Brine pool deposition for the Zn–Pb–Cu massive sulphide deposits of the Bathurst mining camp, New Brunswick, Canada. I. Comparisons with the Iberian pyrite belt

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Ore Geology Reviews 33 (2008) 329 – 351 www.elsevier.com/locate/oregeorev

Brine pool deposition for the Zn–Pb–Cu massive sulphide deposits of the Bathurst mining camp, New Brunswick, Canada. I. Comparisons with the Iberian pyrite belt Mike Solomon ⁎ Centre for Ore Deposit Research (CODES), University of Tasmania, GPO Private Bag 79, Hobart, Tasmania 7001, Australia Received 7 September 2006; accepted 3 April 2007 Available online 19 April 2007

Abstract The Ordovician Zn–Pb–Cu massive sulphide ore deposits of the Bathurst mining camp share many features with those of the Devonian/Carboniferous Iberian pyrite belt, particularly the tendency to large size (tonnage and metal content); shape, as far as can be determined after allowing for deformation; metal content, particularly Fe/Cu, Pb/Zn and Sn; mineral assemblages (pyrite + arsenopyrite ± pyrrhotite and lack or rarity of sulphates); sulphide textures (particularly framboidal pyrite); lack of chimney structures and rubble mounds; irregular metal or mineral zoning; and the low degree of zone refining compared to Hokuroku ores. The major differences between the provinces are the lack of vent complexes and the presence of Sn–Cu ores in the Iberian pyrite belt. There are also similarities in the geological setting of the two camps: both lie within continental terranes undergoing arccontinent and continent–continent collision, and in each case massive sulphide mineralisation followed ophiolite obduction; the ore deposits are associated with bimodal volcanic rocks derived from MORB and continental crust and marine shales; and mineralisation was locally accompanied or followed by deposition of iron formations. Fluid inclusion data from veins in stockworks from at least six of the Iberian massive sulphide deposits point to sulphide deposition having taken place in basins containing mostly spent saline, ore-forming fluids (brine pools), and it is suggested that most of the major features of the Bathurst deposits can be explained by similar processes. The proposed model is largely independent of ocean sulphate and O2 content, whereas low values of each are requisites for the current, spreading-plume model of sulphide deposition in the Bathurst camp. © 2007 Elsevier B.V. All rights reserved. Keywords: Massive sulphides; Bathurst; Iberia; Brine pool

1. Introduction The Bathurst mining camp, New Brunswick, Canada (BMC) includes the relatively well-described deposits such as Brunswick nos. 6 and 12, those of the Heath ⁎ Tel./fax: +61 3 62267208. E-mail address: [email protected]. 0169-1368/$ - see front matter © 2007 Elsevier B.V. All rights reserved. doi:10.1016/j.oregeorev.2007.04.001

Steele zone, Caribou, Canoe Landing Lake, Half Mile Lake, Key Anacon, Taylor Brook and Flat Landing Brook. Several authors (e.g., Franklin et al., 1981; Yang and Scott, 2003; Solomon et al., 2004) have drawn, or implied, certain similarities between the BMC massive sulphide ores — and their host rocks — and their analogues in the Iberian Pyrite Belt of Southwestern Europe (IPB).

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Fig. 1. The major Appalachian terranes of the New Brunswick area showing the approximate location of the Bathurst mining camp; from van Staal et al. (1998). These authors discussed the difficulties of assigning boundaries to terranes. The Red Indian Line separates Gondwanan and Laurentian terranes.

This paper compares the major massive sulphide Zn– Pb–Cu ores of the BMC with those examples from the IPB for which fluid inclusion and other data have led to an improved understanding of the likely manner of sulphide deposition on the sea floor. For most of the deposits the temperature–salinity data of these fluids imply a reversal of buoyancy on mixing with seawater, probably leading to sulphide deposition in brine pools (Turner and Campbell, 1987; Solomon et al., 2002). An Aristotlean syllogism is applied to suggest that the major Bathurst ores have so many features also seen in these IPB ores referred to above that they were probably also deposited in brine pools. Hutchinson (1973) classified volcanic-hosted or volcanogenic massive sulphide ores by mineral or metal content and the nature of the host rocks, and these aspects have been expanded on by Solomon (1976), Franklin et al. (1981, 2005), Franklin (1996) and Barrie and Hannington (1999). A refinement of the metallic classification as follows: Zn–Pb–Cu (Zn/ Pb b 5), Zn–Cu (Zn/Pb ≫ 5), and Cu (Cu N Zn ± Co), places both the IPB and BMC ores in the first group, except for a number of small Zn–Cu types associated with oceanic basalts of the Fournier Group in the BMC. With respect to host rocks, the Zn–Pb–Cu deposits in both camps belong to the bimodal-siliciclastic group of Barrie and Hannington (1999).

2. The geology of the Bathurst mining camp The Bathurst camp largely lies within the Gander Zone, one of several making up the lower Palaeozoic, orogenic collage of the northern Appalachians (van Staal et al., 1998; Fig. 1). This collage contains oceanic and continental arcs and microcontinents within the early Palaeozoic Iapetus Ocean, and continues north and east into the Caledonides through southern Ireland, Wales and England (Mac Niocall et al., 1997; van Staal et al., 1998). To the northwest of the Gander Zone lie the Exploits and Notre Dame sub-zones (of the Dunnage terrane), which flank the Laurentian continent, while to the southeast lie the Avalon and Meguma zones. The Red Indian Line separates the peri-Laurentian Notre Dame and the peri-Gondwanan Exploits sub-zones (Fig. 1). The Exploits sub-zone includes Cambrian to midOrdovician oceanic volcanic arcs and ophiolites. The terranes continue into Newfoundland where the geology has provided a picture of the likely Cambrian– Ordovician history of the northern Appalachians (van Staal et al., 1998). In the New Brunswick region ocean closure with attendant tectonism commenced in the Tremadoc/early Arenig with obduction of the Penobscot arc over the Gander terrane (the start of the Taconic orogeny?). The terranes of Fig. 1 were accreted to Laurentia during the Silurian–Devonian Acadian

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Fig. 2. Highly simplified map of the Bathurst mining district showing the locations of Zn–Pb–Cu massive sulphide deposits mentioned in the text; from the coloured maps of van Staal et al. (2003), except for Key Anacon which lies just east of the map. Small Zn–Cu massive sulphide deposits occur in the Fournier Group, relict ocean crust derived from adjacent oceanic terrane.

orogeny which involved southeast-directed thrusting of continental and oceanic slices over the Gander margin. van Staal et al. (2003) summarised the geology of the camp, describing the main nappes and also areas or groups of nappes of characteristic geology referred to as blocks or slivers (Figs. 2 and 3). Interpretations have been made difficult by folding, brecciation, shearing and internal remobilization during two major periods of deformation (De Roo and van Staal, 2003). The first, more intense phase (phengite dated from ca. 444 Ma) produced noncylindrical, asymmetrical folds and regional thrusting, and the second phase developed steep,

upright folds (van Staal et al., 2003); metamorphism involved temperatures of 350 to 400 °C and pressures of 550 to 800 MPa (Currie et al., 2003). 2.1. The Miramichi Group The oldest rocks found in the Sheephouse Brook, Tetagouche and California Lake blocks, the major mineralised units, belong to the Miramichi Group which consists mostly of feldspathic wacke and shales (oldest first, the Chain of Rocks, Knights Brook and Patrick Brook formations). The latter contains dark grey

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Fig. 3. Summary stratigraphies of the Iberian pyrite belt and the Bathurst mining camp; mainly from Quesada et al. (1994), Leistel et al. (1998a), Fonseca et al. (1999), Tornos (2006) and van Staal et al. (1998, 2003). VS: Volcano–Sedimentary Complex; PQ: Phyllite–Quartzite Formation. See Fig. 2 for location of suprasubduction calc–alkaline volcanics (shown in black) on the Ossa Morena Zone, and the IPB legend. Symbols for Fe formation and ores in the Iberian pyrite belt also apply to the Bathurst mining camp.

to black shales with some units laminated. Units up to 1 m thick with enhanced C and S values indicate occasional anoxic conditions of deposition (Goodfellow et al., 2003). Deposition probably took place before about 476 Ma (McNicoll et al., 2002, in van Staal et al., 2003). A gap of several Ma in the Arenig separates the Miramichi Group from younger formations, and evidence in Newfoundland suggests that this period marks that of the obduction of the Penobscot arc/backarc rocks southeast over the Gander margin (van Staal et al., 1998).

2.2. Tetagouche and California Lake groups In the Tetagouche block the Miramichi Group is overlain, in places conformably and in others disconformably, by the Nepisiguit Falls Formation, the oldest formation of the Tetagouche Group and the most highly mineralised, dated at 471 ± 3 Ma (Sullivan and van Staal, 1990). Younger formations in this group include the Flat Landing Brook, which hosts several massive sulphide deposits, and the Little River and Tomogonops formations (Fig. 3). In the California Lake block, units equivalent to

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the Nepisiguit Falls Formation include the Mount Brittain, Spruce Lake, and Canoe Landing Lake formations of the California Lake Group (Sullivan and van Staal in van Staal et al., 2003). Dacitic to rhyolitic, crystal-rich, volcaniclastic sandstones and mudstones dominate all formations other than the Canoe Landing Lake which contains largely basaltic rocks. U–Pb ages of acidic volcanic rocks range from about 473 to 468 Ma (Rogers et al., 2003). Shales and wackes are more abundant in the California Lake Group than in the Tetagouche, and host several ore deposits. According to Rogers and van Staal (2003) and Rogers et al. (2003), some of the basalts are transitional between MORB and island arc tholeiites and typical of intra-rift or back-arc basins. There is also evidence of extensive fractionation and assimilation of continental crust, and in some, characteristics of a subducted slab; others are closer to E-MORB. The units that followed the mineralised sequences generally include red/green shales (e.g., in the upper part of the Flat Landing Brook Formation of the Tetagouche Group), and maroon Fe–Mn shales and cherts are common in post-ore successions (Goodfellow et al., 2003). Pillow lavas near the top of the Flat Landing Brook Formation are locally interleaved with red shale and siltstone, heralding the overlying Little River (Tetagouche Group) and Boucher Brook formations (California Lake Group), aged about 464 to 451 Ma (van Staal et al., 2003), which consist of shales, siltstones and cherts, and alkalic basalts. The Tomogonops Formation comprises calcareous shale, greywacke and conglomerate, and may be discordant on the underlying rocks at regional scale. Thirty one massive sulphide deposits lie within the Tetagouche Group, 23 on the Brunswick horizon in the Nepisiguit Falls Formation, and 8 on the Stratmat horizon in the Flat Landing Brook Formation. Ten of the 13 in the California Lake Group occur in the Spruce Lake Formation which includes mainly acidic volcanic rocks and minor basalts but also shales and wackes; shales form the footwall to the major Caribou orebody and the Canoe Landing Lake orebody in the Canoe Landing Lake Formation. The Chester deposit in the Sheephouse Brook Group, in the south of the province, previously believed to be older than the others, has recently been dated as 469 Ma, more or less the same age as the Brunswick no. 12 deposit in the Nepisiguit Falls Formation (First Narrows Resources Corporation press release, 2006; www.uno.ca/documents/news/UNO_PR_02-1506_Chester_Age+Map.pdf). Iron formations overlie, and extend beyond, several deposits in the Brunswick ore horizon in the Nepisiguit

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Falls Formation (Goodfellow and Peter, 1996; Goodfellow and McCutcheon, 2003; Peter et al., 2003). They consist of siderite-, magnetite–siderite- and silicatedominated facies; the last, commonly termed “chlorite tuff”, and composed of quartz and a distinctive chlorite, is commonly distal to the ores (Peter et al., 2003). Interbedded hematitic and ferroan carbonate iron formations (hematite facies) overlie only the Austin Brook and Brunswick no. 6 orebodies in the Brunswick horizon. Hematitic and manganiferous bodies occur in the Little River and other post-ore formations. 2.3. Fournier Group This group, in the northern part of the camp, consists of sedimentary and basic igneous rocks that were obducted over the Gander terrane (van Staal et al., 2003). It is probably of late Arenig to Caradoc age, more or less the age of the mineralised sequences of the Tetagouche, California Lake and Sheephouse Brook formations, and is evidence of coexisting ocean. Rock types include those of back-arc basin crust and island arc, and contain a number of small, Cyprus-type, pyrite– chalcopyrite, massive sulphide lenses, generally associated with basalts, such as the Turgeon deposit (van Staal et al., 2003; Thurlow, 1993, in McCutcheon and Walker, 2005).

