Chemical characteristics of zircon from A-type granites and comparison to zircon of S-type granites

Lithos 192–195 (2014) 208–225

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Chemical characteristics of zircon from A-type granites and comparison to zircon of S-type granites Karel Breiter a,⁎, Claudio Nery Lamarão b, Régis Munhoz Krás Borges b, Roberto Dall'Agnol b,c a b c

Institute of Geology of the Academy of Sciences of the Czech Republic, v. v. i., Rozvojová 269, CZ-165 00 Praha 6, Czech Republic Research Group on Granite Petrology, Instituto de Geociências, Universidade Federal do Pará, Caixa Postal 8608, 66075-100 Belém, Pará, Brazil Vale Institute of Technology, Rua Boaventura da Silva, 955, 66055-090 Belém, Pará, Brazil

a r t i c l e

i n f o

Article history: Received 17 October 2013 Accepted 1 February 2014 Available online 7 February 2014 Keywords: Zircon A-type granites S-type granites Wiborg batholith Brazil Krušné Hory/Erzgebirge

a b s t r a c t The trace element content in zircons from A-type granites and rhyolites was investigated by using back-scattered electron images and electron microprobe analyses. The studied Proterozoic (Wiborg batholith, Finland and Pará, Amazonas and Goiás states, Brazil) and Variscan (Krušné Hory/Erzgebirge, Czech Republic and Germany) plutons cover a wide range of rocks, from large rapakivi-textured geochemically primitive plutons to small intrusions of F-, Li-, Sn-, Nb-, Ta-, and U-enriched rare-metal granites. While zircon is one of the first crystallized minerals in less fractionated metaluminous and peraluminous granites, it is a late-crystallized phase in peralkaline granites and in evolved granites that may crystallize during the whole process of magma solidification. The early crystals are included in mica, quartz, and feldspar; the late grains are included in fluorite or cryolite or are interstitial. The zircon in hornblende–biotite and biotite granites from the non-mineralized plutons is poor in minor and trace elements; the zircon in moderately fractionated granite varieties is slightly enriched in Hf, Th, U, Y, and HREEs; whereas the zircon in highly fractionated ore-bearing granites may be strongly enriched in Hf (up to 10 wt.% HfO2), Th (up to 10 wt.% ThO2), U (up to 10 wt.% UO2), Y (up to 12 wt.% Y2O3), Sc (up to 3 wt.% Sc2O3), Nb (up to 5 wt.% Nb2O5), Ta (up to 1 wt.% Ta2O5), W (up to 3 wt.% WO3), F (up to 2.5 wt.% F), P (up to 11 wt.% P2O5), and As (up to 1 wt.% As2O5). Metamictized zircons may also be enriched in Bi, Ca, Fe, and Al. The increase in the Hf content coupled with the decrease in the Zr/Hf value in zircon is one of the most reliable indicators of granitic magma evolution. In the zircon of A-type granites, the Zr/Hf value decreases from 41–67 (porphyritic granite) to 16–19 (equigranular granite) in the Kymi stock, Finland, and from 49–52 (biotite granite) to 18–36 (leucogranite) in the Pedra Branca pluton, Brazil. In the in situ strongly fractionated Cínovec cupola (Erzgebirge), the Zr/Hf value decreases from 33–51 in the protolithionite granite at a depth of 1255 m to 7.5–25 in the zinnwaldite granite at a depth of 40 m. At the scale of individual crystals, the Zr/Hf value decreases from 86 to 68 from the cores to the rims of the zircons from the Teplice rhyolite and from 64 to 33 in the zircons from the biotite granite at Krupka, Erzgebirge. The contents of Hf and U in zircon are dependent mainly on the degree of granite fractionation and the nature and volume of the volatile phases and are independent of the A- or S-character of the parental melt. The zircon Zr/Hf ratios 55 and 25 are proposed to approximately distinguish common, moderately evolved and highly evolved granites. Zircons from the moderately and highly evolved granites of A- and S-type can be discriminated on the basis of their HREE content and the U/Th ratios. Nb, Ta, and W are present in zircon from the highly evolved granites from all studied areas, while high As, Bi, and Sc contents are typical only for the Erzgebirge. © 2014 Elsevier B.V. All rights reserved.

1. Introduction Zircon is an almost ubiquitous and relatively stable accessory mineral in the majority of types of granitoids and is often used for genetic considerations and geochronology (e.g., Hanchar and Hoskin, 2003, and references therein). In spite of its apparently simple chemical composition, (Zr,Hf)SiO4, zircon is able to accept substantial amounts of a number of other minor and trace elements into its crystal lattice. Zircon crystals ⁎ Corresponding author. E-mail address: [email protected] (K. Breiter).

http://dx.doi.org/10.1016/j.lithos.2014.02.004 0024-4937/© 2014 Elsevier B.V. All rights reserved.

that are not affected by intense metamictization provide information about the chemical composition of the melt from which the granite crystallized. The metamictized crystals may accumulate substantial amount of nonformula elements adsorbed from hydrothermal and low-temperature fluids. The routine use of electron microprobe analysis (EMPA) during the last 20 years has produced extensive data concerning the chemical composition of zircon (Breiter et al., 2006; Finch and Hanchar, 2003; Grimes et al., 2007; Hoskin and Schaltegger, 2003; Huang et al., 2002; Johan and Johan, 2005; Pérez-Soba et al., 2007; Pettke et al., 2005; Rubatto, 2002; Uher et al., 1998; Van Lichtervelde et al., 2009; Wang

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et al., 2000). However, in addition to Zr, Hf, and Si, only a few of the most abundant elements found in zircon, including U, Th, Y, some REE, Al, and Ca, are usually analyzed using this technique. Complete analyses for the 20 or more trace elements that contribute to the chemical composition of individual zircon grains are still scarce (Breiter and Škoda, 2012; Breiter et al., 2006, 2009; Förster, 2006; Förster et al., 2011; Uher et al., 2009). A broad trace element spectrum in zircon including the lower concentration elements may be obtained by using the LA-ICP-MS method (Belousova et al., 2002; De Liz et al., 2009; Nardi et al., 2012, 2013). Although A-type granites have recently garnered more attention (cf. Bonin, 2007, 2008; Dall'Agnol and Rämö, 2009; Dall'Agnol et al., 2012; Frost et al., 2007; Rämö, 2005), especially for their potential rare-metal mineralizations (Bastos Neto et al., 2009; Bettencourt et al., 2005; Borges et al., 2009; Costi et al., 2009; Dall'Agnol et al., 2005, 2012; Haapala, 1995; Lamarão et al., 2012; Lenharo et al., 2002), the chemistry of zircon from these granites has not been reported extensively. It is also relevant to compare the characteristics of zircon found in A- and S-type mineralized granites to define an additional tool for the identification of these types of granites that can occur in the same province (Breiter, 2012) and to evaluate their potential as carriers of rare-metal mineralization. The aims of this article are as follows: (i) To characterize the contents of minor and trace elements in zircon from A-type granites from plutons of different ages, chemical compositions, grades of fractionation and ore fertilities, as represented by several tin mineralized provinces; (ii) To identify the behavior of different elements related to areal specialization (protoliths) and magma typology (A-type vs. S-type granitoids); (iii) To propose discrimination tools (diagrams) to distinguish zircon from ore-bearing and barren A-type plutons.

2. Chemical studies on zircon of A-type granites Zircon from granitoids always contains some Hf. The Zr/Hf ratio in chondrites is 33–38 (Anders and Grevesse, 1989; Barrat et al., 2012), but this ratio in zircons varies considerably. A general rule is that the Zr/Hf ratio decreases with progressive fractionation of the melt (e.g., Černý et al., 1985). The content of Hf in zircon from rocks ranging from kimberlites to common granites remains almost the same (0.8– 1.7 wt.% HfO2) and increases significantly only in strongly fractionated granites (Belousova et al., 2002). The highest concentrations of Hf in zircon were found in the Tanco pegmatite in Manitoba, Canada (39 wt.% HfO2, Van Lichtervelde et al., 2009) and in the Steward granitic pegmatite (44 wt.% HfO2, Ma and Rossman, 2005). Hafnon, the Hf-dominant member of the zircon group, was found in a rare-metal pegmatite at Zambezia, Mozambique (Correia Neves et al., 1974) and in the Koktokay No.1 pegmatite, China (Yin et al., 2013). Uher and Broska (1996) analyzed zircon from relatively lessfractionated post-orogenic A-type granites in the Slovak Republic and Hungary and found only low trace element content, with a maximum 1.8 wt.% HfO2. Wang et al. (1996, 2000) reported Hf-rich zircon from A-type granites in Sushou and Laoshan, China. Kempe et al. (2004) noted that extreme Hf-enrichment is typical of zircons with patchy structure from P-poor (more commonly A-type) granites. Johan and Johan (2005) analyzed 16 chemical elements in zircon from the Cínovec granite cupola, Krušné Hory/Erzgebirge, and found important differences between zircons from the zinnwaldite and protolithionite granite facies. Förster (2006) described Th-, U-, and Y-rich zircon and intermediate solid solutions in the system zircon–xenotime–thorite–coffinite from A-type granites in the eastern Erzgebirge (Germany) and Jordan. Lamarão et al. (2010) published an overview of the Hf, Y, U, Th, Nb, and Ca content in zircon from A-type granites of the Amazonian craton and stressed the significance of the Zr/Hf ratio for granite classification.

