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GEOLOGIAN TUTKIMUSKESKUS

7/2016

2.02.2016

Abundance of REE-bearing minerals in

carbonatite and lamprohyre dikes in Kaulus

area, Sokli Carbonatite Complex, NE

Finland

Thair Al-Ani and Olli Sarapää


7/2016

2.02.2016

GEOLOGICAL SURVEY OF FINLAND DOCUMENTATION PAGE

Date / Rec. no.

Authors

Thair Al-Ani

Olli Sarapää

Type of report

Archive report

Commissioned by

GTK

Title of report

Abundance of REE-bearing minerals in carbonatite and lamprohyre dikes in Kaulus area, Sokli Carbonatite Complex, NE

Finland

We report mineralogy of the samples collected from the trenches and the drill cores of the Kaulus target, southern side of the

Sokli carbonatite complex. The studied samples represent carbonatite and lamprophyre dikes of the Fenite zone. The miner-

alogy of the samples was examined by using XRD, MLA, EMPA, SEM and light microscope. X-ray diffraction analysis

show that weathered materials are mainly composed of quartz, feldspar, carbonates (calcite and dolomite), clay minerals

(mainly smectite) and variable amounts of goethite, aegirine tainiolite, phlogopite and monazite. Chemical analyses analy-

ses made by XRF and ICP-MS-methods contain 1.3-9.1 % REE:

MLA and SEM results indicate that monazite is the principal REE-phosphate and bastnäsite is the principal REE-carbonate

in the studied samples. REE-bearing minerals occur either as isolated grains or small aggregates consisting mainly of the

minute needles of crystals. Selected analyses indicate Ce as the most abundant REE-oxide up to 37-46% Ce2O3. Some

samples show high BaO and ThO2 values.

Keywords

Calcite, dolomite, goethite, smectite, tainiolite, monazite, bastnäsite, allanite, pyochlore, carbonatite, lamprophyre Sokli,

Kaulus

Map sheet

U542

Report serial

Archive report

Archive code

7/2016

Total pages

27

Language

English

Price

Confidentiality

public

Signature/name

Thair Al-Ani

Signature/name

Olli Sarapää


2.02.2016

Contents

Documentation page

1 INTRODUCTION 1

2 SAMPLES AND METHODS 1

3 MINERALOGY AND GEOCHEMISTRY 5 3.1 Drill core U5422014R30 5

3.1.1 Whole rock geochemistry 6 3.1.2 Mineralogical analysis by XRD 6

3.1.3 SEM Analysis and Interpretation 10 3.2 Drill core U5422014R38 12

3.2.1 Petrography 12

3.2.2 REE Minerals 12 3.3 Bedrock samples PAT2 and JVPY-2013 14

3.3.1 Mineral Liberation Analyzer (MLA) results 14 3.3.2 Detailed mineralogy by SEM-EDS 20

4 CONCLUSIONS 30

5 REFERENCES 30

6 APPENDICES 1 32 Appendix 1.

GEOLOGIAN TUTKIMUSKESKUS 1

2.02.2016

1 INTRODUCTION

This work describes mineralogy and alteration features of the REE-bearing crosscutting carbonatite and

lamprophyre dikes, and associated fenitic rock within Sokli/Kaulus area. The Sokli carbonatite complex

(ca. 360-380 Ma) in northeastern Finland is part of the Kola alkaline province and hosts an unexploited

phosphate deposit enriched in Nb, Ta, Zr, REE and U (Vartiainen 1980, Kramm et al., 1993, Korsakova

et al., 2012 ).

The carbonatite complex consists of the magmatic carbonatite core surrounded by the metacarbonatite

and the wide fenite aureole, altogether about 9 km in diameter. The late-stage carbonatite dikes in the

central fracture zone and in the fenite zone have high potential for REE mineralisation (Vartiainen, 2001,

Al-Ani and Sarapää 2013). Chemical analyses from the drill cores (R301 and R302) show that the car-

bonatite dikes, 0.5-1.0 m wide in fenites, are enriched in P2O5 (19.9 wt%), Sr (1.9 wt%), Ba (6.8 wt%),

Zn (0.3wt%) and have a high total REE content of 0.5-1.83 wt%, including 0.11-1.81 wt% LREE and

0.01-0.041 wt% HREE (Sarapää et al. 2013). Dominant REE-bearing minerals in the Sokli/Kaulus car-

bonatite dykes are REE carbonates, ancylite-(Ce), bastnäsite-(Ce), Sr-apatite, monazite, strontianite,

baryte and brabantite, which are enriched in LREE, P, F, Sr and Ba (Al-Ani and Sarapää, 2013). Minera-

logical and chemical evidence demonstrates that late stage magmatic and hydrothermal processes were

responsible for the REE mineralisation in the Sokli carbonatite veins and apatite and carbonate minerals

were replaced by various assemblages of REE-Sr-Ba minerals (Al-Ani and Olli Sarapää, 2014).

2 SAMPLES AND METHODS

The samples for mineralogical and chemical studies were selected from the recent drill core

U5422014R30 and U5422014R38, and outcrops from the old trenches of Rautaruukki Oy mapped by

Pertti Telkkälä (PAT-2013) and Juuso Pynttäri (JYPY-2013), see the studied area map in (Fig. 1). These

outcrop samples were selected by using a gamma spectrometer to find high thorium radiation. Table 1

gives descriptions of the studied rocks and the analytical methods.

Light microscope, XRD and Scanning Electron Microscopy (SEM) were used to identify mineralogical

compositions of the main carbonate minerals and REE-bearing phases. XRD-measurements was done by

Mia Tiljander in GTK Mineralogical laboratory at Espoo. MLA analyse were made at GTK Mintek Ou-

tokumpu by Tuula Saastamoinen. All the samples are dominated by calcite and dolomite with minor to

trace amounts of Fe-Ti oxides, pyrite and carbonates, K-feldspar, albite, alkaline pyroxenes, strontianite

and barite. REE-bearing phases are dominated by monazite, bastnäsite, ancylite and apatite, pyro-

chlore(Nb) and thorite (Th).

