Quartz chemistry in polygeneration Sveconorwegian pegmatites, Froland, Norway

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1 Eur. J. Mineral. 2008, 20, Published online June 2008 Paper presented at the symposium Granitic Pagmatites: the State of the Art, Porto, May 2007 Quartz chemistry in polygeneration Sveconorwegian pegmatites, Froland, Norway Axel MÜLLER 1,Peter M. IHLEN 1 and Andreas KRONZ 2 1 Geological Survey of Norway, 7491 Trondheim, Norway *Corresponding author, Axel.Muller@ngu.no 2 Geowissenschaftliches Zentrum Göttingen, Goldschmidtstr. 1, Göttingen, Germany Abstract: Element concentrations in quartz, feldspar and biotite of Sveconorwegian ( Ga) granitic pegmatites in Froland, Norway, were analysed by LA-ICP-MS, EPMA and XRF, respectively, in order to determine chemical variations between different pegmatite types and within individual pegmatitic bodies. A refined classification of the syn-, late- and post-orogenic granitic pegmatites of Froland is presented basing on the pegmatite structure, bulk composition and mineral chemistry. Syn-orogenic pegmatites ( Ga) are relative primitive with respect to granite differentiation. Late-orogenic pegmatites linked to the Herefoss pluton (0.93 Ga) have the most primitive composition and contain Fe phlogopite. Post-orogenic zinnwaldite pegmatites (< 0.93 Ga) are the most evolved. Pegmatitic quartz has an astonishingly consistent trace element signature between and within syn-orogenic pegmatites. Average concentrations are in the range of 6 10 μgg 1 for Li, μgg 1 for Al, 4 8 μgg 1 for Ti, and μgg 1 for Ge. Al, Li, Fe, Ge, and Ti in quartz of late- and post-orogenic and contact-metamorphosed syn-orogenic pegmatites are more variable. Micro-mylonitisation and contact metamorphism caused the lowering of Li and Al and the increase of Ti and Ge in pegmatitic quartz of some syn-orogenic granites. Several generations of secondary quartz replaced pegmatitic quartz at the micro scale (< 1 mm) during retrograde fluid-driven overprint. Secondary quartz is depleted in Al, Ti and Li compared to the host quartz. In contrast to quartz, the feldspar and biotite chemistry depends largely on the differentiation degree of the pegmatites and varies significantly within structurally-zoned pegmatite bodies. Feldspar and biotite chemistry reflects changes in melt composition within pegmatites, which includes a decrease of Mg and Sr and increase of Li, Rb, and Ba. The syn-orogenic pegmatites were formed during the crustal accretion on the western margin of Fennoscandia under constant PTX-conditions causing the homogeneous trace element signature of quartz. Key-words: pegmatite, quartz, LA-ICP-MS, cathodoluminescence, Froland, trace elements. 1. Introduction The pegmatites in southern Norway have attracted the attention of mineralogists for more than a century due to their contents of rare-metal minerals (e.g., Brøgger, 1906), many of them being discovered and described for the first time in the world (e.g., Schetelig, 1922). However, few attempts have been made to give details of the most common pegmatite minerals quartz, feldspar and mica. The chemistry of quartz in the Froland pegmatite field, that developed during the Sveconorwegian orogeny ( Ga) will be the object of this study. The 20 km NE-SW striking and 5-km wide Froland field is in the centre of the south Norwegian pegmatite cluster is framed by the fields of Glamsland- Lillesand, Evje-Iveland, Arendal, and Kragerø (Fig. 1a, b). The mineralogy, mineral chemistry, geochronology, structures and genesis of the pegmatites in these fields have been studied by Andersen (1926, 1931), Bjørlykke (1937), Åmli (1975, 1977), Baadsgaard et al. (1984), Ihlen et al. (2001, 2002), Larsen (2002), Larsen et al. (2004), Henderson & DOI: / /2008/ Ihlen (2004), and Müller et al. (2005). The Froland pegmatites comprise simple abyssal pegmatites with variable contents of quartz, alkali feldspar, plagioclase, biotite, and minor white mica forming about 105 major granitic pegmatite bodies (Ihlen et al., 2001, 2002). REE minerals and other striking accessories are rare and thus the Froland field has been of minor interest for mineralogists, but of large interest for the procelain and glass industry. 76 of the Froland pegmatites were mined for feldspar and/or quartz since the 19th century. Some pegmatites were mined for flaky mica and REE minerals. Pegmatites can display both regional (e.g., Černý, 1992; Malló et al., 1995; London, 1996) and internal compositional zoning (e.g., Cameron et al., 1949; Norton, 1983; London et al., 1989; London, 1996; Roda-Robles et al., 2004) on the basis of characteristic minerals and paragenesis as well as the chemistry of minerals, such as feldspar, mica, tourmaline, garnet and accessory rare-metal minerals. However, the chemistry of quartz has not been considered until the beginning of the 21st century mainly /08/ $ 7.65 c 2008 E. Schweizerbart sche Verlagsbuchhandlung, D Stuttgart

2 448 A. Müller, P.M. Ihlen, A. Kronz Fig. 1. a Location of the pegmatite fields in southern Norway. b Pegmatite occurrences and fields in southern Norway. c Simplified geologic map of the Froland area showing the distribution of major and sampled pegmatite occurrences. Sample localities: 1 Våtåskammen, 2 Haukemyrliene, 3 Lille Kleivmyr, 4 Hellheia Middle, 5 Hellheia North, 6 Bjortjørn, 7 Skåremyr, 8 Sønnristjern, 9 Løvland, 10 Vaselona, 11 Fossheia West, 12 Husefjell, 13 Heimdal, 14 Fossheia East, 15 Metveit. due to analytical limitations. Due to the increasing economic interest for quartz as raw material for high-t glass moulds in the production of solar-grade silicon and other high-tech end uses, the study of pegmatite quartz deposits has been intensified over the last years (e.g., Ihlen et al., 2001, 2002; Larsen et al., 2004; Müller et al., 2005). This is promoted by recent developments of micro-beam techniques enabling the precise determination of trace element in quartz (Flem et al., 2002; Müller et al., 2003b). The aim of this study is to reveal possible variations in the quartz chemistry between different pegmatite types and within individual pegmatites in Froland. For that purpose 14 pegmatite localities were investigated representing different structural and compositional pegmatite types (Fig. 1c; Ihlen et al., 