Geology, petrography, and mineral chemistry of the Vazante non-sulfide and Ambrósia and Fagundes sulfide-rich carbonate-hosted Zn-(Pb) deposits, Minas Gerais, …

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=Ore Geology Reviews 2
Geology, petrography, and mineral chemistry of the Vazante

non-sulfide and Ambrosia and Fagundes sulfide-rich

carbonate-hosted Zn–(Pb) deposits, Minas Gerais, Brazil

Lena Virgınia Soares Monteiro a,*, Jorge Silva Bettencourt b, Caetano Juliani b,

Tolentino Flavio de Oliveira c

aInstituto de Geociencias, Universidade Estadual de Campinas, R. Joao Pandia Calogeras, 51, CEP 13083-970, Campinas, SP, BrazilbInstituto de Geociencias, Universidade de Sao Paulo, Rua do Lago, 562, CEP 05508-900, Sao Paulo, SP, Brazil

cVotorantim Metais, Rodovia LMG 706, Km, CEP 38780-000, Vazante, Minas Gerais, Brazil

Received 12 February 2005; accepted 28 March 2005

Available online 11 July 2005

Abstract

The Vazante–Paracatu region represents the most important Zn district known in Brazil and includes the Vazante hypogene

non-sulfide Zn deposit composed mainly of willemite (Zn2SiO4) and sphalerite-rich carbonate-hosted Zn–(Pb) deposits.

Fagundes is a stratabound deposit, characterized by strong silicification, dolomitization and a Fe-rich carbonate alteration

halo. The main ore is represented by rhythmically banded, colloform, and zoned pyrite, sphalerite and galena, related to wall

rock dissolution and sulfide infilling, which probably occurs late during the burial diagenesis. Later veins and breccia ore types

reflect epigenetic mobilization, related to brittle–ductile structures. The Ambrosia mineralization is mainly fault-controlled and

related to brecciated dolomite, which is tectonically imbricated with black shales and slates. Typical features include host rock

recrystallization, minor silicification, baroque dolomite and ankerite formation. Pyrite, marcasite, sphalerite and minor galena

occur in brecciated comb-veins and veinlets, which overprint stylolites and tectonic fractures, suggesting an epigenetic origin

for the ore. The Vazante deposit differs from all other deposits of the district due to the presence of willemitic ore, which is

composed of willemite, dolomite, siderite, quartz, hematite, Zn-rich chlorite, barite, franklinite and zincite. The willemitic ore

occurs tectonically imbricate to small sulfide ore bodies, which comprises sphalerite and galena, metabasites and hydrother-

malized dolomites within the Vazante Shear Zone. The relationships between willemite formation and the development of

mylonitic structures suggest that willemitic mineralization and deformation are synchronous episodes closely related to the

Vazante Shear Zone. Low Zn/Cd ratios in sphalerite from Vazante (64 to 98) and Fagundes colloform (96 to 244) and zoned

sphalerite (89 to 305) could reflect the regional role of mineralizing fluids with similar low Zn/Cd ratios and low contents of

reduced sulfur (P

Sred). High Ge (up to 2200 ppm) and the low Fe, Cu, Mn and Ag contents in late-diagenetic Fagundes

sphalerite might suggest that this metal-bearing fluid could be derived from the underlying basin fill, which comprise clastic

sediments and organic matter-rich pelitic sequences. Systematic relationships among sphalerite composition and paragenetic

0169-1368/$ - s

doi:10.1016/j.or

* Correspondi

E-mail addre

8 (2006) 201–234

ee front matter D 2005 Elsevier B.V. All rights reserved.

egeorev.2005.03.005

ng author. Fax: +55 19 37885150.

ss: [email protected] (L.V. Soares Monteiro).

L.V. Soares Monteiro et al. / Ore Geology Reviews 28 (2006) 201–234202

evolution of the Fagundes and Ambrosia deposits suggest that progressive fluid mixing processes were important for the genesis

of the sulfide-rich deposits in the district. These mixing processes possibly involved the hot metal-bearing fluid with low

contents of reduced sulfur and moderate-temperature, highly saline fluids, which could represent an important sulfur supply.

The predominance of the highly saline brines in later epigenetic mineralization episodes might be related to episodic migration

of hydrothermal fluids mainly derived from reduced shale sequences during the Brasiliano compressive events. The small

variation in chemical and sulfur isotopic composition of the Vazante sphalerite could imply that the high-temperature metal-

bearing fluid with low Zn/Cd ratios could represent a minor reservoir of reduced sulfur, which permitted only subordinate

sphalerite precipitation in the Vazante deposit. The lack of reduced shale sequences above the Vazante deposit could represent a

limiting factor for H2S supply. Additionally, overall mixture between this hot sulfur-deficient metal-bearing fluid and meteoric

fluids channeled to the Vazante Shear Zone favor the high fO2/S2 conditions responsible for the stability of the Vazante

willemitic assemblage.

D 2005 Elsevier B.V. All rights reserved.

Keywords: Carbonate-hosted Zn–Pb deposit; Non-sulfide zinc deposit; Vazante deposit; Willemite

1. Introduction

The most important Zn-district known in Brazil is

located in the Vazante–Paracatu region, which

extends N–S for up to 250 km in the NW part of

Minas Gerais State (Fig. 1). Within this region,

various carbonate-hosted Zn deposits occur, includ-

ing Vazante, Morro Agudo, Ambrosia, and Fagundes

(Fig. 2). These are currently responsible for all Zn

production in Brazil. Measured reserves have been

estimated at 28.5 Mt with an average grade of 18.3%

Zn (Vazante willemitic ore) and 9.7 Mt with 6.5%

Zn and 2.8% Pb (Morro Agudo sulfide ore) (Viviani

et al., 2001).

The Zn deposits and occurrences are hosted by

metapelitic–dolomitic units of the Vazante Group

(Dardenne et al., 1998). Primary ore types in the

district differ mainly in relative sulfide abundance,

which is a notable feature of the Morro Agudo, Am-

brosia and Fagundes deposits, but is subordinate to

willemitic ore (Zn2SiO4) in the Vazante deposit. Struc-

tural, petrographic, geochemical and stable isotopic

studies carried out in the Vazante mine (Pinho, 1990;

Pinho et al., 1990; Hitzman, 1997; Monteiro, 1997,

2002; Monteiro et al., 1999, 2000, 2003; Hitzman et

al., 2003) have prompted a re-evaluation of the genet-

ic concepts relating to the willemitic mineralization,

which has been, since the 1960s, interpreted to be of

supergene origin. These studies indicate that the will-

emitic ore could have a hydrothermal origin related to

development of the Vazante Shear Zone. Thus, the

Vazante deposit represents the largest known hypo-

gene non-sulfide Zn deposit (Hitzman, 2001; Hitzman

et al., 2003), sharing characteristics with a relatively

small number of other deposits, such as Beltana (Aus-

tralia), Berg Aukus/Abenab (Namibia) and Kabwe

(Zambia).

Furthermore, there is no consensus among workers

about the origin of the carbonate-hosted sulfide depos-

its of this district. The proposed genetic hypotheses

include models similar to the Mississippi Valley Type

(MVT), mainly based on the dolomitic host rocks of

the mineralization and absence of magmatic activity

(Amaral, 1968; Rigobello et al., 1988; Iyer et al.,

1992, 1993). Sulfide textures of the Morro Agudo

ore indicate that mineralization process accompanied

syn-diagenetic, late-diagenetic and epigenetic stages

of the host sequence evolution (Dardenne, 1979;

Dardenne and Schobbenhaus, 2001). The relationship

of sulfide lenses to faults, mineral paragenesis, depo-

sitional temperatures ranging from 100 to 250 8C, andS-isotopic characteristics observed in the Morro

Agudo deposit indicate similarity to Irish-type depos-

its (Hitzman et al., 1995; Hitzman, 1997; Cunha et al.,

2000).

Other deposits in this district, show a predomi-

nance of late-diagenetic (Fagundes) or epigenetic

(Ambrosia) styles of mineralization and evidence of

mobilization, such as partial dissolution, corrosion,

recrystallization, brecciation, and mylonitization, due

to overprinting of later hydrothermal fluids related to

the deformation associated with compressive events

related to the Brasiliano orogeny (Monteiro et al.,

2000; Monteiro and Bettencourt, 2001).

N

Crixás

0 250 500 km

0o

16 So

Atla

ntic

Oce

an

Fold Belts

Craton cover

Cratonic areas

Ara

çuai

Bel

t

BFBPhanerozoicsediments

São FranciscoCraton

São FranciscoBasin

Brazil

SouthAmerica

46 Wo50 Wo

Dianópolis

12 So

São Domingos

Phanerozoic

Neoproterozoic

Paleo/Mesoproterozoic

Sedimentary basins

Orthogneiss

Volcano-sedimentarysequences

Meso/Neoproterozoic

Ibiá Formation

Araxá Group

Felsic and mafic granulitesand orthogneisses

Vazante Group

Paranoá Group

Canastra Group

Estrondo Group

Araí Group

Serra da Mesa Group

Mafic-ultramafic complexes

Volcano-sedimentary sequences

Volcano-sedimentary sequence(Santa Terezinha-type)

Granite-gneiss terranes

Greenstone belt

Paleoproterozoic

Archean

Mara Rosa

Niquelândia

Araxá

Piumhi

UnaíCristalina

Brasília

Goiânia

Paracatu

Vazante

Fig. 2

Patos de Minas

20 So

0 100 200 km

Fortalezade Minas

Três Marias FormationParaopeba Subgroup

Bambuí Group

Fig. 1. Location map and geotectonic setting of the Vazante Group, in the Brasılia Fold Belt (Dardenne, 2000).

L.V. Soares Monteiro et al. / Ore Geology Reviews 28 (2006) 201–234 203

LAGAMAR

PARACATÚ

N46 35'Wo

VAZANTE

Morrodo Ouro

17 20'So

Canastra Group

Paracatu Formation(carbonaceous phyllitewith quartzite layers)

Serra do Landim Formation(green carbonate phyllite)

Vazante Group

Serra da Lapa Member(gray slate, quartzite,and dolomite lenses)

Serra do Velosinho Member(black carbonaceous slateand shale)

Morro do Calcário andSerra do Poço Verdeformations(stromatolitic bioherm,breccia facies, algal-laminateddolomite, gray to pinkish dolomitewith stromatolitic mats, and slate)

Serra do Garrote Formation(black carbonaceous shaleand gray slate)

Pb anomalies

0 8 16 km

Lapa Formation

Fagundes

Morro Agudo

Ambrósia

Vazante

18 00'So

Fig. 2. Geological map of the Vazante Group and location of the Vazante, Ambrosia, and Fagundes deposits (Cia. Mineira de Metais, Votorantim

Metais).



Despite the fact that a number of base–metal pro-

vinces have been studied in detail (Le Huray et al.,

1987; Sangster, 1990; Leach and Sangster, 1993) the

distinction of carbonate-hosted Zn–Pb deposit genetic

models can be rather difficult. Moreover, in the same

district the integrated local stress, regional scale ther-

mal regime, fluid flow and physicochemical condi-

tions, can provide contrasts in mineralizing fluid

characteristics and mineralization styles (syngenetic,

syn-diagenetic or epigenetic), which are used to ad-

dress the problems of carbonate-hosted ore genesis

and modeling. In the Vazante–Paracatu region, the

result is a puzzle of complex relationships among

non-sulfide and different sulfide ore bodies.

The composition of the mineral phases in the

Vazante, Fagundes and Ambrosia deposits, principally

the different generations of sphalerite, could reflect

the evolution of the hydrothermal system related to

late-diagenetic and epigenetic episodes of mineraliza-

tion. The present study was aimed at the identification

of processes responsible for the genesis of each spe-

cific type of mineralization, which can lead to com-

prehensive metallogenic and exploration models for

the Vazante–Paracatu Zn–Pb deposits.

2. Geological setting

The Vazante–Paracatu region is located in the east-

ern part of the Brasılia Fold Belt (Almeida, 1967),

which extends for more than 1000 km over a width of

300 km along the western margin of the Sao Francisco

Craton (Fig. 1). This fold belt represents an unstable

crustal block, whose final structural differentiation

resulted from the closure of a wide oceanic basin

during the Neoproterozoic Brasiliano Orogeny (~600

Ma; Pimentel et al., 2001). The Brasılia Fold Belt

displays sequences of rock thrusted to the east with

increasing deformation and metamorphism to the

west, reflecting the vergence of the Brasılia Fold

Belt with respect to the Sao Francisco Craton (Dard-

enne, 2000).

The Vazante Group (Dardenne et al., 1998), which

hosts the Zn deposits (Figs. 2 and 3), covers a 250 km

long, N–S-striking region in the southern segment of

the Brasılia Fold Belt. This group was affected by low

greenschist facies metamorphism and has a pervasive

cleavage (S1), related to regional folding, which is

overprinted by S2 and S3 cleavages, related to local

D1 isoclinal and D2 open folds, respectively (Mon-

teiro, 1997).

From base to top, the Vazante Group is divided

into: Santo Antonio do Bonito, Rocinha, Lagamar,

Serra do Garrote, Serra do Poco Verde, Morro do

Calcario and Lapa Formations. The basal Santo Anto-

nio do Bonito and Rocinha formations are composed

of metapelitic units with phosphate concentrations

(Dardenne et al., 1998; Dardenne and Schobbenhaus,

2001). The Lagamar Formation represents a metap-

samo-pelitic unit with basal metaconglomerates, do-

lomitic breccia, dark gray limestone and stromatolitic

bioherm with columnar stromatolites of the Conophy-

ton and Jacutophyton type (Moeri, 1972; Cloud and

Dardenne, 1973). The Serra do Garrote Formation

represents a sequence of pyrite-bearing carbonaceous

gray slate and quartzite layers (Madalosso and Valle,

1978).

The Serra do Poco Verde Formation is made of gray

to pink algal-laminated dolomite, gray to green slates,

sericite phyllite, dark gray dolomite with bird’s-eyes,

marls and pyrite-bearing carbonaceous shale. The

Morro do Calcario Formation is composed of stromat-

olitic bioherm facies, intraformational breccias, dolar-

enite, and subordinate carbonaceous shale. These two

formations correspond to the dominantly dolomitic

sequences (Figs. 3 and 4) that host the Zn–(Pb) depos-

its and can represent a continuously deposited dolo-

mitic sequence, according to Dardenne (2000). The

lithostratigraphic columns for this dolomitic sequence

in the regions of Paracatu (A) and Vazante (B) and its

subdivisions (Morro do Pinheiro and Pamplona mem-

bers) as proposed by Rigobello et al. (1988) and

Dardenne (2000) are shown in Fig. 4.

The dolomitic sequence is overlain by the Lapa

Formation, with black rhythmic carbonaceous slate

and phyllite (Serra do Velosinho Member) and ser-

icite–chlorite phyllite, carbonate-bearing metasilt-

stone, dolomite and quartzite lenses (Serra da Lapa

Member). The Canastra Group metasediments (1200

to 900 Ma; Pimentel et al., 2001), which comprise

chlorite-rich calc-phyllite of the Landim Formation

and carbonaceous phyllites and quartzites of the

Paracatu Formation, overthrusts the rocks of the

Vazante Group (Fig. 3), as consequence of the late

Brasiliano collisional event (~630 Ma; Dardenne,

2000).

