Rare earth elements and its applications in geological studies

RARE EARTH ELEMENTS AND ITS
APPLICATIONS IN GEOLOGICAL STUDIES
LECTURES FOR
UNDERGRADUATE STUDENTS
hASSAN Z. HARRAZ
Professor of Economic, Geology Department
Faculty of Science, Tanta University, Egypt
hharraz2006@yahoo.com
@Hassan Z. Harraz 2019
REE & ITS APPLICATIONS IN GEOLOGICAL STUDIES

OBJECTIVES
 To review the geology of rare earth
elements.
 To discuss the various applications
of rare earth elements in
geological studies.

OUTLINE
 Introduction
 Objectives
 Abundance of REEs in Earth’s Crust
 Classification of Rare Earth Elements
 Geology of REEs
 Applications of REES
 Application of REEs in Geological Studies
 Application of REE to Petroleum Systems
 Case Studies
 REE Global Economic Supply and Demand
 Large and Giant Sized Deposits of the Rare Earth Elements

INTRODUCTION
 Rare earth elements (REEs) are a group of 15 chemical elements in the periodic table,
specifically the Lanthanides on the periodic table of elements (atomic number 57 to 71)
(Connelly, 2005).
 Two other elements, Scandium (n=21) and Yttrium (n=39), have a similar
physiochemistry to the lanthanides, are commonly found in the same mineral
assemblages, and are often referred to as REEs.
 Although relatively abundant in the earth’s crust, they rarely occur in concentrated
forms, making them economically challenging to obtain.
 Scandium and Yttrium of Group IIIb on the periodic table of elements are typically included
with the rare earth elements because they share chemical, physical, and application
properties with the lanthanides (Table 1).
 These elements comprise critical components of many of our modern-day
technological devices and everyday electronics.
 These elements constitute critical components of many important technologies and
products, such as hybrid vehicles, wind turbines, and cell phones. Given this global
demand for green and sustainable products in energy, military, and manufacturing
industries, REE demand in the United States and throughout the world is projected to
increase.
 REE demand in the United States is projected to increase given global demand for green
and sustainable products in energy, military, and manufacturing uses. China has been
providing 95 to 97% of REEs worldwide but the United States is increasing its interest in
exploring and mining REEs.

• The International Union of Pure and Applied Chemistry, an
organization devoted to maintaining international
consistency for chemical nomenclature, has identified the15
transition metals from the periodic table of the elements
with atomic numbers 57 (lanthanum) through 71 (lutetium)
as lanthanides or lanthanoids. These 15 elements share
common physiochemical properties and are listed below:
 Lanthanum (57La)  Samarium (62Sm)  Holmium (67Ho)
 Cerium (58Ce)  Europium (63Eu)  Erbium (68Er)
 Praseodymium (59Pr)  Gadolinium (64Gd)  Thulium (69Tm)
 Neodymium (60Nd)  Terbium (65Tb)  Ytterbium (70Yb)
 Promethium (61Pm)  Dysprosium (66Dy)  Lutetium (71Lu).
Due to their similar physiochemistry, these lanthanides often occur together as elemental constituents of their host minerals.
Two other metals commonly found in association with lanthanides in the same mineral assemblages are the following:
 Scandium (21Sc)
 Yttrium (39Y).
These two metals also have physiochemical characteristics that are very similar to the lanthanides.

Table 1: Periodic table of the elements showing Rare Earth Elements (Long et al.,
2010)

Abundance of REEs in
Earth’s Crust
 Together, the lanthanides, yttrium, and scandium are commonly referred to as REEs or REMs, although
this is a misnomer since most of the REEs are common mineral constituents as compared with other
metal elements. The term “rare” is a carryover from metallurgical chemists from around the 1940s
(Gupta and Krishnamurthy, 2004). The metallurgical processes needed to isolate the individual metal
species are complex, and early technology prevented commodity-level production. As a result, lanthanide
metals or metal oxides (i.e., REOs) were difficult to obtain and thus are considered rare. The abundance
of REEs in the earth’s crust relative to other common metals is presented in Table 2-1; these
abundances from Wedephol (1995) are only one of several interpretations, but those presented here are
generally representative. As shown in the comparison, the content of lanthanides relative to other REEs
in rockforming minerals is not rare at all.
 Following a common pattern within the periodic table, the lanthanides with even atomic numbers are
more common in nature. Additionally, early on, geochemists observed a pattern in the occurrence and
crustal abundance of some lanthanides. Lanthanides with lower atomic numbers were noted to be more
common ionic constituents in REE mineral ores and, in general, occurred in greater abundance than the
lanthanide elements with higher atomic numbers.
 These observed trends in crustal abundance among the geochemical models suggest a divide between
light and heavy lanthanide-enriched minerals. Although variation exists, one example of an REE
classification is presented in Figure 2-1 and shows the division between light REEs (LREEs) and heavy
REEs (HREEs) (Schuler et al., 2011). Some investigators classify gadolinium and dysprosium as medium-
weight lanthanides due to their physiochemical properties.

Table 2-1. Abundance of Elements in the Earth’s Crust (Wedepohl, 1995)
Elements
Crustal Abundance
(parts per million)
Nickel (28Ni) 90
Zinc (30Zn) 79
Copper (29Cu) 68
Cerium (58Ce)a 60.0
Lanthanum (57La) 30.0
Cobalt (27Co) 30
Neodymium (60Nd) 27.0
Yttrium (39Y) 24.0
Scandium (21Sc) 16.0
Lead (82Pb) 10
Praseodymium (59Pr) 6.7
Thorium (90Th) 6
Samarium (62Sm) 5.3
Gadolinium (64Gd) 4.0
Dysprosium (66Dy) 3.8
Tin (50Tn) 2.2
Erbium (68Er) 2.1
Ytterbium (70Yb) 2.0
Europium (63Eu) 1.3
Holmium (67Ho) 0.8
Terbium (65Tb) 0.7
Lutetium (71Lu) 0.4
Thulium (69Tm) 0.3
Silver (47Ag) 0.08
Gold (79Au) 0.0031
Promethium (61Pm) 10-18
a Lanthanides (lanthanoids), scandium,
and yttrium are presented in boldface type.

