Characterization of the Wappasini and Kyaska Thrust Sheets in the Eastern –Western Wapiskau River Area of the Western Reindeer Zone

Ryan M. Morelli 1, Yinghui Zhang 2 and Jaida L. Lamming 3

Information from this publication may be used if credit is given. It is recommended that reference to this publication be made in the following form: Morelli, R.M., Zhang, Y. and Lamming, J.L. (2016): Characterization of the Wappasini and Kyaska thrust sheets in the eastern Brabant Lake–western Wapiskau River area of the western Reindeer Zone; in Summary of Investigations 2016, Volume 2, Geological Survey, Saskatchewan Ministry of the Economy, Miscellaneous Report 2016-4.2, Paper A-2, 17p.

This paper is accompanied by the map separate entitled: Morelli, R.M., Lamming, J.L. and Zhang, Y. (2016): Bedrock geology of the eastern Brabant Lake–Lavender Lake areas (parts of NTS 64D/03 and /04, 63M/13 and /14); 1:20 000-scale preliminary map 2016-4.2-(1) with Summary of Investigations 2016, Volume 2, Saskatchewan Geological Survey, Saskatchewan Ministry of the Economy, Miscellaneous Report 2016-4.2.

Abstract Bedrock mapping was undertaken at 1:20 000 scale in the eastern Brabant Lake–western Wapiskau River area in 2016 to better define the geological history of this part of the west-central Reindeer Zone. Two distinct lithostructural sequences are exposed in this area, each likely corresponding to major, previously designated thrust sheets that are integral to the crustal structure of the western Reindeer Zone. The eastern sequence, part of the Wappasini sheet, is underlain by an igneous-dominated assemblage comprising mafic to intermediate volcanic sequences, some with minor felsic components, that are cut by an array of intrusive rocks. The latter include fine- to coarse-grained mafic and intermediate constituents, some of which are probably contemporaneous with the volcanic rocks, though are dominated by widespread medium-grained granodiorite and tonalite plutons. The western sequence, defining the Kyaska sheet, consists of a sedimentary-dominated assemblage of migmatitic psammopelite and pelite, with thin vestiges of calcic sedimentary interlayers associated with minor dioritic constituents. A domal feature exposed within the sedimentary rocks on easternmost Brabant Lake exposes medium-grained felsic to intermediate plutonic rocks of the Eastern Brabant Plutonic Complex (EBPC). Thin, semicontinuous layers of mafic to intermediate volcanic rocks are spatially associated with these plutonic rocks and exhibit both tectonic and intrusive contacts with them. Mylonite zones, some with brittle overprints, are observed at contacts between the sedimentary rocks of the Kyaska sheet and plutonic rocks of the EBPC, as well as in the northeast part of the map area along the Wapiskau River. Though not exposed, the boundary between the sedimentary-dominated western sequence (Kyaska) and the igneous-dominated eastern sequence (Wappasini) is defined by a marked topographic low that is interpreted to represent a tectonized zone. All rocks in the map area have been affected by at least two early isoclinal folding events (D1, D2), a widespread set of later (D3) upright, north-trending, tight to close folds that control the gross structural distribution of lithological units in this area, and later (D4) open, upright, east- southeast–trending folds. The rocks have been metamorphosed under a minimum of upper amphibolite facies conditions, with widespread evidence of metamorphic-derived partial melting. Collectively, the lithological and structural characteristics of the rocks fit well within the existing thrust sheet model and indicate that the EBPC is a structural inlier of Wappasini sheet rocks mantled by sedimentary rocks of the Kyaska sheet. Furthermore, widespread mylonites exposed in the northeast along the Wapiskau River might represent basal portions of the Wappasini sheet, and rocks of a structurally underlying (Cartier?) thrust sheet might be exposed in the vicinity. The main economic potential for rocks of the area is for volcanogenic massive sulphide– related copper and zinc, as indicated by the presence of minor sulphidic zones and possible syngenetic alteration associated with some of the volcanic rocks.

Keywords: Paleoproterozoic, Reindeer Zone, Trans-Hudson Orogen, Kyaska sheet, Wappasini sheet, volcanogenic massive sulphides, base metals

1 Saskatchewan Ministry of the Economy, Saskatchewan Geological Survey, 1000-2103 11th Avenue, Regina, SK S4P 3Z8 2 Institute of Geology, Chinese Academy of Geological Sciences, Beijing, 100037, China 3 University of British Columbia, Okanagan, 3333 University Way, Kelowna, BC V1V 1V7 Although the Saskatchewan Ministry of the Economy has exercised all reasonable care in the compilation, interpretation and production of this product, it is not possible to ensure total accuracy, and all persons who rely on the information contained herein do so at their own risk. The Saskatchewan Ministry of the Economy and the Government of Saskatchewan do not accept liability for any errors, omissions or inaccuracies that may be included in, or derived from, this product.

Saskatchewan Geological Survey 1 Summary of Investigations 2016, Volume 2 1. Introduction Work continued this year on a 1:20 000-scale bedrock mapping transect of the west-central Reindeer Zone between Brabant and Royal lakes (Figure 1). Following mapping of the westernmost portion of the project in 2014-2015, centred on Brabant Lake (Morelli et al., 2015a, 2015b), work in 2016 was focused on the central part of this transect in the area of eastern Brabant Lake–Lavender Lake–western Wapiskau River. The transect crosses the boundary between the sedimentary-dominated Kisseynew Domain and the volcanoplutonic-dominated Glennie Domain. The main objectives are to improve our understanding of the geological history by detailed bedrock mapping and supporting analytical work, and to provide an updated assessment of the economic mineral potential of the area.

Figure 1 – Location of the overall project area, with interpreted boundaries of thrust sheets comprising the Reindeer Zone of northern Saskatchewan (modified by R. Maxeiner from Lewry et al., 1990) as a backdrop. Long arrow shows approximate axial trace of northeast-trending D4 anticlinorium. Inliers of Archean to Siderian4 rocks include Black Bear Island Lake window (BBIL); Hunter Bay window (HW); Iskwatikan window (IW); Nistowiak window (NW); Pelican window (PW). Other abbreviations: BL = Brabant Lake; RL = Royal Lake. Inset: Same view of Reindeer Zone, showing lithotectonic domain subdivisions (SC = Sask craton inliers).