2001, 2002). Larger pegmatites (> 50 m) were sampled along several traverses across different compositional zones. Quartz was investigated by scanning electron microscope cathodoluminescence (SEM-CL) prior to trace element analyses in order to reveal different quartz generations (primary and secondary quartz) at micro-scale (0.001 to 10 mm). Trace elements in quartz (Li, Be, B, Ge, Na, Al, P, K, Ca, Ti, Fe) were analysed with laser ablation inductively coupled mass spectrometry (LA-ICP-MS). Al, Ti, K and Fe of secondary quartz were analysed by electron probe micro analysis (EPMA) due to small volumes of secondary quartz. The chemical signature of quartz is compared with the composition of feldspar and biotite to detect chemical relationships between these co-genetic minerals. This study is a continuation of the work done by Larsen et al. (2004) who provided a general overview of the quartz and feldspar chemistry of the Evje and Froland pegmatite fields. 2. Geological setting The Froland pegmatite field is situated in the Bamble- Lillesand block of southern Norway at the southwestern margin of the Fennoscandian shield (Andersen, 2005; Fig. 1a, b). The pegmatites form large tabular bodies and dykes emplaced in an isoclinally folded sequence of steeply dipping and NNE-SSW striking banded biotite-hornblende gneisses of volcano-sedimentary origin (Alirezaei, 2000). The gneisses are affected by amphibolite facies metamorphism, possibly transitional to granulite facies as indicated by orthopyroxene-bearing felsic gneisses (Elders, 1963) during the Sveconorwegian deformation in the period 1.14 to ca. 0.9 Ga (e.g., Bingen et al., 1998). The precise age of the pegmatites in Froland is uncertain, but U/Pb dating elsewhere in the Bamble-Lillesand block yields ages in the range Ma (Baadsgaard et al., 1984; Cosca et al., 1998). This crustal block representing a segment of the Sveconorwegian orogeny ( Ga) comprises an exhumed mid-crustal portion of a volcanic arc complex (Knudsen & Andersen, 1999), thrusted over the Telemark block along the Porsgrunn-Kristiansand Fault Zone (PKFZ) during the early Sveconorwegian ( Ga; e.g., Bingen et al., 2001, 2002). The 5-km wide Froland pegmatite field is situated in the hanging wall of the PKFZ where it can be followed over a distance of ca. 20 km in NE-SW direction. The PKFZ is interpreted as a northwestdirected long-lived and polyphase fault zone initiated under amphibole facies conditions (Starmer, 1993; Henderson & Ihlen, 2004) when the injection of the majority of pegmatites occurred in the Froland and Glamsland-Lillesand fields (Henderson & Ihlen, 2004). These two pegmatite

3 Quartz chemistry in pegmatites 449 fields, that together comprise a belt of pegmatites with similar bulk compositions, are separated by the Herefoss granite pluton (Ihlen et al., 2002). The circular Herefoss pluton (diameter 18 km) intruded at 0.93 Ga (Andersen, 1997; Andersen et al., 2002) into the central part of the older Glamsland-Lillesand-Froland pegmatite belt (Fig. 1b). The pluton carries mega-enclaves of gneisses (several km in length) in its northern and central part where these gneisses host similar compositional types of pegmatites as in the Froland pegmatite field to the north outside the pluton. 3. Classification of Froland pegmatites The pegmatite field of Froland comprises different types of granitic pegmatites of the abyssal class, some transitional to AB-HREE pegmatites (Černý & Ercit, 2005). Representative localities of the different pegmatite types which were studied are characterised in Table 1, which is deposited and freely available on the EJM website at GeoScience- World ( For more detailed information see Müller et al. (2005). The Froland pegmatites formed during the Sveconorwegian orogeny, i.e. syn-orogenic ( Ga), lateorogenic (0.93 Ga; syn-genetic in respect to the emplacement of the Herefoss pluton) and post-orogenic (< 0.93 Ga; Ihlen et al. 2002). The largest volume of pegmatites formed during the syn-orogenic stage (Henderson & Ihlen, 2004). Ihlen et al. (2002) subdivided the syn-orogenic pegmatites into a number of sub-groups on the basis of their major mineral composition including pegmatitic granites (PGr), granite pegmatites (GP), plagioclase-dominant pegmatites (NaP, Fig. 2a), zoned granitic pegmatites (ZoP, Fig. 2b, c) and K-feldspar-dominant pegmatites (KP), and white mica pegmatites (MP1). Their injection is roughly coeval, although several magma pulses can be distinguished by cross-cutting relationships in the individual areas. The distinction between these pegmatite types is not always obvious, because transitional pegmatites also occur. Some of the ZoP (Vaselona and Fossheia West) which are in the contact aureole of the Herefoss pluton were affected by contact metamorphism and micro-shearing (sheared zoned pegmatites szop). PGr, GP, NaP, and ZoP are crosscut by fine- to medium grained biotite granite dykes (BtGr). The late-orogenic pegmatites form one structural type, i.e. zoned pegmatites linked to the Herefoss pluton emplacement. The Herefoss pluton itself consists of four major granite facies (HGr1-4). HGr1 and HGr2 show development of pegmatite segregations in their interior and frequently along their endocontacts. The pegmatite at Heimdal (HP1) is related to the megacrystic leucogranite HGr1 and the pegmatites at Fossheia East and Metveit (HP2) to the coarse-grained biotite quartz monzonite (HGr2; Fig. 1c). The post-orogenic pegmatites are represented by zinnwaldite pegmatites (MP2) which comprise < 1 m thick dykes. These straight MP2 dykes crosscut all older pegmatite generations. They contain comb quartz and K- feldspar and show internal banding similar to layered pegmatites related to highly fractionated granites rich in Li, FandMn(e.g., Morgan & London, 1999). 4. Analytical methods 4.1. Laser ablation inductively coupled plasma mass spectrometry Laser ablation inductively coupled plasma mass spectrometry, LA-ICP-MS, was applied for the in situ determination of Li, Be, B, Ge, Na, Al, K, Ti and Fe in quartz. The ICP-MS used in this study is a double focusing sector field instrument (model-element-1, Finnigan MAT, Bremen, Germany) combined with a Finnigan MAT UV laser probe. Operating conditions of the LA-ICP-MS are listed in Table 2. The 266-nm laser had a repetition rate of 20 Hz, and pulse energy of mj with continuous ablation on an area of approximately μm. The laser beam was adjusted to give a spot size of approximately 20 μm. External calibration was done using four silicate glass reference materials produced by the National Institute of Standards and Technology (NIST SRM 610, NIST SRM 612, NIST SRM 614, NIST SRM 616). In addition, the standard reference material NIST 1830, soda-lime float glass (0.1 wt.