Morro Agudo,Fagundes and

Ambrósia Zn-(Pb)deposits

Vazante non-sulfideZn deposit

Phosphorite 3Lagamar

Phosphorite 2Rocinha

Phosphorite 1Coromandel

VAZ

AN

TE

GR

OU

PLapa

Morro doCalcário

Serra doPoçoVerde

Serra doGarrote

Lagamar

Rocinha

Sto.Antônio

do Bonito

UpperPamplona

MiddlePamplona

LowerPamplona

UpperMorro doPinheiro

Lower Morrodo Pinheiro

Sumidouro

Arrependido

Gray carbonate-rich slate,lenses of dolomite, blackcarbonaceous phyllite

Stromatolitic bioherm,facies of breccia anddolarenite

Gray and pink dolomite withstromatolitic mats

Gray and green slate,gray and pink dolomite

Dark gray dolomite withstromatolitic mats and bird's eyes

Light gray to pink dolomite withlenses of breccia and dolarenite

Gray slate

Stromatolitic bioherm

Dark gray limestoneDolomitic breccia

Conglomerate

Rhythmite

Dark gray pyritic andphosphatic slate

Rhytmites

Layers of quartzite, phosphorite,diamictite and slate

Serra da Lapa

S. Velosinho

Fig. 3. Schematic lithostratigraphic column (not to scale) of the Vazante Group (Dardenne et al., 1998; Dardenne, 2000).


The ages of the Vazante Group and the Zn miner-

alizing episodes are controversial. Stromatolites of the

Vazante Group indicate relative age intervals of 1650

and 950 Ma (Conophyton Cylindricus Maslov; Moeri,

1972) and 1350 and 950 Ma (Conophyton metula

Kirichenko; Cloud and Dardenne, 1973), suggesting

a correlation with the 1200 to 900 Ma Paranoa Group

(Dardenne et al., 1976). The occurrence of diamictite

units at the base of the Vazante Group, similar to those

of the base of the Bambuı Group (900 to 600 Ma;

Thomaz Filho et al., 1998), also suggests correlation

between these groups (Dardenne, 2000).

A Rb–Sr whole rock isochron for shales from the

Vazante Group yielded an age of 600F50 Ma

(Amaral and Kawashita, 1967), which could represent

the last closing of the isotopic systems, during the

Brasiliano metamorphic event. 207Pb/206Pb analyses

of galena from Vazante and Morro Agudo deposits

yielded model ages based on Stacey and Kramers

(1975) ranging between 929 and 600 Ma (Amaral,

1968; Cassedane and Lasserre, 1969; Iyer et al., 1992,

1993; Freitas-Silva and Dardenne, 1997; Misi et al.,

1997; Cunha et al., 2001, 2003), which have been

considered as the time of mineralization (Iyer et al.,

21

3

4

56

7

8

9

(1) Serra daLapa

(2) Serra doVelosinho

Ser

rad

oG

arro

teF

orm

atio

n

UpperPamplona

MiddlePamplona

LowerPamplona

UpperPamplona

1 - Slate, quartzite, andlenses of dolomite2 - Black carbonaceousphyllite

3 - Dolorudite and dolarenite

4 - Pyrite-rich black shale

5 - Stromatolitic bioherm

6 - Algal-laminated dolomite

8 - Dark gray dolomitewith bird’s eyes,light gray andpink dolomite

7 - Carbonate-rich slateand dolomite lenses

9 - Gray slate withquartzite lenses

3 - Dolorudite

4 - Dolarenite

5 - Stromatolitic bioherm

6 - Light gray algal-laminated dolomite withdolarenite lenses

7 - Gray and green slate,marls, gray and pinkdolomite with stromatoliticmats

8a - Fine dark gray dolomitewith birds eyes, marl, pyrite-bearing black carbonaceousslate

8b - Light gray to pinkinshalgal-laminated dolomite,dolarenite, lamelar breccia

VAZ

AN

TE

GR

OU

P

PARACATU

Ser

rad

oP

oço

Ver

de

Fo

rmat

ion

Lap

aF

orm

atio

n

LowerPamplona

Morro doPinheiro

UpperMorro doPinheiro

9 - .

(A)

9

8b

8a

7

54

3

6

VAZANTE(B)

LowerMorro doPinheiro 50

0m

500

m20

0m

400

m90

0m

Maximumthickness

Member Member

Mo

rro

do

Cal

cári

oF

orm

atio

n

Gray slate with quartzitelenses

Fig. 4. Correlations between the lithostratigraphic columns of the Vazante Group in the Vazante and Paracatu regions (after Oliveira, 1998;

Dardenne, 2000).


1992, 1993; Misi et al., 1997) or as the time of lead

separation. However, according to Cunha et al. (2003)

and Babinski et al. (2005), the Pb-isotopic ratios of

galena from the Vazante–Paracatu region characteris-

tically plot above of the evolution curve of Stacey and

Kramers (1975), indicating that the obtained ages lack

geologic significance.

Additional analyses on galena from the Morro

Agudo deposit resulted in Pb–Pb plumbotectonic

model ages of 1200 to 1000 Ma for early fine-

grained galena, which have been interpreted as the

time of lead separation or as the time of the syndia-

genetic mineralization, and of 600 Ma for epigenetic

coarse-grained galena, considered as the time of

epigenetic mobilization processes (Freitas-Silva and

Dardenne, 1997; Dardenne and Schobbenhaus,

2001).

Sm–Nd analyses carried out on metasediments

from the Vazante Group indicate a uniform distribu-

tion of TDM values between 2100 and 1700 Ma,

which, according to Pimentel et al. (2001), reflect

the overlapping of sources associated with the Para-

noa (TDM=2300 to 2000 Ma) and Bambuı groups

(TDM=1900 to 1400 Ma). This is compatible with

an intermediate stratigraphic position of the Vazante

Group, which could correspond to the top of the

Paranoa passive margin sequence (Pimentel et al.,

2001), or could alternatively represent the sedimenta-

tion in a rapidly subsiding zone forming a depression

in the Brasılia Fold Belt initial thrust fronts (Dard-

enne, 2000).

3. Vazante non-sulfide Zn deposit

The bulk of the Vazante non-sulfide Zn ore is

concentrated close to the contact of two units of the

Serra do Poco Verde Formation: the Upper Morro do

Pinheiro Member (footwall sequence) and the over-

lying Lower Pamplona Member (Figs. 4b and 5),

within the Vazante Shear Zone. Small metabasite

bodies occur tectonically imbricated with brecciated

metadolomites and willemitic ore bodies along the

shear zone (Monteiro, 1997). The Upper Morro do

Pinheiro Member includes gray metadolomites, py-

rite-bearing carbonaceous black shale, and marls

with textures indicating an inter- to subtidal flat

environment. The Lower Pamplona Member is

NW SE

F-551-65 F-543-65 F-364-60

F-379-75

469.20 m

410.35 m

374.75 m

276.80 m

192.00 m

30 0 30 60 90 m

Gray dolomite with microbialmat and teepee structures

Sericite phyllite and dolomitic slate

Pink dolomite with ooids and pellets,intraformational breccia

Light gray dolomite and quartzsericite phyllite

Marl and argillaceous dolomite

Dark gray dolomite with bird's eyesand stromactatis

Pyrite-bearing carbonaceousblack slate

Marl with pyrite and graphite

Metabasic rock

Willemitic ore

Breccia zone

Llimit of the shear zone

Lower Pamplona Member

Upper Morro do Pinheiro Member

Serra do Poço Verde Formation

VAZANTE GROUP

Fig. 5. Cross-section of the Vazante ore zone showing the spatial relationship between host sequence, willemitic ore, and the Vazante shear zone.


made of slate and sericite phyllite interbedded with

light gray to pink metadolomites, which display

features typical of an inter- to supratidal setting

with periods of subaerial exposure (Monteiro et al.,

1999).

The Vazante Shear Zone is approximately 12 km

long, with strike N508E and dip 608NW. It has been

interpreted as an inverse and transcurrent fault de-

veloped during a compressive phase, which was later

reactivated as a normal fault at the final stages of the

Brasiliano Orogeny (Pinho et al., 1990). The shear

zone is characterized by complex zones of irregular

anastomosing geometry that result from the intersec-

tion of C foliation planes and R, RV, P and T Riedel-

type shear fractures.

The metabasites exhibit sub-ophitic texture relicts

with igneous plagioclase, pyroxene and ilmenite par-

tially to totally recrystallized to chlorite, clinozoizite,

epidote, talc, sericite, quartz, rutile, leucoxene and

apatite in low greenschist facies metamorphism. In

the S–C mylonitic structures and brittle structures are

also present hydrothermal Fe-chlorite, hematite, tita-

nite, and dolomite (Monteiro et al., 1999).

3.1. Hydrothermal alteration

Within the Vazante Shear Zone, the hydrothermal

alteration is largely fracture controlled, producing a

complex zone of net veined and hydraulic breccias.

The metadolomites are also bleached and metaso-


matically altered along the contact with the metaba-

site. The hydrothermalized metadolomite of the

Upper Morro do Pinheiro Member displays color

varying from dark gray to pink mainly related to

Fe-dolomite and siderite formation along the mylo-

nitic planes. The micro- and pseudospar textures of

the Pamplona dolostone are replaced by closely

packed anhedral saddle dolomite with undulatory

extinction, siderite and baroque dolomite, which

exhibit strong zoning that is evidenced by blue,

red and orange cathodoluminescence (CL) zones.

Usually, the baroque dolomite is brecciated.

Within the Pamplona metadolomites and slates,

silicification is associated with strongly brecciated

zones cut by hydrothermal veins. These veins dis-

play a crustiform texture related to progressive

infilling of open fractures by successive layers of

texturally and/or mineralogically different precipi-

tates, which include Fe-dolomite, siderite, jasper,

hematite and chlorite.

Pre-mineralization stage

Minerals

GalenaWillemiteQuartz

Hematite

MagnetiteFrankliniteZincite

SideriteBaroque dolomite

Chlorite

BariteApatiteSmithsoniteTalc

Sphalerite

Microspar to pseudospardolomite

Earlydiageneticassociation Euhedral pyrite

Fibrous dolomite

Quartz

Clay-minerals

Latediageneneticassociation

Pyrite (stylolites)

Epigeneticassociation

Spar dolomite

Saddle dolomite

Jasper

Cloudy saddle dolomite

Fig. 6. General paragenetic association of the sulfide and willemitic ore

Vazante Shear Zone development.

3.2. Vazante willemitic and sulfide ore bodies

The willemitic ore (Fig. 6), the main ore type in the

Vazante deposit, displays podiform morphology and is

tectonically imbricated with small sulfide ore bodies,

metabasites and brecciated metadolomites. This ore

type contains willemite (50% to 70%), dolomite (10%

to 30%), siderite (10% to 20%, quartz (10 to 15%),

hematite (5% to 10%), Zn-rich chlorite (5% to 10%),

barite (b5%), franklinite (b5%), zincite (b5%), be-

sides subordinate concentrations of magnetite and

apatite. The willemite is colloform or occurs as fine

to coarse fibrous-radiated crystals associated mainly

with quartz and baroque dolomite (Fig. 7A). The

brittle–ductile deformation of willemitic ore is respon-

sible for its granoblastic texture and mineral stretching

and is accompanied by the formation of hematite and

Zn-rich chlorite (Fig. 8A). Cataclastic breccia com-

prises willemitic fragments surrounded by cloudy

saddle dolomite with zoning characterized by red

Main mineralization stage Late mineralization stage

Brittle- ductilestructures

Brittle-ductile andbrittle structures

bodies in relation to brittle–ductile and brittle structures related to

A

willemite

dolomite

quartz

DC

franklinitefranklinitesiderite

B

barite

sphalerite

sphalerite

sphalerite

willemite

willemite

quartz

quartz

quartz

galena

Fig. 7. (A) Willemitic ore includes willemite, quartz, dolomite, hematite, and zincite. Vazante deposit (width of field=12 cm); (B) replacement

of sphalerite by an assemblage made of willemite, quartz, dolomite, zincite, and barite along mylonitic foliation. Back-scattered electron images,

width of field=6 mm (Vazante deposit); (C) back-scattered electron images in two different contrasts showing franklinite associated to sideritic

and willemitic veins. The willemite is cut by sphalerite veinlets. Width of field, 3.75 mm (Vazante deposit); (D) sphalerite partially corroded,

separated from quartz by a galena film. Franklinite is usually associated with a reaction front. Back-scattered electron images, width of field, 0.6

mm (Vazante deposit).


cathodoluminescence (CL) and non-luminescent

zones, and cut by barite, hematite, and chlorite. Late

veins truncate the breccias and are mainly made of

non-luminescent dolomite.

Sulfide-rich ore occur either as irregular bodies

elongated parallel to C shear planes, with a well-devel-

oped mylonitic fabric, or as late-vein infillings. They

are composed mainly of colorless sphalerite, with ga-

lena, hematite, quartz, and dolomite inclusions. Under

microscope, the sphalerite is brown, quite homoge-

neous, displays strong yellow CL and is strongly de-

formed and stretched along the mylonitic foliation.

The brittle–ductile shear zone development is of

major importance in mechanical mobilization, recrys-

tallization and for the replacement of the sulfides by

the willemitic assemblage (Figs. 6 and 7B). The

initial willemite crystallization in the sulfide bodies

occurs along the mylonitic foliation, as part of two

distinct associations: willemite+sphalerite+ franklini-

te+zincite (without quartz) and willemite+quartz+

dolomite+ franklinite (without sphalerite). Locally,

galena isolated the sphalerite crystals impeding its

total destruction from reaction with quartz (Fig.

7C). These assemblages suggest the formation of

willemite from sphalerite and quartz via reaction

(1), which indicates that fS2 and fO2 may have had

an important role in the stability of this assemblage:

ZnSþ SiO2 þ O2 ¼ ZnSiO4 þ 1=2S2: ð1Þ

The willemite displays strong green CL in all

associations (Fig. 8B). Brittle structures affected wil-

lemite crystals, resulting in cataclastic textures, which

are filled, in turn, by galena and sphalerite. Late

sphalerite veinlets cut all willemite generations

(Figs. 7D and 8B).

The relationship between willemite formation and

the development of microstructures in sulfide orebo-

willemite hematite

dolomite

quartzwillemite

and hematite

sphalerite

willemite

sphalerite

quartz

pyrite

dolomite

dolomiteand quartz

sphalerite (III)and phyllosilicates

dolomite

sphalerite (IV)

sphalerite (III)

galena

pyrite

pyritegalena

sphalerite

galenag

sphalerite (I)

pyrite

sphalerite(I) and (II)

sphalerite (III)

galenag

quartz

sphalerite (III)sphalerite (I)

dolomite

quartz

A B

G H

D

E F

C

Fig. 8. (A) Willemitic ore composed of willemite, dolomite and hematite associated with brittle–ductile microstructures. Plane polarized light,

Vazante deposit; (B) willemite with green CL cut by mobilized sphalerite, with strong yellow CL, Vazante deposit; (C) photomicrograph showing

brecciated sphalerite (I) involved with sphalerite (II), and concentration of late sphalerite (III) along mylonitic planes. Plane-polarized light,

Ambrosia deposit; (D) sphalerite (I) cut by sphalerite (III) veinlets. Plane-polarized light, Ambrosia deposit; (E) colloform texture of sphalerite

(orange to brown) and pyrite, associatedwith later galena. Plane polarized light, Fagundes deposit; (F) colloform sphalerite (brown) associatedwith

later galena. Plane polarized light, Fagundes deposit; (G) Sphalerite (III), pyrite, dolomite and quartz associated with brittle–ductile micro-

structures. Plane polarized light, Fagundes deposit; (H) sphalerite (III) cut by yellow clear sphalerite (IV). Plane polarized light, Fagundes deposit.

