The Wathaman Batholith and Its Relation to the Peter Lake Domain: Insights from Recent Mapping along the Reindeer Lake Transect, Trans-Hudson Orogen

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1 The Wathaman Batholith and Its Relation to the Peter Lake Domain: Insights from Recent Mapping along the Reindeer Lake Transect, Trans-Hudson Orogen D. Corrigan 1, T G. MacHattie 2, and J. Chakungal 3 Corrigan, D., MacHattie, T.G., and Chakungal, J. ( 1999): The Wathaman Batholith and its relation to the Peter_ Lal_(e Domain: Insights from recent mapping along the Reindeer Lake Transect, Trans-Hudson Orogen; in Summary oflnvestlgatlons 1999, Volume 2, Saskatchewan Geological Survey, Sask. Energy Mines, Misc. Rep Introduction In 1997, the Geological Survey of Canada and Saskatchewan Energy and Mines joined in a collaborative effort aimed at enhancing understanding of the "La Ronge~Lynn Lake Bridge" as well as the lithotectonic framework of the northwestern Reindeer Zone of the Trans-Hudson Orogen. During the first two summers, regional mapping at 1: scale (Corrigan et al., l 998a; Corrigan et al., 1999), integrated with local detailed mapping of the Central Metavolcanic Belt (CMB) at I : scale (Corrigan et al., 1997; Harper, 1997, 199 8; Maxeiner 1997, 1998), was completed in a 3000 km 2 corridor extending from the north flanks of Glennie and Kisseynew domains, to the central part of the Wathaman Batholith (Figure 1 ). This past summer was the third field season for the GSC involvement in the project. The first part of the field season was spent reexamining outcrops and collecting more data and samples from newly recognized supracrustal rocks in the Rottenstone Domain, now interpreted in part as the 110'W northern extension of the La Ronge Domain (Corrigan et al., 1999). Results from that work are described in Corrigan et al. (in prep.). The second halfofthe field season was spent in the northern part of Reindeer Lake and entailed a transect, from the interior of the Wathaman Batholith to the Archean Peter Lake Domain, that covered NTS sheet 64E-9 and parts of 64 E-10 and 64 E-16. Results are described below. 2. Regional Geology and Previous Work Reindeer Lake was first explored geologically by Tyrrell and Dowling (1896) and mapped by Stockwell (1929). Parts of the northern area of the lake were subsequently mapped by Weeks ( 1941 ), Shklanka (1962), Potter ( 1979), Stauffer et al., (1981), and MacDougall (1988). More recently, Lafrance and Varga (1996) published a report on the Parker Lake Shear Zone, interpreted as a tectonic boundary separating the Wathaman Batholith from the Peter Lake Domain. Zircon U-Pb ages are available for only Hudson Bay four rock samples from the map area. They are all from the Peter Lake Domain and include a 2582 ± 19 Ma grey megacrystic granite, a 2556 ±22 Ma granitic gneiss, a younger, 1860 ±5 Ma granitic gneiss, and a 1865 ± 10 Ma gab bro pegmatite (Bickford et al., 1986). Further analysis of zircon from the gabbro pegmatite produced a revised age of 1908 ±27 Ma (Bickford et al., 1987). Figure 1- Lithotectonic map of the Trans-Hudson Orogen in Saskatchewan and Manitoba, modified after Lewry el al. (1990). NFSZ, Needle Falls Shear Zone; PLSZ, Parker Lake Shear Zone; and RLSZ, Reilly Lake Shear Zone. The Trans-Hudson Orogen in northern Saskatchewan and Manitoba forms a collage of west-southwest-striking, northerly-dipping juvenile volcanic and sedimentary belts (referred to in the literature as \ithotectonic domains) that were accreted to the Archean Hearne margin during Paleoproterozoic collision (Lewry et al., 1981; I Geological Survey of Canada, 6 l 5 Booth St., Ottawa, ON KI A OE8. 2 Department of Earth Sciences, Memorial University, St. John's, NF AIB 3X5. 1 Department of Earth Sciences, Dalhousie University, Halifax, NS B3H IJ5. /32 Summary of Investigations 1999, Volume 2

2 Bickford el al., 1990). From south to north along Reindeer Lake, or from lowest to highest structural levels, they consist of the Glennie, Kisseynew, La Ronge, and Rottenstone domains. The Glennie and La Ronge domains consist predominantly of ca to 1.80 Ga volcanic rocks and associated sediments, and are interpreted on the basis of protolith type and geochemical signature as remnants of island arcs and arc-flanking sedimentary basins. The Kisseynew Domain is dominated by graphitic meta-turbidites (Bumtwood Group) and penecontemporaneous fluvial and fluvio-deltaic rocks of the McLennan (i.e. Sickle) Group. rt stratigraphically overlies the Glennie Domain and is overthrust on its northern flank by the La Ronge Domain. The Kisseynew Domain contains two major supracrustal units; the Burntwood Group turbidites and McLennan Group fluvial sediments. The Bumtwood Group consists predominantly of gamet±cordieritebearing turbidites locally intruded by granitoid sheets. An apparently older package of supracrustal rocks and tonalitic intrusives was identified near the McLennan/Burntwood transition zone during last summer's mapping (Maxeiner 1998; Corrigan el al. 1998a, 1999). It is characterized by narrow slivers of graphitic, ferruginous, and calcareous sedimentary rocks, interlayered with garnet amphibolite containing calc-silicate alteration bands that are very similar in composition and appearance to those in altered mafic volcanic rocks of the CMB (see Maxeiner, 1996). These supracrustal rocks are referred to informally as the "Levesque Bay assemblage". Preliminary