Fig. 4. The Iberian Peninsula, displaying the main continental terranes involved in the leadup to the Variscan orogeny; arrow shows approximate direction of movement of the South Portuguese Zone based on present cordinates; from Quesada (1998) and Leistel et al. (1998a). OMZ = Ossa Morena Zone.

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3. The geology of the Iberian Pyrite Belt The IPB lies within the Ibero-Armorican orogenic belt on the northern margin of the South Portuguese Zone, thought to represent part of Avalonia. This collided obliquely in the Variscan orogeny with the Iberian massif and Ossa Morena Zone (OMZ), also of Gondwanan affinity, during the closing of the intervening (Rheic) ocean (Dias and Ribeiro, 1995; Oliveira and Quesada, 1998; Sánchez-García et al., 2003; Fig. 4). The collision suture is marked by the Beja-Acebuches ophiolite complex, and an adjacent shale–greywacke assemblage, known as the Pulo do Lobo terrane (Quesada et al., 1994; Fig. 5). The main rock groups of the region are separated from each other by thrusts, and are, from north- to south (approximately from older to younger; Figs. 3 and 5): (a) The Ossa Morena Zone is a continental arc accreted during the late Proterozoic Cadomian orogeny to the southern margin of the Iberian massif. It consists of Neoproterozoic to Devonian sedimentary and volcanic rocks, with the southern part dominated by intrusions of diorite and granodiorite; the metamorphic and basic igneous rocks of the Aracena

metamorphic belt; and a large gabbroic complex known as the Beja Igneous or Gabbroic Complex (Castro et al., 1999; Tornos et al., 2002; SánchezGarcía et al., 2003; Tornos et al., 2005; Fig. 5). Two volcanic complexes crop out in the Portuguese section of the southern Ossa Morena Zone: an island arc sequence near Odivelas, of late Eifelian/ Givetian age (Conde and de Andrade, 1974; Santos et al., 1990), and the bimodal arc complex of the Toca da Moura area, of Viséan age (Santos et al., 1987; Pereira and Oliveira, 2001; Fig. 5). These complexes testify to north-directed subduction. (b) The Beja Acebuches ophiolite complex is up to 1.5 km wide and extends discontinuously along the southern margin of the Ossa Morena Zone. It consists of cherts, pillowed basalts, amphibolitic sheeted dykes, gabbroic cumulates, and serpentinised ultrabasic rocks, and has been interpreted as evidence of a pre-existing ocean (the Rheic) lying between the Ossa Morena Zone and the South Portuguese Zone (Fonseca and Ribeiro, 1993; Quesada et al., 1994). The basal parts of this assemblage show evidence at all scales of north-directed shearing (D1), probably related to

Fig. 5. Simplified geological map of the Iberian pyrite belt; from Quesada (1998), Leistel et al. (1998a) and Fonseca et al. (1999).

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northward obduction over the Ossa Morena Zone margin (Fonseca et al., 1999). Most of the Beja Acebuches basalts have suprasubduction characteristics, but some are transitional to N-MORB in composition, the combination suggesting a back arc origin (Quesada et al., 1994). In addition there are basaltic and dacitic volcanic rocks metamorphosed to eclogitic–bluschist facies and imbricated prior to, or during, D1 within Proterozoic/Cambrian sedimentary rocks. Their emplacement is thought to be related to the ophiolite obduction, suggesting a major collisional event at this time (Fonseca et al., 1999). (c) Further south the Pulo do Lobo terrane occupies a wide zone of similar lateral extent to the ophiolite. The dominant rocks are shales, greywackes, phyllites and sandstones of Frasnian to late Fammenian age, and basal units include amphibolitic basalts with transitional to N-MORB affinities, and minor acid volcanic rocks (Oliveira et al., 1986; Giese et al., 1994; Quesada et al., 1994; Z. Pereira, pers. comm., 2005). The terrane is thought to represent an accretionary prism developed during northerly subduction beneath the Ossa Morena Zone. (d) The oldest rocks of the IPB belong to the Phyllite– Quartzite or PQ Group, of Frasnian to Fammenian age, a variable assemblage of marine grey shale, siltstone, and quartz sandstone (Moreno et al., 1996; Carvalho et al., 1999). The base is not exposed but the formation must be at least several hundred metres thick; towards the top it contains limestone lenses, and increased evidence of tectonic disturbance, with development of small horst-and-graben basins. It is overlain conformably by the Volcano–Sedimentary Complex (VS), a marine assemblage less than 600 m thick of coherent, autoclastic and peperitic basic and acid rocks, reworked volcaniclastic rocks, monomict breccias, pumice-bearing mass flow breccia, and ash-rich, volcanic sandstones, and mudstones and sandstones (Boulter, 1993; Soriano and Martí, 1999; Tornos, 2006). The volcanic rocks are bimodal with respect to silica composition, andesitic rocks being present but relatively rare; acid compositions dominate (Munhá, 1983; Mitjavila et al., 1997; Rosa et al., 2004, 2006). The basaltic rocks are dominantly tholeiitic in composition, with a minority alkaline, while the acid and intermediate rocks are calcalkaline. The tholeiites can be explained by variable degrees of asthenospheric melting, plus mineral fractionation and

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assimilation of continental crust (Munhá, 1983; Mitjavila et al., 1997; Thiéblemont et al., 1998; Rosa et al., 2004, 2006). Purple shales occur near the top of the VS over much of the IPB (Oliveira, 1990). Jasperoid or hematitic chert lenses in the IPB occur just above, or many metres above, some of the ores and locally pass to non-hematitic chert or Mn carbonate–rhodonite lenses (Barriga and Fyfe, 1988; Leistel et al., 1998c). Some 90 massive sulphide bodies lie within the VS below the purple shales. Tornos (2006) subdivided the ores according to host rock, most of the largest lying within shales of varying thickness in the southern part of the belt (e.g., Neves Corvo, Tharsis and Aznalcóllar, Fig. 5) while others lie largely in acidic fragmental volcanic rocks with minor shales mainly in the central and northern zones where volcanic rocks are thickest. Two of the largest belong to the latter group (Aljustrel, Rio Tinto). Three of the shale-hosted deposits (Neves Corvo, Tharsis and Aznalcóllar) have been dated as late Strunian (360.5 to 360.7 Ma) using the palynology of the shales (Oliveira et al., 2004) and lie close to the base of the VS (Lombador stockwork is partly in the PQ Group). Equating the stratigraphies of Aznalcóllar, Los Frailes and Las Cruces (Conde et al., 2003), zircon TIMS ages for Las Cruces and Rio Tinto, near the top of the VS, suggest that the latter deposit is about 6 Ma younger (Barrie et al., 2002). Mineralisation probably occurred in pull-apart basins related to sinistral, sutureparallel, faulting during early stages of the continent– continent collision (Tornos et al., 2002, 2005). The VS is overlain conformably by up to 3000 m of turbiditic flysch facies of late Viséan to Westphalian age and derived largely from the Ossa Morena Zone (Oliveira, 1990), heralding the Variscan orogeny that involved at least two major episodes of south-verging thrust and fold structures and suture-parallel sinistral faulting (Quesada, 1998; Onézime et al., 2002; Soriano and Casas, 2002). Metamorphism ranged from prehnite–pumpellyite to lower greenschist in shear zones, indicating temperatures up to 300–350 °C and pressures ≤ 2 kb (Munhá, 1990). 4. Geological comparisons between the IPB and the BMC There are many similarities between the geological evolutions of each camp, viz. (a) the sedimentary and volcanic rocks of each camp were deposited on marine continental margins of Gondwanan affinity, associated with offshore ocean crust; (b) the margins were deformed

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as they closed with adjacent volcanic and/or continental masses; (c) ophiolite obduction preceded mineralisation; (d) both the IPB and the BMC were affected by several phases of deformation and metamorphism tens of Ma after massive sulphide mineralisation; (e) the ore-bearing sequences at mine scale in both areas are dominated by acidic volcanic rocks, mostly fragmental; interbedded shales occur in many cases and are the immediate host rocks in several of the larger deposits in the IPB (Los Frailes, Neves Corvo, Tharsis), and Orvan Brook and Canoe Landing Lake in the BMC (Goodfellow and McCutcheon, 2003; Tornos, 2006); (f) in each province the syn-mineralisation volcanic rocks are bimodal, with acidic dominant; the tholeiites show evidence of fractionation and assimilation of continental crust, and variable degrees of mantle melting, producing magmas with E- to N-MORB characteristics (Munhá, 1983; Mitjavila et al., 1997; Rogers and van Staal, 2003; Rogers et al., 2003; Rosa et al., 2004, 2006); alkalic rocks occur in each province, but are much more common in the BMC, in sequences that followed the main phases of massive sulphide deposition; (g) massive sulphide mineralisation commenced shortly after the beginning of volcanism; (h) Zn–Pb–Cu mineralisation recurred over periods of 5

to 6 Ma in different parts of each province; (i) based on (Zn + Pb + Cu) content the camps contain the two largest massive sulphide deposits worldwide (Brunswick no. 12, Rio Tinto; Fig. 6). Despite these similarities the proposed tectonic settings for each camp differ markedly. van Staal et al. (2003) favoured a setting like the Sea of Japan, a 1000 km-wide margin that has undergone intermittent extension for at least 50 Ma and contains only Hokurokustyle massive sulphides hosted by subduction-related rocks. The IPB, however, is seen as a margin in which sinistral, steep, belt-parallel faults related to the early stages of oblique continent–continent collision have initiated mantle magmatism and mineralisation in pullapart basins (Quesada et al., 1994; Solomon and Quesada, 2003; Tornos et al., 2005). 5. Fluid inclusions in deposits of the IPB and BMC, and their significance In comparing deposit styles, attention is focused on those IPB ores for which there are fluid inclusion data or the results of recent studies concerned with mechanisms of sulphide deposition. The quartz of stockwork veins of

Fig. 6. Proposed reconstructions of the original shape and scale of A. Rio Tinto massive sulphide body, from Williams (1934), Solomon et al. (1980) and Garçia Palomero (1990); B. The Brunswick no. 12 orebody, from Goodfellow and McCutcheon (2003). Note that no scale is given for B.

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6 deposits yielded fluid inclusion data that allowed Solomon et al. (2002) to predict with reasonable confidence that all or the majority of exhaling fluids would reverse buoyancy on mixing with seawater and pond in basins if they existed. The deposits involved are Aguas Teñidas Este (Sánchez-España et al., 2003; McKee, 2003); Aznalcóllar (Almodóvar et al., 1998); Masa Valverde (Toscano et al., 1997); Rio Tinto (Nehlig et al., 1998); and San Miguel and San Telmo (Sánchez-España et al., 2003). The fluid inclusions have been interpreted as representing the ore-forming fluids, later metamorphic fluids being CO2-bearing and having lower homogenisation temperatures and salinities (Moura et al., 1997; Sánchez-España et al., 2003). As discussed by Solomon et al. (2002), virtually all the fluids observed in fluid inclusions from Aguas Teñidas Este, San Telmo and San Miguel would, on mixing with seawater, have reversed buoyancy and ponded within a sea-floor basin if such existed. For Rio Tinto and Masa Valverde some fluids would remain buoyant on mixing but if early fluids were saline the existing pond would probably have trapped all exhaling fluid, as argued for Hellyer by Solomon and Khin Zaw (1997). At Aznalcóllar the nonreversing are as abundant as the reversing fluids, judging by the inclusion population, and the timing between types, unfortunately unknown, makes brine-pool deposition less assured, but Solomon et al. (2002) proposed that the Aznalcóllar deposits were so similar to the others that a different origin seemed unlikely. In addition to these studies, inclusions have been reported in three samples of quartz associated with the massive sulphide stockwork at Las Cruces (Knight, 2000). One contained low salinity (i.e., buoyant) fluids, the other two mostly saline fluids of reversing type. Moura (2005) found one sample of quartz in the Corvo orebody at Neves Corvo that contained fluids with salinities of about 30 wt.% NaCl equivalent. Relvas et al. (2006) reminded readers that the ore lenses of that deposit appear to have been deposited in basins on the sea floor. Only 38% of the fluid inclusions measured in the Feitais (Aljustrel) orebody by Inverno et al. (in press-a) were of reversing type but these authors and Barrett et al. (in press) argued for sulphide deposition in a basin. Not all IPB ores were necessarily deposited in brine pools: salinities only 50% higher than that of seawater were found by Inverno et al. (2000) in quartz in stockwork-like veins at Salgadinho, Portugal (no massive sulphide ore is present), and fluids with up to 7.4 wt.% NaCl equivalent occur in quartz associated with massive sulphides at the sub-economic Lagoa Salgada deposit (Jaques and Noronha, 2001). Tornos et al. (1998) and Tornos and Spiro (1999) proposed a basinal deposition for the Tharsis lenses, based