% Al 2 O 3 ) from NIST, the high purity silica BCS 313/1 reference sample from the Bureau of Analysed Samples, UK, the certified reference material pure substance No. 1 silicon dioxide SiO 2 from the Federal Institute for Material Research and Testing, Berlin, Germany and the Qz-Tu synthetic pure quartz monocrystal provided by Andreas Kronz from the Geowissenschaftliches Zentrum Göttingen (GZG), Germany, were used. Each measurement consists of 15 scans of each isotope, with a measurement time varying from 0.15 s per scan of K in high resolution to s per scan of, e.g. Li in low resolution. An Ar-blank was run before each standard and sample measurement. The background signal was subtracted from the instrumental response of the standard before normalisation against the internal standard. This was done to avoid memory effects between samples. A weighted linear regression model including several measurements of the different standard was applied for calculation of the calibration curve for each element. 10 successive measurements on the Qz-Tu were used to estimate the limits of detections (LOD). LOD are based on 3 times standard deviation (3σ) of the 10 measurements divided by the sensitivity S. LOD are 1.6 μgg 1 for Li, 0.3 for Be, 0.3 for B, 50 for Na, 4 for Al, 10 for P, 0.2 for Ge, 0.5 for Ti, 1 for K, and 0.2 for Fe. Flem et al. (2002) gave a more detailed description of the measurement procedure Electron-microprobe analysis Electron-microprobe analysis (EPMA) was applied to determine the Al, Ti, K and Fe distribution across domains of secondary quartz, since this method provides in situ trace element data with a very good spatial resolution down to 5 μm. The analysis spot of the LA-ICP-MS is too large

4 450 A. Müller, P.M. Ihlen, A. Kronz Fig. 2. Three cross sections of representative pegmatites exposed by historical mining activity. The insets right below the cross sections simplify the pegmatite zoning. a View of the SE-NW striking wall of the Hellheia Middle quarry. b SW-NE striking wall of the Skåremyr quarry. c SW-NE striking wall of the Sønnristjern quarry. ( μm) to be placed accurately inside secondary quartz which normally forms domains < 100 μm. Moreover, the high number of fluid inclusions within the secondary quartz would probably cause the adulteration of many of the LA-ICP-MS analyses by elements originating from the trapped fluids (e.g., Na,K,B).The microprobe analyses were performed with a JEOL 8900 RL electron microprobe at the Geowissenschaftliches Zentrum Göttingen, Germany. For high precision and sensitivity, a beam current of 80 na, a beam diameter of 5 μm, and counting times of 15 s for Si, and of 300 s for Al, Ti, K, and Fe were used. Detection limits (3σ of single point background) were 60 μgg 1 for Al, 18 μgg 1 for K, 33 μgg 1 for Ti, and 27 μgg 1 for Fe. Müller et al. (2003a, 2003b) gave a more detailed description of the measurement procedure.

5 Quartz chemistry in pegmatites 451 Table 2. Operating parameters of the LA-ICP-MS and key method parameters. Plasma conditions plasma power 1075 W auxiliary gas flow 0.89 l/min sample gas flow l/min cone high performance Ni CD-1 guard electrode yes Data collection scan type E-scan no. of scans Scanning electron microscope cathodoluminescence Scanning electron microscope cathodoluminescence (SEM-CL) images were obtained from polished thin sections coated with carbon using the LEO 1450VP analytical SEM with an attached CENTAURUS BS BIALKALI type cathodoluminescence (CL) detector. The applied acceleration voltage and current at the sample surface were 20 kv and 3 na, respectively. The BIALKALI tube has a CL response range from 300 (violet) to 650 nm (red). It peaks in the violet spectrum range around 400 nm. The CL images were collected from one scan of 43 s photo speed and a processing resolution of pixels and 256 grey levels. The brightness and contrast of the collected CL images were improved with the PhotoShop software. SEM-CL has been applied to quartz in order to reveal on micro-scale (< 1 mm) growth zonation, alteration structures and different quartz generations. Grey-scale contrasts visualised by SEM-CL are caused by the heterogeneous distribution of lattice defects (e.g., oxygen and silicon vacancies, broken bonds) and trace elements in the crystal lattice (e.g., Sprunt, 1981; Ramseyer et al., 1988; Perny et al., 1992; Stevens Kalceff et al., 2000; Götze et al., 2001; 2004, 2005). Although the physical background of the quartz CL is not fully understood, the structures revealed by CL give information about crystallisation, deformation and fluiddriven overprint. 5. Chemical characterisation of major pegmatite minerals The scope of the study is to characterise the the trace element composition of quartz in different pegmatite generations to indentify processes that generate high purity quartz. In this context, the chemistry of feldspar and mica is important in order to evaluate the degree of fractionation of the pegmatitite melts and their precise crystallisation conditions. One sample of K-feldspar, plagioclase, biotite and/or muscovite was taken per sample point, if the mineral occurred less than 0.5 m away from the sampled quartz. Five of the larger pegmatites (Løvland, Hellheia Middle, Skåremyr, Sønnristjern, Lille Kleivmyr) were multiple sampled along longitudinal traverses crossing the pegmatite bodies in order to reveal possible distribution patterns among the elements. The distances between sample points of the traverses were 4 to 65 m depending on pegmatite heterogeneties, structures, size of exposures, and dimensions of the pegmatites.the longest sampling longitudinal traverse of 208 m was taken from the Sønnristjern pegmatite crossing the zoned core (ZoP) and the host granite pegmatite (GP) Composition of feldspars Rb, Sr, and Ba in K-feldspar and plagioclase are