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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)