Mineralium Deposita (2003) 38: 953–967DOI 10.1007/s00126-002-0342-z Klaus Germann Æ Volker Lu¨ders Æ David A. BanksKlaus Simon Æ Jochen Hoefs Late Hercynian polymetallic vein-type base-metal mineralizationin the Iberian Pyrite Belt: fluid-inclusion and stable-isotopegeochemistry (S–O–H–Cl) Received: 16 January 2002 / Accepted: 16 November 2002 / Published online: 6 February 2003 Springer-Verlag 2003 Abstract Late Variscan vein-type mineralization in the quartz–stibnite veins remains unclear. By contrast, Iberian Pyrite Belt, related to the rejuvenation of pre- quartz–galena veins derived sulfide (and metals?) by al- existing fractures during late Variscan extensional tecto- teration of a sedimentary source, most likely shale- nism, comprises pyrite–chalcopyrite, quartz–galena– hosted massive sulfides. The d34S values in galena from the two study sites vary between )15.42 and )19.04&.
Barite which is associated with galena has significantly chalcopyrite, and quartz–manganese oxide mineral different d34S values ()0.2 to 6.44&) and is assumed to assemblages. Studies of fluid inclusions in quartz, have formed by mixing of the ascending fluids with stibnite, and barite as well as the sulfur isotopic com- meteoric water.
positions of stibnite, galena, and barite from threeoccurrences in the central part of the Iberian Pyrite Belt Keywords Pyrite Belt Æ Vein mineralization Æ Fluid reveal compelling evidence for there having been differ- inclusions Æ Infrared microscopy Æ Chlorine isotopes ent sources of sulfur and depositional conditions.
Quartz–stibnite mineralization formed at temperaturesof about 200 C from fluids which had undergone two-phase separation during ascent. Antimony and sulfide are most probably derived by alteration of a deeperlying, volcanic-hosted massive sulfide mineralization, as Regarding their general stratigraphic and structural sit- indicated by d34S signatures from )1.45 to )2.74&. Sub- uation, the vein-type mineralizations of the Iberian critical phase separation of the fluid caused extreme Pyrite Belt (IPB) studied here fit into the common me- fractionation of chlorine isotopes (d37Cl between )1.8 tallogenetic evolution pattern of the European Hercy- and 3.2&), which correlates with a fractionation of the nides. Late and post-Hercynian vein deposits of Zn–Pb, Cl/Br ratios. The source of another high-salinity fluid barite and fluorite are widespread in the central and western regions of the European Hercynian orogen (see,for example, Tischendorf and Schwab 1989; Mo¨ller andLu¨ders 1993). Their ages extend from Late Hercynian to Editorial handling: V. Bouchot Mesozoic times, and underlying sedimentary rocks are thought to be the fluid sources, rather than the granitic Institut fu¨r Angewandte Geowissenschaften – Fachgebiet intrusions. Structurally controlled antimony mineral- Lagersta¨ttenforschung, TU-Berlin, Ernst-Reuter-Platz 1, izations are another typical feature of the Hercynian 10587 Berlin, Germany orogenic belt in Europe (see Wagner and Cook (2000) for NW Germany, Munoz et al. (1992) for the French Paleozoic basement, and Gumiel and Arribas (1987) for the Iberian Peninsula). These antimony deposits can be Telegrafenberg, P.B. 4.3, 14473 Potsdam, Germany considered to be a common and widespread mineral- ization style, all across the European Hercynides School of Earth Sciences, (Wagner and Cook 2000), and can be regarded as a kind University of Leeds, Leeds, LS2 9JT, UK of metallogenic marker characterizing the late Hercy- K. Simon Æ J. Hoefs nian extensional tectonic evolution (Munoz et al. 1992).
Go¨ttinger Zentrum Geowissenschaften, Abt. Geochemie, The IPB is part of the South Portuguese Zone Universita¨t Go¨ttingen, Goldschmidtstr. 1,37077 Go¨ttingen, Germany (Fig. 1), located at the southern edge of the Iberian Fig. 1 Location of deposits in the Spanish part of the Iberian Pyrite Belt (modified after Leistel et al. 1998) Westfalian), rocks and sulfide ores underwent multi-phase deformation and low-grade regional metamor- Hercynian belt and the European Hercynian orogen. It phism (Schermerhorn 1971; Silva et al. 1990; Munha´ extends for some 250 km with widths of 25–70 km, and 1990, One´zime et al. 2002).
is one of the largest provinces of volcanic- and sediment- At the northeastern boundary of the IPB, a plutonic hosted massive sulfide deposits in the world, containing complex (Sierra Norte Batholith) is situated, the age of more than 1,700 Mt sulfide ore (Leistel et al. 1998).
which is still under discussion. Some authors suggest Mining activity dates back to the Chalcolithic era but at that the largest part of the plutonic complex is pre-tec- present only five of the more than 80 mines which op- tonic and related to the first volcanic episode of the VSC erated during the last hundred years are still active, (e.g., Schu¨tz et al. 1987; Thie´blemont et al. 1995). Others namely, Sotiel-Migollas, Aznalco´llar-Los Frailes, Rio consider the batholith's emplacement to be of Late Tinto, Tharsis, and Neves-Corvo (Sa´ez et al. 1999).
Hercynian age and post-date the deformation of the IPB Neves-Corvo is currently the only active mine in the (e.g., De la Rosa et al. 1993; Quesada 1998).
Portuguese part of the belt and is an important source of Besides the massive sulfide deposits, the IPB hosts copper and tin.
several other types of mineralization, namely, stratiform The massive sulfide deposits and their host rocks manganese ores and manganese deposits and vein-type formed under an epicontinental extensional regime base-metal. The latter comprise mineral associations during the Late Devonian–Early Carboniferous, thus such as pyrite–chalcopyrite, quartz–galena–sphalerite, corresponding to a regionally distributed metalliferous ‘‘peak'' around 350 Ma within the Western Hercynides (Lescuyer et al. 1998). Mineralization is hosted by a strongly folded series of rocks composed of felsic and mineralization is known from all three main lithostrati- mafic volcaniites, black shales, siltstones, and cherts of graphic units, i.e., the pre-volcanic PQ, the VSC, and the the Volcano-Sedimentary Complex (VSC) which is in- tercalated between the Late Devonian Phyllite–Quarzite For some of the PQ-hosted, sulfide-bearing quartz veins Group (PQ) and the Lower Carboniferous Culm Group, in the Valverde area (Fig. 1), Bonijoly et al. (1994) the latter consisting of flysch sediments (Schermerhorn proved that the vein structures formed prior to the main phase of deformation, and that their mineralogicaland geochemical composition is similar to that of the Regional geological setting massive sulfides. These oldest veins are thus interpretedto be the roots of massive sulfide bodies, representing From the long list of late vein-type occurrences and paleofaults which controlled the distribution of the small mines compiled by Pinedo Vara (1963) or men- stratiform sulfide deposits in the volcano-sedimentary tioned in other regional publications, three localities in the center of the Spanish part of the Pyrite Belt were The predominant type of disconformable mineral- selected, namely, Mina Nero´n, Mina Aurora and Mina izations in the VSC is represented by stockworks located Silillas (Fig. 1 and Table 1). Geological fieldwork and beneath the stratiform massive sulfides and which acted sampling at these sites was done by Sedler (1989) and as feeder veins. The major structures of these stock- Wipfler (1989) who also presented data on the geo- works, as demonstrated by the Rio Tinto feeder zone, chemistry and mineral parageneses and some fluid-in- are arranged in a regular pattern which can be inter- clusion data from quartz.
