Northern Finland Office M19/3231,3232,3441,3533/2009/32 2.4.2009 Rovaniemi

Concentration and residence of rare earth elements (REE) in kaolin and weathered rocks of Virtasalmi, Taivalkoski and Puolanka deposits, eastern Finland

Thair Al-Ani, Olli Sarapää and Bo Johanson

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

2.4.2009

Type of report

M19 Authors

Thair Al-Ani, Olli Sarapää and Bo Johanson

Commissioned by

GTKTitle of report Concentration and residence of rare earth elements (REE) in kaolin and weathered rock of Virtasalmi, Taivalkoski and Puolanka deposits, in eastern Finland

Abstract

The mineralogical study and microtextures analysis have allowed us to address the factors controlling distribution pattern, residence and behaviour of rare earth elements (REE) during kaolinization of Paleoproterozoic feldspathic rocks in eastern and northern Finland. The kaolin samples for the mineralogical study were selected from drill cores of the Virtasalmi and the Puolanka primary kaolin deposits and the Taivalkoski sedimentary kaolin clay. The sample selection was mainly based on high Ce and La contents in existing analyses. The aim of this study was to find out in which minerals the REE-elements occur in these kaolins. Mineral composition of the deeply weathered samples is dominated by kaolinite and metahalloysite, with minor

amounts of quartz, muscovite-illite, alkaline feldspar and traces of resistant minerals (rutile, zircon and monazite). Variable amounts of Si, Na, Ca, K, Mg and Fe were lost from the weathering profile, as a result of feldspars, mica, amphibole and apatite breakdown, whereas Al, Ti, Zr and REE were concentrated in the residual kaolin. Possible monazite formation and alteration mechanisms found in the course of this study using backscattered scanning electron microscopy (BSE-SEM) and elemental maps obtained by focusing of X-ray beams onto studied samples show similar REE distribution patterns, but differ in concentration levels. Most of monazite crystals in studied kaolin are depleted in thorium and enriched in Ce, La and Nd. Assuming thorium as an immobile element; the depletion Th in monazite crystals suggests the degree of monazite alteration and may be termed Ce-monazite with chemical formula (Ce, La, Nd, Th, Y)PO4. Although the fine fractions are the most important REE reservoir, the lack of correlation between LREE and con-tent of kaolinite in some Virtasalmi kaolins suggested 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 with respect to that of major minerals on the geochemistry evolution of REE during kaolinization as seen in correlative behaviour

among P2O5 and REE in the <2 µm fraction of studied kaolins. Keywords

Rare earth elements, REE, kaolin deposits, ion-adsortion, monazite, kaolinite, halloysite, BSE-SEM, XRD, Geographical area

Virtasalmi; Litmanen, Eteläkylä, Puolanka; Pääkkö, Taivalkoski; Saarijärvi

Map sheet

323109, 323204, 344112, 353309 Other information

Report serial

M19 Archive code

M19/3231,3232,3441,3533/2009/32 Total pages

21 Language

English Price

Confidentiality

Confidential until 31.12.2011

Unit and section

Northern Finland Office, Bedrock Geology and Resources

Project code

2141007

Signature/name

Thair Al-Ani Signature/name

Olli Sarapää Bo Johanson

Contents

Documentation page

1 INTRODUCTION 1

2 EXPERIMENTAL METHODS 2

3 MINERALOGY 3

4 CRYSTAL MORPHOLOGY 4

5 REE ABUNDANCE AND DISTRIBUTION 11

6 THE MECHANISM OF MONAZITE FORMATION 11

7 X-RAY MAPS OBTAINED BY SEM/EDS 15

8 CONCLUSION 18

9 REFERENCES 19 LITERATURE

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1 INTRODUCTION The kaolin samples for the mineralogical study were selected from drill cores of the Virtasalmi; Litmanen and Montola, the Puolanka; Pääkkö primary kaolin deposits and the Taivalkoski; Saarijärvi sedimentary kaolin clay. The sample selection was mainly based on high Ce and La contents of the existing analyses. The topic of this study was to understand how the rare earth elements REE migrate and are even-tually trapped in a near-surface weathering system of kaolinite, involving warm humid climate, oxidation of sulphide minerals, and a high content of CO2 in the atmosphere maintained the groundwater acidity causing kaolinization of aluminum silicate materials. In the other words which minerals do include REE in the kaolins. Monazite, a monoclinic orthophosphate with the general formula (Ce, La, Nd, Th) PO4, is one of the main mineral hosts for rare earth elements (REE) and Th in the continental crust. In addition to being a significant natural resource for the REE (Neary and Highly, 1984), monazite has been used for a long time in geochronology (Tilton and Nicolaysen, 1957). Ceramics with the struc-ture and composition of monazite have been proposed as potential nuclear waste forms (McCarthy et al., 1978). Monazite has been earlier a primary ore of several rare earth metals most notably thorium, ce-rium and lanthanum. All these metals have various industrial uses and are considered quite valu-able. Thorium is a highly radioactive metal and could be used as a replacement for uranium in nuclear power generation. Monazite therefore is an extremely important Th-ore mineral. This mineral is currently the subject of a considerable renewed interest through its use in igneous and metamorphic geothermometry (Ayres et al., 1997; Heinrich et al., 1997) and geochronology via in situ analytical techniques including electron microscope or ion microprobes (Harrison et al., 1995; Zhu et al., 1997; Braun et al., 1998; Cocherie et al., 1998; Crowley and Ghent, 1999). Recent studies have evaluated the behaviour of the U-Pb radiometric systems in monazite during metamorphism and/or interaction with fluids (Hawkins and Bowring, 1997; Bingen and van Breemen, 1998; Schaltegger et al., 1999), the diffusion of Pb at high temperature in the monazite crystallographic structure (Smith and Giletti, 1997), the behavior of the monazite lattice under irradiation (Meldrum et al., 1998), the study of monazite paragenesis during metamorphism (Pan, 1997), and the compositional range of monazite-group minerals (Podor and Cuney, 1997). Mesoproterozoic kaolins of Virtasalmi are lenticular in shape, generally less than a few hundred meters (200-250 m) wide and half to two kilometers long. Kaolin deposits, several tens to 100 meters thick, are located under a 20-30 m thick glacial overburden. According to Sarapää (1996) the heavy rare earth elements are enriched in the basal part of Virtasalmi weathering profiles. In this study Virtasalmi core samples R669 and R529 represent kaolin of Litmanen, R657 and R697 kaolin of Eteläkylä and R334 is from the Montola kaolin occurrence. Kaolinite and halloysite are the main clay minerals and mostly associated with mica-quartz feldspar gneiss, granodiorites and amphibolites. According to the drilling data, these kaolin deposits were formed by in situ weath-ering of bedrock. The Color and quality of kaolin are controlled by the type of the weathered bedrock. White kaolin mainly derives from quartz-feldspar gneiss and mica gneiss, whereas col-ored kaolin from amphibolites and diopside amphibolites. The kaolins consist mostly of kaolinite and halloysite in various proportions and a gradual transition from fresh rock to kaolin is ob-

