Miner Deposita (2011) 46:289–304
DOI 10.1007/s00126-011-0332-0
ARTICLE
An oxygen isotope study of two contrasting orogenic vein
gold 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 gold
deposits of similar geological setting but different ages (The
Ovens, 408 Ma; Dufferin, 380 Ma) in the Meguma Terrane
of Nova Scotia has been done to compare and contrast their
δ18Oquartz 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 with
similar average δ18O values of +15.2±0.9‰ (n=16) for
The Ovens and +15.7±0.6‰ (n=12) for Dufferin. Using an
average δ18O value of +15.4‰ for the two deposits, the
corresponding δ18OH2O values, calculated for 400°C and
350°C based on constraints from mineral assemblages and
fluid inclusion studies, indicate averages of 11.4±0.2‰
and +10.2±0.2‰, respectively. The isotopic data indicate
that: (1) the vein-forming fluids have a metamorphic
signature, (2) all vein types in the two deposits represent
formation from a single, isotopically homogeneous fluid,
and (3) a fluid of similar isotopic signature was generated
by two contrasting tectono-thermal events in the Meguma
Editorial handling: G. Beaudoin
D. J. Kontak (*)
Department of Earth Science, Laurentian University,
Sudbury, ON, Canada P3E 2E6
e-mail: [email protected]
R. J. Horne
Acadian Mining,
1969 Lower Water Street,
Halifax, NS, Canada B3J 2R7
K. Kyser
Department of Geological Sciences and Geological Engineering,
Queen’s University,
Kingston, ON, Canada K7L 3N6
Terrane that were separated by 30 Ma. Integration of these
results with previously published data for 14 Meguma gold
deposits indicate a general stratigaphic dependence in
δ18OH2O values for deposits when arranged in their relative
stratigraphic position such that δ18OH2O values increase
upwards in the stratigraphy. This apparent trend cannot be
explained by models involving either fluid mixing or
cooling of the vein-forming fluids, but instead is modelled
using fluid/rock interaction taking into account a change in
the modal mineralogy of the metasedimentary rocks
upwards in the stratigraphy.
Keywords Nova Scotia . Meguma terrane . Orogenic gold
deposits . The Ovens . Dufferin . Oxygen isotopes
Introduction
Orogenic gold-quartz vein systems occur in rocks from the
Archean onwards, although certain periods of crustal
growth appear to be more endowed than others (Goldfarb
et al. 2001), as well as some tectonic settings and host rocks
(Goldfarb et al. 2005; Bierlein et al. 2006). Despite
extensive study (reviews in Groves et al. 1998; Bierlein and
Crowe 2000; Goldfarb et al. 2005; Dubė and Gosselin
2007), varied opinions have and continue to exist regarding
the source of both fluids and metals. For example, different
models source the mineralizing fluid from the mantle
(Cameron 1988; Colvine 1989), from deep- to mid-crustal
reservoirs during pro-grade metamorphism (Henley et al.
1976; Phillips 1993; Pettke et al. 1999; Jia and Kerrich
1999), magmatic reservoirs (Burrows et al. 1986; de Ronde
et al. 2000), or a mixture of metamorphic and meteoric fluids
(Nesbitt and Muehlenbachs 1995; Craw and Chamberlain
1996). In some cases, there is evidence of multiple sources
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Miner Deposita (2011) 46:289–304
in single veins, presumably due to a protracted history for
vein formation (Pettke and Frei 1996; Ridley and Diamond
2000), 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 gold
setting similar to those mentioned above, has been the
focus of considerable study (e.g. Kontak et al. 1990a;
Sangster 1990; Ryan and Smith 1998). This work has
demonstrated that the vein systems are similar with respect
to their geological setting, structural style, vein mineralogy,
and geochemical attributes (Kontak et al. 1990a). In
addition, well-exposed surface and underground exposures
integrated with robust geochronology (see below) indicate
that the veins formed at two distinct periods. These two
vein-forming events coincided with regional deformation
and subsequent emplacement some 30 Ma later of
voluminous granites; notably, similar multiple ages for vein
emplacement and related gold mineralization has been
established in the Lachlan fold belt of Australia (Arne et
al. 1998; Bierlein et al. 2001). Despite the considerable
efforts directed at the Meguma gold deposits and the
similarities for the many districts, different models have and
continue to be proposed for these deposits, as is the case for
other orogenic gold districts.
In order to address some of the outstanding issues of the
Meguma gold deposits, two well-characterised vein settings
of different ages, based on Re–Os and 40Ar/39Ar dating, but
similar in all other respects, were chosen for a detailed
oxygen isotopic study. The purpose of this work was aimed
specifically at the following two issues: (1) to see if the
apparently different vein types record similar or different
δ18Oquartz signatures which would, therefore, allow addressing 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 the
tectonic evolution of the Meguma Terrane can be distinguished isotopically. Furthermore, by integrating the new
data with previously published results, issues of isotopic
variability within a regional context could be addressed
(e.g. Rushton et al. 1993; Nesbitt and Muehlenbachs
1995; Beaudoin and Pitre 2005).
Fig. 1 Regional geological setting of the Meguma Terrane, southern
Nova 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 shown
as MB. The inset map shows the distribution of terranes in the
Canadian part of the Appalachian orogen, which includes, in addition
to the Meguma terrane (M), the Avalon (A), Dunnage (D), Gander (G)
and Humber (H) terranes. The Liscomb Complex (LC) in the eastern
part of the terrane is discussed in the text
Regional geological setting
The study area is located within the Meguma Terrane of
Nova Scotia, which forms part of the Canadian segment of
the composite Appalachian Orogen (Williams and Hatcher
1983). The terrane is the most easterly of five lithotectonic
zones that comprise the composite orogen (Fig. 1) and was
emplaced against the adjoining Avalon Terrane along the
east–west trending Cobequid–Chedabucto Fault Zone during
the Late Devonian closure of the Rheic Ocean, the dextral
docking of the terrane resulting in the Acadian Orogeny.
