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Regional hydrothermal alteration and [sup.18]O-depletion of the ca. 620 Ma Huntington Mountain pluton and related rocks, Cape Breton Island, Canada.

The ca. 620 Ma Huntington Mountain pluton and East Bay Hills Group, which comprise part of the Avalonian Mira terrane, Cape Breton Island, Nova Scotia, Canada, are characterized by pervasive propylitic alteration (chlorite, epidote, sericite, and Fe-Ti oxides) and low [[delta].sup.18]O values (-3.8 to +6.20). This alteration is a product of interaction with hydrothermal fluids of meteoric and/or meteoric-seawater mixed origin at N300 [degrees]C over a range of water/rock (w/r) ratios. Locally, the propylitic alteration was further overprinted by quartzcalcite-sericite alteration. Such samples have generally higher [[delta].sup.18][O.sub.WR] values (up to +9.5%0), reflecting interaction with evolved meteoric water at lower temperatures (~200 [degrees]C) and very low w/r ratios. The hydrothermal fluids responsible for widespread propylitic alteration of the Huntington Mountain-East Bay Hills complex (and regions beyond) likely entered the crust during initial rifiing of the Mira terrane from Gondwana at ca. 575-550 Ma.

Le pluton du mont Huntington, apparu il y a quelque 620 Ma et la succession volcanique des collines East Bay, qui font partie du terrane Mira d'Avalon, sur l'ile du Cap-Breton, en Nouvelle-Ecosse, au Canada, se caracterisent par une alteration propylitique envahissante (chlorite, epidote, sericite, et oxydes de fer et de titane), et des teneurs faibles en [[delta].sup.18]O (-3,8 a +6,2[per thousand]). Cette alteration est le resultat de l'interaction de fluides hydrothermaux d'origine mixte meteorique ou meteorique et d'eau de mer, ou des deux, a une temperature d'environ 300 [degrees]C, selon divers rapports eau/roche. Au plan local, une alteration de quartz-calcite-sericite s'est superposee a l'alteration propylitique. Ces echantillons ont en regle generale des valeurs de [[delta].sup.18][O.sub.WR] superieures (qui peuvent atteindre +9,5[per thousand]), ce qui rend compte de l'interaction de l'eau meteorique evoluee a de basses temperatures (environ 200 [degrees]C) et de rapports eau/roche tres faibles. Les fluides hydrothermaux a l'origine de l'alteration propylitique tres etendue du complexe du mont Huntington et des collines East Bay (et des regions au-dela) ont probablement penetre la croute terrestre au cours du soulevement initial du terrane Mira, a l'epoque du continent de Gondwana, il y a de cela entre 575 et 550 Ma.

[Traduit par la redaction]

INTRODUCTION

West Avalonia forms a fragmented belt along the eastern margin of the northern Appalachian orogen from Newfoundland to Massachusetts and records the complex tectonic history of several late Proterozoic magmatic arcs that evolved proximal to Gondwana (Murphy et al. 1990; Barr et al. 1998). Like other terranes in West Avalonia, the Mira terrane of southeastern Cape Breton Island is composed of mainly late Proterozoic volcanic-plutonic-sedimentary belts overlain by younger sedimentary cover sequences (Fig. 1).

The tectonic history of the Mira terrane, and especially its relationship to the Ganderian Bras d'Or and Aspy terranes of Cape Breton Island (Fig. 1), have been the subject of longstanding debate (Barr and Raeside 1989; Murphy et al. 1990; Barr et al. 1998). Potter et al. (2008a) added a new dimension to that discussion by showing the Mira terrane to have a distinctive low-[sup.18]O signature relative to other peri-Gondwanan terranes of Cape Breton Island, and Potter et al. (2008b) expanded that observation to other West Avalonian terranes. Potter et al. (2008a, b) concluded that the Avalonian terranes underwent post-magmatic oxygen isotope exchange with meteoric-dominated hydrothermal fluids across the region, and proposed that these fluids infiltrated the crust during regional transtensional faulting associated with initial rifting of Avalonia at ca. 600-550 Ma.

Here we evaluate the hypothesis of Potter et al. (2008a, b) through petrographic and stable isotope analysis of the ca. 620 Ma Huntington Mountain pluton and associated East Bay Hills Group from the Mira terrane (Fig. 1). More detailed examination of a single plutonic-volcanic complex allows testing for local versus regional patterns of hydrothermal alteration and [sup.18]O-depletion that are essential in understanding the exact processes that lead to the noted [sup.18]O-depletion observed on a regional-scale in Potter et al (2008a, b). We also examine the origin(s) of the hydrothermal fluid, and whether its presence in the Huntington Mountain--East Bay Hills area added to the potential for base- and precious-metal mineralization, as is sometimes the case for such mineral deposits associated with porphyry and epithermal systems (Lynch et al. 1990; Sillitoe and Hedenquist 2003; Richards 2009).

GEOLOGICAL SETTING

The Mira terrane is composed of mainly volcanic and plutonic rocks that form linear northeast-southwest trending belts separated by regional-scale faults and younger sedimentary cover sequences (Fig. 1). The majority of the Mira terrane rocks can be subdivided into four magmatic associations: the ca. 680 Ma Stirling Group, the ca. 620 Ma volcanic-plutonic units, which include the East Bay Hills Group and Huntington Mountain pluton, the ca. 575-560 Ma Coastal belt, and the ca. 380 Ma Devonian plutons (Barr et al. 1996).

The ca. 680 Ma Stirling Group consists primarily of andesitic to basaltic lapilli tuff with interbeds of tuffaceous arenite and laminated siltstone. Barr et al. (1996) interpreted it to have formed in an extensional basin within a volcanic arc. The Stirling Group contains zones of pyrite-rich, laminated litharenite-siltstone-chert-dolomite, which is host to the Mindamar Zn-Pb-Cu-Ag-Au deposit (interpreted as an exhalative volcanogenic massive sulphide deposit by Barret al. 1996) (Fig. 1). The ca. 620 Ma volcanic-plutonicse-dimentary belts (East Bay Hills and Huntington Mountain --this study, Coxheath Hills, and Pringle Mountain Group and Chisholm Brook plutonic suite) are composed mostly of granitic to granodioritic rocks and andesitic to rhyolitic tuffs and flows (see next section for detailed descriptions). Barr et al. (1996) interpreted these high-K, calc-alkaline rocks to have formed in a subduction-related convergent margin setting. Mineralization includes sporadic Cu anomalies within an extensive shear zone in the Sporting Mountain pluton and the Coxheath porphyry-style Cu-Mo-Au deposit located in the Coxheath Hills Group and comagmatic Coxheath Hills pluton (Barr et al. 1996; Lynch and Ortega 1997; Kontak et al. 2003) (Fig. 1).