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served. Fresh rocks are mainly composed of quartz, feldspars (microcline, Na plagioclase) and muscovite. Previous workers (Sarapää, 1996; Al-Ani et al., 2006) suggested a residual origin for the kaolins. According to Al-Ani and Sarapää (2004), the kaolinization process seems to follow two alteration paths: (i) K-rich feldspars → kaolinite. (ii) Na-plagioclase → halloysite → kaolin-ite. The sedimentary rocks of the Saarijärvi impact crater are mostly filled with kaolinitic claystone and sandstone (Tynni and Uutela 1985). The samples from the drill cores R311 and R313 as shown in table 2 are typical kaolinitic claystone samples related to high content of kaolinite. In the Kainuu region at Puolanka, there are dozens of kaolin occurrences but most are small and only a few meters in thickness, without any economic potential (Al-Ani and Niemelä 2005). In major occurrences the kaolinite content is highest in the topmost part and decreases downwards and finally kaolinite disappears just before the change into a hard rock. It is obvious that these generally rather thin occurrences; often low in kaolinite are "roots" of thicker layers, whose top-most part was moved away by glacial erosion. The formation of weathered material was mainly caused by chemical weathering especially in fractured bedrock. The quality of kaolin has origi-nally been influenced by the amount of feldspar and dark minerals of the parent rock and later on by the topographic position, because lower on the slopes the kaolins seem to be more coloured. The parent rock of white kaolin occurrences is feldspar-bearing serisitic quartzite. The samples R346 in table 2 are from the Puolanka Pääkkö kaolin occurrence. This report deals with monazite occurrence and alteration in weathering rocks and kaolinitic samples, which they have undergone various fluid-rock interaction conditions and chemical weathering. The different geochemical exchange mechanisms observed during monazite altera-tion have implication for both U-Th-Pb geochronology and for proposed monazite-like nuclear ceramic waste forms.

2 EXPERIMENTAL METHODS The mineralogical composition of bulk rocks and of the clay fractions (< 2 µm) of the samples were determined by X-ray diffraction, using a Philips diffractometer PW1050/25, with Ni-filtered CuKα radiation. Powders from oriented clay-aggregate samples were scanned at 1º 2θ/min from 3 to 50º 2θ. Clay minerals were identified from three XRD patterns (air-dried at 25 ºC, ethylene-glycolated, and heated at 550 ºC for 2θ) of the clay-size fraction (< 2 µm) extracted by the standard sedimentation technique in deionizer water. Monazite’s textures, morphology and chemical composition of its alteration products were de-termined at the Electron optical laboratory at GTK using an scanning electron microscope (SEM) (JEOL JSM 5900 LV), with a backscattered electron BSE imaging, energy dispersive spectrome-ter (EDS). The chemical composition of the minerals was determined using natural standards and 20 kV accelerating voltage with ~1nA beam current. Special analytical conditions with lower beam current and short counting times (10 s) were made of some kaolinite samples from studied areas to obtain some idea of how the REE accumulate and are eventually trapped in a near-surface of kaolinite and accessory minerals such as monazite. Carbon was used to coat most samples, to avoid peak overlap in energy dispersive X-ray spectrometry EDS.

