Petrogenetic and mineralization processes in Paleo- toMesoproterozoic rapakivi granites: examples from Pitinga and

Goias, Brazil

Sara L.R. Lenharo �,1, Marcia A. Moura, Nilson F. Botelho

Universidade de Brasılia, IG/GMP, 70910-900 Brasılia, DF, Brazil

Received 21 May 2001; received in revised form 16 November 2001; accepted 4 May 2002

Abstract

The 1.8 Ga Pitinga granites*/Agua Boa and Madeira massifs*/in Amazonas (northern Brazil) are within-plate,

shallow-level rapakivi granites associated with an extensional fracture system. They comprise an early facies of pyterlitic

to wiborgitic rapakivi granite, a fine- to medium-grained biotite granite, as well as topaz granite (Agua Boa massif) and

albite granite (Madeira massif). The granites are usually metaluminous to peraluminous, the albite granite, however, is

peralkaline. They are enriched in SiO2, K2O, Na2O, F, Rb, Th, Nb, Y, Zr and the rare-earth element (REE) and

impoverished in MgO, TiO2, P2O5 and Sr, as the majority of Sn-mineralized granites. Sn contents range from �/1 ppm

in the rapakivi facies to �/3400 ppm in the albite granite. oNd (at 1.8 Ga) values vary from �/2.2 to �/0.4 and Nd model

ages lie between 2.4 and 2.1 Ga. Mineralization in the Madeira massif includes disseminated magmatic cryolite, zircon,

cassiterite, pyrochlore, columbite-tantalite and xenotime and massive cryolite bodies in the F-rich peralkaline albite

granite. In the Agua Boa massif, Sn mineralization is associated with greisens and episyenite. The 1.77 Ga (g1) and

1.58�/1.57 Ga (g2) rapakivi granites of Goias (central Brazil) are coeval with the Araı rift basin. Granites of the g1 suite

are metaluminous and alkaline, while the g2 suite is metaluminous to peraluminous. Both are enriched in F, Sn, Rb, Y,

Th, Nb, Ga and the REE. Primary micas range from Fe-rich biotite to zinnwaldite. The micas of the more evolved

granites and the metasomatic micas are strongly enriched in F, with F/Li between 2 and 10. The initial oNd values of

both suites show a considerable range (�/�/14 to 0) and indicate substantial compositional variation in source. Sn

deposits in Goias are hosted mainly by greisens. Indium is concentrated in quartz�/topaz rock and albitized g2d granite

of the Mangabeira massif and is always related to a cassiterite-sulfide association. This quartz�/topaz rock is of

metasomatic origin, probably generated by a hydrothermal fluid derived from the topaz�/albite granite. Mineralization

in the studied deposits was essentially associated with F enrichment. In the peralkaline Madeira albite granite,

extremely high F contents favored disseminated mineralization, while in the Goias Tin Province (GTP) and Agua Boa

massif greisenization was related to early fluid saturation. The GTP and Pitinga granites display tectonic, petrogenetic,

geochemical, isotopic and metallogenic similarities that can be applied in search of Sn and rare-metal deposits.

� Corresponding author. Tel.: �/55-22-2773-6565; fax: �/55-22-2773-6564

E-mail address: sara@lenep.uenf.br (S.L.R. Lenharo).1 Present address: LENEP-Universidade Estadual do Norte Fluminense Rod. Amaral Peixoto, Km 163, 27925-310, Macae, RJ,

Brazil.

Precambrian Research 119 (2002) 277�/299

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Keywords: Brazil; Proterozoic; Within-plate magmatism; Rapakivi granite; Sn; In; Rare metals

1. Introduction

The majority of primary Sn and rare-metal

deposits are spatially, temporally and genetically

related to plutonic rocks of granitic composition,

or to their volcanic equivalents. These granitic

rocks typically form composite batholiths and

granites associated with Sn and rare-metal depos-

its are commonly the most evolved and latest

intrusive phases. Sn mineralization is often asso-

ciated with highly fractionated ilmenite-bearing S-

type granites in collisional orogens (Lehmann,

1990; Blevin and Chappell, 1992; Pitcher, 1993;

Sillitoe, 1996). Another important environment is

highly evolved alkaline granites in anorogenic ring

complexes (A-types; Pitcher, 1993). A-type gran-

ites generally occur in continental rift environ-

ments, but they may also be found in oceanic

islands and post-orogenic settings. The Precam-

brian granite association with the greatest capacity

to generate Sn deposits are the Proterozoic rapa-

kivi granites that form a group of anorogenic*/

post-orogenic A-type granite complexes (Haapala,

1988).

Sn deposits are mainly associated with rare-

metal mineralization and the chemical fractiona-

tion processes that concentrate Sn also increase the

rare-metal contents in granitic magmas (Pollard,

1995). Rare-metal granites were distinguished in

three geochemical types by Kovalenko (1978)*/

Li�/F, standard and agpaitic. On the basis of

geochemical signature and geological setting, the

rare-metal granites and pegmatites have been

classified as LCT (for Li, Ce, Ta) and NYF (for

Nb, Y, F) associations (Cerny, 1991).

In Brazil, intra-cratonic Proterozoic granites are

responsible for the most important Sn and rare-

metal mineralization, accounting for �/12% of

western world Sn production during the past 20

years. These granitic bodies are related to anoro-

genic granitoids associated with major fracturing

and rifting of stable cratonic zones (Botelho and

Moura, 1998; Bettencourt et al., 1999; Dall’Agnol

et al., 1999). Within-plate magmatism of rapakiviaffinity is widespread in the Amazonian region,

covering a time interval from �/1.8 to 1.0 Ga and

including world-class Sn deposits associated with

the earliest (Pitinga; Lenharo, 1998; Costi et al.,

2000) and latest (Rondonian Tin Province; Bet-

tencourt et al., 1999) suites. In central Brazil, this

type of magmatism gave rise to a medium-class tin

province coeval with the oldest Amazonian exam-ples.

Given the economic importance of the Brazilian

anorogenic granites, the aim of this paper is to

compare the oldest examples of mineralized Pro-

terozoic within-plate rapakivi granites in Brazil:

the intra-cratonic 1815�/1794 Ma Pitinga granites

in Amazonas and the 1770�/1580 Ma rift-related

granites (e.g. Pedra Branca, Mangabeira) in Goias.Petrographic, geochemical and isotopic features of

these A-type granites are presented, focusing on

their similarities, significance and type of asso-

ciated Sn and rare-metal mineralization.

2. Pitinga granites

2.1. Geologic setting

The Pitinga region is located in the central

Amazonian geochronologic province (Tassinari,1996; Santos et al., 2000) or in central block of

the Amazonian craton (Dall’Agnol et al., 1999).

The anorogenic granites show sharp and discor-

dant contacts with their country rocks and have

been interpreted as having been emplaced at 0.5�/

2.0 kbar (Dall’Agnol et al., 1994). The Pitinga

granites intruded Paleoproterozoic silicic volcanic

rocks of the Uatuma Supergroup�/IricoumeGroup (U�/Pb age of 1962�/429/33 Ma, Schob-

benhaus et al., 1994; and 207Pb/206Pb age of 18889/

3 Ma, Costi et al., 2000). These volcanic rocks

show, at least in some samples, consanguinity with

the less evolved rapakivi facies of the Madeira

massif (Lenharo, 1998).

