509
Petrogenesis of the 1.9 Ga mafic hanging wall
sequence to the Flin Flon, Callinan, and Triple 7
massive 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 Louis
formations, which make up the hanging wall to the volcanogenic massive sulphide deposits at Flin Flon, Manitoba, was
carried 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 the
1920 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) is
characterized by Nb/Thmn = 0.16–0.14, and 204Pb/206Pb = 21.4. The rhyodacitic Tower member (bottom of Louis formation) has Nb/Thmn = 0.23, 3Nd1.9Ga = +4.6, 3Hf1.9Ga = +9.3, and 204Pb/206Pb = 22.2. The basaltic flows that dominate the
Louis 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. The
Hidden and Louis formations show dominantly transitional arc tholeiite signatures, with the 1920 unit having arc tholeiite
characteristics. It is interpreted to have formed through extensive fractional crystallization of differentiated magmas at
shallow levels in oceanic crust. Given the geological, geochemical, and isotopic characteristics of the Hidden and Louis
formations, they are interpreted to represent subducted slab metasomatism with minor contamination from subducted sediments.
Résumé : Une étude détaillée des caractéristiques géochimiques et isotopiques des roches volcaniques des formations de
Hidden et de Louis, lesquelles forment l’éponte supérieure des gisements de sulfures volcanogènes massifs à Flin Flon,
Manitoba, a été effectuée sur un ensemble d’échantillons contrôlés par la stratigraphie. La stratigraphie comprend, tout à
la base, la formation de Hidden, principalement basaltique et la formation de Louis sus-jacente, principalement basaltique.
L’unité 1920, une andésite basaltique, est importante d’un point de vue pétrogénétique; elle possède les valeurs suivantes :
Nb/Thmn = 0.,54–0,62, 3Nd(1.9Ga) = +3,6 à +5,9, 3Hf(1.9Ga) = +8,5 à +9,6, et 204Pb/206Pb = 23.9. Les coulées basaltiques qui
dominent la formation de Hidden ont les valeurs suivantes : Nb/Thmn = 0,16–0.29, 3Nd(1.9Ga) = +1,7 à +4,4, 3Hf(1.9Ga) =
+7,0 à +11,8 et 204Pb/206Pb = 16,9–18,6). L’andésite basaltique Carlisle Lake (sommet de la formation de Hidden) est caractérisée par Nb/Thmn = 0,16–0,14 et 204Pb/206Pb = 21,4. Le membre Tower (bas de la formation de Louis) a les valeurs
suivantes : Nb/Thmn = 0,23, 3Nd1.9Ga = +4,6, 3Hf1.9Ga = +9,3 et 204Pb/206Pb = 22,2. Les coulées basaltiques qui dominent la
formation de Louis ont les valeurs suivantes : Nb/Thmn = 0,18–0,25, 3Nd(1.9Ga) = +3,6 à +4,2, 3Hf(1.9Ga) = +8,4 à +11,3 et
204Pb/206Pb = 17,9. Les formations de Hidden et de Louis présentent des signatures surtout d’arc tholéiitique de transition
où l’unité 1920 a des caractéristiques d’arc tholéiitique. Cette unité se serait formée par la cristallisation fractionnée à
grande échelle de magmas différenciés à de niveaux de faible profondeur dans la croûte océanique. Étant donné les caractéristiques géologiques, géochimiques et isotopiques des formations de Hidden et de Louis, elles représenteraient un métasomatisme de plaque subductée avec une contamination minime par les sédiments subductés.
[Traduit par la Rédaction]
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, Laurentian
University, 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 of
Paleoproterozoic 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.
Can. J. Earth Sci. 46: 509–527 (2009)
doi:10.1139/E09-033
Published by NRC Research Press
510
Introduction
Volcanogenic massive sulphide (VMS) deposits occur in
extensional environments within a variety of tectonic settings, including oceanic, fore-arc, arc, back-arc, continentalmargin, or continental settings (Franklin et al. 1981, 2005;
Barrie and Hannington 1999). They are typically related to
volcanically active submarine environments where metals
are precipitated, at or below the sea floor, from circulating
hydrothermal fluids (Franklin et al. 1981, 2005; Lydon
1988; Gibson et al. 1999). Submarine volcanic successions
that host VMS mineralization are typically bimodal, but can
be dominated by mafic or felsic volcanic rocks or sedimentary rocks (Franklin et al. 1981, 2005; Barrie and Hannington 1999). Volcanogenic massive sulphide deposits often
exhibit a pronounced stratigraphic control that may be related to a specific event, such as caldera or cauldron formation, restricting VMS mineralization to a specific time in the
magmatic and volcanic evolution of submarine volcanoes
(Rytuba 1994; Stix et al. 2003). Given the variety of tectonic settings and geochemical compositions associated with
VMS deposits (e.g., Franklin et al. 1981, 2005; Barrie and
Hannington 1999), it is essential to document the tectonic
and magmatic history of well-preserved, ancient VMS deposit-hosting volcanic rocks.
In Flin Flon, phenomenal surface exposure (up to 80%
outcrop of *200 m of footwall and *800 m of hanging
wall stratigraphy) combined with excellent preservation of
primary volcanic textures and structures make this camp the
ideal location to study an ancient submarine volcanic succession associated with world class massive sulphide deposits. The morphology, texture, and structure of submarine
basaltic volcanoes are important in understanding the physical constraints and manifestations of submarine volcanism.
Geochemical and isotopic data add insight into the tectonic
setting and the petrological history, including details about
the location, temperature, and composition of the magma
source and any changes in composition the magma might
have undergone due to contamination from crustal sources.
The Paleoproterozoic Glennie – Flin Flon complex of
northern Manitoba and Saskatchewan is part of the southeastern Reindeer Zone of the Trans-Hudson Orogen (THO)
and is known for its significant VMS deposits. The complex
contains 25 past- and presently producing mines rich in Zn–
Cu–(Au–Ag) that total over 118 Mt of sulphide, making it
the largest Paleoproterozic VMS district in the world (Syme
et al. 1999). The complex consists of a series of assemblages that range in age from 1.91 to 1.84 Ga and include
arc, back-arc, ocean-floor, and successor-arc successions
(Syme and Bailes 1993; Stern et al. 1995a, 1995b; Lucas et
al. 1996). The Flin Flon and Snow Lake ocean floor and arc
assemblages (1.91–1.87 Ga) contain the majority of the
VMS deposits (Fig. 1), and only the juvenile arc assemblages within the Glennie – Flin Flon complex, not back-arc
basin assemblages, have been found to contain VMS mineralization (Syme et al. 1999).
The regional tectonic environment, stratigraphy, and environment of emplacement of the Glennie – Flin Flon complex have been studied by numerous researchers (Bailes and
Syme 1989; Syme and Bailes 1993; Stern et al. 1995a,
1995b; Lucas et al. 1996; Syme et al. 1999; Ames et al.
Can. J. Earth Sci. Vol. 46, 2009
2002; Devine 2003). Previous geochemical studies of the
Flin 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), Leybourne
et al. (1997), and Syme et al. (1999). Neodymium isotopic
studies have been carried out by Stern et al. (1995a,
1995b). However, since these geochemical and Nd isotopic
studies focussed on the regional tectonic and magmatic evolution of the Glennie – Flin Flon complex, this study and its
companion paper (DeWolfe et al. 2009) provide the first
comprehensive volcanological, geochemical, and Nd isotopic study of the immediate hanging wall to the Flin Flon
VMS deposits. It also provides the first whole-rock Hf and
Pb isotopic data for the Flin Flon arc assemblage. This new
information provides a more detailed evaluation of the volcanic, tectonic, and hydrothermal environment of the dominantly mafic hanging wall rocks to the Callinan, Triple 7,
and Flin Flon orebodies and has led to the interpretation
that they represent primitive arc volcanism in the Early Proterozoic.
