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Natural ResourcesCanada
Ressources naturellesCanada
PRELIMINARY GEOCHRONOLOGICAL STUDY OF ECONOMICALLY PROSPECTIVE UNITS FROM FOXE PENINSULA, SOUTHWEST BAFFIN ISLAND
1 1 2N. Wodicka , M. Sanborn-Barrie , and M.D. Young1M.R. St-Onge , 1 2 Geological Survey of Canada, 601 Booth Street, Ottawa, ON, K1A OE8; Geological Survey of Canada, 625 Robson Street, Vancouver, BC, V6B 5J3
INTRODUCTION
In 2006, regional geological mapping of Foxe Peninsula, southwest Baffin Island, conducted as part of
the joint GSC-CNGO South-West Baffin Integrated Geoscience Project (SWBIG), revealed that this
part of Trans-Hudson Orogen is underlain dominantly by Paleoproterozoic supracrustal and intrusive
rocks with exploration potential for base- and precious-metal mineralization. Three distinct
supracrustal sequences are recognized (see geological map; Sanborn-Barrie et al. in prep. GSC Current
Research). A shelf sequence comprising orthoquartzite, marble, and psammite-semipelite is
lithologically similar to the type <1.93 Ga Lake Harbour Group exposed further southeast in south Baffin
Island. This succession is overlain by a thick, homogeneous succession of well-bedded quartzite and
feldspathic arenite with minor intraformational conglomerate (Lona Bay sequence). Overlying the Lona
Bay sequence is a heterogeneous volcano-sedimentary succession, informally named the Schooner
Harbour belt, comprising chiefly mafic volcanic rocks with subordinate intermediate to felsic volcanic
rocks, siliciclastic rocks, mafic-ultramafic flows and sills, and pyroclastic breccias. This locally
gossanous, economically prospective supracrustal belt extends for ~100 km from Schooner Harbour on
the southwest coast of Foxe Peninsula to the West Foxe Islands off the south-central coast. Another
economic prospect is a suite of mafic to ultramafic sills intrusive into the orthoquartzite-marble-
semipelite succession and which could represent hypabyssal expressions of Schooner Harbour
volcanism.
Greenland
West
SuperiorProvince
??
Hudson Strait
Foxe Basin
BaffinIslandBaffinIsland
UngavaBay
Hudson Bay
SuperiorProvince
SlaveProvince
Hearne
Rae
Rae
Rae NainProvince
Cord
illera
ndefo
rmatio
n fro
nt
0 300km
49°49°
49°49°
55°55°
60°60°65°65°
60°60°
70°70°
125°125°
115°
Carbonate platforms
Grenville orogen
Continental magmatic arcs
Island arcs / oceanic crust
Mafic volcanic rocks
Tertiary basaltsCenozoic
Cratons
2.0-1.8 Ga magmatic arcs(Thelon-Taltson, Great Bear)
Reworked Archean unitsReworked Archean units
Paleozoic
Paleo- to Mesoproterozoic
Paleoproterozoic
Archean
Anorthositic to granitic plutons
Cover sequences
Trans-Hudson Orogen
Continental shelf / foredeep prisms
modified after Wheeler et al. (1996)
100°100°
2.4-1.9 Ga accreted crust
neg
or O nosdns u-HarT
neg
or O nosdns u-HarT
Determining the timing of Schooner Harbour
volcanism and mafic-ultramafic magmatism, and
establishing their temporal relationship with
documented mineralization in northern Quebec and
central Baffin Island, is critical to future mineral
exploration in southwest Baffin Island. Concurrently,
determining the age and provenance of the supracrustal
sequences will be critical to the establishment of
regional tectonostratigraphic correlations. This poster
presents preliminary SHRIMP U-Pb results from key
stratigraphic units from the Schooner Harbour belt,
Lona Bay sequence, and a gabbroic sill intrusive into a
rusty-weathering, sulphide-bearing semipelite.
Location of geochronologysample
Mafic to ultramafic sills
1900
1700
1660
0.26
0.28
0.30
0.32
0.34
0.36
4.0 4.4 4.8 5.2 5.6
207Pb/235U
20
6P
b/2
38U
data-point error ellipses are 2s
18201820
17801780
17401740
18601860
Red = colourless, zoned grainsBlue = brown grains
?Crystallization age: 1876±22 Ma
The gabbro appears to contain two generations of zircon growth. Analyses of brown zircon grains are concordant and give a weighted mean age of 1835 ± 3 Ma (MSWD = 0.57; P = 97%). Based on regional correlations and uniform geochemical composition (generally low Th/U ratios), this age is interpreted as the time of metamorphism. In contrast, colourless
207 206grains give a range of Pb/ Pb ages from 1898 to 1803 Ma. If we assume that a single age exists for this population, which has suffered ancient Pb loss, a possible crystallization age of 1876 ± 22 Ma (MSWD = 1.12; P = 34%) is calculated based on the weighted mean of four replicate analyses on one of the oldest grains from this sample. Alternatively, but considered less likely, the younger 1835 Ma age could represent the crystallization, with the older dates being affected by inheritance.
With the exception of two Archean, brown zircon grains (interpreted as xenocrysts), all 207 206colourless grains yield Paleoproterozoic Pb/ Pb ages ranging from 1878 to 1720 Ma.
