application of rare earth elements in geological studies

APPLICATIONS OF RARE EARTH ELEMENTS IN GEOLOGICAL STUDIES

A SEMINAR PRESENTATIONBY

ADEYINKA, SOLOMON ADEOLAUNIVERSITY OF ILORIN

SUPERVISOR: DR. O.A. ADEKEYE

JANUARY, 2016

OUTLINE

• Introduction• Objectives of Seminar• Classification of Rare Earth Elements • Geology and Abundance of Rare Earth Elements• Application OF REEs in Geological Studies• Case Studies

INTRODUCTION

• Rare Earth Elements (REEs) are seventeen (17) elements, comprising Scandium (n=21), Yttrium (n=39) and the fifteen (15) Lanthanides on the periodic table of elements (atomic number 57 to 71) (Connelly, 2005).

• 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).

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

OBJECTIVES

• To review the geology of rare earth elements

• To discuss the various applications of rare earth elements in geological studies

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

• 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).


Element Symbol AtomicNumber

Upper CrustAbundance,

ppm

Chondrite Abundance,ppm

Scandium Sc 21 16.0 na

Yttrium Y 39 22 na

Lanthanum La 57 30 0.34

Cerium Ce 58 64 0.91

Praseodymium Pr 59 7.1 0.121

Neodymium Nd 60 26 0.64

Promethium Pm 61 na na

Samarium Sm 62 4.5 0.195

Europium Eu 63 0.88 0.073

Gadolinium Gd 64 3.8 0.26

Terbium Tb 65 0.64 0.047

Dysprosium Dy 66 3.5 0.30

Holmium Ho 67 0.80 0.078

Erbium Er 68 2.3 0.20

Thulium Tm 69 0.33 0.032

Ytterbium Yb 70 2.2 0.22

Lutetium Lu 71 0.32 0.034

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


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

Sedi

men

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Met

amor

phic

Ig

neou

s


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


• 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 iron- REE 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).


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


• 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).


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

GEOLOGICAL APPLICATION OF REEs

• Some REE tools used as proxies in geological studies include:

1. La Anomalies,2. Ce Anomalies, 3. Eu Anomalies4. Y/Ho ratios5. Nd isotope ratios (143Nd/144Nd) and 6. Sm/Nd ratios


Geological application of REEs includes:• Paleoenvironmental studies• Provenance studies• Sedimentary processes• Petrogenetic modelling• Geochronology• Paleoclimate reconstruction

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.


3. 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).

GEOLOGICAL APPLICATION OF REEs4. 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.


5. Geochronology • REE isotopes, particularly of neodymium and samarium,

have found use in petrogenetic modelling and geochronology

6. Nd isotopes serve as a pointer to changes in erosional input, sedimentation rates and ocean circulation in marine sediments (Dahlqvist et al., 2005)

7. Neodymium isotopes in planktonic foraminifera records the response of continental weathering and ocean circulation rates to climatic change (Vance and Burton, 1999).

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.

Case study One (cont.)

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.

Case Study Two (cont.)

Figure 1. Correlation chart of all outcrops studied showing their locations, formations and groups.


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).

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.

Case study Three (cont.)

Methodology• Ten samples of the organic matter fraction and 10 samples of the silicate-

carbonate 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• 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. • 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.


• The distribution patterns of REEs in the organic materials normalized to PAAS (post-Archean Australian Shale) had the following significant features:

(1) all but two out of the ten samples had a La-Lu trend with HREE enrichment in general,

(2) all but two samples showed Ho and Tm positive enrichments, (3) only one sample had positive Eu anomalies, (4) three samples had Ce negative anomalies, although one was with a positive Ce

anomaly, (5) all but three out of ten had MREE enrichment by varied degrees.

Summary of Case study 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 Study Four

Evaluating rare earth elements as a proxy for oil-source correlation. A case study from Aer Sag, Erlian Basin, northern ChinaP. 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.

MethodologyThis 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

Case Study Four (cont.)

a, Crude oils from Well YM2 and Well TD2 sourced from the Middle-Upper Ordovician andCambrian marine source rocks, respectively are regarded as two end-member oils in the TarimBasin, China (Jiao et al., 2010). TD2 crude oil became denser by thermal alteration, with a densityof 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 DevonianWoodford (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 Paleogenelacustrine 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 andCambrian marine source rocks, respectively are regarded as two end-member oils in the

TarimBasin, China (Jiao et al., 2010). TD2 crude oil became denser by thermal alteration, with a

densityof 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

DevonianWoodford (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

Paleogenelacustrine 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.


Fig. 2. Cross-plot of REE values against the LaN/YbN ratio of various types of oils or extracts from around the world

Summary of Case study 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.

CONCLUSION 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.

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application of rare earth elements in geological studies

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