Geological setting
The Trans Hudson Orogen comprises five main crustal
components: (i) the reactivated Archean-age Hearne and
Superior cratonic margins and their respective Paleoproterozoic cover sequences; (ii) the ca. 1.92–1.88 Ga Glennie – Flin
Flon complex, that was tectonically accreted in an intraoceanic setting during the interval 1.88–1.87 Ga; (iii) the northwestern Reindeer Zone consisting of ca. 1.92–1.88 Ga
juvenile volcanic arcs, back-arcs, and associated sedimentary
basins thrust onto the Archean Hearne cratonic margin during
the interval 1.92–1.87 Ga; (iv) the Wathaman–Chipewyan
batholith (ca. 1862–1848 Ma), a continental-arc magmatic
suite that was emplaced along the northwestern Reindeer
Zone; and (v) a marginal basin and molasse sub-basins (Kisseynew Domain) developed between the northwestern Reindeer Zone and Glennie – Flin Flon complex during the
interval 1.85–1.84 Ga (Fig. 1; Corrigan et al. 2007).
The Glennie – Flin Flon complex (Ashton 1999) comprises juvenile island arc, ocean floor, ocean plateaus,
evolved arc and associated sedimentary and plutonic rocks
that 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 have
formed at ca. 1.87 Ga by intraoceanic accretion of the
Snow Lake arc assemblage, the Amisk collage, the Hanson
Lake block, and the Glennie Domain (Lewry and Collerson
1990; Lucas et al. 1996). Tectonostratigraphic assemblages
of the complex are fold-repeated, thrust-stacked, and tectonically overlie the Archean to earliest Paleoproterozoic Sask
Craton above a basal décollement that was active as early
as about 1.84 Ga (Ashton et al. 2005).
Rocks of the Flin Flon arc assemblage are interpreted to
have been erupted and emplaced in an island-arc to backarc setting (Syme and Bailes 1993; Syme et al. 1999) and
consist of basaltic flows, basaltic andesite flows and breccias, and lesser rhyolitic flows. Overall the stratigraphy is
dominantly bimodal with the bulk of the stratigraphy being
mafic or felsic with only minor, but significant, basaltic andesite rocks. The Flin Flon, Callinan, and Triple 7 VMS dePublished by NRC Research Press
DeWolfe et al.
511
Fig. 1. Geology of the Flin Flon arc assemblage, showing the locations of known VMS deposits (modified from Syme et al. 1996). Box
indicates area covered by Fig. 2. The inset map shows the location of Flin Flon within the Trans-Hudson Orogen (THO).
posits (Fig. 2), which total more than 92.5 million tonnes
grading 2.21% Cu, 4.25% Zn, 2.11 g/t Au, and 27.22 g/t
Ag, are interpreted to have formed during a period of localized rhyolitic volcanism in a synvolcanic subsidence structure, 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 period
of resurgent basaltic volcanism and subsidence that immediately followed a hiatus in volcanism marked by VMS ore
deposition (DeWolfe et al. 2009.
Previous workers (Stern et al. 1995a, 1995b; Syme et al.
Published by NRC Research Press
512
Can. J. Earth Sci. Vol. 46, 2009
Fig. 2. Geology of the Flin Flon area (modified from Stockwell 1960); see Fig. 1 for location.
1999) described various volcanic units from the Flin Flon
arc assemblage, including five samples taken from the Hidden and Louis formations. They interpreted these samples as
isotopically ‘‘evolved’’ arc rocks, characterized by flat to
slightly enriched chondrite-normalized rare-earth element
(REE) patterns, with depletions of Nb, Zr, Hf, and Ti relative 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) interpreted
that this interval of intraoceanic arc magmatism was characterized by rapid subduction of oceanic lithosphere, relatively
thin arc crust (<20 km) and by extensive back-arc basin formation. They also postulated that these isotopically evolved
arc rocks have incorporated Nd from an older crustal source,
either through subduction of sediments or by intracrustal
contamination. Given the regional nature and the sparse
Published by NRC Research Press
DeWolfe et al.
sampling within the hanging wall of the study by Stern et al.
(1995a, 1995b), this research endeavoured to collect more
systematic data, including data for all units within the Hidden and Louis formations, and to evaluate this data in light
of a new understanding of the stratigraphy, volcanic textures, and structures (DeWolfe et al. 2009), and to compare
this data with that of Stern et al. (1995a, 1995b) to discern if
all units within the hanging wall are of evolved arc origin as
previously interpreted.
Stratigraphy of the hanging wall
The contact between the Hidden and Louis formations is
marked by a plane-bedded, mafic tuff unit that represents a
mappable hiatus in volcanism traceable throughout the Flin
Flon area (Bailes and Syme 1989; Ames et al. 2002;
DeWolfe et al. 2009).
The Hidden formation defines the onset of hanging wall
volcanism and comprises, from oldest to youngest, the 1920
unit, the Stockwell member, and the Reservoir member. The
1920 unit consists of massive, pillowed, and peperite facies
basaltic andesites and is overlain locally by felsic or intermediate volcaniclastic rocks. The Stockwell member is
present only locally and is repeated by a thrust fault
(Fig. 2). In one thrust panel, it overlies the 1920 unit, and
in the other, it overlies aphyric basaltic flows of the Reservoir member (Fig. 2). The Stockwell member is also overlain by aphyric basaltic flows of the Reservoir member. It
is composed of massive, pillowed, and breccia facies, plagioclase-phyric basaltic flows intercalated with mafic lapillistone mass flow deposits (DeWolfe et al. 2009). The
Reservoir member is made up of massive, pillow, breccia,
and peperite facies, aphyric basaltic flows. Where neither
the 1920 unit nor Stockwell members are present, south of
the Railway Faults, it conformably overlies the Millrock
member of the Flin Flon formation (Fig. 2). A basaltic andesite unit occurs at the top of the dominantly basaltic Reservoir member where it is in contact with overlying Louis
formation flows. This unit is called the Carlisle Lake basaltic andesite after its type location.
The Louis formation conformably overlies the Hidden formation and consists of the Tower and Icehouse members, as
well as undivided basaltic flows. The Tower member occurs
at the base of the Louis formation and consists of an areally
restricted massive to in situ–brecciated, aphyric rhyodacitic
flow and associated volcaniclastic rocks overlain by mafic
tuff, and more extensively is represented by the tuff alone.
The Icehouse member, which conformably overlies the
Tower member, consists of a massive, pillowed and brecciated, strongly plagioclase- (£30%) and pyroxene- (£25%)
porphyritic basaltic flow overlain by heterolithic, mafic volcaniclastic rocks. The Louis formation is capped by a thick
(>500 m) succession of undivided plagioclase- (>15%) and
pyroxene- (>5%) porphyritic, dominantly pillowed basaltic
flows (DeWolfe et al. 2009).
Basaltic to basaltic andesite flows and sills of the Hidden
formation are interpreted to have formed a small shield volcano with a synvolcanic graben and volcanic vent for this
edifice located on the northwest limb of the Hidden syncline. The graben and volcanic vent correspond spatially
with the location of the 1920 unit and the flows and inter-
513
flow volcaniclastic units of the Stockwell member. Flows of
the Louis formation are interpreted to represent resurgence
in basaltic volcanism and minor associated subsidence, resulting in the growth of a new small lava shield on what is
now the southern flank of the Hidden volcano. The volcanology of these two volcanoes is described in detail in the
companion paper DeWolfe et al. (2009).
