M19/3231/2009/33 20.5.2009 Rovaniemi

Geochemistry and Mineralogy of REE in Virtasalmi kaolin deposits, SE Finland

Thair Al-Ani and Olli Sarapää

GEOLOGICAL SURVEY OF FINLAND DOCUMENTATION PAGE Date / Rec. no.

20.5.2009

Type of report

M19Authors

Thair Al-Ani and Olli Sarapää Commissioned by GTK

Title of report

Geochemistry and Mineralogy of REE in Virtasalmi kaolin deposits, SE Finland Abstract

The aim of this study was to find out the potential of Virtasalmi kaolins for ionic type REE-deposits. The samples for mineralogical and chemical studies were selected from the drill cores of the Litmanen, Eteläkylä, Vuorijoki and Montola deposits. Analytical methods used include the major/rare earth elements geochemistry (methods 308M and 511; ICP-MS), and mineralogy (XRD, SEM, microprobe). A geochemical and mineralogical study has allowed us to address the factors controlling distribution patterns, residence and behaviour of REE during kaolinization of the parent rocks in Virtasalmi kaolin deposits, SE Finland. Mineral composition of the deeply weathered samples is dominated by kaolinite, with minor amount of quartz, muscovite-illite and traces of resistant minerals (rutile, zircon and mona-zite). There is a gradual transition zone between kaolin and its parent rocks. The transition zone and the primary features show the residual origin of kaolin. Variable amounts of Si, Fe, Ca, Na and K were lost from the weather-ing profiles, whereas Al, Ti, Zr, LOI and REE were concentrated in the residual kaolin. The source of REEs in Virtasalami is diverse, with one or several dominant sources in the specific kaolin profiles. According to the this study and previous study by Olli Sarapää (1996), two factors cause the REEs concentration in Virtasalmi kaolins: The major sources of REEs is the sorption of the rare earth elements (REE) on a kaolinite and about 50-85% of the total REE in Virtasalmi kaolins was adsorbed from solution onto kaolinite and halloysite minerals during kaolinization process. The residual REE-bearing minerals such as Zircon and monazite, which were derived from parent rocks as the second source of REEs enrichment in kaolins. Chondrite-normalized REE patterns of the kaolins show an overall enrichment of LREE (Lan/Smn=3-5 and Lan/Ybn = 6-19), HREE depletion (Gdn/Ybn = 1.3-2.6) and slightly negative Eu anomaly (Eu/Eu* >1), probably inherited from the parent rocks. Similarly, the parent rocks –normalized REE distribution is characterized by a strong depletion in HREE (heavy REE) and a positive Eu anomaly (3.3 in Eteläkylä) due to plagioclase presence in the source rock; tonalite and slightly enriched in LREE. The findings of the present study, such as correlative behaviour among P2O5, kaolinite% and LREE, beside the enrichment of REE in clay-rich layers with depth support the three processes for fractionation and enrichment of REE during weathering and kaolinization: (i) selective leaching of rocks containing both stable and unstable REE-bearing minerals; (ii) adsorption onto clay minerals; and (ii) presence of possible secondary LREE-bearing minerals. The present study also show, that the total REE content of kaolin in basal part of weathering profile reaches maximum 0.1-0.2% in aqua regia soluble form at Litmanen and Eteläkylä deposits.

Keywords

Rare earth elements, REE, mineralogy, geochemistry, mineralogy, kaolin deposits, kaolinite, halloysite, monazite, Geographical area

Virtasalmi, Litmanen, Eteläkylä, Vuorijoki, Montola Map sheet

323109, 323204, Other information

Report serial

Archive code M19/3231/2009/33

Total pages

20 Language

English Price

Confidentiality

Confidential until 31.12.2011 Unit and section

Project code

2141007 Signature/name

Thair Al-Ani Signature/name

Olli Sarapää

Contents

Documentation page

1 INTRODUCTION 1

2 SAMPLES AND ANALYSIS 1 ICP-MS (method 511) 2 ICP-MS (method 308M) 2

3 RESULTS 3 3.1 Mineralogy 3 3.2 Geochemistry 5

3.2.1 Major elements 5 3.2.2 REE behavior in the weathered rocks 6 3.2.3 The partial content of REE in kaolin samples 7 3.2.4 Total REE content in parent rocks and kaolin 11

4 SUMMARY AND CONCLUSION 18

5 REFERENCES 19

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1 INTRODUCTION The aim of this study was to find out the potential of Virtasalmi kaolins for ionic type REE-deposits. The sorption of the rare earth elements (REEs) onto kaolinite is one of the interests to the geo-chemical community. Clay minerals are common products of hydrothermal alteration, chemical weathering and diagenesis. Petrographic evidence indicates that some REE redistribution occurs under these low –temperature conditions (McLennan, 1989). Indeed, some petrographic evi-dences show that REE remobilization may occur during these processes and that adsorption by clay minerals plays important roles in such adsorption and fractionation process (Stephen, 1998). Ionic type REE deposits occur generally in the weathering crusts of the granitic rocks in Jiangxi Province—Longnan and Xunwu, China, the former yielding HREE- and yttrium-rich material and the other, LREE-rich material. This type of deposits covers over 25 % of the REE produc-tion in the world. During weathering rare earth elements with positively charged trivalent ions are considered to be adsorbed on negatively charged surfaces of the clay minerals such as kaolinite and halloysite (Yang et al., 1981). Both of them are polymorphs of Al2Si2O5 (OH) 4. The mineralogical studies of the Virtasalmi kaolins indicate that the clay fraction of kaolin is composed mostly of kaolinite and in places considerable amount of metahalloysite or dehydrated halloysite (Sarapää 1996, Al-Ani et al. 2006). The distribution and behavior of REE in weathering profile depend on several factors, including the physicochemical conditions of the alteration environment and the relative stability of REE-bearing primary minerals in the parent rocks. In the weathering of granitoids as in studied area, most of the REE (Z=57-71) very similar chemical properties, are incorporated in accessory min-erals resistant to chemical weathering of rocks. It is therefore not supervising that REE have tra-ditionally been regarded as relatively immobile during subtropical weathering and clay forma-tion. Galan et al. (2007) considered the kaolin deposit represents a large REE storage reservoir and REE have accumulated in the kaolinized granite at total concentration greater than that ob-served in the fresh granite (24.3 ppm), and their distributed strongly correlates with the grain size of the samples. This study presents the result of mineralogical and geochemical studies on kaolin weathering profiles developed over quartz-feldspar gneiss and tonalite rocks of Virtasalmi kaolin deposits, with a two fold objective. First to determine the abundance and distribution of REE in the stud-ied kaolin profiles, and the second was to address the factors controlling the distribution pattern and behavior of REE during kaolinization process.