S.L.R. Lenharo et al. / Precambrian Research 119 (2002) 277�/299278

Fig. 1. Geological sketch map of (a) the Pitinga area and (b) GTP. Massifs in the RPS of Goias are: (1) Serra do Mendes; (2)

Mangabeira; (3) Mocambo; (4) Pedra Branca; (5) Sucuri; (6) Soledade. Massifs in the RTS are: (7) Serra da Mesa; (8) Serra Branca; (9)

Serra Dourada. Inset shows study areas relative to South America.

S.L.R. Lenharo et al. / Precambrian Research 119 (2002) 277�/299 279

The Agua Boa and Madeira massifs are elon-gate, parallel to one of the dominant regional

orientations, and display vertical contacts (Fig.

1a). The latest phase of the Agua Boa massif

(topaz granite) has a dyke-like geometry. These

features suggest that the emplacement of the

granitic bodies involved brittle fracturing (Clarke,

1992). The latest albite granite phase of the

Madeira massif shows subhorizontal and subver-tical contacts and was probably emplaced in a

similar manner.

The Agua Boa and Madeira massifs are multiple

intrusions and have been described as petrogra-

phically, geochemically and isotopically similar

(Horbe et al., 1991). Recent data, however,

demonstrate that although the granitic massifs

belong to the same suite, they display distinctpetrographic and geochemical features (Lenharo,

1998). The �/350 km2 Agua Boa massif comprises

an early facies of medium- to coarse-grained,

inequigranular, mainly pyterlitic rapakivi granite,

a medium- to coarse-grained biotite granite with a

fine-grained marginal porphyritic phase and a late

elongate and narrow body of fine-grained por-

phyritic topaz granite (Fig. 1a). The contacts ofpyterlitic rapakivi and biotite granites with the

evolved porphyritic topaz granite are transitional

(Lenharo et al., 2000a). The topaz granite displays

oriented phenocrysts suggesting magmatic flow.

SHRIMP U�/Pb zircon data for the Agua Boa

massif indicate ages of 17989/10 and 18159/5 Ma

for the pyterlitic rapakivi facies and topaz granite,

respectively (Lenharo, 1998; Lenharo et al., 1999).The �/60 km2, elongated Madeira massif is

separated from Agua Boa by a 1 km wide corridor

of volcanic rocks (Fig. 1a). It is composed of, from

border to center, an early fine- to coarse-grained,

equigranular to porphyritic, mainly wiborgitic

rapakivi granite; a fine- to medium-grained, equi-

granular and locally porphyritic biotite granite,

and a fine- to coarse-grained porphyritic albitegranite. The latter is found as a �/2.5 km2

subcircular body in the south-central part of the

massif (Fig. 1a). The albite granite is composed of

a nucleus facies surrounded by a ring-shaped

autometasomatically altered border facies (Costi

et al., 1995, 2000). SHRIMP U�/Pb zircon data for

the Madeira massif indicate ages of 18109/6 Ma

and 17949/19 Ma for the biotite granite and albitegranite, respectively (Lenharo, 1998; Lenharo et

al., 1999). Ar�/Ar in micas for the albite granite

indicate that the system was closed at 17829/5.2

Ma (Lenharo, 1998). Costi et al. (2000) obtained207Pb/206Pb zircon ages of 18249/2 and 18189/2

Ma for the rapakivi and albite granite of the

Madeira massif, respectively.

2.2. Petrography

The petrographic characteristics of the granite

facies from Pitinga and Goias are summarized in

Table 1. The pyterlitic and wiborgitic rapakivi

facies in the Agua Boa and Madeira massifs are

composed of perthitic K-feldspar, quartz, plagio-

clase, biotite and locally amphibole. Accessory

minerals include fluorite, zircon, magnetite, ilme-nite, sphalerite, galena, apatite, titanite, chlorite,

sericite, carbonates and minor pyrite. Rounded

phenocrysts of K-feldspar typically consist of

perthite core surrounded successively by plagio-

clase, perthite and granophyric quartz.

The biotite granite facies in both massifs are

composed of perthitic K-feldspar, quartz, plagio-

clase and biotite. Phengite is commonly observed(up to 1 vol.%) and accessory minerals include

fluorite, opaque, zircon, topaz and rarely apatite.

Plagioclase grains are locally absent, suggesting a

near hypersolvus character. Alteration features

such as swapped rims, sericitization of the micas

and plagioclase and oxidation of the feldspars are

common. The biotite facies of the Agua Boa

massif comprises three subfacies (Lenharo, 1998):North-biotite, in which plagioclase is present only

as perthite and swapped rims; South-biotite, con-

taining plagioclase with relatively calcic cores; and

Topaz-biotite, which occurs in association with the

topaz granite and contains calcic and sodic plagi-

oclase and topaz. The porphyritic topaz granite of

Agua Boa is divided into three textural subtypes

that have many similar textural features (Lenharoet al., 2000a).

The albite granite nucleus facies of the Madeira

massif is composed of fine-grained groundmass

and phenocrysts of quartz (diameter up to 3 mm),

zoned perthitic K-feldspar and subordinate rie-

beckite-arfvedsonite. The quartz phenocrysts have

S.L.R. Lenharo et al. / Precambrian Research 119 (2002) 277�/299280

Table 1

Petrographic features of the granitic facies of Pitinga and GTPsa

Agua Boa massif Madeira massif Goias g1 suite Goias g2 suite

Rapakivi Biotite

granite

Topaz

granite

Rapakivi Biotite

granite

Albite

nucleus

g1a g1b g1c g2a g2b g2c g2d TAG

Color Reddish Pink White Reddish Pink Grey to

white

Grey to

pink

Pink Pink Pink to

grey

Pink Pink Pink to grey White

Diagnostic

mineralogy

Biotite &

hornblende

Biotite Primary

topaz

Biotite &

hornblende

Biotite Albite,

riebeckite &

polylithionite

Biotite

(Fe/

Mg�/8)a

Biotite (Fe/

Mg�/24),

REE-bear-

ing apatite

Biotite (Fe/

Mg�/100),

monazite &

xenotime

Biotite &

hornblende

Biotite (Fe/

Mg�/8),

allanite &

apatite

Biotite (Fe/

Mg�/24) &

monazite

Zinnwaldite

& Li-sidero-

phyllite (Fe/

Mg�/100)

Zinnwaldite

(Fe/Mg�/

500), Li-

phengite,

primary to-

paz

General

texture

Medium- to

coarse-

grained,

equigranular

to seriate

Medium- to

coarse-

grained,

seriate

Fine- to

coarse-

grained,

seriate to

porphyritic

Fine- to

coarse-

grained, seri-

ate and por-

phyritic

Fine- to

medium-

grained,

equigranular

to porphyri-

tic

Fine- to

coarse-

grained,

porphyritic

Coarse-

grained,

porphyri-

tic

Coarse-

grained,

porphyri- tic

to equi-

granular

Coarse-

grained,

porphyritic

to equi-

granular

Medium-

grained,

porphyritic

Coarse-

grained, por-

phyritic to

equi-granular

Medium-

to coarse-

grained,

porphyritic to

equigranular

Medium- to

coarse-

grained, por-

phyritic to

equigranular

Medium-

grained,

equigranular

Inter-

growth

Granophyric Rare grano-

phyric

Granophyric

and dendri-

tic

Granophyric Rare grano-

phyric

Snowball

and dendritic

Grano-

phyric

Rare grano-

phyric

Topaz within

albite

Over-

growth

Pyterlitic

rapakivi and

anti-rapakivi

Wiborgitic

rapakivi and

anti-rapakivi

Pyterlitic

and rare

wiborgi-

tic rapa-

kivi

ASIb Metalumi-

nous

Metalumi-

nous to

peralumi-

nous

Peralumi-

nous

Metalumi-

nous

Metalumi-

nous to per-

aluminous

Peralkaline Metalu-

minous

Metalumi-

nous

Metalumi-

nous

Metalumi-

nous

Metalumi-

nous to pera-

luminous

Metalumi-

nous to pera-

luminous

Metalumi-

nous to pera-

luminous

Peralumi-

nous

a, Pitinga Province: Agua Boa and Madeira massifs; GTP: g1 and g2 suites.

a Biotite (Fe/Mg) in atoms per unit formulae.

b Aluminum saturation index, molar Al2O3/(Na2O�/K2O�/CaO).

