Revision Bedrock Geological Mapping of the Northwest Amisk Lake Area (Parts of NTS 63L-9 and -16) 1

8.A. Reilly

Reilly, B.A. (1993): Revision bedrock geological mapping of the northwest Amisk Lake area (parts of NTS 63L·9 and ·16); in Sum· mary of Investigations 1993, Saskatchewan Geological Survey, Sask. Energy Mines, Misc. Rep. 93·4.

Revision bedrock geological mapping, during the 1993 2. General Geology field season in the northwestern part of the Amisk Lake area, covered approximately 105 km2 at 1: 12 500 scale. The area around northwest Amisk Lake lies in the west­ The area is located south of Welsh and Alder lakes, ern part of the Flin Flan-Snow lake greenstone belt, east of Jardine Lake, north of Neagle Creek, and west the most southern exposure of the Trans-Hudson Oro­ of Magdelan Lake. Islands located in the North Channel gen (Lewry and Collerson, 1990; Hoffman, 1990). Su­ of Amisk Lake were mapped; however, mapping in the pracrustal rocks in the map area have been ascribed to West Channel area was restricted to the mainland. the Amisk Group, which is dated at 1888 ±3 Ma in the Neagle Lake area (Heaman et al., this volume). The A major objective of this project is to obtain a better un· stratigraphic sequence appears to consist of older mafic derstanding of the controls on base metal and gold de· volcanic rocks overlain by intermediate volcanic rocks posits in the region. Emphasis is being placed on the with subordinate felsic volcanic rocks (Figure 1). Con­ application of physical volcanology and lithogeochemi· formable sedimentary rocks of the Amisk Group are be­ cal techniques in refining the volcanic stratigraphy, map· lieved to be volcanogenic turbidites. Falsie hypabyssal ping, and geochemical study of intrusive rocks, as well rocks form minor intrusions in the northwest Missi Is­ as detailed structural analysis of the complex folding land area. The Amisk Group is unconformably overlain and fault/shear systems transecting the region. Relative by sedimentary rocks of the Missi Group, a molasse de­ ages for volcanism, sedimentation, plutonism, metamor­ posit which was deposited between 1842 to 1847 Ma phism, and deformation events based on field relation­ (Ansdell, in press). Pre· to syn-tectonic intrusions in­ ships are being tested by high-precision geochronologi­ clude the Neagle Lake Pluton dated at 1837 ±5 Ma cal methods. (Ansdell and Kyser, 1991b) and 1846 +14/-6 Ma (Ashton et al., 1992), the Reynard Lake Pluton dated at Mapping in the Amisk Lake area is a component of the 1853 ±8 Ma (Ansdell and Kyser, 1991b), and smaller Saskatchewan Geological Survey's multidisciplinary, bodies of tonalitic feldspar porphyry dated at 1841 multi-year Project Seagull and includes revision bed­ ±18 Ma (Ansdell and Kyser, 1992) and 1830 +10/-8 Ma rock geological mapping by Reilly (1990, 1991, 1992) (Ashton et al., 1992). Minor intrusions include syn-vol­ and colleagues 0. Thomas (1989, 1990, 1991, 1992, canic bodies of gabbro/diorite and rare quartz feldspar this volume), B. Slimmon (1991, 1992, this volume), porphyry. Post-tectonic dykes of mafic and felsic compo­ K. Ashton (1990), and C. Harper (this volume). Project sition are found locally. Seagull is part of a larger Canada-Manitoba-Saskatche­ wan Shield Margin NATMAP Project focused along the Regional metamorphic grade increases towards the Precambrian Shield-Paleozoic margin. northwest. Contact metamorphism may be associated with emplacement of some of the larger intrusions. Ret­ 1. Previous Work rograde metamorphism is associated with late struc· tures.2 Tyrrell (1902), Mcinnes (1909), and Bruce (1916, 1918) recorded the first reconnaissance geological surveys in Early east-west trending (D 1) folds and high-strain the Flin Flon- Amisk Lake region. These surveys were zones are deformed by north-south trending (02) folds followed by detailed studies by Wright and Stockwell to produce a complex fold interference pattern. The (1934), Pearson (1951). Byers and Dahlstrom (1954), dominant regional fabric found throughout the area is a Fox (1976a and b), Ayres et al. (1981), Pearson (1983), north-south trending axial planar foliation associated de Tombe (1988), Sparks (1990), Wilcox (1990), and with the 02 deformation. Sinistral brittle-ductile shear Ashton (1992). zones developed during 03 deformation are folded by the Embury Lake Antiform (04). Faults and topographic lineaments which transect the area are interpreted as a product of late stage brittle 05 deformation.

(1) Saskatchewan Project A.112 was funded in 1993 under the Canada-Saskatchewan Partnership Agreement on Mineral Development 1990·95. (2) All of the Precambrian rocks In the map area have been metamorphosed and the prefix meta will be omitted when referring to these rocks.

12 Summary of Investigations 1993 Ptog ITE?J ~1 r -.-;1 \...'.._ •__J

bO~ RPyna.r c/ Loke Plvt on [::'.]

Figure 1 - Geological sketch map of the northwest Amisk Lake area. A, Welsh Lake; B, Batty Lake; C, Grassy Lake; D, Jardine Lake; £, Neagle Creek; £LA, Errington Lake Anticline; MLS, Magdalen Lake Syncline; NGA, North Channel Anticline; WIA, Waverly Island Anticline; RCSZ, Robinson Creek Shear Zone; MCFZ, MacDonald Creek Fault Zone; and WCF, West Channel Fault.