Abundance of REEs in Earth’s Crust
…..(contd.)
 The elemental forms of REEs that are extracted from mineral ores, as
oxides (i.e., REOs), are iron-gray to silvery lustrous metals that are
typically soft, malleable, ductile, and usually reactive, especially at
elevated temperatures or when finely divided. The REEs’ unique properties
are used in a wide variety of applications. For example, magnets made
with REEs are much more powerful, weigh less, and can be made smaller
than conventional magnets. Some REEs also have high electrical
conductivity, can withstand extreme heat, and give off intense white light
when heated.
 In aquatic systems, REEs typically occur in the trivalent state. However,
cerium can be present as Ce4+ and europium can occur in both the
divalent and trivalent states. The chemical behaviors of all REEs are very
similar, but smooth variations can be attributed to their atomic number
and ionic radii, which are inversely correlated. These attributes make REEs
well suited to the study of processes such as complexation, sorption,
precipitation, and the formation of colloids (Merten and Büchel, 2004).

Abundance of REEs in
Earth’s Crust …..(contd.)
 Most of the REE are not as rare as the
group’s name suggests. Cerium is the
most abundant REE (Table 4), and it is
actually more common in the Earth’s crust
than copper or lead (Taylor and McLennan,
1985).
 REE-bearing mineral deposits have various
origins and modes of formation (Table 5)
and they occur on all continents of the
world (Figure 1).

Table 4: REEs and their abundances in the Earth crust and in
Chondrites (Taylor and McClennan 1985)

CLASSIFICATION OF RARE EARTH
ELEMENTS
 There are observed distributions for lanthanide group elements in the natural environment
indicating that they will, under the right conditions, separate from the each other. Preferences for
the occurrence of certain lanthanides have been observed in different mineral types. In aqueous
solution, separation also occurs due to variable stability constants, indicating the strength of the
chemical bond of lanthanide-ligand complexes (Weber, 2008). Observations like these have
suggested a subdivision of the lanthanides into various groupings as presented by Gupta and
Krishnamurthy (2004) from other sources and that are presented below. Previously the lanthanides
were categorized into three groups according to Kramers in 1961:
 Light (or cerium) lanthanide group – lanthanum (La) through samarium (Sm);
 Middle (or terbium) lanthanide group – europium (Eu) through dysprosium (Dy);
 Heavy (or yttrium) lanthanide group – holmium (Ho) through lutetium (Lu) and including
yttrium.
 More recently, two other attempts have been made to subdivide the lanthanides into groups: (after
Jackson and Christiansen, 1993):
 Light (or cerium) lanthanide group – lanthanum (La) through gadolinium (Gd); and
 Heavy (or yttrium) lanthanide subgroup – terbium (Tb) through lutetium (Lu), including
yttrium.
 (after Sabot and Maestro, 1995)
 Light lanthanide group – lanthanum (La) through neodymium (Nd);
 Middle lanthanide group – samarium (Sm) through dysprosium (Dy);
 Heavy lanthanide group – holmium (Ho) through lutetium (Lu) and including yttrium.

CLASSIFICATION OF RARE EARTH
ELEMENTS
 REEs are mainly classified into two
groups:
 LIGHT RARE EARTH ELEMENTS
(Lanthanum to Samarium) and
 HEAVY RARE EARTH ELEMENTS
(Europium to Lutetium) (Table 2),
based on their ionic radii and other
physicochemical properties (Table 3):

Table 2: Periodic table of the elements showing the division between LREEs and HREEs (Schuler et al., 2011).

Table 3: Rare Earth elements—overview of selected characteristics (Zepf, 2013)

GEOLOGY OF RARE EARTH ELEMENTS
 REEs do not occur as native elemental metals in nature, only as part of the host mineral’s chemistry. For this reason, the recovery of REMs
must be accomplished through a complex processing method to chemically break down the minerals containing the REEs.
 Despite more than 200 known REE-bearing minerals, only three are considered to be the principal REE mineral ores most feasible for the
extraction of REMs: bastnasite, xenotime, and monazite (Gupta and Krishnamurthy, 2004), as described below:
 Bastnasite, the most abundant among the three REE mineral ores, is a carbonate mineral found mainly enriched in LREEs (e.g., cerium,
lanthanum, and yttrium). Bastnasite is found in vein deposits, contact metamorphic zones, and pegmatites. It forms in carbonate-silicate
rocks occurring with and related to alkaline intrusions (e.g., Mountain Pass mine).
 The two phosphate minerals, xenotime and monazite, can occur together, but crystallize in different temperature and pressure regimes from
a similar igneous environment. While these minerals can contain any of the REEs (i.e., HREEs or LREEs), enrichment of specific REEs is
variable and a function of the temperature and pressure regime in which they formed. Monazite commonly occurs in placer deposits;
xenotime can occur along with monazite, but generally occurs as a more minor constituent of these types of deposits. Deposits of phosphate
rare earth ores provide the opportunity to produce co-products of phosphates and REEs. Thorium and uranium may also be taken advantage
of and produced as a co-product, or may represent a significant management challenge. A further description of these two minerals follows:
 Monazite is generally enriched with the LREEs cerium, lanthanum, and neodymium, but can also contain HREEs, particularly yttrium (Ni et al.,
1995). The predominance of LREEs is due to the lower crystallization temperature and pressures of this mineral; however, it typically contains
more HREEs than bastnasiteore deposits. It occurs in acidic igneous rocks (primarily pegmatites), metamorphic rocks, and some vein deposits.
Monazite is resistant to weathering and occurs in many placer deposits as the host rocks are eroded. Thorium may also be associated with monazite
in various amounts.
 Xenotime crystallizes under higher temperatures and pressures than those of monazite; therefore, its crystalline structure more readily
accommodates a higher ratio of HREEs (terbium through lutetium, and yttrium) than is commonly found in monazite. It is primarily a yttrium
phosphate mineral and occurs as a minor constituent of granitic and gneissic rocks. Although not always present in significant quantities, uranium
and thorium can also occur as constituents of xenotime.
 There are two other important REE-containing minerals in the United States (Long et al., 2010) including:
 Euxenite which contains yttrium, erbium, and cerium. It is found mostly in placer deposits in Idaho, and occurs as a tantaloniobates(e.g., minerals
where Ta and Nb form the compound) of titanium, rare earths, thorium, and uranium.
 Allanite is an epidote mineral and contains cerium, lanthanum, and yttrium. It occurs in igneous, metamorphic, and hydrothermal environments and
is disseminated in pegmatite or occurs in vein deposits.