These younger analyses do not appear to define a single population, as indicated on the
relative probability curve. The majority of analyses (n = 19) occupying the youngest peak
give a weighted mean age of 1793 ± 12 (MSWD = 0.31; P = 99%). The central mode comprises
six analyses with a mean date of 1842 Ma. The seven analyses making up the oldest mode
give a weighted mean of 1864 ± 7 Ma (MSWD = 0.25; P = 96%). Four replicate analyses on
the oldest grain from this group yields a Tukey's biweight mean of 1878 ± 41 Ma (MSWD =
2.7; P = 5%). Albeit imprecise, this age may approximate the time of crystallization of the
andesite pyroclastic breccia, with the younger dates representing the ages of metamorphic
events. Alternatively, if we assume that the older dates reflect inheritance, then the
volcanic rock could be as young as ca. 1793 Ma. Based on the timing or regional metamorphic
events in eastern Trans-Hudson Orogen, this scenario is considered less likely.
Schooner Harbour belt
Lona Bay sequence
2600
2200
1800
1400
1000
0.1
0.2
0.3
0.4
0.5
0.6
0 4 8 12 16
207Pb/
235U
20
6P
b/2
38U
data-point error ellipses are 2s
Red = colourless grainsGreen = brown, xenocrystic grains
All data1950
1550
1450
1350
0.16
0.20
0.24
0.28
0.32
0.36
2.5 3.5 4.5 5.5
207Pb/235U
20
6P
b/2
38U
data-point error ellipses are 2s
1850
1750
1650
Paleoproterozoic grains only
Red = colourless grainsBlue = brown grains
0.000
0.001
0.002
0.003
0.004
0.005
0.006
0.007
0.008
1600
1700
1800
1900
2000
Pb-Pb age (Ma)
Pro
ba
bilit
y
1790
1840
1862
1900
2000
2100
2200
2300
2400
2500
2600
2700
2800
2900
Age (Ma)
0
2
4
6
8
10
12
14
16
2310
2410
20442162 2759
Fre
qu
en
cy
A feldspathic arenite was sampled to provide information on the provenance of the Lona
Bay detritus and on the evolution of the depositional basin.
The andesitic matrix (sample SAB-06-M236) to a pyroclastic breccia was sampled to determine the timing of Schooner Harbour volcanism
A gabbroic top to a layered peridotite sill intrusive into a rusty-weathering,
sulphide-bearing semipelite was sampled to test the temporal relationship
with Schooner Harbour volcanism.
Sampled gabbro with distinctive leucocratic wisps. Underlying rusty-weathering semipelite (left photograph) contains up to ~30% sulphide minerals.
SHRIMP U-Pb results for gabbro SAB-06-Y165
SUMMARY
The predominance of 2.3-2.4 Ga detrital zircon ages in the Lona Bay sequence feldspathic
arenite suggests probable derivation from local basement. The range of detrital ages is broadly
similar to those documented in the Lake Harbour Group as well as in the lower Piling Group. The
youngest detrital zircon grain indicates a maximum depositional age of 2.03 Ga for upper Lona Bay
sedimentation.
Gabbro sill intrusive into sulphidized semipelite is tentatively dated at ca. 1.88 Ga. This age is
characteristic of known base-metal-hosting rocks elsewhere in Trans-Hudson Orogen, namely the
ca. 1.88 Ga, Ni-Cu-PGE-bearing mafic/ultramafic bodies along the northern Superior craton margin.
Andesite matrix to a pyroclastic breccia from the economically prospective Schooner
Harbour belt gives an imprecise age of ca. 1.88 Ga. The SHRIMP results permit a link between mafic-
ultramafic magmatism and Schooner Harbour volcanism, but additional, more precise thermal
ionization mass spectrometry (TIMS) data are required to test this hypothesis.
Sampled feldspathic arenite (SAB-06-Y158) showing decimetre-scale compositional layering. The b iot i te-bear ing fe ldspath i c aren i te occurs near the top of the Lona Bay sequence. Note that based on the new GSC Open File bedrock maps for SW Baffin Island, this feldspathic arenite falls near the base of the Schooner Harbour sequence.
Zircon grains are colourless to brown and show variable morphologies; facets are sharp to mostly s u b r o u n d e d , a n d pitted surfaces are also present.
Interbedded basaltic to andesitic, pyroxene-phyric pyroclastic breccia exposed on West Foxe Islands; younging to left (N) based on variation in lithic fragment size.
Zircon grains comprise almost exclusively colourless, e u h e d r a l t o a n h e d r a l subequant crystals.
Meta Incognita microcontinent
Meta Incognita microcontinent
from Sanborn-Barrie et al. in prep. GSC Current Research
2600
2000
1800
0.2
0.3
0.4
0.5
0.6
4 6 8 10 12 14 16
207Pb/235U
20
6P
b/2
38U
data-point error ellipses are 2�
2400
2200
2800Maximum depositional age: 2026±18 Ma
Upper Lona Bay feldspathic areniten=55/66
Ages from the feldspathic arenite range from 2766 to 2026 Ma. Approximately 80% of SHRIMP analyses yield Paleoproterozoic 207Pb/206Pb ages in the range 2419 to 2296 Ma and define prominent modes at 2409 and 2310 Ma (see relative probability curve). The remaining zircon population yields Archean ages at ca. 2759, 2676, and 2510 Ma, and younger Paleoproterozoic ages at ca. 2161 and 2026 Ma. The latter age, with an uncertainty of ±18 Ma, is taken as the maximum age of deposition of sedimentary strata near the top of the Lona Bay sequence. The abundance of ca. 2.4-2.3 Ga zircon grains suggests derivation from local sources. The grains could be derived from potential basement identified in a number of places north and northeast of the sampling site. Several samples from basement units were sampled to test this hypothesis.
Corresponding author: Tel.: 613-947-4795
E-mail address: nwodicka@nrcan.gc.ca (Natasha Wodicka)
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