geology and extent of the archean swan river complex in ... · which intruded the swan river...

Saskatchewan Geological Survey 1 Summary of Investigations 2003, Volume 2

Geology and Extent of the Archean Swan River Complex in the Patterson Island Area (part of NTS 64E-10), Peter Lake Domain,

Northern Saskatchewan

Ralf O. Maxeiner and Shawna M. Leatherdale 1

Maxeiner, R.O. and Leatherdale, S.M. (2003): Geology and extent of the Archean Swan River Complex in the Patterson Island area (part of NTS 64E-10), Peter Lake Domain, northern Saskatchewan; in Summary of Investigations 2003, Volume 2, Saskatchewan Geological Survey, Sask. Industry Resources, Misc. Rep. 2003-4.2, CD-ROM, Paper A-6, 17p.

Abstract A geological transect at 1:20 000 scale was mapped across the southeast margin of the Peter Lake Domain along the west shore of Reindeer Lake, encompassing part of the 2.562 Ga Swan River Complex. It is less extensive than indicated by previous workers and is intruded by large masses of monzonitic to granitic rocks. The Swan River Complex intruded subordinate mafic to felsic volcanic and migmatitic sedimentary rocks that were metamorphosed at upper amphibolite facies metamorphic grade during Neoarchean times. It comprises two distinct intrusive suites: an older and more deformed and recrystallized gabbroic suite and a younger leucogabbroic suite. These are correlated respectively with the Warner Lake gabbroic suite and the Love Lake leucogabbroic suite in the southwestern part of the Peter Lake Domain. Both have well-preserved primary igneous features common in other layered intrusions, including modal rhythmic layering, cross-bedded layering, colliform layering and layered autoliths. The Lueaza River granitoid, which is closely associated and similar in age to the Warner Lake gabbroic suite of the Swan River Complex, is characterized by foliated megacrystic monzogranite and dioritic to granitic orthogneisses. The Patterson Island Pluton forms part of a larger and more extensive monzonitic-syenitic suite, which intruded the Swan River Complex and is here tentatively correlated with the 2.54 Ga monzonitic intrusion in the Peter Lake area. The pluton consists of an outer megacrystic monzonite phase and an inner megacrystic syenite phase. Both phases have primary igneous layering preserved and grade locally into minor gabbro and leucogabbro. Massive to weakly foliated syenogranite to alkali feldspar granite of unknown age intruded most of the previous lithologies. Some of the granitoid rocks may be Archean; others may be related to the 1.86 Ga Wathaman Batholith, which underlies the southeastern portion of the transect. Two new sulphide occurrences were discovered near the ‘Ant’ Cu-Ni-Pt-Pd showing.

Keywords: Archean, igneous layering, gabbro, leucogabbro, monzonite, syenite, Swan River Complex, Peter Lake Domain, Patterson Island Pluton, Wathaman Batholith.

1. Introduction The Peter Lake Domain mapping project commenced in 2002 with a geological transect along Highway 905, from the Wathaman Batholith into the Wollaston Domain (Maxeiner and Hunter, 2002; Figure 1).

That work identified two distinct suites of mafic intrusive rocks in the extension of the Swan River Complex. Both are cut by later monzonitic and granitic intrusions: the Warner Lake gabbroic suite having components with above-background Cu, Ni, Cr, Pt and Pd; and the Love Lake leucogabbroic suite, that although sulphide-bearing lacks above-background PGEs.

Three episodes of deformation and at least two metamorphic events, including one upper amphibolite facies Archean event, characterized the structural history of the Peter Lake Domain. Recently determined age dates further constrain the thermotectonic history. A preliminary U-Pb zircon age of 2540 ±1 Ma was obtained from a megacrystic monzonite that intrudes upper amphibolite facies migmatitic psammopelites and the Warner Lake gabbroic suite (Heaman et al., this volume).

This year’s mapping covered parts of the Wathaman Batholith near McLean Channel on Reindeer Lake and extended as far as the north end of Pearce Lake in the interior of the Peter Lake Domain (Figure 1). Janet Campbell (this volume) investigated the Quaternary geology. Saskatchewan Industry and Resources in partnership with the

1 Department of Geological Sciences, University of Saskatchewan, 114 Science Place, Saskatoon, SK S7N 5E2.


Geological Survey of Canada began an airborne geophysical survey, and David Corrigan and Nicole Rayner of the Geological Survey of Canada began geochronological investigations.

The Patterson Island area was previously mapped by Stauffer et al. (1981), MacDougall (1988) and Corrigan (2001) and is covered by a regional compilation at 1:250 000 scale (Macdonald and Thomas, 1983). Key findings of this year's work are: the Swan River Complex is less extensive and more heterogeneous than suggested by previous authors (e.g. Stauffer et al., 1981); the primary igneous textures within the Swan River Complex rival those of other layered intrusions in the world; minor screens of Archean high-grade mafic to felsic volcanic rocks and sedimentary rocks are present within the gabbroic complex; the Parker Lake gneisses and a heterogeneous high-strain zone are present along the southeast margin of the domain at least as far as Patterson Island; and Archean monzonitic and quartz-monzonitic rocks are abundant.

Two new mineral occurrences were discovered near the Ant showings (SIR Assessment Files 64E-0008 and 64E10-NE-009R). Assessment of the PGE potential and other metals awaits geochemical analyses.

2. Updated Regional Geological Framework

The Peter Lake Domain is largely Archean (2.54 to

2.63 Ga) and has been subdivided by earlier workers (Figure 2) into the Peter Lake Complex (Lewry et al., 1980; Ray and Wanless, 1980), Parker Lake Gneisses (Ray, 1975), and Campbell River Group (Lewry, 1976; Lewry et al., 1980). In the southwest, the domain is bounded by the Needle Falls and Parker Lake shear zones both of which die out towards the northeast. On Reindeer Lake, the domain boundary is the intrusive contact of the partly megacrystic 1.86 Ga Wathaman Batholith (Ray and Wanless, 1980; Corrigan et al., 2000, 2001; Corrigan, 2001). In the Cook Lake area, approximately 30 km to the northeast of Highway 905, the northern flank of the domain is unconformably overlain by feldspathic psammite, cobble conglomerate, and mafic volcanic rocks of the Paleoproterozoic Courtenay Lake Formation (Delaney et al., 1997; MacNeil et al., 1997) of the Wollaston Supergroup (Yeo et al., in prep.).

