The Wiborg rapakivi batholith (1.64 Ga) in southeastern Finland with documented occurrences of REE, indium and Zn-Cu-Pb sulphide mineralization was studied. Hydrothermal greisen and quartz vein type Fe-Sn and Zn-Cu-Pb are found in the Kymi granite stock as intrusions. They are enriched with indium and rare earth elements, with roquesite (CuInS2) being a major indium- carrier, whereas monazite (Ce), allanite (Ce), bastnäesite (Ce), xenotime-(Y) and thorite are the main REE carriers. Combination of optical and field emission scanning electron microscopy (FE-SEM) and electron probe microanalysis (EPMA) were used to study the indium and REE-bearing mineral assemblages. EPMA of roquesite found in galena had a composition of 26.16% S, 0.02% Fe, 25.06% Cu, 0.03% Zn, 1.06% As, 0.31% Sb and 47.14% In. Substitution reaction Pb2+S2-<->Cu+In3+S2- is the cause of the incorporation of indium in the galena structure. The majority of the LREE are carried by monazite, bastnäesite and allanite, and the HREE by xenotime and zircon. There is a partial solid solution between monazite and xenotime with minor or trace amounts of LREE in xenotime grains (6.0 wt%). LREE (>95 mol% LREE) and less than 5 mol% HREE + Y reflects the enrichment of chondrite-normalized REE of the monazite grains of the Kymi granite stock. The xenotime grains (small and irregular) main composition contains 71 - 76 mol% YPO4, 16 - 27 mol% HREE, and 6 - 8 mol% LREE. It is believed that indium and REE-mineralization presence is due to the combination of magmatic and postmagmatic processes, particularly at later stages by fluid fractionation.
The Wiborg rapakivi batholith (1.64 Ga) in southeastern Finland (
The data presented in this study are the outcome of unique set of boreholes drilling during 2014 as part of a critical minerals project carried out by the Geological Survey of Finland (GTK). The study aimed to assess the potential for indium and REE minerals hosted by rapakivi granite and associated rocks in southern Finland. Here, we provide a detailed description of the accessory phases and mineral chemistry of indium and REE-bearing minerals within late-stage intrusions, which is important not only for the Wiborgite rapakivi granites, but also for other granitic complexes in the Palaeoproterozoic bedrock.
Thin sections were prepared from 14 samples of which 12 were selected from topaz-greisen mineralization veins, stockscheider pegmatite and even aplitic
granite for mineralogical and petrographical studies. Two samples were selected from Pb-Zn-Cu-In dominated quartz veins hosted by Wiborgite rapakivi granites. These samples covered two drilling depth intervals in the drill hole L433R1, between 18.65 to 18.95 m and 20.75 to 21.10, respectively (
Petrographic thin sections and polished thin sections of the heavy mineral concentrates were prepared from representative samples in order to investigate the mineralogical-textural characteristics of the indium- and REE-bearing minerals and their host rocks. REE-bearing minerals were identified from polished thin sections by optical microscopy and further by scanning electron microscopy (SEM) and electron microprobe (EMP).
Backscatter electron images (BSI) and quantitative microanalysis were taken with a JEOL JSM 5900 LV scanning electron microscope equipped with a JED-2300 energy dispersive system at the Electron optical laboratory of GTK, Finland. The operating voltage was fixed at 15 kV with a varying spot size during the qualitative analysis. A total of 20 grains of roquesite (the main host of indium) and REE-bearing minerals (monazite, allanite, bastnäesite and xenotime) were investigated and 320 chemical analyses were carried out using a CAMECA SX100/LKP electron microprobe at the laboratory of the Geological Survey of Finland (GTK), Espoo, Finland. The accelerating voltage was 15 keV with a beam current of 20 nA and a beam size of 5 μm respectively. The spot size was 1 μm in the analyses without fluorine and 5 μm when fluorine was determined.