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3 MINERALOGY XRD of the whole samples give us the mineral composition, but in many cases minor quantities of some minerals such as monazite will not be detected (Table 1 and 2). In Virtasalmi samples, kaolinite content of bulk samples range between 25 – 100 % with an average of 80 %. Additional constituents are quartz ranging between 0 – 40 % with an average of 10 %, muscovite <5 and high content of plagioclase in two of studied samples between 35–55 %, theses samples reflect the transition zone between kaolin and its parent rocks. Small amount of feldspar, calcite, hema-tite, pyrite, anatase and illite and apatite are found in some samples (Table 1). Puolanka Pääkkö raw samples contain quartz, kaolinite, mica, hematite, vermiculite. Kaolinite content of raw material between (0-65 wt %) with an average of 45%. The range of quartz con-tent between (45-100) with an average of 51.6 %. Accessory minerals contents are mica <5 %, hematite 20 % max, traces of vermiculite in few samples. Taivalkoski claystone contains 25-75 % kaolinite, 15-95 % quartz, mica 0-10 %, hematite 0-20 % and occasionally pyrite (max 20 %). Oriented slides of the <2μm fractions of both treated and untreated samples were run with XRD after glycolation, and formamide treatments and heating up to 350ºC (Figure 1). The diffraction patterns showed kaolinite to be the main clay mineral phase in each of the deposits. Kaolinite content increases from the unaltered parent rocks to completely kaolinized rocks. From the X-ray Diffraction patterns and SEM, it is evident that halloysite growths progressively at the expense of kaolinite and were identified using SEM observations and microanalyses. Oriented diffracto-grams of the <2-μm fraction of the Puolanka kaolin deposits show that kaolinite and illite are the major minerals, with traces of vermiculite.

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 Plagioclase Feldspar Calcite Hematite Pyrite Clay Anatase * Rutile F-apatite Wollastonite tot.R529/66.6 100 x 100R529/73.1 100 100R529/84 25 25 35 5 <5 possible possible 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 R529/84 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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Table 2. Mineral composition for raw material of studied samples from Taivalkoski Sarrijärvi claystone (R311,R313) Puolanka Pääkkö kaolin (R346) and Virtasalmi Montola kaolin (R334).

Sample Quartz Kaolinite Mica Feldspar Plagioclase Hematite Calcite Pyrite Vermiculite tot.R311 18.5 65 20 <5 5 - 5 - 95R311 29.2 60 25 <5 5 - 5 5 100R311 35.5 55 40 <5 5 - - - 100R311 41.5 60 30 <5 <5 - 5 - 95R311 44.0 60 30 <5 5 - <5 - 95R311 47.5 95 - - - - - 5 100R311 52.4 70 20 <5 5 - 5 - 100R311 61.25 60 35 <5 5 - - - 100R311 83.5 60 20 <5 5 - 10 <5 95R313 9.5 30 40 <5 10 - - - 20 100R313 16.9 75 15 <5 10 - - - - 100R313 17.5 95 <5 - 5 - - - - 100R313 20.8 25 75 possible - - - - - 100R313 22.9 45 25 <5 5 - 20 - - 95R313 27.0 15 60 possible 5 - - - 20 100R313 32.5 45 25 10 - 20 - - - 100R334 23.5 <5 95 <5 - - <5 - - 95R334 29.5 10 75 - 15 - - - - 100R334 38.1 15 80 5 - - - - - 100R334 41.5 10 90 - - - - - - 100R334 50.3 10 90 - - - - - - 100R334 55.2 0R334 62.0 10 65 <5 10 5 - - - 10 90R346 18.0 X X X - - - - - X 0R346 37.2 X X - - - - - - X 0R346 45.0 65 35 - - - - - - 100R346 52.3 0R346 56.5 45 55 - - - - - - 100R346 65.45 70 25 5 - - - - - 100R346 74.0 55 25 - - - 20 - - 100R346 89.95 X X X - - - - - X 0R346 97.0 85 15 <5 - - - - - 100R346 98.5 100 - possible - - - - - 100R346 130.8 100 - - - - - - - 100

4 CRYSTAL MORPHOLOGY Morphologies, as observed by scanning electron microscopy (SEM), can also be useful in identi-fication of kaolin minerals. Kaolinite shows a variety of morphologies, including platy, pseudo-hexagonal particles, booklets and vermicular stacks (Figure 1). The dimension of kaolinite book up to 7 μm in length and up to 2 μm in width (Fig.1a) Some platelets with rounded semi-hexagonal to irregular hexagonal edges were observed as well, and the ED-spectrum shows that these platelets constitute Al, Si and O without any contamination of Fe and K (Fig. 1b,c). Other categories were tubular aggregates of halloysite particles, the crystals elongated parallel to the C-axis. The halloysite appears dominantly as tubular particles of varying lengths and widths. The length to width ratio is about 20:1(Fig.1d). Halloysite and metahalloysite may reflect different stages of weathering, diagenesis or hydrothermal alteration before altering to kaolinite at a later stage (Al-Ani, et al., 2004).

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Figure 1. Scanning electron microscopic images showing the most common morphologies of kaolin mineral in Virtasalmi Litmanen. (a) Books of kaolin. (b) Vermicular kaolinite. (c) Blocky and stacks of kaolinite (d) conversions of kaolinite to tubular halloysite.