U-Pb ages of 1867 ±4 Ma and 1894 ± 4 Ma (Corrigan, unpubl. rep.) obtained on a homblende-biotite tonalite and gametiferous leucogranite, respectively, cutting the Levesque Bay assemblage, suggest that it may be the same age as some of the older supracrustal rocks in the La Ronge and Glennie domains. The Levesque Bay assemblage is tectonically imbricated with arkosic and turbiditic rocks of the McLennan and Burntwood groups in fold-thrust style (Corrigan et al., 1999). The La Ronge Domain includes volcanic and intercalated sedimentary rocks of the Central Metavolcanic Belt (CMB), and sediments of the Milton Island assemblage (Corrigan et al., 1998a, 1999). These supracrustal rocks have been intruded by numerous calc-alkaline plutons that vary in composition from dioritic to granitic. Most were emplaced between 1865 to 1850 Ma, the time span during which the Wathaman Batholith formed (see Lewry et al., I 990). In last year's report (Corrigan et al., l 998a), evidence was presented that this intrusive suite likely formed as satellite plutons to the Wathaman Batholith. The Rottenstone Domain flanks the La Ronge Domain to the northwest. It has been historically interpreted as a predominantly tonaliticmigmatitic belt that contains supracrustal rocks possibly linked to those of the La Ronge Domain (Lewry et al., 1981 ). rt also contains megacrystic granitoids of the Wathaman Batholith (Johnston and Thomas, 1984 ). During last year's mapping, Corrigan et al. (l 998a, 1999) identified extensive tracts of supracrustal rocks in the Rottenstone Domain along the shoreline and islands of Reindeer Lake. Newly identified metavolcanic, volcaniclastic, and epiclastic rocks were interpreted as northern extensions of the CMB of the La Ronge Domain. A newly recognized succession consisting of magnetite-bearing fluvial to marine sediments, including polymictic conglomerate, arkose and calcareous psammite, was also identified last summer (Corrigan et al., 1998a, 1999). These rocks, infonnally referred to as the "Park Island assemblage", unconfonnably overlie previously folded volcanic and sedimentary rocks of the CMB and Milton Island assemblages, respectively. The ca to 1850 Ma Wathaman Batholith (Ray and Wanless, 1980; Fumerton et al., 1984; Bickford et al., 1986; Meyer et al., I 992) has been interpreted as a continental arc batholith intruding the Rottenstone Domain. It is separated from the Archean Peter Lake Domain and the Wollaston Domain by the Parker Lake and Needle Falls shear zones, respectively, and from the Rottenstone Domain by the Reilly Lake Shear Zone (Lewry et al., 1990; Stauffer and Lewry, 1993). This report presents a summary of field observations in the northern half of the Wathaman Batholith and discusses its relationship to the southeastern margin of the Peter Lake Domain. Evidence is presented that the Wathaman Batholith is intrusive to the margin of the Hearne Province, and that layered mafic-ultramafic sill-like intrusions in the Peter Lake Domain may be early Wathaman-age intrusions. 3. Peter Lake Domain As the main objective of mapping this past summer was to better understand the relationship between the Archean craton margin and the Wathaman Batholith, mapping in the Peter Lake Domain was concentrated in an 8 to IO km strip along its southeastern margin. This part of Peter Lake Domain is underlain by the Lueaza River Granitoids which had been described as comprising highly deformed and metamorphosed biotite±homblende-bearing, high-level intrusives, anatectites, or metasomatized intrusives (map unit 4 of Stauffer et al., 1981 ). Part of the unit had been interpreted as migmatite of possible sedimentary origin. This summer's work, which concentrated mainly on well-exposed shoreline and island outcrops on Reindeer Lake (Figure 2), revealed that the part of the Lueaza River Granitoids examined is indeed composed ofmigmatite of both plutonic and sedimentary origin, but also contains abundant nonmigmatitic, strongly foliated and recrystallized granitoids, as well as minor supracrustal screens. All of these are intruded by amphibolite dykes of likely Archean age, plagioclase-phyric mafic dykes of unknown age, and granitoid plutons related to the Wathaman suite (see below). a) Migmatitic Ortho- and Paragneiss The most northwestern part of the Lueaza River Granitoids mapped, consists of metatexites and diatexites derived predominantly from igneous protoliths of dioritic to granitic composition (migmatitic orthogneiss), as well as minor migmatite of Saskatchewan Geologica{ Survey /33

3 ... a ~ /,, ',..\) Boundary Isl. Reindeer Lake 5 10 Southern limit of Archean gneiss Assumed geological contact Peter Lake Domain (Archean) EJTI Foliated granitoids [--:.c -c.:'.' j Migmatitic ortho- and paragneiss [ITillill Metavolcanic rocks Wathaman Batholith (Proterozoic) 11!111 Ton a lite ~ Foliated granite ~ Megacrystic granite t~~~;~~{;~~j ~ Megacrystic granodiorite Megacrystic monzonite and quartz-monzonite ~ Patterson Island syenite... _ -- ;wan RI~~~- Comple;... (?) Figure 2 - Geological map of the nonhern shore and islands of Reindeer Lake; Gb, gabbro (Swan River Suite). 134 Summary of Investigations 1999, Volume 2