The Kymi granite complex consists mainly of three modes of rocks; these include ovoidal alkali feldspar phenocrysts mantled by sodic plagioclase, quartz-feldspar porphyrtic texture with angular shape phenocrysts and porphyritic hornblende rapakivi texture composed of plagioclase feldspar, K-feldspar, quartz, biotite and hornblende [
Apatite (AP) is present in most of the studied samples as disseminations biotite, quartz and feldspar or in contact with zircon, sulphides, chlorite and REE-bearing minerals. A BSI image of some apatite crystals shows an approximately hexagonal basal section, 70 µm in diameter (
Fluorite (Fl): The late greisen mineralization veins of Kymi granite stock formed fluorite-rich hydrothermal fluids [
Cassiterite (Cst) is the main Sn-bearing mineral concentrator of Sn in the studied Kymi granite stock, southern Finland. It occurs as small bright grains or as inclusions within fluorite (Fl) (
No. | Sample | Al2O3 | FeO | CaO | SrO | P2O5 | F | *−O=F | Total |
---|---|---|---|---|---|---|---|---|---|
Apatite | |||||||||
1 | L434R1/18.95 | 0.04 | 0.01 | 54.04 | 0.11 | 42.27 | 4.87 | −2.05 | 99.62 |
2 | L434R1/18.95 | 0.00 | 0.00 | 54.19 | 0.10 | 42.01 | 4.97 | −2.09 | 99.27 |
3 | L434R1/21.10 | 0.00 | 0.02 | 53.72 | 0.05 | 42.22 | 5.54 | −2.33 | 99.43 |
4 | L443R3/150.4 | 0.00 | 0.06 | 53.48 | 0.06 | 43.49 | 4.14 | −1.74 | 100.13 |
5 | L443R3/150.4 | 0.00 | 0.05 | 53.62 | 0.04 | 42.46 | 4.93 | −2.07 | 99.63 |
Fluorite | |||||||||
6 | L434R1/20.95 | 0.43 | 0.00 | 70.91 | 0.05 | 0.00 | 46.86 | −19.73 | 98.59 |
7 | L434R1/20.95 | 0.01 | 0.21 | 72.87 | 0.06 | 0.00 | 44.08 | −18.56 | 98.72 |
8 | L434R1/21.10 | 0.01 | 0.03 | 72.87 | 0.10 | 0.00 | 41.94 | −17.66 | 97.32 |
9 | L434R1/21.10 | 0.03 | 0.00 | 74.89 | 0.10 | 0.00 | 41.36 | −17.42 | 98.98 |
10 | L434R1/21.10 | 0.00 | 0.02 | 74.02 | 0.03 | 0.00 | 41.19 | −17.35 | 97.97 |
Note: *−O=F: The equivalent of oxygen for halogens was accounted by subtracting it from the total calculated oxides.
No. | Sample | TiO2 | FeO | Nb2O5 | In2O3 | SnO2 | Total |
---|---|---|---|---|---|---|---|
1 | L434R1/21.10 | 0.77 | 0.57 | 0.0179 | 0.0114 | 98.32 | 99.69 |
2 | L434R1/21.10 | 0.68 | 0.49 | 0.0079 | 0.0047 | 97.80 | 98.98 |
3 | L434R1/21.10 | 0.72 | 0.27 | 0.2494 | 0.0100 | 98.65 | 99.90 |
4 | L434R1/21.10 | 0.46 | 0.38 | 0.7630 | 0.0026 | 98.13 | 99.74 |
crystals about 100 µm in length, and in contact with biotite (
Sulphides: Most widespread sulphide minerals found in the studied wiborgite rapakivi granites are sphalerite (Sp), galena (Gn) and chalcopyrite (Cp) are the dominants sulphide phases. Galena and sphalerite are intimately intergrowth and develop a rim replacement texture of sphalerite-galena (
The indium and REE-bearing mineral assemblages were investigated in polished thin sections of separated heavy mineral and petrographic thin sections by using a combination of a combination of optical and electronics microscopies (SEM& EPMA). Roquesite is a major indium carrier, while monazite, bastnäesite, allanite and xenotime are the dominant light rare earth element (LREE) minerals studied Kymi granite stock, southern Finland.