2 SAMPLES AND ANALYSIS The samples for mineralogical and chemical studies were selected from the drill cores of the Litmanen, Eteläkylä, Vuorijoki and Montola deposits. The detailed description of these deposits have been presented in the work of Sarapää 1996 and existing analytical data from that work was also exploited in the selection of drill cores.

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The present study is based on modal mineralogical and geochemical analyses of weathered rocks and kaolin samples from four complete profiles in Virtasalmi deposits. A total of 23 samples were collected from weathered bedrocks and kaolinitic deposits, which mainly originated as weathering products of parent rocks; tonalite, amphibolite and quartz-feldspar gneiss. The min-eralogical study of the samples has been investigated using a combination of optical microscopy, X-ray diffraction (XRD), scanning electron microscopy (SEM) with an EDX system, and elec-tron microprobe X-ray analyzer. Chemical analysis of the REE was done at Labtium laboratory in Espoo. Two different methods have been used for analysis of the rare earth elements: first after partial dissolution (method 511) the REE were analyzed by ICP-MS to measure the partial REE content in kaolin samples or mo-bile REE and secondly by using total REE analyse, method 308M. For more details on analytical techniques and quality control procedures see Niskavaara (1995).

ICP-MS (method 511) 0.3 g subsample was digested for 2 hours at 90 ºC with 3 ml of aqua regia (1:3 HCl and HNO3). After digestion samples were diluted with water to 15 ml, mixed and centrifuged. The clear solu-tion was analysis with ICP-MS technique for 26 elements including REE (La-Y) (Labtium method 511 Niskavaara, 1995).

ICP-MS (method 308M) Total element ICP-MS analyses were preformed by mixing 0.2 g of pulverised sample with 10 ml of 40 % hydrofluoric acid and 4 ml of 70 % perchloric acid in a Teflon dish. After evapora-tion on a hot plate, the residue was dissolved in 20 ml of 8 mol/l nitric acids and 1 ml of 30 % hydrogen peroxide. The solution was filtered and the filtrate was saved. The filter was ashed in a platinum crucible. The residue was fused with 0.2 g of lithium metaborate and 0.02 g of sodium perborate and then dissolved in 5 ml of 0.8 mol/l nitric acid. This solution was added to the fil-trate and the combined solution was made up to 100 ml (1.8 mol/l nitric acid). The ICP-MS de-terminations were performed with a Perkin-Elmer Sciex Elan 5000 instrument using normal resolution and external calibration. All concentrations were determined by one measurement from one dilution of the sample. The acid dissolution followed by fusion used for this method effectively digest most refractory minerals. However, the major disadvantage of all fusion meth-ods is the introduction of large amounts of total dissolved solids, which necessitates increased dilution and may cause some trace element concentrations in the solution to become too low for quantitative analysis (Totland, Jarvis & Jarvis 1992). The method is described by Rautiainen et al. (1996).

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3 RESULTS

3.1 Mineralogy The mineral composition of the bulk samples of the drill core samples of Litmanen and Eteläkylä are shown in Table 1. The main minerals identified by XRD in the kaolin deposits are kaolinite [Al2Si2O5 (OH)4], quartz, plagioclase and mica, with minor amounts of feldspars. Zircon, mona-zite and in few samples a Th-silicate and/or Th–OH silicate are accessory mineral phases identi-fied by XRD or analytical scanning electron microscopy. The kaolinite content of the whole samples decrease gradually downwards from 65-100 wt. % in middle part of profiles into 25-35 wt. % in the lower profile, where the parent rocks retains its original texture and fabric. In the weathered zone, the fine fraction contain appreciable amount of illite/mica. In the highly weath-ered middle part of the studied profile (up to 40 m depth), feldspar and mica have completely removed and altered to kaolinite (Al-Ani et al., 2009). The mineralogical composition of the Vir-tasalmi kaolins shows that the white kaolin is mostly derived from the quartz-feldspar gneiss or tonalite and the colored kaolin from amphibolite or mica gneiss, which contain more mafic min-erals than the former rocks. The SEM-BSE observations and ED’s microanalysis revealed the occurrence of euhedral to sub-hedral micro-size crystals of resistant heavy minerals disseminated in the kaolins, chiefly zircon, rutile ilmenite and Th-bearing monazite (Fig. 1), which are common phases in the accessory as-semblage granitic rocks. Qualitative EDS- spectrum gives in some crystals only spectrum of tho-rium. Table 1. Mineral composition for raw material of studied samples from Litmanen (R529, R669) and Eteläkylä (R656, R697) kaolins at Virtasalmi. Sample Kaolinite Quartz Mica Plag Feldspar Calcite Hematite Pyrite Clay Anatase * Rutile tot.R529/66.6 100 x 100R529/73.1 100 100R529/84 25 25 35 5 <5 90R656/51.8 85 15 <5 x 100R656/89.7 35 < 5 <5 55 5 95R669/47.5-49.5 85 15 x 100R669/77.5-79.5 60 40 100R669/93.5-100.3 80 20 x < 5 100R697/37.5 100 <5 x 100R697/66.25 85 5 <5 possible x 90R697/108.7 100 x *** x 100R697/117.9 90 10 x 100 *Anatase is identified from heated sample (1h 550o C).The amount of anatase is not estimated. **in sample 09-61 there are too many minerals covering each other. The amounts are estimated as noticing only minerals of given values *** Not seen in bulk spectra, exists in heated spectra