Figure 3 summarizes geochronological data for the Peter Lake Domain. The Peter Lake Complex, the largest component of the Peter Lake Domain, is a very heterogeneous, predominantly plutonic assemblage. It was first defined as comprising two plutonic suites, an older dioritic to gabbroic suite and a younger syenogranitic to monzogranitic suite (e.g. Ray and Wanless, 1980). Major felsic plutonism in the Peter Lake Complex is constrained

Figure 1 - Main geological subdivisions of the Peter Lake Domain. Note that all rocks listed in legend have been metamorphosed.


Figure 2 - Chart showing the major subdivisions of the Peter Lake Domain as distinguished by various workers.

to 2580 to 2540 Ma (Ray and Wanless, 1980; Bickford et al., 1986; Annesley et al., 1992; Rayner et al., in review; Heaman et al., this volume).

Later workers have further subdivided the Peter Lake Complex (Figure 2). The Lueaza River granitoid rocks, comprising granite, granodiorite, and granitic gneisses, represent a large component of the Peter Lake Complex on Reindeer Lake. Corrigan et al. (2000) separated them into migmatized granitic to granodioritic orthogneisses, minor paragneisses, and non-migmatized felsic granitoid rocks. Pink granitic gneiss, that intruded older grey gneiss from the Lueaza River granitoids, yielded complex geochronological results, giving U-Pb zircon ages between 2580 ±4 Ma and 2629 ±10 Ma, the oldest dates for the domain obtained so far (Bickford et al., 2002; Rayner et al., in review). There is also evidence for a second generation of zircon growth between 2590 to 2560 Ma and a lower intercept age of 1800 Ma without corresponding zircon growth.

On Reindeer Lake, Corrigan (2001) interpreted minor units of mafic volcanic rocks to be the oldest component of the Peter Lake Complex (Figure 2), in agreement with observations by others (Lewry et al., 1980; Ray and Wanless, 1980; MacDougall, 1988; Maxeiner and Hunter, 2002). Corrigan (2001) defined the Swan River Complex (Swan River gabbroic rocks of Stauffer et al., 1981), as a separate suite intruding the Peter Lake Complex (Corrigan et al., 2000) and including undersaturated syenitic to monzonitic intrusives such as the Patterson Island Pluton (MacDougall, 1988). A 2562 ±4 Ma U-Pb zircon age (Corrigan et al., 2001) from the Swan River Complex on Reindeer Lake gave a precise age for mafic plutonism in the Peter Lake Domain. Previously, a sample of gabbro pegmatite obtained from the shore of Reindeer Lake southwest of Crane Island provided a U-Pb zircon age of 1908 ±27 Ma (Bickford et al., 1987).

Present work shows the Swan River Complex comprises two distinct gabbroic suites (Figure 2): a strongly recrystallized and foliated suite of upper amphibolite-facies dioritic to gabbroic rocks having locally well preserved igneous layering (the Warner Lake gabbroic suite), and a probably younger suite of homogeneous, massive to weakly foliated and little recrystallized leucocratic gabbronorite and gabbro, orthopyroxene gabbro, clinopyroxene gabbro, anorthosite, and pyroxenite (the Love Lake leucogabbroic suite). Both suites, first described in the Highway 905 transect (Maxeiner and Hunter, 2002), are recognized in the Reindeer Lake area, where they are intruded by


Figure 3 - Summary of previous U-Pb geochronological results for the Peter Lake Domain; modified after Maxeiner and Hunter (2002).

megacrystic monzonite and syenite of the Patterson Island Pluton. The monzonitic component of the Patterson Island Pluton bears a strong resemblance to the 2.54 Ga monzonitic intrusive suite documented in the Peter Lake area (Maxeiner and Hunter, 2002; Heaman et al., this volume)

The Parker Lake gneisses (Ray, 1975), subparallel to the Needle Falls and Parker Lake shear zones, are strongly foliated and sheared mafic to felsic rocks interpreted as sheared equivalents of the Peter Lake Complex (Lewry et al., 1980; Macdonald and Thomas, 1983). They are less extensive than previously assumed (Maxeiner and Hunter, 2002). Mylonitic megacrystic quartz monzonite (unit PGd of Maxeiner and Hunter, 2002) from the Parker Lake gneisses gave a U-Pb zircon age of 2566 ±8 Ma (Rayner et al., in review), similar to the previously determined age of felsic plutonism for the Peter Lake Complex (Figures 2 and 3).

The Campbell River Group (Lewry, 1976; Lewry et al., 1980; MacDougall, 1987) is a narrow, synformal, northeast-trending, upper greenschist to lower amphibolite facies supracrustal belt northwest of Spalding Lake. Outliers flank Highway 905 (Maxeiner and Hunter, 2002; Hunter, 2003). Lewry et al.(1980) suggested that the Campbell River Group is Archean on the basis of xenoliths that resemble rocks from the Campbell River Group in


Peter Lake Complex diorite (Lewry et al., 1980; Macdonald and Thomas, 1983). This conclusion is contradicted, however, as the Campbell River Group was not affected by the 2.55 Ga high-grade metamorphic event (Maxeiner and Hunter, 2002) that affected the Peter Lake Complex.

Quartz monzonite, southwest of Peter Lake (unit AGr of Maxeiner and Hunter, 2002) yielded an age of 2529 ±4 Ma from titanite of presumed igneous origin (Annesley et al., 1992). The date was interpreted by Maxeiner and Hunter (2002) to represent a late Archean high-grade metamorphic event, consistent with second generation zircon growth dated between ca. 2.59 to 2.56 Ga (Rayner et al., in review) and with a high-grade metamorphic event dated between 2.55 to 2.50 Ga elsewhere in the Hearne Craton (Davis et al., 2000).

Foliated syenogranite from the northwest margin of the domain gave an age of 2086 +52/-8 Ma (Annesley et al., 1992). Feldspar megacrystic syenogranite of the Wathaman Batholith that intrudes the southeastern margin of the Peter Lake Domain on Reindeer Lake yielded a U-Pb zircon age of 1861 +3/-2 Ma (Corrigan et al., 2001).

