Northern Finland Office
74/2012
Rovaniemi
1.9.2012
REE-mineralogy of arkosic gneisses from
Mäkärä-Vaulo area, Tana Belt, Northern
Finland
Thair Al Ani and Olli Sarapää
GEOLOGICAL SURVEY OF FINLAND
DOCUMENTATION PAGE
Date / Rec. no.
1.9.2012
Authors
Type of report
Thair Al Ani
alIi Sampaa
Commissioned by
GTK
Title of report
REE-mineralogy of arkosic gneisses from Makara-Vaulo area, Tana Belt, Northern Finland
Abstract
The selection of Makarii and Vaulo areas as REE-Au-targets in the Tana Belt was based on LREE- and
HREE-anomalies in regional till and bedrock geochemistry and Au intersections in previous drill holes.
In this study, the mineral chemistry and alteration ofREE-minerals were investigated by EMPA, and
SEM techniques from selected recent outcrop and drill core samples. The anomalous REE contents in
the Tana belt can be explained by the occurrence ofbastnasite, cerite, allanite and fine xenotime grains
in arkosic gneisses. The late stage REE mineralisation is dominated by Ca-REE fluorocarbonates (bastnasite) and REE-silicate (cerite and allanite). These also occur as fill vug space or fractures and replace
chlorite and apatite. The EMPA analysis has shown the REE minerals and their essentially cerium and
lanthanum composition with content of Nd, Pr Sm, and Gd were detected with spectrochemical analysis.
In general, the REE contents according to ICP-MS-analyses are intermediate to high with range from
596.9 to 938.2 ppm. The LREE and HREE contents are relatively high. LREE is higher than HREE
with distinct negative Eu anomalies and REE normalized patterns indicating decreasing abundances
with increasing atomic number.
Mineralogical and mineral chemical evidence demonstrates that hydrothermal processes were responsible for the most REE mineralization in studied rocks. During hydrothermal processes carbonate, phosphate and silicate minerals have been replaced by various assemblages ofREE-minerals.
Keywords
Tana Belt, yttrium, Au, REE-minerals, bastniisite (Ce), allanite, cerite and xenotime (Y)
Geographical area
Lapland province, Sodankyla, Vuotso, Makara,Vaulo
Map sheet
V434,3724
Other infonnation
Report serial
Archive code
7412012
Total pages
Language
36
English
Price
Public
Unit and section
Project code
Northern Finland office Bedrock and resources
2141007
Signature/name
Signature/name
Ph.D Thair Al Ani
~
1l
GTK
'PAI-I~'
Confidentiality
Ph.D 011i Sarapa;;
t
:J;,'
··V
C?=~
GEOLOGIAN TUTKIMUSKESKUS • GEOLOGISKA FORSKNINGSCENTRAlEN • GEOLOGICAL SURVEY OF FINLAND
Contents
Documentation page
1
INTRODUCTION
1
2
SAMPLING AND ANALYTICAL METHODS
1
3
RESULTS
3.1 Petrography
3.2 Mineralogy
3
3
7
3.3
REE Geochemistry
31
4
CONCLUSIONS
35
5
REFERENCES
35
LITERATURE
-
1
1
INTRODUCTION
Geological Survey of Finland (GTK) has started in 2009 a project for mapping potentiality for
'hi-tech' metals in Finland. The Tana belt, immediately to the south of the Lapland Granulite
Belt, northern Finland, was selected as one of the main targets as the area includes prominent
REE anomalies in regional till geochemical and lithogeochemical data (Salminen 1995, Rasilainen et al. 2008). These data indicate high La and Y concentrations in both till and bedrock of
arkosic gneiss belt 200 km in length. Especially interesting is that high Y values in till and rock
samples indicate enrichment of the heavy REE in the bedrock. Simultaneously with the REE exploration, also indications of gold have been redone: The region includes a number of known,
small Au occurrences in hematite-quartz-veins and extensive areas nugget gold in the regolith
(Sarapää and Sarala 2011).
The strongly deformed Tana belt comprises amphibolite, garnet-biotite and arkose gneisses, and
was trusted together with the Lapland Granulite Belt onto the Central Lapland Greenstone Belt
during 1.9-1.8 Ga (Tuisku and Huhma 2006). The present main Au- and REE targets locate in
Mäkärä and Vaulo, 15 and 25 km northwest from the Vuotso village. The area is located in the
latest ice divide zone of the last (late Weichselian) glaciations. Subglacial erosion has been weak
and the till transport distance short. Bedrock is covered by 5-30 m thick kaolinitic saprolite and
the overlying till, usually clay-rich, has a thickness of 0.5-15 m. The aim of this work to find out
in which minerals are rare earth elements hiding.
2
SAMPLING AND ANALYTICAL METHODS
Five outcrop sample and 15 core samples from 9 drill holes (V434-2011-R20, R21, R24, R28,
R29, R6, R9, R11) were selected from the Tana Belt for detailed mineralogical studies (Figure.
1) The outcrop samples were collected by geologists Antero Karvinen(EAK) and Antti Mikkola(AMM$$) during field season 2011 (Table 1), and the drill cores represent Mäkärä and
Vaulo Au-REE-targets. Backscattered electron (BSE) imaging and electron probe microanalysis
(EPMA) were used to describe various REE-mineral phases from ten polished thin sections (Table. 1), investigated by CAMECASX100/LKP electron microprobe at GTK-Espoo. Another ten
drill core were studied by scanning electron microscope (SEM), performed on JEOL JSM 5900
LV. Our SEM analyses concentrated on REE and Y- accessory minerals. The thin sections were
also studied under petrographic microscope. All photographs are taken from thin sections, polished to 0.03 mm thickness, in transmitted white light, both under plane polarized light and under crossed polarizer. More detailed descriptions are presented in the SEM report of Al Ani
2012. Rare earth elements from studied outcrop and drill core samples were determined either by
ICP-MS after hydrofluoric acid-perchloric acid dissolution (method 307PM, order 502924) or
after sodium peroxide fusion (method 720PM, order 503991, 502933).
-
2
Figure 1. Location map of the studied drill core and outcrop samples in the Tana Belt.
Table 1. The selected outcrop and drill core samples from the Tana Belt rocks.
Sample No.
EAK1-2011-118.1
Kariselkä
AMM$-2011-32.1
Kostiajänkä
AMM$-2011-36.1
Peuranippa
AMM$-2011-45.1
Palo-Peuravaara
AMM$-2011-52.1
Haipanrova
V4342011R28/36.0
Vaulo
V4342011R28/43.4
Vaulo
V4342011R28/62.3
Vaulo
V4342011R28/100.9
Vaulo
V4342011R29/113.3
Vaulo
-
X-Coordinate
Y-coordinate
7582880
3457210
7578605
3466448
7578659
3468944
7579592
3468151
7579896
3466670
7572179
3481878
7572179
3481878
7572179
3481878
7572179
3481878
7572400
3483000
Rock type
Felsic volcanic rock
Arkosic gneiss
Arkosic gneiss
Arkosic gneiss
Arkosic gneiss
Granite gneiss
Amphibolite
Arkosic gneiss
Amphibolite
Granite gneiss
3
3
3.1
RESULTS
Petrography
The following petrographic descriptions are based on a set of 10 thin-sections of arkosic and
hornblende gneisses or amphibolites and granitic gneisses from the Tana Belt (Table 1 and Figs.
1-3). The granitic gneisses are fine to medium grained. The mineralogy of these samples is predominantly quartz and plagioclase feldspar and/or K-feldspar with biotite, garnet, ilmenite, titanite, zircon, and other accessory minerals. Alteration of the rocks produces secondary minerals
such as such as chlorite and sercite (Fig. 2). Amphibolites rock samples are composed mainly
from hornblende and plagioclase with some containing amounts of quartz, biotite, garnet, clinoorthopyroxen, zircon and titanite. As with arkosic gneisses, alteration minerals such as sericite
and chlorite are also present (Fig. 4).
