Perspectives for Li- and Ta-Mineralization in the Borborema Pegmatite Province, NE-Brazil: A review

Accepted Manuscript Perspectives for Li- and Ta-Mineralization in the Borborema Pegmatite Province, NEBrazil: A review Hartmut Beurlen, Rainer Thomas, Marcelo R. Rodrigues da Silva, Axel Müller, Dieter Rhede, Dwight Rodrigues Soares PII:

S0895-9811(14)00101-1

DOI:

10.1016/j.jsames.2014.08.007

Reference:

SAMES 1304

To appear in:

Journal of South American Earth Sciences

Received Date: 27 February 2014 Accepted Date: 6 August 2014

Please cite this article as: Beurlen, H., Thomas, R., da Silva, M.R.R., Müller, A., Rhede, D., Soares, D.R., Perspectives for Li- and Ta-Mineralization in the Borborema Pegmatite Province, NE-Brazil: A review, Journal of South American Earth Sciences (2014), doi: 10.1016/j.jsames.2014.08.007. This is a PDF file of an unedited manuscript that has been accepted for publication. As a service to our customers we are providing this early version of the manuscript. The manuscript will undergo copyediting, typesetting, and review of the resulting proof before it is published in its final form. Please note that during the production process errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain.

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ACCEPTED MANUSCRIPT PERSPECTIVES FOR Li- AND Ta-MINERALIZATION IN THE BORBOREMA PEGMATITE PROVINCE, NE-BRAZIL: A REVIEW 1

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Hartmut Beurlen , Rainer Thomas , Marcelo R. Rodrigues da Silva , Axel Müller , Dieter Rhede 4 Dwight Rodrigues Soares

1: Department of Geology, Federal University of Pernambuco, Rua Acad. Helio Ramos, sn, 50740-530 Recife, Brazil [email protected]

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2: Helmholtz-Zentrum Potsdam (GFZ) Telegrafenberg, D -14473 Potsdam, Germany 3: Geological Survey of Norway, Leiv Eirikssons vei 39, 7491, Trondheim, Norway

4: Instituto Federal de Educação, Ciência e Tecnologia da Paraíba (IFPB), R. Tranquilino Coelho Lemos 671, 58100–000, Campina Grande – Paraíba, Brazil

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ABSTRACT The increasing strategic importance of Li- and Ta-ores during the last decades due to the strong consumption growth for rechargeable batteries and high temperature and corrosion resistant capacitors reactivated the interest of studies in pegmatite fields around the world, because these rocks supply respectively 25% and 100% of the world consumption in these elements. Research on petrogenetic issues and major and accessory mineral chemistry variations in rare element (REL)-pegmatites of the Borborema Pegmatite Province in Northeast Brazil were tested as tools for the diagnosis of the metallogenetic potential of rare metals in individual pegmatites and in the province as a whole along the last dozen of years. The results allowed to establish the nearly isobaric (3.8 kbar) crystallization conditions of the REL-pegmatites between approximately 580°C (liquidus) and 400 °C (solidus) from a peraluminous melt saturated in an aquo-carbonic medium to low salinity volatile phase and an immiscible peralkaline flux-enriched (H2O, CO2, F, B, Li etc.) melt fraction, based on melt and fluid inclusion studies. Mineral-chemistry data from 30 selected REL-pegmatites in the province allowed to classify three of them as being of the complex-spodumene or -lepidolite subtype in Černý’s classification. Both subtypes are supposed to be potentially fertile, (highly fractionated, and with good chances to bear Li- and Ta-ore concentrations). It was also possible to identify several pegmatitic granite intrusions with textural and lithogeochemical characteristics also found in source granites of REL-pegmatite provinces elsewhere. Preliminary chemical Pb/U/Th geochronological determinations in uraninite and xenotyme crystals of these granites indicate an age of 520 ± 10 Ma and match recently published Ar/Ar in mica and U/Pb ages in columbite-group minerals (CGM) of the REL-pegmatites between 509 and 525 Ma. Mineral-chemistry data from grains of the outer zones of the pegmatites do not allow to distinguish potentially fertile from barren pegmatites. This discrimination is possible only if samples of the inner intermediate zone, replacement pockets or quartz core are used. From the tested minerals trace-element determinations (mainly Li, Al, Ti, Ge, B among 14 tested elements) by LA-ICP-MS technique in quartz seem to be more efficient than the classical approach (of Rb, K, Cs, Ga, Sr Ta, ) in K-feldspar or micas, due to the susceptibility to hydrothermal or supergene alteration of the latter. Mineral-chemistry variations in CGM, tourmalines, garnet and gahnite turned out to be efficient discriminators but all of them have the disadvantage of an eventual and, if present, random distribution, typical for accessory minerals in pegmatites, not allowing a regular sampling in most cases. Additional tests are recommended to confirm respectively the preliminary results of mineralchemistry as exploration tools on a larger number of pegmatites and geochronological data to confirm the existence of another, older, synorogenetic generation of REL-pegmatites in the BPP. Keywords: Neoproterozoic REL-pegmatites, mineral-chemistry, source granites, petrogenesis.

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ACCEPTED MANUSCRIPT 1. Introduction

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The Borborema Pegmatite Province (Scorza, 1944) (BPP), in northeastern Brazil has been known since World War I, when it was exploited for white mica. At the end of World War II, it became famous as one of the most important Ta-Be producers of the world and for the production of beautiful specimens of “exotic” tantalum-niobium minerals, from the type locality for many of them. Tantalum-exploration activities and the first systematic geological studies in the 1940’ies, produced schematic geological maps of the most important pegmatites, a record of the production data and the distinction between homogeneous (usually sterile) and heterogeneous pegmatites (potentially enriched in Be-Li-Ta). A fourfold zoned internal architecture of the pegmatites was recognized by Johnston Jr. (1945) and Rolff (1946). The recognized zones numbered I to IV, correspond respectively to the border, wall, intermediate and quartz core zones, later distinguished by Cameron et al. (1949) in pegmatite fields of USA. In the 1960s, a French Geological Mission, in collaboration with the regional development agency “Superintendência do Desenvolvimento do Nordeste” (SUDENE), reactivated exploration activities and research in the BPP, culminating in the organization of a database with records of over 400 mineralized pegmatites. Most of them include detailed geological sketches and information of host rocks, mineral paragenesis, controls of mineralization, regional geology and production data. The most important conclusions are discussed in a final report published by Roy et al. (1964). Several new databases developed as late as 1990 expanded the number of known mineralized pegmatites to over 700 bodies, with each record including location on air-photos and mineralogical data, but poor in important geological or petrological information. Most publications about the BPP from 1969 to 1990 were dedicated only to purely mineralogical aspects. The local production of Ta ore concentrates since 1970 oscillated, very much influenced by the very variable market prices and climate changes. During periods of more intensive droughts, a considerable increase of production of tantalum-ore concentrates occurs by informal hand-picking activity, reaching down to 20 or 30 meters below the surface under the light of candles, and becomes the main “economic” supply of people living in areas of known fertile pegmatites. There are no official records about the real Ta-production in the BPP, mostly sold in free markets to be included in the production of some regular mines in southern Brazil. Since the 1990s, the BPP become important again, mainly as supplier of raw materials for the increasing Brazilian ceramics industry, production of dimension stones and the discovery of the “Paraíba tourmaline”. This highly prized turquoise blue copper-bearing tourmaline reaches values up to US$ 20,000 per carat in top-quality specimens and is the most famous product of the BPP nowadays. In addition, the rapidly increasing need of Ta and Li, respectively for high-temperature and chemically resistant capacitors and rechargeable batteries, reinforced the worldwide strategic importance of pegmatites (Linnen et al., 2012) as an exclusive source of high-grade Ta-ores and as important source of Li ore, accounting for about 25% of the world supply (Sweetapple, 2013). In spite of this importance, most research remained almost exclusively dedicated to mineralogical aspects. Several important metallogenic and petrological questions in the BPP still remain unsolved or have never been systematically addressed. These include the understanding of the regional distribution of different pegmatite types, the identification of the granitic (or other) source, a modern classification and an improvement in the ability to distinguish between sterile and fertile REL-pegmatites (REL stands for Rare Element enriched) and a comparison with other better studied pegmatite fields worldwide. The authors along the last 15 years made an attempt to use the classification criteria proposed by Černý (1982, 1989a, 1991), updated by Černý and Ercit (2005)*1), using paragenetic (type minerals) and geochemical properties, geotectonic setting and several mineral-chemical techniques at a few selected well-known pegmatites in the BPP. The final aim of this approach was to improve the efficiency of the prognosis of the

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metallogenic potential of individual pegmatites or groups of them. The results, with support of new field observations, and a few new petrological and geochronological data will be the main focus of this review. *1) In spite of many problems verified in the attempt to use Černý’s classification in the BPP, it will be used along this text because it is nowadays the most widely used in the literature about pegmatites. Its terminology will be therefore easily understould. Details of the main problems verified are discussed with more details in section 2.4 and introduction of section 4.

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2. Geology of the Borborema Pegmatite Province (BPP) 2.1. Regional geological setting of the BPP

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The Borborema Pegmatite Province (BPP) extends NNE between 5°30’ and 7°15’ and 35°45’ and 37°15’ W, over an area of approximately 75 x 150 km, along the eastern part of the Seridó Belt (SB) in the central part of the Northern Tectonic Sub-Province (NTSP) of the Borborema Tectonic Province (Brito Neves and Fuck, 2013) (Fig. 1). The SB and the BPP are limited in the south by the Patos Lineament, a major, transcontinental shear-zone (with prolongation extending NE along the “Nigeria Schist Belts” with the name of Garoua Lineament). The SB is composed by Paleoproterozoic gneissic-migmatitic basement rocks known as the Caicó Complex, with small Archean nuclei, covered by a supracrustal sequence of Neoproterozoic metasedimentary rocks (van Schmuss et al., 2003) preserved in large synformal structures, with very subordinate metavolcanic intercalations, known as Seridó Group. The Seridó Group is composed by a basal unit, the Jucurutú Formation, which consists of calc-silicate gneisses with intercalations of marble and tungsten bearing skarn, hosting several scheelite mines, followed upward by the Equador Formation (quartzites, metaarkoses and metaconglomerates) and the Seridó Formation, with banded garnet-cordierite-sillimanitebiotite-gneisses and schists, with some marble, calc-silicate rock and orthoamphibolite intercalations at the base. The Seridó Group hosts over 90% of the mineralized pegmatites of the BPP, with 80% being hosted by the Seridó Formation, 10% in the Equador Formation and the remaining 10% distributed within granites, the Jucurutú Formation or basement gneisses and granites.

