Ranking and evaluating light to heavy rare earth
deposits worldwide:
exploration considerations to economic assessment
Mushghi Khudag - Mongolia
David Lentz & Anthony N. Mariano

Major Considerations
Assuming a favourable political climate and good logistics, conditions
determining the viability of deposits that can compete in the world market
are as follows…
1) Mineralogy and favourable lanthanide distribution
2) Grade and tonnage
3) Amenability to mining and mineral processing at low costs, and
successful chemical cracking of the individual lanthanides for their
isolation
4) Acceptable low values of accompanying deleterious impurities
5) Minimum impact on the environment
Any lower production costs can significantly reduce the grade
requirements

USGS facts

USGS facts

USGS facts

100
GSC
Carbonatites
10
Grade (wt%)
1.0
0.1
106 107 108 109 1010
Tonnes of Ores Richardson & Birkett 1996

GSC
Peralkalic
Tonnes of ore Richardson & Birkett 1996

GSC
Peralkalic
Richardson & Birkett 1996

GSC
Peralkalic
Tonnes of ore Richardson & Birkett 1996

Kvanefjeld REE-U deposit, Ilimaussaq Complex

Kvanefjeld REE-U deposit, Ilimaussaq Complex
• This new resource statement estimates the inventory of
contained metal within a 457 Mt ore body to be 4.91 Mt
of Total Rare Earth Oxide (TREO), 0.99 Mt and Zinc,
0.12 Mt of Uranium Oxide (283 Mlbs), and 3.09 Mt of
NaF
• Indicated & Inferred
457 Mt
0.028 U3O8%,
1.07 TREO%,
0.22 Zn%, at a
0.15% U3O8% cut off

Kvanefjeld REE-U deposit

Model for Peralkalic Magma Systems
Contact pegmatite/aplite
Breccias/ Endogranitic
diatremes pegmatite
Late aplite-pegmatite
dike(s)

APLITE Welsford Dyke swarms
Riebeckite
K-feldspar
Zircon
(Baddellyite)
Nb-Fe oxide
Aeschynite
Fergusonite
Euxenite
REE carbonate

Welsford model
Marsh (1995)

Major Rare Earth Sources
Mineral Composition Occurrence
 Bastnäsite (Ce) (REE) CO3F Carbonatites
 Monazite (Ce) (REE) PO4 Beach Sands, Hydrothermal
 Xenotime (Y) (Y,REE) PO4 Beach Sands, Hydrothermal
 Loparite (Ce) (REE,Na,Ca) (Ti, Nb,Ta)O3 Alkaline igneous massif
 South China Clays (Ion-adsorbed REE+Y in Clays)
 Uraninite (REE and Y — Released as dissolved elements
in rafinates from uraninite)

Monazite pseudomorph after apatite Monazite pseudomorph after Rhabdophane
Florencite pseudomorph after pyrochlore Churchite YPO4·2H2O
Supergene Minerals – MT. Weld, Australia

Apatite with Substitutional REE
 Oka, Quebec Carbonatite
 Nolan’s Bore, Australia Carbonatite
 Mushgai Khudag, Mongolia Carbonatite
 Phalaborwa, South Africa Carbonatite
 Kola Peninsula Carbonatite and Alkaline
Massifs
 Hoidas Lake, Saskatchewan Hydrothermal in Granites
 Mineville*, New York Tailings from Magnetite
Mining
* Mineville may be the only Y and HREE dominant source currently known

HD - 1.76 mm HD - 4.4 mm
XPL Micrographs
Bastnäsite in Carbonatite
Mountain Pass, CA

Ancylite (Ce) SrREE(CO3)2(OH)·H2O
HD – 0.7 mm
BSE Image Ancylite PPL Micrograph Ancylite
LREE - dominant –  50 wt. % REO
An exploration target in the
Bear Lodge Carbonatite Complex of northeastern Wyoming