Figure 2. Arkosic gneisses outcrop samples from the Tana belt.
-
4
Figure 3. Drill core samples from the Vaulo area.
-
5
Figure 4. Microphotographs of representative granitic gneiss samples (crossed polarized and Normal
lights): (A) coarse amphibolites grain within quartz and plagioclase; (B) titanite grains surrounded by
quartz and ilmenite with some occurrences of biotite; (C) alteration of amphibole to chlorite and occurrences of zircon.
-
6
Figure 5. Microphotographs of representative amphibolites gneiss samples (crossed polarized and
Normal lights): (A) high occurrences of ilmenite and chlorite with plagioclase and K-feldspar; (B, C)
predominant of coarse amphibole grains with some alteration of chlorite and common titanite occurrences.
-
7
3.2
3.2.1
Mineralogy
Electronic microscopic analysis (EPMA)
Ten samples from Vaulo at Tana Belt were studied by EPMA in detail to investigate petrography
and concentration of the REE in the different mineral phases. Most of selected samples are arkosic and granite gneisses and composed mainly of quartz-plagioclase-K-feldspar -garnethornblende-biotite with some accessory minerals such as titanite, zircon, pyroxene and REEbearing minerals.
Outcrop samples from the Tana Belt
Kostiajänkä, arkosic gneiss, AMM$-2011-32.1
Arkosic gneiss rock composed mainly from quartz-plagioclase-K-feldspar and the accessory
minerals are amphibole, biotite, titanite, ilmenite and zircon (Table 2). Few xenotime grains (diameter = 15 x 40 µm and 20 x 25 µm) have been found, as irregular grains and disseminated
within ilmenite and surrounded by K-feldspar (Fig. 6). Electron-microprobe analyses reveal that
most of the xenotime crystals contain significant amounts of Y2O3 (42.36-47.0 wt.%). Xenotime
grains also contain additional WO3 (1.9-3.2 wt.%), Dy2O3 (3.9-4.0 wt.%) and Gd2O3 (4.2-4.3
wt.%) see Table (3).
-
8
Table 2. Representative EMPA results of main minerals in selected AMM$ drill core samples at Tana
Belt.
Sample
Mineral
Kfls
Biotite
Hornblende
Plag
Kfls
Hedenbergite
Albite
SiO2
64.64
33.71
38.71
66.05
64.50
49.32
67.43
TiO2
0.04
1.54
1.07
0.00
0.02
0.12
0.00
Al2O3
18.41
16.77
10.93
21.07
18.10
1.21
20.34
Cr2O3
0.00
0.00
0.00
0.00
0.00
0.01
0.01
V2O3
0.00
0.03
0.03
0.01
0.00
0.01
0.02
FeO
0.00
31.35
29.89
0.05
0.15
0.00
0.26
0.99
0.00
0.00
24.36
0.89
0.10
MnO
MgO
0.02
2.53
1.78
0.00
0.00
2.42
0.00
CaO
0.00
0.11
Na2O
0.25
0.00
10.12
1.83
K2O
SrO
16.23
0.00
8.49
0.00
BaO
0.34
Total
100.00
AMM$-2011-36.1
0.00
2.17
0.01
0.33
18.36
1.90
1.87
10.64
0.11
16.05
0.01
11.51
0.16
0.00
0.00
0.00
0.05
0.02
0.00
0.00
0.00
0.21
0.00
0.01
95.19
97.47
100.14
99.38
98.86
100.63
1.03
Sample
Mineral
FeOx
Hornblende
Plag
Kfls
Kfls
Plag
Titanite
FeOx
Hedenbergite
SiO2
40.71
64.31
65.59
0.00
64.44
64.23
30.18
0.00
49.55
TiO2
0.00
0.00
0.11
0.03
0.05
0.06
17.72
20.84
0.01
18.40
22.00
34.53
2.51
0.02
Al2O3
1.20
9.95
0.06
1.86
Cr2O3
0.01
0.00
0.03
0.01
0.00
0.01
0.00
0.00
0.00
V2O3
0.02
0.01
0.03
0.04
0.01
0.01
0.22
0.05
0.01
FeO
24.27
0.05
0.04
0.10
1.41
91.85
18.94
0.69
0.00
0.00
91.25
0.04
0.04
MnO
0.04
0.00
0.12
1.61
MgO
5.43
0.02
0.00
0.00
0.00
0.02
0.00
0.38
0.00
CaO
10.53
0.02
2.50
0.00
0.02
3.33
0.01
Na2O
1.64
0.42
0.00
0.28
0.00
15.45
0.00
0.00
0.00
0.00
0.04
0.00
16.02
0.00
0.00
SrO
1.61
0.00
9.79
0.35
19.72
1.49
K2O
9.88
0.17
26.98
0.00
0.06
0.03
0.00
BaO
0.00
0.31
0.00
0.00
0.37
0.00
0.00
0.00
0.00
96.5
98.4
99.1
91.5
99.77
99.95
96.54
92.50
99.11
Total
-
AMM$-2011-32.1
AMM$-2011-52.1
AMM$-2011-45.1
0.00
5.53
9
Figure 6. Back-scattered electron (BSE) images of selected xenotime crystals in sample AMM$-201132.1.
-
10
Table 3. Representative EMPA results of xenotime of sample AMM$-2011-32.1and cerite (ce) of sample
AMM$-2011-52.1
Sample
Mineral
Grain
SiO2
TiO2
Al2O3
FeO
CaO
P2O5
SO2
UO2
ThO2
WO3
Y2O3
Ce2O3
Nd2O3
La2O3
Pr2O3
SmO
Gd2O3
Dy2O3
F
Cl
Total
AMM$-2011-32.1
Xenotime
gr1
gr2
1.14
0.87
0.17
0.81
0
0
0.08
0.66
0
0
35.54
32.68
0
0
0.07
0.15
0.08
0
1.91
3.24
47.03
42.36
0
0.11
0.16
0
0
0
0.3
1.1
0.43
0.1
3.95
4.02
4.31
4.23
0.07
0.11
0.01
0.01
95.3
90.5
AMM$-2011-52.1
gr1
Cerite (Ce)
gr2
gr3
gr4
6.31
0.00
1.71
1.12
0.14
1.10
0.04
0.09
0.06
0.10
0.00
75.61
1.41
0.00
0.46
0.19
0.16
0.00
1.36
0.05
6.57
0.00
1.69
1.27
0.13
1.15
0.02
0.06
0.00
0.00
0.00
78.89
1.52
0.00
0.21
0.19
0.00
0.00
1.36
0.06
6.21
0.02
1.80
1.05
0.09
1.06
0.06
0.18
0.09
0.34
0.00
74.35
1.33
0.00
0.44
0.27
0.12
0.00
1.21
0.05
6.56
0.00
1.74
1.06
0.09
1.17
0.00
0.00
0.07
0.15
0.00
77.05
1.43
0.00
0.25
0.00
0.16
0.00
1.44
0.05
89.9
93.1
88.7
91.2
Peuranippa, arkosic gneiss AMM$-2011-36.1
The main minerals are quartz, plagioclase, K-feldspar, and clinopyroxene (hedenbergite). The
colour of hedenbergite is bluish green. Other accessories include titanite, zircon and FeO-oxide
(Table. 2). Small amounts of REE are present in the studied samples such as bastnäsite and xenotime.