4 sedimentary origin (migmatitic paragneiss). The migmatitic orthogneiss is grey to pink, highly to moderately strained, well foliated, compositionally banded at centimetre to metre scale and contains hornblende as well as biotite as the main mafic mineral phases, their relative abundances varying according to protolith composition. Stromatic granitic leucosomes are ubiquitous and are generally transposed parallel to the main regional foliation trend. Mafic boudins of amphibolitic to dioritic composition are common and likely result from the tectonic disaggregation of dykes and smaller intrusions (Figure 3). The heterogeneous nature of this rock unit, and the overall tonalitic/granodioritic composition with minor diorite and granite, suggests that the protolith may have been a calc-alkaline plutonic complex formed by multiple injections. The migmatitic orthogneiss is locally interlayered with a migmatitic, pink coloured, finely layered, biotite quartzofeldspathic gneiss. Paleosomes, where preserved, show a well-banded fabric suggestive of a sedimentary origin. Overall, this rock type forms approximately IO percent of the migmatitic unit. A feature of the Lueaza River Granitoids, that differs from juvenile rocks of the northwestern Reindeer Zone mapped in the previous two summers, is two sets of mafic dykes of different relative ages. The older set, which is composed of fine-grained amphibolite, rarely exceeds 50 cm in width and is tightly to isoclinally folded with limbs sub-parallel to the transposition foliation. The younger set, which consists of fine to medium-grained amphibolite with distinctive centimetre-sized plagioclasc phcnocrysts and preserved chilled margins, crosscuts the folds developed in the older set. The younger mafic dykes are generally thicker (up to 2 m) and although affected by regional ductile deformation, are not as thoroughly transposed as the earlier set. Although field relationships suggest that the earlier set is likely of Archean age, the absolute age of the younger set is unknown. It must have been em placed after Archean deformation, as it cuts the main regional fabric, but before the Wathaman Batholith as it is not present in that body. b) Metavolcanic Rocks Locally, fine-grained, heterogeneous amphibolite with calc-silicate bands and pods is intercalated with migmatites and granitoids of the Lucaza River Granitoids unit (Figure 4). These bands are discontinuous along strike and rarely exceed a few tens of metres in thickness. Composition is predominantly hornblende with <25 percent plagioclase and rare biotite and quartz. Because of their very fine-grained and compositionally heterogeneous nature and association with thin calc-silicate bands, they are interpreted as highly deformed and metamorphosed mafic flows. Three such occurrences are large enough to be identified on the map (Figure 2). The occurrence on the north shore of a small unnamed bay north of Wiley Bay has been described by MacDougall ( 1988). Three other occurrences were found this past summer on the northwestern shore of Feaviour Peninsula and on the west shore of McLean Bay (Figure 2). At these locations, small volumes of grey, fine-grained hornblende-biotite-bearing gneiss of intermediate composition may be derived from andesite and/or dacite associated with the mafic volcanics. Ultramafic rocks outcrop north of Wiley Bay, and on the northwestern shore of Feaviour Peninsula. They consist of actinolite±diopside±plagioclase hornfels and schists. Locally, such as in the north Wiley Bay exposure, asbestos and a pale, greasy green mineral (prehnite?) fill 2 to 6 cm thick fractures. As the supracrustal rocks are spatially associated with granitoids that yielded Archean U-Pb ages (Bickford et al., 1986), they are assumed to be Archean as well. c) Foliated Granitoids Non-migmatitic, foliated granitoids, in two elongate belts, flank the migmatitic para- and orthogneisses to the northwest and southeast. The northwestern belt has a roughly 1 km map width and consists of mixed granodiorite and granite with numerous, transposed diorite enclaves. The plutonic protoliths are fine to medium grained and totally recrystallized. Southeast of the migmatites, the foliated granitoids form a roughly Figure 3 - Outcrop photograph of Lueaza River Granitoid unit showing migmatitic granodiorite orthogneiss (front of picture) intruded by boudined diorite (dark colour) and fine-grained white granite. Geological hammer for scale. Figure 4 - Outcrop photograph of mafic metavolcanic rock with culc-silicute alteration (light coloured patches). Small bay on west shore of Feaviour Peninsula. Hammer for scale. Saskatchewan Geological Survey /35

5 5 km wide, elongate map unit that hosts a number of cross-cutting plutons comprising tonalite, granodiorite, granite, and syenite. They are mainly fine-grained and thoroughly recrystallized. Individual plutons rarely exceed I 00 m in width and are continuous along strike up to a few kilometres. They are generally too small to form mappable units, however, and have thus been grouped as one larger metaplutonic unit on Figure 2. The most abundant rock type consists of a white to light tan, sugary-textured leucogranite containing up to 10 percent biotite. Light grey biotite granodiorite is also associated with the leucogranite. A less abundant rock type, pink biotite granite, occurs as dykes cutting the white granite and granodiorite. A distinctive phase of the intrusive complex consists of salmon pink quartz syenite and syenite with up to 8 percent biotite as the main mafic phase. At one locality in the syenite, a rusty brown mineral resembling altered orthopyroxene has been found, suggesting that this plutonic phase may have originally been anhydrous. Allanite is an important accessory in the syenite, locally forming up to 2 percent of the mineral assemblage. Two granitoids, a granodiorite and a granite sampled on the shore of Reindeer Lake southwest of Crane Island, yielded Archean U-Pb zircon ages (Bickford et al., 1986). 