Width of field is 1.4 mm in (A), (B) and (H) and 5.5 mm in (C)–(G).



dies, mainly associated with the mylonitic foliation,

suggests that the willemitic mineralization and defor-

mation are synchronous episodes inter-related to the

Vazante Shear Zone development.

The stability of the Vazante willemite assemblage,

in a similar way to willemite and zincite reported

from Sterling Hill and Franklin Furnace (Essene and

Peacor, 1987; Johnson et al., 1990), should be re-

stricted to high fO2/fS2 conditions (Monteiro et al.,

1999). According to Brugger et al. (2003), in the

presence of sulfur, willemite is predicted to form

instead of sphalerite under more oxidizing (at or

above the magnetite–hematite buffer) or alkaline

conditions, especially at temperatures exceeding

150 8C. High fO2/fS2 conditions could explain the

predominance of hematite and absence of pyrite (a

common mineral phase in the majority of base metal

deposits) at Vazante. Additionally, the formation of

early sphalerite, which is replaced by willemite, and

late sphalerite that cuts the willemite, could be relat-

ed to variations of the fO2/fS2 ratio during the fluid

evolution.

4. Ambrosia Zn deposit

Within the Ambrosia area, Zn mineralization is

controlled by a fault zone that strikes N308W and

dips 60 to 808SE and is cut across and displaced by

a N208E trending transverse fault system. To the SE,

the main N308W fault zone intersects the contact

between Lower Pamplona and Upper Morro do Pin-

heiro members (Fig. 4a). To the NW, this fault zone

juxtaposes Lower and Upper Pamplona members.

The host rock of the Ambrosia mineralization is a

brecciated dolomite, intimately associated with the

above fault zone, tectonically imbricated into black

shales and slates of the Lower Pamplona Member

(Fig. 9). Relicts of sedimentary and diagenetic tex-

tures of this dolomite include microbial lamination,

irregular fenestrae and bird’s-eyes. The diagenetic

sequence is represented by: (I) marine cementation,

characterized by micritic zones and non-luminescent

spar cementation associated to fenestrae; (II) reflux,

characterized by fine- to medium-grained euhedral

dolomite rhombs; (III) meteoric diagenesis, repre-

sented by dog tooth and drusy mosaic dolomite ce-

mentation; (IV) burial processes, responsible by

saddle dolomite formation, grain–grain dissolution

and stylolites.

The Upper Morro do Pinheiro Member, lying

below this fault zone, includes fine to medium strat-

ified dark gray dolomites with planar stromatolitic

structures, bird’s-eyes, and fenestrae. The Lower

Pamplona Member comprises rhythmic carbonaceous

shale interbedded with siltstone, sandstone, dolare-

nite, marl, and lenses of gray argillaceous dolomite.

Near the contact with the Upper Pamplona Member,

intraformational breccia layers with fragments of

dolomite, phosphorite, and quartz in a matrix of

dolomite, quartz, microcline, and plagioclase have

been identified. The flat-shaped phosphorite clasts

exhibit chalcedony and apatite crystallization on the

borders. Quartz clasts are either angular or rounded,

with evidence of deformation, such as undulatory

extinction, sub-grain formation, and a mantle–core

texture. The matrix quartz grains display rounded

detrital nucleus and euhedral-shaped authigenic crystal

overgrowths.

The Upper Pamplona Member essentially com-

prises reef dolomite with stromatolitic structures and

evaporitic layers. It has fine layers made of detrital

minerals, such as quartz and microcline, and authi-

genic phases, mainly quartz and euhedral pyrite, in a

dolomitic matrix associated with phosphatic material.

Foliation planes (S1) defined by clay mineral, ser-

icite, phlogopite, and chlorite orientation are observed

in all units and have been considered as the products

of regional deformation. This foliation is folded and

cut by a weak crenulation (S2). Microcrystalline

quartz, carbonates, pyrite, and subordinate sphalerite

fill faults and fractures.


Within the fault zone, the lithotypes of Morro do

Pinheiro and Pamplona Members display brecciated

aspects, due to the interaction of different processes,

such as, recrystallization (I), silicification (II), baroque

dolomite and ankerite formation (III), concentration of

veining and faulting (IV). The recrystallization, char-

acterized by a uniform mosaic of medium-crystalline

equant dolomite crystals with straight intercrystalline

boundaries, represents the main process that affects

the dolomites of the Upper and Lower Pamplona

members. Close to, and within the mineralized zone,

PAF - 78 (40 )PAF - 77 (60 )

o

o

PAF - 82

133.70 m

132.80 m

84.70 m

SW NE

0 10 20 30 40 m

VAZANTE GROUPMorro do Calcário FormationUpper Pamplona Member

Lower Pamplona Member

Fault zone

Stromatolitic bioherm

Gray microbial-laminated dolomite

Light gray brecciated dolomite

Pyrite-bearing black shale, slate,phosphatic dolomite, intraformational breccia

Breccia zone

Zn (Pb) ore-

Fig. 9. Cross-section of the Ambrosia ore zone showing the spatial relationship between the mineralization and high-angle fault zone.


and alongside the recrystallization, are complex vein

systems made of baroque dolomite, ankerite, and

quartz, which are mainly pre-date or are synchronous

with base–metal sulfide mineralization. In the foot-

wall zone, the brecciated aspect of the dolomites is

related to silicification. Networks of fractures filled

with dolomite and ankerite are also responsible for in

situ brecciation of the rock. This sequence of process

postdates early dolomitization and burial diagenetic

features indicating that the hydrothermal alteration is

mainly epigenetic.

4.2. Zinc mineralization

The Ambrosia Zn ore is associated with brecciat-

ed dolomite, tectonically imbricated with metasedi-

ments of the Lower Pamplona Member, within the

Ambrosia Fault Zone (Fig. 9). Iron-sulfides (Fig. 10),

Pre-mineralization

stage

Mainmineralization

stage

Latermineralization

stageMineralsBrittle-ductile structures Brittle structures

Earlydiageneticassociation

Saddle dolomiteQuartzClay-minerals

Latediageneneticassociation Pyrite (stylolites)

Baroque dolomiteAnkeriteQuartzChalcedonyPyriteMarcasiteEpigenetic

association Sphalerite (I)Sphalerite (II)Sphalerite (III)GalenaChloriteTalcEuhedral dolomiteApatite

Micritic dolomiteSpar dolomiteEuhedral dolomiteEuhedral pyrite

Fig. 10. General paragenetic association of the Ambrosia sulfide ore.


mainly marcasite and pyrite, are the most abundant

mineral phases near the mineralized zones. The sul-

fides occur in stylolites, in comb-veins, associated

with baroque dolomite and ankerite, and in concen-

tric nodules in dolomites, which were previously

modified by recrystallization, dolomitization and/or

silicification. Within the comb-veins, the Fe-sulfide

textures are rhythmic and coarsen inward, indicating

open-space filling (Fig. 11A). The association be-

tween Fe-sulfides and compaction features, mainly

stylolites, could indicate a burial diagenetic origin for

part of the pyrite.

The orebodies are composed of sphalerite, pyrite,

and lesser galena, all occurring in veins, veinlets and

as fractures fillings. Under the microscope, sphalerite

(I) displays dark brown–reddish color and evidence

of a primary compositional zoning. However, the

predominant granoblastic texture indicates different

recrystallization stages. The sphalerite grain borders

commonly show evidences of partial dissolution and

corrosion, and concentrations of a second fine-

grained and darker sphalerite generation (II). Fre-

quently, the sphalerite (I) and (II) are cut by vein-

bearing yellow and clearer sphalerite (III), associated

with galena (Fig. 8C, D).

Intense mylonitization within the mineralized

zones is responsible for the Fe-dolomite, dolomite,

quartz, pyrite and sphalerite (III) concentrations

along the S–C planes, limiting the more preserved

sphalerite (I) cores. All these features suggest that

significant tectonic transposition cannot be ruled out.

The pyrite associated with sphalerite (I) was affected

by ductile–brittle deformation, which is indicated by

fragmentation, corrosion, dissolution and replace-

ment by sphalerite, galena (Fig. 11B), talc and chlo-

rite. Late ankerite, quartz, euhedric dolomite, apatite

and mobilized sphalerite veins cut the mylonitized

zones (Fig. 10). The base–metal vein sulfides over-

print stylolites and tectonic fractures, suggesting an

epigenetic origin for the primary ore, which was

later mobilized due to fluid-assisted shear zone

transfer.

5. Fagundes Zn deposit

In the Fagundes area, Zn mineralization is hosted

by dolomites of the Upper Pamplona Member (Fig.

12), which is covered by the Serra do Velosinho and

the Serra da Lapa members of the Lapa Formation

pyrite

dolomite

pyrite +marcasite

A

sphalerite

pyrite +marcasite

galena

pyrite

C

apatite

galena

sphalerite

pyrite

dolomite

B

galenasphalerite

pyrite

dolomite

D

Fig. 11. (A) Rhythmic textures involving pyrite, marcasite, and dolomite. Reflected light, Ambrosia deposit (width of field, 1.4 mm); (B) Back-

scattered electron images showing rounded pyrite grains, with evidence of dissolution, partially replaced by sphalerite and subordinate galena.

Width of field, 0.15 mm (Ambrosia deposit); (C) colloform texture of pyrite, associated with sphalerite and galena. Reflected light, Fagundes

deposit (width of field, 5.5 mm); (D) Back-scattered electron images showing cataclase of colloform pyrite, replaced by galena and subordinate

sphalerite. Width of field, 1.5 mm (Fagundes deposit).


(Fig. 4a). The basal Serra do Velosinho Member is

composed of rhythmic graphitic black shale inter-

bedded with argillaceous-carbonate layers, which con-

tain detrital quartz and microcline-rich sub-layers. The

Serra da Lapa Member is made of rhythmic calc-

silicate metapelite interbedded to sericite–chlorite

phyllite and metasiltstone with subordinate quartzite.

Close to the contact with the Upper Pamplona Mem-

ber, these lithotypes display evidence of mylonitiza-

tion, such as strong mineral stretching, ribbon texture

in quartz and carbonates, and extensional fractures

filled with quartz, sericite, phlogopite, chlorite, pyrite,

and ankerite.

The Upper Pamplona Member is represented in

the Fagundes area by a stromatolitic reef complex,

with back and fore-reef facies (Fig. 4a). The fore-

reef facies consists of algal-laminated dolomite,

dolorudite and dolarenite. The dolorudite is com-

posed of a dolarenitic matrix and angular or rounded

fragments of stromatolite dolomite, collophane,

chert, dolomicrite, and dolomicrosparite intraclasts.

The reef facies is composed of gray microbial-lam-

inated dolomite and columnar stromatolite, which

display concave lamination, characterized by dark

lamellae made of cryptocrystalline dolomite and

light lamellae with coarsely crystalline dolomite

and authigenic quartz grains. The back-reef facies

include recrystallized fine-grained gray dolomite

with planar to wavy mats and subordinate layers of

dolarenite and breccia.

The original textures of these lithotypes were

usually obliterated by neomorphism and silicifica-

tion associated with non-planar dolomite, preferen-

tially along the lamination and in the intercolumnar

spaces of the stromatolites. Saddle dolomite and

stylolites with pyrite, chert and clay minerals rep-

resent the burial diagenetic stage. The development

of the S1 foliation took place sub parallel to the

algal lamination, and is accentuated by chert sub-

stitutions along the lamination plans. Mylonitization

and development of S–C structures are also usually

recognized.

W E

0 100 200 m

VAZANTE GROUP

Serra do Velosinho Member

Morro do Calcário Formation

Zn-(Pb) ore

Pyrite-bearing shale with meta-arenite layers

Dolorudite with stromatolitic bioherm fragments and laminated dolomite

Fine-gray dolomite with green slate layer;

Dolarenite and microcrystalline dolomite

Laminated dolomite

Fig. 12. Cross-section of the Fagundes ore zone (Cia. Mineira de Metais, Votorantim Metais).



Replacement and hydrothermal alteration process-

es related to the Upper Pamplona Member dolomites

have taken place close to or within the mineralized

zones. The burial saddle dolomite, which precedes the

base–metal sulfide mineralization, occurs as coarse

space-filling cement and corresponds to anhedral

spar dolomite with undulatory extinction. It shows

strong cathodoluminescense (CL) zoning character-

ized by strong red CL on the borders and cores of

the crystals. The intermediate zones display weak CL,

due to their Fe-rich composition, alternating with

yellow CL zones, with compositions that are more

calcitic.

Silicification is a common intense process of open-

space filling and involves, in some cases, total re-

placement of dolomites by chalcedony, as layered


chert concretions with straight borders between adja-

cent nucleus and polygonal limits, and mosaic quartz.

In the strongly silicified zones, concentric nodules of

chalcedony also occur, associated with spar dolomite

and pyrite. The dolomite observed in the silicified

zones displays commonly fibrous or colloform tex-

ture, indicating rhythmic deposition and replacement

of the precursor chalcedony. The silicification is pos-

terior to the burial saddle-dolomite formation and can

represent a relatively late stage in the diagenetic his-

tory of the sequence. This process is linked to the

base–metal sulfide mineralization, but usually repre-

senting a pre-mineralization stage of the hydrothermal

alteration (Fig. 13).

Baroque dolomite crystallization is mainly related

to comb-vein infilling, which crosscut both the par-

tially preserved dolomites as well as the intensely

silicified ones. These carbonates and the quartz com-

monly display undulatory extinction due to the brittle–

ductile deformation. A late-zoned euhedral carbonate

generation with strong pleochroism is observed in the

core of the chalcedony nodules and veins. Impressive

fragmentation, related to brittle deformation, occurs in

MineralsPre-

mineralizationstage

DolomicriteEarlydiageneticassociation

Euhedral pyrite

Saddle dolomite

EpigeneticAssociation

Pyrite (stylolites)Chalcedony/quartzBaroque dolomite

Zoned euhedral dolomite

Colloform pyriteColloform sphalerite (I)Zoned sphalerite (II)

Mobilized sphalerite (III)Late sphalerite (IV)Galena

Galena

TalcChloriteApatitePhyllossilicates

Latediageneticto epigeneticassociation

Pseudospar to spardolomite

Fig. 13. General paragenetic associat

the strongly silicified dolomites, originating breccia

zones with chert, quartz, and dolomite fragments.

5.2. Zinc mineralization

5.2.1. Primary ore

The ore bodies are usually stratabound and struc-

turally and stratigraphically controlled. The Fagundes

mineralization is hosted by dolorudites, and dolomites

with chaotic stromatolite structures of back-reef facies

of the Upper Pamplona Member (Fig. 12), near the

Serra do Velosinho Member contact. In the better

preserved lithologies, pyrite represents the first gen-

eration of sulfides, deposited along stylolitic surfaces,

borders of chalcedony nodules in strongly silicified

zones, and in baroque dolomite veins. Within miner-

alized areas, the primary Zn ore is stratabound and

comprises mainly pyrite, sphalerite and late galena.

