Towards a Revised Geological Map of Buried Precambrian ......Flin Flon Domain, sub-Phanerozoic, Paleoproterozoic, volcanogenic massive sulphide (VMS). 1. Introduction Historically,

Towards a Revised Geological Map of Buried Precambrian Basement of the Flin Flon and Glennie Domains

R.M. Morelli and K. MacLachlan

Morelli, R.M. and MacLachlan, K. (2008): Towards a revised geological map of buried Precambrian basement of the Flin Flon and Glennie domains; in Summary of Investigations 2008, Volume 2, Saskatchewan Geological Survey, Sask. Ministry of Energy and Resources, Misc. Rep. 2008-4.2, CD-ROM, Paper A-5, 22p.

Abstract The southern extension of the Flin Flon Domain, buried beneath unconformable Phanerozoic sedimentary successions, has long been considered prospective for mineral deposits. In 2008, a joint provincial-federal government project was initiated with the goal of producing a revised, more detailed compilation map of the Precambrian basement southwest of Flin Flon to aid mineral exploration in this region. The boundaries of the map area correspond to the area covered by high-resolution airborne geophysical surveys. In addition to potential field data, several other types of information will aid map construction, including characterization of Precambrian rocks exposed near the shield margin, drill core inspection, geochemical and geochronological studies, and review of public domain assessment files.

Field work this year was focused on reconnaissance geological mapping of exposed Precambrian rocks near the shield margin in the Hanson Lake area. A transect between the Southeast Arm of Deschambault Lake and eastern Hanson Lake was conducted, focusing on characterization of significant lithologic units that can be traced beneath the Phanerozoic cover using geophysical images. Rocks underlying the western leg of the transect, between the Southeast Arm and Tulabi Brook, comprise predominantly interlayered mafic, intermediate, and subordinate felsic volcanic sequences of the Northern Lights Assemblage, compositionally layered clastic sedimentary rocks, and felsic intrusive suites of varying ages. The eastern leg of the transect, between Tulabi Brook and eastern Hanson Lake, consists of a felsic-dominated volcanic sequence (Hanson Lake Assemblage), subvolcanic felsic porphyritic intrusions, distinct sedimentary packages (including quartzites, calc-silicate and cherty horizons, iron formations, and clastic deposits), and a range of intrusive rocks ranging from ultramafic to granitic in composition. Much of the intrusive component is included within the multi-phase Hanson Lake Pluton.

The geophysical properties (magnetic susceptibility, density, electromagnetism) of the basement rocks, together with observations from the exposed rocks and limited drill core inspection, were used collectively to produce a generalized sub-Phanerozoic geological map of a portion of the southwestern Flin Flon Domain. Revisions to this preliminary map will be made as assessment file information is reviewed and as new data are acquired.

Keywords: Flin Flon Domain, sub-Phanerozoic, Paleoproterozoic, volcanogenic massive sulphide (VMS).

1. Introduction Historically, the Flin Flon Belt of the Trans-Hudson Orogen of Saskatchewan and Manitoba has been one of the most important Paleoproterozoic volcanogenic massive sulphide (VMS) mining camps in the world. Initial base metal discoveries in the region date back to the turn of the 20th century, and intensive exploration and discovery in the area continue to the present day. Despite the enormous potential for new discoveries in the belt, exploration has been hindered within its southern extension due to its burial beneath unconformable Phanerozoic sequences of the Western Canada Sedimentary Basin and/or Quaternary glacial deposits (Figure 1). This is also true for the buried southern extension of the adjacent Glennie Domain to the west, which is also considered to have good base metal and gold potential based on historical findings in the exposed shield. Although successful mineral exploration can be carried out in these areas using sophisticated geophysical techniques, an improved understanding of the detailed regional distribution of the buried rocks, including favourable host lithologies, would help to guide exploration programs.

The purpose of this project, which commenced this year in cooperation with the Geological Survey of Canada (GSC) as part of the Targeted Geoscience Initiative 3 program, is to produce a revised geological map of the unexposed Precambrian basement southwest of Flin Flon. This follows initial mapping of the area performed in the mid-1990s as part of the GSC NATMAP project (see Leclair et al., 1997; NATMAP Shield Margin Project Working Group, 1998), with the intent of providing greater lithologic and structural detail to facilitate identification of prospective units for economic mineralization.

Saskatchewan Geological Survey 1 Summary of Investigations 2008, Volume 2

The need for a revised subsurface map of this region is highlighted by the delineation, both historically and in recent times, of significant base metal deposits in the buried shield by exploration companies. Examples include the McIlvenna Bay Deposit (inferred and indicated resources: >12.5 million tonnes (Mt) with approximate grades of 0.85% Cu, 6% Zn) and the Bigstone Deposit (>1.4 Mt at 2.9 % Cu and 0.3 Mt at 11.2% Zn); unofficial reserve/resource values from Saskatchewan Exploration and Development Highlights 2008 (Saskatchewan Ministry of Energy and Resources, 2008), as well as several anomalously mineralized zones (e.g., Balsam, Miskat, Grid B, Twigge Lake, Jazz, Grassberry, Suggi, Windy zones/showings; see Figure 2). Such discoveries, in validating the prospectivity of the region, reveal the need for better characterization of the geological setting.

a) Data Sources and Acquisition

Data used to generate the new subsurface map were collected from a variety of sources, including past provincial and federal government maps and reports, industry, and public domain assessment files (i.e., those submitted more than three

years ago). Potential field geophysical data, including results of regional airborne magnetic surveys, and ground-based gravity surveys, are critical for defining the subsurface geology. The importance of these data for extrapolation of Precambrian rock units beneath the Phanerozoic cover is illustrated by the correlation of the proposed map area with the boundaries of existing high resolution potential field airborne surveys (Figure 2). Magnetic data (Natural Resources Canada, 2008, Canadian Aeromagnetic Data Base) were acquired by the GSC between 1978 and 2006 using 300 to 400 m-line spacing and flight altitude of 150 m mean terrain clearance. Gravity data (Natural Resources Canada, 2008, Canadian Geodetic Information System) are lower resolution, collected using an average line spacing of ~5 km. In addition to potential field data, anomalies from industry-derived electromagnetic geophysical surveys have been digitized from assessment files and added to the map. On the scale of this map, these anomalous features typically reflect graphitic sedimentary units, clay-rich fault gouge, or potential VMS horizons, and thus can be especially useful for defining lithologic traces and/or faults.

Figure 1 - Geological domain map of northern Saskatchewan, showing location of the Reindeer Zone in the Trans-Hudson Orogen.

Inspection of drill core is another fundamental component of the project, important for verifying preliminary interpretations of geophysical data. Significant limitations, however, are the distribution of the collar locations, which tend to be clustered rather than evenly spaced, and an inability to locate the core from many of the older holes. Where the core cannot be located, the original drill logs, obtained from the assessment files, are relied upon. Interpretative maps and cross sections from industry assessment files are also considered in the overall interpretation, as is information obtained from discussion with industry geologists.