Roquesite (Roq) is a major indium carrier (ideal formula CuInS2) from the Kymi granite complex. It mainly occurs as 10 - 30-µm subhedral to anhedral, often found as angular crystals in galena (
No. | Sample | S | Cu | Fe | Ni | Co | Zn | Sb | Bi | Cd | Pb | Ag | Total |
---|---|---|---|---|---|---|---|---|---|---|---|---|---|
Galena | |||||||||||||
1 | L434R1/20.95 | 13.09 | 0.01 | 0.25 | 0.00 | 0.00 | 2.39 | 0.00 | 0.29 | 0.04 | 83.19 | 0.00 | 99.27 |
2 | L434R1/20.95 | 13.14 | 0.00 | 0.29 | 0.00 | 0.00 | 2.28 | 0.01 | 0.31 | 0.02 | 82.28 | 0.01 | 98.35 |
3 | L434R1/20.95 | 13.06 | 0.03 | 0.20 | 0.00 | 0.00 | 3.15 | 0.03 | 0.16 | 0.07 | 81.82 | 0.00 | 98.53 |
4 | L434R1/20.95 | 13.19 | 0.02 | 0.29 | 0.00 | 0.02 | 2.81 | 0.00 | 0.30 | 0.02 | 82.22 | 0.00 | 98.88 |
5 | L434R1/20.95 | 12.99 | 0.00 | 0.25 | 0.00 | 0.00 | 2.45 | 0.00 | 0.20 | 0.01 | 84.17 | 0.02 | 100.09 |
6 | L434R1/18.95 | 13.19 | 0.00 | 0.01 | 0.01 | 0.01 | 0.03 | 0.00 | 0.19 | 0.01 | 85.28 | 0.00 | 98.75 |
7 | L434R1/18.95 | 13.42 | 0.00 | 0.00 | 0.00 | 0.00 | 0.58 | 0.00 | 0.29 | 0.05 | 83.98 | 0.01 | 98.32 |
Sphalerite | |||||||||||||
8 | L434R1/20.95 | 33.54 | 0.01 | 0.21 | 0.00 | 0.00 | 65.58 | 0.00 | 0.00 | 0.24 | 0.00 | 0.00 | 99.59 |
9 | L434R1/20.95 | 33.58 | 0.00 | 0.22 | 0.00 | 0.00 | 64.43 | 0.00 | 0.00 | 0.23 | 0.03 | 0.00 | 98.49 |
10 | L434R1/20.95 | 33.71 | 0.00 | 0.20 | 0.00 | 0.01 | 65.21 | 0.00 | 0.00 | 0.18 | 0.09 | 0.00 | 99.40 |
11 | L434R1/21.10 | 34.22 | 0.01 | 0.13 | 0.01 | 0.00 | 63.66 | 0.00 | 0.10 | 0.37 | 0.06 | 0.00 | 98.58 |
12 | L434R1/21.10 | 34.15 | 0.00 | 0.15 | 0.00 | 0.01 | 63.26 | 0.02 | 0.00 | 0.31 | 0.10 | 0.00 | 98.02 |
13 | L434R1/21.10 | 34.23 | 0.01 | 0.15 | 0.01 | 0.00 | 63.00 | 0.00 | 0.00 | 0.34 | 0.02 | 0.00 | 97.79 |
Chalcopyrite | |||||||||||||
14 | L434R1/21.10 | 34.52 | 32.80 | 30.27 | 0.00 | 0.00 | 0.00 | 0.00 | 0.03 | 0.00 | 0.35 | 0.00 | 97.97 |
15 | L434R1/21.10 | 34.58 | 33.07 | 30.37 | 0.00 | 0.00 | 0.00 | 0.00 | 0.00 | 0.00 | 0.42 | 0.00 | 98.45 |
16 | L434R1/21.10 | 34.71 | 32.94 | 30.26 | 0.00 | 0.00 | 0.00 | 0.00 | 0.00 | 0.00 | 0.41 | 0.00 | 98.32 |
fine grains/crystals within the galena (
Monazite (Mnz) occurs as euhedral to subhedral crystals (diameter 50 - 100 µm) in mineralized greisen of Kymi granite. Monazite was found association with xenotime, needle-shaped bastnäesite and fluorite (
Bastnäesite (Bsn) in the studied rapakivi granite is mostly present as acicular or needle-shaped crystals forming either radial accumulations or intricate cross- cutting grids within a variety of minerals such as monazite, fluorite and biotite (