Table 5: Various Origins of REE-bearing mineral deposits with examples (Long et al., 2010)Sedimentary
Metamorphic
Igneous

GEOLOGY OF RARE EARTH
ELEMENTS …..(contd.)
 The largest known REE resource in the world is The Fe-REE-Nb at Bayan Obo in Inner
Mongolia, China, discovered by Russian geologists in 1927 (Castor and Hedrick, 2006).
 The Bayan Obo Group was deposited unconformably on 2.35-Ga migmatites, and, along
with Carboniferous volcanics, was deformed during a Permian continent-to continent
collision event dominated by folding and thrusting (Drew et al., 1990).
 The two largest are the Main and East ore bodies (Figure 2), each of which include
ironREE resources with more than 1,000 m of strike length and average 5.41% and
5.18% rare earth oxides (REOs), respectively (Yuan et al. 1992).
 Total Reserves have been reported as 48 Mt of REOs (average grade 6%)
 Intrusion of large amounts of Permian granitoid rocks also resulted from this collision. It
has been dated at 1600 Ma (Yuan et al., 1992) and 550 to 400 Ma (Chao et al., 1997).
 The Bayan Obo ore is hosted by dolomite of the Bayan Obo Group, a Middle Proterozoic
clastic and carbonate sedimentary sequence that occurs in an 18-km-long syncline (Qiu et
al., 1983; Chao et al., 1997; Drew et al., 1990).
 The REE ore consists of three major types: REE-iron ore, the most important type; REE
ore in silicate rock; and REE ore in dolomite (Yuan et al. 1992)
 Major oxide chemistries of several Bayan Obo ore types are shown in Table 6. The REEs
are mainly bastnasite and monazite, but at least 20 other REE-bearing minerals have been
identified (Yuan et al. 1992).

Figure 2: Geologic map of the Main and East iron-REE-niobium
ore bodies at Bayan Obo, China (Chao et al. 1997).

Table 6. Minerals that contain REEs and occur in economic or
potentially economic deposits (Mariano,1989a)

APPLICATIONS OF REES
 The REEs and their key applications are identified in Table 2-2.
 Also included in the table are the :
i) key categories of uses by the U.S. Department of Defense
(DoD) and
ii) DOE’s classification of the elements determined to be
critical or near critical due to projected supply risks and their
importance to clean-energy technologies.
 Figure 2-3 graphically presents additional information on the
specific types and quantities of REEs that were reported as
being in use in various products in 2007.
 Table 2-3, taken from USGS data, provides a breakdown by
industrial application on the uses of REEs in the United States in
2008.

Table 2-2. Rare Earth Elements, Their Applications, and Potential Supply Issues for
Clean-Energy Technologies (Source: U.S. DOE, 2011).
Element Applications
Scandium Metal alloys for the aerospace industry.
Yttrium Ceramics; metal alloys; lasers; fuel efficiency; microwave communication for satellite industries; color televisions;
computer monitors; temperature sensors. Used by DoD in targeting and weapon systems and communication devices.
Defined by DOE as critical in the short- and midterm based on projected supply risks and importance to clean-energy
technologies.
Lanthanum Batteries; catalysts for petroleum refining; electric car batteries; high-tech digital cameras; video cameras; laptop
batteries; X-ray films; lasers. Used by DoD in communication devices. Defined by DOE as near critical in the short-term
based on projected supply risks and importance to clean-energy technologies.
Cerium Catalysts; polishing; metal alloys; lens polishes (for glass, television faceplates, mirrors, optical glass, silicon
microprocessors, and disk drives). Defined by DOE as near critical in the shortterm based on projected supply risks
and importance to clean-energy technologies.
Praseodymium Improved magnet corrosion resistance; pigment; searchlights; airport signal lenses; photographic filters. Used by DoD
in guidance and control systems and electric motors.
Neodymium High-power magnets for laptops, lasers, fluid-fracking catalysts. Used by DoD in guidance and control systems, electric
motors, and communication devices. Defined by DOE as critical in the short- and mid-term based on projected supply
risks and importance to clean-energy technologies.
Promethium Beta radiation source, fluid-fracking catalysts.
Samarium High-temperature magnets, reactor control rods. Used by DoD in guidance and control systems and electric motors.
Europium Liquid crystal displays (LCDs), fluorescent lighting, glass additives. Used by DoD in targeting and weapon systems and
communication devices. Defined by DOE as critical in the short- and mid-term based on projected supply risks and
importance to clean-energy technologies.
Gadolinium Magnetic resonance imaging contrast agent, glass additives.
Terbium Phosphors for lighting and display. Used by DoD in guidance and control systems, targeting and weapon systems, and
electric motors. Defined by DOE as critical in the short- and mid-term based on projected supply risks and importance
to clean-energy technologies.
Dysprosium High-power magnets, lasers. Used by DoD in guidance and control systems and electric motors. Defined by DOE as
critical in the short- and mid-term based on projected supply risks and importance to clean-energy technologies.
Holmium Highest power magnets known.
Erbium Lasers, glass colorant.
Thulium High-power magnets.
Ytterbium Fiber-optic technology, solar panels, alloys (stainless steel), lasers, radiation source for portable X-ray units.
Lutetium X-ray phosphors.

