Characterization of the Wappasini and Kyaska Thrust Sheets in the Eastern Brabant Lake–Western Wapiskau River Area of the Western Reindeer Zone
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Characterization of the Wappasini and Kyaska Thrust Sheets in the Eastern Brabant Lake–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, Saskatchewan 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 “Flin Flon–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