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Figure 1 Simplified regional geologic map compiled from Brasil (1998 and 2002) with delimitation of the Borborema Pegmatite Province and location of the studied pegmatites, modified from Beurlen et al. (2011a). 2.2. Possible sources of the pegmatite forming magma A great variety of granite types in the Seridó Belt (SB) were categorized by Jardim de Sá et al. (1981) as phases G1 to G4. The group G1 refers to orthogneisses restricted to the Paleoproterozoic or even older nuclei, which underlie the supracrustal Neoproterozoic Seridó Group. The G2 granites (with three subgroups) were originally considered to be strongly deformed granites (low-angle foliation parallel to isoclinal folding) intruded in the supracrustal sequence as early-tectonic orthogneisses, but were later recognized as being also part of the Caicó Complex (Jardim de Sá, 1994). The G3 granites (including G3A to G3C subgroups) are syn- to late-tectonic granites usually with a distinct vertical to subvertical foliation parallel to axial planes of open folds. Group G4 includes post-deformation granites with only very local weak signs of deformation related to NNE shear zones. Because of their pervasive signs of pre- or early-orogenic deformation, G1 and G2 granites can be excluded as source of the largely undeformed Be-Li-Ta-mineralized pegmatites, which are mostly related

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to tension gashes (NE) and extension related fractures (E-W) coeval with a late-orogenic Neoproterozoic transpressional tectonic regime of the Ediacaran “Brasiliano-Pan African” orogeny (Araújo et al., 2001). Phase G3 and G4 granites occur as several intrusions with random distribution in the SB. Unfortunately, the geological maps of the SB do not provide a clear distinction of the numerous facies types in G3 and G4 intrusions. The G3 granites can probably be excluded because of ages in the range 580 ± 30 Ma (Jardim de Sá, 1994; Legrand et al., 1991; Jardim de Sá et al., 1986; Brito Neves and Fuck, 2013). The G4 granite group, among other types of granites, includes some independent intrusions of so-called “pegmatitic granites” identified by Da Silva (1993) and Da Silva et al. (1995) as GR3A and GR3B granites. Da Silva (1993) considered these to be the most probable source of the Be-Li-Tabearing pegmatites, formally classified as REL-pegmatites according to Černý (1982, 1991). Many of these pegmatitic granite bodies are not distinguished on the available geological maps. Fortunately in the early 2000s some such bodies became well exposed in a few quarries for exploitation as export-quality ornamental dimension stones. This lead to the recognition of a cyclic decimeter- to meter-sized banding of four different facies (Fig. 2). These facies resemble those described by Černý et al. (2005) in the source- and host-granites of Li-bearing pegmatites at Greer Lake, Manitoba Canada, and of other REL- pegmatite fields elsewhere around the world. The four facies, following the nomenclature proposed by Černý et al. (2005), are: 1) “fine grained leucogranite”; 2) “pegmatitic leucogranite” with randomly oriented graphic K-feldspar megacrysts; 3) “layered sodic aplite” (commonly garnetiferous) similar to the line rocks of Webber et al.(1997, 1999); 4) potassic pegmatite (with combstructured wedge-shaped megacrysts of K-feldspar). The comparison of the petrographic and geochemical features, like the presence of garnet and tourmaline as accessory phases, REE distribution (Fig. 3), normative corundum (> 1, up to 4), normative Qz-Ab-Or and An-Ab-Or, plots and {Al-(K+Na+2Ca)} versus {Fe+Mg+Ti}) made by Beurlen et al. (2009b) between the BPP and Greer Lake are striking. These features are typical for S-type leucocratic granites. Some intrusions of this pegmatitic granite in the BPP are localized in Fig. 1. Preliminary dates younger than 540 Ma (see next section) support the supposition of a genetic relationship with the mineralized pegmatites. The pegmatitic granites and the related pegmatites would therefore represent a short recurrent collisional tectonic stage, not yet recognized by Brito Neves and Fuck (2013) in the Borborema Tectonic Province, much younger than the main collision at 580 ± 30 Ma, the “Brasiliano” (= Panafrican, Ediacaran) orogeny, but with a similar counterpart in the Eastern Domain of the Northern Mantiqueira Province as documented by Pedrosa et al. (2011) in the Eastern Brazilian Pegmatite Province (State of Minas Gerais and small parts of Bahia and Espírito Santo). The real genetic relationship between the pegmatites and the pegmatitic granites still needs to be better investigated. As the similar age alone is not sufficient to prove that a) the pegmatites were formed as products of differentiation of several pegmatitic granite intrusions, alternative hypotheses of pegmatite/granite relations must be considered, as: b) both, pegmatitic granites and REL-pegmatites are formed as differentiation products from another hidden larger granite intrusion (indeed, most older contributions to the literature on pegmatites in the BPP implicitly assume the origin of the pegmatites as residual melts from a hidden unknown granitic source); c) some of the REL-pegmatites are derived from a hidden intrusion and others from the pegmatitic granites; d) a still more complex relation, some REL-pegmatites are apophyses of other REL-pegmatites (this relation is observed at the Capoeira 2 pegmatite where fine- to medium-grained quartz-albite-black tourmaline rocks are formed by segregation of residual melt from the still-crystallizing intermediate zone of the main pegmatite, cross-cutting the earlier pegmatite zones and invading the common metaconglomerate host forming meter sized apophyses Fig. 4 ) e) REL-pegmatites and pegmatitic granites are both products of different degrees of “palingenesis”, as initial nearly “in situ”

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Figure 2 Cyclic banding of four typical petrographic facies of the pegmatitic granites, supposed to be the source-granites of the REL-pegmatites in the BPP, modified from Beurlen et al. (2009a). pegs = pegmatitic facies, with centripetal unidirectional texture; PG = pegmatitic granite with unidirectional upward growth texture; BA = banded sodic aplite; LG = leucocratic medium grained granite. At the left above above the head of R. Martin, a magnified insert corresponds to the green rectangle at the right.

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F igure 3 Rare earth element distribution (chondrite normalized according to Nakamura, 1974) A) in the pegmatitic-granites in the BPP compaired with B) counterparts from Canada according to Černý et al. (2005), modified from Beurlen et al. (2009a). Symbols stand for: A) open triangles = GR3B porphiritic and pegmatittic fácies; solid triangles G3B, equigranular fine to médium grained leucogranite facies; gray area data of other granites in the area (Da Silva etal 1995); B) open triangles pegmatite facies; solid triangles banded sodic aplite; solid circles fine grained leuco granite, open circles=pegmatitic leocogranite (Černý et al. 2005).

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The existence of several smaller source intrusions in the BPP, instead of a single large central source granite intrusion (alternative a) above) could explain the apparent lack of a regional distribution of REL-pegmatite types organized according their degree of fractionation, increasing with the distance from the center of the province, as observed in many other provinces elsewhere. A complex, random or even anomalous distribution of RELpegmatite types could be the result of the overlap of normal distribution patterns in several smaller pegmatite fields, each one related to its own smaller granite source, exposed in different erosion levels. This could be in part the reason of the anomalous scheme of distribution of the pegmatite types in the BPP, with an apparent reversal in regional zoning as proposed by Cunha e Silva (1983) (Fig.5) (see section 2.4). It is also important to realize that the possible granite-pegmatite relations described as a) to e) above are not mutually exclusive, and that the combination of them will result in more complex patterns of distribution. Somewhere here insert Fig. 4 1 column wide

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Figure 4 Apophyses of albite-quartz-tourmaline pegmatites formed from residual melts of the lepidolite-spodumene-complex Capoeira 2 pegmatite in the BPP, modified from Beurlen et al. (2011a). IIZ = inner intermediate zone (mainly quartz, albite and some spodumene and black tourmaline fringe); a = quartz + albite dominant apophyses; WZ = wall zone. The insert in the lower right is a view of the floor with albitic apophyses (yellow arrows labeled with a) invading the hosting metaconglomerates (C). Note the black tourmaline strings along the contact of a large apophysis, directly connected with the main pegmatite body. Small white feeder veinlets (v labels) are originated from the IIZ and crosscut the external pegmatite zones to form the apophyses.

2.3. Geochronological support for pegmatite genesis in the BPP The geochronological database for the great variety of granite types and pegmatites in the SB unfortunately is still very poor and, yet more problematic, deficient in more recent (and supposedly more precise) data. The orthogneisses G1 and G2 in the basement of the Seridó

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Belt are mostly Paleoproterozoic in age, but a few samples of Archean ages are known (Dantas et al., 2013). The geochronological data for the syn- to late-tectonic G3 phase range mostly between 580 and 550Ma, with a few dubious older outliers. These results support the hypothesis that these ages represent the peak deformation and metamorphic stages of the Brasiliano orogeny (Jardim de Sá, 1994; van Schmus et al. 2003). Data on G4 pegmatitic granites (only two data are available so far, respectively 528 ± 12 Ma and 520 ±10 Ma) and REL-pegmatites spread even wider, between 460 and 553 Ma according to several authors and methods, as shown in Table 1. The mineralized pegmatites of the BPP are attributed to the same generation of late tectonic pegmatites, based on structural geological observations by Araújo et al. (2001, 2005 and references therein). Taking into account that the complete crystallization of RELpegmatites occurs in very small time intervals, in the order of less than a few thousand years (thick abyssal bodies), in some cases in weeks (meter thick in greenschist terranes) as demonstrated based on cooling models by Webber et al. (1999), the large spread of geochronological data (460 to 553 Ma, see Table 1) observed in the local literature is very probably the result of analytical errors and misinterpretations of data. New, more precise data are urgent to be acquired. The rapid cooling and crystallization of REL-pegmatites are also strong arguments against a relation between the pegmatites and G3 granites. The dominant assumption that all pegmatites in the BPP belong to the same generation (same age and source) is probably an oversimplification, reflecting in part the simplistic distinction between homogeneous (thus sterile) and heterogeneous (thus potentially fertile) pegmatites, without consideration of recent advances in petrogenetic models favoring very rapid crystallization (Fenn and Swanson, 1992, Webber et al., 1999).The classical concept that large crystals need geologically long times to form is no longer accepted. In the BPP, there are homogeneous pegmatites nearly concordant with and interlayered in meta-sediments of the Seridó Group, in the areas of highest metamorphic grade (type a), nearly synchronous with the peak metamorphism and deformation of the SB, with inferred ages between 550 and 580 Ma. These must be clearly distinguished from tabular, discordant, late- or post-tectonic homogeneous sterile pegmatites (type b) emplaced in the same tension gash veins or extension fractures as the heterogeneous Be-Li-Ta-bearing REL-pegmatites. Type b) homogeneous pegmatites are those refered by Johnston Jr (1945) and Rolff (1946), whereas type a) homogeneous pegmatites are actually anatectic, abyssal according to Černý et al., (1982) or forming the neosomes in migmatitic meta-sediments (Ebert 1970). Type a) homogeneous pegmatites are those refered by Agrawal (1992) and Araújo et al. (2001), but were not clearly separated from the other ones during their genetic considerations. Other homogeneous pegmatites in migmatites of the Caicó Complex (type c) must also be distinguished from the former ones, and also from the distal homogeneous rare earth-elementbearing pegmatites (type d) referred by Cunha e Silva, (1983). The observation of some RELpegmatites hosted in biotite schists of the Seridó Formation that were submitted to high-grade metamorphism and deformation, as indicated by the paragenesis chrysoberyl-sillimanitequartz, suggests the existence of an additional older (synorogenic ?) generation of Be-Sn-Ta bearing REL-pegmatites (Beurlen et al., 2013). New geochronological data are necessary to test this possibility.