Element | Roq1 | Roq2 | Roq3 | Roq4 | Roq5 | Roq6 | Roq7 | Roq8 | Roq9 | Roq10 |
---|---|---|---|---|---|---|---|---|---|---|
S | 26.17 | 26.19 | 26.28 | 26.04 | 26.10 | 26.05 | 26.21 | 26.13 | 26.25 | 26.18 |
Fe | 0.04 | 0.00 | 0.01 | 0.01 | 0.00 | 0.00 | 0.05 | 0.06 | 0.01 | 0.03 |
Cu | 25.12 | 25.05 | 25.01 | 24.99 | 25.02 | 24.62 | 25.32 | 25.21 | 25.18 | 24.81 |
Zn | 0.06 | 0.04 | 0.04 | 0.02 | 0.00 | 0.00 | 0.04 | 0.01 | 0.07 | 0.02 |
As | 1.05 | 1.00 | 0.95 | 1.07 | 1.09 | 1.31 | 1.11 | 1.00 | 0.99 | 1.16 |
In | 47.17 | 47.61 | 47.26 | 46.57 | 47.31 | 46.85 | 46.88 | 47.28 | 47.35 | 46.61 |
Sb | 0.17 | 0.33 | 0.43 | 0.29 | 0.33 | 0.25 | 0.34 | 0.34 | 0.30 | 0.37 |
Total | 99.78 | 100.22 | 99.99 | 98.98 | 99.85 | 99.08 | 99.95 | 100.03 | 100.14 | 99.18 |
fluorine-rich hydrothermal solutions resulting in the deposition of REE-minerals (allanite, bastnäesite) and fluorite [
Allanite (Aln) analysed in the present study (
Xenotime (Xnt) is extremely rare and identified as euhedral to anhedral grains (10 - 50 μm) embedded in quartz (
Sample | L443R3/137.6 | L434R1/18.95 | L434R1/21.10 | L434R1/20.95 | ||||||
---|---|---|---|---|---|---|---|---|---|---|
Mineral | Mnz1 | Mnz2 | Mnz3 | Mnz4 | Bsn1 | Bsn 2 | Bsn 3 | Aln1 | Aln2 | Aln3 |
SiO2 (wt%) | 1.53 | 0.93 | 2.89 | 3.21 | 1.86 | 2.26 | 2.80 | 30.16 | 31.40 | 32.22 |
P2O5 | 27.58 | 27.69 | 28.43 | 28.36 | 0.14 | 0.09 | 0.10 | 0.14 | 0.05 | 0.19 |
CaO | 0.39 | 0.20 | 0.25 | 0.24 | 8.99 | 7.49 | 6.19 | 11.79 | 10.52 | 10.68 |
TiO2 | n.d | n.d. | n.d | n.d | n.d | n,d. | n.d | 1.27 | 1.32 | 1.27 |
Al2O3 | n.d | n.d. | n.d | n.d | n.d | n,d. | n.d | 10.29 | 10.67 | 10.19 |
FeO | n.d | n.d. | n.d | n.d | n.d | n,d. | n.d | 10.30 | 9.59 | 8.84 |
UO2 | 0.21 | 0.07 | 0.05 | 0.03 | 0.02 | 0.00 | 0.05 | 0.03 | 0.05 | 0.00 |
ThO2 | 3.40 | 3.21 | 1.59 | 1.53 | 3.82 | 0.36 | 1.20 | 0.80 | 1.32 | 1.51 |
Y2O3 | 1.43 | 1.00 | 1.20 | 1.59 | 2.41 | 1.74 | 3.44 | 0.09 | 0.04 | 0.09 |
Ce2O3 | 30.75 | 30.04 | 33.11 | 33.00 | 22.23 | 33.68 | 31.66 | 18.39 | 20.10 | 20.39 |
Nd2O3 | 12.83 | 10.35 | 12.25 | 12.49 | 7.82 | 11.64 | 11.14 | 5.99 | 5.13 | 5.89 |
La2O3 | 12.33 | 11.82 | 13.20 | 13.58 | 10.43 | 17.94 | 13.70 | 7.99 | 7.19 | 6.37 |
Pr2O3 | 3.27 | 3.30 | 3.57 | 3.37 | 2.19 | 3.23 | 2.95 | 0.65 | 1.02 | 0.76 |
Sm2O3 | 1.99 | 2.07 | 2.22 | 1.92 | 1.11 | 1.33 | 1.99 | 0.41 | 0.51 | 0.38 |
Gd2O3 | 1.51 | 1.34 | 1.55 | 1.43 | 0.95 | 0.80 | 1.72 | 0.11 | 0.25 | 0.08 |
Dy2O3 | 0.45 | 0.26 | 0.45 | 0.56 | 0.55 | 0.22 | 0.79 | 1.40 | 1.37 | 1.65 |
