Geology of the Scimitar Lake Area

New U-Pb and Sm-Nd Results from the Pelican Narrows Area: 1865 to 1857 Ma Successor Arc Sedimentation from Juvenile Sources, 1857 Ma Juvenile Successor Arc Plutonism, and 1837 Ma Missi Group Sedimentation N.M Rayner 1, R.O. Maxeiner, and R.A. Creaser 2 Rayner, N.M., Maxeiner, R.O., and Creaser, R.A. (2009): New U-Pb and Sm-Nd results from the Pelican Narrows area: 1865 to 1857 Ma successor arc sedimentation from juvenile sources, 1857 Ma juvenile successor arc plutonism, and 1837 Ma Missi Group sedimentation; in Summary of Investigations 2009, Volume 2, Saskatchewan Geological Survey, Sask. Ministry of Energy and Resources, Misc. Rep. 2009-4.2, Paper A-9, 15p.

Abstract New U-Pb geochronological and Sm-Nd isotopic results are presented for three samples from the Wunehikun Bay area of Mirond Lake, east of Pelican Narrows and one sample from the Jones Lake area, 30 km to the east near the Manitoba border. A calcic psammopelitic gneiss, intercalated with high-grade tuffaceous rocks, is inferred to be syn-volcanic. Detrital zircons are dominantly 1.865 Ga, with a minor older component at ca. 1.88 Ga. The maximum age of deposition of the calcic psammopelite, constrained by the youngest reproducible detrital zircon population, is 1854 ±16 Ma. A psammitic gneiss, inferred to be part of an early sedimentary succession at Wunehikun Bay, is also dominated by 1.865 Ga detrital zircons and has a maximum age of deposition of 1844 ±19 Ma, based on the youngest detrital zircon population. Subsequent high-grade metamorphism at 1818 ±11 Ma is recorded in high-uranium overgrowths on detrital zircon. A gneissic diorite from central Wunehikun Bay yields a crystallization age of 1857 ±3 Ma and intrudes a layered hornblende-bearing sedimentary succession thought to be equivalent to the dated calcic psammopelite. Prevalent high-uranium overgrowths on zircon constrain the timing of metamorphism to 1817 ±5 Ma. All three samples at Wunehikun Bay have relatively juvenile isotopic signatures with ε143Nd results between +0.59 and +1.46 and model ages ranging from 2.1 to 2.3 Ga, consistent with values obtained for the Sickle and Grass River groups in Manitoba. At Jones Lake an aluminous potassic psammite gneiss from the lower Missi Group yielded a detrital zircon population dominated by 1.85 Ga material, but also a minor component of older material at 1.89 Ga and 2.1 Ga. The maximum age of deposition is 1837±9 Ma, constrained by the youngest reproducible detrital zircon population. A depleted mantle model age of 2.2 Ga is consistent with those observed at Wunehikun Bay. Keywords: U-Pb, geochronology, Paleoproterozoic, Flin Flon Domain, Kisseynew Domain, zircon, Sm-Nd, model age.

1. Introduction This paper provides an update on U-Pb zircon geochronology and Sm-Nd isotopic work carried out in support of the Pelican Narrows bedrock mapping project (Maxeiner, 2007; Maxeiner et al., 2008) in the northwestern Flin Flon Domain (Figure 1). The geochronological component of the Pelican Narrows project forms part of the joint federal-provincial Targeted Geoscience Initiative III (TGI-3) for the Flin Flon area, the objective of which is to sustain and enhance base metal exploration in established mining communities. Previous geochronological results (Rayner and Maxeiner, 2008) provided U-Pb zircon ages of 1841 ±15 Ma and 1846 ±7 Ma for intermediate to felsic subvolcanic units intruding the main Kakinagimak Lake volcanic succession, which is interpreted to have older (>1.87 Ga) crystallization ages. Further dating of zircon overgrowths provided U-Pb ages of 1808 ±4 Ma for an intermediate subvolcanic rock and 1807 ±8 Ma for an anatectic leucogranodiorite sheet, both of which were interpreted as metamorphic ages. The anatectic leucogranodiorite also yielded complex inherited zircons, giving older ages of 1883 to 2039 Ma with a weighted mean of 1.96 Ga. High-uranium overgrowths on these inherited cores were dated at 1868 ±6 Ma (Rayner and Maxeiner, 2008) and were interpreted to likely record an earlier metamorphic event related to amalgamation of the Flin Flon–Glennie Complex at ca. 1.87 Ga (Syme et al., 1998).

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Natural Resources Canada, Geological Survey of Canada, 601 Booth Street, Ottawa, ON K1A 0E8. Department of Earth and Atmospheric Sciences, University of Alberta, 1 - 26 Earth Sciences Building, Edmonton, AB T6G 2E3.