The absence of voluminous volcaniclastic deposits that
typify the underlying Flin Flon formation, within the Hidden
and Louis formations, suggests extension and subsidence had
largely ceased during construction of the Hidden and Louis
shield volcanoes and that they may represent a return to normal arc evolution (DeWolfe et al. 2009). However, synvolcanic structures in the hanging wall do define structural
corridors that can be traced directly into the footwall where
they controlled the location of massive sulphide mineralization (Gibson et al. 2003; DeWolfe et al. 2009). The continuation of these structures into the hanging wall strata indicates
their longevity and reactivation as magma and fluid pathways during the emplacement of the Hidden and Louis volcanoes. The recognition of synvolcanic structural corridors
in the hanging wall allows for targeting massive sulphide
mineralization along the same structures within the footwall.
Geochemical results
Petrographic observations
Samples of volcanic rocks were collected during three
summers of detailed mapping at scales ranging from 1 : 250
to 1 : 2000 (DeWolfe 2007a, 2007b, 2007c, 2007d, 2007e).
Each flow and cryptoflow from the base of the Hidden formation to the top of the Louis formation was sampled, and
the flows and cryptoflows were also sampled along strike at
100 to 500 m over a total strike length of *6 km.
Although primary volcanic textures, such as pillows, flow
banding, autoclastic breccias, hyaloclastite, peperite, and
layering are well preserved in the Hidden and Louis formations, all of the rocks are deformed, and primary minerals,
such as pyroxene and plagioclase, are replaced to a variable
extent by greenschist-facies metamorphic actinolite, epidote,
and muscovite. Most mafic minerals have been replaced by
actinolite; primary plagioclase (albite) is variably replaced
by epidote and muscovite. The groundmass commonly comprises actinolite, epidote, quartz, and chlorite with lesser
amounts of biotite and carbonate. Locally the volcanic rocks
contain strong, patchy, epidote–quartz alteration. These
patches manifest themselves as 5–50 cm wide, rounded to
subrounded, greenish-white patches often forming as halos
around amygdules filled with quartz and epidote. In these
cases, the groundmass almost entirely consists of granular
epidote and quartz (9:1 ratio, respectively) and many of the
phenocrysts, felsic or mafic, are overprinted by granular epidote and quartz. Such features in intermediate to mafic volcanic rocks of Noranda, Quebec, have been attributed to
semi-conformable hydrothermal alteration zones associated
with VMS deposits (Galley 1993; Gibson and Kerr 1993;
Paradis et al. 1993); consequently, we interpret the mineralogically and texturally identical epidote–quartz patches in
the Hidden and Louis formations to have resulted from hydrothermal alteration associated with the massive sulphide
mineralization.
Published by NRC Research Press
514
Can. J. Earth Sci. Vol. 46, 2009
Table 1. Ranges in composition for units of the Hidden and Louis formations.
SiO2 (wt.%)
TiO2
Al2O3
Fe2O3
MnO
MgO
CaO
Na2O
K2O
P2O5
LOI
1920 unit
(Hidden fm.)
48–58
1.0–1.2
14.6–17.8
12.8–17.6
0.21–0.27
1.54–2.37
6.3–8.1
2.8–4.2
0.30–0.83
0.33–0.45
0.1–1.2
Reservoir mb.
(Hidden fm.)
50–56
0.56–0.85
13.8–17.2
11.2–15.7
0.18–0.25
3.3–6.2
6.2–11.7
2.3–4.2
0.13–0.93
0.05–0.15
1.3–3.6
Stockwell mb.
(Hidden fm.)
46–53
0.36–0.90
12.4–19.0
9.4–17.5
0.15–0.23
2.6–6.0
7.1–11.1
2.3–4.2
0.15–0.66
0.05–0.17
0.7–3.9
Carlisle Lake
andesite (Hidden fm.)
51–64
0.49–0.65
14.6–17.0
6.3–14.6
0.09-.18
2.5–4.7
3.2–5.9
2.8–5.8
0.55–1.85
0.21–0.29
1.6–3.1
Tower mb.
(Louis fm.)
73.00
0.24
10.29
7.05
0.07
1.75
1.38
3.00
0.65
0.08
2.10
Icehouse mb.
(Louis fm.)
47–48
0.48
14.5–14.9
11.5–11.9
0.18–0.19
8.2–9.1
9.6–10.3
2.3–2.7
0.17–0.39
0.07
3.50
Undivided flows
(Louis fm.)
46–57
0.36–0.64
14.9–17.3
9.7–13.6
0.14–0.20
3.2–6.2
5.4–10.8
2.1–5.1
0.23–1.16
0.06–0.11
2.1–4.4
Cr (ppm)
Ni
Sc
V
Rb
Cs
Ba
Sr
Nb
Hf
Zr
Y
Th
U
La
Ce
Pr
Nd
Sm
Eu
Gd
Tb
Dy
Ho
Er
Tm
Yb
Lu
5–10
9–30
30–35
26–36
2–17
0.06–0.85
105–644
120–229
2.3–2.9
2.7–3.0
91–114
47.8–58.9
0.48–0.52
0.32–0.44
7.0–8.4
17.7–21.8
2.83–3.38
13.64–16.84
4.49–5.59
1.61–1.89
6.20–7.82
1.14–1.45
8.30–10.29
1.91–2.34
5.77–7.29
0.90–1.12
6.1–7.6
0.96–1.20
33–50
5–27
40.7–62.6
265–434
0.6–11.9
0.08–0.55
27–481
44–291
0.6–1.2
0.62–1.10
18–35
12.5–19.3
0.25–0.96
0.21–0.68
1.80–6.48
4.6–13.9
0.71–1.96
3.67–9.65
1.17–2.75
0.42–1.19
1.81–3.65
0.30–0.62
2.12–4.20
0.49–0.93
1.52–2.74
0.24–0.42
1.61–2.74
0.026–0.43
95–225
9–33
49.5–54.3
275–355
1.5–10.5
0.03–0.36
37–326
45–269
0.5–1.4
0.40–1.20
13–39
8.8–24.0
0.21–0.46
0.16–0.36
1.88–4.99
4.5–11.7
0.58–1.66
2.72–7.99
0.87–2.41
0.32–0.72
1.20–3.23
0.21–0.58
1.49–3.96
0.36–0.88
1.17–2.85
0.17–0.43
1.20–2.81
0.19–0.44
<24–36
14–32
19.2–35.2
174–310
7.6–33.9
0.09–1.23
48–754
58–452
2.9–4.0
1.34–2.27
47–77
15.5–21.7
2.22–3.21
1.01–1.39
14.34–16.79
27.5–35.2
3.36–4.47
13.91–18.41
2.89–3.85
0.66–1.17
2.58–3.55
0.42–0.54
2.70–3.50
0.57–0.79
1.64–2.29
0.28–0.39
1.85–2.58
0.31–0.42
7
5
9.2
0.17
258
97
3.2
2.50
86.4
33.9
1.65
1.07
12.45
25.8
3.35
14.97
3.92
1.36
4.51
0.80
5.46
1.20
3.75
0.57
3.94
0.61
246
71–65
44.0–45.7
262–293
1.8–6.2
0.02–0.8
38–143
267–399
0.6
0.39–0.44
12–14
8.4–9.0
0.28–0.29
0.14–0.15
2.38–2.56
5.3–5.5
0.73–0.79
3.51–3.68
0.97–1.04
0.38–0.42
1.14–1.18
0.20–0.22
1.30–1.40
0.31–0.32
0.86–0.93
0.14–0.15
0.95–0.98
0.15–0.16
<24–94
13–80
29.8–49.3
247–355
3.4–17.3
0.04–0.24
27–629
73–376
0.7–1.7
0.41–1.25
13–46
8.8–18.1
0.25–0.91
0.19–0.51
2.38–6.06
5.2–13.4
0.76–1.76
4.33–8.15
1.25–2.08
0.39–0.66
0.21–0.66
0.21–0.35
1.40–2.80
0.31–0.61
0.99–1.84
0.15–0.30
0.97–1.80
0.16–0.31
Note: fm., formation; mb., member; LOI, loss on ignition.