Ho2O3 | 0.08 | 0.01 | 0.00 | 0.00 | 0.00 | 0.06 | 0.00 | n.d. | n.d. | n.d. |
Er2O3 | 0.10 | 0.12 | 0.03 | 0.10 | 0.18 | 0.17 | 0.29 | 0.17 | 0.01 | 0.30 |
Yb2O3 | 0.01 | 0.00 | 0.00 | 0.00 | 0.05 | 0.00 | 0.03 | 0.05 | 0.00 | 0.14 |
Lu2O3 | 0.00 | 0.00 | 0.02 | 0.15 | 0.03 | 0.07 | 0.04 | 0.21 | 0.05 | 0.00 |
REE | 63.33 | 59.32 | 66.41 | 66.59 | 45.56 | 69.14 | 64.31 | 35.37 | 35.63 | 35.95 |
F | 1.05 | 0.93 | 1.97 | 1.07 | 9.01 | 8.01 | 6.71 | 0.47 | 0.51 | 0.50 |
Total | 97.95 | 99.11 | 100.88 | 101.64 | 72.03 | 89.33 | 84.89 | 100.29 | 100.59 | 100.96 |
Structural formulae based on 4 oxygen atoms | ||||||||||
Si (apfu) | 0.15 | 0.10 | 0.25 | 0.28 | 0.17 | 0.20 | 0.27 | 1.19 | 1.22 | 1.24 |
P | 1.12 | 1.20 | 1.04 | 1.05 | 0.01 | 0.00 | 0.00 | 0.00 | 0.00 | 0.00 |
Ca | 0.04 | 0.02 | 0.02 | 0.02 | 0.90 | 0.71 | 0.63 | 0.50 | 0.44 | 0.44 |
Ti | n.d | n.d. | n.d | n.d | n.d | n,d. | n.d | 0.04 | 0.04 | 0.04 |
Al | n.d | n.d. | n.d | n.d | n.d | n,d. | n.d | 0.24 | 0.24 | 0.23 |
Fe | n.d | n.d. | n.d | n.d | n.d | n,d. | n.d | 0.34 | 0.31 | 0.28 |
U | 0.00 | 0.00 | 0.00 | 0.00 | 0.00 | 0.00 | 0.00 | 0.00 | 0.00 | 0.00 |
Th | 0.07 | 0.07 | 0.03 | 0.03 | 0.08 | 0.01 | 0.03 | 0.01 | 0.01 | 0.01 |
Y | 0.03 | 0.02 | 0.02 | 0.03 | 0.05 | 0.04 | 0.08 | 0.00 | 0.00 | 0.00 |
Ce | 0.54 | 0.56 | 0.52 | 0.53 | 0.38 | 0.55 | 0.55 | 0.13 | 0.14 | 0.14 |
Nd | 0.20 | 0.19 | 0.19 | 0.19 | 0.13 | 0.18 | 0.19 | 0.04 | 0.04 | 0.04 |
La | 0.22 | 0.22 | 0.21 | 0.22 | 0.18 | 0.29 | 0.24 | 0.06 | 0.05 | 0.05 |
---|---|---|---|---|---|---|---|---|---|---|
Pr | 0.06 | 0.06 | 0.06 | 0.05 | 0.04 | 0.05 | 0.05 | 0.00 | 0.01 | 0.01 |
Sm | 0.03 | 0.04 | 0.03 | 0.03 | 0.02 | 0.02 | 0.03 | 0.00 | 0.00 | 0.00 |
Gd | 0.02 | 0.02 | 0.02 | 0.02 | 0.01 | 0.01 | 0.03 | 0.00 | 0.00 | 0.00 |
Dy | 0.01 | 0.00 | 0.01 | 0.01 | 0.01 | 0.00 | 0.01 | 0.01 | 0.01 | 0.01 |
Ho | 0.00 | 0.00 | 0.00 | 0.00 | 0.00 | 0.00 | 0.00 | 0.00 | 0.00 | 0.00 |
Er | 0.00 | 0.00 | 0.00 | 0.00 | 0.00 | 0.00 | 0.00 | 0.00 | 0.00 | 0.00 |
Yb | 0.00 | 0.00 | 0.00 | 0.00 | 0.00 | 0.00 | 0.00 | 0.00 | 0.00 | 0.00 |
Lu | 0.00 | 0.00 | 0.00 | 0.00 | 0.00 | 0.00 | 0.00 | 0.06 | 0.06 | 0.06 |
F | 0.32 | 0.30 | 0.53 | 0.30 | 2.67 | 2.25 | 2.01 | 2.56 | 2.52 | 2.50 |
Total | 2.82 | 2.82 | 2.94 | 2.77 | 4.66 | 4.33 | 4.12 | 7.74 | 4.44 | 5.27 |
(La/Sm)n | 3.89 | 3.59 | 3.74 | 4.44 | 5.88 | 8.48 | 4.33 | 2.58 | 2.27 | 1.79 |
(La/Nd)n | 1.86 | 2.21 | 2.09 | 2.10 | 2.58 | 2.98 | 2.38 | 2.42 | 2.58 | 2.98 |
LREE (6 wt%) in the studied xenotime grains. In addition, monazites show some occurrences of HREE in minor or trace amounts (HREE + Y2O3 between 1.3 to 2.5 wt%).