4. Wathaman Batholith The Wathaman Batholith is a continental magmatic arc that is 900 km long, and between 15 and 150 km wide. It is comparable in size and geochemical characteristics to some of the largest Phanerozoic continental arc-type batholiths (Fumerton et al., 1985; Meyer et al., 1992). ln the Reindeer Lake area, it had been interpreted to form a voluminous plutonic suite dominated by K feldspar megacrystic or coarse-grained monzonite, quartz-monzonite, granodiorite, and granite, with minor diorite and aplite (Stauffer et al., 1981; Fumerton et al., 1984; Meyer et al., 1992). Earlier workers have emphasized that: 1) it is more potassic than most Phanerozoic analogues; 2) it does not contain discreet intrusive phases, but rather phases that grade into one another; and 3) that it is separated from gneisses of the Rottenstone and Peter Lake domains by the Reilly Lake and Parker Lake shear zones, respectively. During the latter part of the 1998 field season, and during most of this past season, part of the batholith was remapped at I : scale and its northern and southern boundaries re-examined. Field observations and preliminary U-Pb zircon ages suggest that magmatism associated with the Wathaman Batholith is not restricted per se to the area outlined in earlier maps and reports ( e.g. Stauffer et al., 1980, I 981; Johnston and Thomas 1984), but comprises a number of large plutons ranging in composition from pyroxenite to biotite granite (Corrigan et al., I 998a, 1999) that extend to the southern edge of the La Ronge Domain. Quartz diorite and diorite are the most common varieties. Investigations of the northern margin of the Wathaman Batholith, along the southeastern margin of Peter Lake Domain, yielded substantial evidence suggesting that the batholith intrudes the Archean craton margin. This includes megacrystic granitoid dykes cutting gneiss of the Lueaza River Granitoid unit and fine-grained, deformed and metamorphosed granitoid rafts in the Wathaman Batholith. Furthermore, we have found evidence suggesting that the Swan River Pluton and a number of similar monzonitic to gabbroic elongate bodies northwest of the Wathaman Batholith could potentially represent the earliest mafic magmas of the Wathaman continental arc batholith. These intrusions were historically inferred to be of Archean age and belong to the Peter Lake Domain (Johnston and Thomas, 1984). In order to group rocks by relative age determined from field relationships, the Swan River Pluton will be described together with the Wathaman Batholith. a) Swan River Complex This map unit, originally named Swan River Pluton by Stauffer et al. (1981), reaches the southwestern comer of our map area. It includes a few elongate, sill-like bodies, dykes and pods of similar composition that intrude gneisses of the Peter Lake Domain, as well as other smaller ones mixed in with the Wathaman Batholith (Figure 2). To account for the great diversity observed in this intrusion, the name has been modified herein to Swan River Complex. Throughout the area, rocks of the Swan River Complex are compositionally heterogeneous and commonly layered (Figure 5). The scale of layering varies from metre to centimetre and is continuous over entire outcrop exposures (up to a few tens of metres). Cross-cutting sets of rhythmic layers are commonly suggesting emplacement in a tectonically active environment. In contrast to the recrystallized and highly metamorphosed nature of the Lueaza River Granitoids, rocks of the Swan River Complex contain mostly original igneous minerals and are at most metamorphosed at greenschist facies. By far, the best exposed outcrops are on a group of islands between Feaviour Peninsula and Crane Island (NTS 64E- l 6). There, the complex consists of a lower ultramafic layer a few metres thick formed of alternating harzburgite and dunite. This grades into massive olivine gabbro with well developed subophitic textures, commonly forming decametres-thick layers containing IO to 15 cm thick bands defined by a gradual upward decrease in olivine content. Overall, textural variations in the gabbro vary from I cm scale rhythmic layering in fine-grained rock, to pegmatitic gabbro layers and dykes up to 1 m thick (Figure 6). Rare leucogabbro and anorthosite layers were observed. In most outcrops, gabbro grades upwards into massive to rhythmically layered diorite composed of approximately equal proportions of plagioclase and homblende±clinopyroxene (Figure 7). Interestingly, the diorite component is locally sub-ophitic, suggesting that it is in part derived from post-crystallization hydration of gabbro. Geochemical analysis will determine whether this rock is truly diorite, or hydrated gabbro. The sub-ophitic diorite and gabbro locally host spectacular pegmatitic pods (Figure 8). These are presumably similar to the pegmatitic gabbro sampled southwest of Crane Island which yielded a preliminary 136 Summary of Investigations I 999, Volume 2

