23
Remobilisation of base metals and gold by Variscan metamorphic fluids in the south Iberian pyrite belt: evidence from the Tharsis VMS deposit Christian Marignac a, * , Bocar Diagana b , Michel Cathelineau b , Marie-Christine Boiron b , David Banks c , Serge Fourcade d , Jean Vallance b a CRPG-CNRS, BP20, 54501 Vandoeuvre-les-Nancy Cedex, France b CREGU and UMR G2R 7566, BP 23, 54 501Vandoeuvre-les-Nancy Cedex, France c School of Earth Sciences, Leeds University, Woodhouse Lane, Leeds, UK d Geosciences Rennes, Campus de Beaulieu, 35042 Rennes Cedex, France Received 14 February 2002; received in revised form 25 June 2002 Abstract The Tharsis massive sulphide deposit, one of the major VMS-type deposits in the Iberian pyrite belt (IPB) was severely deformed by the Variscan tectono-thermal events. The question of whether or not these events affected the metal distribution in the deposit has been addressed by simultaneously studying the mineral parageneses (Tharsis stockwork) and the fluid circulation (at local and regional scales). The results are: (1) The early paragenesis in the stockwork (Q1 quartz – pyrite – chlorite – phengite F cobaltite F ankerite) was strongly overprinted by a late post-kinematic mineral deposition, including new quartz veins (Q3 quartz) and base metal sulphides (chalcopyrite, sphalerite, Bi and Te minerals, pyrite and galena) and gold. (2) At a regional scale, fluids accompanying the peak metamorphism conditions (ca. 300 MPa, ca. 300 jC) were of C – O – H – N – NaCl type, CO 2 -dominated with CH 4 and N 2 , and are considered to be ‘‘metamorphic’’ on the basis of microthermometry and geochemistry. The late- to post-kinematic evolution (‘‘retrograde’’ stage) was characterised by a pressure drop, down to 40 MPa (lithostatic to hydrostatic transition), and a heat input leading to temperatures z 430 jC, then decreasing to temperature around 170 jC. Fluids of the ‘‘retrograde’’ type exhibit both dilution of the C– O– H– N– NaCl fluid by a low salinity ‘‘meteoric’’ water and progressive loss of volatile components. (3) Fluids of the retrograde type pervasively percolated through the Tharsis stockwork and were responsible for the strong mineral overprint on the early (deformed) paragenesis. All the measurable fluid inclusions (f.i.) record these late fluids. There are primary fluid inclusions in Q1, but they are systematically imploded due to the external overpressure generated by the Variscan tectonic events. Although base metal distribution in the stockwork is basically the result of the 0009-2541/02/$ - see front matter D 2002 Elsevier Science B.V. All rights reserved. PII:S0009-2541(02)00275-9 * Corresponding author. E-mail address: [email protected] (C. Marignac). www.elsevier.com/locate/chemgeo Chemical Geology 194 (2003) 143 – 165

Remobilisation of base metals and gold by Variscan metamorphic fluids in the south Iberian pyrite belt: evidence from the Tharsis VMS deposit

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Remobilisation of base metals and gold by Variscan

metamorphic fluids in the south Iberian pyrite belt:

evidence from the Tharsis VMS deposit

Christian Marignaca,*, Bocar Diaganab, Michel Cathelineaub,Marie-Christine Boironb, David Banksc, Serge Fourcaded,

Jean Vallanceb

aCRPG-CNRS, BP20, 54501 Vandoeuvre-les-Nancy Cedex, FrancebCREGU and UMR G2R 7566, BP 23, 54 501Vandoeuvre-les-Nancy Cedex, France

cSchool of Earth Sciences, Leeds University, Woodhouse Lane, Leeds, UKdGeosciences Rennes, Campus de Beaulieu, 35042 Rennes Cedex, France

Received 14 February 2002; received in revised form 25 June 2002

Abstract

The Tharsis massive sulphide deposit, one of the major VMS-type deposits in the Iberian pyrite belt (IPB) was severely

deformed by the Variscan tectono-thermal events. The question of whether or not these events affected the metal distribution in

the deposit has been addressed by simultaneously studying the mineral parageneses (Tharsis stockwork) and the fluid

circulation (at local and regional scales). The results are:

(1) The early paragenesis in the stockwork (Q1 quartz–pyrite–chlorite–phengiteF cobaltiteF ankerite) was strongly

overprinted by a late post-kinematic mineral deposition, including new quartz veins (Q3 quartz) and base metal sulphides

(chalcopyrite, sphalerite, Bi and Te minerals, pyrite and galena) and gold.

(2) At a regional scale, fluids accompanying the peak metamorphism conditions (ca. 300 MPa, ca. 300 jC) were of C–O–H–

N–NaCl type, CO2-dominated with CH4 and N2, and are considered to be ‘‘metamorphic’’ on the basis of microthermometry

and geochemistry. The late- to post-kinematic evolution (‘‘retrograde’’ stage) was characterised by a pressure drop, down to

40 MPa (lithostatic to hydrostatic transition), and a heat input leading to temperatures z 430 jC, then decreasing to

temperature around 170 jC. Fluids of the ‘‘retrograde’’ type exhibit both dilution of the C–O–H–N–NaCl fluid by a low

salinity ‘‘meteoric’’ water and progressive loss of volatile components.

(3) Fluids of the retrograde type pervasively percolated through the Tharsis stockwork and were responsible for the strong

mineral overprint on the early (deformed) paragenesis. All the measurable fluid inclusions (f.i.) record these late fluids.

There are primary fluid inclusions in Q1, but they are systematically imploded due to the external overpressure generated

by the Variscan tectonic events. Although base metal distribution in the stockwork is basically the result of the

0009-2541/02/$ - see front matter D 2002 Elsevier Science B.V. All rights reserved.

PII: S0009 -2541 (02 )00275 -9

* Corresponding author.

E-mail address: [email protected] (C. Marignac).

www.elsevier.com/locate/chemgeo

Chemical Geology 194 (2003) 143–165

‘‘retrograde’’ fluid circulation, it remains unclear whether these metals were newly introduced into the stockwork from

elsewhere or simply redistributed from the existing primary assemblages in the massive sulphide bodies.

D 2002 Elsevier Science B.V. All rights reserved.

Keywords: VMS; Iberian pyrite belt; Gold; Fluid inclusions; Metamorphic fluids

1. Introduction

The Iberian pyrite belt (IPB) is the largest prov-

ince of volcanogenic massive sulphide (VMS) depos-

its in the world. A great deal of structural,

petrological and geochemical data has been published

and were recently summarised (Leistel et al., 1998a;

Saez et al., 1999; and references therein). The depos-

its were formed during the early Carboniferous

(Tournaisian) in a transtensional environment charac-

terised by abundant bimodal volcanism and coeval

sedimentation of black shales (the VS Group) in

several E–W trending troughs. These troughs were

developed through the dislocation of a former plat-

form characterised by the late Devonian shales and

quartzites of the PQ Group. Starting from the Visean,

the IPB was incorporated in a south-verging fold-

and-thrust belt with progressive evolution of the

deformation from North to South (Ribeiro and Silva,

1983; Ribeiro et al., 1990; Quesada, 1998; Onezime

et al., 2001) and coeval sedimentation of syntectonic

flyschs (the ‘‘Culm’’). The VMS deposits suffered

both ductile deformation and thermal overprinting

(e.g., Tornos et al., 1998), under the weak metamor-

phic conditions of the prehnite-pumpellyite facies

(Munha, 1990).

Several fluid inclusion studies have been recently

undertaken in the huge VMS deposits of South Spain,

in an attempt to reconstruct ore-forming conditions

(e.g., Almodovar et al., 1998; Nehlig et al., 1998).

However, the possibility that metamorphic fluids could

have been trapped within the deposits, and possibly

overprinted the earlier, ore-depositing fluids in some

instances, was not considered in these works or was

disregarded (Nehlig et al., 1998). In addition, there are

until now no data on the metamorphic fluids at the

regional scale in the whole IPB. Nevertheless, it has

been shown, in the Neves-Corvo deposit in Portugal

(Moura et al., 1997a,b) that metamorphic fluids had

indeed percolated through the deposit and were res-

ponsible for significant mass transfer, involving ore-

forming elements.

The present study addresses the question of compar-

ing fluid circulating at the regional scale with the fluids

involved in the genesis and subsequent modifications

of the Iberian VMS deposits. For this purpose, the

Tharsis area was chosen because: (i) the Tharsis deposit

is well known through recent publications (Tornos et

al., 1998) and several exploration drill cores were

available (courtesy of SEIEMSA); and (ii) good out-

crops with suitable lithologies are present in the deposit

area. At Tharsis, the study was focused on the stock-

work, since it is currently considered that primary gold

is mainly concentrated in the stockworks of the Iberian

VMS deposits (Leistel et al., 1998b).

The study was conducted on a multi-disciplinary

basis and encompassed ore petrography and fluid

inclusion study (microthermometry and Raman micro-

spectrometry), bulk analysis of the fluids (crush-leach

experiments) and stable isotope (d18O) analysis.

2. Geological setting of the Tharsis deposit

With 120 Mt ore, the Tharsis deposit is one of the

largest VMS ore bodies in the IPB. The deposit is

representative of those Iberian VMS deposits that are

associated more closely with black shales than with

penecontemporaneous acid volcanism (Saez et al.,

1999). It is located in the so-called ‘‘Puebla de Guz-

man anticlinorium’’, in fact an antiformal stack of

nappes (Fig. 1) resulting from the inversion of an

early Carboniferous synvolcanic extensional basin

(Quesada, 1998; Tornos et al.,1998). At the mine

scale, three subunits of the Puebla de Guzman nappe

are stacked onto shales and quartzites of the late

Devonian PQ Group (Fig. 2). These units are dis-

membered parts of the regional Volcano-Sedimentary

(VS) Group of Tournaisian age. From bottom to top:

(i) the lower unit (LU), comprising massive sulphides,

C. Marignac et al. / Chemical Geology 194 (2003) 143–165144

Fig. 1. Geological sketch of the Tharsis area, simplified from the IGME (1982) map and adapted from Quesada (1998) for the nappe structure.