Palopeuravaara, arkosic gneiss, AMM$-2011-45.1
Quartz-plagioclase-K-feldspar and hornblende are the main minerals. Accessories minerals include chlorite, ilmenite, titanite, zircon and cubic FeO-oxide. REE-minerals are not shown in this
sample (Fig. 5).
Haipanrova, arkosic gneiss, AMM$-2011-52.1
The main minerals are quartz-plagioclase-K-feldspar-amphibole, whereas the accessories include
biotite, titanite, zircon Fe-oxide (Fig.5, Table. 2). BSE photo shows a large cluster of REEbearing mineral grains included within studied sample (Fig. 7A). The main REE-bearing mineral
is cerite (Ce), which occurs as inclusions within albite (Fig. 7B). Electron-microprobe analyses
reveal that most of the Cerite (Ce) crystals contain significant amounts of Ce (75-79 wt. %), and
also contain additional Nd (1.3-1.5 wt. %), F (1.2-1.4 wt. %), SiO2 (6.3-6.6 wt. %), Al2O3 (1.71.8 wt. %) and FeO (1.0-1.32 wt. %), see Table (3).
-
11
Figure 7. Back-scattered electron (BSE) images of selected cerite (Ce) in sample AMM$-2011-52.1. (a)
Original sample (low magnification) shows clustering of cerite (Ce) within the sample, (b) cerite (Ce)
within albite mineral.
Kariselkä, felsic volcanic rock, EAK1-2011-118.1
The main minerals are mylonitized quartz, plagioclase, K-feldspar and amphibole. Amphibole is
partly chloritized and the accessories include titanite, zircon (Table. 4). This sample was characterized by high content of different type of REE-minerals. REE-silicate mostly cerite (Ce) was
developed in vugs and fractures within main silicate minerals as quartz to form bright vertical
lines (Fig. 8 A-F). Cerite (Ce) is mostly associated with chlorite as dark colour. Backscattered
electron (BSE) imaging of the studied sample also shows some content of bastnäsite. It´s found
as inclusions in quartz. Bastnäsite grains are enveloped with a chlorite rim against neigh boring
quartz, albite and amphibole (Fig. 9A-C).
Electron-microprobe analyses reveal that most of the Cerite (Ce) crystals contain significant
amounts of Ce (57-77.5 wt. %). These grains also contains minor amounts of Nd (1.4-2 wt. %)
and F (1.2-1.7 wt. %) see Table (5). The chemical data by EMPA of few bastnäsite grains shows
-
12
that bastnäsite have elevated REE and Y with La2O3, Ce2O3, Nd2O3 and Y2O3 contents ranging
from 20.5-26.3 wt.%, 16.1-20.6 wt.%, 17-22.5 wt.% and 5.1-6.1 wt.% respectively (Table. 5). F
content is high with ranging from 5.7 to 6.4 wt. %.
Table 4. Representative EMPA results of main minerals in sample EAK1-2011-118.1.
Sample
-
EAK1-2011-118.1
Mineral
Kfls
Plag
Chlorite
hornblende
SiO2
64.23
67.02
23.84
38.79
TiO2
0.03
0.04
0.00
0.84
Al2O3
18.05
20.22
19.44
13.14
Cr2O3
0.00
0.00
0.00
0.00
V2O3
0.02
0.00
0.00
0.02
FeO
0.02
0.16
36.39
25.55
MnO
0.01
0.00
0.67
0.55
MgO
0.00
0.00
7.13
3.68
CaO
0.04
1.36
0.01
10.96
Na2O
0.17
10.62
0.00
1.28
K2O
16.35
0.14
0.02
2.07
SrO
0.33
0.13
0.12
0.61
BaO
0.38
0.00
0.00
0.00
Total
99.76
99.72
87.74
97.82
13
Figure 8. Backscattered electron micrographs REE-silicate mostly cerite (Ce) was developed in vugs
and fractures within main silicate minerals as quartz to form bright vertical lines.
-
14
Figure 9. Backscattered electron micrographs of Bastnäsite (a, b) fine grains of Bastnäsite filling the
vug space within albite and quartz and associated with chlorite, (c) bright grain of Bastnäsite replacing
the chlorite in center and enclosed by primary silicate minerals.
-
15
Table 5. Representative EMPA results of REE-minerals (cerite and bastnäsite) of sample EAK1-2011118.1.
Cerite-(Ce)
Mineral
-
Bastnäsite
Grain
gr1
gr2
gr3
gr4
gr5
gr6
gr7
gr1
gr2
gr3
SiO2
13.04
12.64
14.50
13.39
22.30
13.91
17.27
1.44
1.20
0.93
TiO2
0.03
0.00
0.11
0.12
0.02
0.00
0.09
0.09
0.11
0.16
Al2O3
1.39
1.18
1.80
1.50
6.37
1.41
2.47
0.73
0.55
0.26
FeO
0.68
0.00
1.07
0.64
2.18
0.17
2.41
0.49
0.18
1.09
CaO
0.35
0.29
0.20
0.08
0.18
0.19
0.13
2.20
2.15
1.88
Cs2O
0.89
0.97
0.89
0.91
0.71
0.84
0.90
0.01
0.09
0.30
P2O5
0.14
0.17
0.13
0.29
0.00
0.03
0.21
0.31
0.27
0.13
SO2
0.09
0.09
0.08
0.18
0.11
0.16
0.10
0.36
0.33
0.27
UO2
0.28
0.43
0.15
0.39
0.10
0.53
0.19
0.10
0.11
0.08
ThO2
0.06
0.07
0.16
0.01
0.03
0.02
0.04
0.86
1.38
1.04
WO3
0.20
0.12
0.00
0.31
0.18
0.07
0.00
0.04
0.01
0.15
Y2O3
0.79
1.09
0.83
0.92
0.76
0.92
1.00
6.05
6.12
5.13
Ce2O3
72.45
77.49
72.12
73.24
57
74.36
69.44
16.11
17.17
20.61
Nd2O3
1.97
1.57
1.39
1.97
1.35
2
1.69
21.20
22.52
17.19
La2O3
0.00
0.00
0.00
0.00
0.00
0.00
0.00
26.33
25.96
20.53
Pr2O3
0.25
0.08
0.09
0.22
0.00
0.35
0.07
4.85
5.05
4
SmO
0.28
0.26
0.44
0.29
0.26
0.29
0.35
2.82
2.96
2.25
Gd2O3
0.53
0.56
0.38
0.34
0.20
0.39
0.33
2.92
2.99
2.11
Dy2O3
0.11
0.55
0.00
0.08
0.00
0.33
0.00
0.49
0.98
0.00
F
1.72
1.31
1.23
1.70
1.09
1.45
1.26
6.34
5.72
5.94
Cl
0.03
0.01
0.03
0.00
0.03
0.06
0.03
0.09
0.15
0.07
Total
95.76
99.34
96.16
97.23
94.84
98.11
98.32
91.37
93.90
82.07
16
Table 6. Representative EMPA results of main minerals in selected V434-2011-R28 samples at Tana
Belt.
