petrogenesis of the 1.9 ga mafic hanging wall sequence to ... · petrogenesis of the 1.9 ga mafic...

Petrogenesis of the 1.9 Ga mafic hanging wallsequence to the Flin Flon, Callinan, and Triple 7massive sulphide deposits, Flin Flon, Manitoba,Canada1

Y.M. DeWolfe, H.L. Gibson, and S.J. Piercey

Abstract: A detailed study of the geochemical and isotopic characteristics of the volcanic rocks of the Hidden and Louisformations, which make up the hanging wall to the volcanogenic massive sulphide deposits at Flin Flon, Manitoba, wascarried out on a stratigraphically controlled set of samples. The stratigraphy consists of the lowermost, dominantly basaltic,Hidden formation, and the overlying, dominantly basaltic, Louis formation. Of importance petrogenetically, is the1920 unit a basaltic andesite with Nb/Thmn = 0.54–0.62, 3Nd(1.9Ga) = +3.6–+5.9, 3Hf(1.9Ga) = +8.5–+9.6, and 204Pb/206Pb =23.9. The basaltic flows that dominate the Hidden formation have Nb/Thmn = 0.16–0.29, 3Nd(1.9Ga) = +1.7–+4.4,3Hf(1.9Ga) = +7.0–+11.8 and 204Pb/206Pb = 16.9–18.6). The Carlisle Lake basaltic–andesite (top of Hidden formation) ischaracterized by Nb/Thmn = 0.16–0.14, and 204Pb/206Pb = 21.4. The rhyodacitic Tower member (bottom of Louis forma-tion) has Nb/Thmn = 0.23, 3Nd1.9Ga = +4.6, 3Hf1.9Ga = +9.3, and 204Pb/206Pb = 22.2. The basaltic flows that dominate theLouis formation have Nb/Thmn = 0.18–0.25, 3Nd(1.9Ga) = +3.6–+4.2, 3Hf(1.9Ga) = +8.4–+11.3 and 204Pb/206Pb = 17.9. TheHidden and Louis formations show dominantly transitional arc tholeiite signatures, with the 1920 unit having arc tholeiitecharacteristics. It is interpreted to have formed through extensive fractional crystallization of differentiated magmas atshallow levels in oceanic crust. Given the geological, geochemical, and isotopic characteristics of the Hidden and Louisformations, they are interpreted to represent subducted slab metasomatism with minor contamination from subducted sedi-ments.

Resume : Une etude detaillee des caracteristiques geochimiques et isotopiques des roches volcaniques des formations deHidden et de Louis, lesquelles forment l’eponte superieure des gisements de sulfures volcanogenes massifs a Flin Flon,Manitoba, a ete effectuee sur un ensemble d’echantillons controles par la stratigraphie. La stratigraphie comprend, tout ala base, la formation de Hidden, principalement basaltique et la formation de Louis sus-jacente, principalement basaltique.L’unite 1920, une andesite basaltique, est importante d’un point de vue petrogenetique; elle possede les valeurs suivantes :Nb/Thmn = 0.,54–0,62, 3Nd(1.9Ga) = +3,6 a +5,9, 3Hf(1.9Ga) = +8,5 a +9,6, et 204Pb/206Pb = 23.9. Les coulees basaltiques quidominent la formation de Hidden ont les valeurs suivantes : Nb/Thmn = 0,16–0.29, 3Nd(1.9Ga) = +1,7 a +4,4, 3Hf(1.9Ga) =+7,0 a +11,8 et 204Pb/206Pb = 16,9–18,6). L’andesite basaltique Carlisle Lake (sommet de la formation de Hidden) est car-acterisee par Nb/Thmn = 0,16–0,14 et 204Pb/206Pb = 21,4. Le membre Tower (bas de la formation de Louis) a les valeurssuivantes : Nb/Thmn = 0,23, 3Nd1.9Ga = +4,6, 3Hf1.9Ga = +9,3 et 204Pb/206Pb = 22,2. Les coulees basaltiques qui dominent laformation de Louis ont les valeurs suivantes : Nb/Thmn = 0,18–0,25, 3Nd(1.9Ga) = +3,6 a +4,2, 3Hf(1.9Ga) = +8,4 a +11,3 et204Pb/206Pb = 17,9. Les formations de Hidden et de Louis presentent des signatures surtout d’arc tholeiitique de transitionou l’unite 1920 a des caracteristiques d’arc tholeiitique. Cette unite se serait formee par la cristallisation fractionnee agrande echelle de magmas differencies a de niveaux de faible profondeur dans la croute oceanique. Etant donne les carac-teristiques geologiques, geochimiques et isotopiques des formations de Hidden et de Louis, elles representeraient un meta-somatisme de plaque subductee avec une contamination minime par les sediments subductes.

[Traduit par la Redaction]

Received 19 January 2009. Accepted 29 June 2009. Published on the NRC Research Press Web site at cjes.nrc.ca on 3 September 2009.

Paper handled by Associate Editor A. Polat.

Y.M. DeWolfe,2,3 H.L. Gibson, and S.J. Piercey.4 Mineral Exploration Research Centre, Department of Earth Sciences, LaurentianUniversity, 933 Ramsey Lake Road Sudbury ON P3E 6C7, Canada.

1This is a companion paper to DeWolfe, Y.M., Gibson, H.L., Lafrance , B., and Bailes, A.H. 2009. Volcanic reconstruction ofPaleoproterozoic arc volcanoes: the Hidden and Louis formations, Flin Flon, Manitoba, Canada. Canadian Journal of Earth Sciences, 46:this issue.

2Corresponding author (e-mail: [email protected]).3Present address: Department of Earth Sciences, Mount Royal College, 4825 Mount Royal Gate SW Calgary, AB T3E 6K6, Canada.4Present address: SJPGeoConsulting, 11 First Ave., St. John’s, NL A1B 1N3, Canada.

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Can. J. Earth Sci. 46: 509–527 (2009) doi:10.1139/E09-033 Published by NRC Research Press

Introduction

Volcanogenic massive sulphide (VMS) deposits occur inextensional environments within a variety of tectonic set-tings, including oceanic, fore-arc, arc, back-arc, continental-margin, or continental settings (Franklin et al. 1981, 2005;Barrie and Hannington 1999). They are typically related tovolcanically active submarine environments where metalsare precipitated, at or below the sea floor, from circulatinghydrothermal fluids (Franklin et al. 1981, 2005; Lydon1988; Gibson et al. 1999). Submarine volcanic successionsthat host VMS mineralization are typically bimodal, but canbe dominated by mafic or felsic volcanic rocks or sedimen-tary rocks (Franklin et al. 1981, 2005; Barrie and Hanning-ton 1999). Volcanogenic massive sulphide deposits oftenexhibit a pronounced stratigraphic control that may be re-lated to a specific event, such as caldera or cauldron forma-tion, restricting VMS mineralization to a specific time in themagmatic and volcanic evolution of submarine volcanoes(Rytuba 1994; Stix et al. 2003). Given the variety of tec-tonic settings and geochemical compositions associated withVMS deposits (e.g., Franklin et al. 1981, 2005; Barrie andHannington 1999), it is essential to document the tectonicand magmatic history of well-preserved, ancient VMS de-posit-hosting volcanic rocks.

In Flin Flon, phenomenal surface exposure (up to 80%outcrop of *200 m of footwall and *800 m of hangingwall stratigraphy) combined with excellent preservation ofprimary volcanic textures and structures make this camp theideal location to study an ancient submarine volcanic suc-cession associated with world class massive sulphide depos-its. The morphology, texture, and structure of submarinebasaltic volcanoes are important in understanding the physi-cal constraints and manifestations of submarine volcanism.Geochemical and isotopic data add insight into the tectonicsetting and the petrological history, including details aboutthe location, temperature, and composition of the magmasource and any changes in composition the magma mighthave undergone due to contamination from crustal sources.

