Mineralogy and geochemistry of the Paleoproterozoic, tin-mineralized Bom Jardim granite of the Velho Guilherme Suite, eastern Amazonian craton

Journal of South American Earth Sciences 38 (2012) 159e173

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Mineralogy and geochemistry of the Paleoproterozoic, tin-mineralized Bom Jardim granite of the Velho Guilherme Suite, eastern Amazonian craton Claudio Nery Lamarão b, c, *, Sabrina Cristina Cordovil Pinho a, b, c, Antonio Lima de Paiva Júnior b, c, Marco Antônio Galarza c, d a

Mineração Buritirama LTDA, Belém, Brazil Group of Research on Granite Petrology, Geosciences Institute, Federal University of Pará, Caixa Postal 8608, 66075-100, Belém, Pará, Brazil Programa de Pós-Graduação em Geologia e Geoquímica, Instituto de Geociências, UFPA, Belém, Brazil d Laboratory of Isotopic Geology, Geosciences Institute, Federal University of Pará, Belém, Brazil b c

a r t i c l e i n f o

a b s t r a c t

Article history: Received 24 June 2011 Accepted 15 May 2012

The Bom Jardim granite is located to the south of São Felix do Xingu town and is intrusive in the intermediate to felsic volcanic rocks of the Uatumã Group. It is formed dominantly of coarse- to mediumgrained isotropic monzogranite and syenogranite, both affected by intense late- to post-magmatic alteration. Biotite, generally chloritized, is the main primary mafic phase, with rare amphibole being found in the monzogranite. Hydrothermally altered and greisenized rocks, containing small primary concentrations of cassiterite þ wolframite, as well as quartz veins with millimeter- to centimeter-sized crystals of wolframite þ pyrite þ fluorite occur in pervasively altered cupolas. Presently, alluvial cassiterite and wolframite (columbite, tantalite) are mined in the Pedra Preta mine, located in the northern part of the pluton. SEM data showed that SneW mineralization is dominantly associated with syenogranite and greisenized rocks. EDS Semi-quantitative analysis revealed that the zircon crystals of the Bom Jardim granite are characteristically enriched in Hf, Y, U, and Th and display Zr/Hf ratios decreasing from monzogranite/leucomonzogranite toward syenogranite and greisenized syenogranite rocks, suggesting that magmatic differentiation significantly contributed for this particular feature. The Bom Jardim granite is slightly peraluminous and displays geochemical affinities with A-type granites. The Bom Jardim granite varieties evolved dominantly by fractional crystallization and their REE patterns are similar to those of the tin-specialized granites of the Velho Guilherme suite. It is concluded that the more evolved granites and associated greisenized rocks of the Bom Jardim pluton are tin-specialized granites. The similarities observed between the granites of the Velho Guilherme suite and the Bom Jardim granite allow to include the latter in this important granite suite. Ó 2012 Elsevier Ltd. All rights reserved.

Keywords: Amazonian craton Paleoproterozoic Tin-specialized granites A-type granites Xingu region

1. Introduction The Amazonian craton was formed by accretion events and amalgamation of micro-plates during the Archean and Proterozoic, and is divided into six different geochronologic provinces (Tassinari and Macambira, 2004): Central Amazonia (>2.5 Ga), Maroni-Itacaiúnas (2.2e1.9 Ga), Ventuari-Tapajós (1.95e1.80 Ga), Rio NegroJuruena (1.8e1.55 Ga), Rondonian-San Ignacio (1.5e1.3 Ga), and Sunsas (1.25e1.0 Ga). The voluminous Proterozoic anorogenic

* Corresponding author. Tel.: þ55 91 3201 8146; fax: þ55 91 3201 7478. E-mail addresses: [email protected] (C.N. Lamarão), [email protected] (S.C. Cordovil Pinho), [email protected] (A.L. de Paiva), [email protected] (M.A. Galarza). 0895-9811/$ e see front matter Ó 2012 Elsevier Ltd. All rights reserved. doi:10.1016/j.jsames.2012.05.004

magmatism of the Amazonian craton is dominated in the Xingu region by granites with associated intermediate to felsic volcanic rocks and subordinated mafic plutonic rocks (Teixeira, 1999; Teixeira et al., 2002; Dall’Agnol et al., 1999a). In the eastern domain of the Amazonia Central province of the Amazonian craton, three important granite suites (Fig. 1) were individualized on the basis of geologic, geochemical, geochronological, and isotope data, the Jamon, Velho Guilherme, and Serra dos Carajás suites (CPRM/ DNPM, 1997; Teixeira et al., 2002; Dall’Agnol et al., 2005). These three suites are composed of w1.89e1.86 Ga (Table 1) undeformed granites forming stocks and batholiths. The absence of deformation, the discordant character of the plutons and the presence of micrographic intergrowths suggest a high level of emplacement, with temperatures and pressures estimated in the range of 890e690  C and 400e80 MPa, respectively (Teixeira, 1999; Teixeira

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Fig. 1. (a) Sketch of the Amazonian Craton with the location of the studied area. (b) Simplified geological map of the Carajás Mineral Province with the distribution of Paleoproterozoic A-type granites of the Jamon, Velho Guilherme and Serra dos Carajás suites (modified from Dall’Agnol et al., 2005).

et al., 2002, 2005). All granites display characteristics of A-type granites and within-plate signature. The three granite suites display important differences in the degree of oxidation of their magmas (Dall’Agnol et al., 2005; Dall’Agnol and Oliveira, 2007). The plutons of the Jamon suite (Dall’Agnol et al., 1999b,c; Almeida et al., 2006; Dall’Agnol and Oliveira, 2007; Oliveira et al., 2009) show oxidized character, while the plutons of the Serra dos Carajás (Barros et al., 1995; Javier Rios et al., 1995) and Velho Guilherme suites (Teixeira, 1999; Teixeira et al., 2002, 2005; Villas, 1999) are moderately reduced and reduced (Dall’Agnol et al., 2005), respectively. The Bom Jardim granite is a SneW mineralized pluton that outcrops in an area of approximately 200 km2 to the south of São

Felix do Xingu city (Fig. 1). In this paper are presented and discussed new geologic, petrographic and geochemical data of the Bom Jardim pluton, which contribute to a better understanding of the Velho Guilherme suite and tin-mineralized granites of the Amazonian craton. 2. The Velho Guilherme Suite The Velho Guilherme suite occurs in the São Felix do Xingu region and is composed so far of the plutons Antonio Vicente, Serra da Queimada, Velho Guilherme, Mocambo, Ubim-sul and Benedita (Fig. 1), which are tin-mineralized granites with local occurrence of wolframite and tantalite. The mineralization is related to the

C.N. Lamarão et al. / Journal of South American Earth Sciences 38 (2012) 159e173 Table 1 Geochronologic data of the Paleoproterozoic granite suites of the Carajás region (compiled from Dall’Agnol et al., 2005). Pluton

Method analyzed

Serra dos Carajás granite suite Cigano UePb Serra dos Carajás UePb Pojuca UePb Jamon granite suite Musa UePb Jamon PbePb Seringa PbePb Redenção PbePb Felsic dikes PbePb Velho Guilherme granite suite Velho Guilherme PbePb Rio Xingu PbePb PbePb Mocambo PbePb Antonio Vicente PbePb PbePb

Material

Age (Ma)

Zircon Zircon Zircon

1883  2 (1) 1880  2 (1) 1874  2 (1)

Zircon Zircon Zircon Whole rock Zircon Zircon

1883  5 (1) 1885  32 (2) 1895  1 (3) 1870  68 (4) 1885  4 (7) 1885  2 (7)

Whole rock Zircon Whole rock Zircon Zircon Whole rock þ fk

1874  30 (5) 1866  3 (6) 1906  29 (6) 1862  32 (6) 1867  4 (6) 1896  9 (6)

Data sources: (1) Machado et al. (1991); (2) Dall’Agnol et al. (1999b); (3) Paiva Júnior (2009); (4) Barbosa et al. (1995); (5) Macambira and Lafon (1995); (6) Teixeira et al. (2002); (7) Oliveira, D.C., unpublished data.

evolved granite facies affected by intense post-magmatic alteration or hosted in small bodies of greisens (Dall’Agnol et al., 1993; Teixeira et al., 2002). These granite plutons are intrusive in Archean granitoids and metavolcano sedimentary sequences or in the Paleoproterozoic Parauari granite and intermediate to felsic volcanic rocks of the Uatumã Group (Fig. 1; Teixeira et al., 2002; Fernandes, 2005; Vasquez et al., 2008; Juliani and Fernandes, 2010). The granitic rocks of the Velho Guilherme suite are dominantly leucocratic to hololeucocratic monzogranite to syenogranite with subordinate alkali-feldspar granite with low contents of TiO2, Al2O3, CaO, MgO, P2O5, Sr, Ba, and Cl (Teixeira et al., 2005). The alkalis