Sample
Mineral
amph
plag
kfls
FeOx
amph
plag
bio
garnet
apt
SiO2
38.28
65.21
65.03
0.00
42.14
61.88
35.93
38.04
0.06
TiO2
1.56
0.01
0.00
0.14
1.74
0.00
5.25
0.03
0.00
Al2O3
11.61
22.09
18.10
0.00
12.30
23.97
14.24
20.91
0.00
Cr2O3
0.02
0.01
0.01
0.01
0.05
0.00
0.05
0.04
0.02
V2O3
0.00
0.00
0.00
0.02
0.09
0.03
0.12
0.01
0.00
FeO
28.84
0.04
0.00
93.07
18.96
0.06
21.95
28.06
0.08
MnO
0.55
0.00
0.00
0.00
0.11
0.02
0.08
1.27
0.00
MgO
2.30
0.00
0.00
0.00
8.25
0.00
8.84
3.08
0.02
CaO
10.62
3.69
0.00
0.02
11.46
5.92
0.01
8.82
54.76
Na2O
1.51
8.86
0.28
0.00
1.26
7.69
0.00
0.00
0.00
K2O
1.98
0.28
16.17
0.01
1.58
0.43
9.50
0.01
0.00
SrO
0.01
0.02
0.00
0.00
0.01
0.12
0.00
0.11
0.10
BaO
0.00
0.00
0.37
0.00
0.00
0.00
0.06
0.00
0.00
NiO
0.00
0.00
0.00
0.01
0.02
0.00
0.01
0.00
0.00
ZnO
0.06
0.16
0.04
0.00
0.00
0.18
0.00
0.00
0.00
SO2
0.10
0.01
0.04
0.00
0.00
0.00
0.04
0.01
0.00
P2O5
0.09
0.00
0.03
0.00
0.16
0.11
0.02
0.15
43.71
F
0.00
0.00
0.00
0.00
0.00
0.00
0.00
0.00
3.37
F=O
0.00
0.00
0.00
0.00
0.00
0.00
0.00
0.00
-1.42
Cl
0.24
0.00
0.00
0.00
0.03
0.02
0.03
0.00
0.06
V434-2011-R28(36.0)
Cl = O
-0.05
0.00
0.00
0.00
-0.01
0.00
-0.01
0.00
-0.01
Total
97.71
100.39
100.08
93.30
98.17
100.41
96.12
100.52
100.75
Sample
-
V434-2011-R28(43.4)
V434-2011-R28(62.3)
V434-2011-R28(100.9)
V434-2011-R28(113.3)
Mineral
amph
plag
kfls
FeOx
titan
amph
plag
bio
garnet
apt
kfls
kfls
SiO2
38.65
66.51
65.48
0.03
30.99
40.82
63.74
35.23
37.82
0.15
64.43
64.72
TiO2
1.12
0.00
0.01
0.09
32.67
1.90
0.04
4.97
0.00
0.00
0.00
0.02
Al2O3
11.14
21.21
18.29
0.02
3.58
12.22
23.04
13.66
20.65
0.00
17.92
18.14
Cr2O3
0.00
0.00
0.01
0.00
0.00
0.02
0.00
0.03
0.00
0.00
0.00
0.00
V2O3
0.00
0.02
0.01
0.00
0.19
0.07
0.03
0.08
0.00
0.00
0.00
0.00
FeO
29.50
0.09
0.02
93.02
1.97
22.13
0.08
25.42
27.80
0.20
0.08
0.08
MnO
0.76
0.01
0.00
0.01
0.13
0.19
0.00
0.08
1.93
0.07
0.00
0.00
MgO
2.22
0.01
0.01
0.00
0.01
6.16
0.01
6.75
1.72
0.02
0.00
0.00
CaO
10.62
2.43
0.02
0.00
27.61
11.38
4.75
0.05
10.12
54.36
0.05
0.05
Na2O
1.74
9.69
0.30
0.00
0.00
1.26
8.11
0.00
0.00
0.00
0.16
0.17
K2O
1.88
0.32
15.34
0.00
0.00
1.78
0.54
9.43
0.00
0.00
16.10
16.31
SrO
0.10
0.02
0.00
0.09
0.00
0.00
0.07
0.00
0.05
0.02
0.01
0.00
BaO
0.00
0.00
0.31
0.00
0.00
0.00
0.00
0.05
0.00
0.00
0.22
0.23
NiO
0.00
0.00
0.00
0.00
0.00
0.00
0.00
0.02
0.00
0.01
0.01
0.00
ZnO
0.11
0.00
0.00
0.00
0.01
0.00
0.03
0.00
0.00
0.00
0.04
0.13
SO2
0.06
0.00
0.01
0.00
0.00
0.05
0.00
0.07
0.01
0.00
0.01
0.01
P2O5
0.13
0.01
0.00
0.01
n.d.
0.08
0.08
0.00
0.11
43.27
0.01
0.01
F
0.00
0.00
0.00
0.00
1.33
0.00
0.00
0.00
0.00
3.00
0.00
0.00
F=O
0.00
0.00
0.00
0.00
-0.56
0.00
0.00
0.00
0.00
-1.26
0.00
0.00
Cl
0.23
0.00
0.00
0.00
0.00
0.12
0.00
0.13
0.01
0.06
0.01
0.00
Cl = O
-0.05
0.00
0.00
0.00
0.00
-0.03
0.00
-0.03
0.00
-0.01
0.00
0.00
Total
98.21
100.32
99.82
93.28
97.92
98.15
100.51
95.95
100.23
99.89
99.03
99.87
17
Drilling core samples
Vaulo, granitic gneiss, V434-2011-R28/36.0
The sample is composed mainly of K-feldspar, plagioclase, amphibole, chlorite, biotite, Feoxide, ilmenite, zircon, apatite and some REE-minerals (allanite, altered allanite, bastnäsite).
Electron microprobe analyses (EMPA) clearly shows that dominance of minerals (about 95%)
that belong to the mineral group of the silicates (Table. 6). Two types of REE minerals have been
discovered in the studied sample (bastnäsite and allanite). The first REE minerals are bastnäsite
which has the empirical formula (REE) CO3F and belongs to the fluoro-carbonates group. The
average contents of the compound compositions in the bastnäsite includes CaO (6.8-9%) with
average 7.8 %, Nd2O3 (9.7-13.3 %) with average11.4 %, Ce2O3 (22.8-30.7 %) with average 26
%, La2O3 (8.9-13.7 %) with average 10 %, Pr2O3 (2.7-3.6 %) with average 3.2 %, SmO (1.1-2.2
%) with average 1.7 % and Gd2O3 (0.8-1.8) with average 1.2 (Table 7). The average sum of
REE2O3 in the studied Bastnäsite is 55 % and the average REE2O3/CaO ratio is 7.2. The Bastnäsite is characterized by the occurrences of Pr, Sm and Gd. The second REE mineral is allanite
with homogeneous chemical composition. The mean contents of allanite are SiO2 (32%), Al2O3
(15 %), Ce2O3 (10 %), Nd2O3 (3.1 %), La2O3 (4.6) and Pr2O3 (1 %) see Table (7). The sum of
REE2O3 in studied allanite is about 20 %.
-
18
Table 7. . Representative EMPA results of REE-minerals (cerite and bastnäsite) of sample V434-2011R28 (36.0).
