Rare Earth Element Deposits: Their

Genesis and Exploration

A.E. Williams-Jones

Department of Earth and Planetary Sciences

McGill University, Montreal, Canada

By

McGillQuébec Mines, 2016

The REE and the Periodic Table

Li3

H1

Na

K

Rb

Cs

Fr

Be

Mg

Ca

Sr

Ba

Ra

Sc

Y

La

Ac

Ti

Zr

Hf

Rf

V

Nb

Ta

Db

Cr

Mo

W

Sg

Mn

Tc

Re

Bh

Fe

Ru

Os

Co

Rh

Ir

Ni

Pd

Pt

Ag

Au

Cd

Hg

B

Al

Ga

In

Tl

C

Si

Ge

Sn

Pb

N

P

As

Sb

Bi

O

S

Se

Te

Po

F

Cl

Br

I

At

He

Ne

Ar

Kr

Xe

Rn

11

19

37

55

87

4

12

20

38

56

88

21 22 23 24 25 26 27 28

Cu Zn29 30 31 32

39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54

36

18

10

2

5 6 7 8 9

1716151413

33 34 35

57 72 73 74 75 76 77 78 79 80 81 82 83 84 85 86

89 104 105 106 107

Hs Mt Ds Uuu Uub Uuq108 109 110 111 112 114

Ce Pr Nd Pm Sm Eu Gd Tb Dy Ho Er Tm Yb Lu58 59 60 61 62 63 64 65 66 67 68 69 70 71

Light REE Heavy REE

Th Pa U Np Pu Am Bk Cf Es Fm Md No Lr90 91 92 93 94 95 97 98 99 100 101 102 103

Cm96

Why we Need the REE

The REE and Wind Power

Wind power now supplies 11.4% of

the European Union’s electricity

(141.6 GW; growing at 15.6% /yr).

Wind turbines are driven by

(Nd,Dy)2Fe14B magnets requiring

730 Kg of Nd and Dy per MW.

In the U.S., wind power supplies

4.4% of electrical energy (74.5

GW); also growing at 15.6%/yr.

In 2015, China overtook the EU with

145.1 GW of installed wind turbine

power capacity, a 27% 1 yr growth

(supplies ~4% of electrical energy)

Not all REE are Equally Critical

Medium term criticality matrix (2015 -2025)

U.S. Department of Energy (2011)

The Strategic Importance of the REE

US Production Chinese Production

Rare Earth Element Deposits

Nechalacho

Strange LakeBayan Obo

Maoniuping

Lovozero

Mt Weld

Mountain

Pass

Lofdal

Bear Lodge Kipawa

CarbonatiteNepheline syeniteGraniteHydrothermal

Ion adsorption clay

Mine

Prospect

Ilímaussaq

Relative Abundance of the REE in

the Earth’s Crust Normalized to

Primitive Mantle

0,1

1

10

100

La Ce Pr Nd Sm Eu Gd Tb Dy Ho Er Tm Yb Lu Y

LREE

HREE

HREE

The Hosts to REE Deposits

Alkaline igneous rocks and carbonatites

Carbonatites; LREE deposits, main ore

minerals, monazite-(Ce), basnäsite-(Ce)

Nepheline syenites;

HREE deposits,

A-type granite pegmatites; HREE

deposits, ore minerals, secondary

gadolinite-(y), bastnäsite-(Ce)

main primary ore mineral,

eudialyte; secondary

fergusonite-(Y)

0,85

0,90

0,95

1,00

1,05

1,10

1,15

1,20

1,25

La Ce Pr Nd Sm Eu Gd Tb Dy Ho Er Tm Yb Lu

Ce4+

Eu2+REE3+

Ionic

radiu

s (

Angstr

om

s)

Y3+

HeavyLightY3+

The Lanthanide ContractionIncompatible elements are concentrated by low degrees of partial melting

Light and Heavy REE deposits

Carbonatite-hosted

deposits are invariably light

REE-rich.

Nepheline-syenite- and A-

type granite-hosted REE

deposits are relatively

enriched in the heavy REE.

Carbonatites are the

products of either very low

degrees of partial melting

or liquid immiscibility, both

of which favour the most

incompatible elements, the

LREE.

Chakhmouradian & Zaitsev. (2012)

Oceanic

Alkaline

Magmatism

Continental

Alkaline

Magmatism

Depleted Upper

Mantle

Undepleted

Lower Mantle

The Source of Alkaline Magmas

Environments of Alkaline

Magmatism

Back Arc Intraplate

Continental Swell

Continental Rift

Mountain Pass Strange LakeMaoniuping Lovozero

Nechalacho

Oka Carbonatite

Nepheline syenite

Carbonatite

Québec Separation and the REE

Mont Saint Hilaire

HREE

LREE

Monteregian Hills deliniate a failed rift – alkaline magmatism

produced nepheline syenites, carbonatites and REE

Carbonatite-hosted REE Deposits

Magma evolutionCalcio-carbonatite magnesio-carbonatite ferrocarbonatite

CaO

MgO FeO + MnO

Ferrocarbonatite

Calcio-carbonatite

Ferruginous

carbonatite

Magnesio-carbonatite

The REE mineralisation

is progressively enriched

from magnesio-

carbonatite to

ferrocarbonatite

The example of the

Eldor carbonatite,

Québec; bulk-rock

compositional data.