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content (Na2O þ K2O) varies between 7.12 and 8.91%, and the K2O/ Na2O ratio varies between 1.01 and 3.14. Their contents of Hf, U, and Zr are moderate and those of Rb, Y, F, Li, Th, Nb, Ta, Ga, and the Rb/ Sr, Rb/Ba, and F/Cl ratios are systematically high, except for the rocks of the Antonio Vicente pluton which have comparatively lower Ga. Geochemically these granites are subalkalineand display a metaluminous to peraluminous character, within-plate signature and affinity with A-type granites of the A2 subgroup (Eby, 1992), with the exception of the Benedita pluton which plots in the A1 subgroup (Teixeira et al., 2005). Geochemical data point to fractional crystallization as the main petrogenetic process governing the evolution of the different granites of the Velho Guilherme suite (Teixeira and Bettencourt, 2000). 3. The Bom Jardim granite 3.1. Geologic aspects Fig. 2 shows the geologic map of the Bom Jardim granite with the areal distribution of the different identified petrographic facies and the location of the Pedra Preta mine (compiled from Pinho, 2009). The Bom Jardim granite is a nearly circular intrusion situated at the right margin of the Xingu River, south of São Felix do Xingu. The pluton covers an area of w200 km2 (Fig. 2) and its rocks are exposed generally as boulders and blocks along hills and drainage flows. The pluton is intrusive in grayish to greenish aphanitic to microporphyritic andesites to dacites flows of the Sobreiro Formation and in rhyolites of the Iriri Formation, or Santa Rosa Formation according to Juliani and Fernandes (2010), both belonging to the Uatumã Group (CPRM/DNPM, 1997; Vasquez et al., 2008). Locally, porphyritic felsic volcanic rocks of the Uatumã Group (Paiva Júnior, 2006) display enclaves of andesite composition and plagioclase, quartz and K-feldspar phenocrysts in a felsitic matrix. Granodioritic rocks similar in petrographic and geochemical characteristics to the

Fig. 2. Geologic map of the Bom Jardim granite showing the areal distribution of the different petrographic facies and the location of the Pedra Preta mine (compiled from Pinho, 2009).

Other minerals: titanite  2 rutile  2 zircon  2 allanite P/A ¼ Plagioclase/Alkali-feldspar Ser-musc ¼ sericite-muscovite. Abbreviations: B ¼ biotite; L ¼ leuco; Grd ¼ granodiorite; MZG ¼ monzogranite; SG ¼ syenogranite.

88.5 11.0 0.45 90.1 10.0 0.31 96.1 3.7 0.39 95.5 4.5 0.55 94.2 5.8 0.52 92.4 7.6 0.47 97.1 2.9 0.48 97.9 1.2 0.7 95.8 4.2 0.8 96.7 3.3 0.9 93.7 6.3 0.7 95.7 4.3 1.1 96.0 4.0 1.0 93.0 7.0 0.7 92.9 7.1 0.9 96.5 3.5 0.9 92.3 7.7 0.8 80.4 19.6 3.0 84.8 15.2 3.0

76.2 23.8 4.2

93.7 6.3 0.9

92.6 7.1 0.8

0.9 0.7 3.0 0.9 0.7 0.6

0.0

4.6 0.2 3.2 0.5

0.8 3.6

98.7 1.3 0.8

0.6 0.0

0.4 0.9

0.7

0.4

0.3

0.2

0.2 0.7 1.2 1.1

0.3 0.6 0.3

0.6 0.8

0.7 1.0

0.5

0.8 0.6

0.2

0.6 1.7 0.2 0.3 1.4 0.6 4.0 0.6 2.1 1.1 0.5 0.8 1.8 0.6

0.8 2.1 0.7 0.4 0.7 0.3 1.7

0.5 1.9 1.1 0.8 0.6 0.1 0.4 2.4 0.8 0.7 0.4 0.1 0.8 1.3 0.9 0.8 5.9

92.4 7.6 0.32

1.2 0.1 0.0 0.0

0.2 0.6

1.3 0.0 0.6

1.5

1.7 0.9

0.5

1.5 1.4 2.3 1.8 0.3 0.3 0.8 0.7 3.5 0.6 1.2 0.2 0.6 1.4 0.5 1.8 1.6 0.3

97.0 3.0 0.21

2.5 1.9 2.1 0.3 0.0 0.3

1.0 2.1 0.4

2.0 0.4 0.9 1.9 0.5

1.3

0.0

0.7 3.0

1.2 0.3 0.8

1.5 5.0

0.1

0.5 3.2 1.6

29.0 31.3 33.6 33.7 39.1 41.8 42.2 43.0 47.4 28.3 32.8 35.9 36.7 43.7 48.2 51.8 1.0 53.5 33.9 35.6 36.4 40.3 42.9

19.5 9.5 2.8 1.0

15.5 18.5

14.0 44.8 17.5 45.0 11.2 52.1 20.1 36.3 18.0 34.4 16.1 34.1 17.6 36.5 11.0 34.0 28.2 41.4 28.6 34.4 29.4 31.4 23.4 33.6 26.9 25.1 23.5 24.3 17.2 24.0 20.1 25.1 27.6 31.4 28.6 32.3 25.3 30.6 23.5 28.8 23.9 26.9 49.0 11.7

20.1 4.3 0.7

SAL 36D

45.5 15.4

BSG

SAL 56 SAL 72 SAL 72B NCBJ 119 NCBJ 124 SAL 70B BLMZG

SAL 32 SAL 42 SAL 29 SAL 62

SAL 35 BMZG

SAL 40B

SAL 41 Grd

48.5 16.2

Plagioclase Alkalifeldspar Quartz Amphibole Biotite Epidote Chlorite Ser-musc White mica Opaques Apatite Fluorite Topaz Albite Other minerals Felsic Mafic P/A

Fig. 3. Q-A-P and Q-(AþP)-M’diagrams (Streckeisen, 1976) showing the distribution of the Bom Jardim granite varieties.

Table 2 Representative modal compositions of the Bom Jardim granite and associated granodiorite, Xingu region.

The studied rocks of the Bom Jardim pluton range from isotropic monzogranite to syenogranite altered in different intensities. In the more intensely altered rocks, represented by syenogranite and greisenized rocks, expressive occurrence of albite, sericite-muscovite, fluorite, and topaz, besides cassiterite, wolframite, and columbite can be observed. These minerals are related to late- to post-magmatic alteration processes that probably culminate with the greisenization of cupola zones of the Bom Jardim granite. Based on mineralogical, petrographic, and textural features, four varieties of rocks were identified: (1) Biotite monzogranite (BMZG), (2) Biotite leucomonzogranite (BLMZG), (3) Biotite syenogranite (BSG), and (4) Greisenized rocks (GR). The Q-A-P and Q(AþP)-M’ diagrams (Fig. 3) show the variation in modal composition and the dominant hololeucocratic to leucocratic (M0  10%) character of the granites of the pluton. A general increase in the plag/Kfeld ratio is observed, associated with the reduction of mafic minerals content toward the more evolved facies (Table 2),

SAL 60A

3.2. Petrography and mineralogy

NCBJ 125

SAL 25

SAL 22

SAL 24A

SAL 65

NCBJ 121

SAL 49

SAL 64A

SAL 73B

Archean sanukitoid granodiorite that occurs in the Rio Maria Granite-Greenstone Terrain (RMGGT; Oliveira et al., 2006, 2009) were identified in the eastern border of the Bom Jardim pluton (Fig. 2). The westernesouthwestern border of the body could not be studied because of the dense vegetal cover and of the proximity with an Indian reservation. This portion of the pluton was referred to the geologic map (Fig. 2) as undifferentiated rocks. The studied rocks of the Bom Jardim pluton are formed dominantly of isotropic pink to reddish monzogranite to syenogranite with coarse- to medium-grained texture. Biotite, now intensely chloritized, was the main primary mafic phase. Amphibole is locally found in the monzogranites. Aplite dikes cut the dominant variety. The monzogranites and syenogranites are affected in different intensities by late- to post-magmatic alteration. Greisenized rocks containing small primary concentrations of cassiterite, besides quartz veins with millimeter to centimeter-sized crystals of wolframite þ pyrite þ fluorite, were identified in pervasively altered cupolas in the center-north of the Bom Jardim pluton (Fig. 2). Alluvial cassiterite and wolframite (columbite, tantalite) are mined actually in the Pedra Preta mine located in that area of the pluton (Fig. 2).

