ARTICLE

An oxygen isotope study of two contrasting orogenic veingold systems in the Meguma Terrane, Nova Scotia, Canada,with implications for fluid sources and genetic models

Daniel J. Kontak & Richard J. Horne & Kurt Kyser

Received: 5 June 2010 /Accepted: 10 January 2011 /Published online: 29 January 2011# Springer-Verlag 2011

Abstract Sampling of quartz vein material from two golddeposits of similar geological setting but different ages (TheOvens, 408 Ma; Dufferin, 380 Ma) in the Meguma Terraneof Nova Scotia has been done to compare and contrast theirδ18Oquartz signatures. Despite different ages of formation,quartz from all vein types in each of the deposits (i.e.saddle-reef, bedding-concordant leg reefs, en echelon,discordant) shows limited intra-deposit variation withsimilar average δ18O values of +15.2±0.9‰ (n=16) forThe Ovens and +15.7±0.6‰ (n=12) for Dufferin. Using anaverage δ18O value of +15.4‰ for the two deposits, thecorresponding δ18OH2O values, calculated for 400°C and350°C based on constraints from mineral assemblages andfluid inclusion studies, indicate averages of 11.4±0.2‰and +10.2±0.2‰, respectively. The isotopic data indicatethat: (1) the vein-forming fluids have a metamorphicsignature, (2) all vein types in the two deposits representformation from a single, isotopically homogeneous fluid,and (3) a fluid of similar isotopic signature was generatedby two contrasting tectono-thermal events in the Meguma

Terrane that were separated by 30 Ma. Integration of theseresults with previously published data for 14 Meguma golddeposits indicate a general stratigaphic dependence inδ18OH2O values for deposits when arranged in their relativestratigraphic position such that δ18OH2O values increaseupwards in the stratigraphy. This apparent trend cannot beexplained by models involving either fluid mixing orcooling of the vein-forming fluids, but instead is modelledusing fluid/rock interaction taking into account a change inthe modal mineralogy of the metasedimentary rocksupwards in the stratigraphy.

Keywords Nova Scotia . Meguma terrane . Orogenic golddeposits . The Ovens . Dufferin . Oxygen isotopes

Introduction

Orogenic gold-quartz vein systems occur in rocks from theArchean onwards, although certain periods of crustalgrowth appear to be more endowed than others (Goldfarbet al. 2001), as well as some tectonic settings and host rocks(Goldfarb et al. 2005; Bierlein et al. 2006). Despiteextensive study (reviews in Groves et al. 1998; Bierlein andCrowe 2000; Goldfarb et al. 2005; Dubė and Gosselin2007), varied opinions have and continue to exist regardingthe source of both fluids and metals. For example, differentmodels source the mineralizing fluid from the mantle(Cameron 1988; Colvine 1989), from deep- to mid-crustalreservoirs during pro-grade metamorphism (Henley et al.1976; Phillips 1993; Pettke et al. 1999; Jia and Kerrich1999), magmatic reservoirs (Burrows et al. 1986; de Rondeet al. 2000), or a mixture of metamorphic and meteoric fluids(Nesbitt and Muehlenbachs 1995; Craw and Chamberlain1996). In some cases, there is evidence of multiple sources

Editorial handling: G. Beaudoin

D. J. Kontak (*)Department of Earth Science, Laurentian University,Sudbury, ON, Canada P3E 2E6e-mail: dkontak@laurentian.ca

R. J. HorneAcadian Mining,1969 Lower Water Street,Halifax, NS, Canada B3J 2R7

K. KyserDepartment of Geological Sciences and Geological Engineering,Queen’s University,Kingston, ON, Canada K7L 3N6

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in single veins, presumably due to a protracted history forvein formation (Pettke and Frei 1996; Ridley and Diamond2000), which is also reflected in models that either couple(e.g. Pitcairn et al. 2006) or decouple (e.g. Large et al. 2009)the source of the vein-forming fluids and gold.

Over the past several decades, the Meguma Terrane,Nova Scotia, a classic slate-belt hosted orogenic goldsetting similar to those mentioned above, has been thefocus of considerable study (e.g. Kontak et al. 1990a;Sangster 1990; Ryan and Smith 1998). This work hasdemonstrated that the vein systems are similar with respectto their geological setting, structural style, vein mineralogy,and geochemical attributes (Kontak et al. 1990a). Inaddition, well-exposed surface and underground exposuresintegrated with robust geochronology (see below) indicatethat the veins formed at two distinct periods. These twovein-forming events coincided with regional deformationand subsequent emplacement some 30 Ma later ofvoluminous granites; notably, similar multiple ages for veinemplacement and related gold mineralization has beenestablished in the Lachlan fold belt of Australia (Arne etal. 1998; Bierlein et al. 2001). Despite the considerableefforts directed at the Meguma gold deposits and thesimilarities for the many districts, different models have andcontinue to be proposed for these deposits, as is the case forother orogenic gold districts.

In order to address some of the outstanding issues of theMeguma gold deposits, two well-characterised vein settingsof different ages, based on Re–Os and 40Ar/39Ar dating, but

similar in all other respects, were chosen for a detailedoxygen isotopic study. The purpose of this work was aimedspecifically at the following two issues: (1) to see if theapparently different vein types record similar or differentδ18Oquartz signatures which would, therefore, allow address-ing the polygenic (e.g. Sangster 1990, 1992) versus singular(Horne and Culshaw 2001) models for vein formation and(2) to see if fluids generated at different times in thetectonic evolution of the Meguma Terrane can be distin-guished isotopically. Furthermore, by integrating the newdata with previously published results, issues of isotopicvariability within a regional context could be addressed(e.g. Rushton et al. 1993; Nesbitt and Muehlenbachs1995; Beaudoin and Pitre 2005).

