Abundance of REE-bearing minerals in carbonatite and lamprohyre

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
GEOLOGIAN TUTKIMUSKESKUS
7/2016
2.02.2016
GEOLOGICAL SURVEY OF FINLAND
DOCUMENTATION PAGE
Date / Rec. no.
Authors
Type of report
Thair Al-Ani
Olli Sarapää
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 mineralogy 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 analyses 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 code
Archive report
7/2016
Total pages
Language
27
English
Price
Confidentiality
public
Signature/name
Signature/name
Thair Al-Ani
Olli Sarapää
GEOLOGIAN TUTKIMUSKESKUS
2.02.2016
Contents
Documentation page
1
INTRODUCTION
1
2
SAMPLES AND METHODS
1
3
MINERALOGY AND GEOCHEMISTRY
3.1 Drill core U5422014R30
3.1.1
Whole rock geochemistry
3.1.2
Mineralogical analysis by XRD
3.1.3
SEM Analysis and Interpretation
3.2 Drill core U5422014R38
3.2.1
Petrography
3.2.2
REE Minerals
3.3 Bedrock samples PAT2 and JVPY-2013
3.3.1
Mineral Liberation Analyzer (MLA) results
3.3.2
Detailed mineralogy by SEM-EDS
5
5
6
6
10
12
12
12
14
14
20
4
CONCLUSIONS
30
5
REFERENCES
30
6 APPENDICES 1
Appendix 1.
32
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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 carbonatite 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 carbonatite 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). Mineralogical 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 Outokumpu 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, pyrochlore(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
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(Method 175X, 811L) and determination of the rare earth elements and trace elements by ICP-MS (Method 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 (normalized 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 REEmineral 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. Mineralogy 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
Weathered carbonatite from the drill hole R30
analyzed by XRD and SEM
Description
U5422014R30/ 4.40
U5422014R30/ 7.40
U5422014R30/ 8.90,
U5422014R30/ 14.40
Drill core samples analyzed
by light microscopes and SEM
Black weathered carbonatite, high in REE, Mn, Zn, Nb, Th, Fe, P
Brown weathered carbonatite REE-rich
Dark brown weathered carbonatite REE-rich
Brown weathered carbonatite REE-rich
U5422014R38(12.4)
U5422014R38(31.8)
U5422014R38(49.35)
U5422014R38(55.40)
U5422014R38(66.85)
U5422014R38(77.70)
Trench sampling concentrate for heavy minerals
analyzed by light microscopes and SEM
Fenitic amphibolite
Dark brown carbonatite dike
Light green lamprophyre dike
Light green porphyric lamprophyre dike
Light brown lamprophyre dike
Greenish lamprophyre dike
Samples were screened in two fraction 32 to 90 µm and +90 µm
PAT2-2013-3.1
PAT2-2013-3.1
PAT2-2013-7.1
PAT2-2013-8.1
JVPY-2013-14.2
JVPY-2013-14.2
Fine fractions (32-90 µm) Brown weathered carbonatite
Coarse fractions (+90 µm)
Coarse fractions (+90 µm) Fenite
Coarse fractions (+90 µm) Fenite
Fine fractions (32-90 µm) Brown weathered carbonatite
Coarse fractions (+90 µm)
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3
3.1
MINERALOGY AND GEOCHEMISTRY
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
Sample
(6-7)
R30
(7-8)
(2-3)
(3-4)
(4-5)
(5-6)
(8-9)
(9-10) (10-11
Ce
7600
10100
25600
52900
45300
12000
22700
14800
7080
5260
13800
10200
La
Dy
2950
180
4370
193
17500
204
33900
155
27200
429
7460
258
11900
381
7670
472
3800
445
2560
164
5970
230
3990
234
Er
51.1
54.3
56.9
45.2
111
77.4
112
117
106
41.7
60
63.3
Eu
Gd
178
445
208
502
234
605
277
747
378
1060
245
623
470
1150
420
1080
329
873
175
413
253
597
213
526
Ho
Lu
24.5
5.13
25.9
3.85
26.4
4.05
18.6
2.29
57.5
4.54
35.4
5.05
51.1
6.46
61.2
7.03
56.9
5.41
20.8
1.9
29.4
2.59
31.1
4.35
Nd
4200
4820
7560
12900
12000
5340
9760
7030
5210
3740
6390
5330
Pr
Sc
993
28.8
1200
19.6
2340
30
4300
20.6
3830
23.1
1460
26.8
2560
33.9
1750
24.8
1210
18.6
864
9.11
1580
11.2
1270
20.8
Sm
Tb
691
45.7
798
49.9
941
55
1280
53.6
1440
106
920
63
1740
103
1460
116
1070
104
654
42.3
1020
58.5
856
56.1
Tm
Sum_REE
Eu/Eu*
4.81
17401
4.74
22357
4.7
55160
2.73
106597
7.46
91958
7.07
28532
9.73
50993
9.54
35044
8.18
20338
3.25
13955
4.42
30016
5.31
22810
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
(Ce/Sm)N
2.685
2.654
3.445
3.055
11.698
6.566
16.66
9.974
11.882
7.592
5.101
3.148
4.302
3.148
3.305
2.446
2.234
1.597
2.462
1.941
3.682
3.265
2.932
2.876
Nb
Th
2050
256
6290
260
4430
576
33.6
1500
445
1200
55.6
448
360
708
43.8
488
43
368
65.7
292
138
648
1110
575
Zn
4610
9460
10300
6720
6670
3910
5140
4410
3580
5460
8200
8740
Mn
P2O5%
23100 20800
7.93 6.12
12700
7.74
25200
5.37
13500
11.60
11200
17.90
25100
17.20
13600
18.70
9000
21.00
13500
19.60
16800
16.80
18000
12.10
Fe2O3%
22.00
29.30
13.60
24.30
16.00
17.20
22.40
15.10
13.90
19.90
27.60
30.40
(11-12) (12-13) (13-14)
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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 abundances 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 fractionation 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
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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 diffractograms of Mg-saturated randomly oriented clay samples given in (Fig. 4), show an abundance of montmorillonite, 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), Kfeldspar, 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 diffractograms 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).