Figure 2-3. In-use stocks of selected REEs by specific
application or industry (in gigagrams) (Du and Graedel, 2011).

Table 2-3. Distribution of REEs by End
Use in 2008 (U.S. DOI/USGS, 2010)
End Use Percentage
Metallurgical applications and alloys 29%
Electronics 18%
Chemical catalysts 14%
Rare earth phosphors for computer monitors, lighting, radar, televisions, and
X-rayintensifying film
12%
Automotive catalytic converters 9%
Glass polishing and ceramics 6%
Permanent magnets 5%
Petroleum refining catalysts 4%
Other 3%

APPLICATION OF REEs IN GEOLOGICAL STUDIES
 Some REE tools used as proxies in
geological studies include:
1) La Anomalies,
2) Ce Anomalies,
3) Eu Anomalies
4) Y/Ho ratios
5) Nd isotope ratios (143Nd/144Nd) and
6) Sm/Nd ratios

APPLICATION OF REEs IN
GEOLOGICAL STUDIES…(contd)
 Geological application of REEs includes:
1) Paleoenvironmental studies
2) Provenance studies
3) Sedimentary processes
4) Petrogenetic modelling
5) Geochronology
6) Paleoclimate reconstruction

APPLICATION OF REEs IN
GEOLOGICAL STUDIES… (contd)
1) Provenance studies and Sedimentary processes
 It has been established that REEs in terrigenous sediments are exceptionally
unreactive, thus making them very useful for provenance studies. Sediments,
especially in rivers are sources of transportation and sinks for REEs (McLennan,
1989).
2) Petrogenetic modeling
 Europium (Eu) anomalies (positive or negative departures of europium from
chondrite- normalized plots) have been found to be particularly effective for
Petrogenetic modeling.
 The relative abundance of individual lanthanide elements has been found useful
in the understanding of magmatic processes and natural aqueous systems.
Comparisons are generally made using a logarithmic plot of lanthanide
abundances normalized to abundances in chondritic (stony) meteorites.
3) Geochronology
 REE isotopes, particularly of neodymium and samarium, have found use in
petrogenetic modelling and geochronology
 Nd isotopes serve as a pointer to changes in erosional input, sedimentation rates
and ocean circulation in marine sediments (Dahlqvist et al., 2005)
 Neodymium isotopes in planktonic foraminifera records the response of
continental weathering and ocean circulation rates to climatic change (Vance and
Burton, 1999).

APPLICATION OF REE TO PETROLEUM
SYSTEMS
1) The Paleodepositional environment reconstruction of Source Rocks (Murray et
al., 1990; Pi et al., 2013).
 REE compositions of kerogens (Petroleum Precursors) could place better constraints on
oceanic redox conditions (Pi et al., 2013)
2) Classification of crude oils or solid bitumens:
 Parnell (1988) found that dysprosium (Dy) contents may be of value in discriminating
between solid bitumens from different sources.
 Akinlua et al. (2008) classified Niger Delta oils of different sources using the contents
and patterns of light rare earth elements (LREE).
 Jiao et al. (2010) analyzed REE compositions of two end-member oils of the Cambrian-
Ordovician in the Tarim Basin, and determined whether the oils were derived from
mixed sources.
 Ramirez-Caro (2013) compared REE patterns of Mississippian oils and Devonian
Woodford shales from Anadarko Basin, and demonstrated that Mississippian oils were
generated from the Woodford shales.
 Manning et al. (1991) evaluated Nd isotope values (143Nd/144Nd) and Sm/Nd ratios as
potential tools for oil-source correlation by comparing both ratios in source rocks,
hydrous pyrolysates from source rocks and crude oils.

Case study One
Preliminary investigation of rare earth element (REE)
composition of shales in the Oshosun Formation exposed in
the Sagamu quarry, eastern Dahomey Basin Southwestern
Nigeria. (O.A. Adekeye et al., 2007)
Introduction
 The Oshosun Formation in eastern Dahomey Basin,
southwestern Nigeria consists of shale sediments, which
are significant for their phosphorite and pyrite
compositions and are fossiliferous. The shales are lower
Eocene-middle Eocene age, are well laminated and
contain glauconitic grains.
 The study area for this work is located at Sagamu quarry
of the West African Portland Cement (WAPCO) where the
sedimentary section is exposed.
 The result of this study was used to predict the shale
sediment precursors and Source rock type to enhance the
geological knowledge of the shale build-up

Methodology
 § Five (5) selected shale samples were analysed for their rare
earth elements by Neutron Instrumental Activation Technique.
This method involves the irradiation of samples together with
a standard with neutron flux. REEs content in the samples
were determined by comparing their residual counts after
cooling from a reference standard irradiated under the same
condition as samples. The standard used in this study is
DMMAS-16-1.
Results and Discussions/Findings
 Results of the rare earth elements (REE) analysis of the five
shale samples from the Eocene Oshosun Formation indicates
REEs values ranging from ~0.5 to 139ppm.
 Strong positive Ce anomalies were consistent in all the six
shale samples analysed. The enrichment of Ce indicates that
the Oshosun shales have undergone some degree of
phosphatization leading to the precipitation of phosphate
minerals.
 The chondrite-normalised REE abundances are generally
lower than those reported for North American shale
composites and for most Mississippian Valley Type Lead-zinc
deposits with strong europium anomalies that were derived
from predominantly arkosic rocks with abundant plagioclase
feldspars.