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Zircons from peralkaline rocks contain in general fewer trace elements. Smith and de St. Jorre (1991) reported Hf-poor (b0.30 wt.% HfO2), but Nb-enriched (up to 6.6 wt.% Nb2O5) zircon from the Thor Lake alkali syenite. In peralkaline A-type granites from eastern coastal China, Xie et al. (2005) distinguished two types of zircon: an early crystallized Th-rich zircon (1–10 wt.% ThO2) and a late recrystallized Th-poor zircon (b1 wt.% ThO2) with thorite microinclusions. Nardi et al. (2012) analyzed zircons from several varieties of A-type granites of the Pitinga tin province of Brazil, including the peralkaline Madeira albite granite, and found that the Madeira granite contains exceptionally high average contents of HfO2 (2–5 wt.%), Nb (8–825 ppm), Th (200–6649 ppm), U (456–2975 ppm) and Y (2003–9211 ppm). 3. Geology of the studied plutons and sampling For our study, we chose three areas with well-known A-type granite magmatism: (i) the Wiborg batholith, the classic area of Proterozoic rapakivi-type granites in southern Finland, (ii) the Proterozoic A-type granite plutons of Xingu (Pará state), Pitinga (Amazonas state), and Goiás tin provinces in Brazil, and (iii) the Krušné Hory/Erzgebirge area in the Czech Republic and Germany with Variscan volcanoplutonic complexes containing Sn–W-bearing A-type rhyolites and granites. All selected plutons are composed of typical A-type granites (Bonin, 2007; Dall’Agnol et al., 2012; Eby, 1990, 1992; Haapala and Rämö, 1992; Loiselle and Wones, 1979). The studied granite complexes are generally metaluminous to marginally peraluminous, ferroan (Frost et al., 2001), both reduced and oxidized (cf. Dall'Agnol and Oliveira, 2007), and are post-orogenic or within-plate (Pearce et al., 1984) granites with relatively high Fe/Mg ratios and high HFSE content (Breiter and Škoda, 2012; Haapala and Rämö, 1992; Rämö and Haapala, 2005). The studied granites are derived predominantly from crustal sources (Anderson and Bender, 1989; Breiter, 2012; Creaser et al., 1991; Dall'Agnol et al., 2005; Heinonen et al., 2010a; Rämö and Haapala, 2005). They belong to the A2 subtype, according to the classification of Eby (1992). Its Alumina saturation index (ASI) generally varies between 0.9 and 1.1, except for greisenized and/or hydrothermally altered rocks. Peralkaline rocks were not included in this study. The only exception is the Pitinga cryolite granite, which is associated with the metaluminous to peraluminous dominant facies of the Madeira pluton (Costi et al., 2009). Most complexes consist of voluminous early non-mineralized facies of geochemically ‘normal’ granites and/or rhyolites followed by smaller later intrusions of fractionated geochemically specialized rare-metal granites, with different grades of enrichment in F, Li, Rb, Sn, W, Nb, Ta, and U. However, some barren plutons are also presented for comparison. 3.1. The Proterozoic A-type Wiborg batholith, Finland The Wiborg batholith is the largest and the most petrologically diversified Proterozoic (1.67–1.54 Ga) rapakivi-type batholith crosscutting the Paleoproterozoic Svecofennian (1.9–1.8 Ga) basement in southern Finland (Heinonen et al., 2010b; Sederholm, 1891, Fig. 1). Wiborgite is the most typical member of the entire rapakivi suite. It is a porphyritic coarse-grained biotite–hornblende granite with cm-sized ovoids of alkali feldspars mantled by plagioclase rims. The ‘dark wiborgite’ differs from the wiborgite s.s. in containing fewer alkali feldspar ovoids and additionally containing megacrysts of basic plagioclase and larger modal contents of mafic minerals. Equigranular biotite, partly hornblende-bearing, granite forms smaller, relatively younger bodies. The contacts between the mentioned rock types are sharp and intrusive, locally with magmatic brecciation (Heinonen et al., 2010b). Samples of the most typical and widespread granite varieties were collected in the southern part of the batholith near the town of Hamina (sample #4717) and the island of Ristisaari (#4711 and 4712). The Ahvenisto complex located at the NW margin of the Wiborg batholith

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of topaz-bearing granite. A comagmatic, ca. 1000 m thick series of porphyritic rhyolites (#4716) and rhyolitic tuffs (#4715) occurs in the NE part of the batholith at the town of Lappeenranta. The most evolved part of the batholith is the Kymi stock situated in the batholith's central part (Lukkari and Holtz, 2007; Lukkari et al., 2009). The stock is zoned and composed of medium-grained porphyritic biotite granite in the center (#4718), medium-grained equigranular Li–mica–topaz granite at the margin (#4719) and marginal pegmatite along the stock contact (#4720).

3.2. Proterozoic A-type granites of Brazil

Fig. 1. Geological sketch of the Wiborg batholith, Finland (Heinonen et al., 2010b, modified).

is composed of a gabbro–anorthosite rim and a granitic core. The granite varieties evolved from coarse-grained hornblende–biotite granite (#4713) through equigranular biotite granite (#4714) to minor bodies

The studied granites from Brazil belong to three major tin provinces located in the states of Pará (Xingu), Amazonas (Pitinga) and Goiás (Goiás province) (Fig. 2). In the Xingu tin province, the Paleoproterozoic mineralized granites were grouped in the reduced Velho Guilherme Suite (Dall'Agnol et al., 1993; Teixeira et al., 2002). The 1.87 Ga Bom Jardim Granite (BJG; Lamarão et al., 2012) is a circular intrusion with approximately 200 km2 of area that crosscuts volcanic rocks of the Uatumã Group (Juliani and Fernandes, 2010). It is composed dominantly of coarse- to medium-grained monzogranite to syenogranite (#SAL-49) affected by different intensities of late- to post-magmatic alteration. Greisenized rocks (#SAL-66) containing small primary concentrations of cassiterite were identified in pervasively altered cupolas (Lamarão et al., 2012; Teixeira et al., 2002). The Pitinga Province belongs to the Central Amazonian Province of the Amazonian craton (Almeida et al., 2000; Santos et al., 2000; Tassinari and Macambira, 1999). The Paleoproterozoic Madeira and Água Boa plutons are the main sources of the tin exploited in the Pitinga

Fig. 2. Location of studied granites from Brazil.

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region (Costi et al., 2000). The earlier, less evolved facies of the Água Boa pluton is an isotropic, coarse-grained hornblende–biotite syenogranite to alkali feldspar granite, with ovoids (up to 2 cm) of K-feldspar, locally surrounded by plagioclase rims (#F-13, 50.4 m). The more evolved facies of the Água Boa pluton is a porphyritic topaz–alkali–feldspar granite (#AMT-10). The earlier-emplaced facies of the Madeira pluton are similar to those of the Água Boa pluton. However, the most evolved facies of the Madeira pluton is a medium-grained, cryolite-bearing peralkaline albite granite (#4894). The Pitinga tin-greisens occur as lens-shaped ore bodies or veins essentially composed of quartz, brown siderophyllite, topaz, and sphalerite, with subordinate amounts of pyrite, chalcopyrite, cassiterite, zircon, fluorite, monazite, xenotime, siderite, and Nb-rich anatase (Borges et al., 2009) (#F-13, 44.7 m). The Mesoproterozoic Pedra Branca granite (PBG), located near Nova Roma city, is a mineralized granite of the Goiás Tin Province (Botelho, 1984). It is elliptical in shape and is intrusive into N2.5 Ga gneisses and schists of the Ticunzal Formation. It is formed dominantly by isotropic porphyritic to equigranular biotite granites (#PB-124), leucogranites (#PB-94) and greisens. The tin deposits associated with the PBG are typical of greisenized granite cupolas. The Jamon and Redenção granites belong to the Paleoproterozoic oxidized A-type Jamon suite of the eastern Amazonian craton. The granites consist of granitic batholiths and stocks emplaced at shallow crustal levels in the Archean Carajás province. The rocks are isotropic, fine- to coarse-grained biotite ± amphibole monzogranites (#AU-382) and subordinate syenogranites and leucogranites (#DC-83b). The typical accessory minerals are apatite, titanite, zircon, allanite, magnetite, and ilmenite. Fluorite appears only in the most evolved facies. Subsolidus processes were limited (Dall'Agnol et al., 2005).

3.3. Variscan A-type granites of the Krušné Hory/Erzgebirge, Czech Republic/Germany The granites of Krušné Hory/Erzgebirge Mts. (Fig. 3) represent one of the classic regions of ore-bearing granites in the world (Breiter et al., 1999; Förster et al., 1999; Hochstetter, 1856; Lange et al., 1972; Štemprok and Šulcek, 1969; Tischendorf, 1989). Alongside the prevailing strongly peraluminous phosphorus-rich granite plutons of S-type, smaller stocks and one volcanoplutonic complex of subaluminous P-poor granitoids of A-type signature were recognized (Breiter, 2008, 2012). The Altenberg–Teplice Caldera located in the eastern Krušné Hory/Erzgebirge (Breiter, 1997; Hoffmann et al., 2013; Mlčoch and Skácelová, 2010) belongs to the largest complexes of A-type granitoids in Variscan Europe, covering approximately 500 km2. The 600 m thick Teplice rhyolite suite shows typical features of A-type chemical composition (#3194, 3198, 3203, and 3210). Following the caldera collapse, several small plutons of A-type biotite granites and albite– zinnwaldite–topaz granites intruded. The subvolcanic character of these intrusions is demonstrated by the existence of pipes of explosive/ intrusive breccia (Beck, 1914; Seltmann, 1994; Seltmann et al., 1992). The upper parts of the granite cupolas and stocks are usually greisenized and mineralized with cassiterite and wolframite. At Cínovec, a huge granite cupola intruded the Teplice rhyolite. Its upper part, to the depth of 735 m, is composed of partly greisenized, dominantly medium-grained zinnwaldite granite (#4674 and 4685). The deeper part (735–1670 m in the borehole CS-1) is composed of porphyritic coarse-grained biotite granite (#4689, 4692, and 4803). In Krupka, two cupolas of zinnwaldite granite (#2153, 2154, 2179, 2180, and 2182) intruded slightly older biotite granite (#2152, 2155, and 2181). Some parts of the zinnwaldite granite were pervasively greisenized. At Sadisdorf, a hidden granite cupola (#4641 and 4643) passed upwards into a steep stock with several episodes of explosive/ intrusive brecciation (#4644) and greisenization (Seltmann, 1994). For locations and descriptions of samples, see Table 1.

Fig. 3. Geological sketch of eastern Krušné Hory/Erzgebirge, Czech Republic and Germany (Mlčoch and Skácelová, 2010, modified).

4. Analytical procedures To study the zircon grains, polished thin sections were made from all collected rock samples. Back-scattered electron (BSE) images were taken prior to analysis to study the internal zoning of individual mineral grains and their textural relationships with associated rock-forming minerals. Zircon and associated minerals, such as monazite, xenotime, thorite, and other similar mineral phases, were analyzed by using an identical set-up and included all of the chemical elements identified in at least one of the above-mentioned minerals. The elemental abundances of W, P, As, Nb, Ta, Si, Ti, Zr, Hf, Th, U, Y, La, Ce, Pr, Nd, Sm, Gd, Dy, Er, Yb, Al, Sc, Bi, Mn, Fe, Ca, Mg, Pb, S, and F in oxide minerals were determined by using a CAMECA SX100 electron microprobe (Masaryk University and Czech Geological Survey, Brno) equipped with five WD spectrometers. The minerals were analyzed at an accelerating voltage and beam current of 15 keV and 40 nA, respectively, and with a beam diameter ranging from 1 to 5 μm. The following standards were used: U — metallic U; Pb — PbSe; Th — ThO2; P — fluorapatite; Y — YAG; La — LaB6; Ce — CeAl2; Pr — PrF3; Nd — NdF3; Sm — SmF3; Gd — GdF3; Dy — DyP5O14; Er — YErAG; Yb — YbP5O14; Al — almandine; Si, Ca, and Fe — andradite; Mn — rhodonite; W — scheelite; S — barite; F — topaz; As — InAs; Nb — columbite; Ta — CrTa2O6; Ti — titanite; Zr — zircon; Hf — metallic Hf; Bi — metallic Bi; Mg — MgAl2O4 and Sc — ScVO4. The analytical results were normalized by the PAP procedure. The empirical formulae of zircon were calculated on the basis of 4 atoms of oxygen in a formula unit (4 O apfu).