Kymi granite stock in southeastern Finland and especially the related greisens are enriched in REE, In, F and Sn and contain various sulphide mineralization such as sphalerite, galena, chalcopyrite and arsenopyrite. An examination of the distribution of REE in the studied rapakivi granites revealed that a large proportion of the LREE were hosted in monazite and bastnäesite, whereas the HREE were commonly hosted in xenotime, thorite and zircon (
normalized REE patterns show that individual HREE tends to be enriched in specific minerals (Figures 4(d)-(f)).
In the studied monazite grains from the Kymi granite stock, the main constituents are La, Ce and Nd (La 0.21 - 0.25 apfu, Ce 0.52 - 0.57 apfu, Nd 0.19 - 0.21 apfu) PO4, with HREE + Y elements between 0.05 - 0.07 apfu. Most of the monazite grains analysed in this study contain more than 95 mol% LREE, and less than 5 mol% HREE + Y (
The solid solution between monazite and xenotime is limited between 6 - 8 mol% LREE in xenotime and between 4 - 5 mol% HREE + Y in monazite (
Mineralized greisen veins and deposits generally occur in association with highly fractionated granitic intrusions [
Sample | L434R1/18.95 | L443R3/133.40 | L434R1/20.95 | L434R1/18.95 | ||||
---|---|---|---|---|---|---|---|---|
Mineral | Xnt1 | Xnt2 | Xnt3 | Xnt4 | Thr1 | Thr2 | Thr3 | Thr4 |
SiO2 (wt%) | 0.52 | 0.50 | 0.48 | 0.20 | 20.74 | 18.23 | 18.06 | 16.06 |
P2O5 | 32.27 | 32.24 | 33.60 | 34.36 | 1.11 | 1.00 | 1.56 | 2.86 |
CaO | 0.04 | 0.05 | 0.00 | 0.03 | 2.25 | 2.25 | 1.87 | 0.70 |
PbO | 0.17 | 0.12 | 0.39 | 0.37 | 0.28 | 0.19 | 2.36 | 0.14 |
UO2 | 0.31 | 0.35 | 0.47 | 0.15 | 1.62 | 1.76 | 0.99 | 8.29 |
ThO2 | 0.26 | 0.29 | 0.46 | 0.17 | 68.12 | 70.19 | 69.57 | 49.09 |
Y2O3 | 42.66 | 41.84 | 38.72 | 40.88 | 0.23 | 0.12 | 0.38 | 10.03 |
Ce2O3 | 0.22 | 0.29 | 0.25 | 0.21 | 1.66 | 1.54 | 1.82 | 0.45 |
Nd2O3 | 0.02 | 0.06 | 0.42 | 0.21 | 0.58 | 0.82 | 0.69 | 0.37 |
La2O3 | 0.40 | 0.52 | 0.00 | 0.05 | 1.07 | 1.14 | 0.73 | 0.02 |
Pr2O3 | 0.54 | 0.54 | 0.00 | 0.03 | 0.20 | 0.15 | 0.08 | 0.03 |
Sm2O3 | 4.55 | 4.77 | 3.96 | 0.72 | 0.19 | 0.11 | 0.11 | 0.35 |
Gd2O3 | 0.00 | 0.08 | 5.27 | 5.12 | 0.23 | 0.06 | 0.12 | 1.58 |
Dy2O3 | 4.57 | 4.67 | 5.53 | 5.49 | 0.06 | 0.00 | 0.00 | 2.26 |
Ho2O3 | 0.58 | 0.81 | 0.56 | 0.61 | 0.00 | 0.17 | 0.01 | 0.39 |
Er2O3 | 3.63 | 3.90 | 4.10 | 3.90 | 0.24 | 0.19 | 0.17 | 1.44 |
Yb2O3 | 4.27 | 4.32 | 4.70 | 4.80 | 0.00 | 0.00 | 0.01 | 0.90 |
Lu2O3 | 0.72 | 0.69 | 0.55 | 0.71 | 0.03 | 0.00 | 0.00 | 0.26 |