Three different groups of samples were prepared for the mineralogical studies (Table 1). The first

group, including four weathered carbonatite samples from the drill hole U5422014R30 (Fig. 2), were

pulverized for XRD analysis using a Siemens D500 diffract meter with a step size of 0.02° 2θ (and a

counting time of 1 s per step, applied over a range of 5–80° 2θ (Appendix 1). The mineralogical study of

these samples has been made by using a combination of X-ray diffraction (XRD) and scanning electron

microscopy (SEM) with an EDX system. These samples were chemically analyzed by Labtium Analytical

Laboratories (order 47667). The major and minor elements of drill cores were determined by XRF


2.02.2016

(Method 175X, 811L) and determination of the rare earth elements and trace elements by ICP-MS (Meth-

od 306PM) . The analytical data of representative samples are presented in Table 2. Rare earth element

(REE) data from the different carbonatite units have been plotted in chondrite normalized diagrams (nor-

malized to chondrite values of Boynton (1984) to visualize trends and signatures (Fig. 3)

Figure 1. Location of the studied drill holes and in the high density thorium aeroradiation map the Kaulus area.


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Figure 2. Black and brown weathered REE-rich carbonatite in the drill core U5422014R30.


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The second group of drill core samples (U5422014R38) include mafic fenite and porfyric carbonatite and

lamprophyre dikes, polished thin sections were prepared for light microscopic investigations and REE-

mineral identification by using a Scanning electron microscopy (SEM-BSE).

The outcrop samples, the third group (PAT, JVPY-2013) were studied for heavy minerals. Each sample

was separated by mechanical sieves into two grain-size fractions, including material greater than 90 µm

and 32 to 90 µm. Heavy minerals (minerals with density > 2.75 g/cm3) were separated from each fraction

with heavy liquids and prepared into polished sections for mineral and texture characterization. Mineral-

ogy of heavy-mineral fractions was determined through Mineral Liberation Analyser (MLA) to identify

and quantify minerals and to determine their association and distribution. The data of modal mineralogy

obtained by this Scanning electron microscopy (SEM) was used to identify the chemical composition

crystal morphology of REE-bearing and accessory minerals

Table 1. Application of different type of studied samples and lithological observations from Sokli/Kaulus area.

Sokli/ Kaulus Sample_ID Description Weathered carbonatite from the drill hole R30

analyzed by XRD and SEM

U5422014R30/ 4.40

Black weathered carbonatite, high in REE, Mn, Zn, Nb, Th, Fe, P

U5422014R30/ 7.40 Brown weathered carbonatite REE-rich U5422014R30/ 8.90, Dark brown weathered carbonatite REE-rich U5422014R30/ 14.40 Brown weathered carbonatite REE-rich Drill core samples analyzed by light microscopes and SEM

U5422014R38(12.4)

Fenitic amphibolite

U5422014R38(31.8) Dark brown carbonatite dike U5422014R38(49.35) Light green lamprophyre dike U5422014R38(55.40) Light green porphyric lamprophyre dike U5422014R38(66.85) Light brown lamprophyre dike U5422014R38(77.70) Greenish lamprophyre dike Trench sampling concentrate for heavy minerals

analyzed by light microscopes and SEM Samples were screened in two fraction 32 to 90 µm and +90 µm

PAT2-2013-3.1

Fine fractions (32-90 µm) Brown weathered carbonatite

PAT2-2013-3.1 Coarse fractions (+90 µm) PAT2-2013-7.1 Coarse fractions (+90 µm) Fenite PAT2-2013-8.1 Coarse fractions (+90 µm) Fenite JVPY-2013-14.2 Fine fractions (32-90 µm) Brown weathered carbonatite JVPY-2013-14.2 Coarse fractions (+90 µm)


2.02.2016

3 MINERALOGY AND GEOCHEMISTRY

3.1 Drill core U5422014R30

Four samples were selected from black weathered carbonatite, rich in Fe, P, Mn, REE, Zn, Nb and Th

for chemical and mineralogical X-ray powder diffraction, SEM-EDX and image analyses.

Table 2. REE, trace (ppm/306 PM), P, Fe (% 175X) and elements ratios of the R30 drill cores in Kaulus/Sokli

carbonatite.

Drillhole

R30

Sample (2-3) (3-4) (4-5) (5-6) (6-7) (7-8) (8-9) (9-10) (10-11 (11-12) (12-13) (13-14)

Ce 7600 10100 25600 52900 45300 12000 22700 14800 7080 5260 13800 10200

La 2950 4370 17500 33900 27200 7460 11900 7670 3800 2560 5970 3990

Dy 180 193 204 155 429 258 381 472 445 164 230 234

Er 51.1 54.3 56.9 45.2 111 77.4 112 117 106 41.7 60 63.3

Eu 178 208 234 277 378 245 470 420 329 175 253 213

Gd 445 502 605 747 1060 623 1150 1080 873 413 597 526

Ho 24.5 25.9 26.4 18.6 57.5 35.4 51.1 61.2 56.9 20.8 29.4 31.1

Lu 5.13 3.85 4.05 2.29 4.54 5.05 6.46 7.03 5.41 1.9 2.59 4.35

Nd 4200 4820 7560 12900 12000 5340 9760 7030 5210 3740 6390 5330

Pr 993 1200 2340 4300 3830 1460 2560 1750 1210 864 1580 1270

Sc 28.8 19.6 30 20.6 23.1 26.8 33.9 24.8 18.6 9.11 11.2 20.8

Sm 691 798 941 1280 1440 920 1740 1460 1070 654 1020 856

Tb 45.7 49.9 55 53.6 106 63 103 116 104 42.3 58.5 56.1

Tm 4.81 4.74 4.7 2.73 7.46 7.07 9.73 9.54 8.18 3.25 4.42 5.31

Sum_REE 17401 22357 55160 106597 91958 28532 50993 35044 20338 13955 30016 22810

Eu/Eu* 0.981 1.005 0.948 0.866 0.935 0.989 1.016 1.023 1.041 1.03 0.991 0.971

(La/Sm)N 2.685 3.445 11.698 16.66 11.882 5.101 4.302 3.305 2.234 2.462 3.682 2.932