C.Marig

nacet

al./Chem

icalGeology194(2003)143–165

145

shales and a stockwork; (ii) the intermediate unit,

(IU), mainly massive spilites (a former sill, with

hydrothermal ankerite-rich breccias); and (iii) the

upper unit of silicified rhyolites. The LU displays a

complex internal structure (Fig. 2), with two massive

sulphide bodies (Filon Norte and San Guillermo) and

an intercalated sheet of shales, containing the pyrite–

chlorite–quartz stockwork (interpreted as the feeder

of the San Guillermo body). It is likely that the Filon

Norte and San Guillermo bodies were initially part of

a single VMS deposit (Tornos et al., 1998).

The massive sulphides are mainly pyrite, with

subordinated sphalerite, chalcopyrite and galena, and

a host of minor sulphides (including Bi minerals) and

sulphosalts (mainly tetraedrite). Arsenic minerals are

rare, mostly expressed in the stockwork, with the

specific presence of cobaltite (thought to be associated

with gold; Leistel et al., 1998b). The massive ores are

mainly of the banded types, including carbonated ores

(with siderite) that are specific to Tharsis. The deposit

is renowned for its numerous ‘‘synsedimentary’’ tex-

tures involving the banded ores (Tornos et al., 1998).

Synkinematic hydrothermalism is present, mainly

in the PQ group (pyrite and chlorite veinlets and

disseminations) (Tornos et al., 1998). However,

although the massive sulphides and the stockwork

evidently suffered strong synfolial deformation, and

the ore minerals display strong evidence of recrystal-

lisation, it is claimed that there was no significant syn-

or post-kinematic ore deposition (Tornos et al., 1998).

Fig. 2. Cross-section of the Tharsis open pit (adapted from Tornos et al., 1998; SEIEMSA, unpublished documents).

C. Marignac et al. / Chemical Geology 194 (2003) 143–165146

3. Paragenetic succession in Tharsis stockwork

The Variscan tectono-thermal events are well

expressed at the sample scale. In good agreement

with the results of structural analysis at the regional

(Onezime et al., 2001) and local (Tornos et al., 1998)

scale, we find consistently two schistosities (often at

right angles) in the studied samples. It is therefore

easy to partition the observed mineral associations

into specific assemblages by considering the timing of

crystallisation relatively to the Variscan deformation,

thus defining three main stages, ante-, syn- and post-

kinematic, respectively (Fig. 3). This is particularly

evident in the stockwork samples where deformation

features are by far more conspicuous than in massive

ore.

(a) The early stage comprises all the ante-kine-

matic minerals and is thought to represent the initial

(syn-VMS) paragenesis in the stockwork. These min-

erals occur as networks of veins and veinlets, with

three types: (i) barren quartz veins (Q1); (ii) frequent

pyrite veinlets with chloritised walls overprinting type

(i); disseminated pyrite within chlorites is also found;

and (iii) rare quartz (Q1)F ankeriteF phengite veins

and veinlets, with sulphides, that are associated to

carbonated wall-rocks. A special mention must be

made for Co-bearing minerals (cobaltite CoAsS,

glaucodot [Co, Fe]AsS) occurring either as isolated

crystals associated with pyrite in the type (iii) veinlets

(Fig. 4a), or as independent veinlets in chloritised

black shales, and being clearly ante-kinematic in both

cases. This early cobalt-bearing paragenesis was first

described by Marcoux et al. (1996) and is thought to

be closely related with gold occurrence in the shale-

hosted deposits of the Tharsis type (Leistel et al.,

1998b).

(b) The synkinematic stage is principally marked by

recrystallisation and neocrystallisation in ‘‘pressure

shadows’’ and/or ‘‘pull apart’’ structures around early

sulphides at the microscopic scale: mainly, quartz

fibres (Q2), and subordinated chlorite (Fig. 4a,b). Mass

transfer remained of limited importance, although a

few synkinematic structures may be found at the out-

crop scale outside the stockwork: mainly tension

gashes filled with Q2 within the massive sulphide ore

(Filon Norte). A synkinematic Q2 stockwork (includ-

ing hydraulic fractures) is locally known at the footwall

of the IU (Fig. 5), but there is no evidence for the

superimposition by a significant Q2 stockwork of the

early stockwork underlying the massive sulphides.

(c) The late- to post-kinematic stage is characterised

in the mineralised stockwork by the inception of

significant fluid circulation, as evidenced by the devel-

opment of new mineralised veins and veinlets and the

crystallisation of a polymetallic sulphide assemblage.

There is a distinct late-kinematic stage, with for-

mation of a network of quartz (Q3), phengite and

chlorite veinlets, that clearly overprint synkinematic

assemblages, but are deformed by some late incre-

ments of the Variscan deformation. In particular, the

Q3 quartz systematically exhibits undulose extinction

typical of a slight plastic deformation (Fig. 4c). Also,

vermicular phengites and/or chlorites (Fig. 4d), that

crosscut plastic deformation features in the Q1 quartz,

are currently kinked, or even foliated in some instan-

ces. In addition, the deformed Q1 quartz or the Q2

fibres are often locally partially recrystallised into

patches of a Q2–3 quartz exhibiting the same defor-

mation features as the Q3 quartz and therefore con-

sidered to be coeval. Arsenopyrite is rare and clearly

crystallised during this late-kinematic stage.

The post-kinematic stage itself is typified by (i) the

crystallisation of a hyaline undeformed Q4 quartz in

small dissolution vugs, together with late chlorite

(undeformed radiated booklets) and calcite; and (ii)

the deposition of polymetallic sulphides in micro-

cracks (particularly, within early pyrite) and dissolu-

tion patches. That the sulphides were coeval with Q4

is demonstrated by their filling of vugs rimmed by Q4

crystals. The main minerals are sphalerite, chalcopyr-

ite (with typical ‘‘chalcopyrite disease’’ features in

sphalerite), pyrite and galena, crystallising in this

order. A few undetermined Bi and Te minerals (likely,

joseite) were found in this study, generally coeval

with chalcopyrite. According to the observations of

Leistel et al. (1998b), gold was deposited together

with this late paragenesis containing chalcopyrite and

Bi–Te minerals.

Thus, to the contrary of earlier conclusions (Tornos

et al., 1998), it seems that a significant hydrothermal

event occurred within the Tharsis stockwork at the end

of the Variscan tectono-thermal event. This hydrother-

mal event was indeed responsible for the late poly-

metallic gold-bearing assemblage that was formerly

considered to represent a late influx of high-temper-

ature (up to 400 jC) fluids at the end of the massive

C. Marignac et al. / Chemical Geology 194 (2003) 143–165 147

Fig. 3. Paragenetic succession in the Tharsis stockwork.

C. Marignac et al. / Chemical Geology 194 (2003) 143–165148

Fig. 4. Details of the paragenetic relationships in the Tharsis stockwork: (a) two generations of Q2 quartz fibres around cobaltite (THA 12–

111.4); (b) same around pyrite (THA 12–111.4); (c) late-kinematic Q3 quartz veinlet with chlorite (chlorite 3) selvages (THA 15–30.20); (d)

late-kinematic chlorite 3 vermicules growing onto grain boundaries of deformed Q3 quartz (THA 15–30.20); (e) late sphalerite overprinting S2

schistosity; note that sphalerite overgrew phengite booklets (THA 12–143.85); (f) late Bi–Te mineral (joseite?) in microcracks in earlier (late

kinematic) arsenopyrite (MIS).

C. Marignac et al. / Chemical Geology 194 (2003) 143–165 149

sulphide deposition (Marcoux et al., 1996; Leistel et al.,

1998b). It may be speculated that the late-kinematic

inception of hydrothermal circulation was related to the

brittle–ductile transition allowing fluid ingress in the

stockworks through the still active thrust planes. Evi-

dencemay be found in the THA 15/120 sample, located

close to the basal contact of the LU (Fig. 1), where late

Q3-chlorite hydrothermal veining is conspicuous.

4. Selection of samples for fluid inclusion and

geochemical studies

For the fluid inclusion and geochemical studies, we

selected representative samples from the Tharsis open

pit and from quartz veins in regional settings.

– At Tharsis (Fig. 2), the samples were taken in the

massive sulphide and the host formations sampled in

the open pit and from one drill core (THA 15) carried

out by SEIEMSA:

(i) In the stockwork: underlying the San Guillermo

body (THA 15–39 and THA 15–105.5) and close

to the phyllonite at the basis of the LU (THA 15–

120).

(ii) In the main open pit (Filon Norte), mainly Q2

quartz: N80jE25jN tension gashes in the massive

pyrite (samples TH1FT, with late sulphides:

sphalerite, chalcopyrite; and THA-1FT3); a

N85jE20jN tension gash in the spilites of the

IU (sample THA-3D); a folded quartz vein (likely,

refolded early tension gash) in the shales from the

IU (sample THA-3C); a tension gash with fibrous

Q2 quartz in the ignimbrite of the UU (THA 5). In

addition, Q4 quartz and an associated dolomite

were sampled from late quartz–chlorite–dolo-

mite veins in the spilite of the IU (sample TH4).

The Tharsis mine samples allowed the study of

fluid inclusions in the Q1, Q2–3, Q3 and Q4 quartz

generations (the Q2 fibres being usually devoid of

fluid inclusions). In the TH1FT and THA-3C samples,

the quartz veins are locally recrystallised into a clear

quartz (cQ), particularly at the quartz grain bounda-

ries; this cQ quartz is likely coeval with Q3. In

TH1FT, a chalcopyrite veinlet overprinted cQ and

was associated with euhedral overgrowths of a hyaline

quartz (hQ) (likely coeval with Q4) on cQ.

Fig. 5. Synkinematic hydraulic fracturing at the footwall of the

intermediate unit (sample THA 3B).

Fig. 6. Typology of fluid inclusions: (a) imploded early fluid inclusions in the Q0 quartz from Virgen de la Pena, (b) stripe of recrystallised clear

cQ quartz with Lc –w inclusions from Valverde, (c) rim of clear cQ quartz with a few secondary (FIP) Lc –w inclusions from Valverde, (d) a

sequence of clear cQ quartz (with Lc –w inclusions) and vuggy hyaline hQ quartz (with rare Lw inclusions in healed planes) from SP 110, (e) a

typical Lc –w inclusion from El Morante, (f) healed planes of Lw inclusions in Q4 associated with sphalerite (Sph) from THA 15–105.5.