Figure 6. XRD pattern of selected sample U5422014R30/ 8.90
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4. U5422014R30 / 14.40 (X14-194):
The sample is composed mainly of quartz, plagioclase, K-feldspar, calcite and possible Ca-Mgphosphate. 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.
Figure 7. XRD pattern of selected sample U5422014R30/ 14.40
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 occurrence, 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. Monazite is the principal REE-phosphate present in the investigated rocks (Fig. 8a-d). Selected analyses indicate 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 monazite, 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 intergrown 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 colour. 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 sodic- 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 redbrown (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 studied sample. The main constituents of the studied lamprophyre dikes are calcite, strontium calcite, dolomite 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. (%)
30.7
54.7
54.7
47.6
53.9
45.4
30.3
34.8
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
>90
90-32
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 3290 µm). The results for each grain size are combined from six individual subsamples, and their mineralogy was determined by an automated SEM-EDS technique (see section Analytical methods). The indicator 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 fraction (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 analysed. In the diagram, the abundances of selected REE-minerals are bastnäsite (23 930 grains) and monazite (21 113 grains) in fine fraction (32-90 µm) of selected sample PAT2-2013-3,1 (Fig. 8a). The fractions 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 concentrated 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 pyrochlore (Nb).
The graph of the studied sample JVPY-2013-14,2 (Fig. 11b) shows, the dominant heavy mineral is tainiolite (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), cerphosphorhuttonite (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
Bastnäsite
Goethite
Monazite
K-feldspar
Fe-oxides
Albite
Hornblende
Goethite(Mn)+Zn
Biotite
Ferrosilite (Se)
Barite (Ba)
Allanite (La)
Aegirine
Quartz
Cerphosphorhuttonite (CeTh)
Chlorite
Stilpnomelane
Aluminoceladonite
Britholite (Ce)
Fayalite-deform
Richterite
Psilomelane
Riebeckite
Augite
Rutile+Nb
Arfvedsonite
Psilomelane (Ba)
Tainiolite (Li)
Muscovite
Aegirine-augite
Ilmenite
Ancylite(La)
Almandine
Thorite (Th)
Pyrolusite
Actinolite
Epidote
Tremolite
Rutile
Serpentine
Schorl (B)
Hyalophane
Pyrochlore (Nb)
Pyrite
Cummingtonite
Apatite
Total
PAT2-2013-3,1 +90
µm
PAT2-2013-3,1 32-90
µm
PAT2-2013-7,1 +90
µm
Wt%
Grain
Count
Wt%
Grain
Count
Wt
%
17.23
7 044
16.3
23 931
14.9
7 167
22.3
41 086
11.20
4 821
12.9
9.07
6 487
7.53
6.43
2 285
8.80
PAT2-2013-8,1 +90
µm
Grain
Count
Wt%
Grain
Count
0.45
193
1.43
549
14.5
7 366
7.46
3 711
21 113
6.13
2 697
9.07
3 653
20 584
3.89
2 931
1.63
1 206
4.05
5 508
6.49
2 432
7.15
2 623
6 111
6.45
17 090
2.18
1 594
0.57
406
4.46
2 828
3.0
7 292
0.74
495
0.26
168
4.13
1 978
6.97
12 833
47.1
23 930
60.1
29 879
3.01
1 780
1.55
3 503
4.68
2 918
1.43
875
2.98
1 473
3.21
6 068
0.24
123
0.60
306
2.55
1 042
2.18
3 411
-
-
-
-
2.78
1 724.00
1.00
2 524
0.07
47.00
0.01
18
2.20
1 143
1.33
2 644
0.07
40
0.02
12
2.19
1 525
1.56
4 160
1.80
1 324
0.69
495
1.76
639
2.57
3 564
0.48
184
0.06
21
1.47
914
0.71
1 688
0.37
245
0.47
304
1.39
911
1.22
3 050
0.15
101
1.63
1 101
1.00
634
0.51
1 228
0.07
47
0.01
7
0.84
363
1.13
1 853
0.13
61
0.02
8
0.78
324
0.87
1 385
0.12
52
0.43
186
0.33
194
0.23
524
0.03
17
0.05
29
0.27
110
0.34
525
6.71
2 850
0.75
313
0.21
114
0.26
539
0.05
31
0.03
19
0.18
98
0.07
144
0.00
1
-
-
0.18
77
0.25
407
0.02
7
0.00
2
0.18
94
0.13
268
0.02
10
0.00
1
0.16
64
0.20
313
2.51
1 064
0.08
32
0.16
102
0.10
238
0.12
80
0.04
24
0.16
101
0.12
285
0.04
29
-
-
0.13
67
0.06
129
0.00
2
-
-
0.12
48
0.14
205
0.02
10
-
-
0.05
26
0.08
154
-
-
-
-
0.05
20
0.02
41
0.02
8
-
-
0.03
10
0.09
112
-
-
0.00
1
0.03
10
0.01
10
-
-
-
-
0.02
15
0.04
90
0.02
10
0.00
1
0.02
11
0.10
196
0.00
2
0.01
4
0.02
11
0.04
82
0.04
25
0.00
3
0.02
10
0.03
46
0.01
6
0.00
1
0.01
7
0.01
16
-
-
-
-
0.01
5
0.01
18
0.00
1
-
-
0.01
5
0.01
16
-
-
-
-
0.01
5
0.04
63
0.15
72
0.73
320
0.01
2
0.00
2
-
-
-
-
0.00
2
0.02
42
0.01
3
0.00
1
0.00
100
2
51 569
2.02
100
52