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Figure 1. SEM image and ED’s spectrum of monazite and xenotime crystals from Taivalkoski Saarijärvi claystone (R311, R313) and Virtasalmi kaolins at Litmanen (R669) and Eteläkylä(R697).

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3.2 Geochemistry

3.2.1 Major elements

In order to measure the variation in chemical composition of the kaolin and weathered rocks relative to those of parent rocks, we used an index normalized by a possible immobile element during weathering. The immobile elements which were considered to be Al, Ti and Zr in the previous works (e.g. Nesbitt, 1979; Nesbitt and Wilson, 1992; Braun et al., 1993), are uniformly distributed in all samples and are remarkably stable with regard to weathering. Al2O3 rather than the other elements is unlikely to introduce significant inter-samples error, because of its excep-tionally high and constant at >10 wt% levels. Al2O3 was selected as the immobile element in the present study and also in other study by Olli Sarapää (1996) from which these analyses were borrowed. The weight percentage variation normalized by Al2O3 is given by equation (1):

Variation% = ((Cs/Al2O3s)/ (Cpr/Al2O3pr))-1) x100 (1)

Hence, the equation yields the percentage of increase or decrease of any element (C) in a sample (s) when compared with its concentration in the parent fresh rock (pr). Average values of major and trace elements and REE for the different parent rocks related to studied areas were utilized in equation (1). The chemical variations that have taken place during weathering and kaolinization processes are summarized in Table (2). Table 2. The chemical variations during weathering and kaolinization processes in different Virtasalmi kaolin deposits. Kaolin derived from quartz-feldspar gneiss (R504, R669) and tonalite (R656 and 697)

Losses GainsVariation % High moderate Low Low/average HighDrill core (66-100%) (33-66%) (0-33%) 0-100 >100%

R504 (Vuorijoki) Na, Ca, Mg,K, Pb SiO2, Fe2O3, P2O5 Zr, La, Nb, Y TiO2, Ce, S, Cr Al2O3, H2OSr, Ba, Rb Cu, Ni, Th

R656(Eteläkylä) SiO2,Ca, Na, K, Mn Fe2O3, Zn, pb P2O5, Zr TiO2, (LREE) Al2O3, H2OSr, Ba

R697(Eteläkylä) SiO2,Ca, Na, K, Mn Fe2O3, Zn, pb P2O5, Cu Zr,TiO2, (LREE) Al2O3, H2OSr, Ba

R669(Litmanen) SiO2, Zn, Rb, Ba Na, Ca, K, Mn, Mg, Zn Fe2O3, P2O5, Zr TiO2, Ga, V, Cr Al2O3, H2O CaO and Na2O are significantly depleted relative to parent rocks in most of studied drillcores in Virtasalmi. The depletion for the elements expressed as percentage changes reach (60-100%). In the studied area, the depletion in SiO2, MgO, CaO, NaO, K2O and MnO tends to be higher at the middle parts of drilling drillcores. K2O, SiO2 and MnO have a lower depletion rate than CaO, and Na2O for most of studied samples. Fe2O3 tend to be moderately depleted in most of studied area. P2O5 also tend to be immobile or depleted in the kaolinitic samples. The weathered rock samples have low increase for P2O5, whereas the element is depleted in the kaolinitic samples. TiO2, Ga, Cr, V and sometimes Zr tend to be enriched in most studied area. The percentage

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change less than 100 % for TiO2, Ga and Cr, with low depleted of Zr in some of studied profiles. Percentage change in Al2O3 and (LOI) are the highest enriched measured components in all kao-linitic samples.

3.2.2 REE behavior in the weathered rocks In general, fractionation of the REE is attributed to be a selective leaching of rocks, which con-tains both stable and unstable REE-bearing minerals. Residual stable minerals, being resistant to weathering, accumulate in the weathered profiles, while REE in unstable minerals is preferen-tially released and subsequently concentrated to yield supergene enrichments (Middelburg et al., 1988). In order to clarify the relationships between degree of weathering and REE content of the weath-ering rocks, the parameter ‘‘R’’ according to Middelburg et al. (1988) is adopted:

R= (CaO+Na2O+K2O)/ (Al2O3+L.O.I)

This ratio is a measured of the degree of weathering and associated with the feldspar breakdown and accumulation and formation of kaolinite (kaolinization). The ratio approaches 0 with in-creasing intensity of weathering. In the kaolin samples the R ratio range between (0.001-0.008), whereas in weathered samples the R ratio is higher with rang between (0.009-0.022). LREE con-tent of the kaolin samples has a negative correlation with the ratio R, indicate enrichment of LREE with kaolinization (Fig. 2a), whereas in weathered rock samples the LREE has a positive relation with the ratio R indicating that LREE increase with decreasing degree of weathering (Fig. 2b).