Regional geological setting

The study area is located within the Meguma Terrane ofNova Scotia, which forms part of the Canadian segment ofthe composite Appalachian Orogen (Williams and Hatcher1983). The terrane is the most easterly of five lithotectoniczones that comprise the composite orogen (Fig. 1) and wasemplaced against the adjoining Avalon Terrane along theeast–west trending Cobequid–Chedabucto Fault Zone duringthe Late Devonian closure of the Rheic Ocean, the dextraldocking of the terrane resulting in the Acadian Orogeny.Geologically, the terrane is dominated by Lower Paleozoicmetasedimentary rocks of the Meguma Supergroup and large

Fig. 1 Regional geological setting of the Meguma Terrane, southernNova Scotia, with the location of the two study areas (The Ovens,Dufferin) and other areas (West Gore, Moose River, regional samples)discussed in the text; note that the Musquodoboit Batholith is shownas MB. The inset map shows the distribution of terranes in the

Canadian part of the Appalachian orogen, which includes, in additionto the Meguma terrane (M), the Avalon (A), Dunnage (D), Gander (G)and Humber (H) terranes. The Liscomb Complex (LC) in the easternpart of the terrane is discussed in the text

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peraluminous granitoid bodies (e.g. South Mountain andMusquodoboit batholiths; Fig. 1). Lesser amounts ofSilurian-Devonian metasedimentary and metavolcanic rocksoverlie the Meguma Supergroup in the western part of theterrane, whereas sedimentary and volcanic rocks of Carbon-iferous and Triassic–Jurassic age occur in the central part ofthe terrane.

The Meguma Supergroup consists of a ca. 10 kmsuccession of the metasandstone-dominated GoldenvilleGroup and the overlying metasiltstone-dominated HalifaxGroup; the transition between the two referred to as theGoldenville–Halifax transition zone. The sequence wasdeformed into upright, shallowly plunging, north- tonortheast-trending folds and metamorphosed to greenschistto amphibolite grade during the Acadian Orogeny, the ageof which is constrained to 400–410 Ma (Keppie andDallmeyer 1995; Kontak et al. 1998). The metasedimentaryrocks were intruded in the Late Devonian by peraluminousgranites (380–375 Ma; Clarke et al. 1993; Kontak et al.2003; Reynolds et al. 2004) which outcrop the length of theterrane; lesser amounts of dioritic and gabbroic phases alsooccur (Clarke et al. 1993). Important in a genetic context tothe gold deposits is that, based on both geophysical dataand regional mapping (see Horne et al. 1992), including theextent of contact aureoles, the contacts of the largebatholiths (e.g. South Mountain and Musquodoboit,Fig. 1) are steeply dipping and do not extend laterallybeneath the stratigraphy.

Although not well constrained, there is some relevantinformation that pertains to the inferred basement to theMeguma Terrane. Complexly folded, high-grade metamor-phic rocks comprising mixed gneisses occur in the centralpart of the terrane and are referred to as the LiscombComplex (Dostal et al. 2006). These high-grade metamor-phic rocks record cooling to below 400–500°C at about380 Ma (Kontak and Reynolds 1994), which coincides withemplacement of the large granitic batholiths in the terrane.Based on geochronologic and chemical constraints, Dostalet al. (2006) argue this complex may represent a corecomplex. Alternatively, White et al. (2009) argue that theserocks are modified Meguma Supergroup with the highmetamorphic grade due to nearby granites. Other potentialbasement rocks to the Meguma Supergroup occur as high-grade (i.e. granulite grade), xenolithic paragneisses in374 Ma lamprophyric dyke rocks outcropping along theeastern part of the terrrane (Owen et al. 1988) or in faultsplays off the regionally extensive Cobequid ChedabuctoFault Zone (Fig. 1; Gibbons et al. 1996). In both examples,the xenoliths record basement metamorphism at 375 Ma(U-Pb dating of zircon and monazite; Gibbons et al. 1996;Greenough et al. 1999). These xenoliths are, therefore,interpreted to represent sampling of high-grade basementrocks that lay beneath the Meguma Supergroup and are

referred to later in the discussion of potential sourcereservoirs for vein-forming fluids (i.e. Tangier xenoliths).

Geological features of Meguma gold deposits

The general features of Meguma gold deposits have beensummarised elsewhere (e.g. Smith and Kontak 1986; Ryanand Smith 1998), thus only a brief summary is providedhere. Deposits occur at or near hinge areas of anticlinalstructures of regional folds where quartz veins are mostabundant and include both concordant and discordant types(see Horne and Culshaw (2001) for a discussion of veintypes). The dominant vein type consists of concordantveins, that includes bedding-concordant, bedding-parallel,and saddle-reef types (Horne and Culshaw 2001), and theseveins show a preference for sandstone siltstone contacts;less abundant discordant-vein types also occur. Thebedding-concordant veins are laterally continuous and showvertical continuity. Gold occurs in all vein types but oftenshows higher grades where discordant vein cut concordantvein types. Veins are quartz dominant (i.e. ≥90–95%) withlesser carbonate and Fe–As sulphides (pyrrhotite, pyrite,arsenopyrite) but also include a variety of silicates(tourmaline, garnet, epidote, plagioclase, K-feldspar, mus-covite, amphibole, biotite, apatite) and other sulphides(galena, sphalerite, stibnite) plus Bi–Te–Ag–Hg phases(e.g. Kontak and Smith 1993). Scheelite can locally beabundant, in one case, there having been production(Moose River, Fig. 1). In addition, antimony was producedin addition to gold from the West Gore Sn–Au deposit(Fig. 1; Kontak et al. 1996) which, interestingly, occurshighest in the stratigraphy of all deposits. Significantly, themineralogy of the veins within a deposit shows a zonaldistribution depending on the spatial association of deposits tointrusions (Newhouse 1936; Smith and Kontak 1986). Forexample, the Beaver Dam deposit, located 1 km of the RiverLake granite and partly cross-cutting its contact aureole(Kontak et al. 1990b), has veins with a high-temperaturemineral assemblage (e.g. amphibole–garnet–tourmaline–plagioclase) and also containing Bi–Te phases, which arenoted to occur in intrusion-related gold settings (Thompsonand Newberry 2000). In general, the conditions of veinformation are estimated at 2–3 kbars and 350–400°C basedon mineralogical, isotopic, and fluid inclusion work (Kontakand Smith 1989a, 1993; Kontak et al. 1990a, 1996).

Geology of The Ovens and Dufferin deposits

The geology of The Ovens and Dufferin districts are brieflydescribed in order to provide a setting for the sampled veins.Of significance in this study is the similarity of the setting of

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the two areas, despite occurring within different parts of thestratigraphy, and occurrence of the same vein types althoughthe amount of veins is greater at the Dufferin deposit.

The Ovens deposit

The Ovens district occurs in the hinge of a tight (interlimbangle 35–50°) regional anticlinal structure, one of severalnortheast-trending fold structures of box- and chevron stylein the region (Fig. 2a). The area is underlain by rocks of thelower Halifax Group, which is dominated by slate andmetasandstone metamorphosed to lower greenschist facies.The closest exposed intrusion is the South MountainBatholith, which lies 25 km to the north and has steepcontacts, and there is no evidence of thermal effects. Thestructural evolution of the area is described in detail byHorne and Culshaw (2001) who note that an early phase offlexural-flow folding was followed by a period of flexural-

slip folding, as indicated by a variety of structural features,most important being bedding-parallel movement horizonswith associated striations and slickenfibres.