The Paleoproterozoic Glennie – Flin Flon complex ofnorthern Manitoba and Saskatchewan is part of the south-eastern Reindeer Zone of the Trans-Hudson Orogen (THO)and is known for its significant VMS deposits. The complexcontains 25 past- and presently producing mines rich in Zn–Cu–(Au–Ag) that total over 118 Mt of sulphide, making itthe largest Paleoproterozic VMS district in the world (Symeet al. 1999). The complex consists of a series of assemb-lages that range in age from 1.91 to 1.84 Ga and includearc, back-arc, ocean-floor, and successor-arc successions(Syme and Bailes 1993; Stern et al. 1995a, 1995b; Lucas etal. 1996). The Flin Flon and Snow Lake ocean floor and arcassemblages (1.91–1.87 Ga) contain the majority of theVMS deposits (Fig. 1), and only the juvenile arc assemb-lages within the Glennie – Flin Flon complex, not back-arcbasin assemblages, have been found to contain VMS miner-alization (Syme et al. 1999).

The regional tectonic environment, stratigraphy, and envi-ronment of emplacement of the Glennie – Flin Flon com-plex have been studied by numerous researchers (Bailes andSyme 1989; Syme and Bailes 1993; Stern et al. 1995a,1995b; Lucas et al. 1996; Syme et al. 1999; Ames et al.

2002; Devine 2003). Previous geochemical studies of theFlin Flon volcanic rocks include those of Stauffer et al.(1975), Bailes and Syme (1989), Syme and Bailes (1993),Stern et al. (1995a, 1995b), Lucas et al. (1996), Leybourneet al. (1997), and Syme et al. (1999). Neodymium isotopicstudies have been carried out by Stern et al. (1995a,1995b). However, since these geochemical and Nd isotopicstudies focussed on the regional tectonic and magmatic evo-lution of the Glennie – Flin Flon complex, this study and itscompanion paper (DeWolfe et al. 2009) provide the firstcomprehensive volcanological, geochemical, and Nd iso-topic study of the immediate hanging wall to the Flin FlonVMS deposits. It also provides the first whole-rock Hf andPb isotopic data for the Flin Flon arc assemblage. This newinformation provides a more detailed evaluation of the vol-canic, tectonic, and hydrothermal environment of the domi-nantly mafic hanging wall rocks to the Callinan, Triple 7,and Flin Flon orebodies and has led to the interpretationthat they represent primitive arc volcanism in the Early Pro-terozoic.

Geological setting

The Trans Hudson Orogen comprises five main crustalcomponents: (i) the reactivated Archean-age Hearne andSuperior cratonic margins and their respective Paleoprotero-zoic cover sequences; (ii) the ca. 1.92–1.88 Ga Glennie – FlinFlon complex, that was tectonically accreted in an intrao-ceanic setting during the interval 1.88–1.87 Ga; (iii) the north-western Reindeer Zone consisting of ca. 1.92–1.88 Gajuvenile volcanic arcs, back-arcs, and associated sedimentarybasins thrust onto the Archean Hearne cratonic margin duringthe interval 1.92–1.87 Ga; (iv) the Wathaman–Chipewyanbatholith (ca. 1862–1848 Ma), a continental-arc magmaticsuite that was emplaced along the northwestern ReindeerZone; and (v) a marginal basin and molasse sub-basins (Kis-seynew Domain) developed between the northwestern Rein-deer Zone and Glennie – Flin Flon complex during theinterval 1.85–1.84 Ga (Fig. 1; Corrigan et al. 2007).

The Glennie – Flin Flon complex (Ashton 1999) com-prises juvenile island arc, ocean floor, ocean plateaus,evolved arc and associated sedimentary and plutonic rocksthat formed during closure of the Manikewan Ocean (e.g.Stauffer 1984; Syme and Bailes 1993; Lucas et al. 1996;Whalen et al. 1999; Ansdell 2005). It’s interpreted to haveformed at ca. 1.87 Ga by intraoceanic accretion of theSnow Lake arc assemblage, the Amisk collage, the HansonLake block, and the Glennie Domain (Lewry and Collerson1990; Lucas et al. 1996). Tectonostratigraphic assemblagesof the complex are fold-repeated, thrust-stacked, and tectoni-cally overlie the Archean to earliest Paleoproterozoic SaskCraton above a basal decollement that was active as earlyas about 1.84 Ga (Ashton et al. 2005).

Rocks of the Flin Flon arc assemblage are interpreted tohave been erupted and emplaced in an island-arc to back-arc setting (Syme and Bailes 1993; Syme et al. 1999) andconsist of basaltic flows, basaltic andesite flows and brec-cias, and lesser rhyolitic flows. Overall the stratigraphy isdominantly bimodal with the bulk of the stratigraphy beingmafic or felsic with only minor, but significant, basaltic an-desite rocks. The Flin Flon, Callinan, and Triple 7 VMS de-

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posits (Fig. 2), which total more than 92.5 million tonnesgrading 2.21% Cu, 4.25% Zn, 2.11 g/t Au, and 27.22 g/tAg, are interpreted to have formed during a period of local-ized rhyolitic volcanism in a synvolcanic subsidence struc-ture, or cauldron, within a much larger, dominantly basaltic,central volcanic complex (Bailes and Syme 1989; Devine et

al. 2002; Devine 2003). The Hidden and Louis formations(Fig. 2) are interpreted to have been erupted during a periodof resurgent basaltic volcanism and subsidence that immedi-ately followed a hiatus in volcanism marked by VMS oredeposition (DeWolfe et al. 2009.

Previous workers (Stern et al. 1995a, 1995b; Syme et al.

Fig. 1. Geology of the Flin Flon arc assemblage, showing the locations of known VMS deposits (modified from Syme et al. 1996). Boxindicates area covered by Fig. 2. The inset map shows the location of Flin Flon within the Trans-Hudson Orogen (THO).

DeWolfe et al. 511


1999) described various volcanic units from the Flin Flonarc assemblage, including five samples taken from the Hid-den and Louis formations. They interpreted these samples asisotopically ‘‘evolved’’ arc rocks, characterized by flat toslightly enriched chondrite-normalized rare-earth element(REE) patterns, with depletions of Nb, Zr, Hf, and Ti rela-tive to adjacent REE on mid-ocean ridge basalt (MORB)-normalized plots, and with initial 3Nd values ranging

from +3.1 to +4.1. Stern et al. (1995a, 1995b) interpretedthat this interval of intraoceanic arc magmatism was charac-terized by rapid subduction of oceanic lithosphere, relativelythin arc crust (<20 km) and by extensive back-arc basin for-mation. They also postulated that these isotopically evolvedarc rocks have incorporated Nd from an older crustal source,either through subduction of sediments or by intracrustalcontamination. Given the regional nature and the sparse

Fig. 2. Geology of the Flin Flon area (modified from Stockwell 1960); see Fig. 1 for location.



sampling within the hanging wall of the study by Stern et al.(1995a, 1995b), this research endeavoured to collect moresystematic data, including data for all units within the Hid-den and Louis formations, and to evaluate this data in lightof a new understanding of the stratigraphy, volcanic tex-tures, and structures (DeWolfe et al. 2009), and to comparethis data with that of Stern et al. (1995a, 1995b) to discern ifall units within the hanging wall are of evolved arc origin aspreviously interpreted.

Stratigraphy of the hanging wallThe contact between the Hidden and Louis formations is

marked by a plane-bedded, mafic tuff unit that represents amappable hiatus in volcanism traceable throughout the FlinFlon area (Bailes and Syme 1989; Ames et al. 2002;DeWolfe et al. 2009).

The Hidden formation defines the onset of hanging wallvolcanism and comprises, from oldest to youngest, the 1920unit, the Stockwell member, and the Reservoir member. The1920 unit consists of massive, pillowed, and peperite faciesbasaltic andesites and is overlain locally by felsic or inter-mediate volcaniclastic rocks. The Stockwell member ispresent only locally and is repeated by a thrust fault(Fig. 2). In one thrust panel, it overlies the 1920 unit, andin the other, it overlies aphyric basaltic flows of the Reser-voir member (Fig. 2). The Stockwell member is also over-lain by aphyric basaltic flows of the Reservoir member. Itis composed of massive, pillowed, and breccia facies, pla-gioclase-phyric basaltic flows intercalated with mafic lapilli-stone mass flow deposits (DeWolfe et al. 2009). TheReservoir member is made up of massive, pillow, breccia,and peperite facies, aphyric basaltic flows. Where neitherthe 1920 unit nor Stockwell members are present, south ofthe Railway Faults, it conformably overlies the Millrockmember of the Flin Flon formation (Fig. 2). A basaltic ande-site unit occurs at the top of the dominantly basaltic Reser-voir member where it is in contact with overlying Louisformation flows. This unit is called the Carlisle Lake basal-tic andesite after its type location.