The volcanic-sedimentary sequences of the ca. 575-560 Ma Coastal Belt are subdivided into the Fourchu and Main-a-Dieu groups. The Fourchu Group consists of mainly dacitic tuffs and flows, with minor basaltic to rhyolitic tuffs and fiows and tuffaceous sedimentary rocks, and was interpreted by Barr et al. (1996) to represent a volcanicarc setting. The Main-a-Dieu Group consists of mainly tuffaceous sedimentary and epiclastic rocks, with minor basaltic and rhyolitic flows, interpreted by Barr et al. (1996) to have formed in an intra-arc extensional setting. Given their close stratigraphic association, the Fourchu and Maina-Dieu groups are inferred to be different facies formed more or less coevally (Barr et al. 1998). The ca. 380 Ma Devonian plutons are composed mostly of monzogranite and are interpreted to have formed in an anorogenic, within-plate setting (Barr and Macdonald 1992).

Geology of the Huntington Mountain area

The ca. 620 Ma Huntington Mountain pluton intruded the northeastern part of the East Bay Hills Group (Fig. 1). The pluton is dominated by diorite, but also contains granodiorite, leucogranite, monzogranite, and syenogranite. The East Bay Hills Group forros an elongate belt along and inland from the southeastern shore of Bras d'Or Lake. This group is dominated by andesitic to dacitic rocks with lesser quantities of basaltic to rhyolitic tuffs and flows and epiclastic sedimentary rocks. Field relationships suggests that the Huntington Mountain diorite was emplaced first, followed by granodiorite, leucogranite, and syenogranite; the small body of monzogranite may have been emplaced at some time between the granodiorite and syenogranite (Barret al. 1996). Earlier basaltic, andesitic-dacitic, and dacitic rocks in the East Bay Hills Group have a thermal overprint attributed to pluton emplacement. Minor pyrite, chalcopyrite, and malachite in the basaltic rocks are associated with the Huntington Mountain pluton (Barr et al. 1996). Later basaltic andesite and rhyolite are considered to be coeval with pluton emplacement as all units are dated at ca. 620 Ma (Barr el al. 1990; Keppie el al. 1990; Bevier et al. 1993). All rocks in the study area are characterized by some degree of post-magmatic alteration.

METHODS

A representative range of pristine to moderately altered volcanic and plutonic rocks were collected (65 in total) in the Huntington Mountain area. These were discriminated in the field on the basis of visible turbid feldspar, veining, and alteration minerals (chlorite, epidote, quartz, calcite, pyrite, and ilmenite). The nature of the alteration was confirmed by petrographic examination of thin sections. A portion of each sample was crushed for mineral separation and powder X-ray diffraction (pXRD). Standard mineral separation techniques (magnetic and heavy liquid separation, handpicking) were used to isolate primary and secondary phases. Separate purity was assessed using high-brilliance pXRD (Rigaku rotating anode diffractometer, CoK[alpha] radiation at 160 kV and 45 mA). Purity was better than 90% for most separates and >95% for quartz. Feldspar separates consisted of alkali feldspar, either albitic plagioclase or potassium feldspar, or mixtures of both.

Stable isotopic compositions are reported in [delta]-notation relative to VSMOW for hydrogen and oxygen and VPDB for carbon (Coplen 1996). Oxygen was liberated from silicates by overnight reaction with [ClF.sup.3] at 550 [degrees]C in sealed Ni reaction vessels, following the method of Clayton and Mayeda (1963), as modified by Borthwick and Harmon (1982). The released oxygen was converted to C[O.sub.2] over a red-hot carbon rod and its oxygen isotopic composition measured using a dual-inlet DeltaPlus XL stable isotope ratio mass-spectrometer. The 8180 values of an internal laboratory standard quartz, NBS-30 (biotite) and NBS-28 (quartz) were +11.4 [+ or -] 0.2[per thousand], +5.1 [+ or -].1[per thousand], and +9.7 [+ or -] 0.3[per thousand], respectively, which compares well with their accepted values of +11.5[per thousand], +5.1[per thousand], and +9.6[per thousand]. Sample reproducibility was generally better than +0.2[per thousand].

Hydrogen was extracted from hydrous silicates following the methods of Bigeleisen et al. (1952), as modified by Vennemann and O'Neil (1993). Following drying at 105 [degrees]C overnight under vacuum, samples were heated to ~1200 [degrees]C using an oxygen-methane torch. Released hydroxyl groups were then converted to [H.sub.2]O by reaction with copper oxide at 400-600 [degrees]C, and [H.sub.2]O then reduced to [H.sub.2] over Cr at 900 [degrees]C. Stable hydrogen-isotope compositions were measured using a dual-inlet VG Prism-II stable isotope ratio mass-spectrometer calibrated to VSMOW and SLAP using four in-house water standards. A [[delta].sup.2]H value of-55 [+ or -][per thousand] was obtained for kaolinite KGa-1 (accepted value = -57[per thousand]). Sample reproducibility was generally better than [+ or -]5[per thousand].

Calcite was placed in glass reaction vials and dried at 60 [degrees]C for 12 hours. It was then reacted under vacuum with orthophosphoric acid at 90 [degrees]C for 10 minutes using a MultiPrep autosampler attached to a dual-inlet VG Optima stable isotope ratio mass-spectrometer. During this study, laboratory standard calcite had [[delta].sup.18]O and [[delta].sup.13]C values of +26.2 [+ or -].1[per thousand] and +0.7[per thousand] [+ or -].1[per thousand], respectively (accepted values, +26.2[per thousand] and +0.8[per thousand]). Sample reproducibility for both oxygen and carbon isotopic compositions was generally better than [+ or -]0.1[per thousand]. common product of interaction with magmatic-dominated fluids in the hottest parts of a hydrothermal system (~ 350-500 [degrees]C; Harris and Golding 2002).

RESULTS

Petrography

Plagioclase and hornblende are the main primary minerals in the Huntington Mountain diorite and granodiorite; K-feldspar, quartz, and biotite occur in lesser quantities. Primary phases in the leucogranite are dominantly perthitic K-feldspar, quartz, and plagioclase, and in the syenogranite, K-feldspar, quartz, and plagioclase. These rocks have undergone weak to strong secondary alteration. Basaltic to andesitic rocks of the East Bay Hills Group are typically aphanitic and massive, with slight to moderate porphyritic textures. Phenocrysts consist mostly of plagioclase and rarely, clinopyroxene. Plagioclase-rich groundmass is commonly overprinted by secondary phases and in a few localities, all primary features have been obscured. Dacite is typically aphanitic to weakly porphyritic, consisting mainly of plagioclase phenocrysts suspended in a plagioclase-rich groundmass with minor quartz. Dacite typically exhibits moderate to strong alteration. Rhyolite samples are dominated by ash to lapilli crystal tuff; aphanitic to weakly porphyritic flow-banded pyroclastic beds are also present. Rhyolite consists of feldspar microlites, quartz, and minor K-feldspar, and exhibits only weak alteration.