These and other relevant compiled data will be augmented by information provided by new mapping/drill core inspection, thin section inspection, and geochemical and geochronological investigations performed during the course of this project.


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Figure 2 - A) Close-up of the southern margins of the exposed Flin Flon and Glennie domains (see Figure 1), where they are unconformably overlain by Phanerozoic sedimentary rocks. Purple dashed line shows extent of coverage by high-resolution geophysical surveys and also represents the proposed map boundary for this project; KN = Kisseynew Domain and PW = Pelican Window. B) Location of reconnaissance mapping transect performed during the summer, and of several known base metal deposits/showings (yellow dots)in the exposed and buried Precambrian rocks (B = Balsam; BS = Bigstone; G = Grassberry Zone; GB = Grid B; J = Jazz Zone; M = Miskat Zone; MB = McIlvenna Bay; S = Suggi; T = Twigge; W = Windy Zone, WN = Western Nuclear mine site; ZZ = Zinc Zone). Lake abbreviations: BL = Bigstone Lake, HL = Hanson Lake, LL = Limestone Lake, ML = McDermott Lake; SL = Suggi Lake, SWR = Sturgeon-weir River, TB = Tulabi Brook, and TL = Twigge Lake. Black dot indicates the location of drill hole FON436.

b) 2008 Project Objectives There were three principal objectives for the 2008 field season:

1) conduct a reconnaissance mapping transect through exposed Precambrian rocks of the Hanson Lake area near the shield margin (i.e., between the Southeast Arm of Deschambault Lake and the Sturgeon-weir River);

2) take inventory of accessible drill core for the majority of the map area; and 3) sample for geochemical and geochronological studies from both exposed rock outcrops and drill core.

2. Geological Setting of the Flin Flon Belt The study area is situated within the internal portion of the Paleoproterozoic Trans-Hudson Orogen (THO). This zone, termed the Reindeer Zone (Stauffer, 1984), comprises a collage of predominantly juvenile volcano-plutonic island arc assemblages and derived sedimentary rocks that reflect closure of an extensive ocean basin. The Flin Flon Domain constitutes the southeast portion of the exposed Reindeer Zone (Figure 1) in Saskatchewan. It includes several individual juvenile arc assemblages, that are separated by younger plutons, sedimentary rocks, and/or faults/suture zones that obscure inter-assemblage relationships (NATMAP Shield Margin Project Working Group, 1998). The Bigstone-Hanson lakes area, the focus of field work for this project in 2008 (Figure 2), is underlain by the greenschist to amphibolite facies Northern Lights and Hanson Lake juvenile arc assemblages (Maxeiner et al., 1999), which were divided into three broad lithotectonic subdivisions by Lucas et al. (1996): i) ca. 1920 to 1870 Ma


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island arc/backarc, ocean plateau, and ocean floor magmatic assemblages; ii) ca. 1870 to 1830 Ma island arc assemblages that were generated within amalgamations of earlier oceanic assemblages (i.e., ‘successor’ arc magmatism); and iii) unconformable, ca. 1850 to 1840 Ma turbiditic (Burntwood Group) and alluvial-fluvial (Missi Group) sedimentary rocks deposited during uplift and erosion of older intra-oceanic assemblages.

During orogenesis, the juvenile rocks were emplaced as allochthonous thrust sheets above the Sask Craton, an Archean (3200 to 2400 Ma) micro-continent first suggested by Lewry (1981) and later named by Ansdell and Norman (1995). The base of the Paleoproterozoic thrust sheets is recognized as a major mylonitic detachment zone, exposed only around small inliers of the Archean basement in the Reindeer Zone (Figure 1). The largest of these is the ‘Pelican Thrust Zone’ (Ashton et al., 2005), which underlies the northeastern Flin Flon Domain. Regional mapping and geophysical investigations have characterized the lowermost Sask Craton, overlying arc assemblages, and the uppermost Burntwood and Missi Group sedimentary successions as a three component, northeasterly dipping crustal stack resulting from southwesterly transport of the allochtons over the Sask Craton (Lewry et al., 1990; Lucas et al., 1997).

Tectonic interaction between the Sask Craton and Paleoproterozoic sequences resulted in the generation of peak metamorphic mineral assemblages in the northwestern Flin Flon Domain after ca. 1845 Ma (Ashton et al., 2005). Prograde regional metamorphism was ongoing during collisions involving the Sask Craton, the Rae-Hearne Craton to the west (present day coordinates), and the Superior Craton to the east, until about 1800 Ma. Subsequent post-collisional shortening caused reorganization of earlier deformational features and regional retrograde metamorphism.

The unconformity between Precambrian rocks of the Reindeer Zone and Lower Paleozoic rocks of the Western Canada Sedimentary Basin marks the transition between cessation of convergent tectonism and the start of a prolonged period of erosion of the continental interior. In the Flin Flon–Hanson Lake area, the angular unconformity is directly overlain by the Cambrian Winnipeg Formation sandstone and the Ordovician Red River Formation dolostone. These rocks have a shallow southerly dip and attain a maximum thickness of ~125 to 150 m at the south end of the map area. These are, in turn, overlain by 0 to 50 m of unconsolidated Quaternary glacial deposits (Fenton et al., 1994).

3. Geological Transect: Description of Principal Units A portion of the 2008 summer field season was spent conducting reconnaissance mapping in a transect along Highway 106 between the Southeast Arm of Deschambault Lake (herein ‘Southeast Arm’) and eastern Hanson Lake. This provided familiarity with important lithologic units to facilitate along-strike extension beneath Phanerozoic cover, and was guided by use of existing 1: 20 000-scale geological maps and accompanying reports. The salient findings of the transect, which has been separated into two legs for ease of discussion (Figure 2B), is provided below. Unit descriptions are reported without consideration of their current domain affiliation, as several units were observed in multiple domains. The unit descriptions are not comprehensive, being based on limited observations of only those lithologic units considered important for extrapolation into the subsurface. Relevant supplementary information (e.g., geochronological, geophysical) has been added to some of the descriptions to enhance unit characterization. The unit codes provided with each description are adopted from the maps of Maxeiner et al. (1994) for transect leg 1 and from Slimmon (1992b) and Maxeiner et al. (1994) for transect leg 2; the reader is referred to these map publications for lithologic boundary positions since no such boundaries were changed during the course of the present investigations. Implications for unit extrapolation beneath the Phanerozoic cover and preliminary interpretations are also discussed.

a) Leg 1: Southeast Arm, Deschambault Lake to Tulabi Brook This area (Figure 3), which encompasses the transition between eastern Glennie Domain and the western Flin Flon Domain across the Tabbernor Fault zone, was most recently mapped by Lewry (1990) and Lewry et al. (1991). The eastern boundary of the area is arbitrarily defined as the Tulabi Brook, which follows the surface trace of the Tulabi Brook Fault, a splay of the Tabbernor Fault zone.