Geochemical limitations
All samples have been screened using field, petrographic
and geochemical attributes. Samples containing patchy epidote–quartz alteration were not used to elucidate petrogenetic processes; however, minor alteration, in general, was
inevitable given the pervasive metamorphic alteration of the
hanging wall. Under upper greenschist metamorphic conditions, 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 typically
immobile (e.g., MacLean 1990; Jenner 1996). Table 1 shows
representative geochemical data for the Hidden and Louis
formations; key major element and trace element ratios are
presented in Table 2. Samples were rejected if the total loss
on ignition exceeded 4.5 wt.%, Na2O < 2 wt.% and (or)
Al2O3/Na2O > 10 (Spitz and Darling 1978), values intended
to eliminate the most altered samples. Variability in ratios of
immobile Zr (MacLean 1990) to the major elements suggests that, as expected, SiO2, Na2O, K2O, CaO, MgO, and
Fe2O3 are mobile, whereas a lack of scatter in the Zr vs.
P2O5, TiO2, Nb, and Sm indicate that they are largely immobile (e.g., Figs. 3a–3h).
Analytical methods
Samples were pulverized in a steel jaw crusher, with a
few samples subsequently powdered in an agate mill. Total
abundances of major oxides were analysed by inductively
coupled plasma – emission spectrometry (ICP–ES) followPublished by NRC Research Press
DeWolfe et al.
515
Table 2. Average values for key element ratios for the units of the Hidden and Louis formations.
Al2O3/Na2O
Al2O3/TiO2
Ti/V
Zr/Y
Zr/Ti
Nb/Y
Ti/Sc
Nb/Lamn
Nb/Thmn
La/Smch
La/Ybch
Sm/Ybch
1920 unit
(Hidden fm.)
3.8–5.3
13.8–15.5
168.2–240.6
1.8–2.0
0.015–0.016
0.05
201–214
0.31–0.35
0.54–0.62
0.9–1.0
0.8
0.8–0.9
Reservoir mb.
(Hidden fm.)
3.7–6.3
16.9–33.7
8.1–14.4
1.2–1.8
0.004–0.007
0.04–0.07
5–127
0.17–0.32
0.11–0.27
0.9–2.1
0.7–1.9
0.8–1.1
Stockwell mb.
(Hidden fm.)
4.2–7.2
17.0–50.0
8.5–18.2
1.2–1.8
0.004–0.007
0.04–0.06
61–134
0.16–0.31
0.15–0.29
1.1–1.7
1.0–1.7
0.8–1.1
Carlisle Lake basaltic
andesite (Hidden fm.)
2.5–5.4
25.5–29.9
11.2–16.9
2.6–3.6
0.014–0.020
0.15–0.19
99–153
0.17–0.26
0.14–0.16
2.7–3.2
4.2–5.7
1.7–2.0
Tower mb.
(Louis fm.)
3.4
42.9
—
2.6
0.060
0.09
—
0.25
0.23
2.1
2.3
1.1
Icehouse mb.
(Louis fm.)
5.3–6.4
30.3–31.2
9.8–11.0
1.4–1.6
0.004–0.005
0.07
63–65
0.22–0.23
0.23–0.25
1.6
1.8–1.9
1.1–1.2
Undivided flows
(Louis fm.)
3.1–7.8
24.3–45.6
7.7–14.3
1.4–2.7
0.005–0.014
0.06–0.10
47–105
0.15–0.30
0.14–0.25
1.5–2.3
1.8–3.3
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 McDonough (1989); fm., formation; mb., member.
ing a lithium metaborate–tetraborate fusion and dilute nitric
digestion at ACME Analytical Laboratories (Vancouver,
British Columbia). Replicate analyses of samples and standards reveal relative standard deviations (%RSD) of <18%
for ICP – mass spectrometry (ICP–MS) determinations.
Samples were analysed for trace elements at the Ontario
Geoscience Laboratories (Sudbury, Ontario) and underwent
a closed beaker digest using four acids (hydrofluoric, hydrochloric, perchloric, and nitric acids) to ensure total dissolution of all solids. The samples were then analysed for trace
elements using ICP–MS. Replicate analyses of samples and
standards reveal relative standard deviations (%RSD)
of <10% for ICP–MS determinations.
Neodymium isotopic geochemistry was completed at the
Pacific Centre for Isotopic and Geochemical Research, Department of Earth and Ocean Sciences, The University of
British Columbia (Vancouver, B.C.) using thermal ionization mass spectrometry (TIMS) following the methods of
Weis et al. (2006). Values for the United States Geological
Survey (USGS) reference standards BCR-2 and G-2 yielded
average 143Nd/144Nd ratios of 0.512628 and 0.512217, respectively, with analytical uncertainties of ± 0.000006 (2s)
for each. Neodymium isotope data are presented relative to
a La Jolla standard value of 143Nd/144Nd = 0.511858. All
143Nd/144Nd values are normalized to 146Nd/144Nd = 0.7219,
and initial 3Nd values are reported relative to a chondritic
uniform 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 ratios
and 3Nd were calculated at 1.9 Ga, the approximate age of
all samples in this study, to facilitate comparison with other
data from the Flin Flon arc assemblage (Stern et al. 1995a,
1995b).
Hafnium isotopic geochemistry was also completed at the
Pacific Centre for Isotopic and Geochemical Research using
TIMS, following the methods of Weis et al. (2007). Values
for the USGS reference standards BHVO-1 and BCR-2
yielded average 176Hf/177Hf ratios of 0.283102 and
0.282869, respectively, with analytical uncertainties of
± 0.0000015 and 0.0000016 (2s), respectively. Hafnium isotope 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 with
present-day values of 176Lu/177Hf = 0.0332 (Vervoot and
Blichert-Toft 1999) and 176Hf/177Hf = 0. 282772 (Vervoot
and Blichert-Toft 1999). Initial 176Hf/177Hf ratios and 3Hf
are again calculated at 1.9 Ga.
Lead isotopic geochemistry was done at Carleton University (Ottawa, Ontario) using a Thermo-Finnigan TRITON
mass spectrometer following the methods of Cousens
(1996). Samples were dissolved using a three acid digestion
and the residue taken up in a hydrogen bromide solution for
Pb separation. Lead was separated in Bio-Rad 10 mL polyethylene columns and Dowex AG1-8X anion resin using hydrogen bromide to elute other elements and hydrochloric
acid to elute Pb. This procedure was repeated. All mass
spectrometer runs are corrected for fractionation using NIST
SRM981, and the average ratios for SRM981 are 206Pb/
204Pb = 16.892 ± 0.010, 207Pb/204Pb = 15.431 ± 0.013, and
208Pb/204Pb = 35.512 ± 0.038 (2 standard deviations), based
on 20 runs. The fractionation correction based on the values
of Todt et al. (1984) is +0.13%/amu (atomic mass units).