Saskatchewan Geological Survey 13 At least seventeen marginally economic gold occur­ The Missi Group unconformably overlies the Amisk rences are found in the map area. The largest include Group and defines the Amisk Basin, one of three major, the Graham, Monarch- Prince Albert, and the Black Dia­ partly fault-bounded, synclinal basins at the western mond deposits. They exhibit characteristics akin to end of the Flin Flon- Snow Lake greenstone belt (Stauf­ mesothermal gold mineralization and are associated fer, 1990). Polymictic boulder conglomerate generally with (03) brittle-ductile shear zones. No significant base marks the base of the sedimentary sequence and is metal occurrences are known in the map area, although overlain by pebbly arkose. Arkose found at the top of nickel-copper mineralization is reported from one show­ the succession is the major rock type in the basin. The ing. Missi Group is considered to have been deposited be­ tween 1842 Ma {Heaman et al., 1992) and 1847 Ma 3. Stratigraphy (Ansdell, in press). Byers and Dahlstrom (1954) recognized two basic sub­ 4. Amisk Group Rocks division~ .~ithin the Amisk Group in the map area, a lower d1v1s1on of basalt and subordinate falsie volcanics, and an upper division of felsic rocks. Fox (1976a and b) a) Mafic Volcanic Rocks re.fined the stratigraphic sequence geochemically, identi­ fying a lower division of juvenile tholeiitic island arc ba­ Mafic volcanic rocks crop out south of the Neagle Lake salts which evolve upwards from olivine- to quartz-nor­ Pluton and north of Neagle Creek in the core of the Er­ mative compositions (finding no traces of subordinate rington Lake _Anticline (F?x, 1976a; Reilly, 1992). Long falsie volcanics) and an upper division of calc-alkaline is­ attenuated slivers of maftc volcanic rock also occur land arc volcanic rocks comprising five mappable rock within the Welsh lake Assemblage, generally in tec­ units. Andesite, which predominates volumetrically, oc­ tonic contact with the sediments. Weathered surfaces curs at the base. of th~ upper division and is overlain by are dark green grey and fresh surfaces are green black. coarse pyroclast,cs, high-alumina basalt, dacite, and The rock is composed of plagioclase, chlorite, actinolite, rhyolite. Present mapping confirmed this stratigraphic and epidotE:. Biotite and_ hornblende are found at higher sequence, with the exception of coarse pyroclastics metamorphic grades. Minor constituents are magnetite, w~ich do ~ot appear to form a distinct mappable unit. leucoxene, and quartz. Massive equigranular flows are ~1gh-alumma basalt was not found in the map area, but dominant, and pillow and pillow breccia flows and pla­ 1s abundant south of Missi Island in the Crater-Vances gioclase porphyritic flows are found locally. Quartz islands area (Fox, 1976a and b). amygdales are present in some of the flow rocks. Highly strained mafic volcanic rocks form tectonites In the Snake Rapids area to the south, Watters and w~ich exhibit millimetre-scale tectono-metamorphic lay­ Ashton (1991) believe that stratigraphicalfy equivalent en_ng accentuated by quartz and carbonate stringers. lower division basalts best represent island arc tholei­ Primary features are obscured or obliterated in this unit. ites. A transitional or back-arc environment for the ba­ salts cannot, however, be ruled out, in which case the b) Felsic to Intermediate Volcanic Rocks tholeiitic basalts may best correlate with the island arc basalts of the Flin Flon Assemblage (Syme et al., Felsic to intermediate volcanic rocks were subdivided in 19~3) i~ the Flin Flon area (Watters, 1990, 1991). Corre­ the field into andesites, dacites, and rhyolites based on lation with MOAB-type or back-arc environment basalts colour index. These are found in the North Channel of the Athapapuskow Assemblage {Syme et al., 1993) area and south of the Neagle Lake Pluton where they in the ~ast Amisk Lake area (Parslow and Gasgarth, form the eastern extension of the West Amisk Assem­ 1988) 1s also possible. blage.

The upper division of predominantly intermediate to fal­ Andesitic rocks weather olive to moderate green grey sie volcanic rocks define a classical well-differentiated and have moderate dark grey fresh surfaces. Plagio­ calc-alkaline island arc sequence {Fox, 1976a and b; clase, quartz, aclinolite, chlorite, biotite, epidote, horn­ Walker and Watters, 1982) which are distinct from the blende, and locally magnetite, are the major constitu­ underlying basalts and are hereafter referred to as the ents of this rock type. Volcaniclaslic andesites are domi­ West Amisk Assemblage. A felsic volcanic tuff breccia nated by heterolithic tuff breccias. These fragmental located at the top of the sequence in the Neagle Lake ro~ks are generally poorly sorted, matrix-supported, de­ area yielded a date of 1888 ±3 Ma (Heaman et al., this void of bedding, and interpreted as debris flows. Subor­ volume). dinate volcaniclastic rocks include heterolithic and monolithic _lapilli tuft and crystal tuff units which vary Volcanogenic sediments between Welsh Lake and the from m~ss1ve to well bedded. Grain size gradation is ob­ West Channel of Amisk Lake form a third division of the served in some of the well bedded units. Andesitic flow Amisk Group, hereafter called the Welsh Lake Assem­ rocks are dominated by massive and plagioclase±horn­ blag«:. This assemblage conformably overlies, and is lo­ blende-phyric units in which phenocrysts comprise up cally intercalated with, the West Amisk Assemblage. to 40 percent of the flow. Individual flows can be distin­ Greywacke and argillite layers represent the dominant guis~ed alon_g _the West Channel where well-exposed rock type. Polymictic pebble conglomerate, and less sections exh1b1t flow top and bottom breccias. Minor commonly cobble conglomerate, occur near the base of flow rocks are pillow and pillow breccia units. Quartz the sedimentary sequence. amygdales are found locally in many of the flow rocks. Like the mafic volcanic tectonites, andesitic tectonites