Eudialyte Na15Ca6(Fe2+,Mn2+)3Zr3(Si,Nb)(Si25,O73)(O,OH,H2O)3(CL,OH)2
Red Wine Complex, Labrador Dora Bay, Alaska
Eudialyite may also contain Y and HREE
in amounts exceeding 4 wt.%. The
mineral is easily dissolved in weak acids
but colloidal silica currently presents a
problem in the isolation of Y, REE and Zr
oxides.
Kipawa, Quebec

Massive Britholite (Ce) Britholite (Ce) Concentrate from Skarn
Oka, Quebec Kipawa, Quebec
Britholite – (REE,Y,Ca)5(SiO4,PO4)3(OH,F)
This mineral has the potential for occurring in ore quantities in
skarn associated with syenite gneiss in Kipawa, Quebec

Allanite (Ce) (Ce,Ca,Y)2(Al,Fe2+,Fe3+)3(SiO4)3(OH)
Allanite – Hydrothermal, Mountain Pass, CA Allanite – Pegmatite, Timmins, Ontario
Allanite is found in abundant quantities in
many different geologic environments,
and in almost all cases is LREE
dominant. Low quantities of ∑REE+Y
relative to bastnäsite, and its refractory
nature diminish its value as an economic
source for REE and Y.

Eudialyte and Mosandrite in Peralkaline Syenite
Kipawa, Quebec

Britholite-Rich Skarn Britholite Concentrate (mm scale)
All brown prisms are britholite
(Horizontal Distance – 46 mm)
Britholite – (Ce,Y,Ca)5(SiO4.PO4)3(OH,F)
Kipawa, Quebec

Cathodoluminescence Macrograph of Iimoriite in Syenite – Bokan Mountain
Mottled light blue and tan clusters - Iimoriite
Red groundmass – Feldspar
(Horizontal distance of rock slab – 46 mm)

Iimoriite (Y) Yttrofluorite
Y2(SiO4)(CO3) (Ca,Y)F2

Iimoriite Concentrate –
Bokan MT (1 mm scale)

Wicheeda Lake Heavy Mineral Composite — (from samples 828951, 52, 53)
These grains range in size between 0.2 and 0.5 mm. The left micrograph consists of
major monazite and parisite and minor grains of pyrite. Dolomite is also attached to
some of these grains. The right micrograph shows selective reflection of the green
part of the visible spectrum under unfiltered shortwave UV examination. This test is
diagnostic for the identification of LREE minerals.

As a final statement it should be emphasized…
1) Carbonatites containing as much as 5 wt. % LREE must compete with
Bayan Obo, Maoniuping, and Mountain Pass which have much higher
grade, and have established physical and chemical processing plants.
2) Deposits that are mineralized with allanite and LREE-enriched apatite
can not compete economically with carbonatites or peralkalic systems
that have the high REE mineralogy.
3) Naturally higher radioactivity in all REE systems makes them easier to
find with airborne and ground gamma-ray spectrometry.
4) Uraniferous systems commonly have anomalous LREE & HREE, which
has been recovered in some deposits, i.e., rafinates from uranium
mining
5) Although ion-adsorbed REE in clays from South China provide the bulk
of HREE to the market place, in other countries, high costs for labor
and necessary supplies, power costs, and environmental restrictions
may render similar deposits uneconomical.

Rare Earth Elements
• Name something of a misnomer
– Rarest REEs are over 200 times more
abundant then gold
• Variation in distribution for two reasons
– Compatibility with common rock forming
materials
– Cosmic/Crustal abundances

Crustal Abundances of Elements

Occurrence
• REEs occur mostly as
substitutional impurities in
many rock forming
minerals
• Only a few, the REE
minerals, have sufficient
quantities to be considered
important sources.
• Defined as minerals
having at least one site
that is filled by REEs
Monazite and/or Yttrium more often
then any other element.

Rare Earth Minerals
• Form by primary crystalization from
magma or by hydrothermal reactions
• Found hosted in carbonate rocks, in
pegmatites and as accessory minerals in
igneous rocks.
• Stable REE minerals and can be
concentrated in weathering zones.