The area contains an abundance of quartz veins (Fig. 3),which importantly are mostly concentrated in the hinge areaof the fold (Fig. 2a). Veins types include both bedding-parallel and discordant varieties, with the former includingveins variably described as bedding-concordant, saddle-reefand buckled vein types. The discordant type includesconjugate veins that may occur either as singular or pairedtypes. Important features of the veins follow: (1) presenceof all vein types (Fig. 3a, c, d), (2) mutual cross-cuttingrelationships of veins (Fig. 3a, c), and (3) crack-sealtextures in both concordant (Fig. 3b) and discordant(Fig. 3c, e) vein types. Importantly, gold has been observedin all vein types, including discordant types (Fig. 3f). Asnoted by Horne and Culshaw (2001), the orientation of theveins, kinematic indicators, mutually cross-cutting relation-

Fig. 2 a Simplified geology ofThe Ovens area which is locatedin the hinge of a northeast-trending anticline (map modifiedafter Horne and Culshaw 2001).Note that the area is underlainby metasiltstone beds of theHalifax Group. The vein sam-ples used in this study camefrom the western part of the areahighlighted as veined area,which is well exposed along thecoastal section at Rose Bay. b, cPlan map and cross-section(facing east) of the Dufferindeposit area (modified afterHorne and Jodrey 2002), whichis underlain by metasandstonesand interbedded metasiltstonesof the Goldenville Group. Notethe change in the wavelength ofthe paired anticlines along theHarrigan Cove Fault. The cross-section is a view looking east atthe west end of the CrownReserve Anticline near the re-cent workings and shows someof the 13 stacked saddles presentbased on a deep drill hole(saddles numbered from 1 at thetop downwards). The plan mapshows the extent of both thehistorical and recent (post-1980s) workings

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ships of veins and similar accessory mineralogy of all veintypes (gold, scheelite, Fe–As sulphides) suggest emplace-ment of all vein types during late-stage tightening of anexisting fold structure by a flexural-slip fold mechanism.

The Dufferin deposit

The Dufferin area (Fig. 2b, c) is underlain by a pair ofanticlinal structures, the Salmon River and Dufferin Minesanticlines, which are offset by a cross-fault, the Harrigan CoveFault with 1.5 km of sinistral displacement. Importantly, thearea is also distant (i.e. >10 km) from the nearest graniticintrusion, which is relevant to the age-dating discussed below.The stratigraphy consists of rocks of the Goldenville Groupand is dominated bymedium to thickly beddedmetasandstonewith lesser metasiltstone and slate. A typical sedimentarycycle of consists of a graded or fining-upward cycle of thick,massive metasandstone (1 m) overlain by metasiltstone (5–10 cm), and capped by black slate (1–2 cm). Althoughmetasandstone dominates, cycles rich in metasiltstone andslate do occur. The cross-section through one of the anticlines(Fig. 2c), based on underground workings and surfacedrilling, indicates a chevron fold with steep limbs and upto 13 stacked saddles (note that in some cases paired veinscount as a single saddle) with 700 m of strike length.

Vein types present at Dufferin (Fig. 4) include bedding-parallel and discordant types, with saddle-reefs and theirdown limb extensions (leg reefs) dominating but with lesseren echelon and discordant types. Important features of theveins follow: (1) all vein types show mutually cross-cuttingrelationships (Fig. 4b, e), (2) en echelon types show reversesense of displacement as expected for the gold geometry(Fig. 4c), (3) en echelon and bedding-concordant types arespatially associated (Fig. 4c), and (4) veins are commonlycomposite (Fig. 4d). As in other good deposits, gold occursin all vein types, but in this case saddle-reef, en echelon andlaminated bedding-concordant veins are most enriched.

The structural evolution of the Dufferin area and veinformation has been discussed by Horne and Jodrey (2002).These authors note the abundance of movement horizons (i.e.fault gouge) at slate–metasandstone contacts, which localisedbedding-concordant veins and striations oriented perpendic-ular to the fold axis. Hence, vein formation is inferred tohave occurred during flexural-slip movement during a late-stage tightening of an existing, tightly folded (i.e. chevronstyle) anticlinal structure.

Relative and absolute timing of vein formationat The Ovens and Dufferin

Timing of vein emplacement at the two deposit sites isconstrained by both field relationships and radiometric

dating (40Ar/39Ar, Re–Os). As noted above, field relation-ships suggest veining was synchronous with flexural-slipfolding late in the deformation history when fold limbswere steepened. Thus, steep orientation of bedding planesand the regional penetrative cleavage, both of which wouldhave been at high angles to the horizontally orientedmaximum compressive stress (σ1; Horne and Culshaw2001), provided favourable conditions for the build-up offluid pressure (Sibson et al. 1988). As discussed by Sibsonet al. (1988), such misorientation of the dominant anisot-ropy (i.e. So and S1 in this case) to σ1 is the basis for thefault-valve mechanism of vein formation. In the studyareas, the steeply dipping bedding-concordant veins, ofmassive and laminated nature (i.e. ribbon or crack-seal typefabric; Figs. 3 and 4), represent the fault veins, whereas theen echelon veins would represent the flat veins. That veinemplacement was late relative to the major folding eventand cleavage development is constrained by the followingfeatures, which are seen in most gold deposit areas: (1)veins truncate the trace of cleavage in adjacent wall rocksand (2) cleaved wall rock fragments occur in the veins. Inaddition, at some localities, vein alteration selvagesretrograde contact mineral assemblages (Kontak et al.,1990b), hence, some veins are syn- to post-emplacementof the 380 Ma granites in the Meguma Terrane.