The stratabound ore type is represented mainly by

rhythmically banded, colloform, and zoned sulfides

(Fig. 11C). Pyrite is present as colloform or euhedral

crystals nuclei that are coated and overgrown by

concentric colloform sphalerite (I), which shows

Mainmineralization

stage

Latemineralization

stageBritle-ductilestructures

Britlestructures

ion of the Fagundes ore types.

Table 1

Main attributes of the Vazante, Ambrosia, Fagundes and Morro Agudo Zn–(Pb) deposits

Deposit Host rocks Ore control Hydrothermal

alteration

Styles of

mineralization

Ore types Mineralogy Salinity (wt.%

equivalent NaCl)/

temperature (8C)

Sulfur source

Ambrosia Brecciated dolomite

(Upper Pamplona

Member)

High-angle fault zone

(N30W/80SW)

Replacement by

baroque dolomite

and ankerite,

silicification

Epigenetic Lode ore py, sp, gn, dol,

qtz, marc, phyll;

apatite

Salinity: 5–22 TH:

122–244(1)Hydrothermal source(2)

Fagundes Dolarenite, dolorudite,

dolarenitic breccia

(Upper Pamplona

Member)

Stratigraphic control;

brittle–ductile

fault zones

Strong silicification

and baroque

dolomite formation

Tardi-diagenetic/

epigenetic

Stratabound ore

(open space filling,

largely replacive),

brecciated ore

py, sp, gn, marc.,

dol, qtz, phyll,

chalcedony

Salinity: 5–15

TH: 120–265(1)Two sulfur sources:

thermochemical

reduction of sulfate

under closed system

conditions and

hydrothermal supply(2)

Vazante Brecciated pink

dolomite and slates

(Lower Pamplona

Member)

Shear zone

(N50/60NW).

Stratigraphic

control

Dolomitization,

silicification,

siderite,

ankerite, hematite,

chlorite formation(3,4)

Epigenetic Willemitic ore

(pods, lode, breccia)

and sulfide ore

(veins, pods)

will, hm, dol, sid,

ank, sp, gn, fk, zc,

qtz, chl barite,

apatite(3,4)

Salinity:3–23(1,5)

TH: 65–232(1,5)

T: 206–294

(stable isotope data)(3,4)

Thermochemical

reduction of seawater

sulfate or hydrothermal

source(3,4)

Morro

Agudo

Breccias, dolarenite

and dolorudites

(Upper Pamplona

Member)

Fault zone

(N10W/75SW);

stratigraphic

control(6,7)

Silicification posterior

to the main

mineralization

Syndiagenetic to

epigenetic

Stratiform ore

breccia

ore, veins(6)

gn, sp, py, cc, dol,

barite, qtz(6)Salinity: 0–23(6);

TH: 80–283(6)

T: 80–386(6)

(stable isotope data)

Two sulfur sources:

from thermochemical

reduction of evaporitic

sulfate and hydrothermal

supply(6,7,8)

Abbreviations: py=pyrite; sp=sphalerite; gn=galena; dol=dolomite; qtz=quartz; marc=marcasite; phyll=phyllossilicate; will =willemite; hm=hematite; sid=siderite; ank=ankerite; fk=franklinite;

zc=zincite; chl=chlorite; cc=calcite; TH: homogenization temperature.

(1) Bettencourt et al. (2001); (2) Monteiro and Bettencourt (2001); (3) Monteiro (1997); (4) Monteiro et al. (1999); (5) Dardenne and Freitas-Silva (1999); (6) Cunha et al., 2000; (7) Misi et al. (1999); (8)

Misi et al. (2000).

L.V.Soares

Monteiro

etal./Ore

GeologyReview

s28(2006)201–234

218


color orange to dark-brown, and by dolomite. Sphal-

erite (II) occurs as medium- to coarse-zoned crystals

on the borders of baroque dolomite infilling. Under

transmitted light sphalerite (II) displays light brown

color in the core of the crystal (Fig. 8E). Red-orange

areas are predominant in intermediate parts of the

crystals, while the borders, in general, have darker

brown color. Galena shows predominantly infilling or

substitution textures (Figs. 8F and 11D), but also

occur in veins and veinlets associated to dolomite,

pyrite and subordinated sphalerite.

The sulfide textures of the stratabound ore indicate

mainly sulfide deposition in open spaces within the

dolomite host rocks, possibly related to fracturing and

dissolution during the mineralizing process. The pri-

mary mineralization postdates the burial saddle-dolo-

mite formation; however it is locally overprinted by

chemical compaction features, such as stylolites (Fig.

13). This could suggest a late-diagenetic to epigenetic

origin for the Fagundes stratabound mineralization.

Table 2

Representative microprobe analyses (wt.%) and calculated cation values f

Sulfide ore Willemiti

Will Frank Mag Hm Will

SiO2 27.16 0.05 0.03 0.02 27.28

Al2O3 0.00 0.61 0.01 0.03 0.00

TiO2 0.02 0.00 0.07

MgO 0.00 0.00 0.00 0.00 0.05

CaO 0.03 0.41 0.00 0.00 0.13

MnO 0.02 0.00 0.00 0.00 0.02

FeO 0.19 1.01 29.92 0.29

Cr2O3 0.03 0.00

CdO 0.08 0.00

Fe2O3 65.60 66.48 93.82

ZnO 74.00 32.24 0.02 5.41 72.59

Total 101.47 99.97 99.29 100.36

Catios assuming: 4 (O) for willemite, franklinite and magnetite; 6 (O) for

Si 0.99 0.00 0.00 0.00 1.00

Al 0.00 0.03 0.00 0.00 0.00

Mg 0.00 0.00 0.00 0.00 0.00

Ca 0.00 0.14 0.00 0.00 0.01

Mn 0.00 0.00 0.00 0.00 0.00

Fe2+ 0.01 0.27 1.00 0.01

Cr 0.00 0.00

Cd 0.00 0.00

Fe3+ 1.97 2.00 3.84

Zn 1.99 7.59 0.00 0.21 1.97

Fe2+ and Fe3+ were calculated assuming full site occupancy.

Abbreviations: Will=willemite; Frank=franklinite; Mag=magnetite; Hm=

5.2.2. Mobilized ore

Mobilization of the sulfides is closely related to

local ductile–brittle faults in the mineralized areas.

Interaction with later hydrothermal fluids results in

the partial obliteration of the originally zoned sulfide

textures, mainly in the proximity of fissures and bor-

ders of the crystals, and homogenization of the sphal-

erite color. Mobilized and deformed sphalerite (III)

usually exhibits a dark brown color, without evidence

of zoning.

Brecciated ore associated with brittle–ductile and

brittle processes contains sphalerite (I) and (II) frag-

ments in a fine-grained brown mobilized matrix of

sphalerite (III). In the more intensely deformed areas,

the sulfides associated with quartz and dolomite with

ribbon structure (Fig. 8G) are oriented parallel to the

mylonitic foliation. Late sphalerite (IV) displays a

clear yellow color, and is associated with galena

(Fig. 8H). The sphalerite (IV) veins are concordant

to mylonitic foliation plains, which cut the primary

or mineral phases from the Vazante deposit

c ore Cataclastic breccia

Will Frank Hm Will Hm

27.15 10.71 0.13 27.34 0.04

0.01 0.52 0.08 0.00 0.03

0.00 0.00 0.00

0.01 0.01 0.06 0.09 0.03

0.02 0.02 0.00 0.01 0.00

0.00 0.00 0.00 0.00 0.00

0.29 7.23 0.10

0.13

0.00 0.00

54.93 99.22 99.78

73.17 27.48 0.66 74.36 0.10

100.65 100.93 100.15 101.88 100.12

hematite

1.00 0.39 0.00 1.00 0.00

0.00 0.02 0.00 0.00 0.00

0.00 0.00 0.00 0.00 0.00

0.00 0.02 0.00 0.00 0.00

0.00 0.00 0.00 0.00 0.00

0.01 0.22 0.00

0.00

0.00 0.00

1.49 3.97 3.99

1.99 0.73 0.03 2.00 0.00

hematite.


sphalerite (I) and (II) aggregates. In some deformed

domains, the sphalerite and pyrite evidence partial

dissolution, being substituted by phyllosilicates and

euhedral dolomite. Table 1 summarizes the main attri-

butes of the deposits of the Vazante–Paracatu region.

Table 3

Representative chlorite analyses (wt.%) from Vazante

Cataclastic breccia/willemitic ore Metabasite

SiO2 28.11 28.56 28.07 33.83 33.78

MgO 20.28 20.57 20.46 30.72 30.11

Al2O3 16.70 16.36 16.86 13.74 15.09

K2O 0.00 0.00 0.01 0.03 0.00

TiO2 0.69 0.02 0.19 0.00 0.00

FeO 3.00 2.97 2.63 7.91 8.10

Cr2O3 0.01 0.03 0.04 0.02 0.03

NiO 0.03 0.04 0.03 0.04 0.00

CaO 0.14 0.56 0.23 0.05 0.11

MnO 0.00 0.00 0.05 0.09 0.13

ZnO 19.68 18.99 19.1 0.16 0.41

Total 88.64 88.10 87.67 86.59 87.75

Cations assuming 28 (O)

Si 5.86 5.97 5.92 6.53 6.44

AlIV 2.14 2.03 2.08 1.47 1.56

AlVI 1.97 2.00 2.11 1.67 1.84

Ti 0.11 0.00 0.03 0.00 0.00

Cr 0.00 0.00 0.01 0.00 0.00

Fe3+ 0.03 0.00 0.05 0.11 0.16

Fe2+ 0.50 0.53 0.41 1.17 1.13

Mn 0.00 0.00 0.01 0.01 0.02

Mg 6.30 6.41 6.43 8.84 8.56

Ni 0.01 0.01 0.01 0.01 0.00

Zn 3.03 2.93 2.83 0.02 0.06

Ca 0.03 0.13 0.05 0.01 0.02

K 0.00 0.00 0.01 0.01 0.00

OH 16.00 16.00 16.00 16.00 16.00

Fe/Fe+Mg 0.08 0.08 0.07 0.13 0.13

Fe2+, Fe3+ and OH were calculated assuming full site occupancy

6. Mineral chemistry

Chemical compositions of willemite, franklinite,

hematite, dolomite, and chlorite were determined by

a CAMECA 50 electron probe microanalyser at the

Universidade de Brasılia. Sulfide compositions were

analyzed using a JEOL, JXA 8600 SuperProbe at the

Instituto de Geociencias, Universidade de Sao Paulo.

The wavelength dispersive technique was employed,

with accelerating voltages of 20 and 15 kV, and probe

currents of 20 and 30 nA, respectively. Estimated

minimum detection limits (mdl) for trace elements

in sulfides are: Cd, Cu, Mn (100 ppm); Ge, Ga, Ag

(120 ppm); Sb (270 ppm); Co (350 ppm); Ni (390

ppm); As (530 ppm); Pb and Se (575 ppm). Analyzed

elements that carried concentrations below these mdl’s

in N95% of samples are not presented. Mean concen-

trations were calculated only if N50% of the analyses

have values above mdl.

6.1. Vazante non-sulfide assemblage

Representative microprobe analyses from willemi-

tic ore are given in Table 2. The structural formulae of

willemite from different ore associations, including

sulfide ore bodies, ranges within a negligible range

[(Zn2+1.97–2.00Fe2+0.00–0.02Ca0.00–0.01)(Si0.99–1.00)O4]. This

purity can be responsible for the strong green CL

observed in willemite from Vazante (Fig. 8A), be-

cause impurities can inhibit the CL effects, according

to Johnson et al. (1990).

Magnetite and franklinite intergrowths can be

taken as indicating an inverse structure for the

Vazante franklinite (Sclar and Leonard, 1992;

Zheng, 1996), which displays the structural formula

(Zn2+0.73–0.95Fe2+0.22–0.03Ca

2+0.05–0.00)(Fe

3+1.49–1.97Al0.03–0.02

Si0.39–0.00)O4 (Table 2).

Hematite presents variable degrees of replacement

of Fe2+ by Zn2+. The Zn-rich hematite occurs as elon-

gated inclusions within the Vazante sphalerite. The

hematite associated with the willemitic ore, including

cataclastic breccias, displays the lowest amounts of Zn

compared to other hematite occurrences.

Chlorite from veins that cut willemite fragments in

cataclastic breccias is characterized by its unusual Zn

content (up to 19.7% ZnO), previously reported by

Monteiro (1997) [and Alain Blot, pers. comm., 1998].

According to the chlorite nomenclature of Bayliss

(1975), it is a zincian clinochlore. The hydrothermal

chlorite from Vazante metabasite (Table 3) is also

classified as clinochlore, but has lower Zn contents

(up to 0.5% ZnO).

The temperature of Vazante chlorite crystallization

was calculated using the method of Cathelineau and

Nieva (1985). Correction for AlIV-T dependence, as

proposed by Kranidiotis and MacLean (1987) and

Zang and Fyfe (1995), was not adopted due to lack

of correlation between AlIV contents and Fe/(Fe+Mg)

ratios in the Vazante chlorite. The estimated tempera-

.


tures for chlorite from hydrothermalized metabasite

(175 to 190 8C) and from cataclastic breccias with

willemite fragments (230 to 245 8C) reflect conditionsrelated to the development of brittle and brittle–ductile

structures. These conditions are consistent with tem-

peratures calculated from stable isotopes by Monteiro

(1997) and Monteiro et al. (1999), which indicate a

temperature range between 250 and 295 8C for will-

emitic ore and 200 to 260 8C for hydrothermal min-

eral phases of veins and breccias within the shear

zone. The d18O of the fluid in equilibrium with chlo-

rite (+12x), at 250 8C, is similar to the estimated

oxygen isotopic composition of fluids responsible for

the willemitic ore (Monteiro, 1997; Monteiro et al.,

1999). This oxygen isotopic signature and the calcu-

lated yD value (�33.5x) could indicate an affinity

with either metamorphic or diagenetically modified

formational fluids.

6.2. Vazante, Fagundes and Ambrosia sulfide

mineralization

6.2.1. Sphalerite

The Vazante sphalerite is characterized by low Fe

(mean 0.09%) and high Cd contents (mean 8410 ppm)

and displays little compositional variation (Table 4).

However, different sphalerite generations in the

Fagundes and Ambrosia deposits show significant

chemical variations (Figs. 14 and 15), as indicated by

their Fe and total trace metal (P

metals=Cd+Ge+

Ag+Cu) contents.

In the Fagundes deposit, Cd-concentrations as high

as 7000 ppm are found in sphalerite types (I) and (II)

and relatively high amounts of Ge are observed in

colloform (I) (up to 1640 ppm), zoned (II) (up to

2200 ppm) and deformed (III) (up to 2390 ppm) sphal-

erite (Table 5). The late sphalerite (IV), however, dis-

plays characteristically lower Cd, Ge and Cu contents

in relation to earlier phases (Table 5).

Ambrosia epigenetic sphalerite (I) has higher Fe-

content (mean 0.78%) and lower average Cd-content

(257 ppm) than Fagundes andVazante sphalerite (Table

6), resulting in the highest Fe/P

metals ratio (Fig. 15).