sensitive to igneous differentiation and to the differentiation of pegmatite-forming melts (Mehnert & Büsch, 1981; Long & Luth, 1986; Cox et al., 1996). Generally, Ba and Sr decrease and Rb increases in feldspar during magmatic differentiation. However, granite magmas crystallise under equlibrium conditions whereas pegmatite melts crystallise under super-cooled conditions far from the equilibrium or granite liquidus (e.g., Chakoumakos & Lumpkin, 1990; Morgan & London, 1999; Webber et al., 1999). Therefore, the crystal and, thus, the element fractionation is different (London, 2005), i.e. of Rb, Sr and Ba. The composition of 79 pegmatitic feldspar crystals between 0.1 and 2.5 m in size were determined. Concentrations of major and trace elements are shown in Fig. 3 to 5. The analytical results for feldspar are listed in Table 3, which is deposited and freely available on the EJM website at GeoScienceWorld ( eurjmin.geoscienceworld.org/). The average bulk composition of K-feldspar and plagioclase from syn- and lateorogenic pegmatites vary from Or 79 Ab 21 to Or 84 Ab 16 and from Ab 82 An 12 Or 6 to Ab 75 An 21 Or 4, respectively. Feldspars from Hellheia North (locality 5) and Vaselona (locality 10) were presumably affected by albitisation resulting in a higher Ab content in K-feldspars (Ab )and plagioclases (Ab ). ZoP, GP and PGr contain the most potassium rich K-feldspars (> 13 wt.% K 2 O) and, thus, the K 2 O content in K-feldspar seems to be related to the pegmatite type. High K 2 O(> 13 wt.%) is the requirement for glass- and ceramic-grade K-feldspar and, thus, the K- feldspar of ZoP, GP, and PGr has high feldspar quality. The bulk composition of K-feldspars from post-orogenic pegmatites and granites (HP) is more variable (Or 75 Ab 24 An 1 to Or 83 Ab 16 An 1 ). Ba, Rb, Sr, Ga, and Pb in K-feldspar and Sr and Rb in plagioclase show only slight variations between the different pegmatite types and distinct variations within the individual pegmatites (e.g., Hellheia Middle, Sønnristjern, Lille Kleivmyr; Fig. 3). The element variation is higher for large ZoP and GP pegmatites than for small pegmatites. K-feldspar of the Lille Kleivmyr locality cover the broadest range of Rb/(Sr+Ba) ratios. Lille Kleivmyr is the largest of the investigated pegmatites. The variation of Rb/Sr across the pegmatites at Løvland (KP) and Våtåskammen (PGr) is minor which is in agreement with the compositional homogeneity of these pegmatites. The Rb/Sr ratios of NaP plagioclase, e.g. Hellheia Middle, are almost constant. Plagioclase from Skåremyr (ZoP) shows a strong increase in differentiation from the SE towards the NW edge of the pegmatite (Fig. 2b). A similar scenario is also obtained

6 452 A. Müller, P.M. Ihlen, A. Kronz Fig. 3. Concentration variation diagrams of major and trace elements in K-feldspar and plagioclase from Froland pegmatites. Grey arrows indicate the general magmatic differentiation trend. from Haukemyrliene PGr. A strong zoning in Rb/(Sr+Ba) of K-feldspar and of Rb/Sr in plagioclase is developed across the Sønnristjern pegmatite (Fig. 4 and 5). The granite pegmatite hosting the zoned core has feldspar with consistently low ratios. The ratios strongly increase within the zoned pegmatite core. Increasing ratios reflect higher fractionation of the residual melt from which the feldspar grew, as long as ratios are not disturbed by secondary feldspar alteration. Generally, the fractionation trends can be better obtained from the Rb/Sr ratios of plagioclase than by Rb/(Sr+Ba) of K-feldspar. Megacrystic feldspars (> 1 m) in the core of ZoP and GP can show internal chemical zoning with higher Rb/Sr and Rb/(Sr+Ba) in the core than at the margin. For example, the core of plagioclase (sample ) from Sønnristjern has a more primitive composition (Rb/Sr = 0.04) than the crystal margin (Rb/Sr= 0.22). The core composition corresponds to the primitive composition of plagioclase from the pegmatite contact (e.g., sample in Fig. 4). Generally, feldspar megacrysts were sampled at their margins to produce comparable data. By summarizing, the following differentiation trends for the Froland pegmatites can be revealed by feldspar chemistry. Feldspars from MP dykes at Skåremyr and Hellheia Middle, Løvland (KP), Hellheia North (NaP), Vaselona (sheared ZoP) have the most evolved chemistry. However, the high degree of differentiation exhibited by the NaP Hellheia North is in conflict with its plagioclasedominance and biotite chemistry (see following chapters) and the primitive composition of the related and neighbouring Hellheia Middle pegmatite. The Hellheia North plagioclases were presumably affected by albitisation which resulted in re-distribution of Sr, Ba and/or Rb. Sønnristjern (ZoP), Skåremyr (ZoP), Våtåskammen (PGr), Lille Kleivmyr (GP), Vaselona (sheared ZoP), Bortjørn (NaP) contain feldspars of chemical composition reflecting moderate differentiation of the pegmatitic melt. Pegmatites related to the Herefoss pluton (HP) exhibit a relative primitive differentiation reflected by high Ba and low Rb/Sr in the feldspars. The chemically most primitive plagioclase occurs at Hellheia Middle (NaP). However, the trace element signature of feldspar in the Froland pegmatite field is relatively primitive compared to feldspars from other granitic pegmatite fields elsewhere in the world (Shearer et al., 1992; Abad-Ortega et al., 1993; Larsen, 2002) Composition of micas The composition of 40 pegmatitic micas were determined and plotted in Fig. 4, 6 and 7. The analytical results for mica are listed in Table 4, which is deposited and freely available on the EJM website at GeoScienceWorld ( Their compositions are used to estimate the degree of fractionation of the