S.L

.R.

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ha

roet

al.

/P

recam

bria

nR

esearch

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9(

20

02

)2

77�

/29

92

81

Table 2

Whole-rock geochemical analyses of Pitinga and Goias granites

S.L

.R.

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roet

al.

/P

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esearch

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20

02

)2

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/29

92

82

Table 2 (Continued )

Major oxides and F in wt.%, trace elements in ppm; na, not analyzed; g1a through g2d denote evolutionary sequence of Goias, TAG,topaz-albite granite.a Analyses of Sucuri and Serra Dourada massifs from Bilal et al. (1997).b Representative analyses of Serra Branca massif from Pinto-Coelho (1996).

S.L

.R.

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/P

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nR

esearch

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20

02

)2

77�

/29

92

83

small plagioclase and cryolite inclusions indicatingcontemporaneous growth of quartz, albite and

cryolite. Quartz phenocrysts also contain inclu-

sions of pale blue mica, dark blue amphibole and

cassiterite. The groundmass is composed of albite,

K-feldspar and minor quartz, polylithionite, rie-

beckite-arfvedsonite and cryolite. Further acces-

sory minerals include zircon, cassiterite,

pyrochlore, columbite, xenotime, thorite and ironoxides.

2.3. Geochemistry

Geochemical data on the Pitinga (and Goias)samples are shown in Table 2 and analytical

methods used to acquire the data are described

in Appendix A. Except for the peralkaline albite

granite, the granites of the Agua Boa and Madeira

massifs range from metaluminous to peraluminous

(Table 3), are enriched in SiO2, K2O, Na2O and F

and depleted in MgO, CaO, MnO, TiO2, Fe2O3

and P2O5. These compositional patterns are simi-lar to those observed in ‘tin granites’ (Tischendorf,

1977). All facies are also enriched in Rb, U, Th,

Nb, Y, Zr, Hf and Pb, and relatively depleted in Sr

(Table 2). The minimum Rb content in Pitinga

granites is also higher than in average A-type

granite (cf. Whalen et al., 1987). Sn content varies

from �/1 ppm in the rapakivi facies to more than

3400 ppm in the albite granite.

The rare-earth element (REE) composition of

the Agua Boa and Madeira granites indicates

progressive enrichment in the heavy REE

(HREE) from the earliest to the latest facies

(Fig. 2; Table 2). The albite granite is depleted in

the light REE (LREE) relative to the HREE,

indicating that the HREE behaved more incom-

patibly in the latest facies. All facies of the Agua

Boa and Madeira massifs show a negative Eu

anomaly that increases from the earliest to the

latest facies (Fig. 2).

The compositional trend from the rapakivi

granite through the biotite granite to the topaz-

bearing granite is marked by increasing SiO2 and

decreasing Fe2O3, MnO, MgO, CaO, TiO2 and

P2O5 (Table 2). Al2O3 displays a decreasing trend

from the rapakivi to the biotite facies but slightly

increases from the biotite to the topaz and albite

granite. In the Madeira massif, Na2O contents

decrease from the rapakivi to the biotite granite

and are high in the albite granite. In the Agua Boa

massif, Na2O contents increase from the rapakivi

granite through the biotite granite to the topaz and

microgranites. Zr versus TiO2 variation (Fig. 3)

displays different trends for the granitic bodies and

for the different facies of each body, indicating

Table 3

Characteristic geochemical features of the granite facies from Pitinga and Goias

Pitinga granites Goias granites

Rapakivi Biotite granite Evolved facies g1 suite g2 suite

Topaz granite Albite granite g1a, g1b,

g1c granitesa

g2a, g2b,g2c,

g2d granitesb

Topaz�/albite granite

ASIc 0.92�/0.98 0.95�/1.07 0.98�/1.15 0.85�/0.86 0.88�/0.98 0.90�/1.30 1.20�/1.50

K2O�/Na2O (wt.%) 8.98�/9.20 8.13�/8.99 8.55�/8.70 9.90�/10.60 7.35�/8.25 7.33�/8.59 8.19�/8.36

SiO2 (wt.%) 69�/73 73�/76 75�/76 68�/69 68�/75 67�/75 73�/75

FeOt/(FeOt�/MgO) 0.90�/0.96 0.91�/0.98 0.95�/0.96 0.97�/0.99 0.89�/0.98 0.85�/0.99 0.95�/1.00

Rb/Sr 3�/12 17�/75 17�/108 49�/164 1�/19 2�/55 94�/182

10 000� Ga/Al 2.81�/3.73 2.87�/5.57 4.51�/5.24 8.48�/8.94 2.68�/4.79 3.23�/5.70 5.99�/12.83

(La/Yb)N 2.80�/10.80 2.22�/15.35 1.82�/2.00 0.20�/0.30 4.09�/14.75 4.00�/9.16 1.15�/2.17

(Eu/Eu�)N 0.19�/0.35 0.14�/0.22 0.10�/0.20 0.07�/0.09 0.05�/0.49 0.02�/0.19 0.004�/0.01

a g1a, g1b, and g1c denote distinct facies of the g1.b g2a, g2b, g2c, and g2d denote distinct facies of the g2.c Molar Al2O3/(Na2O�/K2O�/CaO).

S.L.R. Lenharo et al. / Precambrian Research 119 (2002) 277�/299284

that each facies may have evolved by internal

fractionation and that some of the facies are not

directly related to each other by fractionation

processes.

Whole-rock Nd isotopic data for the Pitinga

granites indicate oNd (at 1.8 Ga) values between

�/2.2 and �/0.4 (Table 4) and, in line with the

geochemical data, suggest variable sources, prob-

ably both crust and mantle with predominant

crustal contribution. The clearly more fractionated

albite granite has a similar initial value (�/0.2) as

the other granites and thus does not point to a

distinct source for the albite granite.

2.4. Mineralization

Mineralization in the Agua Boa massif is

associated with cassiterite�/topaz�/mica�/quartz

greisen and cassiterite-bearing sodic episyenite

(Daoud, 1988; Borges et al., 1996; Costi et al.,

1996). Widespread albitization of the host granites

has been considered a typical pre-greisenization

process (Borges et al., 1996). Greisens and sodic

episyenites are spatially associated with K-feld-

spar-rich zones found in all facies of the massif and

are predominantly related to the topaz granite and

microgranite.