The absolute timing of vein formation is of particularrelevance to the present study given that the setting of thetwo areas is so similar. Previous work at the two sitesincludes 40Ar/39Ar (Kontak et al. 1998) and Re–Os (Morelliet al. 2005) dating. At The Ovens, two samples of whole-rock slate within and adjacent veins yielded 40Ar/39Arplateau ages of 396±3.5 Ma and 399±2 Ma, which areslightly less than 408±5 Ma Re–Os ages (model andisochron) for vein arsenopyrite. These data have beeninterpreted to reflect vein formation at 408 Ma at thermalconditions above the argon blocking temperature ofmicas (i.e. 300–350°C) with subsequent cooling andclosure of argon in micas at ca. 400 Ma. In contrast, atDufferin a whole-rock slate sample from within a saddlereef quartz vein yielded a 40Ar/39Ar plateau age of 382±2 Ma, which is identical to the 380±3 Ma Re–Os isochronand model ages for vein arsenopyrite. In contrast, awhole-rock slate sample from outside the veined areayielded a 40Ar/39Ar plateau age of 390±2 Ma, whichrecorded the effects of regional metamorphism. Thus, atthese two areas, which are similar in their structuralsetting, vastly different ages for the vein formation of 408and 380 Ma are recorded which relate to, respectively,regional deformation and granitic intrusion in theMeguma Terrane. Where other deposits are well con-strained from field relationships, supporting radiometricdating (Ar–Ar) indicates ages of 370–380 Ma (Kontak etal. 1990b; Kontak and Archibald 2002).

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Nature of veins-forming fluid at Dufferin and The Ovensand other Meguma gold deposits

The nature of the vein-forming fluids at The Ovens andDufferin is inferred from a large data base for theMeguma gold deposits, but these data are discussedcollectively below. The sulphide assemblage (pyrrhotite–pyrite–arsenopyrite) and narrow range of δ34Ssulphidewithin individual deposits (±1–2‰) indicate the fluids werereduced, consistent with the sulphide assemblage, andremained so during vein formation (Kontak and Smith1989b). The range of δ34Ssulphide values for all depositsof +10 to +26‰ and their gradual change to positive valuesup stratigraphy mimics the trend of δ34Ssulphide for theMeguma Supergroup (Sangster 1992). Thus, the δ34S dataare interpreted to reflect inheritance of δ34S values of wallrock sulphides due to fluid/rock interaction. Similarly, theoverlap of δ13C values (i.e. −18 to −26‰) for veincarbonates and wall rock carbonate and graphite alsoindicate fluid/rock interaction and inheritance of δ13Cvalues (Kontak and Kerrich 1997). In addition, these

isotopic signatures suggest low fluid/rock ratios existedduring vein formation.

Vein quartz samples from all vein types in deposits,including Dufferin and The Ovens, are dominated by low-salinity (5–8 wt.% equiv. NaCl) aqueous–carbonic (XCO2=0.1–0.2) inclusions; minor saline aqueous types of secondaryorigin occur that are unrelated to the primary vein-formingfluids (Kontak and Smith 1989b, 1988; Baker 1996; Kontaket al. 1996). There is rarely evidence for fluid unmixing,which is expected given the pressures of vein formation(Schmidt and Bodnar 2000), except for the West Gore Au–Sb deposit where fluid unmixing occurred (Kontak et al.1996), but this deposit occurs at the highest stratigraphiclevel in the Meguma Supergroup. The fluid inclusionsconstrain vein formation to 350–400°C and 2–3 kbars.

Sampling and analytical techniques

Sampling at The Ovens and Dufferin deposits was guidedby earlier detailed mapping of Horne and Culshaw (20010

Fig. 3 Photographs of representative vein types from surface outcrops ofThe Ovens study area. a Bedding-concordant (horizontal) and conjugatediscordant (subvertical) veins cutting layered metasiltstone beds. Note thatthe bedding-concordant veins are offset along faults controlling emplace-ment of the inclined veins. b Close-up of crack-seal textured bedding-concordant vein. Coin is 3 cm wide. c Crack-seal textured discordant (actype) vein cutting a thin bedding-concordant vein. Note that the crack-seal

texture only occurs where the discordant vein cuts siltstone beds and notsandstone beds. Coin on left is 3 cm wide. d Fold closure (i.e. The OvensAnticline) with bedding-concordant veins going over the hinge. Hammerin centre is 0.4 m long. e Discordant (ac type) vein in metasiltstone withdextral offset on slip planes, as indicated by arrows. Note that the veincontinues in the lower left of photo. Hammer in centre is 0.4 m long. fClose-up of crack-seal textured discordant (ac type) vein with visible gold

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and Horne and Jodrey (2002), respectively. In each area, allvein types were sampled where relationships could beclearly established. In addition, the same samples were partof a more extensive sampling suite for fluid inclusionstudies, the results of which will be presented elsewhere.Three additional samples from near the Oldham area wereselected for inclusion in this study to complement thealready large data base for Meguma gold veins.

High-purity quartz separates were produced by hand-picking sub-millimetre-size fragments from coarse crushesof quartz vein material using a binocular microscope.Although some of the vein samples contained sulphideand wall rock, such material was absent in the finalseparates prepared. The samples all consist of highlyvitreous, glassy, fresh quartz that is free of impurities.Quartz separates were analysed for δ18O at the Queen’sUniversity Stable Isotopic Facilities, Kingston, Ontario,Canada. Samples were prepared for oxygen isotopic

analysis using the BrF5 method of Clayton and Mayeda(1963), and isotope measurements were performed using aFinnigan MAT 252 mass spectrometer. All values arereported using the δ notation in units of per mil (‰)relative to V-SMOW and have a precision of±0.2 per mil(‰) based on repeated analyses of standards. The results ofdata acquired in this study are compared and contrastedwith earlier δ18O data for Meguma quartz veins reported byKontak and Kerrich (1995, 1997) and Kontak et al. (1996),which were analysed at the University of Saskatchewanusing similar procedures as those used in the present study.

Analytical results

The results of δ18Oquartz values are presented in Table 1,where vein type is provided along with the isotopic data.There are two features of the data which are apparent.

Fig. 4 Photographs of represen-tative vein types from under-ground exposures at theDufferin deposit. Note that theveins are found in the hinge andlimbs of the Crown ReserveAnticlinal structure (see Fig. 2for location). a A view along thefold axis of a mined, auriferoussaddle-reef vein exposed in thefold hinge. b An exposure ofdifferent vein types on the foldlimb showing a bedding-concordant (bc) type vein on theleg of the reef (i.e. continuationof saddle vein on the limb offold), en echelon (ee) veins anddiscordant veins (dv). The ex-posed pipe is about 1 m inlength. c Bedding-concordant(bc) and en echelon (ee) veinson the fold limb. Note the crack-seal or laminated texture of theconcordant-type vein and re-verse sense of shear indicated bythe en echelon veins. d Close-upof a bedding-concordant-typevein in Fig. 4c. e Bedding-concordant vein cut by adiscordant-vein type. f A pair ofsheared (i.e. reverse motion) enechelon veins looking subparal-lel to the fold axis