Three main alteration types were observed. Type 1 consists of fine-grained chlorite, epidote, sericite, and Fe-Ti oxides (Figs. 2a, b, c), which are characteristic of propylitic alteration (Meyer and Hemley 1967). This alteration is widespread and varies in intensity from weak to strong (partial to complete replacement of primary phases). Type 2 consists of fine- to coarse-grained, anhedral quartz, sericite, and calcite, with minor Fe-oxides. This moderate to strong alteration is highly localized, and has partially to completely replaced primary minerals and textures (Fig. 2d). Type 2 alteration appears to overprint the propylitic alteration (Fig. 2e). Type 3, which was observed only rarely, is typical of phyllic alteration (Meyer and Hemley 1967). Most primary minerals have been moderately to strongly overprinted by fine-grained euhedral quartz, sericite, and pyrite (Fig. 2f). Ty-pe 3 alteration occurs mainly in the contact zone between the Huntington Mountain pluton and East Bay Hills Group, suggesting its development during contact metamorphism. Contact metamorphic features in the East Bay Hills dacite, including hornfelsic texture and pyrite mineralization, were previously reported by Barr et al. (1996). Such alteration is a

Stable isotope compositions

The [[delta].sup.18]O.sub.WR] results for the Huntington Mountain pluton range from -1.5 to +7.1[per thousand] (Table la, Fig. 3a, 4): diorite and granodiorite, -1.5 to +4.5[per thousand]; syenogranite, -1.2 to +6.2[per thousand]; leucogranite, +3.8 to +7.1[per thousand] (except for one sample, +0.2[per thousand]). Two leucogranite salnples have [[delta].sup.2][H.sub.WR] values of-60 and -56[per thousand], whereas values are lower for other plutonic rock types (-78 to -61[per thousand]). The East Bay Hills Group has a wider range of [[delta].sup.18]O.sub.WR] values (-3.8 to +9.5[per thousand]) than the plutonic suite: rhyolite-andesite and dacite, -3.8 to +6.5[per thousand]; basaltic rocks, -1.9 to +9.5[per thousand]; rhyolite, +4.6 to +6.9[per thousand] (Table lb, Fig. 3b). The 62HwRValues of the volcanic rocks range from -93 to -70[per thousand]. In Figure 4 no clear pattern is observed between [[delta].sup.18][O.sub.WR] values and the intrusive sequence and/or rock types in this complex.

Primary quartz (qtz) in the plutonic rocks has [[delta].sup.18]O.sub.WR] values ranging from +0.5 to +7.0[per thousand], with leucogranite having higher values ([greater than or equal to] +4.8[per thousand]) than other rock types. The pattern for alkali feldspar (fs) is similar (leucogranite [[delta].sup.18]O.sub.fs], +4.4 to +6.0[per thousand]; other rock types, +1.4 to +4.6[per thousand]). Hornblende (hbl) has [[delta].sup.18]O.sub.hbl]Values of+1.4 to +5.5[per thousand]. The [[delta].sup.18]O values for phenocrysts from volcanic samples also vary widely: quartz, -1.5 to +8.2[per thousand]; alkali feldspar, -0.3 to +6.5[per thousand].

Chlorite (chl) [[delta].sup.18][O.sub.chl] values vary widely: granodiorite, syenogranite and andesite, -6.3 to -4.0[per thousand]; diorite and leucogranite (-5.2 to +3.3[per thousand]). The [[delta].sup.2][H.sub.chl] values for all rock types range from -77 to -69[per thousand]. Disseminated secondary quartz from a diorite sample affected by phyllic alteration has a [[delta].sup.18]O. value of +3.3[per thousand], whereas values for basaltic to andesitic rocks and leucogranite affected by quartz-sericitecalcite alteration are much higher (+11.1 to +15.1[per thousand]). Disseminated calcite (cal) from plutonic rocks has [[delta].sup.18][O.sub.cal] values of +5.4 to +8.4[per thousand], and from volcanic rocks, +5.8 to [[delta].sup.18]C.sub.cal] values of-3.8 to +0.1[per thousand]; values for the volcanic rocks are lower (-7.2 to -4.5[per thousand]).

Rare vein quartz associated with phyllic alteration of diorite has a [[delta].sup.18][O.sub.qtz] value of-2.1[per thousand]. Veins are more abundant in the volcanic rocks, with [[delta].sup.18][O.sub.qtz] values ranging from +6.1 to +10.5[per thousand]. Vein calcite [[delta].sup.18][O.sub.cal] and [[delta].sup.18][C.sub.cal] values range from +6.0 to + disseminated calcite, the vein calcite samples most enriched in [sup.18]O are also the most depleted of [sup.13]C.