18.6 40.9

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SAL 57

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suggesting that processes of fractional crystallization were responsible for the magmatic differentiation of the different facies of the Bom Jardim pluton. Similar differentiation processes were also identified in other plutons of the Velho Guilherme (Teixeira, 1999; Teixeira et al., 2002) and Jamon suites (Dall’Agnol et al., 1999b; Almeida et al., 2006; Oliveira et al., 2009). The granodiorite (Grd) of the southeastern border of the pluton, have a distinct modal composition, including a more mafic character (M0 ¼ 15e24% modal) and the presence of hornblende as the major mafic phase. These rocks are plotted in Fig. 2 for comparison with the granite varieties of the Bom Jardim pluton. These rocks differ in their petrographic and geochemical characteristics of the Bom Jardim granites and probably belong to the Archean or Paleoproterozoic basement rocks. They were included in this study just for comparison. 3.2.1. Biotite monzogranite and leucomonzogranite These rocks are massive, isotropic, coarse- to medium-grained, pink in color and show seriated, hypidiomorphic texture, in thin section. Biotite is the dominant mafic phase (3.5% modal; Table 2) and amphiboles occur only in the biotite monzogranite facies as rare pseudomorphosed crystals. Accessory minerals are preferentially associated with mafic phases and include magnetite, ilmenite, allanite, zircon, apatite, fluorite, and titanite. Chlorite, sericitemuscovite, epidote, and albite are secondary minerals. K-feldspar crystals are dominantly anhedral to subhedral and locally form phenocrysts. They are generally altered to clay minerals and exhibit films, stringers and rods of albite in microperthitic intergrowths. Plagioclase is subhedral, coarse- to medium-grained, displaying normal oscillatory zoning and, sometimes, inclusions of quartz, biotite and K-feldspar. Intense sericitization, especially in the crystal core, precludes the determination of plagioclase composition, but it is indicative of a Ca-poor composition (probably An  30). Quartz occurs as anhedral, rounded phenocrysts, as medium-grained aggregates, and granophyric intergrowths. Biotite is subhedral, medium to fine-grained, intensely altered to chlorite with associate epidote, fluorite, titanite, and iron oxide. Biotite appears sometimes as interstitial crystals denoting later crystallization. Aggregates of white micas are locally present. Albite is common in these rocks and it occurs as albite rims associated to plagioclase crystals, swapped-rims between K-feldspar grains, chessboard albite, and in perthitic intergrowths (Peng, 1970).

163

the syenogranite. The greisens fill fractures within syenogranites and form irregular patches or pockets. Small concentrations of cassiterite and wolframite (columbite, tantalite) were identified. The intensity of greisenization is variable and depends on the amount of fractures. These rocks show hypidiomorphic, heterogranular, coarse- to fine-grained texture and grayish color. Quartz, topaz, fluorite, chlorite, and siderophyllite are the dominant mineral phases. Siderophyllite is commonly associated to fluorite and muscovite. Fine subhedral crystals of topaz are abundant and associated to fluorite and micas. The accessory minerals are zircon, rutile, cassiterite, wolframite, columbite, and rare titanite. Quartz veins containing millimeter to centimeter-sized crystals of wolframite, pyrite, and fluorite are common intersecting greisens, being therefore post-greisenization. 3.2.4. Associated granodiorite These rocks are gray to slightly greenish in color and show medium-grained, hypidiomorphic, textures. Amphibole and subordinate brown biotite are the major mafic minerals, and zircon, apatite, titanite, magnetite, ilmenite, thorite and rare rutile the accessory phases. Chlorite, epidote, sericite, and clay minerals are the dominant secondary minerals. Plagioclase is dominantly anhedral and intensely saussuritized, with fine inclusions of amphibole, biotite, and quartz crystals. Locally synneusis features (Vance, 1965, 1969) are observed. Quartz is dominantly interstitial. K-feldspar is subhedral, medium-grained, perthitic and altered to clay minerals. Titanite is a common primary accessory phase. Magnetite is subhedral to anhedral and commonly associated with amphibole and biotite crystals. Epidote is a common secondary mineral replacing plagioclase and amphibole. Fig. 4 shows microscopic aspects of the different rocks of the Bom Jardim pluton. 3.2.5. Accessory mineralogy Table 3 shows the accessory mineralogy of the different rocks of the Bom Jardim granite and associated granodiorite obtained with Scanning Electron Microscopy (SEM) and Energy Dispersive Spectrometry (EDS) semi-quantitative analyses. Cassiterite, wolframite, columbite, thorite, sphalerite, monazite, galena, fluorite, and topaz are preferentially associated with the syenogranite and greisenized syenogranites, while in the monzogranites they appear only locally. The associated granodiorites have magnetite and ilmenite as the main opaque phases.

3.2.2. Syenogranite Syenogranite is hypidiomorphic heterogranular, coarse- to medium-grained rocks, pink in color. Biotite is the dominant mafic phase but it is scarce (Table 2). The primary accessory minerals are thorite, ilmenite, columbite, cassiterite, wolframite, galena, titanite, allanite, fluorite, zircon and rare magnetite and apatite. Sericitemuscovite, chlorite, clay minerals, albite, white micas, and rare epidote are secondary phases. K-feldspar is similar to that found in the monzogranites. Albite is a common mineral phase in these rocks. It forms anhedral to subhedral crystals, shows sericitization and inclusions of biotite, zircon and rare apatite. Intergranular albite is commonly present along the contacts between K-feldspar crystals. Quartz occurs as anhedral to sub-rounded crystals and as aggregate of thin crystals associated to biotite, epidote, fluorite, and opaque minerals. Biotite consists of anhedral to subhedral crystals, locally interstitial, intensely altered to chlorite, epidote, and iron oxide. Titanite, apatite, fluorite, zircon, and allanite occur associated to biotite or as inclusions in quartz grains.

3.2.6. Compositional variation in zircon The high chemical stability of zircon, associated with the occurrence in its internal structure of trace elements as Hf, Y, Nb, Th, U, REE, Ca, and P, may be useful in the identification of the geochemical nature of source rocks, in the characterization of magmatic fractionation and in provenance studies of detrital zircon grains of crystals from sedimentary rocks. Hf-rich zircon grains of crystals in granitic rocks are typically associated with evolved, rare metals (Sn, W, Nb, and Ta) specialized granites. Zircon grains of crystals of topaz and rare-metal-bearing granites display extremely low Zr/Hf ratios that are interpreted as a magmatic signature inherited of evolved granitic melts or as the result of hydrothermal alteration of the host rocks by F-rich fluids (Murali et al., 1983; Uher et al., 1998; Wang et al., 2000; Belousova and Griffin, 2002; Kempe et al., 2004; Lamarão et al., 2007, 2010). The study of zircon crystals of the Bom Jardim granite is based essentially on backscattered images obtained through SEM and EDS elemental analyses.

3.2.3. Greisenized rocks and quartz veins The greisenized syenogranites are associated with fractures and pervasively altered zones (Taylor and Pollard, 1988) in the cupola of

3.2.6.1. Analytical procedures. Polished sections of the studied rocks (Table 3) were previously coated with carbon. The backscattered (BSE) images and EDS analyses were made at the

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Fig. 4. Photomicrographs showing mineralogical and textural aspects of the Bom Jardim granite varieties. (A, B) Biotite monzogranite and leucomonzogranite: (A) General microscopic aspect; (B) Fluorite crystals associated with chloritized biotite and opaque minerals. (C, D) Biotite syenogranite: (C) swapped-rims of intergranular albite formed along the contact of crystals of perthitic alkali-feldspar; (D) Fluorite, opaques and zircon crystals included in or associated with quartz and chlorite. (E, F) Greisenized syenogranites: (E) Corroded and altered siderophyllite crystal associated with anhedral cassiterite; (F) Aggregate of topaz and fluorite crystals associated with chlorite.

Geosciences Institute of the Federal University of Pará, using a LEO1430 SEM. Operating conditions were as follows: accelerating voltage ¼ 20 kV, beam current ¼ 90 mA, work distance ¼ 15 mm. Were analyzed O, Si, Zr, Hf, Ce, Nb, Y, Th, U, Ba, and Ca. The analyses were performed in the rims and cores of the zircon grains, avoiding, with the aid of the BSE images, fracture, alteration and inclusions. 3.2.6.2. Morphology and composition. The zircon crystals of the different identified varieties show morphological contrasts. In the monzogranites, they vary from euhedral to subhedral and form commonly corroded and zoned well-developed (100e200 mm) crystals. The syenogranites have subhedral to anhedral zircon crystals, which are weakly zoned and show corroded borders and internal Ca-enriched patches. The greisenized rocks have dominantly fractured, corroded, anhedral to subhedral zircon grains, commonly associated with or including thorite and monazite (Fig. 5). Compositionally, zircon of the Bom Jardim granite is characteristically enriched in Hf, Y, U, and Th and displays Zr/Hf ratios decreasing from monzogranite/leucomonzogranite (18.7) toward syenogranite (17.2) and greisenized rocks (10.0). The same behavior

has also been observed in the zircon of tin-specialized granites of the Amazonian craton (Lamarão et al., 2007, 2010), suggesting that magmatic differentiation significantly contributed for this particular feature. On the other hand, the common occurrence of anhedral, corroded zircon grains with patchy internal structure in the syenogranites and greisenized rocks of the Bom Jardim pluton is indicative of intense hydrothermal alteration in these rocks. Compared to the zircon of the different rocks of the Bom Jardim granite, those of the associated granodiorite show lower contents in Hf, Y, U, and Th, and comparatively high Zr/Hf ratios, similarly as observed in zircon of not specialized granites of the Jamon suite (Table 4, Fig. 6; cf. Lamarão et al., 2007). 3.3. Geochronology Six zircon crystals extracted from syenogranite (sample NC-BJ121) of the southeast border of the Bom Jardim pluton were dated by the single grain Pb evaporation method at the isotope geology laboratory of the Federal University of Pará, Brazil. Isotope analyses were performed on a Finnigan MAT262 mass spectrometer in a dynamic mode using an ion counting detector. The

