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GEOLOGIAN TUTKIMUSKESKUS
Yksikkö
Espoo
11.4.2013
115/2013
Mini-Atlas of REE-minerals in Finnish
Bedrocks
Thair Al-Ani and Lassi Pakkanen
GEOLOGIAN TUTKIMUSKESKUS
11.4.2013
GEOLOGICAL SURVEY OF FINLAND DOCUMENTATION PAGE
Date / Rec. no.
Authors
Thair Al-Ani
Lassi Pakkanen
Type of report
Commissioned by
GTK
Title of report
Mini-Atlas of REE- Minerals in Finnish bedrock
Abstract
This High-Tech mineral atlas builds on our analysis of the REE-bearing minerals sector contained in our previous papers
completed by Thair Al-Ani and Olli Sarapää during working in Hi-Tech metal project (2009-2012) of the Geological Survey
of Finland (GTK). The aim of this work is to evaluate the known REE occurrences and exploration potential in Finland based
on existing data (literature, previous reports, databases, and drill cores) combined to new geochemistry and mineralogy
(Hytönen, Kai 1999), heavy mineral studies, geophysical measurements, geological mapping and recent drillings of new tar-
gets. The primary purpose of this report is to build an initial and preliminary archive of High-Tech mineral and resource in-
formation in Finnish deposits. The High-Tech minerals data presented herein could be used to support exploration efforts and
provide an initial database for the use of researchers and investors in the natural resources sector.
Keywords
Allanite, Ancylite-(Ce), Bastnasite- (Ce), Cerite-(Ce), Columbite and Tantalite, Davidite, Euxenite-(Y), Fergusonite-(Y),
Monazite-(Ce), Parisite-(Ce), Thorite
Geographical area
Sokli, Korsnäs, Otanmäki, Iivaara, Lamujärvi, Lehmikari, Vanttaus and Suhuvaara.
Map sheet
Other information
Report serial
Archive report
Archive code
Total pages
42
Language
English
Price
Confidentiality
Unit and section
Southern Finland Office
Project code
2551005
Signature/name
Thair Al-Ani
Signature/name
Lassi Pakkanen
GEOLOGIAN TUTKIMUSKESKUS 2
Contents
Documentation page
1 INTRODUCTION 3
2 RARE EARTH PROPERTIES AND USES 3
3 APPLICATIONS OF RARE EARTH ELEMENTS 4
4 RARE EARTH OXIDE (REO) SUPPLY AND DEMAND FORECASTS 5
5 RARE EARTH ELEMENTS IN FINLAND 5
6 RARE EARTH MINERALS 10 6.1 Allanite-(Ce) 10
6.2 Ancylite-(Ce) 14 6.3 Bastnasite-(Ce) 16
6.4 Cerite-(Ce) 21 6.5 Columbite and Tantalite 22 6.6 Davidite 26
6.7 Euxenite-(Y) 28
6.8 Fergusonite-(Y) 30 6.9 Monazite-(Ce) 33 6.10 Parisite-(Ce) 37
6.11 Thorite 39
7 REFERENCES 41
LITERATURE
GEOLOGIAN TUTKIMUSKESKUS 3
1 INTRODUCTION
The rare earth elements (REE) include fifteen elements with atomic numbers 57 through 71, from lantha-
num to lutetium, plus other elements, such as scandium and yttrium, which are commonly classed as rare
earths because of their natural association with rare earths. REE are classified into two subgroups, as light
rare earth elements (LREE) comprising the first five elements (atomic numbers 57-62); and the heavy rare
earth elements (HREE), comprising the elements with atomic numbers 63-71 as well as yttrium. Despite
its low atomic weight, yttrium is classified with the HREE because it's properties are closer to those of the
HREE subgroup than to LREE.
Although industrial demand for these elements is relatively small in tonnage terms, they are essential for
a diverse and expanding array of high-technology applications. REE-containing magnets, metal alloys for
batteries and light-weight structures are essential for many current and emerging alternative energy tech-
nologies, such as electric vehicles, energy-efficient lightning, and wind power. REE are also critical for a
number of key defense systems and other advanced materials. The most abundant rare earth elements are
cerium, yttrium, lanthanum and neodymium (USGS 2010). They have average crustal abundances that are
similar to commonly used industrial metals such as chromium, nickel, zinc, molybdenum, tin, tungsten
and lead (USGS 2002). Again, they are rarely found in extractable concentrations.