The SEM-BSE observations and ED’s micro-analysis of studied kaolin samples revealed the oc-currences of euhedral to subhedral micro-size crystals of resistant heavy minerals disseminated in the kaolins, chiefly Ce-monazite, Th-bearing monazite, zircon, rutile and pyrite. The only mineral of the studied kaolin samples that contains the elements La, Ce, Nd and Th is monazite (Fig. 2). Microanalyses of sulphide minerals and zircon which are also present reveal that neither of them contains the above elements in detectable amounts (0.01 %). The sample R529 (82.5) from Litmanen kaolin deposit contains (Ce, La, Nd)-rich monazite, intimately associated with LREE-depleted kaolinite flakes (but never with halloysite). Significantly, even when kaolinite and halloysite are intimately mixed together, SEM examination reveals that halloysite never bears monazite micro-crystals. As kaolinite generally forms flat flakes and halloysite coiled tubes, a morphology effect possibly took place. Isolated, graded monazite crystals, down to a few nanometers in length (typically; 5 µm in length and 20 µm in diameter), often exhibit flat-tened prismatic shapes, while crystalline morphology is less obvious in micrometric aggregates (Fig 2). Strongly corroded monazite crystals with porous aggregates in low contrast parts of BSI image were shown in Figure (2a). Regular shaped, dehydrated objects with high contrast in

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backscattered electron images and three-dimensional shape were commonly observed (Fig 2a, b, c). Monazite crystals are found as elongated forms (Fig.2d) and also as rounded, irregular and discrete grains of monazite (Fig.2e, f). Other heavy minerals are essentially resistant’s; occur in studied kaolin such as zircon and rutile. Minor sulphide minerals are also present in the studied kaolin samples, such as chalcopyrite and pyrite; needles and as minute crystals of barite, with poorly developed crystalline morphologies. A backscattered SEM images and EDS-spectrum show that the monazite is characterized by al-teration both at the margin and within the crystal. These areas correspond to different alteration processes, and only the one affecting the core of the crystal is discussed here. The other type of alteration will be studied in the most of kaolin samples an increase in Ce, La, Nd concentrations and a decrease in Th characterize the alteration affecting the inner parts of this grain (Table 1). The alteration here is characterized by a decrease in Th concentrations which is opposite to what was noted in chemical exchange described above. The EDS spectrum (Fig. 3 and 4) from most of studied samples indicates abundant in Ce2O3 and to a lesser degree in La2O3, Nd2O3 and Th2O3; and may be termed Ce-monazite with chemical formula (Ce, La, Nd, Th, Y) PO4. Some SEM analyses of monazite show monazite coexisting with Th-silicate bearing samples (Fig. 5), the remnants of monazite crystals are enriched in Ce, implying thus that Ce remains in the monazite during its alteration to Th-silicate. This process liberated a large proportion of the Th, LREE and P, originally contained in monazites. Although there is a considerable recent lit-erature devoted to the changes monazite undergoes during hydrothermal alteration (e.g. Cath-elineau, 1987; Schandl and Gorton, 1991; Smith et al., 1999; Mathieu et al., 2001), weathering (e.g. Taunton et al., 2000; Putter et al., 2002), and their chemical implications, a more complete understanding of REE chemistry during weathering and hydrothermal alteration would provide additional constraints on the understanding of these processes.

SEM analysis also shows few grains of Xenotime (Yttrium Phosphate YPO4). Xenotime was ob-served in one clay sample R334 (50.3) as seen in Figure (6). The Microanalysis of xenotime (Fig. 6b) shows an increase in Y and a decrease in other rare earth elements (REE). The secon-dary xenotime may be generated from the decomposition of zircon and apatite during late-stage fluid activity (Broska et al., 2005). The size of xenotime ~5µm and ED’s analysis it composed mainly from Y and P with traces of Ca.

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Figure 2. Back-scattered scanning electron micrograph of a monazite crystals and associated alteration phases: (a) highly corroded monazite crystals from the drill coreR529 (82.5); (b) regular shaped of monazite crystal; (c) regular crystal of monazite with partial eroded; (d) elongated crystal (e, f) irregular to rounded grain on Monazite.

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Figure 3. EDS spectrum of different crystals of monazite: (a, b) showing high content of P and Ca content in; (C) spectrum shows a mixed spectrum of kaolinite and monazite; (d) spectrum shows high content of P with Ce, La and Nd.

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Figure 4. SEM image and ED’s spectrum of monazite and xenotime crystals from Taivalkoski Saarijärvi claystone (R311, R313) and Litmanen kaolin (R669).

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(c) Microanalysis of Thorium silicate

Spectrum Al Si P S Ca Ce Th Total

Spectrum 1 14.52 12.57 29.39 2.37 7.35 13.02 20.78 100Spectrum 2 19.22 18.12 20.98 1.74 5.62 7.45 26.87 100Average 16.87 15.345 25.185 2.055 6.485 10.235 23.825 100

Figure 5. SEM image of monazite coexisting with Th-silicate bearing minerals in sample R529 (82.5); (a) BSI of thorium silicate, (b) ED’s spectrum and (d) microanalysis.

(c) Microanalysis of Xenotime (YPO4)

Element Weight% Atomic%O 66.5 86.67P 11.2 7.55Ca 1.3 0.68Y 21 5.11Totals 100 100 Figure 6. SEM image of xenotime in the sample R334 (50.3); (a) BSI of xenotime, (b) ED’s spectrum and (d) microanalysis.