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Figure 2. Relation between the ratio R, light rare earth elements (La+Ce), and Y for studied Virtasalmi kaolin (a, c) and weathered rocks (b, d).

Comparison between the behavior of LREE content and Y content in both kaolin and weathered bedrock samples in the studied drillcores is shown that they have positive correlations together in the weathering and kaolin samples of studied area (Fig. 2c, d). This relation suggest that LREE and Y are considerably enriched during weathering and kaolinization processes.

3.2.3 The partial content of REE in kaolin samples In the weathering process, hydrolysis releases the REE cations and minerals from the parent rock. REE will migrate with water and become concentrated in the favorable sites soon after they have released from unstable REE minerals. The REE in the weathering crust are adsorbed on clay particle fractions in the form of simple cations. Song Yunhua and Shen Lipu (1987) show that the Ce-family (LREE La, Ce, Pr, Nd) are more unsoluble to hydrolysis than the Y-family

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REE, especially Ce+4, which is most unsoluble to hydrolysis than other REE. This has been con-firmed by the facts that the weathered rocks of the studied samples are relatively enriched in the Ce-family REE, Ce content is the highest at the top of the weathered rocks, and the Ce-family REE tend to become enriched during weathering. In the geochemistry of REE, the adsorption on clay minerals has a great importance, as reported by several authors, e.g. Balashov and Girin (1969), and Roaldset and Rosenquist (1971). These works demonstrate that 20-95 % of the total REE in kaolinitic deposits was adsorbed onto clay minerals. In the present study we found that 37-72 % of the total REE in kaolinitic samples of Virtasalmi kaolins was adsorbed from solution onto kaolinite and halloysite minerals during kao-linization process (Table 3). The mobility of REE in natural environments depends largely on their redox potential and the pH of water. Chemical weathering, such as kaolinization of rocks, usually starts in a weakly acidic environment, but liberation of alkalis and alkali earths results in a rapid increase of the pH. Alkalis and alkali earths are quickly removed from the kaolinization environment, thus the last stages of kaolinization proceed in acid environment. This change, from slightly acid to strongly alkaline, and finally to acid conditions is, of primary importance for the migration of several elements in the course of kaolinization. Progressive weathering and According to Wang Xianjue et al. (1984) the adsorption rates of REE on clay particles tend to increase with increasing pH, indicating that the necessary conditions for the formation of REE deposits of the ion-adsorption type in the weathering crust under acid-weakly acid conditions; when pH=7-9, is the most favorable for REE adsorption in the this pH environment. Mobility differences of REEs during weathering may result in REE fractionation in the weather-ing profiles. In general, the lower mobility of LREEs compared to HREEs may result in signifi-cant HREE depleted patterns in weathering products after extensive weathering, and mobility differences between Ce and other REEs usually results in Ce anomalies in upper parts of weath-ering products (Nesbitt, 1979; Nesbitt and Wilson, 1992).

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Table 3. REE analysis of kaolinitic samples in the Virtasalmi deposits; the analysis shows both chemi-cal measurement methods (Labtium 511 and 308M). REE (ppm) La Ce Nd Pr Sm Eu Gd Tb Dy Ho Er Tm Yb Lu Y ΣREEadsorbed REE 511 511 511 511 511 511 511 511 511 511 511 511 511 511 511 511Total REE 308M 308M 308M 308M 308M 308M 308M 308M 308M 308M 308M 308M 308M 308M 308M 308MR669 21.50-23.50 29.1 63.2 29.0 7.44 5.83 1.20 5.39 0.73 3.53 0.63 1.63 0.23 1.40 0.20 15.1 164.6

42.1 89.8 39.6 10.3 7.18 1.47 6.71 0.94 4.83 0.91 2.55 0.37 2.50 0.41 21.6 231.3R669 29.50-31.50 12.9 25.3 14.2 3.17 3.65 1.08 4.04 0.65 3.55 0.63 1.72 0.24 1.69 0.23 13.9 87.0

75.1 157 74.3 18.3 14.3 4.03 14.1 1.93 9.03 1.50 3.69 0.48 2.99 0.43 27.1 404.3R669 37.50-39.50 13.0 27.7 15.9 3.52 3.42 1.19 4.21 0.73 4.29 0.92 2.68 0.39 2.66 0.38 22.4 103.4

40.0 87.7 42.7 10.6 8.47 2.52 8.13 1.26 6.56 1.26 3.83 0.50 3.67 0.53 28.0 245.7R669 45.50-47.50 4.22 9.27 4.71 1.12 1.26 0.42 1.76 0.32 2.14 0.48 1.52 0.24 1.65 0.24 13.0 42.4

9.68 25.0 10.8 2.96 2.53 0.65 2.94 0.53 2.85 0.63 2.08 0.34 2.48 0.39 16.6 80.5R669 53.50-55.50 22.4 48.9 21.1 5.60 4.15 0.74 3.89 0.60 3.29 0.61 1.79 0.26 1.83 0.26 14.9 130.3

63 133 49.5 14.5 8.41 1.53 6.99 1.04 5.46 1.07 3.12 0.49 3.94 0.59 26.5 319.1R669 61.50-65.50 26.6 57.1 24.0 6.43 4.75 0.85 4.63 0.69 3.33 0.62 1.74 0.25 1.60 0.22 16.1 148.9