Rim

BD Zone

A-Zone

MHREO-Zone

B-Zone

Beland & Williams-Jones. (in prep)

Carbonatite-hosted REE Mineralisation

Dolomite 1 (primary); Dolomite

2 (hydrothermally altered

Dolomite 1); and Dolomite 3

(hydrothermal dolomite filling

vugs with bastnäsite-(Ce) and

parisite-(Ce)

XFe = 0.41

XFe = 0.30

XFe = 0.24

The example of the Wicheeda LREE carbonatite Deposit,

British Columbia (11.3 Million tons grading 1.95 wt% REE)

In most carbonatite-hosted deposits, the REE mineralisation is hydrothermal.

Trofanenko et al. (2016)

Carbonatite-hosted REE Mineralisation

At Wicheeda, the calcio-carbonatite has a mantle isotopic signature, the

dolomitic carbonatite an igneous signature and the vug-filling dolomite

accompaning bastnäsite-(Ce), a hydrothermal signature.

A model is proposed in

which the REE

mineralisation was the

product of late

magmatic carbo-

hydrothermal fluids at ~

300 C.

Trofanenko et al. (2016)

Strange Lake Nechalacho

Silica-saturated

magma

Silica-undersaturated

magma

Mafic magma

Mantle

Felsic magma

Crust

Rifts, Plumes and REE-Rich Magmas

Peralkaline granite (A-type) Layered nepheline syenite complex

Nepheline Syenite REE Deposits

REE mineralisation develops in alkaline layered igneous complexes as a

result of extreme fractional crystallisation, which saturates the incompatible

REE, Zr, and Nb as eudialyte in the last aliquot of liquid.

The Ilímaussaq layered complex, Greenland

Eudialyte cumulates (pink)

Na15(Ca, REE)6(Fe,Mn)3Zr3NbSi25O72(O,OH,H2O)3

Cross-Section through the

Nechalacho Layered Suite, NWT

100 m

Long Lake

Basal Zone

Upper Zone

Sodalite Foyaite

Micro-layered Agirine Nepheline Syenite

Thor Lake

Syenite Grace Lake

Granite

Nepheline syenite

Möller & Williams-Jones (2016)

The Ore Zones

Bt

Zrn

Bt, Mt0.5 cm

0.5 cm

Eud

Bt, Mt

Na15(Ca, REE)6(Fe,Mn)3Zr3NbSi25O72(O,OH,H2O)3

Eudialyte

Upper

ore zone

Basal

ore zone

Albitite

Unaltered

aegirine

nepheline

syenite

Sodalite

syenite

Basal Zone REE Mineralisation

Pseudomorphs after eudialyte

0.5 cm

Bt, Mt, Hm

Pseudomorph after eudialyte

in plane polarised light

Qtz

Mt

MnzZrn

Bt

Cal

0.1 cmFer

Yttrium

20µm

Yttrium

100µm

Yttrium

40µm

Zircon

Fergusonite

Progressive alteration of zircon

100µm

Zirconium

100µm

YttriumAlteration of eudialyte to zircon

and REE minerals

Hydrothermally Unlocking the REE

LREE mobilised upwards and

deposited as Bastnäsite-(Ce)

and monazite –(Ce)

Sheard et al. (2012)

HREE deposited locally, mainly

as fergusonite-(Y) {Y,NbO4}

Magmatic concentration of the REE in

Nechalacho Layered Complex

Sodalite

Zr Silicate

Aegirine Nepheline

Crystallisation

from roof down

and floor up

Residual, volatile

(F, Cl)- and HFSE-

rich magma

saturates with

REE-bearing

zirconosilicates

(zircon, eudialyte)

A hydrothermal

fluid is released.

The REE “stew in

this juice” and are

mobilised

Granite-hosted REE Deposits

1 km

Subsolvus

granite

Hypersolvus

granite

B-Zone M-Zone

Hypersolvus

granite

Strange Lake, Québec, the type example

Pegmatite border Pegmatite core

The Strange Lake Pegmatite Ores

REE MineralsTitanite

(CaTiSiO5)

Gittinsite

(CaZrSi2O7) Fluorite

Nb Ce Eu Dy YBeZr

F

Porous

Porous

15

20

25

30

Pegm

atite

Distribution of REE and Zr in Pegmatite

Melt Inclusions in Hypersolvus Granite

Melt Inclusions are evident by their

spherical shape. They vary from

being silicate-only, to fluorite-bearing

to fluorite-only.

