New Results from Mapping in the Flin Flon Mining Camp, Creighton, Saskatchewan
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Stratigraphy, Structure, and Silicification: New Results From Mapping in the Flin Flon Mining Camp, Creighton, Saskatchewan Kate MacLachlan MacLachlan (2006): Stratigraphy, structure, and silicification: new results from mapping in the Flin Flon Mining Camp, Creighton, Saskatchewan; in Summary of Investigations Volume 2, 2006, Saskatchewan Geological Survey, Sask. Industry Resources, Misc. Rep. 2006-4.2, CD-ROM, Paper A-9, 25p. Abstract Two areas in the Flin Flon mining camp were mapped at a scale of 1:5000, one area between Douglas Lake and West Arm Road on the west limb of the Beaver Road Anticline, and the other on the peninsula between Green Lake and Phantom Lake. In the Douglas Lake area, mapping was undertaken in the hanging wall of the west-younging, felsic-dominated Myo member of the Flin Flon formation. Significant findings include, an extrusive felsic unit above the upper contact of the Myo member, abundant peperite at several stratigraphic levels, an up to 100 m wide zone of semi-conformable silicification, and pervasive sinistral shearing that post-dates the Phantom Intrusive Suite. In the Green Lake Peninsula area, three fault-bounded successions with opposing younging directions were recognized. The easternmost succession, east of the newly defined Burley Lake Fault (a modified version of the Phantom Lake Fault), is part of the west-younging Louis formation on the east limb of the Burley Lake Syncline. The east-younging succession between the Burley Lake and Green Lake faults comprises a large component of fine- grained mafic volcaniclastic rocks intercalated with aphyric and plagioclase ± pyroxene porphyritic flows, and is tentatively correlated with the Hidden formation. The west-younging succession west of the Green Lake Fault is tentatively correlated with the west limb of the Beaver Road Anticline. The Green Lake Fault is a fairly late structure that overprinted a multiply reactivated fault zone that runs down the centre of the peninsula and may be a continuation of the Flin Flon Lake Fault. The boundary between the east- and west-facing successions occurs within this complex fault zone and the timing and nature of the original boundary in not known. Keywords: Flin Flon Mining Camp, stratigraphy, structure, silicification, peperite, sinistral shear zones, faulting. 1. Introduction The Flin Flon Mining Camp is in the Paleoproterozoic Flin Flon Belt of the Trans-Hudson Orogen in Manitoba and Saskatchewan (Figure 1). Because it is a world-class volcanogenic massive sulphide (VMS) mining district, the Flin Flon–Creighton area has been the focus of many detailed geological studies over the years (e.g., Stockwell, 1960; Bailes and Syme, 1989; Thomas, 1992; 1994; Fedorowich et al., 1995; Price, 1997; Gale et al., 1999). As a result of the first “Targeted Geoscience Initiative” (TGI) in the Flin Flon Belt, undertaken from 2000-2002, significant progress was made in understanding the volcanological framework of the VMS hosting succession (Gibson et al., 2003b; 2005; Devine et al., 2002; Ames et al., 2002; MacLachlan and Bailey, 2002; Bailey and Gibson, 2004; 2005), and the previous informal stratigraphic nomenclature (e.g., Thomas, 1994) was revised (Devine et al., 2002; Figure 2). A consistent stratigraphic and volcanological framework for the entire camp, however, remains incomplete and is one of the objectives of the present Flin Flon TGI 3 project. The VMS deposits are hosted by a steeply northeast-dipping succession (Figure 2) on the upright, shared limb of the Beaver Road Anticline (BRA; Stockwell, 1960) and Hidden Lake Syncline (HLS; Stockwell, 1960). These regional, inclined, D2 folds are disrupted by several phases of superposed faulting (e.g., Stockwell, 1960; Thomas, 1994; Gale et al., 1999; Fedorowich et al., 1995). The Flin Flon Lake Fault is a northerly-trending regional structure that truncates the shared limb of the anticline-syncline pair and precludes tracing specific units around the BRA to the west-younging, western limb (Figure 2). Breccias of the ‘Blue Lagoon member’1 of the ‘Flin Flon formation’, however, are interpreted to occur on both sides of the Flin Flon Lake Fault (H. Gibson, pers. comm., 2006), thus providing a stratigraphic datum for regional correlations. There also is general agreement that sequences on either limb of the BRA are broadly correlative (K. Gilmore, pers comm., 2002), but lithologically different, and detailed stratigraphic and genetic relationships remain unclear. An M.Sc. thesis (Bailey, 2006) study of the “Myo Rhyolites” 1 Informal nomenclature first appears in single quotation marks; subsequently, the quotation marks are dropped. Saskatchewan Geological Survey 1 Summary of Investigations 