Summary of Case study
one
 The shales of the Oshosun Formation investigated for
their rare earth elements (REE) show a preliminary
pattern of their composition.
 The results show a slight enrichment in the light rare
earth elements but a significant depletion in the heavy
REE similar to the seawater derived shales. This signifies
that the shale precursors are granitic rocks with large
proportions of alkali feldspars and low contents of
plagioclase feldspars.
 The enrichment of Ce indicates that the Oshosun shales
have undergone some degree of phosphatization leading
to the precipitation of phosphate minerals.

Case Study Two
Rare earth elements fingerprints: Implication for provenance,
tectonic and depostional settings of clastic sediments of Lower
Benue Trough, Southeastern Nigeria. (O. C. Adeigbe and A. Y. Jimoh,
2014)
Introduction
 The study areas, Lower Benue Trough is divided
into Asu River Group (ARG) and Cross River Group
(CRG) and it is delimited by longitudes 7°00'E and
8°30'E and latitudes 5°00'N and 6°30'N. ARG
covers Awi, Abakaliki and Mfamosing Formations
while Ekenkpon, Eze-Aku, New Netim, Awgu and
Agbani Formations fall within CRG.
 The study aimed at using geochemical approach
through rare earth elements (REE) to deduce
provenance and depositional environment.

Figure 1. Correlation chart of all outcrops studied showing their locations,
formations and groups (after Adeigbe and Jimoh, 2014).

Methodology
 A total of 56 fresh outcrop samples collected from eight (8) Formations: Awi,
Abakaliki, Mfamosing Formations which constitute ARG and Ekenkpon, Eze-Aku, New
Netim Marl, Awgu, Agbani Formations which constitute CRG were obtained from the
study area.
 The samples were subjected to detailed lithologic description by visual examination.
Geochemical analysis was done using Inductively Coupled Plasma Mass Spectroscopy
(ICP-MS) to determine trace and rare-earth elements using lithium
metaborate/tetraborate fusion method.
Results and Discussions
 The chondrite normalized REE plots shows enrichment in the LREE over the HREE
with negative Eu anomaly for both ARG and CRG. While the (Eu/Eu*) average for
ARG and CRG are 0.74 and 0.73 respectively indicating Quartzose sedimentary,
Intermediate igneous and Felsic igneous provenances for the sediments.
 The Cerium anomaly (Ce/Ce*) values average 1.20 and1.68 in ARG and CRG
respectively indicating oxidizing and shallow marine environment. The REE pattern is
consistent with that of the Upper Continental Crust (UCC).

(after Adeigbe and Jimoh, 2014).

Summary of Case Study Two
 The chondrite normalized values for the rare earth elements of the
three Formations making up the Asu River Group revealed an
appreciable enrichment in the LREE (La-Nd) over the HREE (Er-Lu).
 The average europium anomaly (Eu/Eu*) value of the three Formations
is 0.73 and this coincides with the range of sediments from a felsic
sources. While the cerium anomaly (Ce/Ce*) value of 1.20 shows that
the sediments were deposited in an oxidizing environment and
confirmed that the sediments of the Asu River Group tend towards
felsic sources as earlier confirmed by the europium anomaly.
 The REE pattern of the Cross River Group shows an enrichment of
LREE and depletion of HREE and indicates negative europium anomaly
which is similar to sediments of ARG.
 Evidences from the cerium anomalies with values >1 indicate an
oxidizing environments and that the sediments of Eze Aku, Ekenkpon,
New Netim Marl, Awgu and Agbani Formations were deposited in a
shallow marine environment.

Case study Three
Rare Earth Elements (REE) as Geochemical Clues to Reconstruct
Hydrocarbon Generation History. (D. Ramirez-Caro, 2013)
Introduction
• In this study, REE geochemical investigations were targeted on oils
generated in the Woodford shale and overlaying Mississippian
formation located in the Anadarko Basin, north-central
Oklahoma.
• The REE distribution patterns and total concentrations of the
organic matter of the Woodford shale reveal a potential avenue
to investigate hydrocarbon maturation processes in a source rock.
• This study provides a valuable insight into the understandings of
the REE landscapes in the organic fraction of the Woodford Shale
in northern Oklahoma, linking these understandings to the REE
analysis of an oil generated from the same source bed and
comparing it to oil produced from younger Mississippian oil. The
information gathered from this study may ultimately prove useful
to trace the chemical history of oils generated from the Woodford
Shale source beds.

Regional Paleozoic Stratigraphic column in the Anadarko Basin (after Ramirez-Caro, 2013).

Methodology
 Ten samples of the organic matter fraction and 10 samples of the silicatecarbonate fraction of the
Woodford shale from north central Oklahoma were analyzed by methods developed at Kansas
State University. Thirteen oil samples from Woodford Devonian oil and Mississippian oil samples
were analyzed for REE by inductively coupled plasma mass spectrometry (ICP-MS) and inductively
coupled plasma atomic emission mass spectrometry (ICP-AES). .
Results and Interpretation
1) REE concentration levels in an average shale range from 170 ppm to 185 ppm, and
concentration levels in modern day plants occur in the ppb levels.
2) The REE concentrations in the organic matter of the Woodford Shale samples analyzed ranged
from 300 to 800 ppm. The high concentrations of the REEs in the Woodford Shale, as compared
to the modern-day plants, are reflections of the transformations of buried Woodford Shale
organic materials in post-depositional environmental conditions with potential contributions of
exchanges of REE coming from associated sediments.
3) The distribution patterns of REEs in the organic materials normalized to PAAS (post-Archean
Australian Shale) had the following significant features:
4) all but two out of the ten samples had a La-Lu trend with HREE enrichment in general,
5) all but two samples showed Ho and Tm positive enrichments,
6) only one sample had positive Eu anomalies,
7) three samples had Ce negative anomalies, although one was with a positive Ce anomaly,
8) all but three out of ten had MREE enrichment by varied degrees.

three
 The REE distribution patterns for the Mississippian
oil samples show a general LREE enrichment with a
minor MREE enrichment. Five out of the seven
samples have a Cerium negative anomaly and all of
the samples have a Europium positive anomaly.
 The Devonian oil samples have REE distribution
patterns with a general LREE enrichement, and a
more prominent MREE enrichment is noticeable,
when comparing this samples to the Mississippian
oil samples. Three out of the six samples have
cerium depletion and like the Mississippian oil
samples, they show europium enrichment.