The Louis formation conformably overlies the Hidden for-mation and consists of the Tower and Icehouse members, aswell as undivided basaltic flows. The Tower member occursat the base of the Louis formation and consists of an areallyrestricted massive to in situ–brecciated, aphyric rhyodaciticflow and associated volcaniclastic rocks overlain by mafictuff, and more extensively is represented by the tuff alone.The Icehouse member, which conformably overlies theTower member, consists of a massive, pillowed and brecci-ated, strongly plagioclase- (£30%) and pyroxene- (£25%)porphyritic basaltic flow overlain by heterolithic, mafic vol-caniclastic rocks. The Louis formation is capped by a thick(>500 m) succession of undivided plagioclase- (>15%) andpyroxene- (>5%) porphyritic, dominantly pillowed basalticflows (DeWolfe et al. 2009).

Basaltic to basaltic andesite flows and sills of the Hiddenformation are interpreted to have formed a small shield vol-cano with a synvolcanic graben and volcanic vent for thisedifice located on the northwest limb of the Hidden syn-cline. The graben and volcanic vent correspond spatiallywith the location of the 1920 unit and the flows and inter-

flow volcaniclastic units of the Stockwell member. Flows ofthe Louis formation are interpreted to represent resurgencein basaltic volcanism and minor associated subsidence, re-sulting in the growth of a new small lava shield on what isnow the southern flank of the Hidden volcano. The volca-nology of these two volcanoes is described in detail in thecompanion paper DeWolfe et al. (2009).

The absence of voluminous volcaniclastic deposits thattypify the underlying Flin Flon formation, within the Hiddenand Louis formations, suggests extension and subsidence hadlargely ceased during construction of the Hidden and Louisshield volcanoes and that they may represent a return to nor-mal arc evolution (DeWolfe et al. 2009). However, synvol-canic structures in the hanging wall do define structuralcorridors that can be traced directly into the footwall wherethey controlled the location of massive sulphide mineraliza-tion (Gibson et al. 2003; DeWolfe et al. 2009). The continu-ation of these structures into the hanging wall strata indicatestheir longevity and reactivation as magma and fluid path-ways during the emplacement of the Hidden and Louis vol-canoes. The recognition of synvolcanic structural corridorsin the hanging wall allows for targeting massive sulphidemineralization along the same structures within the footwall.

Geochemical results

Petrographic observationsSamples of volcanic rocks were collected during three

summers of detailed mapping at scales ranging from 1 : 250to 1 : 2000 (DeWolfe 2007a, 2007b, 2007c, 2007d, 2007e).Each flow and cryptoflow from the base of the Hidden for-mation to the top of the Louis formation was sampled, andthe flows and cryptoflows were also sampled along strike at100 to 500 m over a total strike length of *6 km.

Although primary volcanic textures, such as pillows, flowbanding, autoclastic breccias, hyaloclastite, peperite, andlayering are well preserved in the Hidden and Louis forma-tions, all of the rocks are deformed, and primary minerals,such as pyroxene and plagioclase, are replaced to a variableextent by greenschist-facies metamorphic actinolite, epidote,and muscovite. Most mafic minerals have been replaced byactinolite; primary plagioclase (albite) is variably replacedby epidote and muscovite. The groundmass commonly com-prises actinolite, epidote, quartz, and chlorite with lesseramounts of biotite and carbonate. Locally the volcanic rockscontain strong, patchy, epidote–quartz alteration. Thesepatches manifest themselves as 5–50 cm wide, rounded tosubrounded, greenish-white patches often forming as halosaround amygdules filled with quartz and epidote. In thesecases, the groundmass almost entirely consists of granularepidote and quartz (9:1 ratio, respectively) and many of thephenocrysts, felsic or mafic, are overprinted by granular epi-dote and quartz. Such features in intermediate to mafic vol-canic rocks of Noranda, Quebec, have been attributed tosemi-conformable hydrothermal alteration zones associatedwith VMS deposits (Galley 1993; Gibson and Kerr 1993;Paradis et al. 1993); consequently, we interpret the minera-logically and texturally identical epidote–quartz patches inthe Hidden and Louis formations to have resulted from hy-drothermal alteration associated with the massive sulphidemineralization.

DeWolfe et al. 513


Geochemical limitationsAll samples have been screened using field, petrographic

and geochemical attributes. Samples containing patchy epi-dote–quartz alteration were not used to elucidate petroge-netic processes; however, minor alteration, in general, wasinevitable given the pervasive metamorphic alteration of thehanging wall. Under upper greenschist metamorphic condi-tions, most major elements (e.g., SiO2, Na2O, K2O, CaO)and LFSE (low field strength elements: Cs, Rb, Ba, Sr, U)are mobile (MacLean 1990); however, some major elements(e.g., P2O5, Al2O3, TiO2), the transition elements, HFSE(high field strength elements), REE, and Th are typicallyimmobile (e.g., MacLean 1990; Jenner 1996). Table 1 showsrepresentative geochemical data for the Hidden and Louisformations; key major element and trace element ratios are

presented in Table 2. Samples were rejected if the total losson ignition exceeded 4.5 wt.%, Na2O < 2 wt.% and (or)Al2O3/Na2O > 10 (Spitz and Darling 1978), values intendedto eliminate the most altered samples. Variability in ratios ofimmobile Zr (MacLean 1990) to the major elements sug-gests that, as expected, SiO2, Na2O, K2O, CaO, MgO, andFe2O3 are mobile, whereas a lack of scatter in the Zr vs.P2O5, TiO2, Nb, and Sm indicate that they are largely immo-bile (e.g., Figs. 3a–3h).

Analytical methodsSamples were pulverized in a steel jaw crusher, with a

few samples subsequently powdered in an agate mill. Totalabundances of major oxides were analysed by inductivelycoupled plasma – emission spectrometry (ICP–ES) follow-

Table 1. Ranges in composition for units of the Hidden and Louis formations.

1920 unit(Hidden fm.)

Reservoir mb.(Hidden fm.)

Stockwell mb.(Hidden fm.)

Carlisle Lakeandesite (Hidden fm.)

Tower mb.(Louis fm.)

Icehouse mb.(Louis fm.)

Undivided flows(Louis fm.)

SiO2 (wt.%) 48–58 50–56 46–53 51–64 73.00 47–48 46–57TiO2 1.0–1.2 0.56–0.85 0.36–0.90 0.49–0.65 0.24 0.48 0.36–0.64Al2O3 14.6–17.8 13.8–17.2 12.4–19.0 14.6–17.0 10.29 14.5–14.9 14.9–17.3Fe2O3 12.8–17.6 11.2–15.7 9.4–17.5 6.3–14.6 7.05 11.5–11.9 9.7–13.6MnO 0.21–0.27 0.18–0.25 0.15–0.23 0.09-.18 0.07 0.18–0.19 0.14–0.20MgO 1.54–2.37 3.3–6.2 2.6–6.0 2.5–4.7 1.75 8.2–9.1 3.2–6.2CaO 6.3–8.1 6.2–11.7 7.1–11.1 3.2–5.9 1.38 9.6–10.3 5.4–10.8Na2O 2.8–4.2 2.3–4.2 2.3–4.2 2.8–5.8 3.00 2.3–2.7 2.1–5.1K2O 0.30–0.83 0.13–0.93 0.15–0.66 0.55–1.85 0.65 0.17–0.39 0.23–1.16P2O5 0.33–0.45 0.05–0.15 0.05–0.17 0.21–0.29 0.08 0.07 0.06–0.11LOI 0.1–1.2 1.3–3.6 0.7–3.9 1.6–3.1 2.10 3.50 2.1–4.4