Figure 3 - Generalized geological map of transect leg 1, after Maxeiner et al. (1994); BL = Bigstone Lake, LL = Limestone Lake, SE Arm = Southeast Arm of Deschambault Lake, SL = Sarginson Lake, TB = Tulabi Brook, UL = Unser Lake; SLF = Sarginson Lake Fault, and TBF = Tulabi Brook Fault.


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Mafic Volcanic Rocks (unit Bs, Bn) 1

Volcanic and volcaniclastic rocks encountered along this transect leg comprise the Northern Lights Assemblage (Macdonald and Posehn, 1976; Maxeiner et al., 1999). Exposed on the western shore of the Southeast Arm and on the eastern shore of Sarginson Lake, mafic volcanic rocks of this assemblage are typically dark green and composed of 40 to 60% hornblende and 40 to 60% plagioclase. They are fine grained, but locally porphyroblastic, with 3 to 8 mm hornblende porphyroblasts constituting up to 50% of the rock. They are weakly to moderately foliated, though one rare strongly foliated exposure on the western shore of the Southeast Arm contains several 10 to 20 cm-long, strongly weathered calc-silicate pods. Abundant quartz amygdules (up to 10% of rock; Figure 4A) were observed in an exposure at the northern end of Limestone Lake, and pillows and flow-top breccias were reported northeast of Sarginson Lake (Padgham, 1968). The mafic volcanic rocks have a moderate magnetic signature, with magnetic susceptibility (MS) measurements typically averaging between 0.8 to 1.2 (SI x10-3 units) 2.

Intermediate to Felsic Volcaniclastic Rocks (unit I)

This unit is exposed to the east of Sarginson Lake, where it both under- and overlies the mafic volcanic rocks. This is likely an original stratigraphic relationship, as opposed to repetition by folding. These rocks are consistently fine grained and are generally compositionally layered on centimetre- to metre-scale (Figure 4B). Where observed along Highway 106, these layers parallel the foliation. Intermediate interbeds consist primarily of 25 to 35% hornblende (±biotite) and 65 to75 % plagioclase, whereas felsic varieties contain 5 to 10% combined hornblende and biotite, up to 25% quartz (including rare round quartz phenocrysts) and 65% feldspar. Up to 5% pink garnet is also present in both felsic and intermediate varieties. This compositional layering is likely reflective of fine-grained tuffaceous deposits, consistent with the presence at one outcrop of an angular, lapilli-sized (10 cm), epidote-bearing block in an intermediate matrix (Figure 4C). However, the presence of amygdules elsewhere on the same outcrop could reflect the presence of at least some lava flows. Rocks of this unit typically have a weak magnetic signature, with average MS readings of <0.5.

Clastic Sedimentary Rocks (unit Q)

These sedimentary rocks were observed only along a south-southeasterly trending belt along the Southeast Arm; exposures to the east in a northeasterly trending belt between Unser and Sarginson lakes (Maxeiner et al., 1994) were not visited this summer. They are generally light brown to grey and very fine to medium grained, and range between wacke and, less abundantly, argillite, the latter often comprising subordinate compositional layers in the former. The mineralogical composition varies widely, with biotite forming between 5 and 20% of the assemblage, commonly along foliation planes, and quartz between 10 and 60%. The majority of the observed outcrops exhibit a moderate to strong foliation that typically parallels the compositional layering. Granitic/pegmatitic veinlets and quartz veins are common. These rocks are magnetically weak, with average MS readings between 0.2 to 0.3. Exposures of these rocks in the transect area are situated along the southward continuation of Kisseynew Domain rocks (Maxeiner et al., 1994), and are thus considered to be ca. 1.85 to 1.84 Ga Burntwood Group equivalents.

Intrusive Rocks

Biotite Granite (unit G): Exposed along the southwestern shore of the Southeast Arm and north of Unser Lake, this medium- to coarse-grained rock is equigranular, weakly to moderately foliated and contains 20 to 25% quartz and 15% biotite. It locally grades into granodiorite and is magnetically weak with MS readings averaging 0.35.

Granodiorite-Tonalite (units Gd, Gdp): This plutonic suite underlies a large portion of the area between Unser Lake and Tulabi Brook. Where observed along Highway 106, it consists of medium- to coarse-grained, moderately- to well-foliated granodiorite (locally tonalite), containing 30% quartz, 10 to 15% biotite, and trace to 1% magnetite (Figure 4D). Lewry (1990) reports a weakly megacrystic phase of this unit to the northeast of Sarginson Lake. The magnetic susceptibility is variable, ranging from weak (<0.2) to strong (15).

Felsic Tectonite/Gneiss (unit Fg): Only one exposure of this unit was observed in a road cut located immediately west of Tulabi Brook. The protolith of this unit is difficult to determine due to the effects of late brittle faulting

1 All Precambrian rocks discussed in this paper have been metamorphosed; the prefix ‘meta’ has therefore been omitted from rock descriptions throughout.

2 Henceforth, units of magnetic susceptibility readings are omitted to avoid repetition.


Figure 4 - A) Quartz amygdaloidal basalt of Northern Lights Assemblage, northern Limestone Lake at UTM 3 619679 m E, 6061523 m N; B) interlayered intermediate and felsic tuff, Highway 106 at UTM 622639 m E, 6064147 m N; C) epidote-bearing fragment in intermediate volcanic, Highway 106 at 620729 m E, 6063252 m N; D) moderately foliated, coarse-grained granodiorite, Highway 106 at 622073 m E, 6063894 m N; E) fine-grained, garnet porphyroblastic, biotite-quartzofeldspathic rock of uncertain origin, Highway 106 at 624699 m E, 6063779 m N; and F) close-up of massive, equigranular leucogranite, Southeast Arm at 614321 m E, 6065548 m N.

3 All UTM coordinates in this paper are in NAD 83, Zone 13.


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along the Tulabi Brook Fault, with extensive epidote and quartz veining, and rusty alteration indicating extensive fluid permeation. Additionally, where preserved, the original (pre-faulting) features of the rock are locally variable, possibly indicating the presence of multiple rock types. The majority of the highway exposure is interpreted as an equigranular, foliated granodiorite, containing >50% medium-grained feldspar (original mineral proportions are unrecognizable). In some sparse, narrow (1 to 2 m) zones, the rock takes on a gneissic character with alternating medium-grained, mesocratic, hornblende-bearing bands and medium-grained leucotonalitic bands. Elsewhere, the unit has a fine grained, quartzofeldspathic character and contains 10% biotite and pinkish-red garnet porphyroblasts measuring up to 10 mm in diameter (Figure 4E). The magnetic susceptibility is quite variable (<0.1 to >10), though the majority of readings were less than 1.0. Rocks of this unit are strongly sheared at this particular location, possibly indicating that later brittle faulting along the Tulabi Brook Fault partly overprinted an earlier ductile shear zone.