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Table 1 List of studied samples of A-type granites. For “Typology” compare Figs. 10 and 11. Sample

Locality

Description

Associated accessory minerals

Normal Normal Normal Normal Normal Normal Normal Evolved Strongly evolved Strongly evolved

Dark wiborgite (hornblende granite) Biotite granite Hornblende–biotite granite Biotite granite Rhyolite ignimbrite Porphyritic rhyolite Wiborgite (hornblende granite) Porphyritic granite Equigranular granite Border pegmatite

Apatite, ilmenite, thorite, bastnäsite, sulfides Monazite, thorite, xenotime-(Y), fluorite, ilmenite, apatite, pyrite Ilmenite, magnetite, apatite, bastnäsite, chalcopyrite, sphalerite, pyrhotite Fluorite, monazite MagnetiteNN, bastnäsite Hematite, magnetite, ilmenite, bastnäsite Ilmenite, thorite, allanite, bastnäsite, REE-apatite Y-rich fluorite, topaz, monazite, pyrhotite, columbite, galena Y-poor fluorite, topaz, bastnäsite, galena, wolframite, scheelite Topaz, monazite, rutile, columbite, fluorite

Granites from Brazil AU-382 DC-83b SAL-49 SAL-66b Pb-94 Pb-124 AMT-10 F-13, 44.7 m F-13, 50.4 m 4894

Normal Normal Strongly evolved Strongly evolved Evolved Evolved Normal Normal Evolved Strongly evolved

Biotite monzogranite Leucogranite Biotite syenogranite Greisen Leucogranite Biotite granite Porphyritic topaz–alkali–feldspar granite Siderophyllite–sphalerite–topaz–quartz greisen Hornblende–biotite alkali–feldspar granite Cryolite-bearing albite granite

Magnetite, ilmenite, allanite, titanite, apatite, fluorite Magnetite, hematite, ilmenite, titanite, fluorite, REE-epidote, apatite Xenotime, columbite, thorite, cassiterite, fluorite, wolframite Monazite, columbite, thorite, galena, monazite, cassiterite, wolframite Fluorite, bastnäsite, topaz, apatite, cassiterite, monazite, sphalerite Fluorite, REE-fluoride, allanite, apatite Topaz, fluorite, bastnäsite, W,Nb-oxide, columbite, galena Sphalerite, chalcopyrite, rutile, topaz Rutile, allanite, U,Th–silicate Thorite, cassiterite, ThOF-phase, xenotime

Evolved Normal Normal Evolved Strongly evolved Normal Evolved Evolved Evolved Strongly evolved Strongly evolved Strongly evolved Evolved

Rhyolitic ignimbrite TR3 unit Rhyolitic ignimbrite TR2 unit Rhyolitic tuff TR1 unit Fine-grained porphyritic granite Leucogranite Fine-grained matrix of explosive breccia Biotite granite Biotite granite Aplite Zinnwaldite granite Zinnwaldite granite Zinnwaldite granite, depth of 40 m and 205 m Biotite granite, depth of 735 m, 988 m, and 1215 m

Rutile, thorite, monazite, REE-carbonate Rutile, thorite, monazite, REE-carbonate Rutile, thorite, monazite, REE-carbonate Nb-rutile, cassiterite, monazite, columbite, cheralite Cassiterite, molybdenite, uraninite, cheralite Cassiterite, arsenopyrite, lolingite Ilmenite, rutile, xenotime, monazite, fluorite Nb-rutile, columbite, xenotime, monazite Nb-rutile, xenotime, monazite Cassiterite, columbite, Nb-rutile, fluorite, xenotime, monazite Cassiterite, molybdenite, columbite, fluorite, monazite, thorite, bastnäsite, scheelite Cassiterite, columbite, fluorite, topaz, REE-fluoride and carbonate Thorite, Nb-rutile, fluorite, xenotime, monazite

Jamon Redenção Bom Jardim Bom Jardim Pedra Branca Pedra Branca Pitinga Pitinga Pitinga Pitinga

Krušné Hory/Erzgebirge, Czech Republic/Germany 3194, 3198 Mikulov, borehole Mi-4, depth of 50 m and 178 m 3203 Mikulov, borehole Mi-4, depth of 371 m 3210 Mikulov, borehole Mi-4, depth of 578 m 4641 Sadisdorf, open pit 4643 Sadisdorf, open pit 4644 Sadisdorf, open pit 2152, 2155 Krupka, Preiselberg cupola, adit “5. květen” 2181 Krupka, Preiselberg cupola, adit No. 2 2182 Krupka, Preiselberg cupola, adit No. 2 2154 Krupka, Preiselberg cupola, adit “5. květen” 2153, 2179, 2180 Krupka, Knotl stock, adit “Václav” 4674, 4685 Cínovec, borehole CS-1 4689, 4692, 4803 Cínovec, borehole CS-1

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Typology

Wiborg batholith, Finland 4711 Ristisaari 4712 Ristisaari 4713 Ahvenisto complex 4714 Ahvenisto complex 4715 Lappeenranta 4716 Lappeenranta 4717 Hamina 4718 Kymi 4719 Kymi 4720 Kymi

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Fig. 4. BSE-images of zircons from the Wiborg batholith (scale bars 100 μm): a, #4711-zircon (Zrn) overgrows ilmenite (Ilm), dark wiborgite, Ristisaari; b, #4713-zircon (Zrn) and zoned apatite crystals (Ap) enclosed in biotite, hornblende–biotite granite, Ahvenisto complex; c, #4712-zircon (gray) with two hydrothermally heavily altered grains of thorite (white), biotite granite, Ristisaari; d, #4712-zircon crystals (light gray) altered along rim and cracks (darker gray) with thorite inclusions (white), biotite granite, Ristisaari; e, #4714-zircon crystal with slightly altered Hf-depleted rims, biotite granite, Ahvenisto complex; f, #4715-zircon crystal with slightly Hf-enriched rim, rhyolite ignimbrite, Lapperanta; g, #4718-zircon crystal with U, Y, Yb-enriched rim (light gray) and fluorite (gray) enclosed in biotite (black), porphyritic granite, Kymi; h, #4719-small patchy zoned zircon crystals (gray) enclosed in large monazite grain (white), equigranular granite, Kymi; i, #4720-zircon crystals (Zrn), monazite (Mnz) and ilmenite (Ilm), marginal pegmatite, Kymi.

5. Results Zircon was found in all the studied samples (Figs. 4–6), although its modal content varied largely in different varieties of granite. Generally, zircon is common in all the less fractionated studied granites and rhyolites. In the more fractionated granites from Brazil and the Krušné Hory/ Erzgebirge, zircon is abundant, but it is scarce in the topaz granites from the Kymi stock, Finland. Approximately 300 microprobe analyses of zircon were made for this study. Representative analyses are presented in Table 2 and some interesting inter-element relations are shown in Fig. 7. The low totals of some analyses from the strongly fractionated rocks (occasionally down to only 86.5 wt.%) are most likely a consequence of a high degree of hydration and/or partial destruction of the crystal lattice during metamictization of primary U- and Th-enriched mineral grains. 5.1. Shape of zircon crystals Zircons from normal non-mineralized granites, such as the dominant facies of the Wiborg batholith (Finland) and those of the Redenção and Jamon plutons (Brazil), usually form homogeneous prismatic 50–150 μm sized crystals (Fig. 4a,b). Some zircon grains from the Wiborg batholith show thin rims, darker in BSE (Fig. 4c), sometimes associated with radial or irregular cracks (Fig. 4d,e). Dark areas are depleted in Hf, Y, U, and Th. In some zircons from the Jamon granite (Brazil), irregular bright zones slightly enriched in Th, Y, and U were found (Fig. 5a). In all the mentioned rock types, zircon was one of the early crystallized minerals and was subsequently included most often in mica but also in amphibole, magnetite, ilmenite, quartz, and feldspars.

The rhyolites associated with the Wiborg batholith contain large (up to 100 μm), often fragmented zircon grains. These zircons commonly show rims that are bright in BSE and slightly enriched in Hf (Fig. 4f). The Teplice rhyolite (Krušné Hory/Erzgebirge) contains a very heterogeneous assemblage of zircons: grains with thick Hf-enriched rims (Fig. 6a), oscillatory zoned grains (Fig. 6b), homogeneous grains with irregular depleted rims (Fig. 6c), and grains with complicated textures, patchy metamictized cores, and Hf-enriched rims (Fig. 6d). The varied textural aspects of the zircons suggest a complex evolution of the rhyolite melt. Some zircon grains found in the rhyolite could have been assimilated from the surrounding rocks during magma ascent and eruption, as indicated by the Proterozoic ages of some zircon cores (Hoffmann et al., 2013). In evolved granites, zircon may crystallize during the whole solidification process of the rock. The early crystals are embedded in mica, the later grains in fluorite or are interstitial. Within the Kymi stock (Finland), the porphyritic granite contains slightly zoned zircons, up to 50 μm in size, with rims enriched in the xenotime component (Fig. 4g). The equigranular granite from Kymi contains only small patchily zoned zircon grains (b 20 μm, Fig. 4h). In this case, contrasts in BSE are caused by different proportions of the xenotime component. In the marginal pegmatite, zircon forms small (10–20 μm) interstitial homogeneous grains (Fig. 4i). In the Bom Jardim pluton (Brazil), the granite contains small (10–30 μm) patchily zoned zircon crystals, often with thin bright rims, associated with xenotime (Fig. 5b), while zircons from the greisen are homogeneous and associated with monazite and thorite (Fig. 5c). In the Pedra Branca pluton, zircon from the leucogranite forms small columnar homogeneous crystals embedded in fluorite (Fig. 5d). Some zircons from

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Fig. 5. BSE-images of zircons from Brazil (scale bars 100 μm): a, #AU382, Jamon granite, zircon (Zrn) + allanite (Aln); b, #SAL49, Bom Jardim granite, patchy zoned zircon (Zrn) + xenotime (Xnt); c, #SAL66B, Bom Jardim greisen, zircon (Zrn) + monazite (Mnz) + thorite (Thr); d, #PB94, Pedra Branca, small zircons (Zrn) in large fluorite (Fl) grain; e, #PB124, Pedra Branca zoned zircon (Zrn) + REE-fluoride (REE-F, white) with bastnäsite rims (light gray); f, #PB124, Pedra Branca, patchy zoned zircon locally enriched in Hf; g, #4894 Pitinga, cryolite-bearing albite granite, zircon (Zrn) with slightly Hf-enriched rim and tiny inclusions of Th, F-rich phase and hematite (Hem); h, #4894 Pitinga, cryolite-bearing albite granite, zircon with large inclusion of a Th, F-rich phase; i, #F13, Pitinga, greisen, zircon (Zrn) + sphalerite (Sp) + chalcopyrite (Cp).

neighboring biotite granite often contain dark leached zones and are associated with bastnäsite and REE-fluorides (Fig. 5e), while other grains are patchily zoned with irregular outer zones enriched in Hf (Fig. 5f). The largest crystals among all the studied Brazilian zircons were found in the peralkaline cryolite-bearing albite granite from Pitinga. The late crystallized grains, up to 500 μm across, are slightly zoned with Hf-, Y-, and Yb-enriched rims and common inclusions of a Th-rich phase (Fig. 5g,h). The zircon grains from the associated biotite–hornblende granite, topaz granite and greisen are short, columnar, and homogeneous (Fig. 5i). In Cínovec (Krušné Hory/Erzgebirge), zircon in the zinnwaldite granite forms tiny isometric crystals 10–50 μm in size. They are enclosed in quartz and feldspars, but some of the grains that crystallized later occupy the interstices between the earlier minerals. Some crystals contain μm-sized inclusions of quartz and feldspars and numerous tiny cavities. Most of the crystals are not zoned in the BSE images. The internal composition is patchy with domains enriched in Hf, Y, and Th (Fig. 6e), often associated with fluorite and Nb–Ta minerals (Fig. 6f). The cores in a few zoned grains are heterogeneous, porous and enriched with uranium, whereas the rims are compact, homogeneous and enriched with Hf. Individual analyses of crystal cores produce totals significantly lower than 100 wt.%, usually 90–95 wt.%, which indicates a high degree of hydration due to their metamict state. However, analyses of the compact rims produce totals close to 100 wt.%. The majority of the zircon crystals

in the protolithionite granite are enclosed in mica. They are of similar size (10–50 μm), but inhomogeneous crystals displaying a distinct structure with randomly distributed inclusions of phases close to xenotime and thorite in composition are relatively abundant. However, even in this case, the crystal cores are porous (Fig. 6g). The zircons from the stocks of Li-mica granites at Krupka and Sadisdorf (Krušné Hory/ Erzgebirge) are zoned with cores usually rich in U, whereas the rims are enriched in Hf, Y, and HREEs (Fig. 6h). The cores of the U-rich grains are often patchy and metamict (Fig. 6i). 5.2. Chemical composition of zircon Generally, zircons from hornblende–biotite and biotite granites from the non-mineralized plutons in Brazil and from the Wiborg batholith are poor in minor and trace elements and approach chemically pure (Zr, Hf)SiO4. The zircons from the moderately fractionated granite varieties in Brazil and Krušné Hory/Erzgebirge are slightly enriched in Hf, Th, U, Y, and HREEs, whereas the zircons from the highly fractionated ore-bearing granites from all the three studied areas may be strongly enriched in Hf, Th, U, Y, Sc, F, P, As, Bi, Ca, Fe, and Al. The Hf content systematically increases during geochemical evolution of the studied batholiths: from approximately 1.0–1.5 wt.% in the biotite and hornblende–biotite facies of the non-mineralized plutons or facies in Finland and Brazil, through 1.5–3 wt.% HfO2 in the rhyolites