preted as the expression of tectonic activity contempo- The Mina Silillas orebody is located in the northern raneous with emplacement of the orebodies (Bonijoly flank of the Valverde del Camino-Calan˜as anticline et al. 1994).
where it follows a northwest-dipping fault zone, N36E The uppermost VSC sequence and the base of the in direction, between Culm Group shales and fine- overlying turbidite sediments of the Culm Group host a grained sedimentary rocks of the uppermost VSC third type of vein deposit which postdates Hercynian sequence (Sedler 1989). The following primary and sec- transpressional deformation. As Routhier et al. (1980) ondary mineral parageneses were described from Silillas showed, these types of post-massive sulfide and post- folding veins are restricted to a section of the sedimen- 1. Barite, galena, quartz; tary column which corresponds to an important sedi- 2. Quartz, galena, chalcopyrite, fahlore; mentary discontinuity—the Upper Vise´an transgression.
3. Malachite, cuprite, native copper; Their mineralogy and geochemistry is clearly different 4. Quartz, manganese oxides.
from that of the massive sulfides and their stockworks(Leistel et al. 1998). Besides manganiferous quartz veins, The stibnite veins of Mina Nero´n, often taking the base-metal-bearing quartz veins mainly occur.
form of quartz–stibnite banded ores (Fig. 2), are located With the exception of some Cu-rich stockwork ores, about 10 km west of Mina Silillas. They are hosted by vein-type mineralization has been mined intensively at graywackes and shales of the Culm Group and are situ- only a few places due to its low economic importance, ated in the northern limb of the Puebla de Guzma´n an- and is less well studied, in contrast to the massive sulfide ticline. They occupy a north-dipping fault zone N105E deposits. Wipfler and Sedler (1995) suggested that the in direction, which was developed more or less parallel to youngest type of vein mineralization, the post-massive the prevailing direction of the cleavage and thrust planes sulfide manganiferous and sulfide-bearing quartz veins, (Wipfler 1989), and show evidence of repeated opening.
was derived from underlying stratiform manganese and The early mineral assemblage is chalcopyrite, pyrite, massive sulfide deposits, respectively. Quartz-hosted fahlore and frequently idiomorphic quartz, and a ‘‘main fluid inclusions indicate decreasing temperatures for ore'' stage contains stibnite, milky quartz, and subordi- fluids in repeatedly opened vein systems. Our study aims nate arsenopyrite (Wipfler 1989). The hydrothermal ac- to characterize the origin of the ore-forming fluids and tivity ended with the formation of clear quartz which the P–T–X conditions during the formation of some of occurs as euhedral crystals in fissures or replaces older the post-volcanic and post-folding vein-type mineral- milky quartz (Fig. 2a). The Mina Aurora area is situated ization, using fluid-inclusion and stable-isotope data of at the eastern margin of the Puebla de Guzma´n anticline, some previously mined vein deposits in the Spanish part within basal Culm sediments in which mineralized frac- of the IPB (Fig. 1).
ture zones are developed with N60E (according to Pin- Table 1 Location and properties of the vein-hosted mineralizations at Mina Nero´n, Mina Silillas and Mina Aurora, Huelva province,Spain 2.5 km east of Montes de San Benito, 6 km west of Calan˜as, 2–3 km southeast of Alosno, Primary mineralization Stibnite, arsenopyrite, chalcopyrite, Galena, chalcopyrite, fahlore Galena, sphalerite pyrite, tetraedrite, tennantite, freibergite Geochemi calcharacter Pb, Cu, Ba; (As,Sb) Quartz; dolomite, ankerite Graywacke of the Culm Group Shale; fault VS/Culm Group Fault VS/Culm Group Thickness of veins Direction of veins

deformation, including folding and thrusting. Thus,these undeformed mineralized veins are most probablyrelated to the rejuvenation and repeated reopening ofpre-existing fractures during late Variscan extensionaltectonics.
Both the Puebla de Guzma´n and the Calan˜as- Valverde del Camino anticlines host some prominentmassive sulfide deposits. The giant Tharsis deposit,with reserves of about 115 Mt (Sa´ez et al. 1999), islocated some 10 km southwest of Nero´n and about7 km north of Aurora, and the Sotiel-Migollas Groupof massive sulfide deposits (reserves of 117 Mt) liesanother 10 km SE of the Silillas. No published infor-mation is available on possible indications of massivesulfide bodies buried below the Culm sediments in theNero´n-Silillas-Aurora area, whereas east of Valverdethe giant Masa Valverde deposit (120 Mt) has beendiscovered quite recently under Culm sediment cover(Toscano et al. 1993).
Analytical methods Fluid inclusions were studied in quartz and barite in transmittedlight, and in stibnite in near-infrared light using a U.S.G.S. heating-freezing system. The thickness of doubly polished wafers for mic-rothermometric studies was between 200 and 250 lm for quartzand barite, and for stibnite between 100 and 120 lm. For cali- Fig. 2 a Banded quartz–stibnite ore from Mina Nero´n (sample bration, synthetic standards and natural inclusions were used.
10000 in Tables 2 and 3) b Photomicrograph of halite-bearing fluid Hydrogen isotope ratios on bulk fluid inclusions in quartz were inclusions in a clear zone of late-stage chevron quartz from Mina measured by mechanical crushing of about 5 g of quartz grains of 1 Nero´n (sample 16041 in Tables 2 and 3). c Infrared photomicro- to 5 mm in size, according to the method described in detail by graph of a primary two-phase fluid inclusion in stibnite (sample Simon (2001). The released water was trapped, reduced to H2 by 16039 in Tables 2 and 3) orientated parallel to {010} zinc (Bloomington, Indiana University, USA), and measured on aFinnigan MAT 251 gas source mass spectrometer. The absoluteerror of determination is about 5 to 10&.