The 2016 map area (Figure 2) encompasses ca. 180 km2 and includes portions of four National Topographic System (NTS) map sheets (64D/03, 64D/06, 63M/13 and 63M/14). Previous geological maps by Johnston (1968, 1969, 1984) were published at a scale of 1 inch to 1 mile (1:63,360), with the exception of the southeastern portion (NTS 63M/14), which was mapped by Scott (1982) at a scale of 1 inch to ½ mile (1:31,680). Access to the 2016 map area was provided by a combination of float plane, inflatable boats and canoe. Bedrock mapping was completed by a combination of shoreline work from boats, and overland traversing on foot. An extensive forest fire in 2011 resulted in excellent bedrock exposure for mapping in 2016.

4 Subdivision of Paleoproterozoic time from 2.50 to 2.80 Ga from Gradstein et al. (2004).

Saskatchewan Geological Survey 2 Summary of Investigations 2016, Volume 2 2. Regional Geological Context The project area is within the west-central Reindeer Zone of the Trans-Hudson Orogen. The Reindeer Zone represents a collage of rocks originally emplaced in oceanic and peri-oceanic tectonic environments, which were subsequently caught up in the protracted collision between the Rae-Hearne, Superior and Sask cratons during orogenesis. The most common lithological constituents include arc-derived volcanic and plutonic rocks emplaced between about 1900 and 1840 Ma, and clastic sedimentary rocks deposited at discrete intervals during broadly the same time frame. The earliest deformation of rocks in the Reindeer Zone likely occurred at around 1870 Ma, due to amalgamation of intra-oceanic terranes (Lucas et al., 1996). Ongoing subduction resulted in overprinting ‘successor arc’ magmatism and the eventual formation of a protocontinent within the ocean, referred to as the “–Glennie Complex” (FFGC; Ashton et al., 1997). Subduction ultimately resulted in the collision of the FFGC with the Sask craton, causing widespread isoclinal folding and concomitant overthrusting of the former onto the latter along extensive mylonite zones, starting at ca. 1845 Ma (Ashton et al., 2005). Deformation related to this event was long-lived and has been designated as the regional D2 deformation event (Lewry et al., 1990; Ashton et al., 2005). Eventual collision of these rocks with the Rae-Hearne and Superior cratons resulted in the generation of additional deformation fabrics. Regional D3 deformation is recorded as pervasive north-trending, upright, tight to close folds and north-trending shear zones, whereas D4 deformation is manifest as outcrop- to regional-scale, dominantly northeast-plunging, open to close folds (Lewry et al., 1990).

Interference of map-scale F3 and F4 folds has been interpreted as the cause of domal structures that, due to subsequent erosion, allow present-day exposure of Sask craton inliers mantled by extensive D2 mylonite zones (Figure 1; Ashton et al., 2005). According to Lewry et al. (1990), similar high-strain zones represent boundaries between a series of stacked lithostructural sheets (or ‘allochthons’) that are exposed in cross-section within the western Reindeer Zone. These thrust sheets, namely the “Kyaska”, “Wapassini” and “Cartier” sheets (Figure 1), provide a useful present-day framework for interpretation of the tectonic history of the Reindeer Zone. The 2016 study area overlaps the interpreted boundary of the sedimentary rock–dominated Kyaska sheet (west) and the volcanoplutonic rock–dominated Wapassini sheet (east).

3. Local Geology

a) Wappasini Sheet The Wappasini thrust sheet, underlying the eastern half of the 2016 map area, is dominated by igneous rocks5 of unknown absolute age. The rocks inferred to be the oldest are a sequence of compositionally variable volcanic rocks that are exposed in widely distributed folded belts (Figure 2). It is noteworthy that rocks designated as volcanic throughout the map area are not clearly of effusive origin and almost certainly include components of volcaniclastic and intrusive derivation. Such a designation is impossible to make in most cases due to the obliteration of original textures by the cumulative effects of later deformation and high-grade metamorphism. Intermediate volcanic rocks (unit WIV6) are exposed mainly to the north and south of eastern Lavender Lake. They are well-layered and fine- grained rocks (Figure 3A) consisting of plagioclase (60 to 75%), hornblende (15 to 35%), quartz (0 to 5%) and local garnet (up to 5%), along with traces of magnetite and sulphide minerals. Thin (<20 cm) mafic and felsic volcanic interlayers, defined by variable hornblende, plagioclase and quartz contents, are common. Thin diopsidic calc-silicate interlayers are also locally present, possibly derived from addition of calcium during pre-metamorphic hydrothermal alteration. Isolated exposures of mixed volcanic rocks (unit WMx) are similar in character to those assigned to unit WIV but include a higher proportion of felsic volcanic rocks (Figure 3B), which form layers up to several metres thick in rare cases. A unit of weakly layered to homogeneous amphibolite (unit WAm), comprising dominantly hornblende (35 to 75%) and plagioclase (25 to 65%), is most abundant south of the Wapiskau River.

5 All rock units in the map area, with the exception of some of the late intrusive rocks, have undergone high-grade metamorphism; the prefix ‘meta’ has therefore been omitted for simplicity. Classification of sedimentary rocks follows guidelines by Maxeiner et al. (1999). 6 All unit designations in this paper correspond to those in the legend of Figure 2.

Saskatchewan Geological Survey 3 Summary of Investigations 2016, Volume 2

Figure 2 – Simplified version of the new 1:20 000-scale map of the eastern Brabant Lake–Lavender Lake–western Wapiskau River area that accompanies this report. Grey line labelled ‘A-B’ is location of schematic section shown in Figure 10. EBPC = Eastern Brabant Plutonic Complex, BL = Brabant Lake, LL = Lavender Lake, EKB = East Knight Bay (Brabant Lake), WR = Wapiskau River, WKB = West Knight Bay (Brabant Lake), YI = Yaworski Island.