14 Summary of Investigations 1993 exhibit millimetre-scale tectono-metamorphic layering ac­ 5. Missi Group centuated by quartz and carbonate stringers. Primary features are obscured or obliterated in these rocks. a) Sedimentary Rocks Although much less voluminous than the volcaniclastic Polymictic conglomerate, pebbly arkose, and arkose of andesitic units, dacltes have similar characteristics. the Missi Group crop out in the northeast and extend The dacites weather to a pale to light grey and fresh from the Welsh-Batty lakes area to the North Channel. surfaces are moderate light grey. They are chiefly com­ Isolated lenticular wedges of the Missi Group were also posed of plagioclase, quartz, biotite, chlorite, and found in tectonic contact with the Amisk Group in the sericite. Tuff breccia, lapilli luff, and crystal tuff units MacDonald Creek area. Weathered surfaces range also occur in the area. from fight grey to dark green grey in the conglomerate to moderate orange pink in the arkose. Fresh surfaces Rhyolites are rare and found interbedded with interme­ vary from dark green grey to dusky red. Plagioclase, po­ diate volcanic rocks typically near the top of the West tassium feldspar, and quartz are the main minerals in Amisk Assemblage or associated with hypabyssal rocks rocks of the Missi Group and the presence of chlorite, in the Missi Island area. They weather pale orange yel­ biotite, muscovite, and garnet is a function of metamor­ low to very light grey and fresh surfaces are moderate phic grade and composition. Hematite and magnetite dark grey. Plagioclase, quartz, biotite, and chlorite are are typically found in trace amounts. the main components. Similar to the dacitic rocks, the rhyolites are predominantly volcaniclastic and include Polymictlc conglomerate occurs at the base of the se­ tuff breccia, lapilli luff, and crystal luff. quence and as discontinuous beds, up to 200 m thick, higher in the sequence. The clasts are mainly volcanic, c) Sedimentary Rocks but include granitoid and sedimentary rocks of the un­ derlying Amisk Group. Chert and jasper clasts are a mi­ Volcanogenic sedimentary rocks of the Welsh Lake As­ nor but distinctive component, although no source for semblage extend from Welsh Lake in the north to these has yet been identified. The conglomerate is clast­ Neagle Creek in the south and underlie the central por­ supported, massive to thickly bedded, and clasts vary tion of the map area. Weathered surfaces range from from poorly- to well-sorted. Decimetre to metre thick pale light grey to dark green grey and fresh surfaces beds of pebbly arkose and arkose occur locally in the are dark grey to green black. Feldspar, quartz, chlorite, conglomerate units. epidote, and biotite are found at lower metamorphic grades, whereas andalusite, sericite, garnet, stau~olite, Pebbly arkose, a transitional rock type from conglomer­ and sillimanite are dominant at higher metamorphic ate to arkose, is best exposed along the North Channel. grades where quartz±feldspar stringers are abundant. Polymictic matrix-supported pebbles, similar in composi­ tion to the conglomerate, are found as thin to thick The dominant rock type is very thinly to thinly bedded beds. Contacts with the underlying conglomerate and greywacke and arglllite. Locally this unit exhibits me­ overlying arkose are gradational and interbedded. The dium to thick bedding. Normal graded bedding and . maximum thickness of the pebbly arkose is approxi­ Bouma A(B)E internal zonation is typical for the grey­ mately 300 m. Normal graded bedding, scours, and wacke and argillite beds. Other primary features found trough crossbedding are reliable stratigraphic top indica­ locally include scours, rip-up clasts, and flame s!ruc­ tors in this unit. tures. Peculiar elliptical epidote-rich pods found in the greywacke and argillite unit probably ~e~r~sent con?~e­ Arkose is the most abundant rock type in the basin, oc­ tions. Similarly shaped structures of d1ont1c composrt1on, curring at the top of the sedimentary succession. It found in the vicinity of the Neagle Lake Pluton, are inter­ crops out as a rather monotonous unit and is typically preted by Byers and Dahlstrom (1954) as emanations massive to thickly bedded. Thin beds locally contain from the intrusion. sporadic polymictic clasts. Primary structures observed in the pebbly arkose are rarely found in the arkose. The Pebble conglomerate layers averaging 20 cm in thick­ Missi Group is interpreted as a molasse deposit of allu­ ness are interbedded locally with the greywacke and ar­ vial fans and braided streams (Stauffer, 1990). gillite unit. These layers were found to be bes_t expost:d in the Neagle Creek area. The conglomerate rs polym1c­ tic, matrix-supported, and volcanic and sedimenta~ 6. Minor Intrusions clasts comprise up to 60 percent of the rock. Fels1c peb­ bles are generally the most abundant clast type. Cobble­ Synvolcanic gabbro/diorite sills and dykes intrude all size clasts dominate one particular 3 m wide conglomer­ rock types of the Amisk Group and are most common ate layer comprising at least six different clast types. in the mafic volcanic rocks. Weathered surfaces are Normal graded bedding is common in the pebble con­ dusky yellow green to green black and fresh surfaces glomerate unit. Bouma zon~t(on in the greywacke_and are dark green grey to green black. Hornblende and pla­ argillite beds indicate depos1t1on of the Amtsk sedimen­ gioclase are the main minerals and biotite, actinolit~ •. tary rocks by subaqueous density currents. chlorite, and magnetite are common. The gabbro/dtonte bodies vary in width from decimetres to over 100 m. Contacts between intrusion and country rock are locally chilled. Compositional and metamorphic similarities be­ tween the gabbro/diorite bodies and the mafic volcanic