Results
The Hidden and Louis formations can be subdivided into
seven distinct geochemical suites using immobile incompatible elements. This geochemical subdivision corresponds
with subdivision based on petrographic observations (described earlier in the text and including the 1920 unit, basalts and basaltic andesites of the Reservoir member, and
the Stockwell member, all of the Hidden formation, as well
as the Tower member, Icehouse member, and undivided
flows of the Louis formation). The 1920 unit is slightly light
REE (LREE)-depleted, typical of normal arc tholeiites, but
all other units within the Hidden and Louis formations have
geochemical attributes similar to transitional arc tholeiites
with slightly more LREE enrichment than normal arc tholeiites (Jakes and Gill 1970).
1920 unit, Hidden formation
The 1920 unit has Zr/TiO2 and Nb/Y ratios typical of subalkaline basaltic andesite (Fig. 4) with elevated values of total Fe, TiO2, and P2O5 and lower values of Al2O3 than
typical basaltic andesites (Table 1; Fig. 5). Though high in
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516
Can. J. Earth Sci. Vol. 46, 2009
Fig. 3. Zr vs. selected element variation diagrams to demonstrate(a–d) the effects of post-magmatic alteration and (e–h) the limited effects
of alteration on P, Ti, Nb, and Sm. Strong correlation for these elements indicates that they were not significantly mobilized by alteration.
HFSE, the very high TiO2 content (Table 1) of the 1920 unit
results in high Ti/V and Ti/Sc ratios (Table 2; Fig. 6). The
unit has a moderately low Zr/Y ratio (Table 2; Fig. 7). It is
characterized by primitive mantle-normalized patterns with
slight LREE depletion (La/Smch = 0.9–1.0; Table 2), negative Nb anomalies (Nb/Thmn = 0.58) and HFSE depletion
(Fig. 8a). Chondrite-normalized patterns for the 1920 unit
are again flat with slight LREE depletion (La/Ybch = 0.8;
Table 2; Fig. 9a).
Isotopically, the 1920 unit has 3Nd(1.9Ga) values of +3.6
to +5.9 similar to values for the depleted mantle at 1.9 Ga
(Table 3; Goldstein et al. 1984). The 1920 unit has
Published by NRC Research Press
DeWolfe et al.
Fig. 4. Discrimination diagram (Pearce 1996) for the Hidden and
Louis formations. Alk, Alkaline; And, Andesite.
517
Fig. 6. Ti vs. V tectonomagmatic discrimination diagram (Shervais
1982) 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. 5. Al2O3–P2O5–TiO2 systematics of the Hidden and Louis formations. N-MORB, normal mid-ocean ridge basalt; E-MORB, enriched MORB; OIB, ocean-island basalt.
Fig. 7. Zr/TiO2 vs. Y/TiO2 diagram (Piercey et al. 2004) showing
tholeiitic affinity of rocks of the Hidden and Louis formations.
3Hf(1.9Ga) values of +8.5 to +9.6, similar to values for the depleted mantle at 1.9 Ga (Vervoort and Blichert-Toft 1999;
Table 3). Whole-rock Pb isotopic data for the 1920 unit
yields a 206Pb/204Pb value of 23.945 and 207Pb/204Pb value
of 16.172 (Table 4).
Reservoir member, Hidden formation
Basalts of the Reservoir member have subalkaline affinities (Fig. 4), low to moderate Al2O3/TiO2 ratios, and low
P2O5 contents relative to other basalts of the hanging wall
(Table 2; Fig. 5). The basaltic rocks of the Reservoir member also have low Zr/Y, Ti/Sc, and Ti/V ratios (Table 2),
and, as with the Stockwell member, their Ti vs. V systematics are similar to those of modern day island-arc rocks
(Figs. 6, 7). However, basalts of the Reservoir member
have flat, primitive mantle-normalized patterns with slight
LREE enrichment (La/Smch = 0.9–2.1), strong negative Nb
anomalies (Nb/Thmn = 0.11–0.27), and HFSE depletion
(Fig. 8b), suggesting they are transitional island-arc tholeiites. Chondrite-normalized patterns for the basalt of the Reservoir member are again flat to slightly LREE-enriched (La/
Ybch = 0.7–1.9; Table 2; Fig. 9a).
Isotopically, basalts of the Reservoir member have
3Nd(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 depleted mantle at 1.9 Ga (Goldstein et al. 1984; Vervoort and
Blichert-Toft 1999; Table 3). Whole-rock Pb isotopic data
for basaltic rocks of the Reservoir member give 206Pb/204Pb
values of 15.53–15.57 and 207Pb/204Pb values of 15.16–15.18
(Table 4).
Stockwell member, Hidden formation
Basalts 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, they
have slightly higher P2O5 contents than basalts of the Reservoir member and low to high Al2O3/TiO2 ratios that overlap
only partially with basalts of the Reservoir member (Tables 1, 2; Fig. 5). The Stockwell member also has low Zr/
Y, Ti/Sc, and Ti/V ratios (Table 2). The latter suggests they
are similar modern-day island-arc tholeiites (Figs. 6, 7);
however, on a primitive mantle-normalized plot, the StockPublished by NRC Research Press
518
Can. J. Earth Sci. Vol. 46, 2009
Fig. 8. Primitive mantle-normalized trace element plots for various units within the Hidden and Louis formations. Primitive mantle values
from Sun and McDonough (1989).
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 Stockwell
member has flat chondrite-normalized patterns with slight
LREE enrichment (La/Ybch = 1.0–1.7; Table 2; Fig. 9c).
Published by NRC Research Press
DeWolfe et al.
519
Fig. 9. Chondrite-normalized trace element plots for various units within the Hidden and Louis formations. Chondrite values from 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 depleted mantle at 1.9 Ga (Goldstein et al. 1984, Vervoort and
Blichert-Toft 1999; Table 3). Whole-rock Pb isotopic data
for the Stockwell member yields a 206Pb/204Pb value of
17.40 and 207Pb/204Pb value of 15.38 (Table 4).
Published by NRC Research Press
520
Can. J. Earth Sci. Vol. 46, 2009
Table 3. 3Hf and 3Nd values for the Hidden and Louis formations.
Sample
035
004
080
005
092
002
061
095
127
133
144
Unit or member
1920 unitd
1920 unitc
Reservoir memberd
Reservoir memberc
Stockwell memberd
Stockwell memberc
Stockwell memberd
Stockwell memberd
Tower memberd
Icehouse memberd
Undivided, Louis formationd
143Nd/144Nda
147Sm/144Nd
0.512876
0.512645
0.512668
0.512698
0.512603
0.512568
0.512571
0.512825
0.512321
0.512467
0.512250
0.1918
0.1826
0.1862
0.1945
0.1759
0.1795
0.1732
0.1952
0.1525
0.1661
0.1511
(6)
(6)
(6)
(7)
(5)
(6)
(6)
(5)
(6)
(6)
(6)
3Nd(1.9)
5.9
3.6
3.2
1.7
4.4
2.8
4.4
4.0
4.6
4.2
3.6
176Hf/177Hf b
176Lu/177Hf
0.283624
0.281814
0.283890
0.281773
0.284366
0.281879
0.284002
0.284194
0.283093
0.281811
0.281893
0.0567
0.0484
0.0327
0.0573
0.0581
0.0571
0.0495
0.0444
0.0348
0.0510
0.0350
(06)
(06)
(11)
(04)
(18)
(05)
(10)
(14)
(04)
(08)
(05)
3Hf(1.9)
9.6
8.5
8.5
7.0
11.8
10.8
11.4
10.4
9.3
8.4
11.3
a
Number in parentheses is the uncertainty in the last decimal place.