Cr (ppm) 5–10 33–50 95–225 <24–36 7 246 <24–94Ni 9–30 5–27 9–33 14–32 5 71–65 13–80Sc 30–35 40.7–62.6 49.5–54.3 19.2–35.2 - 44.0–45.7 29.8–49.3V 26–36 265–434 275–355 174–310 - 262–293 247–355Rb 2–17 0.6–11.9 1.5–10.5 7.6–33.9 9.2 1.8–6.2 3.4–17.3Cs 0.06–0.85 0.08–0.55 0.03–0.36 0.09–1.23 0.17 0.02–0.8 0.04–0.24Ba 105–644 27–481 37–326 48–754 258 38–143 27–629Sr 120–229 44–291 45–269 58–452 97 267–399 73–376Nb 2.3–2.9 0.6–1.2 0.5–1.4 2.9–4.0 3.2 0.6 0.7–1.7Hf 2.7–3.0 0.62–1.10 0.40–1.20 1.34–2.27 2.50 0.39–0.44 0.41–1.25Zr 91–114 18–35 13–39 47–77 86.4 12–14 13–46Y 47.8–58.9 12.5–19.3 8.8–24.0 15.5–21.7 33.9 8.4–9.0 8.8–18.1Th 0.48–0.52 0.25–0.96 0.21–0.46 2.22–3.21 1.65 0.28–0.29 0.25–0.91U 0.32–0.44 0.21–0.68 0.16–0.36 1.01–1.39 1.07 0.14–0.15 0.19–0.51La 7.0–8.4 1.80–6.48 1.88–4.99 14.34–16.79 12.45 2.38–2.56 2.38–6.06Ce 17.7–21.8 4.6–13.9 4.5–11.7 27.5–35.2 25.8 5.3–5.5 5.2–13.4Pr 2.83–3.38 0.71–1.96 0.58–1.66 3.36–4.47 3.35 0.73–0.79 0.76–1.76Nd 13.64–16.84 3.67–9.65 2.72–7.99 13.91–18.41 14.97 3.51–3.68 4.33–8.15Sm 4.49–5.59 1.17–2.75 0.87–2.41 2.89–3.85 3.92 0.97–1.04 1.25–2.08Eu 1.61–1.89 0.42–1.19 0.32–0.72 0.66–1.17 1.36 0.38–0.42 0.39–0.66Gd 6.20–7.82 1.81–3.65 1.20–3.23 2.58–3.55 4.51 1.14–1.18 0.21–0.66Tb 1.14–1.45 0.30–0.62 0.21–0.58 0.42–0.54 0.80 0.20–0.22 0.21–0.35Dy 8.30–10.29 2.12–4.20 1.49–3.96 2.70–3.50 5.46 1.30–1.40 1.40–2.80Ho 1.91–2.34 0.49–0.93 0.36–0.88 0.57–0.79 1.20 0.31–0.32 0.31–0.61Er 5.77–7.29 1.52–2.74 1.17–2.85 1.64–2.29 3.75 0.86–0.93 0.99–1.84Tm 0.90–1.12 0.24–0.42 0.17–0.43 0.28–0.39 0.57 0.14–0.15 0.15–0.30Yb 6.1–7.6 1.61–2.74 1.20–2.81 1.85–2.58 3.94 0.95–0.98 0.97–1.80Lu 0.96–1.20 0.026–0.43 0.19–0.44 0.31–0.42 0.61 0.15–0.16 0.16–0.31

Note: fm., formation; mb., member; LOI, loss on ignition.



ing a lithium metaborate–tetraborate fusion and dilute nitricdigestion at ACME Analytical Laboratories (Vancouver,British Columbia). Replicate analyses of samples and stand-ards reveal relative standard deviations (%RSD) of <18%for ICP – mass spectrometry (ICP–MS) determinations.Samples were analysed for trace elements at the OntarioGeoscience Laboratories (Sudbury, Ontario) and underwenta closed beaker digest using four acids (hydrofluoric, hydro-chloric, perchloric, and nitric acids) to ensure total dissolu-tion of all solids. The samples were then analysed for traceelements using ICP–MS. Replicate analyses of samples andstandards reveal relative standard deviations (%RSD)of <10% for ICP–MS determinations.

Neodymium isotopic geochemistry was completed at thePacific Centre for Isotopic and Geochemical Research, De-partment of Earth and Ocean Sciences, The University ofBritish Columbia (Vancouver, B.C.) using thermal ioniza-tion mass spectrometry (TIMS) following the methods ofWeis et al. (2006). Values for the United States GeologicalSurvey (USGS) reference standards BCR-2 and G-2 yieldedaverage 143Nd/144Nd ratios of 0.512628 and 0.512217, re-spectively, with analytical uncertainties of ± 0.000006 (2s)for each. Neodymium isotope data are presented relative toa La Jolla standard value of 143Nd/144Nd = 0.511858. All143Nd/144Nd values are normalized to 146Nd/144Nd = 0.7219,and initial 3Nd values are reported relative to a chondriticuniform reservoir with present-day values of 147Sm/144Nd =0.1967 (Jacobsen and Wasserburg 1980) and 143Nd/144Nd =0.512638 (Goldstein et al. 1984). Initial 143Nd/144Nd ratiosand 3Nd were calculated at 1.9 Ga, the approximate age ofall samples in this study, to facilitate comparison with otherdata from the Flin Flon arc assemblage (Stern et al. 1995a,1995b).

Hafnium isotopic geochemistry was also completed at thePacific Centre for Isotopic and Geochemical Research usingTIMS, following the methods of Weis et al. (2007). Valuesfor the USGS reference standards BHVO-1 and BCR-2yielded average 176Hf/177Hf ratios of 0.283102 and0.282869, respectively, with analytical uncertainties of± 0.0000015 and 0.0000016 (2s), respectively. Hafnium iso-tope data are presented relative to a La Jolla (JMC475)standard value of 176Hf/177Hf = 0.282160. Initial 3Hf values

are reported relative to a chondritic uniform reservoir withpresent-day values of 176Lu/177Hf = 0.0332 (Vervoot andBlichert-Toft 1999) and 176Hf/177Hf = 0. 282772 (Vervootand Blichert-Toft 1999). Initial 176Hf/177Hf ratios and 3Hfare again calculated at 1.9 Ga.

Lead isotopic geochemistry was done at Carleton Univer-sity (Ottawa, Ontario) using a Thermo-Finnigan TRITONmass spectrometer following the methods of Cousens(1996). Samples were dissolved using a three acid digestionand the residue taken up in a hydrogen bromide solution forPb separation. Lead was separated in Bio-Rad 10 mL poly-ethylene columns and Dowex AG1-8X anion resin using hy-drogen bromide to elute other elements and hydrochloricacid to elute Pb. This procedure was repeated. All massspectrometer runs are corrected for fractionation using NISTSRM981, and the average ratios for SRM981 are 206Pb/204Pb = 16.892 ± 0.010, 207Pb/204Pb = 15.431 ± 0.013, and208Pb/204Pb = 35.512 ± 0.038 (2 standard deviations), basedon 20 runs. The fractionation correction based on the valuesof Todt et al. (1984) is +0.13%/amu (atomic mass units).

ResultsThe Hidden and Louis formations can be subdivided into

seven distinct geochemical suites using immobile incompat-ible elements. This geochemical subdivision correspondswith subdivision based on petrographic observations (de-scribed earlier in the text and including the 1920 unit, ba-salts and basaltic andesites of the Reservoir member, andthe Stockwell member, all of the Hidden formation, as wellas the Tower member, Icehouse member, and undividedflows of the Louis formation). The 1920 unit is slightly lightREE (LREE)-depleted, typical of normal arc tholeiites, butall other units within the Hidden and Louis formations havegeochemical attributes similar to transitional arc tholeiiteswith slightly more LREE enrichment than normal arc tholei-ites (Jakes and Gill 1970).

1920 unit, Hidden formationThe 1920 unit has Zr/TiO2 and Nb/Y ratios typical of sub-

alkaline basaltic andesite (Fig. 4) with elevated values of to-tal Fe, TiO2, and P2O5 and lower values of Al2O3 thantypical basaltic andesites (Table 1; Fig. 5). Though high in

Table 2. Average values for key element ratios for the units of the Hidden and Louis formations.

1920 unit(Hidden fm.)

Reservoir mb.(Hidden fm.)

Stockwell mb.(Hidden fm.)

Carlisle Lake basalticandesite (Hidden fm.)

Tower mb.(Louis fm.)

Icehouse mb.(Louis fm.)

Undivided flows(Louis fm.)