Sample
Mineral
Grain
SiO2
TiO2
Al2O3
V2O3
FeO
MnO
MgO
CaO
Na2O
SrO
SrO
BaO
Cs2O
P2O5
SO2
ZrO2
HfO2
UO2
ThO2
PbO
SnO2
Nb2O5
Ta2O5
Sc2O3
WO3
Y2O3
Ce2O3
Nd2O3
La2O3
Pr2O3
SmO
Gd2O3
Dy2O3
F
F=O
Cl
Cl = O
Total
-
V434-2011-R28(36.0)
allanite
bastn
bastn
bastn
allanite
bastn
bastn
allanite
bastn
bastn
bastn
gr1_phase1
gr2_phase2
gr2
gr3_phase1
gr3_phase2
gr4
gr5
gr6
gr7
gr8
gr9
30.95
0.81
1.65
0.13
5.77
1.06
4.55
0.31
34.56
0.88
3.29
0.28
5.43
0.48
31.22
0.77
5.20
0.43
1.63
2.46
0.38
14.83
0.00
0.27
0.00
1.34
0.00
1.28
0.00
15.21
0.00
0.73
0.01
1.49
0.00
14.89
0.00
1.33
0.00
0.34
14.74
0.37
0.28
0.55
0.02
0.00
1.52
0.05
0.00
1.52
0.05
0.02
11.39
0.31
0.20
0.82
0.06
0.09
1.45
0.14
0.27
14.83
0.38
0.16
1.57
0.05
0.12
0.22
10.64
0.00
0.00
0.01
0.03
0.18
0.05
0.00
0.00
0.00
0.00
0.80
0.00
0.01
0.00
7.00
0.00
0.00
0.00
0.01
0.40
0.07
0.00
0.00
0.09
0.00
1.27
0.04
0.06
0.00
0.01
0.00
0.05
0.00
7.80
0.00
0.29
0.30
0.06
0.36
0.09
0.00
0.00
0.05
0.01
2.38
0.00
0.01
0.00
0.00
0.00
0.12
0.00
11.96
0.10
0.00
0.00
0.25
0.06
0.31
0.00
0.00
0.00
0.00
0.78
0.34
0.00
0.02
6.83
0.00
0.00
0.00
0.00
0.37
0.12
0.00
0.00
0.00
0.00
1.07
0.18
0.00
0.10
0.00
0.00
0.05
1.29
n.d.
0.00
0.10
0.00
6.59
0.00
0.42
0.42
0.05
0.33
0.14
0.00
0.00
0.00
0.00
0.90
0.06
0.03
0.10
0.00
0.00
0.00
0.00
7.13
n.d.
0.00
0.10
0.00
7.55
0.00
0.37
0.38
0.00
0.43
0.22
0.00
0.00
0.00
0.00
1.00
0.00
0.00
0.00
0.00
0.00
0.03
0.00
10.70
0.00
0.00
0.00
0.00
0.19
0.16
0.01
0.00
0.00
0.00
0.46
0.00
0.01
0.01
n.d.
0.00
0.22
0.29
8.54
0.00
0.06
0.06
0.12
0.40
2.33
0.00
0.01
0.00
0.04
0.46
0.00
0.00
0.00
0.00
0.00
0.00
0.70
11.82
3.45
4.78
1.27
0.19
0.28
0.00
0.23
-0.09
0.00
0.00
96.13
30.67
10.61
13.01
3.10
1.29
0.94
0.00
1.01
-0.43
0.02
0.00
75.55
26.46
10.38
10.44
3.22
1.58
1.41
0.00
0.77
-0.32
0.05
-0.01
72.71
25.11
11.20
8.88
3.00
2.08
1.34
0.00
0.95
-0.40
0.01
0.00
71.36
6.12
2.46
2.43
0.58
0.61
0.66
0.00
0.33
-0.14
0.05
-0.01
89.57
27.60
11.87
9.85
3.24
1.97
0.85
0.00
0.81
-0.34
0.02
-0.01
71.14
24.97
10.97
11.83
3.23
1.33
1.29
0.00
0.73
-0.31
0.04
-0.01
73.34
11.14
2.84
6.17
1.18
0.40
0.11
0.00
0.25
-0.11
0.00
0.00
95.89
26.62
11.34
10.03
2.94
1.77
0.86
0.00
0.70
-0.30
0.05
-0.01
71.75
25.01
0.30
0.00
0.00
0.02
0.00
0.29
0.29
0.15
0.35
0.06
0.00
0.00
0.00
0.00
1.31
0.00
0.00
0.07
0.00
0.00
0.00
0.83
12.46
11.69
3.31
1.89
1.46
0.13
0.69
-0.29
0.02
-0.01
69.38
0.44
0.00
0.45
0.04
0.00
7.18
0.00
0.39
0.39
0.05
0.29
0.19
0.00
0.03
0.00
0.00
1.59
0.03
0.00
0.01
0.00
0.00
0.26
0.66
23.53
12.14
11.66
3.43
2.16
1.46
0.00
0.85
-0.36
0.04
-0.01
69.75
19
The sample V434-2011-R28/36.0 shows an incipient process of replacement of bastnäsite-(Ce) +
allanite (Ce) after chlorite as observed in backscattered electron images. Bastnäsite is dominant
toward the inner portion of the crystal, allanite-(Ce) replacements occur along the outer portion
of the crystals (Figs. 10 and11. The replacement of bastnäsite and allanite are found both within
and occurs in many forms: infilling vugs and fractures; and enveloped with a chlorite rim against
neigh boring quartz, K-feldspar and plagioclase. The allanite appears to be slightly older than the
bastnäsite; and these minerals (Bastnäsite and allanite), replaced earlier minerals such as amphibole or quartz, and in filled fractures in primary K-feldspar and plagioclase. REE-minerals characterized by large crystal agglomerations with anhedral form, measuring up to 200 μm in diameter. These spheroidal aggregates or fine-grained vug-filling structure filled by chlorite, which altered to allanite (in the rim) and later to bastnäsite in the center (Fig. 8c, d) and (Fig. 9).
Figure 10. Backscattered electron micrographs of REE minerals from Tana Belt in sample V434-2011R28/36.0 (a) Sub-anhedral grain of allanite with bright spots of bastnäsite. (b) REE-minerals filling the
vuges show allanite in the rim and bastnäsite in the core as bright colour; associated with zircon and enclosed by amphibole. (C, d) REE- minerals occur as spheroidal aggregates or fine-grained vug-filling
structure, chlorite altered to allanite (in the rim) and later to bastnäsite in the center.
-
20
Figure 11. Backscattered electron micrographs of REE minerals from Tana Belt in sample V434-2011R28/36.0 (a) REE- minerals occur as spheroidal aggregates or fine-grained vug-filling structure, chlorite
altered to allanite (in the rim) and later to bastnäsite in the center. (b) Spheroidal aggregates filled by
altered allanite and chlorite and enclosed by K-feldspar and mica. (C, d) REE- minerals occur as spheroidal aggregates or fine-grained vug-filling structure, chlorite altered to allanite (in the rim) and later to
bastnäsite in the center, spheroidal aggregates also contain black hole related to removal of REEminerals.
Vaulo, amphibolite, V434-2011-R28/43.4 (x=7572179, y=3481878)
The sample is composed mainly of amphibole, biotite, plagioclase, Fe-oxide, ilmenite, zircon
and apatite (Table. 6). Electron microprobe analyses (EMPA) shows that the sample contains
some allanite filling the fractures within quartz and feldspar (Fig. 10a, b). The average contents
of the compound compositions in the allanite includes SiO2 (15.6 %), Al2O3 (10.7 %), Ce2O3
(21.6 %), Nd2O3 (5.7 %), La2O3 (9.1 %) and Pr2O3 (1.8) with total REE2O3 about 40% (Table.
8).
-
21
Table 8. Representative EMPA results of REE-minerals in some selected samples in Tana Belt.
sample
Mineral
Grain
SiO2
TiO2
Al2O3
V2O3
FeO
MnO
MgO
CaO
Na2O
SrO
SrO
BaO
Cs2O
P2O5
SO2
ZrO2
HfO2
UO2
ThO2
PbO
SnO2
Nb2O5
Ta2O5
Sc2O3
WO3
Y2O3
Ce2O3
Nd2O3
La2O3
Pr2O3
SmO
Gd2O3
Dy2O3
F
F=O
Cl
Cl = O
Total
R28(43.4)
allan
gr1
15.66
0.00
10.71
0.00
0.09
0.00
0.00
7.26
1.24
0.23
0.25
0.01
0.22
0.11
0.00
0.00
0.00
0.00
0.02
0.00
0.00
0.00
n.d.