Increases in Fe (up to 2.54%) and Cd (up to 4100 ppm)

are observed in mobilized sphalerite (II) and late sphal-

erite (III) from Ambrosia (Fig. 14; Table 6).

Sphalerite from the different deposits in the

Vazante–Paracatu district shows some compositional

similarities with sphalerite from other Zn–(Pb) depos-

its worldwide. High Cd-contents in sphalerite, similar

to those observed in Vazante and Fagundes, are

reported in MVT deposits (Table 4), veins in carbon-

ate rocks (mean 7260 ppm; Schwartz, 2000) and in

the low-temperature Cd-rich zinc deposit of Niujiao-

tang, China (Liu et al., 1999).

Previous investigations (e.g., Jolly and Heyl,

1968; Barbanson and Geldron, 1983; Liu et al.,

1999) found Ge to be concentrated in sphalerite

from low-temperature epigenetic deposits (e.g.,

MVT deposits and the Ruby Creek, St. Salvy, Niu-

jiaotang deposits), particularly those hosted in sedi-

mentary rocks. Additionally, low Fe, Cu, Mn and Ag

contents in sphalerite, similar to those observed in

the Vazante–Paracatu deposits, are also typical of

MVT deposits (Table 4).

However, available temperature data from fluid in-

clusion (Table 1) and stable isotope data for the depos-

its in Vazante–Paracatu district (Cunha et al., 2000;

Misi et al., 1999, 2000; Bettencourt et al., 2001; Mon-

teiro, 2002; Monteiro et al., 2003) indicate higher

temperatures (i.e., N250 8C) than those usually

reported for MVT deposits. Thus, similarities between

sphalerite composition from the studied deposits and

low-temperature deposits, including theMVT deposits,

could be better explained by a similar source of brines

related to sedimentary sequences. According to Bern-

stein (1985) and Viets et al. (1992), brines leaching

sedimentary sequences would most likely remove as

much loosely bound metal (Fe, Zn, Cd and Ge, etc.)

from clastic or organic-bearing material. Additionally,

the sphalerite composition could indicate lowP

Sredactivities in the mineralizing fluids, which could favor

formation of Cd-rich sphalerite (Schwartz, 2000) and

incorporation of Ge in the sphalerite (Bernstein, 1985).

6.2.2. Galena

Galena from the three studied deposits has rela-

tively elevated Zn contents (Tables 7–9). The Ag

concentration in galena of the three deposits is similar

to that of some MVT deposits (Illinois–Kentucky and

Silesia), but Cd-content in galena is higher than that

described for MVT deposits, showing similarity to the

metamorphic deposit of Cobar, Australia (Table 7).

The main characteristic of the galena in the three

deposits, however, is the uncommon abundance of Ga

(up to 4650 ppm in the Fagundes deposit) and Ge (up

Table 4

Average sphalerite composition (Fe in wt.% and trace-elements in ppm) from different Pb–Zn deposits

Deposits/district Fe Cd Mn Ga Ge Ag Cu Co Ni

Ambrosia(1) 0.78 1190 300 120

Fagundes(1) 0.46 3350 540 210 300

Vazante(2) 0.09 8410 130 120 240

Morro Agudo(3) 0.64 7700 825 10 20 72 10

Mississippi Valley-type

Upper Mississippi Valley(4) 1.41 1678 49 95 102 21 76 15 42

Illinois–Kentucky(4) 2.90 6900 170 290

Kentucky–Tennesseee(5) 0.28 13,344 98 269 2

Northern Arkansas(6) 0.14 6342 21 120 31 321 6

Tri-State(6) 0.23 6583 23 130 85 273 6

Viburnum Trend(6)

Main stage 0.79 9310 33 41 141 328 490 191 50

Cubic galena stage 0.27 5333 19 79 86 2.8 242 73 8

West Fork Mine(7)

Red sphalerite 1.96 6700 330 11

Yellow sphalerite 1.47 3200 32 48 97 64

Central Missouri(6) 0.10 5395 22 122 46 1.2 247 1.2 6

Central Tennessee(8) 4000 230 400 8 100 100

East Tennessee(8) 0.36 4185 220 60 36

Pine Point(9) 527 1.5

Silesia(10) 1.85 4616 15 163 6

Fankou(11) 5.49 1900 310 100 210

Berg Aukas(12) 0.37 1542 494 25 149 90 1014 17

Abenab(12) 0.68 2149 631 56 226 140 1200 38

IRISH

Silvermines(13) 0.19 1700 900

SEDEX

Red Dog (Alaska)(14) 2.87 3250 84 34

Texas Gulf(15) 2050 145 135 825 61

Base–metal vein type deposits

West Shropshire(16) 3.80 5200 2500

Metamorphised SEDEX deposits

Aguilar(17) 9.09 1000 22,900 300

Dugald River(18) 8.58 894 53

Metamorphic Pb–Zn–Cu deposits

Cobar (Australia)(19) 8.10 851 633

Other types

Niujiaotang (China)(20) 1.36 13,800 1825 2900 22

(1) This paper; (2) Monteiro (1997); (3) Bez (1980); Dresch (1987); (4) Hall and Heyl (1968); (5) Jolly and Heyl (1968); (6) Viets et al. (1992);

(7) Mavrogenes et al. (1992); (8) Lenker (1962); Maher and Fagan (1970); (9) Kyle (1980); (10) Haranczyk (1979); (11) Song (1984); (12)

Emslie and Beukest (1981); (13) Zakrzewski (1989); (14) Edgerton (1997); (15) Farkas (1973); (16) Pattrick et al. (1993); (17) Gemmel et al.

(1992); (18) Xu (1998); (19) Brill (1989); (20) Liu et al. (1999).


to 8470 ppm in the Ambrosia deposit), which exceed

the contents observed in sphalerite (Tables 8 and 9).

These represent the main trace elements in galena

from the Fagundes and Ambrosia deposits (Fig. 16),

and are unusual because, according to Moller (1987),

the bulk of Ga and Ge present in the mineralizing

0.00

0.20

0.40

0.60

0.80

1.00

0.00 0.20 0.40 0.60 0.80 1.00

Fe/(Fe + ∑metals)

∑m

etal

s/(F

e +

∑m

etal

s)

(I)

(II)

(III)

(I)(II) orange zones

(II) light brown zones

(II) brown zones

(III)

(IV)

Ambrósia (II)

Ambrósia (I)

Fagundes (I)

Fagundes(II) and (III)

Fagundes(IV)

Increasing Fe2+Vazante

Ambrósia (III)

Vazante Ambrósia Fagundes

Fig. 14. Fe content vs. total trace metal (Ge+Cd+Cu+Ag) content (P

metals) in sphalerite from Vazante, Ambrosia, and Fagundes deposits.

Cd

Fe (Ag + Ge + Cu)

Vazante

Fagundes

Ambrósia

(I)(II)

(III)

(I)

(II) orange zones

(II) light brown zones

(II) brown zones(III)

(IV)

Vazante

Ambrósia

Fagundes

Fig. 15. Cd–Fe–(Ge+Ag+Cu) atomic ratios for sphalerite from Vazante, Ambrosia and Fagundes deposits.


Table 5

Compositional range and average composition (Fe in wt.%, trace-elements in ppm) of different sphalerite varieties from Fagundes deposit

Fagundes Sphalerite (I) Sphalerite (II) Sphalerite (III) Sphalerite (IV)

All sphalerite

types n =75

Colloform

n =08

Orange zones

n =08

Light brown

zones n =04

Brown zones

n =16

Mobilized/deformed

sphalerite n =29

Late veinlets,

Clearer yellow

n =10

Low High Mean Low High Mean Low High Mean Low High Mean Low High Mean Low High Mean Low High Mean

Fe 0.12 0.84 0.46 0.33 0.54 0.42 0.36 0.80 0.52 0.20 0.40 0.31 0.12 0.72 0.47 0.14 0.78 0.45 0.20 0.84 0.56

Cd 1530 7510 3354 3380 7170 5333 2150 3420 2654 3140 4580 3850 2490 7510 3791 1760 4960 2764 1530 4240 3148

Ge b120 2390 540 b120 1640 672 350 2200 790 b120 400 187 b120 1560 599 b120 2390 552 b120 180 *

Cu b100 2650 300 b100 490 175 400 2650 1616 b100 280 * b100 820 280 b100 550 * b100 260 *

Pb b575 2180 * b575 1950 751 b575 2180 868 b575 b575 b575 b575

Ag b120 930 210 b120 930 366 b120 550 138 b120 220 * b120 630 178 b120 910 256 b120 710 *

Mn b100 530 * b100 60 * b100 530 305 b100 b100 110 * b100 120 * b100

*=Percentage of analyses above the minimum detection limit b50%.


fluid is normally captured by the sphalerite during

crystallization. Exceptions have nevertheless been

reported, such as galena from Apex Ga–Ge Mine,

SW Utah, which has the highest Ga content (mean

1100 ppm) relative to the other sulfides from this

deposit (Mahin, 1990).

Evidence of correlation among Ga, Zn, Cu, and Ag

was observed in Vazante and Ambrosia galena, sug-

gesting that finely disseminated Ga-bearing mineral

phases, such as carnevallite [Cu (Ga,Zn,Fe)S2] or

gallite (CuGaS2), may be present as mineral inclu-

sions in galena, or that coupled substitutions may be

responsible for incorporation of Ga, Zn, Cu and Ag. A

correlation between Ge, Cu, and Ag, which might

suggest the presence of the more common Ge-bearing

Table 6

Compositional range and average composition (Fe in wt.%, trace-elemen

Ambrosia deposit

Vazante Ambrosia

All sphalerite

types n =50

All sphalerite

types n =38

Sphalerite (I)

Brown n =11

Low High Mean Low High Mean Low Hig

Fe 0.00 0.93 0.09 0.21 2.54 0.762 0.21 0.4

Cd b100 10390 8411 b100 4100 1181 b100 440

Ge b120 1030 132 b120 1380 319 b120

Cu b100 2870 241 b100 360 * b100 240

Pb b575 b575 1740 * b575 174

Ag b120 570 * b120 830 * b120 470

Mn b100 b100 150 * b100 150

*=Proportion of analyses above the minimum detection limits b50%.

minerals (e.g., germanite and renierite) was not pres-

ent in any of the three deposits.

6.2.3. Pyrite

Pyrite occurs only in Ambrosia and Fagundes

deposits. In Vazante, pyrite is absent in the willemitic

ore and in the sulfide ore bodies, due to high fO2/fS2conditions of ore deposition (Monteiro, 1997). In Am-

brosia and Fagundes, pyrite contains high Pb and Zn

contents (Table 10), which could be due to submicro-

scopic inclusions of galena and sphalerite. The main

differences in comparison with similar deposits, how-

ever, are the presence of Ga in pyrite (up to 520 ppm in

Ambrosia and 610 ppm in Fagundes) and Ge in Am-

brosia pyrite (up to 4630 ppm).

ts in ppm) of Vazante and from different sphalerite varieties from

Sphalerite (II)

Mobilized/deformed

sphalerite n =11

Sphalerite (III) Late veinlets,

clearer yellow n =16

h Mean Low High Mean Low High Mean

8 0.35 0.35 0.99 0.70 0.54 2.54 1.57

257 720 1770 1225 190 4100 1785

b120 1380 312 b120 1110 330

* b100 160 * b100 360 116

0 * b575 b575

* b120 830 * b120 490 150

* b100 b100 150 *

Table 7

Trace-element average contents (in ppm) of galena from different Pb–Zn deposits

Deposits/district Zn As Ga Ge Cd Sb Ag Cu Bi Ni

Ambrosia(1) 1610 3340 7010 420 140

Fagundes(1) 740 3470 4970 420 170

Vazante(2) 3920 120 380 710 230 240

Morro Agudo(3) 10 71 41

Mississippi Valley-type deposits

Tri-State(4) 49 11.2 9.5 52

Missouri SE(5) 340 27 171 85 59 50

Wisconsin–Illinois(6) 7.5 283 15.7 12 1

Illinois–Kentucky (6) 234 15 813 149 105 139

Silesia(7) 609 20 213 173 37 10

Fankou(8) 500 50 1210 1640

Berg Aukas(9) 65,366 220 521

Abenab(9) 22,446 181 320

IRISH type deposits

Silvermines(10) 800 500 400

SEDEX deposits

New Brunswick(11) 3400 850 4100

Metamorphic Pb–Zn–Cu deposit

Cobar(12) 453 491

Other types

Niujiaotang(13) 1770 1.2 1.72 3233 4025

(1) This paper; (2) Monteiro (1997); (3) Bez (1980); Dresch (1987); (4) Hagni (1983); (5) Hall and Heyl (1968); Bhatia and Hagni (1980); (6)

Hall and Heyl (1968); (7) Haranczyk (1979); (8) Song (1984); (9) Emslie and Beukest (1981); (10) Zakrzewski (1989); (11) Boorman (1968);

(12) Brill (1989); (13) Liu et al. (1999).


6.3. Primary sulfide mineralization processes

In spite of the overlapping deformation observed in

the Fagundes deposit, primary sulfide textures in the

Table 8

Variations in the trace element contents (in ppm) of galena from Fagunde

Fagundes

All types n =29 Galena (I) Open-space

filling, replacements n =12

Low High Mean Low High Mean

Fe b100 520 * b100

Cd b100 860 402 b100 700 400

Ag b120 810 183 b120 810 240

Cu b100 210 * b100 210 *

Zn b100 6790 769 b100 1080 196

Ge 3920 6430 4971 3920 4860 4402

Ga 2740 4650 3454 2940 4650 3576

*=Proportion of analyses above the minimum detection limits b50%.

stratabound sulfide ore deposits are still preserved,

including marked compositional zoning in sphalerite.

In Ambrosia, these textures are rare, and in Vazante

the different sphalerite generations, which were affect-

s

Galena (II) Veins, veinlets

in mobilized ore n =08

Galena (III)

Late galena n =09


b100 520 * b100 160 *

270 860 441 b100 640 371

b120 810 165 b120 390 123

b100 130 * b100 190 *

b100 2180 475 b100 6790 1794

4000 6430 5288 5010 5250 5130

3110 3650 3358 2740 3750 3418

Table 9

Variations in the trace element contents (in ppm) of galena from the Vazante and the Ambrosia deposits

Ambrosia Vazante

Galena All types

n =15

Galena (I) Open-space filling,

veins n =09

Galena (II)

Late galena n =06

Galena All types

n =09

Low High Mean Low High Mean Low High Mean Low High Mean

Fe b100 190 * b100 b100 190 * b100 870 214

Cd 110 660 416 110 620 364 180 660 488 b100 2280 853

Ag b120 720 140 b120 b120 720 300 b120 760 167

Cu b100 280 * b100 280 * b100 b100 740 296

Zn b100 6090 1605 b100 3870 590 b100 6090 3026 b100 3400 1622

Ge 4410 8470 7005 4410 8470 6993 7050 7090 7055 b120 960 382

Ga 3000 3810 3343 3000 3810 3391 3040 3700 3276 b120 400 *

*=Proportion of analyses above the minimum detection limit b50%.


ed by the ductile–brittle and brittle deformations, are

quite homogeneous; evidence of primary zoning pat-

terns is conspicuously absent.