(Ce/Sm)N 2.654 3.055 6.566 9.974 7.592 3.148 3.148 2.446 1.597 1.941 3.265 2.876

Nb 2050 6290 4430 33.6 445 55.6 360 43.8 43 65.7 138 1110

Th 256 260 576 1500 1200 448 708 488 368 292 648 575

Zn 4610 9460 10300 6720 6670 3910 5140 4410 3580 5460 8200 8740

Mn 23100 20800 12700 25200 13500 11200 25100 13600 9000 13500 16800 18000

P2O5% 7.93 6.12 7.74 5.37 11.60 17.90 17.20 18.70 21.00 19.60 16.80 12.10

Fe2O3% 22.00 30.40 29.30 13.60 24.30 16.00 17.20 22.40 15.10 13.90 19.90 27.60


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3.1.1 Whole rock geochemistry

Representative chemical analyses for trace and rare earth elements of weathered carbonatite samples from

drill hole R30 are given in Table (2). The studied carbonatites samples are characterized by high abun-

dances of REE and other elements such as, LREE 2.34 % (max 5.5 %), HREE 0.15 % (max 0.3 %), P2O5

10.8 % (max 21.0 %), Nb 0.3 % (max 1.7% XRF), Fe2O3 21.0 % (max 30.4 % XRF), Zn 0.5 % (max

1.0%) and Mn 1.9 % (Appendix 2).

Carbonatite samples show similar REE distribution (Fig. 3), characterized by light-REE enriched and

HREE-depleted patterns. The lack of a strong negative Eu anomaly suggests that silicate minerals may

have not played an important role for REE enrichment in Sokli carbonatites rocks, although apatite frac-

tionation may also have tended to offset the development of a negative Eu anomaly.

Figure 3. Chondrite-normalised REE patterns of the studied samples of drillhole R30.

3.1.2 Mineralogical analysis by XRD

The bulk mineralogy analysis of the studied samples from the Kaulus area, identified by using XRD are

composed of montmorillonite, aegirine, tainiolite, K-feldspar, goethite, quartz , albite and REE minerals

(mainly monazite). XRD data show the presence of montmorillonite as major clay mineral in most of the


2.02.2016

studied samples, as indicated by the presence of a 14-Å reflection that expands to 16-Å upon glycolation

and collapses to 10 Å upon heating. Some separated samples (not chemically analyzed and not shown in

Table 1) had moderate to minor abundances of other clays (besides chlorite or smectite) identified as

poorly crystalline smectite or mixed layer clays of d-spacing of 14 Å to 18 Å in the oven-dried (30°C)

particles, glycolated, and heated (350°C and 550°C) particles. The separation process was repeated until a

pure clay-mineral separate was achieved. Other associated minerals are carbonate minerals as calcite,

dolomite, strontianite and apatite, and tainiolite, goethite and aegirine in some samples.

Following the mineral phases were identified by XRD (Tiljander 2014: EMA-2014-81-X):

1. U5422014R30 / 4.40 (X14-191):

The sample is composed mainly of montmorillonite, goethite, aegirine and monazite. The X-ray diffrac-

tograms of Mg-saturated randomly oriented clay samples given in (Fig. 4), show an abundance of mont-

morillonite, after EG-treatment the peak of 13.5 Å moved to 16.7 Å.

Figure 4. XRD pattern of sample U5422014R30/ 4.40


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2. U5422014R30 / 7.40 (X14-192-1):

The sample is composed mainly of montmorillonite, aegirine, mica (tainiolite and/or phlogopite), K-

feldspar, goethite, and possibly strontianite and quartz. Sample separation was made from the lighter part

(X14-192) and the darker part (X14-192-1) of the material. No difference found between the diffracto-

grams of XRD patterns. EG was added to the darker sample (X14-192-1-1) and the peak moved from

13.3 Å to 16.7 Å (Fig. 5).

Figure 5. XRD pattern of selected sample U5422014R30/ 7.40


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3. U5422014R30 / 8.90 darker material (X14-193):

The sample is composed mainly of K-feldspar, goethite and REE-phosphates monazite and bastnäsite

(Fig. 6).



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4. U5422014R30 / 14.40 (X14-194):

The sample is composed mainly of quartz, plagioclase, K-feldspar, calcite and possible Ca-Mg-

phosphate. Phosphates and carbonates were difficult to identify, because the high amount of other mineral

phases (Fig. 7). To get more accurate identification it is recommend studying the samples with SEM or

EPMA.


3.1.3 SEM Analysis and Interpretation

In addition, selected samples were studied with scanning electron microscopy (SEM) and combined with

bulk and clay XRD analyses. Thin section of each sample is examined by SEM to highlight the occur-

rence, distribution, textural features of REE-minerals. Energy dispersive X-ray (EDX) analysis is also

carried out to get the elemental composition of the samples.

The SEM-BSE observations and ED’s microanalysis revealed the occurrence of euhedral to subhedral

micro-size crystals of resistant heavy minerals disseminated in the clay and weathered materials. Mona-

zite is the principal REE-phosphate present in the investigated rocks (Fig. 8a-d). Selected analyses indi-

cate Ce2O3 as the most abundant RE element, with the concentration going up to 37% in most samples;

that particular sample shows higher BaO values (3.8%). Despite the non-uniform composition of mona-

zite, no systematic variation is indicated for the studied samples. In contrast, smectite forms the matrix of


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these rocks, exhibiting radial textures (Fig.8b); it may also occur in association with calcite, goethite,

chlorite and barite.

Figure 8. Back-scattered electron images of monazite grains and barite within clay materials from Sokli/Kaulus

area.


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3.2 Drill core U5422014R38

The drill core R38 from Kaulus penetrates fenites, silico-carbonatite and porphyric lamprophyre dikes.

The mineralogy of the selected samples was examined by using SEM and light microscopy.

