Flin Flon, 777, Callinan, Trout Lake, Centennial, Schist Lake, Konuto, Westarm, Coronation, Mandy
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The Flin Flon and associated cluster of volcanic hosted massive sulphide (VHMS) copper-zinc-gold deposits are located in northern Manitoba and Saskatchewan in Canada, ~605 km NNW of Winnipeg, and 420 km NE of Saskatoon. The main Flin Flon group of deposits straddle the Provincial border, and are situated within a 25 km radius around the town of Flin Flon. The key deposits include Flin Flon, Trout Lake, 777, Callinan, Centennial, Schist Lake, Konuto, Westarm and Coronation all of which contained >1 Mt of economic ore, as well as the smaller satellite deposits that included Mandy, White Lake, Cuprus, Birch Lake, Flexar, North Star and Don Jon (#Location: Flin Flon - 54° 45' 58"N, 101° 52' 58"W).
The regional setting and context of this group of deposits is described in the Flin Flon-Glennie Complex VHMS Deposits record, as is the district geology.
Flin Flon Deposit
The Flin Flon deposit was discovered in 1914 and brought into production in 1927. Peak production was reached in 1943, with mining largely from pillars and remnants after 1976. The deposit was essentially depleted by 1992 (Trevor, 1998).
The main Flin Flon massive sulphide deposit is hosted by a complex succession of felsic and basalt-dominated heterolithic volcaniclastic rocks, predominantly thick lava flows intruded by synvolcanic mafic dykes and sills. This succession is composed of i). a >1.88 Ga juvenile, oceanic arc assemblage comprising basalt, basaltic andesite, rhyolite and synvolcanic intrusions, the Amisk Group (Syme and Bailes, 1993), and ii). a <1.88 Ga assemblage of calc-alkaline "early successor arc" plutons (pre-Missi intrusive rocks), fluvial sedimentary rocks of the Missi Group, and "late successor arc" intrusions (Bailes and Syme, 1989; Stauffer, 1990; Stern et al., 1999). The structural architecture of the Flin Flon District and the geometry of mapped formations have been influenced by multiple generations of folding, thrusting and strike-slip faulting, such that within the Flin Flon Block, major NNW striking early thrust faults and late strike-slip faults have dissected the block into structural panels (Simard et al., 2010). Lithofacies within each formation can differ somewhat between panels and the correlation of units between panels is not always certain.
The stratigraphic succession in the Flin Flon mine area is as follows, from the base (after Gibson et al., 2011; Pearson et al., 2012):
Flin Flon Formation
• Club Lake Member - is the oldest exposed unit within the sequence, and where exposed, dips shallowly and has an apparent thickness of ~500 m. It is truncated at its base by the Club Lake Fault in the north and is conformably overlain by the Blue Lagoon member to the south and east. It consists of four main units:
i). heterolithic basalt±rhyolite breccia, interpreted to have been the result of proximal re-sedimentation of detritus derived from pre-existing mafic and lesser felsic volcaniclastic lithofacies and their localised accumulation within subsidence basin(s);
ii). dominantly monolithologic rhyolite breccia and rhyolite clast bearing mafic volcaniclastic;
iii). massive, aphyric coherent rhyolite. The coherent rhyolite and the preceding rhyolite breccia and rhyolite clast bearing mafic volcaniclastic lithofacies are interpreted to be part of a series of rhyolite flow or dome complexes and their transported flank breccias (Devine, 2003; Gibson et al., 2005); and
iv). sparsely feldspar-phyric to aphanitic pillowed basalt flows.
• Blue Lagoon Member - conformably overlies the Club Lake member. It is a distinctive unit characterised by a distinctly plagioclase phyric flow lithofacies containing varying amounts and sizes of plagioclase crystals that that range in size from 0.2 to 1 cm, and may make up 5 to 25% of the rock. It contains several subsidiary rock types, including plagioclase crystal-rich volcaniclastic lithofacies, rhyolitic tuff, heterolithic crystal lithic basaltic breccia, and feldspar-phyric massive and pillowed basalt flow and flow breccia. At the base, plagioclase-phyric pillowed lithofacies of the upper unit of the Club Lake member is intercalated with the plagioclase-crystal-rich volcaniclastic lithofacies, suggesting the latter, in part, may be transported autoclastic deposits of the former (Devine, 2003).
The Blue Lagoon member is also characterised by abrupt changes in the thickness and limited lateral continuity of units, interpreted to be due to synvolcanic faulting influencing localised sub-basins in the underlying dominantly mafic flow lithofacies,collectively defining a larger subsidence structure, as well as adjacent uplift, erosion, redistribution and slumping of earlier unconsolidated facies.