Al2O3/Na2O 3.8–5.3 3.7–6.3 4.2–7.2 2.5–5.4 3.4 5.3–6.4 3.1–7.8Al2O3/TiO2 13.8–15.5 16.9–33.7 17.0–50.0 25.5–29.9 42.9 30.3–31.2 24.3–45.6Ti/V 168.2–240.6 8.1–14.4 8.5–18.2 11.2–16.9 — 9.8–11.0 7.7–14.3Zr/Y 1.8–2.0 1.2–1.8 1.2–1.8 2.6–3.6 2.6 1.4–1.6 1.4–2.7Zr/Ti 0.015–0.016 0.004–0.007 0.004–0.007 0.014–0.020 0.060 0.004–0.005 0.005–0.014Nb/Y 0.05 0.04–0.07 0.04–0.06 0.15–0.19 0.09 0.07 0.06–0.10Ti/Sc 201–214 5–127 61–134 99–153 — 63–65 47–105Nb/Lamn 0.31–0.35 0.17–0.32 0.16–0.31 0.17–0.26 0.25 0.22–0.23 0.15–0.30Nb/Thmn 0.54–0.62 0.11–0.27 0.15–0.29 0.14–0.16 0.23 0.23–0.25 0.14–0.25La/Smch 0.9–1.0 0.9–2.1 1.1–1.7 2.7–3.2 2.1 1.6 1.5–2.3La/Ybch 0.8 0.7–1.9 1.0–1.7 4.2–5.7 2.3 1.8–1.9 1.8–3.3Sm/Ybch 0.8–0.9 0.8–1.1 0.8–1.1 1.7–2.0 1.1 1.1–1.2 0.9–1.4

Note: mn, primitive mantle normalized ratios using values of Sun and McDonough (1989); ch, chondrite-normalized ratios using values of Sun and McDo-nough (1989); fm., formation; mb., member.

DeWolfe et al. 515


HFSE, the very high TiO2 content (Table 1) of the 1920 unitresults in high Ti/V and Ti/Sc ratios (Table 2; Fig. 6). Theunit has a moderately low Zr/Y ratio (Table 2; Fig. 7). It ischaracterized by primitive mantle-normalized patterns withslight LREE depletion (La/Smch = 0.9–1.0; Table 2), nega-tive Nb anomalies (Nb/Thmn = 0.58) and HFSE depletion

(Fig. 8a). Chondrite-normalized patterns for the 1920 unitare again flat with slight LREE depletion (La/Ybch = 0.8;Table 2; Fig. 9a).

Isotopically, the 1920 unit has 3Nd(1.9Ga) values of +3.6to +5.9 similar to values for the depleted mantle at 1.9 Ga(Table 3; Goldstein et al. 1984). The 1920 unit has

Fig. 3. Zr vs. selected element variation diagrams to demonstrate(a–d) the effects of post-magmatic alteration and (e–h) the limited effectsof alteration on P, Ti, Nb, and Sm. Strong correlation for these elements indicates that they were not significantly mobilized by alteration.



3Hf(1.9Ga) values of +8.5 to +9.6, similar to values for the de-pleted mantle at 1.9 Ga (Vervoort and Blichert-Toft 1999;Table 3). Whole-rock Pb isotopic data for the 1920 unityields a 206Pb/204Pb value of 23.945 and 207Pb/204Pb valueof 16.172 (Table 4).

Reservoir member, Hidden formationBasalts of the Reservoir member have subalkaline affin-

ities (Fig. 4), low to moderate Al2O3/TiO2 ratios, and lowP2O5 contents relative to other basalts of the hanging wall(Table 2; Fig. 5). The basaltic rocks of the Reservoir mem-ber also have low Zr/Y, Ti/Sc, and Ti/V ratios (Table 2),and, as with the Stockwell member, their Ti vs. V system-atics are similar to those of modern day island-arc rocks(Figs. 6, 7). However, basalts of the Reservoir memberhave flat, primitive mantle-normalized patterns with slightLREE enrichment (La/Smch = 0.9–2.1), strong negative Nbanomalies (Nb/Thmn = 0.11–0.27), and HFSE depletion(Fig. 8b), suggesting they are transitional island-arc tholei-ites. Chondrite-normalized patterns for the basalt of the Res-ervoir member are again flat to slightly LREE-enriched (La/Ybch = 0.7–1.9; Table 2; Fig. 9a).

Isotopically, basalts of the Reservoir member have3Nd(1.9Ga) values of +1.7 to +3.2 and 3Hf(1.9Ga) values

of +7.0 to +8.5, which are both similar to values for the de-pleted mantle at 1.9 Ga (Goldstein et al. 1984; Vervoort andBlichert-Toft 1999; Table 3). Whole-rock Pb isotopic datafor basaltic rocks of the Reservoir member give 206Pb/204Pbvalues of 15.53–15.57 and 207Pb/204Pb values of 15.16–15.18(Table 4).

Stockwell member, Hidden formationBasalts of the Stockwell member overlap with those of

the Reservoir member on a plot of Zr/TiO2 versus Nb/Y,both having subalkaline affinities (Fig. 4). However, theyhave slightly higher P2O5 contents than basalts of the Reser-voir member and low to high Al2O3/TiO2 ratios that overlaponly partially with basalts of the Reservoir member (Ta-bles 1, 2; Fig. 5). The Stockwell member also has low Zr/Y, Ti/Sc, and Ti/V ratios (Table 2). The latter suggests theyare similar modern-day island-arc tholeiites (Figs. 6, 7);however, on a primitive mantle-normalized plot, the Stock-

Fig. 6. Ti vs. V tectonomagmatic discrimination diagram (Shervais1982) for the Hidden and Louis formations. BON, bonninite; IAT,island-arc tholeiitic basalts; BABB, back-arc basin basalt; MORB,mid-ocean ridge basalt; ARC, arc basalt; OFB, ocean-floor basalt.

Fig. 7. Zr/TiO2 vs. Y/TiO2 diagram (Piercey et al. 2004) showingtholeiitic affinity of rocks of the Hidden and Louis formations.

Fig. 4. Discrimination diagram (Pearce 1996) for the Hidden andLouis formations. Alk, Alkaline; And, Andesite.

Fig. 5. Al2O3–P2O5–TiO2 systematics of the Hidden and Louis for-mations. N-MORB, normal mid-ocean ridge basalt; E-MORB, en-riched MORB; OIB, ocean-island basalt.

DeWolfe et al. 517


well member has flat to slightly LREE-enriched patterns(La/Smch = 1.1–1.7), with strong negative Nb anomalies(Nb/Thmn = 0.16–0.28), and HFSE depletion (Fig. 8c) char-

acteristic of a transitional island-arc tholeiite. The Stockwellmember has flat chondrite-normalized patterns with slightLREE enrichment (La/Ybch = 1.0–1.7; Table 2; Fig. 9c).

Fig. 8. Primitive mantle-normalized trace element plots for various units within the Hidden and Louis formations. Primitive mantle valuesfrom Sun and McDonough (1989).



This unit has 3Nd(1.9Ga) values of +2.8 to +4.4, 3Hf(1.9Ga)values of +10.4 to +11.8, both similar to values for the de-pleted mantle at 1.9 Ga (Goldstein et al. 1984, Vervoort and

Blichert-Toft 1999; Table 3). Whole-rock Pb isotopic datafor the Stockwell member yields a 206Pb/204Pb value of17.40 and 207Pb/204Pb value of 15.38 (Table 4).

Fig. 9. Chondrite-normalized trace element plots for various units within the Hidden and Louis formations. Chondrite values from Sun andMcDonough (1989).

DeWolfe et al. 519


Carlisle Lake basaltic andesites, Reservoir member,Hidden formation

Basaltic andesites at the top of the Reservoir memberhave Zr/TiO2 and Nb/Y ratios typical of subalkaline basalticandesites, and higher Nb/Y ratios separate them from the1920 unit (Fig. 4). The basaltic andesites of the Reservoirmember are referred to as the Carlisle Lake basaltic ande-sites after their type locality and to separate them from thebasalts of the Reservoir member. In the field, they are com-monly indistinguishable from the basalts of the Reservoirmember and seldom contain acicular amphibole crystalssimilar to those observed in the 1920 unit. They have mod-erate Al2O3/TiO2 ratios and P2O5 contents that distinguishthem from all other units within the hanging wall (Tables 1,2; Figs. 5, 7). High Zr/Y ratios, low to moderate TiO2 con-tents, and moderate Ti/Sc and Ti/V ratios also distinguishthem from the 1920 unit and basalts of the hanging wall(Tables 1, 2). As with the other units within the Hidden for-mation, the Ti–V systematics of the Carlisle Lake basalticandesites suggest they are similar to modern-day island-arctholeiites (Table 2; Fig. 6). However, rocks from the CarlisleLake basaltic andesite have relatively low HFSE values, aremore LREE enriched than the other units within the Hiddenformation (La/Smch = 2.7–3.2), and have primitive mantle-normalized patterns with distinct negative Nb (Nb/Thmn =0.14–0.16) and Ti anomalies (Table 2; Fig. 8d), suggesting

they are transitional between island-arc tholeiites and calc-alkaline rocks. On a chondrite-normalized plot the CarlisleLake basaltic andesites have LREE-enriched patterns (La/Ybch = 4.2–5.7; Table 2; Fig. 9d).