Titanite and lower intercept ages for the felsic granitoid rocks range between 1830 and 1800 Ma, probably a result of the thermotectonic overprint of the Trans-Hudson orogeny. Growth of titanite suggests that at least lower amphibolite facies conditions were attained during the Trans-Hudson orogenic event. Rayner et al. (in review), however, find no evidence of Paleoproterozoic zircon growth in their Peter Lake Domain samples, concluding that metamorphic grades remained below upper amphibolite facies conditions.

3. Results from Field Work Mapping was carried out by a five-person crew between the beginning of July and the end of August 2003. Access was provided by inflatable boats from Reindeer Lake, and canoes on smaller lakes. Low water levels insured excellent lakeshore exposures and outcrops in the northern half of the map area have been completely cleared of vegetation by recent forest fires

Local Geology The present work has recognized the following subdivisions of the Peter Lake Domain (Figure 2 and 4):

• Archean supracrustal rocks; • Lueaza River granitoid suite (revamped ‘Lueaza River granitoids’ of Stauffer et al., 1981); • Swan River Complex (comprising the Warner Lake gabbroic and the Love Lake leucogabbroic suites); • Patterson Island monzonite-syenite suite; • Campbell River Group (not present in the Patterson Island area); • a younger granitic suite; • Parker Lake gneisses; and • Wathaman Batholith.

Archean Supracrustal Rocks (units with prefix A)

The majority of rock units in the Patterson Island area are of plutonic origin (Figure 4), however, several thin keels of mafic, intermediate, and felsic volcanic rocks 2, as well as psammopelitic to pelitic 3 migmatite are in the Swan River Complex.

Mafic Volcanic Rock 4

A north- to northwest-dipping unit of mafic volcanic rocks is exposed in an unnamed bay west of Wiley Bay southwest of Patterson Island and can be traced westward for several kilometres. Metamorphic grade increases from upper amphibolite facies to lower granulite facies along strike from southwest to northeast, as shown by changes in

2 The prefix ‘meta-’ is not used, as all of the rocks have been metamorphosed at greenschist to amphibolite facies. 3 Classification of clastic sedimentary rocks follows the recommendations of Maxeiner et al. (1999). 4 Only selected units and important observations and relationships are described in detail in this paper. For comprehensive and systematic descriptions of all units, the reader is referred to the legends of the accompanying maps.


Figure 4 - Simplified geological map of the Patterson Island area.


the mineralogy and increases in prevalence of leucosome. It comprises four main lithologic subunits, from structural base to top.

1) The most extensive subunit is a fine-grained, heterogeneous, strongly foliated hornblende-plagioclase rock characterized by colour patterns and structures interpreted as deformed pillows (Figure 5). Local centimetre-scale gradational patches of dioritic leucosome contain coarse hornblende, diopside, and cummingtonite after orthopyroxene. Towards the west, this subunit is characterized by local occurrence of abundant garnet and absence of leucosome.

2) A fine-grained, homogeneous plagioclase-porphyritic mafic rock intruded subunit (1), but has also been affected by partial melting.

3) An eight metre thick subunit of fine- to medium-grained, pale brown-weathering, Mg-rich ultramafic rock characterized by fine-grained tremolite, serpentine, phlogopite, talc and magnetite, and relict olivine, is interpreted as a former peridotitic sill.

4) An eight metre thick subunit of fine-grained, pale green- to dusky green-weathering homogeneous ultramafic rock composed of actinolitic tremolite, spinel, magnetite, and relict olivine, is interpreted as another, more Fe-rich ultramafic sill.

Intermediate Volcanogenic Rock

Intermediate volcanogenic rocks occur as xenoliths and minor units along the northwestern edge of the Patterson Island pluton and in the Love Lake leucogabbroic suite. Three distinct phases of intermediate rocks are present:

1) Grey, fine-grained, laminated ash tuff or calcic psammopelite. It grades locally into mafic compositions characterized by a weak layer-parallel tectonic foliation (S1). Decimeter- to metre-sized xenoliths of it occur in the surrounding syenitic rocks which post-date the S1-foliation, but possess a later fabric (S2).

2) Massive to weakly foliated plagioclase-porphyritic amygdaloidal andesite (Figure 6) that intrudes the laminated rock. Amygdales up to two centimetres in diameter are filled with carbonate, epidote, and/or amphibole. Xenoliths of the porphyritic andesite are in the Love Lake leucogabbroic suite and therefore predate the ca. 2.56 Ga Swan River Complex.

3) Minor intermediate tuff-breccias, containing felsic volcanic clasts in an intermediate hornblendic matrix.

Felsic Volcanogenic Rock

A relatively extensive unit of felsic volcanogenic rocks approximately 30 m thick is traceable for about 4 km along the north edge of one of the Warner Lake gabbroic bodies north of Patterson Island. It comprises a predominant heterogeneous rhyolitic tuff breccia, flow banded rhyolite and a 10 m wide central subunit of migmatitic pelite. The breccia is characterized by strongly flattened lapilli- to bomb-sized subangular fragments of massive to laminated, very fine-grained, light pinkish rhyolite, set in a biotite-rich psammopelitic matrix. Subhedral quartz eyes are in a few fragments. Fine-grained melanocratic clasts are a less common constituent. Some centimetre-scale layering in the rhyolite may represent flow-banding; this is locally crenulated with axial planar biotite (S2) overprinting the layering and layer-parallel S1 fabric

Figure 5 - Possible deformed pillow basalt; west of Wiley Bay; Station 18-16-1; UTM-E: 638444; UTM-N: 6388674 1.

Figure 6 - Plagioclase porphyritic amygdaloidal andesite; west side of ‘Patterson Channel’; Station 13-1-5; UTM-E: 638570; UTM-N: 639317.


(Figure 7). Fine-grained intermediate andesitic dykes cut the rhyolite at low angles.

Migmatitic Psammopelite

The upper amphibolite facies migmatitic pelite subunit sandwiched between the heterogeneous rhyolitic tuff breccia and flow banded rhyolite is a strongly foliated quartzofeldspathic rock containing abundant biotite, garnet and sillimanite, and tonalitic leucosome with biotite-rich melanosome selvages.

