What on Earth are Rare Earth Elements REE’s

Rare Earth Elements – Part One

Rare earth elements (REE) are all the rage at the moment. They’ve pushed gold and copper from the exploration headlines, and a cohort within the junior exploration sector is clamouring for new ground with rare earth elements potential, or re-assaying old samples for rare earth elements …. any opportunity to flag rare earth element credentials and to capture the attention of investors and brokers alike.

This is 100% legitimate! It is what the junior exploration sector does. It moves fast, it takes samples, it drills holes and sometimes it finds a deposit or two.

Australia is not a bad place at all to look for rare earth elements!

Importantly, investors need to get up to speed quickly with the reporting of REE-related exploration results and the jargon associated with it.

Rare earth elements are a group of elements in the Periodic Table also known as the Lanthanides. They are generally heavy metals that tend to be pale in colour (white to silvery) and are soft. Despite their collective name, not all of them are rare.

REE = Rare Earth Elements = sometimes also referred to as Rare Earth Metals

There are seventeen elements considered rare earth elements, the 15 lanthanides, and two extra elements, Scandium and Yttrium (that are not lanthanides).

The 17 REE’s are:

  • Scandium (Sc)
  • Yttrium (Y)
  • Lanthanum (La)
  • Cerium (Ce)
  • Praseodymium (Pr)
  • Neodymium (Nd)
  • Promethium (Pm)
  • Samarium (Sm)
  • Europium (Eu)
  • Gadolinium (Gd)
  • Terbium (Tb)
  • Dysprosium (Dy)
  • Holmium (Ho)
  • Erbium (Er)
  • Thulium (Tm)
  • Ytterbium (Yb)
  • Lutetium (Lu)

 The rare earth elements are divided into different “informal” groupings and each grouping has an acronym. The light rare earth elements, the heavy rare earth elements, the critical rare earth elements, are the main groupings. Sometimes there is a group called medium rare earth elements.

There are seven light rare earth elements (LREE) of the 17 REEs and they are: 

  • Scandium (Sc)
  • Lanthanum (La)
  • Cerium (Ce)
  • Praseodymium (Pr)
  • Neodymium (Nd)
  • Promethium (Pm)
  • Samarium (Sm)

There are ten heavy rare earth elements (HREE) of the 17 REEs and they are:

  • Yttrium (Y)
  • Europium (Eu)
  • Gadolinium (Gd)
  • Terbium (Tb)
  • Dysprosium (Dy)
  • Holmium (Ho)
  • Erbium (Er)
  • Thulium (Tm)
  • Ytterbium (Yb)
  • Lutetium (Lu)

There are five REE that are known as critical rare earth elements (CREE) and they are:

  • Yttrium (Y) – a HREE
  • Neodymium (Nd) – a LREE
  • Europium (Eu) – a HREE
  • Terbium (Tb) – a HREE
  • Dysprosium (Dy) – a HREE

These are considered “critical” because they are all “important” and “rare”. Most are HREE. This explains why explorers like to emphasise the HREE content in reports.

There are also what are informally called the four battery rare earth elements. These are:

  • Lanthanum (La) – a LREE
  • Praseodymium (Pr) a LREE
  • Neodymium (Nd) – a LREE and CREE
  • Terbium (Tb) – a HREE and CREE
  • Sometimes also:
    • Cerium (Ce) a LREE
    • Samarium (Sm) – a LREE
    • Dysprosium (Dy) – a HREE and CREE

When it comes to reporting rare earth element assay results, explorers will almost always refer to rare earth oxides. This is because geochemical laboratories actually test for and subsequently report the levels of the oxides. Incidentally, both the metal and the metal oxide prices are quoted in the metals-markets (typically as USD/Ib or USD/kg).

  • Lanthanum (La) – La2O3 (two Lanthanum atoms and three oxygen atoms)
  • Cerium (Ce) – Ce2O3
  • Yttrium (Y ) – Y2O3
  • Praseodymium (Pr) – Pr6O11
  • Neodymium (Nd) – Nd2O3
  • Promethium (Pm) – Pm2O3 (an extremely rare and radioactive REE generally not tested for)
  • Samarium (Sm) – Sm2O3
  • Europium (Eu) – E2O3
  • Gadolinium (Gd) – Gd2O3
  • Terbium (Tb) – Tb2O3
  • Dysprosium (Dy) – Dy2O3
  • Holmium (Ho) – Ho2O3
  • Erbium (Er) – Er2O3
  • Thulium (Tm) – Tm2O3
  • Ytterbium (Yb) – Yb2O3
  • Lutetium (Lu) – Lu2O3

In ASX announcements, the reader will come across various acronyms referring to rare earth elements, especially in the assay tables. Here’s a list of the common ways explorers will refer to rare earth elements:

  • REE = Rare Earth Elements
  • LREE = Light Rare Earth Elements
  • MREE = Medium Rare Earth Elements (not commonly used)
  • MREE = Magnet Rare Earth Elements
  • HREE = Heavy Rare Earth Elements
  • REEY = Rare Earth Elements including Yttrium (this is a little confusing as Yttrium is considered a REE)
  • TREE = Total Rare Earth Elements
  • REO = Rare Earth Oxides
  • TREO = Total Rare Earth Oxides
  • LREO = Light Rare Earth Oxides (inferring total Light Rare Earth Oxides)
  • HREO = Heavy Rare Earth Oxides (inferring total Heavy Rare Earth Oxides)
  • HREYO = Heavy Rare Earth, including Yttrium Oxides (this doesn’t mean that Y is counted twice, it’s just the case that because Y is not a lanthanide, the explorer wants to make it clear that the data includes yttrium)
  • TREYO = Total Rare Earth, including Yttrium Oxides (the comment above applies here also)
  • CREO = Critical Rare Earth Oxides (meaning total Critical Rare Earth Oxides)

Putting aside the “unfamiliarity” of rare earth elements, their strange names, their hi-tech use and their general paucity in the annals of exploration history, they are not particularly unusual, nor as mentioned above, are they particularly rare.

All rare earth elements, except for one, Promethium, can be assayed by any of the major laboratory service companies. The assay results for rare earth elements can be reported as parts per million (ppm), like most of the precious and base metals are, or as milligrams per kilogram (mg/kg) (which is the same as ppm), or kilogram per tonne [metric tonne]  (kg/mt).

Remember that 1ppm = 1g/t = 1mg/kg

Also remember that 1kg/mt = 1000ppm

And that 10000ppm = 1% (1000ppm = 0.1%)

When rare earth oxide results are used, conversation factors are required to obtain the level (grade) of the actual rare earth element. The conversation factor essentially removes the oxygen component of the rare earth oxide. To understand rare earth element grades, there is no real need for the investor to worry about conversation factors. This is because rare earth element resource/reserve figures are often quoted as oxides, and as mentioned above, rare earth elements are traded as oxides.

When total rare earth oxide (TREO) results are used, the explorer will/should mention which of rare earth oxides are included. Same follows for total HTEO or LREO.

In addition to individual REE/REO assay data, explorers may provide REE/REO grouping totals or grouping ratios, such as:

  • Total rare earth oxides (TREO), or
  • Total heavy rare earth oxides (THREO or more typically HREO), or
  • HREO/LREO ratio data, or
  • HREO to TREO ratio data or
  • CREO to TREO ratio data.

This is nothing to be intimidated by. It’s just simple additions and/or ratios. When explorers use totals though they may not mention all the individual rare earth elements that make up the total figure.

Reporting rare earth element assay results is not that different to reporting precious or base metals results

I’ve included below a couple of examples of published resource figures to understand the results:

Example 1: The Hastings Technology Metals Brockman REE Project has Indicated Resources of 27.1Mt @ 8913ppm ZrO2, 3545ppm Nb2O5, 182ppm Ta2O5, 110ppm Ga2O5, 318ppm HfO2, 186ppm Dy2O3, 1120ppm Y2O3 and 2103ppm TREO (source Geoscience Australia, date of data: 31 Dec 2018).

Firstly. Zr (Zirconium), Nb (Niobium), Ta (Tantalum), Ga (Gallium) and Hf (Hafnium) are not rare earth elements. Dy (Dysprosium) is a HREE and Y (Yttrium) is also considered a HREE.

Now… the resource statement mentions that there is 186ppm Dy2O3, 1120ppm Y2O3 and 2103ppm TREO. Note though that Dy2O3 and Y2O3 are both REO – so why are they specified and not simply made part of the TREO figure? This is simple. The explorer wants to highlight the fact that the deposit contains Dy and Y. Why? Because Y and Dy are both CREO.

Nevertheless, the results can be read either of two ways:

  • 186ppm Dy2O3 + 1120ppm Y2O3 + 797ppm of other unspecified REO = 2103ppm TREO, or
  • 186ppm Dy2O3 + 1120ppm Y2O3 + 2103ppm TREO = 3409ppm TREYO – I think this is the correct interpretation

Example 2: Northern Minerals’ Brown Range Project has Indicated Resources of 4.59Mt @ 0.71% TREO, 0.6kg/t Dy2O3, 3.99kg/t Y2O3, 0.09kg/t Tb4O7 with 86% HREO (source Geoscience Australia, date of data: 31 Dec 2018).

In this case, the resource states that there is 0.71% TREO. This means that grade of the total REO (TREO) is 7100ppm. This includes 0.6kg/t (or 600ppm) Dy2O3, 3.99kg/t (or 3990ppm) Y2O3, 0.09kg/t (90ppm) Tb4O7 and 2420ppm other unspecified REO.

The final figure “with 86% HREO” means that of the total 7100ppm TREO, 6,106ppm is made up of heavy rare earth oxides (7100 x 0.86 = 6106).

There is a bit of care required to understand the assay results and resource/reserve statements but its not too onerous.

Okay… we know what rare earth elements are and how they are reported by exploreres.

How do rare earth elements occur? What are the styles of rare earth element mineralisation? I won’t get into the extraction methods – this is not my expertise.

In Part Two of What on Earth are Rare Earth Elements, I’ll talk about the rare earth occurrence and the main styles of mineralisation,