3.2.1 Petrography

The studied area is mainly composed of fenites and silico-carbonatite, In the surface part they are often

strongly weathered. Basically these rocks consist of silicate, apatite and carbonate minerals. Carbonatites,

often brecciated, fine to coarse-grained, brown-yellowish in colour, consist mainly of calcite, dolomite

and apatite. Goethite and brown biotite grains in fenite occur abundantly as poikiloblastic plates inter-

grown with pyroxene, olivine companied by albite and potassium minerals (K-feldspar). The amphibole

also occurs as acicular to fibrous, anhedral to euhedral crystals which are colourless to pale green in col-

our. The amphibole is likely the sodium bearing tremolite and associated with goethite. Aegirine-augite is

a common sodic pyroxene mineral in fenitic rocks. They are typically found in association with other so-

dic- alkali amphiboles hornblende, glaucophane and richterite. Aegirine occurs as dark green slender

prismatic crystals and distinctly pleochroic – emerald green to yellowish green. A common, widespread,

rock-forming mineral, mica is a significant mineral in the studied rocks. Mica occurs as irregular, tabular

to ragged grains and is characterized by a noticeable pale yellow brown (phlogopitic) core and dark red-

brown (biotitic) rim. Locally, phlogopite flakes are associated with greenish brown chlorite as rich in iron

content.

3.2.2 REE Minerals

Several minerals containing REE, Sr and/or Ba as major elements have been identified in the studied

Sokli/Kaulus samples. The SEM-EDS technique was used to identify the main and REE minerals in stud-

ied sample. The main constituents of the studied lamprophyre dikes are calcite, strontium calcite, dolo-

mite apatite and REE minerals. The principal and most widespread REE minerals at Kaulus carbonate

phosphates (monazite), Ca ± Ba fluocarbonates (bastnäsite), hydrous carbonates (ancylite), and silicates

(allanite and britholite). Monazite-(Ce) occurs most commonly in the form of microcrystalline, sporadic,

isolated equidimensional crystals and associated mainly with calcite, dolomite and chlorite (Fig. 9a-d) .

The crystal habit of bastnäsite in the studied carbonatites samples appears to be acicular or needle-shaped

forming either in radial accumulations or intricate cross-cutting grids within a variety of minerals such as

chlorite and calcite (Fig. 9e,f). Monazite and bastnäsite occur as irregular grains and nodules frequently

intergroup with REE–Sr–Ba-bearing minerals or it’s found as filling the fractures within rocks.

All REE minerals in the Sokli/Kaulus carbonatites are strongly enriched in light REE. Ce is the principal

light REE, however, a La-rich mineral (ancylite-(La)) is also known from the Sokli carbonatites (Thair Al

Ani et al., 2011). The composition of monazite-Ce from studied samples contains between 28.5 and 31.4

wt% Ce, 15.5 and 18.1 wt% La, 5 and 9 wt% Nd. Bastnäsite-Ce is relatively high with Ca 6.5-8.0 wt %

and Sr present only as traces in few sample 2.3 wt %, with high content of Ce more 40 wt%, La 33 wt%,

Nd 9.2 wt% and F 13 wt%.


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Figure 9. BSI of REE with associated minerals, (a, b) monazite overgrowth within calcite and associated with

large assemblage of aegirine, (c) monazite in dolomite, (d) acicular crystals growth of monazite within calcite, (e)

euhedral bastnäsite grains filling the vugs and fractures within calcite, (e) acicular crystals growth of monazite

within chlorite in lamprophyre dikes.


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3.3 Bedrock samples PAT2 and JVPY-2013

3.3.1 Mineral Liberation Analyzer (MLA) results

This group consisted of four samples were collected from the old excavations made by Rautaruukki Oy.

The samples were processed at GTK Mintec/Outokumpu . Each sample was separated by mechanical

sieves into three grain-size fractions, including material greater than 90 µm, 90-32 µm and 32 µm (Table.

3). Heavy minerals (minerals with density > 2.75 g/cm3) were separated from each fraction with heavy

liquids and prepared into polished sections for mineral and texture characterization.

Table 3. Sieving analysis results of the Sokli/Kaulus excavation samples.

Sample_ID PAT2-2013-3.1 PAT2-2013-7.1 PAT2-2013-8.1 JVPY-2013-14.2

Grain size <0,5 mm <0,5 mm <0,5 mm <0,5 mm

Fine fraction( µm ) weight (g) Conc. (%) weight (g) Conc. (%) weight (g) Conc. (%) weight (g) Conc. (%)

>90 30.7 54.7 54.7 47.6 53.9 45.4 30.3 34.8

90-32 9.9 17.6 20.6 17.9 21.0 17.7 14.4 16.5

<32 15.5 27.6 39.7 34.5 43.7 36.8 42.4 48.7

Total 56.1 100.0 115.0 100.0 118.6 100.0 87.1 100.0

Detailed mineralogical investigations were carried out by MLA analysis on selected samples, the data

document enrichment factors (wt.% concentration in bulk sample, as given in Tables 3, 4). The data of

heavy mineral fractions of the test materials are representing two different grain-size classes (+90 and 32-

90 µm). The results for each grain size are combined from six individual subsamples, and their mineral-

ogy was determined by an automated SEM-EDS technique (see section Analytical methods). The indica-

tor mineral species of the heavy density fractions are highlighted in Tables 3 and 4 as grey color.

The composition of indicator heavy mineral varies greatly in the concentrates, from 0.1% to over 22% by

studied samples in the Kaulus area. The dominant heavy mineral is bastnäsite, making up 17% and 16%

of analysed grains, in studied sample PAT2-2013-3,1 in both fractions (>90 and 32-90 µm). The next

most common REE-mineral is monazite, with maximum concentrations of 12.9% of heavies and 0.11.2%

of all scanned minerals in sample PAT2-2013-3,1 (Fig. 10 a). Other REE minerals, such as allanite,

birtholite, cerphosphorhuttonite, ancylite, thorite, pyrochlore and Ba minerals, are dominated but in

lower percentages.