Saskatchewan Geological Survey 4 Summary of Investigations 2016, Volume 2 These rocks are locally compositionally layered with subordinate interlayers of intermediate composition, indicating that they are at least partly of volcanic derivation. Compared to the volcanic rocks mapped in the western part of the Wappasini sheet, they are commonly pervasively injected by later metamorphic leucosome (i.e., ‘injection migmatites’; Figure 3C) and therefore do not consistently form continuous, coherent entities but are more commonly present as discontinuous, isolated exposures. Relative age relationships between the various units listed above are unknown at present. A distinctive unit of heterogeneous diorite to quartz diorite (unit WDh) was identified in a few isolated localities. This rock is fine to medium grained, homogeneous to weakly layered, and typically contains hornblende (15 to 30 %), plagioclase (60 to 80%), quartz (<15%) and, locally, garnet (<5%). It is distinguished as an intrusive rock due to the characteristic presence of 5 to 25 cm long, hornblende (±diopside)-rich mafic to ultramafic xenoliths (Figure 3D). A compositionally variable unit designated as fine-grained quartz diorite, diorite to gabbro (unit WDf) is exposed south of Lavender Lake and consists of hornblende (20 to 60%), plagioclase (40 to 70%) and, locally, quartz (<10%). Rocks of units WDh and WDf generally lack significant internal compositional layering. Contact relationships between these mafic to intermediate intrusive rocks and the more strongly layered volcanic rocks are not well defined, and at least some of the former are thought to be high-level synvolcanic intrusions.

Figure 3 – Outcrop photographs of igneous rock units of the Wappasini thrust sheet exposed on Lavender Lake and the western Wapiskau River: A) Layered, fine-grained intermediate volcanic rock with thin mafic interlayers, UTM7 592295E, 6209953N. B) Example of mixed volcanic unit exhibiting adjacent intermediate and felsic interlayers and containing thin, layer-parallel leucosome injections, UTM 592152E, 6205215N. C) Weakly layered to homogeneous, fine-grained mafic volcanic rock that has been infiltrated and dismembered by later leucosomal melt injections, UTM 594546E, 6203829N. D) Medium-grained, heterogeneous quartz diorite containing subangular xenoliths composed of coarse-grained hornblende and diopside, UTM 596955E, 6207923N.

7 All UTM coordinates are in Zone 13, NAD83.

Saskatchewan Geological Survey 5 Summary of Investigations 2016, Volume 2 The majority of the Wappasini sheet investigated in 2016 is underlain by an extensive intermediate to felsic plutonic suite that intruded the volcanic rocks. These plutons are also thought to have intruded aforementioned intrusive rocks (units WDh and WDf), though direct contacts were not observed. The most common rock type is gneissic granodiorite to tonalite (unit WGd; Figure 4A), which typically consists of medium-grained plagioclase and K-feldspar, quartz (20 to 35%) and hornblende (10 to 20%). Widespread injections of lit par lit leucosome, along with thermotectonic-induced mineral segregation, have resulted in a prominent gneissosity in most of these rocks. Compositional variants of this pluton are also present, including medium- to coarse-grained quartz diorite to diorite (unit WDi), which is generally homogeneous and contains less quartz (<15%) and more hornblende (Figure 4B) relative to granodioritic and tonalitic components. All of these plutonic rocks clearly intrude the volcanic sequences, as evidenced by the common presence of xenoliths (Figure 4C).

Figure 4 – Outcrop photographs of plutonic rocks of the Wappasini thrust sheet exposed between Lavender Lake and the western Wapiskau River: A) Medium-grained, weakly gneissic hornblendic tonalite, UTM 589634E, 6204788N. B) Medium- grained, foliated quartz diorite, UTM 595432E, 6209450N. C) Locally derived xenoliths of layered mafic to intermediate volcanic rock in tonalite, UTM 592151E, 6205215N. D) Gradational internal change in hornblende-rich gabbro from coarse-grained margin to fine-grained interior, UTM 590730E, 6205656N. E) Amphibolite pervasively infiltrated by relatively late leucogranitic intrusion of unit WLgt, UTM 595562E, 6206304N. F) Cluster of very coarse magnetite crystals near margin of leucogranitic pegmatite dyke, UTM 595002E, 6209337N.