2 RARE EARTH PROPERTIES AND USES
The world supply of rare earths is dominated by China, which provides 97% of the world’s production.
However, China only has 48% of the world’s known reserves of rare earths, according to the USGS Min-
eral Commodity Summaries 2011. The data shows that until significant rest-of-world production comes
on-stream in the next three to five years, there will be a near-term supply shortfall for Rest-of-World
(ROW) rare earth users (Kingsnorth/IMCOA, 2011). Both the short- and medium-term supply/demand
balance for rare earths depend heavily on Chinese export and domestic production policies, due to the
overwhelming Chinese domination of rare earth supply. This is further reinforced by the current lack of
rare earth production infrastructure and processing knowledge in the rest of the world. Also, because each
rare earth deposit is unique and contains various REEs in different proportions, individual elements are
produced in different quantities. Some rare earths may be in short supply even though the total supply is
forecast to exceed total demand by 2015.
GEOLOGIAN TUTKIMUSKESKUS 4
3 APPLICATIONS OF RARE EARTH ELEMENTS
Design after koengeth, 2011 http://enercar2.wordpress.com/
GEOLOGIAN TUTKIMUSKESKUS 5
4 RARE EARTH OXIDE (REO) SUPPLY AND DEMAND FORECASTS
Source: IMCOA, Roskill
5 RARE EARTH ELEMENTS IN FINLAND
Rare earth metals were first found by Finnish scientist Johan Gadolin in 1794, and he named them Rare
Earths, thus leaving a misnomer for the group of elements, that is not earth at all, but a group of typical
metallic elements with chemical activity only next to alkaline and alkaline earth metals. Finland has been
a REE- producer in 1960’s but nowadays mineable deposits are missing. Several small REE deposits are
known in Finland. The rock types with the most promising exploration potential include carbonatites
(Sokli, Korsnäs), alkaline rocks (Otanmäki, Iivaara and Lamujärvi), Paleoproterozoic appinite intrusions
(Lehmikari, Vanttaus and Suhuvaara) in Lapland, pegmatites in Mesoproterozoic rapakivi granites in
southern Finland and kaolin weathering crusts in eastern and northern Finland. The highest REE concen-
trations are in carbonatite veins in Siilinjärvi apatite ore, which contain (0.4% weight-% REO), Korsnäs
Pb-ore (0.9 weight- % REO) and Sokli fenite zone (1-2 % weight-% REO) and alkaline gneiss in
Katajakangas (2.4 weight- % REO) (Neary and Highley, 1984). REO is an abbreviation of RE-oxides.
GEOLOGIAN TUTKIMUSKESKUS 7
Rare earth element deposits in Finland
Deposit location Geological information
Siilinjärvi
Geographic location
Deposit type
Age of deposit
REE minerals
Ore minerals
Gangue minerals
Host rock types
Status
Company
Ore content
References
Sokli
Geographic location
Deposit type
Age of deposit
REE minerals
Ore minerals
Gangue minerals
Host rock types
Status
Company
Ore content
References
27.6667, 63.0833
Carbonatite
Late Archean-- 2580 (U-Pb)
Apatite, monazite and pyrochlore
Zircon, sulphides and Fe-oxides
Phlogopite, calcite and dolomite
Carbonatite, glimmerite, syenite, diabase, fenite and dioritic dykes
Phosphorus, lime and phlogopite producer
Yara Suomi Oy
Apatite contains 0.4% weight-% REE-oxides
USGS, 2001, MASMILS database
Isokangas, Pauli, 1978, Finland, in Bowie, S.H.U., Kvalheim, A., and
Haslam, H.W., eds., Mineral deposits of Europe, volume1: Northwest
Europe: London, The Institution of Mining and Metallurgy and The Minera-
logical Society, p. 39-92.
Puustinen, K., 1970. The carbonatite of Siilinjärvi in the Precambrian of
Eastern Finland. A preliminary report. Lithos, 3, s. 89 - 92.
29.2534, 67.7485
Carbonatite and regolith
334-392 Ma; Devonian
Apatite, rhabdophane and francolite
Apatite, magnetite, pyrochlore, zircon, carbonate-fluorapatite, baddeleyite,
sulphides and Ti-, Zn- and Sr-bearing minerals
Goethite, calcite, tremolite, phlogopite, serpentine and clinohumite
Carbonatite
Phosphorus deposit
Yara Suomi Oy
REE content of the apatite is similar to that of the Khibina complex
USGS, 2001 and 2002, MASMILS database
Isokangas, Pauli, 1978, Finland, in Bowie, S.H.U., Kvalheim, A., and
Haslam, H.W., eds., Mineral deposits of Europe, volume1: Northwest
Europe: London, The Institution of Mining and Metallurgy and The Minera-
logical Society, p. 39-92.