Geologically, the terrane is dominated by Lower Paleozoic
metasedimentary rocks of the Meguma Supergroup and large
Miner Deposita (2011) 46:289–304
peraluminous granitoid bodies (e.g. South Mountain and
Musquodoboit batholiths; Fig. 1). Lesser amounts of
Silurian-Devonian metasedimentary and metavolcanic rocks
overlie the Meguma Supergroup in the western part of the
terrane, whereas sedimentary and volcanic rocks of Carboniferous and Triassic–Jurassic age occur in the central part of
the terrane.
The Meguma Supergroup consists of a ca. 10 km
succession of the metasandstone-dominated Goldenville
Group and the overlying metasiltstone-dominated Halifax
Group; the transition between the two referred to as the
Goldenville–Halifax transition zone. The sequence was
deformed into upright, shallowly plunging, north- to
northeast-trending folds and metamorphosed to greenschist
to amphibolite grade during the Acadian Orogeny, the age
of which is constrained to 400–410 Ma (Keppie and
Dallmeyer 1995; Kontak et al. 1998). The metasedimentary
rocks were intruded in the Late Devonian by peraluminous
granites (380–375 Ma; Clarke et al. 1993; Kontak et al.
2003; Reynolds et al. 2004) which outcrop the length of the
terrane; lesser amounts of dioritic and gabbroic phases also
occur (Clarke et al. 1993). Important in a genetic context to
the gold deposits is that, based on both geophysical data
and regional mapping (see Horne et al. 1992), including the
extent of contact aureoles, the contacts of the large
batholiths (e.g. South Mountain and Musquodoboit,
Fig. 1) are steeply dipping and do not extend laterally
beneath the stratigraphy.
Although not well constrained, there is some relevant
information that pertains to the inferred basement to the
Meguma Terrane. Complexly folded, high-grade metamorphic rocks comprising mixed gneisses occur in the central
part of the terrane and are referred to as the Liscomb
Complex (Dostal et al. 2006). These high-grade metamorphic rocks record cooling to below 400–500°C at about
380 Ma (Kontak and Reynolds 1994), which coincides with
emplacement of the large granitic batholiths in the terrane.
Based on geochronologic and chemical constraints, Dostal
et al. (2006) argue this complex may represent a core
complex. Alternatively, White et al. (2009) argue that these
rocks are modified Meguma Supergroup with the high
metamorphic grade due to nearby granites. Other potential
basement rocks to the Meguma Supergroup occur as highgrade (i.e. granulite grade), xenolithic paragneisses in
374 Ma lamprophyric dyke rocks outcropping along the
eastern part of the terrrane (Owen et al. 1988) or in fault
splays off the regionally extensive Cobequid Chedabucto
Fault 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 basement
rocks that lay beneath the Meguma Supergroup and are
291
referred to later in the discussion of potential source
reservoirs for vein-forming fluids (i.e. Tangier xenoliths).
Geological features of Meguma gold deposits
The general features of Meguma gold deposits have been
summarised elsewhere (e.g. Smith and Kontak 1986; Ryan
and Smith 1998), thus only a brief summary is provided
here. Deposits occur at or near hinge areas of anticlinal
structures of regional folds where quartz veins are most
abundant and include both concordant and discordant types
(see Horne and Culshaw (2001) for a discussion of vein
types). The dominant vein type consists of concordant
veins, that includes bedding-concordant, bedding-parallel,
and saddle-reef types (Horne and Culshaw 2001), and these
veins show a preference for sandstone siltstone contacts;
less abundant discordant-vein types also occur. The
bedding-concordant veins are laterally continuous and show
vertical continuity. Gold occurs in all vein types but often
shows higher grades where discordant vein cut concordant
vein types. Veins are quartz dominant (i.e. ≥90–95%) with
lesser carbonate and Fe–As sulphides (pyrrhotite, pyrite,
arsenopyrite) but also include a variety of silicates
(tourmaline, garnet, epidote, plagioclase, K-feldspar, muscovite, amphibole, biotite, apatite) and other sulphides
(galena, sphalerite, stibnite) plus Bi–Te–Ag–Hg phases
(e.g. Kontak and Smith 1993). Scheelite can locally be
abundant, in one case, there having been production
(Moose River, Fig. 1). In addition, antimony was produced
in addition to gold from the West Gore Sn–Au deposit
(Fig. 1; Kontak et al. 1996) which, interestingly, occurs
highest in the stratigraphy of all deposits. Significantly, the
mineralogy of the veins within a deposit shows a zonal
distribution depending on the spatial association of deposits to
intrusions (Newhouse 1936; Smith and Kontak 1986). For
example, the Beaver Dam deposit, located 1 km of the River
Lake granite and partly cross-cutting its contact aureole
(Kontak et al. 1990b), has veins with a high-temperature
mineral assemblage (e.g. amphibole–garnet–tourmaline–
plagioclase) and also containing Bi–Te phases, which are
noted to occur in intrusion-related gold settings (Thompson
and Newberry 2000). In general, the conditions of vein
formation are estimated at 2–3 kbars and 350–400°C based
on mineralogical, isotopic, and fluid inclusion work (Kontak
and Smith 1989a, 1993; Kontak et al. 1990a, 1996).
Geology of The Ovens and Dufferin deposits
The geology of The Ovens and Dufferin districts are briefly
described in order to provide a setting for the sampled veins.
Of significance in this study is the similarity of the setting of
292
the two areas, despite occurring within different parts of the
stratigraphy, and occurrence of the same vein types although
the amount of veins is greater at the Dufferin deposit.
The Ovens deposit
The Ovens district occurs in the hinge of a tight (interlimb
angle 35–50°) regional anticlinal structure, one of several
northeast-trending fold structures of box- and chevron style
in the region (Fig. 2a). The area is underlain by rocks of the
lower Halifax Group, which is dominated by slate and
metasandstone metamorphosed to lower greenschist facies.
The closest exposed intrusion is the South Mountain
Batholith, which lies 25 km to the north and has steep
contacts, and there is no evidence of thermal effects. The
structural evolution of the area is described in detail by
Horne and Culshaw (2001) who note that an early phase of
flexural-flow folding was followed by a period of flexuralFig. 2 a Simplified geology of
The Ovens area which is located
in the hinge of a northeasttrending anticline (map modified
after Horne and Culshaw 2001).