68.5 146 60.9 16.7 10.9 2.07 9.79 1.62 6.33 1.15 3.29 0.50 3.64 0.53 28.4 360.3R669 69.50-71.50 32.6 68.4 28.1 7.53 5.24 0.74 5.16 0.78 3.81 0.69 1.82 0.24 1.57 0.22 18.6 175.5

66.1 139 57.5 15.6 10.7 1.75 9.55 1.37 6.66 1.25 3.55 0.51 3.58 0.55 30.1 347.8R669 77.50-79.50 25.2 52.5 22.6 5.79 4.35 0.74 4.25 0.64 3.14 0.56 1.49 0.21 1.30 0.18 13.2 136.2

58.0 127 56.4 14.5 10.5 2.00 10.0 1.32 6.30 1.13 3.29 0.43 3.37 0.50 25.1 319.8R669 85.60-87.50 27.4 51.1 20.9 5.64 3.69 1.14 3.81 0.56 2.79 0.50 1.27 0.15 1.04 0.14 12.7 132.8

529 874 266 84.6 37.8 12.5 34.6 4.64 18.8 3.17 7.28 0.78 5.44 0.72 66.9 1946.2R669 93.50-100.30 - - - - - - - - - - - - - - 0.0

23.4 48.9 22.1 5.67 4.56 1.11 5.91 0.89 5.23 1.13 3.00 0.42 2.78 0.38 29.5 155.0R697 13.80-17.75 9.52 20.8 8.98 2.36 1.63 0.57 1.49 0.23 1.25 0.23 0.69 0.11 0.74 0.09 6.14 54.8

20.9 49.9 20.1 5.59 3.45 1.06 2.68 0.35 1.87 0.34 1.03 0.12 1.07 0.16 7.67 116.3R697 27.20-29.50 4.04 8.86 3.63 0.98 0.73 0.25 0.80 0.11 0.70 0.16 0.54 0.08 0.59 0.09 4.60 26.2

19.5 44.1 16.9 4.86 3.12 1.14 3.03 0.40 1.90 0.40 1.14 0.17 1.28 0.20 8.11 106.3R697 37.50-40.50 8.16 19.7 10.7 2.47 2.01 0.68 1.93 0.26 1.40 0.28 0.69 0.10 0.67 0.09 6.34 55.5

39.4 83.9 32.1 9.10 5.45 1.76 4.73 0.65 2.71 0.50 1.24 0.16 1.24 0.16 9.58 192.7R697 49.15-52.10 49.9 120 52.1 13.6 9.42 2.81 8.49 1.23 5.75 1.03 2.81 0.37 2.41 0.30 23.6 293.8

60.5 139 55.5 15.3 9.48 2.92 8.59 1.16 5.33 0.98 2.56 0.33 2.51 0.38 21.6 326.1R697 60.55-63.60 13.6 30.2 16.2 3.80 3.27 1.26 3.63 0.56 2.80 0.49 1.14 0.12 0.70 0.08 9.79 87.6

25.0 58.5 26.5 6.84 4.78 1.63 5.10 0.70 3.27 0.60 1.44 0.16 1.09 0.15 11.5 147.3R697 72.30-75.30 10.3 22.9 11.9 2.84 2.40 0.92 2.71 0.37 1.95 0.38 1.09 0.14 0.86 0.12 10.5 69.4

24.4 51.2 21.0 5.81 3.74 1.28 3.77 0.52 2.71 0.51 1.39 0.19 1.45 0.21 12.1 130.3R697 84.30-87.30 176 415 229 57.2 43.6 9.36 39.7 5.80 28.3 5.03 13.8 1.89 12.4 1.65 117 1155.7

179 432 238 59.3 45.5 9.58 41.3 5.97 28.4 5.36 14.5 1.93 13.5 1.80 114 1190.1R697 96.45-99.50 153 352 171 42.7 33.5 9.29 35.3 5.37 29.2 5.94 17.0 2.33 14.6 2.06 176 1049.3

142 326 160 40.1 31.4 8.53 33.5 4.84 26.6 5.64 16.0 2.22 13.9 2.02 155 967.8R697 108.70-112.0 92.0 225 106 27.4 20.0 5.16 19.6 2.90 14.9 2.83 7.69 1.07 7.03 0.94 72.4 604.9

85.8 215 102 26.6 20.1 5.04 19.1 2.90 14.8 2.78 7.71 1.11 7.41 1.02 67.0 578.4R697 117.25-120.5 42.7 94.0 42.5 11.0 8.62 1.87 8.15 1.27 6.36 1.13 3.11 0.46 3.00 0.40 27.5 252.1

38.4 88.5 40.5 10.7 8.25 1.97 8.34 1.25 6.07 1.19 3.42 0.49 3.48 0.49 26.4 239.5ion adsorbtion % 37 % 42 % 50 % 46 % 56 % 52 % 58 % 61 % 66 % 65 % 67 % 69 % 63 % 60 % 72 % The enrichment of REE in the clay sediments likely corresponds to abundance of clay minerals such as kaolinite. Coppin et al. (2002) noted that kaolinite can play an important role in remov-ing REE from aqueous solution by sorption. Wan and Liu (2006), however, reported that a high concentration of humic acid in the solution increase the adsorption of LREE (Σ La-sm) onto kao-linite. The linear relation between LREE content of kaolinite percentage in rich-kaolinite layer at the Virtasalmi area, suggests that the ion adsorption of REE onto kaolinite play a dominant role controlling the REE budget in the weathering profiles (Figure 3). On the other hand the lack of correlation between LREE and content of kaolinite in the other studied kaolin samples suggest that adsorption onto surfaces of clay minerals is probably not a prevailing mechanism of REE retention, but accessory minerals (as monazite) play a key role

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with respect to that of major minerals on the geochemistry evolution of REE during kaoliniza-tion. Monazite is the only LREE-rich mineral found as an accessory phase in the studied kaolin samples. It is a very low-solubility mineral that remained stable during kaolinization process, as confirmed by SEM-BSE observation (Al-Ani et al., 2009).The positive relation between LREEs and P2O5 and also between HREE and P2O5 in kaolin samples of (R669) Litmanen kaolin and (R697) Eteläkylä kaolin suggest control by phosphate minerals, such as occurrences of monazite, during weathering and kaolinization processes (Figure 4).