Saskatchewan Geological Survey 6 Summary of Investigations 2016, Volume 2 A unit of coarse-grained gabbro to pyroxenite (unit WGa), exposed in discontinuous belts along eastern Lavender Lake, is of uncertain relationship with other intrusive rocks in the area. This rock consists of 70 to 90% coarse hornblende, likely pseudomorphed after subhedral pyroxene crystals, separated by interstitial plagioclase. It commonly exhibits gradational changes into a fine-grained compositional equivalent (Figure 4D). Though its age relative to other rocks is unknown, its massive appearance and apparent crosscutting relationship at map-scale suggests that it may postdate formation of the main regional fabric, which has strongly affected most other rock types. The youngest rock type encountered in the area was light pink to pink leucogranite to leucogranodiorite (WLgt), composed primarily of feldspar (50 to 60%; predominantly K-feldspar), quartz (25 to 40%) and biotite (<5%). Thought to have originated as a metamorphic melt product, this rock is widespread throughout the eastern half of the 2016 map area. Although some exposures are of sufficient size to form map units, it is particularly prevalent as centimetre- to metre-scale pervasive injections within other rock types, particularly units WGd and WAm (Figure 4E) in the vicinity of the Wapiskau River. Where it has intruded rocks of mafic composition, it commonly exhibits relatively high amounts of hornblende near the contact. In general, this rock is not strongly deformed and thus likely postdated formation of the main regional foliation. A suite of randomly oriented, massive, leucogranitic pegmatite intrusions has also intruded into rocks of the Wappasini sheet and might be contemporaneous with or postdate emplacement of rocks of the leucogranite to leucogranodiorite. These pegmatites are rich in K-feldspar and locally contain abundant magnetite crystals, 1 to 10 cm in diameter (Figure 4F), which tend to be concentrated along the intrusion margins. Though individual intrusions are generally not of sufficient size or continuity to be represented at 1:20 000 scale, collectively they are a common suite and are especially prevalent in the easternmost part of the 2016 map area. b) Kyaska Sheet Between the eastern edge of Brabant Lake and western Lavender Lake, rocks of the Kyaska thrust sheet predominate. These rocks are dominated by metatexitic psammopelite-pelite (unit Psp), which consists of a matrix of fine-grained quartz (20 to 40%), biotite (10 to 25%), feldspar (30 to 65%), garnet (5 to 15%) and, locally, traces of graphite. This unit is typically compositionally layered with subordinate foliation-parallel, 5 to 40 cm thick interlayers of diatexitic pelite along with minor psammite and calc-silicate rock interlayers, the latter likely derived from calcareous sedimentary layers. The rock generally contains 15 to 60% quartzofeldspathic ±garnet-bearing leucosome, 5 to 20% melanosome that is rich in biotite and fine- to coarse-grained garnet porphyroblasts, and 20 to 80% paleosome. The leucosome is a combination of in situ, in-source and injected components, which commonly have a lit par lit distribution. Compositional interlayers and lit par lit leucosome give the rock a stromatic texture in many cases (Figure 5A) and are commonly boudinaged. At map scale, the metatexitic psammopelitic rocks are conformably interlayered with thick beds of diatexitic pelite (unit Pl), which forms several semicontinuous map units throughout the area. The diatexitic pelite is typically grey to brownish grey and ranges from fine to coarse grained. It characteristically lacks a paleosome (<10%) and contains >90% neosome, including 25 to 40% garnet and biotite and, locally, sillimanite and/or cordierite (Figure 5B). Fine grains of disseminated graphite (1 to 3%) are also typically present along the foliation planes. In situ leucosome is ubiquitous and consists of coarse-grained plagioclase feldspar, quartz and K-feldspar in varying proportions; garnet and coarse (1 to 2 cm in diameter) cordierite porphyroblasts are commonly present in the leucosome. The leucosome generally imparts a massive (unlayered to weakly layered) texture to the rock. Rocks of the pelitic unit locally contain 10 to 20% psammitic to psammopelitic interlayers that are <20 cm in thickness and commonly boudinaged. Subordinate lithological constituents in this part of the Kyaska sheet include calcic psammopelite to psammite (±diorite; unit CPs). This partly migmatitic rock forms isolated interlayers within unit Psp and is internally weakly to moderately compositionally layered at the centimetre to metre scale (Figure 5C). It is generally fine grained and contains hornblende (5 to 25%), biotite (5 to 10%), quartz (10 to 25%) and plagioclase (40 to 60%), and locally contains garnet (5 to 10%). In one location northeast of Lavender Rapids, this unit is associated with metre-thick interlayers of calc-silicate rock, comprising diopside (5 to 15%), hornblende (5 to 25%) and plagioclase, with local calcite-rich pods. Though dominantly of sedimentary origin, this unit locally exhibits internal variability and probably includes minor igneous components. In such cases the well-layered sedimentary rocks exhibit relatively sharp contacts with metre-scale homogeneous interlayers comprising dominantly fine- to medium-grained plagioclase, quartz, biotite and hornblende. These possibly represent minor synsedimentary dioritic components.

Saskatchewan Geological Survey 7 Summary of Investigations 2016, Volume 2

Figure 5 – Outcrop photographs of common rock units of the Kyaska thrust sheet on east-central Brabant Lake: A) Typical outcrop appearance of stromatic psammopelite, UTM 586293E, 6209423N. B) Diatexitic pelite containing porphyroblasts of garnet, cordierite and abundant in situ neosome, UTM 590113E, 6210128N. C) Layered hornblende- and garnet-bearing calcic psammopelite, UTM 588389E, 6208998N. D) Example of very coarse-grained leucotonalite injection within psammopelite, UTM 585801E, 6205770N.

The preponderance of Kyaska sheet rocks are migmatitic and contain centimetre- to metre-scale dykes and pods derived from in situ or injected partial melt. In places these injections form larger accumulations of coarse-grained to pegmatitic, leucocratic tonalite to granodiorite (Figure 5D) that are of sufficient dimensions to show at the scale of mapping (unit Lgt).

c) Eastern Brabant Plutonic Complex The Eastern Brabant Plutonic Complex (EBPC; Morelli et al., 2015b) comprises an assemblage of rocks exposed within a north-northeast–trending elongate dome structure (Figure 2) that is distinct from the mantling sedimentary- dominated rocks of the Kyaska sheet. The EBPC mainly comprises medium-grained gneissic granodiorite to tonalite (unit EBGd; Figure 6A), consisting of quartz (20 to 30%), variable amounts of plagioclase and K-feldspar, and hornblende (5 to 20%). This rock commonly contains lit par lit injections of leucogranodiorite to leucogranite that give it a gneissic appearance, though it is also homogeneous in places. Apparently contemporaneous quartz diorite (EBQD), compositionally similar to the granodiorite-tonalite except for lower quartz (5 to 20%) and K-feldspar (<10%) contents (Figure 6B), is present as sheets within the granodiorite.

Saskatchewan Geological Survey 8 Summary of Investigations 2016, Volume 2

Figure 6 – Outcrop photographs of rock units within, or spatially associated with, the Eastern Brabant Plutonic Complex (EBPC) on east-central Brabant Lake: A) Foliated gneissic granodiorite with folded leucosome injections, UTM 584975E, 6211360N. B) Moderately to strongly foliated gneissic quartz diorite with injected leucosome stringers and dykes, UTM 583603E, 6205965N. C) Compositionally layered fine-grained mafic volcanic rock with thin diopside-bearing calc-silicate layers and layer-parallel stringers of injected leucotonalitic leucosome, UTM 583875E, 6206642N. D) Example of mixed volcanic unit consisting of interlayered intermediate (right) and garnetiferous felsic (left) components; contact approximated by yellow dashed line, UTM 584835E, 6215045N. E) Silicified high strain zone in granodiorite marking the contact (yellow dashed line) with layered mafic volcanic rocks (MV), UTM 584686E, 6209239N. F) Xenoliths (red dashed lines) of layered mafic volcanic (MV) rock in granodiorite (EBGd) of the EBPC, UTM 584975E, 6211360N.