Gagarinite-(Y) NaCaY(F,Cl)6

Elpidite Na2ZrSi6O15·(3H2O)

Vasyukova & Williams-Jones (2014)

Fluoride-bearing Melt Inclusions

after Heating and Quenching

Transmitted Light SEM Image

1 – Silicate glass;

~3 wt.% Zr

2 – Ca-fluoride glass;

~10 wt.% REE

3 – REE-fluoride glass;

~47 wt.% REE

Acidic Alteration and REE Mobilisation

Autometasomatism

lead to acidic

alteration by HCl-HF-

bearing fluids that

destroyed the

primary mineralogy,

creating porosity

REE were mobilised,

replacing earlier

minerals and filling

vugs

Flc - fluocerite (REEF3)

Gysi & Williams-Jones (2013)

Mobilisation of the REE

Gysi et al. (2016)

The LREE were mobilised preferentially leaving the HREE concentrated

closer to the pegmatites (LREE are more mobile than HREE, discussed later)

Model of REE Accumulation

Al, Na, K, Fe + Zr

Ca, REE, F

Fractional crystallizatio

n

Silicate melt

Fluoride melt

c o o l i n g

Subsolvus

granite Pegmatite

Hydrothermal fluid

REE Mobilised

F

Porous

Porous

Zr Y

Hydrothermal REE Deposits

Monazite (LREEPO4) and bastnäsite

(LREECO3F), together with magnetite,

hematite and fluorite replaced H8 dolomite .

Fluids 5 – 15 wt% NaCl eq., T > 400 C.

Smith & Henderson (2000)

The Bayan Obo deposit, China, is thought by some to be carbonatite-hosted

and others to be hosted by dolomitic marble that was replaced by magnetite,

hematite, REE minerals, aegirine, and fluorite.

Bayan Obo replacement ore.

The Lofdal HREE Deposit, Namibia

The Lofdal HREE deposit is associated with 750 Ma

nepheline syenites and calcio-carbonatites that were

emplaced during intracontinental rifting which

preceded amalgamation of Gondwana.

REE-Mineralised StructuresThe REE-mineralised structures give the appearance of ferrocarbonatite

dykes but are instead fault-controlled sodic fenites (albitites) that have been

altered to calcite and/or ankerite. The red colour reflects pyrite oxidation.

Lithogeochemical SurveyThe potential ore deposit with zones of strong fenitisation/carbonate

alteration (dark grey) and weaker fenitisation (light grey). The coloured

dots show the distribution of Dy in surface rock samples. Xenotime-(Y)

concentrates in the structure and bastnäsite-(Ce) distally from it.

>700

300-700

100-300

<100

Dy ppm

106 ppm Ce

2987ppm Y

1124ppm Th

REE Mineralisation in Core

Albitite clast containing xenotime-(Y) in a dolomite-cemented breccia

Ce 152ppm

Y 1470ppm

Albitite containing HREE-enriched, biotite-filled shears

Dolomite Albite

Xenotime-(Y) Mineralisation

Albitite cut by xenotime-(Y)-zircon-biotite veins and then replaced by

calcite.

Calcite

Rutile

CalciteRutile

AlbiteXenotime

and zircon

100 µm

Calcite

Calcite

Albite

Why is the Lofdal Deposit So Enriched

in the HREE? The light REE were preferentially mobilised as chloride complexes by

hydrothermal fluids leaving behind the heavy REE.

Williams-Jones et al. (2012)

Control on REE Fractionation

Ion Adsorption Clay DepositsThe REE are leached by humic acids and transported down the soil profile

into the B-zone where they are concentrated by adsorption as the REE3+ onto

the surfaces of clay minerals, mainly kaolinite. Many of the deposits are

HREE-rich with grades between 0.2 and 0.35 wt.% REE2O3

A

B

C

Solution Mining For HREE, China

1) Ammonium sulphate is dripped

into weathered granite hill-tops, 2)

ion adsorbed REE leached, 3)

solutions collected down slope and

channeled into holding tanks,

4)REE precipitated with oxalic acid.

Recovery of the REE

(NH4)2SO4 + REE3+ = REESO4+ + 2(NH4)

+

The REE are dissolved to form REE sulphate complexes according to the

ion exchange reaction (NH4+ displaces the REE3+ on the clay mineral

surface):

and precipitate in the holding tanks as a result of the addition of oxalic acid.

2REESO4+ + 3H2C2O4 = REE2(C2O4)3 + 6H+ + 2SO4

2-

The REE oxalate precipitates

settle to the bottom of the

tanks and after draining of the

fluid, they are removed, dried

and bagged for transport to a

refinery.

The resulting concentrate

contains 60 – 90 wt% REE.

“These elements [the rare earths] perplex us in our researches, baffle us in our speculations and haunt us in our very dreams. They stretch like an unknown sea before us, mocking, mystifying and murmuring strange revelations and possibilities.”

(Sir William Crookes, February 16th, 1887)

Thank You