0.00
0.15
0.00
21.63
5.72
9.14
1.76
0.26
0.09
0.00
0.32
-0.13
0.05
-0.01
74.77
allan
gr1
34.92
0.00
5.08
0.20
4.92
2.59
1.22
0.39
0.00
0.00
0.00
0.02
0.53
0.24
0.02
0.00
0.01
0.00
0.02
0.19
0.00
0.06
n.d.
0.01
0.00
1.73
37.82
1.01
0.00
0.00
0.46
0.77
0.00
0.82
-0.35
0.05
-0.01
92.71
R28(62.3)
Cerite
gr2
22.26
0.26
2.19
0.15
0.51
0.94
0.10
0.26
0.00
0.00
0.00
0.06
0.65
0.42
0.00
0.03
0.11
0.32
0.21
0.29
0.00
0.01
n.d.
0.01
0.43
3.63
55.61
2.92
0.09
0.38
1.18
1.51
0.51
0.86
-0.36
0.02
-0.01
95.55
Cerite
gr3
16.54
0.36
1.68
0.05
0.24
0.93
0.13
0.41
0.00
0.00
0.00
0.00
0.99
0.06
0.00
0.00
0.13
0.09
1.53
0.95
0.00
0.00
n.d.
0.00
0.41
0.35
69.86
2.00
0.22
0.00
0.36
0.37
0.11
1.21
-0.51
0.02
-0.01
98.49
R28(100.9)
bastn
bastn
gr1
1.68
0.01
0.45
0.00
0.62
0.01
0.00
4.60
0.00
0.05
0.06
0.11
0.47
0.21
0.09
0.00
0.12
0.00
1.09
0.15
0.00
0.00
0.00
0.00
0.16
0.35
32.71
9.73
18.71
1.48
0.70
0.32
0.00
5.41
-2.28
0.05
-0.01
77.07
gr2
0.80
0.12
0.01
0.01
2.03
0.07
0.00
4.04
0.00
0.00
0.00
0.09
0.43
0.28
2.76
0.04
0.00
0.12
0.65
0.00
0.00
0.06
0.04
0.00
0.02
0.65
34.09
9.47
16.08
0.00
0.83
0.74
0.00
6.22
-2.62
0.06
-0.01
77.06
Vaulo, arkosic gneiss, V434-2011-R28/62.3
The sample is composed mainly of quartz, K-feldspar, plagioclase, amphibole, biotite, Fe-oxide,
titanite, zircon and apatite (Table. 6). The studied sample characterized by occurrences of minor
cerite (Ce) and allanite; these minerals occur as isolated grains filling fractures within quartz
(Fig. 12b, c). Electron microprobe analyses (EMPA) shows that cerite composed mainly from
SiO2 (20 %) and Ce2O3 (65 %) with content of Nd, Pr, Sm, Y and Th (Table. 8).
-
22
Figure 12. Backscattered electron micrographs of REE minerals from Tana Belt selected samples (a, b )
Allanite disseminated within quartz, (c) subhedral Cerite grain within plagioclase, (d) Bastnäsite and
allanite intergrowth with chlorite and surrounded by plagioclase and quartz.
Vaulo, amphibolites, V434-2011-R28/100.9
The mineralogical composition of the studied sample includes plagioclase, hornblende, biotite,
garnet, quartz, chlorite, zircon, ilmenite, chalcopyrite and pyrite (Table 6). Few grains of Bastnäsite and allanite are occur as filling the vugs within silicate minerals and associated with chlorite (Fig 12d). The Bastnäsite composed from CaO (4.5 %), Ce2O3 (34 %), Nd2O3 (9.5), La2O3
(18 %) and Pr2O3 (1.5 %) with REE2O3 about 65 % and high REE2O3/CaO ratio (14.5) Table (8).
Vaulo, granitic gneiss, V434-2011-R28/113.3
The studied sample composed mainly from mosaic of quartz, K-feldspar and plagioclase with
trace occurrences of biotite and hornblende. The accessory minerals include garnet, apatite, zircon and chlorite. The sample is characterized by dominant of Ca-REE fluorocarbonates as bastnäsite-(Ce) due to EPMA data for thin section of sample. The chemical analysis of bastnäsite(Ce) is reported in Table (9); Ca content ranges from 5.6 to 7.3 wt% CaO; Ce from 24 to 28.5
wt% Ce2O3; La from 10.5 to 13 wt% La2O3; Nd from 11.3 to 12 wt% Nd2O3; Pr from 2.7 to 3.4
wt% Pr2O3; Sm from 1.5 to 1.7 wt% Sm2O3; Gd from 1 to 1.6 wt% Gd2O3; Y from 1.2 to 2.7
-
23
wt% Y2O3; Th from 1.9 to 5.9 wt% ThO2; and F content in the range from 4.2 to 6.4 wt%. Regarding the chemical analysis of bastnäsite-(Ce), the high REE2O3/CaO ratios (8.3) indicates that
the REE dominance of bastnäsite-(Ce) is always present at Tana Belt samples.
Table 9. Representative EMPA results of Bastnäsite (Ce) in sample R28 (113.3).
sample
Mineral
Grain
SiO2
TiO2
Al2O3
V2O3
FeO
MnO
MgO
CaO
Na2O
SrO
SrO
BaO
Cs2O
P2O5
SO2
ZrO2
HfO2
UO2
ThO2
PbO
SnO2
Nb2O5
Ta2O5
Sc2O3
WO3
Y2O3
Ce2O3
Nd2O3
La2O3
Pr2O3
SmO
Gd2O3
Dy2O3
F
F=O
Cl
Cl = O
Total
bastn
bastn
R28(113.3)
bastn
bastn
bastn
bastn
bastn
bastn
gr1
2.64
0.35
0.87
0.00
1.27
0.08
0.03
6.13
0.00
0.00
0.00
0.03
0.44
0.11
0.00
0.13
0.05
0.21
4.63
0.03
0.00
0.02
0.75
0.00
0.00
2.16
25.59
11.38
12.93
3.24
1.64
1.28
0.00
4.21
-1.77
0.04
-0.01
78.46
gr2
2.78
0.54
0.64
0.00
1.58
0.10
0.00
6.37
0.00
0.00
0.00
0.01
0.39
0.47
0.00
0.21
0.05
0.05
3.51
0.00
0.00
0.09
0.00
0.00
0.28
0.00
27.14
11.33
12.09
3.18
1.59
0.98
0.00
4.74
-2.00
0.02
0.00
76.14
gr3
2.92
0.59
0.72
0.02
1.14
0.05
0.05
6.52
0.00
0.00
0.00
0.10
0.32
0.22
0.00
0.12
0.06
0.13
3.91
0.00
0.02
0.00
0.00
0.00
0.13
1.17
26.98
11.98
12.48
3.25
1.56
0.98
0.00
5.63
-2.37
0.08
-0.02
78.75
gr5
4.44
0.10
0.52
0.04
2.52
0.02
0.06
7.30
0.00
0.00
0.00
0.04
0.36
0.09
0.00
0.00
0.18
0.20
1.89
0.00
0.00
0.00
0.09
0.00
0.19
0.00
26.88
11.49
11.05
3.06
1.47
1.20
0.00
5.00
-2.11
0.06
-0.01
76.12
gr6
2.58
0.35
0.46
0.00
0.56
0.04
0.00
5.62
0.00
0.00
0.00
0.00
0.30
0.18
0.00
0.25
0.00
0.00
3.73
0.11
0.00
0.00
0.00
0.00
0.12
1.31
23.99
11.26
10.53
2.73
1.57
0.99
0.00
4.67
-1.97
0.09
-0.02
69.47
gr7
2.88
0.17
0.43
0.11
1.02
0.08
0.00
7.24
0.00
0.00
0.00
0.09
0.49
0.00
0.00
0.03
0.00
0.11
1.90
0.02
0.00
0.09
0.03
0.00
0.00
2.69
28.49
11.68
11.75
3.23
1.70
1.60
0.00
6.36
-2.68
0.07
-0.01
79.57
gr8
2.49
0.26
0.51
0.00
0.71
0.07
0.01
6.92
0.00
0.00
0.00
0.12
0.30
0.34
0.00
0.22
0.07
0.27
5.91
0.08
0.00
0.00
0.05
0.00
0.06
1.98
24.41
11.63
12.03
3.22
1.49
1.24
0.00
5.55
-2.34
0.07
-0.02
77.67
gr4
2.56
0.35
0.48
0.00
1.24
0.09
0.00
5.72
0.00
0.00
0.00
0.00
0.36
0.13
0.00
0.31
0.16
0.18
4.07
0.05
0.00
0.06
0.00
0.00
0.02
1.39
28.02
11.28
11.69
3.43
1.53
0.97
0.00
5.01
2.11
0.04
0.01
81.25
Backscattered electron micrographs of bastnäsite from the sample V434-2011-R28/113.3 show
that coarse-grained (100–500 µm) bastnäsite filling the interstices fractures and vug space and
replace apatite in quartz-K-feldspar-dominated rock sample (Fig. 11a, b). Bastnäsite occurs also
as isolated subhedral crystal within quartz and associated with apatite and zircon (Fig. 13c, d).