Late Granite/ Granite Pegmatite (unit Gj): This suite intrudes all other rock types in the area, with the largest mass underlying an area immediately surrounding the Southeast Arm. Typical rocks include massive, predominantly medium-grained, K-feldspar-rich leucogranites to leucogranodiorites (<5% biotite; Figure 4F)), with broadly coeval aplitic to pegmatitic phases being common. Overall, this suite is non-magnetic, with typical MS values of <0.1.

b) Leg 2: Tulabi Brook to Eastern Shore of Hanson Lake The second leg of the transect (Figure 5) covered an area most recently mapped by Slimmon (1992b) and Maxeiner et al. (1994).

Supracrustal Rocks

Mafic to Intermediate Volcanic Rocks (units B, A): In contrast to volcanic rocks of the Northern Lights Assemblage, mafic volcanic rocks in the Hanson Lake area (Hanson Lake Assemblage; Maxeiner et al., 1999) are a minor constituent, with dacites and rhyolites comprising the bulk of the exposed extrusive pile. Mafic/intermediate volcanic rocks were encountered at only two locations along the transect, both along a drill road immediately west of Hanson Lake. These rocks are medium to dark greyish green, fine grained, and composed of 25 to 45% hornblende (including 0.5 cm hornblende porphyroblasts), 55 to 75% plagioclase, and trace garnet. No primary volcanic textures were observed, suggesting they might have been emplaced as hypabyssal intrusions; however, Maxeiner et al. (1994) report amygdaloidal, fragmental, and other volcanic/volcaniclastic textures in these rocks elsewhere in the Hanson Lake area. Rocks of this unit have moderate magnetic susceptibilities, averaging 0.8 to 1.0.

Dacite (unit D): Dacites underlie much of the area on the western side of Hanson Lake. They are typically light brown to light grey, very fine to fine grained quartzofeldspathic rocks with 5 to 10% biotite (±hornblende), ±garnet, ±magnetite. They are commonly massive, but also can have a weakly layered character. Subangular felsic lapilli, ranging from 1 to 10 cm, are common and indicate a pyroclastic component (Figure 6A). The dacites are typically weakly magnetic, with average MS readings of 0.2 to 0.3, though a few rare examples are moderately to strongly magnetic (MS = 5 to 20). A minimum crystallization age of 1848 Ma was obtained from a dacitic rock in the Mine Bay area (Figure 5; Heaman et al., 1994).

Rhyodacite/Rhyolite (units Rd, R): Rhyolitic/rhyodacitic rocks form a north-south–trending, easterly dipping belt situated on the western shore of central Hanson Lake. These rocks are generally light grey to pink, aphanitic to very fine-grained, and essentially composed of quartz, K-feldspar, and plagioclase, with <5% muscovite and/or biotite (Figure 6B). Quartz and/or feldspar phenocrysts, 1 to 2 mm across, were noted at some locations. Overall, these rocks are quite massive, though some fine-scale layering (flow banding?) was noted in places, and quartz veining is prevalent at some outcrops. The rhyolites/rhyodacites consistently have a very weak average magnetic susceptibility (0.1 to 0.2). Crystallization of the rhyolite exposed in the western Mine Bay area has been dated at ca. 1875 ±1 Ma (Heaman et al., 1993).

Exhalites and Associated Sedimentary Rocks (units If, Sm): The only exposures of these rocks are in western Hanson Lake, within a very thin belt along the central part of Agnew Bay and on the northern part of One-Mile (Bluebird) Island (Figure 5). This package collectively comprises a mixture of distinct clastic and chemical sedimentary rocks, including sericite-garnet schists, chert, quartzite, calc-silicate horizons (Figure 6C), and silicate-/oxide-/sulphide-facies iron formation. These rocks are commonly associated with anomalous base metal concentrations. Though not directly observed during this study, Maxeiner et al. (1994) also reported the presence of anthophyllite-cordierite-garnet gneisses within this package. They also noted the presence of a very thin unit of interbedded greywacke and silicate facies iron formation extending northwards from Fly Lakes (Figure 5). Rocks of this sequence typically yield low MS readings (<0.3) with the exception of the oxide-facies iron formation, which is very highly magnetic (MS >100).

Clastic Sedimentary Rocks (unit Q/Hgw): A sequence of clastic sedimentary rocks defines a north-south–trending belt underlying much of the west-central portion of Hanson Lake. This variable sedimentary unit is dominated by


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Figure 6 - Supracrustal rocks, Hanson Lake: A) felsic fragments in dacitic volcaniclastic rock at 638577 m E, 6064275 m N; B) massive, aphanitic to very fine-grained rhyolite at 638893 m E, 6066905 m N; C) heterogeneous rock comprising quartzitic interlayers within fine-grained calc-silicate rock at 638480 m E, 6065613 m N; and D) fine-grained, garnetiferous psammite at 641251 m E, 6064714 m N.

light brown, fine-grained psammite that comprises 15 to 20% quartz, 5 to 10% biotite, and ±2 to 3% pink garnet (Figure 6D). It is typically compositionally layered on a centimetre-scale with a well-developed bedding-parallel main foliation. Quartz veining is prevalent in some outcrops. Lithologic variants within this unit include a light brown, massive, hornblende-bearing (20%) calcic psammopelite and a polymictic, matrix-supported conglomerate containing 5 to 25 cm clasts stretched parallel to the main foliation. These sedimentary rocks are generally weakly magnetic (MS = 0.1 to 0.3).

Intrusive Rocks

An array of intrusive rocks underlie the Hanson Lake area, ranging widely in both age and composition. These include:

Biotite-Microcline Granite (unit Gb): This intrusion forms a series of narrow, elongate bodies along the western shore of Hanson Lake. It is light pink and contains 5 to 10% biotite and trace magnetite. It is equigranular, weakly foliated (Figure 7A), and strongly magnetic, giving average MS readings of 7 to 9. This granite is the oldest of all dated intrusions in the Hanson Lake area, providing an age of 1870 +7/-5 Ma in a weakly deformed variety, whereas a highly sheared phase yielded a crystallization age of 1873 ±2 Ma (Heaman et al., 1994; 635762 m E, 6063710 m N).

Granodiorite-Tonalite (units Gd, Gdg, Gdm): This felsic intrusive suite is compositionally equivalent to unit Gd (and variants) in transect leg 1. However, on the eastern side of the Tulabi Brook Fault, some zones of this unit exhibit a strong gneissosity, including melt leucosome layers (Figure 7B), indicating an increased metamorphic grade. Another well-defined zone along Highway 106 has a strongly mylonitic character, containing abundant


A B

C D

Figure 7 - Intrusive rocks of the Hanson Lake area: A) early foliated granite/granodiorite injected by late, massive granite pegmatite at 638287 m E, 6066191 m N; B) gneissic equivalent of granodiorite unit ‘Gd’ at 626411 m E, 6064033 m N; C) mylonitized and recrystallized granodiorite, with numerous K-feldspar porphyroclasts along foliation planes (Highway 106 near intersection with Highway 135 at 637848 m E, 6074940 m N); D) quartz feldspar porphyry (qfp) intruding fragmental dacite (da) at 638320 m E, 6064063 m N; E) medium-grained, equigranular diorite phase of the Hanson Lake Pluton at 641691 m E, 6060239 m N; and F) coarse-grained, equigranular granodiorite phase of the Hanson Lake Pluton at 642511 m E, 6063237 m N.