• Millrock Member - the uppermost unit of the Flin Flon formation which unconformably, and locally, conformably overlies the previously deposited footwall strata. It hosts the Flin Flon, Callinan and 777 VMS deposits, and includes coherent porphyritic basaltic pillowed flows, heterolithic and monolithic basaltic megabreccia, breccias and volcaniclastic rocks, chlorite schist, aphyric to quartz-feldspar phyric rhyolite and contemporaneous volcaniclastic rocks. These lithofacies are discontinuous and define syn-volcanic basins that range from tens to several hundreds of metres in width (Gibson et al., 2006; 2009). The member is exposed east and west of the major, north-south Flin Flon Lake Fault. East of the fault, it is traceable over a strike length of >5 km, where it varies in thickness from <10m in the north to >500m in the south, locally in excess of 1000 m. It dips moderately and faces to the NE and east, steepening to the north. Coherent and monomictic rhyolite breccia yielded a U-Pb zircon age of 1888.9 M± 1.6 Ma (Rayner, et al., 2010).
Within the Millrock Member the coherent and volcaniclastic rhyolite units define localised "felsic volcanic centres". Massive sulphide lenses at the Flin Flon, 777 and Callinan deposits occur principally at or near the top, but also within, below, and lateral to rhyolite flow dome complexes indicating a long-lived hydrothermal event where felsic volcanism was accompanied by ore deposition (Gibson et al., 2011). A bedded tuff unit caps the Millrock Member, and represents a significant hiatus in effusive volcanism that followed emplacement of rhyolite domes and cryptodomes, and formation of the VHMS deposits (Devine, 2003; Gibson et al., 2003b; Gibson et al., 2009).
Detailed reconstruction and distribution mapping of the coherent basaltic flow, basaltic megabreccia and volcaniclastic and rhyolitic lithofacies are interpreted to indicate the Flin Flon, Callinan and 777 deposits formed within a large, subaqueous subsidence structure or cauldron, where they are spatially and temporally associated with the construction of rhyolite flow and dome complexes that were emplaced during the waning stage of Flin Flon formation volcanism (Devine, 2003; Gibson, et al., 2006; 2009). Millrock rhyolitic volcanism and VMS ore-formation was followed by a period of explosive basaltic volcanism from vents located primarily at, and south of Millrock Hill (Gibson et al., 2009). The bedded tuff lithofacies that extends across the cauldron is a product of these eruptions (Gibson et al., 2011).
Hidden Formation - composed of mafic flows, sills and volcaniclastic rocks, with subordinate basaltic-andesite flows, rhyolite flows and felsic volcaniclastic rocks. The base of the unit is placed at the last occurrence of tuff and/or rhyolite of the underlying Millrock member. Localised, alteration associated with the Flin Flon-Callinan-777 ore system has been identified into the Hidden formation (Ames et al., 2002; 2003; Tardif; 2003), divided into five members.
• 1920 Member - comprises a 50 to 200 m thick massive to pillowed aphyric Fe-Ti-P basaltic andesite cryptoflows, locally with 25 to 50% randomly oriented acicular amphibole porphyroblasts, and aphyric to sparsely plagioclase-phyric Fe-Ti-P basalt flows and sills (DeWolfe et al., 2009).
• Reservoir Member - a steeply to moderately dipping succession with an apparent thickness of 400 to 800m, comprising aphyric, plagioclase phyric and pyroxene-plagioclase-phyric basalt flows, with minor volcaniclastic rocks. The flows are are mainly massive (>70% by volume, usually 5 to 15 m thick) and pillowed (>30% by volume, usually 10 to 50 m thick) and contain some large lava tubes (DeWolfe et al., 2009).
• Stockwell Member - comprises massive, pillowed and breccia facies of strongly plagioclase (15 to 50%) and pyroxene (>5%) porphyritic basalt flows and is locally overlain by a mafic volcaniclastic unit. Where present it occurs as a generally south facing moderately-dipping sequence with an apparent thickness up to 300 m that is thrust-repeated with portions of the Reservoir and 1920 members (DeWolfe et al., 2009).
• Carlisle Lake Member - with an apparent thickness >40 to >800 m, comprises aphyric to sparsely plagioclase-phyric, plagioclase-phyric basalt flows, mafic volcaniclastic rocks,and minor amount of felsic volcanic rocks and is interpreted to represent a lateral equivalent to the Reservoir member (DeWolfe, 2008; Simard, 2006a).
Louis Formation - composed of basalt flows and mafic volcaniclastic rocks, with subordinate rhyolitic flows and felsic volcaniclastic rocks, representing a second episode of mafic volcanism following the Hidden Formation (DeWolfe et al., 2009). It isa divided into
• Tower Member - consists of massive to in situ-brecciated, aphyric or sparsely plagioclase- and quartz-phyric rhyolite overlain by, and locally underlain, by mafic tuff. Where the coherent rhyolite is absent, it is defined by a laterally extensive mafic tuff, including lapilli-tuff beds containing rhyolite fragments derived from the coherent rhyolite portions (DeWolfe et al., 2009).
• Icehouse Member - where present, is a steeply-dipping, east-facing sequence 25 to 100 m thick sequence of strongly plagioclase pyroxene phyric basaltic, pillowed to massive flows and mafic volcaniclastic rocks, which from north to south changes from a thick (~100 m) single facies massive flow to a thin (~25 m) multifacies flow with a massive bottom and a pillowed top (DeWolfe et al., 2009).