DISCUSSION

Fluid composition

Most Huntington Mountain area samples have [[delta].sup.18][O.sub.WR] values that are lower than typical for "normal" (+6 to +10 [per thousand], Taylor 1974) igneous rocks, thus following the pattern of [sup.18]O-depletion reported for the Avalon terrane by Potter et al. (2008a, b). Most commonly, igneous rocks with abnormally low [[delta].sup.18]O values have experienced post-crystallization alteration (see Taylor 1974), but crystallization from a low-[[delta].sup.18]O magma (see Taylor 1986; Bindeman and Valley 2000) cannot be ruled out a priori. In the latter case, high-temperature oxygen isotopic equilibrium should produce primary compositions in which (i) [MATHEMATICAL EXPRESSION NOT REPRODUCIBLE IN ASCII.] and (ii) values of [MATHEMATICAL EXPRESSION NOT REPRODUCIBLE IN ASCII.]) are small and positive (~+1 to +2 [per thousand], Taylor and Epstein 1962). Hydrothermally altered igneous rocks, by comparison, typically lack consistent high-temperature oxygen-isotope equilibrium between coexisting primary phases (Criss and Taylor 1986; Liu 2000). While some samples from the study area have [MATHEMATICAL EXPRESSION NOT REPRODUCIBLE IN ASCII.] values within the range of magmatic systems, others--most particularly diorite, granodiorite, and syenodiorite--display oxygen isotopic disequilibrium, as manifested by negative values for [MATHEMATICAL EXPRESSION NOT REPRODUCIBLE IN ASCII.] and [MATHEMATICAL EXPRESSION NOT REPRODUCIBLE IN ASCII.], Such reversals are a hallmark of postcrystallization, hydrothermal alteration. The leucogranite and rhyolite exhibit the least alteration and, except for one sample, have relatively high [MATHEMATICAL EXPRESSION NOT REPRODUCIBLE IN ASCII.] values ([greater than or equal to] +4[per thousand]); samples of mafic to intermediate composition, in which mineral phases are more susceptible to alteration, generally have lower [MATHEMATICAL EXPRESSION NOT REPRODUCIBLE IN ASCII.] values (Fig. 3, Table la, b). The few samples retaining mineralogical and textural characteristics of phyllic alteration have among the lowest [MATHEMATICAL EXPRESSION NOT REPRODUCIBLE IN ASCII.] (<2[per thousand]) and [MATHEMATICAL EXPRESSION NOT REPRODUCIBLE IN ASCII.] values (<3[per thousand], Fig. 5, Table la, b), despite their potential association with magmatic fluids during contact metamorphism. The isotopic results suggest that these samples were overprinted by low-[sup.18]O hydrothermal fluids. Samples affected by moderate to strong propylitic alteration display the largest range of [MATHEMATICAL EXPRESSION NOT REPRODUCIBLE IN ASCII.] values, with the majority falling between -2 and +4[per thousand] (Fig. 5); primary quartz affected by propylitic alteration likewise has a wide range of [MATHEMATICAL EXPRESSION NOT REPRODUCIBLE IN ASCII.] values (-2 to +7[per thousand], Table la, b). Samples moderately to strongly affected by the later quartz-sericitecalcite alteration have higher [[delta].sup.18]O.sub.WR] values (+4 to +10[per thousand], Fig. 5), as does associated vein quartz ([[delta].sup.O][O.sub.qtz] = +6 to +11[per thousand]) (Table la, b). The [MATHEMATICAL EXPRESSION NOT REPRODUCIBLE IN ASCII.] values (-93 to -56[per thousand]) fall close to or within the normal range for igneous rocks (-85 to -50[per thousand], Sheppard 1986). However, interaction with midto low-latitude meteoric water or seawater can also produce such compositions (Longstaffe 1982). With the exception of hornblende, hydrous minerals in the Huntington Mountain area are of secondary origin (chlorite > epidote > sericite). Where comparisons are possible, the [MATHEMATICAL EXPRESSION NOT REPRODUCIBLE IN ASCII.] values are very similar to the [[delta].sup.2][H.sub.WR] values (Table la, b), indicating that chlorite--and fluids that formed it--control the bulk hydrogen-isotope composition of most samples.

The oxygen isotopic results for minerals formed and/ or re-equilibrated during both the propylitic and quartzsericite-calcite alteration stages have been used to estimate fluid [[delta].sup.18]O values (Fig. 6). Over the 300-450 [degrees]C temperature range typical for propylitic alteration (Ferry 1985; Criss and Taylor 1986), [[delta].sup.18][O.sub.H2O] ovalues range from -9 to -2[per thousand] at 300 [degrees]C, to -5 to +1[per thousand] at 450 [degrees]C (Fig. 6a). Coexisting propylitic quartz and chlorite for syenogranite and granodiorite samples (CBI-6-6-55 and CBI-8-5-22) yield virtually identical [[delta].sup.18][O.sub.H2O] values of -6 to -5[per thousand] at 300 [degrees]C as does coexisting secondary feldspar and chlorite for andesite sample CBI-6-6-52 (Fig. 6a). Hence we use 300 [degrees]Cas the propylitic alteration temperature in the discussion that follows. These results suggest that meteoric water ([[delta].sup.18][O.sub.H2O] < 0[per thousand]) comprised a significant ffaction of the propylitic alteration fluid. Some estimates based on brachiopod carbonate suggest [[delta].sup.18]O values of-8 to -6[per thousand] for late Precambrian-early Cambrian seawater (Veizer et al. 1986). However, evidence from ophiolite, greenstone, and massive sulphide deposits overwhelmingly suggests open ocean [[delta].sup.18]O values that varied no more than +2[per thousand] from its present composition since at least 3 Ga (Muehlenbachs 1986; Johns et al. 2006). Accordingly, we accept a seawater [[delta].sup.18]O value of 0[per thousand] in the discussion that follows.

Quartz-sericite-calcite alteration is generally known to occur at temperatures ranging from 200 to 300 [degrees]C (Ferry 1985; Criss and Taylor 1986). For the Huntington geothermometer. The apparent trend towards higher [[delta].sup.18][O.sub.H2O] values from propylitic (-6[per thousand]) to quartz-sericite-calcite (0[per thousand]) alteration is suggestive of either [sup.18]O -enrichment of meteoric water during water-rock interaction and/or an increasing contribution of seawater (~0[per thousand]) as the system cooled and waned. Combined consideration of the hydrogen- and oxygen-isotope compositions of altered whole-rock samples and associated chlorite allows evaluation of these two possibilities. Figure 7 compares propylitic fluid hydrogen-and oxygen-isotope compositions at 300 [degrees]C for chlorite and whole-rock samples to results calculated for a range of molar oxygen water/rock (w/r) ratios in a simple hydrothermal system (following Ohmoto and Rye 1974; see caption to Figure 7 for details). The oxygen- and hydrogen-isotope compositions predicted for meteoric water at ~560 Ma, based on Avalonia paleolatitude estimates (Murphy et al. 2004) closely match the values calculated using the Ohmoto and Rye (1974) model (see caption to Figure 7 for details). Fluid compositions for chlorite range flora -5.3[per thousand] ([[delta].sup.18][O.sub.H2O] and -37[per thousand] [[delta].sup.18][H.sub.H2O], which cluster near the Global Meteoric Water Line (GMWL; Craig 1961) at very high w/r ratios, to +3.3[per thousand] [delta].sup.18][O.sub.H2O] and---33[per thousand] [[delta].sup.2]H at very low w/r ratios. Many whole-rock samples follow the same trend. This shift away from the GMWL towards higher [delta].sup.18][O.sub.H2O] values at lower w/r ratios is typical of many modern geothermal systems. Meteoric-dominated hydrothermal fluids become enriched in [[sup.18]O as w/r ratios decrease whereas [delta].sup.18][O.sub.H2O] values are largely unchanged, except at very low w/r ratios, because of the low initial molar hydrogen content of the rock (Craig 1963; Taylor 1974; Longstaffe 1989; Cole 1994). Addition of seawater as the hydrothermal fluid evolved would not produce such a pattern. One sample (CBI-6-6-11), which is dominated by the lower temperature quartz-sericite-calcite alteration, plots just beyond the end of the trend calculated for propylitic alteration at very low w/r ratios (<0.001). ti his positioning is consistent with a waning flux of hydrothermal fluid.