REE Minerals
• The most important REE
minerals is bastnäsite
REE(CO3)F.
• Other notable sources are
– Monazite REE(PO4)
– Xenotime YPO4,
• All may contain radioactive
species, such as thorium
and uranium
– are avoided as source
materials.

Bastnesite
• Bastnasite
[(REE)(CO3)F], is the
world’s most important
source of rare earth
elements
• Containing 60 to 70%
rare earth oxides
(REOs)
• REE site is most
commonly filled by
LREEs and Y

Other REE minerals
• Monazite [(LREE,Y,Th)PO4]
– Contains about 50–78% rare earth oxides.
– Forms in heavy mineral sands; placer deposits
associated with beach environments
• Xenotime [(YPO4)]
– Contains 54–65% rare earth oxides
– Yttrium, Erbium and Cerium most common
– Found in heavy mineral sands; can also be a
component in pegmatite and igneous rocks.

Electron Configuration
• The similarities in chemical and physical
properties arise due to the group’s common
electron configuration
• REEs have same outer electronic configuration
(+3), they differ in their number of 4f electrons

Electron Configuartion

REE Behavior
• Because of their shared behaviour, REEs tend to be
present in nature as a group. All REEs commonly
substitute for one another in minerals.
• Yet, the REEs are capable of showing great variation in
their distributions.
• Comes about due to:
– Differences in ionic radius;
– Crystal structure (Coordination Number)
– Basicity of the mineral
– The element’s solubility and ability to migrate in the environment
– Content of REEs in source fluids,

Ionic Radius
• The ionic radius of the REEs is inversely related to atomic number
• The heavy rare earths are smaller
– more similar to Mn2+ (ionic radius 0.08 nanometers)
• LREEs are larger
– more comparable in size to Ca2+ (ionic radius 0.1 nanometer)
• Charge balance achieved through some sites being left vacant, or by
coupled substitution with lower charged mineral (Na+)
In nanometers

Coordination Number
• Coordination number: the number of
atoms touching a particular atom in a
crystal lattice.
• Coordination number
for this structure is 8.

Coordination Number
• The heavy and light REEs differ in the coordination
numbers (CN) with oxygen
– HREEs have CN between six to nine
– LREEs have higher CNs
• Minerals with high CNs associated with REE site will
favor LREEs
– Bastnasite CN = 11
– Monazite CN = 9
• Those with low CNs will preferentially select HREEs.
– Xenotime has a value of 8

Other Factors
• Minerals basicity
– Alkalic rocks host minerals with elevated LREE content
– Rocks with lower basicity have lower amounts of LREEs relative
to their HREE content
• Solubility
– LREEs are more soluble in water then the HREEs
– Important characteristic for hydrothermally derived minerals
• Magma/Hydrothermal fluid composition
– Minerals will take what they can get

REEs and Economics
• The REEs and Yttrium have a
very broad range of applications,
mostly in high technology fields
• 84% of Y acquired by the United
States used in light and cathode
ray tube phosphors. The
remainder was used in ceramics
(7%), electronics (7%) and
metallurgy (2%)
• REEs used primarily for
automotive (25%), petroleum
(22%) and metallurgic (20%)

HREEs and Magnetism
• HREEs exhibit complex magnetic
behaviour on account of electron structure
– They share the same outer shell electron
configuration (valence = +3)
– Differ in number of 4f electrons

Applications in Magnetism
• Terbium and Dysprosium
• Components of Terfenol-D, alloy with the formula Tb(0.3) Dy(0.7) Fe(1.9).
• Has the higher magnetostriction then any other alloy
– expands and contracts in magnetic field.
• Developed by American Navy for sonar systems
– Now has applications in magnetomechanical sensors and other electronic devices

Applications in Magnetism
• Holmium
• Possesses the highest magnetic moment
(10.6µB) of any of the naturally-occurring
elements
• Creates the strongest artificially generated
magnetic fields
– In research where strong magnetic fields are needed

HREEs and Nuclear Technology
• Dysprosium, Homium, Erbium
• High neutron absorption cross-section
– Measure of probability of neutron capture
• Used in neutron-absorbing control rods in
nuclear reactors

HREEs and Nuclear Technology
• Lutetium
• Radioactive isotope used in radiometric
dating.
• Thulium
• Stable thulium used as a radiation source
in portable X-ray devices.

