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.

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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 6

Location map of REE-minerals in Finland

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.

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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.

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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.

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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).

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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.

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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.

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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.

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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.

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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.

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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-%.

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GEOLOGIAN TUTKIMUSKESKUS 41

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