A separate and more extensive 50 m thick unit of migmatitic psammopelite associated with the Wiley Bay mafic volcanic rocks is traceable for about 4 km. It comprises partly layered, medium grey, fine-grained psammopelitic and psammitic rocks. Aluminosilicate mineral content (including biotite and up to 5 percent garnet) ranges between 5 and 25 percent5. Gneissosity is created by layer-parallel tonalitic leucosome. Both gneissic layering and bedding are cut by phases of the Warner Lake gabbroic suite (Figure 8).

Lueaza River Granitoid Suite (units with prefix R)

The Lueaza River granitoids (Stauffer et al., 1981) are here reinterpreted to comprise mostly megacrystic monzogranite6; some phases merge in the southwest into the Ettle Creek granite (Macdonald and Thomas, 1983). The monzogranite is light pink- to pink-weathering, coarse- to very coarse-grained, inequigranular and weakly to strongly foliated. Megacrysts are mostly 1 to 3 cm long microcline, and compose 30 to 40 percent of the rock. Locally, smaller white to light grey plagioclase porphyroblasts are common. Mafic mineral content varies between 10 and 15 percent, biotite predominating over lesser variable amounts of hornblende, magnetite, and titanite. Moderately to strongly foliated varieties have an augen texture.

Age relationships between the Lueaza River monzogranite and the Swan River Complex are unclear. Dioritic and gabbroic xenoliths are widespread in the augen monzogranite, and it is intruded by narrow, partly feldspar-phyric mafic dykes. Conversely, granitoid xenoliths are generally absent from the Swan River Complex, but granitic intrusions are common. The close relationship of the megacrystic monzogranite with the Warner Lake gabbroic suite of the Swan River Complex suggests that they are temporally related. Syenogranite (see below) and fine-grained aplitic dykes intruded and clearly post-date the megacrystic monzogranite.

Strongly deformed and mixed dioritic to granitic orthogneisses form a distinct component of the Lueaza River granitic suite at the south end of Pearce Lake. They are characterized by protomylonitic to ultramylonitic foliates (Ashton and Leclair, 1990) and gneisses of alkali feldspar granite (Figure 9), porphyroblastic monzogranite, diorite (Figure 10), amphibolitized mafic dykes, granodiorite, and monzonite interlayered on a scale of metres to tens of metres. Locally, interlayering is on a centimetre scale. The age of shearing is ambiguous, but post-dates at least in part the emplacement of the syenogranitic suite.

5 Mineral percentages were estimated in the field and some of the lithologies were later verified with the help of a petrographic microscope. 6 All rock names for intrusive rocks follow Streckeisen’s (1976) recommendations on the classification of plutonic rocks.

Figure 7 - Andesitic dyke cutting folded flow-banded rhyolite and overprinted by axial planar biotite; bay north of Patterson Island; Station 28-3-3; UTM-E: 642198; UTM-N: 6399256.

Figure 8 - Gabbro cutting gneissic layering and bedding in psammite; west of Wiley Bay; Station 7-3-2; UTM-E: 637944; UTM-N: 6389209.


Swan River Complex

Warner Lake Gabbroic Suite (units with prefix W)

This unit was first described in the Peter Lake area (Maxeiner and Hunter, 2002), where it is between the Love Lake leucogabbro and the Parker Lake shear zone and consists of several highly flattened, largely recrystallized dioritic to gabbroic intrusions, extensively invaded by monzonitic and later granitic intrusive suites. Igneous layering is locally preserved. The intrusion is interpreted as an older component of the Swan River Complex.

Units of gabbro and diorite, located between a homogeneous, massive leucogabbro and the Wathaman Batholith (Figure 4) in the present map area is massive to weakly foliated and extensively recrystallized, but preserves some of the best igneous layering of the entire area.

The gabbroic component is greenish black or mottled black and white, medium to coarse grained, and massive to moderately foliated. Mafic mineral content generally varies between 35 and 50 percent though there are local melagabbroic, pyroxenitic, and anorthositic phases. Metamorphic hornblende generally has replaced the primary ferromagnesian minerals and was subsequently replaced by biotite. Plagioclase was strongly sericitized. Accessory minerals include epidote, magnetite, pyrite, and titanite. The gabbro is generally homogeneous, equigranular, granoblastic and locally hornblende porphyroblastic. Relict ophitic to subophitic textures (Figure 11) occur locally. Secondary textures include pyroxene replacement by hornblende, porphyroblastic hornblende, acicular amphibole overgrowing rhythmic layering (Figure 13), strong sericitization of plagioclase, and new growth of Na-rich plagioclase.

Spectacular primary layering is preserved in many places and stratigraphic up or, as is the case in layered intrusions, the centre of the pluton, can often be reconstructed. Weak rhythmic layering (Figure 13; see photos for detailed descriptions); colliform layering (Figure 12) defined by convex inward layers with outward pointing cusps as described at the Skaergaard intrusion (Irvine et al., 1998); rhythmic zebra layering (Figure 13), and trough cross-bedding (Figure 14) are all represented. Adjacent ‘way-in indicators’ commonly vary in orientation indicating that the Warner Lake gabbroic suite has been affected by early folding.

Diorite is a mottled black and white rock, medium to coarse grained, homogeneous, equigranular, and massive to weakly foliated. Fine-grained ‘salt and pepper’ textured diorite and microdiorite form local variants. Mafic minerals (20 and 35 percent) include hornblende, epidote and biotite, and accessory magnetite, pyrite, and titanite.

The Warner Lake gabbroic suite intrudes upper amphibolite facies mafic volcanic rocks and migmatitic psammopelite to pelite. The dioritic and gabbroic

Figure 9 - Ultramylonitic granite; south end of Pearce Lake; Station 22-2-3; UTM-E: 634506; UTM-N: 6400090.

Figure 10 - Mylonitic diorite-granite gneiss; south end of Pearce Lake; Station 3-15-2; UTM-E: 633120; UTM-N: 6398295.

Figure 11 - Relict ophitic texture in Warner Lake gabbro; northeast of Porter Bay; Station 8-19-2; UTM-E: 637087; UTM-N: 6399359.


components are themselves locally invaded by coarse-grained tonalite some possibly derived by in situ melting. In general, the dioritic components postdate the gabbroic ones. Both were intruded by later monzonitic and syenogranitic units. The Wathaman Batholith encloses and intrudes large screens of Warner Lake gabbro and contains smaller xenoliths of gabbro that show rhythmic zebra layering (Figure 15). One of the gabbroic screens displays autoliths of rhythmically layered diorite-anorthosite (Figure 16).