The analysis data of the studied sample JVPY-2013-14,2 (Fig. 10b), showing the dominant heavy mineral

is tainiolite (Li), making up to 8% in coarse fraction (>90 µm) and 6% in fine fraction (32-90 µm) of the

studied sample. The common mineral is ferroselite (Se), with maximum concentration 3.8% in fine frac-

tion (32-90 µm). The most common REE-mineral is monazite, with maximum concentrations of 3.5 % in


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fraction (>90 µm) and 3% in fine fraction (32-90 µm). Other REE minerals, such as rutile (Nb), allanite,

britholite, bastnäsite cerphosphorhuttonite, thorite, microlite (Ta), pyrochlore and Ba mineral, are

founded, but they have very low percentages.

The graphs (Figure 11a) illustrates the compositional variation of the concentrates numbers of grains ana-

lysed. In the diagram, the abundances of selected REE-minerals are bastnäsite (23 930 grains) and mona-

zite (21 113 grains) in fine fraction (32-90 µm) of selected sample PAT2-2013-3,1 (Fig. 8a). The frac-

tions are also dominated by such as ferrosillite (Se), barite (Ba), allanite (La), cerphosphorhuttonite (Ce,

Th), apatite and birtholite (Ce). The fine fraction of the selected sample PAT2-2013-3,1 shows more con-

centrated in heavy minerals than other selected samples. They also contain less than 500 of each mineral

grains, such as rutile, psilomelane (Ba), tainolite (Li), ancylite (La), thorite (Th), schorl (B) and pyro-

chlore (Nb).

The graph of the studied sample JVPY-2013-14,2 (Fig. 11b) shows, the dominant heavy mineral is tainio-

lite (Li), making up to 4 400 grains in coarse fraction (>90 µm) and up to 10 540 grains in fine fraction

(32-90 µm). The common minerals are ferroselite(Se) with maximum 5 112 grains, monazite with

maximum 3 384 grains, allanite with maximum 1 478 grains , rutile (Nb) with maximum 807 grains and

psilomelane (Ba) with maximum 527 grains. Other minerals, such as britholite, zektzerite (Li, Zr), cer-

phosphorhuttonite (Ce, Th), bastnäsite, microlite (Ta), pyrochlore (Nb) and thorite, are extremely rare.


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Table 4. Modal mineralogy of studied samples PAT2-2013 determined by MLA on Polished sections (indicator

heavy mineral labeled as grey color). Measured at GTK Mintec by Tuula Saastaoinen.

Mineral PAT2-2013-3,1 +90

µm PAT2-2013-3,1 32-90

µm PAT2-2013-7,1 +90

µm PAT2-2013-8,1 +90

µm

Wt%

Grain Count

Wt% Grain Count

Wt%

Grain Count

Wt% Grain Count

Bastnäsite 17.23 7 044 16.3 23 931 0.45 193 1.43 549

Goethite 14.9 7 167 22.3 41 086 14.5 7 366 7.46 3 711

Monazite 11.20 4 821 12.9 21 113 6.13 2 697 9.07 3 653

K-feldspar 9.07 6 487 7.53 20 584 3.89 2 931 1.63 1 206

Fe-oxides 6.43 2 285 4.05 5 508 6.49 2 432 7.15 2 623

Albite 8.80 6 111 6.45 17 090 2.18 1 594 0.57 406

Hornblende 4.46 2 828 3.0 7 292 0.74 495 0.26 168

Goethite(Mn)+Zn 4.13 1 978 6.97 12 833 47.1 23 930 60.1 29 879

Biotite 3.01 1 780 1.55 3 503 4.68 2 918 1.43 875

Ferrosilite (Se) 2.98 1 473 3.21 6 068 0.24 123 0.60 306

Barite (Ba) 2.55 1 042 2.18 3 411 - - - -

Allanite (La) 2.78 1 724.00 1.00 2 524 0.07 47.00 0.01 18

Aegirine 2.20 1 143 1.33 2 644 0.07 40 0.02 12

Quartz 2.19 1 525 1.56 4 160 1.80 1 324 0.69 495

Cerphosphorhuttonite (CeTh) 1.76 639 2.57 3 564 0.48 184 0.06 21

Chlorite 1.47 914 0.71 1 688 0.37 245 0.47 304

Stilpnomelane 1.39 911 1.22 3 050 0.15 101 1.63 1 101

Aluminoceladonite 1.00 634 0.51 1 228 0.07 47 0.01 7

Britholite (Ce) 0.84 363 1.13 1 853 0.13 61 0.02 8

Fayalite-deform 0.78 324 0.87 1 385 0.12 52 0.43 186

Richterite 0.33 194 0.23 524 0.03 17 0.05 29

Psilomelane 0.27 110 0.34 525 6.71 2 850 0.75 313

Riebeckite 0.21 114 0.26 539 0.05 31 0.03 19

Augite 0.18 98 0.07 144 0.00 1 - -

Rutile+Nb 0.18 77 0.25 407 0.02 7 0.00 2

Arfvedsonite 0.18 94 0.13 268 0.02 10 0.00 1

Psilomelane (Ba) 0.16 64 0.20 313 2.51 1 064 0.08 32

Tainiolite (Li) 0.16 102 0.10 238 0.12 80 0.04 24

Muscovite 0.16 101 0.12 285 0.04 29 - -

Aegirine-augite 0.13 67 0.06 129 0.00 2 - -

Ilmenite 0.12 48 0.14 205 0.02 10 - -

Ancylite(La) 0.05 26 0.08 154 - - - -

Almandine 0.05 20 0.02 41 0.02 8 - -

Thorite (Th) 0.03 10 0.09 112 - - 0.00 1

Pyrolusite 0.03 10 0.01 10 - - - -

Actinolite 0.02 15 0.04 90 0.02 10 0.00 1

Epidote 0.02 11 0.10 196 0.00 2 0.01 4

Tremolite 0.02 11 0.04 82 0.04 25 0.00 3

Rutile 0.02 10 0.03 46 0.01 6 0.00 1

Serpentine 0.01 7 0.01 16 - - - -

Schorl (B) 0.01 5 0.01 18 0.00 1 - -

Hyalophane 0.01 5 0.01 16 - - - -

Pyrochlore (Nb) 0.01 5 0.04 63 0.15 72 0.73 320

Pyrite 0.01 2 0.00 2 - - - -

Cummingtonite 0.00 2 0.02 42 0.01 3 0.00 1

Apatite 0.00 2 2.02 52 0.07 28 7.56 2 171

Total 100 51 569 100 189 846 100 51 424 100 605


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Figure 10. Mineral composition of indicator heavy mineral concentrates produced from the Sokli/Kaulus samples

