Geology of the Birch Point (Reindeer Lake) Area, Northeastern La Ronge Domain Ralf 0. Maxeiner Maxeiner, R.O. ( 1998): Geology of the Birch Point (Reindeer Lake) area. northeastern La Ronge Domain; in Summary of Investigations 1998. Saskatchewan Geological Survey. Sask. Energy Mines, Misc. Rep. 98-4. In 1996, the Saskatchewan Geological Survey initiated Mineral Resources {Innes et al., 1964). Fox and a mapping project in the southern Reindeer Lake area, Johnston ( 1980) discussed the characteristics of a belt aimed at providing I :20 000 scale coverage of the "La of ultramafic rocks that cross the map sheet. An Ronge-Lynn Lake Bridge" (Maxeiner, 1996, 1997; aeromagnetic map of the Southend area at I :63,360 Harper, 1996, 1997; Corrigan et al., 1997). During the scale was issued in 1965. past summer, mapping between the 1996 and 1997 map sheets covered an approximately 340 km 2 area centered on Birch Point, Reindeer Lake, about 30 km northeast of Southend and 210 km northeast of the 2. General Geology town of La Ronge (Figure I). This year's map area offers a unique cross-section through the northwestern part of the Reindeer Zone, Mapping by the Geological Survey of Canada (GSC) at from the Central Metavolcanic Belt of the La Ronge I :50 000 was carried out in adjoining areas to the east Domain into the Burntwood Group of the Kisseynew and south (Corrigan et al., this volume), and also Domain (Figure I). From northwest to southeast the extended farther north as part of a regional study study area is underlain by the following supracrustal designed to enhance understanding of the lithotectonic assemblages (Figure 2): evolution of the northwestern Reindeer Zone within the Trans-Hudson Orogen. I) volcanic and minor sedimentary rocks of the Central Metavolcanic Belt, intruded by abundant In 1997, David Mac Dougall commenced a tonalitic, granodioritic, and minor granitic plutons; metallogenic study as part of the project (MacDougall, 1997), this year focusing on the Henry Lake­ 2) psammitic to pelitic sedimentary gneisses of the Stackhouse Bay and the Birch Point I :20 000 scale Duck Lake assemblage, located structurally below map areas (Maxeiner, 1996; MacDougall, this report). the Central Metavolcanic Belt and separated from For detailed description of mineral occurrences the it by a high-strain zone; reader is referred to MacDougall's report and maps. 3) a magnetite-rich sequence of 'arkose' 1 and minor conglomerate in the Macfarlane Island area (in part McLennan Group equivalents), intruded by 1. Previous Work minor granodiorite and tonalite plutons; Geological reconnaissance surveying of the shoreline 4) magnetite-free psammitic and psammopelitic and islands of Reindeer Lake was carried out in 1928 gneiss in the Jones Peninsula area; by Stockwell ( 1929) at a scale of I :380, l 60. The entire 5) a sequence of intercalated calcareous sedimentary Reindeer Lake south map sheet (NTS 640) was rocks in the Price Island area, including calc­ subsequently mapped by Alcock ( 1938) for the GSC at silicate gneiss, impure calcareous quartzite, minor a scale of I :253,440. Previous work by the marbles, and thin layers of mafic rocks; and Saskatchewan Geological Survey (SGS) includes I :63,360 mapping of the west half of the Milton Island 6) graphite-rich pelitic to psammopelitic turbidites in sheet {NTS 640-10) in 1971 by Sibbald ( 1977) and the the Deep Bay area (Bumtwood Group Southend sheet (NTS 640-6) in 1970 and 1972 by equivalents). Johnston ( 1983). As part of larger 1: I 00 000 scale The area has been affected by at least three phases of mapping projects for the SGS, Lewry et al. ( l 980a) ductile deformation and late, brittle faulting associated with the University of Regina, mapped the east half of with the Tabbernor Fault zone. The regional foliation is the Ghana Lake sheet (640-11) in 1975 and Gilboy for the most part moderately to steeply northwest to (1980) mapped the Finlayson sheet (64D-7) in 1976. north dipping. Metamorphic grade increases from Compilation maps at 1:250 000 scale of the bedrock north to south. Lower to upper amphibolite, and locally geology (Johnston and Thomas, 1984) and granulite, facies metamorphism accompanied ductile metallogenesis (Scott, 1991) for the Reindeer Lake south map sheet (NTS 640) have also been published. Between 1956 and 1962, a study of'The Deep Bay Crater" was undertaken by M.J.S. Innes and J.W. I Geuer of the Dominion Observatory of Canada and by In order to be consistent with nomenclature of earlier workers, the term 'arkosc' in this report is used for pinkish grey weathering. W.J. Pearson of the Saskatchewan Department of microclinc-bearing. magnetite-rich aluminous psammites (sec Table l ) Saskatchewan Geological Survey 81 Lawrence Bay 1997 CARSWELL ~TURE ATHABASCA BASIN Birch Point 1998 _... 0 5 10 15 Henry Lake kilometres 1996 Figure 1 - Location ofthe Birch Poilll (Reindeer Lake) map area with respect to the mai11 lithotecto11ic eleme11ts ofth e Precambria11 Shield ofnorthern Saskatchewan and previous mappi11g by the author ofthis five year project. Unit symbo/ogy as in Figure 2. 