2006, Volume 2 E NAIN V A RAE L S NE AR Hudson HE Bay HO T 50 N 50 N 60 W 130 W SUPERIOR G Flin Flon TGI study area N I M Atlantic O Y Ocean W <1.8 Ga Orogens Archean Cratons Cu-Zn MINES Paleoproterozoic Orogens B - Birch Lake C - Callinan Ce - Centennial T NE Arm shear zone Co - Coronation Cu - Cuprus C Bear Lake block TR D - Don Jon Flin Flon N F - Flin Flon F D Fl - Flexar Cu K - Konuto M WL M - Mandy S N - North Star Ce S - Schist Lake T - Trout Lake Scotty Lake block Fl TR - Triple 7 K W - Westarm B W WL - White Lake Amisk Lake Co ake w L ko us ap Phanerozoic cover p o a 102 15' W th Phanerozoic cover o 10 km A 54 30' N Sask. Man. PRE-ACCRETION ASSEMBLAGES (1.92 to 1.88 Ga) POST-ACCRETION ROCKS (1.87 to 1.84 Ga) Missi Group Major mafic-felsic tholeiitic SUCCESSOR BASINS sandstone, conglomerate JUVENILE ARC intrusive rocks Schist-Wekusko suite Calc-alkaline volcanic rocks 1.90 to greywacke, mafic sills 1.88 Ga Arc rift basalt Tholeiitic, mafic-felsic SUCCESSOR ARC Felsic volcanic rocks INTRUSIVE ROCKS Intermediate-mafic OCEAN FLOOR Layered mafic-ultramafic complex (BACK-ARC) N-type MORB/E-type MORB 1.90 Ga OCEANIC PLATEAU Tholeiitic basalt (age unknown) Accretion-related Younger shear zones shear zones (D >1.87 Ga) and/or faults (D -D ) Felsic plutonic rocks 1 25 'EVOLVED ARC' (~1.920 to 1.903 Ga) F VMS deposit (see inset key) ARCHEAN SLICES Granitic rocks (~2.5 Ga) Figure 1 - Tectonic assemblage map of the Flin Flon Belt. Inset shows location of the Flin Flon Belt within the Trans- Hudson Orogen (modified from Syme et al., 1998). Saskatchewan Geological Survey 2 Summary of Investigations 2006, Volume 2 0 km 1 Legend C Intrusive Rocks FF VMS deposit C FF=Flin Flon F F Phantom Intrusive Suite C=Callinan L Tr=Triple 7 C C Boundary Intrusions RF M=Mandy C S=Schist Lake 10 Bootleg Pluton Tr Mine shaft Tr H Annabel Pluton 106 Tailings N=North Main Pond L S=South Main S Cliff Lake Pluton Tr= Triple 7 Tr F Missi Group Highway L 167 F Ross F Lake 2007 Provincial Flin Flon Assemblage Border N Louis formation 10A Fault FF Manitoba 10 Hidden formation Saskatchewan F1 Syncline/ Anticline B R Douglas formation A X S F2 Syncline/ Anticline 2007 X X Flin Flon formation P Younging L Millrock member R direction 167 W Myo member (felsic/mafic) A Study Areas R Creighton member Blue Lagoon member MacLachlan CL 02 Club member Bailey 20 R Schist B M Simard L Lake Douglas L F F Lake S Unassigned volcanic rocks X Lewis D L 2006 R Potter Bay PLF M 2007 Phantom Lake F 2006 R S Burley 2006 Lake Figure 2 - Simplified geological map and informal stratigraphic subdivisions of the Flin Flon-Creighton area, showing locations of previous G and ongoing Flin Flon Targeted Geoscience Initiative 3 studies; BLS, Burley Lake Syncline; BRA, Beaver Road Anticline; CCF, Creighton LF Creek Fault; CL, Carlisle Lake; CLF, Club Lake Fault; DLR, Douglas Lake Road; FFLF, Flin Flon Lake Fault; GLF, Green Lake Fault; HLS, Hidden Lake Syncline; MF, Mandy Fault; PLF, Phantom Lake Fault; PLR, Phantom Lake Road; RF, Railway Fault; RLF, Ross Green Lake Fault; and WAR, West Arm Road. Lake Saskatchewan Geological Survey 3 Summary of Investigations 2006, Volume 2 (Thomas, 1994), the potential time-stratigraphic equivalent of the VMS-hosting rhyolites, resulted in redefinition of the rhyolite-bearing succession as the ‘Myo member’ of the Flin Flon formation (Bailey, 2006). More work remains to be done on the successions above and below the Myo member. The first part of this report describes the stratigraphy and geology of part of the western limb of the BRA, in the hanging wall of the Myo member. The second part focuses on a structurally and stratigraphically complex area south of the Phantom Lake Fault (Stockwell, 1960; Figure 2), where a rhyolite on the western shore of the Green Lake Peninsula, is thought to be a lateral continuation of the Myo member (K. Bailey, pers. comm., 2006). This potential correlation infers that younging in the western part of the peninsula is toward the west, whereas the succession youngs to the east in the eastern part of the peninsula (Stockwell, 1960). There is currently no interpretation of how or where the younging change occurs. During the summer of 2006, a joint mapping project by Saskatchewan Industry and Resources (SIR) and the Manitoba Geological Survey (MGS) was initiated in the Green Lake Peninsula and adjacent Burley Lake–Carlisle Lake areas (Figure 2). This paper reports on the results of the SIR component of 1:5000 scale mapping and how it integrates with the MGS mapping to resolve some of the stratigraphic and structural issues in the area. 2. Regional Geology The Flin Flon Belt is a collage of 1.92 to 1.87 Ga, predominantly juvenile oceanic rocks and 1.87 to 1.83 Ga successor arcs, basins and plutonic rocks (Lucas et al., 1996; 1999; Syme et al., 1998; Stern et al., 1999).