Oxygen isotope ratios were measured by the laser ablation edo Vara 1963) and N100E (Routhier et al. 1980) strike.
continuous flow technique described in Fiebig et al. (1999) and The mineral paragenesis comprises quartz, barite, galena Wiechert et al. (2002). A 300-lm spot size was ablated by a 193-nm and sphalerite.
ArF Excimer laser (Lambda Physik), with an average energy of In terms of their structural and lithostratigraphic 20 J/cm2 on the sample surface. The resulting oxygen was analyzedby a Finnigan Delta plus mass spectrometer.
position, all three vein deposits occur at or near to the Sulfur isotope analyses of sulfides were performed by preparing flanks of anticlines and are hosted either by the Basal sulfur dioxide through combustion at 1,000 C with V2O5. Sulfur Shaly Formation (Moreno and Sequeiros 1989; Moreno isotopic analyses of sulfates were carried out on H2S prepared by 1993) of the Culm Group, which overlies the third and reaction at 350 C with Kiba solution. H2S is precipitated as CdS,converted to Ag uppermost volcanic sequence of the VS Complex, or by 2S, and oxidized with V2O5 at 1,000 C to produce SO2 which was used for the mass spectrometer measurements.
the first turbidite facies of the Culm Group.
Sulfur isotope ratios are reported as d34S relative to the Can˜on Wipfler and Sedler (1995) have demonstrated that Diablo Troilite (CDT).
the strike direction of undeformed quartz veins is ap- Chemical analysis of the fluid inclusions was carried out at the proximately parallel to the main foliation in the study University of Leeds using the bulk crush-leach method as detailed inBanks et al. (2000a). Quartz, barite and stibnite samples were crushed area. Structural analysis of the central part of the Py- to 1–2 mm grain size and the quartz samples cleaned in aqua-regia, rite Belt by Routhier et al. (1980) indicated a time se- followed by nitric acid. All samples were then boiled several times in quence of fractures and related veins from N90/100E 18.2 MW water and dried prior to analysis. Approximately 0.5 to 1 g to N40/60E and finally N140/150E. In addition, a of material was crushed, transferred to a suitable container and lea-ched with 18.2 MW water for anion and Na, K and Li analysis, or close temporal and spatial relationship between the with acidified LaCl3 solution for the analysis of other cations. Anions observed Variscan folding phases and their subsequent were determined by ion chromatography, Na, K and Li by flame relaxation periods, represented by fractures, was as- emission spectroscopy, and other cations by inductively coupled sumed by Routhier et al. (1980). However, neither the plasma emission spectroscopy. Replicate analyses show the precisionto be on average 5% RSD for the analysis of these samples. The 35Cl Pb-Cu-barite veins nor the quartz-Sb veins which, ac- and 37Cl isotopes were determined by thermal ionization mass cording to the Routhier scheme, would belong to the spectrometry on aliquots of the water-extracted salts, following the oldest fracture generation, are affected by polyphase method of Banks et al. (2000b).
phase and a vapor bubble at room temperature. Some well-crystallized, late-stage quartz samples from MinaNero´n, with chevron structures, contain two-phase fluid inclusions in the milky growth zones and polyphaseinclusions, i.e., two-phase fluid inclusions with cubes of Milky gangue quartz samples from quartz–stibnite halite crystals and/or other daughter minerals of un- banded ores from Mina Nero´n and from the studied known composition, in their clear zones (Fig. 2b). The occurrences contain numerous fluid inclusions, but their inclusions are preferentially orientated in milky growth sizes generally do not exceed 2 lm. Due to the high zones or arranged parallel to crystal planes in clear number of fluid inclusions in milky quartz, a clear zones and, therefore, they appear to be of primary or- classification, i.e., primary vs. secondary origin of the igin (Roedder 1984). They are highly variable in size inclusions, is impossible. The shapes of the inclusions (20–100 lm) and shape (irregular and rounded–elon- are irregular or rounded and they either consist of a gated forms). Barite samples from Mina Aurora always liquid phase and a vapor bubble or, in the case of Mina contain monophase aqueous fluid inclusions. They Nero´n, they are often vapor-rich. Only a few combined generally have a rounded–elongated form and sizes be- microthermometric data of Tmice and Th were obtained tween 10 and 30 lm.
from such samples (Fig. 3 and Table 2). Fluid inclu- FTIR spectroscopic investigations of stibnite samples sions in younger quartz crystals, in small vugs within from Mina Nero´n indicate a transmittance of 15–25% to milky quartz, are considerably larger (up to 15 lm) and near-infrared radiation in the studied wavelength range show rounded to elongated forms, consisting of a liquid between 880 and 1,300 nm. Under the IR microscope, Fig. 3 Tmice vs. Th diagram offluid inclusions in stibnite,quartz, and barite from vein-type mineralization in theIberian Pyrite Belt. Note: baritecontains only monophaseaqueous inclusions, probablydue to low formationtemperatures Table 2 Summary of microthermometric data derived from studies of fluid inclusions in quartz, stibnite, and barite (m massive quartz, xcrystallized quartz) Locality Sample no. Material Te (n) Mean Tmclath/hydr. (n) )2.5 11.3 to 14.7 (6) 153 to 200 (19) 178 )3.6 to )0.8 (17) 141 to 217 (17) 176 )62 to )44 (14) )49.3 to )19.7 (27) )29.2 0.1 to 16.3 (4) 125 to 152 (27) 142 )3.2 to )1.1 (10) 133 to 192 (10) 165 )20.8 to )14 (5) )7.3 to )0.6 (15) )3.7 )2.1 to )1.5 (5) 142 to 189 (15) 165 )30 to 24.3 (13) )16 to 13.9 (13) )23.1 to )7.8 (7) the samples mostly show striation in the direction of homogenization temperatures and halite dissolution growth. Primary two-phase fluid inclusions are elon- temperatures (Bodnar and Vityk 1994).
gated (Fig. 2c), and orientated parallel to crystallo- Fluid inclusions in quartz from Mina Silillas have graphic planes, {110} and/or {010}, as observed in moderate to high salinity but lower homogenization stibnite from other occurrences (Lu¨ders 1996; Bailly et al.
temperatures compared with the fluid inclusions from 2000). The size of primary fluid inclusions in stibnite Mina Nero´n, whereas fluid inclusions in quartz from varies between 30 and 70 lm. Secondary fluid inclusions Mina Aurora have slightly lower salinities but the of smaller size (<25 lm) occasionally occur along trails highest homogenization temperatures of the three oc- crosscutting the samples in various directions.
currences (Fig. 3). Monophase aqueous inclusions inbarite from Mina Aurora have ice melting temperaturesvarying between )16 and )1.5 C. The absence of a vapor bubble in fluid inclusions in barite may be indi-cative of a low formation temperature of <80 C.