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Firstly, the results for the two deposit areas are very similar interms of their averages with values of +15.7±0.6‰ (n=12)for Dufferin and +15.2±0.9‰ (n=16) for The Ovens.Secondly, there is a limited spread for each of the data setsdespite a variety of vein types having been analysed at bothlocalities. Thus, although veins are discriminated based on

their structural setting or appearance (e.g. laminated versusnon-laminated, saddle veins versus limb veins, strataboundvein versus discordant veins), their δ18O values are similar.For example, even where there is a change of vein type,such as from a laminated vein to massive, non-laminatedvein, there is no significant difference in δ18Oquartz values

Table 1 Summary of oxygen isotope data for quartz vein samples from The Ovens and Dufferin districts, Nova Scotia

Sample Vein type Comments δ18O (‰)Quartz

δ18OH2O

(‰) 400°Cδ18OH2O

(‰) 350°C

Dufferin

DUFF 2 ds <30 cm; massive white vein 15.3 11.2 10.0

DUFF 3 ds <20 cm; flat vein; massive white 16.0 11.9 10.7

DUFF 4A bc <10 cm; some slate inclusions and trace pyrite 15.5 11.4 10.2

DUFF 4B bc Quartz euhedra in bc vein on opposite side of hinge as 4A 15.3 11.2 10.0

DUFF 5B ds 10–20 cm; vein is between two bc veins, including #5 C 16.0 11.9 10.7

DUFF 5 C sd Near hinge of fold; massive white vein with faint cs textures 15.2 11.1 9.9

DUFF 6A fs <6 cm; laminated cs textured vein 16.7 12.6 11.4

DUFF 6B fs <4 cm; massive white vein adjacent vein #6A 15.9 11.8 10.6

DUFF 7A ee, peg <3–4 cm; deformed ee veins 16.0 11.9 10.7

DUFF 7B fs <6–8 cm; massive white 16.1 12.0 10.8

DUFF 7 C fs Extension of vein 7B where cs texture occurs 15.7 11.6 10.4

DUFF 7D ee <3–4 cm; extended ee veins 14.4 10.3 9.1

15.7±0.6 11.6 10.4

The Ovens

OV-99-1A bc <1–2 mm vein in slate; on limb of fold; early vein (?) 14.5 10.4 9.2

OV-99-1A bc Duplicate of 1A 14.5 10.4 9.2

OV-99-1B bc thurst relatedvein below 1A withgood cs texture

16.0 11.9 10.7

OV-99-03 ac <4 cm; good cs texture developed; cuts shale-sst package 15.2 11.1 9.9

OV-99-04 fs 4–6 cm; pinches-swells on strike; thin slate bands in the vein 12.3 8.2 7.0

OV-99-05 ds 4–6 cm; steep discordant vein with trace pyrites 15.4 11.3 10.1

OV-99-06 fs <6 cm; some slate inclusions and pyrite, coarse scheelite 15.4 11.3 10.1

OV-99-07 fs <4–6 cm; contains arsenopyrite crystals that fill vein 15.5 11.4 10.2

OV-99-08 fs <2–3 cm, tightly buckled vein in hinge of fold 15.3 11.2 10.0

OV-99-09 ds 4 cm; cuts early bc veins(#6) and is cut by #9 15.1 11.0 9.8

OV-99-10 ds 3–4 cm; cuts bc veins (#11) 16.4 12.3 11.1

OV-99-11 fs <3–4 cm; cs texture developed; is cut by vein #10 15.6 11.5 10.3

OV-99-12 ds 4 cm; cuts bc veins; has vs texture and trace pyrite 15.7 11.6 10.4

OV-99-13 fs <1–2 cm; ribbon texture with slate inclusions 15.2 11.1 9.9

OV-99-14 ds <1–2 cm; massive texture with no cs texture 15.9 11.8 10.6

OV-99-15 fs <2 cm; some slate inclusions and pyrite 15.4 11.3 10.1

15.2±0.9 11.2 9.9

Regional samples

OGR-99A 13.8 9.7 8.5

EO3-70 14.9 10.8 9.6

OV-99-DG 15.0 10.9 9.7

Vein types and textures: bc bedding-concordant, ac discordant vein with plane perpendicular to fold axial plane, orientation, fs flexural-slip vein,ds discordant vein with conjugate, sd saddle vein in hinge zone (Dufferin samples), cs crack-seal texture, δ18 OH2O values calculated using thefractionation equation of Matsuhisa et al. (1979)

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(Fig. 5a, b). The very limited spread δ18Oquartz fromwithin and between veins for a single deposit is similar tothose reported by Beaudoin and Pitre (2005) in theircomprehensive analysis of the δ18O composition oforogenic quartz veins in the Archean of Val-d’Or,Quebec. Although not as thorough as this latter study,many other studies on orogenic quartz vein systems havealso noted a limited spread of δ18Oquartz values withindeposits (e.g. Goldfarb et al. 1991; Ansdell and Kyser1992; Rushton et al. 1993).

Also shown in Table 1 are three samples from bedding-concordant-type veins of similar structural setting as thetwo deposit areas. The samples are come from near theOldham gold district (Fig. 1) and occur near the top of theGoldenville Group. This material is included since it addsto the regional data base for the Meguma gold districts and,as is seen below, is included in the analysis of thestratigraphic variation of δ18Oquatz values. These sampleshave δ18Oquartz between +13.8 and +15.0‰, thus similar tothose in the two study areas.

Discussion

δ18O of vein-forming fluids

The δ18OH2O values for the vein-forming fluids for thetwo districts are assessed using the δ18Oquartz data,inferred temperature of vein formation (400°C to 350°C;see discussion above for justification of these temper-atures) and appropriate mineral–H2O fractionation equa-tion; results are summarised in Table 1. For The Ovenssamples, the δ18OH2O values range from +12.3 to +9.2‰with averages for 400°C and 350°C of +11.2‰ and +9.9‰,respectively. For the Dufferin samples, the δ18OH2O valuesrange from +12.6‰ to +9.1‰ with averages for 400°Cand 350°C of +11.6‰ and +10.4‰, respectively.

The fractionation equation has been used to calculate theδ18OH2O values for fluids in isotopic equilibrium withquartz having known 18O values for a given temperature,and this is displayed graphically in Fig. 6 along with thedata for the two deposits. It is apparent from Fig. 6 that therange for δ18OH2O values is +9‰ to +12‰ for deposition at350°C to 400°C. However, an alternative way to use thisdiagram is to examine the maximum change in temperaturethat is required to account for the range in δ18Oquartz values.Based on this approach, a temperature variation of about50°C is inferred for both deposits. Thus, the data indicatethat at both deposits vein quartz precipitated from fluids ofsimilar δ18OH2O and that this occurred over a very narrowtemperature interval of about 50°C.