Figure 3. Plot showing the linear correlation between LREE and kaolinite content of the Virtasalmi kaolin samples.

Figure 4. The linear relation between REE content and P2O5 % in the studied kaolin samples.

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Table 4. Geochemical data for the kaolinitic samples in the four studied profiles of Virtasalmi deposits. REE(ppm) R504 (Vuorijoki) R656(Eteläkylä) R697(Eteläkylä) R669(Litmanen)

Kaolin Parnet Rx enrichement Kaolin Parnet Rx enrichement Kaolin Parnet Rx enrichemen Kaolin Parnet Rx enricheLa 66.5 52.9 1.3 105.9 24.1 4.4 63.5 24.1 2.6 97.5 32.7 3.0Ce 139.8 104.0 1.3 195.0 35.4 5.5 148.8 35.4 4.2 182.7 75.1 2.4Nd 17.1 12.0 1.4 26.4 3.2 8.3 71.3 3.2 22.3 68.0 9.8 6.9Pr 68.2 46.9 1.5 104.5 9.5 11.0 18.4 9.5 1.9 19.4 43.4 0.4Sm 11.7 9.1 1.3 18.3 1.0 18.3 13.5 1.0 13.5 11.5 9.3 1.2ΣLREE 303.3 224.9 1.4 450.0 73.2 9.5 315.5 73.2 8.9 379.1 170.3 2.2Eu 3.4 2.7 1.3 5.1 0.9 5.6 3.5 0.9 3.9 3.0 2.9 1.0Gd 10.7 8.4 1.3 17.9 0.7 25.6 13.0 0.7 18.6 10.9 9.4 1.2Tb 1.5 1.2 1.2 2.6 0.1 25.5 1.9 0.1 18.7 1.6 1.5 1.0Dy 7.6 6.2 1.2 14.5 0.4 36.1 9.4 0.4 23.4 7.2 8.7 0.8Ho 1.4 1.2 1.2 3.2 0.1 32.3 1.8 0.1 18.3 1.3 1.7 0.8Er 4.0 3.2 1.2 10.4 0.3 34.7 5.0 0.3 16.8 3.6 4.5 0.8Tm 0.6 0.5 1.3 1.6 0.0 40.0 0.7 0.0 17.2 0.5 0.7 0.7Yb 3.8 3.0 1.3 11.2 0.3 37.3 4.7 0.3 15.6 3.4 4.3 0.8Lu 0.6 0.5 1.2 1.7 0.1 16.5 0.7 0.1 6.6 0.5 0.6 0.8ΣHREE 33.5 26.9 1.2 68.0 2.9 28.2 40.7 2.9 15.5 31.9 34.3 0.9Y 36.2 30.6 1.2 96.7 2.5 38.7 43.3 2.5 17.3 30.0 42.5 0.7ΣREE 373.0 282.4 614.7 78.6 399.0 78.6 441.0 247.2HREE/ΣREE 0.1 0.1 0.1 0.0 0.1 0.0 0.1 0.1LREE/HREE 9.1 8.4 6.6 24.9 7.8 24.9 11.9 5.0(La/Sm)n 3.6 3.7 3.7 15.2 3.0 15.2 5.3 2.2(Gd/Yb)n 2.3 2.3 1.3 1.9 2.2 1.9 2.6 1.8(La/Yb)n 11.9 11.9 6.4 54.3 9.1 54.3 19.2 5.2(Eu/Eu*)n 0.9 0.9 0.9 3.3 0.8 3.3 0.8 0.9

ment

(Eu/Eu*) n = Eun/(Sm n x Gd n) 11//22, where subscript n = chondrite normalized

3.2.4 Total REE content in parent rocks and kaolin

The ΣREE (ppm) can be used as a measure of absolute REE content. The average ΣREE in sam-ples of the kaolin samples from Virtasalmi is much higher than parent rocks especially in Eteläkylä kaolin deposits (Fig. 5). The parent rocks of Virtasalmi rocks (n = 4; Table 4) have dif-ferent average ΣREE of 78, 247 and 282 ppm for Eteläkylä tonalite, Litmanen and Vuorijoki quartz-feldspar gneiss respectively. The kaolins of Eteläkylä have the highest average ΣREE of 615 ppm in drillcore R656 and 399 ppm in drillcore R697(n=10; Table 4): These ΣREE are ap-proximately 8-fold and 5- fold higher than the tonalite source rocks (78 ppm). The parent rocks of Eteläkylä have a higher LREE/HREE ratio, with 24.9, than those of the Vuorijoki (8.3) and Litmanen (4.9) granitic rocks, indication LREE enrichment. In the Litmanen kaolin the weathered kaolin samples (n = 10; Table 4) have an average ΣREE of 441ppm. There is a high concentration in REE of the kaolin relative to the original rocks (247 ppm). In particular, clay-rich layers have a higher total REE content (ΣREE> 1946ppm; at least 7.5-fold higher than the parent rock at the depth of 85.6-87.5 m in the drillcore R669 of Litma-nen deposit. Several REE-enriched clay layers in Eteläkylä deposit have also higher total REE at depth range (84.3-99.5 m; at least 15- fold higher than parent rocks with a maximum content of ΣREE 1190 at depth of 99.5 m. The LREE/HREE ratio (Table 4) is a good indicator of the original rock source (Taylor and McLennan 1985). In the studied kaolins, this ratio fluctuates between 5 and 25; the Eteläkylä kaolin samples have average LREE/HREE ratios of 7.7, while the ratio in tonalite, source rock,