In general, Fagundes sphalerite crystals belonging

to a single generation of ore deposition display color-

banded growth zones, which can be correlated to

oscillatory variations in the content of the minor ele-

ments (Emslie and Beukest, 1981; Hagni, 1983; Viets

et al., 1992). Light-brown zones in the crystal cores

display lower Fe, Ge and Cu contents and higher Cd

concentration than orange zones in intermediate parts

of the crystals (Fig. 17; Table 5). Brown zones, mainly

on the crystal borders, may exhibit increase in the Ag

and Cd concentrations.

The usual distribution of minor and trace-elements

in sphalerite from MVT deposits (e.g., the Tri-State

district, USA; Hagni, 1983; Viets et al., 1992) is

Table 10

Variations in the trace element contents (in ppm) of pyrite from Fagundes

Fagundes

All types

n =34

Pyrite (I) Colloform,

open-space filling n =19


Cu b100 430 130 b100 430 157

Pb b575 35,480 4812 b575 35,480 6931

Zn b100 8590 973 b100 2130 266

Cd b100 b100 150 *

Ag b120 620 152 b120 620 172

As b530 3590 * b530 3590 *

Mn b100 5710 652 b100 5710 1058

Ga b120 610 * b120 190 *

Ge b120 360 * b120 360 *


characterized by higher concentrations of compatible

elements in the crystal core and highest concentration

of incompatible elements, such as Ge, Ga and Ag, in

the more external crystal zones (Hagni, 1983). This

pattern is associated with enrichment of incompatible

elements in the residual mineralizing fluid during

crystal formation. However, Fe concentration, which

is relatively more compatible, increases markedly in

the outer crystal zones, reflecting introduction of Fe-

rich fluid pulses in the Tri-State deposits (Hagni,

1983; Viets et al., 1992).

The observed patterns in Fagundes sphalerite could

reflect that Fe and Cd readily substitute for Zn in the

sphalerite lattice during initial crystallization. Howev-

er, the increase in Fe content in intermediate parts of

the crystals may reflect introduction of Fe-rich fluids.

The incorporation of Ge and Cu in intermediate parts

Pyrite (II) Brecciated,

mobilized pyrite n =3

Pyrite (III) Late pyrite

n =12


b100 b100 290 111

b575 2480 827 b575 13,390 2453

210 2900 1767 b100 8590 1870

b100 b100

b120 200 * b120 480 133

b530 b530

b100 180 117 b100 520 143

b120 140 * b120 610 133

b120 b120

Ga Ge

Zn + Cd + Ag

Vazante

FagundesAmbrósia

Fig. 16. Ga–Ge–(Zn+Cd+Ag) atomic ratios for galena from

Vazante, Ambrosia and Fagundes deposits.

100

1000

10000

Lightbrown

Brown

pp

m

Orange

Rim RimCoreOrange

Cd

Ge

Fe

Ag

Cu

Lightbrown

Fig. 17. Trace-element variations in Fagundes zoned sphalerite.


of the crystal could have consumed a large part of

these elements from the fluid, resulting in their de-

crease on the crystal borders. The final Cd increase

could suggest hydrothermal fluid pulses with varia-

tions in Zn/Cd ratio, reflecting changes in the fluid

source or degree of mixing of hydrothermal fluids.

Colloform pyrite also displays trace element distri-

bution variations, expressed as higher Mn contents in

the core of the structures, an increase of Pb and As in

marginal areas and by oscillations in the Ag and Cu

contents in intermediate parts.

6.4. Deformation, mobilization and related sulfide

mineralization

The Vazante sphalerite textures indicate that ductile

and brittle deformations were quite intense, resulting

in recrystallization, homogenization and mobilization

processes, which were accompanied by the willemitic

mineralization. In the Fagundes and Ambrosia depos-

its, the observed features reflect several intermediate

stages of mobilization, which could be related to

interaction of pre-existing sulfide phases with later

hydrothermal fluids.

Changes in sphalerite chemical composition were

observed in relicts of primary sphalerite from

Fagundes and Ambrosia, which display evidence of

corrosion and partial replacement on the crystal rims.

Decrease of Cu, Ag and Ge concentrations is recorded

along the borders of these relicts. Minor fragments,

with evidence of large fluid interaction, also display

low contents of these elements, even in the crystal

cores. Sphalerite (IV) from Fagundes, which precipi-

tated directly from the later hydrothermal fluid, also

exhibits a decrease of Cu and Ge concentrations rel-

ative to those of the primary phase (Table 5). This

could indicate low concentration of these elements in

the overprinting fluid.

Mobilized sphalerite (II) and late sphalerite (III)

from Ambrosia are significantly richer in Fe and Cd

(Table 6) relative to primary sphalerite (I). In spite of

the similarity in the Fe/P

metals ratios of the late

sphalerite phases from Fagundes and Ambrosia (Fig.

14), the observed sphalerite compositions could re-

flect variations in the concentrations of Fe and Cd in

the overprinting fluids or significant differences in the

temperature, Eh, fS2 or pH in the fluid system, which

may be responsible for the incorporation of Cd and Fe

in mobilized and late Ambrosia sphalerite.

Zn is enriched in galena affected by processes

related to the deformation, mobilization, and in late

galena (Tables 8 and 9). Due to deformation, pyrite is

commonly brecciated or shows evidence of dissolu-

tion. In the Fagundes deposit, there is an increase of

Zn and decrease of Mn contents in mobilized and late

pyrite (Table 10). The Ambrosia late pyrite exhibits an

increase in Pb (Table 11).

6.5. Zn/Cd ratio in sphalerite

Sphalerite Zn/Cd ratio values, (Zn/Cd)sph, for the

studied deposits vary from 64 to 98 (Vazante), 89 to

439 (Fagundes), and 157 to 8269 (Ambrosia). Such

Table 11

Variations in the trace element contents (in ppm) of pyrite from Ambrosia

Ambrosia

All types n =28 Pyrite (I) Open-space filling n =17 Pyrite (II) Late pyrite n =12

Low High Mean Low High Mean Low High Mean

Cu b100 300 * b100 300 * b100 120 *

Pb b575 11,720 891 b575 2350 * b575 11,720 1943

Zn b100 2160 334 b100 2160 343 b100 950 320

Cd b100 500 * b100 500 * b100 160 *

Ag b120 1160 140 b120 1160 162 b120 390 *

As b530 5860 * b530 5850 * b530 670 *

Mn b100 800 * b100 800 * b100 300 *

Ga b120 520 * b120 390 * b120 520 129

Ge b120 4630 298 b 120 3046 506 b 120 260 *


Table 12

Zn/Cd ratios in sphalerite from Zn–(Pb) deposits

Mineral (Zn/Cd)sph

Range Average

Fagundes(1)

Colloform sphalerite (I) 96–244 140

Zoned sphalerite (II) 89–305 207

Orange zones 192–305 252

Yellow zones 146–213 178

Brown zones 89–269 192

Mobilized sphalerite (III) 134–384 265

Late sphalerite (IV) 154–439 226

All types 89–439 225

Ambrosia(1)

Sphalerite (I) 1515–8269 3398

Mobilized sphalerite (II) 372–911 615

Late sphalerite (III) 157–3498 1536

All types 157–8269 1510

Vazante(2) 64–98 78

Morro Agudo(3) 68–121 83

Magmatic–hydrothermal deposits(4) 104–214

Sediment-hosted and carbonate-hosted

Pb–Zn deposits (MVT, SEDEX) (4,5,6)

252–330

Volcanogenic deposits(4,5,6) 417–531

Metamorphised/remobilized deposits(6,7) 273–1310

Base–metal vein-type deposit(8) 69–380

Others types (Niujiaotang, China)(9) 31–75

(1) This paper; (2) Monteiro (1997); (3) Bez (1980); (4) Song

(1984); (5) Jonasson and Sangster (1978); (6) Brill (1989); (7) Xu

(1998); (8) Pattrick et al. (1993); (9) Liu et al. (1999).


broad variation in (Zn/Cd)sph has not been previously

reported from the same district (Jonasson and Sang-

ster, 1978; Song, 1984; Brill, 1989; Xu, 1998). In

comparison with available data from other Pb–Zn

deposits (Table 12), the mean Fagundes (Zn/Cd)sph(255) is similar to those observed in carbonate- and

sediment-hosted Pb–Zn deposits, including the meta-

morphosed ones (Song, 1984).

The lowest (Zn/Cd)sph observed in Fagundes–in

colloform (I) (96 to 244) and zoned (II) sphalerite

(89 to 305)–are similar to those of the Vazante (64 to

98) and Morro Agudo sphalerite (Table 12). Mobi-

lized (III) and late (IV) sphalerite from Fagundes

display (Zn/Cd)sph higher than the early sphalerite

phases (Table 12).

Low (Zn/Cd)sph from Vazante and Fagundes

could reflect the regional role of mineralizing fluids

with similar low Zn/Cd ratios and, possibly, with

low contents of reduced sulfur (P

Sred), which

according to Schwartz (2000), shift the total distri-

bution coefficient Kt(ZnS, Cd) to higher values, and

hence favor formation of Cd-rich sphalerite. These

conditions could have major importance for the low

sulfidizing capacity of the Vazante willemitic ore,

but also imply a key role of an additional sulfur

supply for the genesis of the sulfide-rich deposits in

the district.

The mean (Zn/Cd)sph (1510) of Ambrosia epige-

netic sphalerite is the largest described in the litera-

ture. Brill (1989) and Xu (1998) mention Zn/Cd

ratios up to 1300 in the Cu–Pb–Zn Cobar and Zn–

Pb–Ag Dugald River deposits (both Australia),

which are genetically linked to hydrothermal replace-

ment related to metamorphism. Available petrograph-

ic and geochemical evidences indicate that epigenetic

mineralization related to fluid-assisted mobilization


process might have been more intense in Ambrosia

than in Fagundes, which could be related to late

expulsion of hydrothermal fluids during the Brasi-

liano compressive events.

6.6. Geothermometry

The formation temperature of sphalerite–galena

cogenetic pairs from the Vazante deposit, estimated

by Monteiro (1997), based on Cd distribution (Gele-

tii et al., 1979; Bortnikov et al., 1995), range from

317 8C (sulfides related to brittle–ductile structures) to

110 8C (sulfides related to brittle structures). Stable

isotopic geothermometers indicate temperatures of

257 to 330 8C for sulfide bodies (sphalerite–galena),

254 to 294 8C for willemitic ore (willemite–quartz,

hematite–quartz) and 206 to 260 8C for hydrothermal

mineral phases (siderite–quartz) of veins and breccias

(Monteiro, 1997; Monteiro et al., 1999). The lack of

reversals and the agreement of temperatures obtained

by O- and S-isotope- and mineral chemistry

geothermometer were utilized as an indication of

chemical and isotopic equilibrium. Minimum tem-

peratures of the mineralization estimated from fluid

inclusions in willemite (up to 180 8C) and sphalerite

(up to 230 8C) are lower than those indicated by stableisotopic systematic and mineral chemistry (Dardenne

and Freitas-Silva, 1999; Bettencourt et al., 2001;

Monteiro, 2002).

Temperatures calculated from cadmium sphaler-

ite–galena geothermometers from Fagundes and

Ambrosia samples are unreasonably high, ranging

from 573 8C (sphalerite II) to 706 8C (sphalerite IV)

in the Fagundes deposit and between 629 8C (sphal-

erite I) and 802 8C (sphalerite III) in the Ambrosia

deposit. These results are in disagreement with the

fluid inclusion data, which range from 120 to 265

8C (Monteiro, 2002), implying disequilibrium be-

tween coexisting galena and sphalerite with respect

to Cd partition. This could reflect, particularly in the

Fagundes deposit where colloform and zoned tex-

tures are preserved, that equilibrium was not

attained during mineral deposition due to the rapid

crystallization and to diffusion rates slower than

crystal growth rates. Additionally, the lack of equi-

librium is also consistent with textural observations

indicative of incomplete reaction and mobilization

process, similar to those reported by Brill (1989)

and Wagner and Boyce (2001) for base–metal

mineralizations overprinted by hydrothermal–meta-

morphic fluids.

7. Discussion

7.1. Timing of Zn mineralizations in the Vazante–

Paracatu region

The occurrence of different styles of mineralization

in the Vazante–Paracatu region, in a similar way to

those reported for carbonate-hosted deposits of the

Irish Midlands and of the McArthur River district,

could be related to local stress regimes, which repre-

sent a major mineralization style and ore control. In

this case, the compressional regimes favor the epige-

netic end-member styles of mineralizations (Le Huray

et al., 1987).

Despite the intrinsic difficulties concerning the

timing of carbonate-hosted mineralizations, the iden-

tification of the relationships among different miner-

alization styles in the same deposit, could allow the

recognition of the different mineralization episodes in

the district.

Syndiagenetic mineralization stages, represented

by early sulfide cementation of unconsolidated allo-

chemical grains, progressive replacement of diagenet-

ically modified coated grains and relationships

between sulfides and convolute or compactation struc-

tures (Dardenne, 1979; Hitzman, 1997), have been

recognized only in the Morro Agudo deposit. Collo-

form sulfides and coarse-grained zoned sphalerite

associated with pyrite, galena and baroque dolomite

represent a minor late mineralization stage at Morro

Agudo (Dardenne, 1979; Hitzman, 1997), and the

main stage of the Fagundes deposit. This later stage,

related to wall rock dissolution and sulfide infilling,

probably occurs late during the burial history of the

sedimentary sequence.

The Morro Agudo and Fagundes deposits share

some characteristics, besides the late-diagenetic sul-

fide textures, such as the stratigraphic positioning

related to back-reef facies overlaid by reduced carbo-

naceous pyrite-bearing shales, temperature (100 to

N250 8C), low to moderate salinity of mineralizing

fluids and wide variation of sulfur isotopic composi-

tions (d34S=�8x to +40x; Misi et al., 1999; Cunha


et al., 2000; Monteiro, 2002; Monteiro et al., 2003).

These characteristics could indicate similarity to Irish-

type deposits (Hitzman, 1995, Hitzman and Beaty,

1996), suggesting a syn- to late-diagenetic replace-

ment origin for these deposits.

The emplacement of epigenetic–hydrothermal

mineralizations and the occurrence of mobilization

of ore phases related to migration of late hydrothermal

fluids during the late Brasiliano collisional event

(~630 Ma; Dardenne, 2000) are also ubiquitous in

the Vazante–Paracatu Zn–(Pb) district.

The Ambrosia deposit represents an example of

epigenetic mineralization, whose characteristics

could reflect the mineralization fluid evolution during

the host sequence deformational history, related to the

continuous transition between burial diagenesis and

low greenschist facies metamorphism. The Vazante

non-sulfide Zn deposit represents also a syntectonic

mineralization episode, synchronous and inter-related

to the Vazante Shear Zone development, which was

subsequent to the low greenschist facies metamor-

phism of the Vazante Group.

7.2. Sulfide-rich carbonate-hosted Zn–(Pb) deposits:

fluid mixing evidences

Colloform and zoned sphalerite textures and the

strong silicification observed in Fagundes deposit

might imply in rapid fluid cooling and ore deposition,

which could be explained by fluid mixing processes.