Samples were analyzed for Pb-isotopes yielding 206Pb/204Pb values of 14.77–15.58 and 207Pb /204Pb values of15.12–15.19 (Tables 3, 4).

Tower member, Louis formationThe Tower member plots as a subalkaline rhyodacite

(Fig. 4) and is characterized by a high Al2O3/TiO2 ratio andlow P2O5 content (Tables 1, 2; Fig. 5); although this is a sin-gle sample, it is likely representative of the Tower member.The primitive mantle-normalized plot of the Tower memberhas a flat to LREE-enriched (La/Smch = 2.1) pattern, with astrong Nb (Nb/Thmn = 0.23) and Ti anomaly (Table 2;Fig. 8e). A chondrite-normalized plot of the Tower memberagain shows that it is moderately enriched in the LREEs(La/Ybch = 2.3; Table 2; Fig. 9e).

A sample from the Tower member yielded an 3Nd(1.9Ga)value of +4.6 and an 3Hf(1.9Ga) value of +9.6, again both aresimilar to values for the depleted mantle at 1.9 Ga (Gold-stein et al. 1984; Vervoort and Blichert-Toft 1999; Table 3).The Tower member was also analyzed for Pb isotopes andyielded a 206Pb/204Pb value of 15.82 and 207Pb/204Pb valueof 15.21 (Table 4).

Table 3. 3Hf and 3Nd values for the Hidden and Louis formations.

Sample Unit or member 143Nd/144Nda 147Sm/144Nd 3Nd(1.9)176Hf/177Hf b 176Lu/177Hf 3Hf(1.9)

035 1920 unitd 0.512876 (6) 0.1918 5.9 0.283624 (06) 0.0567 9.6004 1920 unitc 0.512645 (6) 0.1826 3.6 0.281814 (06) 0.0484 8.5080 Reservoir memberd 0.512668 (6) 0.1862 3.2 0.283890 (11) 0.0327 8.5005 Reservoir memberc 0.512698 (7) 0.1945 1.7 0.281773 (04) 0.0573 7.0092 Stockwell memberd 0.512603 (5) 0.1759 4.4 0.284366 (18) 0.0581 11.8002 Stockwell memberc 0.512568 (6) 0.1795 2.8 0.281879 (05) 0.0571 10.8061 Stockwell memberd 0.512571 (6) 0.1732 4.4 0.284002 (10) 0.0495 11.4095 Stockwell memberd 0.512825 (5) 0.1952 4.0 0.284194 (14) 0.0444 10.4127 Tower memberd 0.512321 (6) 0.1525 4.6 0.283093 (04) 0.0348 9.3133 Icehouse memberd 0.512467 (6) 0.1661 4.2 0.281811 (08) 0.0510 8.4144 Undivided, Louis formationd 0.512250 (6) 0.1511 3.6 0.281893 (05) 0.0350 11.3

aNumber in parentheses is the uncertainty in the last decimal place.bNumber in parentheses is the uncertainty in the last two decimal places.cLeast altered sample.dWeakly altered sample.

Table 4. Pb isotopic data for the Hidden and Louis formations.

Sample Unit or member Formation 206Pb/204Pba 207Pb/204Pba 208Pb/204Pbb

004 1920 unitc Hidden 23.945 (7) 16.172 (5) 39.879 (11)006 Reservoir member c Hidden 16.161 (4) 15.227 (3) 35.313 (08)002 Reservoir memberd Hidden 16.881 (2) 15.320 (1) 35.724 (03)005 Stockwell memberc Hidden 18.566 (5) 15.503 (4) 36.269 (10)202 Carlisle Lake basaltic andesitec Hidden 21.468 (2) 15.846 (1) 37.849 (04)203 Carlisle Lake basaltic andesited Hidden 17.811 (3) 15.437 (2) 36.386 (06)133 Icehouse memberc Louis 17.903 (1) 15.441 (1) 36.327 (02)127 Tower memberc Louis 22.166 (3) 15.903 (2) 37.120 (05)

aNumber in parentheses is the uncertainty in the last decimal place.bNumber in parentheses is the uncertainty in the last two decimal places.cLeast altered sample.dWeakly altered sample.



Icehouse member, Louis formationSubalkaline basalts (Fig. 4) of the Icehouse member have

Zr/TiO2 ratios that overlap with the basalts of the Reservoirand Stockwell members, but with distinctly higher Nb/Y ra-tios (Table 2; Fig. 4). The Al2O3/TiO2 ratios of the Icehousemember overlap with the higher Al2O3 ratios of the Stock-well member but are markedly higher than those within theReservoir member (Table 2). Rocks belonging to the Ice-house member have slightly lower P2O5 values than the ba-salts of the Reservoir and Stockwell members (Table 1;Fig. 5). Moderate to high Ti/Sc and Ti/V ratios (Table 2)also differentiate these basalts from those of the Reservoirmember, and Ti–V systematics, low Zr/Y ratios, and lowHFSE contents indicate an island-arc tholeiite affinity(Figs. 6, 7). The Icehouse member is similar to basalts ofthe Reservoir and Stockwell members having flat primitivemantle-normalized patterns with only slight LREE enrich-ment (La/Smch = 1.6), strong negative Nb anomalies (Nb/Thmn = 0.23–0.25), and HFSE depletion (Fig. 8f). On achondrite-normalized plot, the Icehouse member againshows slight LREE enrichment (La/Ybch = 1.8–1.9; Table 2;Fig. 9f), possibly indicating that it is transitional between is-land-arc tholeiites and calc-alkaline rocks.

A sample of the Icehouse member has 3Nd(1.9Ga) = +4.2and an 3Hf(1.9Ga) value of +8.4, again both are similar to val-ues for the depleted mantle at 1.9 Ga (Goldstein et al. 1984;Vervoort and Blichert-Toft 1999; Table 3). The same sam-ple yielded a 206Pb/204Pb value of 15.39 and 207Pb/204Pbvalue of 15.16 (Table 4).

Undivided volcanic flows, Louis formationThe undivided volcanic flows that form a thick sequence

at the top of the Louis formation have Zr/TiO2 ratios similarto the Reservoir, Stockwell, and Icehouse members and fallwithin the subalkaline basalt field; however, they can beseparated based on their Nb/Y ratios from other basaltswithin the hanging wall (Table 2; Fig. 4). They overlapwith Al2O3/TiO2 and P2O5 values of the Stockwell and Ice-house members but differ in this respect from the Reservoirmember (Tables 1, 2; Fig. 5). Low TiO2 content and low Zr/Y, Ti/Sc, and Ti/V values are similar to the other basaltswithin the hanging wall and lie within the island-arc tholei-ite field in Figs. 6 and 7. The undivided basaltic flows haverelatively low HFSE contents (Table 1) and slightly LREE-enriched (La/Smch = 1.5–2.3; Table 2) primitive mantle-nor-malized patterns with distinctive negative Nb (Nb/Thmn =0.14–0.25; Table 2; Fig. 8g). On chondrite-normalized plots,the undivided basalts of the Louis formation again showmoderate LREE enrichment (La/Ybch = 1.8–3.3; Table 2),suggesting they are transitional in nature (Fig. 9g).

With 3Nd(1.9Ga) = +3.6 and an 3Hf(1.9Ga) value of +11.3,the undivided basalts of the Louis formation are similar tovalues for the depleted mantle at 1.9 Ga (Goldstein et al.1984; Vervoort and Blichert-Toft 1999; Table 3).

