Bedrock Geological Mapping, Hatle Lake Area (Part of NTS 64M-13 and -14) B.A. Reilly Reilly, BA (1989): Bedrock geological mapping, Ennadai Domain (part of NTS 64M-13 and -14); in Summary of Investigations 1989, Saskatchewan Geological Survey; Saskatchewan Energy and Mines, Miscellaneous Report 89-4. The map area is located in the northeastern part of Sas­ release of aeromagnetic maps for the map area katchewan (NTS 64M-13 and -14), adjacent to the (Geological Survey of Canada 1961a, 1961 b). Agarwal Northwest Territories border, and is centred 160 km (1962) completed a regional correlation of geological northeast of Stony Rapids. Approximately 335 km2 were and geophysical data, which included the map area. mapped at a scale of 1:50,000. Pace and compass The Ennadai Domain was mapped by Tremblay (1960), traverses were conducted at approximately 0.5 km spac­ part of the Phelps lake area (NTS 64M), at a 1:253,440 ing in the central portion of the map area where scale. bedrock exposure is estimated at 20 percent. Else­ where, less than 2 percent exposure is found and traverse spacing approximated 1.5 km. A base camp 1. Ennadai Group was established at Hatle Lake from August 8 to August 27, during which time mapping was completed. a) Mafic to Intermediate Metavolcanic Rocks The map area is predominantly underlain by supracrus­ Mafic to intermediate metavolcanic rocks (unit Evb) are tal rocks that extend from northeastern Saskatchewan, the dominant rock type in the Ennadai Domain through the Snowbird Lake area (Taylor 1963). to (Figure 1). Both flow rocks and pyroclastic rocks are Rankin Inlet in the Northwest Territories. These rocks present, the former being more abundant. Flow rocks form the Ennadai - Rankin (or Rankin - Ennadai) vary from massive to pillowed and include local pillow greenstone belt (Wright 1967). Macdonald (1984) breccia, as well as vesicular, amygdaloidal and coined the term Ennadai Domain for the Saskatchewan plagioclase porphyritic units. Pyroclastic rocks are portion of the greenstone belt. The Ennadai Domain is dominated by tuffs and crystal tufts which are generally chiefly composed of metavolcanic and metasedimentary devoid of bedding. Pyroclastic breccia contains frag­ rocks of the Ennadai Group (Macdonald 1984) and ments which are more felsic in composition than the lesser carbonates and catc-silicates which are correlated matrix material. An extensive heteroJithic and pyroclastic with the Hurwitz Group. A U-Pb zircon age date of 2682 breccia unit crops out between lethridge and Frampton ± 5.9 Ma obtained from the Ennadai Group (Chiarenzel­ Lakes. A monolithic pyroclastic breccia is interlayered li and Macdonald 1986) is consistent with Archean ages with tuffaceous rocks between Tindall Lake and Macken­ (2697.5 ± 1.4 Ma and 2692.0 ± 1.0 Ma) recorded by zie Creek. Epidote pods, comprising less than 5 percent Mortensen and Thorpe (1987) in the Northwest Ter­ of the rock, occur locally in the mafic to intermediate ritories portion of the belt. The Hurwitz Group is of metavolcanic rocks. Proterozoic age (Bell 1970a, 1970b). The Ennadai Domain is enveloped by a granitoid-gneiss complex of A strongly layered mafic to intermediate (subunit Evbl) the Mudjatik Domain. The boundary between the En­ rock is located near the southern segment of Mclintock nadai Domain and the Mudjatik Domain is ill-defined Lake. Centimetre-scale layering is defined by alternating both to the east and west, and supracrustal rocks may mafic-rich (dark green) and mafic-poor (light to medium extend further in both directions. green) bands. This layering is interpreted as a well­ developed tectono-metamorphic layering which Aspler et al. (1989) point out that the term Ennadai obliterates primary textures. Group was used by Eade and Chandler (1975) and Wan­ less and Eade (1975) for a unit of Proterozoic con­ A hornblende-plagioclase gneiss (subunit Evbg) is glomerate and arkose that unconformably overlies the present proximal to the contact between the greenstone Hurwitz Group. They proposed a new name, the Kiyuk belt and the enveloping granitoid-gneiss complex of the Group, for this sedimentary unit. The term Ennadai Mudjatik Domain. Alternating hornblende-rich and Group is informally used in this report for Archean plagioclase-rich layers are typically millimetre scale and metavolcanic and metasedimentary rocks of the En­ discontinuous in strike length. The hornblende­ nadai Domain. plagioclase gneiss is predominantly derived from mafic to intermediate metavolcanics. Local amphibolites are Previous work in the area is limited (see Reilly other ar­ associated with the hornblende-plagioclase gneiss. ticle this volume). Tyrrell (1898) explored to the west of the Ennadai Domain, along the Wholdaia River system, and to the northeast in the Kasba lake area. A Federal­ Provincial sponsored aeromagnetic survey included the Saskatchewan Geological Survey 11 b) Felsic to Intermediate Metavolcanics Rocks strained equivalents. The psammitic schist exhibits no primary structures. Although the contact with the Felsic to intermediate metavolcanic rocks (unit Eva) are