Love Lake Leucogabbroic Suite (units with prefix L)

The Love Lake leucogabbroic suite was first described in the ‘Love’ Lake area south of Peter Lake at the southwestern end of the domain (Maxeiner and Hunter, 2002; Leatherdale et al., this volume). In that area, the Love Lake leucogabbroic bodies differ from the Warner Lake gabbroic bodies in being less flattened in shape and having preserved relict igneous minerals

Figure 12 - Colliform layering defined by convex inward layers with outward pointing cusps suggests that the interior of the intrusion is at the bottom of the picture, (i.e. towards the west); west side of Patterson Island; Station 13-14-7; UTM-E: 639330; UTM-N: 639384.

Figure 13 - Spectacular rhythmic zebra layering defined by changes in modal content; secondary acicular amphibole post-dates layering; west side of Patterson Island; Station 13-14-1; UTM-E: 639330; UTM-N: 639384.

Figure 14 - Cross-bedded igneous layering (formed near the bottom of a magma chamber, where increased fluid shear stress (a function of velocity and pressure in the magma chamber) within the intrusion causes rhythmically layered dunes and scours. The interior of the pluton is to the top of the picture. Another world-class example of primary layering, rivaling those seen in the ‘cross-bedded belt’ of the Skaergaard Intrusion (Irvine et al., 1998); west side of small bay north of Patterson Island; Station 28-8-2; UTM-E: 642166; UTM-N: 6398924.

Figure 15 - Rhythmically layered gabbro xenolith in Wathaman Batholith quartz monzonite; Rocky Island area; Station SL26-10-1; UTM-E: 648142; UTM-N: 6398523.


including orthopyroxene and clinopyroxene. In the Patterson Island area, the Love Lake leucogabbro comprises two separate plutons; a large one southeast of ‘Ant’ Lake and a smaller one 7 km northeast of Swan River.

The larger pluton west of Patterson Channel, comprises leucogabbro (possibly a gabbronorite), gabbro, microgabbro, minor pyroxenite, and anorthosite. These intruded intermediate volcanic rocks and are intruded by the partly megacrystic monzonitic phase of the Patterson Island Pluton and granitic pegmatite dykes.

The main leucogabbro phase weathers a characteristic mottled light bluish grey to greenish black, is medium to coarse grained, homogenous, equigranular and massive to weakly foliated. Mafic mineral content (15 to 35 percent) is dominated by hornblende, actinolite, relict pyroxene, biotite, epidote and magnetite, and accessory ilmenite, pyrite, and chalcopyrite. Pyroxene has been replaced by actinolite and hornblende leaving relict cores of pyroxene. Hornblende in turn was partially replaced by biotite and epidote fills relatively late fractures. Coarse tabular calcic plagioclase shows little sign of recrystallization or sericitization. Plagioclase composition (An50) confirms the gabbroic to anorthositic nature of these rocks despite their low mafic mineral content. Locally, abundant xenoliths include mafic and intermediate volcanic rocks, porphyritic andesite, and hornblende-porphyroblastic gabbroic rocks (Figure 17). Xenoliths are angular to subrounded, up to 50 cm in diameter and have a tectonic fabric that predates emplacement of the pluton. The leucogabbro also has many examples of igneous layering. Centimetre to decimeter-scale rhythmic layering consists of repeated thin anorthositic and thicker gabbro layers (Figure 18).

A smaller pluton of leucogabbro occurs at the southwest corner of the map near McLean Channel. It is also massive to weakly foliated, but less magnetic and primary features were not observed.

Monzonite-Syenite Suite, Including the Patterson Island Pluton (units with prefix M)

Monzonitic rocks, dated at approximately 2.54 Ga (Heaman et al., this volume), were also recognized in the Peter Lake area (Maxeiner and Hunter, 2002) and termed the monzonitic intrusive suite. The Patterson Island Pluton, comprises an outer monzonitic phase and an inner syenitic phase.

Monzonitic Phase

Monzonite forms the marginal phase of the Patterson Island pluton, and intruded dioritic and gabbroic rocks of the Swan River Complex, and next to granitoid rocks represents one of the most pervasive units. Locally, monzonite grades into monzodiorite, diorite and gabbro, and in part these rocks are interlayered.

Figure 16 - Autoliths of a rhythmically layered gabbro-anorthosite within a homogeneous Warner Lake gabbro screen in Wathaman Batholith quartz monzonite; west shore of Reindeer Lake, east of Wiley Bay; Station 21-7-6; UTM-E: 640233; UTM-N: 6383430.

Figure 17 - Compositionally and texturally variable foliated xenoliths within the Love Lake leucogabbroic suite; south of ‘Ant’ Lake; Station 16-10-3; UTM-E: 634367; UTM-N: 6391059.

Figure 18 - Poorly defined rhythmic modal layering in the Love Lake leucogabbroic suite; south of ‘Ant’ Lake; Station 11-25-1; UTM-E: 634596; UTM-N: 6391320.


The monzonite is light grey to light pink, medium to coarse grained, homogeneous, equigranular to more commonly megacrystic, and massive to weakly foliated. Mafic mineral content ranges from 15 to 25 percent and includes abundant hornblende, biotite and epidote, minor carbonate, and variable amounts of magnetite. Megacrystic varieties are characterized by 2 to 3 cm grey to pink perthitic K-feldspars (Figure 19).

Along the northeast shore of Patterson Island and elsewhere, the monzonitic rocks contain thin layers of pyroxenite, diorite, and gabbro. This cumulate igneous layering is not only defined by changes in modal composition, but also by distinct changes in composition and grain size (Figure 20). Layering in this locality is overprinted at a low angle by a weak northwest-dipping tectonic foliation. A later northwest-trending set of mafic dykes cut the layered succession and are sheared parallel to the trend of the dyke emplacement (Figure 21). Xenoliths a few centimetres to metres long, usually tectonically flattened, are abundant throughout this unit. In a few examples xenoliths with internal xenoliths were observed.