Fig. 2. Chondrite-normalized REE patterns for (a) Madeira massif of Pitinga; (b) Agua Boa massif of Pitinga; (c) Goias g1 suite; (d)

Goias g2 suite. For Goias, distinct facies (g1a, g1b, g1c, g2a, g2b, g2c and g2d) are denoted. Abbreviations: rapakivi, rapakivi facies;

TAG, topaz�/albite granite; biotite, biotite�/granite; N-biotite, north-biotite facies; S-biotite, south-biotite facies; T-biotite, topaz-

biotite facies; albiteNuc, albite granite nucleus facies; albiteBor, albite granite border facies; and Topaz, topaz granite.

S.L.R. Lenharo et al. / Precambrian Research 119 (2002) 277�/299 285

In the Madeira massif, mineralization associated

with greisen and other alteration types is minor

and confined to the contact of the wiborgitic

rapakivi and biotite facies and the albite granite.

The albite granite contains, however, disseminated

magmatic cryolite�/zircon�/cassiterite�/pyrochlore

�/columbite�/tantalite�/xenotime mineralization.

The F- and Na-rich peralkaline albite granite

Fig. 3. TiO2 vs. Zr diagram for Pitinga indicating the evolution of the Agua Boa and Madeira massifs. Lower plot shows the

lowermost part of the upper diagram in detail. Abbreviations: N, north-biotite facies; S, south-biotite facies; T, topaz�/biotite facies.

S.L.R. Lenharo et al. / Precambrian Research 119 (2002) 277�/299286

also contains two massive cryolite bodies located

approximately 150 m below the roof of the granite(Lenharo et al., 1997; Costi et al., 2000). These

bodies may reflect formation of immiscible fluo-

ride melts during crystallization of the albite

granite (Lenharo et al., 2000b). The albite granite

can be classified as a mixed NYF�/LCT fertile

granite in the sense of Cerny (1991).

3. Goias tin granites

3.1. General characteristics

At least three generations of Sn-related granites

have been recognized in the Goias state: Paleo-

proterozoic syn- to post-tectonic peraluminous

granites, Paleo- to Mesoproterozoic within-plate

granites and Neoproterozoic syn- to late-tectonic

granites (Marini and Botelho, 1986; Pimentel et

al., 1991; Botelho and Moura, 1998; Pimentel et

al., 1999). The northern Goias state includes the

Goias Tin Province (GTP), which is separated into

the Rio Tocantins subprovince (RTS) in the west

and Rio Parana subprovince (RPS) in the east

(Fig. 1b). The main Sn deposits are related to

within-plate granites that are divided in two

geochemical and geochronological suites, the 1.77

Ga g1 and the 1.58�/1.57 Ga g2 (Pimentel et al.,

1991; Botelho, 1992; Rossi et al., 1992).

These granite suites intruded Archaean-Paleo-

proterozoic granite gneisses and mylonitic rocks

Table 4

Nd isotopic composition of Pitinga and Goias granites

Rock type Massif Sample Sm (ppm) Nd (ppm) 147Sm/144Nda 143Nd/144Nd (9/2 S.E.)b oNd (T)c TDM (Ga)d

Pitinga

Rapakivi Madeira MDRG-2 13.92 75.09 0.112 0.511603 (05) �/0.8 2.16

Rapakivi Agua Boa AgBG-39 21.65 118.91 0.110 0.511579 (03) �/0.8 2.16

Biotite Agua Boa AgBG-49 9.04 49.54 0.110 0.511643 (05) �/0.4 2.07

Biotite Madeira MDRG-39 13.75 66.68 0.125 0.511677 (08) �/2.2 2.35

AlbiteN. Madeira MRDG-11 13.74 24.70 0.336 0.514272 (06) �/0.2 �/

Goias e

RPS-g1 Mangabeira MM-1A 13.17 68.75 0.116 0.511386 (05) �/6.1 2.58

RPS-g1 Mendes ME-08 13.43 66.44 0.122 0.511769 (06) 0.0 2.10

RPS-g1 Mendes ME-01A 19.57 78.79 0.150 0.511388 (05) �/13.9 �/

RPS-g1 Sucuri SU-06A 28.73 132.3 0.131 0.511675 (05) �/3.9 2.50

RPS-g1 Soledade SS-1 17.06 88.62 0.116 0.511479 (04) �/4.3 2.43

RPS-g1 Pedra Branca PB-188A 21.35 83.12 0.155 0.511824 (03) �/6.5 �/

RPS-g2 Pedra Branca PB-75A 27.97 148.8 0.114 0.511423 (06) �/3.9 2.47

RPS-g2 Pedra Branca PB-02 72.40 175.5 0.249 0.512639 (04) �/11.9 �/

RPS-g2 Mocambo MO-06 greis 26.87 81.86 0.198 0.512307 (06) �/6.3 �/

RTS-g2 Serra da Mesa 84-GD-SM2 27.57 138.0 0.121 0.511356 (04) �/7.9 2.77

RTS-g2 Serra Branca SB-322 25.51 116.1 0.133 0.511796 (04) �/3.4 2.34

RTS-g2 Serra Dourada PE-283 19.19 96.26 0.120 0.511761 (05) �/1.4 2.07

RTS-g2 Serra da Mesa SM-20 17.73 89.21 0.120 0.511572 (03) �/5.0 2.38

Diorite Pedra Branca PB-152 2.55 12.19 0.126 0.512003 (10) �/3.6 1.80

Abbreviations, RPS, Rio Parana subprovince; RTS, Rio Tocantins subprovince; Rapakivi, pyterlitic and wiborgitic rapakivi facies;

Biotite, biotite facies; AlbiteN., albite granite nucleus facies.a Estimated error on 147Sm/144Nd is better than 9/0.05% (1s ) for Pitinga samples.b Normalized to 146Nd/144Nd�/0.7219, estimated error on 143Nd/144Nd is better than 9/0.00001 (1s ) for Pitinga samples.c Initial oNd values calculated at 1.8 Ga (Pitinga), 1.77 Ga (Goias g1) and 1.58 Ga (Goias g2), using chondritic ratios of

143Nd/144Nd�/0.512638 and 147Sm/144Nd�/0.1967.d Depleted mantle model age calculated according to DePaolo (1981).e Data from Pimentel et al. (1999), Pimentel and Botelho (2001).

S.L.R. Lenharo et al. / Precambrian Research 119 (2002) 277�/299 287

and are coeval with the development of the Araı

rift basin. Rift sequences, represented by the Araı

Group, surround the plutons and were, together

with the granites, deformed and weakly metamor-

phosed during the Brasiliano-Pan-African orogeny

(Alvarenga et al., 2000). According to Liverton

and Botelho (2001), these granites are shallow, as

evidenced by miarolitic cavities, associated volca-

nic rocks and existence of conglomerates in the

surrounding Araı Group with fragments of the Sn-

mineralized granites.

The g1 suite Soledade granite and cogenetic

dykes of the RPS represent the rapakivi magma-

tism in the GTP. The rocks are dark grey,

granophyric and porphyritic with ovoidal K-

feldspar and blue quartz phenocrysts, commonly

show pyterlitic and, rarely, wiborgitic textures

(Table 1). Early, weakly Sn-mineralized granites

(the g1 suite) are found only in the RPS. The most

important Sn deposits are related to the youngest

g2 suite that is present in both subprovinces

(Botelho and Moura, 1998).

Granites of g1 suite are potassic and show

alkaline affinity, while the g2 suite granites are

metaluminous to peraluminous, have lower K/Na

ratios and higher Li, Rb, Sn and Ta contents

(Table 2). Both suites are enriched in F, Sn, Rb, Y,

Th, Nb, Ga and REE (Table 2). REE patterns of

Fig. 4. Geological map of the Pedra Branca massif, GTP.