The results of fluid-inclusion studies in quartz, stibniteand barite are shown in Fig. 3 and Table 2. From the Thvs. Tm diagram (Fig. 3), two groups of fluid inclusions Crush-leach analyses can be distinguished: (1) low-salinity fluid inclusionswith homogenization temperatures between 150 and The results of the crush-leach analysis are presented in 245 C, and (2) high-salinity fluid inclusions with Table 3. The data show the fluids to be dominated by homogenization temperatures between 100 and 150 C.
Na and Cl with significant but variable amounts of Ca Some fluid inclusions in quartz and monophase inclu- and K, and lesser amounts of Li, Mg and Br. Fluorine sions in barite from Mina Aurora vary in salinity was not detected and, although SO4 was present, there between that of these two groups.
was a strong possibility that the analyses were influenced All fluid inclusions in stibnite from Mina Nero´n have by oxidation of sulfides during crushing and leaching, low salinities, i.e., 1.6–4.9 wt% equivalent NaCl. The and so the data have been omitted.
first melting of ice was observed at about )20 C, close There is a large variation in the Cl/Br ratio of the to the eutectic of the pure H2O–NaCl system. Addi- fluid inclusions (Fig. 4). Quartz and stibnite (paired tionally, the melting of clathrate between 10 and 14 C samples) have similar Cl/Br and Na/Br ratios, but within in a few inclusions indicates traces of a dissolved gaseous the whole sample suite the fluid inclusions have a large component in the fluid. Final homogenization temper- range of values. This is despite the samples having es- atures were not obtained from these gas-bearing inclu- sentially the same gross salinity. There is a correlation with salinity, as can be seen from the bulk analyses of homogenization. The homogenization temperatures of quartz sample 16041 (*), where selective cutting and aqueous two-phase inclusions in stibnite were generally analyzing parts of this sample which contains different observed between 150 and 200 C.
salinity inclusions (a=high salinity+halite, b=high Fluid inclusions in milky gangue quartz from Mina salinity, c=dominantly low-salinity fluids) was carried Nero´n, which is associated with stibnite (Fig. 2a), have out. Halite-bearing inclusions are the most Br-enriched similar salinities and homogenization temperatures as and the lowest-salinity fluid inclusions (salinity equiva- the fluid inclusions in stibnite (Fig. 3). Melting of lent to that of the quartz–stibnite mineralization) the clathrate was not observed in low-salinity inclusions in least. However, the range of Cl/Br and Na/Br ratios, in milky quartz. Fluid inclusions in euhedral late-stage the whole sample suite, is much larger than that covered quartz crystals with chevron structures (quartz II in by these three different salinity fluids in sample 16041.
Fig. 3) from vugs contain low-salinity fluid inclusions in Quartz and barite from Mina Aurora have different Cl/ milky growth zones whereas clear zones contain high- Br and Na/Br ratios, the fluid inclusions in quartz being salinity or even halite-bearing fluid inclusions (Fig. 2b).
more Br-rich, and are within the range of values from The high-salinity fluid inclusions show ice melting tem- Mina Nero´n. The quartz from Mina Silillas has Cl/Br peratures as low as )27 C. In some of these inclusions, and Na/Br ratios which are the same as those of the melting of hydrate was observed between )2 and +4 C halite-bearing fluid from Mina Nero´n.
(metastable?). The homogenization of the vapor phase in Cation ratios, Na/K, Na/Li and Na/Ca also show halite-bearing inclusions occurs at temperatures of considerable variation (Figs. 5 and 6). Low-salinity fluid about 150 C, always prior to the homogenization of the inclusions from the quartz–stibnite mineralization of daughter mineral (170 to 175 C). From the final melting Mina Nero´n have lower Na/K and Na/Li ratios com- temperatures of halite daughter crystals, a salinity of up pared to the high-salinity fluids, and are especially dis- to about 30.5 wt% equiv. NaCl can be inferred for these tinct in terms of their Na/K ratios. The fluid inclusions inclusions (Bodnar 1994). Although this salinity estimate in quartz and barite from Mina Aurora have the same is only valid for inclusions where Th vapor and Tm Na/K ratios but markedly different Na/Li ratios, with halite occur at the same temperature, the error range fluids in barite being depleted in Li relative to the other from an underestimate of salinity will be less than samples. There is no correlation of Cl/Br with Na/K 1.3 wt% for the measured difference between vapor (Fig. 7) or Na/Li. However, fluid inclusions in quartz Table 3 Crush-leach analyses of fluid inclusions hosted by the different vein minerals with the d37Cl, dD and d34S of the fluids and minerals(anion and cation data reported in ppb (as analyzed); n.a. not analyzed, cont. analyses contaminated by minerals not removed prior tocrushing) Locality Sample no. Mineral Na d37Cl FIs. dD FIs.
(&)CDT (&)SMOC (&)SMOW 4,900 18.2 n.a.
<20 3,909 23.1 n.a.
127 <20 8,925 47 2,100 33.2 105 35 59 <20 17,429 127.2 333 58 cont. 3 cont. <20 15,371 33.6 cont.
1,764 50.5 126 42 113 <20 24,029 61.2 915 30 cont. 11 cont. <20 5,122 17.2 cont.
126 <20 51,264 639.4 cont.
<20 9,385 131.6 115 <20 2,855 27.9 142 <20 13,730 89.9 173 <20 3,859 24.4 n.a.
<20 34,097 99.2 n.a.
<20 1,125 14.9 n.a.
<20 1,161 14.4 n.a.
Fig. 4 Fluid-inclusion compositions compared to the trend shown Fig. 5 Comparison of the fluid-inclusion temperatures using the by evaporating seawater. Sample marked * is the bulk analysis of crush-leach analyses and equations for the Na/K and Na/Li fluid inclusions in sample 16041 which contains halite daughter geothermometers derived by Verma and Santoyo (1997). Samples crystals. Samples marked a–c represent halite-bearing, high-salinity designated by *, a, and c belong to the different portions of sample and low-salinity portions of sample 16041 16041 as identified in Fig. 4. Sample b contained too little K foranalysis and is not shown from Mina Nero´n show a good correlation of Cl/Br andNa/Ca, with the most Br-rich fluids having the lowest an excellent correlation with Cl/Br (r2=0.91). The halite- Na/Ca ratio.