Seawater may have been important earlier in the alteration history at higher w/r ratios. A handful of samples, including some with sericite as the main hydrous phase, have [delta].sup.18][H.sub.H2O] values plotting well above the meteorichydrothermal fluid w/r trend-line for 300 [degrees]C (Fig. 7). Such compositions could indicate alteration of these samples at >300 [degrees]C. Calculated [delta].sup.18][H.sub.H2O]values at 450 [degrees]C for these samples would plot closer to the trend-line, albeit at higher [delta].sup.18][H.sub.H2O] values and lower w/r ratios. However, the main alteration phases in two of these samples (CBI-6-6-55 and CBI-8-5-22) are in oxygen isotopic equilibrium at 300 [degrees]C. An alternate explanation is that the hydrothermal fluid affecting these samples comprised a mixture of seawater and (evolved) meteoric water (Fig. 7). Based on petrographic, isotopic and fluid-inclusion thermometric data, Potter et al. (2012) have suggested that seawater was a significant component of the hydrothermal fluid associated with early vein assemblage formation during the Mira terrane alteration.

The carbon isotopic compositions of disseminated and vein calcite samples (-7.4 to +0.1[per thousand]) are not uniquely diagnostic of a particular source (e.g., seawater, magmatic fluids, organic matter oxidation). Further confounding the situation is that Neoproterozoic marine carbonates at 575-550 Ma ranged widely in [[delta].sup.13]C (-6 to +4[per thousand]) (Des Marais 2001, Deines 2002). The majority of samples analyzed here lie within this range (-5.2 to +0.1[per thousand]); only those samples with the very highest [[delta].sup.18]O values, and which are unrelated to propylitic or quartz-sericite-calcite alteration, have lower [[delta].sup.13]C values.

Local versus regional alteration and mineralization potential

Potter et al. (2008a) proposed two scenarios to explain the regional [low.sup.-18]O character of the Mira terrane: (1) a series of local meteoric water-dominated geothermal systems associated with convergent subduction, associated volcanism, and emplacement of individual plutons, or (2) a single event involving regional infiltration of hydrothermal fluids during transcurrent rifting of Avalonia at the Gondwanan margin at ca. 575-550 Ma. Potter et al. (2008a, b) preferred the second model, given the widespread [sup.18]O-depletion of Avalonia, and absence of such [[sup.18]O-depletion for the associated inboard Neoproterozoic peri-Gondwanan terranes of the region (e.g., Bras d'Or terrane).

The observations reported here for the Huntington Mountain pluton and East Bay Hills metavolcanic rocks are not typical of a localized hydrothermal system. The putative concentric pattern of progressively cooler alteration zones (potassic, phyllic, propylitic, argillic; Meyer and Hemley 1967; Sheppard et al. 1971; Taylor 1997) that would have been associated with emplacement at ca. 620 Ma is absent--or at the very least--not preserved at present exposure levels. Nor is there a zonation of oxygen isotopic compositions that would be predicted for intrusion-driven water-rock interaction--magmatic fluids near the intrusive centres followed progressively outwards by [[sup.18]O-depletion (propylitic alteration) and then [[sup.18]O-enrichment (argillic alteration), as meteoric-hydrothermal waters became dominant in the cooling system through circulatory fluid flow above the brittle-ductile boundary as is evident in the distribution of [[delta].sup.18][O.sub.WR] values in Figure 4. The minor variations in alteration assemblages across the study area and the absence of any systematic patterning of [[delta].sup.18]O values are more consistent with the regional model for [sup.18]O-depletion across West Avalonia, in which fluid infiltration into deep extensional basins occurred during transition from a subduction to a transtensional rifting environment (Potter et al. 2008a, b). In this model, initial rifting of West Avalonia resulted in the formation of large-scale extensional fault networks, which provided conduits for deep infiltration of meteoric water (and/or seawater during earlier stages). Continued volcanism during the initial stages of rifting served to heat and circulate these fluids. Direct evidence exists throughout West Avalonia for extensional-related volcanism and associated transtensional faulting, including volcanic-sedimentary sequences of the ca. 575-560 Ma Coastal Belt in the Mira terrane, the ca. 560-550 Ma Coldbrook Group of the Caledonia terrane in New Brunswick, and the ca. 580-570 Ma and younger units of the Avalon terrane in Newfoundland (Barr et al. 1996; O'Brien et al. 1996).

Many economic accumulations of base and precious metals are known to form in epithermal systems, commonly as the product of circulation of metal-laden hydrothermal fluids associated with pluton emplacement. To the best of our knowledge, the Huntington Mountain pluton and East Bay Hills Group are barren of significant mineralization (Barr et al. 1996). The hydrothermal fluids responsible for regional [sup.18]O-depletion may not have been metal-rich, perhaps because of the lack of a magmatic fluid component. The [MATHEMATICAL EXPRESSION NOT REPRODUCIBLE IN ASCII.] and [MATHEMATICAL EXPRESSION NOT REPRODUCIBLE IN ASCII.] values calculated for the Huntington Mountain alteration assemblages certainly do not reveal any strong association with magmatic water (Fig. 7). Alternatively or additionally, it may be that the processes needed to focus the flow of the hydrothermal fluids and/ of precipitate metals efficiently were not operating in this system (Simmons and Brown 2007). Whether regional movement of hydrothermal fluids of meteoric/seawater origin lead to leaching and/or redistribution of pre-existing metals of economic interest in this area, and hence, West Avalonia more widely is worthy of further enquiry.

CONCLUSIONS

The ca. 620 Ma cogenetic Huntington Mountain pluton and East Bay Hills Group comprise rocks of mainly intermediate composition (mostly diorite and andesite), which have undergone regional propylitic alteration and more localized overprinting by quartz-sericite-calcite alteration. These rocks are most commonly characterized by anomalously low [[delta].sup.18]O values, which are attributed to propylitic alteration at ~300 [degrees]C from fluids of dominantly meteoric [+ or -] seawater origin over a range of w/r ratios. Lower temperatures (~200 [degrees]C), lower w/r ratios and higher [[delta].sup.18][O.sub.H2O] values characterized the evolved meteoric hydrothermal water responsible for later, more localized quartz-sericitecalcite alteration. The widespread [sup.18]O-depletion, which is also characteristic of other Neoproterozoic rocks from the Mira terrane, likely occurred at ca. 575-550 Ma during large-scale transtensional faulting and extensional-related volcanism, during initial rifting of Avalonia from Gondwana. This alteration appears not to be associated with mineralization in the Huntington Mountain pluton or East Bay Hills Group.

doi: 10.4138/atlgeol.2012.003

Date received 21 November 2011 [paragraph] Date accepted 21 March 2012

ACKNOWLEDGEMENTS

We are grateful to Kim Law and Li Huang for assistance in the laboratory, and Sam Russell for his assistance in the field. Norm Duke is thanked for discussions regarding intrusion-related hydrothermal systems. We thank journal reviewers David Lentz and Michael Dorais for their helpful comments and suggestions. Financial support was provided by Natural Sciences and Engineering Research Council of Canada Discovery Grants to FIL and SMB. This is Laboratory for Stable Isotope Science Contribution # 268.