6 U-Pb age of 1865 ± l O Ma (Bickford et al., 1986), later revised at 1908 ±27 Ma (Bickford et al., 1987). Another important component of the Swan River Complex is small plutons and pods of coarse-grained, pitted diorite. Numerous, ovoid-shaped cavities on the outcrop surface characterize this rock. They were produced by concentration of igneous biotite in small spherical zones 1 to 4 cm in diameter. This characteristic texture has been observed in rafts of the Swan River Complex in the Wathaman Batholith and in intrusions in the Peter Lake Domain. Very similar, possibly related intrusions have also been observed in the La Ronge Domain near Laxdal and Doucet islands and in the Cowie Pluton, south of the Wathaman Batholith (Corrigan et al., 1999). Another common feature is igneous breccia with fine-grained, footballsized gabbro and/or diorite pods injected by either: 1) thin ultramafic veins composed mainly of homblendite or orthopyroxenite; and/or 2) a net veinwork of medium- to coarse-grained diorite to K feldspar megacrystic monzodiorite. The texture of this rock is quite characteristic (Figure 9) and is observed on many outcrops within the Peter Lake Domain. Figure 5 - Outcrop photograph showing centimetre-sized rhythmic layering in gabbro of the Swan River Complex. Bands are outlined by variations in the relative abundance of plagioclase versus mafic minerals. Small island west of Feaviour Peninsula. Hammer for scale. Figure 7 - Rhythmic layering in diorite showing the highly contrasting black and white layers of igneous hornblende and plagioclase, respectively. North shore of Patterson Island. Figure 6 - Layering in coronitic metagabbro, crosscut by a gabbro pegmatite dyke. The dyke is similar in texture and composition to some of the concordant layers. Small island west of Feaviour Peninsula. Figure 8 - Pegl?llltitic pod in hydrated gabbro showing welldeveloped sub-ophitic textures. Minerals are mainly hornblende after pyroxene and unrecrystallized plagioclase. Hand flare projector for scale. Saskatchewan Geological Survey 137

7 feldspar over plagioclase and the greater abundance of biotite (10 to 15 percent) over hornblende (0 to 10 percent). In addition, titanite and epidote are either rare or absent from the accessory minerals. The proportion ofk-feldspar megacrysts varies much more in the granite than in any other rock type commonly grading into homogeneous, medium- to coarse-grained granite. Figure 9 - Outcrop photograph of a characteristic component of the Swan River Complex showing ultramafic veins (dark colour) and coarse-grained monwdiorite related to the Wathaman Batholith, intruding fine-grained diorite. Hammer for scale. b) Wathaman-type Megacrystic Granitoids Five different compositional types ofk-feldspar megacrystic granitoids have been identified in the Wathaman Batholith (Figure 2). In order of decreasing volume their composition consists of granodiorite, granite, monzonite (±quartz), syenite, and monzodiorite. Included in this group are plutons previously interpreted to belong to the Peter Lake Domain, which show similar field relationships to the Wathaman Batholith. These include the Patterson Island syenite/monzodiorite and the Ettie Creek granite (Figure 2). Feldspar megacrysts are pink microcline and range in maximum length from I to 8 cm. Growth zoning is commonly visible in hand specimen, especially in the larger crystals. Rapakivi texture is also locally present. Primary igneous textures such as accumulated megacrysts (Figure I 0) demonstrate that the crystals are igneous and not the end product of later metasomatism. Although the foliation in the batholith is parallel to the regional southwest-northeast trend in wallrock tectonites, it is commonly outlined by feldspar megacrysts set in an unrecrystallized matrix and is thus demonstrably magmatic, consistent with observations made farther to the southwest (Lewry et al., 1981). This suggests a broad correspondence between regional deformation and magma emplacement. Megacrystic monzonite to quartz-monzanite occurs at three locations, all close to the boundary of the Peter I.ake Domain. This rock is in all aspects (except for the relative abundance of quartz, plagioclase and potassic feldspar), identical to the megacrystic granodiorite into which it appears to grade locally. This unit, as well as the megacrystic granite, are crosscut by the granitic phase of the batholith. Megacrystic syenite forms part of a well-exposed pluton on Patterson Island, where a multiphase gabbro to syenomonzonite pluton was mapped by MacDougall ( 1988). This oval-shaped intrusion is virtually Figure IO - Outcrop photograph showing high concentration of K-feldspar megacrysts in a layer parallel to the magmatic layering in a granitic phase of the Wathaman Batholith. Rest of outcrop contains only about 5 percent of scattered megacryst.f. Small island northeast of Ba/lentin Islands. Megacrystic granodiorite underlies most of the central portion of the Wathaman Batholith. The rock is light grey, coarse grained, and comprises 15 to 60 percent pink K-feldspar megacrysts (Figure 11) set in a matrix of plagioclase, quartz, hornblende, and biotite. Hornblende is either equal to or more abundant than biotite, but together they form up to 25 percent of the rock volume. Titanite, titanomagnetite, allanite, and epidote are ubiquitous accessory minerals. Megacrystic granite occurs mainly in a large band separating the granodiorite from the Peter Lake Domain. It is light pink and differs from the megacrystic granodiorite only in the abundance of K- Figure I I - large K-fe/dspar megacryst in moderately foliated granodiorite. Igneous wning is visible as faint crystal-parallel layers. Small island of the Ballen tin Islands group. Coin is 2.8 cm in diameter. /38 Summary of Investigations I 999. Volume 2