7 Quartz chemistry in pegmatites 453 Fig. 4. Sønnristjern pegmatite with outline of the 10-m deep quarry and access tunnel. The exploited zoned pegmatite core is hosted by granite pegmatite which intruded hornblende gneisses. The black columns illustrate the relative values of Rb/(Ba+Sr), Rb/Sr, and (Mg- Li)/Fe# in K-feldspar, plagioclase and biotite, respectively. Columns are placed at the sampling point. pegmatites since micas are useful monitors of PTX during magmatic processes (e.g., Černý & Burt, 1984). Generally, the biotites in the Froland pegmatites have a relatively homogeneous composition which is characteristically primitive in respect to granitic differentiation. All biotites plot in the Mg-siderophyllite and Fe-phlogopite field in the discrimination diagram of Tischendorf et al. (2001; Fig. 6). Biotites in different pegmatite types exhibit slight compositional variations. The most primitive compositions (Fe-phlogopite) are comprised by the micas from pegmatites related to the Herefoss pluton. NaP has micas transitional between Fe-phlogopite and Mg-siderophyllite. Biotites of GP and ZoP plot exclusively in the Fe-phlogopite field reflecting a slightly evolved differentiation. A number of pegmatites are crosscut by zinnwaldite pegmatites (MP1 and MP2). The mica of these dykes have zinnwaldite (Fe polylithionite) composition except for the mica occurring in the Vaselona pegmatite that represents a Li-Fe muscovite with relative high Ti. Sampling profiles across the Hellheia Middle, Skåremyr, Sønnristjern and Lille Kleivmyr pegmatite reveal no obvious zonation across pegmatites due to the limited chemical variation of biotite (Fig. 4). In Fig. 7 Rb/Sr in plagioclase and Rb/(Ba+Sr) in K-feldspar are plotted against Mg-Li of associated biotite. The plots reveal poorly defined tends although the small Mg-Li variation. Mg-Li of biotite decreases with increasing Rb/Sr and Rb/(Ba+Sr) of feldspar during progressive fractionation. Thus, biotites of the four localities show weak chemical zonation in pegmatites that follows the compositional zonation of feldspar Micro-textures in cathodoluminescence images of quartz Late- to post-magmatic fluid-driven overprint causes smallscale quartz dissolution and precipitation (healing) along grain boundaries and micro-cracks resulting in the formation of newly crystallised (secondary) quartz which appears dark grey to black in SEM-CL images. If the CL intensity of the primary quartz is low or if the CL intensity decreases during electron bombardment these structures are hard to detect. For this study the knowledge about different quartz generations and abundance of secondary quartz is a necessity in order to interpret the trace element analyses of quartz properly (e.g.,müller et al., 2002a). Different CL intensities may indicate variable trace element contents (e.g.,götzeet al., 2001). Henderson (2002) gave an overview of secondary micro structures observed in pegmatitic quartz from Froland.

8 454 A. Müller, P.M. Ihlen, A. Kronz Fig. 5. Stacked column diagram of Rb/(Ba+Sr) and Rb/Sr in feldspars (upper part) and of Al, Ti, Li and Ge in pegmatite quartz along a 210 m long profile crossing the Sønnristjern pegmatite. Concentrations of trace elements in quartz are the average of two LA- ICP-MS measurements. The numbers between the columns in the lower line corresponds to distance between two sample points in meter. n.d. not determined due to lack of feldspar at the sample point. Fig. 7. Minor element plots of biotite versus plagioclase (a) and K-feldspar (b). The dashed lines of exponential regression defines poorly differentiation trends. Fig. 6. Compositions of micas from the Froland pegmatite field plotted in classification diagram of Tischendorf et al. (2001). MP1 micas of the Hellheia Middle, Hellheia North, Skåremyr, and Vaselona pegmatite plot in the Fe polylithionite and Li-Fe muscovite fields. tfe Fe total. Four major types of secondary quartz (sqz1 to sqz4) replacing primary pegmatitic quartz (pqz) can be distinguished. The features and abundance of the secondary quartz generations are summarised for the different pegmatites in Table 5. The different types of secondary quartz are described in the order from young to old: sqz1: Thin (< 5 μm), intra- and transgranular healed cracks connecting non-luminescent domains around secondary fluid inclusions. These structures appear black in the SEM-CL image (Fig. 8a, b, c, e). sqz2: Irregular domains of low-luminescent quartz extending from and commonly enveloping sqz1. Occasionally, the envelops extend outwards as preferentially oriented zones in certain directions which may correspond to the crystallographic plans or sets of micro-fractures. Similar to sqz1, sqz2 originates in grain and sub-grain boundaries (Fig. 8a, d), spz1-healed micro-fractures (Fig. 8b) or fluid inclusions (Fig. 8c). These structures appear grey in the SEM-CL image. sqz3: Diffuse alteration rims of relative constant width parallel to grain and sub-grain boundaries and contacts to feldspar and mica. In contrast to sqz1, sqz3 is not transgranular and it exhibits sporadically diffusional, wavy zoning. However, in some cases sqz1 and sqz3 are hard to distinguish. Sqz3 structures appear dark grey in the SEM-CL image (Fig. 8a and d). sqz4: Non-luminescent (black), thin crystal coatings and interstitial fillings at triple-junction boundaries of recrystallised quartz (Fig. 8g and h). Sqz4 dominates the quartz samples from the Fossheia West and Vaselona pegmatites.

9 Quartz chemistry in pegmatites 455 Fig. 8. SEM-CL images of pegmatitic quartz. a Quartz from Bjortjørn showing the distribution and spatial relations of sqz1, sqz2 and sqz3. The network of sqz1 is more dense and irregular than in other pegmatitic quartz. b Quartz from Sønnristjern showing network of sqz1 and sqz2, the latter with preferred orientation. c Fluid inclusion (FI) in quartz bordered by thin film of sqz1 (black). The fluid inclusion and sqz1 are hosted by sqz2. d Strongly altered quartz (pqz) from Lille Kleivmyr which is nearly totally replaced by sqz2. Mica appears black. The structure of sqz3 corresponds the former fluid pathway. The inset shows the enlargement of the bright CL halo around a zircon inclusion. e Quartz from Metveit. Sqz1 forms straight thin healed cracks connecting non-luminescence domains around secondary fluid inclusions. f Detailed SEM-CL image of granite quartz from Husefjell. The quartz exhibits non-luminescent spots (black; some spots are marked with white arrows) which are interpreted as hydrogen-rich defect clusters. g Mylonitised and recrystallised quartz from Vaselona. Boundaries of recrystallised quartz are covered and healed with non-luminescent (black) sqz4. h Mylonitised and recrystallised quartz from Fossheia West. The grain size of recrystallised grains, which are healed with sqz4, is much smaller than in quartz of Fossheia West.

