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 103 5-10 2ranite leucosome Psammitc
(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. Distinct units of garnet lava flow are present. Sediments, altered volcanics, and anthophyllite schist (unit CAv) also occur and are iron formation form a minor component. The believed to represent metamorphosed hydrothermal supracrustal rocks are intruded by sheets of alteration zones. Small amounts of sulphides, including granodiorite, megacrystic granodiorite, diorite, pyrite, pyrrhotite, and chalcopyrite, are mainly pyroxenite, and minor mafic dykes. responsible for the rusty weathering.
l Informal names of lakes and islands appear in single quotation marks when first mentioned; subsequently. the quotes arc dropped from all references to that lake or island.
84 Summary of fnvesllgations 1998 ~ Table 2- Characteristics of the main rock units in the Birch Point (Reindeer Lake) area; MS=magnetic susceptibility, NA=not available; typ.=typical. "';,,,- ~ <; ;:,- Map ;;,"' Ro<'k Type Colour (weathered Mineralogy (numbers in brackets arc Thick- s::, Code surface) Grain-size Tcxrure Struc1ure M~ ;:: percenUigcs) neu () e INTRUSIVE ROCKS rs c Light grey 10 yel lowish lncquigranular with subhedral Feldspar Porphyry Fp Fine plagiodase phenocrysts (2~5mm), Massive to strongly Low(---02) grey foliated Plagioclase, quartz. biorite (<5), ±muscoi.·ite, ±garnet NA ~;:; homoaeneous 0.05-0J Coarse to M3$sive to weakly Leucotonallte Li White tu very light grey Equigranular, homogeneous Plagioclase. quanz (25-}5), biotite/hornb lende (<5). NA H,gh (- 2 0) e. medium foliated-lineated magnetite 0 .2 -7 5 Tonalite T Ughtgrey Coarse to Massi ...· e to slrongly Plagioclase, quanz (20-JO), microcline («5), High (- 16) medium Equlgranular, homogeneous folia1ed.lineated ho rnblende > biotite >eoidote (5-l S). ma,i:netite NA 0.2-8.5 r Leucogranite Pinkish grey to moderate Medium w Massive to weakly Plagioclase, microcline (20-30), quartz (20-30), Lg High(- 14) orange pink Equlgranular, homogeneous NA ~ coarse fo!iated-lineated bio1ite ( <5 ), ma1metite, ±hornblende 0 .1-7.8 Light grey, medium grey Granodiorite Gd Massi\le 10 5,trOngly Plagioclase, quartz (15-20). microcline (10-15}, High (-2 O) lo li~hl pinkish ~re,..· Medium Equigranular, homogeneous fol iated-lineated hornblende> biotite > eaidote (5- 15), magnetite NA 0.1-9.8 lnequigranular, with I -5 cm Megacrystic Granodiorire Gdm Pin kish grey Medium to ·,ery Massive to weakly Plagioclase, quartz ( 15-20). microcline ( I0 -15), 0 11 coarse subhedrat plagioclase megacrysts. NA auite friable fohated-1 ineated hornblende > biotite > epidote(5-15), sphene 0.09-0 25 Diorite/Quartz-diorite Di Medlurn grey to Coarse to very Massive to weakly Plagiocla.se, hornblende > retrograde biotite > 0.4} brownish grey, peppered Homogeneous coarse foliated-lineated ecidote (15-JO), ouanz(0-15) NA 02-0 9 Dark greenish grey LO Commonly hornblende Gab bro Ga Medium to Massive LO weakly Hornblende (40-65), plagiocla.se, retict pyroxene, 0.49 greenish black coarse porphyroblastic, gradational into NA nvroxenite foliated-lineated ±quanz. 0 .25-1.0 Dusky green to greenish Medium to Pyroxenire Upx Homogeneous. gradationaf into Massive to weakly Hornblende (>90), relict pyroxene plagiocla.se, Very high black coarse gab bro folia1ed-lir1eated serpentine, magnetile. ±pyrite, ±pyrrhotite NA 0 4-90 Bluish grey to brownish Inequigranular, knobby weathering, Serpentinite Usp Fine to very Serpentine, relict olivine-orthopyroxene-chro mlte. grey coarse mesh-textured o livine with Strongly foliated NA Very high magnetite veinlel!i magnetite, anthophy!lite, talc 5-90 Ern erald green to dusky AcLmollte Schist Uac Strongly foliated, 0.4 (lyp) yel luw 1.1;reen Fine to medium Rare relict olivine crystals Trcmolite-actinolite. relict oJi,..·ine, t-;A schistose 02-40 • YOU~'GER SUPRACRlSfAL ROCKS
7 Deep Bay ,uccession
Diatexite BDt Grey Medium to very Jnequigraular, heterugeneous. Migmatitic, >50%, Plagioclase. quartz. biolite (20-25), garnet (5-10). - 0 .20 coarse 200m neoblastic tonalilic leucosome \!.raphite 0 15-025 MigmatitlC, gn~issic, Pehtic Gneiss BPp Grey to dark grey Plagioclase. quartz, biotite (20-25 ). gMnet (5-10), ---0 20 Fine to med!um Heterogeneous, granoblastk 20-40% tonaliuc 100 -JOO m leucosome graphite, ±hypersthene. ±Jiopside 0 .15-0.25 Migmatitic, gneissic, PsamrnopelitlC Gneiss BPsp M edium grey Fine to medium Heterogeneous, granoblastic J0 .20'Vi, tonaltric Plagioclase, quartz. biotite ( 10-20). game\ (<5), 400- -020 leucosorne graphite. ±hypemhene, :1::diopside >lOOOm 0 . I 5-0.25 ~ Price bland 1uc:ct:S5ion
Light grey, greenish grey Fine (to Thin to medium bedded, m part Quan, (>60), plagioclase granule,, ±graphite, Impure Quartzite PQz --0.6 (typ) to brown medium) calcareous quanzite, in pan minor Well foliated ±pyrrhotite, ±pyrite, ±chalcopyrite, ±~phalerite. I0-50m ~arnet-amohibolite lavers ±dionside 0 1-1 2 Thin to medium bedded, Well foliated, with Plagioclase. micrndine (up to 50 in part), quartz, Calcareous Psammopelite PPcs Grey to greeniiih grey, in Fine (to - 0.3 (typ.) part rusty b rown medium) g.ranoblastic, interlayered with thin 20o/o Lonalitic > diopside, hornblende, sphene, ='=magnetJte. ±bio1ite, --400-500 m 0.2-0 5 beds of marb k auartzJte '1.ranitic leucosome ±Qamet :1::nvrrhotite. ±oranhite also 20-50 Well foliated and Banded greenish black, Banded, granobhstic, in part boudinaged layers. Plagioclase. hornblende - diopside (40-50). quartz (0- Mafic Calc-sil icate Gneiss PCm Fine (to -o 50 pale green, r"USty brown medium) homogeneous, garnet-amphibolite 10% orthopyro}< ene- 20), ±garnet, ±carbonate, ±cummingtonJre, ±blotite -20-40 m (PCmg) diopside-bearlng th.ypersthene-brown hornblende 0.4-0.7 leucosome ~ Jones Peninsula 1ucce.s!iiion
Medium to thickly bedded, P.sammitic Gneiss JP, Medium grey granoblastic, up to 50o/. I O"/c iit-pur-lit tonalitic Plagiodase. quaru.. biatite (5- 10), garnet (<5}, -0.20 Fine lo medium 1200 m psammopeliric beds, rare thin leucosome graphite or sil limanite or diopside and/or epidote 0 .15-0.25 caJcareous beds Psammopelitlc Gneiss JPsp Medium grey Fine to med,um Medium bedded, .granoblastic. more 10-20% N-par-lir - 0 .20 PlaH>0clase, quartz, biotite [ 10-15), garnet (5-10) 200-300 m 1han to 50% psammooel ihc beds tonahlic leucosome 015-025
~ & Table 2 (continued)- Characteristics ofth e main rock units in the Birch Poillt (Reindeer lake) area; MS=magnetic susceptibility, NA=not available; typ.=typical.