Saskatchewan Geological Survey 15 rocks suggest that these early intrusions may have dark grey. The porphyritic gabbro is medium- to coarse­ served as feeders providing the source material for the grained, composed of plagioclase phenocrysts up to volcanic flows. one centimetre, hornblende, biotite, magnetite, serpen­ tine, chlorite, and epidote. Pre- to syn-tectonic minor felsic intrusions, which are rare in this area, weather light grey to moderate or­ ange pink and fresh surfaces are moderate light grey to 7. Major Intrusions dark grey. Quartz, plagioclase, and potassium feldspar The Neagle Lake Pluton is a large, compositionally are the main minerals and minor biotite is common. and texturally heterogeneous, oval-shaped pluton which Quartz±plagioclase phenocrysts are dominant and grain crops out between Neagle Lake and Welsh Lake. It size ranges from aphanitic to medium. The felsic intru­ ranges in composition from a diorite core m'.1n~led by sions are typically concordant and measure several me­ quartz diorite which is enveloped by granod1onte along tres in width. the northern and eastern margins (Reilly, 1992). Subor­ dinate components include quartz monzonite, tonalite, Minor intrusions of felsic rocks, that occur along the and gabbro. Internal contacts are gradationaf. Massive, southeast margin of the area, are part of a larger m~ss coarse-grained, locally plagioclase porphyritic textures centred around Missi Island. Exhibited features are inter­ are common except for the southeast portion of the plu­ mediate between plutonic and extrusive rocks. Weath­ ton where it is well foliated. Small dykes of pegmatite, ered surfaces are light grey to orange grey and fresh aplite, gabbro, diorite, lamprophyre, and amphibolite in­ surfaces are moderate dark grey to yellow grey. Pfagio­ trude the main intrusion and are also found as apo­ clase, potassium feldspar, quartz, biotite, and muscovite physes in the adjacent country rock. Small satellit~ i~tru­ are the chief components. The typical rock type is ho­ sions in the West Channel area, and dykes and srlls rn mogeneous and quartz±feldspar porphyritic. L!nequivo­ the MacDonald Creek area, are similar and probably re­ cal extrusive features, such as fragments, define subor­ lated to the Neagle Lake Pluton. Granodiorite and dinate volcaniclastic rocks which are associated with quartz diorite components of the Neagle Lake Pluton this suite. A felsic volcanic lapilli tuft from the Laural from the Neagle Lake area have been dated at 1837 Lake area was dated at 1887 ±3 Ma (Heaman et al., ±5 Ma (Ansdell and Kyser, 1991a) and 1846 +14/-6 Ma this volume). A detailed examination of hypabyssal fel­ (Ashton et al., 1992), respectively. sic rocks in the West Missi Island area is provided by Harper (this volume). Ashton et al. (1992) suggested that the Neagle Lake Pluton is not post-tectonic as proposed by Byers a~d. Tonalitic feldspar porphyry crops out in the map area Dahlstrom (1954) and Reilly (1992), who based therr in­ southwest of Batty Lake as a lenticular body, hereafter terpretation on the general shape of the main ?o~y. the referred to as the Batty Lake porphyry, and south of marked discordance between the structures w,thrn the the Graham Gold deposit as a smaller body, named the intrusion and those in the country rocks, and the mas­ Graham Trail porphyry (Ansdell and Kyser, 1992). sive coarse-grained texture of the pluton. Although The porphyry weathers moderate orange pink and fresh these features are true for part of the pluton, especially surfaces vary from dark green grey to dark grey. ~e­ immediately around Neagle Lake, the southeast is well- dium-grained plagioclase phenocrysts, up to 1 cm in • foliated and lineated. Apophyses of the main body are places, occur in a fine-gr~ine~ ~atrix consisti_ng of pla­ also well foliated and focally exhibit two fabrics (S1 and gioclase, quartz, muscovite, brotrte, and chlonte. The S2). This contrast can be explained by multiple !ntrusi~e porphyry is spatially restricted to the Missi Group where phases of different ages or,. more proba~ly, strain parti­ centimetre- to decimetre-scale apophyses demonstrate tioning within the pluton dunng deformation. The Neagle an intrusive relationship. These feldspar porphyry bod­ Lake Pluton is consequently interpreted here as pre- to ies have been are interpreted as hypabyssal (Wilcox, syn-tectonic. It is also cut by the West Channel Fault. 1990), and may be the intrusive equivalents to the felsic volcanics recognized in the Missi Group in the Wekusko The Reynard Lake Pluton is a large lenticular-shaped Lake area, Manitoba (Gordon et al., 1990). The Gra­ multiphase intrusion which extends over 30 km from ham Trail porphyry has been dated at 1841 ±18 Ma Mystic Lake, southeast of the map area, to Amy Lake, (Ansdell and Kyser, 1992). A similar porphyry found north of the map area (Reilly, 1991 ; Thomas, 1991 ). In north of the map area near Annabel Lake has been the Alder Lake area, weathered surfaces are grey or­ dated at 1830 + 10/-8 Ma (Ashton et al., 1992). ange to moderate orange pink and fresh surfaces dark grey to grey orange. The pluton crops out as a med1un:,­ A large tadpole shaped porphyritic gabbroic to ul· grained, plagioclase porphyritic tonalite co~p~sed of b_r­ tramafic body, referred to as the Magdalen Lake intru· otite, plagioclase, quartz, and muscovite .. It 1s 1n t~ctonic slon (Slimmon, this volume), crops out south of the Gra­ contact with the Missi Group and according to Wilcox ham Gold deposit and extends southeast of the map (1990) dykes similar in comp~sition to t_he _main intru­ area to Magdelan Lake. A second large body crops out sion were not observed intruding the M1ss1 Group. A gra­ in the North Channel area, along the southeast margin nitic phase located in the central part of the pluton was of the map area. Numerous centimetre- to metre-wide dated at 1853 ±8 Ma (Ansdell and Kyser, 1991b), thus dykes and sills intrude both the Missi Group and Amisk supporting a pre-Missi age of emplacement. Group in the North Channel area. _Wilcox (1990) re-. . ported that the porphyritic gabbro intrudes the tonahtLc feldspar porphyry. Weathered surfaces are light olive grey to dark green and fresh surfaces are moderate to