• Undivided Louis formation rocks - which account for >90% of the formation, and comprise aphyric to sparsely plagioclase-phyric, plagioclase-phyric, and plagioclase-pyroxene-phyric massive and pillowed basalt flows intercalated with subordinate amount of mafic volcaniclastic rocks (DeWolfe, 2008).
The Flin Flon orebody is/was composed of massive and disseminated sulphides in 6 individual lenses that strike at 330° and dip 70°E, extending for about 1600 m down the 45°SE plunge. Individual lenses averaged 270 m in width, by 21 m thick and 760 m in length down plunge.
The massive bodies are spatially and temporally associated with the construction of rhyolite flow and dome complexes that were emplaced within the upper Millrock Member during the waning stage of Flin Flon formation volcanism. The sulphides are fine-grained pyrite, sphalerite and chalcopyrite and are banded parallel to to wall-rock contacts. The massive bodies are zoned, with chalcopyrite-pyrrhotite in the footwall and sphalerite, occasionally banded with pyrite, towards the hanging wall (Byers et aI., 1965; Howkins and Martin, 1970. Minor gangue minerals include arsenopyrite, magnetite, galena, tetrahedrite, argentite and electrum. Disseminated chalcopyrite, pyrrhotite and cubanite are found in the altered footwall rhyolite and volcaniclastic rocks (Koo and Mossman, 1975), and accounted for ~30% of the ore mined (Gale and Eccles, 1988). Metal ratios are similar in both the massive and disseminated ores (Koo and Mossman, 1975).
Hydrothermal alteration associated with massive sulphide deposit is only poorly exposed on surface, where the footwall Club Member basalt most commonly has been subjected to intense epidotisation, accompanied by local zones of chlorite and sericite. Distributed zones of silicification, and gossan zones characterised by anastomosing chlorite- and pyrite-filled fractures, are also present. Underground, Koo and Mossman (1975) outlined a 2000 x 1000 x 200 m schistose chloritic zone that transects Millrock Member volcaniclastic rocks, rhyolites, and the massive sulphide deposit, and terminates against the Hidden Formation basalt in the stratigraphic hanging wall. The chloritic zone is interpreted as a deformed hydrothermal alteration pipe (after Sangster, 1972). Rocks within the alteration pipe are depleted in Si02 and alkalis, and enriched in CaO, FeO, and particularly MgO, relative to less altered wall rocks (Koo and Mossman, 1975). In the mine workings the alteration zone is characterised by abundant dark greenish-black Mg chlorite, locally enclosing remnants of quartz phenocrysts (altered rhyolite) and quartz amygdules (altered basalt). Altered basalt contains talc, albite, stilpnomelane, sphene, leucoxene, dolomite, quartz and pyrrhotite. Altered rhyolitic rocks includes assemblages of quartz, albite, phengite, calcite, chlorite and epidote (Koo and Mossman, 1975).
The Mine Rhyolite is overlain by a 35 m thick felsic volcaniclastic rock, interpreted to represent a debris flows. These are in turn overlain by the >3000 m thick Hidden Lake basalt, characterised by pillow flows.
The geological section of this summary is largely drawn from "Gibson, H., Pehrsson, S., Lafrance, B., DeWolfe, M., Syme, R., Bailes, A., Gilmore, K., Devine, C., Simard, R-L., MacLachlan, K., and Pearson, B., 2014 - The volcanological and structural evolution of the Paleoproterozoic Flin Flon and Snow Lake mining districts: Field Trip 3B: Joint Annual Meeting, Geological Association of Canada-Mineralogical Association of Canada-Society of Economic Geologists-Society for Geology Applied to Mineral Deposits, Ottawa 2011; Geological Survey of Canada, Open File 7116, 88p.
The 777 deposit is semi-parallel to the Flin Flon orebody, ~1200 m to the NE, on the opposite side of the north-south oriented Flin Flon Lake fault. They two form an en echelon pair, with 777 to the east and offset to the north. The surface projection of the Flin Flon deposit is ~1500 m long, while 777 has a similar lateral extent. Laterally, the smaller Callinan begins just beyond the northern extremity of 777 on the same trend. 777 is 500 m south of the underground workings at Callinan Mine. The top of the ore body is at approximately 900 m below surface, dipping at an average of 41°.
The 777 mine is an underground mining operation that commenced commercial production in 2004 and that has a life of mine to beyond 2021.
Both the 777 and Callinan deposits are hosted within an east-facing sequence of tholeiitic and basalt-dominated volcanic rocks, although the immediate host rocks of the mineralisation, are quartz-phyric and quartz-feldspar-phyric volcaniclastic rhyolite flows. The hanging wall is made up of basaltic flows and intrusive volcanics of the overlying Hidden formation. The Millrock member at 777 has been subdivided into five main units, namely:
i). Fragmental Basalt, which is typically dark green, fine-grained to aphanitic, amygdaloidal aphyric, with sparse, subangular to well rounded, 1 to 10 cm feldspar phyric basalt clasts within a finer-grained, light to medium green basaltic matrix.