Vartiainen, H.,1989, The phosphate deposits of the Sokli Carbonatite Com-
GEOLOGIAN TUTKIMUSKESKUS 8
Korsnäs
Geographic location
Deposit type
Age of deposit
REE minerals
Ore minerals
Gangue minerals
Host rock types
Status
Company
Ore content
References
plex, Finland, in Notholt, A.J.G., Sheldon, R.P., and Davidson, D.F., eds.
Phosphate deposits of the world, Volume 2-- Phosphate rock resources:
Cambridge, Cambridge University Press, p. 398-402.
Thair Al Ani, Torppa Akseli and Lassi Pakkanen, 2013, Mineralogy and Pe-
trography of Siilinjärvi Carbonatite and Glimmerite Rocks, Eastern Finland,
GTK report.
15.4300, 60. 3500
Pb –REE deposit
Proterozoic
Monazite
Galena and apatite
Calcite, feldspar and diopside
Gneiss, skarn and carbonatite
REE byproduct producer (1988)
Outokumpu Oy
0.86 - 0.91 wt% REE-oxides in monazite
USGS, 2001, MASMILS database
Roskill Information Services, 1988, The economics of rare earths & yttrium,
1994, seventh edition: London, Roskill Information Services, 359 p. + ap-
pendices.
Neary, C.R., and Highley, D.E., 1984, The economic importance of the rare
earth elements, in Henderson, P., ed., Rare earth element geochemistry: New
York, Elsevier, Developments in Geochemistry 2, p. 423-466.
Himmi, R. 1975. Outokumpu Oy:n Korsnäsin ja Petolahden kaivosten vai-
heita. Vuoriteollisuus 33, 35–38.
More than twenty REE minerals were identified and analyzed in detail with electron microprobe and
compared with analyses from literature. The minerals identified include phosphates (monazite-Ce), fluor-
carbonates (bastnaesite-Ce), hydrated carbonates (ancylite-Ce), hydrated aluminium silicates, allanite,
oxides, fergusonite and U-Pb rich minerals. The REE mineralization processes were complex in most tar-
gets and included both primary REE minerals and late stage hydrothermal processes.
GEOLOGIAN TUTKIMUSKESKUS 9
Table 1. The most important REE-mineral occurrences in Finland
Locality Rock type Dominant REE-mineral phases
Jammi, Sokli Carbonatite veins F-apatite, Sr-apatite, monazite, bastnasite, ancylite,
strontianite and baryte
Iivaara Nepheline-syenite Apatite and allanite
Otanmäki Alkaline-gneiss Fergusonite(Y), fergusonite(U), allanite and columbite
Katajakangas Alkaline schists and gneisses Ferugsonite-(Y), allanite, bastnasite-(Ce) and columbite
Korsnäs Carbonatite Apatite, monazite, carbocernaite, calcio-ancylite, bastnasite
and baryte
Uuniniemi Carbonatite and albitite Apatite, euxenite, Fe-columbite and Fe-thorite
Mäkärä Arkosic gneiss Euxenite, columbite, monazite, xenotime and zircon
Lamujärvi Syenite Apatite, calcite and monazite
Vanttaus Appinitic diorite Apatite, allanite, sphene and zircon
Lehmikari Appinitic diorite F-apatite, monazite, allanite, ancylite, thorite, zircon and
baryte
Palkiskuru Albitite Apatite, bastnasite, allanite, monazite, ancylite, davidite,
masuyite and sayrite,
Palovaara Albite-carbonate-rock Allanite, ancylite, bastnasite and xenotime
Honkilehto Carbonate -sericite schist Bastnasite, allanite, davidite, U-Pb minerals and U-Si
minerals
Kortejärvi Carbonatite Apatite, allanite, monazite, bastnasite and columbite
Laivajoki Silicocarbonatite Apatite, monazite, allanite and bastnasite
Suhuvaara Appinitic diorite Monazite and allanite
Eurajoki Rapakivi granite Bastnasite, monazite, Y-xenotime, thorite, Nb-Ta oxides and
zircon
Kovela Monazite- granite Th-monazite, thorite and REE-carbonate
Karhukoski
(Puumala)
Garnet-cordierite-mica
gneisses
Monazite and zircon
Virtasalmi Kaolin Monazite, kaolinite and zircon
GEOLOGIAN TUTKIMUSKESKUS 10
6 RARE EARTH MINERALS
Rare earth minerals contain one or more rare earth elements as significant metal constituents. REE min-
erals are usually found in association with carbonatite, alkaline to peralkaline igneous rocks, and in
pegmatites. Mantle derived carbonatite magma is also a carrier of the rare earths and enrichment can oc-
cur by fractionation. Hydrothermal deposits associated with alkaline magmatism contain a variety of rare
earth minerals. Commercially, the three main REE ore mineral species are: bastnaesite, a LREE
fluorocarbonate; monazite, a light/heavier rare earth phosphate that also contains radioactive thorium; and
xenotime, the HREE yttrium phosphate.