10 456 A. Müller, P.M. Ihlen, A. Kronz Table 5. Observed micro-textures of secondary quartz in pegmatitic quartz and their roughly estimated abundance in vol.%. The volume of sqz2 and sqz3 is summed up, because these generations are often hard to distinguish. Loc. Nr Sub-type Sqz1 (vol.%) Sqz2+3 (vol.%) Sqz4 (vol.%) Specific micro-textures 1 PGr GP < GP NaP < NaP < sporadic inclusions of rutile needles 6 NaP wide-spread sqz1, sqz2 and sqz3 7 ZoP very low CL intensity contrast between pqz and sqz2 8 ZoP < KP < strongly recrystallised Qtz and wide-spread formation of sqz4 along newly formed grain boundaries; healed fluid inclusion trails up to 500 μm wide 10 szop mylonitised, pre-mylonitisation textures are not preserved 11 szop mylonitised, pre-mylonitisation textures are not preserved 12 HGr non-luminescent defect clusters (< 5 μm) 13 HP HP wide-spread sqz1, no sqz2, sporadic inclusions of rutile needles 15 HP non-luminescent defect clusters (< 5 μm), pqz with very unstable CL Loc. Nr. = locality number, Peg. Type = pegmatite type, Qtz = quartz, x = present, - = absent. Quartz in both pegmatites is completely mylonitised and recrystallised which caused the deletion of pre-existing secondary structures (sqz1 3) and the formation of microcrystalline quartz (< 1 to 20 μm). The degree of quartz mylonitisation is more intense in the Fossheia West sample than in the sample from Vaselona. Additonally two types of CL structures have been identified in the Froland quartz: Bright circular radiation halos around radioactive inclusions, e.g. zircon (Fig. 8d) and non-luminescent circular spots 1 5 μm in diameter (Fig. 8f). The radiation halos are caused by α-radiation emitted from radioactive minerals resulting in the damage of the quartz structure and the increase of quartz CL intensity (e.g., Botis et al., 2005). The pegmatite quartz from Metveit (HP2) and the granite quartz from Husefjell (HGr2) show non-luminescent 1 5-μm spots (Fig. 8f). These spots are not related to fluid inclusions or mineral inclusions. Some of the spots disappear after several minutes of electron bombardment. Stenina et al. (1984) described similar spots and identified these structures as amorphous (non-crystalline) micro-domains or defect clusters using TEM imaging. In summary, the portion of secondary quartz replacing primary quartz during at least four different events ranges from 1 to 30 vol.% (Table 5). The approximate volume ratio of primary and secondary quartz is required to draw the correct conclusion regarding the results of the trace element analyses of quartz by LA-ICP-MS. The differences in the CL properties of primary and secondary quartz indicate different trace element signatures as will be shown below. In addition, secondary quartz sqz1, 2 and 3 is the main carrier of fluid inclusions Trace elements in pegmatitic quartz The concentrations of Ti, Li, K, Na, P, and Ge in quartz from the different pegmatite types are listed in Table 6, which is deposited and freely available on the EJM website at GeoScienceWorld ( Be, Na and P are mostly below the detection limit of 0.3, 50 and 10 μgg 1, respectively Variations in quartz chemistry between pegmatite types Average trace element concentrations of quartz in the different pegmatite types are summarised in Table 7. Concentrations in secondary quartz (spz) are not considered in the average value of the deposits due to its commonly low total modal contents. The Al versus Ti plot in Fig. 9 illustrate the concentration fields for the different pegmatite types. Al contents in quartz of the syn-orogenic pegmatites PGr, GP (including GtGr), NaP, ZoP and KP show consistently the same levels (Table 7). Ti is low in PGr, GP, NaP, and KP comprising 3.8 to 6.1 μgg 1. Quartz of ZoP has slightly higher average Ti of 7.2 μgg 1. PGr quartz exhibits the highest average Li of 10.2 μgg 1 followed by GP and NaP with 8.7 and 8.3 μgg 1, respectively. Quartz of K- rich pegmatites (ZoP and KP) has low average Li (6.9 and 5.9 μgg 1 ). Concentrations of trace elements in the mylonitised pegmatitic quartz of Vaselona and Fossheia (szop) show significant differences compared to contents in undeformed ZoP quartz. The quartz of Fossheia West has high

11 Quartz chemistry in pegmatites 457 Table 7. Average concentration of trace elements in quartz of the different pegmatite and granite types. Analyses of secondary quartz are not considered (see Table 6). Average concentrations of quartz from the Vaselona and Fossheia pegmatite are given separately due to their different degree of deformation. Na is below the detection limit of 50 μgg 1. Type Sub-Type Locality name n Li Be B Al Ge Ti K Fe Syn- PGr Våtåskammen < 0.30 < < 1 < 0.24 orogenic GP Sønnristjern, Lille Kleivmyr, < 0.30 < < 1.8 < 0.24 Haukemyrliene NaP Hellheia Middle and North, < 0.32 < < 2.8 < 0.42 Bjortjørn ZoP Skåremyr, Sønnristjern < 0.31 < < 2 < 0.30 GtGr Lille Kleivmyr < 0.30 < < 1 < 0.22 KP Løvland < 0.30 < < 1 < 0.21 szop Vaselona < 0.30 < szop Fossheia West < 0.30 < BtGr Skåremyr, Sønnristjern < 0.30 < < 1 < 0.20 MP1 Hellheia Middle, Skåremyr < 0.30 < < 1.7 < 0.21 Late- HGr1 Husefjell, Heimdal < 0.30 < < 0.68 orogenic HP1 Heimdal < 0.30 < HGr2 Fossheia West, Metveitl < 0.30 < < 0.54 HP2 Fossheia East, Metveit < 0.30 < < Post- MP2 Haukemyrliene < 0.35 < < 1.00 orogenic n = number of analyses. Fig. 9. Al versus Ti plot of pegmatitic quartz grouped according to pegmatite type. Increasing Ti in quartz indicates increasing crystallisation temperature (Wark & Watson, 2006) and, therefore, quartz in Herefoss quartz monzonites and pegmatites (HGr1 and HGr2) and high-temperature deformed pegmatites (szop) have the highest levels of Ti. Ge (2.4 μgg 1 )andti(29μgg 1 ), and exceptional low Li (0.3 μgg 1 ) and Al (26.2 μgg 1 ). The Vaselona quartz has highest Ge (2.8 μgg 1 ), high Ti (16.3 μgg 1 ), and relatively low Li (4.3 μgg 1 ). The mylonitisation combined with contact metamorphism which affected the Fossheia West pegmatite more intensely may have caused the redistribution of trace elements whereby Ti and