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Editorial responsibility: David P. West

DUANE C. PETTS (1) *, FREDERICK J. LONGSTAFFE (1), JOANNA POTTER (1), SANDRA M. BARR (2), AND CHRIS E. WHITE (3)

(1.) Western University, London, Ontario N6A 5B7, Canada

(2.) Department of Earth and Environmental Science, Acadia University, Wolfville, Nova Scotia B4P 2R6, Canada

(3.) Nova Scotia Department of Natural Resources, P.O. Box 698, Halifax, Nova Scotia B3J 2T9, Canada

* Corresponding author: <dpetts@uwo.ca>

Table 1a. Oxygen-and hydrogen-isotope results for the Huntington
Mountain pluton.

Sample          Map Unit       (a) Alteration

Huntington Mountain pluton

CBI-8-5-23      Leucogranite   1--weak
CBI-6-6-81      Leucogranite   1--weak
CBI-6-6-105     Leucogranite   1--weak to moderate
CBI-6-6-106     Leucogranite   1--weak
dEB91-014       Leucogranite   2--undetermined
dF16C-1582      Leucogranite   1--undetermined
CBI-6-6-54      Syenogranite   1--weak to moderate
CBI-6-6-55      Syenogranite   1--moderate to strong
(d) F16C-1631   Syenogranite   1--undetermined
(d) F16C-1635   Syenogranite   1--undetermined
(d) F16C-1782   Syenogranite   1--undetermined
CBI-8-5-2I      Granodiorite   1--moderate
CBI-8-5-22      Granodiorite   1--moderate
CBI-8-5-25      Diorite        1--moderate
CBI-8-5-26      Diorite        1--moderate
CBI-8-5-27A     Diorite        1--weak to moderate
CBI-8-5-27B     Diorite        1--weak to moderate
CBI-6-6-56      Diorite        1--moderate to strong
CBI-6-6-82      Diorite        1--moderate
CBI-6-6-83      Diorite        1--moderate
CBI-6-6-84      Diorite        1--moderate to strong
CBI-6-6-86      Diorite        1--moderate
CBI-6-6-87      Diorite        1--moderate
CBI-6-6-102     Diorite        1--strong, 2--weak,
                               3--moderate
CBI-6-6-103     Diorite        3--strong
CBI-6-6-I04     Diorite        1--strong, 3--moderate
(d) F16C-1751   Diorite        1--undetermined

Sample          [delta][sup.18]   [delta][sup.2]        [delta]
                  [O.sub.WT]      [H.sub.WT]       [sup.18][O.sub.qts]

Huntington Mountain pluton

CBI-8-5-23            5.9               --                6.4
CBI-6-6-81            5.8               --                6.2
CBI-6-6-105           3.8              -56                4.8
CBI-6-6-106           5.4               --                7.0
dEB91-014             7.1              -60               615.1
dF16C-1582            0.2               --                 --
CBI-6-6-54            6.2              -71                4.3
CBI-6-6-55            1.4              -61                0.5
(d) F16C-1631         4.3               --                 --
(d) F16C-1635        -1.2              -70                 --
(d) F16C-1782         5.5               --                 --
CBI-8-5-2I            --                --                1.3
CBI-8-5-22            1.2              -62                1.5
CBI-8-5-25            2.7              -69                 --
CBI-8-5-26            --                --                 --
CBI-8-5-27A           --                --                4.8
CBI-8-5-27B           --                --                 --
CBI-6-6-56            1.7              -72                 --
CBI-6-6-82            3.8               --                 --
CBI-6-6-83            4.5              -78                 --
CBI-6-6-84            2.2               --                 --
CBI-6-6-86            3.6              -69                 --
CBI-6-6-87            3.6               --                 --
CBI-6-6-102           1.0               --                 --
CBI-6-6-103           1.9               --             {b,3) 3.3
CBI-6-6-I04          -1.5              -68             (c,l] -2.1
(d) F16C-1751         3.1               --                 --

Sample          [delta] [sup.18]   [delta][sup.18]   [delta][sup.18]
                   [O.sub.fs]        [O.sub.hbl]     [O.sub.chl]

Huntington Mountain pluton

CBI-8-5-23            5.2                --          (b,1) 1.0
CBI-6-6-81            5.0                --          (b,1) -1.2
CBI-6-6-105           4.4                --          (b,1) -3.3
CBI-6-6-106           5.2                --          (b,1) -0.2
dEB91-014             6.0                --          --
dF16C-1582             --                --          --
CBI-6-6-54            3.5                --          (b,1) -4.8
CBI-6-6-55            1.8                --          (b,1) -6.3
(d) F16C-1631          --                --          --
(d) F16C-1635          --                --          --
(d) F16C-1782          --                --          --
CBI-8-5-2I            2.9                --          (b,1) -4.0
CBI-8-5-22            3.1                --          (b,1) -5.3
CBI-8-5-25            2.5                3.9         (b,1) -0.8
CBI-8-5-26            3.6                --          --
CBI-8-5-27A           3.8                --          (b,1) -l.7
CBI-8-5-27B            --                --          (b,1) -l.0
CBI-6-6-56            2.5                1.7         (b,1) -5.2
CBI-6-6-82            3.9                4.6         (b,1) 0.1
CBI-6-6-83            4.3                5.5         (b,1) 3.3
CBI-6-6-84            2.4                3.5         --
CBI-6-6-86            4.6                3.3         (b,1) 0.6
CBI-6-6-87            3.8                4.5         --
CBI-6-6-102           1.4                1.4         --
CBI-6-6-103            --                --          --
CBI-6-6-I04            --                --          --
(d) F16C-1751          --                --          --

Sample          [delta][sup.2]   [delta][sup.18]   [delta][sup.2]
                [H.sub.chl]      [O.sub.ser]       [O.sub.ser]