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on their morphology, textures, and other factors, and followed this with a study of the chemical composition of the host shales (Tornos et al., in press). The S/C, metal content, and other chemical data of the shales that host the main Tharsis lenses give a confused picture but data from a supposedly equivalent, pyritised shale sequence allowed conclusions relating to the oxicity of the ambient ocean water. The data indicate that (a) prior to sulphide precipitation ambient seawater was oxic or dysoxic, (b) during and for a period following sulphide deposition it was apparently anoxic, and (c) after deposition of about 50 m of shales it reverted to oxic. The anoxic phase was attributed to formation of a brine pool filled with spent ore-forming fluid rather than a coincidental, sudden change in ocean Eh. Owing to the more severe deformation and metamorphism of the BMC, the few fluid inclusion data available are of doubtful significance, as pointed out by Goodfellow and McCutcheon (2003). Goodfellow and Peter (1999) reported the finding of fluid inclusions in the Brunswick no. 12 stockwork with salinities between 3 and 8 wt.% NaCl equiv., very like the range found in modern massive sulphide systems. They also identified three-phase inclusions containing mostly silicates, carbonates and oxides, and CO2-bearing inclusions, both groups described as of metamorphic origin. Lusk and Krouse (1997) assumed that all the fluid inclusions they observed in sulphide ore from the same deposit were of metamorphic origin but they are unlike those observed outside the ores (Goodfellow and Peter, 1999). Th values ranged up to 440 °C and the salinities from about 4 to 10 wt.% NaCl equiv., plus a small group of 32 to 38 wt.%; the temperature range is almost certainly reflecting regional metamorphism (see Section 2) but the salinity range is not dissimilar to that found in the IPB studies described above, and also at Hellyer, Tasmania. The Lusk and Krouse inclusions do not contain CO2 which is found in inclusions in the stockwork and in later veins distant from the massive sulphides and thought to be of metamorphic origin (Goodfellow and Peter, 1999), thus there would appear to be a possibility that the saline inclusions are in fact primary fluids reworked during metamorphism. 6. Comparisons of Zn–Pb–Cu mineralisation style in the IPB and the BMC No two orebodies are exactly alike, either between or within massive sulphide provinces, but it is noted in this section that there are many similarities between the major deposits in the BMC and IPB (Table 1). The focus is on those features likely to be related to the mode of deposition.

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Table 1 Comparative features of the massive sulphide deposits of the Bathurst mining camp, the Iberian pyrite belt and the Hokuroku basin Feature

Bathurst mining camp

Iberian pyrite belt

Hokuroku Basin

Maximum size (Zn + Pb + Cu), Mt; total tonnage, Mt Original shape Metal ratios of ore Sn content, ppm Sulphur, wt. % Major ore types

25.6 (Brunswick 12); 230

20 (estimate) (Rio Tinto); 500?

2.1 (Matsumine); 30

Probably sheet-like High Fe/Zn, Fe/Cu, Pb/Zn Averages up to ca. 900 Average 40 Massive pyrite; massive py–sp–gn–ccp “bedded ore”; “vent complex” breccia; silica– py–ccp stockwork py, sp, gn, ars, po, tetr, cass, stan carbonates, quartz, phyllosilicates Largely stratigraphic

Sheet-like High Fe/Zn, Fe/Cu, Pb/Zn Samples up to 5000 35–51 Massive pyrite; massive py–sp– gn–ccp; silica–py–ccp stockwork. Sn and Sn–Cu at Neves Corvo py, sp, gn, ars, tetr, cass, stan, rare po quartz, carbonates, phyllosilicates Largely stratigraphic

Mound Low Fe/Zn, Fe/Cu, Pb/Zn v.low Average 16 Barite–gn–sp (kuroko); py–ccp (oko); silica–py–ccp (keiko) stockwork kuroko: sp, gn, py, ccp, tetr. oko: py, ccp, sp barite, quartz oko replaces earlier, overlying kuroko

Variable late Cu enrichment

Variable late Cu enrichment

Marked basal Cu and Fe enrichment py–barite? Framboids uncommon Yes

Metallic mineral content of ores Gangue minerals Relative ages of ore types (zoning) Zone refining

fO2 ore-forming fluid py–ars–po Textures Mineral banding, framboids, colloform Chimneys? No

py–ars Framboids, colloform, banding No

Data from Tanimura et al. (1983), Carvalho et al. (1999); Goodfellow and McCutcheon (2003); Solomon et al. (2004); Tornos (2006). Py: pyrite; sp: sphalerite; gn: galena; ccp: chalcopyrite; ars: arsenopyrite; tetr: tetrahedrite; cass: cassiterite; stan: stannite; po; pyrrhotite.

6.1. Classification and overall style Broadly speaking, the main massive sulphide lenses in each camp are stratiform and stratabound, sheet-like to lensoid, lie within shales and/or volcanic rocks, have hydrothermally altered footwalls containing stockwork vein systems, and can be classified as belonging to the Zn–Pb–Cu and bimodal-siliciclastic groups (Sáez et al., 1996, 1999; Goodfellow and McCutcheon, 2003; Tornos, 2006). Many deposits consist of more than one lens, for example, there are five at Neves Corvo in the IPB and six at Caribou in the BMC (Relvas et al., 2006; Goodfellow, 2003), though those at Caribou may be deformed relics of an earlier single lens (McCutcheon et al., 2005). The footwall stockwork zones appear to be of considerable lateral extent, unlike the equivalent zones in the Hokuroku Basin in which fluid flow appears to have been more focused (Bryndzia et al., 1983; Eldridge et al., 1983). This may partly due to smearing out of the footwall during deformation, but few stockworks have been investigated in depth. One of the least deformed in the IPB, the San Dionisio at Rio Tinto, has a cone-like stockwork zone that has been mined for Cu ore to a stratigraphic depth of about 400 m below the massive sulphide, however, shallower and less intensely mineralised zones stretch laterally beneath gossan assumed to have been derived from a massive sulphide sheet (Garçia Palomero, 1990; Fig. 7). Thus the wide spread of stockwork veining observed in both camps may be due to the deflection at shallow depth

of the rising ore-forming fluids by the overlying massive sulphide. Major differences in the ore types between the two camps are the lack of Sn and Sn–Cu ores like those of Neves Corvo (Relvas et al., 2006) in the BMC, and the presence of vent complexes overlying stockworks in the BMC (e.g., Fig. 12), there being no equivalent in the IPB. The vent complexes are breccias with clasts of pyrite, pyrrhotite, magnetite, chalcopyrite and stockwork material cemented by pyrite, pyrrhotite, chalcopyrite and other minerals. Goodfellow and McCutcheon (2003), after reviewing earlier ideas, suggested that the bodies

Fig. 7. The approximate Zn+ Pb+ Cu contents of the 10 largest Zn+ Pb+ Cu deposits worldwide, and the two comparable Zn–Cu types; from Garçia Palomero (1990), Leistel et al. (1998a), Large and Blundell (2000) and Tornos (2006).

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are of hydrothermal origin and part of the ore-building process. The presence of footwall clasts suggests that the breccias may have been caused by overpressured fluids disrupting the upper footwall and early formed sulphides (evidence of fluid overpressuring in the IPB has been described by Nehlig et al., 1998). 6.2. Sea floor deposition versus replacement The BMC massive sulphides are thought to have been deposited on the sea floor because of (a) primary bedding in pyritic layers, (b) the presence of iron formations overlying and extending laterally from the orebodies, and (c) the similarity of the overall structure (massive lenses over stockwork zones) to that of modern, sea floor, massive sulphide deposits (Goodfellow and McCutcheon, 2003). These authors also included the presence of lenses of framboidal pyrite as indicating sea floor biological processes. While this is supported as evidence for sea floor deposition in massive sulphide deposits, it seems more likely that rather than biological activity the framboids are the products of quenching of FeS-supersaturated fluids (Solomon and Gaspar, 2001). The criteria put forward by Goodfellow and McCutcheon (2003) to support open-cast sulphide deposition can also be applied to most of the IPB ores (Solomon et al., 2004; Tornos, 2006). In addition, slump, grading and breccia textures have been recorded in many deposits (references in Sáez et al., 1999) and particularly at Rio Tinto (Williams et al., 1975), Tharsis (Tornos et al., 1998; in press) and Aljustrel (Gaspar, 1996; Inverno et al., in press-a). Solomon et al. (2002) also included the contrast between the (mild) hydrothermal alteration that affected the hanging wall rocks with the (severe) alteration of the footwall, and Tornos and Conde (2002) described a subcylindrical burrow and supposed biological escape structures at the base of a Tharsis lens. Goodfellow and McCutcheon (2003) described local sulphide replacement of the footwall rocks in the BMC. In the IPB, replacement by pyrite of altered rocks immediately below massive sulphide bodies is common, for example a significant part of the stockwork zone has been replaced near the Lago pit, Rio Tinto (Solomon et al., 1980) and at San Miguel (Tornos, 2006); both examples are hosted by fragmental, acid, volcanic rocks. Almodóvar et al. (1998) suggested that the Aznalcóllar ore lenses were formed by replacement of shales and Sáez et al. (1999), adapting a genetic model of Lydon (1988), proposed that the shales in many other deposits acted as a cap below which replacement took place. In addition, Tornos (2006) proposed that many of the massive sulphide bodies situated along the northern

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margin of the IPB, where shales are minor or absent (including Feitais, Aguas Teñidas Este, San Miguel and San Telmo), were of replacement origin. However, Allen (2001) found no supporting field evidence for replacement at Aznalcóllar, and Tornos (2006) provided no evidence from the northern deposits other than local footwall replacement. A strong case for sea floor deposition was presented for Feitais by Inverno et al. (in press-a), and McKee (2003) was unable to decide between brine-pool deposition and sub-seafloor replacement for Aguas Teñidas Este. Both Inverno et al. (in press-a) and Tornos et al. (in press) criticised the model of Barriga and Fyfe (1988) that envisaged sulphide deposition in open space beneath chert caps at Feitais and Tharsis; this model was partly put forward because of the lack of evidence for more than small-scale sulphide replacement of the host rocks. 6.3. Shape of the massive sulphide lenses Considerations concerning the original form of the massive lenses have to take into account the effects of deformation, which in the BMC, and locally in the IPB, can be severe. Solomon et al. (2004) were able to present only a few reliable figures for primary aspect ratio from the IPB, including Rio Tinto which is one of the least deformed deposits though folded into a broad anticline and locally affected by thrusting and post-ore dykes (Williams et al., 1975; Solomon et al., 1980). Solomon et al. (2004) gave an estimate of 30 to 35 for the aspect ratio (maximum length/average thickness) of the original massive sulphide, using data from Garçia Palomero (1990). Despite the intense deformation and metamorphism in the BMC, and obvious brecciation and reorganisation (De Roo and van Staal, 2003), Goodfellow and McCutcheon (2003) concluded that there had not been sulphide remobilization and transfer greater than the deposit scale. The preservation of delicate textures suggests that internally the ores underwent less rearrangement than the strongly cleaved wall rocks, a feature seen in many massive sulphide provinces. The Canoe Landing Lake deposit in the BMC has a strike length of 1.2 km with an aspect ratio N 250, and the Caribou deposit is N1.5 km long with an aspect ratio N 30. Although the original shapes are unknown an original high aspect ratio seems likely, judging by reconstructions (Goodfellow, 2003; McCutcheon and Walker, 2005). Goodfellow and McCutcheon (2003) modelled the Brunswick no. 12 orebody with a vent complex overlain by layered pyrite– sphalerite–galena ore and, above, a pyrite-dominant assemblage (Fig. 6).