Ge were introduced to the quartz lattice and Al and Li expelled. The chemistry of the quartz in the biotite granite dykes (BtGr) crosscutting the pegmatites is characterised by lower average Al (18.3 μgg 1 )andge(1.0μgg 1 )and slightly higher Ti (7.4 μgg 1 ) compared to that of their pegmatite hosts. However, the differences in concentration between the syn-orogenic pegmatites and the biotite granite dykes are minor. The two subtypes of zinnwaldite-bearing pegmatite dykes MP1 and MP2, subdivided on the basis of textural features (Table 1), show significant differences in their Li, Al, Ti, K and Fe content (Table 7). However, both of them have high average Ge (2.0 and 2.1 μgg 1 ) compared to the other pegmatite types. The MP2 at Haukemyrliene exhibits a very distinct element signature characterised by high Al (122 μgg 1 ), Ti (15.5 μgg 1 ), and K (18.2 μgg 1 )andlow Li (3.6 μgg 1 ). Quartz of the Herefoss leucogranite (HGr1) and quartz monzonite (HGr2) is characterised by high average Ti (33.4 and 24.6 μgg 1 ) and K (5.4 and 4.2 μgg 1 )andlowge (0.8 μgg 1 ). The Herefoss pluton related HP1 and HP2 pegmatitic quartz has high Ti (26.3 and 17.5 μgg 1 ) and K and relative low Li compared to the syn-orogenic pegmatites. Similar Li, Al, K and Fe concentrations in the quartz of Herefoss granites and related pegmatites underline their genetic relationship. The slightly lower Ti in the HPs is related to the lower formation temperature (Wark & Watson 2006) of the pegmatite quartz compared to the granite quartz. Most syn-orogenic pegmatites (Løvland, Hellheia Middle and North, Bjortjørn, Skåremyr Sønnristjern, Lille Kleivmyr) represent quartz of medium quality in a raw material context (Harben, 2002; Müller et al., 2005) with relatively similar trace element concentrations independently of pegmatite type (Fig. 9). However, syn-orogenic pegmatites, which occur in the contact aureole of the Herefoss

12 458 A. Müller, P.M. Ihlen, A. Kronz yield much lower Ti than the other samples (Table 6). This sample contains more than 25 vol.% of secondary quartz, which causes the general lowering of the average trace element concentration (see below). Summarising, there appears to be no clear systematic variations of the trace element contents of quartz across the pegmatites. The results testify to a rather homogeneous distribution of the tested trace elements Al, Ti, Li, Ge, Fe in quartz across different pegmatite zones Quartz chemistry of primary versus secondary quartz Fig. 10. Pegmatites with stacked columns of the Al, Ti, Li, and Ge concentration (average of 2 analyses) in pegmatitic quartz, a Skåremyr pegmatite, b Sønnristjern pegmatite. pluton and in mega enclaves within the Herefoss pluton (szop) are characterised by relative high Ti. Most of the HPs contain low quality quartz apart from the Fossheia East pegmatite which contains medium quality quartz Variations in quartz chemistry within pegmatites Quartz samples were taken along traverses in the individual pegmatite bodies in order to reveal possible distribution patterns among the trace elements. Figure 5 and 10 illustrates the distribution of Al, Ti, Li and Ge in pegmatite quartz in form of stacked concentration columns across the Sønnristjern and Skåremyr pegmatites. Generally, the trace element contents of quartz show small variations across the pegmatites. However, there are some exceptions. For example, analyses of sample of the Løvland pegmatite Al, Ti, K and Fe distribution across domains of secondary quartz was determined by EPMA. Figure 11 shows 3 concentration profiles of Al across structures of secondary quartz in pegmatitic quartz from Bjortjørn, Sønnristjern and Lille Kleivmyr. Al is systemically depleted in secondary quartz in relation to the primary quartz. The depletion is stronger in sqz1 (Bjortjørn and Sønnristjern) than in sqz3 (Lille Kleivmyr). Beside Al the Ti concentration in secondary quartz sqz1 and sqz3 is distinct lower than in the primary host quartz (Fig. 12). The LA-ICP-MS analyses (Løvland) and (Skåremyr) which are placed in primary quartz with high portion of secondary quartz (sqz1 to sqz3) have lower Al, Ti and Li than primary quartz in the same deposit. It can be concluded that secondary quartz sqz1 to sqz3 revealed by SEM-CL is depleted in Li, Al and Ti (Fig. 11 and 12). The films of sqz4 around recrystallised quartz grains are too thin to be analysed by LA-ICP-MS and EPMA. Bright luminescent quartz around radioactive inclusions shows no significant redistribution of trace elements (Botis et al., 2005). Summarising, the presence of secondary quartz (sqz1 to sqz3) in primary quartz leads to a slight decrease in the average concentration of trace elements when using LA- ICP-MS analyses depending on the volume portion of secondary quartz (Table 5). 6. Implications of quartz chemistry for pegmatite crystallisation The two major findings of this study are the insignificant trace element variation in pegmatitic quartz of the synorogenic pegmatites on regional scale and the homogeneous trace element content of quartz within these pegmatites, which are in part compositionally zoned. The general explanations could be that the melts originated from a relatively homogeneous source, pegmatites emplaced at the same crustal level during a relatively short time period at similar PT conditions, the determined trace elements in quartz are not very sensitive to internal fractionation processes, and/or the water-enriched highly viscous pegmatitic melt enables the almost free diffusion of Li, B, Al, Ge, and K(e.g., London, 2005). Different populations of pegmatitic quartz, e.g. quartz graphically intergrowth with primitive plagioclase at the pegmatite contacts

13 Quartz chemistry in pegmatites 459 Fig. 11. Al concentration profiles crossing primary and secondary quartz. The SEM-CL images of quartz above show the location of EPMA sampling spots. Fig. 12. Concentration profiles of Al across structures of secondary quartz in pegmatite quartz from Bjortjørn, Sønnristjern and Lille Kleivmyr analysed by EPMA.