Note that the area is underlain
by metasiltstone beds of the
Halifax Group. The vein samples used in this study came
from the western part of the area
highlighted as veined area,
which is well exposed along the
coastal section at Rose Bay. b, c
Plan map and cross-section
(facing east) of the Dufferin
deposit area (modified after
Horne and Jodrey 2002), which
is underlain by metasandstones
and interbedded metasiltstones
of the Goldenville Group. Note
the change in the wavelength of
the paired anticlines along the
Harrigan Cove Fault. The crosssection is a view looking east at
the west end of the Crown
Reserve Anticline near the recent workings and shows some
of the 13 stacked saddles present
based on a deep drill hole
(saddles numbered from 1 at the
top downwards). The plan map
shows the extent of both the
historical and recent (post1980s) workings
Miner Deposita (2011) 46:289–304
slip folding, as indicated by a variety of structural features,
most important being bedding-parallel movement horizons
with associated striations and slickenfibres.
The area contains an abundance of quartz veins (Fig. 3),
which importantly are mostly concentrated in the hinge area
of the fold (Fig. 2a). Veins types include both beddingparallel and discordant varieties, with the former including
veins variably described as bedding-concordant, saddle-reef
and buckled vein types. The discordant type includes
conjugate veins that may occur either as singular or paired
types. Important features of the veins follow: (1) presence
of all vein types (Fig. 3a, c, d), (2) mutual cross-cutting
relationships of veins (Fig. 3a, c), and (3) crack-seal
textures in both concordant (Fig. 3b) and discordant
(Fig. 3c, e) vein types. Importantly, gold has been observed
in all vein types, including discordant types (Fig. 3f). As
noted by Horne and Culshaw (2001), the orientation of the
veins, kinematic indicators, mutually cross-cutting relation-
Miner Deposita (2011) 46:289–304
ships of veins and similar accessory mineralogy of all vein
types (gold, scheelite, Fe–As sulphides) suggest emplacement of all vein types during late-stage tightening of an
existing fold structure by a flexural-slip fold mechanism.
The Dufferin deposit
The Dufferin area (Fig. 2b, c) is underlain by a pair of
anticlinal structures, the Salmon River and Dufferin Mines
anticlines, which are offset by a cross-fault, the Harrigan Cove
Fault with 1.5 km of sinistral displacement. Importantly, the
area is also distant (i.e. >10 km) from the nearest granitic
intrusion, which is relevant to the age-dating discussed below.
The stratigraphy consists of rocks of the Goldenville Group
and is dominated by medium to thickly bedded metasandstone
with lesser metasiltstone and slate. A typical sedimentary
cycle 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). Although
metasandstone dominates, cycles rich in metasiltstone and
slate do occur. The cross-section through one of the anticlines
(Fig. 2c), based on underground workings and surface
drilling, indicates a chevron fold with steep limbs and up
to 13 stacked saddles (note that in some cases paired veins
count as a single saddle) with 700 m of strike length.
Vein types present at Dufferin (Fig. 4) include beddingparallel and discordant types, with saddle-reefs and their
down limb extensions (leg reefs) dominating but with lesser
en echelon and discordant types. Important features of the
veins follow: (1) all vein types show mutually cross-cutting
relationships (Fig. 4b, e), (2) en echelon types show reverse
sense of displacement as expected for the gold geometry
(Fig. 4c), (3) en echelon and bedding-concordant types are
spatially associated (Fig. 4c), and (4) veins are commonly
composite (Fig. 4d). As in other good deposits, gold occurs
in all vein types, but in this case saddle-reef, en echelon and
laminated bedding-concordant veins are most enriched.
The structural evolution of the Dufferin area and vein
formation 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 localised
bedding-concordant veins and striations oriented perpendicular to the fold axis. Hence, vein formation is inferred to
have occurred during flexural-slip movement during a latestage tightening of an existing, tightly folded (i.e. chevron
style) anticlinal structure.
Relative and absolute timing of vein formation
at The Ovens and Dufferin
Timing of vein emplacement at the two deposit sites is
constrained by both field relationships and radiometric
293
dating (40Ar/39Ar, Re–Os). As noted above, field relationships suggest veining was synchronous with flexural-slip
folding late in the deformation history when fold limbs
were steepened. Thus, steep orientation of bedding planes
and the regional penetrative cleavage, both of which would
have been at high angles to the horizontally oriented
maximum compressive stress (σ1; Horne and Culshaw
2001), provided favourable conditions for the build-up of
fluid pressure (Sibson et al. 1988). As discussed by Sibson
et al. (1988), such misorientation of the dominant anisotropy (i.e. So and S1 in this case) to σ1 is the basis for the
fault-valve mechanism of vein formation. In the study
areas, the steeply dipping bedding-concordant veins, of
massive and laminated nature (i.e. ribbon or crack-seal type
fabric; Figs. 3 and 4), represent the fault veins, whereas the
en echelon veins would represent the flat veins. That vein
emplacement was late relative to the major folding event
and cleavage development is constrained by the following
features, which are seen in most gold deposit areas: (1)
veins truncate the trace of cleavage in adjacent wall rocks
and (2) cleaved wall rock fragments occur in the veins. In
addition, at some localities, vein alteration selvages
retrograde contact mineral assemblages (Kontak et al.,
1990b), hence, some veins are syn- to post-emplacement
of the 380 Ma granites in the Meguma Terrane.