bearing fluid is quite distinct from these others, having a The d37Cl values of fluid inclusions in quartz (Fig. 8) much lower Cl/Br ratio and a d37Cl value which is within cover a large range from )1.8 to +3.2& (SMOC). The the range expected from evaporation of seawater. Saline low-salinity fluids associated with the mineralization have brines trapped in quartz from other Spanish Pb–Zn Fig. 6 The Na/Ca vs. Cl/Br ratios of quartz-hosted fluid inclusions Fig. 8 Cl/Br vs. d37Cl. The d37Cl values of fluid inclusions in from Mina Nero´n show a good correlation which may indicate massive gangue quartz from Mina Nero´n plot on a trend line either fluid mixing or immiscibility. Only the bulk analysis of typical for fluids which underwent two-phase separation, as sample 16041 is shown, plotting at one extreme. However, because observed for seafloor mineralization (Lu¨ders et al. 2002). Samples of its d37Cl value (Fig. 8), the highest-salinity inclusions found in with vapor-rich inclusions have negative d37Cl values whereas the this sample could not be involved, either through mechanical residual fluid becomes more enriched in 37Cl. Evaporation alone mixing or by dilution with other fluids, in producing the observed would only result in d37Cl fractionation of ±0.5& (shown by the correlation of the other samples two dashed lines). The bulk analysis of sample 16041 from MinaNero´n (identified by *), which is dominated by high-salinity, halite-bearing fluid inclusions in late-stage quartz, had a different originto the other fluids or different formation conditions. Forcomparison, high-salinity fluid inclusions in quartz from SpanishPb–Zn brines in the Maestrat Basin (Banks 2001) differ clearlyfrom the data in this study. The error bars represent 2r errors provide information on the origin of the salinity. In theabsence of evaporite minerals, Cl and Br behave con-servatively during fluid flow because they are not sig-nificantly involved in fluid–rock interactions (Banks et al.
1991; Bohlke and Irwin 1992). In addition, they can beused to determine if fluid mixing or evaporation duringfluid flow and mineral deposition has occurred. The Cl/Br and Na/Br ratios of fluid inclusions in differentminerals from the studied deposits are shown in Fig. 4relative to the seawater evaporation line based on datacompiled by Fontes and Mattray (1993). The dashed line Fig. 7 Na/K vs. Cl/Br ratios of the fluid inclusions relative to the in the Na/Br versus Cl/Br plot represents Na to Cl ratios trend expected for evaporating seawater. Samples designated by *, of 1, and any removal or addition of halite produces a a, and c belong to the different portions of sample 16041 as data array parallel to this line.
identified in Fig. 4. Sample b contained too little K for analysis and High-salinity and halite-bearing inclusions from is not shown. The variation in Cl/Br at constant Na/K for somequartz and stibnite samples from Mina Nero´n is due to fluid Mina Silillas and Mina Nero´n (late fluids in vug quartz) immiscibility. Other samples which contain variable proportions of plot close to the seawater evaporation line, with Cl/Br the late high-salinity fluid have quite different ratios and Na/Br ratios which would be generated whenalmost all the halite had been precipitated from sea- mineralization, in the Maestrat Basin, have quite different water. The lower-salinity fluids, associated with the distributions of Cl/Br ratios and d37Cl values, and show quartz–stibnite mineralization and quartz from Mina no correlation between the chlorine isotopic composition Aurora, also plot close to or on the seawater evapora- and the Cl/Br ratios (Banks 2001).
tion line, albeit with higher Cl/Br and Na/Br ratios.
However, the salinity of these fluid inclusions is too lowfor them to represent only evaporated seawater, and Origin of the fluids they would have to have been diluted by a low-salinityfluid. Fluids which plot on the seawater evaporation line Determination of halogen concentrations, especially Cl at these points should have approximately 35 wt% total and Br, and their ratios in fluid inclusions can be used to dissolved solids, whereas the salinity of these fluids is less than 5 wt%. To maintain these Cl/Br and Na/Br ratios, are much higher, between 300 and 450 C but most are the diluting fluid must have had a very low salinity.
close to 350 C. Fluid inclusions in quartz and stibnite Quartz samples and the barite from Mina Aurora have at Mina Nero´n have homogenization temperatures of Cl/Br and Na/Br ratios which are close to seawater about 185 C, and the late-stage high-salinity fluids values, and their salinity would be consistent with such have halite dissolution temperatures of about 170 C.
an origin. Other samples have significantly higher Cl/Br At Mina Aurora, homogenization temperatures of ca.
and Na/Br ratios which would be consistent with a 240 C were recorded for fluid inclusions in quartz.
contribution from the dissolution of halite in the fluid.
The two mineral geothermometers give different tem- However, an origin for the fluids which involves sea- peratures, and this may be due to the fluids not water evaporation, halite dissolution and dilution by a achieving equilibrium with the appropriate mineral low-salinity fluid is not compatible with the Cl isotope assemblages. However, it is also possible that both are data (Fig. 8). d37Cl values should be within the range of correct but reflect the temperature at different stages of +0.3 to )0.5& if the fluids were derived by evaporation the fluid's history. The temperatures obtained from of seawater or dissolution of halite (Eggenkamp et al.
Na/K ratios are almost identical to the fluid-inclusion 1995). However, the values of the fluids are between )1.8 temperatures, and we suggest they may be reflecting and +3.2& and show an excellent correlation with the equilibration of the fluid at the site of mineral depo- Cl/Br ratios. The linear regression through the data in sition. Sodium and K are more readily re-equilibrated Fig. 8 passes within error of each sample and of sea- than Li which is essentially conservative once in solu- water. The late quartz, which contains the highest-sa- tion (Fontes and Matray 1993). Therefore, the tem- linity halite-bearing fluid inclusions, does not plot close peratures obtained from the Na/Li ratios may be to the other samples. This has the lowest Cl/Br ratio and reflecting the maximum temperature reached by the a d37Cl value both of which are consistent with a sea- fluid prior to its ascent. We believe that the initial water evaporation origin for the fluid. The same origin is temperature of the ore-forming fluids was approxi- likely for the quartz-hosted fluid inclusions from Mina mately 300 C, and that the Na/K geothermometer probably indicates the true temperature of the mineralformation whereas the Na/Li geothermometer morelikely reflects the initial temperature of the hydrother- mal fluids. Consequently, if the mineralization occurredin a near-surface environment (<500 m), as indicated Unlike the halogens, the cation content of the fluid is by the stratigraphic position of the deposits, it is very more likely to reflect some degree of re-equilibration likely that the ascending fluids locally underwent par- with rocks along the flow path and at the site of min- tial two-phase separation.
