The southeast quarter of the Reindeer Lake area is centred about 330 km north- 2

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1 Project 6: Reindeer Lake North (SE Quarter) Area Reconnaissance Geological Mapping of 64E - l,2,7, and 8 by M.R. Stauffer, L.C. Coleman, F.F. Langford and D.J. Mossman * The southeast quarter of the Reindeer Lake area is centred about 330 km north- 2 east of the town of La Ronge, Saskatchewan. Approximately 2140 km were mapped during this project. The area is easily accessible by boat from Southend, Saskatchewan via Highway 102, by road via Lynn Lake, Manitoba and by float plane from Lac La Ronge, Saskatchewan (2 hrs.) or Lynn Lake, Manitoba (Yz hr.). The terrain is of low relief with few hills more than 50 m high and few rock cliff outcrops greater than 10 m high. Traversing varies from easy in open mature forest to extremely difficult in some muskegs and deadfall areas caused by recent forest fires. Most of the mapping was done along lake shore where exposure is locally excellent. General Geology The area is underlain by Precambrian gneisses and intrusive rocks locally mantled with Pleistocene glacial deposits. The Precambrian lithological units comprise intrusive rocks ranging from granite to diorite (including common pegmatites), metasedimentary gneisses, and migmatites derived from both intrusive and metasedimentary rocks. most abundant, and these are extensively migmatitic. Of the metasedimentary rocks, biotite gneisses are The most abundant intrusive rock is a dominantly porphyroblastic granitic complex(the Wathaman Complex) that underlies the northern half of the area. stratigraphic sequence has been established within the metasedimentary gneisses, but a chronological sequence has been determined for the intrusive rocks. All rock types have been deformed and metamorphosed to the amphibolite facies, although there has been little textural modification of most of the pegmatites. The history of small-scale folding can be divided into two general phases: (Pl) isoclinal folding about E-W trending, north-dipping axial surfaces and northplunging axes (more than one such phase may be present) and (P2) isoclinal to kink folding in various directions. The dominant metamorphic foliation parallels axial surfaces of the early isoclinal folds, though foliations parallel to the axial surfaces of one or more of the kink fold sets are well developed locally. N-S trending folds readily apparent on the geological map and the few late faults * University of Saskatchewan No

2 trending N-S across the area may be related to the small-scale P2 folds. Metamorphism and intrusion appear to have begun early in the isoclinal folding phase and continued throughout the kink folding phase; although metamorphism appears to have outlasted intrusion. Due to the local variation of most rock types and the high degree, but variable nature, of migmatization, all lithological boundaries shown on the map are approximate. Metasedimentary Rocks Biotite Gneiss (Unit 1). The most common metasedimentary unit is fine to mediumgrained, well-foliated, light to medium grey, quartz-feldspar-biotite gneiss (la). Most of these gneisses contain 10-20% biotite, although in some places leucocratic layers of probable sedimentary origin (arkose) up to several metres thick occur. Throughout most of the area this gneiss is fairly uniform except for variable amounts of lit-par-lit pegmatite injections comprising up to 20% of the rock. Thin bands (up to a metre thick) of this gneiss locally contain scattered leucocratic ellipsoidal nodules up to 3 cm long which consist of quartz, feldspar and sillimanite. Thin bands and lenses of amphibole-bearing and calc-silicate rocks also occur locally. Migmatites (lb) derived from unit la contain 30-50% leucocratic neosome as lit-par-lit quartz veins and aplite to pegmatite injections mostly 0.5 to 5 cm thick. Layering is on the scale of several centimetres. Mega-layered migmatite (le) derived from unit la contains large lit-par-lit injections of granodiorite similar to unit 7 (see page 27). These granodiorite bodies are up to about SO m thick, are spaced up to about 100 m apart and make up 30-50% of the unit. Biotite-Arnphibole Gneiss (Unit 2). Rocks of unit 2a are similar to those of unit la except that they contain mainly 10-25% mafic minerals. Locally, amphibolites and/or calc-silicate rocks are present, mostly in bodies up to 100 m across. The ratio of biotite to amphibole (hornblende) varies widely and amphibole-dominated rocks are commonly interlayered with biotite-dominated rocks. Leucocratic lenses and layers, dominantly lit-par-lit pegmatite bodies, are common as in unit la. Migmatite (2b) derived from unit 2a is similar to rocks of unit lb except that the paleosome consists of the fine-to medium-grained amphibole-bearing gneisses of unit 2a.