The following rare earth minerals were identified from different locations of Finnish bedrock with signif-
icant amount of rare earth elements: +3
6.1 Allanite-(Ce)
Formula (Ce,Ca,Y)2(Al,Fe +3 )3(SiO4)3(OH)
Crystal System monoclinic
Cleavage None
Color Brown, Black
Class Prismatic - Crystals Shaped like Slender Prisms
Fracture Brittle - Conchoidal
Hardness 6
Mineral Chemistry
(Otanmäki)
MgO Al2O3 SiO2 CaO FeO La2O3 Ce2O3 Nd2O3 ThO2 Total
2,9 7,5 24,1 10,4 6,6 13,6 24,9 9,0 3,1 99,1
Allanite is the most abundant rare-earth element (REE)-bearing mineral. It belongs to epidote group
(Armbruster et al. 2006). It is a common accessory in many types of evolved igneous rocks, as well as in
a variety of metamorphic rocks of both igneous and sedimentary origin (Table 1). Allanite shows a strong
preference for light rare-earth elements (LREE) over heavy rare-earth elements (HREE), while the REE
distribution in metamorphic allanite is highly variable and ultimately depends on the specific REE activi-
ty in the precursor rock (Giere & Sorensen 2004). Quantitative electron microprobe analyses yielded light
REE contents of 25–50 weight-% as REE- oxide, in studied allanites. The allanite-(Ce) typically occurs as
euhedral tabular or thin-tabular crystals. Allanite shows large variety of flaky and acicular crystal forms.
GEOLOGIAN TUTKIMUSKESKUS 14
6.2 Ancylite-(Ce)
Formula CeSr(CO3)2(OH)·H2O
Crystal System Orthorhombic
Cleavage None
Color Brown, brown red, colorless, gray, grayish pink
Class Orthorhombic- Dipyramidal
Fracture Brittle
Hardness 4.5
Mineral Chemistry
(Jammi)
CaO SrO BaO Nd2O3 ThO2 La2O3 Ce2O3 P2O5 F Total
1.1 23.2 0.5 8.5 3.1 12.7 32.8 0.1 0.7 83.6
Ancylite commonly has curved and rounded crystal shapes. In ancylite composition Ce predominates
over other rare earth elements. Ancylite-(Ce) is a rare mineral that can be found as an accessory mineral
in different rock types such as nepheline syenite and carbonatites. Ancylite-(Ce) usually occurs as well-
formed fine grained crystals. Sometimes crystals may have a pyramidal form. Ancylite occurs in Korsnäs
lead ore cavities (Kinnunen, 1976; Rehtijärvi & Kinnunen, 1979), in Savukoski Sokli carbonatites
(Vartiainen, 1975 and 1980) and in Lehmikari and Palovaara.