Map Colour (wut~red Mineratoo (numben in brac.kEts are Thick- Rock Typo Grain-Jiu Tt1turt Structure Code sur"f.ace) i,crctnUge,) ntss MS
~ Macflrl1Re bland sut(tHion Light grey IO lighr Gra.noblastic, up to I oo;. siHirnanitc
~ Duck Lake Assemblage
Plagioclasc, qua11z, biotite (20· 25}, sillimanite (< 10), - 0.2 Pelitc DPp Grey Fine to medium Thinly to medium bedded Well foliated < SOOm ~arnet ( ~ Central Md nolcanic Btlt Hetcro~eneous. includes calcareous Plagioclase, hornblende, lremolitc-acti11oli1e, Light grey, light greenish Fine (to ps.amm,te, psammopelite. minor 0 70 Mixed ('..ale-silicate Schis1osc. well foliated diopside. quartz. g arnet, carbon.ate, ±bio1i1e, - IOO m cc, grey 10 medium grey medium) felsic cuffs. chen iron formatK>n, 0 2-1.7 ±graphite. zpyrrhotite, ±pyrite m arble Silicate-racies (CSfi) and oxide· Dark grey to b rownish Quartz (40-SO), grunerite ( 10-50), game< (S,50), Very high Fine to coarse facies (CSfo); Jam;nated 10 thinly Well foliared 20-60 m Iron Formation csr bio tite. magneti1e, ±pyrrhotite, ±chalcop~·rite l!)"Oy bedded 1·100 Medium grey 10 Fine (10 Poorly layered, in part well Plagiocl= . qua,tz, bio Figure 3 - Flow banded dacite from 500 m north ofZed Figure 5 - Heterogeneous rock with light coloured Lake. intermediate components, surrounded by dark coloured 'pelitic' components from 500 m east of Numa bin Bay at north end ofmap area; see text for explanation. Figure 4 - Bomb-sized vesicular rhyolite clasts in a dacitic Figure 6 - Silicate-facies iron formation with layers of luffbreccia; 1 km east ofNumabin Bay at north end of chert, 'garnetite' and grunerite-rich rock; 2 km east of map area. Numabin Bay at north end ofmap area. Saskatchewan Geological Survey sheets of unmappable intermediate and mafic dykes. Birch Point Area A 40 m thick band of silicate facies iron formation In order of decreasing abundance, the Birch Point area fringes a tonalite pluton along the edge of the Numabin is underlain by mafic volcanic rock, mafic calc-silicate Bay volcanics and extends over a strike length of some gneiss, hornblendic psammopelite, ferruginous 6 km into the Cowie Lake area. The grey to brown psammite, mixed calc-silicate rock, intermediate weathering, medium- to coarse-grained iron formation volcanic rock, dacitic volcanic rock, and thin slivers of is thin to medium bedded. Distinctive banding (Figure serpentinite contained within the mafic rocks. 6) is defined by layers of intermediate ash tuff, 'gametite' (60 to 80 percent), gedrite-rich rock, and Compared to other parts of the Central Metavolcanic chert. Magnetite, pyrrhotite, hornblende, and biotite Belt, the state of strain is quite high albeit account for the remainder of the rock. heterogeneous. Protornylonitic to rnylonitic fabrics were observed in many places and as a consequence Overall, the volcanic environment in which the virtually no primary features are preserved. Numabin Bay and Zed Lake rocks were emplaced was felsic and largely subaerial; some subaqueous Mafic volcanics (unit CMv) of this belt most likely deposition is indicated by pelitic intercalations, iron originated as lava flows as they are quite homogeneous formation, and possible cross-bedding in a felsic and fine-grained. Pillow-like features were observed in volcaniclastic rock. A possible analogue might be a the laterally equivalent Stackhouse Bay volcanics Crater Lake-type caldera (Cas and Wright, 1987). High (Maxeiner, 1996) and again this year in the low-strain magnetite content of the volcanics may be further hinge-zone of the Birch Point synform, but these are evidence of a subaerial depositional environment, as it not convincing (Figure 7). Mafic calc-silicate gneiss indicates a high oxidation state. This depositional (unit CCrn), a prominently colour-banded rock environment contrasts strongly with that of rocks in the characterized by alternating centimetre-scale greenish Duck Lake area of the Birch Point volcanic belt, which black hornblende-rich layers and light greenish grey were largely deposited in a subaqueous environment. diopside-actinolite-rich layers (Figure 8), is closely associated with the mafic volcanics. The calc-silicate mineral content varies from IO to 20 percent, but may b) 'Birch Point Volcanic Belt' locally drop below 10 percent. Contacts with adjacent A predominantly mafic volcanic succession at least mafic volcanics appear to be gradational. In 1996, 600 m thick with a strike extension of some 20 km is unequivocal pillows were observed in identical rocks tightly folded around the Birch Point synform. In the to the west (Maxeiner, 1996) and therefore they are vicinity of ' Marge' Island and 'Homer' Point, the interpreted as pillowed basaltic flows that were Birch Point volcanic belt thickens due to fold affected by syngenetic Ca-metasomatism possibly due interference and its position in the pressure shadow of to hydrothermal alteration shortly after their deposition the Numabin Bay megacrystic granodiorite. on the seafloor. Alternatively, this alteration might Northeastward it pinches out, but its strike extension have been caused by metasomatism during shearing. continues along the northwest side of Duck Lake from where it can be traced into the Lawrence Point volcanic The mafic rocks are overlain and merge laterally into belt (Maxeiner, 1997). Towards the west, it passes into intermediate (unit Clv) and dacitic (unit CFv) volcanic the Stackhouse Bay volcanics (Maxeiner, 1996). rocks in the Marge Island area. Fragmental textures in isolated outcrops identify these as predominantly pyroclastic rocks, including tuff breccias and lesser ash tuffs. Many of the felsic and intermediate volcanic Figure 7 - Tectonically disrupted pillow selvages or Figure 8 - Banded mafic calc-silicate gneiss with secondary veining in mafic volcanic rocks. alternating greenish black hornblende-rich layers and light greenish grey diopside-actinolite-rich layers; Jones Peninsu[(I. 88 Summary oflnvesrigations 1998 rocks in this area, however, lack primary features, Serpentinite is typically pale bluish grey to pale contain abundant garnet and are rusty weathering, due brownish grey weathering, but bluish black on fresh to small amounts of disseminated pyrrhotite; Mg-rich surface. Original coarse-grained textures have been arnphiboles (both cummingtonite and anthophyllite) completely recrystallized into a fine-grained mosaic of are also present. These rocks might represent serpentine, tremolite, and magnetite. Least deformed metamorphosed alteration zones within a succession of and serpentinized examples show that the serpentinites pyroclastic volcanics. An alternate interpretation is that are derived from coarse-grained peridotites, with they are resedimented volcanic rocks. evidence of igneous layering and multiple intrusive events (Figures 9). On the basis ofpetrography, both The volcanic rocks are structurally overlain by a harzburgitic and lherzolitic peridotites have been succession of mixed syn volcanic sediments, including identified. The harzburgites show relict grains of calcareous psammites, homblendic and graphitic igneous (?) orthopyroxene, olivine, and chromite psammopelites, and ferruginous psammites. All of (Figure I 0). Magnetite is commonly found as thin these have most likely been deposited in a subaqueous streaks within relict olivine crystals, due to the environment. redistribution of iron as it is expelled from olivine during serpentinization. Duck Lake Area Preliminary geochemical data characterizes the serpentinized harzburgites as possibly mantle-derived Exposure in this area is spectacular because of a recent melts, with relatively flat, strongly refractory (-10) bum. North of Duck Lake, within the (up to 600 m chondrite-normalized REE patterns and highly elevated wide) Duck Lake high-strain zone, strongly tectonized Mg, Cr, and Ni concentrations (Maxeiner et al. , 1998). mafic rocks are interleaved with serpentinite, mafic to ultramafic actinolite schist, fe lsic to intermediate volcanic rocks, oxide