Case four study:
Evaluating rare earth elements as a proxy for oil-source
correlation. A case study from Aer Sag, Erlian Basin,
northern China (P. Gao et al., 2015)
Introduction
 Traditional geochemical tools for oil-source correlation such as biomarkers and carbon isotopes
can be hampered by thermal maturation and secondary alteration (including biodegradation and
water washing) and can lose their original significance. Less attention has been paid to the
application of REE to the petroleum system.
 The newly found Aer Sag, located on the northeast margin of the Erlian Basin, first produced
commercial oil in 2006. It is a NE trending half-graben, covering an area of 2000 km2, with 800
km2 in China and the rest in Mongolia.
Methodology
 This study analyzed organic extracts and their corresponding whole rock materials for REE
compositions by inductively coupled plasma–mass spectrometry (ICP–MS). Twenty-one samples
were collected from the Lower Cretaceous of the Aer Sag, Erlian
 Basin, northern China, including 14 mudstone samples and 7 oil sand
a, Crude oils from Well YM2 and Well TD2 sourced from the Middle-Upper Ordovician and
Cambrian marine source rocks, respectively are regarded as two end-member oils in the
Tarim Basin, China (Jiao et al., 2010). TD2 crude oil became denser by thermal alteration,
with a density of 1.0217 g/cm3 1010 falling into the category of heavy oil (Xiao et al., 2004).
b , Mississippian crude oils from Kansas State and Anadarko Basin, USA sourced from Devonian
Woodford (Chattanooga) shale enriched in marine organic matter (Ramirez- Caro, 2013;
McIntire, 2014; 1013 Kwasny, 2015).
c , Dushanzi oil seeps from southern margin of Junggar Basin mainly derived from Paleogene
lacustrine source rocks (Clayton et al., 1997; Li et al., 2013).
d , Organic extract samples of marine influenced coals from China can represent transitional oil.
e , Niger delta crude oils with substantial terrestrial organic matter input can represent terrestrial
oil (Akinlua et al., 2008).

a, Crude oils from Well YM2 and Well
TD2 sourced from the Middle-Upper
Ordovician and Cambrian marine source
rocks, respectively are regarded as two
end-member oils in the Tarim Basin,
China (Jiao et al., 2010). TD2 crude oil
became denser by thermal alteration,
with a density of 1.0217 g/cm3 1010
falling into the category of heavy oil (Xiao
et al., 2004). b , Mississippian crude oils
from Kansas State and Anadarko Basin,
USA sourced from Devonian Woodford
(Chattanooga) shale enriched in marine
organic matter (Ramirez-Caro, 2013;
McIntire, 2014; 1013 Kwasny, 2015). c ,
Dushanzi oil seeps from southern margin
of Junggar Basin mainly derived from
Paleogene lacustrine source rocks
(Clayton et al., 1997; Li et al., 2013). D,
Organic extract samples of marine
influenced coals from China can
represent transitional oil., e, Niger delta
crude oils with substantial terrestrial
organic matter input can represent
terrestrial oil (Akinlua et al., 2008).

Fig. 1. PAAS normalized plots of the rare earth elements in various
types of oils or extracts from the world. REE patterns are plotted
according to median values of available data (after Gao et al., 2015).

Fig. 2. Cross-plot of REE values against the LaN/YbN ratio of various types of
oils or extracts from around the world (after Gao et al., 2015)

four
 An attempt was made using rare earth
elements (REE) for oil-source correlation
 REE cannot be used alone for oil-oil and/or
oil-source correlations. Oil-source
correlations using REE were not consistent
with conclusions based on biomarker data
and trace element ratios. Only one pair of
oil-source rock relationships was
successfully established using REE.

REE GLOBAL ECONOMIC SUPPLY AND
DEMAND
 From the 1960s until the 1980s, the United States was the world leader in REO production. In fact,
in 1984, the Mountain Pass Mine in California supplied 100 percent of U.S. demand and 33 percent
of the world’s demand for rare earths. In the late 1970s, China started increasing production of
REEs, and as illustrated in Figure 2-4, rapidly became the world’s dominant producer. Active mining
operations at Mountain Pass Mine were suspended in 2002. Since 2007, separation of REE from
stockpiles at the site has continued. As REE production in the U.S. has declined, China has become
the world’s leading producer of REEs and is currently responsible for more than 95 percent of global
production.
 Annual global production of REEs totaled about 124,000 tons in 2008, according to a recent report
by the U.S. Congressional Research Service (Humphries, 2010). According to this same report,
analysis of the future supply and demand for each of the REEs indicates that, by 2014, global
demand could exceed 200,000 tons per year, which would exceed current production by over 75,000
tons per year. Additional analysis by others indicates the high likelihood of shortages of neodymium,
dysprosium, terbium, and praseodymium and the potential for shortages of lanthanum, yttrium, and,
europium by 2014 (Schuler et al., 2011). This information, combined with the data shown in Figure
2-3, indicates that the uses most likely to be impacted by future shortages are magnets for use in
computers, audio systems, wind turbines, and automobiles; motors/generators; batteries;
metallurgy; and catalysts. The critical nature of these uses is driving the push for increased mining,
expanded recycling and research into alternatives, and changes in U.S. and international policy.
 In 2008, the United States consumed 7,410 metric tons of REEs (U.S. DOI/USGS, 2010). Currently,
this demand is met mainly through imports from China, industry inventories, and stockpiles.