Oscillatory variations in minor and trace-elements of

the Fagundes zoned sphalerite could also suggest

hydrothermal fluid pulses with variations in Zn/Cd

ratio, reflecting changes in the fluid source or degree

of mixing of hydrothermal fluids. Additionally, the

relationship between minor and trace-elements in

sphalerite and the paragenetic evolution of Fagundes

and Ambrosia deposits could also reflect progressive

fluid mixing.

According to Monteiro (2002), chemical variations

in sphalerite may be correlated with d34S values of

sphalerite from these deposits. The Fagundes early

sphalerite (I) is characterized by the highest d34Svalues (+36.3x), low average Fe content (0.42%)

and low (Zn/Cd)sph (140). The decrease in d34S values

(+14.8x) in late sphalerite (IV) is accompanied by

slight increase in mean Fe content (0.56%) and (Zn/

Cd)sph (226), whereas sphalerite associated with epi-

genetic mineralization of Ambrosia is 34S-depleted

(d34S=+12.2x to �5.4x), Fe-rich (up to 1.57%)

and has the highest (Zn/Cd)sph (1510). These relation-

ships are systematic and might suggest that mixing

processes involving two distinct fluid bearing sulfur

sources may be important for the genesis of the sul-

fide-rich deposits of the district. Fluid mixing is also

supported by fluid inclusion studies in Fagundes and

Ambrosia deposits (Monteiro, 2002; Monteiro et al.,

2003). These studies permitted the characterization of

a high-temperature (N250 8C) and moderate salinity

(~15 wt.% NaCl equiv.) fluid, mainly in sphalerite

from early mineralization stages of the Fagundes de-

posit, and a moderate-temperature (140 to 190 8C) andhigh salinity (N23 wt.% NaCl equiv.) fluid, which is

associated mainly with the late mineralization stage of

Fagundes and Ambrosia. Thus, progressive mixing

between hot metal-bearing fluid with low contents

of reduced sulfur (P

Sred) and moderate temperature,

highly saline basinal fluids could be suggested, in a

similar way to that reported for the Morro Agudo

deposit (Hitzman, 1997; Misi et al., 1999; Cunha et

al., 2000).

The predominance of isotopically light sulfur in

epigenetic stages of mineralization, mainly in Am-

brosia deposit, may result from expulsion of moder-

ate temperature, highly saline basinal fluids from the

Vazante basin, related with Brasiliano compressive

events. Alternatively, reduced shales that cover the

host dolostones in Fagundes, Ambrosia and Morro

Agudo deposits might be mobilized by descending

fluids, representing a potential sulfur source. This

could enhance the importance of shale units for

localization of sulfide deposits in the district.

7.3. Vazante non-sulfide Zn deposit

The Vazante sphalerite, which occurs in subordinat-

ed ore-bodies imbricated with the predominant will-

emitic ore, displays chemical homogeneity and also

shows a narrow range of d34S values between

+11.8x and +14.4x (Monteiro, 1997; Monteiro et

al., 1999). This is a distinct sulfur isotopic signature in

relation to sulfides from the other deposits in the dis-

trict, such as Ambrosia (d34S=�5.4x to +12.2x) and

Fagundes (d34S=+14.8x to +36.3x), which display

a remarkable wide sulfur isotopic variation and a com-

plex isotopic distribution related to the textural and


paragenetic evolution of each deposit (Monteiro, 2002;

Monteiro et al., 2003). This could imply that the high-

temperature metal-bearing fluid with low Zn/Cd ratios

could represent a minor reduced sulfur reservoir. Pro-

gressive consumption of sulfur from this fluid would

yield early sphalerite precipitation followed by willem-

ite deposition, explaining the paragenetic sequence

observed at Vazante and in others hypogene non-sul-

fide Zn deposits, such as Berg Aukas, as previously

proposed by Hitzman et al. (2003).

Furthermore, the colloform willemite also sug-

gests rapid mineral precipitation, which could be

induced by mixing between the hot metal-bearing

and meteoric fluids, as indicated by stable isotope

(Monteiro, 1997; Monteiro et al., 1999) and fluid

inclusion studies (Monteiro, 2002; Monteiro et al.,

2003). This could be an important factor for the

establishment of high fO2/fS2 conditions, which are

necessary for the willemite stability (Monteiro, 1997;

Brugger et al., 2003).

8. Conclusions

The carbonate-hosted Zn–(Pb) deposits of the

Vazante–Paracatu district present different mineraliza-

tion styles, which may be attributed to the overprint-

ing of syndiagenetic and epigenetic–hydrothermal

processes, related to the long-term hydrothermal sys-

tem evolution associated to diagenesis and deforma-

tion of the Vazante Group, during the Brasiliano

Orogeny.

These characteristics may reflect common miner-

alizing processes, involving the regional migration of

high temperature metal-bearing brine with low Zn/

Cd ratios and, possibly, with low contents of reduced

sulfur (P

Sred). High Cd- and Ge- and low Fe-, Cu-,

Mn- and Ag-contents, which characterize the late-

diagenetic Fagundes sphalerite, suggest that the

source of this metal-bearing fluid could be, in part,

derived from the underlying basin fill, which com-

prise dolomitic units, clastic sediments and organic

matter-rich pelitic sequences. This could indicate

similarity of this brine with deeply circulating oxi-

dized basinal brines, which have been considered

important in the formation of Irish-type deposits.

According to Cooke et al. (2000), they are the

preferred metal carrier and are more likely to pro-

duce large tonnage Zn–Pb deposits at moderate tem-

peratures (~200 8C).Systematic relationships among sphalerite compo-

sition, S-isotopic composition and paragenetic evo-

lution of the Fagundes and Ambrosia deposits

suggest that progressive fluid mixing processes in-

volving oxidized metal-bearing fluid and sulfur-rich,

saline hydrothermal fluids were important for the

genesis of the sulfide-rich deposits in the district.

The predominance of the highly saline brines in

later epigenetic mineralization episodes, such as in

Ambrosia deposit, might be related to episodic mi-

gration of hydrothermal fluids mainly derived from

reduced shale sequences during the Brasiliano com-

pressive events.

The Vazante non-sulfide Zn deposit results from the

overall mixture between oxidized sulfur-deficient

metal-bearing fluid and meteoric fluids channeled to

the Vazante Shear Zone, which enable the high fO2/S2conditions responsible for the stability of the Vazante

willemitic assemblage and the intense fissural hydro-

thermal alteration, mostly accompanied by hydraulic

breccia and veins infilling by siderite, dolomite, Fe-

dolomite, hematite and jasper. These high fO2/S2 con-

ditions would also be favored by the lack of reduced

sequences above the Vazante deposit, which could

represent a limiting factor for H2S supply.

Acknowledgments

This paper is part of a Doctorate thesis of the first

author. We are grateful to Votorantim Metais for

continuous support and hospitality at the mine and

permission to publish. We are greatly indebted to D.F.

Sangster, S.S. Iyer, Nigel J. Cook, and an anonymous

referee for their reviews of the manuscript, which

significantly improved this paper. Special thanks are

due to the Microprobe laboratories in the Institute de

Geociencias of the Universidade de Sao Paulo and in

the Universidade de Brasılia. The financial support

was provided by Fundacao de Amparo a Pesquisa do

Estado de Sao Paulo, Brazil (Research Grant 96/

3941-3 and Doctorate Scholarship 98/0412-5),

which we acknowledge with appreciation. This

study is a contribution to the IGCP 450—Proterozoic

Sediment-hosted Base Metal Deposits of Western

Gondwana.


References

de Almeida, F.F.M., 1967. Origem e evolucao da plataforma brasi-

leira. Boletim-Departamento Nacional da Producao Mineral 243

(36 pp.).

Amaral, G., 1968. Geologia e depositos de minerio na regiao de

Vazante, Estado de Minas Gerais. Unpublished Doctorate thesis,

Escola Politecnica Universidade de Sao Paulo, Brasil, 133 pp.

Amaral, G., Kawashita, K., 1967. Determinacao da idade do Grupo

Bambuı pelo metodo Rb/Sr. Congresso Brasileiro de Geologia,

21, Anais. Sociedade Brasileira de Geologia, 214–217.

Babinski, M., Monteiro, L.V.S., Fetter, A.H., Bettencourt, J.S.,

Oliveira, T.F., 2005. Isotope geochemistry of the mafic dikes

from the Vazante Nonsulfide Zinc Deposit, Brazil. Journal of

South American Earth Sciences 18, 293–304.

Barbanson, L., Geldron, A., 1983. Distribution du germanium, de

l’argent et du cadmium entre les schistes et les mineralisations

stratiformes et filoniennes a blende-siderite de la region de

Saint-Salvy (Tarn). Chronique de la Recherche Miniere 51

(470), 33–42.

Bayliss, P., 1975. Nomenclature of the trioctahedral chlorites. Ca-

nadian Mineralogist 13, 178–180.

Bernstein, L.R., 1985. Germanium geochemistry and mineralogy.

Geochimica et Cosmochimica Acta 49, 2409–2422.

Bettencourt, J.S., Monteiro, L.V.S., Bello, R.S., Oliveira, T.F.,

Juliani, C., 2001. Metalogenese do zinco e do chumbo na regiao

de Vazante–Paracatu, Minas Gerais. In: Pinto, C.P., Martins-

Neto, M.A. (Eds.), Bacia do Sao Francisco, Geologia e Recursos

Naturais. SBG-MG, Belo Horizonte, pp. 159–196.

Bez, L., 1980. Evolucao mineralogica e geoquımica do deposito de

zinco e chumbo de Morro Agudo, Paracatu, MG. Congresso

Brasileiro de Geologia, 31, Anais. Sociedade Brasileira de

Geologia, Balneario de Camburiu 3, 1402–1416.

Bhatia, D.M.S., Hagni, R.D., 1980. Laser probe determinations of

trace-element concentrations in sulfide minerals from the Mag-

mont Mine, Viburnum Trend, Southeast Missouri. Transactions

of the American Institute of Mining, Metallurgical, and Petro-

leum Engineers 268, 1847–1855.

Boorman, R.S., 1968. Silver in some New Brunswick galenas. New

Brunswick Production Council Report Note, vol. 11. 11 pp.

Bortnikov, N.S., Dobrovol’skaya, M.G., Genkin, A.D., 1995. Sphal-

erite–galena geothermometers: distribution of cadmium, manga-

nese, and the fractionation of sulfur isotope. Economic Geology

90, 155–180.

Brill, B.A., 1989. Trace-element contents and partitioning of ele-

ments in ore minerals from the CSA Cu–Pb–Zn deposit, Aus-

tralia. Canadian Mineralogist 27, 263–274.

Brugger, J., McPhail, D.C., Wallace, M., Waters, J., 2003. Forma-

tion of willemite in hydrothermal environments. Economic Ge-

ology 98, 819–836.

Cassedane, J., Lasserre, M., 1969. Etude geologique et analyse

isotopique, par la methode au plomb, de quelques galenes du

Bresil. Bulletin du Bureau de Recherches Geologiques et Mini-

eres (Section 2: Geologie des Gites Mineraux) 1, 71–83.

Cathelineau, M., Nieva, D., 1985. A chlorite solid solution

geothermometer: the Los Azufres (Mexico) geothermal system.

Contributions to Mineralogy and Petrology 91, 235–244.

Cloud, P.E., Dardenne, M.A., 1973. Proterozoic age of the Bambuı

Groupe in Brazil. Geological Society of America Bulletin 84,

1673–1676.

Cooke, D.R., Bull, S.W., Large, R.R., Mcgoldrick, P.J., 2000. The

importance of oxidized brines for the formation of Australian

Proterozoic stratiform sediment-hosted Pb–Zn (Sedex) deposits.

Economic Geology 95, 1–18.

Cunha, I.A., Coelho, C.E.S., Misi, A., 2000. Fluid inclusion study

of the Morro Agudo Pb–Zn deposit, Minas Gerais, Brazil.

Revista Brasileira de Geociencias 30, 318–321.

Cunha, I.A., Misi, A., Babinski, M., 2001. Lead isotope signatures

of galenas from Morro Agudo Pb–Zn deposit, Minas Gerais,

Brazil. In: Misi, A., Teixeira, J.B.G. (Eds.), Proterozoic Base

Metal Deposits of Africa and South America. Proceedings of the

First IGCP 450 Field Workshop. CNPq/UNESCO/IUGS, Belo

Horizonte and Paracatu (MG), Brazil, pp. 45–47.

Cunha, I.A., Babinski, M., Misi, A., 2003. Pb isotopic constraints

on the mineralization from the Vazante Group, Minas Gerais,

Brazil. South American Symposium on Isotope Geology, 4,

Salvador, Short Papers, pp. 727–730.

Dardenne M.A., 1979. Les mineralisations plomb-zinc du Groupe

Bambui et leur contexte geologique. Doctorate thesis, Universite

Paris VI, France. 275 pp.

Dardenne, M.A., 2000. The Brasılia fold belt. In: Cordani, U.G.,

Milani, E.J., Thomaz-Filho, A., Campos, D.A. (Eds.), Tectonic

Evolution of South America. 31st International Geological Con-

gress, Rio de Janeiro, pp. 231–263.

Dardenne M.A., Freitas-Silva F.H., 1999. Pb–Zn ore deposits of

Bambui and Vazante Groups, in the Sao Francisco Craton and

Brasılia Fold Belt, Brazil. In: Silva M. da G. da, Misi, A. (Eds.),

Base metal deposits of Brazil. Ministerio de Minas e Energia/

Companhia de Pesquisa de Recursos Minerais Minerais/Depar-

tamento Nacional de Producao Mineral, pp. 75–83.

Dardenne, M.A., Schobbenhaus, C.S., 2001. Metalogenese do Bra-

sil. Editora Universidade de Brasılia/CNPq, Brasılia. 392 pp.

Dardenne, M.A., Faria, A., Andrade, G.F., 1976. Occurrence de

stromatolithes collumnaires dans le Groupe Bambuı (Goias,

Bresil). Anais da Academia Brasileira de Ciencias 48, 555–566.

Dardenne, M.A., Freitas-Silva, F.H., Souza, J.C.F. de, Campos,

J.E.G., 1998. Evolucao tectono-sedimentar do Grupo Vazante

no contexto da Faixa de Dobramentos Brasılia. Congresso

Brasileiro de Geologia, 40, Anais, Sociedade Brasileira de

Geologia, Belo Horizonte, Resumos, 26.

Dresch, R.A.C., 1987. Aspectos geoquımicos da Jazida de Morro

Agudo, Paracatu, MG. Congresso Brasileiro de Geoquımica., 1,

Porto Alegre, Proceedings, vol. 1, pp. 5–27.

Edgerton, D., 1997. Reconstruction of the Red Dog Zn–Pb–Zn–Ba

orebody, Alaska: implications for the vent environment during

the mineralizing event. Canadian Journal of Earth Sciences 34,

1581–1602.

Emslie, D.P., Beukest, G.J., 1981. Minor- and trace-element distri-

bution in sphalerite and galena from the Otavi Mountainland,

South West Africa. Annals of the Geological Survey, Republic

of South Africa 15 (2), 11–28.

Essene, E.J., Peacor, D.R., 1987. Petedunnite (CaZnSi2O6), a new

clinopyroxene from Franklin, New Jersey, and phase equilibria

for zincian pyroxenes. American Mineralogist 72, 157–166.


Farkas, A., 1973. A trace element study of the Texas Gulf ore body,

Timmins, Ontario. Unpublished MSc thesis, University of

Alberta, Edmonton, AB, Canada. 149 pp.