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is more than 24. In Vuorijoki kaolin samples, the ratio is 9 and 8.4 for parent rock; quartz-feldspar gneiss. The Litmanen deposits have an average LREE/HREE ratio of 11.9, and quartz-feldspar gneiss source rock about 5, and are more enriched in LREE than weathered and parent rocks in all studied area. Several REE-enriched kaolin samples have higher HREE enrichment than LREE in some studied kaolins. As seen in Table (4) the HREE enrichment at R656 about 28- fold more than parent rocks, while the LREE enrichment about 9.5-fold relative to parent rocks in same profile. The same thing showed in R697 whereas, the HREE enriched at least 15-fold than parent rocks, while the LREE enriched only 8.9-fold. The REE variations among sam-ples within each studied kaolin deposit could possibly be due to differences in the initial REE content of the source rocks, to differences in intensity and duration of weathering, to exchange reactions during kaolinization, to digenesis, and to contamination of the clay minerals with small amounts of resistant, detrital minerals enriched in the REE. The REE are released from primary minerals (i.e., feldspars) and taken up by the secondary phases during kaolinization (Nesbitt, 1979). REE adsorption onto kaolin surfaces shows clear pH dependence. Dominant electrostatic interaction and specific site binding due to the negatively charged kaolinite surface occur at low pH from 3 to 4 (needed for kaolin formation) which enhanced the REE adsorption (Wan and Liu, 2006; Coppin et al., 2002). The acidic environment involved by oxidation reactions of sulfide minerals (pyrite and marcasite) and induced quite low pH values in this environment. Considering the chondrite-normalized patterns of the REE distribution in the kaolins and com-paring them with the REE abundance in the unaltered feldpathic rocks, a relatively small shift is observed. The parent rocks have REE patterns essentially parallel to each, indicating that these parent rocks have probably the same provenance (Fig 6a). The chondrite-normalized REE pat-terns of the kaolins are identical with LREE enrichment, a positive Nd anomaly and relatively flat HREE content, but showing higher contents than normalized parent rocks (Fig 6b). Indeed, the REE patterns are quite similar and resemble to that of the parent rocks, which is consist of quartz-feldspar gneiss in Vuorijoki, Litmanen and tonalite in Eteläkylä deposits. The most remarkable features are the uniformity of the REE patterns. In fact, the shape of the REE patterns is identical for all studied samples, and they are characterized by a slight LREE enrichment in Vuorijoki (Lan/Smn =3.5) and Eteläkylä (Lan/Smn =3.6, 3.0) with high enrichment in Litmanen (Lan/Smn =5.3), HREE depletion (Gdn/Ybn= 1.8-2.3) and slight to moderate negative Eu anomalies they don’t have anomalous average values of Eu in most chondrite-normalized curves (Eu/Eu* = 0.9), except for a high positive Eu anomaly (EuP/EuP* = 3.3) in parent rock of Eteläkylä deposit sample; a feature directly linked to the plagioclase content of tonalite source rocks. The kaolin patterns have also Nd anomaly, with its least rate is assumed to be immobile. In comparison, the concentration of REE in kaolinite of Eteläkylä (R656 and R697) with parent rocks show that the enrichment both in LREE and HREE and the concentration is getting up over the tonalite concentration (Fig 6c). This enrichment is greater for Nd, and also for Yb and Y. The kaolin samples from Vuorijoki (R504) are relatively flat to slightly enrich in both LREE and HREE compared to quartz-feldspar source rocks. The REE pattern of Litmanen kaolin samples are characterized by LREE enrichment patterns and depleted HREE with negative Pr anomaly. This suggests that most REE have been transformed from the parent rock to kaolin, which pre-serves the REE signature of the source rocks, indicating of REE leaching by local meteoric wa-ters from the upper levels of the profiles and concentrated in deeper zones, probably in the form of complexes, or REE may accumulate by adsorption in kaolinite surface (Sarapää 1996). The behavior of the REE is quite similar as Nesbitt (1979) observed in the weathering profile at

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Torrongo. The selective leaching of stable and unstable minerals is probably one reason for the fractionation of REE. When a mineral is weathered, REE are librated and may be subsequent be concentrated as supergene enrichment in alkaline conditions, a basic pH environment is also known to fractionate LREE-HREE, as the HREE are preferentially retained in solution, where they form soluble complexes (Cantrell and Byrne, 1987). The normalization of REE concentra-tion (Fig 6d) gets rid of the inherently zig-zaggy pattern shown by the rare earth elements be-cause the abundances of elements with even atomic numbers are larger than elements with odd atomic numbers.

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Figure 5. Average content of Y, HREE and LREE in kaolin and parent rocks at each studied area: (a) Vuorijoki; (b, c) Eteläkylä and (d) Litmanen.

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Figure 6. Rare earth element plots of Virtasalmi kaolin samples normalized to (a) parent rocks data of studied profile , (b) kaolin samples data comparing with average parent rocks, (c) normalized of REE in kaolin related to parent rock in each profile and (d) REE concentrations of kaolin and parent rocks The kaolins show a general LREE enrichment with a Nd positive anomaly.