C.N. Lamarão et al. / Journal of South American Earth Sciences 38 (2012) 159e173 Table 3 Accessory mineralogy of the different rocks of the Bom Jardim granite and associated granodiorites identified with Scanning Electron Microscopy (SEM) and Energy Dispersive Spectrometry (EDS) semi-quantitative analyses. Rock type

Sample

Acessory mineralogy

Greisens

SAL-66c SAL-66B SAL-68 SAL-100 SAL-66A SAL-49 SAL-65 SAL-64A NC-BJ-123 NC-BJ-121 SAL-72 SAL-62 SAL-72B SAL-56 SAL-29 NC-BJ-124 SAL-36 SAL-36D SAL-40A

Mnz, Col, Gn Thr, Mnz, Col Mz, Col, Gn Thr, Fl, Mnz, Gn, Py, Sp, Toz, Wol Thr, Cst, Fl, Col, Mlb, Mnz Thr, Col, Cst, Fl, Thr, Cst, Fl, Wol, Gn, Mnz Mgt, Col Thr, Mgt Thr, Ilm Col, Wol, Xnt Thr, Fl, Xnt, Mt Thr, Col, Wol Thr, Fl, Rt, Mz, Ilm Thr, Fl, Cst Thr, Fl, Rt, Xnt Mgt, Thr, Ap, Tnt, Ilm, Rut Mgt, Thr, Py, Ap, Tnt Mgt, Thr, Py, Ap

Biotite syenogranite

Biotite monzogranite to leucomonzogranite

Granodiorite

Ap ¼ apatite; Col ¼ columbite; Cst ¼ cassiterite; Fl ¼ fluorite; Gn ¼ galena; Ilm ¼ ilmenite; Mgt ¼ magnetite; Mlb ¼ molybdenite; Mnz ¼ monazite; Py ¼ pyrite; Rt ¼ rutile; Sp ¼ sphalerite; Thr ¼ thorite; Tnt ¼ titanite; Toz ¼ topaz; Xnt ¼ xenotime; Wol ¼ wolframita.

selected yellowish and translucent crystals, showing some inclusions and fractures, yielded an age of 1867  1 Ma (Table 5), interpreted as crystallization age (Pinho, 2005). Similar ages have also been obtained in other mineralized plutons of the Velho Guilherme suite (Table 1). 3.4. Geochemistry Chemical analyses (Table 6) of the different rocks of the Bom Jardim granite and associated granodiorites were made in the ACMEdAnalytical Laboratories LTD. SiO2, Al2O3, Fe2O3, CaO, MgO, K2O, Na2O, TiO2, P2O5 and MnO were analyzed by ICP-ES (Inductively Coupled Plasma-Emission Spectrometry). Trace elements, including rare earth elements (REE), were analyzed by ICP-MS (Inductively Coupled Plasma-Mass Spectrometry), F by SIE (Specific Ion Electrode) and Li by wet chemistry. 3.4.1. General aspects The Bom Jardim granites are high-silica rocks (73e77 wt% of SiO2), generally with K2O/Na2O ratios higher than one and relatively low contents of mafic components (Table 6). The Al2O3 contents vary generally between 12 and 13 wt% and are similar to those of A-type granites described by Whalen et al. (1987). The average contents of Na2O and K2O are, respectively, of 3.53 wt% and 5.31 wt% in the BMZG and of 3.4 wt% and 4.74 wt% in the BLMZG. In the BSG both oxides display averages of 4.35 wt%. Fe2O3 rarely is >2.0 wt% in the BMZG/BLMZG and in the BSG it decreases to an average value of 0.72 wt%. Except for sample SAL 42 (a leucomonzogranite geochemically akin to the BMZG), the BMZG samples show similar silica contents (ca. 73 wt%) and are enriched in TiO2, MgO, CaO, Ba, Sr, Zr, and LREE, and impoverished in Rb, Nb, Li, F, W, U, HREE, and Sn, compared with the leucomonzogranites and syenogranites. Ba/Rb, Zr/Hf, Th/U and Eu/Eu* ratios are higher and Rb/Sr, FeOtot/MgO and Rb/Zr ratios lower in the BMZG compared to the other varieties of granite (Table 6). Two geochemically distinct groups of greisens were recognized. The first (GR1) is represented by SAL-100 and SAL-66a samples, and the second (GR2) by SAL-68 and SAL-66c samples. The two GR varieties are extremely poor in Na2O (0.02e0.08%), but they have

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distinct contents of K2O (1.7 wt% in GR1 and 4.58 wt% in GR2). The average values of Fe2O3 are of 7.17 wt% in GR1 and 3.72 wt% in GR2 (Table 6). These values are higher than those found in the granites and should be related to the significant modal contents of siderophyllite observed in the greisens. The associated granodiorites have SiO2 contents of w62 wt% and they are enriched in TiO2, MgO, CaO, Al2O3, and Fe2O3, compared with the Bom Jardim granites (Table 6). The Bom Jardim granite is slightly peraluminous (Fig. 7A) and geochemically similar to the Phanerozoic within-plate granites (Fig. 7B), as defined by Pearce et al. (1984). In the Rb  (Y þ Nb) plot, the BMZG plot in the within-plate field near the field of granites related to volcanic arc. The BLMZG and BSG fall on the limit between within-plate and syn-collisional granites, as a consequence of their accentuated Rb-enrichment, which is probably a reflex of fractional crystallization governing the evolution of the different facies of the pluton and post-magmatic alteration processes. In the plot FeO*/MgO  (Zr þ Nb þ Y þ Ce) the rocks of the Bom Jardim granite fall in the field of A-type granites as defined by Whalen et al. (1987), near the fractionated granites field (Fig. 7C). The associated granodiorites are geochemically distinct of the Bom Jardim granites as can be seen in the same diagrams (Fig. 7AeC). 3.4.2. Trace elements Rb shows enrichment from the BMZG (262e325 ppm; Table 6) toward the BLMZG and BSG (513e936 ppm), the more evolved rocks, behaving as a typical incompatible element. In the GR1 the concentrations of Rb are similar to those found in BLMZG and BSG, varying from 791 to 956 ppm, whereas in the GR2, the Rb contents are comparatively higher (ca. 1850 ppm). Contrarily to Rb, Ba and Sr decrease toward the more evolved facies, showing compatible behavior. The GR also show low Sr contents, similar to those observed in the BLMZG. In the Rb  Sr and Sr  Ba plots (Fig. 7D,E), the effects caused in the liquid composition by the fractionation of hornblende, biotite, plagioclase, and potassium feldspar can be estimated (vectors compiled from Dall’Agnol et al., 1999b). The increase of Rb from the BMZG to BLMZG and BSG and greisenized rocks can be partially explained by the fractionation of plagioclase and, in lower proportion, of K-feldspar. The decrease of Ba is dominantly linked to the fractionation of alkali-feldspar and that of Sr is mostly due to plagioclase fractionation. In the Rb  Ba plot (Fig. 7F), the rocks tend to show similar behavior to that observed in the Rb  Sr diagram (Fig. 7D). The Rb/Sr, Ba/Rb and Ba/Sr ratios are good indicators of fractional crystallization in felsic magmas (Blevin and Chappell, 1995). Effectively, in the studied granites, the Rb/Sr ratios increase toward the more evolved rocks, while Ba/Rb and Ba/Sr ratios decrease (Fig. 7G,H). Zr also shows a compatible behavior, but with a less defined evolution trend if compared to Ba and Sr (Figs. 7F, 8A). The reduction in the Zr contents is certainly linked to zircon fractionation because it is an early crystallized mineral. Nb contents tend to increase to the more evolved rocks (Fig. 8B), whereas those of Y show some overlapping in the different varieties and a less evident trend (Fig. 8C). In the GR, there is a clear contrast in Nb and Y contents between the GR1 (high content of Y and moderate of Nb; Table 6; Fig. 8B, C), compared to the GR2 (high Nb and extremely low Y; Table 6; Fig. 8B,C). Ga contents increase toward the more evolved facies and greisenized rocks (Table 6), with average values of 20.45 ppm in the BMZG, 28.72 ppm in the BLMZG, 29.30 ppm in the BSG, and 34.00 and 42.70 ppm in the GR1 and GR2, respectively. In a general way, Li, Sn, and W show enrichment from BMZG/ BLMZG toward BSG and GR, with some superposition (Table 6). The highest F contents are found in the GR1 and in some samples of the

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Fig. 5. Backscattered (BSE) images of zircon grains from different varieties of the Bom Jardim pluton. Note the euhedral to subhedral, zoned and well developed crystals of the less evolved rocks (BMZG/BLMZG), compared to the zircon of the more evolved biotite syenogranite (BSG) and greisens (GR), and the frequent thorite inclusions in the zircon crystals of the latter.