S.L.R. Lenharo et al. / Precambrian Research 119 (2002) 277�/299288

the less evolved biotite granites are highly fractio-

nated [(La/Yb)N �/20], while the later leucogra-

nites display nearly flat REE patterns (Fig. 2). The

high concentrations of Nb, Y and F, and the high

Nb/Ta and F/Li ratios show that g1 and g2

comprise a fertile NYF granite�/pegmatite associa-

tion (cf. Cerny, 1991). Primary micas range from

very Fe-rich biotite to zinnwaldite, with composi-

tions close to annite in the less evolved granites.

The most evolved tin granites in the g2 suite are

Li-siderophyllite- to zinnwaldite-bearing granite

and topaz�/albite granite of the Mangabeira and

Pedra Branca massifs. In the RTS, evolved g2-type

granites are present only in the Serra Brancamassif (Pinto-Coelho, 1996). In both subprovinces,

these granites have the highest magmatic Sn

concentrations (Table 2). The massifs display

prominent greisen zones in margin of leucogranite

bodies (Mangabeira) or along linear strike-slip

shear zones (Pedra Branca).

Sn and In deposits associated with the within-

plate Goias granites are hosted in greisenizedcupolas and fractures (Serra Branca in RTS, Pedra

Branca and Mangabeira massifs in RPS), albitized

zones (Serra Dourada in RTS and Sucuri massifs

in RPS) and greisenized granite�/mylonite country

rocks (Mocambo in RPS). The main mineraliza-

tion was related to fluorine-rich hydrothermal

alteration that gave rise to mineral associations

with quartz, fluorite, topaz, phengite, siderophyliteand minor zinnwaldite. The best known examples

of these deposits are found in the Pedra Branca

and Mangabeira massifs that are described in

more detail below.

Whole-rock Nd isotopic data on the Goias tin

granites indicate initial oNd values between �/13.9

and 0 for RPS and between �/7.9 and �/1.4 for

RTS (Table 4). There is no substantial differencein oNd between g1 (�/13.9 to 0) and g2 (�/11.9 to

�/1.4), indicating similar, heterogeneous, source

characteristic for the two suites. The initial oNd and

TDM values (Table 4) are compatible with the idea

that the Goias tin granites were generated by

melting of a heterogeneous Archean-Paleoproter-

ozoic crust or by different degrees of mixing

between mafic and felsic (crust-derived) magmas.

3.2. Pedra Branca massif

The Pedra Branca massif includes five of the

lithologic facies (g1b, g1c, g2b, g2c and g2d)

recognized in the GTP (Fig. 4). The g1 suite is

composed of biotite granites that show substantial

variation in biotite composition (2�/0.5 wt.%

MgO) and in the character of REE-bearingaccessory minerals*/apatite and allanite are found

in the early facies, monazite in the late facies. The

granites of the g2 suite are biotite and zinnwaldite

granites that are more aluminous than the g1

granites, and are directly related to Sn mineraliza-

tion.

Fig. 5. TiO2 vs. MgO (a) and Nb vs. Ta (b) diagrams for Goias

tin granites indicating the evolution of the g1 and g2 suites, (a)

separates different facies (g1a, g1b, g1c, g2a, g2b, g2c and g2d)

of the g1 and g2 suites, (b) displays general trends.

S.L.R. Lenharo et al. / Precambrian Research 119 (2002) 277�/299 289

3.2.1. Petrography

The dominant facies in the Pedra Branca massif

is a biotite granite rich in zircon, apatite and

allanite (named g1b by Botelho, 1992). Further

accessory minerals are ilmenite, monazite and

xenotime. The greisens derived from g1b facies

are rich in chlorite and magnetite and do not host

Sn mineralization. The other facies are biotite

granites (g1c, g2b and g2c) or biotite/zinnwaldite

granite (g2d; Table 1). The g1c facies is composed

of microcline, bluish quartz and rare biotite as

phenocrysts and an overall composition of 40%

Fig. 6. Geological map of the Mangabeira massif, GTP. The MGZ indicates the metasomatic aureole in the g2d granite.

S.L.R. Lenharo et al. / Precambrian Research 119 (2002) 277�/299290

microcline, 30% quartz, 25% albite and 5% biotite.Accessory minerals are fluorite, zircon, ilmenite,

magnetite, allanite, monazite and thorite. g1c is

commonly greisenized and the metasomatic rocks

are characterized by the association of topaz-Li-

siderophyllite and quartz-Li-phengite.

The g2b facies is composed of strongly perthitic

microcline, quartz, plagioclase and biotite. The

main accessory minerals are zircon, allanite, fluor-ite, apatite and xenotime. g2c is similar to g2b,

except for the absence of allanite and apatite and

the lower MgO contents in biotite (1.5 wt.% in g2c

vs. 4.5 wt.% in g2b). The g2d facies is the most

evolved granitic phase in the massif with strongly

perthitic microcline, quartz, albite (An0�2) and

biotite. Accessory minerals are fluorite, ilmenite,

zircon, monazite and thorite. The greisenized g2dfacies and greisens contain light green phengitic

mica, quartz, rare topaz, niobium-tantalates and

Nb-rich ilmenite.

3.2.2. Geochemistry

The MgO versus TiO2 diagram (Fig. 5a) can be

used to discriminate the g1 and g2 suites in Pedra

Branca as trends with variable slopes are observed.For a given MgO value, the g1 suite granites are

more enriched in TiO2. The behavior of Ta, Th

and Nb is also specific for each suite, g1 shows

large variation in Nb and small variation in Ta, g2

displays opposite trends (Fig. 5b). Also, the g1

granites are always richer in Ba than the g2

granites. The g1 granites show an increase of

both LREE and HREE with increasing SiO2,and display a weak decrease of LREE in the latest

facies (Fig. 2). In the g2 suite, the decrease of

LREE is more pronounced.

3.2.3. Mineralization

The highest Sn concentrations in the RPS are

found in the greisens related to the g2d granite in

the Pedra Branca massif. The g2d facies has given

rise to albitized and greisenized granites andgreisens with or without topaz. Two mineralized

zones are recognized, a 10 km2 area hosting topaz-

Li-siderophyllite greisen swarms at the roof of a

granite cupola and a 5 km long and 100 m wide

fractured zone containing topaz-Li-siderophyllite

greisens.

3.3. Mangabeira massif

3.3.1. Petrography

The Mangabeira massif is located in the RPS

(Fig. 1) and is composed of a biotite granite related

to the g1 suite, and a Li-siderophyllite granite and

a minor topaz�/albite granite of the g2 suite. The

topaz�/albite granite is responsible for Sn and In

mineralization in the main greisenized zone

(MGZ) of the massif (Fig. 6). The MGZ is

composed of several g2 suite granite facies, grei-sens and a quartz�/topaz rock. The dominant Li-

siderophyllite granite is composed of quartz (30%),

microperthitic microcline (30�/35%) and albite

(An0, 30�/35%), and represents the less evolved

facies of the g2 suite within the MGZ (Botelho,

1992). Primary Li-siderophyllite has commonly

Fig. 7. TiO2�/10 000/Zr vs. Nb/Ta diagram for Pitinga (a) and

Goias (b). TAG denotes topaz�/albite granite.