(a, b). Density >2.75 g·cm-3, grain size <90 µm and 32-90 µm, PM = polished epoxy mount, GM = grain prepa-

rate, Data : Mineral Liberation Analyser (MLA), GTK Mintec/Outokumpu.

(a)

(b)


2.02.2016

Table 5. Modal mineralogy of studied samples JVPY-2013-14,2 determined by MLA on polished sections (indica-

tor heavy mineral labelled as grey colour)

.

Mineral JVPY-2013-14,2 +90 µm JVPY-2013-14,2 32-90 µm

Wt% Grain count Wt% Grain count

Goethite 35.55 13788 48.29 63492 K-feldspar 16.6 9 731 13.2 26 040

Tainiolite (Li) 8.35 4 403 6.0 10 547

Quartz 7.58 4 322 2.91 5 586

Albite 7.9 4478 4.41 8394 Stilpnomelane 2.93 1 565 2.92 5 248

Ferroselite(Se) 3.3 1 329 3.8 5 112

Monazite (Ce) 3.5 1 195 3.0 3 384

Goethite (Mn) 2.07 814 2.23 2 951

Goethite (Mn)+Zn 1.89 743 3.10 4 114

Fayalite 1.98 675 2.24 2 576

Riebeckite 1.25 552 1.39 2 065

Rutile+Nb 1.0 346 0.7 807

Aegirine 0.75 319 0.70 1 008

Allanite (La) 0.7 261 1.10 1 478

Hornblende 0.58 299 0.70 1 212

Psilomelane (Ba) 0.62 204 0.47 527

Biotite 0.40 192 0.45 735 Ilmenite 0.54 172 0.45 483

Aluminoceladonite 0.20 102 0.16 278

Chlorite 0.24 116 0.34 538 Britholite (Ce) 0.24 86 0.12 141

Muscovite 0.15 78 0.13 237

Richterite 0.12 57 0.17 272

Apatite 0.07 33 0.07 112

Actinolite 0.06 30 0.06 102

Zektzerite (Li, Zr) 0.05 25 0.04 68

Arfvedsonite 0.06 24 0.04 58

Epidote 0.05 22 0.15 226

Cerphosphorhuttonite (Ce, Th) 0.06 19 0.09 87

Augite 0.04 18 0.01 10

Staurolite 0.04 17 0.02 28

Bastnäsite (Ce) 0.06 17 0.05 51

Mascovite 0.03 15 0.02 42

Aegirine-augite 0.03 13 0.01 8

Baddeleyite 0.04 11 0.06 55

Almandine 0.03 9 0.03 32

Microlite (Ta) 0.03 8 0.06 54

Tremolite 0.01 4 0.03 49

Serpentine 0.00 2 0.00 5

Pyrochlore(Nb) 0.01 2 0.02 25

Nepheline 0.00 1 0.00 2

Zircon 0.00 1 0.02 22


2.02.2016

Figure 11. The main mineral phases of the heavy mineral concentrates (>1%), grain size <90 and 90-32µm frac-

tions from the Sokli/Kaulus samples (a, b).

(a)

(b)


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3.3.2 Detailed mineralogy by SEM-EDS

Detailed mineralogical investigations were carried out by FE-SEM-EDS on selected samples that have

been analysed by MLA for trace elements. Accessory and REE minerals are challenging and require a lot

of manual SEM-EDS (scanning electron microscope + energy dispersive spectrometer) work to analyze

the selected individual grains for chemical composition. The searching for and the analysis of the indica-

tor minerals can be also automated by using a modern SEM and suitable software. The analyses are done

from the polished sections of the heavy mineral concentrates. The EDS chemical analysis and SEM im-

ages of the various heavy mineral particles separated from >90 to 32 µm fractions show in Figures (12-

18). The majority of the heavy mineral separates are dominated by bastnäsite, goethite, monazite, K-

feldspar, Fe-oxides, albite, hornblende and tainiolite.

Heavy mineral of studied samples from Kaulus/Sokli area contain several type of REE-bearing. REEs are

mainly in bastnasite and monazite, but at least three other REE-bearing minerals have interesting distribu-

tions in the studied samples as allanite, britholite, cerphosphorhuttonite, ancylite, thorite, pyrochlore

xenotime and apatite (Tables 4, 5).

Bastnäsite is the main REE-bearing mineral identified in the sample PAT2-2013-3,1 both size fractions.

For comparison, the high concentration of bastnäsite was observed in the fine fraction (32-90 µm) of

sample PAT2-2013-3.1, containing 234931 bastnäsite grains, while only 7 044 grains counted in the

coarse fraction>90 µm (Table 4). Many of bastnäsite grains from the heavy mineral particles separated

from >90-32 µm fractions of the studied samples have been analysed by SEM, to investigate the size,

morphology and chemical composition of the grains. Bastnäsite appears as isolated crystals or thin-

tabular crystals, shows large variety of flaky/acicular/needle-like and aggregates of radiating individual

crystal habits forms elongated crystals (100 x 300 μm), though it can also form rounded hexagonal or sub

rounded crystals (Figures 12, 13). Bastnäsite is commonly associated with allanite and goethite, with

which it may be intergrown. Also, inside of the bastnäsite-(Ce) there occur small bright grains of thorite,

with ~ 60 wt% Th2O3 (Figures 12a-d). The majority of bästnasite grains in the studied samples are

strongly enriched in the LREE with approximately 70 wt% REE in its structure, as Ce (36.5 wt%), La

(32.5 wt%) and Nd (9.5 wt. %). The replacement of bastnäsite and allanite are noted in most of the stud-

ied bastnasite grains and causing increasing of REE content. The allanite-(Ce) is quite commonly attacked

by F-rich fluids and transformed into REE fluorcarbonates minerals, most often into bastnasite-(Ce) see

Figures (12c-d). Allanitization process of REE carbonates can form on bastnäsite-(Ce) and this transfor-

mation process is reversible and maybe causes decreasing of REE contents. Allanite-(Ce) is formed under

conditions with higher SiO2 activity and higher concentrations of Al, Ca and Fe than that the conditions

favourable for the crystallization of the other REE-silicates shown above.