Summary of Investigations 1993 16 8. Structure obscured or obliterated by the shearing. Kinematic indi­ cators such as S-C fabrics, boudinaged and rotated 01 Structures: The earliest recognizable deformation quartz veins, rotated clasts, and asymmetric shear folds event in the map area (01) is considered to have pro­ indicate a sinistral shear sense, confirming the interpre­ duced a bedding-parallel flattening fabric (S1) and bed­ tation of Byers and Dahlstrom (1954) and Wilcox ding-parallel high-strain zones (SZ1 ). (1990). Difficulty has been experienced distinguishing shear-related stretching lineations in SZ3 from linea­ The S1 fabric is defined by flattened primary features tions produced during 02; in any case, they appear to such as clasts, fragments, amygdales, pillows, and phe­ be collinear, indicating west-side-up oblique movement nocrysts, and by preferred mineral orientations. espe­ along the high-strain zones. Reverse-sinistral displace­ cially aligned phyllosilicates such as chlorite, biotite, ment is consistent with the observations of faults in the and muscovite. S1 is penetrative but variably devel­ western part of the Flin Flon greenstone belt (Stauffer oped. Massive competent units exhibit a weak fabric, and Mukherjee, 1971). The major SZ3 high-strain zones whereas less competent rocks are well foliated. Linea­ in the map area are the West Channel Fault (Byers tion has not been observed in association with S1 fabric. and Dahlstrom, 1954). the MacDonald Creek Fault Zone, and the Robinson Creek Shear Zone (Wilcox, The SZ1 fabric is manifest as zones of a well-devel­ 1990). These are comparable to the block-bounding oped ductile penetrative fabric which obscures or obliter­ faults described by Bailes and Syme (1989) in Mani­ ates primary lithological features. No shear sense has toba. Stauffer and Mukherjee (1971) suggested that been deduced for these high-strain zones. The best ex­ they resulted from northwest-southeast shortening. Nu­ posed SZ1 fabrics were found in the Monarch Mine merous smaller structures have also been found area. throughout the map area.

The orientation of S1 and SZ1 is variable and deline­ 04 Structures: The high-strain zones of 03 are folded ation of major folds and high-strain zones is made diffi­ about the Embury Lake Antiform. This antiform is an cult by subsequent folding and shearing. The geometry open northeasterly flexural fold which plunges moder­ of these 01 structures is more complex than previously ately to the east. No fabric associated with this fold has recognized in the Neagle-Errington lakes area (Reilly, been recognized in the map area. Wilcox (1990) ex­ 1992). Fold train envelopes of folded S1 and 821 sur­ plained the structure in terms of passive folding of the faces indicate that 01 major folds and shear zones northern limb of the Embury Lake Antiform by sinistral were originally oriented east-west. This is best exhibited shearing during a northeast-southwest shortening in areas of low strain, such as hinge zones of 02 folds, event. Alternatively, folding and shearing may have otherwise 81 and 82 are indistinguishable along the been unrelated and the Embury Lake Antiform could limbs of 02 folds. Reversals in stratigraphic younging di­ have been produced by active folding during northwest­ rection define at least two major 01 folds in the map southeast shortening. area, the Errington Lake Anticline (Fox, 1976a and b; Reilly, 1992) and the Magdalen Lake Syncline (see 05 Structures: Strong negative topographic line­ Slimmon, this volume). 01 structures are a product of aments, which transect the area and displace lithologi­ north-south shortening. cal contacts, are interpreted as due to late stage fault­ ing. These lineaments form a regional northeast and 02 Structures: A steeply dipping foliation occurs northwest conjugate set. Some ground observations throughout the map area. This is predominantly north­ show evidence of ductile shearing, but generally there south-trending in the south and swings toward the north­ is no associated pervasive fabric and the lineaments west in the north. It is axial planar to the minor and ma­ are interpreted as steeply dipping brittle faults. jor Ught upright 02 folds and is manifest as a discontinu­ ous spaced or crenulation cleavage (82) defined by cen­ timetre-scale micaceous laminae. 82 fabrics produced 9. Metamorphism during this event are best developed in rocks which are well layered and are commonly refracted at bedding Metamorphic grade increases from the south towards contacts. 02 folds plunge gently to moderately to the the northwest. This is interpreted as due to a regional northwest based on the orientation of 02 minor folds, metamorphic event which was probably initiated dur­ and stretching and S1/S2 intersection lineations. Major ing 01 folding and peaked during 02 folding. Similar in­ 02 folds in the map area are the Waverley Island Anti· terpretations have been made in the area by Ashton cline, the North Channel Anticline, and the Lookout (1990, 1992), de Tombe (1988) and Wilcox (1990). At Island Syncline. East-west shortening is responsible least three metamorphic facies are provisionally recog­ for the formation of 02 structures. nized in the Amisk Group of the area as follows:

03 Structures: Zones of brittle-ductile high strain (823) 1. Upper greenschist facies is found in the south crosscut all rock types, postdating 02 folding. These (West and North channels, Amisk Lake area). Sedi­ zones strike north-south in the south and swing toward mentary rocks are dominated by biotite±chlorite. the northwest in the north. The S23 structures comprise Mafic volcanic rocks consist of chlorite±biotite± numerous shear zones and splays. An associated well­ actinolite±epidote. Biotite±chlorite are the chief com­ developed shear foliation, defined by the alignment of ponents of felsic to intermediate volcanic rocks. micaceous minerals in mica schists, generally dips steeply to moderately to the west. Primary features are