Mountain Pass
• Bastnasite is the major REE mineral
• High grade accessory mineral of igneous or hydrothermal origins.
• 31 million tons of 8.86 % by weight of rare earth oxides (REO);
• Mining stopped in 1994
– Thorium content of waste rock
– Availability of inexpensive REEs from China
San Bernardino County

Bayan Obo
• The world’s primary source for both
yttrium and the rare earth elements
• 37 million tons of ore
• Main REE source there is Bastnasite

World Production

Exploration
• 84% of REE imports to US
are from China
• Increasing demand for high
tech applications spurred
increase in exploration in
2007.
• Economic assessments of
known deposits such as
Canadian Thor Lake and
Hoidas Lake, as well as in
Malawi, Africa

Environmental Considerations
• REE soil and food contamination
• Acid Mine Drainage and groundwater
systems
• Radioactive elements

REE Fertilizer
• In China, REE enriched fertilizer has been used in crop
fields since 1990.
• At the turn of the century, 50 to 100 million tons of REEs
were being applied to an area of about 4 million hectares
every year.
• Research and agricultural practice that provides
evidence that REEs will improve crop quality an yield.
• The ramifications environmental and human exposure to
REEs are not well understood.

Investigation by T. Liang et al.
• Revealed that the average
concentration of total
REEs in Chinese soil is
176.8 mg/kg, ranging
between 85.0 to 522.7
mg/kg
• In wheat grains, the REE
distribution as similar to
that of the soil, with a
content about 3 or 4
orders of magnitude

Implications
• Human health effects not
completely understood.
• REE soil content shown to be
detrimental to some plant
species
– 100% of ryegrass specimens
involved in the study that were
reared with REE fertilizer
showed poor development
relative to the control group
that was reared without
elevated exposures to REEs

Acid Mine Drainage (AMD)
• Rain waters contacts waste rock, facilitating acid forming
reactions
• Increases the capacity of the water to leach potentially
harmful elements from waste piles.
• Process mobilizes established ecotoxins (lead and
mercury) as well as elements whose effects are less
understood, namely the rare earth elements.
• Historically dismissed as minor environmental risk

Radioactive Elements
• REEs associated with uranium and
thorium
• Bastnesite: 3.2% thorium
• Monazite sands: 6 to 12% thorium oxide
• Ores containing radioactive elements are
avoided as sources of REEs

Radioactive Hazards
• Mountain Pass
• Accidents
– In 1977, major pipeline break spilled over 2 million gallons of radioactive
water
• Health Effects
– inflammatory bowel disease
– Prolonged seizures
– Cysts
– Cancers
• Waste Disposal
– Yucca Mountain

Summary
• REE concentrations in the crust are rare
• Several geochemical factors influencing distribution, including ionic
radius and coordination number
• Main REE minerals are bastnasite, monazite and xenotime
• Most important deposits are found at Bayan Obo, China and
Mountain Pass, USA.
• Important electronic and nuclear applications
• Environmental concerns associated with REE production and use
are exposure to the environment and people, liberation and water
system contamination though acid mine drainage, association with
radioactive elements.

References
• E. Orvini, M. Speziali, A. Salvini, C. Herborg, “Rare earth elements determination in environmental matrices by
INAA”, Microchemical Journal, 67, 2000, 97-104
• Tao Liang et al., “Environmental biogeochemical behaviors of rare earth elements in soi-plant systems”,
Environmental Geochemistry and health, 27, 2005, 301-311
• G. Protano and F. Riccobono, “High contents of rare earth elements (REEs) in stream wates of a CU-Pb-Zn
mining area”, Environmental Pollution, 117, 2002, 499-514
• B Lipin “Geochemistry and mineralogy of rare earth elements”, Mineralogical Association of America, 1989
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