Syenitic Phase

The oval central syenitic part of the Patterson Island Pluton (Figure 4) has a unique and distinctive grey to violet-grey colour and coarse-grained megacrystic texture. Grey to light pink K-feldspar megacrysts, up to 5 cm long, account for 40 to 70 percent of the rock (Figure 22). The matrix consists of plagioclase, hornblende, biotite, abundant magnetite, and minor carbonate. Mafic mineral content is about 20 percent. The syenite is interlayered in places on an outcrop and map scale with leucogabbro and gabbro, which contain relict augite crystals rimmed by hornblende. In the west side of Patterson Island, megacrystic syenite is rhythmically interlayered with thin leucogabbroic layers. The layering is partially interrupted by fine- to medium-grained inclusions (possibly autoliths) of equigranular syenitic rocks up to 10 by 40 cm in maximum dimensions, flattened at a low angle to the igneous layering (Figure 23). A heterogeneous syenite unit along the east shore of Patterson Island, containing abundant inclusions, multiple mafic dykes and erratic megacryst content is regarded as a separate phase of the Patterson Island Pluton (Figure 4). One outcrop in this heterogeneous syenite revealed three generations of cross-cutting mafic dykes (Figure 24). Early, zoned ultramafic-mafic dykes parallel the foliation or are transposed within it. These are cut by heterogeneous mafic dykes containing xenoliths of a more mafic fine-grained rock (possibly the previous dyke generation). The youngest dykes are aplitic.

The leucogabbroic and gabbroic components in the syenitic rocks of the Patterson Island Pluton resemble in many respects the rocks of the Love Lake leucogabbroic suite. Both have large, relatively fresh, plagioclase crystals, cores of variably amphibolitized pyroxenes, and abundant magnetite. It is possible that the syenitic rocks of the Patterson Island Pluton

Figure 19 - Perthitic K-feldspar megacrysts in monzonite; northeast side of Patterson Island; Station 9-4-1; UTM-E: 642099; UTM-N: 6394625.

Figure 20 - Layers of cumulate megacrystic monzonite, pyroxenite and gabbro; northeast side of Patterson Island; Station 9-17-1; UTM-E: 641923; UTM-N: 6394970.

Figure 21 - Mafic dykes cross-cutting igneous layering at a high angle; dykes are sheared parallel to their emplacement direction; northeast side of Patterson Island; Station 9-17-3; UTM-E: 641923; UTM-N: 6394970.


crystallized from the same basaltic magma as the Love Lake leucogabbroic suite, albeit at a slightly later stage.

Late Syenogranite to Granite

A suite of relatively late syenogranite to alkali feldspar granite intruded all of the previously described rocks of the Peter Lake Domain. One contact between syenogranite and Warner Lake gabbro north of Patterson Island, however, suggests immiscibility of co-existing melts representing the two rather than intrusion.

These intrusions are abundant in the northern half of the domain (see also Maxeiner and Hunter, 2002). It accounts for approximately 20 percent of the bedrock in the Patterson Island area. The syenogranite is pink to brick red, coarse to very coarse grained, homogeneous, equigranular and massive to weakly foliated. Mafic minerals (5 to 10 percent) comprise biotite, magnetite and titanite, with or without hornblende, and chlorite.

Parker Lake Gneisses (units with prefix P)

Even at 1:20 000 scale, certain outcrops were geologically too complex and were lumped into a map unit of Parker Lake gneisses, which represent strongly deformed and transposed rocks of the Swan River Complex, Monzonite-syenite suite, Syenogranitic suite, and the Wathaman Batholith. The rocks are strongly foliated to sheared, compositionally heterogeneous, and include granodiorite, granite, monzonite, and quartz-diorite to diorite. They also contain distinct intrusive layers of strongly deformed and transposed augened quartz-monzonite related to the Wathaman Batholith.

The Southeast Margin of the Peter Lake Domain: The Wathaman Batholith and Parker Lake Shear Zone

Quartz-monzonite, monzonite, and granodiorite of the 1855 Ma Wathaman Batholith intruded the southeast margin of the Peter Lake Domain. Strain is heterogeneous throughout this part of the batholith: high-strain zones several metres to tens of metres wide are common and likely represent a more diffuse extension of the dextral Parker Lake shear zone (LaFrance and Varga, 1996).

The quartz-monzonite is light pink to white, coarse to very coarse grained and commonly megacrystic with up to 5 cm long pink microcline megacrysts (Figure 25), that can account for 20 to 30 percent of the rock. Quartz content varies between 5 and 10 percent and mafic minerals, including biotite, hornblende and epidote, vary between 15 and 20 percent. Accessory minerals include magnetite, titanite, and allanite. Late cross-cutting granite pegmatite dykes contain larger crystals of allanite. Locally, these are cumulate layers of microcline megacrysts (Figure 26).

Figure 22 - Typical violet-grey-weathering megacrystic syenite of the central phase of the Patterson Island pluton; east side of Patterson Island; Station 15-24-2; UTM-E: 640712; UTM-N: 6392139.

Figure 23 - Fine-grained grey syenitic inclusions, flattened at a low angle to igneous layering; west side of Patterson Island; Station 13-7-1; UTM-E: 638800; UTM-N: 6391475.

Figure 24 - Two generations of mafic dykes intruding megacrystic monzonite; all rocks are overprinted by steeply west-dipping foliation; small island southeast side of Patterson Island; Station 21-14-1; UTM-E: 641429; UTM-N: 6392440.


Discontinuous sheets of diorite and gabbro in the northwest margin of the batholith (Figure 15) represent rafts of the Swan River Complex.