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ACCEPTED MANUSCRIPT Insert Table 1, may be as a whole page in landscape format Rock

Method

Mineral

Age Ma

Source

Capoeira Mamões Malhada Vermelha Combi Carnaubinha Trigueiro

pegmatite pegmatite pegmatite

Pb/U s Pb/U Pb/U

Columbite* columbite columbite

509±2.9 514±1.2 510±0.4

Baumgartner et al. Baumgartner et al. Baumgartner et al.

pegmatite pegmatite pegmatite

Pb/U Pb/U Pb/U

columbite columbite columbite

513.7±1.5 514.9±1.1 511.6±2.6

Baumgartner et al. Baumgartner et al. Baumgartner et al.

Boqueirão

pegmatite

Ar/Ar

523.4±1.1

Araujo et al. (2005)

several several several Boqueirão, Seridozinho several

pegmatite pegmatite pegmatite pegmatite

Rb/Sr Rb/Sr K/Ar K/AR K/Ar, Rb/Sr U/Pb

biotite thorianite white mica K-feldspar white mica Lepidolite muscovite

483 to 514 540 450 to 520 450 to 462 475 to 512 460 to 510

Almeida et al. (1968 Almeida et al. (1968 Almeida et al. (1968 Dirac and Ebert (19

Carnaúba dos Dantas Picuí

pegmatitic granite pegmatitic granite pegmatite other granites

528±12

Baumgartner et al.

U/Pb EMP

Monazite, “Brabantite”* xenotime- uraninite -

520±10

Beurlen et al. (2009

Ar/Ar Pb/U

biotite zircon

553±4 555 to 580

Santiago et al. (201 Jardim de Sá (1994

Pb/U

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uraninite

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Lages (Bonfim) several

pegmatite

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Locality

Ebert (1970)

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Table 1 Synopsis of geochronological data describing the Borborema pegmatites. *by columbite is meant a member of the columbite group minerals; new valid name for Brabantite is Cheralite. 2.4. Internal zonal structure and classification

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The classical distinction of heterogeneous (potentially mineralized) versus homogeneous (sterile) pegmatites as proposed by Johnston Jr (1945) and still used in the BPP until recently, does not account for the many transitional types of internal zonal architecture observed in pegmatites. Another problem with the classification of pegmatites simply as homogeneous or heterogeneous, or also as types and subtypes according to Černý and Ercit (2005), is that there are at least four different types of Neoproterozoic homogeneous pegmatites in the BPP, as discussed in detail in the last paragraph of section 2.3. In a more elaborate classification based on internal architecture, Vlasov (1952) distinguishes: A) equigranular or graphic homogeneous pegmatites; B) poorly zoned pegmatites with blocky K-feldspar zone in the center; C) well-zoned pegmatites with a quartz core and incipient replacement pockets; D) well-zoned pegmatites with rare-element minerals concentrated in common replacement pockets or albite-rich inner intermediate zone at the transition between the blocky feldspar zone and quartz core; and E) albite -spodumene pegmatites with erased primary zonal structure due to intensive replacement. This scheme puts the different types side by side, almost forming a continuum with increasing degree of fractionation, replacement and potential of accessory minerals of economic interest in this order: sterile, Be-bearing, Be-Li-Ta-bearing etc. This scheme is not a real geological map of a single pegmatite but suggests that a single pegmatite may change its internal zonal structure along strike or depth. A comparison of this scheme with the actual detailed geological map of the Boqueirão Pegmatite (also referred to as Cabeço in the literature) in the BPP (Fig. 6)

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seems to be a very striking demonstration that this can occur in real cases and certainly is not rare. A vertical change in the zonal structure and accessory mineral contents was confirmed in Somewhere here insert Fig. 5 2columns wide Figure 5 Regional distribution of pegmatite types a) according to Cunha e Silva (1983) and b) comparison with a complex distribution model due to overlapping.

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some other pegmatites in the BPP, where records of the historical evolution of the production are available. This is the case of the Quintos Pegmatite, known under the name “Beryl mine” in the 1970s, because this was the only mineral of economic interest found at the surface at that time, with no mention of tourmaline as an accessory mineral. Two decades later, the exploitation advanced 20 to 30 meters below surface and the color-zoned elbaite was discovered. Since then the pegmatite became a mine of “Paraíba tourmaline”, very rich in albite, lepidolite, elbaite and spodumene at the transition between the intermediate zone and the quartz core and in black tourmaline at the border zone. A similar history reported by Heitor Barbosa (the discoverer of the occurrence) is mentioned by Wilson ( 2002): at the famous S. José da Batalha mine, originally mined near the surface only for kaolin, there was a very small production of tantalite-(Mn) as by-product and no reference to elbaite. A few years later and 20 to 40 m below surface the first “Paraíba” elbaite was found and the pegmatite became the first and most famous “Paraíba tourmaline” mine. The inverse story occurred at the Carrascão pegmatite, very enriched in black tourmaline at the border zones and explored at surface for green elbaite (some with a Paraíba tourmaline core) at the transition of the inner intermediate, albite-lepidolite rich zone to the quartz nucleus. A few years after the discovery and 20 m below surface, this pegmatite became sterile for colored elbaite and very poor in black tourmaline, restricted to the border zone in the roof. These examples are a clear demonstration that the classification of a pegmatite based only on near-surface evidence does not really work well for exploration purposes, even if very helpful for classification of well known and deeply mined cases.

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Here at the end of a page insert Fig. 6 Figure 6 Detailed geological sketch of the Boqueirão (= Cabeço) pegmatite (modified from Tavares, 2001) compaired with the model of the classification of pegmatites based on internal structure proposed by Vlasov (1952).

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There is an additional complicating factor of the simplistic model of internal zonal architecture of pegmatites and the presence of diagnostic-type accessory minerals and its use for the prognosis of the metallogenetic potential: many (perhaps most) zoned pegmatites do not present a regular symmetrical zoning. It is well known from many examples worldwide that in low-dip tabular pegmatites, a quite asymmetric zoning is the rule rather than the exception. The famousTanco pegmatite and “layered pegmatites” (e.g., Little Three and many others) in general (London, 2008) are clear examples. In these gently dipping pegmatites, the more fractionated and fertile zones, replacement bodies and miaroles, and therefore parts richer in accessory minerals of economical interest (Ta and Cs in Tanco, Stilling et al., 2006) are thicker or restricted to the upper part of the pegmatite, e.g., as the almost monomineralic Cs- (pollucite-) and lepidolite-zones in Tanco. This is also observed in the BPP, where a few low-dip pegmatites, like Tanquinhos (synformal) are referred as those with the highest production in Ta ore concentrates (Johnston Jr, 1945). Other strikingly similar examples in the BPP are aquamarine-producing pegmatites in the fields of Tenente Ananias (200 km northwest of the BPP, in the northwest of the State of Rio Grande do Norte, where the pockets rich in gem-quality aquamarine are restricted to low-dipping and plunging portions (inflexions identified as “canoes” in the local terminology) alternating with steeply dipping portions poor in beryl (Barreto, 1999). The same “pinch and swell” pattern is found in the

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BPP in the Pitombeira pegmatite group, also exploited for aquamarine. Here, the better zoned and more gently dipping pegmatite portions are the preferred loci of gem-quality bearing pockets found along the contacts of discontinuous shallowly plunging pod-shaped segments of the quartz core, enveloped by a thin intermediate zone. These better zoned portions alternate with thinner nearly homogeneous steeply dipping portions of the pegmatite (Beurlen et al., 2006; 2007). The same pinch and-swell pattern is repeated at the Corredor – Roncadeira pegmatite group (Beurlen et al., 2013) and probably at the “Paraíba tourmaline” (“PT”) mine of the Quintos pegmatite, where the inner intermediate zone of “PT” + albite + quartz follows along 30 meters with a smooth dip in contact with the quartz core, in a generally steeply dipping pegmatite Beurlen et al. (2011a). A tentative classification of BPP pegmatites according to the first proposal by Černý (1982, based in part on Ginzburg and Rodionov, 1960 and references therein) and updated by Černý and Ercit (2005), was tested on over 30 remapped Be-Li-Ta bearing pegmatites by Da Silva (1993) and Beurlen et al. (2008), in addition of several homogeneous supposedly sterile pegmatites with columbite-(Fe) as only minor accessory ore-mineral. Five subtypes of heterogeneous REL-pegmatites could be recognized, namely: a) homogeneous (columbite(Fe) bearing, without beryl, e.g Fazenda Turmalina; b) beryl-columbite subtype{columbite(Fe) + beryl-bearing} e.g. Pitombeiras; c) beryl-columbite-phosphate subtype, e.g., Serra Branca; d) complex- spodumene subtype (columbite-(Mn) + tantalite-(Mn) ± microlite) e.g., Boqueirão, Capoeiras 1 and Quintos pro-parte; e) complex lepidolite subtype (+elbaite ± columbite- tantalite), e.g., Carrascão, Capoeiras 2 and Quintos pro parte; f) albite (+cassiterite ± wodginite), e.g., Corredor, Roncadeira, Pedras Pretas. It must be noted, however, that the attribution of a particular pegmatite to a type or subtype of this classification is neither simple nor unequivocal, because of the complete lack of quantitative minimum limits of the proportion of the various name-giving accessory minerals by Černý (1982) or by Černý and Ercit (2005) on one hand and, on the other, by the importance of vertical or longitudinal variations of the internal zoned structure of the pegmatites and consequently on the modal proportion of these minerals. As consequence, a correct classification is possible only for those pegmatites completely known in three dimensions or exposed in the best fractionated parts. Many other pegmatites belonging to the most fractionated type in a pegmatite field will not be recognized as such. The existence of different types of mostly sterile homogeneous pegmatites in the area, some of them belonging to older generations and others belonging to the late orogenic RELpegmatite generation and another one possibly to an earlier, syn-orogenic REL-generation certainly will enhance the difficulty to recognize eventual patterns of regional zonal distribution of pegmatite types. This must always be considered to avoid misunderstandings when a classification of the Borborema pegmatites is discussed. 2.5. Regional distribution

The only attempt to establish a model of regional distribution of the REL-pegmatites in the BPP was published by Cunha e Silva (1983). This author distinguishes five roughly concentric zones of pegmatite “types” according to the main accessory minerals of economic interest (at that time, Li-minerals were not included). The proposed zones, from the center to the more distal zone are respectively: a) Ta-bearing; b)Ta-Be-bearing, c)Be-bearing; d) Snbearing; e) Rare-Earth-Elements bearing pegmatites (Fig. 5a). This model, however, failed a statistical evaluation by Da Silva (1993), who considered the more recent records of over 700 mineralized pegmatites because: i) there are many pegmatites in the so-called “tin zone” that bear no cassiterite but are rich in Ta- and Li-minerals; ii) cassiterite or wodginite occur as accessory minerals together with Ta- and Be-minerals in the Ta-Be-zone or Ta-zone; iii) the expected large central granite intrusion or other source was not identified. The proposed