2.02.2016

Figure 12. Back-scattered electron (BSE) images of REE mineral from sample PAT2-2013-3.1 (a-d) Bastnäsite

crystals have a distinctly lamellar structure, acicular aggregate and irregular aggregates (e, f) Replacement of bast-

näsite by acicular aggregate allanite.


2.02.2016

Figure 13. Back-scattered electron (BSE) images of REE mineral from sample PAT2-2013-3.1 (a-c) Spheri-

cal growths of acicular bastnäsite crystals (d) Replacement of bastnäsite by acicular aggregate allanite, (e) Spheri-

cal to subrounded aggregates of allanite associated with bastnäsite and iron oxides (f) subhedral monazite crystal

associated with bastnäsite.


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Similarly the monazite crystals more abundance in the fine fraction (32-90 µm) of sample PAT2-2013-3,1

(more than 21 110 grains) than in the coarse fraction (>90 µm) of the same sample (4 820 grains). Mona-

zite considered as the main REE-minerals in the sample PAT2-2013-8,1 (more than 3 650 grains) and in

the sample PAT2-2013-7,1 (2 697 grains) (Table 4). The selected monazite grains for searching and

analysis in studied samples tend to appear as rounded to subrounded, ranging from 50-300 µm in size

(Figures 13, 14). The chemical composition of monazite-(Ce), determined with SEM-EDAX is:

P2O5=33.2-38.0, CaO=3.9-8.2, Ce2O3=33.5-45.0, La2O3= 24 - 33.6, Nd2O3= 8.0-14.2 (%wt). Also,

some monazite grains are observed with elevated Th content (5.6- 20.0 wt%), or with high content of Ba

(5 wt%) as seen in many studied samples.

In most studied samples the monazite crystals occur in various shapes and sizes, such as radial fibrous

aggregates and then grading completely into a dendritic network (Figures. 12a-d). Monazite crystals occur

as acicular, columnar and radial aggregates and commonly associated with iron-oxides, barite and chlorite

(Figure 13e, f and Figure 14 a, b). In some studied samples the monazite occurs completely as spherical

aggregates or as clustering crystals (Figure. 15a, b).

In some cases, grains of monazite and bastnasite are characterized by presence of Th, REE-rich mineral,

showing clear and bright grains called as britholite. Britholite primarily grew directly on the surface of the

monazite or bastnäsite grains. This embayed contact between britholite and monazite-bastnäsite may be

the product of a reaction between F-, P-, REE-enriched fluid and the silicate minerals (Halden & Fryer

1999). The monazite shows a relatively high Th and Ca content: 14.6-18.9 % ThO2 and 1.4-3.4 % CaO.

Although this indicates the dominant britholite substitution with monazite, britholite occurs as irregular

forms and visible as small bright inclusions in the monazite and bastnäsite (Figures 15 a-e). The chemical

composition of britholite, determined with SEM-EDAX is: 1.4-3.4 % CaO, 11.0-18.54 % La2O3, 26.4-

32.5% Ce2O3, 20.5-38.0 % ThO2, 14.6-18.9 % SiO2, 4.5-6.2 % P2O5, 2.4-9.3 % Nd2O3, 0.50 % F.

Several other REE minerals have interesting distributions in some studied samples includes cerphos-

phorhuttonite (Ce, Th), Pyrochlore(Nb), ancylite(La), and thorite. Pyrochlore (commonly comprising a

U–Ta-rich and Nb-bearing rutile) typically occurring as scarce minute crystals, composed predominantly

of sector-zoned prismatic crystals measuring of 50-100 µm (Figure 16e, f).

Other distinctive heavy minerals were counted by MLA in minor amounts or only in a few samples such

as Ferroselite(Se), zektzerite (Li, Zr), aegirine, augite riebeckite, perovskite, aluminosilicates, microlite

(Ta), psilomelane (Ba), schorl (B) and rutile (Ti, Nb). Aluminosilicates (used here in to refer to kyanite,

sillimanite, and andalusite) were abundant in some studied samples. These minerals occurred at 1-2% of

the individual heavy mineral fractions (90-32 μm) see Tables (4, 5). Goethite, albite, chlorite and ae-

girine-augite are generally present (and locally abundant) in the studied samples. Distribution and Mor-

phology of the minerals are shown in Figure (17a-f).

The most abundant heavy mineral in the studied sample JVPY-2013-14,2 is tainiolite, which was occurs

in abundance in coarse fraction (>90 µm) as 8.35 wt% with 4 403 grains and in fine fraction (32-90 µm)

as 6.0 wt% with 10 547grains see Tables (5). While in studied samples PAT2-2013, tainiolite was ob-

served in minor amounts with many hundred grains and less than 1 wt% of the individual heavy mineral


2.02.2016

fractions. Over 500 tainiolite grains from the heavy mineral particles separated from >90-32 µm fractions

of the studied samples have been analysed by SEM, to investigate the size, morphology and chemical of

the tainiolite grains. Tainiolite appears as aggregates of acicular or flaky crystals closely spaced to form

elongated crystals (50 x 200 μm), in most studied samples (Figure 18a-f). The chemical composition of

Li-bearing phase (Tainiolite), determined with SEM-EDAX is: 5-9.8% K2O, 4-16wt% MgO, 54-59%

SiO2, 1-2.2% Al2O3, 2-5.4wt% BaO, 2-6% F (Li2O not detected by SEM, but around 4wt%). A similar

mineral is referred to as tainiolite in literature and was described for the first time in 1938 in the alkaline

district of Magnet Cove, USA, by Miser and Stevens (Foster 1960, Erd et al. 1983).