C. Marignac et al. / Chemical Geology 194 (2003) 143–165150

C. Marignac et al. / Chemical Geology 194 (2003) 143–165 151

– For an overview of the fluids percolating at a

regional scale, two sets of samples were selected:

(i) From the close vicinity of the Tharsis deposit, in

rocks from the same major tectonic unit that the

deposit (the Puebla de Guzman nappe) or from

the underlying Almendro nappe (Fig. 1):

– Quartzites from the PQ Group of the Virgen

de la Pena subunit in the Puebla de Guzman

nappe. The sample was taken at the top of the

Virgen de la Pena hill, in huge quartzite

masses containing a stockwork of ante-kine-

matic (folded) subvertical quartz veins with

the N30j, N150j and N170jE directions

(sample Vir Pe). At the microscopic scale,

the early Q0 quartz exhibits evidence of

plastic deformation, overprinted by a clear

quartz (cQ) in healed fractures and at

recrystallised grain boundaries. A late hyaline

more or less vuggy quartz (hQ) occurs in

recrystallisation/dissolution patches.

– Ignimbrites from the VS Group, at Villanue-

va de las Castilleros, in the Almendro nappe,

close to the thrust contact with the under-

lying Culm (Fig. 1). The sample comes from

a set of ante-kinematic quartz veins (sample

SP 110). At the microscopic scale, the early,

plastically deformed, Q0 quartz is over-

printed by a series of tension veins with

palissadic quartz (likely coeval with Q2 at

Tharsis), that exhibits late recrystallisation

features, with a clear quartz (cQ) at quartz

grain boundaries and eventually a vuggy

hyaline quartz (hQ) (Fig. 6d), that are likely

to be coeval with similar features in the Vir

Pe, THA-1FT and THA-3C samples.

(ii) From a late south verging thrust within the

Valverde nappe (Fig. 1), a probable equivalent of

the Puebla de Guzman nappe. These shales of

the PQ Group are upthrusted onto shales of the

VS Group. In the PQ shales, the S1 foliation is

folded (F2 folds, Onezime et al., 2001) and

contains, about 30 cm above the main thrust, a

series of synfolial quartz lenses (10 cm� a few

cm) paralleling the thrust plane. These are

deemed to be coeval with the thrusting and are

therefore considered to be representative of Q2

(sample VA).

(iii) From a Mn-bearing chert lens of the VS Group, in

the Berrocal nappe (Fig. 1), a probable equivalent

of the Paymogo nappe that overlies the Puebla de

Guzman nappe. The sample was taken at the top

of the El Morante hill, from a set of quartz-filled

tension gashes (Q2) inside the chert lens (El

Morante sample).

In both the VA and El Morante samples, the Q2

quartz displays the features of late recrystallisation

that were described above, with development of clear

quartz (cQ) along grain boundaries.

5. Fluid inclusion study

5.1. Methods

Petrography of fluid inclusions has been carried out

on 300-Am thick double-polished wafers. Microther-

mometric characterisation of the fluids was performed

using a Chaix-meca heating-freezing stage (Poty et al.,

1976) at low temperature (V 30 jC) and a Fluid Inc.

Stage for measurements at higher temperatures. The

accuracy was of F 0.1 jC at low temperature and of

F 2 jC at high temperature. Salinity, expressed in

equivalent wt.% NaCl, and fluid density of gas-free

fluid inclusions, are determined from melting temper-

atures of ice using the regression of Bodnar (1993). In

volatile-bearing fluid inclusions, CO2 was identified

by melting of a solid at TV� 56.6 jC. The volumetric

fractions of the volatile phase(s) (/vol) was estimated

at room temperature by reference to the volumetric

chart of Roedder (1984). Molar fractions of CO2, CH4,

N2 and H2S were determined in individual fluid

inclusions using a DILOR LABRAM Raman spec-

trometer following the procedure given by Dubessy

(1984). Molar fraction of NaCl, molar volume, bulk

composition and P–T parameters were determined by

combining results from microthermometry and Raman

analysis using the computer code by Bakker (1997).

The P–V–T properties of volatile-bearing inclu-

sions were modelled in the system H2O–CO2–CH4

using the V–X data and the equation of state of

Kerrich and Jacobs (1981) and Jacobs and Kerrich

(1981). For the purely aqueous fluids, the data from

Zhang and Frantz (1987) for the H2O–NaCl system

have been used.

C. Marignac et al. / Chemical Geology 194 (2003) 143–165152

5.2. Typology and relationships

Nomenclature follows that of Boiron et al. (1992).

Briefly, the fluid inclusions (f.i.) are named first on

the basis of the mode of their final homogenisation as

either liquids (noted L) or vapour (noted V); then

according to the nature of their components, noted by

a subscript, c for CO2-dominated volatile species, w

for water; for instance two-phase aqueous f.i. homog-

enising in the liquid phase are noted Lw. A specific

case must be made for mixed inclusions. For

instance, three-phase f.i. at room temperature that

finally homogenise in the liquid phase are noted as

Lc–w, whereas those inclusions homogenising to the

liquid that remain apparently two-phase even at low

temperature, but display the presence of volatile

species (more commonly as clathrates) are noted

Lw–c. In the case of the volatiles being only detect-

able by Raman microspectroscopy, the notation

becomes Lw–(c). Similar notations hold for V-type

inclusions.

5.2.1. Early fluid inclusions

In the Tharsis stockwork, there is evidence of some

primary f.i., in early Q1 with preserved growth zones.

However, these inclusions display features of post-

trapping modifications typical of implosion processes

according to the experimental data of Vityk and

Bodnar (1995), in particular, they frequently exhibit

stellar or annular morphologies. It is likely that these

inclusions imploded during the Variscan tectono-

metamorphic events. Unfortunately, as a result, these

primary inclusions have become unsuitable for micro-

thermometric measurements. Consequently, any P–

T–X information relevant to the deposition of the

massive sulphides is lost.

In the Vir Pe sample, numerous similarly imploded

inclusions are also observed (Fig. 6a), in healed

planes with secondary inclusions (FIP). Since the

host quartz veins are apparently ante-kinematic, it

may be speculated that they were coeval with the

primary f.i. in the Q1 quartz from the Tharsis stock-

work, i.e., that the early Q0 quartz stockwork in the

PQ quartzites could have resulted from the same

hydrothermal event that was responsible for the

VMS formation.

5.2.2. Volatile-rich inclusions

Lc–w inclusions were systematically found in the

clear quartz (cQ) from the Vir Pe, VA and El Morante

samples (Fig. 6b–e). There they mainly occur in

healed microfractures (‘‘fluid inclusion planes’’: FIP;

Roedder, 1984; Cathelineau et al., 1994), but are

locally present as isolated clusters. Vc–w inclusions

are also found, equally in FIP, but seem to be

restricted to cQ quartz in sample Vir Pe. Significantly,

no volatile-rich inclusions were found in the samples

from the Tharsis stockwork.

5.2.3. Aqueous-dominated inclusions

Lw type f.i. are found in all samples and all types of

quartz, generally in planar arrays cross-cutting grain

boundaries or as clusters in hyaline hQ quartz and in

Q4. Lw–c and Lw–(c) inclusions are also observed in

Table 1

Summary of the microthermometric data for the different types of fluid inclusions

Fluid inclusion type Location Tm CO2 Th CO2 Tm cl Tm ice Th

Lc–w Virgen de la Pena � 56.8/� 58.2 25/29 (L) 7.5/8.5 � 3.2/� 5.4 265/300

Valverde (VA) � 56.6/� 58.2 24/29 (L/V) 6.5/7.7 � 5/� 3 220/250

El Morante � 57.6/� 57.2 20/24 (V) 8/12 � 4.2/� 5.7 200/280

Lw– c Tharsis 3.3/3.6 � 3

Lw– (c) Tharsis � 1/� 3.9 140/360

Vw– c Tharsis 4.4/8.2 � 2/� 2.6 250/380

Vw– (c) Tharsis � 2.2/� 2.8 340/380

Villanueva � 3.4/� 3.5 330/420

Lw Virgen de la Pena � 3.2/� 4.3 150/250

Tharsis � 1/� 5.9 130/240

Tm CO2: melting temperature of CO2; Tm ice: melting temperature of ice; Tm cl: melting temperature of clathrate; Th CO2: homogenization

temperature of CO2, Th: total homogenization temperature. L: liquid, V: Vapor. All temperatures are given in jC.

C. Marignac et al. / Chemical Geology 194 (2003) 143–165 153

Table 2

Chemical composition of typical fluid inclusions from the studied areas obtained by Raman microprobe analysis and corresponding