A B

C

E F

D

qfp

da

recrystallized hornblende porphyroblasts and rotated K-feldspar porphyroclasts (Figure 7C), and represents a splay of the Pelican Thrust Zone (Lewry and Macdonald, 1988; Ashton et al., 2005). The rocks are variably magnetic, ranging from weak (<0.2) to strong (>10), with the exception of the mylonite zone, which is weakly magnetic (MS <0.25).

Quartz-Feldspar Porphyry (Gp): These subvolcanic bodies are exposed along the western side of Hanson Lake and intrude the volcanic sequence (Figure 7D). They comprise light grey to pink, very fine- to fine-grained quartzofeldspathic rocks with 10 to 15% phenocrysts of K-feldspar and quartz, 1 to 3 mm in diameter. A crystallization age of ca. 1861 Ma has been determined for the Mine Bay (639649 m E, 6063557 m N) and the Agnew Bay (639535 m E, 6067265 m N) intrusions (Heaman et al., 1997). A smaller unit of sheared quartz-feldspar porphyry (originally interpreted as a felsic volcanic rock) collected on the western shore of Mine Bay had previously provided an age of 1888 ±12 Ma (Bickford et al., 1986; 638693 m E, 6059194 m N). Another minor, geochemically distinct felsic porphyritic unit (unit Gdg), containing only quartz phenocrysts as well as 2 to 3% garnet porphyroblasts, is exposed as thin dykes in southern Bertrum Bay of Hanson Lake (Figure 5; Maxeiner et al., 1999). The relative timing of emplacement of the ca. 1860 Ma quartz-feldspar porphyry and the garnet-bearing quartz porphyry is uncertain, though Maxeiner et al. (1999), based on geochemical observations, suggested that the garnet-bearing suite might be synvolcanic (i.e., >1875 Ma). Both types of felsic porphyries are magnetically weak, characterized by measured magnetic susceptibilities of 0.1 to 0.3.

Ultramafic Intrusions (units U, Ue, Upx, Hpx): A number of small exposures of ultramafic intrusions are scattered throughout the Hanson Lake area. Where observed, these intrusions consist predominantly of black to dark green, medium- to coarse-grained pyroxene, commonly replaced by hornblende and/or chlorite, and generally contain magnetite. Field relationships suggest that these intrusions post-dated volcanism and are likely related to post-1870 Ma successor arc magmatism. They range from moderately to very strongly magnetic (MS = 1 to 30).

Hanson Lake Pluton (units Ga/Hgb, Di/Hdi, Qdi/Hqd, Hgd): This multi-phase intrusive suite (Slimmon, 1992a), which dominates rock exposures on the southern and eastern sides of Hanson Lake, includes gabbro, diorite, quartz diorite, and granodiorite. These rocks are typically medium to coarse grained, massive to weakly foliated and equigranular (Figure 7E). They have variable magnetite contents, reflected in their variable (moderate to high) magnetic susceptibilities of between 0.5 and 10; the more highly magnetic rocks are typically the more mafic plutons. The granodioritic phase, exposed discontinuously along the eastern shore of Hanson Lake, is pink, medium to coarse grained, equigranular, and contains 10% hornblende + biotite (Figure 7F). Observed exposures were homogeneous and magnetically weak, yielding MS readings of <0.3. Results of U-Pb zircon dating of both mafic (1844 ±2Ma; Heaman et al., 1993; 640856 m E, 6060416 m N) and felsic (1843 ±2 Ma; Heaman et al., 1994; 642991 m E, 6064944 m N) rocks of the Hanson Lake Pluton confirm a cogenetic origin of these phases during successor arc magmatism.

c) Metamorphism Rocks along the transect west of the Tulabi Brook Fault (Leg 1) were metamorphosed at lower to upper amphibolite facies, with metamorphic grade generally decreasing from west to east and from north to south (Lewry, 1990). This is evidenced by the presence of sillimanite and partial melt leucosomes in the higher grade rocks of the northern part of the Southeast Arm, in contrast to andalusite-bearing sedimentary rocks in the southern part of the Southeast Arm (Lewry et al., 1991) and the retention of primary volcanic textures in lower grade rocks of the Sarginson-Limestone lakes area. Metamorphic grade appears to increase again to the immediate east of the Tulabi Brook Fault (Leg 2), as indicated by the presence of a strong gneissosity in granodioritic unit Gd. Consistent with the pattern observed to the west, exposed rocks in the Hanson Lake area decrease in metamorphic grade from the north end (upper amphibolite facies) to the south end of Hanson Lake and into the subsurface, in the McIlvenna Bay deposit area (upper greenschist facies). This distribution is evidenced by metamorphic mineral assemblages in the north-south–trending sedimentary belt in central Hanson Lake (Maxeiner et al., 1995). Metamorphic grade increases southeast of Hanson Lake, reaching middle amphibolite facies in the vicinity of the Balsam deposit (Sask. Ministry of Energy and Resources (SMER) Assessment File 63L10-SE-0125).

d) Structure The detailed structural character of rocks in the Southeast Arm–Hanson Lake area is described by Lewry et al. (1990) and Ashton et al. (2005). The earliest recognized deformational event (D1) in the transect area is represented by the regional foliation/gneissosity, transposition of compositional layering, and rare east-west–trending isoclinal fold closures (e.g., west of Jackpine Lake; Maxeiner et al., 1994). Reorientation of D1 fabrics/structures occurred during D2 deformation, which was a protracted event that was synchronous with peak regional metamorphism and caused the development of tight to isoclinal, generally southwest-plunging (F2) folds in the Deschambault–Hanson Lake area, as well as southwest-verging thrust faults/mylonite zones that splay off the main detachment zone at the boundary between the Archean Sask Craton and overlying Paleoproterozoic thrust sheets (e.g., Sturgeon-weir Shear


Zone; Ashton et al., 2005). Following this D2 deformational event, D3 resulted in the formation of close to tight, north-trending folds, and D4 resulted in upright, open, northeast-trending and plunging regional-scale folds. The sinistral Tabbernor Fault, a north-south–oriented brittle fault system that transects the entire eastern portion of the province, is also attributed to this late (D4), northwest-southeast–shortening event (Lewry et al., 1990). The Tulabi Brook Fault is part of the Tabbernor system. Interference between F3 and F4 folds is responsible for map-scale fold interference patterns, including the structural dome, referred to as the Pelican Window, in which the Sask Craton is exposed (ibid.).