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Table 2 Approximate average tonnages and grades of the ore deposits of the Iberian pyrite belt and the Bathurst mining camp, and of four individual examples, including a resource identified within the Feitais deposit Province

Mt

wt.% Zn

wt.% Pb

wt.% Cu

Ag, ppm

Au, ppm

Iberian pyrite belt (Leistel et al., 1998a; Carvalho et al., 1999) Bathurst mining camp (Goodfellow and McCutcheon, 2003) Caribou (Goodfellow, 2003) Brunswick no. 12 (Goodfellow and McCutcheon, 2003) Los Frailes (Leistel et al., 1998a; Tornos, 2006) Feitais, Aljustrel Leistel et al. (1998a), total Dawson et al. (2001)

1765 497 69 230 70

2.0 4.7 4.3 7.7 3.9

0.7 1.8 1.6 3.0 2.2

1.3 0.6 0.5 0.5 0.3

26 51 51 91 62

0.5 0.5 1.7 0.5 0.4

3.7 6.0

1.2 1.8

0.4 0.2

44 66

0.7

6.4. Size On the basis of (Zn + Pb + Cu) content, the IPB and BMC camps account for 8 of the largest 10 Zn–Pb–Cu deposits worldwide, the remaining two being Rosebery and Hellyer in the Mount Read province, Tasmania (Table 1; Fig. 7). The first two, Brunswick no. 12 and Rio Tinto, are the two biggest massive sulphide deposits of any type, though there is considerable uncertainty about the tonnage data for the latter. Kidd Creek and Gaiskoye are only slightly smaller but are of Zn–Cu type. The (Zn + Pb + Cu) content of the IPB is estimated at 70 (Leistel et al., 1998a; Carvalho et al., 1999), and of the BMC about 35 Mt (Goodfellow and McCutcheon, 2003; Table 1). No other Zn–Pb–Cu province can match these figures, and particularly provinces with Hokuroku Basin-type ores, e.g., the total Zn + Pb + Cu content of the Hokuroku Basin is 7.7 Mt (Tanimura et al., 1983; Table 1). 6.5. Metal content By comparison with Australian Phanerozoic ores (Large, 1992), metal grades in both camps tend to be

54.5 18.4

low, though the BMC ores appear to be richer overall (Goodfellow and McCutcheon, 2003; Tornos, 2006). They are dominated by pyrite, with sulphur contents mostly 35 to 51 wt.% S in the IPB, and an average ca. 40 wt.% S in the BMC (Carvalho et al., 1999; Goodfellow and McCutcheon, 2003). Approximate average ore grades in the IPB and BMC are given in Table 2, together with three current resource grades. By contrast, the ores of the Hokuroku Basin, which include significant barite, average 16 wt.% S (Tanimura et al., 1983). The ores of each camp are characterised by high Fe/Cu values, with the BMC ores tending to higher values, perhaps related to lower Cu contents (Fig. 8). These values set the ores apart from those of the Hokuroku Basin, and may be related in some degree to the oxidation potential of the ore-forming fluids, the ratio Fe/Cu decreasing with increasing fO2 at constant pH (Solomon et al., 2004; Fig. 9). The reduced nature of the fluids in the IPB is indicated by the pyrite–arsenopyrite ± pyrrhotite assemblage in, for example, the stockwork veins and/or massive sulphides of Feitais and Moinho (Aljustrel), Tharsis, Aznalcóllar and Rio Tinto, and in a number of other deposits (Marcoux et al., 1996; Gaspar, 1996). For

Fig. 8. Zn/Cu versus Fe/Cu for the Zn–Pb–Cu ores of the Hokuroku Basin, the Iberian pyrite belt (filled circles) and the Bathurst mining camp (open circles); from Tanimura et al. (1983), Goodfellow and McCutcheon (2003) and Solomon et al. (2004).

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averaging 0.85 ppm (Leistel et al., 1998a,b; McClenaghan et al., 2003). There are wide variations within deposits in each camp, but in each Au occurs in two associations: As + Ag and Co + Bi. 6.6. Metal zoning

Fig. 9. Fe–S–Cu–Zn diagram at the conditions shown, with Zn, Fe and Cu solubilities in equilibrium with sphalerite, pyrite and chalcopyrite respectively. Drawn from Walshe and Solomon (1981) and Cooke et al. (2000).

the BMC, Goodfellow et al. (2003) reported arsenopyrite contents in the bedded pyritic ores, and apparently primary (though metamorphosed) minor pyrite–pyrrhotite assemblages in the stringer veins and vent complexes. Pyrrhotite–pyrite assemblages occur in both stockwork and massive bedded ore at the Halfmile Lake deposit and the Taylor Brook deposits and pyrrhotite is commonly present as inclusions in pyrite, for example, the Murray Brook deposit (Adair, 1992; McCutcheon and Walker, 2005). Yang and Scott (2003) showed that the ores of both camps shared a range in Pb/Zn ratio of 0.3 to 0.6, setting them apart from Hokuroku massive sulphides with b 0.3. The difference may be due to the greater involvement of continental crust beneath the IPB and the BMC in the generation of volcanic rocks and/or greater crustal involvement in supplying the Pb and Zn of the oreforming fluids. There are Sn values for single samples for the IPB ores other than the high grade Corvo and Graça orebodies at Neves Corvo, values ranging from about 5 to 5000 ppm, with the highest values from Rio Tinto, the largest orebody. There is a crude positive size-grade correlation (Leistel et al., 1994; Marcoux et al., 1996; Leistel et al., 1998a; Fig. 10). BMC massive sulphide lenses have average Sn contents from about 20 to 900 ppm, also with a positive correlation between size and Sn grade; individual samples range up to several thousand ppm, and the Sn appears to be associated with sphalerite and galena (Goodfellow and McCutcheon, 2003). The Sn values are high compared to other Zn– Pb–Cu provinces such as Mount Read. In the IPB, Au contents range between 0.1 to about 4.0 ppm, and in the BMC from 0.018 to 3.07 ppm,

The Cu/(Zn + Pb) ratio is generally higher in stringer zones than in overlying massive sulphides, and in some ore lenses the trend continues towards the top of the massive sulphide. However, the style of zone refining seen in Hokuroku massive sulphide deposits, resulting from replacement of early-formed minerals by later ones at higher temperature, and producing pronounced vertical metal and mineral zoning, is not a feature of the deposits of either camp. In the IPB the lower parts of a number of the massive sulphide lenses are richer in Cu (Marcoux et al., 1996) but generally without a uniform Cu-rich layer, for example, San Dionisio at Rio Tinto (Williams, 1934 and figure 136 therein; Garçia Palomero, 1990), Aguas Teñidas Este (Pons et al., 1999), and Feitais (Dawson et al., 2001; Barrett et al., in press). Above the Cuenriched zones there is no consistent variation in Zn and Pb; for example, in the Feitais lens the Cu zone is overlain by a low grade pyritic zone which grades up to a Zn–Pbenriched zone (Dawson et al., 2001). At Tharsis there is little evidence of basal Cu enrichment, and chalcopyritic lenses occur near the hanging wall (Tornos et al., in press). Cu, Pb and Zn distributions at Masa Valverde, Aznalcóllar and Las Cruces vary between lenses but metal distribution has been complicated by ore-parallel thrusting (Almodóvar et al., 1998; Ruiz et al., 2002; Doyle et al., 2003).

Fig. 10. Average Sn contents of massive sulphide ores in the BMC (filled circles) versus size (production + reserves) and the ranges of individual analyses (vertical lines) from various IPB massive sulphide ores (Leistel et al., 1994, 1998a; Marcoux et al., 1996). Values from Rio Tinto reach 5000 pp Sn; the Lombador line is the average composition of the orebody.

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In the BMC the vent complexes are richer in Cu and poorer in Zn and Pb than overlying massive sulphides. At Caribou and other deposits, there is a lateral decrease of Cu/(Cu + Pb + Zn) away from the vent complex (Goodfellow, 2003). The most striking zoning in the BMC is in the Brunswick no. 12 ore, in which the upper zones (Bedded Pyrite) are strongly pyritic and lower in Zn and Pb than underlying massive sulphide (Bedded Ore), which overlies the vent complex (Goodfellow and Peter, 1996). At Caribou, Zn and Pb tend to be enriched towards the top at least in parts of the lenses, though with little apparent variation stratigraphically in the Pb/Zn value (Goodfellow, 2003; Fig. 6). The Key Anacon deposit is zoned from a Cu-rich base to Zn–Pb-rich top (McCutcheon and Walker, 2005). A similar pattern has been observed at the Camelback deposit and Ag is enriched in the tops of the lenses (McCutcheon and Walker, 2005); similar Ag enrichment occurs in the Restigouche ores (Goodfellow and McCutcheon, 2003; Goodfellow, 2003; McCutcheon and Walker, 2005). 6.7. Mineral content All massive sulphide and stockwork vein mineral assemblages in both camps are dominated by pyrite, which is generally associated with sphalerite, galena, chalcopyrite and tetrahedrite–tennantite, in order of abundance (Marcoux et al., 1996; Goodfellow and McCutcheon, 2003). In some of the IPB massive sulphides, arsenopyrite is an essential mineral (e. g., at Feitais, Gaspar, 1996) but in others it is rare (e.g., Tharsis, Marcoux et al., 1996); Marcoux et al. (1996) described it as “ubiquitous without ever being truly abundant”. Pyrrhotite and magnetite occur in a few (e.g., Aznalcóllar, Rio Tinto, Moinho and Feitais, Yamamoto et al., 1993; Marcoux et al., 1996; Gaspar, 1996). Arsenopyrite is common in the bedded ores in the BMC and magnetite less so (Goodfellow and McCutcheon, 2003) while several contain pyrrhotite (e.g., Jambor, 1979; Adair, 1992; McCutcheon and Walker, 2005); pyrrhotite and magnetite appear also in the vent complexes and stringer zones. It is not clear how much pyrrhotite and magnetite is primary and how much due to metamorphism. There do not appear to be any consistent spatial variations in mineral compositions, such as the FeS content of sphalerite, within the massive sulphides in either province. Cassiterite and to a lesser extent stannite is present in highly variable proportions in many massive sulphides and stockworks in both camps, and cassiterite is the main Sn component of the high grade Sn ore lenses in and below the Corvo orebody at Neves Corvo. Marcoux et al. (1996) reported unusual mineral assemblages confined to the stockwork veins of several IPB ores (e.g., Tharsis,

Aznalcóllar, Rio Tinto), predominantly early Co sulpharsenides and later, higher temperature, Bi sulphides. Barite has been recorded from several mines in the IPB. At Feitais it is present in very small amounts in the massive sulphide, being more common near the hanging wall and extremities, and as late veins (Barriga, 1983; Gaspar, 1996); at Rio Tinto it occurs in late veins in massive ore (Williams, 1934). It is a minor component of the gangue at Las Cruces, along with quartz and carbonate (Knight, 2000; Doyle et al., 2003). The main barite occurrence is at San Telmo where it is common in banded, sphalerite-rich ore (Yamamoto et al., 1993). At Aguas Teñidas Este it occurs only in late structures (McKee, 2003). Barite is very rare in the BMC, occurring only in the vent complex associated with pyrite at Brunswick no. 12 mine, and in the massive sulphide and the hanging wall of the small, very low grade Louvicourt deposit (Goodfellow and McCutcheon, 2003). Other gangue minerals in the IPB massive sulphides include quartz, carbonates, phyllosilicates, Fe oxides and rutile (e.g., Barriga, 1983; Gaspar, 1996; Tornos et al., 1998); with barite, they make up only a few wt. percent of the ores. Barriga and Kerrich (1984) were able to obtain depositional temperatures by measuring oxygen isotope fractionation between quartz and chlorite separated from massive ore at Feitais. Goodfellow and McCutcheon (2003) described the gangue in the BMC bedded ores as including carbonates, barite, magnetite, quartz and phyllosilicates (or metamorphic equivalents). 6.8. Textures There are a number of textures common to the massive sulphides of both camps that are visible in less deformed areas or samples, particularly framboidal and colloform pyrite, mineral banding, bedding and small-scale breccias; also common to both groups is the absence of chimney structures. Framboidal pyrite may be observed in most IPB deposits, and in some cases framboidal pyrite bands are interleaved with polymetallic bands (Almodóvar et al., 1998; Velasco et al., 1998; Sáez et al., 1999). Read (1967) pictured continuous framboidal pyrite texture extending over areas of N 1 mm2 from the San Dionisio massive sulphide at Rio Tinto, observations that match closely those of Solomon and Gaspar (2001) on Hellyer ore. Framboidal textures occur in bedded polymetallic ores and bedded pyrite assemblages in the BMC, commonly associated with colloform structures (Chen, 1978; Goodfellow and McCutcheon, 2003). Mineral banding is localised in the IPB ores but sphalerite–galena- and pyrite-rich bands have been found