F | 0.15 | 0.17 | 0.11 | 0.14 | 0.87 | 1.21 | 1.49 | 0.56 | ||||
---|---|---|---|---|---|---|---|---|---|---|---|---|
Total | 95.90 | 96.19 | 99.57 | 98.15 | 99.47 | 99.12 | 99.92 | 96.86 | ||||
Structural formulae based on 4 oxygen atoms | ||||||||||||
Si (apfu) | 0.050 | 0.047 | 0.045 | 0.019 | 1.050 | 0.967 | 0.959 | 0.957 | ||||
P | 1.304 | 1.304 | 1.330 | 1.373 | 0.024 | 0.022 | 0.035 | 0.072 | ||||
Ca | 0.004 | 0.005 | 0.000 | 0.003 | 0.122 | 0.128 | 0.106 | 0.044 | ||||
Pb | 0.004 | 0.003 | 0.010 | 0.009 | 0.004 | 0.003 | 0.034 | 0.002 | ||||
U | 0.007 | 0.008 | 0.010 | 0.003 | 0.018 | 0.021 | 0.012 | 0.110 | ||||
Th | 0.006 | 0.006 | 0.010 | 0.004 | 0.785 | 0.848 | 0.840 | 0.666 | ||||
Y | 0.957 | 0.939 | 0.850 | 0.906 | 0.003 | 0.001 | 0.005 | 0.140 | ||||
Ce | 0.004 | 0.005 | 0.004 | 0.004 | 0.015 | 0.015 | 0.018 | 0.005 | ||||
Nd | 0.000 | 0.001 | 0.007 | 0.004 | 0.005 | 0.008 | 0.007 | 0.004 | ||||
La | 0.007 | 0.009 | 0.000 | 0.001 | 0.010 | 0.011 | 0.007 | 0.000 | ||||
Pr | 0.009 | 0.009 | 0.000 | 0.001 | 0.002 | 0.001 | 0.001 | 0.000 | ||||
Sm | 0.075 | 0.078 | 0.064 | 0.012 | 0.002 | 0.001 | 0.001 | 0.004 | ||||
Gd | 0.000 | 0.001 | 0.082 | 0.080 | 0.002 | 0.001 | 0.001 | 0.016 | ||||
Dy | 0.070 | 0.072 | 0.083 | 0.084 | 0.000 | 0.000 | 0.000 | 0.022 | ||||
Ho | 0.009 | 0.012 | 0.008 | 0.009 | 0.000 | 0.001 | 0.000 | 0.004 | ||||
Er | 0.054 | 0.059 | 0.060 | 0.058 | 0.002 | 0.002 | 0.001 | 0.013 | ||||
Yb | 0.062 | 0.063 | 0.067 | 0.069 | 0.000 | 0.000 | 0.000 | 0.008 | ||||
Lu | 0.010 | 0.010 | 0.008 | 0.010 | 0.000 | 0.000 | 0.000 | 0.002 | ||||
F | 0.047 | 0.052 | 0.034 | 0.042 | 0.140 | 0.204 | 0.251 | 0.105 | ||||
Total | 2.680 | 2.684 | 2.671 | 2.690 | 2.184 | 2.234 | 2.277 | 2.175 | ||||
(La/Sm)n | 0.054 | 0.068 | 0.000 | 0.041 | 3.450 | 6.673 | 4.158 | 0.044 | ||||
(La/Nd)n | 31.750 | 18.556 | 0.000 | 0.429 | 3.557 | 2.679 | 2.079 | 0.129 | ||||
the surrounding rapakivi granites. These intrusions are commonly enriched in REE, indium, lithium, fluorine and beryllium, and contain sulphide minerals of Cu, Pb, Zn, As, Sn and W [
Recently, Valkama et al. [
The main accessory minerals hosted in these greisens are fluorite, cassiterite, wolframite, genthelvite, galena, sphalerite and chalcopyrite. The present study demonstrated that indium was initially concentrated in galena, and we have discovered new occurrences of the copper-indium sulphide mineral roquesite (nominally CuInS2) as minute grains included in galena. This enrichment of galena in indium indicates the availability of Cu, In, Zn and Pb as isomorphic substitutions in natural sulphide systems. The indium substitution in galena are unknown, although it might be expect a considerable solid solution between galena and roquesite (Pb2+S2− ↔ Cu+In3+S2−), given their comparable structures. An investigation into the solubility of indium in hydrothermal synthesized galena and sphalerite was carried out by [
