy independence and computational capability accelerates, the gap between a REE deposit discovery to mine development is proving much wider than for almost any other commodity and here is why.
Deposition and exploration methods
REE deposits can form through crystal fractioning in magma chambers, originating from deep metasomatised lithospheric mantle and commonly emplaced within stable continental shields or failed rifts.
Non-magmatic REE ores form in unconformity-related hydrothermal alteration systems and are typically confined by fault zones at basin boundaries, with strike lengths of 200 – 300 m. Another source is Ion-adsorption Clay Deposits and tectonic uplift or sustained tropical rainfall post-formation can erase the deposit.
So, what explorative methods other than rigorous mapping of potential host rocks or fertile alteration halos are viable? Most common ore types have a well understood geochemical or geophysical signature. This is not necessarily the case for REE metals, but their immediate environment provides proxy signatures that can be explored.
Magmatic systems are good geophysical targets that introduce dense and magnetic igneous rocks often affiliated with distinct hydrothermal alteration haloes and radioactive mineral signatures; magnetics and Gamma-Ray Spectrometry (radiometrics) are among the methods used.
In non-magmatic systems geophysical methods are used for structural, stratigraphic, and alteration mapping, including Induced Polarisation, Magnetotellurics, and Electrical Resistivity Tomography.
Among common geochemical methods, field-portable XRF is unreliable for REEs, and standard acid digestion is often insufficient to dissolve refractory REE minerals. One non-intrusive technique that has shown more success for detection when combined with geophysical exploration is hyperspectral analysis (imaging spectroscopy).
Multiple methods exist to find new sources for global REE supplies. So why is it still such a concern and source of contention? Let’s discuss the economics.
Grade and economic feasibility
High grade means nothing if the mineralogy is wrong. In copper or gold exploration, a high-grade anomaly tied to few sulphide species is half the battle. In comparison, REEs can substitute into more than 200 different minerals and when they are locked inside refractory silicates such as eudialyte or zircon, the extensive pre-treatment, energy, and acid required to extract them can render an impressive-looking deposit entirely uneconomical. As such, only a handful of minerals, primarily bastnäsite, monazite, and xenotime, are processable at viable cost but they bear another issue: they can all be highly radioactive.
The realities of rare earth element supply
REEs can be further subdivided into light and heavy REEs (LREEs and HREEs) based on their atomic weight and number. LREEs are geologically more abundant while HREEs have a true low natural abundance and face more severe structural supply deficits, which are at the core of some geopolitical concerns observed today. HREE deposits known and mined today are heavily concentrated in regions like southern China (49%) and Myanmar (% unknown). China controls up to 94% of the REE market.
If the world wants to build a more diversified REE market, it needs not only to find new economically feasible deposits but also to build the infrastructure for a vertically integrated supply chain and to produce and sell at a competitive price.
One area where the economics may eventually shift is rare earth extraction from brines. Geothermal fluids, oilfield-produced waters, and other subsurface brines can contain dissolved rare earth elements, creating the possibility of recovering critical minerals alongside existing energy operations.
Final thoughts
In conclusion, the REE supply problem is not their scarcity. The elements are there. What is rare is the integrated capability to find deposits reliably, characterise them accurately, and extract their value economically and with minimal environmental impact.
Advancing geophysical and geochemical scanning methods combined with a holistic data integration approach is key. Only then can the exploration-to-production timeline be minimised enough to allow a more globally competitive REE market to begin developing within this decade.
Author note
Dr Janina Elliott, Segment Director Mining, Seequent.