K. Breiter et al. / Lithos 192–195 (2014) 208–225

215

Fig. 6. BSE-images of zircons from the Erzgebirge (scale bars 100 μm): a, #3208 zircons with parchy zoned cores and irregular Hf-enriched rims, Teplice rhyolite; b, #3201 oscillatory zoned zircon, Teplice rhyolite; c, #3203 homogeneous zircon with altered rim, Teplice rhyolite; d, #3194 zircon with altered patchy zoned core and Hf-enriched rim, Teplice rhyolite; e, #4372 patchy zoned Hf, Y, Yb-rich zircon from the upper part of the zinnwaldite granite, Cínovec; f, #4686 zircon (Zrn) + Nb-rich rutile (Rt) + Y-rich fluorite (Fl) from the deeper part of the zinnwaldite granite, Cínovec; g, #4689 zircon + thorite from the biotite granite, Cínovec; h, #2152 zircon with Hf, Y, Yb-enriched rim and xenotime, Krupka; i, #4641 zircon with patchy zoned core and Hf-enriched rim, Sadisdorf.

and albite–biotite granites in the Krušné Hory/Erzgebirge, 3–5 wt.% HfO2 in the most evolved rare-metal granites in Finland and Brazil, to 3–10 wt.% in the mineralized granites in the Krušné Hory/Erzgebirge (Fig. 7a). Along with increasing Hf content, the atomic ratio of Zr/Hf in zircon systematically decreases. Because the Zr/Hf ratio in zircon is a good indicator of the degree of fractionation in the parent melt (Černý et al., 1985; Hanchar and Hoskin, 2003), this ratio is used as a basis for visualizing the behavior of other analyzed elements during the evolution of individual plutons (Fig. 7b,c,d,e,f,g,h). For example, in the Wiborg batholith, the atomic ratio of Zr/Hf in zircon decreases from 100–80 in the wiborgite and hornblende–biotite granite through 80–60 in the biotite granites, 70–40 in the porphyritic Kymi granite, to less than 25 in the younger phases of the Kymi stock. In the zircons from the volcanic rocks at Lappeenranta, the Zr/Hf ratio varies between 120 and 70. In Brazil, the Zr/Hf ratio decreases from 108–60 in the non-mineralized Jamon and Redenção granites to 25–16 in the Sn-mineralized Bom Jardim granite. Within the Pitinga magmatic system, the Zr/Hf ratio decreases from 128–68 in the hornblende–biotite granite to 41–11 in the cryolite-bearing albite granite. Finally, in the Krušné Hory/Erzgebirge, this value decreases from mostly 60–40 in the Teplice rhyolite through 40–20 in the biotite granites to 20–10 in the topaz–zinnwaldite granites. According to the Zr/Hf ratio in zircon (see below for a more detailed discussion), the studied A-type granites can be divided into three main groups: (i) ‘normal’ granites with Zr/Hf N 55; (ii) moderately evolved granites with Zr/Hf varying between 55 and 25; and (iii) strongly evolved granites with Zr/Hf b 25. The content of Y in the zircons (Fig. 7b) from all ‘normal’ granites is low (b0.1–0.5 wt.% Y2O3), but the Y contents become systematically higher in the moderately and strongly evolved granites (commonly

2.0–2.5 wt.% Y2O3, with maximums of 9 wt.% in the Teplice rhyolite of the Krušné Hory/Erzgebirge, 11 wt.% in the Pedra Branca granite of Goiás and 12 wt.% in the Kymi granite of Finland). With regards to the REEs, zircon dominantly accommodates HREEs. Nevertheless, the contents of Dy, Er, and Yb (Fig. 7c) in zircon from ‘normal’ granites are low (b 0.1 wt.% Dy2O3, Er2O3, and Yb2O3), whereas significant enrichment was found in the highly evolved granites (0.4– 2.0 wt.% Dy2O3, 0.2–1.8 wt.% Er2O3 and 1–5 wt.% Yb2O3). The highest contents were encountered in the Pedra Branca and Bom Jardim granites (Brazil), Kymi stock (Finland) and the Krupka area (Krušné Hory). The contents of LREEs are significantly lower, but relatively high contents (0.2–0.4 wt.% Ce2O3, 0.05–0.4 wt.% Nd2O3 and 0.1–0.2 wt.% Sm2O3) were occasionally found in the strongly evolved granites from all areas, with a maximum in the topaz granite from the Kymi stock (up to 0.94 wt.% Ce2O3, 1.21 wt.% Nd2O3 and 0.96 wt.% Sm2O3). The contents of the radioactive elements U and Th (Fig. 7 d,e), which are responsible for the metamictization of zircon structure, are low in the ‘normal’ A-type granites (b 0.5 wt.% UO2, b0.1 wt.% ThO2). Both elements are substantially enriched in the moderately evolved granites (0.5–1.5 wt.% UO2 and 0.5–1.0 wt.% ThO2) and even more in the strongly evolved granites (up to 10 wt.% UO2 and 5 wt.% ThO2 in the Krušné Hory/Erzgebirge and 9.5 wt.% ThO2 in the Kymi stock, Finland). In Brazil, the highest U-content has been found in zircon from the Bom Jardim granite (up to 2.4 wt.% UO2). The zircons from the Pitinga province are relatively U poor, with a maximum 1 wt.% UO2 in zircon from the topaz granite. The Sc content in zircon from ‘normal’ granites from Brazil and Finland is very low, usually at the detection limit of the microprobe. The zircons from the ore-bearing granites from Brazil are also Sc poor (max. 0.2 wt.% Sc2O3), while the zircons from the strongly evolved

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Table 2 Chemical composition (wt.%) and empirical furmulae (apfu) of zircon. For localization of samples see Table 1). Sample

DC-83b

AU-382

SAL-49

SAL-66b

F-13, 44.7

AMT-10

4894

Pb-94

Pb-94

Pb-124

4711

4712

4715

4717

Rock

Leuco granite

Bt monzo granite

Bt syeno granite

greisen

greisen

Toz-Afs granite

cryolite granite

Leuco granite

Leuco granite

Bt granite

wiborgite

Bt granite

rhyolite

wiborgite

Area

Redencao

Jamon

Bom Jardim

Bom Jardim

Pitinga

Pitinga

Pitinga

Pedra Branca

Pedra Branca

Pedra Branca

Wiborg

Wiborg

Wiborg

Wiborg

SO3 WO3 P2O5 As2O5 Nb2O5 Ta2O5 SiO2 TiO2 ZrO2 HfO2 ThO2 UO2 Al2O3 Sc2O3 Y2O3 La2O3 Ce2O3 Pr2O3 Nd2O3 Sm2O3 Gd2O3 Dy2O3 Er2O3 Yb2O3 Bi2O3 FeO MnO MgO CaO PbO F F = O2 Total S W P As Nb Ta Si Ti Zr Hf Th U Al Sc Y La Ce Pr Nd Sm Gd Dy Er Yb Bi Fe Mn Mg Ca Pb F Zr/Hf atomic

0.00 0.00 0.02 0.01 0.00 0.00 31.86 0.02 65.29 1.26 0.01 0.01 0.00 0.00 0.00 0.00 0.01 0.00 0.06 0.03 0.00 0.00 0.00 0.08 0.08 0.04 0.02 0.01 0.00 0.02 0.00 0.00 99.13 0.000 0.000 0.001 0.000 0.000 0.000 0.993 0.000 0.992 0.011 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.001 0.000 0.000 0.000 0.000 0.001 0.001 0.001 0.001 0.000 0.000 0.000 0.000 89

0.00 0.00 0.00 0.02 0.00 0.00 32.13 0.02 65.85 1.04 0.01 0.00 0.00 0.01 0.00 0.00 0.01 0.00 0.05 0.02 0.00 0.00 0.02 0.02 0.03 0.01 0.00 0.01 0.00 0.00 0.01 0.00 99.25 0.000 0.000 0.000 0.000 0.000 0.000 0.994 0.001 0.994 0.009 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.001 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.001 108

0.00 0.00 0.25 0.01 0.01 0.00 25.96 0.00 46.37 4.24 0.49 2.02 2.73 0.06 0.54 0.03 0.19 0.06 0.04 0.03 0.03 0.23 0.29 1.10 0.07 0.54 0.35 0.01 2.66 0.04 0.41 0.17 88.93 0.000 0.000 0.008 0.000 0.000 0.000 0.934 0.000 0.814 0.044 0.004 0.016 0.116 0.002 0.010 0.000 0.003 0.001 0.001 0.000 0.000 0.003 0.003 0.012 0.001 0.016 0.011 0.000 0.103 0.000 0.046 19

0.07 1.56 1.84 0.00 0.19 0.00 23.75 0.02 30.36 2.51 2.16 2.40 9.05 0.10 2.40 0.02 0.26 0.00 0.15 0.15 0.23 0.74 0.66 1.62 0.71 2.74 0.20 0.04 0.81 0.01 0.83 0.35 85.29 0.002 0.015 0.057 0.000 0.003 0.000 0.867 0.000 0.540 0.026 0.018 0.020 0.390 0.003 0.047 0.000 0.003 0.000 0.002 0.002 0.003 0.009 0.008 0.018 0.007 0.084 0.006 0.002 0.032 0.000 0.096 21

0.01 0.00 0.02 0.00 0.00 0.00 31.93 0.01 65.44 1.19 0.00 0.01 0.00 0.00 0.00 0.01 0.00 0.04 0.04 0.00 0.00 0.05 0.01 0.00 0.07 0.11 0.02 0.00 0.00 0.02 0.01 0.00 99.25 0.000 0.000 0.001 0.000 0.000 0.000 0.993 0.000 0.992 0.011 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.001 0.003 0.000 0.000 0.000 0.000 0.001 94