4. Preliminary Observation from Drill Core Inspection About three weeks of the field season were spent locating, taking inventory of, and inspecting drill core that intersected units within the map area. The majority of the core inspected were from an area between southern Hanson Lake and the northern shore of Suggi Lake, specifically from the McIlvenna Bay deposit (Foran Mining Corp., Copper Reef Mining Corp.), the Windy, Jazz, and Grassberry zones, and drill hole FON436 (HudBay Minerals Inc.; see Figure 2B). A generalized overview of observations from each zone is presented below.

a) McIlvenna Bay The McIlvenna Bay deposit consists of one main massive sulphide lens (#2) and two peripheral lenses (#3 and #4). The massive sulphide mineralization consists primarily of subhedral, fine-grained pyrite grains set within a very fine-grained matrix of sphalerite (10 to 20%), pyrite, quartz, and carbonate (Koziol and Ostapovich, 1990). Chalcopyrite is less abundant, typically comprising <1% of the total sulphide mineralization; disseminated pyrrhotite, galena, and magnetite are also locally present. The ore lenses are typically underlain by alteration zones containing sulphide stringers and/or disseminated sulphides. The lenses are tabular bodies that plunge moderately to the northwest and, along with the host rocks, are east-northeast striking and steeply dipping to the north (SMER Assessment File 63L10-NW-0145).

Inspection of core from multiple drill holes at McIlvenna Bay reveals a sequence of predominantly felsic volcanic and volcaniclastic rocks, with subordinate mafic igneous rocks and exhalative horizons. The intersection of the mineralized zone that was observed in core this summer, presumed to be lens #2, consists of 1 to 3 m-thick, semi-massive and massive sulphide (pyrite + chalcopyrite + sphalerite) and chalcopyrite stringer zones, structurally overlying a disseminated sulphide zone of several metres thickness. Rounded/spheroidal to subangular chert and pyrite grains and nodules within the massive sulphide (Figure 8A) suggest localized, syn- to slightly post-depositional reworking of the mineralized layer. The mineralized zones are hosted by well layered felsic, in part crystal, tuffs containing abundant 3 to 5 mm feldspar crystals and crystal fragments (Figure 8B). Beneath the sulphide zone is a sequence of strongly sericitized felsic volcanic rocks (MS <0.2), sometimes containing 1 to 2 mm feldspar and blue quartz phenocrysts (Figure 8C), which is similar to partially flow-banded rhyolitic rocks exposed in the Mine Bay area of Hanson Lake. Less extensive chlorite and garnet alteration assemblages were also noted to have a spatial association with sulphide mineralization. The predominance of alteration below the mineralized zone suggests that this is the footwall sequence, indicating that the stratigraphy is not overturned at this location. Above the observed mineralized zone, layered felsic tuffs and crystal tuffs are interlayered with chert horizons, oxide-facies and sulphide-facies iron formation (MS = 20 to >100), and fine-grained mafic igneous rocks (MS = 0.75 to 1.0). These mafic rocks are massive, contain ubiquitous 1 to 2 mm-wide carbonate veins and generally lack definitive volcanic textures, with the exception of sparse quartz amygdules; it is unclear whether these rocks represent massive mafic volcanic flows or hypabyssal intrusions. The upper part of the hanging-wall sequence is dominated by relatively unaltered felsic volcanic and volcaniclastic rocks (MS <0.3), as well as massive mafic volcanic/hypabyssal rocks and subordinate mafic tuffaceous layers (MS = 0.75 to 1.0 consistently for all mafic rocks). Despite ambiguity of contact relationships, at least some of the mafic rocks are interpreted to be intrusive (gabbroic) due to a slight grain coarsening and the presence of 2 to 3 mm hornblende (replacing pyroxene?) phenocrysts (Figure 8D). The host sequence at McIlvenna Bay is largely devoid of felsic intrusive rocks, with the exception of common feldspar-porphyritic granitic dykes (MS = 0.5), generally <3 m wide.

b) Drill Hole FON436 Drill core from this hole, located 5 km due east of McDermott Lake (Figure 2B), represents the only currently accessible core from this general area. The core reveals a sequence of predominantly mafic volcanic and volcaniclastic rocks, with minor mafic intrusive intervals. The rocks are weakly to moderately foliated, with vague compositional layering, generally containing 35 to 40% green hornblende, 60 to 65% plagioclase, and, in places, 3 to 5% pink garnet porphyroblasts up to 3 mm in diameter (Figure 9). They contain abundant rounded to subangular felsic lapilli, 0.5 to 2.5 cm in diameter, and are probably of pyroclastic origin, although metamorphic recrystallization has resulted in resorption of fragment and phenocryst boundaries. Some 0.5 to 5 m intervals are medium grained and hornblende porphyroblastic, and likely of intrusive origin. These rocks are moderately


Figure 8 - Drill core from the host sequence of the McIlvenna Bay deposit: A) rounded to subangular quartz/chert nodule in massive sulphide ore horizon of the McIlvenna Bay deposit (hole MB08-129); B) well layered felsic tuff and feldspar crystal fragment tuff layers immediately overlying ore horizon (hole MB08-132); C) blue quartz phenocrysts (arrows) in sericitized felsic volcanic rock structurally underlying the McIlvenna Bay deposit (hole MB99-92); and D) massive hornblende phyric microgabbro (hole MB99-92).

magnetic, yielding MS readings of 0.5 to 2.0. The mafic volcanic rocks are locally cut by thin (1 to 3 m) granite and granite pegmatite dykes, which are magnetically weak (MS <0.2).

c) Grassberry/Jazz/Windy Zones

Figure 9 - Garnet porphyroblastic, weakly foliated mafic volcanic rock from drill hole FON436 (see Figure 2B for location).

Preliminary inspection and comparison of drill core from several holes in each of these zones indicates a lithologically similar sequence of rocks. Although no diagnostic metamorphic mineral assemblages were identified, the strongly recrystallized character of these rocks indicate a relatively high (amphibolite) metamorphic grade. Most of the core is dominated by pink, medium- to coarse-grained granite/granodiorite, containing 5 to 10% biotite, and trace to 1% magnetite. The rock is well foliated to gneissic (Figure 10A), locally epidote-bearing (up to 5%), and consistently magnetic (MS 5 to >20). Though contact relationships are somewhat ambiguous, this granitic rock appears to intrude a package of mafic to felsic volcanic/volcaniclastic and/or sedimentary rocks, though these are not well represented in most holes. Where observed, mafic volcanic rocks are dark green, fine grained and massive, and composed mainly of


layered tuff

crystal tuff

BA

C D

Figure 10 - Drill core from the host sequence of the Jazz/Grassberry/Windy zones, northern Suggi Lake: A) magnetite-bearing biotite granodiorite gneiss (Jazz Zone, hole JZS009); B) massive, fine-grained mafic volcanic or mafic hypabyssal intrusion (Grassberry Zone, hole GBS002); C) compositionally layered biotite-quartzofeldspathic gneiss of volcaniclastic and/or sedimentary parentage (Jazz Zone, hole JZS002); D) close-up of compositional layering in biotite-quartzofeldspathic gneiss (Jazz Zone, hole JZS009); E) chlorite and garnet alteration assemblage in compositionally layered paragneiss proximal to sulphide mineralization (Jazz Zone, hole JZS009); and F) massive, pink, coarse-grained leucogranite intruding granodiorite gneiss (Windy Zone, hole WZS001).