Discussion

The geological characteristics of the Hidden and Louisformations of the Flin Flon arc assemblage suggest thatthey record the evolution of two dominantly basaltic juve-nile arc volcanoes in a Paleoproterozoic island arc. Geologi-

cal characteristics of the base of the Hidden formation implyeruption and emplacement in an extensional environmentwhere flows, intrusions, and volcaniclastic deposits werecontrolled by synvolcanic faulting and associated subsidencestructures (DeWolfe et al. 2009). However, the upper por-tion of the Hidden formation and the Louis formation havegeological characteristics that imply emplacement in an en-vironment dominated by effusive basaltic volcanic activitywith only minor evidence for extension and associated sub-sidence (DeWolfe et al. 2009).

Regional geological and geochemical studies have con-strained the overall tectonic environment of the rocks in theFlin Flon area to island-arc settings comprising mainly tho-leiitic, with lesser calc-alkaline basalt and basaltic andesiteand rare high-Ca boninites (Stern et al. 1995a; Syme et al.1999). Geochemical similarities between Flin Flon arc as-semblage rocks and those in modern primitive, intraoceanicarc systems have been recognized and have resulted in theinterpretation that Paleoproterozic arc processes in Flin Flonwere broadly similar of those in modern arc environments(Stern et al. 1995a; Syme et al. 1999). Geochemical charac-teristics have also suggested that the mantle source duringeruption of rocks in Flin Flon was highly depleted, possiblyresidual after MORB or back-arc basin basalt extraction, andthat variations in Nd isotopic data and LREE contents sug-gest small amounts (0%–8%) of recycling of crust throughsediment subduction and intracrustal contamination (Sternet al. 1995a).

Evidence for a juvenile arc and minor crustalcontamination

In modern intraoceanic island arcs, there are a variety ofprocesses that explain the geochemical and isotopic system-atics found in arc volcanic rocks. Commonly, there is themixing between depleted- and enriched-mantle sources withvariable contributions from crustal sources and the sub-ducted slab (e.g., Pearce and Peate 1995; Pearce 2008). Thedata from Hidden and Louis formations support models in-volving mantle mixing, slab metasomatism, and crustal con-tamination within a Paleoproterozoic juvenile oceanic arcsystem. To test the potential for mantle mixing, Zr, Nb, andYb systematics have been utilized as these elements are im-mobile, largely unaffected by crustal contamination and slabmetasomatism, and sufficiently incompatible; hence, ratiosof them provide a proxy for the mantle source of the maficrocks (Pearce 1983; Pearce and Peate 1995). In Nb/Yb–Zr/Yb space, samples from the Hidden and Louis formationsform a linear array from depleted mantle sources to moreenriched mantle sources, respectively. Most of the units liewithin the normal (N-)MORB field, the exception beingrocks from the Carlisle Lake andesite, which lie halfway be-tween N-MORB and enriched (E-)MORB values (Fig. 10).These data imply that rocks of the Hidden formation, at thebase of the hanging wall succession, were derived from themost depleted mantle source, whereas the overlying rocks ofthe Louis formation were derived from more enriched man-tle sources.

The degree of crustal contamination and input from slabmetasomatism is evaluated using Pb isotopic data, Th–Nb–La systematics, and Sm/Nd isotopic data. Given that theleast altered sample from each unit was analysed and that

DeWolfe et al. 521


there is no correlation between the Pb isotopic data and theHashimoto alteration index (e.g., 100*(MgO + K2O)/(MgO+ K2O + CaO + Na2O) vs. 206Pb/204Pb, 207Pb/204Pb, or208Pb/204Pb), the isotopic ratios cannot be due to alteration,and likely represent primary petrological variance. The Pbreference isochron lies between model N-MORB and uppercrust isochrons (Fig. 11a; Kramers and Tolstikhin 1997), in-dicating that the source for these flows was end-member de-pleted mantle, but was contaminated either through slab-derived fluids and melts or by sediment subduction. On aplot of Nb/Yb versus Th/Yb, flows of the Hidden and Louisformations form a linear array parallel to the MORB–OIB(ocean-island basalt) array but with elevated Th (higher Th/Nb ratios) and lie within the volcanic-arc array, suggestingcrustal input via subduction processes (Fig. 11b; Pearce1983, 2008; Pearce and Peate 1995). All units of the Hiddenand Louis formations also display negative Nb anomalies onprimitive mantle-normalized diagrams (Figs. 8a–8g). Theseanomalies have been interpreted to represent an ‘‘arc’’ signa-ture, the result of subducted-slab metasomatism of the over-lying subarc mantle wedge (Gill 1981; Pearce 1983; Pearceand Peate 1995). However, there is much debate about theorigin of Nb anomalies in arc magmas, and it has also beenargued that these anomalies are a result of contamination ofa mafic magma by crust during emplacement, or a combina-tion of both processes (e.g., Stern et al. 1995a; Pearce2008). Given the fact that the Hidden and Louis formationsshow volcanological evidence for localized rifting and suba-queous, dominantly basaltic eruptions (DeWolfe et al. 2009)and that Sm/Nd and Lu/Hf isotopes indicate they represent aprimitive arc, we suggest that any contamination is due toslab metasomatism and, possibly, minor sediment subduc-tion.

It is important to note that the relatively high initial 3Ndand 3Hf values of the Hidden and Louis formation suggestthat the amount of crustal input through sediment subductionmust be very low. To examine the amount of crustal con-tamination, we plotted Nb/Yb versus initial 3Nd values(Fig. 12; Stern et al. 1995a). The results suggest that therocks of the Hidden and Louis formations contain only mi-nor (£3.5%) input from crustal sources, and their low Nb/Yb

values suggest they formed from a depleted mantle source(i.e., MORB-like mantle source). This agrees with conclu-sions from Stern et al. (1995a), where the authors suggestedthat sediment subduction rather than intracrustal recyclingwas the dominant process involved in introducing an oldercrustal component within tholeiitic rocks of the Hidden–Burley suite (the Hidden and Louis formations in thisstudy).

Evidence for arc evolutionGeochemical variations in the stratigraphy of the Hidden

and Louis formations suggest changes in the mantle sourceand degree of input from crustal sources. Elucidating varia-tions in these processes temporally during the formation ofthe hanging wall stratigraphy in Flin Flon is important inunderstanding the evolution of this juvenile Paleoproterozoicarc. Variations in Nd, Hf, and Pb isotopic values do not dif-fer appreciably with stratigraphic height, hence, are not usedin deciphering changes in mantle source or crustal input dur-ing emplacement of the hanging wall stratigraphy.

To address the question of whether or not there was achange in mantle source during construction of these ancientarc volcanoes, we have plotted Nb/Zr versus stratigraphicheight again using Nb–Zr as a proxy for mantle source(Pearce 1983; Pearce and Peate 1995). Lower Nb/Zr ratiossuggest depleted mantle sources (i.e., MORB-like sources)and higher Nb/Zr ratios suggest more enriched mantle sources(i.e., OIB-like sources; Pearce 1983, 2008; Pearce and Peate1995). Initially low Nb/Zr ratios generally increase up stratig-raphy (Fig. 13a). Nb–Zr systematics suggest derivation ofearly Hidden formation rocks (1920 unit) from depleted man-tle sources with subsequent flows (Reservoir and Stockwellmembers) being derived from more incompatible-element-enriched sources with the most incompatible-element-enriched rocks occurring within the Carlisle Lake basalticandesites at the top of the Hidden formation (Fig. 13a). Thehiatus in effusive volcanic activity that marks the contact be-tween the Hidden and Louis formations coincides with a re-turn to more depleted mantle Nb/Zr ratios (Fig. 13a) forflows of the Louis formation.

The enriched Carlisle Lake basaltic andesites can be ex-plained by variable degrees of melting of a heterogenousmantle that contains blobs of fertile material in a depletedmatrix (‘‘plum pudding’’ model of Zindler et al. 1984). Asthe fertile material will melt first, melts produced by lowerdegrees of partial melting contain a greater component ofLREE-enriched material. This would result in the hanging-wall rocks changing from incompatible element enriched atthe bottom to incompatible element depleted at the top, butdoes not account for the return to more depleted signaturesobserved within the Louis formation. Perhaps a more likelyscenario is re-fertilizing the mantle with slab melts, then re-melting these re-fertilized portions forming Nb-enriched ba-salts (Sajona et al. 1996). This model could explain depletedmantle signatures at the base of the Hidden formation, moreenriched signatures for the Carlisle Lake basaltic andesitesat the top of the Hidden formation, and a return to more N-MORB-like signatures in the Louis formation.