In Figure (14) bastnäsite occurs as filling vug space and associated with chlorite (Fig. 142b)
and/or clustering as larger bladed and tubular crystals within large vug spaces (Fig. 14 c, d).
-
24
Figure 13. Backscattered electron micrographs of REE minerals from sample V434-2011-R28/113.3,(a,
b) Bastnäsite filling the interstices fractures and vug space and associated with apatite, (c) Euhedral
coarse bastnäsite grain with apatite within quartz, (d) Elongated Bastnäsite surrounded by quartz and Kfeldspar.
-
25
Figure 14. Backscattered electron micrographs of REE minerals from sample V434-2011-R28/113.3,
(a) Small bastnäsite and removing the bastnäsite from filling spaces show black holes, (b) Rounded bastnäsite grain associated with chlorite, (c, d) Euhedral Bastnäsite grains filling the vugs and fractures.
-
26
3.2.2
Scanning electron analysis (SEM)
Ten drill core samples were selected from Vaulo and Mäkärä for REE-mineralogical study by
SEM (Table 10). These samples are mainly arkosic and granite gneisses. The main difference
between these banded rock types is that arkosic gneiss has finer grain size. They are composed of
quartz, albite or plagioclase?, K-feldspar, biotite, hornblende, magnetite, titanite and sericite with
accessory minerals as zircon, chlorite, allanite and xenotime. Back scattered electron images
BSE) and EDS analyzer of the studied sample revealed two types of allanite: allanite-(Ce) and
allanite-(Y), Allanite from the studied sample is characterized by compositional zoning, the zoning controlled by the abundance of light rare-earth elements (LREE) and Fe from core to the
edge of the crystal (Figs. 15, 16 and 17).
The Ce-dominated allanite is locally the dominated REE-bearing minerals in studied samples. It
is dominated by Ce (<10%) and incorporates small amounts of La and Nd (Tables 11 and 12),
whereas the Y-dominated allanite, allanite (Y) is dominated by Y (~30%) with low content of Nd
and Gd (Table 13).
The xenotime-(Y) crystals are identifiable under the scanning electronic microscope (SEM) and
with BSE images (Fig. 12). They form fine grain size (10-30 µm) overgrowth on prismatic zircon crystals, 30–120 mm in diameter. Three analyses of xenotime-(Y) overgrowths with zircon
in sample V4342011R8 (135.85) were analysis by EDS (Table 14). The xenotime grains were
composed as an average of Y (38 %), P (34 %), Si (19 %), Al (4 %), Ca (2.5 %) and Na (2 %).
Table 10. Drill core samples were selected to study by SEM.
Drill core samples
Mäkärä
V4342011R6 58.85
V4342011R6 179.8
V4342011R8 135.85
V4342011R9 98.5
V4342011R11 6.95
Arkosic gneiss
Arkosic gneiss
Arkosic gneiss
Granite gneiss
Granite gneiss
Vaulo
V4342011R20 70.15
V4342011R20 93.5
V4342011R21 72.7
V4342011R21 125.5
V4342011R24 103.05
Arkosic gneiss
Granite gneiss
Granite gneiss
Granite gneiss
Granite gneiss
-
27
Figure 15. Backscattered electron micrographs of REE minerals from Mäkärä samples (a, b, c ) Subhedral allanite grains associated with the main silicate minerals, (d)Fine monazite grain disseminated
within K-feldspar, (e) Xenotime intergrowth with zircon and surrounded by Ti-Nb mineral, (f) Zoning allanite disseminated within quartz and K-feldspar.
-
28
Figure 16. Backscattered electron micrographs of allanite from Vaulo samples (a, b, c ) Allanite occur
as spheroidal aggregates or fine-grained vug-filling structure, (d) Allanite associated with biotite, (e, f)
spheroidal allanite forms associated with amphibole and K-feldspar.
-
29
Figure 17. Backscattered electron micrographs of allanite from Vaulo samples (a, b ) Allanite grains
associated with biotite and K-feldspar, (c, d)Allanite occurs as spheroidal aggregates or vug-filling
structure, chlorite altered to allanite (in the rim), (f) spheroidal aggregates filled by altered allanite and
chlorite and enclosed by K-feldspar and mica. (c, d) Coarse allanite grain with quartz inclusion, (f)
Prismatic zircon grain contains apatite and clay minerals as inclusions.
-
30
Table 11. Selected EDS- analyses of allanite (Ce) from the Mäkärä samples.
R6/179.8
Spectrum Allanite (Ce)
R8/ 135.85
Allanite (Ce) 3
Allanite (Ce) 4
Allanite (Ce) 5
1
Allanite (Ce)
2
Allanite (Ce) 6
Al
14.42
16.78
13.16
2.27
16.42
15.19
Si
K
Ca
Ti
54.39
53.49
61.34
79.96
52.82
56.41
1.29
1.75
1.74
13.18
12.23
8.8
8.64
10.13
Fe
Ce
Nd
11.72
9.71
9.35
10.94
8.78
5
6.04
7.36
9.17
7.34
Total
100
100
100
3.78
8.38
3.86
100
100
100
Table 12. . Selected EDS- analyses of allanite (Ce) from the Vaulo samples.
R21/72.7
Spectrum Allanite (Ce)
1
-
Allanite
(Ce) 2
R28/36.0
Allanite (Ce) 3
Allanite (Ce)
4
Allanite (Ce)
5
Allanite (Ce) 6
Al
14.37
15.34
16.82
17.49
9.86
17.74
Si
61.54
61.05
60.22
47.41
62.96
54.91
K
1.29
Ca
8.99
10.04
9.96
11.95
5.72
10.49
Fe
6.88
7.85
7.5
14.66
10.08
10.71
Ce
6.92
5.72
4.47
8.49
11.38
6.15
Total
100
100
100
100
100
100
1.03
31
Table 13. Selected EDS- analyses of allanite (Y) from the Mäkärä sample V434 2011 R6/58.85.
Spectrum
Allanite(Y) 1
Allanite(Y) 2
Allanite(Y) 3
Na
Al
3.45
3.43
4.38
2.26
2.64
Si
Ca
48.38
9.96
48.4
8.36
42.84
12.26
Ti
Fe
Y
Nd
Gd
Total
3.02
4.26
30.93
2.75
3.27
3.31
33.42
100
23.55
4.14
4.97
100
100
Table 14. Selected EDS- analyses of xenotime (Y) from the Mäkärä sample V434 2011 R8/ 135.85.