Saskatchewan Geological Survey 9 Summary of Investigations 2016, Volume 2 d) Undesignated Rocks Other rock types, though not genetically related, are spatially associated with the exposure of the EBPC. The most common of these comprises metre-scale, attenuated layers of mafic to intermediate volcanic rock (unit UMV). These rocks are fine grained and, though locally homogeneous, commonly exhibit subtle compositional layering defined by variance in mafic mineral content (Figure 6C). These rocks consist mainly of hornblende (20 to 80%) and plagioclase (20 to 70%), and locally contain diopside (<15%), garnet (<10%) and/or traces of pyrite and pyrrhotite. Homogeneous constituents of this unit may represent synvolcanic dykes or sills. Leucotonalitic leucosome is common in these rocks as lit par lit injections or, less commonly, as in situ pods that contain coarse hornblende porphyroblasts locally cored by dark brown orthopyroxene. Rock types presumably related to the mafic volcanic rocks include mixed volcanic rocks (unit UMx) and diorite-gabbro (UDi). The mixed volcanic rocks are similar to those of the mafic to intermediate volcanic rock unit but are more strongly compositionally layered, containing a more prevalent component of intermediate and felsic volcanic interlayers (Figure 6D), some of which are strongly garnetiferous. Rocks of the diorite-gabbro unit are fine grained and contain primarily hornblende (20 to 70%) and plagioclase (25 to 75%), with local enrichment of fine garnet (up to 20%). In contrast to the volcanic rocks, they are compositionally homogeneous at outcrop scale. This indicates that these rocks could represent high-level intermediate to mafic intrusions that are genetically related to the volcanic rocks, though direct contact relationships were not observed. Where observed, contacts between the sedimentary rocks of the Kyaska sheet (i.e., units Psp, Pl) and the plutonic components of the EBPC are highly strained, suggesting that these rocks were originally disparate and were brought together spatially during later tectonism. The relationship between the plutonic and spatially associated volcanic rocks is, however, less clear at present. Although some of the observed contacts between these rocks were structural in nature (Figure 6E), metre-scale xenoliths of layered volcanic rocks were observed in granodiorite (Figure 6F). This suggests that at least some of the volcanic rocks formed the crustal substrate at the time of EBPC intrusion.

Figure 7 – Outcrop photographs of sedimentary rocks exposed in the western Wapiskau River area: A) Layered migmatitic psammopelite with in situ, layer-parallel leucosome stringers, UTM 593838E, 6206349N. B) Fine-grained, weakly layered garnetiferous psammite with injected leucogranitic melt stringers, UTM 592970E, 6205056N.

Thin vestiges of clastic sedimentary rocks underlie the area near the channel joining Lavender Lake to the Wapiskau River (Figure 2). A unit of migmatitic psammopelite to pelite (unit UPsp) comprises quartz (20 to 35%), feldspar (30 to 60%), biotite (10 to 20%), garnet (1 to 15%) as well as up to 1% graphite. Thin (<20 cm) interlayers of pelite and, rarely, amphibolite are present. The presence of up to 30% in situ and injected leucosome give the rock a gneissic texture (Figure 7A). A few laterally discontinuous exposures of psammite (unit UPs) were also observed (Figure 7B) and consist of quartz (30 to 35%), feldspar (50 to 65%), biotite (5 to 10%) and garnet (1 to 5%). This rock is weakly layered and contains up to 20% injected stringers of leucogranitic leucosome. Contact relationships between these siliciclastic rocks and surrounding plutonic rocks are unclear, though the observed presence of high-strain zones in nearby plutonic rocks suggests they are at least partly tectonic.

Saskatchewan Geological Survey 10 Summary of Investigations 2016, Volume 2 4. Structure and Metamorphism Most of the rocks investigated are strongly deformed and of high metamorphic grade. The earliest identified deformation fabric (D1) is a pervasive, layer-parallel foliation defined by alignment of constituent minerals, including quartz, feldspar, biotite and/or hornblende (e.g., Figures 5A, 7A). Thin layers of in situ or injected leucosome, which impart a gneissic texture to the rocks, are commonly parallel to this foliation. Subsequent isoclinal folding during D2 deformation resulted in generation of a composite S1/S2 regional foliation in the majority of rocks except in F2 fold hinges, where a distinct axial planar S2 fabric is locally observed (Figure 8A). The orientation of F2 folds is variable across the map area owing mainly to the effects of subsequent deformation. The D3 deformation event led to widespread north-northeast–trending, tight to close folding throughout the area (Figure 2), including an interpreted series of map-scale synforms and antiforms. Though some variation exists, observed F3 folds are generally steeply inclined to upright and moderately to shallowly plunging (Figure 8B). An axial planar foliation (S3) is observed sporadically and dips moderately to steeply to the west throughout most of the map area, though it locally dips moderately to steeply east. A shallow to moderate (5 to 35°), dominantly north-northwest- to north-northeast– trending mineral lineation (L3) is commonly observed and generally parallels the axes of F3 folds. As opposed to rocks in the western Brabant Lake area (Morelli et al., 2015b), the effects of D3 deformation are much stronger in and east of eastern Brabant Lake and are thought to be responsible for the prominent north to north-northeast trend of lithological units (Figure 2). The youngest folding event to have affected the area (F4) produced open to gentle, upright folds that refold D1 to D3 fabrics. These folds, observed only at outcrop scale at a few locations, are generally west-northwest–trending. They may be responsible for local plunge reversals in the axes of F3 folds, as inferred from sporadic variation in the plunge direction of both L3 lineations and minor F3 fold axes to shallowly south plunging. Superposition of at least three fold generations resulted in the development of complex interference structures, creating locally complex map patterns. At both outcrop and map scale, hybrid Type 2 and 3 (Figure 8C) and Type 1 (Figure 8D) fold interference patterns (Ramsey, 1967) are evident. The Type 2/3 patterns are thought to be derived from interference of variably oriented isoclinal F2 folds and north-trending tight to close F3 folds, whereas Type 1 patterns are thought to be derived from interference of F3 and open east- to southeast-trending F4 folds. Another possibility, though not directly supported from existing mapping, is that such patterns could result from some F3 folds being originally doubly (north and south) plunging. In addition to folding, a long-lived history of shearing and faulting is evident. The earliest such structures observed are zones of ductile high strain that parallel the trend of lithological units and the regional foliation. These metre-scale zones are observed sporadically throughout the map area but are especially prevalent along the margins of the Eastern Brabant Plutonic Complex and in granodiorite of the Wappasini sheet along the Wapiskau River in the northeastern corner of the map area (Figure 2). In both locations, mylonitic fabrics are characterized by ribboned quartz, reduction in size of feldspar grains, increased biotite content, strongly boudinaged compositional layering, and/or the presence of feldspar porphyroclasts or ‘beading’ (Figure 8E). These fabrics have undergone F3 folding at both outcrop (Figure 8B) and map scales, and are interpreted to have formed during or prior to D2 deformation.