facies iron formation, and pelitic rock. Strain was heterogeneous and zones of intense mylonitization alternate with less deformed ones. The most deformed parts are strongly banded on a centimetre-scale with transposed rnafic to ultramafic and minor felsic components; no primary textures are preserved. Least deformed parts of the Duck Lake high-strain zone allow recognition of greenish black, fine-grained and homogeneous to poorly layered mafic volcanics (unit CMv), which are cut by conformable light grey to buff weathering feldspar porphyry dykes and emerald green weathering ultramafic dykes. Locally, the mafic volcanics contain garnet in amounts of up to 20 percent, in part accompanied by anthophyllite, cummingtonite, and/or cordierite (unit CAv), and minor amounts of chalcopyrite (e.g. Rosie North and Rosie South showings) and siliciftcation. One exposure (2 m by 2 m) of oxide-facies banded iron Figure 9 - Thin sheet ofdark greeni.fh grey weathering /herwlitic peridotite cutting ligllt brownish weathering, formati on with alternating laminae of magnetite and coarse-grained and layered hun.burgitic peridotite: 300 m chert occurs within thematic tectonite succession, as northwest of Duck lake in recent burn. do isolated layers of pelite. Towards the northwest, the mafic volcani c rocks are structurally overlain and intercalated with equally highly strained intermediate and fe lsic volcanics which can be traced into less deformed felsic volcanics north of Zed Lake (Numabin Bay volcanic belt). Serpentinitc and Actinolite Schist Abundant discontinuous and boudinaged layers of serpentinite (unit Usp) and actinolite schist (unit Uac) characterize part of the Birch Point volcanic belt. Individual layers of serpentinite range in thickness from IO to 150 m. Emerald green weathering mafic to ultramatic actinolitc schist is clost:ly associated with the serpentinite, but less abundant. Figure JO - Serpentinizec/ han.burgite with centimetre-sized sublleclral orthopyroxene crystals set in an olivine matrix: 300 m northwest of Duck l ake i11 recent burn. Saskatchewan GeoloRical Survey 89 Actinolite schist is an emerald green weathering, fine Fp), from 10 cm to several tens of metres in width, grained mafic to ultramafic rock that comprises up to intrude the sediments of the Duck Lake assemblage, as 80 percent tremolite-actinolite, 10 to 30 percent well as mafic volcanics of the Lawrence Point volcanic antigorite, calcite, diopside and plagioclase. No relict belt. minerals or textures are preserved. Actinolite schist occurs as thin bands (10 to 20 cm) in mafic volcanic The western contact of the assemblage is relatively rocks north of Duck Lake and relationships in several abrupt and defined by a high-strain zone that separates outcrops suggest that they are intrusive. They are mafic volcanics of the Central Metavolcanic Belt from therefore interpreted as strongly recrysta\lized pelites of the Duck Lake assemblage. The southeastern metamorphosed pyroxenite. contact is defined by a polymictic conglomerate, which appears to unconformably overlie the assemblage. Rocks of the Duck Lake assemblage are interpreted as 4. Sedimentary Rocks synvolcanic turbiditic sediments. Several distinct successions of predominantly b) Macfarlane Island Succession sedimentary rocks were mapped this summer and are described by area from north to south. Detailed The Macfarlane Island area lies in the centre of an descriptions of the individual lithologic units are given approximately 2 km thick succession of generally in Table 2 and in the legend of the map that magnetite-bearing polymictic conglomerate, arkose, accompanies this report. calcareous arkose and sillimanite arkose. These rocks are correlated with parts of the McLennan Group and Sickle Group (Table 3). a) Duck Lake Assemblage In 1997, a thin wedge of psammitic to pelitic rocks and A unit ofpolymictic conglomerate (unit MCg) minor calcareous psammite was mapped to the structurally underlies and truncates units of the Duck southeast and structurally below the Central Lake assemblage and the Central Metavolcanic Belt. Metavolcanic Belt and was informally referred to as The conglomerate is best exposed on the north side of the Duck Lake assemblage (Maxeiner, 1997). These an island 3 km northeast of Macfarlane Island in the sediments extend into this year's map sheet, where 1997 map area. Another set of excellent, but less they were traced for 8 km along strike, before pinching accessible, exposures is located 800 m to the southeast out north of Jones Peninsula. The rocks are best of the channel that connects Duck Lake to Reindeer exposed at Duck Lake, where they reach a maximum Lake. Although this unit is up to JOO m thick in the thickness of approximately 1 km within the core of an nose of a regional fold closure east of Duck Lake, it is F fold. typically 50 to 100 m thick. It comprises thick beds of 3 polymictic conglomerate, that are intercalated with thin The Duck Lake assemblage is subdivided into four sandy beds. The conglomerate is characterized by units (Table 2). Psammite (unit DPs) can be best strongly deformed pebble- to boulder-sized clasts in a observed in shoreline exposures west and east of fine-grained matrix (Figure 12). The clasts, stretched at Lawrence Point in the 1997 map area. It comprises a ratio of approximately I 0: I to in part 200: 1, predominantly poorly layered to monotonous comprise: fine-grained white felsic rocks, possibly psammitic gneiss with minor intercalated thin felsic volcanics; fine-grained, intermediate hornblendic psammopelite beds. rocks, possibly intermediate volcanics; biotite-rich rocks, possibly psammopelites and petites; medium On the southeast side of Duck Lake, psammopelite grained granitoid clasts; medium-grained dioritic (unit DPsp) is interlayered on a small scale with minor clasts; and rare quartz pebbles. Only rare amphibolite psammitic and pelitic beds and on a larger scale with pelite (unit DPp). The pelite is best exposed on the northwest side of Duck Lake, approximately 300 m from shore. It comprises rhythmically layered, thinly to medium-bedded pelite and psammopelite (Figure 11). Pelitic layers are rich in biotite, sillimanite, and relict staurolite; psammopelitic layers contain only biotite. Calcareous psammopelite (Unit DPcs) is best exposed on the east side of Lawrence Point in the 1997 map area. Compositional layering is typically well developed and marked by variations in hornblende, diopside, and biotite contents. Some outcrops exhibit numerous thin- to medium-bedded calcareous layers which are in part spectacularly contorted and isoclinally folded. Leucosomal melt material, from 5 to 10 percent and locally up to 30 percent, typically forms injections into Figure 11 - Thin- to medium-heddetl petite of the Duck the sedimentary rocks. Feldspar porphyry dykes (unit Lake assemblage; 300 m northwest of Duck Lake. Summary of1nvestigations I 99H 90 clasts and no ultramafic clasts were observed. The co_nglomerate is apparently matrix-supported, although this might be due to recrystallization causing certain clasts to blend in with the matrix. The quartzofeldspathic matrix is fine grained, medium grey and for the most part biotitic and less commonly hornblen Grey to light pink weathering muscovitic arkose (unit increases resulting in the disappearance of muscovite MAr), which can best be observed along the northern and the formation of sillimanite in the presence of shore of Macfarlane Island and on the island to the quartz. As a_ result, a unit of sillimanite arkose (unit west, stratigraphically overlies the polymictic MArs) was identified. The rock is identical to arkose conglo~erate. The arkose is usually well layered, thin but c~mtains up to IO percent sillimanite, in part to medium _bedded, with rare lag deposits, trough formmg large (10 cm by 2 cm) faserkiesel knots. cross-beddi~g, and graded bedding (Maxeiner, 1997). Several layers of sillimanite arkose exist in the map Cross-beddmg shows northwest younging