microthermometric data

Sample IF Type Microthermometry Raman data Bulk Composition

numberTm

CO2

Th

CO2

Mode Tm

ice

Tm cl Th Mode CO2 CH4 N2 H2S H2O CO2 CH4 N2 NaCl

Tharsis

TH1/1ft 11 Vw– c no no – � 2.4 5.2 285 V 74.3 25.7 nd nd

TH1/1ft b Vw– c no no – � 2.5a 5.2 273 V 82.6 17.4 nd nd 92.1 6.5 1 nd 0.4

TH1/1ft 12 Lw– (c) no no – � 2.3 193 L 76.6 23.4 nd nd

TH1/1ft 13 Lw– (c) no no – � 2.3 146 L 83.3 16.7 nd nd

THA 15/39 1 Lw– c no no – � 3a 3.3 90.5 5.6 3.9 nd 95.7 3.4 0.1 0.1 0.7

THA 15/39 2 Lw– c no no – � 3a 3.6 84.4 6.4 9.2 nd 96 3.1 0.1 0.1 0.7

THA 15/39 12b Lw– (c) no no – � 2.6 276.5 L 95.1 3.2 1.7 nd

THA 15/39 11 Lw– (c) no no – � 5.8 176.2 L 94.3 5.7 nd nd

THA 15/120 17 Lw– (c) no no – � 1.8 221.5 L 24.5 18.5 57 nd

THA 15/120 24 Lw– (c) no no – � 1.6 198.2 L 16.3 18.2 65.5 nd

THA-3C 1 Lw– (c) no no – � 2.6 254.8 L 87 4 9 nd

THA-3C 12 Lw– (c) no no – � 2.6 219.6 L 88.4 2.3 9.3 nd

THA-3C 9 Lw– (c) no no – � 2.8 220.2 L 93.8 6.2 nd nd

THA-3C 13 Lw– (c) no no – � 2.8 282.3 L 86 5.6 8.4 nd

THA-3C 1v Lw– (c) no no � 3.6 245 L 81.6 5.2 13.2 nd

THA-3C 4v Lw– (c) no no � 3.3 d 65.3 10.7 24 nd

THA-3C 3 Vw– (c) no no – � 2.6 345.2 V 92.8 3.1 4.1 nd

THA-3C 22 Vw– c no no – � 2.6 8.2 250.3 V 73.1 6.2 20.7 nd 82.3 13.4 1 3.2 0.1

THA-3C 7 Vw– c no no – � 2.4 4.9 380 V 95.0 nd 5.0 nd 89.5 9.8 nd 0.4 0.3

THS 20 HS1 Vw– c no no – � 2 4.4 254.3 V 91.2 8.8 nd nd 90.3 8.9 0.7 nd 0.1

THS 20 HS2 Lw– (c) no no – � 1.8 167.6 L 71.5 28.5 nd nd

THS 20 HS13 Lw– (c) no no – � 1.7 152.5 L 78.4 21.6 nd nd

THS 20 HS3 Lw– (c) no no – � 1.2 174.3 L nd 100.0 nd nd

Villanueva

SP 110 1 Vw– (c) no no – � 5.5 8.2 375.7 V 85.8 3.5 10.7 nd 92.1 6 0.2 0.4 1.3

SP 110 2 Vw– (c) no no – � 4.9 8.5 380.2 V 87.5 5 7.5 nd 92.4 6 0.2 0.3 1.1

SP 110 3 Vw– (c) no no – � 5.2 8.5 375.6 V 88.3 5.2 6.5 nd 91.1 7.3 0.3 0.4 1

SP 110 1v Vw– (c) no no no 449 V 85.9 11.1 3 nd

SP 110 7v Vw– (c) no no no 405 V 81.6 5 13.4 nd

SP 110 2v Lw– (c) no no � 3.5 331 L 69 5.7 25.3 nd

Virgen de la Pena

Vir Pe -Sp2 a Lc –w � 58.1 22.7 L � 4.3 7.7 302.2 L 96.2 1.6 2.2 nd 84.6 13 0.2 0.2 2

Vir Pe -Sp2 b Lc–w � 57.2 22.8 L � 4.4 7.6 285.5 L 93.1 nd 6.9 nd 77.2 19.6 nd 1.3 1.9

Vir Pe -Sp2 c Lc –w � 57.2 24 L � 5.1 7.7 285.2 L 96.8 1.5 1.7 nd 80.1 17.7 0.2 0.3 1.8

Vir Pe -Sp2 h Lc–w � 57.2 22.8 L � 4.8 7.7 285.4 L 98.4 1 0.6 nd 73 25.2 0.2 0.1 1.5

Vir Pe -Sp2 s Lc –w � 57.3 24 L � 4.2 8.4 285.1 L 98.3 1.1 0.6 nd 83.9 13.7 0.1 0.1 2.1

Vir Pe -Sp2 q Lc–w � 56.8 24 L � 4.7 8.4 283.5 L 97.9 1.5 0.6 nd 86.3 11.4 0.1 0.1 2.1

Vir Pe -Sp2 1 Lc–w � 57.2 26.3 V – 8.5 286.5 L 98.4 1.6 nd nd 87 9.8 0.1 0 3.1

Vir Pe -Sp2 11 Lc–w � 57.2 no – � 4.1 8.4 283.9 L 96.9 nd 3.1 nd 94.7 4.2 nd 0.05 1.05

Valverde

VA 4 Lc–w � 57.6 25.3 L � 4.4 6.5 250.5 V 99.3 0.7 nd < 0.1 92.3 5.45 0.05 nd 2.2

VA 10 Lc–w � 57.8 24.3 L � 5.2 6.5a 230.5 L 99.2 0.7 nd 0.1 83.6 14.3 0.1 nd 2.0

VA 8 Lc–w � 57.2 25.2 L � 3.9 6.5a 230.4 L 99.5 0.4 nd 0.1 83.7 14.2 0.1 nd 2.0

C. Marignac et al. / Chemical Geology 194 (2003) 143–165154

healed fractures, mainly in Q2–3, Q3 or cQ quartz.

They are absent from the Q4 or hQ quartz, where only

the Lw inclusions may be found (Fig. 6f) (they are

sometimes also present as isolated clusters). Thus, the

Lw–c or Lw–(c) inclusions appear more akin to the

volatile-rich inclusions, whereas the Lw inclusions are

seemingly coeval with Q4 and therefore with the post-

kinematic stage of fluid circulation and ore deposition

(polymetallic sulphides and gold).

In the SP 110 sample, some patches of clear cQ

quartz exhibit healed fractures with vapour-rich

inclusions, containing a low-density volatile phase

when examined by Raman microspectrometry, and

therefore representative of the Vw–(c) class of inclu-

sions.

5.3. Microthermometry and Raman analysis

A summary of the main f.i. types and microther-

mometric measurements is given in Table 1. For all

the measured inclusions, the first melting temperature

was found to be close to � 21 jC, indicating that the

fluid salinity may be modelled by considering only

the NaCl content in all cases.

5.3.1. Volatile-rich inclusions

5.3.1.1. Lc–w inclusions. Lc–w f.i. have melting

temperatures of CO2 (Tm CO2) ranging from

� 56.6 to � 58.2 jC and homogenisation temper-

atures of CO2 (Th CO2) to the liquid or to the vapour

phase in the range of 20–29 jC (Table 1). Tm CO2

values are significantly lower than the melting point

of pure CO2 and indicate the presence of volatile

compounds other than CO2. The melting temperature

of ice (Tm ice) ranges from � 3.2 to � 5.7 jC with

a mode around � 4.5 jC. The melting temperature of

clathrate (Tm cl) is in the range of 6.5–12 jC with a

mode around 8 jC. The total homogenization tem-

perature (Th to the liquid phase) ranges from 200 to

300 jC.

5.3.2. Aqueous-dominated inclusions

5.3.2.1. Volatile-bearing aqueous inclusions. Most

volatile-bearing aqueous inclusions in the Tharsis

samples are aqueous two-phase inclusions homoge-

nising in the liquid or the vapour state (/vap from 0.1

to 0.8). They are usually small (8–13 Am). Clath-

rates are observed in a few cases (rare Lw–c inclu-

sions, see Table 1; more frequent Vw–c inclusions).

However, in many inclusions with apparently no

clathrate formation upon freezing, Raman micro-

spectrometry revealed the presence of low-density

volatile components (CO2[N2–CH4) (Table 2).

These are either liquid- or vapour-rich, although

most vapour inclusions appear to be pure water.

Vw–c fluid inclusions show Tm cl in the range of

4.4–8.2 jC. Tm ice ranges from � 2 to � 2.6 jC.The total homogenisation temperatures (Th to the

vapour phase) are rather scattered and range from

250 to 380 jC.

Table 2 (continued )

Sample IF Type Microthermometry Raman data Bulk Composition

numberTm

CO2

Th

CO2

Mode Tm

ice

Tm cl Th Mode CO2 CH4 N2 H2S H2O CO2 CH4 N2 NaCl

El Morante

El Morante 8 Lc –w � 56.7 22.5 V � 5.3 9.5 230.5 L 99.2 0.8 nd nd 94.3 5.3 0.02 nd 0.4

El Morante 5 Lc –w � 57.2 24 V � 4.3 8 250 L 99.7 0.3 nd nd 95.3 5.4 0 nd 1.3

El Morante 17 Lc –w � 57.5 20.5 V � 5.5 10a 240.3 L 99.2 0.5 0.1 nd 94.8 5.1 0.02 nd 0.1

El Morante 7 Lc –w � 56.7 24 V � 5.4 9 254.6 L 100 nd nd 0.1 94.1 5.3 0 nd 0.6

El Morante 14 Lc –w � 57.2 22 V � 5.5 9.5 265 L 100 nd nd nd 94.6 5.1 nd nd 0.3

El Morante 15 Lc –w � 57.5 24 V � 5.3 9.5 250.6 L 99 0.6 0.4 nd 92.4 7.1 0.03 0.01 0.4

El Morante 21 Lc –w � 57.2 20 V � 4.9 8.5 200.6 L 100 nd nd nd 92.8 6.3 nd nd 0.9

El Morante 20 Lc –w � 57.5 22.5 V � 5.6 10a 250.6 L 99.2 0.6 0.1 0.1 93 6.9 0.02 nd 0.1

Compositions are given in mol%. Abbreviations are the same as in Table 1. nd: not determined. no: not observed. Inclusion types are defined in

the text.a Indicates that temperatures have been estimated.

C. Marignac et al. / Chemical Geology 194 (2003) 143–165 155

5.3.2.2. Vw– (c) and Lw– (c) inclusions. Both types of

inclusions have similar melting temperatures of ice

(Tm ice comprised between � 1 and � 3.9 jC), butdiffer significantly when total homogenisation temper-

atures are considered. The Vw–(c) inclusions of the SP

110 (Villanueva) sample homogenise at rather constant

high temperatures (Th from 330 to 420 jC), whereasall the Lw–(c) (including those from SP 110) display

lower temperatures, scattered from 340 to 380 jC.

5.3.2.3. Lw inclusions. Tm ice varies from � 1

to� 5.9 jC, corresponding to low to moderate salin-

ity, between 2 and 9 wt.% eq. NaCl. The homoge-

nisation temperatures (Th) are largely variable, from

150 to 250 jC. Part of this variation may be ascribed,

in some cases, to a pronounced necking-down effect.

The highest Th are found in Q1, Q2–3, Q3 and cQ

quartz and span the same Th interval as the associated

Lw–(c) inclusions.

6. Fluid geochemistry

6.1. Crush leach data on bulk quartz

Small quartz grains have been analysed by the

crush-leach method (Banks and Yardley, 1992).