Another interesting result of this study is the distribution and content of the light REE within kaolinite samples, Ce and La are generally much more abundant than other REE. It is noted that the percentage content of Ce and La to be more than 50% comparing to other REE as seen in cir-cular form (Figure 7). The behaviour of REE with depth (Fig. 8) strongly suggests that a very large proportion of REE enriched in kaolinite and depleted in parent rocks. In particular, kaolinite-rich layers at lower part of the profile have a higher LREE content with maximum content of LREE>1790 ppm at depth 87.9 m in R669 Litmanen deposit (Fig.8a), while in Vuorijoki deposit the kaolin layers are slightly enriched of LREE> 505 ppm at depth 69 in profile (R504) (Fig 8b) . Several kaolin-rich layers in Eteläkylä deposit have high LREE especially in profile R697 at depth between 85-100 m with LREE content of 700-950 ppm (Fig 8 c, d). The behaviour of HREE and Y with the depth are quite similar to LREE distribution but in slightly enriched, the HREE and Y are strongly in Eteläkylä profile R697 at depth 85-100 with content of (113-122 ppm) for HREE and (114-155 ppm) for Y.

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Figure 7. REE constituents in studied Virtasalmi kaolins.

One of the reasons for obvious REE zoning in the studied kaolin profiles is that the speed and intensity of water permeating downward tend to slow down and weaken with increasing depth. This suggestion indicated by the decrease of kaolinite with depth in Virtasalmi kaolin deposits. In the upper-middle part of the weathering profile REE and other soluble elements (Mg, Ca, Na and K) have been leached out, and in going to the middle-lower parts both permeating speed and leaching intensity tend to decrease progressively. Under such circumstances, REE cations of higher concentration in the aqueous solution have attained enough time to be adsorbed on kaolin surfaces under appropriate medium conditions. This has resulted in the relative depletion of REE in the uppermost and lower parts, and relative enrichment of REE in the middle or middle-lower parts. Relatively unstable independent REE minerals, such as feldspar titanite, zircon and biotite are considered as the main sources of the REE in the weathering crust of the studied area. On the other hand there are also other REE minerals accessible to weathering such as bastnaesite, pa-risite and britholite, but these need to be more details mineralogical studies for the parent rocks of studied area. The enrichment of REE in the studied kaolin deposits is probably associated with mainly adsorption of most REE onto kaolinite surface and partly formation of possible sec-ondary LREE-bearing minerals such as monazite.

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Figure 8. Variations of LREE (Σ La-sm), HREE (Σ Eu-Yb) and Y content and anomalies of kaolinitic samples throughout the four weathering profiles with depth.

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4 SUMMARY AND CONCLUSION This study has established that during the kaolinization of the Virtasalmi parent rocks, significant amount of Si, Mg, Na, Ca, K, Fe and P were readily removed as result of the breakdown of feld-spars and biotite, whereas Al, Ti, Zr, LOI and REE remained relatively immobile, linked to resis-tant heavy minerals (zircon, monazite and titanium oxides) that tended to be residually concen-trated in the fine fractions of the kaolinite. The parent rock-normalized REE patterns are very similar to each other, and show LREE enrichment, a slight positive Eu and HREE depletion in all studied profiles. Compared to Virtasalmi kaolins show a slightly negative Eu anomaly. The chondrite-normalized REE patterns of the kaolins are identical with LREE enrichment, a positive Nd anomaly and HREE depletion. However, Eteläkylä kaolin samples (R656 and R697) show more REE contents than Vuorijoki and Litmanen kaolin samples. The LREE enrichment reflects the results of extreme weathering. A continuously declining water-table caused mobiliza-tion of REE by acid solutions from the altered zone and their re-precipitation and efficient con-centration at lower levels giving rise to pronounced supergene REE enrichment. REE were leached by acid solutions in the high altered groundwater zone of the profile. The REE were complexes and the LREE complexes became increasingly unstable as the solutions encountered increasing pH and higher alkalinity conditions in lower parts of the profile. Under such circum-stances, REE cations of higher concentration in the aqueous solution have attained enough time to be adsorbed on kaolin surfaces under appropriate medium conditions. This has resulted in the relative depletion of REE in the uppermost and lower parts, and relative enrichment of REE in the middle or middle-lower parts. Relatively unstable independent REE minerals, such as feld-spar titanite, zircon and biotite are considered as the main sources of the REE in the weathering crust of the studied area. On the other hand there is also deposition of LREE occurred principally in the form of monazite mineral. The HREE and Y complexes remained in solution, separated from the LREE and subsequently precipitated at deeper levels of weathering profiles. High HREE contents in some studied profiles were also favoured by adsorption of REE and Y onto kaolinite surfaces. Evidence for mobilization and redistribution within the studied profiles are characterized by the by a slight LREE enrichment in Vuorijoki (Lan/Smn =3.5) and Eteläkylä (Lan/Smn =3.6, 3.0) with high enrichment in Litmanen (Lan/Smn =5.3), HREE depletion (Gdn/Ybn= 1.8-2.3) and slight to moderate negative Eu anomalies they don’t have anomalous average values of Eu in most chon-drite-normalized curves (Eu/Eu* = 0.9), except for a high positive Eu anomaly (EuP/EuP* = 3.3) in parent rock of Eteläkylä deposit sample; a feature directly linked to the plagioclase content of tonalite source rocks. The kaolin patterns have also Nd anomaly, with its least rate is assumed to be immobile. The present study also show, the total REE content of kaolin in basal part of weathering profile reaches maximum 0.1-0.2 % in aqua regia soluble form at Litmanen and Eteläkylä deposits.

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