LMZG with concentrations attaining ca. 20,000 ppm, and >3000 ppm, respectively. In the other varieties, the contents of F vary largely but are always <3000 ppm. The behavior of F is better visualized in the F  SiO2 diagram (Fig. 8E). Monzogranites and syenogranites have variable contents of Sn. In the BMZG, BLMZG, and BSG the average concentrations of Sn are of 1.50, 12.80 and 12.67 ppm, respectively, and there is a clear superposition between the BLMZG and BSG in the Sn  SiO2 plots

(Fig. 8F). GR1 and GR2 display the highest concentrations of Sn, with average values of 120 and 190 ppm, respectively. The W contents have a more erratic distribution compared to Sn. The highest average content of W is shown by GR2, whereas those found in the GR1, BSG, BLMZG, and BMZG are similar. A positive correlation between F and Sn is indicated in the F  Sn plot (Fig. 8G) where the Bom Jardim varieties show enrichment toward GR, although with some superposition. A similar behavior

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Table 4 Elementary zircon compositional variation of the Bom Jardim granitic rocks and associated granodiorites obtained through SEM and EDS semi-quantitative analyses (wt%). Sample Zr/Hf Hf (number of analyses) Greisenized rocks

SAL-66c (10) SAL-66B (14) SAL-68 (5) SAL-100 (13) SAL-66A (23) Average (65) Biotite syenogranite SAL-49 (16) SAL-65 (25) SAL-64A (21) SAL-NC-BJ-123 (14) SAL-NC-BJ-121 (8) Average (84) Biotite monzogranite SAL-72 (18) to leucomonzogranite SAL-62 (20) SAL-72B (10) SAL-56 (22) SAL-29 (27) SAL-NC-BJ-124 (17) Average (114) Granodiorite SAL-36 (17) SAL-36D (27) SAL-40A (17) Average (61)

6.7 7.2 7.4 11.7 17.0 10.0 9.0 17.3 17.5 20.8 21.2 17.2 12.8 16.2 17.2 19.4 19.5 27.1 18.7 30.5 34.7 35.5 33.6

8.40 7.70 9.20 6.50 4.80 7.3 7.2 4.0 4.1 3.6 3.5 4.5 5.9 4.1 5.0 4.2 3.4 2.8 4.2 2.4 2.0 2.0 2.1

Y

U

Th

6.10 4.20 4.30 1.7 1.4 3.5 4.8 2.9 3.1 1.3 1.6 2.7 5.4 3.0 5.5 2.2 1.9 0.9 3.1 1.2 1.7 1.6 1.5

5.0 3.40 4.1 2.1 1.00 3.1 2.0 1.8 1.0 1.0 0.6 1.3 2.3 1.4 1.6 1.1 1.9 0.7 1.5 0.4 0.4 0.4 0.4

5.8 3.7 6.0 0.6 0.4 3.3 1.5 0.6 0.4 0.4 0.2 0.6 0.8 0.5 0.8 0.8 1.7 0.3 0.8 0.4 0.5 0.5 0.5

has been described in the rocks of the Antonio Vicente pluton (Teixeira et al., 2005) of the Velho Guilherme suite (Fig. 1). There is no clear correlation trend between F and W (Fig. 8H), but the higher contents of W are found in the GR. This geochemical evidence suggests that post-magmatic F-enriched fluids had a direct involvement in the origin of the Sn and W mineralization associated with the Bom Jardim granite. In the associated granodiorites, Rb contents are significantly lower and of Ba and Sr are quite higher compared to those observed in the Bom Jardim granite (Fig. 7DeF). Nb, Y, F, Sn, and Ga contents are also lower in the granodiorites than in the Bom Jardim granites (Fig. 8BeF; Table 6). The geochemical contrast between the granodiorites and the Bom Jardim granites cannot be explained only by magmatic differentiation processes and point to an independent origin for the granodiorite and the Bom Jardim granites. 3.4.3. Rare Earth Elements REE analytical data and chondrite normalized plots of the Bom Jardim granite are shown in Table 6 and Fig. 9. SREE are high in the Bom Jardim granites and decrease from BMZG toward BLMZG-BSGGR. BMZG are enriched in light rare earth elements (LREE) in relation to heavy rare earth elements (HREE), show a flat pattern of the HREE and a moderate negative Eu anomaly (average Eu/ Eu* ¼ 0.29; Table 6). The (La/Yb)n varies from 14.02 to 5.47 denoting a moderate fractionation of HREE in relation to LREE (Fig. 9A). BLMZG and BSG have variable contents of SREE (872e289 ppm and 642e253 ppm, respectively) and show similar patterns (Fig. 9B) with deep negative Eu anomalies (average Eu/Eu* of 0.06; Table 6) and (La/Yb)n varying from 2.75 to 0.42, indicating a very weak or even absent fractionation of the HREE compared to LREE. The gradual decrease of the LREE from BMZG toward the more evolved facies, accompanied by gradual increase of the HREE, give rise to a gull-shaped pattern, indicative of important feldspar fractionation and characteristic of tin-specialized A-type granites. Similar features were described by Teixeira et al. (2005) in tin-specialized granites of the Velho Guilherme suite. The presence of relatively large amounts of fluorine in the fluid phase associated to the Bom

Fig. 6. Compositional variations in zircon crystals of the Bom Jardim pluton varieties, compared with tin-granites of the Velho Guilherme suite (Mocambo, Serra da Queimada, Antonio Vicente and Velho Guilherme plutons of the Xingu region), Água Boa pluton (Pitinga province) and Bom Futuro mine (Rondônia province), as well as with non specialized granites of the Rio Maria region (Redenção and Bannach plutons of the Jamon suite). (A) Zr/Hf  Hf þ Y þ Th þ U (wt%); (B) Granite types  average Zr/Hf ratios. A and B based on Lamarão et al. (2007). B ¼ biotite; L ¼ leuco; MZG ¼ monzogranite; SG ¼ syenogranite; GR ¼ greisenized rock; Grd ¼ associated granodiorite. On parentheses: number of zircon EDS analyses for each pluton.

Jardim granites could be responsible for these features, because F tends to concentrate HREE in the late liquids (Collins et al., 1982; Teixeira, 1999; Dall’Agnol et al., 2005). Another alternative would be the absence of mineral carries of REE, such as monazite,

Table 5 Zircon single-crystal evaporation Pb isotopic data from syenogranite (sample NC-BJ121) of the Bom Jardim granite. Zircon

Temp. Number of ratios ( C)

204

NCBJ21/1 NCBJ21/3 NCB121/4 NCBJ21/5 NCBJ21/6 NCBJ21/7

1550 1550 1550 1500 1500 1550

0.000034 0.000036 0.000082 0.000051 0.000053 0.000072

38 32 36 36 36 38

Pb/206Pb

207

Pb/206Pb

0.11479 0.11474 0.11538 0.11495 0.11458 0.11521

207

Pb/206Pb

0.11427 0.11424 0.11427 0.11421 0.11403 0.11418 Medium age

Age 2s (Ma) 1869 1868 1869 1868 1865 1867 1867

3 4 5 3 3 4 1

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Table 6 Chemical composition of the Bom Jardim granite and associated granodiorites, São Félix do Xingu region, Carajás Province Granodiorite

Biotite Monzogranite

Greisenized rocks 1

Greisenized rocks 2

Samples

SAL-40A

SAL-41

SAL-35

SAL-29

SAL-32

SAL-42

Biotite Leucomonzogranite SAL-60

SAL-56

SAL-70B

SAL-60A

Biotite Syenogranite SAL-57

SAL-73B

SAL-64A

SAL-49

SAL-100

SAL-66A

SAL-68

SAL-66C

SiO2 (% wt) TiO2 Al2O3 Fe2O3 MnO MgO CaO Na2O K2O P2O5 LOI Total Rb (ppm) Ba Sr Zr Nb Y Ga F Li Sn W La Ce Nd Sm Eu Gd Dy Ho Er Yb Lu Rb/Sr Ba/Rb Rb/Zr FeOt/(FeOt þ MgO) SREE SLREE SHREE (La/Yb)n (Gd/Yb)n Eu/Eu*

60.8 0.8 15.0 6.6 0.1 3.0 4.2 3.4 4.3 0.2 1.2 99.6 165 1626 462 207 9 22 18 730 20 1 73 197 154 82 44 21 22 14 12 13 12 12.6 0.4 9.9 0.8 0.7 583.7 477.4 85.8 11.3 1.5 0.7

63.2 0.8 14.5 5.9 0.1 2.8 3.8 3.7 3.8 0.2 1.1 99.7 128 1267 361 245 10 21 18 390 21 1 19 177 141 77 40 20 20 13 12 12 11 13.0 0.4 9.9 0.5 0.7 535.3 434.3 80.7 10.9 1.4 0.7