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in most deposits. They have been interpreted as primary or the product of deformation (Barriga, 1983; Garçia Palomero, 1990; Sáez et al., 1996, 1999; Doyle et al., 2003; Inverno et al., in press-a; Tornos et al., in press). Barriga (1983) and Gaspar (1996) described small scale slumping and graded bedding at Feitais, and Sáez et al. (1999) referred to slump, graded bedding and breccias in many IPB deposits; numerous massive sulphide bodies in the IPB include stratiform lenses of shale. Inverno et al. (in press-b) pictured graded bedding, and described the fragmental, bedded nature of the Lombador ore at Neves Corvo. For the BMC Goodfellow and McCutcheon (2003) described “bedded ore” and “bedded pyrite” as major ore types in the BMC; streaky lenses of sphalerite (±galena) lie in “brecciated and fractured” pyrite to give a crude banded effect. Though much of the mineral layering in the bedded (polymetallic) ores is the product of intense shearing (De Roo and van Staal, 2003), less deformed samples appear to show pre-deformational layers of sphalerite–galena and pyrite that have the appearance of bedding; some samples also contain layers of shale-like material. The more obscure banding in the “bedded pyrite” appears to be due to variation of grain size difficult to distinguish from structural foliation (see Fig. 10 of Goodfellow and McCutcheon, 2003). Davies (1980, in Franklin et al., 1981) reported slump fold and other soft sediment structures in the Zn–Pb ores. In the IPB, breccias suggestive of reworking of newly deposited sulphides are not uncommon, for example, at Feitais (Barriga, 1983). At Tharsis there are fragmental pyritic rocks with shale matrices that show conspicuous simple, graded and cross bedding, testifying to open-cast

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reworking of sulphide bodies and/or particle settling (Tornos et al., 1998). While many breccias in the BMC ores have been interpreted as due to deformation, at least one, the Canoe Landing Lake deposit, exhibits evidence of reworking because there are shales with clasts of pyrite and banded mixed sulphides (McCutcheon and Walker, 2005). 6.9. Sulphur isotopes The sulphur isotope ranges of the sulphides in the deposits in the the two camps are different (Fig. 11). In the IPB they have a total range of about −33 to 12‰ (Velasco et al., 1998), unusually wide for volcanic-hosted massive sulphide provinces (Huston, 1999) and thought to involve contributions from bacterially reduced seawater sulphate (Velasco et al., 1998). For individual orebodies the bulk of the data have smaller ranges, for example, San Dionisio at Rio Tinto ranges from −1.3 to 7.3‰, n = 13 (Eastoe et al., 1986); for Tharsis the spread is mostly from −10.1 to 1.4‰, together with 4 samples extending to −33‰, n = 67 (Tornos et al., in press); for Feitais it is from about −7 to 4.7‰, with a tail of 5 samples extending to −15.4‰, n = 32 (Inverno et al., in press-a). Significant biogenic contributions are apparent in Tharsis and Sotiel, both lying in relatively thick shale sequences, the biogenically reduced sulphur probably at least partly derived from H2S generated by seawater sulphate reduction in the orebody footwall (Tornos et al., in press). δ34S values for massive sulphides in the BMC range between about zero and 20‰ (Goodfellow and McCutcheon, 2003), but, as with the IPB, individual deposit ranges

Fig. 11. The approximate distributions of δ34S values from massive sulphide ores in the Iberian pyrite belt and the Bathurst mining camp; from Velasco et al. (1998) and Goodfellow and McCutcheon (2003). ‘n’ indicates the number of analyses.

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are mostly smaller, for example, in the Tetagouche Group bedded massive sulphides at Brunswick no. 12 lie between 13.1 and 18.1‰, n =18 (Goodfellow and Peter, 1996), and at Heath Steele between 7 and 16‰, n = 254 (Lusk and Crocket, 1969). However, in the California Lake Group the ranges are greater, for example, Caribou is from 1.1 to 9.6‰, n =35 (Goodfellow, 2003) while Nepisiquit ‘A’ is about 3 to 17‰, n= 8, apparently the maximum variation in the BMC (Goodfellow and McCutcheon, 2003). There are no significant spatial differences in δ34S within massive sulphide bodies in either camp except for an increase of several per mil in passing upwards from the bedded ores to the bedded pyritic ores at Brunswick no. 12 (Goodfellow and Peter, 1996) and a smaller decrease upwards at Heath Steele B-1 (Lusk, 1972). The narrower range overall for the BMC sulphides may be in part the result of regional metamorphism (Lusk and Crocket, 1969; Lusk, 1972). In several of the IPB deposits, and more generally in the BMC, the stockwork (and vent complex) sulphides have consistently more positive values than the massive sulphides by 1–2‰. Solomon (1999) suggested that the stockwork values might reflect sulphide deposition under equilibrium conditions, with 1 to 2‰ being a likely fractionation effect, while the quenched sulphides in the massive ore reflect a lack of isotopic equilibration, the sulphides returning the isotopic composition of the ore-forming fluid. This suggestion assumes that all the sulphides are more or less coeval. Barite δ34S values in the two camps are close to those of coeval seawater sulphate except at San Telmo in the IPB where they are, for reasons unknown, 5 to 6‰ lower. There is only one value for the BMC, from barite at Brunswick no. 12. There appears to be general agreement that seawater sulphate is one of the major sources of sulphur (Velasco et al., 1998; Goodfellow and McCutcheon, 2003). The difference in the bulk δ34Ssulphide values for the two camps is partly explained by the difference between seawater sulphate values during the Ordovician and at the Devonian/Carboniferous boundary (Claypool et al., 1980; Fig. 11) but may also partly result from different values for ΔH2S-SO4. Ohmoto and Goldhaber (1997), using data from Cambrian–Ordovician sedimentary rocks in Nova Scotia, concluded that the ΔH2S-SO4 value in this period could be about 20‰, compared to the apparent 40 to 50‰ of the Devonian/Carboniferous. If the Ordovician figure is correct then δ34Ssulphide data for the BMC ores could include biogenically derived values, and the Caribou data (above), for example, might be interpreted as due to biogenic reduction of seawater sulphate in a more or less open system. Several stockworks in the IPB have δ34Ssulphide values close to zero (e.g., Tharsis, Aznalcóllar), and in

the Sn–Cu-rich Neves Corvo deposit the Lombador ore lens yielded values close to the mantle-like signatures seen in proximal Sn and Sn–W deposits in eastern Australia (Inverno et al., in press-b). Thus the spread of δ34Ssulphide values in the IPB may be influenced by a magmatic, mantle-derived component. 7. A brine-pool model for sulphide deposition in the Bathurst mining camp 7.1. Previous models As outlined in a review by McCutcheon et al. (2003), the Bathurst Zn–Pb–Cu deposits were linked with those of the Hokuroku Basin (the “Kuroko” ores) by the early 1960's, following recognition of their syngenetic nature (Stanton, 1959); volcanic exhalative models of sulphide deposition have since prevailed. During the last decade several workers have proposed that sulphide deposition occurred from stagnating buoyant plumes within the anoxic layer of a stratified ocean. Goodfellow and Peter (1996), Goodfellow and McCutcheon (2003) and Goodfellow et al. (2003) suggested that during BMC mineralisation the ambient ocean was stratified, with a bottom anoxic layer within which sulphate was largely converted to aqueous sulphide, and that this sulphide-rich fluid was the source of the reduced sulphur in the mineral deposits (Fig. 12). The exhaling fluids were taken to be of buoyant, non-reversing type, allowing sulphide-laden plumes to rise until a neutral buoyancy level was reached and then spread laterally, depositing the bedded ores and bedded pyrites by settling (Fig. 12). The anoxic ocean layer inhibits oxidation of the suspended particles and the accumulated sulphide mass. This meretricious proposal can explain the shape and the bedded nature of the ores, and the absence of contemporaneous oxidation, however, Solomon (1999) suggested that brine-pool deposition equally satisfies the evidence. The likely ocean composition during Bathurst mineralisation, a vital part of the model, is tackled in the accompanying paper (Solomon, 2008) from which it is concluded that there is considerable doubt about an anoxic, sulphate-deficient ocean during mineralisation. Even if the ocean was anoxic, advanced reduction of sulphate is unlikely so the proposed buoyant fluids would have precipitated sulphates on mixing with ambient seawater, leading to development of chimney and mound structures. The lack of these features, the paucity of evidence for involvement of ambient seawater, and the sulphur isotope data are incompatible with the postulate.

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Fig. 12. A simplified version of the sulphide depositional model for Bathurst massive sulphide deposits, from Goodfellow and McCutcheon (2003).

7.2. The brine pool Empirical similarities between the massive sulphides of the IPB and BMC camps suggest that depositional models developed for the IPB ores using fluid inclusion and other data may apply to those of the BMC. Similarities that may be related to depositional mechanisms include (a) primary shape or form (as far as can be determined); (b) size relative to other styles of massive sulphide deposition; (c) metal content, overall grades and Pb/Zn, Fe/Cu, Zn/Cu and Sn values; (d) mineral composition of ore and gangue; (e) mineral and metal zoning, or lack thereof, (f) textures, and (g) lack of penecontemporaneous oxidation. These features mostly set the IPB and BMC ores apart from those of the Hokuroku Basin (Table 1). The only major differences observed between the BMC and IPB camps are the lack of vent complexes and the presence of high grade Sn– Cu ore in the IPB (although the ores of both camps have high Sn contents). The brine-pool model (Fig. 13) can account for many aspects relating to the size, shape, composition (particularly the scarcity of barite), textures and lack of oxidation of the major BMC deposits. It is based on knowledge of processes in the Atlantis II Deep and the related theoretical and experimental modelling of McDougall (1984) and others. Sulphide deposition by basin-filling has the capacity to trap all or most of the exhalative metal content, assuming sufficient sulphur, potentially accounting for the large tonnages of this type of orebody compared to black-smoker-type deposits (see discussion in Solomon et al., 2004). The final primary aspect ratio and size of the ore deposit are controlled by the shape and extent of the confining

basin, the depth of the pool and the volume flux of the exhalative system, for example, a high volume flux and wide pool would allow the plume to spread laterally for a considerable distance and carry sulphide particles over a large area, over and beyond the stockwork feeder zone. Settling of very fine sulphide particles from currents circulating within the pool would normally be very slow but flocculation would dramatically increase settling rates (Solomon and Gaspar, 2001); the circulating currents carry much of the suspended material to the bottom of the basin (Fig. 13). The nature of the prominent mineral banding (pyrite and sphalerite– galena bands) in the massive sulphide ores cannot reflect simple gravitational settling (Solomon et al., 2004) and has yet to be properly explained. Framboidal textures appear to be characteristic of BMC ores. Butler and Rickard (2000) have shown that Fe-monosulphides precipitated from strongly supersaturated solutions form framboidal and euhedral pyrites probably via oxidation of mackinawite by H2S in stoichiometric reactions; framboidal as well as euhedral forms are favoured when the level of supersaturation is high. Solomon and Gaspar (2001) related the abundance of framboidal textures in the Hellyer massive sulphide to the quenching of hot fluids in a brine pool, with the most favourable conditions (i.e., more oxidising) occurring near the double-diffusive interface with oxic seawater. Brine pool-type processes only involve ambient seawater during (a) early growth of the pool as exhaling fluid mixes with seawater, (b) subsurface entrainment into the stockwork veins, (c) diffusion of components across the seawater/brine interface and (d) plumes overshooting that interface. If Ba is present in the rising ore-forming fluids then in the early stages anhydrite and

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Fig. 13. A. An alternative model for sulphide deposition in the BMC involving development of a brine pool, based on McDougall (1984) and Solomon and Gaspar (2001). The pool surface is also an anoxic/oxic boundary. Pf N Ph + Pl + T refers to overpressured fluids rising in the stockwork pipe. B. Outflow at the lowest level of the basin walls could lead to transport of soluble metal species and metal sulphide particles into larger, shallower basins, forming small sulphide bodies or reduced iron formation.