Freitas-Silva, F.H., Dardenne, M.A., 1997. Pb/Pb isotopic patterns

of galenas from Morro do Ouro (Paracatu Formation), Morro

Agudo/Vazante (Vazante Formation) and Bambuı Group depos-

its. South American Symposium on Isotope Geology, Extended

Abstracts, pp. 118–120.

Geletii, V.F., Chernisher, L.V., Pastushkova, T.M., 1979. Distribu-

tion of cadmium and manganese between galena and sphalerite.

Geologiia Rudnykh Mestorozhdenii 21, 66–75.

Gemmel, J.B., Zantop, H., Meinert, L.D., 1992. Genesis of the

Aguilar Zinc–Lead–Silver Deposit, Argentina: contact metaso-

matic vs. sedimentary exhalative. Economic Geology 87,

2085–2112.

Hagni, R.D., 1983. Minor elements in Mississippi Valley-Type ore

deposits. In: Shanks, W.C. (Ed.), Cameron volume on uncon-

ventional mineral deposits. American Institute of Mining, Met-

allurgical and Petroleum Engineers, Society of Mining

Engineers, New York, pp. 71–88.

Hall, W.E., Heyl, A.V., 1968. Distribution of minor elements in ore

and host rock, Illinois–Kentucky fluorine district and upper

Mississippi Valley zinc–lead district. Economic Geology 63,

655–670.

Haranczyk, C., 1979. Development of the Variscan mineral para-

genesis in Poland. Freiberger Forschungshefte, Reihe C: Geo-

wissenschaften, Mineralogie-Geochemie 354, 7–17.

Hitzman, M.W., 1995. Mineralization in the Irish Zn–Pb–(Ba–Ag)

orefield. In: Anderson, K., Ashton, J., Earls, G., Hitzman, M.,

Tear, S. (Eds.), Irish Carbonate-hosted Zn–Pb Deposits, Society

of Economic Geologists Guidebook Series, vol. 21, pp. 25–61.

Hitzman, M.W., 1997. Sediment hosted Zn–Pb and Au deposits in

the Proterozoic Paracatu–Vazante Fold Belt, Minas Gerais, Bra-

zil. Abstracts with Programs-Geological Society of America 29,

A408.

Hitzman, M.W., 2001. Zinc oxide and zinc silicate deposits—a new

look. Abstracts with Programs-Geological Society of America

33, A336.

Hitzman, M.W., Beaty, D.W., 1996. The Irish Zn–Pb–(Ba)

orefield. In: Sangster, D.F. (Ed.), Carbonate-hosted Lead–zinc

Deposits, Society of Economic Geologists Special Publication,

vol. 4, pp. 112–143.

Hitzman, M.W., Thorman, C.H., Romagna, G., Oliveira, T.F., Dard-

enne, M.A., Drew, L.J., 1995. The Morro Agudo Zn–Pb deposit,

Minas Gerais, Brazil: a Proterozoic Irish-type carbonate hosted

sedex replacement deposit. Abstracts with Programs-Geological

Society of America 27, A408.

Hitzman, M.W., Reynolds, N.A., Sangster, D.F., Allen, C.R., Car-

man, C.E., 2003. Classification, genesis, and exploration guides

for nonsulfides zinc deposits. Economic Geology 98, 685–714.

Iyer, S.S., Hoefs, J., Krouse, H.R., 1992. Sulfur and lead isotope

geochemistry of galenas from Bambuı Group, Minas Gerais,

Brazil: implications on ore genesis. Economic Geology 87,

437–443.

Iyer, S.S., Krouse, H.P., Babinski, M., 1993. Isotope investigations

on carbonate rocks hosted lead–zinc deposits from Bambuı

Group, Minas Gerais, Brazil: implications for ore genesis and

prospect evaluation. Simposio do Craton do Sao Francisco, 2,

Anais, Salvador, pp. 338–339.

Johnson, C.A., Rye, D.M., Skinner, B.J., 1990. Petrology and stable

isotope geochemistry of the metamorphosed zinc–iron–manga-

nese deposit at Sterling Hill, New Jersey. Economic Geology

85, 1133–1161.

Jolly, J.L., Heyl, A.V., 1968. Mercury and other trace-elements in

sphalerite and wall-rocks from central Kentucky, Tennessee, and

Appalachian zinc districts. United States Geological Survey

Bulletin 1252-F, 1–29.

Jonasson, I.R., Sangster, D.F., 1978. Zn:Cd ratios for sphalerites

separated from some Canadian sulfide ore samples. Paper-Geo-

logical Survey of Canada 78-1B, 195–201.

Kranidiotis, P., MacLean, W.H., 1987. Systematics of chlorite al-

teration at the Phelps Dodge massive sulfide deposit, Matagami,

Quebec. Economic Geology 8, 1888–1911.

Kyle, J.R., 1980. Controls of lead–zinc mineralization, Pine Point

district, Northwest Territories, Canada. Mining Engineering 32,

1617–1626.

Leach, D.L., Sangster, D.F., 1993. Mississipi Valley-type lead–zinc

deposits. In: Kirkhan, R.V., Sinclair, W.D., Thorpe, R.I., Duke,

J.M. (Eds.), Mineral Deposit Modeling, Geological Association

of Canada Special Paper, vol. 40, pp. 289–314.

Le Huray, A.P., Caulfield, J.B.D., Rye, D.M., Dixon, P.R., 1987.

Basement controls on sediment-hosted Zn–Pb deposits: a Pb

isotope study of Carboniferous mineralization in Central Ireland.

Economic Geology 82, 1695–1709.

Lenker, E.S., 1962. A trace element study of selected sulfide

minerals from the Eastern United States. Unpublished PhD

thesis, Pennsylvania State University, University Park, United

States. 160 pp.

Liu, T., Lin, Y., Chen, G., 1999. Geochemical characteristics of the

independent cadmium deposit, Niujiaotang, Duyun, Guizhou.

Chinese Science Bulletin 44, 61–63.

Madalosso, A., Valle, C.R.O., 1978. Consideracoes sobre a estrati-

grafia e sedimentologia do Grupo Bambuı na Regiao de Para-

catu-Morro Agudo (MG). Congresso Brasileiro de Geologia, 30,

Anais, Sociedade Brasileira de Geologia, vol. 2, pp. 622–631.

Maher, S.W., Fagan, J.M., 1970. Trace element content of some ore

deposits in the southeastern states. Information CircularTennes-

see Department of Conservation, Division of Geology, Nash-

ville, TN, United States. 16 pp.

Mahin, R., 1990. The mineralogy and geochemistry of the Apex

gallium–germanium Mine, Southwestern Utah, MSc thesis, Uni-

versity of Utah. 102 pp.

Mavrogenes, J.A., Hagni, R.D., Dingess, P.R., 1992. Mineralogy,

paragenesis, and mineral zoning of the West Fork mine, Vi-

burnum Trend, Southeast Missouri. Economic Geology 87,

113–124.

Misi, A., Tassinari, C.C.G., Iyer, S.S., 1997. New isotope data from

the Proterozoic lead–zinc (Ag) sediment-hosted sulfide deposits

of Brazil: implications for their metallogenic evolution. South-

American Symposium on Isotope Geology, 1, Extended Ab-

stract, pp. 201–203.

Misi, A., Iyer, S.S., Kyle, J.R., Coelho, C.E.S., Franca-Rocha,

W.J.S., Gomes, A.S.R., Cunha, I.A., Carvalho, I.G., 1999.

Geological and isotopic constraints on the metallogenic evolu-


tion of the Proterozoic sediment-hosted Pb–Zn (Ag) deposits of

Brazil. Gondwana Research 2, 47–65.

Misi, A., Iyer, S.S., Kyle, J.R., Coelho, C.E.S., Tassinari, C.C.G.,

Franca-Rocha, W.J.S., Gomes, A.S.R., Cunha, I.A., Toulkeri-

dis, T., Sanches, A.L., 2000. A metallogenic evolution model

for the lead–zinc deposits of the Meso- and Neoproterozoic

sedimentary basins of the Sao Francisco Craton, Bahia and

Minas Gerais, Brazil. Revista Brasileira de Geociencias 30,

302–305.

Moeri, E., 1972. On a columnar stromatolite in the Precambrian

Bambuı Group of Central Brazil. Eclogae Geologicae Helvetiae

65, 185–195.

Moller, P., 1987. Correlation of homogenization temperatures of

accessory minerals from sphalerite-bearing deposits and Ga/Ge

model temperatures. Chemical Geology 61, 153–159.

Monteiro, L.V.S., 1997. Contribuicao a genese das mineralizacoes

de zinco da Mina de Vazante, MG. Unpublished MSc thesis,

Instituto de Geociencias, Universidade de Sao Paulo, Brazil.

159 pp.

Monteiro, L.V.S., 2002. Modelamento metalogenetico dos depositos

de zinco de Vazante, Fagundes e Ambrosia, associados ao

Grupo Vazante, Minas Gerais. Unpublished PhD thesis, Uni-

versidade de Sao Paulo, Brazil. 317 pp.

Monteiro, L.V.S., Bettencourt, J.S., 2001. Genesis of the Vazante,

Ambrosia and Fagundes Zn–(Pb) deposits (Minas Gerais, Bra-

zil): Geologic and stable isotopic constraints. In: Misi, A.,

Teixeira, J.B. (Eds.), Proterozoic base metal of Africa and

South America. CNPq and UNESCO/IUGS, Belo Horizonte,

pp. 79–81.

Monteiro, L.V.S., Bettencourt, J.S., Spiro, B., Graca, R., Oliveira,

T.F., 1999. The Vazante zinc mine, MG, Brazil: constraints on

fluid evolution and willemitic mineralization. Exploration and

Mining Geology 8, 21–42.

Monteiro, L.V.S., Bettencourt, J.S., de Oliveira, T.F., 2000. The

Vazante, Ambrosia, and Fagundes (MG, Brazil) Neoproterozoic

epigenetic zinc deposits: similarities, contrasting features, and

genetic implications. 31st International Geological Congress,

Rio de Janeiro, Brazil, Abstract volume (CD-ROM).

Monteiro, L.V.S., Bettencourt, J.S., Bello, R.M. da S, Juliani, C.,

Oliveira, T.F., 2003. Fluid inclusions and stable isotopic con-

straints on the genesis of the non-sulfide and sulfide zinc deposits

in the Vazante–Paracatu Belt, Brazil. In: Cailteux, J.L.H. (Orga-

nizer), Proterozoic Sediment-hosted Base Metal Deposits of

Western Gondwana, UNESCO/IUGS, pp. 163–167.

Oliveira, T.F. de, 1998. As Minas de Vazante e de Morro Agudo.

Workshop depositos minerais brasileiros de metais base. Uni-

versidade Federal da Bahia e Agencia para o Desenvolvimento

Tecnologico da Industria Mineral Brasileira (ADIMB), Salva-

dor, pp. 48–57.

Pattrick, R.A.D., Dorling, M., Polya, D.A., 1993. TEM study of

indium- and copper-bearing growth-banded sphalerite. Canadian

Mineralogist 31, 105–117.

Pimentel, M.M., Dardenne, M.A., Fuck, R.A., Viana, M.G., Junges,

S.L., Fischel, D.P., Seer, H.J., Dantas, E.L., 2001. Nd isotopes

and the provenance of detrital sediments of the Neoproterozoic

Brasılia Belt, central Brazil. Journal of South American Earth

Sciences 14, 571–585.

Pinho, J.M.M., 1990. Evolucao tectonica da mineralizacao de zinco

de Vazante. Unpublished MSc thesis, Universidade de Brasılia,

Brasil. 180 pp.

Pinho, J.M.M., Dardenne, M.A., Rigobello, A.E., 1990. Caracter-

izacao da movimentacao transcorrente da falha de Vazante,

Vazante, MG. Congresso Brasileiro de Geologia, 36, Anais,

vol. 5. Sociedade Brasileira de Geologia, Natal, pp. 2284–2295.

Rigobello, A.E., Branquinho, J.A., Dantas, M.G. da S., de Oliveira,

T.F., Neves Filho, W., 1988. Mina de zinco de Vazante. In:

Shobbenhaus, C., Coelho, C.E.S. (Eds.), Principais depositos

minerais do Brasil, DNPM 3, pp. 101–110.

Sangster, D.F., 1990. Mississippi Valley-type and sedex lead–zinc

deposits: a comparative examination. Transactions-Institution of

Mining and Metallurgy. Section B. Applied Earth Science 99,

21–42.

Schwartz, M.O., 2000. Cadmium in zinc deposits: economic geol-

ogy of a polluting element. International Geology Review 42,

445–469.

Sclar, C.B., Leonard, B.F., 1992. Quantitative chemical relation-

ship in franklinite–magnetite exsolution intergrowth from

Franklin, Sussex County, New Jersey. Economic Geology 87,

1180–1183.

Song, X.X., 1984. Minor elements and ore genesis of the Fankou

lead–zinc deposit, China. Mineralium Deposita 19, 95–104.

Stacey, J.S., Kramers, J.D., 1975. Approximation of terrestrial lead

isotope evolution by a two-stage model. Earth and Planetary

Science Letters 26, 207–221.

Thomaz Filho, A., Kawashita, K., Cordani, U.G., 1998. A origem

do Grupo Bambuı no contexto da evolucao geotectonica e de

idades radiometricas. Anais da Academia Brasileira de Ciencias

70, 527–548.

Viets, J.G., Hopkins, R.T., Miller, B.M., 1992. Variations in minor

and trace metals in sphalerite from Mississippi Valley-Type

deposits of the Ozark region: genetic implications. Economic

Geology 87, 1897–1905.

Viviani, C., Almeida, D.R., Romagna, G., Lopes, J.A., de Souza,

J.C.F., de Oliveira, T.F., Bessa, V., 2001. The Vazante and

Morro Agudo Zn–Pb mines, Minas Gerais, Brazil. In: Misi,

A., Teixeira, J.B. (Eds.), Proterozoic Base Metal of Africa and

South America. CNPq and UNESCO/IUGS, Belo Horizonte,

pp. 115–132.

Wagner, T., Boyce, A.J., 2001. Sulphur isotope characteristics of

recrystallisation, remobilisation and reaction processes: a case

study from the Ramsbeck Pb–Zn deposit, Germany. Mineralium

Deposita 36, 670–679.

Xu, G., 1998. Geochemistry of sulfide minerals at Dugald River,

NW Queensland, with reference to ore genesis. Mineralogy and

Petrology 63, 119–139.

Zakrzewski, M.A., 1989. Members of the freibergite–argentoten-

nantite series and associated minerals from Silvermines, County

Tipperary, Ireland. Mineralogical Magazine 53, 293–298.

Zang, W., Fyfe, W.S., 1995. Chloritization of the hydrothermally

altered bedrock at the Igarape Bahia gold deposit, Carajas,

Brazil. Mineralium Deposita 30, 30–38.

Zheng, Y.-F., 1996. Oxygen isotope fractionation in zinc oxides and

applications for zinc mineralization in Sterling hill deposit,

USA. Mineralium Deposita 31, 98–103.

Geology, petrography, and mineral chemistry of the Vazante non-sulfide and Ambrósia and Fagundes sulfide-rich carbonate-hosted Zn-(Pb) deposits, Minas Gerais, …

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