82 Summary of Investigations 1998 deformation and is associated with variable amounts of stretches from Duck Lake through Zed Lake to the east in situ tonalitic and granitic partial melt. side of Numabin Bay and is informally referred to as the Numabin Bay volcanic belt. Both these strands can be traced into the neighbouring map sheets. Table l 3. Central Metavolcanic Belt presents the classification scheme used in the field to distinguish between different types of volcanic and Two highly attenuated and folded strands of volcanics sedimentary rocks. of the Central Metavolcanic Belt occur in the map area and are intruded by leucotonalite to pyroxenite plutons. a) "Numabin Bay Volcanic Belt" One strand is located on Birch Point and is informally referred to as the Birch Point volcanic belt, the other This belt of intermediate to felsic volcanic rocks 0 2 3 4 5 Supracrustals kHomelres Deep Bay pelite. / airphoto lineament/ fault psammopelite & diotexite Price Island calcareous psammopelite Jones Peninsula psammite & psammopelite Macfarlane Island sillimanite 'arkose' .:.. ; Macfarlane Island c 'arkose' laa E Macfarlane Island conglomerate Duck Lake assemblage psammite to pelite ~ Central Metavolcanic Belt Intrusions Leucotonalile 2 Granite E ~ Tona lite N -0 Megacrysllc granodiorile ~ Granodiorite ~ Diorite & quartz-diorile Deep Bay ~ Ultramatic rocks 620000 mE 103°00· Figure 2 - Generalized geological sketch map ofthe Birch Point (Reindeer Lake) area. Saskatchewan Geological Survey 83 Table I - Field classification scheme ofrocks, as used in this report: 1 recommended in part by Gilboy (1981); 1 aluminum silicate mineral content does not include feldspars, but includes calc-si/icate minerals, as well as garnet, biotite, sillimanite, etc; 3 Plagioclase >K-feldspar; 4 recommended by Trowell et al., 1978. Al-silicate2 Mineral Calc-si Ii catc Clastic Sediments1 Content K-fcldspar Minerals Comments Arkosc <IO >!OJ <<S granite leucosome Calcareous Arkose <10 >103 5-10 2ranite leucosome Psammitc <IO <<5 tonalite leucosome Calcareous Psammite <10 <<5 5-10 tonalite leucosome Imoure Ouartzite <10 nil <10 >60 oercent quartz Psammooclitc 10-25 <<5 tonalile lcucosomc Calcareous Psammopelite 10-25 <<5 10-20 tonalitic lcucosome Pe lite >25 <<5 tonalite leucosomc Mafic Mineral Volcanics Content4 Quartz Rhvolitic <5 >30 Felsic 5-15 >25 Intermediate 15-35 <10 Mafic >35 <<5 Ultramafic >90 nil (Figure 2) is highly attenuated between the Lawrence Intermediate volcanics (unit Clv) are interlayered with Point granite, the Numabin Bay megacrystic the dacites and are largely nondescript, except for granodiorite, and the Stackhouse Bay Pluton (Lewry et several outcrops of thinly bedded tuff breccia. The al., 1980a). Towards its southeastern margin in the hornblend ic, intennediate matrix of these rocks 'Duck' Lake2 area, it is in contact with highly strained contains abundant lapilli- to bomb-sized lithic and mafic tectonites and serpentinites which are laterally intermediate clasts. continuous into the Lawrence Point volcanic belt (Maxeiner, 1997). Overall, the Numabin Bay strand of Towards the Numabin Bay area, intermediate volcanics the Central Metavolcanic Belt has a strike extension of are intercalated with petites and psammopelites on both some 15 km, its thickness ranging from as little as large and small scales. These fine-grained rocks 300 m to as much as 2 km in the low-strain lozenge of typically weather in shades of grey, brown or brownish the Lawrence Point granite. grey, and are thinly bedded to laminated. Thin layers of grey, hornblende-rich intennediate ash tuffs (?) or Intennediate to felsic volcanic rocks (Table 2) account epiclastic layers are interbedded with brown garnet­ for about 80 percent of the belt, the remainder is made biotite-rich muddy layers, indicating reworking of a up of mafic tectonite, serpentinite, and minor elastic volcanic source. sediments and iron fonnation. Numabin Bay Area 'Zed' Lake Area Outcrop quality in this area is superb as most of it A relatively thick succession of felsic to intermediate appears to have been burnt twice within the last 15 volcanics and volcaniclastics are exposed on Zed Lake years. Outcrops are without lichen cover and bedrock and the area to the north. Pyroclastic rocks including exposure is estimated to be in the vicinity of 50 tuffbreccias, Japilli tuffs, and ash tuffs are most percent. common; flow banded units are minor (Figure 3). The rock types are essentially the same as in the Zed Dacitic volcanics (unit CFv) predominate and are Lake area, but the level of detail on the map is far typically light grey to buff weathering fine-grained greater due to the amount and quality of exposure. rocks, that are locally brownish grey to rusty brown Abundant felsic to intennediate volcanics, including weathering and accompanied by small amounts of ash tuff, lapilli tuft~ tuff breccia, debris flow, and minor garnet and anthophyllite.