1) The occurrence of greisen intrusions within the Kymi granite stock and as well in the surrounding wiborgite rapakivi granites, such as albite-topaz-REE microgranite dikes and mineralization greisen veins of F-Sn-Zn-Pb-Cu, is due to primary magmatic fluids and postmagmatic processes, which strongly enriched in fluorine and tin, respectively. These intrusions host In-REE minerals, with roquesite (CuInS2) being a major indium carrier, whereas monazite (Ce), allanite (Ce), Bastnäesite (Ce), xenotime-(Y) and thorite are the main REE carriers.
2) Mineralogical investigations show the dominating LREE-bearing minerals of monazite, allanite and bastnäesite, while the HREE-bearing minerals include thorite, xenotime and zircon. F-rich granitic melt has been intruded and cross-cutting magmatic system at later stages, which plays an important role in the genesis of REE mineralization.
3) The studied Kymi granite stock may include variable amounts of sulphides, such as galena, sphalerite, pyrite and chalcopyrite. These sulphide assemblages occur in variable amounts and may be precipitated from hydrothermal solutions during the late stage of crystallization as filling of fractures, of open vugs and of the spaces within the studied rapakivi granites. Indium association with sulphide, mainly galena, can be distinguished on the basis of a microanalytical study of the sulphide assemblages. The results demonstrate that indium prefers galena over sphalerite and chalcopyrite. This could be due to possible substitution of copper and indium with lead in galena. A probable substitution is Pb2+S2− ↔ Cu+In3+S2−, which gives a similar ionic radius and the same charges. Furthermore, the strong correlation between copper, iron and zinc in galena could also play an important role. However, another likely suggestion is that zinc presented in galena is replaced by indium, although the coupled substitution 2(Pb2+Zn+) = Cu+In3+ is also present.
Al-Ani, T., Ahtola, T., Kuusela, J. and Al-Ansari, N. (2018) Mineralogical and Petrographic Characteristics of Indium and REE-Bearing Accessory Phases in the Kymi Granite Stock, Southern Finland. Natural Resources, 9, 23-41. https://doi.org/10.4236/nr.2018.92003