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zoning model is also in disagreement with the usual regional distribution of pematite types in pegmatite provinces or fields elsewhere, organized with the less fractionated pegmatites (sterile, REE, muscovite or beryl-bearing) closer to the center or even intra-apical in the source granite, and the more fractionated pegmatites in the more distal zones successively of Be-Nb-, and complex Ta-Li-Cs-minerals bearing pegmatites, as documented by Varlamoff (1959), Schneiderhöhn (1961), Černý (1989b), among others. With the identification (Da Silva et al., 1995; Beurlen et al., 2009b) of several small intrusions of late- to post-tectonic pegmatitic granites petrographically and geochemically identical to supposed source granites in other pegmatite fields around the world, as already discussed in section 2.2.1, it seems that the anomalous or even lack of a regional zonation and the inexistence of a single large central source granite in the BPP is consistent with the supposition that several small pegmatitic granite intrusions, each of them are the source of pegmatites in normal peri-plutonic zonal distribution, may mutually overlap and simulate anomalous zoning patterns (Fig. 5b). This hypothesis must be considered in any attempt to understand the regional zoned distribution in the BPP. The recognition of these “mixed patterns”, if they exist as expected, will be possible only after a revision of all geological maps of the area, with special attention to the different granite types and particular focus on possible source granites. In addition, it will be necessary to update the records in the existing databases, with special attention to the presence and identification of primary magmatic Li-minerals, and the later phases (in veins, vugs or replacement bodies), and the existence of albite dominant zones and its relative importance in the pegmatite. Unfortunately, this information, base of Černý’s classification is almost always lacking in the records of the pegmatites in the BPP, most of them copied from the old databases. For better efficiency of this update of the databases, minimum modal contents of the type-minerals should be considered in this classification (e.g. > 5 or 10 % in a particular pegmatite zone). The presence of phosphates, other replacement bodies and an inner intermediate albite-rich zone must also be registered. 3. Conditions of pegmatite crystallization in the BPP 3.1. Fluid inclusion approach

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A fluid inclusion (FI) study by Beurlen et al. (2001) verified the presence of five types of FI in quartz, garnet, tourmaline, tantalite-(Mn), beryl and euclase, from six different RELpegmatites in the BPP, with total homogenization temperatures (always to the liquid phase) in aqueous-carbonic and aqueous fluid inclusions ranging between 320 and 120 °C (Fig. 7). In some idiomorphic quartz crystals from miarolitic cavities along the transition of the homogeneous or graphic quartz zone to the blocky K-feldspar zone it was possible to observe all these types of FI along successive growth zones, allowing the authors to recognize without any doubt the primary or pseudo-secondary nature and relative age. Type-A inclusions are aqueous-carbonic with two liquid and one vapor phase at room temperature with eventual accessory accidentally-trapped solids in growth zones (primary) and linear (pseudosecondary) trails, always restricted to an irregularly shaped milky quartz core, overgrown by successive Somehere here insert Fig 7, 2 columns wide Figure 7 P/T conditions of REL-pegmatite crystallization in the BPP according to fluid inclusion studies (modified from Beurlen et al., 2001). Fig. 7 A) Total homogenization temperatures {Th(total)} versus salinity of primary fluid inclusions from successive growth zones of a quartz crystal (from core to rim) from the Boqueirão pegmatite. The respective isochores are labeled 1, 2, 3 and 4 in Fig 7B. Fig 7B isochores of FI (1 to 4, from the Qtz crystal in A); isochores 5a and b in morganite, 6 in tantalite-(Mn) from Alto do Giz, 7 and

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8 in core and rim of a quartz crystal and its euclase inclusions from Mamões. Isochores 9 to 11 represent three successive generations from graphic quartz in the Boqueirão Pegmatite. The red line15 represents the stability limit between spodumene and petalite (according to London, 1984). The vertical gray bar represents the maximal temperature for the coexistence of euclase + quartz (left side) instead of Beryl (right) according to Barton (1984) and Barton and Young (2002). Stars 13 and 15 represent regional peak and retrometamorphic stages of the host rocks.

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hyaline quartz growth zones. Type-A inclusions present the highest total homogenization temperatures around 300 °C, circa 20 mol% CO2 and medium to low salinity around 5% NaCl (eq.). Type B inclusions are also aqueous-carbonic, but with CO2 restricted to the vapor phase, mostly restricted to secondary trails in the milky quartz core but eventually found as primary inclusions together with type-Ca inclusions in the first growth-zones enveloping the milky core. Type-B and type-Ca inclusions have lower homogenization temperatures decreasing from 280 to 210 °C in successive growth-zones. Type-Cb aqueous inclusions with homogenization temperatures between 180 and 220 °C, present higher salinity values, around 15 NaCl % (eq), and increasing contents of K+, Ca+, and possibly Li+, documented by very low eutectic temperatures (down to -70 °C). The outermost growth-zones in these quartz crystals have two-phase aqueous FI with homogenization temperatures below 180 °C and decreasing salinity NaCl % (eq) values, down to around 3%. Trapping conditions for type A inclusions were estimated at 580 °C and circa 3.8 kbar by applying a pressure correction based on the stability of spodumene (observed as primary mineral in the same pegmatites) instead of petalite. These conditions are slightly higher than the late-tectonic retrograde metamorphic conditions in the area, but below the conditions of peak metamorphism. They agree with the usually estimated conditions of the liquidus curve of a pegmatite-forming melt. A nearly isobaric cooling to circa 380 °C is proposed on the basis of type-Cb FI in euclase and coexisting quartz, homogenizing around 200°C. This proposition is based on the the maximal equilibrium temperature for the stability of euclase+quartz instead of beryl (Barton, 1986; Barton and Young, 2002). These data agree roughly with the usual estimates of the pegmatite solidus (Sirbescu and Nabelek 2003, London 2008, 2014 and references therein). The milky quartz core rich in Type -A inclusions is supposed to be corroded quartz from the zone II of the pegmatite, because of its irregular shape, its position always in the root of the zoned crystals, and the same FI assemblage in the common quartz of this pegmatite zone. The hyaline and sometimes smoky quartz overgrowth zones represent the different later stages of the pegmatite crystallization. In only a few of these crystals was an additional FI type-D observed with pure CO2 inclusions (monophase vapor dominant at room temperature) in the outernmost growth zone, side by side with type-Cc inclusions. 3.2. Melt inclusion approach Recent observations made by Thomas et al. (2011a) in tantalite-(Mn) and quartz from the same pegmatites showed that type-A FI commonly coexist with two melt-inclusion types, respectively a peraluminous melt with up to 25% mol of H2O and another peralkaline melt with more than 40 mol % H2O, similar to those found in several other pegmatite fields around the world (Thomas and Davidson, 2012a). These results indicate an early saturation of the source pegmatite-forming melt in volatiles and fluxing elements in the presence of two immiscible melt fractions, possibly forming an emulsion-like liquid at the stage of the zone II crystallization or earlier. Ongoing studies allowed to identify frequent melt and fluid inclusions with unusual high alkali carbonate contents and frequent presence of variable amounts of nahcolite [NaHCO3] as daughter phase at room temperature. Such inclusions were recognized both, in quartz from

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pegmatites (so far at Capoeira 2, Alto do Giz, Boqueirão and Fazenda Turmalina) and from pegmatitic granites (Marcação, Galo Branco, and Picuí quarries). The bulk CO3-2 content determined by micro-Raman spectrometry in more than 100 of these fluid inclusions ranges between 0.24 and 3.25 mol/L , with two main groups at 0.88 ± 0.30 and 1.24 ± 0.09 mol/L. The two main groups are equivalent to concentrations of 9.3 and 13.1 % (g/g) Na2CO3, respectively. Note that the solubility of Na2CO3 at 20°C is 17.9 % (g/g). A small number of inclusions contain between 1.7 and 3.2 mol/l CO3-2, corresponding to 18 and 33.9 % (g/g) Na2CO3. That means that these inclusions must have significant amounts of other highsoluble alkali carbonates (e.g. K2CO3, Rb2CO3, Cs2CO3) in addition to the carbonate daughter crystal. The same fluid and melt inclusion assemblage was also observed elsewhere and indicates that the beginning of the melt-dominated pegmatite stage is represented by very volatile-rich melt inclusions of type-A and type-B characteristics (Thomas et al. 2006a) and syngenetic high-temperature fluid inclusions very rich in alkali carbonate (Fig. 8). The following equation represents the evolution to form the nahcolite-bearing inclusions: first the carbonaterich silicate melt with excess alkalis as sodium disilicate (Thomas et al. 2011b) reacts at high temperature in the presence of water according to the equation

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Na2Si2O5 + CO3-2 + H2O = Na2CO3 + 2 SiO2 +2OH-. and, in a subsequent stage, is followed at lower temperature and presence of CO2 ,by the breakdown of natrite [Na2CO3] to form nahcolite: Na2CO3 + CO2 + H2O → 2 NaHCO3

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This explains also the formation of MI (apparent FI at room temperature), with silica precipitating as quartz at the inclusion walls.

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The presence of this peculiar type of MI and FI in both, mineralized pegmatites, and pegmatitic granites in the BPP reinforces their supposed genetic link, the latter being the probable source of the pegmatites. The high solubility of HFSE, SiO2 , and fluxing components in melts represented by the peralkaline melt and fluid inclusions indicates that these may play an important role in the formation of the latest higher mineralized pegmatite units (inner intermediate zone, replacement bodies and pockets) and of the quartz core. Figure 9 shows these types of MI and FI in the Marcação pegmatitic granite at room temperature. Somewhere fere insert Figs 8 & 9, may be aas a whole page at the side with the text (back page and Figs front page) Figure 8 a) Type-A melt inclusion in pegmatite quartz of sample CP-1, unheated. V= vapor phase, L = alkali-rich aqueous solution. b) Type-A melt inclusion from the same quartz sample, re-homogenized at 700°C and 3 kbar and quenched: V = CO2 – vapor, G – silicate glass. c) Type-B melt inclusion, re-homogenized at the same conditions as (b): CO2-L = liquid CO2, CO2-V = CO2 – vapor, G – silicate glass, the H2O-rich phase is also rich in alkali carbonates. d) A silicate-,CO2- and CO32--rich fluid inclusion in pegmatite quartz (CP-1). The aqueous solution (Laq) contains 0.84 mol/L alkali carbonate.The bubble is a complex CO2H2O system. The glass phase (G) formed after re-homogenization at 700°C and 3 kbar and quenching. Figure 9 Melt inclusions from the Marcação quarry: a) shows a quartz grain in the pegmatitic granite from Marcação with melt (MI) and nahcolite-rich fluid inclusions. The insert in a) is such a nahcolite-rich fluid inclusion. The arrow shows the position. MI (bright spots) marked

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by the MI arrow. b) is a typical melt inclusion in quartz and c) a nahcolite-rich melt inclusion in the same sample.