189 846
0.07
100
28
51 424
7.56
100
2 171
605
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(a)
(b)
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 preparate, Data : Mineral Liberation Analyser (MLA), GTK Mintec/Outokumpu.
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Table 5. Modal mineralogy of studied samples JVPY-2013-14,2 determined by MLA on polished sections (indicator heavy mineral labelled as grey colour)
Mineral
JVPY-2013-14,2 +90 µm
JVPY-2013-14,2 32-90 µm
Wt%
Grain count
Wt%
35.55
13788
48.29
63492
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
Goethite
K-feldspar
Albite
Grain count
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
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
Ilmenite
0.40
192
0.45
735
0.54
172
0.45
483
Aluminoceladonite
0.20
102
0.16
278
Chlorite
Britholite (Ce)
0.24
0.24
116
86
0.34
0.12
538
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
Aegirine
.
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(a)
(b)
Figure 11. The main mineral phases of the heavy mineral concentrates (>1%), grain size <90 and 90-32µm fractions from the Sokli/Kaulus samples (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 indicator 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 images of the various heavy mineral particles separated from >90 to 32 µm fractions show in Figures (1218). The majority of the heavy mineral separates are dominated by bastnäsite, goethite, monazite, Kfeldspar, 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 distributions 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 thintabular 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 studied 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 transformation 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.
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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 bastnäsite by acicular aggregate allanite.
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Figure 13. Back-scattered electron (BSE) images of REE mineral from sample PAT2-2013-3.1 (a-c) Spherical growths of acicular bastnäsite crystals (d) Replacement of bastnäsite by acicular aggregate allanite, (e) Spherical 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). Monazite 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, 26.432.5% 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 cerphosphorhuttonite (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 aegirine-augite are generally present (and locally abundant) in the studied samples. Distribution and Morphology 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 observed in minor amounts with many hundred grains and less than 1 wt% of the individual heavy mineral
GEOLOGIAN TUTKIMUSKESKUS
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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).
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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 prismatic iron oxide mineral, (f) Needles of monazite growth within chlorite.
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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
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Figure 16. Back-scattered electron (BSE) images of REE mineral from samples PAT2-2013-8.1 and PAT2-20137.1 (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.
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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, prismatic crystal of aegirine, (d) Rutile showing two episodes of oscillatory zoning(e) Prismatic crystal of aegirine, (f)
bladed albite crystal.
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Figure 18. Back-scattered electron (BSE) images of tainiolite mineral from sample JVPY-2013-14.2, (a-d) Tainiolite 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.
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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 riebeckite and arfvedsonite, quartz is progressively removed. Other marks of fenite include growth of apatite, 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 sample 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 emplacement. 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
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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 potential 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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