The absolute timing of vein formation is of particular
relevance to the present study given that the setting of the
two areas is so similar. Previous work at the two sites
includes 40Ar/39Ar (Kontak et al. 1998) and Re–Os (Morelli
et al. 2005) dating. At The Ovens, two samples of wholerock slate within and adjacent veins yielded 40Ar/39Ar
plateau ages of 396± 3.5 Ma and 399± 2 Ma, which are
slightly less than 408 ±5 Ma Re–Os ages (model and
isochron) for vein arsenopyrite. These data have been
interpreted to reflect vein formation at 408 Ma at thermal
conditions above the argon blocking temperature of
micas (i.e. 300–350°C) with subsequent cooling and
closure of argon in micas at ca. 400 Ma. In contrast, at
Dufferin a whole-rock slate sample from within a saddle
reef quartz vein yielded a 40Ar/39Ar plateau age of 382±
2 Ma, which is identical to the 380± 3 Ma Re–Os isochron
and model ages for vein arsenopyrite. In contrast, a
whole-rock slate sample from outside the veined area
yielded a 40Ar/39Ar plateau age of 390 ±2 Ma, which
recorded the effects of regional metamorphism. Thus, at
these two areas, which are similar in their structural
setting, vastly different ages for the vein formation of 408
and 380 Ma are recorded which relate to, respectively,
regional deformation and granitic intrusion in the
Meguma Terrane. Where other deposits are well constrained from field relationships, supporting radiometric
dating (Ar–Ar) indicates ages of 370–380 Ma (Kontak et
al. 1990b; Kontak and Archibald 2002).
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Fig. 3 Photographs of representative vein types from surface outcrops of
The Ovens study area. a Bedding-concordant (horizontal) and conjugate
discordant (subvertical) veins cutting layered metasiltstone beds. Note that
the bedding-concordant veins are offset along faults controlling emplacement of the inclined veins. b Close-up of crack-seal textured beddingconcordant vein. Coin is 3 cm wide. c Crack-seal textured discordant (ac
type) vein cutting a thin bedding-concordant vein. Note that the crack-seal
texture only occurs where the discordant vein cuts siltstone beds and not
sandstone beds. Coin on left is 3 cm wide. d Fold closure (i.e. The Ovens
Anticline) with bedding-concordant veins going over the hinge. Hammer
in centre is 0.4 m long. e Discordant (ac type) vein in metasiltstone with
dextral offset on slip planes, as indicated by arrows. Note that the vein
continues in the lower left of photo. Hammer in centre is 0.4 m long. f
Close-up of crack-seal textured discordant (ac type) vein with visible gold
Nature of veins-forming fluid at Dufferin and The Ovens
and other Meguma gold deposits
isotopic signatures suggest low fluid/rock ratios existed
during vein formation.
Vein quartz samples from all vein types in deposits,
including Dufferin and The Ovens, are dominated by lowsalinity (5–8 wt.% equiv. NaCl) aqueous–carbonic (XCO2 =
0.1–0.2) inclusions; minor saline aqueous types of secondary
origin occur that are unrelated to the primary vein-forming
fluids (Kontak and Smith 1989b, 1988; Baker 1996; Kontak
et 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 stratigraphic
level in the Meguma Supergroup. The fluid inclusions
constrain vein formation to 350–400°C and 2–3 kbars.
The nature of the vein-forming fluids at The Ovens and
Dufferin is inferred from a large data base for the
Meguma gold deposits, but these data are discussed
collectively below. The sulphide assemblage (pyrrhotite–
pyrite–arsenopyrite) and narrow range of δ34Ssulphide
within individual deposits (±1–2‰) indicate the fluids were
reduced, consistent with the sulphide assemblage, and
remained so during vein formation (Kontak and Smith
1989b). The range of δ34Ssulphide values for all deposits
of +10 to +26‰ and their gradual change to positive values
up stratigraphy mimics the trend of δ34Ssulphide for the
Meguma Supergroup (Sangster 1992). Thus, the δ34S data
are interpreted to reflect inheritance of δ34S values of wall
rock sulphides due to fluid/rock interaction. Similarly, the
overlap of δ13C values (i.e. −18 to −26‰) for vein
carbonates and wall rock carbonate and graphite also
indicate fluid/rock interaction and inheritance of δ13C
values (Kontak and Kerrich 1997). In addition, these
Sampling and analytical techniques
Sampling at The Ovens and Dufferin deposits was guided
by earlier detailed mapping of Horne and Culshaw (20010
Miner Deposita (2011) 46:289–304
295
Fig. 4 Photographs of representative vein types from underground exposures at the
Dufferin deposit. Note that the
veins are found in the hinge and
limbs of the Crown Reserve
Anticlinal structure (see Fig. 2
for location). a A view along the
fold axis of a mined, auriferous
saddle-reef vein exposed in the
fold hinge. b An exposure of
different vein types on the fold
limb showing a beddingconcordant (bc) type vein on the
leg of the reef (i.e. continuation
of saddle vein on the limb of
fold), en echelon (ee) veins and
discordant veins (dv). The exposed pipe is about 1 m in
length. c Bedding-concordant
(bc) and en echelon (ee) veins
on the fold limb. Note the crackseal or laminated texture of the
concordant-type vein and reverse sense of shear indicated by
the en echelon veins. d Close-up
of a bedding-concordant-type
vein in Fig. 4c. e Beddingconcordant vein cut by a
discordant-vein type. f A pair of
sheared (i.e. reverse motion) en
echelon veins looking subparallel to the fold axis
and Horne and Jodrey (2002), respectively. In each area, all
vein types were sampled where relationships could be
clearly established. In addition, the same samples were part
of a more extensive sampling suite for fluid inclusion
studies, the results of which will be presented elsewhere.
Three additional samples from near the Oldham area were
selected for inclusion in this study to complement the
already large data base for Meguma gold veins.
High-purity quartz separates were produced by handpicking sub-millimetre-size fragments from coarse crushes
of quartz vein material using a binocular microscope.
Although some of the vein samples contained sulphide
and wall rock, such material was absent in the final
separates prepared. The samples all consist of highly
vitreous, glassy, fresh quartz that is free of impurities.
Quartz separates were analysed for δ18O at the Queen’s
University 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 a
Finnigan MAT 252 mass spectrometer. All values are
reported 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 of
data acquired in this study are compared and contrasted
with earlier δ18O data for Meguma quartz veins reported by
Kontak and Kerrich (1995, 1997) and Kontak et al. (1996),
which were analysed at the University of Saskatchewan
using 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.