4. Economic Geology Three mineral occurrences are known in the Patterson Island area, two Cu-Ni-Pt-Pd showings (Ant and Antoine) hosted in gabbroic rocks of the Swan River Complex and a Cu-showing (Wiley Bay) hosted in mafic volcanic rocks (SMDIs 2373, 2374, and 569). The Ant and Antoine showings are among the best PGE occurrences in the Peter Lake Domain on record (SIR Assessment File 64E10-NE-009R). Two additional sulphide occurrences were discovered during mapping near the ‘Ant’ Lake showing. Analyses from grab samples are not yet available.

a) The ‘Ant’ Lake Cu-Ni-Pt-Pd Showing (SMDI 2373)

Discovered in 1985 by Lacana Exploration Inc., this showing returned up to 1% Cu and up to 250 ppb Pt plus Pd (SIR Assessment File 64E-0008). The two trenches at the ‘Ant’ Lake showing that were visited are within 10 m of each other and trend at 100°. They are in a relatively homogeneous and massive, yet strongly amphibolitized part of the Love Lake leucogabbroic suite. The gabbro contains less than 5 percent disseminated or in part fracture-bound pyrite, pyrrhotite, and chalcopyrite.

b) The Antoine Cu-Ni-Pt-Pd Showing (SMDI 2374)

This showing was also discovered by Lacana Exploration Inc. in 1985 and trench samples returned values of up to 1.5% Cu, up to 4910 ppb Pd, and 477 ppb Pt (SIR Assessment Files 64E-0008 and -0009). The one Antoine showing trench that was located, trends at 190°. It is in an isolated unit of gabbroic rocks, completely surrounded by heterogeneous, xenolith-rich monzonitic rocks related to the Patterson Island Pluton. The gabbro, containing approximately 50 percent mafic minerals is mottled black and white to rusty brown, coarse grained, relatively homogeneous and massive. Pyrite and chalcopyrite (less than 5 percent) are disseminated and fracture-controlled.

c) New Sulphide Occurrences Two additional sulphide occurrences were located near the Ant trenches; one is 300 m to the southeast and the other about 200 m to the southwest. Both occur in the Love Lake leucogabbroic suite within 10 m of recognizable rhythmic layering and contain about 5 percent combined disseminated and fracture-bound sulphides, comprising (in order of decreasing abundance) pyrite, chalcopyrite, and pyrrhotite. Several percent magnetite and hematite are also present. The sulphides appear to be restricted to a few square metres.

5. Thermotectonic History and Discussion Based on this year’s mapping and on one new age constraint, the thermotectonic synthesis (see Maxeiner and Hunter, 2002) of the Peter Lake Domain is refined (Figure 27).

An early fabric (S1) related to a deformation event predating the emplacement of the Warner Lake gabbroic suite is recognized. The main tectonic fabric in the area is likely a composite fabric of S2 and S3, with S3 being the overprint related to the Parker Lake shear zone, a post-Wathaman Batholith feature. Major fold closures were not

Figure 25 - Typical Wathaman Batholith megacrystic quartz monzonite; west shore of Reindeer Lake; Station SL27-1-1; UTM-E: 638437; UTM-N: 6384616.

Figure 26 - Cumulate layering in Wathaman Batholith quartz monzonite; west shore of Reindeer Lake; Station 2-1; UTM-E: 640776; UTM-N: 6386821.


Figure 27 - Schematic illustration of the thermotectonic history of the Peter Lake Domain; modified after Maxeiner and Hunter (2002).

observed, although some of the repetitions of units in the Warner Lake gabbroic suite might be due to early tight folding (a feature documented in the southwest part of the domain). Concentric foliation in the Patterson Island pluton that locally overprints primary igneous layering and flattens xenoliths predates emplacement of the Wathaman Batholith and is likely an S2 fabric. Northeast-trending open folds are largely related to the D3 event.

Small shear zones several tens of metres wide within the southeastern Peter Lake Domain and adjacent Wathaman Batholith are likely related to the Trans-Hudson aged Parker Lake shear zone. Other shear zones towards the interior of the domain are of unknown age. Locally, the granitic rocks are transected by ductile shear zones, producing mylonitic orthogneisses tens of metres wide within otherwise homogeneous and massive units of syenogranite and monzogranite.

Geochronological results obtained northeast of the Patterson Island area (Rayner et al., in review), suggest that an older granitic component (>2.60 Ga) is present in the Peter Lake Domain, possibly a constituent of the Lueaza River granitoids. Archean supracrustal rocks including mafic to felsic volcanic rocks, migmatitic psammopelite, and pelite were apparently metamorphosed at upper amphibolite facies grades during a Neoarchean metamorphic event,


possibly between 2.56 and 2.54 Ga. The Swan River Complex is currently dated at 2.562 Ga, but possibly comprises an older Warner Lake gabbroic suite and a younger Love Lake leucogabbroic suite. Both these suites have been metamorphosed, although the Warner Lake gabbroic suite seems more recrystallized than the rest of the Swan River Complex. Supracrustal rocks have at least one tectonic fabric that predates the Swan River Complex. The monzonite-syenite suite that includes the Patterson Island pluton post-dates most of the dioritic to gabbroic rocks of the Swan River Complex. It is tentatively correlated with a 2.54 Ga megacrystic monzonite (Heaman et al., this volume), that intrudes the Warner Lake gabbroic suite in the Peter Lake area. The monzonite-syenite suite is possibly syn- to post-metamorphic. The syenogranitic suite post-dates earlier megacrystic granites (Lueaza River granitic suite), the Swan River Complex and the monzonite-syenite suite, and is possibly related to the Wathaman Batholith or an approximately 2.1 Ga partly fluorite bearing granitic suite recognized in the Courtenay Lake area.

6. Acknowledgments Amanda Perrot, Rachel Sulz, Lance Kostiw, Murray Lungal, and Mike Pollock provided excellent and cheerful field assistance during the entire summer. Field visits by Greg Dunning of Memorial University and Kate MacLachlan were very helpful in improving the map.

7. References Annesley, I.R., Madore, C., and Krogh, T.E. (1992): U-Pb geochronology of some granitoids from the Peter Lake

Domain: A summary; in Summary of Investigations 1992, Saskatchewan Geological Survey, Sask. Energy Mines, Misc. Rep. 92-4, p168-171.

Ashton, K.E. and Leclair, A.D. (1990): Foliate: A useful term to complement the textural classification of foliated metamorphic rocks; Can. J. Earth Sci., v27, p1095-1097.

Bickford, M.E., Van Schmus, W.R., Macdonald, R., Lewry, J.F., and Pearson, J.G. (1986): U-Pb zircon geochronology project for the Trans-Hudson: Current sampling and recent results; in Summary of Investigations 1986, Saskatchewan Geological Survey, Sask. Energy Mines, Misc. Rep. 86-4, p101-107.

Bickford, M.E., Van Schmus, W.R., Collerson, K.D., and Macdonald, R. (1987): U-Pb zircon geochronology project: New results and interpretation; in Summary of Investigations 1987, Saskatchewan Geological Survey, Sask. Energy Mines, Misc. Rep. 87-4, p76-79.