8 undefonned, with abundant, randomly oriented K feldspar megacrysts set in a predominantly hornblende (±augite) rich matrix. Hornblende (locally augite as well) (20 to 30 percent) is much more abundant than biotite (I to 5 percent). The only accessory mineral visible in hand specimen is titanomagnetite. This pluton had previously been interpreted as forming part of the Swan River Complex, and had therefore been informally assigned an Archean age (Macdonald and Thomas, 1983). Because of its low state of strain and unnoticeable metamorphic overprint (Figure 12), we believe that it more likely belongs to the Wathaman suite; a hypothesis that is currently being tested at the U-Pb Geochronology Laboratory at the Geological Survey of Canada. Megacrystic monwdiorite forms the least abundant rock type of the Wathaman suite. It occurs in close association with the Swan River Complex where it typically grades into, and locally intrudes gabbro/diorite in a vein network. It consists of rare K feldspar megacrysts ( <10 percent) in a medium- to coarse-grained hornblende-plagioclase±biotite matrix. The relationship between the megacrystic monzodiorite and the Swan River Complex forms the most convincing argument that the latter is an integral part of the Wathaman suite. c) Other Granitoids Related to the Wathaman Batholith Both granite and granodiorite occur without K-feldspar megacrysts. These commonly grade into megacrystic varieties of the same composition, suggesting that the formation of megacrysts is due to local conditions in the magma chamber. Large areas without K-feldspar megacrysts are identified on the map (Figure 2). The only other non-megacrystic granitoid consists of a large tonalite pluton on Cumines Island (Figure 2). It is grey, medium grained, equigranular and contains both hornblende (-5 percent) and biotite (-5 percent) as mafic phases. It crosscuts megacrystic granitoids of the Wathaman Batholith and thus appears to form one of Figure 12 - Close-up photograph of the Patterson Island megacrystic syenile showing the unrecrystal/ized state of minerals and a few mafic cognate xenoliths. Dark groundmass is predominantly hornblende with minor augite and biotite. Pen for scale is 12 cm the youngest phases. In the field, granitoids related to the Wathaman Batholith generally can be separated from those related to the Archean age Lueaza River Granitoids by their better state of preservation (relict igneous crystals such as coarse-grained potassic feldspars) and the occurrence ofmafic cognate xenoliths. 5. Structure Three major sub-parallel fabrics are observed in the map area. These include: an earlier, penetrative, highmetamorphic grade fabric affecting only Archean rocks of the Peter Lake Domain (D 1 ), and two younger, lower grade, localized fabrics post-dating the emplacement of the Wathaman Batholith (D 2 and 0 3 ). The earlier fabric consists of a well-developed transposition foliation into which all previous planar elements have been rotated. Tight to isoclinal folds and total recrystallization were developed during this deformation event(s). Associated extension lineations are down-dip. Transposition of leucosomes and annealing of mylonitic fabrics during D 1 suggests that it was accompanied by at least middle to upper amphibolite facies pressure and temperature (P-T) conditions. Locally, rocks of the Wathaman Batholith, including mafic plutonic rocks of the Swan River Complex, clearly crosscut this earlier, presumably Archean age fabric. At least two tectonic fabrics, younger than the one described above, occur in the Wathaman Batholith and its satellite intrusions. They consist of: I) a strong- to moderately-developed mineral foliation that can be observed throughout most (but not all) of the Wathaman-age intrusions (D 2 ); and 2) a younger, more localized mylonitic foliation associated with the Parker Lake Shear Zone (D 3 ) (Lafrance and Varga, 1996). The D 2 fabric consists of a weak to moderate biotite foliation and a down-dip mineral and extensional lineation defined by elongate strain shadows surrounding K-feldspar megacrysts. The primary magmatic foliation is parallel to the D 2 tectonic foliation, reflecting emplacement during regional deformation (also see Lewry et al., 1981 and Lafrance and Varga, 1996). D2 mostly overprints the magmatic foliation, suggesting that defonnation and cooling continued after the emplacement of the batholith. The latest deformation event included strike-slip shearing along the Parker Lake Shear Zone (see also Lafrance and Varga, 1996). It is interpreted as a northeastern splay of the Needles Falls Shear Zone (Figure I), a major transcurrent structure that separates the Wollaston Fold Belt and underlying Archean basement of the Hearne Province from the Wathaman Batholith (Lewry and Sibbald, 1980; Stauffer and Lewry 1993; Lafrance and Varga, 1996). The Parker Lake Shear Zone separates, at least in part, the Peter Lake Domain from the Wathaman Batholith. Lafrance and Varga (1996) examined the Parker Lake Shear!:one in the Reindeer Lake area and concluded that it was the locus of mainly dextral strike-slip motion, with local evidence of sinistral movement as well. They also Saskatchewan Geological Survey 139