S.L.R. Lenharo et al. / Precambrian Research 119 (2002) 277�/299 291

been transformed to phengite. The accessory

minerals are zircon, monazite, magnetite and

locally ilmenite. When greisenized, the granite

becomes richer in phengite (10%) and contains

metasomatic anhedral topaz, monazite, fluorite

and disseminated cassiterite. The phengite�/quartz

greisen also contains late arsenates.The topaz�/albite granite is intrusive into the Li-

siderophyllite granite and has caused a metaso-

matic aureole (Fig. 6). The granite contains 35%

quartz, 20% microperthitic microcline, 20% pure

albite, 5�/20% magmatic topaz and 10% zinnwal-

dite; zircon, monazite and cassiterite are rare

(Table 1). Magmatic albite contains euhedral

topaz inclusions (Moura and Botelho, 2000).

Two types of greisen are present, one containing

quartz, topaz and up to 10% zinnwaldite and the

other mainly zinnwaldite.

The quartz�/topaz rock is found within the

topaz�/albite granite as a white elongated body

composed mainly of quartz, topaz, zinnwaldite,

arsenopyrite and cassiterite. Other minerals in-

clude monazite, zircon, fluorite, sphalerite, wol-

framite, lollingite, chalcopyrite, bismuthinite,

galena, stannite and tennantite. Late scorodite,

malachite, covellite and In, Bi, Ba, K, Pb, U and

Sn arsenates are also present.

Three groups of micas can be distinguished in

the MGZ; these belong to the phengite-zinnwaldite

series of Foster (1960). Group A micas occur in the

quartz�/topaz rock and the topaz�/albite granite

and are rich in total FeO (�/10 wt.%), F (�/6.0

wt.%), Rb and Mn, and are poor in Al. Group B

micas in the g2 pink granite have total

FeO between 5 and 9.5 wt.%, F between 2.0 and

4.5 wt.% and low Rb, Li and Mn and high Al.

Group C micas are found in some metasomatized

topaz�/albite granites and are characterized by

intermediate contents of F, FeO, Mn, Al, Li and

Rb.

Fig. 8. Nd isotopic composition of the Proterozoic granites of Pitinga and Goias plotted in an oNd vs. age diagram. Evolution paths of

Paleoproterozoic rocks from the Sao Francisco craton (Pimentel and Botelho, 2001) and the central Amazonian geochronologic

province of the Amazonian craton (Tassinari, 1996) are also shown.

S.L.R. Lenharo et al. / Precambrian Research 119 (2002) 277�/299292

3.3.2. Geochemistry

The topaz�/albite granite is richer in Na2O than

in K2O (molar Na/K is predominantly �/1), while

g2d granite of the MGZ has K2O�/Na2O. The less

altered samples of the topaz�/albite granite have A/

CNK between 1.3 and 1.5 (Table 3) and are rich in

F, Li, FeO, Al2O3, Rb Zn, Ta, Nb and Sn and

poor in TiO2, MgO, P2O5, CaO, Zr, Ba and Sr.

The MGZ granites, together with other evolved g2granite facies of the province, are Ta-rich,

although they still contain more Nb than Ta

(Botelho and Moura, 1998; Moura and Botelho,

2000). In many variation diagrams, the topaz�/

albite granites and the g2d granites define linear

trends that have been interpreted to reflect mag-

matic evolution from g2d to the topaz�/albite

granites (Moura, 1993). In the case of Li, F, Rband Fe, the trends reflect increasing mica specia-

lization toward topaz�/albite granite (Moura and

Botelho, 1994). The MGZ granites are enriched in

REE, as are the other granites in the RPS (Fig. 2).

The topaz�/albite granite and g2d granites, in

particular, have flat REE patterns, with strong

negative Eu anomalies (Table 2).

3.3.3. Hydrothermal alteration and mineralization

The topaz�/albite granite and g2d granites have

undergone pervasive greisenization related to the

emplacement of the topaz�/albite granite. This

involved remobilization of several elements and

resulted in economic concentrations of Sn; Al2O3,

SiO2, K2O, Fe2O3, P2O5, Y, Zr, F, Zn, Li, Rb, Be,

Sn and W were enriched and Na2O depleted in theprocess. The REE, specially the LREE, were also

mobile during the greisenization, probably owing

to formation of F complexes which gave rise to

hydrothermal monazite.

Fluid inclusion data for the quartz�/topaz rock

(Pontes et al., 2001) have revealed two cogenetic

fluid systems: H2O�/NaCl and H2O�/CO2�/NaCl.

Field, textural and fluid inclusion data favor ametasomatic origin for this rock, involving crystal-

lization from a hydrothermal fluid derived from

the topaz�/albite granite magma at P�/T conditions

similar to those involved in greisen formation. The

Sn mineralization is mainly hosted by two types of

greisen veins: Li-phengite9/quartz and Li-

phengite9/zinnwaldite9/topaz�/quartz. Cassiteriteand minor wolframite are the main ore minerals.

Anomalous contents of In are restricted to the

quartz�/topaz rock and albitized g2d granite and

are always related to a cassiterite�/sulphide asso-

ciation. Economic concentrations (30�/4100 ppm)

are found only in the quartz�/topaz rock. Overall,

the granites of the MGZ have less than 20 ppm In,

while the greisens are richer (20 ppm in the g2dgreisen and 57 ppm in the greisen related to the

topaz�/albite granite), suggesting enrichment of In

at the magmatic stage and subsequent mobiliza-

tion during greisenization. In-bearing minerals

present are roquesite (CuInS2), dzhalindite

(In(OH)3) and yanomamite (InAsO4 �/ 2H2O; Bo-

telho et al., 1994). The associated cassiterite

contains 0.3 wt.% In2O3 on average.

4. Discussion

The Sn- and rare-metal-mineralized granites

from Pitinga and Goias provinces have similar

Nb/Ta and TiO2/Zr signatures with a character-

istic decrease in TiO2/Zr from the earlier to the

evolved facies (Fig. 7; Table 2). The Pitinga albitegranite has very low Ti/Zr and does not have a

counterpart in the GTP. This is in line with the

proposed specialized source for the albite granite.

Goias topaz�/albite granite data define a separated

cluster in Fig. 7b, but the evolutionary trend

suggests that this granite could represent a residual

liquid evolved from g2. This is also indicated by

the MgO�/TiO2 and Nb�/Ta correlations (Fig. 5)and REE patterns (Fig. 2). Furthermore, the

relations in Figs. 3 and 7 suggest that the Pitinga

topaz granite is an evolved phase of the biotite

granite.

The overall results from Goias and Pitinga

suggest that the late specialized peraluminous

granites may have been formed by fractionation

of granite magmas with alkaline affinities. How-ever, for the most alkaline rock in the studied

provinces, the peralkaline albite granite from

Pitinga, no geochemical correlation with the ear-

lier granite phases seems to exist, and a different

model involving partial melting of a specific source

is suggested. Lenharo (1998) proposed that the

S.L.R. Lenharo et al. / Precambrian Research 119 (2002) 277�/299 293

albite granite could either represent a residual meltfrom a peralkaline magma or a magma from a

very peculiar source. Fractionation processes in

peralkaline magma are generally invoked to lead

to the increase of F, alkalis and lithophile trace

elements and high HREE/LREE ratio. The only

obvious case for the origin of the albite granite

through differentiation would be related to the

peralkaline Europa granite located �/15 kmnortheast of the albite granite (Fig. 1; Lenharo,

1998). The south-eastern border of the Europa

granite has been dated at 18299/1 Ma (Pb�/Pb

zircon age; Costi et al., 2000) and was not

considered a valid candidate for the initial magma

of the albite granite by Costi et al. (2000).