4. Mineral chemistry and degree of pegmatite fractionation

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One of the main characteristic features of REL-pegmatites is the very irregular distribution of minerals and large size of some crystals. This applies also to the minerals of economic interest in pegmatites, which may also be found in small grains making up large nearly monomineralic aggregates in pockets with a random distribution in an almost sterile host pegmatite. Pegmatites or zones within them with more or less regular disseminated finegrained ore minerals, like Tanco (Canada), Greenbushes (Australia), Volta Grande (SE Brazil), are rather the exception than the rule. Therefore (owing to this “nugget effect”) usual methods of exploration (regular superficial sampling, drilling etc., and the estimate of representative mean ore grades and reserves) are almost always unsuccessful in the search for fertile pegmatites. These features make a correct classification of a pegmatite according to Černý’s model also often difficult. This is why the discovery of efficient indirect indicators of the degree of fractionation and consequently the economic potential of pegmatites and its classification was always considered as an important challenge in pegmatite research and the main reason why research on mineral chemistry (variation of main or trace element contents in minerals) occupies a considerable space of the literature on pegmatites during the last decades. The pegmatite minerals most commonly studied for this purpose are K-feldspar and white mica (mainly K/Rb, Cs, Ga, Rb, Rb/Sr ), tourmaline-supergroup species (Li, Al, Mn/Fe), columbite-tantalite group (Ta/Nb and Mn/Fe), garnet and, more recently, quartz (Li, Al, Ti, Ge, B). The variation of spinel (Fe, Mn, Zn, Al) and zircon (Zr/Hf) also correlates well with the degree of fractionation. Chemical variations in most of these minerals (where possible, collected along different zones of the hosting pegmatites) from some pegmatites of the BPP, selected according to a pre-supposed variable metallogenic potential, were determined with the aim to test its efficiency as indirect exploration tool and as help for pegmatite classification. The results are discussed in the next subsections 4.1 to 4.5 and are of preliminary nature owing to the small number of pegmatites studied. Its application to systematic routine exploration in the BPP should be preceded by additional tests on a larger number of pegmatites and samples per pegmatite. Details on sampling procedure and analytical methods can be found in the papers quoted in each subsection. 4.1. Trace elements in K-feldspar and white mica from the BPP Mineral-chemistry data for K-feldspar and white mica by Da Silva (1993) and Da Silva et al. (1995), were obtained using the classical approach of bulk analyses of samples composed of nearly 50 g chips collected along cross-sections along zone III, ground to <2 mm grain size and homogenized, followed by selection of hand-picked (supposedly) pure grains. The results of circa 15 pegmatites were plotted on the classical diagrams (Kb/Rb versus Cs, Rb, Ga. They showed low degrees of fractionation for the pegmatites studied in comparison with other pegmatite fields. All data plot in the fields of sterile to Be-Nb-phosphate pegmatite types (according to Trueman and Černý, 1982; Morteani and Gaupp, 1989; Morteani et al., 2000 and references therein), indicating a very low potential for Li-Ta-Cs mineralization. This result is clearly in disagreement with the fact that the BPP was known as a worldwide important producer of Ta-ore concentrates, mainly in the decades of 1940 to 1950, and that the chosen pegmatites included a few bodies with good historical Ta-ore production data (e.g.

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Mamões and Feio, both for Ta, Seridozinho and Espera for Ta and Li). This could possibly be due to the degree of inversion from monoclinic to triclinic K-feldspar and to supergene alteration. As most of these pegmatites were “mined” since the 1940s, Soares (2004) obtained data from five additional pegmatites, two of them rich in Li, at the time of sampling mined for “Paraíba Tourmaline” (Fig. 10). Using the same sampling procedure, the data for K-feldspar and white mica from the blocky K-feldspar zone from two Li-rich pegmatites, were found to plot in the areas of the complex Li-Ta-Cs-type in the discrimination diagrams. Data on Kfeldspar from the wallzone of more fractionated and less fractionated pegmatites all plot in the fields of poorly fractionated sterile pegmatites. These results indicate that in the BPP, the study of trace elements in K-feldspar or muscovite of the intermediate zone in superficial samples and in old abandoned prospects or mines will not distinguish between highly fractionated (possibly fertile) and poorly fractionated (probably sterile) pegmatites. Trace elements in feldspar from the wall zone are also inefficient to distinguish among pegmatites that show an increasing degree of fractionation at depth, even if the samples are fresh.

4.2. Trace elements in quartz

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Here insert Fig. 9, two columns wide Figure 10 Trace element (Rb, Cs, Ga) distribution in K-feldspar and white micas from selected pegmatites of the BPP, modified from Soares (2004). Limits between barren and fertile pegmatites are according to Gordienko (1971).

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The investigation of the behavior of trace elements in quartz became efficient only after the advances of the mass-spectrometry with coupled plasma and laser-ablation technique (LA-ICP-MS) lowering the detection limits for many elements to levels down to a few or even fractions of g/tonne in pegmatite quartz (Li, Al, Ti, B, Ge, Be, P, and others, Flem et al., 2002; Larsen et al., 2002, 2004; Müller et al., 2008a, 2008b), improving the analytical precision. The advantage of this technique in comparison to usual hand-picked whole-grain wet-chemical analyses is that it is really possible to exclude supposed analytical “errors”. These in fact are mostly “sampling errors”, caused by micrometric inclusions (fluid or solid) almost invariably present in pegmatite quartz (and specially also in cleavage-rich minerals like feldspar or mica). These errors can never be avoided completely in mm-sized grains selected by hand-picking under binocular microscope (almost all muscovite or feldspar grains from pegmatites if observed in thin sections with petrographic microscope are plenty of secondary FI). In addition to the efficient selection of inclusion-free areas with the normal petrographic microscope, allowed by the perfect transparency of quartz (also in contrast to feldspar and mica), the coupled use of cathodoluminescence (CL) allows an easy textural distinction of primary quartz and later overgrowths or recrystallization. The additional advantages in the use of quartz in comparison with other pegmatite minerals are its resistance to chemical alteration during late hydrothermal events (almost always present in highly fractionated pegmatites) and during weathering, and its omnipresence as major mineral component in all pegmatite zones. The use of this technique in quartz samples from the different zones of six pegmatites covering several types of different degrees of fractionation (Beurlen et al., 2009a, 2011b) confirmed the efficiency of the method. By this means it was possible to distinguish between samples of the quartz core of the pegmatites and, if present, of replacement pockets of highly fractionated pegmatites (higher Al > 300ppm, Li >50 up to 150ppm, Ge > 5 and B > 4 and very low Ti -< 4ppm) from quartz core samples of poorly fractionated pegmatites (Al < 300 ppm, Li < 50, Ti 5 to 25 ppm) as seen in Figure 11. A very good positive linear correlation of Li/Al observed close to the 1/1 atomic ratio indicates that Li + Al contents represent the

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coupled substitution of Si atoms in the structure of quartz (Al in the place of Si and Li retained in intersticial sites for charge compensation. The trace element contents of quartz grains from the border, wall and outer intermediate zones of both, well and poorly fractionated pegmatites, are nearly the same. Therefore, it seems possible only to distinguish potentially mineralized heterogeneous pegmatites where the quartz core or replacement bodies are exposed. High precision for the Li-contents in quartz are certainly a good indication for the prognosis of lithium mineralization. Unfortunately, the method is yet not able to produce reliable results for eventual Ta contents in quartz. Here insert Fig 11, one column wide, side by side in the same page as the text Figure 11 Trace element distribution (Al, Ti, Li) in quartz from different zones of six selected REL-pegmatites of the BPP, according to Beurlen et al. (2011b). CA2 in the legend stands for Capoeira 2, CR for Carrascão, HB 31 for Pitombeiras, HB33 for Fazenda Turmalina and QB for Quintos pegmatites. The roman numbers stand for quartz form the different zones in the pegmatites, respectively border (I), wall (II), intermediate (III) and inner intermediate + transition to quartz core or replacement unit (IV). The two doted lines in the Li/Al diagram correspond to atomic proporcions of 1/1 and 6/10, respectively.

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4.3. Mineral-chemistry of columbite-tantalite group minerals (CGM)

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The possibility to use the compositional variation in CGM as an indicator of the degree of fractionation of the host pegmatite based on Ta/(Ta+Nb) and Mn/(Mn+Fe) values (cationic ratios, simplified expressed respectively as Ta* and Mn*) plotted in the “columbite-tantalite quadrilateral” was proposed early in the research on pegmatites (Černý and Ercit,1985), and became routinely used since the electron-microprobe analysis (EMPA) became widely available. More than 550 EMPA data-points in CGM ore concentrate and some crystals collected in situ of over two dozen (28) pegmatites of the BPP allowed Beurlen et al. (2008) to distinguish clearly the same two trends ascribed to beryl – columbite and complex spodumene or lepidolite subtype pegmatites by Černý (1989b) or to the Fe-rich and manganoan trends by (Tindle and Breaks, 1998) evolving respectively from columbite-(Fe) to tantalite-(Fe) and tapiolite-(Fe) and from manganoan columbite-(Fe) to columbite-(Mn) up to near end-member tantalite-(Mn) (Fig. 12). These results are in contrast with the conclusions by Da Silva et al. (1995) based on trace elements in K-feldspar and mica indicating a lack of complex REL-pegmatites in the BPP as discussed above (section 4-2). As CGM are the only important Ta- and Nb-bearing minerals formed during the early stages of pegmatite crystallization (of at least the first 80% of the pegmatite-forming melt), the possibility of important assimilation of these elements from the regional or local hostrocks is very low. On the other hand, Fe- and Mn-contents of a pegmatite melt may be influenced by assimilation from regional rock units crossed by the melts during ascent or later by direct host-rock assimilation during emplacement. The fixation of Fe- and Mn-proportions in crystallizing CGM also depends on this proportion in other previously or simultaneously crystallized mafic pegmatite minerals, most commonly biotite, garnet, and tourmaline. The Fe/(Fe+Mn) (or Fe* number) values observed in CGM of pegmatites therefore do not reflect only the evolution of fractional crystallization of the source melt in a completely closed system, but may be also strongly dependent on other external factors and other fractionated pegmatite minerals. The use of the Fe* number for the prognosis of the degree of fractionation of the host pegmatite is therefore less reliable than the Ta* value. The existence of the two, respectively, ferroan or manganoan fractionation trends observed for CGM in the BPP may be related with the host rocks, the ferroan trends being observed more commonly in pegmatites of the Seridó Formation rich in biotite and less frequent in the quartzite-hosted pegmatites in the Equador Formation. Therefore, the variation of the Ta/(Ta+Nb) value more

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likely represents the true magmatic fractionation trend. The gradual enrichment of Ta/(Ta+Nb) from the pegmatite border zones inward is explained by the higher solubility of Ta in the pegmatitic melt (van Lichtervelde et al., 2010 and references therein), specially if F and Li rich, and explains why primary Ta-dominant CGM, namely tapiolite-(Fe) in the ferroan trend and tantalite-(Mn) in the manganoan trend, are found only in highly fractionated complex REL-pegmatites, formed from the last residual melt fractions. A late-stage reverse trend with enrichment of Nb, Ti, Fe and Ca is observed in zoned end-member tantalite-(Mn) crystals (millimeter to sub-millimeter opaque rims on translucent red-wine colored crystals) of many pegmatites in the BPP and culminates during the hydrothermal stages with the formation of replacement rims with microlite, pyrochlore and fersmite. Similar observations were made by Tindle and Breaks (1998, 2000) at the Separate Rapids pegmatite field (Ontario Canada). This reverse trend is also observed in tourmaline of the BPP with a late increase of Fe+Mg+Ca (recognized as“acid reflux”, Martin and De Vito 2014). The problem using compositional trends of CGM for exploration purposes, with the aim of making a diagnosis of the economic potential of a particular pegmatite is that a systematic sampling along cross sections of pegmatite outcrops is mostly impossible owing to the erratic distribution of these minerals: if possible, a very large volume and therefore expensive samples would be necessary to be representative. This applies also to other frequently encountered accessory minerals like garnet, spinel, tourmaline, beryl and zircon. The CGMchemistry approach may, however, be very useful as complement to eventual heavy-mineral exploration programs (in alluvium and elluvium) using the Ta* value of the CGM grains to indicate the possible existence of “up-stream” complex spodumene or lepidolite pegmatites. Its use in known pegmatites as in the present case, will allow corroboration of the degree of fractionation of the hosting pegmatite as established based on other criteria.