0.03 0.00 0.47 0.10 0.00 0.00 26.64 0.00 49.17 2.95 0.81 1.05 1.36 0.15 2.38 0.01 0.15 0.03 0.14 0.09 0.15 0.81 0.57 1.13 0.09 1.83 0.59 0.01 0.34 0.05 0.89 0.37 91.92 0.001 0.000 0.014 0.002 0.000 0.000 0.940 0.000 0.846 0.030 0.007 0.008 0.057 0.005 0.045 0.000 0.002 0.000 0.002 0.001 0.002 0.009 0.006 0.012 0.001 0.054 0.018 0.000 0.013 0.000 0.099 28

0.00 0.00 0.45 0.00 0.00 0.00 30.03 0.02 54.59 8.61 0.38 0.10 0.07 0.00 0.29 0.00 0.00 0.00 0.03 0.02 0.00 0.22 0.36 0.89 0.06 0.40 0.26 0.00 0.01 0.02 0.21 0.09 97.39 0.000 0.000 0.013 0.000 0.000 0.000 0.992 0.000 0.880 0.081 0.003 0.001 0.003 0.000 0.005 0.000 0.000 0.000 0.000 0.000 0.000 0.002 0.004 0.009 0.001 0.011 0.007 0.000 0.000 0.000 0.022 11

0.03 0.00 1.92 0.07 0.16 0.00 24.37 0.05 45.50 2.17 1.66 0.15 0.14 0.03 8.02 0.01 0.02 0.02 0.03 0.00 0.12 0.69 1.05 2.30 0.07 0.69 0.19 0.02 0.58 0.08 0.48 0.20 90.41 0.001 0.000 0.059 0.001 0.003 0.000 0.888 0.001 0.809 0.023 0.014 0.001 0.006 0.001 0.156 0.000 0.000 0.000 0.000 0.000 0.001 0.008 0.012 0.026 0.001 0.021 0.006 0.001 0.023 0.001 0.055 36

0.04 0.00 0.94 0.04 0.24 0.00 23.43 0.07 40.18 3.89 1.60 0.29 0.32 0.06 9.65 0.03 0.04 0.00 0.07 0.05 0.18 0.85 1.16 2.54 0.08 0.86 0.20 0.02 0.96 0.07 0.84 0.35 88.81 0.001 0.000 0.031 0.001 0.004 0.000 0.899 0.002 0.752 0.043 0.014 0.003 0.014 0.002 0.197 0.000 0.001 0.000 0.001 0.001 0.002 0.010 0.014 0.030 0.001 0.028 0.007 0.001 0.039 0.001 0.102 17

0.08 0.00 0.38 0.02 0.00 0.00 27.82 0.04 54.05 1.81 0.16 0.53 0.13 0.00 0.99 0.03 0.05 0.00 0.05 0.01 0.04 0.12 0.18 0.29 0.10 0.85 0.18 0.02 2.70 0.07 0.06 0.02 90.73 0.002 0.000 0.011 0.000 0.000 0.000 0.959 0.001 0.909 0.018 0.001 0.004 0.005 0.000 0.018 0.000 0.001 0.000 0.001 0.000 0.000 0.001 0.002 0.003 0.001 0.025 0.005 0.001 0.100 0.001 0.006 51

0.02 0.00 0.04 0.00 0.00 0.00 32.25 0.01 65.08 1.16 0.04 0.08 0.00 0.00 0.04 0.00 0.03 0.00 0.01 0.02 0.02 0.04 0.04 0.09 0.09 0.22 0.00 0.01 0.01 0.02 0.00 0.00 99.32 0.000 0.000 0.001 0.000 0.000 0.000 0.998 0.000 0.982 0.010 0.000 0.001 0.000 0.000 0.001 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.001 0.001 0.006 0.000 0.000 0.000 0.000 0.000 96

0.00 0.00 0.07 0.00 0.00 0.00 32.22 0.00 65.18 1.85 0.00 0.12 0.00 0.00 0.00 0.00 0.01 0.00 0.02 0.02 0.02 0.00 0.09 0.06 0.06 0.32 0.01 0.01 0.02 0.03 0.00 0.00 100.13 0.000 0.000 0.002 0.000 0.000 0.000 0.993 0.000 0.980 0.016 0.000 0.001 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.001 0.001 0.000 0.008 0.000 0.000 0.001 0.000 0.000 60

0.01 0.00 0.01 0.00 0.00 0.00 32.07 0.00 64.83 1.28 0.00 0.02 0.00 0.01 0.04 0.00 0.01 0.00 0.00 0.00 0.02 0.00 0.05 0.06 0.05 0.09 0.00 0.00 0.00 0.00 0.00 0.00 98.56 0.000 0.000 0.000 0.000 0.000 0.000 0.999 0.000 0.985 0.011 0.000 0.000 0.000 0.000 0.001 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.001 0.000 0.002 0.000 0.000 0.000 0.000 0.000 87

0.02 0.00 0.01 0.00 0.00 0.00 32.42 0.01 66.15 1.17 0.01 0.00 0.00 0.00 0.00 0.01 0.00 0.01 0.10 0.00 0.00 0.00 0.00 0.05 0.11 0.25 0.02 0.00 0.01 0.00 0.00 0.00 100.37 0.001 0.000 0.000 0.000 0.000 0.000 0.994 0.000 0.989 0.010 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.001 0.000 0.000 0.000 0.000 0.000 0.001 0.006 0.000 0.000 0.000 0.000 0.000 97

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217

Table 2 Chemical composition (wt.%) and empirical furmulae (apfu) of zircon. For localization of samples see Table 1). 4718

3210

4641

4643

granite granite granite pegmatite Rhyolite

4719

4719

4720

3194

Rhyolite

Granite

Leucogranite Bt granite

Kymi

Kymi

Kymi

Kymi

Teplice rhyolite

Teplice rhyolite

Sadisdorf Sadisdorf

0.20 0.56 2.64 0.00 1.14 0.00 22.54 0.23 30.83 1.10 2.42 0.79 2.19 0.19 12.11 0.10 0.29 0.02 0.24 0.24 0.63 1.97 2.21 4.21 0.06 1.81 0.08 0.03 0.55 0.22 1.54 0.65 90.43 0.006 0.005 0.084 0.000 0.019 0.000 0.850 0.006 0.567 0.012 0.021 0.007 0.097 0.006 0.243 0.001 0.004 0.000 0.003 0.003 0.008 0.024 0.026 0.048 0.001 0.057 0.003 0.002 0.022 0.002 0.183 48

0.05 0.00 0.27 0.00 0.00 0.00 26.48 0.00 48.28 4.38 0.83 2.07 2.90 0.30 0.00 0.08 0.45 0.11 0.31 0.15 0.05 0.17 0.24 0.68 0.05 0.87 0.28 0.09 1.16 0.16 1.05 0.44 91.01 0.001 0.000 0.008 0.000 0.000 0.000 0.934 0.000 0.830 0.044 0.007 0.016 0.121 0.009 0.000 0.001 0.006 0.001 0.004 0.002 0.001 0.002 0.003 0.007 0.000 0.026 0.008 0.004 0.044 0.002 0.117 19

0.33 3.53 0.57 0.00 1.82 0.11 19.97 0.00 28.79 2.62 5.95 9.46 1.61 1.11 1.34 0.02 0.15 0.05 0.34 0.86 0.95 2.11 1.49 3.50 0.06 0.40 0.04 0.05 0.69 1.12 0.95 0.40 89.58 0.010 0.039 0.020 0.000 0.035 0.001 0.844 0.000 0.594 0.032 0.057 0.089 0.080 0.041 0.030 0.000 0.002 0.001 0.005 0.013 0.013 0.029 0.020 0.045 0.001 0.014 0.001 0.003 0.031 0.013 0.127 19

0.02 0.00 0.30 0.00 0.00 0.00 25.62 0.00 47.80 5.17 0.57 1.36 2.63 0.29 0.00 0.04 0.22 0.10 0.04 0.05 0.05 0.12 0.15 0.82 0.05 0.97 0.30 0.11 2.12 0.03 0.88 0.37 89.44 0.001 0.000 0.009 0.000 0.000 0.000 0.919 0.000 0.836 0.053 0.005 0.011 0.111 0.009 0.000 0.001 0.003 0.001 0.001 0.001 0.001 0.001 0.002 0.009 0.000 0.029 0.009 0.006 0.081 0.000 0.099 16

0.03 0.00 0.49 0.09 0.00 0.00 29.60 0.01 55.97 3.22 0.36 2.85 0.10 0.04 0.68 0.03 0.01 0.00 0.01 0.03 0.04 0.10 0.35 0.90 0.05 0.01 0.00 0.01 0.16 0.11 0.06 0.03 95.27 0.001 0.000 0.014 0.002 0.000 0.000 0.987 0.000 0.910 0.031 0.003 0.021 0.004 0.001 0.012 0.000 0.000 0.000 0.000 0.000 0.000 0.001 0.004 0.009 0.000 0.000 0.000 0.000 0.006 0.001 0.006 30

0.00 0.00 0.04 0.04 0.00 0.00 31.71 0.01 64.26 1.81 0.00 0.14 0.00 0.02 0.00 0.02 0.00 0.00 0.00 0.00 0.00 0.03 0.02 0.06 0.08 0.08 0.00 0.01 0.00 0.00 0.00 0.00 98.34 0.000 0.000 0.001 0.001 0.000 0.000 0.995 0.000 0.983 0.016 0.000 0.001 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.001 0.001 0.002 0.000 0.000 0.000 0.000 0.000 61

0.09 0.00 10.83 0.32 0.00 0.00 14.97 0.04 44.34 0.86 0.68 3.03 1.32 0.50 5.56 0.01 0.07 0.03 0.16 0.21 0.43 0.99 0.77 1.05 0.05 1.11 0.07 0.02 2.26 0.14 2.19 0.92 91.15 0.002 0.000 0.329 0.006 0.000 0.000 0.537 0.001 0.775 0.009 0.006 0.024 0.056 0.016 0.106 0.000 0.001 0.000 0.002 0.003 0.005 0.011 0.009 0.011 0.000 0.033 0.002 0.001 0.087 0.001 0.248 88

0.00 0.00 3.64 0.32 0.00 0.00 22.78 0.01 46.77 7.47 1.33 4.14 0.06 3.52 0.20 0.00 0.01 0.00 0.00 0.02 0.03 0.33 0.29 1.05 0.08 0.63 0.12 0.00 0.37 0.14 0.02 0.01 93.30 0.000 0.000 0.109 0.006 0.000 0.000 0.808 0.000 0.809 0.076 0.011 0.033 0.003 0.109 0.004 0.000 0.000 0.000 0.000 0.000 0.000 0.004 0.003 0.011 0.001 0.019 0.004 0.000 0.014 0.001 0.003 11

2152

2153

2180

4674

4674

4674

4685

4803

Zi granite

Zi granite

Zi granite

Zi granite

Zi granite

Zi granite

Bt granite

Krupka

Krupka

Krupka

Cinovec

Cinovec

Cinovec

Cinovec

Cinovec

0.12 0.56 4.55 0.15 0.22 0.00 19.25 0.29 34.10 0.62 15.99 4.29 0.65 0.06 4.69 0.02 0.21 0.00 0.12 0.23 0.61 0.72 0.45 0.54 0.09 0.78 0.10 n.a. 4.63 0.00 1.11 0.47 94.87 0.003 0.006 0.147 0.003 0.004 0.000 0.736 0.008 0.636 0.007 0.139 0.037 0.029 0.002 0.095 0.000 0.003 0.000 0.002 0.003 0.008 0.009 0.005 0.006 0.001 0.025 0.003 0.000 0.190 0.000 0.135 94