ii). Quartz Porphyry Rhyolite (QP), hosts the bulk of the mineralisation at 777, and comprises a coherent and volcaniclastic lithofacies which may contain sub-angular to sub-rounded QP fragments inside a finer grained matrix that also contain quartz crystals. The QP is typically aphanitic to very fine grained with up to 10% blue to clear quartz eyes with varying amounts of plagioclase phenocrysts. Minor to pervasive sericite and chlorite alteration is found throughout much of the QP.
iii). Chlorite Schist, which has a schistose fabric and comprises near massive chlorite with sections of very strongly foliated and chloritised mafic and felsic volcaniclastic lithofacies. Locally this lithofacies contains pyrrhotite, chalcopyrite and magnetite mineralisation. It only occurs within the footwall to the main 777 deposit, although it does include footwall sulphide zones 15, 50, and 70 (see below). This schist is interpreted to represent a hydrothermally altered equivalent of the Fragmental Basalt (and locally the Quartz Porphyry Rhyolite unit) and to define the footwall alteration pipe (Gibson et al., 2011).
iv). Mafic/Felsic Tuffs, mainly mafic in composition, but including some felsic tuffs. This lithofacies comprises both massive, thick to medium bedded, and thinly bedded to laminated tuffs. They contain lapilli sized clasts of QP, chlorite and/or sericite altered QP, amygdaloidal and massive sulphide in a finer grained tuff sized matrix. These tuffs mark the top of the Millrock member. Overlying flow units mark the base of the overlying Hidden Formation. These flows are fine grained to aphanitic basalts that vary between massive and amygdaloidal with up to 15% white quartz/carbonate amygdules, and include both basaltic flows and sills.
v). Intrusives (typically diorite), which are dark green, fine-grained to aphanitic, and are usually not foliated. The diorites frequently cross-cut the mineralised zones and can contain varying amounts of pyrrhotite, pyrite, chalcopyrite, sphalerite and magnetite. Mineralisation typically occurs as remobilisations or as xenoliths, being concentrated near the contacts. Diorite dykes vary in thickness from a few cm to tens of metres.
The 777 deposit has been divided into two main SE plunging trends, the North and the South Limb, as well as the West Zone. All three are within the same stratigraphic sequence with the same lithofacies, with the West Zone lying in the footwall in what is interpreted to be a lower thrust slice. Horizontal widths/thickness within the deposit range from 2.5 to 70 m, and are thicker when two or more zones overlap. Eight distinct sulphide lenses are recognised within the 777 deposit. These lenses are Zones 10, 15, 20 and 30 (North Limb), Zones 40, 50, 60 and 70 (South Limb), and Zone 33 (West Zone). Zone 10 is composed of varying amounts of pyrrhotite, pyrite and chalcopyrite with local sphalerite, arsenopyrite, chalcocite and chlorite. Zones 15, 50, and 70 are chlorite schist hosted and typically pyrrhotite and chalcopyrite with minor sphalerite, pyrite, arsenopyrite and magnetite. Zones 30, 33, 40 and 60 are zinc rich with variable amounts of pyrite, sphalerite and chalcopyrite, and locally minor pyrrhotite, magnetite and arsenopyrite (Gibson et al., 2011). In general each trough is relatively zinc rich on the hanging wall and grading towards copper rich in the footwall. Each lens is distinguished on the basis of grade and ore type as well as their spatial location. Lenses are in general fairly continuous with the exception of scattered diorite intrusions. The 777 deposit covers an area of ~1300 m down plunge by 550 m across, varying in depth from ~870 to 1600 m below the surface. Lenses in general are fairly continuous with the exception of scattered diorite intrusions (Pearson et al., 2012).
The 777 description is largely drawn from "Pearson, B., Lyhkun, D., Spence, C., West, S. and Carter, R., 2012 - Technical Report, 777 Mine, Flin Flon, Manitoba, Canada; an NI 43-101 Technical Report prepared for Hudbay Minerals Inc."
Callinan is hosted by the same sequence as described above. Two mineralised rhyolite horizons are recognised, the East-QP and the West-QP. The East-QP is host to the lenses of the North Zone, East Zone and is on the same horizon as the 777 mineralisation. The West-QP hosts the South Zone and its associated lenses. Each zones is further subdivided into a number of mineralised lenses. The zones are subdivided into lenses on the basis of spatial distribution of the mineralisation. A total of 20 sulphide lenses are contained within the three broad zones of the Callinan deposit, which is a distal deposit that has a matrix supported breccia with variable amounts of wallrock fragments in a fine to medium grained sulphide matrix. The wallrock fragments are intensely altered to chlorite, talc and sericite with some degree of pyritisation and carbonation. These lenses contain variable amounts of pyrite, sphalerite, chalcopyrite and minor pyrrhotite. The Callinan mineralisation occurs as a matrix supported breccia with variable amounts of wallrock fragments in a fine to medium grained sulphide matrix. The wallrock fragments are intensely altered to chlorite, talc and sericite with varying development of pyrite and carbonate minerals. The individual lenses contain variable amounts of pyrite, sphalerite, chalcopyrite and minor pyrrhotite. Most have comparable metal grades, typically averaging 1% copper and 4% zinc , with the Dan Zone being the notable exception with an estimated grade of 0.27% copper and 8.60% zinc (Pearson et al., 2012).