14 460 A. Müller, P.M. Ihlen, A. Kronz and massive quartz in the core zone have similar trace element contents. The graphic quartz crystallised earlier (at least some hours or days; e.g., Webber et al., 1999) than the massivequartz (e.g., Fig. 9b). In contrast, plagioclase coexisting with the two quartz populations has different Rb/Sr ratios indicating the internal fractionation of these elements within the crystallising pegmatite melt. However, the uptake of the determined trace elements into the quartz lattice seems not to be affected by the internal melt fractionation defined by decreasing Mg and Sr and increasing of Li, Rb, and Ba. Wark & Watson (2006) proved the temperature dependence of the Ti 4+ Si 4+ substitution in the presence of rutile and established a geothermometer for the temperature range of 400 to 1000 C at 1.0 GPa. The temperature dependence of Ti in quartz explains its constant values in quartz of syn-orogenic pegmatites, and the higher content in the Herefoss pluton related (HP1 and HP2) and contactmetamorphosed pegmatites (szop). Systematic temperature gradients from the contact to the core of pegmatites which are described, e.g. for the Little Three pegmatite, California (Morgan & London, 1999) could not be demonstrated for the Froland pegmatites due to the small variations in Ti content of quartz. The thermometer of Wark & Watson (2006) can be applied even in the absence of rutile if the TiO 2 activity of the system is known. However, in the case of the Froland pegmatites the TiO 2 activity is difficult to determine due to uncertainties of the pegmatite bulk composition. The bulk composition however of the syn-orogenic pegmatitic granite from Våtåskammen could be determined due to the homogeneous rock structure formed of 1 to 10 cm large crystals. The TiO 2 activity of the Våtåskammen melt was a TiO2 = 0.68 based on a new TiO 2 saturation model for granitic melts (Hayden et al., 2005). The crystallisation temperatures of quartz in the syn-orogenic pegmatites are in the range of C. However, there is an uncertainty in the activity of Ti in the pegmatitic melts and the data from Våtåskammen are probably not representative for all syn-orogenic pegmatites. The presence of secondary quartz slightly lowers the total Ti determined by LA-ICP-MS resulting in the underestimation of the primary crystallisation temperature. The obtained temperatures are not unexpected lower than those determined for the granulite facies peak metamorphism at C in the Bamble-Lillesand block (Touret, 1971a, 1971b; Nijland & Maijer, 1993). However, the temperatures fall well within amphibolite-greenschist facies conditions when the pegmatitites successively were emplaced during progressive crustal shortning and tectonic uplift of the Bamble-Lillesand block, leading to early syn-orogenic folded dykes and late weakly deformed dykes (Henderson & Ihlen, 2004). Processeses which control the uptake of Al into the quartz lattice seem to be more complex (e.g., Müller et al., 2000, 2002a, 2003b). Al 3+ substituting Si 4+ may either be paired with P 5+ or with the monovalent ions Li +,Na +,K + and H + and, thus, Al may form different defect centres in the quartz lattice. Jacamon & Larsen (2006) simply suggest that Al in igneous quartz increases with increasing aluminium saturation index. Li in quartz is presumably buffered by Libearing phases coexisting with quartz which are micas in the Froland pegmatites. Similar mineral assemblages of the Froland pegmatites and their insignificant regional fractionation explains the constant Li content in quartz. Ge shows a incompatible character and becomes enriched in granitic and pegmatitic quartz during fractionation (Schrön et al., 1988; Larsen et al., 2004; Jacamon & Larsen, 2006). Consequently, Larsen et al. (2004) detected significant Ge variations in pegmatitic quartz from the Froland and Evje pegmatite field which have different fractionation trends and stages. Due to the similar fractionation degree of the syn-orogenic Froland pegmatites Ge is almost constant. Fluid-driven, post-crystallisation overprint resulted in replacement of bright luminescent primary quartz by low to non-luminescent secondary quartz during at least four different events. Micro-fractures providing the pathways for fluids can be related to external deviatoric stress, but also to internal stress at grain scale as a consequence of strong thermal contraction of quartz (Vollbrecht et al., 1991, 1994). Structures formed during these sub-solidus processes include fracture-bound replacement that are comprised by secondary quartz, usually as several generations. Thermal contraction triggered probably the development of sqz1 and sqz2 because these structures are common in igneous quartz elsewhere (e.g., Sprunt & Nur, 1979; Behr & Frentzel-Beyme, 1989; Van den Kerkhof & Hein, 2001; Van den Kerkhof et al., 2001, 2004; Müller et al., 2000, 2002b). Sqz3 may result from diffusional processes along existing grain boundaries (Müller et al., 2005). In the case of sqz4 the systems of micro-fractures were formed by shearing and tensional strain. Secondary quartz sqz1, 2 and 3 is systematic depleted in Al, Ti and K compared to the primary quartz hosting them. The trace element depletion has been described previously (Müller et al., 2002a, 2002b; 2003a, Van den Kerkhof et al., 2004) and the process of quartz purification during retrograde, fluid-driven overprint seems to be a common phenomena in igneous and pegmatitic rocks (e.g., Ihlen & Müller, 2007). However, the influence of the chemistry of secondary quartz on the bulk quartz composition is minor in the case of the Froland quartz due to the commonly low volume (< 5vol.%)of secondary quartz. In samples, in which the volume of secondary quartz exceeds 10 vol.%, the average trace element concentration is significantly lowered, e.g. sample from Løvland. Summarising, the PTX-conditions during formation of the syn-orogenic pegmatites were constant and stable for the time of the pegmatite emplacement over an area of at least 100 km 2. Henderson & Ihlen (2004) showed that the syn-orogenic pegmatites are structurally related to Sveconorwegian fold geometries associated with peak metamorphism between 1.14 and 1.12 Ga and are kinetically related to overthrust geometries associated with the initial overthrusting phase of the Porsgrumm-Kristiansand Fault when the Bamble complex docked with the underlying Telemark block. The thrusting lead to amphibolite facies transitional to granulite facies conditions causing the partial anatexis of biotite-hornblende gneisses. Themelts were extracted at short periods of brittle fracturing interspersing ductile deformation (Henderson & Ihlen, 2004) resulting