To evaluate the extent of crustal input either through slabmetasomatism or sediment subduction during formation ofthe hanging wall, Nb/Th was plotted versus stratigraphic

Fig. 10. Zr/Yb vs. Nb/Yb diagram that discriminates between rocksderived from depleted-mantle to enriched-mantle sources. Diagramfrom Pearce and Peate (1995). Values for N-MORB (normal mid-ocean ridge basalt), E (enriched)-MORB, and OIB (ocean-islandbasalt) are from Sun and McDonough (1989).



height (Fig. 13b), again Th–Nb can be used as a proxy forcrustal input (Pearce 1983, 2008; Pearce and Peate 1995). Adecrease in the Nb/Th ratio from bottom to top of the Hid-den formation suggests an increasing amount of crustal con-tamination during the emplacement of the Hidden formation(Fig. 13b). Following the hiatus in effusive volcanism thatmarks the contact between the Hidden and Louis formations(DeWolfe et al. 2009), the rocks of the Louis formationyield intermediate Nb/Th ratios, lower than the ratio for theCarlisle Lake basaltic andesites, but higher than the ratiosobserved for the base of the Hidden formation. This suggestsan increase in crustal contamination through slab metasoma-

tism and (or) sediment subduction during emplacement ofthe hanging wall.

Genetic implications of the 1920 unit and Stockwellmember

Fe–Ti basalts have been documented in the hanging wallto some VMS deposits hosted by bimodal volcanic sequen-ces (e.g., Kam-Kotia, Barrie and Pattison 1999; Kidd Creek,Wyman et al. 1999; Galapagos, Embly et al. 1988; Perfit etal. 1999). These basalts have enrichments in Fe and Ti (andoften P) with SiO2 values = 46–54 wt.% (Perfit et al. 1999;Barrie and Pattison 1999).

Embly et al. (1988), Perfit et al. (1999), and Barrie andPattison (1999) attributed the occurrence of Fe–Ti basaltsassociated with massive sulphide deposits at Galapagos andKam-Kotia to extensive low-pressure fractional crystalliza-tion and contamination by hydrothermally altered oceaniccrust in a shallow-level (<2 km) magma chamber.

Geochemical data presented herein illustrate that the 1920unit is a basaltic andesite enriched in Fe, Ti, and P withREE patterns characteristic of island-arc tholeiites and thatthe overlying units have geochemical characteristics similarto transitional arc tholeiites. Geological evidence also showsthat the 1920 unit and the overlying Stockwell member wereemplaced in an extensional environment (DeWolfe et al.2009), where localized rifting of a juvenile arc resulted in athinned crust that consequently allowed the rise of magmato high levels in the crust.

Geochemical similarities of the 1920 unit to Fe–Ti basaltsat Galapogos, Kam-Kotia and Kidd Creek (Embly et al.1988; Perfit et al. 1999; Barrie and Pattison 1999), and thedocumentation through isotopic and trace element geochem-istry of juvenile arc magmatism, as well as the geologicalevidence for localized rifting, support the hypothesis that1920 unit formed through extensive fractional crystallizationof differentiated magmas at shallow levels in oceanic crust.This high-level magma chamber would have allowed littleor no mixing with a deeper, long-lived magma chamber andmore contamination by hydrothermally altered oceanic crust.

The presence of this shallow-level magma chamber would

Fig. 11. Diagrams for rocks of the Hidden and Louis formations that illustrate crustal input either from subducted slab metasomatism or thesubduction of sediments. (a) Common Pb diagram for whole-rock samples. Artifical normal mid-ocean ridge basalt (N-MORB) isochron andupper crust isochron calculated using enriched mantle values for the evolution of Pb from Collerson and Kamber (2000). (b) Th/Yb vs. Nb/Yb diagram from Pearce (1983), Pearce and Peate (1995), and Pearce (2008). N-MORB, E (enriched)-MORB, and OIB (ocean-island basalt)from Sun and McDonough (1989).

Fig. 12. Nb/Yb vs. 3Nd(1.9Ga) diagram of rocks from the Hidden andLouis formations with contours showing calculated % of older crustNd in the samples. For samples with low Nb/Yb (0% older crust),the juvenile mantle melt end-member was assumed to have 5 ppmNd and 3Nd = +5, and for rocks with higher Nb/Yb, the juvenilemelt was assumed to have 10 ppm Nd and 3Nd = +2.5. The oldercrustal component was modelled with 50 ppm Nd and 3Nd = –7after the 2.5 Ga Beaverhouse Granodiorite. Hidden – Burley Lakeand older crustal component fields and mixing calculations fromStern et al. (1995a).

DeWolfe et al. 523


have also provided a high-temperature environment thatcould generate and sustain a high-temperature convectivehydrothermal system necessary for the formation of massivesulphide mineralization. Thus, this study’s findings are con-sistent with the suggestion by Franklin et al. (2005) that thepresence of Fe–Ti basalts and other evolved rocks in bimo-dal sequences may be a good indicator of prospective areasfor VMS-type mineralization.

Conclusions

(1) Major and trace element geochemistry and Nd, Hf, andPb isotopic data show that the volcanic flows and syn-

volcanic intrusive rocks of the Hidden and Louis forma-tions that make up the hanging wall to the Flin FlonVMS deposits were emplaced in a juvenile island-arcenvironment. Mantle sources range from depleted mantle(N-MORB-type) to slightly more enriched mantlesources (E-MORB-type). The rocks are variably con-taminated (£3.5%) by crustal sources either throughsubducted-slab metasomatism or sediment subduction.

(2) Geochemical variations in the strata of the Hidden andLouis formations record a change from depleted mantlesources to more enriched mantle sources and a return toa more depleted mantle source during emplacement ofthe units. The process responsible for this change in

Fig. 13. Stratigraphic height versus key elemental ratios illustrating (a) variations in mantle source, and (b) crustal contamination. Eachpoint represents the average value for that unit, error bars through the data points represent natural variance within each unit, and error barsbelow each point represent analytical variance within each unit using precision for Nb (5% precise), Th (7% precise), and Zr (5% precise)from MacDonald et al. 2005.



mantle source may be a re-fertilizing of the arc mantlewedge with slab melts, and then re-melting these re-fertilized portions forming Nb-enriched basalts (Sajonaet al. 1996). Variations in geochemical characteristics ofthe hanging wall also indicate broadly increasingamounts of crustal contamination from the base to thetop of the hanging wall, suggesting an increase in theamount of crustal input from slab metasomatic processesor sediment subduction as the hanging wall was em-placed.

(3) Geochemical and geological observations of the 1920unit confirm that it has a composition similar to Fe–Tibasalts associated with VMS–type mineralization atKidd Creek, Kam-Kotia, and Galapagos and that it wasemplaced in a localized rift within a dominantly juvenilearc environment. The geological and geochemical char-acteristics of the 1920 unit suggest it formed though ex-tensive low-pressure fractionation in a high-level magmachamber with associated assimilation of hydrated ocea-nic crust. This high-level magma chamber, occurring ina rifted-arc environment, would have also provided thestructures (synvolcanic faults associated with rifting)and heat source required to drive high-temperature hy-drothermal cells needed for the formation of directly un-derlying VMS deposits in Flin Flon. As such, thepresence of Fe–Ti basalts or similarly evolved rocks, inthis case an Fe–Ti-rich basaltic andesite, is excellent evi-dence for the presence of a high-level magma chamberneeded to provide the heat necessary to drive a hydro-thermal system and, combined with evidence of rifting,is a useful tool in exploring for VMS deposits.

AcknowledgmentsThe Natural Sciences and Engineering Research Council

of Canada (NSERC), HudBay Minerals, and the ManitobaGeological Survey provided funding for this project. TheManitoba Geological Survey also provided logistical supportand field assistance. The authors would like to thank P. Len-ton, E. Wright, E. Fitzsimmons, and C. Devine for providingorthorectified airphoto coverage of the field area, and B.Janser, R.-L. Simard, T. Penner, and K. MacLachlan for dis-cussion on and of the rocks. The authors would also like tothank George Jenner and Anthony Fowler for comprehen-sive reviews of this manuscript.

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