GEOLOGIAN TUTKIMUSKESKUS 16
6.3 Bastnasite-(Ce)
Formula (Ce, La)(CO3)F
Crystal System hexagonal
Cleavage Distinct to perfect and {010}
Color White, beige, pale pink, pale gray and black
Class Ditrigonal Dipyramidal
Fracture Irregular/Uneven
Hardness 4 - 4½
Mineral Chemistry
(Otanmäki)
SiO2 FeO P2O5 ThO2 Y2O3 Ce2O3 Nd2O3 La2O3 SmO Gd2O3 F Cl Total
0.80 2.03 0.28 0.65 0.65 34.09 9.47 16.08 0.83 0.74 6.2 0.06 77.0
GEOLOGIAN TUTKIMUSKESKUS 17
Bastnasite is the most important source of REE in carbonatite occurrences, and it commonly occurs in late
magmatic to hydrothermal assemblages. Bastnasite is the most important economic REE-mineral contain-
ing 60-70 weight-% of REE oxides. Bastnasite appears either as isolated crystals or as aggregates formed
with other accessory minerals. In the case of isolated crystals, bastnasite occurs as subhedral elongated
crystals (< 30 x 100 µm), generally within calcite. Bastnasite occurs also as acicular crystals and aggre-
gates of radiating individual crystals, as fracture fillings or in veins between other minerals. Bastnasite
has been found in Sokli, Otanmäki, Eurajoki, Korsnäs, Lehmikari, Honkilehto, Kortejärvi and Laivajoki.
GEOLOGIAN TUTKIMUSKESKUS 21
6.4 Cerite-(Ce)
Formula Ce9Fe3+
(SiO4)6(SiO3)(OH)4
Crystal System Trigonal
Cleavage None
Color White, brown, dark brown, cherry red, grey
Class Ditrigonal Pyramidal
Fracture Uneven - Flat surfaces
Hardness 5½
Mineral Chemistry
(Tana Belt)
SiO2 Al2O3 FeO P2O5 ThO2 Y2O3 Ce2O3 Nd2O3 La2O3 F Cl Total
6.5 1.7 1.1 1.1 0.1 0.0 76.8 1.4 0.0 1.4 0.1 91.0
Cerium is the most abundant of the rare earth elements, having average content of 46 ppm in the Earth's
crust. It occurs in allanite, monazite, bastnasite and cerite-(Ce) etc. Bastnasite is presently the second
most important source of cerium.
GEOLOGIAN TUTKIMUSKESKUS 22
6.5 Columbite and Tantalite
Formula [(Fe,Mn)(Ta,Nb) 2O6]
Crystal System Orthorhombic
Cleavage {010} Distinct
Color Black, Brownish black
Class Ditrigonal Pyramidal
Fracture Sub Conchoidal
Hardness 6
Mineral Chemistry
(Kaustinen)
FeO MnO TiO2 Nb2O5 Ta2O5 SnO Total
7.2 11.3 0.35 53.5 27.6 0 .1 99.9
The columbite-tantalite series minerals are the most common Nb-Ta species in rare-element pegmatites.
Columbite and tantalite have similar properties since they have the same structure and similar chemistry
(Ta and Nb are very similar elements). Tantalite is the more Ta-rich end member and columbite is the
more Nb-rich end member. Minerals of columbite-tantalite series are used primarily for the production of
tantalum capacitors, which are used in many electronic devices. It is also used in high temperature alloys
for air and land based turbines. Columbite-tantalite series minerals occur in various units of complex
pegmatites in Finland including Kaustinen pegmatite (Thair Al-Ani, et al., 2008) and in of the Eräjärvi
pegmatite (Seppo Lahti, 1987). Pegmatite in Kuortane Kaatiala contained large amounts of columbite.
Tons of columbite was processed in 1950-60 (Hietala, Satu 2012).
Complex zoning patterns occur in columbite-tantalite series minerals, which can be seen by backscattered
electron images. Variations in Nb and Ta content are readily observed as darker and lighter regions within
individual crystals. Oscillatory zoning is considered to be a primary feature, produced by magmatic
growth of columbite-tantalite (Cerny et al. 1992). In contrast, convolute and ‘patchy’ zoning are second-
ary features, which overprint the primary zoning. These secondary zones are thought to be produced by
an abundance of highly reactive residual fluids that subject pegmatite minerals to partial or complete re-
placement during the late stages of pegmatite formation (Cerny et al. 2004).
GEOLOGIAN TUTKIMUSKESKUS 26
6.6 Davidite
Formula (Ce,La)(Y,U)(Ti,Fe+3
) 20O38
Crystal System Hexagonal
Cleavage None
Color Brown, brownish black, red, black.