Nd isotopic composition of the Pitinga and

Goias tin granites is illustrated in an oNd versusage diagram in Fig. 8. Initial oNd values for the two

provinces show quite different ranges. Pitinga has

relatively little variation, �/2.2 to �/0.4, Goias is

much more heterogeneous, �/13.9 to 0. On aver-

age, the Goias granites are clearly less radiogenic

than the Pitinga granites. Pimentel et al. (1999)

interpreted the large range in the initial oNd values

of Goias granites as a result of different degrees ofmixing of mafic and felsic magmas. The composi-

tion of the juvenile mafic component could be

provided by the dioritic intrusions with oNd (at

1.77 Ga) of �/3.9 (Table 4; Fig. 8). These diorites

are probably related to the basalts of the Araı

Group that represents the mafic member of the

bimodal magmatism in the rift environment.

Another interpretation for the large spread in theinitial oNd values for g1 and g2 granites would be

considerable heterogeneity of the crustal (sialic)

source (Pimentel and Botelho, 2001). For both

models, a predominant crustal component is

required.

In Fig. 8, Pitinga and Goias granites plot within

the evolution path of the Paleoproterozoic rocks

from the Sao Francisco craton. Pitinga graniteshave a considerably smaller variation in initial oNd

(close to zero values) suggesting a more important

contribution from the mantle or a different and

more homogeneous crustal source compared with

Goias granites. Geochemical data of Pitinga

granites suggest different sources for the majority

of the facies (Figs. 3 and 7) and isotopic data

indicate that these sources are almost similar intheir Nd isotopic characteristics. The TDM model

ages for both granitic suites are within similar

range, 2.4�/2.1 Ga for Pitinga, and 2.5�/2.1 Ga for

most of the Goias samples. However, some TDM

values for the g1 and g2 Goias granites are older,

up to 2.77 Ga, implying, together with more

negative initial oNd values, that there was a

significant contribution of older crustal material.Recent structural, geochemical and geochrono-

logic data for syn- to post-tectonic peraluminous

granites and pegmatites surrounding some of the

Goias g1 and g2 granites indicate ages of 2.2�/2.1

Ga (Botelho et al., 1999; Sparrenberger and

Tassinari, 1999). These data imply that the begin-

ning of the within-plate magmatism in Goias took

place at least 300 Ma after the main compressiveevent of the Trans-Amazonian orogeny. Thus the

Goias rapakivi granites cannot be regarded as

direct products of the Trans-Amazonian orogenic

processes. Similarly, the 1.65�/1.54 Ga rapakivi

granites of southeastern Fennoscandia (Finland),

with petrographic and geochemical characteristics

similar to the Goias g1 and g2 suites, are 150�/250

million year younger than the post-orogenic grani-tic magmatism, and a direct connection between

the rapakivi granites and the Svecofennian oro-

geny (1.9�/1.87 Ga) has been considered improb-

able (Haapala and Ramo, 1992).

Two different processes of metal concentration

have operated in Pitinga and Goias, resulting in

magmatic and greisen-type mineralizing systems.

In Pitinga, mineralization in the Madeira massifresulted in disseminated magmatic cryolite�/

zircon�/cassiterite�/pyrochlore�/columbite�/tanta-

lite�/xenotime or in massive cryolite bodies in the

F-rich peralkaline albite granite. In the Agua Boa

massif, Sn mineralization is associated with hydro-

thermal processes and includes cassiterite�/topaz�/

mica�/quartz greisen and cassiterite-bearing sodic

pisyenite styles. In Goias, Sn and In deposits arerelated to hydrothermal processes and are hosted

mainly by greisenized cupolas, greisen veins and

albitized zones in the granites. The main miner-

alization processes were related to F-rich hydro-

thermal alteration and they gave rise to mineral

associations with quartz, fluorite, topaz, phengite,

siderophylite and minor zinnwaldite. Despite dif-

S.L.R. Lenharo et al. / Precambrian Research 119 (2002) 277�/299294

ferences in the mineralizing processes in Pitingaand Goias, the concentration of metals in both

regions is essentially related to F enrichment.

The data obtained for the Goias and Pitinga

deposits accord with the experiments of Manning

and Pichavant (1988) who examined the system

Qz�/Ab�/Or�/H2O with F contents between 0 and 4

wt.% and noted that increasing F leads to reduc-

tion in liquidus and solidus temperatures ofgranitic melts. Volatile-enriched residual granitic

melts may thus persist to relatively low tempera-

tures (below 700 8C at 1 kbar) and may become

enriched in incompatible elements, especially me-

tals of economic interest. In these systems, Sn can

partition with F into the melt. In the Agua Boa

and Goias Sn and rare-metal deposits, fluorine

enrichment controlled the evolution of the granitesat shallow crustal levels and also enhanced the

concentration of metals; the majority of the

mineralization occurred as a consequence of early

fluid saturation and subsequent greisenization. As

a result of the early metal-bearing fluid separation,

Sn enrichment in the magmatic stage was not so

important: the Pitinga topaz granite has 38 ppm

Sn, Goias g2d granite 30 ppm and Goias topaz-albite granite 25 ppm. In the Mangabeira massif,

an extremely F-rich phase separated from the

topaz�/albite granite and partitioned the metals,

giving rise to the Sn- and In-mineralized quartz�/

topaz rock.

In the Madeira deposit, the high F contents in

the albite granite (up to 9 wt.%) favored metal

concentration throughout the crystallization his-tory of the highly evolved granitic magma. Pre-

cipitation of ore minerals occurred

contemporaneously with crystallization of the

albite granite and led to a magmatic disseminated

mineralization. The presence of magmatic cassi-

terite and rare-metal minerals indicates that the

melt became saturated in these metals prior to

fluid saturation. Thus, fluid saturation was con-trolled by F and alkalis, as high F increases the

solubility of H2O in the melt (cf. Holtz et al.,

1993).

F-saturated phases, such as topaz and cryolite,

may have precipitated when the fluid segregated

from the granitic melt to constitute a hydrother-

mal phase. In this context, magmatic cryolite and

topaz are likely quench phases for F saturation ingranitic melts (Manning, 1981). Before the forma-

tion of the Goias and Agua Boa greisen systems,

topaz precipitated in topaz granites as a magmatic

phase, lowering the vapor phase solubility and

leading to subsequent exsolution of metal-bearing

fluids. In the Madeira albite granite, cryolite seems

to be the main indicator of F saturation.

5. Conclusions

The Pitinga and Goias granites are typical

Proterozoic rapakivi granites of Brazil. A rifting

environment is inferred for the emplacement of the

Goias granites, while the Pitinga granites probably

represent within-plate magmatism associated withextensional fracture systems. The TDM model ages

of both Pitinga and Goias rapakivi provinces are

in a similar range (2.5�/2.1 Ga) and the beginning

of this within-plate magmatism in Goias took

place at least 300 Ma after the main compressive

event of the Trans-Amazonian orogeny. Thus, the

Goias rapakivi suite is not considered as a direct

result of that orogenic event. The Nd isotopic dataindicate a predominant Archean-Paleoproterozoic

crustal source component for the Goias rapakivi

granites, while for the Pitinga granites a source

with more significant mantle component or with

different younger crustal characteristics is pro-

posed.