Saskatchewan Geological Survey 17 2. Metamorphic grade increases to lower amphibollte associated with the gold are pyrite and arsenopyrite, facies in the centre of area (Grassy Lake area). and extensive gossanous zones are common. Isotopic Sedimentary rocks are composed of biotite±garnet± studies by Ansdell and Kyser (1992) indicate that the staurolite±andalusite. Volcanic rocks of mafic compo­ gold is associated with H20-C02-NaCI fluids deposited sition are dominated by biotite±hornblende. at a temperature of between 360° and 420°C at a pres­ sure of about 2 kbars. 3. Middle amphibollte facies is found in the north­ west (Welsh Lake area). Biotite±garnet±sillimanite The gold occurrences in the map area, although found are the chief constituents of the sedimentary rocks. along 03 structures, may in some places have been formed by remobilization of early mineralization. For ex­ The varied aluminous rocks of the Welsh Lake Assem­ ample, extensive carbonatization is found along some blage provide potentially good indicators of regional con­ of the early SZ1 shear zones. Ankerite±calcite has also ditions in comparison to the limited compositional range been observed to be deformed by 02 deformation. This of the Missi Group. Nonetheless, metamorphic grade is is best exhibited in the area around the Monarch­ observed in the Missi Group to increase to the north­ Prince Albert Mine. The nearby Laural Lake deposit, a west. Biotite and garnet isograds constructed by Wilcox distinct gold-silver deposit in the northwest part of Missi (1990) support this observation. Island, exhibits early sericitization and pyritization asso­ ciated with mineralization which predates metamor­ Contact metamorphism, associated with emplacement phism and deformation (Ansdell and Kyser, 1991 a). of the Neagle Lake Pluton was first proposed by Byers and Dahlstrom (1954), who described andalusite por­ b) Base Metals phyroblasts along the east and north margin of the plu­ ton. As previously reported (Reilly, 1992), these occur­ Although falsie volcanic rocks of the West Amisk As­ rences of andalusite were not confirmed on the north­ semblage host the FON Zone (Zn) (Schwann, 1992) ern margin of the intrusion in the Welsh Lake area. An­ and the Abbott Lake Showing (Cu) to the west (Reilly, dalusite grains along the east margin are foliated and 1992), no significant base metal occurrences have yet lineated, forming part of the regional metamorphic as­ been found in the area, which is dominated by sedimen­ semblage, as suggested by de Tombe (1988). Ran­ tary and plutonic rocks. The predominantly calc-alkaline domly oriented, coarse hornblende porphyroblasts de­ island arc volcanic rocks of the West Amisk Assem­ fine narrow (metre-scale) contact aureoles in country blage contrasts with the tholeiitic MOAB or back-arc vol­ rocks adjacent to some of the larger gabbro/diorite bod­ canic rocks of the Athapapuskow Assemblage in the ies. East Amisk Lake area and the tholeiitic island arc vol­ canic rocks of the Flin Flon Assemblage in the Flin Flon Retrograde metamorphic assemblages of lower green­ area which host Cypress- and Kuroko-type volcano­ schist facies, associated with 0 3 brittle-ductile shear genic massive sulphide deposits, respectively. Fox zones and composed of calcite±ankerite±chlorite± ( 1976a and b) suggested that because of these differ­ sericite±fuchsite±epidote, represent a post-peak meta­ ences, potential massive sulphide deposits in the West morphic event. Mafic to intermediate rocks have been Amisk Assemblage may be richer in lead and are likely retrogressed to chlorite schists and other chlorite-rich to have a different stratigraphic style as compared with assemblages. Felsic rocks have produced sericite those in the Athapapuskow and Flin Flon assemblages. schists and other sericite-rich assemblages. Carbonate generally occurs in all assemblages. The MacDonald Creek Cu-Ni Showing, as described by Byers and Dahlstrom (1954), is located approxi­ mately 800 m west of MacDonald Creek and about 10. Mineral Occurrences 3.2 km southeast of Welsh Lake. The showing was not found during mapping, however, it is summarized here a) Gold after Byers and Dahlstrom (1954). Nickel-copper miner­ alization is associated with two sill-like bodies of gabbro Gold occurrences in the area (Ansdell and Kyser, 1992; and pyroxenite. The sulphide mineralization occurs in Pearson, 1983; Coombe, 1984; Byers and Dahlstrom, isolated patches through the intrusive rock and spar­ 1954) exhibit characteristics akin to epigenetic ingly in sedimentary rocks adjacent to the contact. Dia­ mesothermal mineralization. similar to shear-hosted mond drill holes from the showing returned a best as­ lode gold deposits found in the Archean (Colvine et al., say for combined Ni-Cu content of 0.41 percent. 1988). At least 17 marginally economic gold occur­ rences are present (Figure 2). The largest of these in­ clude the Graham, Monarch-Prince Albert, and Black 11 . Acknowledgments Diamond deposits. Darren Anderson and Jin Hong provided cheerful and competent assistance in the field. Field visits by Bob The gold is hosted in auriferous veins of quartz±ankrite± Macdonald, Bill Slimmon, Charlie Harper, Ken Ashton, chlorite±tourmaline±rnuscovite occurring in brittle-ductile John Lewry, Richard Stern, Steve Lucas, and Kevin shear zones (S23) transecting all units, including Amisk Ansdell proved helpful. and Missi groups, as well as the Neagle lake Pluton. Associated alteration includes silicification, carbonatiza­ tion, chloritization, and sericitization which overprints re­ gional metamorphic assemblages. The main sulphides