A south-trending mylonitic fabric was locally observed to clearly crosscut D2 fabrics and to be affected by an F4 fold, and is therefore thought to be related to the D3 deformation event. This fabric was unambiguously observed only at the northernmost bay of the eastern branch of Lavender Lake (Figure 8F), and is therefore thought to have a relatively limited expression in the map area. It may be responsible, however, for the local reorientation of some lithological units into a more northerly orientation (e.g., south of where Lavender Lake joins the Wapiskau River), and provide the topographic control on the north-south orientation of the eastern branch of Lavender Lake and the western portion of the Wapiskau River. Extensive chloritization, rock brecciation and pseudotachylyte overprint earlier mylonitic fabrics in places. This collectively suggests overprinting of ductile fabrics by later brittle faulting at shallower crustal levels and lower temperatures. These brittle textures are especially concentrated in the easternmost Brabant Lake area, where they are consistently northerly trending and steeply dipping and correspond to the previously recognized Stanley Fault zone (Johnston, 1969). It seems most probable that these late structures are reactivating zones of earlier (?D1 and/or D2) ductile deformation, possibly along steeply west-dipping limbs of major F3 folds.

Saskatchewan Geological Survey 11 Summary of Investigations 2016, Volume 2

Figure 8 – Outcrop photographs showing structural characteristics of rocks: A) Compositional layering and S1 foliation defining an isoclinal F2 fold closure, with coarse sillimanite clots (s) defining an axial planar S2 foliation, UTM 585855E, 6205278N. B) View down-plunge (looking north) of an outcrop-scale F3 fold in ultramylonitic granodiorite gneiss containing strongly attenuated mafic interlayers of unknown derivation, UTM 596303E, 6207516N. C) Hybrid Type 2 and 3 fold interference pattern in granodiorite gneiss interpreted to be produced by interference of F2 (axis = red dashed line) and F3 (axis = blue dashed line) folds, UTM 584693E, 6209268N. D) Approximate Type 1 fold interference pattern in layered volcanic rock interpreted to be produced by interference of F3 (axis = blue dashed line) and F4 (axis = yellow dashed line) folds, UTM 595076E, 6204184N. E) Ductile, D2-related high strain resulting in boudinage and development of feldspar porphyroclasts in granodiorite gneiss, UTM 598513E, 6207675N. F) D3-related mylonite zone (trend shown by dashed green lines) overprinting regional S1/S2 foliation (pink dotted line); dotted white line shows shear zone margin, UTM 591649E, 6206815N.

Saskatchewan Geological Survey 12 Summary of Investigations 2016, Volume 2 Morelli et al. (2015b) had concluded that peak metamorphic assemblages at west-central Brabant Lake correspond to lower granulite facies metamorphism, with subsequent back reaction to upper amphibolite facies assemblages. Similar assemblages were observed in 2016 between Brabant Lake and Lavender Lake. For example, pelite exposed on western Lavender Lake exhibits a paragenesis of garnet, sillimanite, cordierite and in situ leucosome (Figure 9A). Furthermore, coarse orthopyroxene was observed in and adjacent to in situ leucosome in mafic volcanic rocks in the East Knight Bay area (Figure 2).

Figure 9 – Metamorphic features of rocks in the map area: A) Paragenesis of metamorphic minerals in pelite of the Kyaska sheet exposed on the south shore of western Lavender Lake that includes cordierite (c), garnet (g), sillimanite (s), and in situ leucosome (m) in apparent equilibrium, UTM 588543E, 6207417N. B) Gneissic granodiorite of the Wappasini sheet exposed on the southeastern shore of eastern Lavender Lake exhibiting thin margin of melanosome on margin of layer-parallel leucosome, indicating effects of in situ partial melting, UTM 591952E, 6202813N. C) Gneissic granodiorite of the Wappasini sheet exposed on the western Wapiskau River showing undeformed hornblende porphyroblasts overprinting earlier fabrics, UTM 597248E, 6207921N.

Eastward from central Lavender Lake, however, igneous-dominated rocks of the Wappasini thrust sheet generally do not contain mineral assemblages that readily allow diagnosis of peak metamorphic conditions. Rocks in this area are migmatitic, as indicated by widespread leucosome in orthogneisses. This leucosome is dominantly injected as lit par lit and crosscutting layers, but is locally paired with a thin melanosome in the felsic to intermediate rocks (Figure 9B), thus indicating partial melting of the host rock and suggesting that, at minimum, upper amphibolite facies conditions were attained. Small psammopelitic vestiges exposed along the westernmost channel of the Wapiskau River are garnetiferous and contain in situ leucosome layers, but no other diagnostic metamorphic minerals were identified. The presence of 2 to 5 mm diameter, randomly oriented hornblende porphyroblasts (Figure 9C) overgrowing deformational—including mylonitic— fabrics and neosome in rocks in the easternmost portion of the map area suggests that at least some of this high temperature metamorphism outlasted D2 deformation.

Saskatchewan Geological Survey 13 Summary of Investigations 2016, Volume 2 5. Regional Lithotectonic Considerations Although not exposed in the 2016 map area, the contact between sedimentary-dominated rocks in the west (Kyaska thrust sheet) and igneous-dominated rocks in the east (Wappasini thrust sheet) is interpreted here as a significant structural break. This boundary is marked by a prominent, north-northeasterly trending topographic lineament that transects the area (white dotted line on Figure 2). Just southwest of the map area, air photograph analysis indicates that this lineament curves to the west, ostensibly around a south-closing (F3) fold. This apparent closure corresponds to the location of the previously designated Ray Lake syncline (Johnston, 1969), and indicates a relatively early (pre- D3) history for this structural discontinuity. This also indicates that this boundary predates the effects of relatively late cataclastic deformation associated with the Stanley Fault, exposed to the west on eastern Brabant Lake (Figure 2).