9 suggested that, contrary to what is observed along strike to the southwest, the Parker Lake Shear Zone in the Reindeer Lake area does not bound the Peter Lake Domain with the Wathaman Batholith, but cuts into the latter. This agrees with our observations that the Wathaman Batholith intrudes rocks of the Peter Lake Domain, providing unequivocal evidence that it is a stitching pluton, as had been suggested earlier by Lewry et al. (1981). This summer, we have investigated the Parker Lake Shear Zone beyond the area investigated by Lafrance and Varga (1996) and have found no evidence that it extends much further to the northeast, suggesting that this structure terminates somewhere along the north shore of Reindeer Lake. 6. Economic Geology Exploration activity has been sparse and was concentrated at two localities. Husky Oil drilled and trenched a ground EM anomaly near a graphitic shear zone on the shore of Reindeer Lake west of Patterson Island (Wiley Bay showing, Saskatchewan Mineral Deposits Index No. 569). Lacana Exploration Inc. (1986) investigated the Wiley Bay showing and parts of the Swan River gabbroic suite for platinum group elements (PGE) potential west of the map sheet, inland from Patterson Island, and reported assay values of91 to 4000 ppb Pd and 84 to 561 ppb Pt. More detail for these locations is provided by MacDougall (1988). This summer, more outcrops of the Swan River Complex were identified and a few, rare, sulphidebearing horizons in the layered mafic and ultramafic rocks were noted. Some of the better exposed outcrops are on small islands west offeaviour Peninsula in NTS 64E-16, at UTM coordinates N, E and N, E. 7. Discussion The aims of this past summer's mapping were to: 1) investigate the compositional and structural framework of the Wathaman Batholith; 2) map the southeastern margin of the Peter Lake Domain with emphasis on its relationship with the Wathaman Batholith; and 3) continue the on-going sampling program for U-Pb dating at the Geological Survey of Canada in order to determine ages of protolith formation, metamorphism, and deformation. One of the fundamental questions that arose in earlier studies of the Wathaman Batholith was whether or not it was composite, as is the case for most modem analogues ( e.g. Meyers et al., 1992). Within the batholith, we have found that most phases, especially the megacrystic granodiorite, quartz-monzonite, and monzonite, appear to grade into one another (albeit within a short distance), as was observed by earlier workers. The key to this question lies not only on how to interpret the batholith per se, but whether to include all other "satellite" intrusions as well, including the Swan River Complex and ca to 1.85 Ga calcalkaline plutons that are scattered throughout the La Ronge/Rottenstone domains (Corrigan et al., 1999). The field evidence presented here, suggests that K feldspar megacrystic monzodiorite grades into diorite of the Swan River Complex. Furthermore the observation that a texturally distinct pitted diorite of the Swan River Complex also occurs in the La Ronge domain, strongly suggests that the batholith includes a wide range of intrusive types, from layered maficultramafic sills to granite. Another significant contribution from this summer's work was on the nature of the boundary between Peter Lake Domain and Wathaman Batholith. Attempts at mapping out the Parker Lake Shear Zone beyond about 10 km northeast from the western shore of Reindeer Lake failed. Instead, it was noted that strain, in general, decreases northeasterly across the map area. This is consistent with the observation of Lafrance and Varga (1996) that the Parker Lake Shear Zone diverges near the western shore of Reindeer Lake and continues solely within the Wathaman Batholith, separating nearly identical rocks on either side, suggesting minimal displacement. North of this structure, abundant evidence indicates that the Wathaman Batholith (including the Swan River Complex) intrudes gneisses of the Peter Lake Domain. This, coupled with documentation in last year's report that the Wathaman Batholith intrudes rocks of the La Ronge/Rottenstone Domain along its southern margin (Corrigan et al., l 998a, 1999), lends support to the long held view that the Wathaman Batholith stitches the La Ronge arc to the Archean Hearne margin (Lewry et al., 1981; Bickford et al., 1990). 8. Acknowledgements Field work this summer was facilitated with the able assistance of Melanie Bathalon and William Matthews. The crew at La Ronge Aviation provided excellent logistical and fixed-wing support. We wish to extend special thanks to Ralf Maxeiner, Dave Mac Dougall, Charlie Harper, and Gary Delaney for their great company and generously sharing their knowledge of the Trans-Hudson Orogen. 9. References Bickford, M.E., Collerson, K.D., Lewry, J.F., Van Schmus, W.R., and Chiarenzelli, J.R. (1990): Proterozoic collisional tectonism in the Trans Hudson Oro gen, Saskatchewan; Geo!., v 18, p Bickford, M.E., Van Schmus, W.R., Collerson, K.D., and Macdonald, R. (l 987): U-Pb zircon geochronology project: New results and interpretations; in Summary of Investigations 1987, Saskatchewan Geological Survey, Sask. Energy Mines, Misc. Rep. 87-4, p 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 140 Summary of Investigations Volume 2