in the area and extend over a strike length of more than northern .Macfar.lane Island area, which is in agreement 20 km. The unit is best exposed between Hodgson and with earher findmgs (Sibbald, 1977), but cross-bedded Sandfor? !slands, ~he~e it re~ches a thickness ofup to arkose with southerly younging direction were also ~ km. S1_ll1m_amte 1s oriented m the axial plane and co found (see also Corrigan et al., 1997). These lmear with tight, northeasterly plunging F2-folds, but relationships suggest major fold closures in the unit. cr~nl!lated by open, northerly plunging F3-folds. This umt 1s also characterized by boudinaged calcareous Mixed calcareous arkose (unit MArc) is characterized beds described previously. by thin to medium-bedded calcareous layers within the ar~ose. Calcareous layers account for 5 to 10 percent Arkosic rocks _a~e typ(cally recrystallized and in part of the rock, are up to 40 cm thick, generally widely resemble granitic gneiss, with abundant pink granitic spaced a~d boud~naged. The beds are light greenish leuco~ome. Up to 40 cm wide bands of fine-grained, grey, typically with a maroon to purple reaction rim greenish black to dusky green weathering mafic to ar~rnnd them and contain up to 10 percent calc-silicate ultramafi~ rock, presumably recrystallized dykes, are mmerals, mainly diopside and epidote. Calcite may common m the Macfarlane Island area. also be present, resulting in recessive weathering of the beds (Figure 13). The quartz to feldspar ratio in these c) Jones Peninsula Succession beds is quite high. Ps_ammitic and psammopelitic gneisses that range in Towards the southeast, the metamorphic grade thickness from 200 to 1600 mare intercalated with Ta~/e 3 - Stratigraphic relationships between the Reindeer Lake area and other lithotectonic subdivisions ofthe northern Remdeer Lake Zone. ...--..u,--ry(l91J) ---- ··---~Dffl.u.(i9i{~- ·--- ~ili.u( l99-i;J991 .. ('.orti. ;n,1.J.fi'9_'7_)--· ·---- ····----· Gil~r• n "'· (t910) Mcl..f:11n.111 - hy•milh l••n 1rr1: Ourr l.11J.c, •rn; RrindeitJ' c.-~, n : 1 1 Lyun lJ~ •"'•· M1ni1oh•: I.. Ron~ Dom1in f M,UI..Hn Lakr Brit L• Ro111" bonuin I Mad.ran l..Ak1- Helt Lii Ro11gc Dom&.111 / Mul.Hn Lall.t Mt f Ki'M'J"""' Domiin L~·nn Lak( Dem•in I IOncy•N" D11mltin >-,h:Li:nn, nGroup MacLeanL1.ke Md ,cnn,1.nGroup M~ h1rl,im::: Sicli.lt: rOl!p (gm ,itOtd me11-uko'W', (K -spar·:-,· plagiocl.ue l"M11-;ucn ii~. ~ IJla~ Jonei;; (11n::yw• ckc. cooslomcr;11c. cron-b.edded ;ukv;sc, me11-arkoK, u t:oslc ~pnmrnltic mctaconglomerate, mt"la·arilose; alSl.l g,,_r,ili, SllCU!l'ioton f'enin~~la succession biotitegneis.i;, 1:alc.areom taJ1dstone. ;arnl 11rko1ic 8r9w~ h. arko,ic scmipc:litic ~1,1bo< din•lc quart.zjtic mcta.,n (osc. meta· (m.il!jJJ-C:lir.: !;OCCCUl{)n ~~ JU~CC:IS JOfl HmlslOn.ej quartzit e, arko.~ic ~ greyw,-clt(bK'litc arl:DSiC waclc and meota·arko1i cmus¢.w11 c conglnmcratc. p,1mmopclilc. co n11,lomcr&1c) ~. ~ .! gnei:m:sf,pclitc 1,;d1i ~1) arkrnic. sill.· ~Ulr'rlrTJopditc) and imriurc pelite ari(I 1 afkasc) qu1:rtz11e rs"mr110p,elite) ~ :;~i:i~~; cdc- unc:onfom1able, In part ah.. r.-d amJ'l'l,ilx,tite) § tilicateg,,.ci~~) ·- (clltn11l ~c1.11voln nic Belt <:critu1J MacLcati i.i.h M£TA\"OI C BELT (~'l)lc11 nics 111,:I syn\"Oicanic ~lc:irnicHelt Nuni~iJJB... ,- k ocd l.11.,c: Duck I.ale tedime111-~) j ~ (v-0lo11 i~:,and {i:alC~ la.li!S !O 11olcanic bel1 ~... 1, ~ ll. siinvo l~ lliC rooncakaroou~ • ~d iment..s) ~~am1n1t,c ru p,diii~ (f, lltclo ini.:::rmcdiate Cn:wL1.k:e BcJ1 mc,a11 reyw1ct:e, Stad:boui e Bi,d1 Point L" wr,c:n,;e ( peli1.c. Wuclw-n Group R1,1rntwood Ucoup metarot,glumc,,.t,e. Bay>"o lcaniq ~ "oluinlc belt ~anic J>.,llmmQVClite ("oluni...-: ruc:ks ,1,nd (¥raph11icpeli1e a~ rn.eu..,eJimcrio) hornhlrlll!cgr>ei5~. ,1,ndpu1nini1e) ~ynvok anj( udimcn!l) p~amn111pcli1c) amphibolitc, cak- ~ 1i!ic1tc ,g1icin) ( matic .-»lc Saskatchewan Geological Survey 91 sillirnanite arkose and are best exposed on Jones They are poorly layered with thin beds of marble and Peninsula and islands to the east. They also occur as quartzite and with up to ten percent lit-par-lit granite less extensive units to the southeast of Hodgson Island Ieucosome. In many outcrops, psammopelite grades and to the northeast of Graham Island. These into graphitic petites. sedimentary rocks resemble Mac Lean Lake gneisses, as defined by Lewry et al. ( I 980b). A thin unit of microcline- and magnetite-rich calcareous arkose is interlayered with mixed The psammitic gneisses (unit JPs) are grey calcareous psammopelite. These rocks contain up to 40 weathering, fine- to medium-grained granoblastic percent microcline, 10 percent hornblende, and up to 5 gamet-biotite-quartz-plagioclase rocks (Table 2) that percent diopside, and well-rounded detrital magnetite may locally contain graphite or sillimanite. They are grains. thickly bedded and intercalated with up to 50 percent psammopelite beds, and typically contain IO to 20 Beds of impure quartzite (unit PQz) are also percent lit-par-lit tonalitic leucosome (Figure 14). The interlayered with calcareous psammopelite. Some beds gneisses contain rare calcareous beds that are up to of quartzite are calcareous and/or graphitic; most are 40 cm thick with small amounts of diopside and/or sulphide bearing. Interlayered thin units of epidote. garnetiferous amphibolite may be metamorphosed silicate-facies iron formation. Psammopelitic gneiss (unit JPsp) is medium to thick bedded and closely associated with the psammitic Banded mafic calc-silicatc gneiss (unit PCm) fonns 50 gneisses. It contains more than 50 percent to I 00 m thick layers within the calcareous psammopelite beds and up to 20 percent lit-par-lit psammopelite succession, and is indistinguishable from tonalitic leucosome, which produces the gneissosity. banded ca le-silicate gneisses of the Central Metavolcanic Belt. Similar rocks elsewhere (e.g. Dusky green to greenish black, fine-grained, Gilboy, 1980) are described to mark the contact conformable, in part strongly boudinaged ultramafic to between Burntwood and Sickle groups. Banding is on mafic dykes are common within the Jones Peninsula the centimetre scale and is produced by alternating succession. greenish black hornblende-rich layers and pale green diopside-rich layers. Mafic mineral content is between d) Price Island Succession 40 and 60 percent, and quartz is less than 5 percent. North of Deep Bay, on the east shore of Price Island Mafic calc-silicate gneiss is closely associated with up and the large unnamed peninsula to the east, an to 50 m thick layers of more homogeneous, greenish approximately 600 m thick succession of calcareous black, fine-grained quartz-bearing amphibolite. These sediments and intercalated quartzite and amphibolite is mafic rocks are interlayered in many places on a small exposed. The sediments, which appear to be fold- and and large scale with calcareous psammopelite, petite possibly fault-repeated, underlie a 3 km by 3 km large and impure quartzite. Locally, amphibolite grades into area. a brownish grey to greenish grey weathering, hypersthene-diopside-quartz-bearing mafic rock, The dominant rock type of is mixed calcareous interpreted to mark the onset of granulite-facies psammopelite (unit PPcs). These greenish grey to grey metamorphism. Feldspar in these rocks often has a weathering, fine- to medium-grained rocks comprise waxy green colour in outcrop; hornblende is olive plagioclase, quartz, diopside, hornblende, carbonate, green to brown in thin section. Garnet occurs locally, sphene, and minor amounts of sulphides and graphite. and cummingtonite-grunerite selvages fringe both Figure 13 - Boudinaged calcareous bed with recessively Figure 14 - Typical psammitic gneisses with abundant lit weathering core in mixed calcareous arkose; on small par-lit tonalitic leucosome; shoreline expo~·ure on Jones island southwest of Macfarlane Island. Peninsula. 92 Summary of Investigations 1998 garnet and hypersthene; quartz content is relatively diameter (Figure 16). The leucosome constitutes from high and may reach 15 percent. 