Reconstructed compositions (in mmol/kg solution)

are given in Table 3. Na/K (molar ratios) are between

15 and 80, Na/Li in the range of 50–300, Cl/SO4

f 120 to 560. The Na/Li and Na/K ratios are con-

sistent with those expected at temperatures from 150

to 250 jC (Fig. 7A), using the Fournier (1979) and

Fouillac and Michard (1981) empirical geothermom-

eters for geothermal systems, as revised by Verma and

Santoyo (1997). The halogens, Cl, Br and to a lesser degree I, can be used to identify the sources of fluid

(Bohlke and Irwin, 1992), because they are conserva-

tive in solution and are relatively unaffected by fluid–

rock interactions (Banks et al., 1991). With log (Br/

Cl) between � 3 and � 2.1 and log (I/Cl) in the range

of � 3.5 to � 2.8, the Tharsis fluids differ signifi-

cantly from both seawater and granite-related fluids

(Fig. 7B). They are similar to evolved basinal fluids.

6.2. Stable isotope (18O) geochemistry

The same samples that were used for crush-leach

experiments have been chosen for isotopic analysis.

Table 3

Reconstructed composition (in mmol/kg solution) of fluid inclu-

sions from crush-leach analyses

Sample Na K Li F Cl Br SO4 I

THA-1FT 370 13 3 11 691 2.4 6 0.23

THA-1FT3 379 13 2 3 468 0.5 2 0.72

THA 4 Quartz 332 18 2 6 381 0.8 3 nd

THA 4 Dolomite 254 5 1 0.2 388 0.1 1 0.14

THA 5 375 29 2 2 386 0.4 2 nd

THA 15–30.2 1008 79 4 1 1335 7.1 5 0.86

THA 15–120 485 6 9 2 569 3.8 1 0.26

nd: not determined.

Fig. 7. Ionic ratios (mol) of fluids determined from crush-leach

analyses. (A) Na/K–Na/Li diagram. Full line temperature estimation

deduced from the geothermometric cation relationships (Verma and

Santoyo, 1997). (B) log (Br/Cl)– log (I/Cl) diagram with reference

fluid compositions from literature. (1) Seawater (Fontes and Matray,

1993), (2) bulk earth (Bohlke and Irwin, 1992), (3) Au-bearing

quartz veins from NW Iberia (Boiron et al., 1996), (4) oil field

(Carpenter et al., 1974; Kharaka et al., 1987), (5) Canadian shield, (6)

Baltic shield (Frape and Fritz, 1987), (7) SW England fluids from

granites (Bottrell and Yardley, 1988).

C. Marignac et al. / Chemical Geology 194 (2003) 143–165156

The analytical procedure follows the conventional

fluorination method of Clayton and Mayeda (1963).

Two types of samples were analysed: (i) bulk quartz

samples (ca. 7 mg); (ii) chips of quartz (down to ca. 1

mg) extracted from the fluid inclusion wafers. These

chips correspond exactly to the material on which FI

studies were carried out. The uncertainties (estimated

from duplicates performed on different Ni fluorination

tubes) are generally on the order of 0.1–0.2xfor the

bulk samples. Duplicates could not be performed on

the chip samples but it is known from similar studies

that the uncertainties may be higher (Essarraj et al.,

2001). In this paper, we consider a conservative value

of 0.3xfor the uncertainties associated with the

quartz chips extracted from fluid inclusion wafers. A

summary of the data (d18O vs. SMOW) is presented in

Table 4.

The results suggest a rather clear-cut distinction

between the Q3 quartz on one hand (d18O in the

narrow 13.0–13.9xrange) and regional quartz

(mainly Q2 type) on the other hand (d18O in the

narrow 17.7–19.5xrange). Other samples from the

Tharsis mine are either consistent with the regional

range (THA-1FT–THA 4) or display intermediate

isotopic compositions (d18O spread from 14.6xto

16.5x). When the nature of quartz in the Tharsis

mine is considered, it may be concluded that Q2

quartz (or, more precisely, Q2-dominated, since minor

fractions of Q3 or cQ quartz may be present in the

bulk samples) everywhere display high d18O values,

comprised between 15.8xand 19.5x, whereas the

Q3 quartz are characterised by distinctly lower values

(13.0–13.9x) and the Q4 quartz stands in a some-

what intermediate range (14.6–17.4x).

These results are rather different from those ob-

tained for the Rio Tinto quartz stockwork by Halsall

and Sawkins (1989), with a range of d18O values

between 8.2xand 13.2x. The reasons for this

discrepancy may stem from the differences between

the analysed quartz: at Rio Tinto, mainly Q1 quartz

was sampled. On the other hand, the values found

by Tornos et al. (1998) for syntectonic quartz within

the phyllonite zones (17.4x) and for ‘‘quartz

vesicles’’ within the vulcanites of the LU (17.8–

18.5x) are consistent with our findings. In addition,

Tornos et al. (1998) reported d18O values for anker-

ites of the Tharsis mine: 15.0xfor a tension gash

within the phyllonites (likely coeval with Q2) and

18.2xto 20.9xfor veins in the spilites from the

LU.

7. Fluid evolution and P–T–t reconstruction

7.1. Volatile-bearing fluids

7.1.1. Bulk compositions and chemical evolution

All the volatile-bearing fluids in the Tharsis area

appear to be rich in CO2. Most of them are also rich

in N2 and poor in CH4, defining a ‘‘main trend’’

including both ‘‘regional’’ and ‘‘Tharsis mine’’ fluids

(Fig. 8a). However, some fluids trapped in Lw–(c),

Vw–c and Vw–(c) inclusions from the Tharsis mine are

on the contrary enriched in CH4 and poor in N2.

When bulk compositions are considered (Fig. 8b), it

is seen that ‘‘regional’’ fluids display a ‘‘dilution

trend’’ from a volatile-rich end-member (z 30

mol%) towards a water-dominated end-member, with

the ‘‘Tharsis mine’’ fluids being similar to the latter.

7.1.2. P–T–t path

Peak metamorphic conditions are apparently re-

corded by those VA and Vir Pe Lc–w inclusions

Table 4

Stable isotope data for the quartz from the Tharsis area

Sample number Type of

sample

Quartz

type

d18O quartz

xSMOW

Tharsis

THA-1FT bulk Q2 18.3F 0.1

THA-1FT3 bulk Q2 16.55F 0.2

THA-3C wafer Q2 17.3F 0.3a

THA 4 bulk Q4 17.40F 0.15

THA 5 bulk Q2 15.75F 0.2

THA 15–30.20 wafer Q3 13.0F 0.3a

THA 15–105.5 wafer Q4 14.6F 0.3a

THA 15–120 bulk Q3 13.5F 0.15

THA 15–120 wafer Q3 13.9F 0.3a

THA 15–120 wafer Q3 13.3F 0.3a

Virgen de la Pena bulk Q2 18.4F 0.1

SP2 wafer Q2 17.3F 0.3a

Villanueva, SP 110 bulk Q2 17.0F 0.3a

Valverde wafer Q2 19.5F 0.3a

El Morante bulk Q2 17.7F 0.3a

The different types of quartz are described in the text.

The ‘‘bulk’’ samples are from the same samples that were used for

the crush-leach analyses (see Table 3).a Estimated uncertainties for nonduplicated analyses (see text).

C. Marignac et al. / Chemical Geology 194 (2003) 143–165 157

trapped in cQ quartz that exhibit the highest minimal

trapping pressures (Fig. 9). This may be checked by

comparing with the regional petrographic studies.

From metamorphic mineral associations, oxygen iso-

tope data and epidote compositions from buffered

assemblages, Munha (1983, 1990) concluded that

the limiting conditions for the IPB were 290 jC and

180 MPa. However, the characteristic assemblage is

prehnite + chlorite + albiteF pumpellyite, which is in

fact bracketed by 210 jCV TV 290 jC and 200

MPaVPV 300 MPa (Bucher and Frey, 1994). As

may be seen in Fig. 9, these pressure estimates are

consistent with the range of minimal trapping pres-

sures displayed by the VA and Vir Pe fluid inclusions

and, consequently, we consider that P was lower than

300 MPa in the Tharsis area (Fig. 9). However,

whereas the VA isochores are also consistent with

the regional temperature estimations, the temperature

at Virgen de la Pena could have been slightly higher,

up to 320–330 jC (Fig. 9). This may be interpreted as

resulting from heat advection by the circulating fluids

and would therefore point to the CO2-rich fluids being

generated at a greater depth in the Variscan crust of

the IPB.

– The ‘‘retrograde’’ path should not have been

associated with a significant temperature drop, as

indicated by the Lc–w and Vc–w inclusions with the

lowest trapping pressures (Fig. 9). On the other hand,

decompression could have been significant, down to

ca. 100 MPa. These findings are corroborated by the

El Morante isochores (Fig. 9).

A further refinement of the late stages of the

‘‘retrograde’’ path is possible by considering the

aqueous-dominated volatile-bearing fluids. Most sig-

nificant are the Vw– (c) inclusions in the SP 110

sample, with high Th in the 405–420 jC range. These

temperatures are likely to be close to the true trapping

temperatures, since biotite was never a stable phase in

the mineral assemblages. Consequently, these low-

density volatile-bearing fluids circulated at pressures

around 40 MPa (Fig. 9). Such a low pressure is likely

to be hydrostatic in nature (thus implying a depth of

ca. 4 km). On the other hand, there is neither textural

nor microthermometric evidence of a phase separation

Fig. 8. Composition of the volatile-bearing fluid inclusions from regional and Tharsis samples: (a) composition of the volatile phase in the

CO2–CH4–N2 diagram; (b) bulk compositions in the H2O–CO2– (CH4 +N2) diagram.

C. Marignac et al. / Chemical Geology 194 (2003) 143–165158

process for the origin of ‘‘vapour’’ or ‘‘liquid’’ inclu-

sions. Therefore, the Lw–c and Lw–(c) inclusions are

best interpreted as recording a (more or less) isobaric

condensation trend, down to ca. 270 jC, as seen in

Fig. 9.