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Miner Deposita (2011) 46:289–304
Table 1 Summary of oxygen isotope data for quartz vein samples from The Ovens and Dufferin districts, Nova Scotia
δ18OH2O
(‰) 400°C
δ18OH2O
(‰) 350°C
15.3
16.0
15.5
15.3
16.0
15.2
16.7
15.9
16.0
16.1
15.7
14.4
11.2
11.9
11.4
11.2
11.9
11.1
12.6
11.8
11.9
12.0
11.6
10.3
10.0
10.7
10.2
10.0
10.7
9.9
11.4
10.6
10.7
10.8
10.4
9.1
15.7±0.6
11.6
10.4
Sample
Vein type
Comments
δ18O (‰)
Quartz
Dufferin
DUFF 2
DUFF 3
DUFF 4A
DUFF 4B
DUFF 5B
DUFF 5 C
DUFF 6A
DUFF 6B
DUFF 7A
DUFF 7B
DUFF 7 C
DUFF 7D
ds
ds
bc
bc
ds
sd
fs
fs
ee, peg
fs
fs
ee
<30 cm; massive white vein
<20 cm; flat vein; massive white
<10 cm; some slate inclusions and trace pyrite
Quartz euhedra in bc vein on opposite side of hinge as 4A
10–20 cm; vein is between two bc veins, including #5 C
Near hinge of fold; massive white vein with faint cs textures
<6 cm; laminated cs textured vein
<4 cm; massive white vein adjacent vein #6A
<3–4 cm; deformed ee veins
<6–8 cm; massive white
Extension of vein 7B where cs texture occurs
<3–4 cm; extended ee veins
The Ovens
OV-99-1A
OV-99-1A
OV-99-1B
<1–2 mm vein in slate; on limb of fold; early vein (?)
Duplicate of 1A
14.5
14.5
16.0
10.4
10.4
11.9
9.2
9.2
10.7
OV-99-03
OV-99-04
OV-99-05
OV-99-06
OV-99-07
OV-99-08
OV-99-09
OV-99-10
OV-99-11
OV-99-12
OV-99-13
bc
bc
bc thurst related
vein below 1A with
good cs texture
ac
fs
ds
fs
fs
fs
ds
ds
fs
ds
fs
<4 cm; good cs texture developed; cuts shale-sst package
4–6 cm; pinches-swells on strike; thin slate bands in the vein
4–6 cm; steep discordant vein with trace pyrites
<6 cm; some slate inclusions and pyrite, coarse scheelite
<4–6 cm; contains arsenopyrite crystals that fill vein
<2–3 cm, tightly buckled vein in hinge of fold
4 cm; cuts early bc veins(#6) and is cut by #9
3–4 cm; cuts bc veins (#11)
<3–4 cm; cs texture developed; is cut by vein #10
4 cm; cuts bc veins; has vs texture and trace pyrite
<1–2 cm; ribbon texture with slate inclusions
15.2
12.3
15.4
15.4
15.5
15.3
15.1
16.4
15.6
15.7
15.2
11.1
8.2
11.3
11.3
11.4
11.2
11.0
12.3
11.5
11.6
11.1
9.9
7.0
10.1
10.1
10.2
10.0
9.8
11.1
10.3
10.4
9.9
OV-99-14
OV-99-15
ds
fs
<1–2 cm; massive texture with no cs texture
<2 cm; some slate inclusions and pyrite
15.9
15.4
15.2±0.9
11.8
11.3
11.2
10.6
10.1
9.9
13.8
14.9
15.0
9.7
10.8
10.9
8.5
9.6
9.7
Regional samples
OGR-99A
EO3-70
OV-99-DG
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 the
fractionation equation of Matsuhisa et al. (1979)
Firstly, the results for the two deposit areas are very similar in
terms 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 sets
despite a variety of vein types having been analysed at both
localities. Thus, although veins are discriminated based on
their structural setting or appearance (e.g. laminated versus
non-laminated, saddle veins versus limb veins, stratabound
vein 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-laminated
vein, there is no significant difference in δ18Oquartz values
Miner Deposita (2011) 46:289–304
(Fig. 5a, b). The very limited spread δ18Oquartz from
within and between veins for a single deposit is similar to
those reported by Beaudoin and Pitre (2005) in their
comprehensive analysis of the δ18O composition of
orogenic 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 have
also noted a limited spread of δ18Oquartz values within
deposits (e.g. Goldfarb et al. 1991; Ansdell and Kyser
1992; Rushton et al. 1993).
Also shown in Table 1 are three samples from beddingconcordant-type veins of similar structural setting as the
two deposit areas. The samples are come from near the
Oldham gold district (Fig. 1) and occur near the top of the
Goldenville Group. This material is included since it adds
to the regional data base for the Meguma gold districts and,
as is seen below, is included in the analysis of the
stratigraphic variation of δ18Oquatz values. These samples
have δ18Oquartz between +13.8 and +15.0‰, thus similar to
those in the two study areas.
Fig. 5 Line drawings based on underground photographs tracing out
the geology of veins and host rocks at the Dufferin gold deposit. In the
figures are shown the locations of vein quartz samples and their
corresponding δ18O values (see Table 1). Abbreviations follow: ee en
echelon vein, cs crack-seal or laminated vein, bc bedding-concordant
297
Discussion
δ18O of vein-forming fluids
The δ18OH2O values for the vein-forming fluids for the
two districts are assessed using the δ18Oquartz data,
inferred temperature of vein formation (400°C to 350°C;
see discussion above for justification of these temperatures) and appropriate mineral–H2O fractionation equation; results are summarised in Table 1. For The Ovens
samples, 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 values
range from +12.6‰ to +9.1‰ with averages for 400°C
and 350°C of +11.6‰ and +10.4‰, respectively.
The fractionation equation has been used to calculate the
δ18OH2O values for fluids in isotopic equilibrium with
quartz having known 18O values for a given temperature,
and this is displayed graphically in Fig. 6 along with the
data for the two deposits. It is apparent from Fig. 6 that the
range for δ18OH2O values is +9‰ to +12‰ for deposition at
350°C to 400°C. However, an alternative way to use this
diagram is to examine the maximum change in temperature
that is required to account for the range in δ18Oquartz values.
Based on this approach, a temperature variation of about
50°C is inferred for both deposits. Thus, the data indicate
that at both deposits vein quartz precipitated from fluids of
similar δ18OH2O and that this occurred over a very narrow
temperature interval of about 50°C.