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5 REE ABUNDANCE AND DISTRIBUTION Monazite is the only LREE-rich mineral found as an accessory phase in the studied kaolin sam-ples. It is a very low-solubility mineral that remained stable during the kaolinization process, as confirm by SEM-EDS observation. In fact, monazite occurs as isolated crystals with flattened prismatic shape, and show partially of alteration. Also, the microanalysis revealed that monazite contain appreciable amount of Ce, La, Nd with traces or sometimes without Th content (Table 3 and 4). The partially alteration of monazite to other phases during kaolinization process would have significant by liberated or depleted of Th. The primary monazite contain appreciable amount of Th in the crystal structure, which is noted in few grains of monazite, whereas the most of remaining monazite crystals are enriched in Ce, La and Nd (Table 3 and 4) and this enrich-ment in the altered samples is attributed to the high mobility of other elements such as Th. An-other source of REE element in kaolin sample is due to absorption of these elements by kaolinite. Kaolinite flakes absorb a large part of the released Ce, La, and Nd during kaolinization and weathering (Fig 6). Halloysite absorb less REE than kaolinite because of its crystal form (Pa-poulis et al., 2004). The very high correlation between P2O5 and Ce, La, Nd strongly suggests that these elements are primarily in monazite, and the Ce, La, Nd follow the same geochemical path (Fig. 8). Phosphorus in the parent rocks is accommodated exclusively in the monazite and apatite structures. Phosphorus was found to be the only element with an immobile behavior, it is therefore suggested that it may be used as a measure for the depletion in the weathering envi-ronment. Depletion measurements based on P by Sarapää (1996) suggest a loss of almost 60-85% of the original rock constituents. Decomposition of apatite has released phosphorus into so-lution. Many form mechanism of monazite formation will be discuses in next paragraph. Some microanalysis of monazite coexisting with Th-silicate samples show that the some monazite crystals are enriched in Th and depleted in Ce, La, Nd.

6 THE MECHANISM OF MONAZITE FORMATION The mechanism of monazite precipitation in chemical weathering rocks and especially in kaolin-ite deposits takes place when the pH of the fluid most probably increased (to pH~6), due to the fluid neutralization at the carbonate karst wall (see also De Putter et al., 2000). In this pH range, the stability of LaCO3+ strongly increases, and dominates the REE transport, in surface waters (Wood, 1990; Millero, 1992). Lee and Byrne (1992), however, demonstrated that the relative importance of REE species in groundwater is strongly dependent on both pH, and the REE atomic number. For LREE, La3+ dominates up to pH~7, while LaCO3+ stability increases at higher pH, while for the HREE, dominates up to pH~ 6, then passing to LuPO4. Moreover, it is known that monazite solubility is very low (K0sp=10-26.2 at 25 ºC; see Liu and Byrne, 1997): hence, very small quantities of LREE, as La3+, and PO4

-3 ions in the solution allow monazite to form. It is quite interesting that, the monazite REE pattern and ED spectrum are most probably results from the fact that the co-precipitation of REE and phosphate removes these elements from solu-tion in variable proportions (according to their atomic numbers). Co-precipitation is maximum for La-Sm, important for LREE, and much weaker for HREE, because these elements are more strongly complexes than LREE, favouring their retention in the solution (Galan et al, 2007). Most of monazite crystals in the studied kaolin samples are depleted in thorium and enriched in Ce, La and Nd. Assuming thorium as an immobile element; the depletion Th in monazite crystals suggests the degree of monazite alteration.

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Monazite crystals are isolated and very fine crystals; they are very rich in Ce2O3 and to a lesser degree in La2O3 and Nd2O3 and may be termed monazite (Ce) with chemical formula (Ce, La, Nd, Th, Y) PO4 (Table 3). The highest ThO2 content found in the investigated unaltered mona-zite crystals is 5.0 wt. % and decreases with advancing alteration (Table 3, analyses 1, 2 and 3). The microanalyses of monazite crystals from the studied kaolins revealed that there is a remark-able difference in REE content between the unaltered and altered parts of the monazite. The un-altered monazites have lower total REE than the altered residual grains.

Table 3. Representative microanalysis of monazite (Ce) and EDS analyses of monazite from selected Litmanen kaolin sample R529 (82.5).

(A) Sample R529/82.5Analysis 1 2 3 4 5 6 7 8 9 10 11 12P2O5 43.51 28.56 43.19 43.79 43.65 33.46 41.96 44.65 42.94 43.94 45.97 28.67CaO 5.37 6.81 5.25 5.36 5.44 5.64 7.11 6.34 6.83 5.81 5.95 7.19La2O3 11.52 16.72 12.89 12.8 13.4 16.85 15.9 11.41 13.03 12.61 10.64 15.29Ce2O3 27.79 33.46 28.09 28.51 28.13 30.65 29.23 27.32 27.61 28.8 24.91 33.21Nd2O3 11.81 14.45 10.59 9.53 9.39 13.4 6.36 10.28 9.6 8.84 12.54 15.64Total 100 100 100.01 99.99 100.01 100 100.6 100 100.01 100 100.01 100

(B) Sample R529/82.5Analysis 1 2 3 4 5 6 7 8 9 10 11P2O5 55.27 55.47 25.36 50.42 32.94 50.42 32.94 46.67 47.84 43.31 41.4 38.44CaO 7.77 7.42 7.15 6.12 6.17 6.12 6.17 4.86 5.09 9.3 7.11 6.9La2O3 19.63 17.94 17.94 11.54 11.67 11.18 15.9 15.26

1337.87.4713.2330.2111.29100

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Ce2O3 23.35 23.12 36.38 26.48 32.05 26.48 32.05 24.97 26.48 26.75 29.23 28.34Nd2O3 13.62 13.99 11.47 16.98 10.89 16.98 10.89 11.95 8.91 9.45 6.36 11.06

(C) Total 100.01 100 99.99 100 99.99 100 99.99 99.99 99.99 99.99 100 100Sample R529/82.5Analysis 1 2 3 4 5 6P2O5 43.2 42.21 39.51 43.63 37.97 42.21CaO 4.96 7 5.06 5.77 5.66 7S 3.11 2.64 4.05 3.28 3.86 2.64La2O3 13.19 15.02 14.12 13.79 13.28 15.02Ce2O3 26.49 27.26 27.73 24.79 30.08 27.26Nd2O3 9.04 4.33 9.53 8.74 9.15 4.33ThO2 1.54Total 99.99 98.46 100 100 100 100

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Table 4. Representative microanalysis of monazite (Ce) and the abundances of Th and Nd s in the unal-tered monazite in: (A) Eteläkylä Litmanen kaolin sample R697 (98.7); (B) Puolanka kaolin samples.