These kilometre-scale, northerly trending F3 folds appear to exert significant control on the overall crustal structure in this part of the Reindeer Zone. Exposure of rocks of the EBPC, for example, are interpreted to be the result of a domal structure caused by interference of F3 and F4 folds, or possibly by an antiformal culmination of a doubly- plunging F3 fold. The EBPC is mantled by ductile high-strain zones, which are thought to be the refolded equivalent of the inferred structural contact zone separating the Wappasini and Kyaska thrust sheets to the east. Thus, the rocks exposed in this dome are interpreted to be roughly equivalent to those of the Wappasini sheet in the eastern part of the map area (Figure 10). Likewise, clastic sedimentary rocks exposed at the western limit of the Wapiskau River (units UPsp, UPs; Figure 2) may be equivalent to those exposed on Brabant Lake, representing infolded erosional remnants of the Kyaska sheet situated in an F3 synclinal keel. Supplemental work (e.g., structural analysis, geochemistry, geochronology) will help test this model.

Figure 10 – Schematic cross-section from west to east across the 2016 map area showing interpretation of the regional crustal structure, following the model of Lewry et al. (1990). Red dashed lines indicate interpreted locations of F3 fold traces; dark blue dotted lines represent schematic examples of F2 fold axial planes; black dashed lines represent mylonitic soles of major thrust sheets. EBPC = exposure of the Eastern Brabant Plutonic Complex; LL/WR = location at which Lavender Lake drains into the Wapiskau River; RLF = Ray Lake fold; SF = Stanley Fault.

In general, the observed lithological and structural characteristics of rocks in the eastern Brabant Lake–western Wapiskau River area align well with the model of the gross crustal architecture of the western Reindeer Zone proposed by Lewry et al. (1990). This model viewed the stacked thrust sheets comprising the western Reindeer Zone to be soled by extensive and relatively early (regional D1 and D2) high strain zones. One important prediction of this model is that the likelihood of the presence of Archean–Siderian cratonic inliers increases in areas exposing deeper levels of the crust. The possible presence of such an inlier in the general project area can be inferred from the interpretation of Lithoprobe seismic reflection data acquired ~15 km west (line S2b; Corrigan et al., 2005), from which it can be inferred that the Sask craton may project to surface somewhere in this region. Previous investigations in the Otter–Mountain–Nistowiak lakes area (Chiarenzelli et al., 1998; Maxeiner et al., 2013) 70 km to the southwest, just north of Lac , provide a useful basis for comparison in this respect. This area north of Lac La Ronge reveals an eastward transition from Kyaska sheet sedimentary rocks into Wappasini sheet igneous rocks, but also includes the transition across mylonite zones into exposed ortho- and paragneissic rocks of the underlying Cartier sheet. Furthermore, at the base of this crustal section, strongly deformed rocks of the Sask craton (Chiarenzelli et al., 1998) are exposed as inliers mantled by mylonitic rocks of the Cartier sheet.

Saskatchewan Geological Survey 14 Summary of Investigations 2016, Volume 2 In the Nistowiak Lake area, rocks of the Cartier sheet comprise an assemblage consisting predominantly of migmatitic psammopelite, mafic to intermediate volcanic rocks, and mafic to intermediate plutonic rocks, with subordinate felsic plutonic rocks (Maxeiner et al., 2013). Mapping to date has revealed no clear indication that equivalent rock assemblages are exposed between Lavender Lake and the Wapiskau River. This suggests that the lowest structural level exposed in this part of the Reindeer Zone is the Wappasini sheet. Mylonitic rocks exposed in the vicinity of the Wapiskau River in the northeasternmost part of the map area could, however, mark the transition into the basal units of the Wappasini sheet. If so, it is possible that rocks of the Cartier sheet, as well as inliers of Sask craton crust, could be exposed to the east of the 2016 map area. Alternatively, this high strain zone could mark a splay off of a more deeply rooted structure that has projected to higher structural levels, analogous to the Sturgeon–Weir thrust exposed in the Hanson Lake area of the southern Reindeer Zone (Lewry et al., 1990). Future work on the project will test these hypotheses.

6. Economic Considerations The main mineral commodities known in the general project area are gold and base metals. For the 2016 map area specifically, two minor copper showings are listed in the Saskatchewan Mineral Deposits Index (#0435 and #0436; Figure 2), both of which were discovered during government mapping by Johnston (1969). It is currently unclear whether this paucity of known economic mineralization is reflective of actual mineral potential or, rather, the lack of past exploration activity. According to the Saskatchewan Mineral Assessment Database, the only documented exploration work performed in the immediate area was a regional airborne radiometric survey completed by Canadian Aero Mineral Surveys in 1968. In the present campaign, mafic to intermediate rocks were seen to typically contain small amounts of pyrite and pyrrhotite, commonly resulting in a slight rusty-coloured weathering expression. A few strongly oxidized zones8 within mafic igneous rocks or in sedimentary rocks proximal to mafic rocks, were observed (Figure 11A; see accompanying preliminary map for locations). In some such cases, the nearby volcanic rocks were locally strongly garnetiferous (Figure 11B). This is perhaps indicative of minor pre-metamorphic hydrothermal alteration, though no other metamorphic minerals indicative of strongly metamorphosed chloritic or argillic alteration (e.g., cordierite, anthophyllite, cummingtonite, etc.) were observed at these locations.

Figure 11 – A) Example of a strongly oxidized, sulphidic zone in mafic volcanic rock containing mainly pyrite and pyrrhotite, UTM 595745E, 6206178N. B) Strongly garnetiferous felsic interlayer proximal to an oxidized weathering zone in layered volcanic sequence, possibly indicating effects of pre- metamorphic hydrothermal alteration, UTM 595076E, 6204184N.

With respect to gold, although several quartz veins of varying orientation were observed, none appeared to contain gold8 or significant amounts of sulphides. The

8 Analysis of grab samples is in progress.

Saskatchewan Geological Survey 15 Summary of Investigations 2016, Volume 2 sole indication of anomalous gold concentration in the area is from a 6 ppb value from a lake sediment gold analysis taken from the easternmost arm of Lavender Lake (Geological Survey of , 1984). It is currently unclear whether the perceived lack of potential for economic gold mineralization in the northern Glennie Domain is warranted, or whether it instead reflects the lack of focused exploration activity and/or inaccurate exploration paradigms.