18 Summary of Investigations 1993 12. References ____ (1976b): Volcanic stratigraphy and mineralization in the Amisk Group; Geol. Assoc. Can./Min. Assoc. Can., Ansdell, K.M. (in press): U-Pb zircon constraints on the timing Jt. Annu. Meet., Edmonton, Prog. Abstr., v1 . p72. and provenance of fluvial sedimentary rocks in the Flin Flon and Athapapuskow basins, Flin Flon Domain, Trans Gordon, T.M., Hunt, P.A., Bailes, A.H., and Syme, E.C. (1990): Hudson Orogen, Manitoba and Saskatchewan; in Radio­ U-Pb ages from the Flin Flon and Kisseynew belts, Mani­ genic Age and Isotopic Studies. Rep. 7, Geol. Surv. Can. toba: Chronology of crust formation at an Early Proterozoic accretionary margin; in Lewry, J.F. and Stauffer, M.R. Ansdell, K.M. and Kyser, T.K. (1991a): The geochemistry and (eds.), The Early Proterozoic Trans-Hudson Orogen of fluid history of the Proterozoic Laural Lake Au-Ag deposit, North America, Geol. Assoc. Can, Spec. Pap. 37, p1n- Flin Flon greenstone belt; Can. J. Earth Sci., v28, p155- 199. 171 . Hearnan, L.M., Kamo, S.L., Ashton, K.E., Reilly, B.A., Slim­ ____ (199lb): Plutonism, deformation, and metamor­ mon, W.L., and Thomas, D.J. (1992): U-Pb geochronologi· phism in the Proterozoic Flin Flon greenstone belt, Can­ cal investigations in the Trans-Hudson Orogen, Saskatche· ada: Limits on timing provided by the single-zircon Pb­ wan; in Summary of Investigations 1992, Saskatchewan evaporation technique: Gaol., v19, p518-521. Geological Survey, Sask. Energy Mines, Misc. Rep. 92-4, p120-123. ____ (1992): Mesothermal gold mineralization in a Pro­ terozoic greenstone belt: Western Flin Flon Domain, Sas­ Hoffman. P.F. (1990): Subdivision of the Churchill Province katchewan, Canada; Econ. Geol., v87, p1496-1524. and extent of the Trans-Hudson Orogen; in Lewry, J.F. and Stauffer, M.A. (eds.), The Early Proterozoic Trans-Hud· Ashton, K.E. (1990): Geology of the Snake Rapids area, Flin son Orogen of North America, Geo!. Assoc. Can., Spec. Flon Domain (parts of NTS 63L-9 and -10); in Summary of Pap. 37, p15·39. Investigations 1990, Saskatchewan Geological Survey, Sask. Energy Mines, Misc. Rep. 90-4, p4-12. Lewry, J.F. and Collerson, K.D. (1990): The Trans-Hudson Oro· gen: Extent, subdivision, and problems; in Lewry, J.F. and _ ___ (1992): Geology of the Mari Lake area. Saskatch­ Stauffer, M.A. (eds.), The Early Proterozoic Trans-Hudson ewan, Gaol. Surv. Can., Open File Rep. 2444, 1 map, Orogen of North America, Geol. Assoc. Can .. Spec. Pap. scale 1 :50 000. 37, p1-14.

Ashton, K.E., Hunt, P.A. , and Froese, E. (1992): Age con­ Mcinnes, W. (1909): Explorations on the Churchill River and straints on the evolution of the Flin Fton volcanic belt and South Indian Lake; Geol. Surv. Can., Summ. Rep., 1908, the Kisseynew gneiss belt, Saskatchewan and Manitoba; p87-92. in Radiogenic Age and Isotopic Studies, Rep. 5, Geo!. Surv. Can., Pap. 91-2, p55-69. Parslow, G.R. and Gaskarth, J.W. (1988): Proterozoic rocks of east-central Saskatchewan: Geochemistry, structure, and Ayres, L.D., van Wagoner. N., and van Wagoner, S. (1981): mineralization controls; in Summary of Investigations 1988, Physical volcanology of the Amisk Lake Volcano; in Sum­ Saskatchewan Geological Survey, Sask. Energy Mines, mary of Investigations 1981 , Saskatchewan Geological Sur­ Misc. Rep. 88-4, p127-139. vey, Sask. Energy Mines, Misc. Rep. 81-4, p47-51 . Pearson, J.G. (1983): Gold metallogenic studies: Flin Flon­ Bailes, A.H. and Syme, E.C. (1989): Geology of the Flin Flon­ Arnisk Lake Area; in Summary of Investigations 1983, Sas­ White Lake area; Mani!. Energy Mines, Geol. Rep. 87-1, katchewan Geological Survey, Sask. Energy Mines, Misc. 313p. Rep. 83-4, p67-74.

Bruce, E.L. (1916): Amisk-Athapapuskow Lake area; Gaol. Pearson, W.J. (1951): The origin and history of the Neagle Surv. Can., Summ. Rep. 1915, p126·130. Lake pluton in the Amisk Lake area; unpubl. M.A. thesis, Univ. Sask., 72p. ____ _ (1918): Amisk-Athapapuskow Lake district; Gaol. Surv. Can., Mem. 105, 91p. Reilly, B.A. (1990): Bedrock geological mapping, Mystic Lake­ West Arm, Schist Lake area (part of NTS 63K-12); in Sum­ Byers, A.A. and Dahlstrom, C.D.A. (1954): Geology and min­ mary of Investigations 1990, Saskatchewan Geological Sur­ eral deposits of the Amisk-Wildnest lakes area, Saskatche· vey, Sask. Energy Mines, Misc. Rep. 90-4, p25-35. wan; Sask. Dep. Miner. Resour., Rep. 14, 177p. ____ (1991): Revision bedrock geological mapping, Colvine, AC., Fyon, J.A. , Heather, K.B., Marmont, S., Smith, Mystic-Kaminis lakes area (parts of NTS 63K·12 and 63L- P.M., and Troop, D.G. (1988): Archean lode gold deposits 9); in Summary of Investigations 1991, Saskatchewan Geo­ in Ontario; Ont. Geol. Surv., Misc. Pap. 139, 136p. logical Survey, Sask. Energy Mines, Misc. Rep. 91-4, p9- 15. Coombe, W. (1984): Gold in Saskatchewan; Sask. Energy Mines, Open File Rep. 84·1, 134p. ____ (1992): Revision bedrock geological mapping, Neagle Lake-Errington Lake area (parts of NTS 63L-9 and de Tombe, J . (1988): The metamorphic stability fields of the -16); in Summary of Investigations 1992, Saskatchewan Welsh Lake Area in east-central Saskatchewan; Queen's Geological Survey, Sask. Energy Mines, Misc. Rep. 92·4, Univ. , unpubl. B.Sc. thesis, 46p. p16-22.