A consideration regarding the δ18OH2O values must bethe possibility of modification of the fluid at the site of veinformation due to fluid/rock interaction or fluid mixing suchthat the values observed are not primary values. Thisscenario is illustrated in Fig. 6 where two possible end-member migration paths of a fluid having an initial δ18O valueof +8‰ are shown since exchange with another reservoirmay happen at any temperature. That such a scenario mayhave happened is considered unlikely for the followingreasons: (1) the degree of modification would have had to bethe same not only for individual veins within the samedeposit, but also at different deposits to give similar δ18Odata for all vein types; (2) although some wall rock alterationis observed in these deposits, it is highly variable andgenerally cryptic; and (3) there is no evidence that fluidmixing existed in these deposits based on our fluid inclusionstudies, as noted above. An alternative to this scenario, thisbeing some fluid/rock alteration along the fluid pathway tomodify the δ18OH2O values, is addressed later.

In summary, the δ18OH2O values for the vein-formingfluids in the two districts were similar at +9‰ to +12‰. Itis emphasised that this similarity occurs despite the fact thatthe settings formed at vastly different times, at 408 Ma and380 Ma, and in quite different lithological units, that is,

Fig. 5 Line drawings based on underground photographs tracing outthe geology of veins and host rocks at the Dufferin gold deposit. In thefigures are shown the locations of vein quartz samples and theircorresponding δ18O values (see Table 1). Abbreviations follow: ee enechelon vein, cs crack-seal or laminated vein, bc bedding-concordant

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metasandstone at Dufferin versus metasiltone-slate at TheOvens.

Source reservoir(s) of the vein-forming fluids

The origin of the vein fluids is evaluated based on theestablished ages for vein formation and the reservoirspresent at the time of vein formation. In the case of TheOvens, where vein formation occurred at 408 Ma, igneousactivity was absent and instead the age overlaps the time ofregional deformation. In contrast, vein emplacement atDufferin is constrained to 380 Ma and overlaps emplace-ment of the granitic batholiths. There is, however, a spatialargument against a granitic source for the vein fluids (seeFig. 1) despite the fact that the nearest granites haveδ18OH2O values overlapping those of the gold veins values(+7‰ to +12‰ at 400°C; Carruzzo et al. 2004; Kontak andKyser 2010), and these latter values overlap the field formagmatic fluids (Sheppard 1986).

Given the different ages for vein emplacement, butsimilar apparent δ18OH2O values, two scenarios are possi-ble: (1) the same reservoir was tapped, but at two differenttimes, or (2) different source reservoirs fortuitously generatedfluids with similar δ18O values. Before addressing thesescenarios, it is first relevant to review the implications of thefluid inclusion assemblages in the vein systems discussedpreviously. Quartz-hosted fluid inclusions in the veins aresimilar in the two areas and are of the aqueous–carbonictype (XCO2=0.1–0.2, 5–8 wt.% NaCl equiv.), which corre-sponds to the fluid generally associated with orogenic

auriferous quartz vein systems globally (e.g. summary inGoldfarb et al. 2005). Importantly for the Dufferin samples,this fluid composition contrasts markedly with aqueoussaline, carbonic-poor fluids associated with granite-hostedvein systems in the 380 Ma intrusions of the MegumaTerrane (Carruzzo et al. 2000; Kontak et al. 2001). Alsosignificant is that the only exception to this generalisationoccurs in vein systems located at the contact of granites withMeguma Supergroup rocks where a carbonic component isnoted which is considered to reflect local wall rock influence(Carruzzo et al. 2000). Based on the foregoing discussion, adirect connection to a dominantly magmatic fluid reservoir isdiscounted.

Previous discussion concluded that a direct magmaticcontribution to the vein fluids is unlikely, hence ametamorphic fluid is inferred, which requires a link tolarge-scale tectonic processes. For The Ovens area, this canbe related to regional Acadian deformation throughout theMeguma Terrane, hence a classic orogenic-type model forvein formation (Goldfarb et al. 2005). Whereas suchprocesses are not coincident with vein formation atDufferin, emplacement of the 380 Ma granites in theMeguma Terrane was widespread and must have lead todevolitisation of the crust. In fact, generation of these meltsmay have been coincident with formation of 380 Magranulite facies metamorphic rocks which occur as melangein fault zones (e.g. Cobequid Fault Zone in Fig. 1; Gibbonset al. 1996) and xenoliths in 374 Ma lamprophyric dykes(Greenough et al. 1999) in the eastern Meguma Terrane.Thus, it is suggested that this later fluid of metamorphic

Fig. 6 Plot of temperature (°C) versus δ18Oquartz with isopleths ofδ18OH2O (in boxes) calculated using the quartz–H2O fractionationequation of Matsuhisa et al. (1979). The δ18O vein quartz data forDufferin and The Ovens are shown as tick marks. The shaded boxesindicate δ18OH2O values based on quartz precipitation at 350–400°C,

as discussed in the text. The dashed black arrows in the Dufferin plotrepresent the possible evolution of a fluid with an initial δ18OH2O

value of +8‰ which reacts with host rocks with a δ18O valueof +16‰ to +18‰ such that the δ18OH2O of the vein-forming fluid isincreased (see text for discussion)

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character was generated as part of the widespread generationof granitic magmas at this time. Although not conclusive, thegeneral similarity of the fluid chemistry and δ18OH2O valuesat the two areas is a strong argument that the same sourcerocks were twice tapped to generate the fluids which havegiven rise to the Meguma vein deposits.