0.00 2.82 4.48 0.00 1.56 0.04 16.67 0.00 27.99 2.22 1.93 9.76 0.09 0.80 4.99 0.00 0.23 0.00 0.11 0.19 0.33 1.84 1.82 5.36 0.08 0.68 0.08 n.a. 1.62 0.00 1.02 0.43 86.35 0.000 0.031 0.164 0.000 0.030 0.000 0.718 0.000 0.588 0.027 0.019 0.094 0.004 0.030 0.114 0.000 0.004 0.000 0.002 0.003 0.005 0.025 0.025 0.070 0.001 0.025 0.003 0.000 0.075 0.000 0.138 22

0.27 0.00 3.09 0.42 0.27 0.00 21.55 0.03 41.80 8.26 1.18 3.38 1.06 0.55 1.75 0.00 0.16 0.05 0.16 0.10 0.19 0.68 0.65 1.91 3.56 0.98 0.12 n.a. 1.49 0.02 1.58 0.66 94.63 0.007 0.000 0.097 0.008 0.005 0.000 0.795 0.001 0.752 0.087 0.010 0.028 0.046 0.018 0.034 0.000 0.002 0.001 0.002 0.001 0.002 0.008 0.008 0.021 0.034 0.030 0.004 0.000 0.059 0.000 0.184 9

0.08 0.15 2.03 0.97 0.45 0.00 24.75 0.04 44.38 9.76 0.49 0.90 0.84 1.47 2.07 0.00 0.24 0.00 0.05 0.11 0.18 0.69 0.72 1.74 0.26 0.96 0.35 0.02 1.29 0.05 1.24 0.52 95.75 0.002 0.001 0.060 0.018 0.007 0.000 0.862 0.001 0.754 0.097 0.004 0.007 0.034 0.045 0.038 0.000 0.003 0.000 0.001 0.001 0.002 0.008 0.008 0.018 0.002 0.028 0.010 0.001 0.048 0.000 0.136 8

0.05 1.93 1.66 1.14 4.37 1.07 13.67 0.05 14.99 1.03 3.47 9.26 0.75 0.07 0.50 0.00 0.05 0.04 0.00 0.09 0.06 0.36 0.22 0.51 29.02 0.44 0.02 0.17 1.12 0.07 0.55 0.23 86.49 0.002 0.026 0.074 0.031 0.104 0.015 0.721 0.002 0.385 0.015 0.042 0.109 0.047 0.003 0.014 0.000 0.001 0.001 0.000 0.002 0.001 0.006 0.004 0.008 0.394 0.019 0.001 0.000 0.063 0.001 0.092 25

0.04 2.31 1.81 0.99 4.84 1.03 12.71 0.03 14.08 1.22 3.29 10.76 0.55 0.09 0.54 0.00 0.01 0.00 0.11 0.05 0.07 0.34 0.18 0.51 35.15 0.44 0.02 0.05 1.54 0.07 0.53 0.22 93.13 0.001 0.031 0.079 0.027 0.113 0.015 0.659 0.001 0.356 0.018 0.039 0.124 0.034 0.004 0.015 0.000 0.000 0.000 0.002 0.003 0.001 0.006 0.003 0.008 0.470 0.019 0.001 0.004 0.086 0.001 0.087 20

0.21 0.20 1.56 0.78 0.57 0.00 23.00 0.01 46.74 3.37 1.49 1.21 0.74 0.27 3.62 0.00 0.36 0.02 0.06 0.14 0.24 1.17 1.16 3.05 0.10 0.66 0.16 0.00 0.81 0.00 1.59 0.67 92.62 0.006 0.002 0.048 0.015 0.009 0.000 0.841 0.000 0.833 0.035 0.012 0.010 0.032 0.009 0.070 0.000 0.005 0.000 0.001 0.002 0.003 0.014 0.013 0.034 0.001 0.020 0.005 0.000 0.032 0.000 0.184 24

0.04 0.00 0.13 0.01 0.00 0.00 30.94 0.01 62.08 2.06 0.18 0.83 0.00 0.01 0.33 0.00 0.04 0.00 0.00 0.00 0.03 0.11 0.09 0.16 0.11 0.07 0.13 0.08 0.00 0.00 0.03 0.01 97.47 0.001 0.000 0.004 0.000 0.000 0.000 0.989 0.000 0.968 0.019 0.001 0.006 0.000 0.000 0.006 0.000 0.000 0.000 0.000 0.000 0.000 0.001 0.001 0.002 0.001 0.002 0.003 0.004 0.000 0.000 0.003 51

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Kymi stock, Finland, are Sc rich (up to 1.5 wt.% Sc2O3). In the Krušné Hory/Erzgebirge, the zircons from the least evolved rhyolite contain 0.05–0.1 wt.% Sc2O3, the zircons from the biotite and Li-mica granites contain usually 0.3–1.0 wt.% Sc2O3 and the zircons from the albite granite from Sadisdorf reach 2–3 wt.% Sc2O3. This indicates that the Krušné Hory/Erzgebirge is a Sc-enriched province. Traces of Bi are present in many analyzed zircon grains, but relatively high contents are rare. Contents in the range 0.5–3 wt.% Bi2O3 were occasionally found in zircons from Krupka (Krušné Hory). Metamict zircons with up to 35 wt.% Bi2O3 (0.47 Bi apfu) were found in Cínovec (Krušné Hory). The presence of significant Nb content in zircon is limited to the highly evolved granites: up to 1.5 wt.% Nb2O5 in the Pedra Branca granite (Brazil), up to 3.4 wt.% Nb2O5 in zircon from the Kymi stock (Finland) and up to 4.8 wt.% Nb2O5 in zircon from the zinnwaldite granite from Cínovec, the Krušné Hory. In the Krušné Hory/Erzgebirge, contents in the range of 0.2–0.5 wt.% Nb2O5 are quite common. Contrarily, in the Pitinga province, zircons are Nb-free also in the strongly fractionated cryolite albite granite. This can be explained by the fact that this granite has pyrochlore as an important accessory phase (Costi et al., 2009) and Nb preferentially concentrates in it. Tantalum behaves similarly to Nb, but its content is ca. 5 times lower; 1 wt.% Ta2O5 in zircon from Cínovec is the maximum. High values of Nb and Ta are not correlated with Fe- and Mn-enrichment, which excludes the presence of columbite microinclusions. Tungsten is present only in zircon from the highly evolved orebearing granites. Contents in the range of 0.5–3.0 wt.% WO3 were found relatively often in the Kymi stock (Finland) and in all plutons in the Krušné Hory/Erzgebirge, whereas W was found only sporadically in zircon from the Xingu tin province (max. 2.5 wt.% WO3 in the Bom Jardim granite). Phosphorus may substitute for Si, forming PO4-tetrahedrons. The P content in zircons from ‘normal’ granites is negligible, but many zircons from the evolved granites from Brazil and Finland contain 1–2 wt.% P2O5, and in the Krušné Hory/Erzgebirge, zircons often contain up to 3–4 wt.% P2O5. The highest content, 10.8 wt.% P2O5 (0.33 apfu P), has been found in the Sadisdorf albite granite (Fig. 7f). Despite the higher P contents in some zircon of the evolved A-type granites in Brazil and Finland, it is clear that the zircons from the Krušné Hory/Erzgebirge are enriched in P compared to those of other studied provinces. However, the zircons of different granite facies in Pitinga have low phosphorus contents, which are consistent with the whole rock composition (Costi et al., 2009). Arsenic is chemically similar to P, but its content in zircon is generally much lower and usually below the detection limit of the EMPA. Nevertheless, some zircons from the evolved to highly evolved granites were found to be surprisingly rich in As: up to 0.25 wt.% As2O5 in the Pedra Branca pluton (Brazil) and 1.1 wt.% As2O5 (0.03 apfu As) in the Krušné Hory/Erzgebirge. In the Krušné Hory/Erzgebirge, significant As contents have been found in nearly all analyzed zircon crystals. Sulfur in the form of SO4-tetrahedrons is present only in zircon from the highly evolved granites: contents up to 0.08 wt.% SO3 were occasionally found in the Bom Jardim and Pedra Branca granites (Brazil), 0.1–0.5 wt.% SO3 in the Kymi stock (Finland) and up to 0.7 wt.% SO3 (0.02 apfu S) in the evolved granites from the Krušné Hory/Erzgebirge. Fluorine is another typical element of zircon in evolved granites, while zircon in ‘normal’ granites is F-free. Contents in the range 0.3–0.8 wt.% F were found in the fractionated facies of all the studied granites from Brazil, in the ranges 0.5–1 wt.% F and 0.5–2.4 wt.% F (up to 0.3 apfu F) in rhyolites and granites, respectively, from the Krušné Hory/Erzgebirge (Fig. 7g). The zircons from common granites are usually free of Al, but zircons from moderate to strongly evolved granites are often distinctly Alenriched: Al2O3 varies in the range of 0.5–1.0 wt.% Al2O3 in the Krušné Hory/Erzgebirge, 0.5–2.7 wt.% Al2O3 in Brazil, and 1.5–3.4 wt.% Al2O3 (up to 0.137 apfu Al) in the Kymi stock (Fig. 7h). The Al content does

not correlate with the uranium and/or phosphorus content; thus neither “berlinite” substitution (P + Al↔Si + Si) nor metamictization alone can explain the accommodation of Al into the zircon structure. Contents of Fe and Mn in zircon are highly variable. Values in the range of 0.1–0.5 wt.% FeO are usually found in ‘normal’ granites. The zircons from evolved and strongly evolved granites often contain up to 2 wt.%, and in the Teplice rhyolite (Krušné Hory), zircons occasionally contain up to 5.4 wt.% FeO (0.16 apfu Fe). The zircons from ‘normal’ granites are usually Mn-free, but the zircons from evolved granites may contain 0.2–0.6 wt.% MnO, and zircons from the Teplice rhyolite reach up to 1.63 wt.% MnO (0.049 apfu Mn). Ca contents are very low in zircons from ‘normal’ granites (b0.1 wt.% CaO), but contents in the range of 0.5–1.5 wt.% CaO are dominant in the evolved granites, with a maximum of up to 3.7 wt.% CaO (0.14 apfu Ca) in the Pedra Branca granite. 6. Discussion 6.1. Comparison with published analyses of zircon from A-type granites Contents of the most important trace elements (Hf, U, Th, Y, REEs, and P) in zircon from A-type granites are well constrained in the literature, but data about elements such as W, S, Nb, Ta, As, Sc, and Bi are still scarce. Uher and Broska (1996) and Uher et al. (2009) analyzed zircon from post-orogenic A-type granites in the Slovak Republic and Hungary and found only low trace element contents (up to 3.5 wt.% HfO2, 0.77 wt.% Y2O3 and 0.46 wt.% UO2). Wang et al. (1996) found an extremely high Hf content (up to 34.8 wt.% HfO2, 0.353 apfu Hf) in zircon from an A-type granite in Suzhou, China. This zircon is U- and Th-free, and Y- and P-poor (b0.5 wt.% Y2O3, b 1 wt.% P2O5). Wang et al. (2000) reported zircon from A-type granites in Laoshan, China with as much as 12.4 wt.% HfO2 and 4.3 wt.% ThO2, but with only small amounts of UO2 (b 0.4 wt.%), Y2O3 (b 1.4 wt.%) and P2O5 (b 0.75 wt.%). Johan and Johan (2005) analyzed zircon from the Cínovec granite cupola (Krušné Hory) and found, among others, 1.3–5 wt.% HfO2, b0.8 wt.% ThO2, up to 3.2 wt.% UO2, up to 9 wt.% Y2O3, and up to 0.3 wt.% Sc2O3. A detailed investigation of the zircon from a 1596 m long borehole at Cínovec (Breiter and Škoda, 2012) found enrichment in HfO2 (from ca. 2 wt.% to 5–10 wt.% HfO2), Th, U, Y, HREEs, Sc, and Bi from the deeper protolithionite granite to the zinnwaldite granite in the uppermost part of the granite cupola. Lamarão et al. (2010) published an overview of the Hf, Y, U, Th, Nb, and Ca contents in zircon from A-type granites of the Amazonian craton and stressed the significance of the Zr/Hf ratio for granite classification. Finally, Nardi et al. (2013) published average zircon trace element contents for four Neoproterozoic A-type granites from Brazil analyzed by LA-ICP-MS. Example contents include 8623–17883 ppm Hf, 209–2118 ppm Th, 439–3568 ppm U, 1945–9492 ppm Y, 7–293 ppm Nb, and 2–26 ppm Ta. With the exception of the extreme Hf-enrichment in zircon from Suzhou (Wang et al., 1996), all other aforementioned published data for Hf, U, Th, Y, and REEs are within the ranges found in this study. 6.2. The substitution mechanisms in zircon The tetravalent chemical elements Hf, Th, U, and (in small amounts) Ti substitute for the zirconium in the zircon crystal lattice (Hanchar and Hoskin, 2003). The common minor trivalent elements (Y and REEs) usually enter the zircon structure as the “xenotime component” YPO4 because xenotime is isostructural with zircon and has similar lattice dimensions (Speer, 1982). Similarly, Sc and Bi substitute on the basis of the ScPO4 (pretulite) and BiPO4 (ximengite) components (Bernhard et al., 1998; Shi, 1989). The A-type rocks are generally poor in phosphorus, and thus zircons from these rocks are also expected to be very poor in P. Surprisingly, zircon from the more evolved A-type granites is often P-enriched. Fig. 8a shows a generally positive correlation between P and Y + REE in zircon with a predominance of Y + REE in samples from