eralization, and ultimately may bear no resemblance to We suggested above that the highest-salinity fluid its original composition. An assessment of the closeness inclusions were derived from seawater which evaporated to equilibration can be made by comparing tempera- past the point of halite precipitation. If this were the tures derived from mineral geothermometers and case, then the fluid should contain little Ca and large amounts of Mg. However, we observe the opposite homogenization temperatures are the minimum tem- (Table 3), and this is common for most high-salinity, peratures of the fluid and corrections for pressure have low-temperature brines where dolomitization controls to be applied, which are often difficult to determine the Ca and Mg contents of the fluids. In Fig. 8 there is a exactly. The temperatures obtained from mineral geo- good correlation between the highest-salinity fluid thermometers are only valid if the fluid has reached (marked with *) and the lower-salinity mineralizing equilibrium with the appropriate mineral assemblage fluids. We assume that in these fluids the variation in Cl/ and, using only one geothermometer, this is difficult to Br ratios was due to phase separation. It is possible the assess. In this study (Fig. 5) we have used the Na/K and correlation of Cl/Br and Na/Ca was caused by this Na/Li geothermometers of Fournier (1979) and Fouillac process, but we are unaware of data on the behavior of and Michard (1981), which have improved equations Ca in these circumstances. However, in Fig. 7 there is determined by Verma and Santoyo (1997) to estimate not a similar correlation of Na/K and Cl/Br for the the temperature of the different fluids. None of the fluids we suggest have undergone phase separation. It is samples plot on the combined geothermometer line, and not possible that the correlation is caused by the pres- the Na/K and Na/Li geothermometers give markedly ence of small amounts of the late highest-salinity fluids (as secondary inclusions) which were mixed with the The majority of quartz and stibnite from Mina low-salinity fluids during crushing, based on the evi- Nero´n, and of quartz and barite from Mina Aurora dence from the Cl isotopes. If the highest-salinity fluids give temperatures of between 250 and ca. 180 C using at Mina Nero´n represent evaporated seawater, they the Na/K geothermometer. Halite-bearing fluid inclu- should plot on the seawater evaporation trend line in sions from Mina Nero´n have much larger Na/K ratios Fig. 7. They clearly do not, as they have ca. 7 to 9 times which are outside the validity of the geothermometer.
less K than expected. This could be explained if, for Temperatures obtained with the Na/Li geothermometer example, illite was produced from the fluid.

Fig. 9 Cl/Br vs. dD diagram Deuterium and oxygen isotopes Fig. 10 d18O distribution in a chevron quartz of the late The dD values of fluid inclusions hosted in quartz and mineralization stage from Mina Nero´n (sample 16041x in Tables 2 stibnite from Mina Nero´n, obtained by mechanical ex- traction, fall within a narrow range of )24.7 to )8.9&and are not correlated with the Cl/Br ratios (Fig. 9).
known massive sulfide deposit in the IPB with negative Considering a 2 sigma uncertainty of 5 to 10& (Simon sulfur isotopic signatures, the d34S values are between 2001), all samples could have formed from a single fluid )10.7 and +1.3& (Tornos et al. 1998). At some mas- with a mean dD composition of about 15&.
sive sulfide deposits, the d34S values of barite lie between A profile through a well-crystallized quartz sample +15 and +20&, which leads to the assumption that from Mina Nero´n indicates a correlation between the sulfate was derived from seawater. By contrast, sulfur salinity of fluid inclusions, in distinct growth zones, and isotopes in barite from Mina Aurora have d34S values the d18O isotopic composition (Fig. 10). The lowest d18O between )0.2 and +6.4&, indicating a different source values of 19.3 to 20.7& were measured in growth zones containing low-salinity fluid inclusions which have a Cl/Br ratio of 153. By contrast, growth zones containinghigh-salinity fluid inclusions without a halite daughter mineral have a lower Cl/Br ratio of 103 and d18O valuesbetween 20.8 and 21.6&. In the uppermost zone of the The differences in sulfur isotopic compositions indicate quartz crystal where high-salinity fluid inclusions pre- that stibnite, galena, and barite either derived their sul- dominantly contain halite daughter crystals, a further fur from distinctly different sources, or formed under increase of the d18O values up to 23.4& occurs, ac- quite different physico-chemical conditions. Sulfur iso- companied by a decrease of the Cl/Br ratio to 72.
topic fractionation in hydrothermal ore deposits is afunction of temperature, pH, ƒO2, isotopic compositionof the ore-forming fluid, and/or dissolved element spe- Sulfur isotopes in galena and stibnite cies in the fluid (Ohmoto and Rye 1979). Assuming ahomogeneous sulfur source for all three deposits, sig- Stibnite samples from Mina Nero´n have d34S values nificant changes in ƒO2 and pH would have been re- from )1.45 to )2.74&, and clearly differ from the d34S quired to change the d34S values of sulfides and barite values of galena samples from Mina Silillas and Mina during ore deposition. Ohmoto (1972) has demonstrated Aurora which have considerably lower d34S values that for a fluid with d34SSS=0& and T=250 C, the (Table 3). Galena from Mina Silillas has d34S values of d34S values for sphalerite could vary between +5.8 and about )15.5&, and galena from Mina Aurora between )24&, and for coexisting barite between 0 and +24.2&, )17.6 and )19.6&, the latter being lower than the within geologically reasonable limits for ƒO2 and pH. Atreported d34S values of )15 to +10& from sulfides of low ƒO2 and pH values, the d34S values of sulfides will be the massive sulfide deposits in the IPB (Sa´ez et al. 1999).
similar to d34SSS whereas at high ƒO2 values, the d34S For example, at the Tharsis deposit, which is the only values of minerals can differ significantly from d34SSS.
However, at high ƒO2 values the proportion of aqueous Metallogenic model sulfate in the fluid will increase significantly with respectto H2S in the fluid, and considerable amounts of sulfates The data obtained from studies of sulfur isotopes and should precipitate. Small changes in ƒO2 and pH would fluid inclusions in quartz, stibnite and barite show there cause large changes in the d34S values of either sulfate or to be different sources of metals and sulfur, and different sulfide (Ohmoto and Lasaga 1982). Assuming a com- depositional conditions for some vein-type mineraliza- mon sulfur source for all three deposits, the variations of tions in the IPB. Vein-type deposits in the study area are the d34S values can be explained by changes in ƒO2 and situated along E-W-striking (normal) fault zones which pH. The variation of the large negative d34S values of were active during the transition from Hercynian uplift galena (Table 2) from Mina Aurora and Mina Silillas to extensional tectonism. Therefore, the vein mineral- can be attributed to a significant increase in ƒO2, con- ization seems to be related to a late stage of metamor- sidering an initial d34SSS=0& for the parental ore- phism (Routhier et al. 1980). Extensional tectonics forming fluid (Ohmoto 1972). The small negative d34S allowed fluids from deeper reservoirs to ascend along values of stibnites from Mina Nero´n would have re- faults to higher crustal levels, accompanied by fluctua- quired only a slight increase in ƒO2 or a decrease in pH.
tions in pressure and temperature (Cathelineau et al.