Class Pyramidal
Fracture Conchoidal - Uneven
Hardness 6
Mineral Chemistry
(Palkaskuru)
MgO SiO2 CaO TiO2 FeO Y2O3 La2O3 Ce2O3 ThO2 SrO ZrO2 V2O3 Cr2O3 PbO UO2 Total
0.1 0.0 0.3 44.1 16.9 0.6 3.1 2.8 0.1 0.9 0.4 3.1 11.3 1.4 5.6 91.4
Davidite from Palkaskuru is characterized by large zoned grains (up to 1mm in diameter) due to composi-
tional variation. Minerals most intimately associated with the davidite include: chromite, titanite, zircon,
allanite, monazite and pyrite. In Palkaskuru the main U-Pb rich minerals are davidite (Y) and
masuyite/sayrite, which contain UO2 (6.4 weight-%), PbO (1.7 weight-%) and UO2 (66.1 weight-%),
PbO (14.7 weight-%) respectively. These two minerals show zoned texture in studied Enontekiö davidite.
Whereas in Kuusamo (Honkilehto), two phases of U-rich minerals are recognized; firstly U-Pb rich min-
eral (richetite) contains 75 weight-% UO2, 20 weight-% PbO and 5 weight-% Y2O3 and FeO , secondly
the U-Si rich mineral (bijvoetite) contains less UO2 (~65 weight-%) with SiO2 (~15 weight-%). Inter-
growth of these two minerals has occurred to form cauliflower (kukkakaali in finnish) texture in most
studied U-Pb and U-Si phases.
GEOLOGIAN TUTKIMUSKESKUS 28
6.7 Euxenite-(Y)
Formula (Y,Ca,Ce,U,Th)(Nb,Ta,Ti) 2O6
Crystal System Orthorhombic
Cleavage None
Color Black, greenish or brownish
Class Dipyramidal
Fracture Conchoidal, Sub-Conchoidal
Hardness 5½ - 6½
Mineral Chemistry
Kuusamo (Honkilehto)
SiO2 TiO2 Fe2O3 CaO Y2O3 UO2 Ta2O5 Nb2O5 Total
5,8 1,3 1,0 4,2 19,5 4,6 1,0 37,6 93
Euxenite belongs to Rare Earth Oxides (REO). Other rare earth oxides such as fergusonite, aeschynite and
samarskite have very similar properties with euxenite; they are often associated with each other, compli-
cating the identification problem. Even the common oxide rutile, when found as larger grains can be
mixed optically with rare earth oxides. Euxenite is associated with quartz, feldspars, columbite, tantalite,
monazite and other rare earth minerals. Euxenite is used as an ore mineral for its rare earth metals and
uranium. Euxenite has been found in many locations in Finland, including Otanmäki, Uuniniemi,
Eurajoki, Mäkärä, and other places in Tana Belt.
GEOLOGIAN TUTKIMUSKESKUS 30
6.8 Fergusonite-(Y)
Formula YNbO4
Crystal System Tetragonal
Cleavage Poor/Indistinct
Color Grey, yellow, brown
Class Dipyramidal
Fracture Sub-Conchoidal
Hardness 5½ - 6½
Mineral Chemistry
(Otanmäki)
SiO2 FeO CaO UO2 ThO2 WO3 Ta2O5 Nb2O5 Y2O3 F Tot
2.1 1.5 3.2 2.0 2.0 1.5 0.2 37.6 23.0 0.9 91.0
Fergusonite-(Y) is the major host for Nb and Y. Grain diameter varies between 100-400 µm in studied
Finnish deposits. It fills fractures and forms replacement textures and inclusions in other minerals.
Fergusonite-(Y) is not chemically homogeneous; many crystals display growth zoning, with a core that is
brighter than the rim in the BSE images, which itself may consist of two separate zones. The bright core
marks enrichment in U and/or Th, and the gray colored rim a deficiency in these radioactive elements, but
high contents of Y and Nb instead. Irregular or patchy zoning as well as sector zoning are also observed
in some of the crystals. In Katajakangas alkaline gneiss, fergusonite-(Y) contains very fine grained allan-
ite (grain diameter 1-10 µm) inclusions. Sometimes fergusonite-(Y) may have an allanite overgrowth,
which appears dark in the BSE images. The diameter of these fergusonite grains ranges mostly between
100 and 200 μm, and they show corroded boundaries.
GEOLOGIAN TUTKIMUSKESKUS 33
6.9 Monazite-(Ce)
Formula (Ce,La,Nd,Th)PO4
Crystal System Monoclinic
Cleavage {001} Distinct, {100} Indistinct
Color Brown, Colorless, Greenish, Gray white, Yellow.