Thus, the end of the ‘‘retrograde’’ path in the Tharsis

area was indeed characterised by both a significant heat

input at the origin of a (re)-heating of the circulating

fluids, and a transition from lithostatic to hydrostatic

conditions. A detailed appraisal of the time relation-

ships between the decompression and the heat input is

not possible with the presented data—there is a lack of

f.i. recording the transition. The heat input may as well

have been progressive (path A in Fig. 9) or ‘‘instanta-

neous’’ (path B).

7.2. Aqueous fluids

A Th–Tm ice plot was drawn for all the aqueous-

dominated fluid inclusions from the Tharsis mine,

including the Lw, Lw–c, Lw– (c), Vw–c and Vw– (c)

types (Fig. 10).

In Fig. 10, a clear-cut distinction appears between

two groups of fluid inclusions, according to their

setting. The first group (group 1—white and grey

symbols in Fig. 10) comprises the inclusions that are

restricted to quartz generations earlier than Q4, all

being found in Q3. The second group (group 2—black

symbols in Fig. 10) consists of inclusions that are

present either in all generations of quartz or only in

Q4. For any given salinity, inclusions of the first

Fig. 9. Reconstruction of the Variscan P–T– t path for the fluids in the Tharsis area. For a given set of fluid inclusions, the shaded area

represents the permitted trapping conditions. The limiting conditions are either a maximum pressure of ca. 300 MPa (corresponding to the

estimated maximum pressure of the regional metamorphism, see text) or a maximum temperature of ca. 430 jC as fixed by the absence of biotite

in the studied area. The black field corresponds to the conditions of peak regional metamorphism. The arrows labelled A or B are for the

possible ‘‘retrograde’’ paths in the Tharsis area (see text).

C. Marignac et al. / Chemical Geology 194 (2003) 143–165 159

group consistently exhibit higher Th than inclusions

of the second group. This is true whatever the content

of the fluid inclusions, either pure water or containing

a minor volatile component. It may be considered that

the first group is representative of the fluids coeval

with Q3, whereas the second group is representative

of the fluids coeval with Q4. A similar distinction may

be observed for the regional aqueous-dominated

inclusions, with a ‘‘high temperature’’ group restricted

to cQ and a ‘‘low temperature’’ group characteristic of

hQ.

– As seen in Fig. 10, the group 2 inclusions

exhibits a clear trend of varying salinity (from 9 to

1.7 wt.% eq. NaCl) with fluctuating Th (between 150

and 230 jC, when the necking-down effects are

smoothed by removing the extremal Th values). This

trend may be interpreted as resulting from the mixing

of a ‘‘hot’’ saline fluid (z 9 wt.% eq. NaCl, z 230

jC) with a ‘‘cold’’ low-salinity fluid (V 1.7 wt.% eq.

NaCl, V 150 jC). The mixing may have occurred

under fluctuating pressures, as recorded by the fluc-

tuating Th at a given salinity. A range of Th up to 60

jC for a given salinity (Fig. 10) is consistent with the

pressures fluctuating above a hydrostatic pressure of

ca. 40 MPa, up to the corresponding lithostatic value

of 110 MPa (Fig. 9). The 40 MPa value is assumed

taking into account the pressure estimates of the

preceding section.

– The group 1 inclusions typically correspond to the

end of the ‘‘retrograde’’ path discussed in the preceding

section; therefore, the large range of Th displayed by

these inclusions really records the overall temperature

decrease from the ‘‘peak’’ 400–430 jC discussed

above. Nonetheless, when restricted ranges of Th are

considered, a significant dispersion of the salinity is

observed (Fig. 10). Furthermore, trends similar to the

group 2 trend may be observed: for instance, for the

inclusion in the sample THA 15–120 (Fig. 10). There-

fore, it is possible to interpret the dispersion pattern of

the group 1 inclusions as recording a continuous

Fig. 10. Tm ice–Th plot for aqueous-dominated fluid inclusions from the Tharsis mine.

C. Marignac et al. / Chemical Geology 194 (2003) 143–165160

process of fluid mixing at regionally decreasing Th,

according to the following scheme: (i) at each time (i.e.,

for each small given range of Th) a ‘‘hot’’ saline fluid

mixes with a ‘‘cold’’ low-salinity fluid; and (ii) the bulk

temperatures of the two corresponding reservoirs

decrease simultaneously with time.

7.3. Conclusion: fluids at the ‘‘retrograde’’ stage

Combining the interpretations of the two preceding

sections, it may be concluded that, in the Tharsis area,

at the end of the Variscan thermal event, the fluids

circulated at decreasing pressures but under temper-

atures that were increased up to 400–430 jC before

their progressive lowering. These fluids evolved from

early rather saline volatile-bearing fluids (CO2-domi-

nated) towards complex fluids exhibiting simultane-

ously (i) the mixing of the volatile-bearing fluids with

a low-salinity purely aqueous end-member; and (ii) a

progressive loss of the volatile content in the volatile-

bearing fluids.

8. Discussion

8.1. Source of fluids

The two types of fluids involved in the ‘‘retro-

grade’’ stage of fluid circulation at the regional scale

(volatile-rich and purely aqueous) may be readily

interpreted. The volatile-rich fluids are characterised

by a low, but significant, content in CH4 and N2

together with CO2, and exhibit CO2 to CH4 ratios that

are consistent with equilibrium with graphite in the

source region (at temperatures near 400 jC: Dubessy,1984; Dubessy et al., 1989). They are therefore likely

of ‘‘metamorphic’’ derivation: either, true devolatili-

sation fluids or fluids of any pristine source that

equilibrated with graphite (‘‘pseudo-metamorphic’’

fluids). In any case, it is worth underlining the

abundance of black shales in the IPB (Saez et al.,

1999) that are an accessible source of organic-derived

carbon. The low-salinity, purely aqueous end-member

is likely a fluid rooted in a shallow-level reservoir, i.e.,

a more or less evolved ‘‘meteoric’’ fluid. These

interpretations are consistent with the fact that the

volatile-bearing fluids are constantly hotter than the

purely aqueous fluids throughout the mixing process

that characterises the ‘‘retrograde’’ stage, meaning that

the former are deeper fluids than the latter.

The results of the geochemical studies lend some

support to these contentions.

– Calculation of the d18O of the waters associated

with the quartz (d18Ow), using the fractionation coef-

ficients given by Zheng (1993), leads to the following

results: for the Q2 stage, for a temperature of 300 jC,the d18Ow are in the range of 8.9–12.6x; for the Q3

stage, the d18Ow are either in the range of 9.7–8.8x,

if the maximum temperature of 420 jC is considered,

or in the range of 4.0–4.9xif the low temperature of

250 jC is taken into account; and for the Q4 stage, at

temperatures of 200 jC, the d18Ow are in the range of

3.0–5.8x. A global trend of lowering d18Ow with

time is apparent, which is entirely consistent with the

mixing model presented in the previous section. It is

worth noticing that the d18O values reported for the

syntectonic ankerites by Tornos et al. (1998) are

equally consistent with our findings, since, using the

fractionation coefficients of O’Neil et al. (1969), the

d18Ow calculated at 300 jC for these ankerites is in

the range of 9.9–11.3x.

– The ion ratios obtained by crush-leach analyses

of the brine +meteoric fluid mixtures are obviously

dominated by the saline end-member (dilution by

meteoric water reduces salinity but is not expected

to change cation ratios). Therefore, the cation signa-

ture of the regional and Tharsis fluids, as presented

above, reflects an origin as a deep-seated ‘‘basinal’’

fluid. The ‘‘basinal’’ nature of the deep fluids suggests

that they may represent evolved connate waters remo-

bilised by the Variscan thermal events, thus explaining

their rather high salinity.

8.2. Relevance for the VMS deposits of the IPB

The ‘‘retrograde’’ fluids were responsible for sig-

nificant mineral genesis and ore (re)-deposition in the

Tharsis deposit and, particularly, within the early

deformed stockwork:

– The volatile-bearing fluids that spanned the Q2–

Q3 (or cQ) stages of quartz deposition, both at the

regional and mine scales, were mainly related to

the formation of Q3 quartz and associated silicates

(phengite and/or chlorite) at Tharsis, marking the

late-kinematic influx of externally derived fluids

C. Marignac et al. / Chemical Geology 194 (2003) 143–165 161

into the mineralised structures (see above). How-

ever, late-kinematic sulphides (arsenopyrite and

sphalerite) were also probably deposited by the

same fluids.

– The aqueous-dominated fluids that circulated

during the deposition of Q4 (clusters of primary

f.i.) or thereafter (FIP) are therefore most likely

responsible for the deposition of polymetallic

sulphides and gold, since metal deposition and Q4

were coeval.

These results may be contrasted with the conclu-

sions of Leistel et al. (1998b). These authors, while

clearly identifying the chalcopyrite + Bi-minerals +

gold assemblage as a late paragenesis mainly formed

in the stockwork just beneath the massive sulphide ore

body, were of the opinion that it was a late high

temperature pulse of the syn-VMS (Tournaisian)

Variscan hydrothermalism. In reality, as far as the

stockwork is concerned, we show that: (i) the late

polymetallic stage at Tharsis was basically a Variscan

post-kinematic feature; and (ii) the temperatures

spanned a ca. 400–170 jC interval, with chalcopyrite

and Bi-minerals possibly deposited in the higher range

of temperatures (300–400 jC), whereas galena (and

gold?) could have been deposited at lower temper-

atures (170–250 jC).These conclusions, drawn for the Tharsis deposit,

are likely to be of a general validity for the VMS of

the whole IPB, because:

(i) The sequence of fluid circulation and ore (re)-

deposition that we have found at Tharsis and in

the surroundings is basically the same as was

described for the Neves-Corvo deposit by Moura

et al. (1997a,b).

(ii) The fluids found at Tharsis in the Q3 and Q4

quartz are very similar to those described by

previous workers in the Aznalcollar (Almodovar

et al., 1998), Rio Tinto (Nehlig et al., 1998) and

several northern (Sanchez-Espana et al., 2000)

deposits and deemed to be representative of the

deposition conditions for the VMS deposits. It

seems therefore that these studies were in reality

concerned with the post-kinematic stage of ore

deposition. This is logical, since, given the

generally accepted P–T conditions of ore depo-

sition in the Kuroko-type VMS deposits (V 350

jC, V 30 MPa, e.g., Franklin, 1993), and the

peak conditions of the Variscan tectono-thermal

event (similar temperatures, but up to 300 MPa),

implosion of primary inclusions trapped in the

early quartz was unescapable. Indeed, as stated in

a previous section, primary imploded inclusions

are effectively observed at Tharsis; they were also

described at La Zarza and Rio Tinto (Diagana,

2001) and at Neves-Corvo (Moura et al.,

1997a,b), and are likely to be discovered in the

other deposits of the IPB.