A consideration regarding the δ18OH2O values must be
the possibility of modification of the fluid at the site of vein
formation due to fluid/rock interaction or fluid mixing such
that the values observed are not primary values. This
scenario is illustrated in Fig. 6 where two possible endmember migration paths of a fluid having an initial δ18O value
of +8‰ are shown since exchange with another reservoir
may happen at any temperature. That such a scenario may
have happened is considered unlikely for the following
reasons: (1) the degree of modification would have had to be
the same not only for individual veins within the same
deposit, but also at different deposits to give similar δ18O
data for all vein types; (2) although some wall rock alteration
is observed in these deposits, it is highly variable and
generally cryptic; and (3) there is no evidence that fluid
mixing existed in these deposits based on our fluid inclusion
studies, as noted above. An alternative to this scenario, this
being some fluid/rock alteration along the fluid pathway to
modify the δ18OH2O values, is addressed later.
In summary, the δ18OH2O values for the vein-forming
fluids in the two districts were similar at +9‰ to +12‰. It
is emphasised that this similarity occurs despite the fact that
the settings formed at vastly different times, at 408 Ma and
380 Ma, and in quite different lithological units, that is,
298
Miner Deposita (2011) 46:289–304
Fig. 6 Plot of temperature (°C) versus δ18Oquartz with isopleths of
δ18OH2O (in boxes) calculated using the quartz–H2O fractionation
equation of Matsuhisa et al. (1979). The δ18O vein quartz data for
Dufferin and The Ovens are shown as tick marks. The shaded boxes
indicate δ18OH2O values based on quartz precipitation at 350–400°C,
as discussed in the text. The dashed black arrows in the Dufferin plot
represent the possible evolution of a fluid with an initial δ18OH2O
value of +8‰ which reacts with host rocks with a δ18O value
of +16‰ to +18‰ such that the δ18OH2O of the vein-forming fluid is
increased (see text for discussion)
metasandstone at Dufferin versus metasiltone-slate at The
Ovens.
auriferous quartz vein systems globally (e.g. summary in
Goldfarb et al. 2005). Importantly for the Dufferin samples,
this fluid composition contrasts markedly with aqueous
saline, carbonic-poor fluids associated with granite-hosted
vein systems in the 380 Ma intrusions of the Meguma
Terrane (Carruzzo et al. 2000; Kontak et al. 2001). Also
significant is that the only exception to this generalisation
occurs in vein systems located at the contact of granites with
Meguma Supergroup rocks where a carbonic component is
noted which is considered to reflect local wall rock influence
(Carruzzo et al. 2000). Based on the foregoing discussion, a
direct connection to a dominantly magmatic fluid reservoir is
discounted.
Previous discussion concluded that a direct magmatic
contribution to the vein fluids is unlikely, hence a
metamorphic fluid is inferred, which requires a link to
large-scale tectonic processes. For The Ovens area, this can
be related to regional Acadian deformation throughout the
Meguma Terrane, hence a classic orogenic-type model for
vein formation (Goldfarb et al. 2005). Whereas such
processes are not coincident with vein formation at
Dufferin, emplacement of the 380 Ma granites in the
Meguma Terrane was widespread and must have lead to
devolitisation of the crust. In fact, generation of these melts
may have been coincident with formation of 380 Ma
granulite facies metamorphic rocks which occur as melange
in fault zones (e.g. Cobequid Fault Zone in Fig. 1; Gibbons
et 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
Source reservoir(s) of the vein-forming fluids
The origin of the vein fluids is evaluated based on the
established ages for vein formation and the reservoirs
present at the time of vein formation. In the case of The
Ovens, where vein formation occurred at 408 Ma, igneous
activity was absent and instead the age overlaps the time of
regional deformation. In contrast, vein emplacement at
Dufferin is constrained to 380 Ma and overlaps emplacement of the granitic batholiths. There is, however, a spatial
argument against a granitic source for the vein fluids (see
Fig. 1) despite the fact that the nearest granites have
δ18OH2O values overlapping those of the gold veins values
(+7‰ to +12‰ at 400°C; Carruzzo et al. 2004; Kontak and
Kyser 2010), and these latter values overlap the field for
magmatic fluids (Sheppard 1986).
Given the different ages for vein emplacement, but
similar apparent δ18OH2O values, two scenarios are possible: (1) the same reservoir was tapped, but at two different
times, or (2) different source reservoirs fortuitously generated
fluids with similar δ18O values. Before addressing these
scenarios, it is first relevant to review the implications of the
fluid inclusion assemblages in the vein systems discussed
previously. Quartz-hosted fluid inclusions in the veins are
similar in the two areas and are of the aqueous–carbonic
type (XCO2 =0.1–0.2, 5–8 wt.% NaCl equiv.), which corresponds to the fluid generally associated with orogenic
Miner Deposita (2011) 46:289–304
character was generated as part of the widespread generation
of granitic magmas at this time. Although not conclusive, the
general similarity of the fluid chemistry and δ18OH2O values
at the two areas is a strong argument that the same source
rocks were twice tapped to generate the fluids which have
given rise to the Meguma vein deposits.