Regional and stratigraphic variation of δ18OH2O

The δ18O data presented in this study are integrated withprevious δ18O data to examine δ18Oquartz variation due toproximity to granitic intrusions and stratigraphic positionwithin the Meguma Supergroup. With respect to the former,it is noted that an apparent spatial association between veingold deposits and intrusions has been inferred previouslybased on a zonation of mineralogy proximal the intrusions(Newhouse 1936; Smith and Kontak 1986; Kontak andSmith 1993). For example, the presence of garnet,amphibole, tourmaline and epidote are more abundant inveins proximal granites. In this regard, the δ18OH2O datahave been plotted versus distance from the nearest graniticintrusion (Fig. 7) and following points are noted:

1. There is a suggestion that a general trend of decreasingδ18OH2O for deposits nearer to granitic intrusions exists,but further study would be required to confirm this. Thetwo deposits with the lowest δ18OH2O values occur atthe deepest and shallowest part of the stratigraphy andare discussed below. Also plotted in this diagram aresamples from small vein occurrences (Table 1; the Xsymbols in Fig. 7), which are similar in their structuralsettings to the veins at Dufferin and The Ovens;

2. The lowest δ18OH2O value is recorded for the BeaverDam deposit, which is ≤1 km distance from the 374-MaRiver Lake granite. This deposit is noted for its veinmineralogy, including calcic plagioclase, K-feldspar,garnet, tourmaline, amphibole, epidote and biotite

along with Bi–Te–Ag phases and sulphides (Kontakand Smith 1993). In addition, some quartz veins areobserved to post-date schistose rocks (andalusite–cordierite–staurolite schist) that define an aureolearound the intrusion (Kontak et al. 1990b);

3. Data for West Gore is also noted to have some lowδ18OH2O values, although distant from an intrusion andlocated highest in the stratigraphy. The vein mineralogyof quartz–chlorite–carbonate–muscovite–sulphide istypical of Meguma veins and contrasts with that atBeaver Dam.

Thus, the data currently available are equivocal in termsof suggesting a genetic relationship to the nearest graniticintrusions.

In order to examine the possible relationship between theδ18Oquartz values of veins and stratigraphic position ofdeposits within the Meguma Supergroup, the data havebeen converted to δ18OH2O values for 400°C and 350°Cand plotted as a function of stratigraphy (Fig. 8). We firstnote that the data for the different deposits shows littleintra-deposit variation, which suggests a uniform δ18OH2O

value for the fluid and that vein formation must haveoccurred over a narrow temperature interval in all cases.Although there is a trend of increasing δ18OH2O withstratigraphic height, there are some departures from thegenerally uniform increase, notably for Dufferin and WestGore. Three possible explanations are explored to accountfor this trend: (1) fluid mixing; (2) fluid cooling; and (3)fluid/rock interaction.

1. Fluid mixing: Evidence for presence of different fluidsin hydrothermal systems is commonly preserved asmixing trends in temperature-salinity plots based onfluid inclusion data, in addition to variable XCO2 wheresuch fluids occur. Available data for fluid inclusionsfrom Meguma vein gold deposits (Kontak et al. 1988;Kontak et al., 1996; Bierlein and Smith, 2003; Kontakand Horne 2010) indicate the fluids are uniform withrespect to their chemistry, with low-salinity aqueous–carbonic fluids dominating. An aqueous fluid is rarelyobserved, but there is no petrographic evidence toindicate coexistence of this fluid with the primaryaqueous–carbonic fluid. Thus, that mixing fortuitouslyoccurred at all deposits without leaving any evidencewhile possible is considered an unlikely explanation.

2. Fluid cooling: Given that the trend observed reflects amulti-kilometre section through the stratigraphy of theMeguma Supergroup, it might be expected that coolingof the vein-forming fluids may account for somevariation. In this regard, we note that, in order tochange the δ18O signature of vein quartz by the amountobserved, a fluid with an initial δ18O value of +9‰, as

Fig. 7 Plot of δ18OH2O versus distance to the nearest outcroppinggranite based the provincial geological map of Nova Scotia andisotopic data in Fig. 6. Sample sites labelled are from West Gore (WG)and Beaver Dam (BD). The X symbols represent the small quartzveins occurrences included in this study (see Fig. 1 and Table 1)

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calculated for 400°C, would have to cool to near 250°C.Although this may seem reasonable, there are severalreasons to exclude this scenario: (1) at this temperature(i.e. 250°C to 300°C), inferred pressure (2–3°kbars) andfluid composition, fluid unmixing is expected based onphase equilibria (Schmidt and Bodnar 2000), which isnot observed in the fluid inclusion studies; (2) for thedeposits with highest δ18OH2O values (Dufferin, TheOvens), fluid inclusion data indicate vein formationexceeded these lower temperatures of 250–300°C; and(3) for the deposit at the highest stratigraphic level(West Gore), fluid inclusion data constrain veinformation to≥350–400°C. Thus, although some cool-ing of the fluid is likely, it was not systematic throughthe stratigraphy. It is also noted that in recent fluid/rockmodelling studies of metasedimentary rock hosted veingold systems, Mernagh and Bierlein (2008) noted thatfluid cooling was not an important part of themineralizing systems.

3. Fluid/rock interaction: In order to address the possibleinfluence of wall rock, the data have been modelledfor interaction of an initial vein-forming fluid withδ18O=+9‰ with a model wall rock at temperatures of500°C, 400°C and 300°C using the equations of Taylor(1978). The δ18O values for whole-rock samples(Longstfaffe et al. 1980) are +11.7‰±1.2 (1σ) formetasandstone and +11.5‰±0.7 (1σ) for slate; a valueof +11.5‰ was used as the starting δ18O value for thewhole rock. For the calculations, variable modalcompositions were used, essentially mixtures of thedominant silicate phases in the Meguma rocks, thesebeing quartz, albite, muscovite and chlorite. Althoughcarbonate is present, it occurs at the expense of albite,and these two minerals have similar Δmineral–H2Ovalues, thus similar results occur regardless of thealbite/carbonate ratio. Also relevant is that lower partof the Meguma Supergroup is dominated by meta-sandstone and metasiltstone, whereas the upper part ismetasiltstone and shale dominant (e.g. Horne andPelly 2007), thus modal proportions used reflect this.This change in lithology is manifested in an overallincrease in the modal amount of muscovite andchlorite present in the wall rocks. We also note thatchlorite is also present as a product of wall rockalteration, particularly where shale forms part of thewall rock.