5 0 to I 00 percent of the rock and comprises plagioclase, quartz, biotite, garnet, and graphite. Metre Amphibolite and gametiferous amphibolite may derive sized xenoliths of poorly 'digested' psammopelitic to from intrusive quartz-diorite sills, volcanics, or from psammitic gneiss occur locally. These rocks are silicate-facies iron formation. identical to Burntwood Group graphitic pelite exposed at the north end of Deep Bay. Where less affected by As much as 20 percent tonalitic leucosome is quite anatexis, the pelitic gneisses appear to be interlayered common in the amphibolitic rocks and locally the with arkoses, possibly reflecting stratigraphic leucosome contains up to 2 cm large crystals of interbedding of the two rock types. orthopyroxene and diopside. Thin retrograde fringes of cummingtonite crystals generally surround the orthopyroxene. Sphene is also commonly in the leucosome. 5. Intrusive Rocks Intrusive rocks (Table 2) underlie large parts of the e) Deep Bay Succession northern half of the map area. Leucotonalite, tonalite, and granodiorite predominate over leucogranite, Highly graphitic sedimentary rocks, exposed on the diorite, gabbro, and pyroxenite. In the southern half of northeastern shore and the islands north of Deep Bay, the map, tonalite is the predominant intrusive rock. The are likely equivalents of the Burntwood Group of the following description of plutonic rocks is organized by Kisseynew Domain. In the map area, these pelitic to composition and area, irrespective of age relationships. psammopelitic gneisses have an estimated thickness in excess of I km and a strike extension of at least 12 km. In the Stackhouse Bay and the northern Numabin Bay They are interlayered with and grade laterally into the areas, the predominantly tonalitic Stackhouse Bay calcareous Price Island sedimentary package. Pluton (Lewry et al., l 980a) comprises leucotonaiite, tonalite, and diorite (units Lt, T, and Di). A sample Pelitic gneisses (unit BPp) are characterized by (HUD-84-115) of a "strongly lineated medium grained abundant graphite, biotite, and garnet. They are grey granodiorite" from the southeastern part of that pluton weathering, fine to medium grained and highly yielded a U-Pb zircon age of 1837 ±8 Ma (Bickford et migmatized typically with 20 to 30 percent tonalitic al., 1986; p 103 ). The sample was taken from a "small leucosome (Figure 15). Locally, melt increases to well island on the west branch ofNumabin Bay (approx. above 50 percent and the gneisses grade into diatexite Lat. 56°32'N, Long. 103°15'W)". This places the (unit BDt). Primary layering, defined by compositional sample location on an island between Stackhouse Bay variations, is present locally. On both small and large and the entrance to Creswell Bay, approximately 200 scales, the pelites are interlayered with graphitic to 500 m west of the western boundary of the present psammopelitic gneisses (unit BPsp), which contain map. Extrapolating lithological boundaries westward Jess aluminum-silicate minerals and Jess melt, but are places the sample in a unit of leucotonalite (Lt). In otherwise essentially identical to the pelites. part, leucotonalite looks quite nebulous, with swirls and schlieren of mafic minerals apparently defining an An outlier of graphitic pelitic gneiss and diatexite earlier, folded fabric that has been largely obliterated. occurs on the large island to the southwest of Birch Locally, it is gradational into tonalite, from which it Point. Diatexite (unit BDt), best exposed on the south appears to have been derived by partial melting; side of the island, is grey, medium to very coarse alternatively it may have intruded and partially grained, and contains up to 30 percent white assimilated the tonalite. Either way leucotonalite plagioclase neoblasts, typically from 5 to IO cm in appears to be one of the youngest rocks in the area and Figure I 5 - Strongly deformed pelitic metatexite. Figure 16 - Neoblastic diatexite ofpelitic composition; from west shore oflarge island southwest of Birch Point. Saskatchewan Geological Survey 93 was possibly formed during peak metamorphism A highly attenuated, > 15 km long and I km wide, (Maxeiner, 1997). The U-Pb zircon age derived for this biotite-hornblende tonalite (unit T) intrudes rock (Bickford et al., 1986) may represent a mixing predominantly arkosic rocks between Pearson Islands age between the emplacement age of the younger and Hodgson Island and is continuous into the leucotonalite and an older tonalite suite. Granodiorite neighbouring map sheets. The tonalite is light medium of the Macoun Lake Pluton, a mainly granodioritic grey, medium grained, and homogeneous with textures intrusion centered approximately 30 km west of the varying from massive to strongly foliated. It contains map area, provided a U-Pb zircon age of 1849 ± 10 Ma rafts of sillimanite arkose and amphibolite several (Bickford and Van Schmus, 1985). kilometres in length. The southeastern margin of the intrusion coincides with a high-strain zone several A small intrusion ofleucogranite (unit Lg) that locally hundred metres in width, developed entirely within the grades into aplite is exposed on islands in Numabin supracrustals. It is unclear whether the intrusion post Bay and the mainland to the east. This pink to orange dates the high-strain event. The tonalite is cut by pink rock is medium to fine grained, typically contains straight-walled, east- to southeast-trending undeformed 30 percent microcline and up to 5 percent biotite. It granite pegmatite. postdates diorite and tonalite intrusions of that area. Diorite intrudes small bodies of dusky green to black Small intrusions of gab bro (unit Ga) and pyroxenite weathering, medium- to coarse-grained pyroxenite (Table 2) occur west of Zed Lake, along the southern (unit Upx), which occur along the edge of the end of Cowie Lake and in the Numabin Bay area Stackhouse Bay Pluton. within the Central Metavolcanic Belt. Another leucogranitic intrusion underlies the northeastern comer of the map and forms part of the 6. Structure and Metamorphism Lawrence Bay leucogranite (Maxeiner, 1997), where it intrudes intermediate volcanic and dioritic rocks. It a) First Generation Structures also truncates mylonites of the Duck Lake high-strain zone. Most of the rocks in the map area show a weakly to well-developed foliation oriented parallel to S0 . The The central part of the map is dominated by a 4 km by age of this fabric is generally uncertain, as it is the 8 km large megacrystic granodiorite pluton (unit product of either 0 1 or D2, or a composite of both Gdm). This pinkish grey weathering, very friable events. In 1997, a layer parallel schistosity (S1) was granodiorite is characterized by subhedral to euhedral, documented in supracrustal xenoliths contained within partly zoned plagioclase megacrysts ( l to 5 cm in size) the Butler Island diorite (Corrigan et al., 1997; which form up to 20 percent of the rock. Its relatively Maxeiner, 1997; Corrigan et al., 1998). This first low quartz content (20 percent), ubiquitous sphene ( 1 deformation episode (D1) is interpreted to be restricted to 2 percent), and extremely low magnetic to rocks of the Central Metavolcanic Belt and predates susceptibility are distinctive. Textures are generally 1858 ±2 Ma (Corrigan, pers. comm., 1998), the massive to weakly foliated and/or lineated. preliminary U-Pb zircon age of the Butler Island diorite. Small-scale isoclinal, intrafolial F 1 minor folds A large body of leucotonalite (unit Lt) intrudes the occur rarely and major structures of this age are not southeastern part of the Central Metavolcanic Belt and recognized on the present map. the sedimentary rocks of the Duck Lake assemblage. Northeast of Duck Lake, relationships between b) Second Generation Structures leucotonalite and feldspar porphyry appear gradational, suggesting that the leucotonalite may be the feeder to The main penetrative foliation (S 2) is typically the porphyries. In