F

D

A B

C

E

hornblende and plagioclase (Figure 10B). As at McIlvenna Bay, it is difficult to determine whether these mafic rocks are of volcanic or plutonic origin, due to a lack of diagnostic textures and because metamorphic recrystallization has obscured primary textural features. Felsic tuffs (and lava flows?) and/or layered sedimentary rocks consist of grey to pink, fine- to medium-grained, strongly foliated to gneissic quartzofeldspathic rocks with 10 to 15% biotite (Figure 10C). Compositional layering is also apparent (Figure 10D), though it is unclear whether it is of primary origin or metamorphically induced. In the observed core, mineralization is spatially associated with felsic supracrustal rocks that exhibit a garnet ±sericite ±chlorite alteration assemblage (Figure 10E). Mineralization generally consists of 0.5 to 3 m-thick zones of semi-massive to massive sulphide (pyrite, pyrrhotite, chalcopyrite, sphalerite) or sulphide veinlets/stringers and minor magnetite.

Subordinate units intersected in these zones include foliated, fine- to medium-grained diorite and quartz diorite, and massive, highly magnetic, coarse-grained pyroxenite (Jazz Zone only). Fine-grained mafic dykes are also common, and late, pink, coarse-grained to pegmatitic leucogranite veins and dykes are ubiquitous (Figure 10F).

5. Discussion/Preliminary Interpretations The following discussion provides preliminary interpretations of the subsurface geology south of Hanson Lake proximal to the unconformity margin. These interpretations are generalized and derived mainly from preliminary observations from reconnaissance mapping of exposed rocks and geophysical data, but are also supplemented by observations from drill core and assessment file information, where applicable. The accompanying preliminary map (Figure 11) will serve as a starting point from which revisions can be made as new information is collected.

Figure 12 shows, in shaded colour, the first vertical derivative of the magnetic intensity of rocks in the 2008 study area. One of the most obvious features in the image is the subsurface extension of the north-south–trending Tulabi Brook Fault. There is a clear change in magnetic signature of the rocks on either side of this discontinuity, confirming that this is a significant structural feature. Correlation of lithologic contacts across the fault indicates a sinistral strike-slip component of movement of at least 3 km (Maxeiner et al., 1995), though a substantial vertical component is also inferred (Padgham, 1968). The apparent sharp increase of metamorphic grade from west to east across the fault suggests an upward movement of the east block relative to the west block. Other less extensive discontinuities that run subparallel to or splay off of the Tulabi Brook Fault are also evident, some of which also have a sinistral oblique sense of movement (e.g., East and West Sarginson Lake faults; Lewry et al., 1991). Collectively, this faulting demonstrates that the Tabbernor Fault system had a profound effect on the lithologic redistribution of units south of Hanson Lake.

West of the Tulabi Brook Fault, distinct magnetic highs correlate with northwest- and southwest-trending exposures of mafic volcanic units in the Southeast Arm and Sarginson Lake areas, respectively. Beneath the Phanerozoic cover, these units appear to join, forming a close to tight synformal structure (Figure 12) that is subparallel to the axes of a series of F3 anticline-syncline pairs in the exposed shield to the northeast (Figures 3 and 5; Lewry, 1990). One of the magnetic highs can also be traced continuously north-westwards into the Glennie Domain, indicating continuity of the Northern Lights volcanic assemblage across this domain boundary (Figure 12) and suggesting that the boundary has no geological relevance, as previously pointed out by Maxeiner et al. (1999). Low to moderate magnetic signatures adjacent to the mafic volcanic rocks appear to correlate with the interlayered intermediate and felsic volcanic/volcaniclastic rocks, which can be traced several kilometres to the south, where these rocks host the Bigstone Cu-Zn deposit. This interpretation is generally consistent with geochemical data from the deposit host sequence (Adamson, 1988) and interpretative geological maps derived from drill core data (SMER Assessment File 63L10-SE-0077). Maxeiner et al. (1999) also had suggested stratigraphic continuity of the Northern Lights volcanic assemblage into the Bigstone Lake area. Prominent magnetic highs within and to the south of the Bigstone sequence likely represent mafic/ultramafic intrusions that are hosted in a separate supracrustal succession with an anomalously low-magnetic, high-density signature.

To the east of the Bigstone host sequence and west of the Sarginson Lake Fault, aeromagnetic patterns of the subsurface rocks change abruptly from the alternating high and low intensity, linear patterns of the volcanic sequence to a more evenly distributed, moderate intensity pattern. This moderate magnetic signature is interpreted to derive from the same magnetite-bearing, foliated to gneissic granodiorite (unit Gd) that is exposed along the transect between the north end of Limestone Lake and western Hanson Lake. A lithologic change is also evident in the airborne gravity survey (Figure 13) as a marked contrast between the low-density felsic intrusions and the more mafic (i.e., higher density) supracrustal succession. The intrusion, widely exposed north of the Phanerozoic unconformity, is interpreted to occupy most of the area between the presumed subsurface extensions of the Sarginson Lake and Tulabi Brook faults (Figure 11).


Figure 11 - Generalized, preliminary map of the sub-Phanerozoic Precambrian rocks of the western Flin Flon domain; see Figures 3 and 5 for close-ups of exposed geology in the map area. Lake and mineral showing/deposit abbreviations are given in Figure 2 caption; TBF, SLF = interpreted subsurface trace of Tulabi Brook and Sarginson Lake faults, respectively.


Legend (sub-Phanerozoic)

felsic gneiss of uncertain derivation

granodiorite

biotite granite

felsic porphyry

massive/pegmatitic leucogranite

foliated to gneissic granite/granodiorite

mafic/ultramafic intrusion

quartz diorite-quartz monzonite-monzonite

ultramafic intrusion

felsic volcanic

mafic volcanic

intermediate volcanic

greywacke, age unknown

exhalites/iron formation

undifferentiated supracrustals

fault/shear zone

unconformitysurface trace

mapping transect

SL

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HL

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?

mineral showing

drill hole FON436

fold axial trace

G

S

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J

M

GBB

MB

WNZZ

BS

diorite

m E m Em Em Em Em E

m N

m N

m N

m N

m N

TB S

WR

Figure 12 - First vertical derivative aeromagnetic map of the map area. Line colours: white = lake shoreline; solid black = unconformity surface trace; dashed black = interpreted faults; dashed yellow = interpreted subsurface fold closure; orange solid = interpreted fold axial trace. See Figure 2 (and caption) for abbreviations and mineral showing/drill hole names; TBF = interpreted subsurface extension of Tulabi Book Fault; SLF = interpreted subsurface extension of Sarginson Lake Fault.