The positive d34S values of barite samples from Mina 2000). However, it should be noted that rocks of the Aurora (Table 3) could also have resulted from signifi- uppermost VS Complex and of the Culm sequence host cant changes in ƒO2. However, the data from quartz- all the studied vein-type deposits. The thickness of flysch hosted fluid inclusions (associated with galena) and sediments in the eastern part of the IPB (in the Huelva massive barite from Mina Aurora (Fig. 3) do not sup- province) certainly does not exceed some 500 m, ac- port the contemporaneous formation of both minerals cording to Schermerhorn and Stanton (1969). Therefore, from the same fluid.
it can be considered that mineral deposition occurred Alternatively, the observed variation in the sulfur close to the paleosurface, in the upper 1 km of the crust isotopic compositions of galena, stibnite, and barite where the hydrothermal fluids were likely to have been could indicate different sources of sulfur. The large hydrostatically pressured (Hedenquist and Henley 1985).
negative d34S values of the galena samples from Mina At Mina Nero´n, banded quartz–stibnite ore (Fig. 2a) Aurora and Mina Silillas (Table 3) are comparable to was deposited from low- to moderate-salinity fluids d34S values of sediment-hosted massive sulfide deposits probably containing small proportions of dissolved (Sa´ez et al. 1999) and sedimentary sulfides in the Iberian gases. Similar fluids are present in late metamorphic- Pyrite Belt (Routhier et al. 1980). Therefore, deeply stage quartz from dissolution vugs and small veinlets circulating fluids could have derived sulfur as well as within the massive sulfide orebodies, where it is associ- metals by alteration of sedimentary rocks and/or pre- ated with polymetallic sulfide assemblages, and/or late existing sediment-hosted massive sulfide deposits. Mar- chlorite and carbonates (Cathelineau et al. 2001). The coux et al. (1994) and Wipfler and Sedler (1995) have precipitation of milky gangue quartz seems to have oc- shown that galena samples from late vein-type miner- curred at temperatures similar to that of stibnite. A alization have a more radiogenic Pb isotopic composi- similar low-salinity fluid precipitated gangue quartz at tion than the massive sulfide mineralization. At Mina Mina Aurora but at slightly higher temperatures Aurora, barite seems to have precipitated at a late stage (Fig. 3). By contrast, well-crystallized quartz with of mineralization. The variations in sulfur isotopic chevron structures from Mina Nero´n contains low-sa- compositions between )0.2 and 6.4& can be explained linity fluid inclusions with Th values generally above by mixing of a cold SO2 -dominant fluid, probably re- 150 C in the milky zones, and high-salinity fluid in- sidual evaporated seawater, with variable amounts of clusions with lower Th values in the clear zones. Fluid dissolved biogenic sulfide with ascending, hydrothermal inclusions with halite daughter crystals can be found in Ba-bearing fluids.
the outermost parts of the quartz crystals (Fig. 2b). Such The small negative d34S values of the stibnite samples a significant variation in salinity of the fluid inclusions from Mina Nero´n are similar to those of volcanic-hosted within a single deposit can either be produced by con- massive sulfide deposits in the IPB (Routhier et al. 1980; tinuous, non-adiabatic boiling in the vein structure, thus Sa´ez et al. 1999). These deposits are characterized by indicating near-surface depositional conditions, or it is a anomalously high concentrations of mobile elements result of fluid mixing. In the latter case, a high-salinity such as As, Sb Tl, and F (Mo¨ller et al. 1983) which are fluid (>30 wt% NaCl equiv.) must have been the assumed to be secondary dispersion haloes from un- dominant fluid which mixed with the metal-bearing low- derlying orebodies resulting from the action of diage- salinity fluid. Both scenarios are discussed in the light of netic or metamorphic fluids. Therefore, it seems the results of fluid-inclusion studies.
plausible that the stibnite mineralization at Mina Nero´nwas deposited from fluids which altered the volcanic-hosted massive sulfides and derived metals and sulfur Fluid mixing model from deeper orebodies, under the assumption that onlysmall isotopic fractionation occurred from the leaching A simple mixing model requires at least two fluids, with stage to the deposition stage.
different compositions, from different sources to explain the observed variations in temperature, salinity, and hosted in barite from the Mina Aurora. Furthermore, isotopic compositions. It is likely that the ore-forming the strong fractionation of the d37Cl values cannot be fluids ascended from depth due to the opening of the explained by evaporation and mixing alone. Solomon shear zones during late stages of metamorphism. In the et al. (2002) suggested that brine pools developed by case of fluid mixing this hot, metal-bearing fluid must exsolution of supercritical fluids from magmas during have mixed in differing proportions with a colder (de- the main period of volcanism in the Spanish Pyrite Belt.
scending?), highly saline brine. The source of this brine The origin of highly saline fluids in such brine pools at in the study area is unclear. However, the Cl/Br ratios of depth is reasonable. However, in our case, these brines the high-salinity inclusions exclude the dissolution of must have formed by seawater evaporation rather than evaporites and strongly indicate that the fluid was a re- magmatic fluids. In the latter case, the Cl/Br ratios of the sidual brine derived from seawater evaporation past the brines should be considerably higher than observed point of halite precipitation (Fig. 4). If these brine-type (Bohlke and Irwin 1992), and the chlorine isotopic fluids were derived from evaporated seawater, from a composition should show a magmatic signature (Banks near-surface reservoir such as a sabkha, one would ex- et al. 2000b).
pect that such a brine was enriched in heavy isotopes Dand 18O, as illustrated by water from the Red Sea (Craig1966). For oxygen such a trend can be observed by the Phase-separation model clear zones in quartz hosting highly saline fluid inclu-sions with heavier d18O values, compared to milky zones Under a hydrostatic pressure regime, an ascending fluid which host fluid inclusions with considerably lower sa- with a salinity of about 3 wt% NaCl equiv. and an ini- linity (Fig. 10) whereas no positive dD values were tial temperature of about 300 C (mean temperature measured (Fig. 9 and Table 3). If we assume that quartz derived from Na/Li and Na/K geothermometers) would precipitated under a hydrostatic pressure regime at a start boiling at a depth of about 900 m (Cunningham depth of about 500 m, a pressure correction for the 1978). In any case, if the pressure at the site of miner- mean Th values of about 180 C for the low-salinity alization was less than 90 bar, as indicated by the fluid inclusions would be negligible. The mean d18O stratigraphic position of the deposits (<500 m), the value of quartz in the growth zone hosting this type of hydrothermal fluid responsible for the vein-type deposits inclusions is about 20&, and the d18O value of water in must have undergone phase separation into a low-sa- equilibrium with the quartz at 180 C would be about linity vapor and a saline brine (Fig. 11). In the temper- 7.0& (Zheng 1993). By contrast, clear zones in the ature range under consideration for the ore-forming studied chevron quartz sample, hosting the high-salinity fluid (250±50 C), any dD variation will be less obvious fluid inclusions which were trapped at minimum tem- and fractionation scatters around 0±10& (Driesner and peratures of about 175 C (as indicated by halite disso- Seward 2000). If some equilibration with the country lution after homogenization of the vapor phase), are rock and boiling processes had occurred, a variation of associated with a fluid which had an initial d18O value of 10& of the dD values is possible.
about 10&. The fractionation between quartz and pure A phase-separation model would also account for water is 13& at 170 C, and 13.8& at 180 C (Zheng both the observed variations in the Cl/Br ratios and the 1993). High concentrations of salts such as NaCl and/or KCl would lower the fractionation to about 0.5&(Horita et al. 1993). If high amounts of CaCl2 are con-tained in the fluid, the fractionation between quartz andthe fluid can be lowered to about 2& (Horita et al.