Number in parentheses is the uncertainty in the last two decimal places.
c
Least altered sample.
d
Weakly altered sample.
b
Table 4. Pb isotopic data for the Hidden and Louis formations.
Sample
004
006
002
005
202
203
133
127
Unit or member
1920 unitc
Reservoir member c
Reservoir memberd
Stockwell memberc
Carlisle Lake basaltic andesitec
Carlisle Lake basaltic andesited
Icehouse memberc
Tower memberc
Formation
Hidden
Hidden
Hidden
Hidden
Hidden
Hidden
Louis
Louis
206Pb/204Pba
207Pb/204Pba
208Pb/204Pbb
23.945
16.161
16.881
18.566
21.468
17.811
17.903
22.166
16.172
15.227
15.320
15.503
15.846
15.437
15.441
15.903
39.879
35.313
35.724
36.269
37.849
36.386
36.327
37.120
(7)
(4)
(2)
(5)
(2)
(3)
(1)
(3)
(5)
(3)
(1)
(4)
(1)
(2)
(1)
(2)
(11)
(08)
(03)
(10)
(04)
(06)
(02)
(05)
a
Number in parentheses is the uncertainty in the last decimal place.
Number in parentheses is the uncertainty in the last two decimal places.
c
Least altered sample.
d
Weakly altered sample.
b
Carlisle Lake basaltic andesites, Reservoir member,
Hidden formation
Basaltic andesites at the top of the Reservoir member
have Zr/TiO2 and Nb/Y ratios typical of subalkaline basaltic
andesites, and higher Nb/Y ratios separate them from the
1920 unit (Fig. 4). The basaltic andesites of the Reservoir
member are referred to as the Carlisle Lake basaltic andesites after their type locality and to separate them from the
basalts of the Reservoir member. In the field, they are commonly indistinguishable from the basalts of the Reservoir
member and seldom contain acicular amphibole crystals
similar to those observed in the 1920 unit. They have moderate Al2O3/TiO2 ratios and P2O5 contents that distinguish
them from all other units within the hanging wall (Tables 1,
2; Figs. 5, 7). High Zr/Y ratios, low to moderate TiO2 contents, and moderate Ti/Sc and Ti/V ratios also distinguish
them from the 1920 unit and basalts of the hanging wall
(Tables 1, 2). As with the other units within the Hidden formation, the Ti–V systematics of the Carlisle Lake basaltic
andesites suggest they are similar to modern-day island-arc
tholeiites (Table 2; Fig. 6). However, rocks from the Carlisle
Lake basaltic andesite have relatively low HFSE values, are
more LREE enriched than the other units within the Hidden
formation (La/Smch = 2.7–3.2), and have primitive mantlenormalized 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 calcalkaline rocks. On a chondrite-normalized plot the Carlisle
Lake 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 of
15.12–15.19 (Tables 3, 4).
Tower member, Louis formation
The Tower member plots as a subalkaline rhyodacite
(Fig. 4) and is characterized by a high Al2O3/TiO2 ratio and
low P2O5 content (Tables 1, 2; Fig. 5); although this is a single sample, it is likely representative of the Tower member.
The primitive mantle-normalized plot of the Tower member
has a flat to LREE-enriched (La/Smch = 2.1) pattern, with a
strong Nb (Nb/Thmn = 0.23) and Ti anomaly (Table 2;
Fig. 8e). A chondrite-normalized plot of the Tower member
again 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 are
similar to values for the depleted mantle at 1.9 Ga (Goldstein et al. 1984; Vervoort and Blichert-Toft 1999; Table 3).
The Tower member was also analyzed for Pb isotopes and
yielded a 206Pb/204Pb value of 15.82 and 207Pb/204Pb value
of 15.21 (Table 4).
Published by NRC Research Press
DeWolfe et al.
Icehouse member, Louis formation
Subalkaline basalts (Fig. 4) of the Icehouse member have
Zr/TiO2 ratios that overlap with the basalts of the Reservoir
and Stockwell members, but with distinctly higher Nb/Y ratios (Table 2; Fig. 4). The Al2O3/TiO2 ratios of the Icehouse
member overlap with the higher Al2O3 ratios of the Stockwell member but are markedly higher than those within the
Reservoir member (Table 2). Rocks belonging to the Icehouse member have slightly lower P2O5 values than the basalts 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 Reservoir
member, and Ti–V systematics, low Zr/Y ratios, and low
HFSE contents indicate an island-arc tholeiite affinity
(Figs. 6, 7). The Icehouse member is similar to basalts of
the Reservoir and Stockwell members having flat primitive
mantle-normalized patterns with only slight LREE enrichment (La/Smch = 1.6), strong negative Nb anomalies (Nb/
Thmn = 0.23–0.25), and HFSE depletion (Fig. 8f). On a
chondrite-normalized plot, the Icehouse member again
shows slight LREE enrichment (La/Ybch = 1.8–1.9; Table 2;
Fig. 9f), possibly indicating that it is transitional between island-arc tholeiites and calc-alkaline rocks.
A sample of the Icehouse member has 3Nd(1.9Ga) = +4.2
and an 3Hf(1.9Ga) value of +8.4, again both are similar to values for the depleted mantle at 1.9 Ga (Goldstein et al. 1984;
Vervoort and Blichert-Toft 1999; Table 3). The same sample yielded a 206Pb/204Pb value of 15.39 and 207Pb/204Pb
value of 15.16 (Table 4).
Undivided volcanic flows, Louis formation
The undivided volcanic flows that form a thick sequence
at the top of the Louis formation have Zr/TiO2 ratios similar
to the Reservoir, Stockwell, and Icehouse members and fall
within the subalkaline basalt field; however, they can be
separated based on their Nb/Y ratios from other basalts
within the hanging wall (Table 2; Fig. 4). They overlap
with Al2O3/TiO2 and P2O5 values of the Stockwell and Icehouse members but differ in this respect from the Reservoir
member (Tables 1, 2; Fig. 5). Low TiO2 content and low Zr/
Y, Ti/Sc, and Ti/V values are similar to the other basalts
within the hanging wall and lie within the island-arc tholeiite field in Figs. 6 and 7. The undivided basaltic flows have
relatively low HFSE contents (Table 1) and slightly LREEenriched (La/Smch = 1.5–2.3; Table 2) primitive mantle-normalized 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 show
moderate 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 to
values 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 Louis
formations of the Flin Flon arc assemblage suggest that
they record the evolution of two dominantly basaltic juvenile arc volcanoes in a Paleoproterozoic island arc. Geologi-
521
cal characteristics of the base of the Hidden formation imply
eruption and emplacement in an extensional environment
where flows, intrusions, and volcaniclastic deposits were
controlled by synvolcanic faulting and associated subsidence
structures (DeWolfe et al. 2009). However, the upper portion of the Hidden formation and the Louis formation have
geological characteristics that imply emplacement in an environment dominated by effusive basaltic volcanic activity
with only minor evidence for extension and associated subsidence (DeWolfe et al. 2009).