In the Hanson Lake area to the east, volcanogenic rocks of the Hanson Lake Assemblage can be traced as aeromagnetic lows below the shield margin. This interpretation is corroborated by observations from drill core at the McIlvenna Bay deposit, which consists largely of felsic volcanic and volcaniclastic rocks. Layered felsic tuffs and crystal tuffs are probably distal equivalents of the felsic volcanic centre interpreted by Maxeiner et al. (1995) to be represented by rhyolites and felsic porphyry intrusions exposed on southwestern Hanson Lake. Although mafic in composition, volcanogenic rocks intersected in drill hole FON436 to the east are tentatively considered to be part of the same overall volcanic assemblage. Based on geochemical similarities between volcanic rocks of the Hanson Lake and Northern Lights assemblages, Maxeiner et al. (1999) proposed that these sequences were once part of a continuous belt.

The structural complexity of the rocks in the map area is also evident in the magnetic patterns. A prominent, linear magnetic high extending southwards from the southern tip of Hanson Lake and proximal to the McIlvenna Bay deposit likely reflects the presence of oxide-facies iron formation, as observed in drill core intersecting the deposit. This unit and the mantling magnetic lows, interpreted to represent felsic volcanic rocks, appear to wrap around and define an (F2?) isoclinal fold (Figure 11). Locally, known VMS occurrences have a spatial association with this exhalative horizon, and it is possible that several such showings scattered throughout southern Hanson Lake area (e.g., Western Nuclear, McIlvenna Bay, Balsam, Zinc Zone deposits) are on opposing limbs of this fold (S. Masson, pers. comm., 2008). In addition, a change in the trend of the main regional foliation from north-south to northeast-


SL

HL

BL

LL

SE ARM

TB

F

SL

F?

m Em E m E m E m E

m N

m N

m N

m N

m N

Figure 13 - First vertical derivative of Bouguer gravity airborne survey. Line colours: white = lake shoreline; solid black = unconformity surface trace; dashed black = interpreted faults. See Figure 2 (and caption) for abbreviations and mineral showing/drill hole names; TBF = interpreted subsurface extension of Tulabi Brook Fault; SLF = interpreted subsurface extension of Sarginson Lake Fault.

southwest is apparent just south of Hanson Lake, suggestive of a subsequent (F3?), approximately northeast-trending refolding event. This contrasts with an interpretation by Sibbald (1989) and Maxeiner et al. (1999), who interpreted the Hanson Lake Assemblage as a homoclinal east-facing succession that may contain two separate mineralized horizons.

In the Suggi Lake area to the south, the regional structural grain appears to change from north-south in the west to approximately east-west in the east, based on the regional magnetic signatures. From limited drill core observations, this portion of the map area is at least partially underlain by a supracrustal sequence including volcanic rocks, represented by linear magnetic lows, intruded by moderately to highly magnetic granodiorite gneiss and subordinate, highly magnetic mafic and ultramafic intrusions. The lower density signature of this area compared to that of the Hanson Lake Assemblage to the north likely reflects the more extensive presence of felsic intrusive rocks. The Suggi Lake supracrustal sequence, into which the felsic intrusions were emplaced, is tentatively interpreted to be continuous with the Hanson Lake Assemblage to the north based on the lack of a significant discontinuity (fault/shear zone) in the magnetic signatures between southern Hanson Lake and northern Suggi Lake. At present, insufficient information exists to define lithological (volcanogenic vs. sedimentary) and/or compositional variants within this supracrustal succession.


SL

HL

LL

BL

SEARM

TB

F

SL

F?

m E m Em E m E m E

m N

m N

m N

m N

m N

6. Conclusions The following conclusions are either newly identified or substantiated from previously published interpretations:

1) Magnetic anomalies representing folded volcanic rocks of the Northern Lights Assemblage in the Deschambault Lake area can be traced continuously westwards into the Glennie Domain, and southwards where they form the host sequence to the Bigstone VMS deposit.

2) Moderately magnetic, low-density felsic intrusions underlie much of the area west of the Northern Lights Assemblage and east of the Tulabi Brook Fault.

3) The sub-Phanerozoic extension of the Tulabi Brook Fault clearly truncates magnetic and gravity patterns, suggesting significant displacement along this splay of the Tabbernor Fault system.

4) Volcanic rocks of the Hanson Lake Assemblage are traceable beneath the Phanerozoic cover, as is oxide-facies iron formation that is spatially associated with several VMS occurrences (e.g., McIlvenna Bay deposit).

5) Much of the covered basement immediately north of Suggi Lakes comprises a succession of undefined supracrustal rocks, tentatively interpreted to be a continuation of the Hanson Lake Assemblage, mafic to ultramafic intrusions, and regionally extensive, well-foliated to gneissic granites/granodiorites.

7. Acknowledgements A successful outcome to this project requires the support of exploration companies that are active in the study area: Copper Reef Mining Corp., Exploration Syndicate Inc., Foran Mining Corp., HudBay Minerals Inc., and Murgor Resources Inc. are gratefully acknowledged for their cooperation. Thank you to the Manitoba Geological Survey for providing accommodation at the Centennial Mine site trailer camp in August. Carson Turnbull is thanked for providing valuable field assistance. Mandy Hordos and Monica Tepes provided important office support for the project during the summer. Ralf Maxeiner and Ken Ashton are thanked for sharing their knowledge of the study area during field trips and/or discussions. Thomas Love, Dustin Zmetana, and Bill Slimmon are gratefully acknowledged for providing GIS support.

8. References Adamson, D.W. (1988): Volcanogenic mineralisation in the Limestone Lake area, Saskatchewan, Canada; unpubl.

Ph.D. thesis, Aston Univ., Birmingham, 238p.

Ansdell, K.M. and Norman, A.R. (1995): U-Pb geochronology and tectonic development of the southern flank of the Kisseynew Domain, Trans-Hudson Orogen, Canada; Precamb. Resear., v72, p147-167.

Ashton, K.E., Lewry, J.F., Heaman, L.M., Hartlaub, R.P., Stauffer, M.R., and Tran, H.T. (2005): The Pelican Thrust Zone: basal detachment between the Archean Sask Craton and Paleoproterozoic Flin Flon–Glennie Complex, western Trans-Hudson Orogen; Can. J. Earth Sci., v42, p685-706.

Bickford, M.E., Van Schmus, W.R., Macdonald, R., Lewry, J.F., and Pearson, J.G. (1986): U-Pb zircon geochronology project for the Trans-Hudson: current sampling and recent results; in Summary of Investigations 1986, Saskatchewan Geological Survey, Sask. Energy Mines, Misc. Rep. 86-4, p101-107.

Fenton, M.M., Schreiner, B.T., Nielsen, E., and Pawlowicz, J.G. (1994): Quaternary geology of the Western Plains; in Mossop, G. and Shetsen, I. (comp.), Geological Atlas of the Western Canada Sedimentary Basin, Can. Soc. Petrol. Geol./Alta. Resear. Counc., Calgary, p413-420.

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