Regional and stratigraphic variation of δ18OH2O
The δ18O data presented in this study are integrated with
previous δ18O data to examine δ18Oquartz variation due to
proximity to granitic intrusions and stratigraphic position
within the Meguma Supergroup. With respect to the former,
it is noted that an apparent spatial association between vein
gold deposits and intrusions has been inferred previously
based on a zonation of mineralogy proximal the intrusions
(Newhouse 1936; Smith and Kontak 1986; Kontak and
Smith 1993). For example, the presence of garnet,
amphibole, tourmaline and epidote are more abundant in
veins proximal granites. In this regard, the δ18OH2O data
have been plotted versus distance from the nearest granitic
intrusion (Fig. 7) and following points are noted:
1. There is a suggestion that a general trend of decreasing
δ18OH2O for deposits nearer to granitic intrusions exists,
but further study would be required to confirm this. The
two deposits with the lowest δ18OH2O values occur at
the deepest and shallowest part of the stratigraphy and
are discussed below. Also plotted in this diagram are
samples from small vein occurrences (Table 1; the X
symbols in Fig. 7), which are similar in their structural
settings to the veins at Dufferin and The Ovens;
2. The lowest δ18OH2O value is recorded for the Beaver
Dam deposit, which is ≤1 km distance from the 374-Ma
River Lake granite. This deposit is noted for its vein
mineralogy, including calcic plagioclase, K-feldspar,
garnet, tourmaline, amphibole, epidote and biotite
Fig. 7 Plot of δ18OH2O versus distance to the nearest outcropping
granite based the provincial geological map of Nova Scotia and
isotopic data in Fig. 6. Sample sites labelled are from West Gore (WG)
and Beaver Dam (BD). The X symbols represent the small quartz
veins occurrences included in this study (see Fig. 1 and Table 1)
299
along with Bi–Te–Ag phases and sulphides (Kontak
and Smith 1993). In addition, some quartz veins are
observed to post-date schistose rocks (andalusite–
cordierite–staurolite schist) that define an aureole
around the intrusion (Kontak et al. 1990b);
3. Data for West Gore is also noted to have some low
δ18OH2O values, although distant from an intrusion and
located highest in the stratigraphy. The vein mineralogy
of quartz–chlorite–carbonate–muscovite–sulphide is
typical of Meguma veins and contrasts with that at
Beaver Dam.
Thus, the data currently available are equivocal in terms
of suggesting a genetic relationship to the nearest granitic
intrusions.
In order to examine the possible relationship between the
δ18Oquartz values of veins and stratigraphic position of
deposits within the Meguma Supergroup, the data have
been converted to δ18OH2O values for 400°C and 350°C
and plotted as a function of stratigraphy (Fig. 8). We first
note that the data for the different deposits shows little
intra-deposit variation, which suggests a uniform δ18OH2O
value for the fluid and that vein formation must have
occurred over a narrow temperature interval in all cases.
Although there is a trend of increasing δ18OH2O with
stratigraphic height, there are some departures from the
generally uniform increase, notably for Dufferin and West
Gore. Three possible explanations are explored to account
for this trend: (1) fluid mixing; (2) fluid cooling; and (3)
fluid/rock interaction.
1. Fluid mixing: Evidence for presence of different fluids
in hydrothermal systems is commonly preserved as
mixing trends in temperature-salinity plots based on
fluid inclusion data, in addition to variable XCO2 where
such fluids occur. Available data for fluid inclusions
from Meguma vein gold deposits (Kontak et al. 1988;
Kontak et al., 1996; Bierlein and Smith, 2003; Kontak
and Horne 2010) indicate the fluids are uniform with
respect to their chemistry, with low-salinity aqueous–
carbonic fluids dominating. An aqueous fluid is rarely
observed, but there is no petrographic evidence to
indicate coexistence of this fluid with the primary
aqueous–carbonic fluid. Thus, that mixing fortuitously
occurred at all deposits without leaving any evidence
while possible is considered an unlikely explanation.
2. Fluid cooling: Given that the trend observed reflects a
multi-kilometre section through the stratigraphy of the
Meguma Supergroup, it might be expected that cooling
of the vein-forming fluids may account for some
variation. In this regard, we note that, in order to
change the δ18O signature of vein quartz by the amount
observed, a fluid with an initial δ18O value of +9‰, as
300
Miner Deposita (2011) 46:289–304
Fig. 8 a Plot of δ18Oquartz for Meguma gold deposits (Kontak et al.
1996; Kontak and Kerrich 1997; this study) versus relative stratigraphic position in the Meguma Supergroup. b Plot of δ18OH2O values
for Meguma deposits calculated for 350°C and 400°C using the
quartz–H2O fractionation equation of Matsuhisa et al. (1979) and
δ18Oquartz vein data from Fig. 7a. The shaded box is the temperaturedependent difference of δ18OH2O for a fluid at 400°C and 300°C; see
text for further discussion. Note that for West Gore there are two
distinct populations for δ18Oquartz and, hence, δ18OH2O. The deposits
plotted are from base to top: MR Moose River, TG Tangier, BD
Beaver Dam, FMS Fifteen-Mile Stream, MOL Molega, EC Ecum
Secum, ML Mile Lake, USH Upper Seal Harbour, DUFF Dufferin, SH
Sheet Harbour, CAR Caribou, LCH Lochaber, OV The Ovens, WG
West Gore GH. The GHT refers to the Goldenville–Halifax transition
zone, as discussed in the text
calculated for 400°C, would have to cool to near 250°C.
Although this may seem reasonable, there are several
reasons to exclude this scenario: (1) at this temperature
(i.e. 250°C to 300°C), inferred pressure (2–3°kbars) and
fluid composition, fluid unmixing is expected based on
phase equilibria (Schmidt and Bodnar 2000), which is
not observed in the fluid inclusion studies; (2) for the
deposits with highest δ18OH2O values (Dufferin, The
Ovens), fluid inclusion data indicate vein formation
exceeded these lower temperatures of 250–300°C; and
(3) for the deposit at the highest stratigraphic level
(West Gore), fluid inclusion data constrain vein
formation to≥350–400°C. Thus, although some cooling of the fluid is likely, it was not systematic through
the stratigraphy. It is also noted that in recent fluid/rock
modelling studies of metasedimentary rock hosted vein
gold systems, Mernagh and Bierlein (2008) noted that
fluid cooling was not an important part of the
mineralizing systems.
3. Fluid/rock interaction: In order to address the possible
influence of wall rock, the data have been modelled
for interaction of an initial vein-forming fluid with
δ18O=+9‰ with a model wall rock at temperatures of
500°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) for
metasandstone and +11.5‰±0.7 (1σ) for slate; a value
of +11.5‰ was used as the starting δ18O value for the
whole rock. For the calculations, variable modal
compositions were used, essentially mixtures of the
dominant silicate phases in the Meguma rocks, these
being quartz, albite, muscovite and chlorite. Although
carbonate is present, it occurs at the expense of albite,
and these two minerals have similar Δmineral–H2O
values, thus similar results occur regardless of the
albite/carbonate ratio. Also relevant is that lower part
of the Meguma Supergroup is dominated by metasandstone and metasiltstone, whereas the upper part is
metasiltstone and shale dominant (e.g. Horne and
Pelly 2007), thus modal proportions used reflect this.