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Somewhere here insert the Fig. 12, two columns wide Figure 12 Main trends of Mn* and Ta* values (atomic proportions) in the “Ta-Nb-Fe-Mn columbite quadrilateral” for selected REL-pegmatites in the BPP, modified from Beurlen et al. (2008). Trend 1 and trend 2 are respectively the ferroan and manganoan trends according to Tindle and Breaks (1998), or beryl-columbite and complex Be-Li-Ta-Cs pegmatite types according to Černý. Several pegmatites in the BPP follow trend 2, with good potential for TaLi-Cs mineralization. Trend 3 is a reverse trend at the end of fractionation. 4.4. Mineral-chemistry in tourmaline

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The wide range of stability of tourmaline-supergroup minerals (TGM) and large compositional variation were pointed out by several authors as possible tracers of the degree of fractionation in granite magmas or as useful indicators of the source rocks in metamorphic systems (e.g. Henry and Guidotti, 1985). The frequency of tourmaline minerals as important accessory or, in a few cases, even as major component in BPP pegmatites, motivated the test of a possible correlation of its chemical composition (using EMPA) with the degree of fractionation and economic potential of the host pegmatite (Soares et al., 2008), again using samples from different zones of several pegmatite types of supposedly variable degrees of fractionation. The study aimed also to contribute to the origin of the famous highly prized gem quality “Paraíba tourmaline”. First of all, the results showed that the usual trends of variation of the tourmaline composition and substitution mechanisms observed in pegmatites elsewhere were confirmed in the BPP, with ferroan dravitic tourmalines observed in the border zones, and magnesian schorlitic to ferroan schorlitic tourmalines occurring in the wall and outer intermediate zones or, in moderately fractionated pegmatites also in the quartz core. Ferroan elbaitic to near endmember elbaitic compositions are found only in the inner intermediate pegmatite zones,

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quartz cores or vugs and replacement pockets of supposed highly fractionated pegmatites. In terms of element substitution mechanisms this means that there is a first stage with substitution at the Y site of YMg by YFe followed by substitution of Y(Fe+Mg) by YAl (dravite→schorl and schorl→{foitite+olenite}), and a second stage with the substitution of 2Y(Fe+Mg+Mn) by Y(Al + Li) ({schorl+olenite+foitite}→ferroan elbaite→end member elbaite). The last stage in color-zoned elbaite crystals is characterized by the very low (Fe+Mg < 0.1 apfu) values and a small increase in Mn and F values for (earlier) pink crystal cores, followed by decrease of (Fe+Mg+Mn) values (< 0.01 apfu) in “Paraíba”-blue zones, enriched in F and Cu, in some cases followed by a last green rim with a reversal trend of increasing (Fe+Mg) contents (Beurlen et al., 2011a). The continuous linear trend of the compositional variation indicates that the “Paraíba-tourmaline” represents the culmination of a normal magmatic evolution trend of tourmaline compositions and not an independent hydrothermal stage with external B and Cu source. This conclusion is corroborated by strong textural evidence (Beurlen et al. 2011a) and by the similarity of the 11/10B isotope ratios (d ≈ 14 ± 1 ‰, based on coupled SIMS- for B and Li - and EMPA – 14 elements data) of the “Paraíba tourmaline” and the other schorlitic tourmalines in the BPP (Trumbull et al., 2013). The best chemical indicator for the degree of fractionation of the host pegmatite in tourmaline seems to be YAl, which presents a continuous nearly linear increase from less than 0.1 to 1.8 at expense of the decrease of Y(Fe+Mg+Mn) from 2.9 to nearly 0.01. The problem with the use of tourmaline composition as tracer for fractionation is that it is rarely present in all zones of the pegmatite. Furthermore there is no difference in composition of tourmaline of the outer zones of poorly and highly fractionated pegmatites (e.g., the same problems as in other main and accessory minerals). 4.5. Mineral-chemistry in garnet and spinel

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Very preliminary EMPA data (95 data-points) on garnet from the Boqueirão, Capoeira 1, 2 and 3, Quintos and Ermo pegmatites do not present significant variation in composition from core to border of single crystals, and only small variations between different pegmatite zones in the same pegmatite. The spessartine values increase from 61 mol % at Boqueirão to 65 mol % at Capoeira 1, 65 to 68 mol % at Capoeira 2, 69 mol% at Capoeira 3 and 80 to 88 mol % at Quintos (Soares and Beurlen, 2004) and reach over 90 mol % at Ermo (Eeckhout, 2002). These values are coherent with the relative degree of fractionation estimated according to field criteria as proposed by Černý and Ercit (2005), like main primary lithium minerals (spodumene at Boqueirão, amblygonite at Capoeira 1, lepidolite, spodumene and elbaite at Capoeira2 and Quintos), intensity of albitization, and frequence of replacement pockets. A historical citation of an “important” production of Ta-ore concentrate in the BPP, however, exists only for the Boqueirão pegmatite, which is supposed to be the least fractionated one of the examined bodies according to Garnet, TGM and field criteria. This could be an indication that the degree of fractionation is not always to be directly correlated with the potential for Ta ore. Thirty-eight EMPA data points on gahnite crystals from Capoeira 2 (one grain in the wall zone), Quintos (2 grains in the albitized outer intermediate zone) and Ermo (two grains from replacement pockets) revealed high (90 to 95) mol % of gahnite in the spinel, typical of highly fractionated pegmatites. Linear trends with increasing Mn and Zn contents but nearly constant Fe/Mg ratios in each pegmatite are observed, with the usual decrease in Fe-contents of both minerals with fractionation from core to rim in zoned crystals, and from outer (external) zones of the pegmatites inward (Soares et al., 2007). Oscillatory zoning in zoned crystals was also observed and may be explained with the fact that the evolution of Fe, Mg and Mn content in spinel (and garnet) is also influenced by the onset or cessation of

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crystallization of other mafic phases, most likely tourmaline or biotite (London, 2008, and others therein). Unfortunately all these data are from different pegmatite subtypes of the REL Be-Li complex type and there are still no data available for garnet and gahnite from less fractionated pegmatites for comparison, which would allow at least a preliminary evaluation of the efficiency of this approach as tool for a prognosis of the economic potential for Ta and Li.

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5. Petrogenetic considerations

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The petrogenesis of granitic REL-pegmatites still includes several controversial and unsolved questions. The most typical (London, 2008; 2009) but also enigmatic and paradoxical textural characteristics observed in granitic REL-pegmatites are: a) unidirectional (centripetal) solidification textures “UST”, b) banded sodic aplites with cyclic compositional banding (“line rocks”, Webber et al., 1997), c) the frequent presence of up to several metersized “megacrysts” and d) an almost monomineralic quartz core. Each of these textural features would be easy to understand and accepted if formed by open hydrothermal systems, in which the crystallization occurs with slow growth-rates from aqueous solutions with moderate to high solubility of the components necessary for the crystal growth and precipitation, these being caused by local change in P-T-X conditions, in great part due to interaction with the host-rocks (therefore open system conditions). Although similar hydrothermal processes were historically admitted for pegmatite genesis (e.g., Ramberg, 1952; Gresens, 1967; see revision in London 2008 p 8), they are nowadays considered to be incompatible with a) the low solubility of aluminosilicates in aqueous solutions; b) the short time-span of pegmatite solidification (Webber et al., 1999), and c) the almost inexistent or weak signs of interaction with the host rocks, typical for closed or nearly closed system conditions; d) the usual low contents of rare metals in the host rocks. The frequent obvious spatial relation (intra- or peri-apical position) of REL-pegmatites with a larger source granite intrusion and the similarity of the bulk composition of pegmatites not exactly but close to the minimum melt composition of granitic systems lead most researchers since the beginning of the last century to suppose a magmatic origin of RELpegmatites, as result of the solidification of residual aluminosilicate melts generated with progressive crystallization of larger granite intrusions. The direct origin of REL-pegmatites by anatexis (e.g. Ebert, 1970; Grew et al., 2000) is hardly compatible with 1) the predominance of medium- or low-grade metamorphic hostrocks in most REL-pegmatite fields; 2) the considerable enrichment of Li and Ta in the RELpegmatites; 3) the usually normal low contents of these elements in the host-rocks. The possibility may explain particular cases, but certainly is not applicable in most cases. Jahns (1953), and Jahns and Burnham (1969 and references therein), used an experimental simulation departing from a water-saturated mixture of synthetic components in similar proportions as found in pegmatites, were able to replicate the zonal architecture found in natural many pegmatites and since then argued in favor of the origin of REL-pegmatites by fractional crystallization from water saturated and flux-enriched melts under (almost completely) closed-system conditions. Fast circulating volatile bubbles and long crystallization times would enable the formation of large crystals and enrichment of REL in the upper parts of the system. The problem of this model is the low solubility of Si, Al and incompatible elements in the aqueous volatile phase and the assumed long crystallization times, which are in contrast with modeling of pegmatite crystallization times by Webber et al. (1999) demonstrated to be very short in the order of weeks to months or a few years, depending on thickness and temperature differences of pegmatites and host rocks at the time of emplacement.

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London (2008, 2013) and London and Morgan (2012 and references therein), based on own experiments, first with natural volcanic Li-rich rhyolithic glass and later with synthetic components, building on the replication of graphic quartz/K-feldspar intergrowths (Swanson and Fenn, 1986) and modeling of banded quartz/albite “line rocks” by Fenn and Swanson (1992 and references therein), argued in favor of a rapid crystallization of pegmatites from strongly undercooled H2O-undersaturated highly viscous peraluminous melts. A peralkaline low-viscosity boundary layer formed at the crystallization front, enriched in incompatible elements by a zone-refinement process, with high diffusion rates of ions that would promote the possibility of the formation of megacrystals and graphic intergrowths in short time-spans. Some typical features of REL-pegmatites still remain difficult to be explained with this model, such as 1) the formation of a typical, nearly monomineralic quartz core; 2) the frequent regional zonal distribution of pegmatite types; 3) long distances (up to 10 km) of migration from the granite source, contrasting with the supposed highly viscous undersaturated, under-cooled, rapidly crystallizing pegmatite forming melt. Thomas et al. (2006b),Thomas and Davidson (2012a) and Thomas et al. (2012, and references therein) concluded on the basis of fluid and melt-inclusion studies in several granitic REL-pegmatite fields that the pegmatite-forming melts are formed by a mixture of a peralkaline melt fraction (with strong enrichment of REL, fluxing elements and more than 40 mol% water- “type-B melt inclusions”) and a peraluminous melt fraction (type-A melt inclusions with up to 20 mol % H2O) saturated in a dominantly aqueous-carbonic volatile phase. The coexistence of Type-A and Type B-melt inclusions in presence of normal aqueous-carbonic fluid inclusions in early pegmatite minerals was also confirmed in the Borborema BPP (Thomas et al., 2011a). This emulsion-like melt, with several orders of magnitude lower viscosity than an undersaturated homogeneous peraluminous melt, would be easier to conciliate with long migration distances and regional zoning in relation with the source granites, and also with the supposition that the pegmatite-forming melts are residual melts produced after long-time fractionation from the crystallizing peraluminous (usually Stype) source-granite intrusion.