The Goias and Pitinga rapakivi granites have Sn

and rare-metal mineralization essentially asso-ciated with specialized F-rich system. In the GTP

and in the Agua Boa massif of Pitinga, the

specialized metaluminous to peraluminous gran-

ites seem to have been formed by fractionation of

granitic magmas with alkaline affinities. The

Mangabeira massif displays the most peculiar

mineralization, with high concentration of In. In

Pitinga, the peralkaline albite granite of theMadeira massif displays no geochemical correla-

tion with the earlier granite phases and a different

generation model is envisaged. In the Goias

granites and the Agua Boa massif, the mineraliza-

tion is related to greisen systems. In the albite

granite of the Madeira massif the system formed a

S.L.R. Lenharo et al. / Precambrian Research 119 (2002) 277�/299 295

disseminated polymetallic body probably owing tohigher amount of F and alkalis in the magma.

The characteristics of the studied provinces have

important implications for exploration of Sn and

rare-metal deposits both on regional and local

scale. Regionally, they are related to granitic

magmatism in a Paleo- to Mesoproterozoic

within-plate tectonic environment. Locally, the

mineralization is genetically associated with themost evolved granitic facies of rapakivi magma-

tism, with enrichment of F and alkalis crucial for

the metal concentration and style of mineraliza-

tion.

Acknowledgements

The authors acknowledge financial support

from FAPESP (Project 95/4732-6), CAPES and

CNPq (Project 400620/95-2). Thanks are also due

to Geochronological Lab of the University of

Brasılia and the IGCP-426 Committee. Special

thanks go to Sylvia M. Araujo and Fabio C.

Mendonca for helping in manuscript organization.

The authors express their thanks to the journalreferees, Ilmari Haapala and Valdecir de Assis

Janasi, and to the editors, Jorge S. Bettencourt and

O. Tapani Ramo, for constructive and thorough

reviews of this paper.

Appendix A: Analytical methods: elemental

geochemistry

Geochemical data on representative samples are

presented in Table 2. The complete data set (in

total, 140 samples on Pitinga, 150 samples on

Goias) is available from the senior author upon

request.

For Pitinga, the samples were split and pulver-

ized in both tungsten carbide and chrome steel

mills. Using tungsten carbide crush, the majorelements and the majority of trace elements were

analyzed by X-ray fluorescence (XRF) at the

Advanced Analytical Center, James Cook Uni-

versity, Townsville, Australia. The measurements

were carried out using a Siemens XRF sequential

spectrometer, SRS303, fitted with an end-window

Rh tube. Major element analysis was carried outon fused glass discs and trace element analysis was

determined on pressed powder pellets. Precision,

expressed at the 2s level, is better than 1% for

major elements and better than 10% for most trace

elements: SiO2 1.02%, TiO2 1.91%, Al2O3 1.16%,

Fe2O3 1.18%, MnO 10.0%, MgO 2.7%, CaO

1.22%, Na2O 2.15%, K2O 0.66%, P2O5 2.04%, F

10.0% (detection limit 0.02%), Rb 5.7% (3 ppm),Sr 4.2% (3 ppm), Y 4.0% (3 ppm), Zr 2.6% (3

ppm), Nb 4.6% (3 ppm), Ga 4.5% (3ppm), Sn 6.5%

(10 ppm), Ba 7.1% (10 ppm). Yttrium in samples

from the albite granite was also determined by

ICP-AES. The remaining trace elements and REE

were determined by neutron activation analyses

(NAA) at Becquerel Laboratories, New South

Wales, Australia. Detection limits and precisionare: Ta 1.0 ppm and 9.6%, La 0.50 ppm and 4.1%,

Ce 2.0 ppm and 8.0%, Sm 0.20 ppm and 3.0%, Eu

0.50 ppm and 8.0%, Tb 1.0 ppm and 8.9%, Yb 0.50

ppm and 3.7%, Lu 0.20 ppm and 4.5%. Neutron

activation analysis was carried out on the splits

crushed in chrome steel mill.

The Goias were pulverized in agate mill. The

major elements were analyzed by XRF [SiO2,Al2O3, Fe2O3(t), MnO, CaO, K2O, P2O5] and

ICP-AES (Na2O, TiO2 and MgO) at the Geo-

chemical Laboratory in the Ecole de Mines de

Saint-Etienne, France, and at GeoLab-Geosol and

Lageq at the University of Brasılia, Brazil. In some

samples, F was determined by specific ion elec-

trode. The majority of trace elements (Zr, Y, Sr,

Ba, Rb, Nb and Sn) were also analyzed by XRF atthe same laboratories. Major and trace elements

analyses were carried out by lithium borate fusion

and pressed powder pellets, respectively. Ta was

determined by NAA at the Pierre Sue Laboratory,

Saclay, France. REE were analyzed by ICP-AES.

Precision is better than 3% for major elements and

better than 10% for most trace and RE elements.

Analytical methods: Nd isotopes.Nd isotopic analyses of five samples from

Pitinga granites were carried out at University of

Texas, Austin. Rock powders were dissolved in

Teflon pressure dissolution capsules at 210 8Cusing HF and HNO3. These solutions were dried

and re-dissolved in the same capsules in 2.3 N

HCl. REE were separated from these solutions

S.L.R. Lenharo et al. / Precambrian Research 119 (2002) 277�/299296

using standard cation exchange techniques. Nd

and Sm were separated from REE fractions on

HDEHP columns. All reagents were purified by

sub-boiling distillation and all chemical proce-

dures were conducted in laminar flow HEPA

filtered air. Blank contributions of about 30 pg

of Nd are inconsequential compared with the

hundreds of ng Nd samples. Nd and Sm were

analyzed as the metal on the Finnigan MAT 261

multicollector mass spectrometer using dynamic

data collection routine for Nd and a static config-

uration for Sm. Standards ran with each set of

samples included CIT B Nd and Ames Sm. The

CIT B standard averages oNd of �/14.409/0.29 2s

(n�/40). The oNd values at the time of emplace-

ment are based on the SHRIMP U/Pb in zircon

age of 1800 Ma derived by Lenharo (1998). The

TDM model ages were calculated according to

DePaolo (1981).

Nd isotopic analyses of 14 samples from Goias

tin granites were carried out at the Geochronology

Laboratory of the University of Brasılia. The Sm

and Nd analytical procedures as described by

Pimentel and Botelho (2001) followed the techni-

que of Richard et al. (1976), in which separation of

the REE as a group using cation-exchange col-

umns precedes reversed-phase chromatography for

the separation of Sm and Nd using columns

located with HDEHP supported on Teflon pow-

der. Recently, the laboratory is using the RE-Spec

and Ln-Spec resins for REE and Sm�/Nd separa-

tion. Sm and Nd were analyzed as the metal on the

Finnigan MAT 262 using static configuration and

a mixed 149Sm�/150Nd spike. Sm and Nd samples

were loaded onto Re evaporation filaments of a

double filament assembly. Uncertainties on Sm/

Nd and 143Nd/144Nd ratios are considered to be

better than 9/0.05% (1s) and 9/0.00001 (1s),

respectively, based on repeated analyses of inter-

national rock standards BCR-1 and BHVO-1.143Nd/144Nd ratios were normalized to a146Nd/144Nd ratio of 0.7219. Nd procedure blanks

were smaller than 100 pg. The oNd values at the

time of emplacement are based on the U/Pb zircon

ages of 1770 and 1580 Ma derived by Pimentel et

al. (1991). The TDM model ages were calculated

according to DePaolo (1981).

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