3 Coarse-grained migmatite (2c) derived from unit 2a is similar to those of unit 2b except that the grains in the paleosome are larger (mainly 2-4 mm across). There is also a higher proportion of thick felsic gneiss layers (meta-arkose?) within this unit. Intrusive Rocks Intrusive rock types can be categorized into those (1) found within the Wathaman Complex (units 3,4,&5) and (2) those which occur in bodies outside Wathaman Complex (units 6,7,8,9&10). All intrusive bodies except the late pegmatites are foliated and generally gneissic in most outcrops. (1) Wathaman Complex This complex granitic body comprises dominantly porphyroblastic granite and is a northeasterly extension of the Wathaman Granite named by Ray (1975). The term "complex" has been preferred in this area due to the variety of rock types encountered. Diorite to Gabbro (Unit 3). Bodies of fine-to medium-grained, dark greenish grey, diorite to gabbro comprise the oldest igneous rocks in the area. These occur only as xenoliths within other intrusive bodies, although some within the Wathaman Complex are large enough to map, ranging in size from several centimetres to approximately 2 km. Many of the larger bodies contain xenoliths of metasedimentary gneiss. Porphyroblastic Granitic Rocks (Unit 4). Porphyroblastic granite to granodiorite is the main rock type within the Wathaman Complex. This rock contains 15-30% pink to white orthoclase porphyroblasts, mostly 2 x 4 cm in size, set in a light-to medium-pinkish grey, medium-to coarse-grained groundmass of 40-60% feldspar, 10-20% quartz and 15-30% mafics (commonly biotite and/or hornblende). Both sphene and magnetite are locally visible in some hand specimens. Xenoliths of mafic-rich diorite and/or quartz diorite are present in most outcrops. Granite (Unit 5). The porphyroblastic rocks of unit 4 are intruded by pink to light grey, dominantly fine-to medium-grained granite which contains less than 10% mafics (mainly biotite, although locally amphibole is dominant). In some places, this rock is an alaskite. Local brick red rocks may belong to a younger intrusive phase. The commonest variety of this granite, unit Sa, contains scattered orthoclase porphyroblasts, mostly 1 cm in diameter, which commonly make up less than 1% of the

4 rock. However, in a less abundant variety, unit Sb, the porphyroblast content is greater than 5% (locally up to 30%) and in some places the rock resembles unit 4 except for the usually lower mafic content. (2) Other Intrusive Rocks Quartz Diorite (Unit 6). Medium to coarse grained, spotted light to dark grey quartz diorite (6a) occurs in several bodies both outside and inside the Wathaman Complex. Mafic minerals make up 15-30% of this rock and although hornblende is most common, biotite is locally dominant. This rock is porphyritic in a few places with scattered phenocrysts of hornblende up to 2 cm across making up to 15% of the rock. Although mainly homogeneous, this rock locally contains 1-4 cm thick mafic layers. Small xenoliths of diorite, quartz diorite, amphibolite and/or metasedimentary gneiss are present in many outcrops. Locally, within the Wathaman Complex, scattered plagioclase porphyroblasts up to 3 cm across make up to 20% of quartz diorite outcrop. Migmatite (6b) derived from the quartz diorite has a neosome of predominantly granodiorite lit par lit injections similar to unit 7, though pegmatite lenses occur locally. Neosome constitutes 30-50% of the rock and occurs in layers up to about 10 cm thick. Migmatite (6c) is similar to unit 6b except that the paleosome is predominantly rich in xenoliths of metasedimentary gneisses as well as diorite to amphibolite probably derived from rocks of unit 3. Locally, the paleosome is an agmatite. Granodiorite (Unit 7). Pink to light grey, mainly fine-to medium-grained granodiorite occurs in several bodies. This rock is mainly homogeneous but locally contains 1-2 cm thick layers of more felsic material. Locally also, the granodiorite grades into a massive unfoliated pegmatitic granite. The tapered ends of some of the plutons comprise migmatite with at least 30% pegmatite neosome injections up to about 10 cm thick. Diorite (Unit 8). A medium-grained, mid-grey diorite body crops out in the northwest corner of the area and is separated from the Wathaman Complex by a thick shear zone. The age relations of this diorite are unknown. Pegmatite (Unit 9). Pink to white granitic pegmatite injections are common throughout the area, occurring as lit-par-lit to oblique veins and irregular bodies ranging in size from several cm to several km across, and locally forming migmatite

5 zones. The time of emplacement appears to range from syn-pl isoclinal folding to mainly late and even post-p2 kink folding. In some places, crystals up to 1 m across are common and xenoliths of all rock types may be found locally. Although feldspar, quartz, muscovite and biotite are the main minerals, magnetite and/or garnet occur locally. Sheared Rocks (Unit 10). Mylonites and blastomylonites occur in a NE-SW trending zone several kilometers wide separating the Wathaman Complex from the diorites of unit 8 in the NW corner of the area. These rocks commonly have a slaty-like foliation and consist of both layered felsic and amphibole-rich gneisses. Some small late- to post-shearing quartz diorite dikes occur parallel to the shear foliation. Leucogranite (Unit 11). This is a white to minor light pinkish-grey, fine to medium grained, mafic-poor granite to trondjemite. There are three varieties: Type ll(a), xenoliths of mainly metasedimentary gneisses are present locally and are migmatitic (with dominantly leucogranite neosome) and highly assimilated, garnet is locally present in trace amounts. Jype ll(b) contains numerous xenoliths of mainly metasedimentary gneisses up to several metres across, but most show little alteration by the leucogranite. Type ll(c) is similar to ll(b) but the leucogranite locally contains up to 30 percent potassium feldspar porphyroblasts. Economic Geology Showings of base metals (Zn, Cu & Pb) have been reported near the Saskatchewan Manitoba border on the east side of the area north of Paskwachi Bay (Rice, 1953). Small gossan zones, apparently caused by the weathering of pyrite, are present in numerous places within the amphibole-bearing gneisses of unit 2. References Ray, G.E. (1975): Foster Lake (NE) - Geikie River (SE) area, Reconnaissance Geological Mapping of 74A-15(E)-16, and 74H-l, and -2, in summary report of Geological Investigations 1975 by the Saskatchewan Geological Survey, Sask. Dept. Mineral Resources. Rice, H.M.A. (1953): Geological Survey of Canada Map No. 1016A, Paskwachi Bay.