73.0 0.2 13.7 1.6 0.0 0.2 0.8 3.7 5.6 0.1 1.0 99.8 291 603 93 158 14 34 20 1530 9 2 36 241 198 85 45 10 23 21 18 20 20 20.5 3.1 2.1 1.8 0.9 702.6 569.1 123.2 7.9 0.9 0.3

73.5 0.2 13.7 1.3 0.0 0.2 0.8 3.7 5.5 0.1 1.0 100.0 300 873 112 215 15 37 21 2060 23 1 30 348 271 119 55 14 30 24 20 23 21 21.3 2.7 2.9 1.4 0.9 947.0 793.4 139.2 11.3 1.2 0.4

73.8 0.3 13.0 2.1 0.0 0.3 1.0 3.7 4.7 0.1 1.0 99.8 262 705 107 233 17 34 20 1810 18 2 29 390 309 141 67 13 31 23 18 20 19 17.7 2.4 2.7 1.1 0.9 1049.3 907.4 128.9 14.0 1.3 0.3

76.1 0.2 12.4 1.4 0.1 0.2 0.3 3.1 5.5 0.1 0.8 100.0 325 497 53 217 17 34 20 500 10 1 81 210 233 77 42 6 21 20 19 23 26 28.4 6.1 1.5 1.5 0.9 707.1 562.6 138.3 5.5 0.7 0.2

75.0 0.0 14.1 1.2 0.1 0.0 0.0 3.9 4.7 0.0 0.9 99.9 860 33 13 55 81 23 34 310 22 12 53 36 38 15 13 1 9 22 23 31 52 55.5 66.2 0.0 15.6 1.0 297.0 102.6 193.5 0.5 0.1 0.1

75.1 0.1 12.8 0.9 0.0 0.1 0.6 3.7 5.1 0.0 1.5 99.9 513 154 21 138 29 67 24 3450 61 2 35 187 165 78 51 4 34 34 33 41 46 47.7 24.1 0.3 3.7 0.9 720.1 479.8 236.2 2.8 0.6 0.1

75.9 0.1 12.6 1.6 0.0 0.0 0.8 3.5 4.3 0.0 1.2 99.9 654 45 22 116 56 127 28 6260 117 28 113 179 143 95 77 2 55 52 46 53 59 60.7 29.5 0.1 5.6 1.0 820.9 493.1 325.7 2.0 0.7 0.0

75.9 0.0 13.5 1.3 0.1 0.0 0.0 3.7 4.6 0.0 0.9 100.1 851 31 14 60 79 23 33 380 22 12 54 33 35 14 12 1 10 22 23 31 53 56.3 63.1 0.0 14.3 1.0 289.5 93.2 195.5 0.4 0.1 0.1

76.9 0.1 12.1 1.6 0.1 0.1 0.7 2.1 5.0 0.0 1.1 99.9 677 172 26 189 34 83 24 4760 27 10 94 215 194 97 65 2 42 45 43 51 59 61.1 26.3 0.3 3.6 1.0 872.2 570.6 299.7 2.5 0.6 0.0

75.6 0.0 13.8 0.6 0.0 0.0 0.2 4.6 4.3 0.0 1.0 99.9 684 12 5 170 60 51 30 890 51 8 52 108 115 53 40 1 24 41 41 54 81 83.9 129.0 0.0 4.0 1.0 642.3 316.3 325.1 0.9 0.2 0.0

76.6 0.1 13.0 0.9 0.0 0.0 0.2 3.9 4.7 0.0 0.5 99.9 753 26 10 110 39 41 27 2400 129 15 27 80 94 34 25 1 15 24 27 35 49 51.6 78.4 0.0 6.8 1.0 435.5 231.8 202.8 1.1 0.3 0.1

76.8 0.0 13.6 0.7 0.0 0.1 0.1 4.6 4.1 0.0 0.3 100.2 936 16 5 53 67 14 31 1940 223 15 56 45 56 16 12 1 6 13 14 19 34 37.0 176.6 0.0 17.6 0.9 253.5 129.2 123.4 0.9 0.1 0.1

71.0 0.1 15.9 7.6 0.3 0.0 1.0 0.0 1.2 0.0 2.8 99.8 791 2 24 98 28 76 35 24,460 698 22 12 130 120 63 48 1 33 39 39 47 61 60.7 32.4 0.0 8.1 1.0 643.3 361.2 280.8 1.4 0.4 0.0

75.2 0.1 12.9 6.8 0.2 0.0 0.8 0.0 2.2 0.0 1.8 100.0 958 17 22 90 34 74 33 18,630 699 218 87 138 132 76 56 2 38 40 38 45 46 50.0 43.5 0.0 10.6 1.0 661.6 402.9 256.5 2.0 0.7 0.1

74.7 0.0 14.0 3.5 0.3 0.0 0.0 0.1 4.7 0.0 2.5 99.9 1848 23 13 42 96 3 46 2410 128 315 179 20 28 12 10 1 2 3 2 4 10 12.6 140.0 0.0 43.8 1.0 104.5 69.9 33.8 1.4 0.2 0.2

75.4 0.0 12.7 4.0 0.4 0.0 0.0 0.1 4.4 0.0 3.0 99.9 1823 16 21 35 57 3 40 2980 213 83 73 16 22 10 7 1 2 4 3 5 12 12.6 85.6 0.0 52.7 1.0 94.0 55.1 38.0 0.9 0.2 0.2

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Rock type

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Fig. 7. Geochemical diagrams for the rocks of the Bom Jardim granite and associated granodiorites. (A) A/CNK  A/NK (Maniar and Piccoli, 1989); (B) Rb  Nb þ Y (Pearce et al., 1984); (C) FeO*/MgO  Zr þ Nb þ Y þ Ce (Whalen et al., 1987); (D) Rb  Sr; (E) Sr  Ba; (F); Rb  Ba; (G) Rb/Sr  Ba/Rb; (H) Rb/Sr  Ba/Sr. The vectors in D, E and F indicate the influence of the fractionated mineral phases in the composition of the residual liquids (compiled from Dall’Agnol et al., 1999b). Abbreviations as in Fig. 6.

xenotime and apatite, providing REE enrichment in residual melt. The two varieties of GR show distinct REE patterns. GR1 has a REE pattern similar to that of BLMZG and BSG (Table 6, Fig. 9C). On the other hand, GR2 samples are impoverished in both LREE and HREE compared to the other studied rocks and their negative Eu

anomalies are less accentuated (Eu/Eu* w 0.70). The REE behavior suggests that the processes responsible for the origin of GR1 did not affect significantly the REE, whereas those forming the GR2 caused important mobility of REE with reduction of both LREE and HREE (Fig. 9C).

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Fig. 8. Trace element geochemical diagrams for the rocks of the Bom Jardim granite and associated granodiorites. (A) Zr  SiO2; (B) Nb  SiO2; (C) Y  SiO2; (D) Ga  SiO2; (E) F  SiO2; (F) Sn  SiO2; (G) F  Sn; (H) F  W. Symbols and abbreviations as in Fig. 6.

The REE patterns of the Bom Jardim granite are very similar to those of granites of the Velho Guilherme suite (Fig. 9E,F). BMZG of the Bom Jardim pluton is similar to the less evolved varieties of the Antonio Vicente pluton (Eu/ Eu* ¼ 0.21e0.35 and 0.20e0.33, respectively). BLMZG, BSG and

GR1 (Eu/Eu* between 0.03 and 0.1) display REE patterns extremely similar to those of Velho Guilherme, Mocambo, Benedita, and Ubim-sul plutons (Eu/Eu* ¼ 0.0e0.03), and also to the more evolved granites of the Antonio Vicente pluton (Eu/Eu* ¼ 0.06e0.2).

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Fig. 9. Chondrite normalized (Evensen et al., 1978) REE patterns for samples of the Bom Jardim granite and associated granodiorites (AeD), and granites of the Velho Guilherme suite (E,F, according to Teixeira et al., 2005) for comparison. Abbreviations as in Fig. 6.