K. Breiter et al. / Lithos 192–195 (2014) 208–225

219

Fig. 7. Chemical composition of zircon from A-type granites: a, Zr vs. Hf, the dashed line show ideal occupation Zr + Hf = 1 apfu; b, Zr/Hf vs. Y; c, Zr/Hf vs. Yb; d, Zr/Hf vs. U; e, Zr/Hf vs. Th; f, Zr/Hf vs. P; g, Zr/Hf vs. F; h, Zr/Hf vs. Al. Samples are distinguished according to their geographical provenance. Samples from the Pitinga region are divided into older biotite granites + greisen and younger albite and cryolite-bearing granites.

Finland, Brazil and the Teplice rhyolite, while P predominates in samples from Sadisdorf. The zircons from Cínovec and Krupka are highly scattered. Taking all trivalent elements into account (Fig. 8b), the

general predominance of trivalent elements (Y + REE + Sc + Bi + Al) over P is clear. In this case, the substitution (Y,REEs)3 + + (Nb, Ta)5 + ↔ Zr4 + + Zr4 + proposed by Eskova (1959) may play a partial

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role. Hanchar et al. (2001) found that in synthetic REEs N P-doped zircon, minor amounts of Li and Mo are supposed to provide charge balance for the excess REEs over P. Ushikubo et al. (2008) also found Li in natural zircons from the Black Hills, Australia. At the other end of the spectrum, in the case of the predominance of P, the berlinite substitution P5 + + Al3 + ↔ Si4 + + Si4 + is probable (Breiter et al., 2006). The studied (Y + REEs)-enriched grains usually have low totals (Fig. 8c), which is believed to result from “hydration,” and are also enriched in fluorine (Fig. 8d). Therefore, the following substitutions are also possible: (ZrO)2 + ↔ (YOH)2 + and/or (ZrO)2 + ↔ (YF)2 +. 6.3. Low totals, metamictization and hydrothermal alteration The zircons from all the studied common granite plutons (i.e., the not strongly fractionated and not ore bearing granites, e.g., the Wiborg batholith in Finland and the Redenção and Jamon granites in Brazil) have analytical totals near the ideal 100 wt.%. Relatively high totals of 97–99 wt.% were also found in some samples from the Pitinga ore district (e.g., the hornblende granite, topaz-alkali feldspar granite, and greisen). All the other studied granites contain zircons with generally low totals, mostly in the range 92–96 wt.% and occasionally down to 86 wt.%. Low analytical totals are supposed to result from metamictization. Negative correlations between the U-content and analytical totals support this consideration (Nasdala et al., 2009). The Al, Ca, Fe, Mn, and F contents are positively correlated with uranium and negatively correlated with analytical totals. These tri- and divalent elements are most likely not the primary constituents of the zircon lattice, but were incorporated into the zircon only after its partial metamictization. Similarly, the enrichment in the slightly exotic element Bi has been found only in zircons with analytical totals b96 wt.%.

6.4. Hf-enrichment during pluton evolution The Zr/Hf ratio in chondrites is ca. 33–38 by weight (Anders and Grevesse, 1989; Barrat et al., 2012), which corresponds to ca. 65–74 by atoms. Substantially lower values should be expected in continental crust and granites. Increases in the Hf content of zircon (i.e., lowering of the Zr/Hf ratio) during magma fractionation have been reported from many granitoid plutons, e.g., the Sweetwater Wash Pluton, California (Wark and Miller, 1993), the Boggy Plain, Australia (Hoskin et al., 2000), the Suzhou granite, China (Wang et al., 1996), the Povážský Inovec granite, Slovakia (Chudík et al., 2008) and the Kukulbei Complex, Transbaikalia (Zaraisky et al., 2008). Wang et al. (2000) and Kempe et al. (2004) interpreted the high content of Hf in the rims of some zircon crystals as resulting from fluid-related postmagmatic metasomatism and considered this feature to be specific to zircon from A-type granites. Nevertheless, Linnen and Keppler (2002) experimentally proved the fully magmatic origin of Hf-enrichment during zircon crystallization from a granitic melt. The partitioning coefficients of Zr and Hf between zircon and the melt are nearly equal for depolymerized peralkaline melts, whereas in polymerized metaluminous and peraluminous melts, DHf/DZr for zircon is 0.5 to 0.2. Thus, the fractionation of early zircon will strongly decrease the Zr/Hf ratio in the residual melt and increase the Hf content in later-crystallized zircon. Our results, consistently expressed as atomic Zr/Hf ratio in zircon, are in full agreement with the experimental data. The decrease in the Zr/Hf ratio is well documented at all scales of the investigation. At the scale of A-type granite plutons, the Zr/Hf ratio decreases from 67–41 (porphyritic granite) to 19–16 (equigranular granite) in the Kymi stock, Finland; from 52–49 (biotite granite) to 36–18 (leucogranite) in the Pedra Branca pluton, Brazil; and from 94–33 (biotite granite) to 34–9 (zinnwaldite granite) at Krupka, the Krušné Hory. Within one

Fig. 8. Substitution in zircon: a, Y + REE vs. P; b, M3+ vs. P; c, Y + REE vs. total; d, Y + REE vs. F. Line of ideal substitution is shown in the pictures a, b. Enrichment of particular grains in Al, Bi and Y is mentioned in the picture b.

K. Breiter et al. / Lithos 192–195 (2014) 208–225

intrusion, the Zr/Hf ratio decreases, for example, from 51–33 in protolithionite granite at a depth of 1255 m to 25–7.5 in the zinnwaldite granite at a depth of 40 m in the Cínovec granite cupola, the Krušné Hory. Even at the scale of individual crystals, from core to rim, the Zr/Hf ratio decreases from 86 to 68 in zircon from the Teplice rhyolite (Fig. 6a) and from 64 to 33 in zircon from the biotite granite at Krupka, the Krušné Hory (Fig. 6h). Wang et al. (2010) found low Zr/Hf ratios in zircon to be typical for granites with low solidus temperatures and for zircon crystallized from strongly evolved undercooled pegmatitic melt. Similarly, Yin et al. (2013) demonstrated that Hf-enrichment in zircon is related to high F and Li contents in the residual melt. The most Hf-enriched zircon rims (Fig. 6 h,i) were found in samples immediately associated with explosive brecciation followed by fast cooling (undercooling) of the fluid-rich melt (Breiter et al., 2009). The magmatic crystallization of these Hf-rich rims is in agreement with the aforementioned interpretation by Wang et al. (2010) and Yin et al. (2013). Finally, it should be mentioned that in some samples of highly fractionated granites displaying generally low Zr/Hf ratio zircons, some individual zircon grains with high to very high Zr/Hf were also found. These Hf-poor grains most likely represent the earliest zircon population, crystallized at the beginning of the melt evolution.

6.5. Chemical elements typical for zircon from the strongly fractionated granites Niobium, tantalum, tungsten and bismuth are present only in zircons from the highly evolved rare-metal granites, which are associated with Nb–Ta-enriched rutile and/or columbite. Rarely, high content of Nb (6.6 wt.% Nb2O5) have been reported from the Thor Lake alkali syenite (Smith and de St. Jorre, 1991). Hoskin and Schaltegger (2003) exclude the possibility of Nb, Ta and W as components of the zircon crystal lattice, and these elements instead form inclusions. However, Hoskin and Ireland (2000) supposed that the coupled substitution of Nb, Ta, and the REEs in the Zr site is a possible mechanism for the incorporation of REEs in excess of P. We occasionally found more than 1 wt.% of Nb, Ta, W, and Bi-oxides in zircons that are homogeneous in BSE and lacking any visible inclusions. The analyzed Nb, Ta and W contents do not correlate with Fe and/or Mn, as might be expected in the case of microinclusions of columbite or wolframite. Another hypothesis to explain the Nb-, Ta-, and W-enrichment in zircon is their adsorption to amorphous metamict domains within the crystal. However, these elements are effectively transportable only in the high-temperature late- to post-magmatic fluids, which means that they are transportable only during the short time interval following intrusion and prior to the effective metamictization (Breiter et al., 2009). We conclude that in the highly evolved F-rich melt, zircon is able to incorporate these elements into its structure in the range of 0.1–1 wt.%. Traces of scandium are present in zircons from common granites, but Sc strongly increased in some rare-metal granites. In metamorphosed sedimentary Fe-ores, Moëlo et al. (2002) found zircon with up to 0.45 apfu Sc and assumed a full miscibility between scandian zircon and pretulite. Breiter et al. (2006) reported zircon with 3.45 wt.% Sc2O3 from a fractionated S-type granite at Podlesí (Krušné Hory). In this study, we found a maximum of 3.5 wt.% Sc2O3 (0.11 apfu Sc) in zircon from an A-type leucogranite in Sadisdorf (Erzgebirge). Contents in the range 0.5–1.5 wt.% Sc2O3 were found in the Kymi stock (Finland) and at several localities in the Krušné Hory/Erzgebirge. Arsenic in zircon is only rarely analyzed. Contents in the range 0.1– 0.4 wt.% As205 (up to 1.65 wt.% As2O5, 0.03 apfu As) have been found only in fractionated A-type granites from the Krušné Hory/Erzgebirge (this study) and in the range 0.1–0.2 wt.% As2O5 in the Beauvoir S-type granite, France (Breiter and Škoda, 2012). The As-bearing zircon is interpreted as a secondary product of hydrothermal alteration of some rare-metal granites (Breiter et al., 2009; Förster et al., 2011).