8.3. Cause of the ‘‘retrograde’’ heat input

The significant ‘‘retrograde’’ heat input found in

the Tharsis area is worth further discussion. Consid-

ering the high temperature (400–420 jC at least)

reached by the fluids in the very upper continental

crust (estimated depth of ca. 4 km), we are evidently

dealing with the inception of a high-enthalpy geo-

thermal system, and the source of heat must therefore

be sought in some kind of magmatic activity, most

likely a shallow-level granite intrusion. There is a

plutonic complex (Sierra Norte batholith) to the north-

east of the IPB. Made up of tonalites and granites,

with subordinated gabbros and diorites involved in

magma mixing and mingling, this batholith was

considered either as late Variscan (e.g., Schermerhorn,

1987) or as coeval with the bimodal volcanism of the

VS Group in the IPB (Schutz et al., 1987; Thieble-

mont et al., 1994; Stein et al., 1996). Most recently,

structural investigation of the Sierra Norte batholith

lead Onezime et al. (2001) to conclude that the

intrusion was late kinematic. Such a timing is con-

sistent with the timing of heat input at Tharsis, and it

is therefore likely that other plutonic complexes

underlie the IPB and were responsible for the late-

kinematic (‘‘retrograde’’) reheating that we observe at

the regional scale.

It is interesting to note that a comparable situation

was found for the Hajjar VMS deposit in Morocco,

which is very similar to the VMS deposits in the IPB

(Hibti and Marignac, 2001). There, synsedimentary

hydrothermal activity occurred during the late Visean,

and the tectono-thermal Variscan event is supposed to

be of Westphalian age. Nevertheless, primary syn-

VMS f.i. are imploded at Hajjar like at Tharsis, and

late- to post-kinematic fluids record both a pressure

C. Marignac et al. / Chemical Geology 194 (2003) 143–165162

decrease (from peak conditions at 240 MPa) and a late

heat in pulse (from 360 to more than 430 jC, biotitebeing a post-kinematic mineral at Hajjar) (Essarraj et

al., 1999).

9. Conclusions

(1) At Tharsis, there is no evidence of fluids related to

the deposition of the massive sulphides within the

available transparent minerals displaying fluid

inclusions. Deformation is such that early fluid

inclusions in the earliest quartz (Q1) have im-

ploded. Fluids trapped in recrystallised ores as

primary inclusions in newly formed quartz or in

healed fractures are post-deformational and are

therefore synchronous or posterior to the peak of

metamorphism. Fluid production began under P–

T conditions close to those at the peak meta-

morphism, but fluid movements within the

Tharsis orebody and stockwork seem to have

been favoured by decompression after a pressure

drop linked either to the basement uplift and/or

tectonic events.

(2) Peak metamorphic conditions were close to 300

MPa and 300 jC. A strong pressure decrease is

then documented by the aqueous–carbonic fluids,

and can be attributed to the sudden uplift of the

area. Coeval with the transition from lithostatic to

hydrostatic pressure, at a depth of ca. 4 km, a

strong reheating of the circulating fluids (up to at

least 430 jC) is documented (‘‘retrograde’’

stage).

(3) Fluids circulating at decreasing temperatures and

fluctuating pressures during the ‘‘retrograde’’

stage were aqueous–carbonic fluids (similar to

those of the earlier stages, but with a progressive

loss in the volatile-component) that mixed with a

low-salinity purely aqueous fluid. Microthermo-

metric and geochemical evidence indicate that the

volatile-bearing fluids are of metamorphic (or

‘‘pseudo-metamorphic’’) derivation, whereas the

low-salinity water is likely to be meteoric in

origin.

(4) ‘‘Retrograde’’ fluids have played a significant role

in the textural and mineralogical changes that

affected the ores and the stockwork of the Tharsis

massive sulphide deposit. Microtextures indicate

clearly the recrystallisation or the crystallisation

of newly formed quartz and sulphides (arsenopyr-

ite, chalcopyrite, Bi–Te–sulphides, sphalerite,

pyrite, galena, native gold). In particular, the

primary paragenesis of the Tharsis stockwork was

mainly quartz–pyrite–chlorite–phengite (and,

locally, ankerite and cobaltite). Base metals (and

gold) were quantitatively introduced in the stock-

work during the ‘‘retrograde’’ stage of the

Variscan tectono-thermal event. It remains open

as to whether these metals were newly introduced

into the stockwork from elsewhere or were simply

remobilised from the existing primary assemb-

lages in the massive sulphide bodies.

(5) Fluid inclusion studies in other deposits of the IPB

have reported results very similar to those found in

the present study. Excepted for the Neves-Corvo

deposit, for which the reported fluids and relation-

ships with Variscan events are the same as for

Tharsis (Moura et al., 1997a,b), the authors of

these earlier studies claimed to have studied the

pristine fluids associated with the massive sulphide

deposition (Almodovar et al., 1998; Nehlig et al.,

1998; Sanchez-Espana et al., 2000). However,

considering that (i) the synhydrothermal fluid

inclusions are unlikely to escape implosion when

submitted to the peak metamorphic conditions;

and (ii) that the observed inclusions yield basically

the same microthermometric data that in the

Tharsis and Neves-Corvo deposits; it seems likely

that these earlier studies equally dealt with the

‘‘retrograde’’ stage of fluid circulation in the IPB.

Acknowledgements

This work was supported by the GDR ‘‘Metal-

logenie no. 514’’, BRGM, La Source; and SEIEMSA.

J.-P. Milesi, Y. Deschamps and M. Joubert are thanked

for their technical and scientific assistance during the

visit of the Tharsis open pit, and sampling of the

SEIEMSA loggings. The company ‘‘Minas de Tharsis

S.A.’’ is thanked for having permitted sampling in the

open pit. E. Marcoux provided representative thin and

polished sections of the early stockwork ores and J.

Onezime provided the Villanova del Castillo sample.

F. Martineau is thanked for help in the O isotope

measurements. L. Diamond, J. Munha and F. Noronha

C. Marignac et al. / Chemical Geology 194 (2003) 143–165 163

carefully reviewed the manuscript and greatly helped

to its improvement. [RR]

References

Almodovar, G.R., Saez, R., Pons, J.M., Maestre, A., Toscano, M.,

Pascual, E., 1998. Geology and genesis of the Aznalcollar mas-

sive sulphide deposit, Iberian Pyrite Belt, Spain. Miner. Depos.

33, 111–136.

Bakker, R.J., 1997. Clathrates: computer programs to calculate fluid

inclusion V–X properties using clathrate melting temperatures.

Comput. Geosci. 23, 1–18.

Banks, D.A., Yardley, B.W.D., 1992. Crush-leach analysis of fluid

inclusions in small amount and synthetic samples. Geochim.

Cosmochim. Acta 56, 245–248.

Banks, D.A., Davies, G.R., Yardley, B.W.D., McCaig, A.M., Grant,

N.T., 1991. The chemistry of brines from an Alpine thrust sys-

tem in tne Central Pyrenees: an application of fluid inclusion

analysis to the study of fluid behaviour in orogenesis. Geochim.

Cosmochim. Acta 55, 1021–1030.

Bodnar, R.J., 1993. Revised equation and table for determining the

freezing point depression of H2O–NaCl solutions. Geochim.

Cosmochim. Acta 57, 683–684.

Bohlke, J.K., Irwin, J.J., 1992. Laser microprobe analyses of noble

gas isotopes and halogens in fluid inclusions: analyses of micro-

standards and synthetic inclusions in quartz. Geochim. Cosmo-

chim. Acta 56, 187–201.

Boiron, M.C., Essarraj, S., Sellier, E., Cathelineau, M., Lespinasse,

M., Poty, B., 1992. Identification of fluid inclusions in relation

to their host microstructural domains in quartz by cathodolumi-

nescence. Geochim. Cosmochim. Acta 56, 175–185.

Boiron, M.C., Cathelineau, M., Banks, D., Yardley, B., Noronha, F.,

Miller, F.M., 1996. P–T–X conditions of fluid penetration in

the basement during retrograde metamorphism and uplift: a

multidisciplinary investigation of bulk and individual fluid in-

clusion chemistry from NW Iberian quartz veins. Geochim.

Cosmochim. Acta 60, 43–57.

Bottrell, S.H., Yardley, B.W.D., 1988. The composition of a pri-

mary granite derived ore fluid from S.W. England, determined

by fluid inclusion analysis. Geochim. Cosmochim. Acta 52,

585–588.

Bucher, K., Frey, M., 1994. Petrogenesis of Metamorphic Rocks.

Springer, New York.

Carpenter, A.B., Trout, M.L., Pickett, E.E., 1974. Preliminary report

on the origin and chemical evolution of lead- and zinc-rich oil

field brines in central Mississippi. Econ. Geol. 69, 1191–1206.

Cathelineau, M., Lespinasse, M., Boiron, M.C., 1994. Fluid inclu-

sion planes: a geochemical and structural tool for the reconstruc-

tion of paleofluid migration. In: De Vivo, B., Frezzotti, M.L.

(Eds.), Short Course ‘‘Fluid Inclusions in Minerals: Methods

and Applications’’. Virginia Tech, Blacksburg, Virginia, USA,

pp. 271–282.

Clayton, R.N., Mayeda, T.K., 1963. The use of bromine pentafluor-

ine in the extraction of oxygen from oxides and silicates for

isotopic analysis. Geochim. Cosmochim. Acta 27, 43–52.

Diagana, B., 2001. L’importance des remobilisations des metaux

(Cu, Zn, Au) lors du metamorphisme retrograde: Etude des

paleofluides et des assemblages mineralogiques des amas sul-

fures sud-iberiques de Tharsis et La Zarza. Unpubl. Thesis Doct.

Univ. Henri Poincare (Nancy I), 308 pp.