Huntington Mountain pluton

CBI-8-5-23      --               --                --
CBI-6-6-81      --               --                --
CBI-6-6-105     --               --                --
CBI-6-6-106     --               --                --
dEB91-014       --               --                --
dF16C-1582      --               --                --
CBI-6-6-54      --               --                --
CBI-6-6-55      --               --                --
(d) F16C-1631   --               --                --
(d) F16C-1635   --               --                --
(d) F16C-1782   --               --                --
CBI-8-5-2I      --               --                --
CBI-8-5-22      --               --                --
CBI-8-5-25      (b,1] -73        --                --
CBI-8-5-26      --               --                --
CBI-8-5-27A     --               --                --
CBI-8-5-27B     --               --                --
CBI-6-6-56      (b,1) -73        --                --
CBI-6-6-82      --               --                --
CBI-6-6-83      (b,1) -69        --                --
CBI-6-6-84      --               --                --
CBI-6-6-86      (b,1) -77        --                --
CBI-6-6-87      --               --                --
CBI-6-6-102     --               (b,1) l.4         (b,1, *) -73
CBI-6-6-103     --               (b,1) 2.0         (b,1) -61
CBI-6-6-I04     --               --                --
(d) F16C-1751   --               --                --

Sample          [delta][sup.18]   [delta][sup.13]
                [O.sub.cal]       [O.sub.cal]

Huntington Mountain pluton

CBI-8-5-23      --                --
CBI-6-6-81      --                --
CBI-6-6-105     --                --
CBI-6-6-106     --                --
dEB91-014       (b) 68.4          (b) -3.8
dF16C-1582      --                --
CBI-6-6-54      --                --
CBI-6-6-55      --                --
(d) F16C-1631   --                --
(d) F16C-1635   --                --
(d) F16C-1782   --                --
CBI-8-5-2I      --                --
CBI-8-5-22      --                --
CBI-8-5-25      --                --
CBI-8-5-26      --                --
CBI-8-5-27A     --                --
CBI-8-5-27B     --                --
CBI-6-6-56      --                --
CBI-6-6-82      --                --
CBI-6-6-83      --                --
CBI-6-6-84      --                --
CBI-6-6-86      --                --
CBI-6-6-87      --                --
CBI-6-6-102     (b,2) 5.4         (b,2) 0.1
CBI-6-6-103     --                --
CBI-6-6-I04     --                --
(d) F16C-1751   --                --

Notes: calcalcite, chl = chlorite, fs = feldspar, hbl = hornblende,
qtz=quartz, ser=sericite; (a) = alteration types: (1) propylitic, (2)
quartz, sericite and calcite, and (3) phyllic; (b) = disseminated
secondary mineral; (c) = vein mineral; (d) = previously reported by
Potter et al. (2008a); * =ser>fs mixture taken from Table 1b.

Table 1b. Oxygen-and hydrogen-isotope results for the East Bay Hills
Group.

Sample         Map Unit            (a) Alteration

East Bay Hills Group

CBI-8-5-30     Rhyolite            1--weak, 2--moderate
                                   2--qtz-cal vein
CBI-6-6-17     Rhyolite            1--weak, 2--moderate
                                   2--qtz-cal vein
CBI-6-6-80     Rhyolite            1--weak, 2--moderate
(d) FS91-53    Rhyolite            2--undeternlined
CBI-8-5-28     Dacite              1--strong, 3--moderate

CBI-6-6-98     Dacite              1--moderate
CBI-6-6-99     Dacite              1--strong
CBI-6-6-101    Dacite              1--strong
CBI-6-6-93     An&site-Rhyolite    1--moderate, 2--weak
CBI-6-6-94     Andesite-Rhyolite   1--weak, 2--moderate
CBI-6-6-95     Andesite-Rhyolite   2--qtz-cal vein
CBI-6-6-96     Andesite-Rhyolite   1--weak, 2--moderate
CBI-6-6-118    Andesite-Rhyolite   weak, 2--moderate
CBI-6-6-119    Andesite-Rhyolite   weak, 2--moderate
CBI-6-6-121    Andesite-Rhyolite   1,2--weak to moderate
CBI-6-6-50     Andesite            1--moderate to strong
CBI-6-6-51     Andesite            1--moderate to strong
CBI-6-6-52     Andesite            1--moderate to strong,
                                   2--weak
CBI-6-6-89     Andesite            1--moderate to strong
CBI-6-6-90     Andesite            1--moderate, 2--weak
(d) EB87-037   Andesite            1--undetermined
CBI-6-6-11     Basalt-Andesite     2--strong
CBI-6-6-88     Basalt-Andesite     1--strong
CBI-6-6-110    Basalt-Andesite     1--strong
CBI-6-6-111    Basalt-Andesite     1--weak to moderate,
                                   2--weak
CBI-6-6-112    Basalt-Andesite     1--strong, 2--weak
CBI-6-6-112A   Basalt-Andesite     2--qtz-cal vein
CBI-6-6-112B   Basalt-Andesite     2--qtz-cal vein
CBI-6-6-112C   Basalt-Andesite     2--qtz-calvein
CBI-6-6-114    Basalt-Andesite     1--weak, 2--moderate
CBI-6-6-38     Basalt              2--qtz-cal vein
CBI-6-6-39     Basalt              1--moderate, 2--weak

CBI-6-6-40     Basalt              1--moderate, 2--weak
CBI-6-6-107    Basalt              1--weak, 2--moderate
CBI-6-6-122    Basalt              2--moderate to strong
(d) MT6-397    Basalt              2--undetermnined

Sample         [delta][sup.18]   [delta]             [delta][sup.18]
               [O.sub.wr]        [sup.2][H.sub.wr]   [O.sub.qtz]

East Bay Hills Group

CBI-8-5-30     6.6               --                  8.2
               --                --                  (c,2) 10.1
CBI-6-6-17     5.5               --                  --
               --                --                  (c,2) 9.1
CBI-6-6-80     6.9               --                  --
(d) FS91-53    4.6               --                  --
CBI-8-5-28     -2.6              -70                 -1.5
               --                --                  --
CBI-6-6-98     -0.1              --                  --
CBI-6-6-99     0.6               --                  --
CBI-6-6-101    -3.8              --                  --
CBI-6-6-93     1.8               --                  --
CBI-6-6-94     4.1               --                  --
CBI-6-6-95     --                --                  (c,2) 7.7
CBI-6-6-96     4.0               --                  --
CBI-6-6-118    3.6               --                  --
CBI-6-6-119    3.9               -77                 --
CBI-6-6-121    6.5               --                  --
CBI-6-6-50     -0.5              --                  --
CBI-6-6-51     -0.7              --                  --
CBI-6-6-52     -0.6              --                  (b,2) 11.1

CBI-6-6-89     -1.1              --                  --
CBI-6-6-90     -1.9              --                  --
(d) EB87-037   0.5               -82                 --
CBI-6-6-11     9.5               -93                 (b,2) 11.7
CBI-6-6-88     -1.9              -79                 --
CBI-6-6-110    0.0               --                  --
CBI-6-6-111    3.3               --                  # 6.4