Figure 7. Triangular diagram shows the variation of Ce, La and Nd concentrations in monazite crystals.

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Figure 8. A plot showing a positive correlation between: (a) Ce and P2O5; (b) Nd and P2O5 (c) La and P2O5; (d) Ce and La; (e) La and Nd; Ce and Nd abundances in the unaltered monazite (Monazite) par-tially altered to Th-silicate bearing samples (Th-silicate), from studied area.

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The usefulness of this accomplishment is realized when these small X-ray beams are coupled with an automated micrometer-resolution stage, such as commonly found on scanning electron microscopes (SEM). An added bonus is that most SEM have energy dispersive X-ray spec-trometers (EDS) attached to them. Photonic excitation of samples produces X-ray characteristic of the elements within the sample similar to electronic excitation, however with less background because atomic particle interactions do not take place (ref).

7 X-RAY MAPS OBTAINED BY SEM/EDS Elemental maps obtained by focusing of X-ray beams onto samples with beam diameters less than a micrometer (Cross and Witherspoon, 2006). In this investigation, the element distribution maps were generated to check for the presence of monazite and other phases mineral hosts for rare earth elements (REE). X-ray maps of up to 8 elements can be obtained simultaneously. The fine particle size of several dispersion kaolin samples led to the use of a beam energy of 15 kV and an energy-dispersive current of 200 pA to ensure high resolution X-ray mapping. Electron beam were scanning pictures of phosphates of La, Ce, Nd and Na, Al, Ca, Si, Ti Fe in Figures (9 and 10) shows that they are evenly distributed in the areas photographed. The elemen-tal maps allow us to determine the nature of the inhomogeneous distribution of REE in the stud-ied samples. The relative intensity and the absolute intensity of the REE patterns varied from the center to the edge of the slide suggesting that the major portion of these elements is either pre-sent in non-kaolinite minerals or is concentrated preferentially in certain kaolinite flakes. The elemental maps reveal compositional zoning patterns that demonstrate multiple occurrences of REE generations even within single grains due to dark and light regions. The dark regions for major elements such as (Al, Si, Na and Fe) in the center of image, indicated the lower element content and hence lower X-ray emission of these elements; while the light regions in the margin of image show that most of Al and Si are present in the internal structure of kaolin flakes. Figure 8 shows the backscattered image of monazite crystals, which clearly shows the higher atomic number of REE containing. P and the mapped REE are distributed homogeneously across the monazite crystal surface. This even distribution indicates these elements are present in the monazite structure or are present in other minerals which are fine grained and homogeneously distributed. Importantly, the fact that different elements are concentrated in different locations argues against their being artifacts. The maps are exceptional when the concentration of several of the elements (Al, Si, and Ti) occur only at high concentrations within the kaolin particles and therefore must be much lower in the matrix minerals. The Fe is homogeneously distributed though occasionally there is a slight concentration in some of the TiO2 particles. The Na is pre-sent in minor amounts and is evenly distributed. The high X-ray emission of Ca distribution in-dicates the Ca is present in monazite crystals associated with P rather than in kaolinite grains. This means that, the X-ray mapping gives elemental distributions that reflect the known micro-structure of the material with a high degree of accuracy. More lighter distribution of P and Ce comparing to distribution of La and Nd, due to monazite crystals analyzed have Ce as the domi-nant cation and may be termed monazite-(Ce). Electron beam scanning pictures of Al, Si, Ti, Ca (Fig. 10) shows, they are evenly distributed in the areas photographed. This even distribution indicates these elements are present in the kaolin-ite structure or are present in other minerals which are fine grained and homogeneously distrib-uted. The maps clearly showed that most of the Al and Si are present in as large particles of kao-

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linite books. Ti, pattern varied from the center to the edge of the slide suggesting that a major portion of these elements is either present in non-kaolinite minerals or is concentrated preferen-tially in certain kaolinite flakes. Lighter distribution of P and Ce related to the same geochemical path of these elements and are primarily found in monazite.

Figure 9. SEM backscattered electron image, Na, Al, Ca, Si, Ca and Fe X-ray map comparing with REE (P, La, Nd, Ce) x-ray map. Note the loss of Na, Al, Si, Ca and Fe in monazite crystal sample R697 (98.7) as a dark area in middle of the BSI image.

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Figure 10. Backscattered electron image and elemental X-ray maps of the monazite grain found in stud-ied kaolin sample R529 (82.5). Note the loss of Na, Al, Si, Ca and Fe within monazite crystal as a dark area and a REE-phosphate (elevated La, Ce, Th and P) as light area.