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Summary of Investigations 2009, Volume 2

LEGEND

RAE

Supracrustal Rocks Fw Fwn Psammopelite

ORDOVICIAN

HEARNE

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PALEOPROTEROZOIC Missi, Ourom Groups Kr,Fr Arkosic rocks

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Scimitar Lake area

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Burntwood Group Kwg Diatexitic psammopelite

R ZO EIN NE DE E

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Kisseynew Domain Flin Flon Domain

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Plutonic Rocks FJ Jan Lake granite Kgg Granodiorite Fgd

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Fbb Gabbro, diorite Fbq Tonalite, diorite

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Mylonite

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Migmatitic pelite

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Sahli granite

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55° 15’

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Figure 3

Pelican Narrows

Pelican Lake

Fgd

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Sedimentary Schist

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kilometres

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Sandy Bay ARCHEAN (Sask Craton) Granite, granodiorite, tonalite

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Fva Felsic volcanic rock Intermediate Fvi volcanic rock Fvb Mafic volcanic rock

Kwn Migmatitic psammopelite Fh Fm

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Red River Formation

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Figure 2

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Mirond Lake

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Deschambault Lake

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Flin Flon Creighton

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103°00’

Hanson Lake Fbq

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Fbb Orr

102°30’

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Amisk Lake

Denare Beach

Fbb102°

Figure 1 - Simplified geology of the northwestern Flin Flon Domain and southern Kisseynew domains, outlining the Wunehikun Bay (Figure 2) and Jones Lake (Figure 3) areas. Heavy dashed line delineates the limits of the airborne geophysical survey (from Maxeiner et al., 2008).

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In 2008, additional geochronological sampling on Wunehikun Bay of Mirond Lake was undertaken to study the relationships between clastic sedimentary rocks and volcanic units inferred to be part of the 1.92 to 1.88 Ga “Amisk Collage” (Lucas et al., 1996). At Jones Lake, the objectives were to examine the relationship between the younger Burntwood and Missi Group rocks, and to search for evidence of older volcanic components. The rocks at Wunehikun Bay are located in the hanging wall of the Pelican thrust, are characterized by strong transposition of units and abundant mylonitic textures, and have been metamorphosed to upper amphibolite facies (Figure 2). Recent mapping allows subdivision of the exposed lithologies into four groups (Maxeiner et al., 2008; Figure 2): 1) Volcanic and associated rocks are dominated by mafic units, although intermediate volcanic gneisses are abundant and commonly intercalated with mafic layers on a centimetre to decimetre scale. Felsic volcanic gneisses are rare and locally garnet rich, as a result of syngenetic alteration. 2) A succession of compositionally layered, mixed calcic sedimentary gneisses and minor intermediate to mafic tuffaceous components, are interpreted to represent synvolcanic detritus. This mixed sedimentary assemblage is inferred to be overlain by a succession of more aluminous pelitic to psammitic gneisses that are characterized by the near-ubiquitous presence of garnet, biotite, and graphite. The aluminous rocks may also represent synvolcanic detritus or, alternatively, be part of the younger Burntwood Group. Two detrital zircon profiles from this succession are reported here, one from the proposed lower, calcic subdivision, the other from a psammitic gneiss of the more aluminous succession. 3) Arc and successor arc plutons, dominantly granodioritic in composition, intrude the supracrustal rocks and have been subsequently partially melted. Intrusions of intermediate to mafic composition (dominated by diorite) are less common. 4) Syn- to post-tectonic plutons are the youngest mapped component. Within this four-fold division of rocks, UPb geochronological and Sm-Nd isotopic studies are aimed at characterizing the detrital zircon profiles and isotopic signatures of two sedimentary rocks at Wunehikun Bay and the crystallization age of the successor arc suite. The Jones Lake area (Figure 3) exposes the transition between the Flin Flon Domain and the southern flank of the Kisseynew Domain, just west of the Manitoba border. Details of the geology can be found in Maxeiner et al. (2008). There is a minor component of rocks predating deposition of the sedimentary rocks, which is characterized by garnet-rich intermediate volcanogenic rocks with disseminated sulphides and one unit of strongly foliated granodiorite gneiss. The area is dominated by graphite-bearing migmatitic psammopelite to pelite interpreted as Burntwood Group. At the proposed stratigraphic top of the Burntwood Group, near the contact with the Missi Group, a thin unit of quartzitic rocks can be traced for hundreds of metres. The overlying Missi Group is consistently magnetite bearing, and is dominated by migmatitic potassic psammite. Other phases include migmatitic polymictic conglomerate, calcic and aluminous psammite-psammopelite, and a stratigraphically overlying aluminous feldspathic quartzite. These units are intruded by plutons post-dating deposition of the Missi Group. The detrital zircon profile and isotopic signature of a sample of Missi Group aluminous potassic psammite is reported here.

2. Methods U-Pb geochronology was carried out using the Sensitive High-resolution Ion MicroProbe (SHRIMP) at the Geological Survey of Canada in Ottawa. SHRIMP analytical procedures followed those described by Stern (1997), with standards and U-Pb calibration methods following Stern and Amelin (2003). The internal features of the zircons (such as zoning, structures, alteration, etc.) were characterized in back-scattered electron mode (BSE), utilizing a Zeiss Evo 50 scanning electron microscope. Analyses were carried out over three separate analytical sessions and details related to the analytical conditions and calibration parameters for each session are listed in the footnotes to Table 1. Analyses of secondary standard z1242 were interspersed through the analytical sessions and the measured mean 207Pb/206Pb age compared with the accepted age determined by thermal ionization mass spectrometry (2679.7 Ma, B. Davis, pers. comm., 2009). Isoplot v. 3.66 (Ludwig, 2003) was used to generate concordia plots and calculate weighted means. All errors reported in the text are given at the 2σ uncertainty level. Isotopic ratios and ages in Table 1 are given at 1σ uncertainty. AgeDisplay (Sircombe, 2004) was used to generate probability density diagrams. Sm-Nd analytical work was carried out at the University of Alberta. Sample preparation, dissolution, and chemical procedures followed those outlined by Creaser et al. (1997) and Unterschutz et al. (2002). Chemical processing blanks were