the southeast corner of Duck Lake, moderately to steeply northwest to north dipping. In where leucotonalite is in contact with volcanics to the supracrustal rocks of the Central Meta volcanic Belt, S2 west, my lonitic textures are developed within the is generally parallel to S1 and primary compositional ). intrusion. layering (S0 In younger sedimentary rocks southeast of the polymictic conglomerate, metamorphic minerals The area southwest of Cowie Lake is underlain by a such as muscovite, sillimanite or biotite grow slightly peculiar tonalite intrusion (unit Tq). The tonalite oblique to S0 along the long limbs of tight to isoclinal weathers light grey and is coarse to very coarse folds, and parallel to the S2 axial plane in fold hinges. grained. Elongate resistant weathering quartz ribs Most tonalitic and granitic leucosomal melts are folded impart a corrugated appearance on weathered surfaces. by F2 minor folds but also occur parallel to the axial Quartz content is relatively high overall and can reach plane of F2 folds, suggesting that they were developed . up to 40 percent. Protomylonitic fabrics are commonly during 0 2 Foliation in plutonic rocks is generally developed along its southeastern margin, and are poorly defined, and marked either by a weak alignment accompanied by enrichment in quartz and garnet. of biotite and/or hornblende or by gneissic segregations Nebulous and ghosted, somewhat migmatitic features of mafic and felsic components. are typical. Near a unit of silicate-facies iron formation, the tonalite is very quartz-rich, garnetiferous and also A large-scale, tight F2 synformal-antiformal fold pair in quite magnetite rich indicating that it partially resorbed the Duck Lake~Macfarlane Island area refolds pelites the iron formation. of the Duck Lake assemblage and younger sedimentary rocks. Small wavelength parasitic s-folds deform the 94 Summary oflnvestiRalions 1998 northwestern normal limb of the fold and symmetrical e) Metamorphism folds exist in the hinge areas. Metamorphic grade increases from north to south and is generally in the middle to upper amphibolite facies c) Third Generation Structures range, but locally attains granulite facies conditions. F3 folds are open to close, north to northeasterly plunging structures with north-trending subvertical Within the Central Metavolcanic Belt, in mafic and axial surfaces. In th e arkosic assemblages, F folds intermediate volcanic rocks, garnet-hornblende 3 plagioclase-bearing metamorphic mineral assemblages crenulate the S2 schistosity, and exhibit a weak axial planar flattening of quartz-aggregates in folded quartz are typical. Pelitic to psammopelitic rocks contain feldspar veins. Sillimanite faserkiesel knots are also abundant garnet and biotite. Sillimanite and in situ partial melting are generally absent from Central crenulated by F3 minor fold structures. New growth of muscovite along northerly trending, steeply dipping Metavolcanic Belt rocks, suggesting that middle amphibolite facies conditions were not surpassed. axial cleavages, overgrows S2 peak metamorphic assemblages. Most mineral lineations and rodding, are typically coaxial with third generation minor folds, and Pe lites of the Duck Lake assemblage are characterized generally plunge gently to moderately north to north by a metamorphic paragenesis of sillimanite-garnet northeast. biotite and relict staurolite signaling that upper amphibolite facies conditions of 650° to 670°C were The Birch Point-Watt Island area is underlain by an attained (Winkler, 1979). antiformal-synformal fold pair, called the Birch Point Folds (Lewry et al., 1980), which pass westward into Arkosic rocks west of Macfarlane Island are typified the Sucker Point folds (Johnston, 1983; Maxeiner, by biotite-muscovite-quartz±sillimanite-bearing assemblages, indicating that muscovite is stable in the 1996). The Birch Point synform is an F2 fold that was presence of quartz, and sillimanite has started to form. tightened during the D3 fold episode. Rare examples of small scale Type-3 fold interference patterns (Ramsay With the appearance of abundant sillimanite and and Huber, 1987) throughout the area imply coaxiality granitic leucosome in arkoses farther to the southeast of the second and third phase of deformation. Map muscovite disappears from the rock suggesting that the patterns within the Numabin Bay volcanic succession, second sillimanite isograd was reached and that also suggests Type-3 fold interference. muscovite and quartz react to form microcline, sillimanite, and melt. Psammopelitic rocks in this part of the map are characterized by garnet-biotite-quartz d) High-strain Zones plagioclase bearing mineral assemblages and Zones of high strain (indicated on the map by cross development of tonalitic leucosome. hatching) occur throughout the area. The Duck Lake high-strain zone (Maxeiner. 1997) extends into this Hypersthene, in an interbedded succession of pelite, year's map sheet and coincides with the boundary calcareous psammopelite and minor amphibolite between the Central Metavolcanic Belt and the Duck northeast of Deep Bay, can have two explanations: it lake assemblage. In the Duck Lake area, the high signalizes the onset of granulite facies metamorphism strain zone follows the normal limb of a large scale F, where temperatures of 750°C were obtained; or it is . due to an influx of CO, into the rocks which could fold, indicating that it may have formed during D2 The southwestward continuation of the high-strain zone is cause the formation o(orthopyroxene at considerably lower temperatures. As there is an abundance of folded about the F2 -F3 Birch Point synform. On the wesJern limb of the Birch Point synform, the high carbonate i_n the system (calcareous psammopelite), the stram zone appears to be 'climbing' through the second option would appear to be the most viable. stratigraphy and earlier structures, confirming that it Feldspars within the orthopyroxene-bearing rocks, post-dates the first deformation. Several other high-strain zones cut the younger sedimentary succession southeast of Macfarlane Island. The Hodgson Island high-strain zone, which follows the southeastern shoreline of Hodgson Island, is several hundreds o(metres wide. It is developed within pink to grey (arkos1c to psammitic) quartzofeldspathic metasedimentary rocks (Figure 17). A generally northeast-plunging stretching lineation is well d_e"'.elope~ and most shear sense indicators suggest sinistral displacement along this fault, i.e., oblique thrusting with the northwestern hanging wall moving over the southeastern footwall. Figure 17 - Highly strained arkosic gneiss; on southeast shore of large island southeast ofHodgson Islam!. Saskatchewan Geological Survey 95 however, have a waxy green colour in outcrop and water deposits are also present as indicated by some of the amphiboles appear brown in thin section, occurrence of iron forrnation and cross-bedding in both characteristics of granulite facies metamorphism. volcaniclastics. Also, pelites have been affected by >50 percent anatexis, leading to the formation of diatexite. In b) Sediment-hosted Sulphides (Price Island) addition, granulite facies metamorphism is consistent with the southerly increase in metamorphic grade from Another area with abundant gossan development is lower amphibolite to upper amphibolite facies. Biotite located north of Deep Bay, on Price Island and the and green amphibole are still largely stable in the peninsula to the east. Here, an intercalated succession orthopyroxene-bearing rocks, however, suggesting that of arkose, calcareous arkose, calcareous psammopelite, peak metamorphism only reached the onset of granulite marble, impure quartzite, minor mafic rock, and facies conditions presumably at relatively low graphitic petite marks the transition from a shelf pressures. sequence to deeper parts of an ocean. Some of the quartzite and calcareous sedimentary rocks contain f) Late Faulting abundant disseminated pyrrhotite causing