Bickford, M.E., Rayner, N.M., and Stern, R.A. (2002): The exotic origin of the Sask craton, Trans-Hudson Orogen revealed by new SHRIMP zircon U-Pb ages; Geol. Assoc. Can./Miner. Assoc. Can., Joint Annual Meeting, Saskatoon, Abstr. Vol. 27, p10.

Corrigan, D. (2001): Geology, Northern Reindeer Lake, Saskatchewan; Geol. Surv. Can., Open File 1394, 1:100 000 scale map.

Corrigan, D., MacHattie, D.G., and Chakungal, J. (2000): The nature of the Wathaman Batholith and its relationship to the Archean Peter Lake Domain along the Reindeer Lake Transect, Saskatchewan; in Current Research 2000-C13, Geol. Surv. Can., p1-10.

Corrigan, D., Maxeiner, R.O., and Harper, C.T. (2001): Preliminary U-Pb Results from the La Ronge–Lynn Lake Bridge Project; in Summary of Investigations 2001, Volume 2, Saskatchewan Geological Survey, Sask. Energy Mines, Misc. Rep. 2001-4.2, CD-ROM, p111-115.

Davis, W.J., Hanmer, S., Aspler, L., Sandeman, S., Tella, S., Zaleski, E., Relf, C., Ryan, J., Berman, R., and MacLachlan, K. (2000): Regional differences in the Neoarchean crustal evolution of the Western Churchill Province: Can we make sense of it?; GeoCanada 2000, conference CD.

Delaney, G., Jankovic, Z., MacNeil, A., McGowan, J., and Tisdale, D. (1997): Geological investigation of the Courtenay Lake–Cairns Lake Fold Belt and the Hills Lake Embayment, Johnson River Inlier, Wollaston Domain, Saskatchewan; in Summary of Investigations 1997, Saskatchewan Geological Survey, Sask. Energy Mines, Misc. Rep. 97-4, p90-102.

Hunter, R.C. (2003): Geological setting of the Campbell River Group, southwestern Peter Lake Domain; unpubl. B.Sc. thesis, Univ. Sask., 52p.


Irvine, T.N., Andersen, J.C.Ø., and Brooks, C.K. (1998): Included blocks (and blocks within blocks) in the Skaergaard Intrusion: Geological relations and the origins of rhythmic modally graded layers; Geol. Soc. Amer. Bull., v110, p1398-1447.

LaFrance, B. and Varga, M. (1996): Structural studies of the Parker Lake shear zone and the Reilly Lake shear zone, Reindeer Lake; in Summary of Investigations 1996, Saskatchewan Geological Survey, Sask. Energy Mines, Misc. Rep. 96-4, p119-124.

Lewry, J.F. (1976): Reindeer Lake north (SW quarter) area: Reconnaissance geological mapping of 64E-3, -4, and -6; in Summary of Investigations 1976, Sask. Dep. Miner. Resour., Misc. Rep. 76-4, p29-35.

Lewry, J.F., Roberts, K., and Rees, C.J. (1980): Geology of the Area Around Spalding Lake; Sask. Miner. Resour., Rep. 199, 18p.

Macdonald, R. and Thomas, M.W. (1983): Compilation Bedrock Geology, Reindeer Lake North, NTS Area 64E; Sask. Energy Mines, Rep. 232, 1:250 000 scale map with marginal notes.

MacDougall, D.G. (1987): Bedrock geological mapping Campbell River area (part of NTS 64E-6); in Summary of Investigations 1987, Saskatchewan Geological Survey, Sask. Energy Mines, Misc. Rep. 87-4, p34-45.

__________ (1988): Bedrock geological mapping, Patterson Island area, Reindeer Lake (part of NTS 64E 10); in Summary of Investigations 1988, Saskatchewan Geological Survey, Sask. Energy Mines, Misc. Rep. 88-4, p61-66.

MacNeil, A., Delaney, G.D., and Ansdell, K. (1997): Geology of the Courtenay Lake Formation in the Cook Lake area, Wollaston Domain, Saskatchewan; in Summary of Investigations 1997, Saskatchewan Geological Survey, Sask. Energy Mines, Misc. Rep. 97-4, p115-120.

Maxeiner, R.O. and Hunter, R. (2002): A geological transect across the southwestern Peter Lake Domain, Saskatchewan; in Summary of Investigations 2002, Volume 2, Saskatchewan Geological Survey, Sask. Industry and Resources, Misc. Rep. 2002-4.2, CD-ROM, Paper A-3, 24p.

Maxeiner, R.O., Gilboy, G.F., and Yeo, G.M. (1999): Classification of metamorphosed clastic sedimentary rocks: A proposal; in Summary of Investigations 1999, Saskatchewan Geological Survey, Sask. Energy Mines, Misc. Rep. 99-4.1, p89-92.

Ray, G.E. (1975): Geology of the Foster Lake (northeast) and Geikie River (southeast) area; in Summary of Investigations 1975, Sask. Dep. Miner. Resour., Misc. Rep. 75-4, p13-18.

Ray, G.E. and Wanless, R.K. (1980): The age and geological history of the Wollaston, Peter Lake and Rottenstone domains in northern Saskatchewan; Can. J. Earth Sci., v17, p333-347.

Rayner, N.M., Stern, R.A., and Bickford, M.E. (in review): Tectonic implications of new SHRIMP and TIMS U-Pb geochronology of rocks from the Sask Craton, Peter Lake Domain, and Hearne margin, Trans-Hudson Orogen, Saskatchewan; Can. J. Earth. Sci.

Stauffer, M.R., Fumerton, S.L., Langford, F.F., Coleman, L.C., and Mossman, D.J. (1981): Geology of the Ballentin Island Vicinity, Reindeer Lake; Sask. Dep. Miner. Resour., Rep. 206, 22p.

Streckeisen, A. (1976): To each plutonic rock its proper name; Earth Sci. Rev., v12, p1-33.

Van Schmus, W.R., Bickford, M.E., Lewry, J.F., and Macdonald, R. (1987): U-Pb geochronology in the Trans-Hudson Orogen, northern Saskatchewan, Canada; Can. J. Earth Sci., v24, p407-424.

geology and extent of the archean swan river complex in ... · which intruded the swan river...

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