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The detailed discussion of the advantages and problems of these three main petrogenetic models is beyond the available space, but it seems evident that many characteristic features of the REL-pegmatites are still enigmatic and need further research efforts. The main problem in the BPP and in many REL-pegmatite fields worldwide is to conciliate large distances in the order of several km observed between the (often unraveled and supposed) granite source and the REL-pegmatites, in some cases themselves more than one km in length, with constant thickness of a few meters, with regular internal zoning and without visible connection with the source. These field features, also observed in many other pegmatite provinces (e.g. Little Nahani, NWT in Canada, Groat et al., 2003), seem hardly compatible with the crystallization from very-high-viscosity normal granitic, undersaturated peraluminous homogeneous bulk melts, mainly if the ultrashort (in geologic time-scales) crystallization times (a few weeks to months for meter thick dykes Webber et al., 1999), in addition to an enhanced viscosity due to 200 °C melt undercooling (responsible for the graphic and layered aplite textures) are considered. Note that the genetic models proposed respectively by London (2008, 2013) and by Thomas et al. (2012) and Thomas and Davidson (2012a), both propose the coexistence of a highly viscous peraluminous and a low-viscosity peralkaline melt during the pegmatite crystallization, respectively in the form of a boundary layer or of an emulsion,. Both are supported by experimental approachs, one in part performed with Li-rich rhyolitic Macusani Glass and in part on mixtures of synthetic components, the other on melt inclusions, supposed

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The review of the remaining petrogenetic problems for the understanding of RELpegmatite formation under the light of observations in the BPP leads to the conclusion that there does not yet exist an all explaining complete model for the formation of RELpegmatites. Much is yet to be done to reach a complete understanding of the multitude of genetic processes involved. Apart of the controversy concerning petrogenesis, it seems urgently necessary to develop efficient exploration strategies for the recognition of the rare ore-grade Li- and Ta-rich pegmatite deposits and its distinction from the remaining “barren” pegmatites (usually around 98% according to estimates by Ginzburg, as cited in Černý,1989b, in known REL-pegmatite fields, as the BPP. The same need applies for the discovery of new REL-pegmatite fields related to fertile granites. In addition to the usual field criteria (like the heterogeneous zonal distribution of modal composition and textures in the pegmatites, high contents of type-minerals, frequency of replacement bodies and sodic aplites, large size and low dip, etc.) proposed by Černý (1989b), whose recognition however is strongly dependent on the outcrop conditions and erosion level of the pegmatite, the establishment of indirect criteria independent of the outcrop conditions would be highly desirable Chemical variations of composition of pegmatite minerals are outstanding candidates for this purpose. Preliminary tests developed with mineral chemistry in K-feldspar, white mica, CGM, tourmaline and garnet in selected pegmatites covering several subtypes with supposedly variable degrees of fractionation in the BPP indicated that Li, Al, Ge and B contents in quartz determined by the LA-ICP-MS technique are the most efficient tracers for the degree of fractionation of the hosting pegmatites, with the advantage over the classical use of trace element contents in feldspar and muscovite, because the latter are much more susceptible to meteoric or hydrothermal alteration and with advantage over the use of accessory minerals due to the irregular distribution of the last ones. The data on mineral-chemistry variation obtained in the BPP in CGM, tourmaline, garnet and quartz along the last decade support the recognition of complex-spodumene and complexlepidolite pegmatites and allow a revision of the pessimistic diagnosis of a low metallogenetic potential for Ta- and Li-ores by Da Silva et al. (1995) to a more optimistic one, compatible with the historical production data during the second world war. Further investigations are necessary for consolidation of mineral-chemistry as potential indirect exploration tool in the BPP. Their use in systematic exploration programs for pegmatitic Ta- and Li-ore in the BPP are therefore strongly recommended, due to the trend of increasing consumption and strategic importance of these rare metals. The regional exploration strategy should include in a first stage, an upgrade of the records with rapid visits of all mineralized pegmatites to complement the data upon internal structure, type minerals and other geological features lacking in the existing files.The visits could include sampling of quartz and accessory minerals (for eventual later mineral chemistry studies). During this stage the existence of eventual still unidentified pegmatitic granite intrusions should be checked and the spatial relation between pegmatite types/subtypes and pegmatitc granite intrusion should be reanalised, searching for promising smaller areas for detailed exploration, in a follow up stage. Finally, the recovery of Ta-ore concentrates in the BPP is very irregular because: a) of the lack of a large active pegmatite mine with regular Ta-ore grade distribution and production; b) it is also dependent on the strongly oscillating Ta-price; c) it depends on climate variation

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because in draught years due to the reduction of other economic activities unemployed people goes back to the old-known Ta-bearing pegmatites and scavenges up to 20 m deep with manual instruments and candles for recovery of a pound of concentrate earning usually a dozen dollars a week. This is why the manual individual extraction of Ta-ore concentrates is also important of the social point of view. Some times the exceptional discovery of a “bonanza” happens, like the finding (2003) of a pocket with an aggregate of large Tapiolite(Fe) crystals weighting nearly 400 kg in the Boqueirão Pegmatite, after nearly 60 years without any significant production of Ta-ore in this occurrence. Acknowledgements

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The first author dedicates this paper to Robert F. Martin who stimulated my research on the Borborema pegmatites along the last decade with important scientific discussions on pegmatology. Additional thanks are dedicated to the GFZ-Potsdam (Center for Geoscientific Research - Helmholtz-Zentrum Potsdam, Germany) for the permission of the free acquisition of a great part of the analytical data (EMPA, Raman, FI-lab). We acknowledge strongly Oona Appelt for their assistance at the EMPA facility at the GFZ, Dailto Silva for the use of the SEM and Raman facility in the Department of Mineral Resources of the Unversity of Campinas, São Paulo, the Geological Survey of Norway at Trondjheim for the LA-ICP-MS data acquisition and R. Trumbull for the SIMS B-isotope data at the GFZ. We gratefully express our gratitude to several co-authors of previous papers listed in the references. This work was supported by grants APQ 471064/2006-8, PQ 302-348/2007-7, 302076/2010-7 and 307204/2013-8 of the Brazilian Council for Scientific Research (CNPq).

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Müller, A., Ihlen, P.M. and Kronz, A., 2008a. Quartz chemistry in polygeneration Sveconorwegian pegmatites, Froland, Norway. European Journal of Mineralogy, 20, 447463. Müller, A., Wiedenbeck, M., Flem, B. and Schiellerup, H., 2008b. Refinement of phosphorus determination in quartz by LA-ICP-MS through defining new reference material values. Geostandards and Geoanalytical Research, 32, 361-376. Nakamura, N., 1974. Determination of REE, Ba, Fe, Mg, Na and K in carbonaceous and ordinary chondrites. Geochimica et Cosmochimica Acta, 38, 757-775. Pedrosa-Soares, A.C., De Campos, C.P., Noce, C., Silva, L.C., Novo, T., Roncato, J., Medeiros, S., Castañeda, C., Queiroga, G., Dantas, E., Dussin, I., Alkmim, F., 2011. Late Neoproterozoic-Cambrian granitic magmatism in the Araçuaí orogen (Brazil), the Eastern Brazilian Pegmatite Province and related mineral resources. Geological Society, London, Special Publications 350: 25-51. Ramberg, H., 1952. The origin of metamorphic and metassomatic rocks. University of Chicago Press, Chicago, 317 pp. Rolff, P.M.A., 1946. Minerais dos pegmatitos da Borborema. Departamento Nacional de Produção Mineral (DNPM), Divisão de Fomento da Produção Mineral (DFPM), Rio de Janeiro, Boletim 78, 23-76. (“Minerals of pegmatites from Borborema” in portuguese). Roy, P.L., Dottin, O., Madon, H.L., 1964. Estudo dos pegmatitos do Rio Grande do Norte e da Paraíba. Brasil, Superintendência do Desenvolvimento do Nordeste (SUDENE), Série Geologia Economica. 1, 1-124. (“Study of the pegmatites in the States of RioGrande do Norte and Paraíba” in Portuguese). Santiago, J.S., Souza, V. S., Dantas, E. L., Oliveira, C.G., Neto, L.R., Barreto, R.O. 2014Mineralização de esmeralda durante a orogenia brasiliana: depósito na Fazenda Bonfim, Estado do Rio Grande do Norte. 47th Brazilian Geological Congress, Abstracts, PAP 015969. Schneiderhöhn, H., 1961. Die Erzlagerstätten der Erde. Band II: Die Pegmatite. Gustav Fischer, Verlag, Stuttgart, Germany. Scorza, E.P., 1944. Província Pegmatitica da Borborema. Departamento Nacional de Produção Mineral (DNPM), Divisão de Geologia (DGM), Boletim 112. Rio de Janeiro, 55p. (Borborema Pegmatite Province”, in portuguese). Sirberscu, M-L., C., Nabelek. P. I., 2003. Crustal melts below 400°C. Geology, 31, 685-688. Sirberscu, M-L., C., Wilke, M., Veksler, I., Whittington, A. 2010. Experimental crystallization of Li-B-pegmatites. 20th General Meeting, International Mineralogical Association, Acta Mineralogica-Petrographica Abstract Series, 6, 606. Soares, D.R., 2004. Contribuição à petrologia de pegmatitos mineralizados em elementos raros e elbaítas gemológicas da Província Pegmatítica da Borborema, NE-Brasil. PhD Thesis. Federal University of Pernambuco (UFPE) Recife, Pernambuco, Brazil (271 pp) (Contribution to the petrology of rare element mineralized pegmatites and gemologic elbaites in the Borborema Pegmatite Province”, in Portuguese). Soares, D. R., Beurlen, H., 2004. Química mineral de espessartitas da Província Pegmatítica da Borborema. 9° Congresso Brasileiro de Geoquímica, Extended Abstracts Volume, 667668. (“Mineral-chemistry of spessartite from the Borborema Pegmatite province”, in portuguese). Soares, D. R., Beurlen, H., Ferreira, A. C. M., Da Silva, M.R. R., 2007. Gahnite mineral chemistry and pegmatite fractionation in the Borborema Province, northeast Brazil. Anais da Academia Brasileira de Geociências, 181, 395-404. Soares, D.R., Beurlen, H., Barreto, S.B., Da Silva, M.R.R., Ferreira, A.C.M., 2008. Compositional variation of tourmaline-group minerals in the Borborema Pegmatite Province, northeastern Brazil. The Canadian Mineralogist, 46, 1097-1116.