Class Prismatic
Fracture Conchoidal
Hardness 5 - 5½
Mineral Chemistry
(Jammi)
CaO P2O5 SrO Ce2O3 La2O3 Nd2O3 ThO2 Total
5.1 22.3 4.0 33.0 15.3 13.5 6.1 99.3
Monazite, (Ce,La,Nd,Th)PO4, is a common REE- mineral in many rock types and, as such, is an impor-
tant host for rare earth elements (REE) especially in placer deposits. Monazite has been earlier a primary
ore of cerium and lanthanum. All these metals have various industrial uses and are considered quite valu-
able. Thorium is a highly radioactive metal and could be used in future as a replacement for uranium in
nuclear power generation. Monazite is therefore an extremely important Th-ore mineral (Clark, 1993).
Monazite is widespread in Finnish bedrock, and best known from acid igneous and high grade metamor-
phic rocks and as detrital grains in Virtasalmi kaoline deposit; however, it is easily overlooked under the
microscope because of its general optical similarity to the more common zircon, which sometimes also
occurs as coarse grains. Significant amount of monazite has been observed in gold bearing gravels in
Lemmenjoki area.
BSE images of monazite from Kovela granite show large monazite crystals (< 200 μm) with complex
zoning, which reflects variation in chemical composition. Based on EMPA data, studied monazites be-
long mainly to Th-rich type (14.9-19.6 weight-% ThO2). LREE concentration is generally approximately
50% of the total cation proportion (exclusive of P) in studied monazites. Ce2O3-, La2O3-, Nd2O3-,
Pr2O3- and Sm2O3-contents are 26.6 weight-%, 9.6 weight-%, 9.5 weight-%, 2.5 weight-% and 1.5
weight-% , respectively.
GEOLOGIAN TUTKIMUSKESKUS 37
6.10 Parisite-(Ce)
Formula Ca(Ce,La) 2 (CO3) 3F2
Crystal System Trigonal
Cleavage {001} Distinct
Color Brown, Colorless, Greenish, Gray white, Yellow.
Class Prismatic, Acicular
Fracture Brittle
Hardness 4½
Mineral Chemistry
(Vanttaus)
CaO SrO UO2 ThO2 Y2O3 Ce2O3 Nd2O3 La2O3 Pr2O3 F total
5.5 0.3 0.1 1.6 0.4 33.5 8.7 17.5 4.5 5.9 78.0
Parisite, which is named for J.J. Paris, mine proprietor at Muzo, north of Bogota, Columbia, is one of the
few rare earth carbonate minerals. Parisite is closely related to three other distinct minerals; synchysite,
bastnasite and rontgenite-(Ce). Parisite is found in few places in Finland including Vanttaus appinitic dio-
rite and in Lumijärvi alkaline rocks. Back-scattered electron (BSE) images show that parisite occurs for
example as radial cavity filling in titanite or associated with allanite.
GEOLOGIAN TUTKIMUSKESKUS 39
6.11 Thorite
Formula ThSiO4
Crystal System Tetragonal
Cleavage poor
Color black, but also brownish black, yellow
Class Prismatic, rounded
Fracture conchoidal
Hardness 4½ - 5
Mineral Chemistry
(Vanttaus) SiO2 FeO CaO UO2 ThO2 Y2O3 Ce2O3 Nd2O3 Gd2O3 La2O3
P2O5 F Total
14.7 0.9 1.8 1.6 58.1 2.4 3.3 1.4 1.2 0.3
4.3 0.3 92.2
Thorite is the most common thorium mineral. Uranium and thorium are considered to be the primary
sources of the internal heat of the Earth through their radioactive decay. Specimens of thorite generally
come from pegmatites and volcanic rocks, hydrothermal veins, contact metamorphic rocks, and as small
grains found in detrital sands. Crystals are rare, but when found can produce nicely shaped short prismatic
crystals with pyramidal terminations. Remember, this is a radioactive mineral and should be stored away
from other minerals, which are subject to damage because of radioactivity and of course human exposure
should be limited!
Within Uuniniemi-Kuusamo Schist Belt, Fe-thorite was found in high amounts as isolated grains and also
as inclusions within monazite and apatite. Thorite is often anhedral and forms grain aggregates measuring
up to 200 μm in diameter. According to more than 20 microprobe analysis, the composition of the thorite
is characterized by SiO2 (~17.5 weight- %), ThO2 (~60 weight- %), FeO (10.5 weight- %) and UO2 (~3.5
weight- %). Concentrations of the light rare-earth elements (LREE) are less than 1.0 weight-%.
GEOLOGIAN TUTKIMUSKESKUS 41
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