Regional geological and geochemical studies have constrained the overall tectonic environment of the rocks in the
Flin Flon area to island-arc settings comprising mainly tholeiitic, with lesser calc-alkaline basalt and basaltic andesite
and rare high-Ca boninites (Stern et al. 1995a; Syme et al.
1999). Geochemical similarities between Flin Flon arc assemblage rocks and those in modern primitive, intraoceanic
arc systems have been recognized and have resulted in the
interpretation that Paleoproterozic arc processes in Flin Flon
were broadly similar of those in modern arc environments
(Stern et al. 1995a; Syme et al. 1999). Geochemical characteristics have also suggested that the mantle source during
eruption of rocks in Flin Flon was highly depleted, possibly
residual after MORB or back-arc basin basalt extraction, and
that variations in Nd isotopic data and LREE contents suggest small amounts (0%–8%) of recycling of crust through
sediment subduction and intracrustal contamination (Stern
et al. 1995a).
Evidence for a juvenile arc and minor crustal
contamination
In modern intraoceanic island arcs, there are a variety of
processes that explain the geochemical and isotopic systematics found in arc volcanic rocks. Commonly, there is the
mixing between depleted- and enriched-mantle sources with
variable contributions from crustal sources and the subducted slab (e.g., Pearce and Peate 1995; Pearce 2008). The
data from Hidden and Louis formations support models involving mantle mixing, slab metasomatism, and crustal contamination within a Paleoproterozoic juvenile oceanic arc
system. To test the potential for mantle mixing, Zr, Nb, and
Yb systematics have been utilized as these elements are immobile, largely unaffected by crustal contamination and slab
metasomatism, and sufficiently incompatible; hence, ratios
of them provide a proxy for the mantle source of the mafic
rocks (Pearce 1983; Pearce and Peate 1995). In Nb/Yb–Zr/
Yb space, samples from the Hidden and Louis formations
form a linear array from depleted mantle sources to more
enriched mantle sources, respectively. Most of the units lie
within the normal (N-)MORB field, the exception being
rocks from the Carlisle Lake andesite, which lie halfway between N-MORB and enriched (E-)MORB values (Fig. 10).
These data imply that rocks of the Hidden formation, at the
base of the hanging wall succession, were derived from the
most depleted mantle source, whereas the overlying rocks of
the Louis formation were derived from more enriched mantle sources.
The degree of crustal contamination and input from slab
metasomatism is evaluated using Pb isotopic data, Th–Nb–
La systematics, and Sm/Nd isotopic data. Given that the
least altered sample from each unit was analysed and that
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522
Fig. 10. Zr/Yb vs. Nb/Yb diagram that discriminates between rocks
derived from depleted-mantle to enriched-mantle sources. Diagram
from Pearce and Peate (1995). Values for N-MORB (normal midocean ridge basalt), E (enriched)-MORB, and OIB (ocean-island
basalt) are from Sun and McDonough (1989).
there is no correlation between the Pb isotopic data and the
Hashimoto alteration index (e.g., 100*(MgO + K2O)/(MgO
+ K2O + CaO + Na2O) vs. 206Pb/204Pb, 207Pb/204Pb, or
208Pb/204Pb), the isotopic ratios cannot be due to alteration,
and likely represent primary petrological variance. The Pb
reference isochron lies between model N-MORB and upper
crust isochrons (Fig. 11a; Kramers and Tolstikhin 1997), indicating that the source for these flows was end-member depleted mantle, but was contaminated either through slabderived fluids and melts or by sediment subduction. On a
plot of Nb/Yb versus Th/Yb, flows of the Hidden and Louis
formations 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, suggesting
crustal input via subduction processes (Fig. 11b; Pearce
1983, 2008; Pearce and Peate 1995). All units of the Hidden
and Louis formations also display negative Nb anomalies on
primitive mantle-normalized diagrams (Figs. 8a–8g). These
anomalies have been interpreted to represent an ‘‘arc’’ signature, the result of subducted-slab metasomatism of the overlying subarc mantle wedge (Gill 1981; Pearce 1983; Pearce
and Peate 1995). However, there is much debate about the
origin of Nb anomalies in arc magmas, and it has also been
argued that these anomalies are a result of contamination of
a mafic magma by crust during emplacement, or a combination of both processes (e.g., Stern et al. 1995a; Pearce
2008). Given the fact that the Hidden and Louis formations
show volcanological evidence for localized rifting and subaqueous, dominantly basaltic eruptions (DeWolfe et al. 2009)
and that Sm/Nd and Lu/Hf isotopes indicate they represent a
primitive arc, we suggest that any contamination is due to
slab metasomatism and, possibly, minor sediment subduction.
It is important to note that the relatively high initial 3Nd
and 3Hf values of the Hidden and Louis formation suggest
that the amount of crustal input through sediment subduction
must be very low. To examine the amount of crustal contamination, we plotted Nb/Yb versus initial 3Nd values
(Fig. 12; Stern et al. 1995a). The results suggest that the
rocks of the Hidden and Louis formations contain only minor (£3.5%) input from crustal sources, and their low Nb/Yb
Can. J. Earth Sci. Vol. 46, 2009
values suggest they formed from a depleted mantle source
(i.e., MORB-like mantle source). This agrees with conclusions from Stern et al. (1995a), where the authors suggested
that sediment subduction rather than intracrustal recycling
was the dominant process involved in introducing an older
crustal component within tholeiitic rocks of the Hidden–
Burley suite (the Hidden and Louis formations in this
study).
Evidence for arc evolution
Geochemical variations in the stratigraphy of the Hidden
and Louis formations suggest changes in the mantle source
and degree of input from crustal sources. Elucidating variations in these processes temporally during the formation of
the hanging wall stratigraphy in Flin Flon is important in
understanding the evolution of this juvenile Paleoproterozoic
arc. Variations in Nd, Hf, and Pb isotopic values do not differ appreciably with stratigraphic height, hence, are not used
in deciphering changes in mantle source or crustal input during emplacement of the hanging wall stratigraphy.
To address the question of whether or not there was a
change in mantle source during construction of these ancient
arc volcanoes, we have plotted Nb/Zr versus stratigraphic
height again using Nb–Zr as a proxy for mantle source
(Pearce 1983; Pearce and Peate 1995). Lower Nb/Zr ratios
suggest 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 Peate
1995). Initially low Nb/Zr ratios generally increase up stratigraphy (Fig. 13a). Nb–Zr systematics suggest derivation of
early Hidden formation rocks (1920 unit) from depleted mantle sources with subsequent flows (Reservoir and Stockwell
members) being derived from more incompatible-elementenriched sources with the most incompatible-elementenriched rocks occurring within the Carlisle Lake basaltic
andesites at the top of the Hidden formation (Fig. 13a). The
hiatus in effusive volcanic activity that marks the contact between the Hidden and Louis formations coincides with a return to more depleted mantle Nb/Zr ratios (Fig. 13a) for
flows of the Louis formation.
The enriched Carlisle Lake basaltic andesites can be explained by variable degrees of melting of a heterogenous
mantle that contains blobs of fertile material in a depleted
matrix (‘‘plum pudding’’ model of Zindler et al. 1984). As
the fertile material will melt first, melts produced by lower
degrees of partial melting contain a greater component of
LREE-enriched material. This would result in the hangingwall rocks changing from incompatible element enriched at
the bottom to incompatible element depleted at the top, but
does not account for the return to more depleted signatures
observed within the Louis formation. Perhaps a more likely
scenario is re-fertilizing the mantle with slab melts, then remelting these re-fertilized portions forming Nb-enriched basalts (Sajona et al. 1996). This model could explain depleted
mantle signatures at the base of the Hidden formation, more
enriched signatures for the Carlisle Lake basaltic andesites
at the top of the Hidden formation, and a return to more NMORB-like signatures in the Louis formation.