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Stilling, A., Černý, P., Vanstone, P.J., 2006. The Tanco pegmatite at Bernic Lake Manitoba. XVI. Zonal and bulk compositions and their petrogenetic significance. The Canadian Mineralogist, 44, 599-624. Swanson, S.E., Fenn, P.M ., 1986. Quartz crystallization in igneous rocks. American Mineralogist, 71, 331-342. Sweetapple, M., 2013. Mineralogy meets economics: how does pegmatology interface with the mineral industry, society and market forces. 6th International Symposium on Granitic Pegmatites PEG 2013. Abstracts, 139-140. Tavares, J.F., 2001. Relatório de grafuação. (undergraduate report). UFPB (Federal University of Paraíba, Campina Grande, Mining Engineering Course). (in portuguese). Thomas, R., Webster, J.D., Davidson, P., 2006a. Understanding pegmatite formation: the melt and fluid inclusion approach. Mineralogical Association of Canada Short Course 36, 189209. Thomas, R., Webster, J.D., Rhede, D., Seifert, W., Förster, H.J., Heinrich, W. and Davidson P., 2006b.The transition from peraluminous to peralkaline granitic melts: Evidence from melt inclusions and accessory minerals. Lithos, 91, 137-149. Thomas, R., Davidson, P., Beurlen, H., 2011a. Tantalite-(Mn) from the Borborema Pegmatite Province, northeastern Brazil: conditions of formation and melt- and fluid-inclusion constraints on experimental studies. Mineralium Deposita, 46, 749-759. Thomas R., Davidson P., Schmidt C., 2011b. Extreme alkali bicarbonate- and carbonate-rich fluid inclusions in granite pegmatite from the Precambrian Rønne granite, Bornholm Island, Denmark. Contributions to Mineralogy and Petrology 161, 315-329. Thomas R., Davidson P., Beurlen H., 2012. The competing models for the origin and internal evolution of granitic pegmatites in the light of melt and fluid inclusion research. Mineralogy and Petrology, 106, 55–73. Thomas, R., Davidson, P., (2012a) Water in granite and pegmatite-forming melts. Ore Geology Reviews, 46, 32–46. Thomas R, Davidson, P., 2012b. The application of Raman spectroscopy in the study of fluid and melt inclusions. Zeitschrift der Deutschen Gesellschaft für Geowissenschaften, 163, 113–126. Tindle, A.G., Breaks, F.W., 1998. Oxide minerals from the Separation Rapids rare-element granitic pegmatite group, northwestern Ontario. The Canadian Mineralogist, 36, 613- 636. Tindle, A.G., Breaks, F.W., 2000. Columbite-tantalite mineral chemistry from rare element granitic pegmatites: Separation Lake area, NW Ontario, Canada. Mineralogy and Petrology, 70,165-198. Trueman D.L., Černý P., 1982. Exploration for rare-element granitic pegmatites. In: P. Černý (Ed) Mineralogical Association of Canada, Short Course 8; 463-493. Trumbull R.B., Beurlen H., Wiedenbeck, M., Soares D.R., 2013. The diversity of B-isotope variations in tourmaline from rare-element pegmatites in the Borborema Province of Brazil. Chemical Geology 352, 47–62. van Schmus, W.R., Brito Neves, B.B., Williams, I.S., Hackspacher, P. C., Fetter, A.H., Dantas, E.L., Babinski, M., 2003. The Seridó Group of NE Brazil, a late Neoproterozoic pre- to syn-collisional basin in West Gondwana: insights from SHRIMP U-Pb detrital zircon ages and Sm-Nd crustal residence (TDM) ages. Precambrian Research, 127, 287327. van Lichtervelde, M., Holtz,, F., Hanchar, J.M., 2010. Solubility of tantalite-(Mn), zircon and hafnon in highly fluxed peralkaline to peraluminous pegmatitic melts. Contributions to Mineralogy and Petrology, 160, 17-32. Varlamoff, N., 1959. Zonéographie de quelques champs pegmatitiques de l’Afrique Centrale et les classifications de K.A.Vlasov et de Guinsbourg. Annales de la Sociétée Géologique Belgique, 82, 55-87.

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Vlasov, K.A., 1952. Textural-paragenetic classification of granitic pegmatites. Izvestiya, 3344. Apud Routhier, P., 1963. (original in russian). Texturelle und paragenetische Gliederung der Pegmatite. Mitteilungen der Akademischen Wissenschaften USSR, Geol. Ser.2, 30-55. Wark, D.A., Watson, E.B., 2006. TitaniQ: a titanium-in-quartz geothermometer. Contributions to Mineralogy and Petrology, 152, 743-754. Webber, K.L., Falster, A.U, Simmons, Wm.B., Foord, E.E., 1997. The role of diffusion controlled oscillatory nucleation in the formation of line rock in pegmatite-aplite dikes. Journal of Petrology, 39, 1777-1791. Webber, K.L., Simmons, Wm.B., Falster, A.U., Foord, E.E., 1999. Cooling rates and crystallization dynamics of shallow level pegmatite-aplite dikes, San Diego County, California. American Mineralogist, 84, 708-717. Wilson, W.E., 2002. Cuprian elbaite from the Batalha mine, Paraíba, Brazil. The Mineralogical Record, 33, 127-137.

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Ta- & Li-potential in the Borborema pegmatites reviewed based on mineral chemistry. Trace elements in quartz as indicators of Be-Li-Ta bearing complex pegmatites. Compositional trends in COLTAN (CGM) group minerals in complex type REL-pegmatites. Melt-melt immiscibility in rare element bearing pegmatites and their source granites.

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Figure 1 Simplified regional geologic map compiled from Brasil (1998 and 2002) with delimitation of the Borborema Pegmatite Province and location of the studied pegmatites, modified from Beurlen et al. (2011a). Figure 2 Cyclic banding of four typical petrographic facies of the pegmatitic granites, supposed to be the source-granites of the REL-pegmatites in the BPP, modified from Beurlen et al. (2009a). pegs = pegmatitic facies, with centripetal unidirectional texture; PG = pegmatitic granite with unidirectional upward growth texture; BA = banded sodic aplite; LG = leucocratic medium grained granite. At the left above above the head of R. Martin, a magnified insert corresponds to the green rectangle at the right. Figure 3 Rare earth element distribution (chondrite normalized according to Nakamura, 1974) A) in the pegmatitic-granites in the BPP compaired with B) counterparts from Canada according to Černý et al. (2005), modified from Beurlen et al. (2009a). Symbols stand for: A) open triangles = GR3B porphiritic and pegmatittic fácies; solid triangles G3B, equigranular fine to médium grained leucogranite facies; gray area data of other granites in the area (Da Silva etal 1995); B) open triangles pegmatite facies; solid triangles banded sodic aplite; solid circles fine grained leuco granite, open circles=pegmatitic leocogranite (Černý et al. 2005). Figure 4 Apophyses of albite-quartz-tourmaline pegmatites formed from residual melts of the lepidolite-spodumene-complex Capoeira 2 pegmatite in the BPP, modified from Beurlen et al. (2011a). IIZ = inner intermediate zone (mainly quartz, albite and some spodumene and black tourmaline fringe); a = quartz + albite dominant apophyses; WZ = wall zone. The insert in the lower right is a view of the floor with albitic apophyses (yellow arrows labeled with a) invading the hosting metaconglomerates (C). Note the black tourmaline strings along the contact of a large apophysis, directly connected with the main pegmatite body. Small white feeder veinlets (v labels) are originated from the IIZ and crosscut the external pegmatite zones to form the apophyses.

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Figure 5 Regional distribution of pegmatite types a) according to Cunha e Silva (1983) and b) comparison with a complex distribution model due to overlapping. Figure 6 Detailed geological sketch of the Boqueirão (= Cabeço) pegmatite (modified from Tavares, 2001) compaired with the model of the classification of pegmatites based on internal structure proposed by Vlasov (1952). Figure 7 P/T conditions of REL-pegmatite crystallization in the BPP according to fluid inclusion studies (modified from Beurlen et al., 2001). Fig. 7 A) Total homogenization temperatures {Th(total)} versus salinity of primary fluid inclusions from successive growth zones of a quartz crystal (from core to rim) from the Boqueirão pegmatite. The respective isochores are labeled 1, 2, 3 and 4 in Fig 7B. Fig 7B isochores of FI (1 to 4, from the Qtz crystal in A); isochores 5a and b in morganite, 6 in tantalite-(Mn) from Alto do Giz, 7 and 8 in core and rim of a quartz crystal and its euclase inclusions from Mamões. Isochores 9 to 11 represent three successive generations from graphic quartz in the Boqueirão Pegmatite. The red line15 represents the stability limit between spodumene and petalite (according to London, 1984). The vertical gray bar represents the maximal temperature for the coexistence of euclase + quartz (left side) instead of Beryl (right) according to Barton (1984) and Barton and Young (2002). Stars 13 and 15 represent regional peak and retrometamorphic stages of the host rocks. Figure 8 a) Type-A melt inclusion in pegmatite quartz of sample CP-1, unheated. V= vapor phase, L = alkali-rich aqueous solution. b) Type-A melt inclusion from the same quartz sample, re-homogenized at 700°C and 3 kbar and quenched: V = CO2 – vapor, G – silicate glass. c) Type-B melt inclusion, re-homogenized at the same conditions as (b): CO2-L = liquid CO2, CO2-V = CO2 – vapor, G – silicate glass, the H2O-rich phase is also rich in alkali carbonates. d) A silicate-,CO2- and CO32--rich fluid inclusion in pegmatite quartz

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(CP-1). The aqueous solution (Laq) contains 0.84 mol/L alkali carbonate.The bubble is a complex CO2-H2O system. The glass phase (G) formed after re-homogenization at 700°C and 3 kbar and quenching Figure 9 Melt inclusions from the Marcação quarry: a) shows a quartz grain in the pegmatitic granite from Marcação with melt (MI) and nahcolite-rich fluid inclusions. The insert in a) is such a nahcolite-rich fluid inclusion. The arrow shows the position. MI (bright spots) marked by the MI arrow. b) is a typical melt inclusion in quartz and c) a nahcolite-rich melt inclusion in the same sample. Figure 10 Trace element (Rb, Cs, Ga) distribution in K-feldspar and white micas from selected pegmatites of the BPP, modified from Soares (2004). Limits between barren and fertile pegmatites according to Gordienko (1971). Figure 11 Trace element distribution (Al, Ti, Li) in quartz from different zones of six selected REL-pegmatites of the BPP, according to Beurlen et al. (2011b). CA2 in the legend stands for Capoeira 2, CR for Carrascão, HB 31 for Pitombeiras, HB33 for Fazenda Turmalina and QB for Quintos pegmatites. The roman numbers stand for quartz form the different zones in the pegmatites, respectively border (I), wall (II), intermediate (III) and inner intermediate + transition to quartz core or replacement unit (IV). The two doted lines in the Li/Al diagram correspond to atomic proporcions of 1/1 and 6/10, respectively. Figure 12 Main trends of Mn* and Ta* values (atomic proportions) in the “Ta-Nb-Fe-Mn columbite quadrilateral” for selected REL-pegmatites in the BPP, modified from Beurlen et al. (2008). Trend 1 and trend 2 are respectively the ferroan and manganoan trends according to Tindle and Breaks (1998), or beryl-columbite and complex Be-Li-Ta-Cs pegmatite types according to Černý. Several pegmatites in the BPP follow trend 2, with good potential for Ta-Li-Cs mineralization. Trend 3 is a reverse trend at the end of fractionation. .

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Table 1 Synopsis of geochronological data describing the Borborema pegmatites. *by columbite is meant a member of the columbite group minerals; new valid name for Brabantite is Cheralite.

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Highlights (to HB Peg Review JSAESci.doc)

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Ta- & Li-potential in the Borborema pegmatites reviewed based on mineral chemistry. Trace elements in quartz as indicators of Be-Li-Ta bearing complex pegmatites. Compositional trends in COLTAN (CGM) group minerals in complex type RELpegmatites. Melt-melt immiscibility in rare element bearing pegmatites and their source granites.