The results for fluid/rock interaction using three modelcompositions are summarised in Fig. 9, along with detailsused in their construction. Although the diagram indicatesthe δ18O values for altered whole rock, they also indicate,by inference and mass balance, the general trend forδ18OH2O. Two important points emerge from the calcu-lations: (1) in order for a fluid of δ18O=+9‰ to increaseto +10‰ or +11‰, the temperature of the fluid must be inthe 400°C to 500°C range, otherwise the wall rock becomestoo enriched in δ18O at lower temperatures and, hence, thefluid depleted, which is opposite to what is observed; and(2) chlorite must be present in the wall rock in order toincrease the δ18Ofluid. As seen in the model plots, withoutchlorite (Fig. 9a versus 9b, c), there is very little decrease inthe δ18O values of the wall rock, hence the fluid cannotincrease in δ18O, which is what is observed. The estimatedmodal amounts of chlorite required are between 10% and20%, which are not unrealistic and consistent with ourobservations of wall rocks in the deposit areas. Impor-tantly, the requirement of chlorite in the wall rock isconsistent with the known increase in the amount ofsiltstone and slate upwards in the Meguma Supergroupand presence of chlorite as an alteration phase. Althoughthe modelling indicates temperatures higher than antici-pated for the veins, this may indicate that there was, in

Fig. 8 a Plot of δ18Oquartz for Meguma gold deposits (Kontak et al.1996; Kontak and Kerrich 1997; this study) versus relative strati-graphic position in the Meguma Supergroup. b Plot of δ18OH2O valuesfor Meguma deposits calculated for 350°C and 400°C using thequartz–H2O fractionation equation of Matsuhisa et al. (1979) andδ18Oquartz vein data from Fig. 7a. The shaded box is the temperature-dependent difference of δ18OH2O for a fluid at 400°C and 300°C; seetext for further discussion. Note that for West Gore there are twodistinct populations for δ18Oquartz and, hence, δ

18OH2O. The depositsplotted are from base to top: MR Moose River, TG Tangier, BDBeaver Dam, FMS Fifteen-Mile Stream, MOL Molega, EC EcumSecum, ML Mile Lake, USH Upper Seal Harbour, DUFF Dufferin, SHSheet Harbour, CAR Caribou, LCH Lochaber, OV The Ovens, WGWest Gore GH. The GHT refers to the Goldenville–Halifax transitionzone, as discussed in the text

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fact, cooling of the fluid from this temperature commen-surate with vein formation.

In summary, the δ18O data for vein quartz does notshow a demonstrably obvious relationship to graniticintrusions, although it is noted that the deposit closest toan intrusion does record the lowest δ18Oquartz value and,by inference, the lowest δ18OH2O values. However, thereis an apparent trend of between δ18OH2O values fordeposits and their stratigraphic position such that valuesincrease upwards. This trend cannot be accounted forby models of fluid mixing or simple cooling, butinstead is modelled to reflect the fluids having inter-acted with the host rocks within which there is a changein their modal composition, in particular, an increase inthe amount of chlorite.

Implications for models of vein formation

A long-standing issue for the Meguma vein gold systemshas been on whether a singular or multiple model isrequired to explain the coexistence of the concordant versusdiscordant styles of quartz veining. The multiple orpolygenetic vein model, as reviewed by Sangster (1990,1992), advocates an early vein-forming event during theinitial stages of the Acadian Orogeny while the strata wasstill horizontal, thus pre-dating the regional folding of thehost rocks and peak metamorphism that coincided withlater introduction of veins. In contrast, a singular vein-forming event (Mawer 1987; Kontak et al. 1990a), based inpart on the mutual cross-cutting relationships of all veintypes, attributed vein formation to a single event with veinformation occurring syn- or post-folding of the stratigraphy,thus into an upright stratigraphy. Most recently, Horne andCulshaw (2001), based on a detailed structural analysis ofMeguma vein systems, favoured a single vein-forming eventand concluded that it was consistent with a flexural-slipfolding mechanism (Tanner 1989). The same mechanismhas been used to explain the nature of veining in somewhatanalogous settings in gold deposits of Victoria, Australia(Jessell et al. 1994; Fowler 1996; Fowler and Winsor 1996,1997). The results of the present study add further supportto the singular model of vein formation since this favours afluid uniform not only in isotopic composition, but alsotemperature. We also note that since a multiple-vein modelwould presumably be commensurate with increasingtemperatures as metamorphism progressed, then this wouldmanifest itself in a range of δ18Oquartz values due to thetemperature-dependent fraction of 18O between mineral–H2O. Our conclusion is also consistent with the findings ofBeaudoin and Pitre (2005) who, based on multiple analysesof different vein types within the same vein field, foundsimilar δ18Oquartz values that suggest deposition of quartzfrom a fluid uniform in both its δ18OH2O and temperature.

Conclusions

The Meguma gold deposits, Novas Scotia, represent aclassic example of slate-belt hosted auriferous quartz veins.Detailed sampling of two structurally similar, but tempo-rally distinct (i.e. 408 versus 380 Ma) deposit areas hasshown that all the vein types present, including discordantand concordant arrays, have the very similar δ18Oquartz

values. These results are consistent with earlier structuralstudies suggesting the veins represent a single vein-formingevent, having formed during flexural-slip in response tolate-stage tightening of the folded host rocks. The similarδ18Oquartz values and P-T conditions for vein formation alsoinfer similar δ18OH2O values and, thereby, possibly similar

Fig. 9 Plots of fluid/rock ratio (X axis) versus calculated δ18Oaltered rock

(Y axis) for interaction of rock of shown modal composition (Qtz–Alb–Chl–Musc) having an initial δ18O=+12‰ that reacts with a fluid withδ18O=+9‰. Note that a temperature of 500°C is required in order forthe fluid to increase its δ18O value, as reflected by the decrease in δ18Ofor the altered rock. The plots were generated using the equation ofTaylor (1978) governing fluid/rock interaction and the followingfractionation equations: quartz–H2O (Matsuhisa et al. 1979), albite–H2O (O’Neil and Taylor 1969), muscovite–H2O (O’Neil and Taylor1969) and chlorite–H2O (Savin and Lee 1988)

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source reservoirs. Thus, vein fluids of similar isotopiccomposition were generated during the two major tectono-thermal events in this terrane which coincide with regionaldeformation (408 Ma) and intrusion of large graniticbatholiths (380 Ma). Integration of these new data with anexisting data set for the Meguma deposits indicates aprogressive upwards increase in δ18OH2O for differentdeposits. This variation cannot be accounted for by simplecooling of the fluid and, instead, can be modelled based onfluid/rock interaction to reflect interaction of the fluid withthe host stratigraphy.

Acknowledgments The field work for this study was done when D.J. Kontak and R.J. Horne worked for the Nova Scotia Department ofNatural Resources, Halifax, Nova Scotia. Completion of the researchwas supported by a Laurentian University Start-up Grant to D. Kontakand Natural Science and Engineering Research Council (NSERC)Discovery Grants to D. Kontak and T.K. Kyser. The manuscriptbenefited from insightful comments by P. Williams, G. Beaudoin, F.Bierlein and an anonymous reviewer for which we are grateful.

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