CBI-6-6-112    -1.7              --                  --
CBI-6-6-112A   --                --                  (c,2)8.6
CBI-6-6-112B   --                --                  (c,2)10.5
CBI-6-6-112C   --                --                  (c,2)7.9
CBI-6-6-114    5.4               --                  --
CBI-6-6-38     --                --                  (c,2)6.1
CBI-6-6-39     3.0               --                  --

CBI-6-6-40     1.9               -70                 --
CBI-6-6-107    3.1               --                  --
CBI-6-6-122    5.7               --                  --
(d) MT6-397    6.2               --                  --

Sample         [delta][sup.18]   [delta][sup.18]   [delta][sup.2]
               [O.sub.fs]        [O.sub.hbl]       (O.sub.chl]

East Bay Hills Group

CBI-8-5-30     6.5               --                --
               --                --                --
CBI-6-6-17     --                --                --
               --                --                --
CBI-6-6-80     --                --                --
(d) FS91-53    --                --                --
CBI-8-5-28     --                --                --
               --                --                --
CBI-6-6-98     --                --                --
CBI-6-6-99     --                --                --
CBI-6-6-101    --                --                --
CBI-6-6-93     --                --                --
CBI-6-6-94     --                --                --
CBI-6-6-95     --                --                --
CBI-6-6-96     --                --                --
CBI-6-6-118    --                --                --
CBI-6-6-119    --                --                --
CBI-6-6-121    --                --                --
CBI-6-6-50     --                --                --
CBI-6-6-51     --                --                --
CBI-6-6-52     -0.3              (b,1) -5.3        (b,1) -69

CBI-6-6-89     --                --                --
CBI-6-6-90     --                --                --
(d) EB87-037   --                --                --
CBI-6-6-11     --                --                --
CBI-6-6-88     --                --                --
CBI-6-6-110    --                --                --
CBI-6-6-111    #3.3              --                --
                                 --                --
CBI-6-6-112    --                --                --
CBI-6-6-112A   --                --                --
CBI-6-6-112B   --                --                --
CBI-6-6-112C   --                --                --
CBI-6-6-114    --                --                --
CBI-6-6-38     --                --                --
CBI-6-6-39     --                --                --
                                 --                --
CBI-6-6-40     --                --                --
CBI-6-6-107    --                --                --
CBI-6-6-122    --                --                --
(d) MT6-397    --                --                --

Sample         [delta][sup.2]   [delta][sup.18]   [delta][sup.2]
               [H.sub.chl]      [O.sub.ser]       [H.sub.ser]

East Bay Hills Group

CBI-8-5-30     --               --                --
               --               --                --
CBI-6-6-17     --               --                --
               --               --                --
CBI-6-6-80     --               --                --
(d) FS91-53    --               --                --
CBI-8-5-28     --               --                --
               --               --                --
CBI-6-6-98     --               --                --
CBI-6-6-99     --               --                --
CBI-6-6-101    --               --                --
CBI-6-6-93     --               --                --
CBI-6-6-94     --               --                --
CBI-6-6-95     --               --                --
CBI-6-6-96     --               --                --
CBI-6-6-118    --               --                --
CBI-6-6-119    --               --                --
CBI-6-6-121    --               --                --
CBI-6-6-50     --               --                --
CBI-6-6-51     --               --                --
CBI-6-6-52     --               --                --
                                                  --
CBI-6-6-89     --               --                --
CBI-6-6-90     --               --                --
(d) EB87-037   --               --                --
CBI-6-6-11     --               --                --
CBI-6-6-88     --               --                --
CBI-6-6-110    --               --                --
CBI-6-6-111    --               --                --
               --               --                --
CBI-6-6-112    --               --                --
CBI-6-6-112A   --               --                --
CBI-6-6-112B   --               --                --
CBI-6-6-112C   --               --                --
CBI-6-6-114    --               --                --
CBI-6-6-38     --               --                --
CBI-6-6-39     --               --                --
               --               --                --
CBI-6-6-40     --               --                --
CBI-6-6-107    --               --                --
CBI-6-6-122    --               --                --
(d) MT6-397    --               --                --

Sample         [delta][sup.18]   [delta][sup.13]
               [O.sub.ca1]       [C.sub.cal]

East Bay Hills Group

CBI-8-5-30     --                --
               (c,2) 12.1        (c,2) -7.3
CBI-6-6-17     (b,2) 9.4         (b,2) -5.0
               (c,2) 7.3         (c,2) -5.2
CBI-6-6-80     --                --
(d) FS91-53    --                --
CBI-8-5-28     --                --
               --                --
CBI-6-6-98     --                --
CBI-6-6-99     --                --
CBI-6-6-101    --                --
CBI-6-6-93     --                --
CBI-6-6-94     --                --
CBI-6-6-95     --                --
CBI-6-6-96     --                --
CBI-6-6-118    --                --
CBI-6-6-119    (c,2) 6.0         (c,2) -3.2
CBI-6-6-121    --                --
CBI-6-6-50     --                --
CBI-6-6-51     --                --
CBI-6-6-52     --                --

CBI-6-6-89     --                --
CBI-6-6-90     --                --
(d) EB87-037   --                --
CBI-6-6-11     (b,2) 9.8         (b,2) -4.5
CBI-6-6-88     --                --
CBI-6-6-110    --                --
CBI-6-6-111    --                --
               --                --
CBI-6-6-112    --                --
CBI-6-6-112A   --                --
CBI-6-6-112B   (c,2) 14.3        (c,2) -7.4
CBI-6-6-112C   --                --
CBI-6-6-114    --                --
CBI-6-6-38     --                --
CBI-6-6-39     --                --
               --                --
CBI-6-6-40     --                --
CBI-6-6-107    (b,2) 11.7        (b,2) -7.2
CBI-6-6-122    (b,2) 5.8         (b,2) -4.5
(d) MT6-397    --                --

Notes: cal = calcite, chl--chlorite, fs = feldspar, hbl = hornblende,
qtz = quartz, set = sericite; (a) = alteration types: (1) propylitic,
(2) quartz, sericite and calcite, and (3) phyllic; (b) = disseminated
secondary mineral; (c) = vein mineral; (d) = previously reported by
Potter et al. [delta]2008a); # = porphyritic quartz-feldspar
rhyolite.
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Author:Petts, Duane C.; Longstaffe, Frederick J.; Potter, Joanna; Barr, Sandra M.; White, Chris E.
Publication:Atlantic Geology
Article Type:Report
Geographic Code:1CANA
Date:Jan 1, 2012
Words:8568
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