10 Orogen: Current sampling and recent results; in Summary of Investigations 1986, Saskatchewan Geological Survey, Sask. Energy Mines, Misc. Rep. 86-4, plol-107. Corrigan, D., Bash forth, A., and Lucas, S. ( 1997): Geology and structural evolution of the La Ronge-Lynn Lake Belt in the Butler Island area (parts of and -10), Reindeer Lake, Saskatchewan; in Summary of Investigations 1997, Saskatchewan Geological Survey, Sask. Energy Mines, Misc. Rep. 97-4, p Corrigan, D., MacHattie, T.G., Piper, L., Wright, D., Pehrsson, S., Lassen, B., and Chakungal, J. (l 998a): La Ronge-Lynn Lake Bridge Project: New mapping results from Deep Bay (parts of 64D-6 and -7) to North Porcupine Point (parts of 64E-7 and -8), Reindeer Lake; in Summary of Investigations 1998, Saskatchewan Geological Survey, Sask. Energy Mines, Misc. Rep. 98-4, pl I Corrigan, D., Maxeiner, R., Bashforth, A., and Lucas, S. (1998b): Preliminary report on the geology and tectonic history of the Trans-Hudson Orogen in the northwestern Reindeer Zone, Saskatchewan; in Current Research, Part C, Geol. Surv. Can., Pap C, p95- J 06. Corrigan, D., Pehrsson, S.J., MacHattie, T.G., Piper, L., Wright, D., Lassen, B., and Chakungal, J. (1999): Lithotectonic framework of the Trans Hudson Orogen in the northwestern Reindeer Zone, Saskatchewan: An update from recent mapping along the Reindeer Lake transect; in Current Research, Part C, Geo\. Surv. Can., Pap C, p Fumerton, S.L., Stauffer, M.R., and Lewry, J.F. (1984): The Wathaman Batholith: Largest known Precambrian pluton; Can. J. Earth Sci., v21, p Harper, C.T. (1997): Sucker Lake-Fleming Lake update; in Summary of Investigations 1997, Saskatchewan Geological Survey, Sask. Energy Mines, Misc. Rep. 97-4, p (1998): The La Ronge Domain-Glennie Domain transition: Street Lake area (parts ofnts 64D-3 and -6); in Summary of Investigations 1998, Saskatchewan Geological Survey, Sask. Energy Mines, Misc. Rep. 98-4, p Johnston, W.G.Q. and Thomas, M.W. (1984): Compilation Bedrock Geology Series, Reindeer Lake South, NTS Area 640; Sask. Energy Mines, Rep. 230, I : scale map with marginal notes. 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, pl Lewry, J.F. and Sibbald, T.I.I. (1980): Thermotectonic evolution of the Churchill Province in northern Saskatchewan; Tectonophysics, v68, p Lewry, J.F., Stauffer, M.R., and Fumerton, S.L. (1981 ): A Cordilleran-type batholithic belt in the Churchill Province in Northern Saskatchewan; Precamb. Resear., vl4, p277-3 l3. Lewry, J.F., Thomas, D.J., Macdonald, R., and Chiarenzelli, J. ( 1990): Structural relations in accreted terranes of the Trans-Hudson Orogen, Saskatchewan: Telescoping in a collisional regime?; in Lewry, J.F. and Stauffer, M.R. (eds.), The Early Proterozoic Trans-Hudson Orogen of North America, Geol. Assoc. Can., Spec. Pap. 37, p Macdonald, R. and Thomas, M.W. (1983): Compilation Bedrock Geology, Reindeer Lake North, NTS Area 64E; Sask. Energy Mines, Rep. 232 (1 : scale map with marginal notes). MacDougall, D.G. (1988): Bedrock geological mapping, Patterson Island area, Reindeer Lake (part ofnts 64E-l0); in Summary of Investigations 1988, Saskatchewan Geological Survey, Sask. Energy Mines, Misc. Rep. 88-4, p Maxeiner, R.O. (1996): Bedrock geology of the Henry Lake area (parts ofnts 64D-6 and -11 ), northern La Ronge Domain; in Summary of Investigations 1996, Saskatchewan Geological Survey, Sask. Energy Mines, Misc. Rep. 96-4, p5 l-65. -~~~(1997): Geology of the Lawrence Bay (Reindeer Lake) area, northeastern La Ronge Domain; in Summary of Investigations 1997, Saskatchewan Geological Survey, Sask. Energy Mines, Misc. Rep. 97-4, p ~~~(1998). Geology ofthe Birch Point (Reindeer Lake) area, northeastern La Ronge Domain; in Summary of Investigations 1998, Saskatchewan Geological Survey, Sask. Energy Mines, Misc. Rep. 98-4, p8 l-99. Meyer, M.T., Bickford, M.E., and Lewry, J.F. (1992): The Wathaman Batholith: An early Proterozoic arc in the Trans-Hudson orogenic belt, Canada; Geol. Soc. Amer. Bull., vl 04, p Potter, D. (1979): Investigations of basic igneous rocks, Peter Lake Domain; in Summary of Investigations 1979, Saskatchewan Geological Survey, Sask. Dep. Miner. Resour., Misc. Rep , p Ray, G.E., and Wanless, R.K. (1980): The age and geological history of the Wollaston, Peter Lake, Saskatchewan Geological Survey 141

11 and Rottenstone domains in northern Saskatchewan; Can. J. Earth Sci., v17, p Shklanka, R. ( 1962): The geology of the McLean Bay area, Saskatchewan; Sask. Dep. Miner. Resour., Rep. 74 (1 :63,360 scale map with marginal notes). Stauffer, M.R., Fumerton, S.L., Coleman, L.C., Mossman, D., and Langford, F.F. (1981): Geology of the Ballentin Island vicinity, Reindeer Lake (part ofnts area 64E); Sask. Miner. Resour., Rep. 206, 22p. Stauffer, M.R., Langford, F.F., Coleman, L.C., and Mossman, D. (1980): Geology of the Reindeer Lake North (Southeast) Area; Sask. Dep. Miner. Resour., Rep. 200, 2Ip. Stauffer, M.R. and Lewry, J.F. (1993): Regional setting and kinematic features of the Needle Falls Shear Zone, Trans-Hudson Orogen; Can. J. Earth Sci., v30, p1338-l354. Stockwell, C.H. ( 1929): Reindeer Lake area, Saskatchewan and Manitoba; Geo!. Surv. Can., Summary Report 1928, pt. B, p Tyrrell, J.B. and Dowling, D.B. (1896): Report on the country between Athabasca Lake and Churchill River; Canada Geo!. Surv. Can., Annual Report (New Ser.), Vol. VIII, 1895, Report D. Weeks, L.J. (1941): Reindeer Lake, northern Saskatchewan; Canada Geo!. Surv. Can., Map 595A. /42 Summary of /nvesli~ ations Volume 2

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