Fox, J.S. (1976a): Some comments on the volcanic stratigra­ Schwann, P.L. (1992): The geology of the FON zinc deposit; in phy and economic potential of the West Amisk Lake area, Summary of Investigations 1992, Saskatchewan Geologi­ Saskatchewan; Sask. Research Council, Circ. 9, 30p. cal Survey, Sask. Energy Mines, Misc. Rep. 92-4, p87-91 .

Saskatchewan Geological Survey 19 Slimmon, W.L. (1991): Revision bedrock geological mapping, ____ (1991): Revision bedrock geological mapping, Table Lake area (part of NTS 63L·9); in Summary of Inves­ Bootleg Lake-Birch Lake area (part of NTS 63K-12 and tigations 1991 , Saskatchewan Geological Survey, Sask. 63L·9); in Summary of Investigations 1991, Saskatchewan Energy Mines, Misc. Rep. 91·4, p16·20. Geological Survey, Sask. Energy Mines, Misc. Rep. 91·4, p2-8. ____ (1992): Bedrock geological mapping, Hanson Lake-Sturgeon-weir River area; in Summary of Investiga­ _ _ __ (1992): Highlights of investigations around the tions 1992, Saskatchewan Geological Survey, Sask. En­ Flin Flon Mine: Reassessment of the structural history; in ergy Mines, Misc. Rep. 92-4, p23·29. Summary of Investigations 1992, Saskatchewan Geologi­ cal Survey, Sask. Energy Mines, Misc. Rep. 92·4, p3·15. Sparks, D. (1990): Geology of the Raine-Walker Gold Show­ ing. Amisk Lake, Saskatchewan; unpubl. B.Sc. thesis, Tyrrell, J.B. (1902): Explorations in the northeastern portion of Univ. Regina, 30p. the district of Saskatchewan and adjacent parts of·the Dis· trict of Keewatin; Geol. Surv. Can., Ann. Rep., v8, 1900, Stauffer, M.A. (1990): The Missi Formation: An Aphebian mo­ Rep. F, 48p. lasse deposit in the Reindeer Lake zone of the Trans-Hud· son Orogen, Canada; in Lewry, J.F. and Stauffer. M.A. Walker, D. and Watters, B.R. (1982): Geochemistry of metavol· (eds.), The Early Proterozoic Trans-Hudson Orogen of canic rocks, Amisk Lake west area; in Summary of lnvesti· North America, Geol. Assoc. Can, Spec. Pap. 37, p257· gations 1982, Saskatchewan Geological Survey, Sask. En· 281 . ergy Mines, Misc. Rep. 82-4, p24·30.

Stauffer, M.A. and Mukherjee, A.C. (1971): Superimposed de­ Watters, B.R. (1990): Lithogeochemical studies in the Flin formations in the Missi metasedimentary rocks near Flin Flon-Amisk lake area; in Summary of Investigations 1990, Flon, Manitoba; Can. J. Earth Sci., v12, p2012·2035. Saskatchewan Geological Survey, Sask. Energy Mines, Misc. Rep. 90-4, p44-47. Syme, E.C., Thomas, D.J., Bailes, A.H., Reilly, 8.A., and Slim­ mon, W.L. (1993): Geology of the Flin Flon area; Geol. ____ (1991): Lithogeochemical studies, East Amisk Surv. Can., Open File 2658, 1 :50 000 map. Lake area; in Summary of Investigations 1991 , Saskatche­ wan Geological Survey, Sask. Energy Mines, Misc. Rep. Thomas, D.J. (1989): Geology of the Douglas Lake-Phantom 91-4, p21·27. lake area (part of NTS 63K·12 and -13); in Summary of In­ vestigations 1989, Saskatchewan Geological Survey, Watters, B.R. and Ashton, K.E. (1991): Geochemistry and tec­ Sask. Energy Mines, Misc. Rep. 89-4, p44-54. tonic setting of metabasaltic rocks from the Snake Rapids area, Flin Flon Domain; in Summary of Investigations ____ (1990): New perspectives of the Amisk Group 1991 , Saskatchewan Geological Survey, Sask. Energy and regional metallogeny, Douglas Lake-Phantom lake Mines, Misc. Rep. 91-4, p130·134. area; in Summary of Investigations 1990, Saskatchewan Geological Survey, Sask. Energy Mines, Misc. Rep. 90-4, Wilcox, K.H. (1990): Geology of the Amisk-Welsh lakes area, p13·20. Saskatchewan; unpubl. M.Sc. thesis, Univ. Calgary, 245p.

Wright J.F. and Stockwell C.H. (1934): West half of Amisk Lake area, Saskatchewan; Geo!. Surv. Can., Summ. Rep., 1933, ptC., p12·22.

20 Summary of Investigations 1993