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8 CONCLUSION This study has established that during the kaolinization of parent rocks (quartz-feldspar gneiss and amphibolites), significant amount of Na, Ca, K and P were easily removed as result of the breakdown of feldspars, biotite, plagioclase and apatite, whereas Ti, Zr and REE remained rela-tively immobile, linked and/or incorporated to resistant heavy minerals (such as monazite) that tended to be residually concentrated in the kaolins. The main factors controlling the abundance and distribution of REE in the studied kaolin depos-its of Virtasalami are: (a) the concentration of accessory mineralogy such as monazite and other secondary phosphate phase minerals; (b) concentration of the REE in parent rocks and the stabil-ity of REE-bearing primary minerals during kaolization processing; and (c) adsorption of REE onto kaolinite and halloysite minerals, whereas REE behaving as positively charged trivalent ions during weathering and they are considered to be adsorbed on negatively charged surfaces of clay minerals such as kaolinite and halloysite. Another interesting result of this study is the appearance of monazite is the only LREE-rich minerals found as an accessory phase in the studied kaolin. It is a very low-solubility mineral that remained stable during the kaolinization process, as confirmed by SM_BSE observations. In fact, monazite occurs as isolated crystals with flattened prismatic shape, and it does shown very low alteration or some times without any sign of alteration. Also the SEM-EDS analysis revealed that monazite of Th in few monazite crystals structure, which is a typical feature of primary monazites. X-ray microanalysis element mapping has been used to characterize the distribution of REE in kaolin samples Monochromatic elemental maps allow us to determine the nature of the inhomo-geneous distribution of REE in accessory mineral hosts for rare earth elements. All monazite crystals analyzed have Ce as the dominant cation and may be termed monazite-(Ce). Aside from the REE oxide content, which closely approaches the theoretical value, minor amounts of CaO have been detected in some crystals. We have shown that monazite concentrations in weathered rocks and kaolin samples can be very heterogeneous and that abundances are distributed only in few of studied samples and are con-trolled by the behavior of phosphate and vice versa. We attribute the complexes (Ce, La, and Nd) and phosphate distribution patterns to the low solubility products for REE phosphate phases, the low solubility of tetravalent Ce, and the phosphate removes these elements from solution in vari-able proportions according to their atomic numbers. The second source of REE enrichment in kaolin samples is related REE adsorption onto kaolin surfaces. 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 en-hanced the REE adsorption. Accordingly, REE were mainly adsorbed on kaolinite in the weath-ering crust of Virtasalmi parent rocks. These dates will clarify in next report after geochemical analysis of kaolin samples is ready.

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9 REFERENCES Al-Ani, Thair and Sarapää, Olli, 2004. Occurrence of halloysite in Virtasalmi kaolin and its

effect on rheological properties. 26 s., 25 liites. Geologian tutkimuskeskus, arkistoraportti, M 19/3231-3232/2004/1/82.

Al-Ani, Thair and Niemelä, Mauri, 2005. Mineralogy and geochemistry of some kaolin

occurrences in the Kainuu region, Northeastern Finland. 22 s. Geologian tutkimuskeskus, arkistoraportti, M19/3441/2005/1/82.

Al-Ani, Thair, Sarapää, Olli; Lehtinen, Markku J., 2006. Mineralogical and chemical study

of some kaolin samples from the Kahdeksaisiensuo and Hyväjärvi occurrences, Virtasalmi SE Finland Geologian tutkimuskeskus, arkistoraportti, M19/3232/2006/1/82.

Ayres, M., Harris, N., and Vance, D., 1997. Possible constraints on anatectic melt residence

times from accessory mineral dissolution rates: An example from Himalayan leucogranites. Mineral. Mag. 61, 29–36.

Bingen, B. and van Breemen, O., 1998. U-Pb monazite ages in amphibolites to granulite-facies

orthogenesis reflect hydrous mineral breakdown reactions: Sveconorwegian Province of SW Norway. Contrib. Mineral. Petrol. 132, 336–353.

Braun, I., Montel, J. M., and Nicollet, C. (1998). Electron microprobe dating of monazites

from high-grade gneisses and pegmatites of the Kerala Khondalite Belt, southern India. Chem. Geol. 146, 65–85.

Broska, I., Kubiš, M., Siman, P., Lipka, J., 2005. Characterization of accessory titanite of

West-Carpathian granites. Polskie Towarszystwo Mineralogiczne, Prace Specjalne, 25, 269-272.

Cathelineau, M., 1987. U–Th–REE mobility during the albitization and quartz dissolution in

granitoids: evidence from south-east French Massif Central. Bulletin of Mineralogy 110, 249–259.

Cocherie, A., Legendre, O., Peucat, J. J., and Kouamelan, A. N., 1998. Geochronology of

polygenetic monazites constrained by in situ electron microprobe Th-U-total lead determination: Implication for lead behavior in monazite. Geochim. Cosmochim. Acta 62, 2475–2497.

Cross, B. J., and Witherspoon, K. C., 2006. Advancing EDS Analysis in the SEM with in-situ

Quantitative XRF. Proceedings of the International Micrsocopy Congress 16, Sapporo, Japan.

Crowley J. L. and Ghent, E. D., 1999. an electron microprobe studies of the U-Th-Pb

systematic of metamorphosed monazite: The role of Pb diffusion versus overgrowth and recrystallization. Chem. Geol.157, 285–302.

20

Galan, E., Fernandez, J., Miras, A., Aparicio, P., and Marquez, G., 2007. Residence and fractionation of REE during kaolinization of alkaline peraluminous graites in NW Spain, clay Minerals, 42, 341-352.