rusty weathering. In some cases, however, the pyrrhotite is Several splays of the Tabbernor Fault system, a late associated with minor amounts of chalcopyrite and brittle to ductile north-south-trending structure sphalerite, as seen in one thin section of a graphitic extending over much of the province, transect the map quartzite. area. The main splay of the fault, which follows Numabin Bay, is clearly visible on the map. It is partly c) Volcanic-hosted Copper (Duck Lake) parallel to, and superposed on, a high-strain zone along the western limb of the Birch Point synform. Farther The area north of Duck Lake hosts a number of copper north, however, the true brittle nature of the Tabbernor showings in highly strained and strongly altered mafic Fault in this area becomes evident. Displacement along volcanic rocks. The showings are associated with zones the Numabin Bay splay of the Tabbemor Fault is in the of strong garnet enrichment, accompanied by cordierite order of 200 to 1000 m sinistral offset. Rocks flanking and Mg-rich amphiboles (cummingtonite or the fault are characterized by an abundance of anthophyllite), and are interpreted as metamorphosed hematite-, epidote-, or chlorite-coated fractures, and syngenetic alteration zones. These alteration mineral potassic alteration of plagioclase. assemblages occur in discrete bands and patches, and appear to be transposed into the foliation, indicating that they predate the shearing event (D2). The Mg-rich nature of these zones in association with chalcopyrite 7. Economic Geology mineralization is consistent with their formation in a For a detailed discussion of mineral showings the syngenetic, subseafloor hydrothermal environment reader is referred to the companion report by (e.g. Lydon, 1988). One occurrence of oxide-facies MacDougall (this volume). The following briefly banded iron formation in the same sequence of rocks discusses the mineral potential of three areas, from the further supports this idea. The Stackhouse Bay Cu-Zn perspective of the regional mapper. showings (Maxeiner, 1996; MacDougall, this volume) are essentially a strike equivalent of the same package of rocks and further emphasize the potential for the a) Volcanic-hosted Gold? (Numabin Bay) occurrence of volcanogenic massive sulphide deposits The potential for metamorphosed epithermal gold in this part of the Central Metavolcanic Belt. deposits exists in the northwestern comer of the map area, east ofNumabin Bay. The volcanic rocks in this Approximately 80 km to the east, the Fox River Cu-Zn area are exceptionally well exposed due to a double mine in Manitoba is located within strike equivalent bum resulting in approximately 50 percent bedrock rocks. The mines in the Lynn Lake area are located exposure. Many outcrops are rusty weathering and another 30 km to the northeast. contain abundant gossans some of which are tens of metres in diameter. Most of the rust appears to be derived from the weathering of small amounts of 8. Summary and Discussion disseminated pyrrhotite. The host rocks are felsic to intermediate volcanic and volcaniclastic rocks. Most of Two splays of the Central Metavolcanic Belt in the the felsic volcanic rocks are of pyroclastic origin with Birch Point area, here informally termed Numabin Bay abundant dacitic tuff breccias. There is, however, also and Birch Point volcanic belts, comprise approximately evidence of thin intercalated subaerial rhyolitic flows. 40 percent mafic volcanics and 60 percent intermediate Signs of syn genetic hydrothermal alteration are to felsic volcanics. The belts also contain about 20 present: garnet is abundant in the dacitic and percent synvolcanic sediments. Felsic to intermediate intermediate volcanic rocks, and gamet-anthophyllite volcanic rocks are predominantly pyroclastic in origin bearing assemblages occur locally. and were deposited in a subaerial setting; subaqueous volcanics and volcaniclastics are minor. Mafic to Overall, this area may also be favourable for the ultramafic rocks of the Birch Point volcanic belt, which formation of volcanogenie massive sulphides. is continuous with the Lawrence Point volcanic belt to Although most of the volcanic rocks here appear to be the northeast, are interpreted to be the highly strained the product of subaerial deposits, shallow to deeper remnants of a slice of oceanic crust, into which mantle- 96 Summary ofInvestigations 1998 derived harzburgites and lherzolites were intruded. rocks between Macfarlane Island and Price Island have Further geochemical characterization of the volcanic similar descriptions to those of the Sickle Group (e.g. rocks will establish in which lithotectonic environment Gilbert et al., 1980; Zwanzig, 1990). Thick units of the rocks originated. Minor synvolcanic turbidites of calcareous psammopelite and intercalated quartzite and the Duck Lake assemblage have been tectonically graphitic pelite may represent the break between the juxtaposed against the Birch Point-Lawrence Bay shelf edge (Price Island area) and the adjacent deeper volcanic belts. basin (Deep Bay area). D1 high-strain zones disrupt the sequence, resulting in imbrication and stacking of A broad zone of partially imbricated sedimentary rocks units. Fold repetition of units is also possible and structurally underlies rocks of the Central likely, although field evidence is equivocal. Overall, Metavolcanic Belt and Duck Lake assemblage (Figure this interpretation is largely consistent with earlier ones 18). Polymictic conglomerate in the Duck Lake area by Corrigan et al. ( 1998). forms the structural top of this sedimentary stack, but forms the stratigraphic base of a predominantly Understanding of geological relationships in the Price quartzofeldspathic succession of sediments and is Island area is hindered by complex geology and believed to have been deposited in a shallow water, structure combined with poor outcrop quality. It seems possibly flu vial to deltaic setting. A regional obvious from the present map and previous mapping unconformity is inferred at the base of the (Gilboy, 1980), however, that rocks here are unique conglomerate, as its clasts have apparent Central when compared with both the Bumtwood Group and Metavolcanic Belt provenance and the conglomerate the Sickle Group. Gilboy ( 1980) mapped the rocks at appears to cut out structurally overlying units to the Price Island as metaquartzites and meta-arkosic north. The conglomerate is stratigraphically overlain gneisses and suggested that they mark the boundary by cross-bedded muscovite-microcline-bearing 'pink between the two groups; he included them largely in arkose' that was also deposited in a shallow water the Bumtwood Group. From present mapping it is environment. proposed that the change from pelite to calcareous psammopelite, quartzite and arkose records a Southeastward, in the Jones Peninsula area (Figure 18), prograding shelf sequence and that the arkosic rocks the depositional setting changed to a slightly deeper are essentially facies equivalents of the petites. A water shelf environment, with intercalation of arkose, similar depositional setting was described by Ansdell et psammopelite and thin calcareous beds. Sedimentary al. ( 1995) for the contact between Missi and O cross-bedded arkose c:;;:) calcareous psammopelite, quartzite Q conglomerate @ arkose I psammite U graphitic pelite, psammopelite Central Metavolcanic Belt Duck Lake assemblage volcanics and ~ psammitic to minor sediments "'-="' pelitic sediments N 'Duck' s vvvv vvvv vvv v vvv vvvvvv vvvvv vv vv vv vvv vvv vvvv vvv vv vvvvvvvvv v vv vvv vvvv vvvvv vv vvvv vvv vv vvv high-strain zone zone Figure 18 - Schematic composite stratigraphic diagram of supracrustal rocks in the southern Reindeer lake area. Saskatchewan Geological Survey 97 Bumtwood groups on the south side of the Kisseynew Survey, Sask. Energy Mines, Misc. Rep. 86-4, Domain. plOl-107. In the past, the McLennan Group has commonly been Cas, R.A.F. and Wright, J.V. (1987): Volcanic equated with the Sickle Group (e.g. Lewry et al., 1990 Successions, Modern and Ancient; Allen and and references therein), but based on Lewry's (1983) Unwin Ltd., London, 528p. and Thomas' (] 985) initial definition of McLennan Group arkoses, this correlation is only partly Corrigan, D., Bash forth, A., and Lucas, S. ( 1997): warranted, as the Sickle Group includes a much wider Geology and structural evolution of the La Ronge spectrum of quartzofeldspathic sedimentary rocks Lynn Lake Belt in the Butler Island area (parts of (Table 3) including conglomerate, sandstone (biotite 640/9 and 640/10), Reindeer Lake, gneiss, sillimanite biotite gneiss), and calcareous Saskatchewan; in Summary of Investigations sandstone (homblende-diopside gneiss). 