3.5. Discussion 3.5.1. Petrographic and mineralogic evidences of the specialized character of the Bom Jardim granite The Bom Jardim monzogranites to syenogranites were altered in different intensities by post-magmatic processes. Biotite is the principal mafic mineral and amphibole occurs sporadically as pseudomorphosed crystals in the monzogranite rocks. Monzogranites and leucomonzogranites are the more abundant facies. Syenogranites and greisenized syenogranites dominate in the northern portion of the pluton and are mineralized in Sn and W (Ta, Nb). Small economic deposits were reactivated in the last years and are presently mined. The accessory mineral phases of the BMZG/BLMZG are fluorite, apatite, ilmenite, hematite, columbite, wolframite, thorite, xenotime, monazite, rutile, and rare cassiterite. In the BSG and GR, the main accessory phases are cassiterite,

wolframite, fluorite, topaz, sphalerite, thorite, columbite, galena, xenotime, monazite, rutile, ilmenite, and rare pyrite. Morphological and compositional variations of zircon crystals were investigated in all granitic facies. The BMZG/BLMZG display euhedral to subhedral zoned crystals, sometimes weakly altered and corroded. In the BSG the zircon crystals are subhedral to anhedral, slightly zoned and with corroded borders, commonly showing internal Ca-enriched patches. Zircon of the GR is comparatively smaller and anhedral, fractured, corroded, and commonly associated to monazite or with thorite inclusions. Zircon of the Bom Jardim granite is generally enriched in Hf, Y, Th, and U, showing low Zr/Hf ratios. This enrichment tends to increase from monzogranite toward syenogranite, while Zr/Hf decreases in this same direction. On the other hand, Hf-rich zircon grains from greisens may be alternatively explained as result of higher grade of granite fractionation within the upper part of the cupola prior

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greisenization. These are typical geochemical characteristics of Snspecialized granites. The SEM data showed that zircon of the Bom Jardim granite is similar to those of the other specialized granites of the South Pará, Pitinga and Rondônia tin provinces (Lamarão et al., 2007, 2010), suggesting that analyses of SEM-EDS can be used not only in the identification of detrital zircon grains derived from these rocks, but as a useful guide to a preliminary evaluation of the metallogenetic potential for tin of granites. In other words zircon compositional studies can be an important tool for exploration surveys of tin-specialized granites. 3.5.2. The Bom Jardim granites as a member of the Velho Guilherme suite The Bom Jardim granite is subalkaline, slightly peraluminous, shows within-plate signature and affinity with fractionated A-type granites (Fig. 7). Post-magmatic F-enriched fluids certainly played an important role in the origin of Sn and W mineralization associated with the more evolved facies and greisenized rocks of the Bom Jardim pluton. The alteration processes have modified the original compositions of the more evolved rocks, but they preserve their dominant geochemical characteristics. Teixeira et al. (2005) showed that the tin-mineralized members of the Velho Guilherme suite are extremely evolved, silica-rich rocks (SiO2 > 75 wt%) produced by magmatic fractionation and interaction with Fenriched fluids. Trace elements plots indicate that the Bom Jardim magma also evolved dominantly by fractional crystallization (Figs. 7 and 8) with subsolidus changes due to interaction with fluids. A similar behavior was also identified in the tin-specialized granites of the Velho Guilherme suite (Teixeira et al., 2002, 2005). Moreover, the REE fractionation patterns (Fig. 9) of the Bom Jardim granites are extremely similar to those of similar varieties of the Velho Guilherme suite. The Velho Guilherme suite is comprised of the Antonio Vicente, Serra da Queimada, Velho Guilherme, Mocambo, Ubim-sul and Benedita plutons, which include tin-specialized granite varieties (Teixeira et al., 2002). The Bom Jardim granites have similar mineralogy, geochemical compositions, REE patterns, and crystallization age, compared to the Velho Guilherme suite granites. Moreover, the more evolved granites and the greisens of the Bom Jardim pluton are mineralized in tin and W and plot in the field of Sn-bearing granites, coincidently with the evolved rocks of the Velho Guilherme suite, as indicated in the Sr  Rb/Sr plot (Fig. 10). The similarities observed between the granites of the Velho

Guilherme suite and the Bom Jardim granite allow to consider the latter as a pluton of this granite suite. 3.5.3. The relationships between the granodiorite and the Bom Jardim granites The granodiorite outcropping in the eastern border of the Bom Jardim pluton display distinct petrographic, mineralogical and geochemical characteristics when compared with the Bom Jardim granites, suggesting that they do not have any genetic link, even if apparently associated in the same pluton. Geochemically, these granodiorites are akin of the Archean sanukitoid rocks that occur in the Rio Maria Granite-Greenstone Terrain (Oliveira et al., 2006, 2009). 4. Conclusions The Bom Jardim pluton is a subcircular Paleoproterozoic anorogenic granite, intrusive in intermediate to felsic volcanic rocks of the Uatumã Group, formed of monzogranite and syenogranite varieties, affected in different intensities by post-magmatic alteration. The central-north part of the pluton is dominated by syenogranites and greisens mineralized in cassiterite, wolframite, fluorite, topaz, sphalerite, thorite, columbite, galena, xenotime, monazite and rutile. The granodiorite exposed in the eastern border of the pluton are petrographic and geochemically distinct of the Bom Jardim granite and should have an independent origin. The morphological and compositional variation identified through SEM-EDS analyses in the zircon crystals of the Bom Jardim granite can be a useful guide to evaluate the metallogenic potential of evolved granites for Sn-W, being an important tool for exploration surveys. In terms of geology, petrography, geochemistry, metallogenesis, and age, the Bom Jardim granite resembles the plutons that constitute the Velho Guilherme suite and should be included in this important granite suite. Acknowledgments The authors express special thanks to Roberto Dall’Agnol for helpful discussions, to colleagues of the Group of Research on Granite Petrology for support in petrographic work, and to the Geosciences Institute of Federal University of Pará. This research received financial support from PRONEX/CNPq (Proj. 103/98-Proc. 66.2103/1998), CNPq (R. Dall’AgnoldProc. 484524/2007-0) and CAPES/PROCAD (Proj. 0096/05-9). This paper is a contribution to the Brazilian Institute of Amazonia GeosciencesdGEOCIAM (INCT programdCNPq/MCT/FAPESPAdgrant. 573733/2008-2). References

Fig. 10. Sr  Rb/Sr plot (Lehmann and Mahawat, 1989) showing the distribution of the rocks of the Bom Jardim granite and associated granodiorites. Field of the Velho Guilherme suite is shown for comparison. Black circles indicate Ca-rich granites and Ca-poor granites according to Turekian and Wedepohl (1961). Modified from Teixeira et al. (2005). Symbols as in Fig. 6.

Almeida, J.A.C., Dall’Agnol, R., Oliveira, D.C., 2006. Geologia, petrografia e geoquímica do granito anorogênico Bannach, Terreno granito-greenstone de Rio Maria, Pará. Revista Brasileira de Geociências 36 (2), 282e295. Barbosa, A.A., Lafon, J.-M., Neves, A.P., Vale, A.G., 1995. Geocronologia Rb-Sr e Pb-Pb do Granito Redenção, SE do Pará: Implicações para a evolução do magmatismo proterozóico da região de Redenção. Boletim do Museu Paraense Emílio Goeldi. Série Ciências da Terra 7, 147e164. Barros, C.E.M., Dall’Agnol, R., Vieira, E.A.P., Magalhães, M.S., 1995. Granito Central da Serra dos Carajás: avaliação do potencial metalogenético para estanho com base em estudos da borda oeste do corpo. Boletim do Museu Paraense Emílio Goeldi, Série Ciências da Terra 7, 93e123. Belousova, E.A., Griffin, W.L., 2002. Igneous zircon: trace element composition as an indicator of source rock type. Contributions to Mineralogy and Petrology 143, 602e622. Blevin, P.L., Chappell, B.W., 1995. Chemistry, origin, and evolution of mineralized granites in the Lachlan Fold Belt, Australia: the metallogeny of I- and S-type granites. Economic Geology 90, 1604e1619. Collins, W.J., Beams, S.D., White, A.J., Chappell, B.W., 1982. Nature and origin of Atype granites with particular reference to southeastern Australia. Contributions to Mineralogy and Petrology 80, 189e200.