metavolcanic rocks was not observed, the unit posses­ much less voluminous than the mafic to intermediate ses a conformable penetrative foliation and metamor­ rocks, and appear to occur interlayered with mafic to in· phic mineral assemblage of similar grade as the metavol· termediate metavolcanic rocks only in the southern and canic rocks, which suggests that it conformably overlies eastern portions of the Ennadai Group (Figure 1). Typi­ the metavolcanic rocks. cally these units are only a few metres thick, except for an area east of Lichfield Lake where a minimum thick­ d) Chemical Metasedimentary Rocks ness of 400 m is attained. The unit is generally pyroclas· tic, comprising tuffs or crystal tuffs. A local millimetre­ Chemical metasedimentary rocks (unit Eif) are inter­ scale gneissosity is present in places where the unit is in· layered with the elastic metasediments and are best ex­ terlayered with hornblende-plagioclase gneiss. posed southeast of Kanten Lake at the Nirdac Creek Quartzofeldspathic-rich layers, which comprise greater gold occurrence (Figure 1). Iron formation consists of than 60 percent of the rock, alternate with hornblende­ predominantly silicate facies and lesser sulphide facies. rich layers to define the gneissosity. Individual horizons of iron formation are less than one metre thick. Silicate facies iron formation comprises c) Clastic Metasedimentary Rocks coarse garnet porphyroblasts within massive to thinly bedded amphibole-rich layers. Chert beds, locally sul­ Clastic metasedimentary rocks (unit Es) are restricted to phide bearing, and garnetiferous psammitic schist occur the western portion of the map area (Figure 1). Psam· in places. Subordinate sulphide facies iron formation, as- mitic schist (quartz.feldspar-biotite schist) is the dominant rock type. Sericite is present in more highly N ·· · 1 F E L SI C -INTER M ETAVOL CA NI CS 0 2 3 r, r MA F I C - I N TE R. M ~T A VOLC A NI CS Figura 1 - Geological sketch map of the Hatle Lake area. 12 Summa,y of Investigations 1989 sociated with the silicate facies, is defined by the 4. Late Felsic Intrusions presence of pyrite and pyrrhotite. The Ennadai Domain is intruded by a series of small fal­ e) Early Mafic Intrusions sie bodies (unit GI) which vary in composition and tex­ ture, but are consistently unfoliated. West of Mclintock Medium- to coarse- grained gabbroic bodies (unit Eb) in­ lake, a long 300 m thick sill-like body intrudes the trude the mafic to intermediate metavolcanic rocks. The metavolcanic rocks. Subhedral feldspar phenocrysts, texture of these rocks is massive, homogeneous and 1 to 2 cm in size, comprise approximately 50 percent of equigranular. Contacts are generally concordant with the rock and define a megacrystic texture. Other late fel­ the stratigraphy and may be sheared, however, where sic intrusions, comprising homogeneous equigranular contacts were not observed it is uncertain whether these medium-grained granitoids crop out west of Hamson bodies represent gabbroic intrusions or coarse-grained Lake and on the northwest shore of Hamill Lake mafic to intermediate flow centres. (Figure 1). The composition of these granitoids ranges from syenite to granodiorite. These relatively massive un­ The mafic intrusions possess a metamorphic mineral as­ deformed and unmetamorphosed felsic intrusions post­ semblage and local foliation similar to those in the mafic date regional deformation and metamorphism. to intermediate metavolcanic rocks and have been sub­ jected to the same regional metamorphic and deforma­ tional event. Field relations suggests that the mafic in­ 5. Diabase Dykes trusions may have served as a feeder system to the Steeply dipping diabase dykes (unit Dd) which occur in metavolcanic sequence. Intrusion breccia is present in isolated outcrops are similar in composition and texture some of the gabbroic bodies. to those identified in the Misaw Lake area (Reilly, other article this volume) and are believed to cross-cut all rock f) Early Felsic Intrusions units in the map area. Feldspar porphyries (unit Egp) crop out in only a few localities within the metavolcanic sequence. They are 6. Contact Relationships generally less than one metre thick, exhibit concordant contacts which are typically sheared, and possess a a) Mudjatik Domain - Ennadai Group similar metamorphic grade and foliation to the felsic metavolcanic rocks. Like the early mafic intrusions, the Emplacement of the granitoid-gneiss complex of the feldspar porphyries are interpreted as synvolcanic in­ Mudjatik Domain has superimposed a contact strain trusions. and metamorphic aureole on the supracrustal rocks of the Ennadai Group averaging approximately 1 km and up to 3 km wide. This is manifest in the production of 2. Mudjatik Domain hornblende-plagioclase gneisses, predominantly derived Enveloping the Ennadai Domain is a granitoid-gneiss from mafic to intermediate metavolcanic rocks, and complex (unit Mg) which forms part of the Mudjatik quartz-feldspar-hornblende gneisses, originating from fel­ Domain. In the map area, this complex is represented sic to intermediate metavolcanic rocks.