Trout Lake Deposit
The Trout Lake deposit, situated 8 km NE of Flin Flon, was discovered in 1977, and went into production in 1982 and closed in late 2012.
Like the other VHMS deposits of the Flin Flon district, Trout Lake lies conformably within lower greenschist facies Palaeoproterozoic Amisk volcanic strata of the Flin Flon-Glennie Complex or Flin Flon Greenstone Belt.
Ore occurs in six known zones, each of which contains more than one lens. There are 32 known lenses, distributed over a strike length of 1600 m and to a depth of at least 1400 m. The average strike of the deposit is 310° with a dip of 60°NE.
During production, the host sequence was subdivided as follows, from the base (Trevor, 1998, Unpub):
• Footwall Mafics - which are >600 m thick and generally massive, and occasionally feldspar phyric. This unit hosts a narrow band of chalcopyrite, pyrrhotite mineralisation known as the 'Shaft Cu Zone'.
• Footwall Rhyolite Flow - which is 80 to 200 m thick and comprises a massive, highly siliceous, homogeneous moderately foliated rhyolite with a siliceous sericitised fine grained matrix with 1 to 4 mm subrounded light grey to blue quartz eyes. It hosts the uneconomic 'Trout 2' zone at the bottom of the unit, which is dominantly pyrite with minor chalcopyrite and sphalerite. The contact with the overlying graphitic argillite is sharp.
• Footwall Graphitic Argillite - an extensively developed unit which ranges from 90 to 130 m in thickness, and has a sharp contact with the underlying Footwall Rhyolite Flow. It is black, fine grained, laminated, crenulated and sheared, with intercalated brecciated thin cherty and dacitic tuffaceous lenses, and accommodates a major strike slip fault zone.
• Host Seriticised and Chloritised Quartz Phyric Fragmental Rhyolite - which is 350 to 400 m thick, and hosts the main Trout Lake Orebodies. It is cut by mafic sills and dykes and has a sharp contact with the underlying graphitic argillite, although the hanging wall contact with the Hangingwall Graphitic Argillite is generally gradational. This unit is composed of 20 to 80% felsic lapilli sized fragments in a fine grained seriticised and chloritised myolitic tuffaceous matrix. The lapilli are elongated, angular to subrounded, 0.3 to 5.0 cm in width and loosely to tightly packed. It also contains 1.0 to 2.5 mm diameter subangular to rounded light blue to light grey quartz eyes throughout. Rocks above and below the individual ore lenses are of this same lithology with varying degrees of alteration and shearing. In the upper part of the mine, the orebodies are in the upper part of the unit, closer to the hanging wall graphitic argillite/greywacke unit. However, with depth, they orebodies step down through the unit to become closer to the footwall graphitic unit.
• Hanging Wall Graphitic Argillite - a >700 m thick, dark grey to black, fine grained unit composed of intercalated graphitic argillite to fine greywacke and sandstone, which been thickened by folding and faulting, illustrated by indicators of stratigraphic tops (graded bedding) changing rapidly over short distances.
Four episode of deformation have been recognised within the mine, although D1 may have involved several separate phases.
D1 was a major syn-metamorphic, ductile deformation, that generated near-isoclinal folding and strong fabrics (foliation and/or lineation) in the volcanic rocks on a regional scale and resulted in the widespread distribution of the potential ore horizons in the Flin Flon district. The major influence of this event on the Trout Lake sulphide lenses appears to have been flattening and elongation, possible isoclinal folding and the generation of a pattern of semicontinuous but, apparently, discrete, ore lenses.
D2 was also a ductile event, generating a series of NNW-trending (335°), relatively low angle (32°NE) faults/shear zones, defined by a ductile-brittle shear fabric. These structures are commonly marked by the presence of a 'diorite' dykes that are variably foliated and/or lineated and highly carbonate altered, with a Cr-Ni geochemistry suggesting an ultramafic protolith. Fault gouge within the fault/shear zones suggest later brittle movement along the initially more ductile fault. The D2 fault zones normally dip more shallowly than the ore body, but ramps and become steeper where cutting the mineralisation. These structures have a reverse sinistral movement, displacing the ore up the fault 'ramp'.
D3 is evident in the mine as an extensive, NNW (347°) trending, ~75°NE dipping, brittle fault, with a distinctive fault plane at least partly marked by gouge. This structure clearly terminates lenses and is believed to have dextral reverse movement.
D4 is represented in the mine by a NE trending open fold (the Embury Lake Fold) which has a NE trending joint set/fracture cleavage, steeply dipping crenulation lineation in the mica schists, and subhorizontal slickenlides. This event caused reactivation of the earlier faults, and is probably a drag fold of the Annabel shear zone.
Five main ore types were defined, as follows (where massive sulphides have >80%, semi-massive 50 to 80& and disseminated <50% sulphide):
• Banded sphalerite-pyrite ore - principally composed of sphalerite, pyrite and chalcopyrite, with minor galena, pyrrhotite, magnetite, marcasite, arsenopyrite, silver sulfosalts and trace electrum. This type has an elemental association of Cd, Sb, Pb. Ag. Hg, In, Sn and As, and is characterised by banding, some degree of schistosity and pyrite porphyroblasts.