1993). However, the initial d18O value of the brine can beassumed to be between 8.5 and 10&. Thus, the initiald18O values as well as the dD values of both fluids aretypical for formation waters or metamorphic fluids, andtherefore have probably been modified by water–rockinteractions in the sub-surface from the typical valuesexpected of sabkha-type fluids. A mixing model where ahot, low-salinity fluid mixes with considerable amountsof a cold, near-surface brine would not account for thevariations in the d18O of the quartz and temperatures of175 C indicated by the high-salinity fluid inclusions. Ifwe assume that the temperature of the high-salinity fluid Fig. 11 Temperature–pressure–depth diagram showing the two- was less than 50 C, the fluctuation in temperature must phase boundary for a H2O–NaCl solution of seawater salinity be considerably higher than observed. Such a mixing (3.2 wt% NaCl equiv.; modified after Cunningham 1978; Bischoff model would only account for the observed variations in and Pitzner 1985). The shaded field marks the range of trappingtemperature fluid inclusions in quartz and stibnite from Mina salinity and temperatures (indicated by the presence of Nero´n. High-salinity fluids are probably the product of extreme monophase, aqueous inclusions) of fluid inclusions boiling (for details see text) exception of the sample which contains halite daughter different sources of sulfur (and metals) as well as dif- crystals in the fluid inclusions, all the other four quartz ferent depositional conditions.
samples from quartz–stibnite ores from Mina Nero´n There is strong evidence that quartz–stibnite miner- have a large variation in chlorine isotopes which corre- alization is the product of a non-adiabatic phase-sepa- lates with a large variation in Cl/Br ratios (Fig. 8). A ration (boiling) process under a hydrostatic pressure similar correlation was first observed for sphalerite- regime (<100 bar). Phase separation caused pro- hosted fluid inclusions from modern seafloor mineral- nounced fractionation of chlorine isotopes which cor- ization, where fluid-inclusion microthermometric data relate with the fractionation of Cl/Br ratios. The have revealed compelling evidence for two-phase sepa- chlorine isotope data clearly differ from other Spanish ration (Lu¨ders et al. 2002). However, negative d37Cl Pb–Zn mineralization which is assumed to have depos- values were not measured in fluid inclusions from sea- ited from brines similar to those in this study.
floor mineralization, due to the escape of significant The sources of antimony and sulfide are assumed to amounts of vapor from the systems. At the Mina Nero´n come from a hidden, underlying volcanic-hosted massive site, it seems that considerable amounts of vapor (and sulfide orebody. High-salinity fluids which are involved condensed vapor?) are trapped as fluid inclusions in vein in the formation of late-stage quartz, and the Pb–Zn quartz, as indicated by the presence of numerous, small mineralization at other localities, are not derived from vapor-rich inclusions besides aqueous two-phase inclu- dissolution of evaporites. They most closely resemble sions. These samples have negative d37Cl values and formation waters which originated as residual brines.
larger Cl/Br ratios when compared with the aqueous The sulfur isotopic compositions of galena samples two-phase fluid inclusions (Fig. 8). In this scenario, the from two occurrences indicate a sedimentary source of most saline fluids should have the most positive d37Cl sulfide, as it is also proposed for the metals from the Pb values. This is not the case at the Mina Nero´n where the isotopic signatures in galena (Marcoux et al. 1994). It is late-stage fluid trapped in clear zones of chevron quartz also likely that boiling occurred during the formation of has the lowest Cl/Br ratio and a d37Cl value close to 0&.
quartz–galena mineralization. Barite is thought to have This fluid clearly originated from a different source or formed by mixing of the ascending fluids with meteoric was produced by a different process, and indicates that at least two different fluid sources were involved during From detailed studies of vein-type deposits in the the formation of late-stage quartz II at the Mina Nero´n Iberian Pyrite Belt, it may be possible to trace deeper- site. The halogen data are most consistent with its origin lying massive sulfide orebodies. Although there are dif- being that of a highly evaporated seawater, but there is ferent sources for the metals and sulfur and different still the question of how the fluid became so hot. As depositional conditions for the polymetallic ores, their mentioned above, a simple mixing model where a cold, origin is apparently linked to the older massive sulfide near-surface brine mixed with an ascending hydrother- mal fluid should have produced a larger temperaturedecrease than observed. Therefore, the mixed brine ap- Acknowledgements We are particularly indebted to I.K. Sedler and pears to have had a temperature similar to that of the E.L. Wipfler for providing sample material from the studied vein ascending fluid. This brine may represent a formation mineralizations. We are grateful to M. Cathelineau and another water heated by the escape of steam from the upflowing anonymous Mineralium Deposita referee for their constructivereviews of the manuscript and useful comments.
fluid. The large bromine enrichment in the fluid mayhave been caused by halite precipitation. However, wecan exclude the possibility that this saline brine wasderived from the same ascending hydrothermal fluid which underwent extreme boiling at higher levels closeto the surface. If this had occurred, the d37Cl values Bailly L, Bouchot V, Be´ny C, Mile´si JP (2000) Fluid inclusion study of stibnite using infrared microscopy: an example from the would be expected to be even more positive than those we recorded in other samples, which is not the case.
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1ASSAY TECHNOLOGIES Anuradha RoyDel Shankel Structural Biology Center, High Throughput Screening Laboratory, Lawrence, Kansas Gerald H. LushingtonMolecular Graphics and Modeling Laboratory, University of Kansas, Lawrence, Kansas; LiS Consulting, Lawrence, Kansas James McGee Quantitative Biology, Eli Lilly and Company, Indianapolis, Indiana

Pre-IBC Special • September 2009 Cooke First Look: Cooke Panchros Like the Phoenix rising in Harry Potter, the venerable Cooke In September 9, 1926, Kinematograph Weekly reported: "Over Panchro name is being revived, or should we say, reinvented. a hundred Taylor-Hobson Cooke lenses of various focal lengths Film and Digital Times has learned that Cooke is working on a

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