7. Acknowledgments Mapping in 2016 could not have been completed without the hard work of junior field assistants Bryn Gelowitz, Justine Jaeb and Brett Williams. Discussions stemming from a field trip in the project area with Dr. Guo Lei and Dr. Zhu Xiaosan from the Institute of Geology, Chinese Academy of Geological Sciences provided insight into several aspects of the geology, and were appreciated. Technical discussions with Saskatchewan Geological Survey geologists Ralf Maxeiner and Jason Berenyi were also beneficial. Technical review of this report by Ralf Maxeiner and Ken Ashton were appreciated.

8. References Ashton, K.E., Card, C.D. and Harvey, S.E. (1997): Geology of the Mokoman (Knife) Lake-Reindeer River area: The Scimitar Complex and its relationship to the Glennie Domain; in Summary of Investigations 1997, Saskatchewan Geological Survey, Saskatchewan Energy and Mines, Miscellaneous Report 97-4, p.55-64. Ashton, K.E., Lewry, J.F., Heaman, L.M., Hartlaub, R.P., Stauffer, M.R. and Tran, H.T. (2005): The Pelican thrust zone: basal detachment between the Archean Sask craton and Paleoproterozoic Flin Flon-Glennie complex, western Trans-Hudson Orogen; Canadian Journal of Earth Sciences, v.42, no.4, p.685-706. Chiarenzelli, J.R., Aspler, L.B., Villeneuve, M. and Lewry, J. (1998): Early Proterozoic evolution of the Saskatchewan Craton and its allochthonous cover, Trans-Hudson Orogen; Journal of Geology, v.106, p.247-267. Corrigan, D., Hajnal, Z., Nemeth, B. and Lucas, S.B. (2005): Tectonic framework of a Paleoproterozoic arc-continent to continent-continent collisional zone, Trans-Hudson Orogen, from geological and seismic reflection studies; Canadian Journal of Earth Sciences, v.42, no.4, p.421-434. Geological Survey of Canada (1984): Regional lake sediment geochemical reconnaissance data, east-central Saskatchewan; Geological Survey of Canada, Open File 1129, 146p., doi:10.4095/129940. Gradstein, F.M., Cooper, R.A., Sadler, P.M., Hinnov, L.A., Smith, A.G., Ogg, J.G., Villeneuve, M., McArthur, J.M., Howarth, R.J., Agterberg, F.P., Robb, L.J., Knoll, A.H., Plumb, K.A., Shields, G.A., Strauss, H., Veizer, J., Bleeker, W., Shergold, J.H., Melchin, M.J., House, M.R., Davydov, V., Wardlaw, B.R., Luterbacher, H.P., Ali, J.R., Brinkhuis, H., Hooker, J.J., Monechi, S., Powell, J., Röhl, U., Sanfilippo, A., Schmitz, B., Lourens, L., Hilgen, F., Shackelton, N.J., Lasker, J., Wilson, D., Gibbard, P. and van Kolfschoten, T. (2004): Geologic Time Scale 2004; Cambridge University Press, Cambridge, UK, 589p. Harper, C.T. (1998): The La Ronge Domain-Glennie Domain transition: Street Lake area (parts of NTS 64D-3 and -6); in Summary of Investigations 1998, Saskatchewan Geological Survey, Saskatchewan Energy and Mines, Miscellaneous Report 98-4, p.66-80. Johnston, W.G.Q. (1968): The Geology of the Kelly Lake Area; Saskatchewan Department of Mineral Resources, Report 106, 64p. Johnston, W.G.Q. (1969): The Geology of the Eastern Portion of the Waddy Lake Area, Saskatchewan; Saskatchewan Department of Mineral Resources, Report 127, 43p. Johnston, W.G.Q. (1984): Geology of the Royal Lake and Laird Lake (east) areas; Saskatchewan Energy and Mines, Open File Report 83-1, 80p. 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 The Early Proterozoic Trans-Hudson Orogen of North America, Lewry, J.F. and Stauffer, M.R. (eds.), Geological Association of Canada, Special Paper 37, p.75-94.

Saskatchewan Geological Survey 16 Summary of Investigations 2016, Volume 2 Lucas, S.B., Stern, R.A., Syme, E.C., Reilly, B.A. and Thomas, D.J. (1996): Intraoceanic tectonics and the development of continental crust: 1.92-1.84 Ga evolution of the Flin Flon Belt, Canada; Geological Society of America Bulletin, v.108, no.5, p.602-629. Maxeiner, R.O., Gilboy, C.F. and Yeo, G.M. (1999): Classification of metamorphosed clastic sedimentary rocks: a proposal; in Summary of Investigations 1999, Volume 1, Saskatchewan Geological Survey, Saskatchewan Energy and Mines, Miscellaneous Report 99-4.1, p.89-92. Maxeiner, R.O., Matthews, M. and Morelli, R. (2013): La Ronge 'Horseshoe' project: bedrock geology of the Nistowiak-Mountain- Otter lakes area, Glennie and Kisseynew domains (parts of NTS 73P/07, /08, /09, /10); in Summary of Investigations 2013, Volume 2, Saskatchewan Geological Survey, Saskatchewan Ministry of the Economy, Miscellaneous Report 2013-4.2, Paper A-7, 22p. Morelli, R.M. and MacLachlan, K. (2012): Saskatchewan Gold: Mineralization Styles and Mining History; Saskatchewan Ministry of Energy and Resources, Report 262, 171p. Morelli, R., Bachynski, R. and Zhang, Y. (2015a): Bedrock geology of the Brabant Lake area (parts of NTS 64D/04 and 63M/13): 1:20 000-scale preliminary map 2015-4.2-(1) with Summary of Investigations 2015, Volume 2, Saskatchewan Geological Survey, Saskatchewan Ministry of the Economy, Miscellaneous Report 2015-4.2. Morelli, R.M., Zhang, Y. and Bachynski, R.D. (2015b): Geological character and economic mineral potential of the Reindeer Zone in the Brabant Lake area; in Summary of Investigations 2015, Volume 2, Saskatchewan Geological Survey, Saskatchewan Ministry of the Economy, Miscellaneous Report 2015-4.2, Paper A-9, 21p. Ramsay, J.G. (1967): Folding and Fracturing of Rocks; McGraw-Hill, New York, 568p. Scott, B.P. (1982): Geology of the Laird Lake (West) Area; Saskatchewan Energy and Mines, Report 196, 10p.

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