Dubessy, J., 1984. Simulation des equilibres chimiques dans le

systeme C–O–H. Consequences methodologiques pour les in-

clusions fluides. Bull. Mineral. 107, 155–168.

Dubessy, J., Poty, B., Ramboz, C., 1989. Advances in C–O–H–N–

S fluid inclusions geochemistry based on microRaman spectro-

metric analysis of fluid inclusions. Eur. J. Mineral. 1, 517–534.

Essarraj, S., Hibti, M., Marignac, C., Cathelineau, M., Boiron,

M.C., Dubessy, J., 1999. Hercynian metamorphism of the Hajjar

Pb–Zn–Cu massive sulfide deposit, Guemassa, Morocco: pre-

liminary results from fluid inclusion study. ECROFI XV Ab-

stracts, Terra Nostra 99/6, 95–96. Alfred-Wegener-Stiftung,

Koln.

Essarraj, S., Boiron, M.-C., Cathelineau, M., Fourcade, S., 2001.

Multistage deformation of Au-quartz veins (Laurieras, French

Massif Central): evidence for late gold introduction from micro-

structural, isotopic and fluid inclusion studies. Tectonophysics

336, 79–99.

Fontes, J.C., Matray, J.M., 1993. Geochemistry and origin of for-

mation brines from Paris Basin, France: 1. Brines associated

with triassic salts. Chem. Geol. 109, 149–175.

Fouillac, C., Michard, G., 1981. Sodium/lithium ratio in water ap-

plied to geothermometry of geothermal reservoirs. Geothermics

10, 55–70.

Fournier, R.O., 1979. A revised equation for Na/K geothermometer.

Geotherm. Resour. Counc. Trans. 3, 221–224.

Franklin, J.M., 1993. Volcanic-associated massive sulphide depos-

its. In: Kirkham, R.V., Sinclair, W.D., Thorpe, R.I., Duke, J.M.

(Eds.), Mineral Deposits Modeling. Geological Assoc. Canada

Spec. Pap., vol. 40, pp. 315–334.

Frape, S.K., Fritz, P., 1987. Geochemical trends from groundwaters

from the Canadian Shield. In: Fritz, P., Frape, S.K. (Eds.), Saline

Waters and Gases in Crystalline Rocks. Geol. Assoc. Canada

Spec. Paper, vol. 33, pp. 19–38.

Halsall, C.E., Sawkins, F.J., 1989. Magmatic-hydrothermal origin

for fluids involved in the generation of massive sulphide depos-

its at Rio Tinto, Spain. In: Miles, L. (Ed.), Water-Rock Inter-

action. Balkema, Rotterdam, pp. 285–288.

Hibti, M., Marignac, C., 2001. The Hajjar deposit of Guemassa

(SW Meseta, Morocco): a metamorphosed syn-sedimentary

massive sulphide ore body of the Iberian type of volcano-

sedimentary massive sulphide deposits. In: Piestrzynski, A.,

et al. (Eds.), Mineral Deposits at the Beginning of the 21st

Century. A.A. Balkema Publishers, Lisse/Abingdon/Exlan

(DA)/Tokyo, pp. 281–284.

IGME, 1982. Sintesis geologica de la faja piritica del SO de Espa-

na. Mem. IGME 98, 1–106.

Jacobs, G., Kerrich, D., 1981. Methane: an equation of state with

application to the ternary system H2O–CO2–CH4. Geochim.

Cosmochim. Acta 45, 607–614.

Kerrich, D., Jacobs, G., 1981. A remodified Redlich–Kwong equa-

tion for H2O–CO2–NaCl mixtures at elevated pressures and

temperatures. Am. J. Sci. 281, 735–767.

C. Marignac et al. / Chemical Geology 194 (2003) 143–165164

Kharaka, Y.K., Maest, A.E., Carothers, W.W., Law, L.M., Lamothe,

P.J., Fries, T.L., 1987. Geochemistry of metal-rich brines from

central Mississippi Salt dome Basin, USA. Appl. Geochem. 2,

543–561.

Leistel, J.M., Marcoux, E., Thieblemont, D., Quesada, C., Sanchez,

A., Almodovar, G.R., Pascual, E., Saez, R., 1998a. The vol-

canic-hosted massive sulphide deposits of the Iberian Pyrite

Belt. Review and preface to the Thematic Issue. Miner. Depos.

33, 2–30.

Leistel, J.M., Marcoux, E., Deschamps, Y., Joubert, M., 1998b. An-

tithetic behaviour of gold in the volcanogenic massive sulphide

deposits of the Iberian Pyrite Belt. Miner. Depos. 33, 92–97.

Marcoux, E., Moelo, Y., Leistel, J.M., 1996. Bismuth and cobalt

minerals: indicators of stringer zones to massive sulfide de-

posits, Iberian Pyrite Belt. Miner. Depos. 31, 1–26.

Moura, A., Noronha, F., Cathelineau, M., Boiron, M.C., 1997a.

Fluids from the Neves-Corvo Volcanic Massive Sulphide de-

posit, Portugal. European Current Research on Fluid Inclu-

sions—ECROFI XIV, 1–4 July, CREGU, Nancy, France,

pp. 220–221. Abstracts.

Moura, A., Noronha, F., Cathelineau, M., Boiron, M.C., Ferreira,

A., 1997b. Evidence of metamorphic fluid migration within the

Neves-Corvo ore deposits: the fluid inclusion data. SEG Neves

Corvo Field Conference. Abstracts and program, May 11–14,

Lisbon, Portugal. Society of Economic Geologists, Littleton,

Colorado, USA, p. 92.

Munha, J., 1983. Low-grade regional metamorphism in the Iberian

Pyrite Belt. Comun. Serv. Geol. Port. 69, 3–35.

Munha, J., 1990. Metamorphic evolution of the South Portu-

guese/Pulo do Lobo Zone. In: Dallmeyer, R.D., Martinez,

E. (Eds.), Pre-Mesozoic Geology of Iberia. Springer, Berlin,

pp. 363–368.

Nehlig, P., Cassard, D., Marcoux, E., 1998. Geometry and genesis

of feeder zones of massive sulphide deposits: constraints from

the Rio Tinto ore deposit. Miner. Depos. 33, 137–149.

O’Neil, J.R., Clayton, R.N., Mayeda, T.K., 1969. Oxygen isotope

fractionation in divalent metal carbonates. J. Chem. Phys. 51,

5547–5558.

Onezime, J., Charvet, J., Faure, M., Chauvet, A., Panis, D., 2001.

Structural evolution of the southernmost segment of the west

European variscides: the south Portuguese zone (SW Iberia). J.

Struct. Geol. 24, 451–468.

Poty, B., Leroy, J., Jachimowicz, L., 1976. Un nouvel appareil pour

la mesure des temperatures sous le microscope: l’installation de

microthermometrie Chaixmeca. Bull. Mineral. 99, 182–186.

Quesada, C., 1998. A reappraisal of the structure of the Spanish

segment of the Iberian Pyrite Belt. Miner. Depos. 33, 31–44.

Ribeiro, A., Silva, J.B., 1983. Sructure of the south Portuguese

zone. Mem. Serv. Geol. Port. 29, 83–89.

Ribeiro, A., Quesada, C., Dallmeyer, R.D., 1990. Geodynamic

evolution of the Iberian Massif. In: Dallmeyer, R.D., Martinez,

E. (Eds.), Pre-Mesozoic Geology of Iberia. Springer, Berlin,

pp. 399–409.

Roedder, E., 1984. Fluid inclusions. Reviews in Mineralogy, vol.

12. Mineral. Soc. of America, Washington, D.C., USA, 644 pp.

Saez, R., Pascual, E., Toscano, M., Almodovar, G.R., 1999. The

Iberian type of volcano-sedimentary massive sulphide deposits.

Miner. Depos. 34, 549–570.

Sanchez-Espana, J., Velasco, F., Yusta, I., 2000. Hydrothermal alter-

ation of felsic volcanic rocks associated with massive sulphide

deposition in the northern Iberian pyrite belt (SW Spain). Appl.

Geochem. 15, 1265–1290.

Schermerhorn, L.J.G., 1987. The Hercynian gabbro-tonalite-gran-

ite-leucogranite suite of Iberia: geochemistry and fractionation.

Geol. Rundsch. 76, 137–145.

Schutz, W., Ebneth, J., Meyer, K.D., 1987. Trondhjemites, tonalites

and diorites in the South Portuguese Zone and their relations to

the vulcanites and mineral deposits of the Iberian Pyrite Belt.

Geol. Rundsch. 76, 201–212.

Stein, G., Thieblemont, D., Leistel, J.M., 1996. Relations volca-

nisme/plutonisme dans la Ceinture pyriteuse iberique, secteur

de Campofrio, Espagne. C. R. Acad. Sci. Paris 322, 1021–1028.

Thieblemont, D., Marcoux, E., Tegyey, M., Leistel, J.M., 1994.

Genese de la province sud-iberique dans un paleo-prisme d’ac-

cretion? Arguments petrologiques. Bull. Soc. Geol. Fr. 165,

407–423.

Tornos, F., Gonzalez Clavijo, E., Spiro, B., 1998. The Filon Norte

orebody (Tharsis, Iberian Pyrite Belt): a proximal low-temper-

ature shale-hosted massive sulphide in a thin-skinned tectonic

belt. Miner. Depos. 33, 150–169.

Verma, S., Santoyo, E., 1997. New improved equations for Na/K,

Na/Li and SiO2 geothermometers by outlier detection and re-

jection. J. Volcanol. Geotherm. Res. 79, 9–23.

Vityk, M.O., Bodnar, R.J., 1995. Textural evolution of synthetic

fluid inclusions in quartz during reequilibration, with applica-

tions to tectonic reconstruction. Contrib. Mineral. Petrol. 121,

309–323.

Zhang, Y., Frantz, J., 1987. Determination of the homogenization

temperatures and densities of supercritical fluids in the system

NaCl–KCl–CaCl2–H2O using fluid inclusions. Chem. Geol.

64, 335–350.

Zheng, Y.F., 1993. Calculation of oxygen isotope fractionation in

anhydrous silicate minerals. Geochim. Cosmochim. Acta 56,

1079–1091.

C. Marignac et al. / Chemical Geology 194 (2003) 143–165 165