• High-grade chalcopyrite-sphalerite ore - principally composed of sphalerite, chalcopyrite, pyrite and pyrrhotite, with minor galena, pyrrhotite, magnetite, marcasite, arsenopyrite, silver sulfosalts and electrum. This type has an elemental association of Pb, Ag and Au, and is characterised by deformation textures, coarse banding, replaced pyrite.
• High grade chalcopyrite-pyrrhotite-pyrite ore - principally composed of chalcopyrite, pyrrhotite and pyrite, with minor sphalerite, magnetite and electrum. This type has an elemental association of Se, Te and Co, and is characterised by very coarse-grained deformation-annealing textures.
• Disseminated sphalerite-pyrite ore - principally composed of sphalerite and pyrite, with minor chalcopyrite and pyrrhotite. This type has an elemental association of Cd, Sb, Pb, Ag, Hg, In, Sn and As, and is usually highly contorted and characterised by medium to fine grained, highly foliated with chloritic talc schist.
• Disseminated chalcopyrite-pyrite ore - principally composed of chalcopyrite and pyrite, with minor sphalerite, galena, marcasite, magnetite, cubanite, electrum, clausthalite and tellunde minerals. This type has an elemental association of Se, Te, Co, Au and Ag, and is characterised by being highly foliated, with coarse grained chalcopyrite, strongly deformed pyrite and annealing textures.
The individual ore lenses are markedly elongated down the plunge of ~50°E, with down plunge to strike length dimensions of ~4:1 or greater.
This summary is drawn from Trevor, 1989
Schist Lake and Mandy Deposits
The Mandy mine was the first mine in the Flin Flon area, discovered in 1915 and brought into production in 1916. The open pit operation closed in 1919, to be reopened temporarily in 1943, until finally being closed in 1944. The Schist Lake mine was an underground operation that produced from 1954 until 1976 (Gilmore, 2002).
The volcanic strata that hosts the Schist Lake deposit area have undergone significant deformation and are strongly foliated, and have been metamorphosed to lower greenschist facies, containing a mineral assemblage dominated by chlorite, actinolite and albite, with localised epidote patches.
The dominant structure in the Schist Lake-Mandy mines area is the NNW-SSE trending East Mandy Road Fault (which merges with the west arm of the same fault to the north of Mandy). This structure is interpreted to be a sinistral east-side-up shear.
The rocks in the area exhibit two foliations, defined by the alignment of chlorite: i). a fabric striking ~north-south, dipping steeply to the east, and ii). a second, more dominant foliation striking at 145 to 160° and dipping 75 to 85°E, which is a mylonitic S-fabric. The stretching lineation defined by the elongation of clasts trends at 110 to 150° and plunges 48 to 55°. These foliations and the stretching lineation increase in intensity in proximity to the Mandy Road Fault (Cole et al., 2007). Sulphide stringers exposed near the old Schist Lake headframe strike 160° and dip at 85 to 87°E, parallel to the dominant, mylonitic S-fabric foliation in the area
The rocks to the west of the West Mandy Road Fault are interpreted to belong to the Hidden Formation, as described in the Flin Flon summary above, and consist of aphyric to plagioclase-phyric basalt flows, intercalated with mafic and heterolithic volcaniclastic rocks. Basaltic flows are the dominant lithofacies to the north, whilst volcaniclastic rocks dominate to the south (Simard, 2006; DeWolfe, 2009; DeWolfe, 2011). These rocks are most likely stratigraphically younger than the sequence to the east of the fault.
The sequence to the East of the Mandy Road Fault, which hosts the Mandy and Schist Lake deposit, consist of mafic and heterolithic volcaniclastic rocks with minor basaltic
flows, and occupies the interval between the fault and the western shores of Schist Lake ~50 to 100 m to the east. These rocks trend ~north-south, dip steeply to the east or west, and young to the west.
To the south, in the vicinity of and presumably hosting the Schist Lake deposit, much of this sequence east of the Mandy Road Fault is a heterolithic tuff breccia to lapillistone unit, with a maximum exposed thickness of 220 m. It is continues south from the Schist Lake shaft and along strike for ~310 m north towards Mandy (which is ~500 m NNW of the Schist Lake shaft). It is clast supported and crudely bedded, with beds ranging from 1 to 10 m in thickness. It is dominated by beds of 60% pale brown, rounded, quartz-feldspar-phyric rhyolite lapilli; with 5 to 10% dark grey, aphyric basalt lapilli; and 5% dark grey, aphyric, quartz-amygdaloidal basalt lapilli and blocks, set in a matrix is dark green, strongly chloritic tuff. Locally, this unit contains two, massive felsic lapillistone beds, each ~10 m thick, dominantly composed of subrounded rhyolite lapilli and blocks, also in a dark green, strongly chloritic matrix.