2.02.2016

Figure 14. Back-scattered electron (BSE) images of REE mineral from sample JVPY-2013-14.2 (a-d) Irregular

forms of monazite grains, intergrowth with thorite and associated with chlorite, (e) Monazite surrounded by pris-

matic iron oxide mineral, (f) Needles of monazite growth within chlorite.


2.02.2016

Figure 15. Back-scattered electron (BSE) images of REE mineral from sample JVPY-2013-14.2 (a-e) Spherical to

ellipsoidal forms of monazite grains, intergrowth with small white bright thorite grains (britholite) inside monazite


2.02.2016

Figure 16. Back-scattered electron (BSE) images of REE mineral from samples PAT2-2013-8.1 and PAT2-2013-

7.1 (a, b) Multiple bastnäsite-(Ce)grains grow marginally and on the cracks filling within barite and monazite,

(c, d) Spherical aggregates of monazite, (e, f) Prismatic and zoning crystals of pyrochlore.


2.02.2016

Figure 17. Back-scattered electron (BSE) images of selected accessory mineral from sample JVPY-2013-14.2, (a)

Zoning and banded goethite, (b) Chlorite plate contains white grains of monazite ( c) Needle-like crystals, pris-

matic crystal of aegirine, (d) Rutile showing two episodes of oscillatory zoning(e) Prismatic crystal of aegirine, (f)

bladed albite crystal.


2.02.2016

Figure 18. Back-scattered electron (BSE) images of tainiolite mineral from sample JVPY-2013-14.2, (a-d) Tainio-

lite appears as aggregates of acicular or flaky crystals closely spaced to form elongated crystals(50 x 200 μm),

(e, f) Acicular crystals aggregates of tainiolite rich in barite.


2.02.2016

4 CONCLUSIONS

Fourteen samples from the southern part of Sokli/Kaulus area were submitted for mineralogical XRD and

MLA analysis and also analyzed by SEM. The samples consist bedrock samples from old trenches and

drill cores from R30 and R38. The samples are representing REE-rich carbonatite dikes and lamprophyre

dikes taken from thorium-anomalies in the Fenite Zone of Sokli.

The mineralogical and petrographical of studied carbonatic rocks and fenites show that, most of feldspars

in the primary material are replaced by albite and amphiboles are replaced by sodic varieties such as rie-

beckite and arfvedsonite, quartz is progressively removed. Other marks of fenite include growth of apa-

tite, carbonate minerals and goethite. Process of this type of metasomatism is often called ‘fenitization’.

In addition to common heavy minerals, the feature analyzer shows monazite, bastnasite, allanite, ancylite

and birholite are typical REE-bearing in the heavy mineral fractions of the studied carbonatite dikes.

Many of them were found in even high concentrations such as bastnäsite (16.3%), monazite (12.9%),

birtholite (1.3%), allanite (1%) and ancylite (<1%) of heavy minerals in the some selected samples. The

main lithium-bearing minerals include tainiolite (Li) was found in high concentrations (8.3%) in the sam-

ple JVPY-2013-14, 2.

The REE prospect contains total concentrations of Ce, La and Nd, ranging from 40 to 60 wt%, which are

present in monazite bastnäsite and allanite minerals that formed during the late stages of carbonatite em-

placement. Carbonatites - ranging in composition from calcio-, magnesio- to ferro-types - and mica-rich

rocks.

5 REFERENCES

Al-Ani Thair & Sarapää Olli 2013. Mineralogical and geochemical study on carbonatites and fenites

from the Kaulus drill cores, southern side of the Sokli Complex, NE Finland, Geologian tutkimuskeskus,

arkistoraportti, 145/2013.

Al-Ani, T. & Sarapää, O. 2014. REE‐minerals in carbonatite, alkaline and hydrothermal rocks, northern

and central Finland. ERES2014: 1st European Rare Earth Resources Conference|Milos|04‐07/09/2014,

333-342.

Erd RC, Czamanske GK & Meyer CE. 1983. Taeniolite an uncommon lithium-mica from Coyote

Peak County, California. The Mineralogical Record 14: 39-40.

Foster, M.D. 1960. Interpretation of the composition of lithium micas. U.S. Geol Surv, Prof. Paper 354

E, 115-147.

Kramm, U., Kogarko, L.N., Kononova, V.A., Vartiainen, H. 1993. The Kola Alkaline Province of the

CIS and Finland: Precise Rb–Sr ages define 380–360 Ma age range for all magmatism. Lithos 30, 33-44.

Korsakova, M., Krasotkin, S., Stromov, V., Iljina, M., Lauri, L., Nilsson, P., 2012. Metallogenic ar-

eas in Russian part of the Fennoscandian shield, in: Eilu, P. (Ed.), Mineral deposits and metallogeny of

Fennoscandia. Geological Survey of Finland, Special Paper 53, 343–395.

Sarapää O., Al Ani T., Lahti S.I., Lauri, L. S., Sarala P., Torppa, A. 2013. Rare earth element poten-

tial in Finland. Journal of Geochemical Exploration, Volume 133, 25-41.


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Tiljander, M. 2014. Indentification of mineral phases from 4samples using XRD. Research report,

Southern Finland office/ Research laboratory. EMA-2014-81-X. 2 p.

Vartiainen, H., 1980. The petrography, mineralogy and petrochemistry of the Sokli carbonatite massif,

northern Finland. Geological Survey of Finland, Bulletin 313, 126 p.

Vartiainen, H., 2001. Sokli carbonatite complex, northern Finland. Res Terrae. Ser. A 20, University of

Oulu, 8-24.


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6 APPENDICES 1


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