This change in lithology is manifested in an overall
increase in the modal amount of muscovite and
chlorite present in the wall rocks. We also note that
chlorite is also present as a product of wall rock
alteration, particularly where shale forms part of the
wall rock.
The results for fluid/rock interaction using three model
compositions are summarised in Fig. 9, along with details
used in their construction. Although the diagram indicates
the δ18O values for altered whole rock, they also indicate,
by inference and mass balance, the general trend for
δ18OH2O. Two important points emerge from the calculations: (1) in order for a fluid of δ18O=+9‰ to increase
to +10‰ or +11‰, the temperature of the fluid must be in
the 400°C to 500°C range, otherwise the wall rock becomes
too enriched in δ18O at lower temperatures and, hence, the
fluid depleted, which is opposite to what is observed; and
(2) chlorite must be present in the wall rock in order to
increase the δ18Ofluid. As seen in the model plots, without
chlorite (Fig. 9a versus 9b, c), there is very little decrease in
the δ18O values of the wall rock, hence the fluid cannot
increase in δ18O, which is what is observed. The estimated
modal amounts of chlorite required are between 10% and
20%, which are not unrealistic and consistent with our
observations of wall rocks in the deposit areas. Importantly, the requirement of chlorite in the wall rock is
consistent with the known increase in the amount of
siltstone and slate upwards in the Meguma Supergroup
and presence of chlorite as an alteration phase. Although
the modelling indicates temperatures higher than anticipated for the veins, this may indicate that there was, in
Miner Deposita (2011) 46:289–304
301
Implications for models of vein formation
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 with
δ18O=+9‰. Note that a temperature of 500°C is required in order for
the fluid to increase its δ18O value, as reflected by the decrease in δ18O
for the altered rock. The plots were generated using the equation of
Taylor (1978) governing fluid/rock interaction and the following
fractionation equations: quartz–H2O (Matsuhisa et al. 1979), albite–
H2O (O’Neil and Taylor 1969), muscovite–H2O (O’Neil and Taylor
1969) and chlorite–H2O (Savin and Lee 1988)
fact, cooling of the fluid from this temperature commensurate with vein formation.
In summary, the δ18O data for vein quartz does not
show a demonstrably obvious relationship to granitic
intrusions, although it is noted that the deposit closest to
an intrusion does record the lowest δ18Oquartz value and,
by inference, the lowest δ18OH2O values. However, there
is an apparent trend of between δ18OH2O values for
deposits and their stratigraphic position such that values
increase upwards. This trend cannot be accounted for
by models of fluid mixing or simple cooling, but
instead is modelled to reflect the fluids having interacted with the host rocks within which there is a change
in their modal composition, in particular, an increase in
the amount of chlorite.
A long-standing issue for the Meguma vein gold systems
has been on whether a singular or multiple model is
required to explain the coexistence of the concordant versus
discordant styles of quartz veining. The multiple or
polygenetic vein model, as reviewed by Sangster (1990,
1992), advocates an early vein-forming event during the
initial stages of the Acadian Orogeny while the strata was
still horizontal, thus pre-dating the regional folding of the
host rocks and peak metamorphism that coincided with
later introduction of veins. In contrast, a singular veinforming event (Mawer 1987; Kontak et al. 1990a), based in
part on the mutual cross-cutting relationships of all vein
types, attributed vein formation to a single event with vein
formation occurring syn- or post-folding of the stratigraphy,
thus into an upright stratigraphy. Most recently, Horne and
Culshaw (2001), based on a detailed structural analysis of
Meguma vein systems, favoured a single vein-forming event
and concluded that it was consistent with a flexural-slip
folding mechanism (Tanner 1989). The same mechanism
has been used to explain the nature of veining in somewhat
analogous 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 support
to the singular model of vein formation since this favours a
fluid uniform not only in isotopic composition, but also
temperature. We also note that since a multiple-vein model
would presumably be commensurate with increasing
temperatures as metamorphism progressed, then this would
manifest itself in a range of δ18Oquartz values due to the
temperature-dependent fraction of 18O between mineral–
H2O. Our conclusion is also consistent with the findings of
Beaudoin and Pitre (2005) who, based on multiple analyses
of different vein types within the same vein field, found
similar δ18Oquartz values that suggest deposition of quartz
from a fluid uniform in both its δ18OH2O and temperature.
Conclusions
The Meguma gold deposits, Novas Scotia, represent a
classic example of slate-belt hosted auriferous quartz veins.
Detailed sampling of two structurally similar, but temporally distinct (i.e. 408 versus 380 Ma) deposit areas has
shown that all the vein types present, including discordant
and concordant arrays, have the very similar δ18Oquartz
values. These results are consistent with earlier structural
studies suggesting the veins represent a single vein-forming
event, having formed during flexural-slip in response to
late-stage tightening of the folded host rocks. The similar
δ18Oquartz values and P-T conditions for vein formation also
infer similar δ18OH2O values and, thereby, possibly similar
302
source reservoirs. Thus, vein fluids of similar isotopic
composition were generated during the two major tectonothermal events in this terrane which coincide with regional
deformation (408 Ma) and intrusion of large granitic
batholiths (380 Ma). Integration of these new data with an
existing data set for the Meguma deposits indicates a
progressive upwards increase in δ18OH2O for different
deposits. This variation cannot be accounted for by simple
cooling of the fluid and, instead, can be modelled based on
fluid/rock interaction to reflect interaction of the fluid with
the 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 of
Natural Resources, Halifax, Nova Scotia. Completion of the research
was supported by a Laurentian University Start-up Grant to D. Kontak
and Natural Science and Engineering Research Council (NSERC)
Discovery Grants to D. Kontak and T.K. Kyser. The manuscript
benefited from insightful comments by P. Williams, G. Beaudoin, F.
Bierlein and an anonymous reviewer for which we are grateful.
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