Harrison, T. M., McKeegan, K. D., and LeFort, P., 1995. Detection of inherited monazite in

the Manaslu leucogranite by 208Pb/232Th ion microprobe dating: Crystallization age and tectonic implications. Earth Planet. Sci. Lett. 133, 271–282.

Heinrich, W., Andrehs, G., and Frantz, G., 1997. Monazite-xenotime miscibility gap

thermometer. 1. An empirical calibration. J. Metamorph. Petrol. 15, 3–16. Hawkins, D. P. and Bowring, S. A., 1997. U-Pb systematics of monazite and xenotime: Case

studies from the Paleoproterozoic of the Grand Canyon, Arizona. Contrib. Mineral. Petrol. 127, 87–103.

Lee, J. H., Byrne, R. H., 1992. Examination of comparative rare earth element complexation

behavior using linear free-energy relationships. Geochim. Cosmochim. Acta 56, 1127–1137. Mathieu, R., Zetterstrom, L., Cuney, M., Gauthier-Lafaye, F., Hidaka, H., 2001. Alteration

of monazite and zircon and lead migration as geochemical tracers of fluid paleocirculations around the Oklo-Okelobondo and Bangombe natural nuclear reaction zones (Franceville basin, Gabon). Chemical Geology 171, 147–171.

McCarthy, G. J., White, W. B., and Pfoertsch, D. E., 1978. Synthesis of nuclear waste

monazites, ideal actinide hosts for geologic disposal. Mat. Res. Bull. 13, 1239–1245. Meldrum, A., Boatner, L. A., Weber, W. J., and Ewing, R. C., 1998. Radiation damage in

zircon and monazite. Geochim. Cosmochim. Acta 62, 2509–2520. Millero, F.J., 1992. Stability constants for the formation of rare earth inorganic complexes as a

function of ionic strength. Geochim. Cosmochim. Acta 56, 3123–3132. Neary, C. R. and Highley, D. E., 1984. The economic importance of the rare earth elements. In

Rare Earth Elements Geochemistry (ed. P.Henderson), 2, 423–466. Elsevier. Pan, Y., 1997. Zircon and monazite-forming reactions at Manitouwadge, Ontario. Can. Mineral.

35, 105–118. Papoulis, D., Tsolis-Katagas, P., Katagas, C., 2004. Monazite alteration mechanisms and

depletion measurements in kaolins. Applied Clay Science 24, 271– 285. Podor, R. and Cuney, M., 1997. Experimental study of Th-bearing LaPO4 (780°C, 200 MPa):

Implications for monazite and actinide orthophosphate stability. Am. Mineral. 82, 765–771. Putter, T.D., Andre, L., Bernard, A., Dupuis, C., Jedwab, J., Nicaise, D., Perruchot, A.,

2002. Trace element (Th, U, Pb, REE) behaviour in a cryptokarstic halloysite and kaolinite deposit from Southern Belgium: importance of ‘‘accessory’’ mineral formation for radioactive pollutant trapping. Applied Geochemistry 17, 1313–1328.

21

Sarapää, Olli, 1996. Proterozoic primary kaolin deposits at Virtasalmi, southeastern Finland.

Espoo: Geological Survey of Finland. 152 p. + 6 app. Schandl, E. S., Gorton, M. P., 1991. Postore mobilization of rare earth elements at Kidd Creek

and other Archean massive sulfide deposits. Economic Geology 86, 1546–1553. Schaltegger, U., Fanning, C. M., Günther, D., Maurin, J. C., Schulmann, K., and Gebauer,

D., 1999. Growth, annealing and recrystallization of zircon and preservation of monazite in high-grade metamorphism: Conventional and in-situ U-Pb isotope, cathode-luminescence and microchemical evidence. Contrib. Mineral. Petrol. 134, 186–201.

Smith, M.P., Henderson, P., Peishan, Z., 1999. Reaction relationships in the Bayan Obo Fe–

REE–Nb deposit, Inner Mongolia, China: implications for the relative stability of rare-earth element phosphates and Fluor carbonates. Contributions to Mineralogy and Petrology 134, 294– 310.

Smith, H. A. and Giletti, B. J., 1997. Lead diffusion in monazite. Geochim. Cosmochim. Acta

61, 1047–1055. Taunton, A. E., Welch, S. A., Banfield, J. F., 2000. Microbial controls on phosphate and

lanthanide distributions during granite weathering and soil formation. Chemical Geology 169, 371– 382.

Tilton and Nicolaysen, 1957. The use of monazites for age determination. Geochim.

Cosmochim. Acta 11, 28–40. Tynni, Risto and Uutela, Anneli, 1985. Myöhäis-prekambrinen ajoitus Taivalkosken

savikivelle mikrofossiilien perusteella. Summary: Late Precambrian shale formation of Taivalkoski in northern Finland. Geologi 37 (4-5), 61-65.

Zhu, X. K., O’Nions, R. K., Belshaw, N. S., and Gibb, A. J., 1997. Significance of in situ

SIMS chronometry of zoned monazite from the Lewisian granulites, northwest Scotland. Chem. Geol. 135, 35–53.

Wood, S. A., 1990. The aqueous geochemistry of the rare earth elements and yttrium, 1. Review

of available low temperature data for inorganic complexes and the inorganic REE speciation of natural water. Chem. Geol. 82, 159–186.