Figure 1. Map showing the global distribution of REE (BGS, 2011)

REE GLOBAL ECONOMIC SUPPLY AND DEMAND
Figure 2-4. Global production of rare earth oxides (Du and Graedel, 2011).

Introduction to Large and Giant Sized Deposits of the Rare Earth
Elements
 The rare earth elements (REE) are currently a focus of global attention because of geopolitical controls on their supply (Hatch, 2012),
which have led to them being included in recent and current lists of critical metals (US Department of Energy, 2011; British Geological
Survey, 2012; European Commission, 2014). Their importance comes from their use in the production of high strength magnets,
fundamental to a range of low carbon energy production approaches, and in a wide range of high technology applications. Reviews
are given in Chakhmouradian and Wall (2012), Gunn (2014), and Wall (2014). Production is currently limited to a small number of
large deposits (e.g. Bayan Obo, China; Mountain Pass, USA; Mount Weld, Australia; Lovozero, Russia), by-products (e.g. mineral
sands, India) or to deposits that have enrichments in specific elements of current high demand, notably dysprosium (Dy), terbium (Tb)
and other HREE (e.g. the so called ion absorption deposits in weathered granite of southern China; Kanazawa and Kamitani, 2006).
However, a number of deposits are known from relatively recent past production, are currently at the stage of feasibility studies, are at
advanced stages of exploration or have been the focus of research. Of these, given the small size of the REE market, most are large
enough to have a significant impact on global supply, although only Bayan Obo may truly be considered as giant.
 The formal definition of a giant ore deposit was proposed by Laznicka (1999) on the basis of the tonnage accumulation index
(Laznicka, 1983). This is the amount of metal in a defined ore body divided by its average crustal concentration (or ‘Clarke value’). The
aim of this was both to show the relative enrichment of different metals in a directly comparative manner, removing the absolute
variation of concentration between different metals, and to remove economic bias from discussion of the scale of ore bodies. The latter
aim can only ever be partly successful as it is dependent on the cutoff grade used to define an ore bodyean inherently economic
consideration. However, this approach remains the most clearly defined way to address the problem. Laznicka (1999) defined a giant
ore deposits as having a tonnage accumulation index of 1 x 1011, and a large ore body a tonnage accumulation index of 1 x 1010. For
these values, and using an average REE crustal concentration of 1.5 x 102 ppm (Wedepohl, 1995), a large REE deposit would have 1.7
x 106 tonnes of contained REE2O3, and a giant deposit would have 1.7 x 107 tonnes of contained REE2O3 (calculated assuming an
intermediate atomic mass for REE of 150). The available data for resources in REE deposits from Orris and Grauch (2002) and Long et
al. (2010) and other sources are shown in Fig.1A, and the deposits of large size or greater are shown in Fig.1B. Because of the current
scarcity of data for many of these deposits, resource estimates are commonly not JORC/NI43101 compliant, and for simplicity in this
review we have used the figures quoted by those authors. Where compliant data are available they are mentioned below. Of all
currently known REE deposits, only Bayan Obo, China, with the ore grade defined at 4.1 wt.% REE2O3, counts as a truly giant
deposit. A number of deposits classify as large, however, and these are likely to have a significant impact on the production of the
REE in the near future.

Figure 1. Grade-tonnage
plot for resource estimates
in REE deposits from Orris
and Grauch (2002) and
Long et al. (2010). Size
classifications after
Laznicka (1999)

Deposit types
 Rare earth element deposits are developed in virtually all major rock types with examples from igneous,
metamorphic and sedimentary (weathering profiles, residual deposits and placers) host rocks (Orris and
Grauch, 2002; Long et al., 2010) from settings worldwide (Fig. 2). Large and giant deposits for the whole REE
group, however, with the exception of Olympic Dam, are developed in association with alkaline igneous rocks e
either carbonatite or syenite. Individual HREE have potentially large deposits sensu stricto within the
weathered granitoid deposits of SE China (Chi and Tian, 2008).
 Carbonatite is an igneous rock with 50 modal% carbonate (sensu lato) and containing less than 20 wt.% SiO2
(Le Maitre et al., 2002), although Mitchell (2005) argued for a broader definition. Mitchell (2005) went on to
specify a distinction with genetically related carbothermal residua- that is rocks derived from CO2-rich
hydrothermal fluids. Syenite is an igneous rock with <20 modal% quartz, and alkali feldspar >65% of the total
feldspar content (Streckeisen, 1976). Rare earth enrichments are typically associated with quartz-free,
feldspathoid syenites. Such rocks are also commonly peralkaline (mole fraction Na2O / K2O > Al2O3) and as
such may contain sodic pyroxene (e.g. aegirine) and amphibole (arfvedsonite and riebeckite). Extreme
fractional crystallization of such rocks may lead to molal (Na2O/ K2O)/Al2O3 > 1.2, and the formation of
complex Zr and Ti minerals such as eudialyte - such rocks are termed agpaitic (Le Maitre, 1989; Sørensen,
1997). Syenites and carbonatites may be related in some composite intrusions, either by extreme
differentiation (Wyllie and Tuttle, 1960), or liquid-liquid immiscibility (e.g. Lee and Wyllie, 1998).
 Olympic Dam stands alone as the only iron oxide-copper-gold (IOCG) deposit that hosts significant REE
mineralization (Lottermoser, 1995). These REE resources hold currently uneconomic reserve estimates, but may
have the potential as by-products in the future. Iron oxide-copper-gold systems are hydrothermal deposits,
defined by the dominance of iron oxides rather than sulphide gangues, economic Cu and possibly Au
mineralisation, and an association with sodium-rich alteration haloes, and specific trace metal enrichments,
including the REE (Hitzman et al., 1992; Williams et al., 2005). The hydrothermal fluids involved are not simply
related to coeval magmatic sources, although magmatic-hydrothermal fluids are implicated in the formation of
a number of deposits (e.g. Pollard, 2001), and may involve high salinity brines derived from interaction with
evaporites, formation waters or highly saline surface waters (Barton and Johnson, 1996, 2000). The
characteristics of key large and giant sized deposits are summarized in Table 1.