Spectrum
Xenotime (Y) 1
Xenotime (Y) 2
Xenotime (Y) 3
Na
Al
Si
1.9
4.81
19.4
2.55
4.57
18.35
2.6
3.72
20.66
P
Ca
Y
33.99
2.32
37.57
34.62
1.27
38.64
32.95
5.41
34.66
100
100
100
Total
3.3
REE Geochemistry
Five samples of the arkosic gneiss and nine drill core samples from Tana Belt have been chosen
to perform REE analyses and the results are listed in Tables 15, 16, 17. The ΣREE contents of
the Tana Belt outcrop samples range from 596.9 to 938.2 ppm (average 781 ppm). The chondrite-normalized REE patterns of the studied samples exhibit trends similar to the normalized
REE patterns of international magmatic standard rock samples and display a decrease from
LREE towards HREE. The chondrite-normalized REE patterns for the studied samples also show
an increase in LREE, distinct negative Eu anomalies moderately steep with depletion of HREE
and a sharp negative Eu anomaly (Fig. 13). On the other hand, all the studied samples have positive Ce anomalies that may have resulted from the high concentration of Ce-minerals as bastnäsite-Ce and cerite-Ce. The Ce/Yb ratio is rather high and varies from 3.3 to 5.2, the Ce/Sm ratio from 2.3 to 4.2, La/Yb 2.1 to 7.1, La/Sm 1.7 to 3.8 and Eu/Eu* from 0.4 to 0.5.
The whole-rock chemical data of the studied sample in Tana Belt shows high concentrations of
Y, ranging from 155-210 ppm, and averaging about 1000 ppm ∑REE + Y oxides. Scanning electron microscopy indicates REE and Y residence in xenotime, bastnäsite, cerite and allanite, sug-
-
32
gesting that the heavy rare earth element (HREE) mineralisation in the form of xenotime was
accompanied by a second phase of the LREE mineralisation in the studied bedrocks. In general
the drill core samples from Vaulo were showing higher REE contents than Mäkärä samples.
Table 15. REE contents of the outcrop samples from Tana Belt.
REE/Sample
AMM$-2011-52.1
AMM$-2011-36.1
AMM$-2011-32.1
AMM$-2011-45.1
EAK1-2011-118.1
Ce
427
328
La
80.4
146
367
321
282
193
56.5
110
Nd
112
156
173
73.2
129
Pr
27.5
39.6
46.5
18.8
33.5
Sm
30
32
31.6
18.5
29.3
Gd
32.2
33.4
34.1
21.9
26.4
Dy
40.1
33.5
31
28.9
34.8
Er
26.8
22.3
21.1
20.1
22.8
Eu
4.55
4.51
4.83
3.27
3.72
Ho
8.73
7.26
6.67
6.3
7.37
Lu
3.29
2.97
2.67
2.52
3.51
Tb
6.18
5.52
5.46
4.43
5.07
Tm
3.67
3.06
2.91
2.94
3.3
Yb
22.4
19.7
18.4
18.5
22.2
Y
824.82
209
833.82
179
938.24
183
596.86
154
712.97
172
Th
27.7
20.7
25.9
27.1
28.2
U
4.97
4.35
4.47
5.63
15.2
Eu/Eu*
0.4
0.4
0.5
0.5
0.4
La/Yb
2.4
5.0
7.1
2.1
3.3
La/Sm
1.7
2.9
3.8
1.9
2.4
Ce/Yb
4.9
4.3
5.2
4.5
3.3
Ce/Sm
3.4
2.5
2.8
4.2
2.3
Eu/Yb
0.6
0.7
0.7
0.5
0.5
REE
-
33
Figure 18. Chondrite-normalized (Boynton, 1984) REE patterns of the Tana Belt samples.
-
34
Table 16. REE contents of Mäkärä drill core samples.
Drill core
R6 58.85–58.95
R6 179.70–179.80
R8 135.75–135.85
R9 98.35–98.45
R11 6.85–6.95
Ce
124
247
122
183
128
La
58.5
116
57.3
89.9
82
Nd
62.6
112
58.1
82.6
77.9
Pr
15.3
28.9
14.5
21.5
19.5
Sm
14.4
22.2
12.9
16.6
15.8
Gd
15.9
22.7
14.8
16.6
17
Dy
17.8
21.5
15.9
14.9
16.4
Er
11.3
12.3
10.3
8.73
10.2
Eu
2.7
2.77
2.15
2.93
2.59
Ho
3.77
4.28
3.36
2.98
3.44
Lu
1.6
1.62
1.51
1.26
1.36
Tb
2.77
3.48
2.51
2.55
2.72
Tm
1.66
1.81
1.54
1.3
1.49
Yb
10.9
11.5
10.2
8.46
9.34
REE
343.2
608.06
327.07
453.31
387.74
Y
95.5
103
86.4
73.9
90.3
Th
9.17
18.4
10.7
12.9
11.1
U
1.85
3.47
1.94
3.06
1.62
Table 17. REE contents of Vaulo drill core samples.
Drill core
R28 36.50-38.80
R28 43.30-46.50
R28 61.20-63.65
R28 107.80-110.30
Ce
371
99.9
341
280
La
128
37.7
131
126
Nd
137
52.1
135
127
Pr
35.9
12.1
35.2
32.2
Sm
27.7
11.4
27.2
24.3
Gd
26.3
11.5
25.4
23.3
Dy
28.2
11.2
25.6
23.4
Eu
4.33
2.79
3.68
3.69
Er
18.2
6.83
16.3
14.8
Ho
5.89
2.29
5.4
4.75
Lu
2.26
0.88
2.11
1.87
Tb
4.67
1.92
4.36
3.91
Tm
2.51
0.9
2.22
2.04
Yb
15.8
6.2
14.2
13.1
807.76
257.71
768.67
680.36
Y
157
65.6
145
125
Th
38.5
9.04
30.8
27
REE
-
35
4
CONCLUSIONS
1) The composition of REE minerals from the Tana Belt samples indicating, that the main
REE-minerals are bastnäsite, allanite and cerite. Comparisons between the studied samples indicate that the studied EAK1-2011-118.1, V434-2011-R28/36.0 and V434-2011R28/113.3 samples are dominated by REE-minerals.
2) The REE composition of the minerals is characterized by enrichment in Ce, La and to a
lesser extent Nd. The total REE content decreases from 75 wt % in cerite (Ce), 60% in
bastnaesite to 25 wt % in allanite.
3) SEM –BSE of the studies of s arkosic gneiss core samples from Mäkärä and Vaulo reveals the yttrium phosphate mineral xenotime as scattered grains within Ti-minerals and
as overgrowths on zircon. Allanite as the main REE-bearing mineral in studied samples
occurs as spheroidal aggregates or vug fillings structure, and the chlorite and bastnäsite
replacing the allanite grains.
4) The BSI images have shown that the secondary REE minerals are bastnäsite filling the
interstices fractures and vug space and replace apatite and chlorite within quartz and Kfeldspar.
5) REE contents are intermediate to high with range from 596.9 to 938.2 ppm in outcrop
samples. The LREE contents are dominantly higher than HREE contents with distinct
negative Eu anomalies and REE normalized patterns indicate decreasing abundances with
increasing atomic number.
6) Mineralogical and mineral chemical evidence demonstrates that hydrothermal processes
were responsible for the most REE mineralization in studied rocks. During hydrothermal
processes carbonate, phosphate and silicate minerals have been replaced by various assemblages of REE–minerals.
5
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