From ~100 m south of the Mandy mine, the sequence between the Lake shore and Mandy Road Fault is a plagioclase crystal-rich, mafic tuff breccia unit. The interval between the two units is an embayment of the lake masking the contact. This unit has a maximum thickness of 100 m and a strike length of ~520 m, extending north from the shaft of the former Mandy mine. It is massive, monolithic and clast supported, 60% blocks and 35% lapilli in a tuff matrix. It comprises beds containing 25% purple, subrounded to subangular, plagioclase-phyric basalt blocks and lapilli; and 45% green, rounded to subrounded, plagioclase-phyric, quartz-amygdaloidal basalt blocks and lapilli. These rocks are overlain by a mafic tuff breccia, locally separated by a plagioclase-phyric mafic sill.
Approximately halfway between the Mandy and Schist Lake mines, a malachite stained sulphide-stringer zone is exposed at surface, with massive sulphide stringers from 0.1 to 3.5 m in width, generally oriented at 340°. Each sulphide stringer has an associated 1 to 3 m alteration halo of intense chlorite and randomly oriented quartz-stockwork veining (1 to 5 cm wide in the enclosing host rocks. Locally, near the old Schist Lake mine the heterolithic tuff breccia displays strong chlorite and pyrite alteration.
A Mafic tuff breccia unit with a maximum thickness of 30 m and strike length of ~1 km occurs above both of the main units east of the Mandy Road Fault described immediately above. It is characterised by intercalated, finely laminated beds separated by coarser, massive tuff beds containing basalt blocks and basalt lapilli.
A mafic tuff unit, with a maximum thickness of 90 m and strike length of ~1 km occurs on both sides of and within the Mandy Road Fault. The unit is dominated by parallel-laminated tuff beds, intercalated with thin plagioclase crystal-rich beds.
The Schist Lake and Mandy deposits, appear to be hosted along strike from one another, within a sericite carbonate schist, derived from a fine-grained, grey, quartz porphyry. Level plans and sections of the Schist Lake mine, compiled and interpreted when the mine was in production, show the orebodies occurring within a quartz porphyry unit and localised sericite schist (Cotter, 1969).
Both the Schist Lake and Mandy orebodies occur within a few to 30 m to the east of the Mandy Road fault.
The Schist Lake deposit consisted of two main zones (the North and South zones), each composed of several lenses. The individual lenses were tabular to lens-shaped. and plunged at ~70°S. The North Zone contained three discontinuous ore lenses, each with a maximum size of 60 x 300 m, whereas the South Zone contained four discontinuous lenses that ranged from 60 to 120 m in strike length and 300 to 600 m down plunge. Howkins and Martin (1970) suggested that the four lenses of the south zone may have been part of one sulphide lens that was segmented by faults. The envelope enclosing the North Zone plunges slightly more shallowly than the South Zone, although the individual lenses have the same overall plunge in both zones. The major metallic minerals were pyrite, chalcopyrite and sphalerite, occurring in three main types of ore: massive sphalerite-pyrite, massive chalcopyrite-sphalerite, and disseminated chalcopyrite-pyrite. Minor arsenopyrite and galena were also present and a little native gold was reported.
The Mandy orebody consisted of several zones: an inner core rich in chalcopyrite, surrounded by a sphalerite-rich zone of mixed sulphide, and an outer zone dominated by pyrite (Bailes and Syme, 1989). Only the chalcopyrite-rich zone was mined. The orebody was 30 m in strike length and 4 m wide, and extended to a depth of 60 m (Davies et al., 1962). The ore lenses were elongate parallel to the strike of the foliation and dipped steeply to the east. The orebody was reported to also contain gold and silver (Bruce, 1918).
This summary is drawn from Manitoba Geological Survey Report of Activities papers by Simard, 2006; Cole et al., 2007; 2008; DeWolfe, 2011, largely the latter).
Reserve + production figures for these deposits are as follows:
• Flin Flon - 62.485 Mt @ 2.21% Cu, 4.11% Zn, 2.72 g/t Au, 41.28 g/t Ag, (production + remnants following closure, Gibson et al., 2011)
• 777 - 21.904 Mt @ 2.59% Cu, 4.39% Zn, 2.12 g/t Au, 26.94 g/t Ag, - 1.2 km NE of Flin Flon, (Gibson et al., 2011)
12.12 Mt @ 2.56% Cu, 5.19% Zn, 32.68 g/t Ag, 2.29 g/t Au (Measured + indicated resource, Pearson et al., 2012)
0.569 Mt @ 1.75% Cu, 6.80% Zn, 49.11 g/t Ag, 2.31 g/t Au (Inferred resource, Pearson et al., 2012)
• Callinan - 7.774 Mt @ 1.36% Cu, 4% Zn, 2.06 g/t Au, 24.63 g/t Ag, - 2.5 km NNE of Flin Flon, (Gibson et al., 2011)
2.174 Mt @ 2.56% Cu, 1.20% Zn, 29.30 g/t Ag, 1.91 g/t Au (Measured + indicated resource, Pearson et al., 2012)
0.615 Mt @ 1.13% Cu, 4.23% Zn, 29.97 g/t Ag, 1.64 g/t Au (Inferred resource, Pearson et al., 2012)
• Trout Lake - 21.612 Mt @ 1.74% Cu, 4.97% Zn, 1.56 g/t Au, 16.02 g/t Ag, - 7 km NNE of Flin Flon,
• Schist Lake - 1.847 Mt @ 4.3% Cu, 7.27% Zn, 1.3 g/t Au, 37.03 g/t Ag, - 6.5 km SSE of Flin Flon,
• Mandy - 0.125 Mt @ 8.22% Cu, 11.38% Zn, 3.02 g/t Au, 60.15 g/t Ag, - 6 km SSE of Flin Flon.