To evaluate the extent of crustal input either through slab
metasomatism or sediment subduction during formation of
the hanging wall, Nb/Th was plotted versus stratigraphic
Published by NRC Research Press
DeWolfe et al.
523
Fig. 11. Diagrams for rocks of the Hidden and Louis formations that illustrate crustal input either from subducted slab metasomatism or the
subduction of sediments. (a) Common Pb diagram for whole-rock samples. Artifical normal mid-ocean ridge basalt (N-MORB) isochron and
upper 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 and
Louis formations with contours showing calculated % of older crust
Nd in the samples. For samples with low Nb/Yb (0% older crust),
the juvenile mantle melt end-member was assumed to have 5 ppm
Nd and 3Nd = +5, and for rocks with higher Nb/Yb, the juvenile
melt was assumed to have 10 ppm Nd and 3Nd = +2.5. The older
crustal component was modelled with 50 ppm Nd and 3Nd = –7
after the 2.5 Ga Beaverhouse Granodiorite. Hidden – Burley Lake
and older crustal component fields and mixing calculations from
Stern et al. (1995a).
height (Fig. 13b), again Th–Nb can be used as a proxy for
crustal input (Pearce 1983, 2008; Pearce and Peate 1995). A
decrease in the Nb/Th ratio from bottom to top of the Hidden formation suggests an increasing amount of crustal contamination during the emplacement of the Hidden formation
(Fig. 13b). Following the hiatus in effusive volcanism that
marks the contact between the Hidden and Louis formations
(DeWolfe et al. 2009), the rocks of the Louis formation
yield intermediate Nb/Th ratios, lower than the ratio for the
Carlisle Lake basaltic andesites, but higher than the ratios
observed for the base of the Hidden formation. This suggests
an increase in crustal contamination through slab metasoma-
tism and (or) sediment subduction during emplacement of
the hanging wall.
Genetic implications of the 1920 unit and Stockwell
member
Fe–Ti basalts have been documented in the hanging wall
to some VMS deposits hosted by bimodal volcanic sequences (e.g., Kam-Kotia, Barrie and Pattison 1999; Kidd Creek,
Wyman et al. 1999; Galapagos, Embly et al. 1988; Perfit et
al. 1999). These basalts have enrichments in Fe and Ti (and
often 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 and
Pattison (1999) attributed the occurrence of Fe–Ti basalts
associated with massive sulphide deposits at Galapagos and
Kam-Kotia to extensive low-pressure fractional crystallization and contamination by hydrothermally altered oceanic
crust in a shallow-level (<2 km) magma chamber.
Geochemical data presented herein illustrate that the 1920
unit is a basaltic andesite enriched in Fe, Ti, and P with
REE patterns characteristic of island-arc tholeiites and that
the overlying units have geochemical characteristics similar
to transitional arc tholeiites. Geological evidence also shows
that the 1920 unit and the overlying Stockwell member were
emplaced in an extensional environment (DeWolfe et al.
2009), where localized rifting of a juvenile arc resulted in a
thinned crust that consequently allowed the rise of magma
to high levels in the crust.
Geochemical similarities of the 1920 unit to Fe–Ti basalts
at Galapogos, Kam-Kotia and Kidd Creek (Embly et al.
1988; Perfit et al. 1999; Barrie and Pattison 1999), and the
documentation through isotopic and trace element geochemistry of juvenile arc magmatism, as well as the geological
evidence for localized rifting, support the hypothesis that
1920 unit formed through extensive fractional crystallization
of differentiated magmas at shallow levels in oceanic crust.
This high-level magma chamber would have allowed little
or no mixing with a deeper, long-lived magma chamber and
more contamination by hydrothermally altered oceanic crust.
The presence of this shallow-level magma chamber would
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524
Can. J. Earth Sci. Vol. 46, 2009
Fig. 13. Stratigraphic height versus key elemental ratios illustrating (a) variations in mantle source, and (b) crustal contamination. Each
point represents the average value for that unit, error bars through the data points represent natural variance within each unit, and error bars
below 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.
have also provided a high-temperature environment that
could generate and sustain a high-temperature convective
hydrothermal system necessary for the formation of massive
sulphide mineralization. Thus, this study’s findings are consistent with the suggestion by Franklin et al. (2005) that the
presence of Fe–Ti basalts and other evolved rocks in bimodal sequences may be a good indicator of prospective areas
for VMS-type mineralization.
Conclusions
(1) Major and trace element geochemistry and Nd, Hf, and
Pb isotopic data show that the volcanic flows and syn-
volcanic intrusive rocks of the Hidden and Louis formations that make up the hanging wall to the Flin Flon
VMS deposits were emplaced in a juvenile island-arc
environment. Mantle sources range from depleted mantle
(N-MORB-type) to slightly more enriched mantle
sources (E-MORB-type). The rocks are variably contaminated (£3.5%) by crustal sources either through
subducted-slab metasomatism or sediment subduction.
(2) Geochemical variations in the strata of the Hidden and
Louis formations record a change from depleted mantle
sources to more enriched mantle sources and a return to
a more depleted mantle source during emplacement of
the units. The process responsible for this change in
Published by NRC Research Press
DeWolfe et al.
mantle source may be a re-fertilizing of the arc mantle
wedge with slab melts, and then re-melting these refertilized portions forming Nb-enriched basalts (Sajona
et al. 1996). Variations in geochemical characteristics of
the hanging wall also indicate broadly increasing
amounts of crustal contamination from the base to the
top of the hanging wall, suggesting an increase in the
amount of crustal input from slab metasomatic processes
or sediment subduction as the hanging wall was emplaced.
(3) Geochemical and geological observations of the 1920
unit confirm that it has a composition similar to Fe–Ti
basalts associated with VMS–type mineralization at
Kidd Creek, Kam-Kotia, and Galapagos and that it was
emplaced in a localized rift within a dominantly juvenile
arc environment. The geological and geochemical characteristics of the 1920 unit suggest it formed though extensive low-pressure fractionation in a high-level magma
chamber with associated assimilation of hydrated oceanic crust. This high-level magma chamber, occurring in
a rifted-arc environment, would have also provided the
structures (synvolcanic faults associated with rifting)
and heat source required to drive high-temperature hydrothermal cells needed for the formation of directly underlying VMS deposits in Flin Flon. As such, the
presence of Fe–Ti basalts or similarly evolved rocks, in
this case an Fe–Ti-rich basaltic andesite, is excellent evidence for the presence of a high-level magma chamber
needed to provide the heat necessary to drive a hydrothermal system and, combined with evidence of rifting,
is a useful tool in exploring for VMS deposits.
Acknowledgments
The Natural Sciences and Engineering Research Council
of Canada (NSERC), HudBay Minerals, and the Manitoba
Geological Survey provided funding for this project. The
Manitoba Geological Survey also provided logistical support
and field assistance. The authors would like to thank P. Lenton, E. Wright, E. Fitzsimmons, and C. Devine for providing
orthorectified airphoto coverage of the field area, and B.
Janser, R.-L. Simard, T. Penner, and K. MacLachlan for discussion on and of the rocks. The authors would also like to
thank George Jenner and Anthony Fowler for comprehensive reviews of this manuscript.
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