C.N. Lamarão et al. / Journal of South American Earth Sciences 38 (2012) 159e173 CPRM/DNPM, 1997. Programa levantamentos Geológicos básicos do Brasil. São Félix do Xingu, Folha SB-22-Y-B, Programa Grande Carajás. MME/SMM, Brasília-DF. Dall’Agnol, R., Costi, H.T., Leite, A.A.S., Magalhães, M.S., Teixeira, N.P., 1999a. Rapakivi granites from Brazil and adjacent areas. Precambrian Research 95, 9e39. Dall’Agnol, R., Oliveira, D.C., 2007. Oxidized, magnetite-series, rapakivi-type granites of Carajás, Brazil: implications for classification and petrogenesis of A-type granites. Lithos 93, 215e233. Dall’Agnol, R., Rämö, O.T., Magalhães, M.S., Macambira, M.J.B., 1999b. Petrology of the anorogenic, oxidized Jamon and Musa granites, Amazonian craton: implications for the genesis of Proterozoic A-type granites. Lithos 46, 431e462. Dall’Agnol, R., Scaillet, B., Pichavant, M., 1999c. An experimental study of a Lower Proterozoic A-type granite from the Eastern Amazonian craton, Brazil. Journal of Petrology 40, 1673e1698. Dall’Agnol, R., Teixeira, N.P., Magalhães, M.S., 1993. Diagnostic features of Tinspecialized anorogenic granites of the eastern Amazonia. Anais da Academia Brasileira de Ciências 65 (1), 33e50. Dall’Agnol, R., Teixeira, N.P., Rämö, O.T., Moura, C.A.V., Macambira, M.J.B., Oliveira, D.C., 2005. Petrogenesis of the Paleoproterozoic, rapakivi, A-type granites of the Archean Carajás Metallogenic Province, Brazil. Lithos 80, 101e129. Eby, G.N., 1992. Chemical subdivision of the A-type granitoids: petrogenesis and tectonic implications. Geology 20, 641e644. Evensen, N.M., Hamilton, P.J., ÓNions, R.K., 1978. Rare-earth abundances in chondritic meteorites. Geochimica & Cosmochimica Acta 42, 1199e1212. Fernandes, C.M.D., 2005. Geologia, geoquímica e geocronologia das vulcânicas do Grupo Uatumã, região de São Félix do Xingu (PA), Província Mineral de Carajás. M.Sc. thesis, Centro de Geociências, Universidade Federal do Pará, Belém, 136 p. Javier Rios, F., Villas, R.N.N., Dall’Agnol, R., 1995. O Granito Serra dos Carajás: 1. Fácies petrográficas e avaliação do potencial metalogenético para estanho no setor norte. Revista Brasileira de Geociências 25, 174e182. Juliani, C., Fernandes, C.M.D., 2010. Well-preserved Late Paleoproterozoic volcanic centers in the São Félix do Xingu region, Amazonian Craton, Brasil. Journal of Volcanology and Geothermal Research 191, 167e179. Kempe, U., Gruner, T., Renno, A.D., Wolf, D., René, M., 2004. Discussion on Wang et al. (2000) “Chemistry of Hf-rich zircons from the Laoshan I- and A-type granites, Eastern China”. Mineralogical Magazine 64, 867e877. Lamarão, C.N., Dall’Agnol, R., Silva, J.S., Soledade, G.L., 2010. Morphological and compositional variation in zircons of tin-specialized Paleoproterozoic A-type granites of the Amazonian craton: metallogenic implications. In: Tapani Ramo, O., Lukkari, Sari, Heinonen, Aku (Eds.), International Conference on Atype Granites and Related Rocks Through Time (IGCP-510); Helsinki-Finland, 2010. University HelsinkieDepartmente of Geosciences and Geography. Helsinki University Print, Abstract Volume. Lamarão, C.N., Dall’Agnol, R., Soledade, G.L., Silva, J.S., 2007. Variações composicionais de zircão em granitos anorogênicos proterozóicos do Cráton Amazônico: implicações metalogenéticas. Revista Brasileira de Geociências 37 (4), 693e704. Lehmann, B., Mahawat, C., 1989. Metallogeny of tin in central Thailand: a genetic concept. Geology 17, 426e429. Maniar, P.D., Piccoli, P.M., 1989. Tectonic discrimination of granitoids. Geological Society of American Bulletin 101, 635e643. Macambira, M.J.B., Lafon, J.M., 1995. Geocronologia da Província Mineral de Carajás: síntese dos dados e novos desafios. Boletim Museu Paraense Emílio Goeldi 7, 263e288. Machado, N., Lindenmayer, Z.G., Krogh, T.E., Lindenmayer, D., 1991. U-Pb geochronology of Archean magmatism and basement reactivation in the Carajás area, Amazon shield, Brazil. Precambrian Research 49, 329e354. Murali, A.V., Parthasarathy, R., Mahadevan, T.M., Sankar Das, M., 1983. Trace element characteristics, REE patterns and partition coefficients of zircons from different geological environmentsda case study on Indian zircons. Geochimica & Cosmochimica Acta 47, 2047e2052. Oliveira, M.A., Dall’Agnol, R., Althoff, F.J., 2006. Petrografia e geoquímica do Granodiorito Rio Maria da região de Bannach e comparações com as demais ocorrências no terreno Granito-Greenstone de Rio Maria-Pará. Revista Brasileira de Geociências 36 (2), 313e326.

173

Oliveira, M.A., Dall’Agnol, R., Althoff, F.J., Leite, A.A.S., 2009. Mesoarchean sanukitoid rocks of the Rio Maria Granite-Greenstone Terrane, Amazonian Craton, Brazil. Journal of South American Earth Sciences 27, 146e160. Paiva Júnior, A.L., 2006. Petrografia e petrologia magnética de rochas vulcânicas porfiríticas a SSE de São Félix do Xingu (PA), Província Mineral de Carajás. Trabalho de Conclusão de Curso. Instituto de Geociências, Universidade Federal do Pará, Belém, 50 p. Paiva Júnior, A.L., 2009. Geologia, Petrografia, Geocronologia e Geoquímica do Granito Anorogênico Seringa, Província Mineral de Carajás, SSE do Pará. M.Sc. thesis, Instituto de Geociências, Universidade Federal do Pará, Belém, 123 p. Pearce, J.A., Harris, N.B.W., Tindle, A.G., 1984. Trace element discrimination diagrams for the tectonic interpretation of granitic rocks. Journal of Petrology 25, 956e983. Peng, C.C.J., 1970. Intergranular albite in some granites and syenites of Hong Kong. American Mineralogist 55, 270e282. Pinho, S.C.C., 2005. Petrografia e Geocronologia da borda ENE do Granito Serra da Queimada e da borda SE do Granito Bom Jardim, Província Estanífera do Sul do Pará. Trabalho de Conclusão de Curso. Instituto de Geociências, Universidade Federal do Pará, Belém, 41 p. Pinho, S.C.C., 2009. Geologia, petrografia e geoquímica do Granito Bom Jardim, região de são Félix do Xingu, Província Mineral de Carajás. M.Sc. thesis, Instituto de Geociências, Universidade Federal do Pará, Belém, 121 p. Streckeisen, A.L., 1976. To each plutonic rock its proper name. Earth Science Review 12, 1e33. Tassinari, C.C.G., Macambira, M.J.B., 2004. Evolução tectônica do Cráton Amazônico. In: Manteso-Neto, V., Bartorelli, A., Carneiro, C.D.R., Brito-Neves, B.B. (Eds.), Geologia do Continente Sul-Americano: evolução da obra de F.F.M. Almeida. BECA, São Paulo, pp. 471e486. Taylor, R.G., Pollard, P.J., 1988. Pervasive hydrothermal alteration in tin-bearing granites and implications for the evolution of ore-bearing magmatic fluids. Recent Advances in the Geology of Granite-Related Mineral Deposits. Canadian Institute Mining Metallurgy Special Volume 39, 86e95. Teixeira, N.P., 1999. Contribuição ao estudo das rochas granitóides e mineralizações associadas da Suíte Intrusiva Velho Guilherme, Província Estanífera do Sul do Pará. Doctoral thesis, Instituto de Geociências USP, São Paulo, 508 p. Teixeira, N.P., Bettencourt, J.S., 2000. Velho Guilherme Intrusive Suite, Pará, Brazil: petrogenetic aspects and associated mineralization. In: International Geologic Congress, 31, Rio de Janeiro. Abstract. Granite Systems and Proterozoic Lithospheric Processes, IGCP-426, IAGC/IMA. Teixeira, N.P., Bettencourt, J.S., Dall’Agnol, R., Moura, C.A.V., Fernandes, C.M.D.F., Pinho, S.C.C., 2005. Geoquímica dos granitos paleoproterozóicos da Suíte Intrusiva Velho Guilherme, Província Estanífera do Sul do Pará. Revista Brasileira de Geociências 35 (2), 217e226. Teixeira, N.P., Bettencourt, J.S., Moura, C.A.V., Dall’Agnol, R., Macambira, E.M.B., 2002. Archean crustal sources for Paleoproterozoic tin-mineralized granites in the Carajás province, SSE Pará, Brazil: Pb-Pb geochronology and Nd isotope geochemistry. Precambrian Research 119, 257e275. Turekian, K.K., Wedepohl, K.H., 1961. Distribution of the elements in some units of the Earth’s crust. Geological Society of America Bulletin 72, 172e202. Uher, P., Breiter, K., Klecka, M., Pivec, E., 1998. Zircon in highly evolved Hercynian Homolka Granite, Moldanubian Zone, Czech Republich: indicator of magma source and petrogenesis. Geologica Carpathica 49 (3), 151e160. Vance, J.A., 1965. Zoning in igneous plagioclase: “Patchy Zoning”. Journal of Geology 73 (4), 636e651. Vance, J.A., 1969. On Synneusis. Contributions on Mineralogy and Petrology 24, 7e29. Vasquez, M.L., Macambira, M.J.B., Armstrong, R.A., 2008. Zircon geochronology of granitoids from the western Bacajá domain, southeastern Amazonian craton, Brazil: Neoarchean to Orosirian evolution. Precambrian Research 161, 279e302. Villas, R.N.N., 1999. Granito Pojuca, Serra dos Carajás (PA): composição mineralógica, química mineral e controles químicos da alteração hidrotermal. Revista Brasileira de Geociências 29 (3), 393e404. Wang, R.C., Zhao, G.T., Lu, J.J., Chen, X.M., Xu, S.J., Wang, D.Z., 2000. Chemistry of Hfzircons from the Laoshan I- and A-type granites, Eastern China. Mineralogical Magazine 64, 867e877. Whalen, J.B., Currie, K.L., Chappell, B.W., 1987. A-type granite: geochemical characteristics, discrimination and petrogenesis. Contributions to Mineralogy and Petrology 95, 407e419.