barite are likely to be precipitated in chimneys and mounds. As the basin fills with reduced, ore-forming fluid having negligible sulphate the early sulphates are replaced or dissolved. The lack of more than scarce barite (see Section 6.7) within the BMC and IPB massive sulphides is in stark contrast to Hokuroku ores, but its presence, though minor, is considered to be evidence that ambient seawater contained sulphate. The Goodfellow and McCutcheon (2003) model requires an almost sulphate-free ocean which is thought (Solomon, 2008 — part II of this contribution) to be unlikely, even in an anoxic ocean. The relatively minor involvement of ambient seawater compared to Hokuroku and modern black smoker systems might explain the lower apparent oxidation potential of the ore-forming fluids in brine pool-type deposits, as discussed by Solomon et al. (2004), because rapid mixing with seawater can dramatically increase f O2 (Ohmoto et al., 1983). However, the low f O2 (near the CO2/CH4 boundary) of the BMC and IPB fluids may be due to interaction with carbonaceous shales in the

continental margin successions, or reflect expulsion of reduced fluids from Sn–W-type magmas (Relvas et al., 2006; Inverno et al., in press-b) or Earth's core (Walshe et al., 2005), so it is possible that the higher f O2 of the Hokuroku fluids simply reflects limited interaction with such powerful reductants. Goodfellow and McCutcheon (2003) suggested that the scarcity of quartz in the ores did not favour brinepool deposition. Silica enrichment is characteristic of the central column of the stockwork zones in each camp (e.g., Lentz and Goodfellow, 1996; Inverno et al., in press-a) but average SiO2/Al2O3 ratios in the BMC massive sulphides range from only 4 to 6 (no comparable data is available for the IPB). This is put down to the kinetics of silica precipitation, residence time for the spent ore-forming fluids in the main basin being short, a thesis based on the lack or scarcity of extraneous material such as sediment being introduced during sulphide mineralisation. Ohmoto et al. (1983) argued similarly for the Hokuroku ores, the silica being largely lost to the buoyant plumes. In the model of

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Fig. 12 it is not clear why in many cases the more silica is not deposited from the proposed laterally spreading plumes. Following sulphide precipitation the spent pool fluid protects the sulphides from oxidation. Oxidation could be achieved by protracted exchange across the doublediffusive brine–seawater interface but the pool is likely to be dispersed as a result of tectonic or volcanic disturbance, both possible processes in the BMC. It is not clear why the metal zoning and zone refining patterns are different from those in the Hokuroku ores; it seems likely that these patterns are related to the nature of the fluid source and its evolution, presumably involving more than the groundwater convection over magmatic plutons proposed for Hokuroku ore genesis. Spent ore-forming fluids venting the basin may have contributed to the non-hematitic iron formations that are found at Brunswick no. 12 and along the Heath Steele belt (Peter et al., 2003). These reduced iron formations may indicate the presence of subsidiary or shallower adjacent basins in which relatively dense fluids collected still separated from overlying oxic seawater by intermediate pool layers (Fig. 13). In those cases where hematitic iron formation occurs the overspill perhaps entered oxic ocean water. In summary, some of the features of the BMC ores can be explained within the anoxic ocean model of Fig. 12, for example, the large size, framboidal textures in pyrite and the mineral banding (though settling would be slow) and lack of contemporaneous and subsequent oxidation but the scarcity of barite and lack of evidence for rubble mounds requires an anoxic, almost sulphate-free anoxic ocean is considered unlikely (Solomon, 2008 — part II of this contribution). A major advantage of the brine pool proposition is that it is largely independent of the sulphate content and Eh of the ocean. 8. Conclusions The BMC massive sulphide deposits have many morphological, mineralogical and chemical features in common with the IPB ores. The commonality extends to the types of host rock, the facies and composition of the associated volcanic rocks, the overall tectonic setting, and the sequence of ophiolite obduction, mineralisation and deformation. Fluid inclusion data and other data suggest that a number of massive sulphide deposits in the IPB were deposited in brine pools on the sea floor (Solomon et al., 2002, 2004; Inverno et al., in press-a; Tornos et al., in press), and brine-pool sulphide deposition can explain many of the salient features of the BMC deposits.

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Acknowledgements I thank Wayne Goodfellow and Steve McCutcheon for helpful reviews, Dave Cooke, Bruce Gemmell, Carlos Inverno, Ross Large, David Rickard and Fernando Tornos for their insights into massive sulphide genesis, June Pongratz for drafting assistance, and Ore Geology Reviews Editor Nigel Cook and Associate Editor Yuanming Pan for guidance. The research was supported by the Australian Research Council's Centre of Excellence Programme. References Adair, R.N., 1992. Stratigraphy, structure, and geochemistry of the Halfmile Lake massive-sulphide deposit, New Brunswick. Exploration and Mining Geology 1, 151–166. Allen, R.L., 2001. Volcanic facies in VHMS districts and their use in reconstructing stratigraphy: an example from Los Frailes-Aznalcóllar, Iberian Pyrite Belt. GEODE Workshop “Massive sulphide deposits in the Iberian Pyrite Belt: New advances and comparison with equivalent systems”. University of Huelva, Huelva, pp. 1–3. Almodóvar, G.R., Sáez, R., Pons, J.M., Maestre, A., Toscano, M., Pascual, E., 1998. Geology and genesis of the Aznalcóllar massive sulphide deposits, Iberian Pyrite Belt, Spain. Mineralium Deposita 33, 111–136. Barrett, T.J., Dawson, G.L., MacLean, W.H., in press. Volcanic stratigraphy, alteration and setting of the Paleozoic Feitais massive sulphide deposit, Aljustrel, Portugal. Economic Geology. Barrie, C.T., Hannington, M.D., 1999. Classification of volcanicassociated massive sulphide deposits based on host-rock composition. Reviews in Economic Geology 8, 1–11. Barrie, C.T., Amelin, Y., Pascual, E., 2002. U–Pb geochronolgy of VMS mineralisation in the Iberian Pyrite Belt. Mineralium Deposita 37, 684–703. Barriga, F.J.A.S., 1983. Hydrothermal metamorphism and ore genesis at Aljustrel, Portugal. Unpublished PhD Thesis, University of Western Ontario, London, Ontario, Canada, 386 pp. Barriga, F.J.A.S., Fyfe, W.S., 1988. Giant pyritic base–metal deposits: the example of Feitais (Aljustrel, Portugal). Chemical Geology 69, 331–343. Barriga, F.J.A.S., Kerrich, R., 1984. Extreme 18O-enriched volcanics and 18O-evolved marine water, Aljustrel, Iberian Pyrite Belt: transition from high to low Rayleigh number convective regimes. Geochimica et Cosmochimica Acta 48, 1021–1031. Boulter, C.A., 1993. High-level peperitic sills at Rio Tinto, Spain: implications for stratigraphy and mineralization. Transactions, Institution of Mining and Metallurgy (Section B: Applied Earth Sciences) 102, 30–38. Bryndzia, L.T., Scott, S.D., Farr, J.E., 1983. Mineralogy, geochemistry, and mineral chemistry of siliceous ore and altered footwall rocks in the Uwamuki 2 and 4 deposits, Kosaka mine, Hokuroku district, Japan. Economic Geology Monograph 5, 507–522. Butler, I.B., Rickard, D., 2000. Framboidal pyrite formation via the oxidation of iron (II) monosulphide by hydrogen sulphide. Geochimica et Cosmochimica Acta 64, 2665–2672. Carvalho, D., Barriga, F.J.A.S., Munhá, J., 1999. Bimodal-siliclastic systems — the case of the Iberian Pyrite Belt. Reviews in Economic Geology 8, 375–408.

348

M. Solomon / Ore Geology Reviews 33 (2008) 329–351

Castro, A., Fernandez, C., El-Hmidi, H., El-Biad, M., Diaz, M., de la Rosa, J., Stuart, F., 1999. Age constraints to the relationships between magmatism, metamorphism and tectonism in the Aracena metamorphic belt, southern Spain. International Journal of Earth Science 88, 26–37. Chen, T.T., 1978. Colloform and framboidal pyrite from the Caribou deposit, New Brunswick. Canadian Mineralogist 16, 9–16. Claypool, G.E., Holser, W.T., Kaplan, I.R., Sakai, H., Zak, I., 1980. The age curves of sulfur and oxygen isotopes in marine sulfate and their mutual interpretation. Chemical Geology 28, 199–260. Conde, L.E.N., de Andrade, A.A.S., 1974. Sur la faune meso et/ou neodevonienne des calcaires du Monte das Cortes, Odivelas (Massif de Beja). Memorias e Noticias, Publicacoes do Museu e Laboratorio Mineralogico e Geologico da Universidade de Coimbra 78, 141–145. Conde, C., Tornos, F., Doyle, M., 2003. Encuadre estratigráfico de los sulfuros masivos de la parte suroriental de la faja piritica: Aznalcóllar-Los Frailes, y Las Cruces. Boletin Sociedad Española de Mineralogia 26-A, 161–162. Cooke, D.R., Bull, S.W., Large, R.R., McGoldrick, P.J., 2000. The importance of oxidized brines for the formation of Australian Proterozoic stratiform sediment-hosted Pb–Zn (Sedex) deposits. Economic Geology 95, 1–17. Currie, K.L., van Staal, C.R., Peter, J.M., Rogers, N., 2003. Conditions of metamorphism of the main massive sulphide deposits and surrounding rocks in the Bathurst mining camp. Economic Geology Monograph 11, 65–78. Dawson, G.L., Caessa, P., Alverca, R., Sousa, J.C., 2001. Geology of the Aljustrel mine area, southern Portugal. GEODE workshop “Massive sulphide deposits in the Iberian Pyrite Belt: New advances and comparisons with equivalent systems”, Aracena, Spain, October 2001. Aljustrel Field Trip Guidebook. Eurozinc Mining Corporation, Aljustrel. 28 pp. De Roo, J.A., van Staal, C.R., 2003. Sulphide remobilization and sulphide breccias in the Heath Steele and Brunswick deposits, Bathurst mining camp, New Brunswick. Economic Geology Monograph 11, 479–496. Dias, R., Ribeiro, A., 1995. The Ibero-Armorican Arc: a collision effect against an irregular continent? Tectonophysics 246, 113–128. Doyle, M., Morrisey, C., Sharp, G., 2003. The Las Cruces orebody, Seville province, Andalucia, Spain. In: Kelly, J.G., Andrew, C.J., Ashton, J.H., Boland, M.B., Earls, G., Fusciardi, J., Stanley, G. (Eds.), The Geology and Genesis of Europe's Major Base Metal Deposits. Irish Association for Economic Geology, Dublin, pp. 381–390. Eastoe, C.J., Solomon, M., Garçia Palomero, F., 1986. Sulphur isotope study of massive and stockwork pyrite deposits at Rio Tinto, Spain. Transactions, Institution of Mining and Metallurgy (Section B: Applied Earth Sciences) 95, 201–207. Eldridge, C.S., Barton Jr., P.B., Ohmoto, H., 1983. Mineral textures and their bearing on formation of the Kuroko orebodies. Economic Geology Monograph 5, 241–281. Fonseca, P., Ribeiro, A., 1993. Tectonics of the Beja-Acebuches ophiolite: a major suture in the Iberian Variscan foldbelt. Geologisches Rundschau 82, 440–447. Fonseca, P., Munhá, J., Pedro, J., Rosas, F., Moita, P., Araújo, A., Leal, N., 1999. Variscan ophiolites and high-pressure metamorphism in southern Iberia. Ofioliti 24, 259–268. Franklin, J.M., 1996. Volcanic-associated massive sulphide base metals. In: Eckstrand, O.R., Sinclair, W.D., Thorpe, R.I. (Eds.), Geology of Canadian mineral deposit types. Geology of Canada, vol. 8. Geological Survey of Canada, Ottawa, pp. 158–183.