Figure 2. Locations of main large and giant REE deposits

Fig. 1. Classification of global REE deposits based on current
exploitation status and geological setting. Contains British
Geological Survey materials ©NERC [2017].

Table 1: Approximate resource estimates and description of large and giant REE
deposits by the criteria of Laznicka (1999). Data from Orris and Grauch (2002) and
Long et al. (2010), with other references as cited.

CONCLUSION
 The series of 15 lanthanide metals, plus scandium and yttrium, have been designated as REEs; however, it should be noted that other elements
also are sometimes referred to as REEs. Rare earth oxides (REOs), and rare earth metals (REMs). While these elements are widely dispersed and
generally common in nature, minable concentrations of REEs are less common than for most other metal ores. Rare earths have become
important in modern commercial and industrial processing and products. Metallurgical processing, alloying, and electronics applications (e.g., cell
phones, computer components, electric motors, specialty glass and lenses) represent the most significant uses of REEs. In addition, due to the
dependence on several of these elements for military applications, REEs are considered a national strategic resource. Analysis of the future
supply and demand for each of the REEs indicates that, by 2014, global demand could exceed 200,000 tons per year, which would exceed
current production by over 75,000 tons per year. It is reported that if the new mines under development are able to meet their projected
production levels, world-wide demand for REEs will be met from these new sources.
 What precisely counts as a large or giant sized ore body for the REE is dependent on the size definition used. For total REE content, using the
size definitions of Laznicka (1999) only one deposit truly classes as giant in size e Bayan Obo in China. However, a number of other deposits can
be classified as large in this sense, although for many the definition of resources and reserves is tentative because of limitations in reliable data
and resource assessments. Only a few such deposits are currently mined, but those that are not are currently at the stage of exploration or
feasibility study, or in some cases mined for other commodities. The commonality in all these deposits (with the possible exception of Olympic
Dam) is an association with alkaline igneous rocks e either carbonatites, syenites or both. The total resource of such deposits must be a function
of the size of the parent intrusion, and the availability of enriched mantle sources. This typically limits them to areas of long term,
metasomatically enriched, lithospheric mantle. Metasomatism of the lithospheric mantle in this context may be linked to either past plume
activity, or to mantle enriched by subduction zone processes. The subsequent tectonic settings of melting range from post-orogenic collapse to
lithospheric extension. The formation of enriched mantle domains, means that in some cases repeated tectonic activity over long geological time
scales may have generated REE-enriched magmas at widely separated times in spatially restricted areas. Bayan Obo may be the key example of
this, with multiple stages of activity, alongside metamorphic and metasomatic reworking, being responsible for the unique scale of the REE
resource. Rare earth rich systems appear to have occurred throughout geological time. There do, however, appear to be distinctions in the grade
and tonnage of deposits that may reflect the generation of enriched mantle domains in the Proterozoic. Increases in grade may also be related to
enrichment of ore zones by the potential hydrothermal and weathering processes in specific deposits. A critical factor in what constitutes a large
or giant REE deposit is whether the grade for total REE or individual REE is used to define the size of the resource relative to average crustal
values. The HREE are up to two orders of magnitude less abundant than Ce, the most abundant REE. Deposits of Nd, Eu, Dy, Tb and Y in
agpaitic nepheline syenites and lateritic weathering profiles may class as large for the individual metals, and may have economic impact in
coming years.
 REEs can be of Primary origin (Carbonatites, Alkaline igneous rocks, Iron-REE, Hydrothermal veins and Stockworks) or Secondary origin
(Laterites, Marine, Alluvial and Paleo-placers).
 REEs are essential tools in geological research for paleoenvironmental studies, geochronology, oil-source correlation in petroleum systems,
petrogenetic modelling, provenance studies, sedimentary processes, paleoclimate reconstruction and ocean water circulation.

References
 Chi, R., Tian, J., 2008. Weathered Crust Elution-deposited Rare Earth Ores. Nova Science Publishers, New York, p.
308.
 Du, X. and T. E. Graedel. (2011). Global in-use stocks of the rare earth elements: A first estimate. American
Chemical Society. Environ. Sci. Technol. 45: 4096-4101.
 Gunn, G., 2014. Critical Metals Handbook. Wiley, British Geological Survey. American Geophysical Union, p. 454.
 Gupta, C. K. and N. Krishnamurthy. (2004). Extractive Metallurgy of Rare Earths. CRC Press.
 Hatch, G.P., 2012. Dynamics in the global market for rare earths. Elements 8, 341-346.
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United States - a Summary of Domestic Deposits and a Global Perspective. US Geological Survey Scientific
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 Lottermoser, B.G., 1995. Rare earth element mineralogy of the olympic dam Cu-U-Au-Ag deposit, Roxby Downs,
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 Ni, Y., J. M. Hughes, et al. (1995) Crystal chemistry of the monazite and xenotime structures. American
Mineralogist 80, 21-26.
 Orris, G.J., Grauch, R.I., 2002. Rare Earth Element Mines, Deposits, and Occurrences. U.S. Geological Survey
Open-File Report 2002; 02-189, U.S. Geological Survey, Tucson, AZ.
 Schüler, D., M. Buchert, et al. (2011). Study on rare earths and their recycling. OKO-insititut e.v., January.
 Smith, M.P. et al. (2016). From mantle to critical zone: A review of large and giant sized deposits of the rare
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 U.S. Department of the Interior, U.S. Geological Survey. (2010). Mineral commodities summary 2010. January 26.
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