1997, Saskatchewan Geological Survey, Sask. Energy Mines, Misc. Rep. 97-4, p 18-30. MacLean Lake gneisses, commonly interpreted as Bumtwood Group equivalents (e.g. Lewry et al., 1990 Corrigan, D., Maxeiner, R.0., Bashforth, A., and and references therein), comprise rocks which could be Lucas, S.B. (1998): Preliminary report on the equivalents of either Bumtwood or Sickle groups. geology and tectonic history of the Trans-Hudson Graphitic pelites of the MacLean Lake gneisses in the Orogen in the northwestern Reindeer Zone, Otter Lake area likely do represent Bumtwood Group Saskatchewan; in Current Research, Part C, Geo!. equivalents. MacLean Lake psammite, calcareous Surv. Can., Pap. 98-1 C, p95-l 06. psammite and conglomerate of the same area (Thomas, 1993), however, could be equivalents of the Sickle Fox, J.S. and Johnston, W.G.Q. (1980): Komatiites, Group and/or Missi Group, and may represent the boninites and tholeiitic picrites in the Central attenuated southern margin of the Kisseynew Basin in Metavolcanic Belt, Saskatchewan and Manitoba, Saskatchewan. and their possible economic significance; Sask. Resear. Counc., Pub!. G-741-1-G-80, 51 p. Gilbert, H.P., Syme, E.C., and Zwanzig, H.V. (1980): 9. Acknowledgments Geology of the metavolcanic and volcaniclastic Jason Cosford, Brett Pearson, and Greg Helman metasedimentary rocks in the Lynn Lake area; provided excellent and cheerful field assistance during Min. Resour. Div., Manit. Energy Mines, GP80-I, the entire summer. Exchanging ideas and sharing l l8p. logistical costs with David Corrigan, the GSC party chief, was fruitful both to the map and budget. Gilboy, C.F. (1980): Geology of the Reindeer Lake Discussions with David MacDougall, Gary Delaney, South (southeast) Area; Sask. Dep. Miner. and Charlie Harper both during and after the field Resour., Rep. 198, 62p. season were extremely helpful in improving the map and report. Osprey Wings of Missinipe provided ----~ ( 1982): Classification of elastic excellent air services. metasediments; Sask. Dep. Miner. Resour., Open File Rep. 82-3, 33p. Harper, C. T. ( 1996): La Ronge-Lynn Lake Bridge 10. References Project: Sucker Lake-Flemming Lake area; in Alcock, F.J. (1938): Reindeer Lake South Map-area, Summary of Investigations 1996, Saskatchewan Saskatchewan; Geol. Surv. Can., Pap. 38-15, l 7p. Geological Survey, Sask. Energy Mines, Misc. Rep. 96-4, p66-78. Ansdell, K.M., Lucas, S.B., Connors, K., and Stem, R.A. ( 1995): Kisseynew metasedimentary gneiss ( 1997): Sucker Lake-Flemming Lake belt, Trans-Hudson Orogen (Canada): Back-arc update; in Summary of Investigations 1997, origin and collisional inversion; Geol., v23, Saskatchewan Geological Survey, Sask. Energy p\039-1043. Mines, Misc. Rep. 97-4, p42-SO. Bickford, M.E. and Van Schmus, W.R. (1985): Innes, M.J.S., Pearson, W.J., and Gueur, J.W. (1964): Preliminary U-Pb age data for the Trans-Hudson The Deep Bay crater; Pub!. Dom. Obs., v3 I, no2, Orogen in northern Saskatchewan: New and 52p. revised results; in Summary of Investigations 1985, Saskatchewan Geological Survey, Sask. Johnston, W.G.Q. ( 1983): Geology of the Southend Energy Mines, Misc. Rep. 85-4, p63-66. area; Sask. Energy Mines, Open File Rep. 82-4, 15 lp. Bickford, M.E., Van Schmus, W.R., Macdonald, R., Lewry, J.F., and Pearson, J.G. (1986): U-Pb zircon Johnston, W.G.Q. and Thomas, M.W. (1984): geochronology project for the Trans-Hudson: Compilation Bedrock Geology, Reindeer Lake Current sampling and recent results; in Summary South, NTS Area 640; Sask. Energy Mines, Rep. of Investigations 1986, Saskatchewan Geological 230 ( l :250 000 scale map with marginal notes). 98 Summary of Investigations 1998 Lewry, J.F. ( 1983): Character and structural relations Ramsay, J.G. and Huber, M.I. (1987): The Techniques of the McLennan Group meta-arkoses, McLennan of Modern Structural Geology, Vol. 2: Folds and Jaysmith lakes area; in Summary of Investigations Fractures; Academic Press, London, 264p. 1983, Saskatchewan Geological Survey, Sask. Energy Mines, Misc. Rep. 83-4, p49-55. Scott, B.P. (] 991 ): Metallogenic Map Series, Reindeer Lake South, NTS Area 640; Sask. Energy Mines, Lewry, J.F., Curry, A. , and Roberts, K. (1980a): Rep. 253, 18p (accompanied by I :250 000 scale Geology of an Area Around Ghana Lake (NTS map). area 640-NW); Sask. Dep. Miner. Resour., Rep. 191 , 29p. Sibbald, T.1.1. (] 977): The Geology of the Milton Island Area (west half); Sask. Dep. Miner. Lewry, J.F., Abraham, A., and Wilson, G.B. (1980b): Resour., Rep. 153, 38p. La Ronge Project; in Summary of Investigations 1980, Saskatchewan Geological Survey, Sask. Stockwell, C.H. ( 1929): Reindeer Lake area, Dep. Miner. Resour., Misc. Rep. 80-4, p23-28. Saskatchewan and Manitoba; Geol. Surv. Can. Summ. Rep., p46-72. Lewry, J.F., Thomas, D.J., Macdonald, R., and Chiarenzelli, J. (1990): Structural relations in Thomas, D.J. ( 1985): Geological mapping, Roundish accreted terranes of the Trans-Hudson Orogen, Bervin lakes area (part ofNTS 73P- l 5 and -16); in Saskatchewan: Telescoping in a collisional Summary of Investigations 1985, Saskatchewan regime?; in Lewry, J.F. and Stauffer, M.R. (eds.), Geological Survey, Sask. Energy Mines, Misc. The Early Proterozoic Trans-Hudson Orogen of Rep. 85-4, p 18-27. North America, Geol. Assoc. Can., Spec. Pap. 37, p75-94. _ _ __ (1993): Geology of the Star Lake-Otter Lake Portion of the Central Metavolcanic Belt, La Lorenz, V. (1974): Vesiculated tuffs and associated Ronge Domain; Sask. Energy Mines, Rep. 236, features; Sediment, v2 I, p273-29 I. 132p. Lydon, J.W. (1988): Volcanogenic massive sulphide Trowell, N.F., Pirie, J., and Jensen, L.S. (1978): deposits, Part n genetic models; Geosci. Can., Volcanic rock classification in Precambrian v 15, p43-65. geology reports; Ont. Geol. Surv., Informational Manual 1, for internal use, 23p. MacDougall, D.G. ( l 997): Mineral occurrences in the south Reindeer Lake area, NTS 640-1 O; in Winkler, H.G .F. ( 1979): Petrogenesis of Metamorphic Summary of Investigations 1997, Saskatchewan Rocks; fifth edition, Springer Verlag, New York, Geological Survey, Sask. Energy Mines, Misc. 348p. Rep. 97-4, p3 l-42. Zwanzig, H.V. (1990): Kisseynew gneiss belt in Maxeiner, R.O. ( 1996): Bedrock geology of the Henry Manitoba: Stratigraphy, structure, and tectonic Lake area (parts ofNTS 640-6 and -11 ), northern evolution; in Lewry, J.J. and Stauffer, M.R. (eds.), La Ronge Domain; in Summary of Investigations The Early Proterozoic Trans-Hudson Orogen of 1996, Saskatchewan Geological Survey, Sask. North America, Geol. Assoc. Can., Spec. Pap. 37, Energy Mines, Misc. Rep. 96-4, p51-66. p95- I 20. _____ (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, p3-17. Maxeiner, R.O. and Sibbald, T.I.J. (1995): Controversial rocks in the Hebden-MacKay lakes area, southern La Ronge Domain; in Summary of Investigations 1995, Saskatchewan Geological Survey, Sask. Energy Mines, Misc. Rep. 95-4, p79-86. Maxeiner, R.O., MacDougall, D.G., Corrigan, D., and Lucas, S. B. ( 1998): Serpentinites, actinolite schists, and mafic volcanogenic rocks in the La Ronge Domain, northeast Saskatchewan: Mafic ultramafic intrusive complex, or remnants of an ophiolite?; GAC/MAC Annual Meeting, Quebec City, May 1998, Abst. Vol., v23, pA-121. Saskatchewan Geolog1cal Survey 99