Franklin, J.M., Lydon, J.W., Sangster, D.F., 1981. Volcanic-associated massive sulphide deposits. Economic Geology 75th Anniversary Volume, pp. 485–627. Franklin, J., Gibson, H.L., Jonasson, I.R., Galley, A.G., 2005. Volcanogenic massive sulphide deposits. Economic Geology 100th Anniversary Volume, pp. 523–560. Garçia Palomero, F., 1990. Rio Tinto deposits — geology and geological models for their exploration and ore-reserve estimation. In: Gray, P.M.J., Bowyer, G.J., Castle, J.F., Vaughan, D.J., Warner, N.A. (Eds.), Sulphide deposits — Their origin and processing. Institution of Mining and Metallurgy, London, pp. 17–35. Gaspar, O.C., 1996. Ore microscopy and petrology applied to the genesis, exploitation and beneficiation of Aljustrel and Neves Corvo massive sulphide deposits. Estudos Notas Trabalhos, Instituto Geológico e Mineiro Tomo, vol. 38, pp. 3–195. Giese, U., von Heogen, R., Hoymann, K.H., Kramm, U., Walter, R., 1994. The Palaeozoic evolution of the Ossa Morena Zone and its boundary to the South Portuguese Zone in SW Spain: geological constraints and geodynamic interpretation of a suture in the Iberian Variscan orogen. Neues Jahrbuch für Geologie und Palaëontologie Abhandlungen 192, 383–412. Goodfellow, W., 2003. Geology and genesis of the Caribou deposit, Bathurst mining camp, New Brunswick, Canada. Economic Geology Monograph 11, 327–360. Goodfellow, W.D., McCutcheon, S.R., 2003. Geologic and genetic attributes of volcanic-hosted massive sulphide deposits of the Bathurst mining camp, northern New Brunswick. Economic Geology Monograph 11, 245–311. Goodfellow, W.D., Peter, J.M., 1996. Sulphur isotope composition of the Brunswick No. 12 massive sulphide deposit, Bathurst Mining Camp, New Brunswick: implications for ambient environment, sulphur source, and ore genesis. Canadian Journal of Earth Science 33, 231–251. Goodfellow, W.D, Peter, J.M., 1999. Reply: Sulphur isotope composition of the Brunswick N. 12 massive sulphide deposit, Bathurst Mining Camp, New Brunswick: implications for ambient environment, sulphur source, and ore genesis. Canadian Journal of Earth Science 36, 127–134. Goodfellow, W.D, Peter, J.M., Winchester, J.A., van Staal, C.R., 2003. Ambient marine environment and sediment provenance during formation of massive sulphide deposits in the Bathurst mining camp: importance of the reduced bottom waters to sulphide precipitation and preservation. Economic Geology Monograph 11, 129–156. Huston, D.L., 1999. Stable isotopes and their significance for understanding the genesis of volcanic-hosted massive sulphide deposits: a review. Reviews in Economic Geology 8, 157–179. Hutchinson, R.W., 1973. Volcanogenic sulphide deposits and their metallogenic significance. Economic Geology 68, 1223–1246. Inverno, C., Lopes, C.J.C.D., d'Orey, F.L.C., Carvalho, D., 2000. The Cu (-Au) stockwork deposit of Salgadinho, Cercal, Pyrite Belt, SW Portugal — paragenetic sequence and fluid inclusion investigation. In: Gemmell, J.B., Pongratz, J. (Eds.), Volcanic environments and massive sulfide deposits. Centre of Ore Deposit Research Special Publication, vol. 3. University of Tasmania, Hobart, pp. 99–101. Inverno, C.M.C., Solomon, M., Barton, M.D., Foden, J., in press-a. The Cu-stockwork and massive sulphide ore of Feitais, Aljustrel. Iberian Pyrite Belt, Portugal. Economic Geology. Inverno, C.M.C., Solomon, M., Gaspar. O.C., Pacheco, N., Noiva, P.C., Barriga, G., Ferreira, A., in press-b. Evidence supporting an exhalative magmatic origin for the Lombador orebody, Neves Corvo, Iberian Pyrite Belt, Portugal. SGA Biennial Meeting, Dublin, August 2007.

M. Solomon / Ore Geology Reviews 33 (2008) 329–351 Jambor, J.L., 1979. Mineralogical evaluation of proximal–distal features in New Brunswick massive-sulphide deposits. Canadian Mineralogist 17, 649–664. Jaques, L., Noronha, F., 2001. Fluid evolution related to disseminated ores of the Lagoa Salgada deposit (Portugal). XVI ECROFI European Current Research on Fluid Inclusions. Porto, 2001, pp. 217–218. Knight, F.C., 2000. The mineralogy, geochemistry and genesis of the secondary mineralisation of Las Cruces, Spain. Unpublished PhD Thesis, University of Wales (Cardiff), 434 pp. Large, R.R., 1992. Australian volcanic-hosted massive sulphide deposits: features, styles and genetic models. Economic Geology 87, 471–510. Large, R.R., Blundell, D. (Eds.), 2000. Database of Global VMS Districts. Centre of Ore Deposit Research, University of Tasmania, Hobart. 179 pp. Leistel, J.M., Bonijoly, D., Braux, C., Freyssinet, P., Kosakevitch, A., Leca, X., Lescuyer, J.L., Marcoux, E., Milési, J.P., Piantone, P., Sobol, F., Tegyey, M., Thiéblemont, D., Viallefond, M., 1994. The massive sulphide deposits of the South Iberian Pyrite Province: geological setting and exploration criteria. Bureau de Recherches Géologiques et Miniéres Documentaire, vol. 234. 236 pp. Leistel, J.M., Marcoux, E., Thiéblemont, D., Quesada, C., Sánchez, A., Almodóvar, G.R., Pascual, E., Sáez, R., 1998a. The volcanichosted massive sulphide deposits of the Iberian Pyrite Belt: review and preface to the thematic issue. Mineralium Deposita 33, 2–30. Leistel, J.M., Marcoux, E., Deschamps, Y., Joubert, M., 1998b. Antithetic behaviour of gold in the volcanogenic massive sulphide deposits of the Iberian Pyrite Belt. Mineralium Deposita 33, 82–97. Leistel, J.M., Marcoux, E., Deschamps, Y., 1998c. Chert in the Iberian pyrite belt. Mineralium Deposita 33, 59–81. Lentz, D., Goodfellow, W.D., 1996. Intense silicification of footwall sedimentary rocks in the stockwork alteration zone beneath the Brunswick no. 12 massive sulphide deposit, New Brunswick. Canadian Journal of Earth Science 33, 284–302. Lusk, J., 1972. Examination of volcanic–exhalative and biogenic origins for sulfur in the stratiform massive sulphide deposits of New Brunswick. Economic Geology 67, 169–183. Lusk, J., Crocket, J.H., 1969. Sulfur isotope fractionation in coexisting sulphides from the Heath Steele B-1 orebody, New Brunswick, Canada. Economic Geology 64, 147–155. Lusk, J., Krouse, H.R., 1997. Comparative stable isotope and temperature investigation of minerals and associated fluids in two regionally metamorphosed (Kuroko-type) volcanogenic massive sulphide deposits. Chemical Geology 143, 231–253. Lydon, J.W., 1988. Ore deposit models 14. Volcanogenic massive sulphide deposits Part 2. Genetic models. Geoscience Canada 15, 43–65. McClenaghan, S.H., Goodfellow, W.D., Lentz, D.R., 2003. Gold in massive sulphide deposits, Bathurst mining camp: distribution and genesis. Economic Geology Monograph 11, 303–326. McCutcheon, S.R., Walker, J., 2005. The Turgeon deposit, IGCP project 502: global comparisons of volcanic-hosted massive sulphide districts. Geological Association of Canada and Mineralogical Association of Canada Conference, Bathurst Mining Camp Workshop, pp. 4–7. McCutcheon, S.R., Luff, W.M., Boyle, R.W., 2003. The Bathurst mining camp, New Brunswick, Canada: history of discovery and evolution of geologic models. Economic Geology Monograph 11, 17–35. McCutcheon, S.R., Walker, J., Bernard, P., Lentz, D., Downey, W., McClenaghan, S., 2005. Stratigraphic setting of base-metal

349

deposits in the Bathurst mining camp, New Brunswick. GACMAC-CSPG-CSSS Meeting, Halifax, Canada, Field Trip, vol. B4. 105 pp. McDougall, T.J., 1984. Fluid dynamic implications for massive sulphide deposits of hot saline fluid flowing into a submarine depression from below. Deep-Sea Research 31, 145–170. McKee, G.S., 2003. Genesis and deformation of the Aguas Teñidas Este massive sulphide deposit and implications for the formation, structural evolution and exploration of the Iberian Pyrite Belt. Unpublished PhD Thesis, University of Birmingham, U.K., 413 pp. Mac Niocall, C., van der Pluijm, B.A., van der Roo, R., 1997. Ordovician paleogeography and evolution of the Iapetus ocean. Geology 25, 159–162. Marcoux, E., Moëlo, Y., Leistel, J.M., 1996. Bismuth and cobalt indicators of stringer zones to massive sulphide deposits, Iberian Pyrite Belt. Mineralium Deposita 31, 1–26. Mitjavila, J., Martí, J., Soriano, C., 1997. Magmatic evolution and tectonic setting of Iberian pyrite belt volcanism. Journal of Petrology 38, 727–755. Moreno, C., Sierra, S., Saéz, R., 1996. Evidence for catastrophism in the Fammenian–Dinantian boundary in the Iberian pyrite belt. In: Strogen, P., Somerville, I.D., Jones, G.L. (Eds.), Recent advances in Lower Carboniferous geology Geological Society of London Special Publication, vol. 107, pp. 153–162. Moura, A., 2005. Fluids from the Neves Corvo massive sulphide ores (Iberian pyrite belt, Portugal). Chemical Geology 223, 153–167. Moura, A., Noronha, F., Cathelineau, M., Boiron, M.-C., Ferreira, A., 1997. Evidence of metamorphic fluid migration within the NevesCorvo ore deposit: the fluid inclusion data. Society of Economic Geologists Field Conference, Lisbon- Neves Corvo, Portugal, May 1997, p. 92. Abstracts and Programme. Munhá, J., 1983. Hercynian magmatism in the Iberian Pyrite Belt. Memorias Servicio Geologico Portugal 29, 39–81. Munhá, J., 1990. Metamorphic evolution of the South Portuguese/Pulo do Lobo Zone. In: Dallmeyer, R.D., Martínez-Garcia, E. (Eds.), PreMesozoic geology of Iberia. Springer-Verlag, 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 (Spain). Mineralium Deposita 33, 137–149. Ohmoto, H., Goldhaber, M.B., 1997. Sulfur and carbon isotopes, In: Barnes, H.L. (Ed.), Geochemistry of Hydrothermal Ore Deposits, 3rd edition. John Wiley and Sons, New York, pp. 517–611. Ohmoto, H., Drummond, S.E., Eldridge, C.S., Pisutha-Arnond, V., Lenagh, T.C., 1983. Chemical processes of ore formation. Economic Geology Monograph 5, 570–604. Oliveira, J.T., 1990. South Portuguese Zone:introduction. Stratigraphy and suynsedimentary tectonism. In: Dallmeyer, R.D., Martínez García, E. (Eds.), Pre-Mesozoic Geology of Iberia. Springer Verlag, Berlin, pp. 333–347. Oliveira, J.T., Quesada, C., 1998. A comparison of stratigraphy, structure and paleogeography of the South Portuguese Zone and Southwest England, European Variscides. Proceedings of the Ussher Society 9, 141–150. Oliveira, J.T., Cunha, T.A., Streel, M., vanguestaine, M., 1986. Dating the Horta da Torre Formation, a new lithostratigraphic unit of the Ferreira-Ficalho Group, South Portuguese Zone; geological consequences. Comunicacoes dos Servicos Geologicos de Portugal 72, 129–135. Oliveira, J.T., Pereira, Z., Pedro, C., Pacheco, N., Kora, D., 2004. Stratigraphy of the tectonically imbricated lithological succession of the Neves Corvo mine area, Iberian Pyrite Belt, Portugal. Mineralium Deposita 39, 422–436.