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6.6. Differences between zircons from A- and S-type granites In common I- and S-type granites, zircon is one of the first crystallizing minerals, frequently included in biotite and other early mafic phases. Some slightly Hf-enriched grains may precipitate during the final stage of rock crystallization. On the contrary, in strongly fractionated peraluminous S-granites, generally low in Zr, zircon is one of the latecrystallizing minerals. It is interstitial and usually enriched with U, P, F, and, in some cases, also with Nb, Ta, W, Sc, Bi, etc. (Breiter et al., 2006). In the A-type granites, zircon crystallizes during the whole process of the melt differentiation (Breiter and Škoda, 2012). To clarify the major differences in the chemical compositions of zircon from A- and S-type granites, we compare our A-type zircon data (this work, Breiter and Škoda, 2012; Breiter et al., 2009; together ca. 500 analyses) with extensive datasets of ca. 540 zircon analyses from European Variscan S-type plutons, obtained by using the same methodology in the same laboratory during the earlier projects. For comparison, we used zircon from the highly fractionated peraluminous P-, F-, Li-, Sn-, and Ta-enriched Beauvoir granite, France (Breiter and Škoda, 2012), the strongly fractionated P-, F-, Li-, Sn-, W-, Nb-, and Ta-enriched Podlesí granite, the Krušné Hory, Czech Republic (Breiter et al., 2006), and the common peraluminous two-mica granites from the Moldanubian domain of the Bohemian Massif, Czech Republic/ Austria (author's unpublished data). We evaluated altogether more than 1000 analyzes of zircon. Major differences between S- and A-type zircons were found in the contents of Th, Y and the HREEs (Fig. 9). For example, 55% of zircon grains from the A-type granites contain more than 0.003 apfu Yb, but only 1% of zircon grains from the S-type granites reach this value. In contrast, there is no significant difference in the Hf, U and F contents. With regards to the Zr/Hf ratio, zircons from the most fractionated unit B in the Beauvoir granite (France) produce a mean ratio of Zr/ Hf = 21 (56 analyses in range 4–35), while zircons from the less evolved B' unit (classification according to Raimbault et al., 1995) have ratios of Zr/Hf = 30 (33 analyses in the range 18–45). The zircons from the common two-mica granites in the Moldanubian Pluton (Czech Republic/Austria) produce a value of Zr/Hf = 72 (144 analyses in the range 48–105). We conclude that, despite the still rather limited datasets, the zircon Zr/Hf ratios 55 and 25 (proposed to approximately distinguish the common, moderately evolved and the highly evolved A-type granites) are also valid for the S-type granites. Fig. 10 demonstrates increasing differences between the A- and S-type zircons from the common to the highly fractionated granites. HREE contents (here represented by Yb; Fig. 10a) are very low (b0.003 apfu Yb) in zircon from all the investigated S-type granites, but systematically increase in zircons from the common to the evolved A-type granites (0.002 to 0.075 apfu Yb). Zircons from A- and S-type granites also differ in the trends of Th and Y evolution (Fig. 10b,c). The contents for both elements systematically increase in the A-type rocks from the common granites (mostly b0.001 apfu Th, b0.002 Y) to the strongly evolved ones (often 0.02–0.05 apfu Th, max. 0.09 apfu Th; often 0.05–0.20 apfu Y, max. 0.24 apfu Y). On the contrary, in S-type granites, contents of Th and Y in zircon decrease. Therefore, zircon from the common and moderately evolved S-granites is often slightly Th- and Y-enriched (0.005–0.10 apfu Th and 0.02–0.10 apfu Y in biotite granites from the Krušné Hory/Erzgebirge and some two-mica granites from the southern Bohemian Massif), while zircon from the strongly evolved Li-mica granites from the Krušné Hory/Erzgebirge and Beauvoir is Th- and Y-free. Similarly in zircon from the peraluminous LCTpegmatites from the Western Carpathians, Uher and Černý (1998) usually found less than 0.1 wt.% Y2O3, with only sporadic enrichment up to 1.7 wt.% Y2O3 (0.13 apfu Y). Hoskin and Ireland (2000) tried to use the REE, U and Th contents in zircon as indicators of provenance. They concluded that neither the REE patterns nor the U/Th ratios are suitable for this purpose. The HREE contents in granitoids were generally found to be within a narrow range

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103–104 times those of chondritic values (ca. 0.02–0.2 wt.% Yb2O3) and the U/Th ratios in the range 1.0–2.5. This field is shown in Fig. 11a. Our data are much more scattered. The HREEs, represented here by Yb, are in the range 103–2 × 105 times those of chondritic values, while the U/Th ratio varies between 0.1 and 900 (Fig. 11a). Among the 198 A-type zircon grains analyzed for U and Th in this study, only 66 grains (33%) lie in the interval predicted by Hoskin and Ireland (2000), whereas 30% of the grains have a U/Th ratio b 1 and 37% of the grains N 2.5. Among the S-type zircons, 15% of the grains have U/Th b1, 17% of the grains are in the proposed interval 1–2.5, and 68% of the grains have U/Th N 2.5 (grains with U- or Th-content under detection limit were not considered). The U/Th values proposed by Hoskin and Ireland (2000) are most likely generally valid in common, geochemically non-specialized granites. In fractionated and mineralized granites, the dispersion of the U/Th value is much larger: from b 0.1 to N100 (cf. Table 2). Differences in the U/Th ratio between the A- and

Fig. 9. Histogram of the contents of HfO2, UO2, ThO2, Y2O3 and Yb2O3 in zircon from A- and S-type granites. See text for the source of data.

Fig. 10. Comparison of the contents of minor elements in zircons from A- and S-type granites of different degree of geochemical evolution: a, Yb vs. Zr/Hf; b, Th vs. Zr/Hf; c, Y vs. Zr/Hf. Samples are distinguished acc. to grade of geochemical evolution of their parental granites.

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met the narrow field defined for zircon of common granites by Hoskin and Ireland (2000). Taken together, zircons from the majority of geochemically nonevolved granites of all types show a similar trace-element spectrum, but the zircons from the strongly fractionated A- and S-type granites can be discriminated on the basis of the HREE contents and the U/Th ratios. The U/Th vs. Yb plot (Fig. 11b) is proposed to be the best diagram for discrimination of zircons from the A- and S-type granites. 8. Conclusions The main results of our investigation of the chemical composition of zircon from post-orogenic or anorogenic/within-Plate A-type granites can be summarized as follows:

Fig. 11. Discrimination diagram for zircons from the A- and S-type granitoids. Gray field shows the area of common zircon composition acc. to Hoskin and Ireland (2000): a, zircons from the A- and S-type granites are distinguished acc. to their geographical provenance; b, zircons from the A- and S-type granites are distinguished acc. to grade of geochemical evolution of their parental granites. Classification of granites was made on the basis of the prevailing Zr/Hf-ratio of their zircons: normal granites with Zr/Hf N 55, evolved granites with Zr/Th 25–55, strongly evolved granites with Zr/Hf b 25.

S-type zircons generally resemble differences between the bulk-rock U/Th values of the parental rock. For example, in the Krušné Hory/ Erzgebirge, the U/Th values in fractionated S-type granites are 2–5, whereas in the A-type granites, the values are only 0.2–1 (due to substantially higher Th-contents, Breiter, 2012; Breiter et al., 1991, 1999; Förster et al., 1999). Some trace elements are typically enriched in particular areas, without a clear dependence of the geochemical type of granite. For example, Bi and Sc are scarce in Brazil (A-type) and France (S-type), but strongly enriched in the Krušné Hory/Erzgebirge (both A- and S-types). Arsenic is poor in all Brazilian plutons, but commonly enriched in the Beauvoir (S-type) and the Krušné Hory/Erzgebirge (A-type) granites. The enrichment of Nb, Ta and W was found only in zircon from the strongly fractionated A-type granites in the Krušné Hory/Erzgebirge and in lesser amounts in the Kymi stock. Nardi et al. (2013) proposed to use diagrams constructed on the basis of Th, Nb, Yb, Eu*/Eu, Nb, Ce and (Y/100) + (Lu/10) + Nb coordinates to discriminate zircons from the I-type, A-type, and shoshonitic granitoids. These diagrams separate most of the A-type zircons from zircons of other geochemical types, but the necessary use of the LA-ICP-MS method because the Nb, Ce, Eu and Lu contents in zircon are often lower than the detection limit of EMPA is a large disadvantage of these graphs. When we put the data published by Nardi et al. (2013) into our interpretation diagram using U/Th vs. Yb, zircons from all the studied rocks

• Zircon is a common constituent in all the studied A-type granites and rhyolites. In evolved granites, zircon may crystallize during the entire solidification process of the rock. • Zircon from common biotite and hornblende–biotite granitoids is poor in minor and trace elements. Zircon from the moderately fractionated granite varieties is slightly Hf-, Th-, U-, Y-, and HREEenriched, while zircon from the highly fractionated rare-metal granites may be strongly enriched in Hf, Th, U, Y, Sc, F, P, As, Bi, Ca, Fe, and Al. • Nb, Ta, and W are present in zircon from the highly evolved rare-metal granites from all the studied areas, while high Sc, As and Bi contents are typical for the Krušné Hory/Erzgebirge. • The decrease in the zircon Zr/Hf value during fractionation of the silicate melt is well documented at all scales of the investigation: at the scale of whole plutons, from the early to late intrusions; within single intrusions, from the early to the late solidified portions; and at the scale of individual crystals, from core to rim. • The Hf and U contents in zircon from A- and S-type granites display good correspondence in similar varieties (common, moderately evolved or highly evolved granites) and are apparently relatively independent of the source of the parental melt. • The zircon Zr/Hf ratio values of 55 and 25 are proposed to approximately distinguish common, moderately evolved and highly evolved granites. These values are valid for both the A- and S-type studied granites and should be tested in other occurrences of similar granites. • The zircons from geochemically non-evolved A- and S-type granites possess similar trace-element spectrums, but the zircons from the strongly fractionated A-type granites contain substantially more Th, Y, and HREEs than zircons from S-type granites of similar fractionation grade. The zircons of A-type and S-type can be discriminated on the basis of their HREE contents and U/Th-ratios. Acknowledgments We would like to thank Mrs. Zuzana Korbelová (Geological Institute AS CR Praha) for the BSE images, Mr. Radek Škoda (Masaryk University Brno) for the technical help with the microprobe and Mr. H. T. Costi (Belém) for the supply of the cryolite-bearing albite granite sample from Pitinga. Pavel Uher (Bratislava) and one anonymous reviewer are thanked for their detailed and helpful review. Inspiring comments by the handling editor Nelson Eby are highly acknowledged. This investigation was supported by the RVO 67985831 in the Czech Republic. This paper is a contribution to the Brazilian Institute of Amazonia Geosciences (INCT program – CNPq/MCT/FAPESPA – Proc. 573733/ 2008-2). References Almeida, F.F.M., Brito Neves, B.B., Carneiro, C.D.R., 2000. The origin and evolution of the South American Platform. Earth-Science Reviews 50, 77–111. Anders, E., Grevesse, N., 1989. Abundances of the elements: Meteoritic and solar. Geochimica et Cosmochimica Acta 53, 197–214.

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