350

M. Solomon / Ore Geology Reviews 33 (2008) 329–351

Onézime, J., Charvet, J., Faure, M., Chauvet, A., Panis, D., 2002. Structural evolution of the southernmost segment of the West European Variscides: the South Portuguese zone (SW Iberia). Journal of Structural Geology 24, 451–468. Pereira, Z., Oliveira, J.T., 2001. The Viséan age of the orogenic volcanic complex of Toca da Moura, Ossa Morena Zone, Portugal: preliminary results based on palynostratigraphy. Abstracts, 15th International Senckenberg Conference, Frankfurt am Main, p. 7. Peter, J.M., Kjarsgaard, I.M., Goodfellow, W.D., 2003. Hydrothermal sedimentary rocks of the Heath Steele belt. Bathurst mining camp, New Brunswick: Part 1. Mineralogy and mineral chemistry. Economic Geology Monograph 11, 361–390. Pons, J.M., Hidalgo, R., Guerrero, V., Anderson, K., 1999. Geology, structure, genetic and geological model of Aguas Teñidas Este massive sulphide deposit. In: Gemmell, J.B., Pongratz, J. (Eds.), Volcanic environments and massive sulfide deposits. Centre of Ore Deposit Research, Special Publication, vol. 3. University of Tasmania, Hobart, pp. 163–164. Quesada, C., 1998. A reappraisal of the structure of the Spanish segment of the Iberian pyrite belt. Mineralium Deposita 33, 31–44. Quesada, C., Fonseca, P.E., Munhá, J., Oliveira, J.T., Ribeiro, A., 1994. The Beja-Acebuches ophiolite (southern Iberia Variscan fold belt): geological characterization and geodynamic significance. Boletin Geológico y Minero 105, 3–49. Read, R.A., 1967. Deformation and metamorphism of the San Dionisio pyritic orebody, Rio Tinto, Spain. Unpublished PhD Thesis, Royal School of Mines, London, 297 pp. Relvas, J.M.R.S., Barriga, F.J.A.S., Ferreira, A., Noiva, P.C., Pacheco, N., Barriga, G., 2006. Hydrothermal alteration and mineralization in the Neves-Corvo volcanic-hosted massive sulfide deposit, Portugal. I. Geology, mineralogy and geochemistry. Economic Geology 101, 753–790. Rogers, N., van Staal, C.R., 2003. Volcanology and tectonic setting of the northern Bathurst mining camp: Part II. Mafic volcanic constraints on back-arc opening. Economic Geology Monograph 11, 181–201. Rogers, N., van Staal, C.R., McNicoll, V., Thériault, R., 2003. Volcanology and tectonic setting of the northern Bathurst mining camp: Part I. Extension and rifting of the Popelogan arc. Economic Geology Monograph 11, 157–159. Rosa, D.R.N., Inverno, C.M.C., Oliveira, V.M.J., Rosa, C.J.P., 2004. Geochemistry of volcanic rocks, Albernoa area, Iberian pyrite belt, Portugal. International Geology Review 46, 366–383. Rosa, D.R.N., Inverno, C.M.C., Oliveira, V.M.J., Rosa, C.J.P., 2006. Geochemistry and geothermometry of volcanic rocks from Serra Branca, Iberian Pyrite Belt, Portugal. Gondwana Research 10, 328–339. Ruiz, C., Arribas, A., Arribas Jr., A., 2002. Mineralogy and geochemistry of the Masa Valverde blind massive sulphide deposit, Iberian Pyrite Belt (Spain). Ore Geology Reviews 19, 1–22. Sáez, R., Almodóvar, G.R., Pascual, E., 1996. Geological constraints on massive sulphide genesis in the Iberian Pyrite Belt. Ore Geology Reviews 11, 429–451. Sáez, R., Pascual, E., Toscano, M., Almodóvar, G.R., 1999. The Iberian type of volcano–sedimentary massive sulphide deposits. Mineralium Deposita 34, 549–570. Sánchez-España, J., Velasco, F., Boyce, A.J., Fallick, A.E., 2003. Source an evolution of ore-forming hydrothermal fluids in the northern Iberian Pyrite Belt massive sulphide deposits (SW Spain): evidence from fluid inclusions and stable isotopes. Mineralium Deposita 38, 519–537.

Sánchez-García, T., Bellido, F., Quesada, C., 2003. Geodynamic setting and geochemical signatures of Cambrian–Ordovician riftrelated igneous rocks (Ossa-Morena Zone, SW Iberia). Tectonophysics 365, 233–255. Santos, J.F.H.P., Mata, J., Gonçalves, F., Munhá, J., 1987. Contribuiçaõ para o conhecimento geológico-petrológico da regiáo de Santa Susana: o complexo volcano-sedimentar da Toca da Moura. Communicações Serviços Geológicos de Portugal 73, 29–314. Santos, J.F., de Andrade, A.S., Munhá, J., 1990. Magmatismo orogénico Varisco no limite meridional da Zona de Ossa-Morena. Communicações Serviços Geológicos de Portugal 76, 91–124. Solomon, M., 1976. ‘Volcanic’ massive sulphide deposits and their host rocks—a review and an explanation. In: Wolf, K. (Ed.), Handbook of stratabound and stratified ore deposits, vol. 6. Elsevier, Amsterdam, pp. 21–54. Solomon, M., 1999. Discussion: sulphur isotope composition of the Brunswick no. 12 massive sulphide deposit, Bathurst mining camp, New Brunswick: implications for ambient environment, sulphur source, and ore genesis. Canadian Journal of Earth Science 36, 1–5. Solomon, M., 2008. Brine pool deposition for the Zn-Pb-Cu massive sulphide deposits of the Bathurst mining camp, New Brunswick, Canada. II. Ocean anoxia during mineralisation. Ore Geology Reviews 33, 352–360 (this issue). Solomon, M., Gaspar, O.C., 2001. Textures of the Hellyer volcanichosted massive sulphide deposit, Tasmania — the ageing of a sulphide sediment on the sea floor. Economic Geology 96, 1513–1534. Solomon, M., Quesada, C., 2003. Zn–Pb–Cu massive sulphide deposits: brine pool types occur in collisional orogens, black smoker types in back arc/arc basins. Geology 31, 1029–1032. Solomon, M., Zaw, Khin, 1997. Formation of the Hellyer volcanogenic massive sulphide deposit on the sea floor. Economic Geology 92, 686–695. Solomon, M., Walshe, J.L., Garçia Palomero, F., 1980. Formation of massive sulphide deposits at Rio Tinto, Spain. Transactions, Institution of Mining and Metallurgy (Section B: Applied Earth Sciences) 89, 16–24. Solomon, M., Tornos, F., Gaspar, O.C., 2002. Explanation for many of the unusual features of the massive sulphide deposits of the Iberian pyrite belt. Geology 30, 87–90. Solomon, M., Tornos, F., Large, R.R, Badham, J.N.P., Both, R.A., Zaw, Khin, 2004. Zn–Pb–Cu volcanic-hosted massive sulphide deposits: criteria for distinguishing brinepool-type from black smokertype sulphide deposition. Ore Geology Reviews 25, 259–283. Soriano, C., Casas, J.M., 2002. Cross section through the central part of the Iberian Pyrite Belt, South Portuguese zone (Spain). Geological Society of America, Special Paper 364, 183–197. Soriano, C., Martí, J., 1999. Facies analysis of volcano–sedimentary successions hosting massive sulfide deposits in the Iberian Pyrite Belt, Spain. Economic Geology 94, 867–882. Stanton, R.L., 1959. Mineralogical features and possible mode of emplacement of the Brunswick Mining and Smelting orebodies, Gloucester County, New Brunswick. Canadian Institute of Mining and Metallurgy Bulletin 52, 631–643. Sullivan, R.W., van Staal, C.R., 1990. Age of a metarhyolite from the Tetagouche Group, Bathurst, New Brunswick, from U–Pb isochron analyses of zircons enriched in common Pb. Geological Survey of Canada, Paper 89–3, 109–117. Tanimura, S., Date, J., Ohmoto, H., 1983. Geologic setting of the kuroko deposits. Part II. Stratigraphy and structure of the Hokuroku district. Economic Geology Monograph 5, 24–38.

M. Solomon / Ore Geology Reviews 33 (2008) 329–351 Thiéblemont, D., Pascual, E., Stein, G., 1998. Magmatism in the Iberian Pyrite Belt: petrological contraints on a metallogenic model. Mineralium Deposita 33, 98–110. Tornos, F., 2006. Environment of formation and styles of volcanogenic massive sulphides: the Iberian pyrite belt. Ore Geology Reviews 27, 133–163. Tornos, F., Conde, C., 2002. La influencia biogénica en la formación de sulfuros masivos de la Faja Pirítica Ibérica. Geogaceta 32, 235–238. Tornos, F., Spiro, B., 1999. The genesis of shale-hosted massive sulphides in the Iberian Pyrite Belt. In: Stanley, C.J., et al. (Ed.), Mineral Deposits: Processes to Processing. Balkema, Rotterdam, pp. 605–608. Tornos, F., Clavijo, E.G., Spiro, B., 1998. The Filon Norte orebody (Tharsis, Iberian Pyrite Belt): a proximal low-temperature shalehosted massive sulphide in a thin-skinned tectonic belt. Mineralium Deposita 33, 150–169. Tornos, F., Casquet, C., Relvas, J.M.R.S., Barriga, F.J.A.S., 2002. The relationship between ore deposits and oblique tectonics: the SW Iberian variscan belt. In: Blundell, D.J., Neubauer, F., von Quadt, A. (Eds.), The timing and location of major ore deposits in an evolving orogen Geological Society of London Special Publication, vol. 204, pp. 179–198. Tornos, F., Casquet, C., Relvas, J.M.R.S., 2005. Transpressional tectonics, lower crust decoupling and intrusion of deep mafic sills: a model for the unusual metallogenesis of SW Iberia. Ore Geology Reviews 27, 133–163. Tornos, F., Solomon, M., Conde, C., Spiro, B., in press. The formation of the Tharsis massive sulphide deposit on the seafloor, Iberian Pyrite Belt: Evidence for deposition in a brine pool from geology, host-rock compositions, and stable isotope data. Economic Geology. Toscano, M., Sáez, R., Almodóvar, G.R., 1997. Multi-scale fluid evolution in the Masa Valverde stockwork (Iberian Pyrite Belt): evidence from fluid inclusions. Society of Economic Geologists Field Conference, Lisbon- Neves Corvo, Portugal, May 1997, p. 101. Abstracts and Programme. Turner, F.J., Campbell, I.H., 1987. Temperature, density and buoyancy fluxes in “black smoker” plumes, and the criterion for buoyancy reversal. Earth and Planetary Science Letters 86, 85–92. van Staal, C.R., Dewey, J.F., Mac Niocall, C., McKerrow, W.S., 1998. The Cambrian–Silurian tectonic evolution of the northern

351

Appalachians and British Caledonides: history of a complex, west and southwest Pacific-type segment of Iapetus. In: Blundell, D.J., Scott, A.C. (Eds.), Lyell; The Past is the Key to the Present Geological Society of London Special Publication, vol. 143, pp. 199–242. van Staal, C.R., Wilson, R.A., Rogers, N., Fyffe, L.R., Langton, J.P., McCutcheon, S.R., McNicoll, V., Ravenhurst, C.E., 2003. Geology and tectonic history of the Bathurst Supergroup, Bathurst mining camp, and its relationship to coeval rocks in southwestern New Brunswick and adjacent Maine — a synthesis. Economic Geology Monograph 11, 37–60. Velasco, F., Sánchez-España, J., Boyce, A.J., Fallick, A.E., Sáez, R., Almodóvar, G.R., 1998. A new sulfur isotopic study of some Iberian Pyrite Belt deposits: evidence of a textural control on sulphur isotope composition. Mineralium Deposita 34, 4–18. Walshe, J.L., Solomon, M., 1981. An investigation into the environment of formation of the volcanic-hosted Mt. Lyell copper deposits using geology, mineralogy, stable isotopes, and a six-component chlorite solid solution model. Economic Geology 76, 246–284. Walshe, J.L., Cooke, D.R., Neumayr, P., 2005. Five Questions for fun and profit: a mineral systems perspective on metallogenic epochs, provinces and magmatic hydrothermal Cu and Au deposits. In: Mao, J., Bierlein, F. (Eds.), Mineral Deposit Research: Meeting the Global Challenge. Springer, pp. 477–480. Williams, D., 1934. The geology of the Rio Tinto mines, Spain. Transactions Institution of Mining and Metallurgy 43, 593–640. Williams, D., Stanton, R.L., Rambaud, F., 1975. The Planes-San Antonio pyretic deposit of Rio Tinto, Spain: its nature, environment and genesis. Transactions Institution of Mining and Metallurgy (Section B: Applied Earth Sciences) 84, 73–82. Yamamoto, M., Kase, K., Carvalho, D., Nakamura, T., Mitsuno, C., 1993. Ore mineralogy and sulfur isotopes of the volcanogenic massive sulphide deposits in the Iberian Pyrite Belt. Resource Geology Special Issue 15, 67–80. Yang, K., Scott, S.D., 2003. Geochemical relationships of felsic magmas to ore metals in massive sulphide deposits of the Bathurst mining camp, Iberian pyrite belt, Hokuroku district, and the Abitibi belt. Economic Geology Monograph 11, 457–478.