Reserve + production figures for the other significant and satellite deposits of the Flin Flon district are listed in the Flin Flon-Glennie Complex VHMS Deposits record.
The most recent source geological information used to prepare this summary was dated: 2012.
Record last updated: 13/11/2014
This description is a summary from published sources, the chief of which are listed below.
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References to this deposit in the PGC Literature Collection:
Ames, D.E., Galley, A.G., Kjarsgaard, I.M., Tardif, N. and Taylor, B. T., 2016 - Hanging-Wall Vectoring for Buried Volcanogenic Massive Sulfide Deposits, Paleoproterozoic Flin Flon Mining Camp, Manitoba, Canada: in Econ. Geol. v.111, pp. 963-1000|
Bleeker W 1990 - Thompson Area - General Geology and Ore Deposits: in Galley A G, Bailes A H, Syme E C, Bleeker W, Macek J J, Gordon T S, (Eds), Geology & Mineral Deposits of the Flin Flon and Thompson Belts, Manitoba, International Association on the Genesis of Ore Deposits Guide Book No. 10 Geological Survey of Canada, Open File 2165 pp 93-136|
Cole E M, Gibson H L and Lafrance B, 2007 - Preliminary description of the lithofacies and structure of the Schist Lake mine area, Flin Flon, Manitoba (part of NTS 63K12): in Report of Activities 2007, Manitoba Geological Survey Manitoba Science, Technology, Energy and Mines, GS-3 pp. 33-42|
DeWolfe Y M, 2011 - Geology east and west of the Mandy Road Fault in the Schist Lake–Mandy mines area, Flin Flon, west-central Manitoba (part of NTS 63K12): in Report of Activities 2011, Manitoba Geological Survey, Manitoba Innovation, Energy and Mines, GS-5 pp. 43–54|
Galley A G, et. al., 1990 - Introduction: in Galley A G, Bailes A H, Syme E C, Bleeker W, Macek J J, Gordon T S, (Eds), Geology & Mineral Deposits of the Flin Flon and Thompson Belts, Manitoba, International Association on the Genesis of Ore Deposits Guide Book No. 10 Geological Survey of Canada, Open File 2165 pp 1-5|
Koo J and Mossman D J, 1975 - Origin and metamorphism of the Flin Flon stratabound Cu-Zn sulfide deposit, Saskatchewan and Manitoba : in Econ. Geol. v.70 pp. 48-62|
Lafrance, B., Gibson, H.L., Pehrsson, S., Schetselaar, E., DeWolfe, Y.M. and Lewis, D., 2016 - Structural Reconstruction of the Flin Flon Volcanogenic Massive Sulfide Mining District, Saskatchewan and Manitoba, Canada: in Econ. Geol. v.111, pp. 849-875|
Ordonez-Calderon, J.C., Lafrance, B., Gibson, H.L., Schwartz, T. S., Pehrsson, J. and Rayner, N.M,. 2016 - Petrogenesis and Geodynamic Evolution of the Paleoproterozoic (~1878 Ma) Trout Lake Volcanogenic Massive Sulfide Deposit, Flin Flon, Manitoba, Canada: in Econ. Geol. v.111 pp. 817-847|
Schetselaar, E., Pehrsson, S., Devine, C., Lafrance, B., White, D. and Malinowski, M., 2016 - 3-D Geologic Modeling in the Flin Flon Mining District, Trans-Hudson Orogen, Canada: Evidence for Polyphase Imbrication of the Flin Flon-777-Callinan Volcanogenic Massive Sulfide Ore System: in Econ. Geol. v.111, pp. 877-901|
Syme E C, Bailes A H 1993 - Stratigraphic and tectonic setting of early Proterozoic volcanogenic massive sulfide deposits, Flin Flon, Manitoba: in Econ. Geol. v88 pp 566-589|
Trevor S M 1998 - Geology of the Trout Lake Mine: in Unpub. Hudson Bay Mining & Smelting Report 11p|
Whalen, J.J.B., Pehrsson, S.J. and Rayner, N.M., 2016 - Significance of Pre-1860 Ma Granitoid Magmatism for Crustal Evolution and Exploration Targeting in the Flin Flon Assemblage, Trans-Hudson Orogen, Canada: in Econ. Geol. v.111, pp. 1021-1039|
White, D.J., Malinowski, M., Devine, C., Gilmore, K., Schetselaar, E. and Pehrsson, S., 2016 - Drill Targeting with 3-D Seismics for Volcanogenic Massive Sulfide Exploration in the Flin Flon Mining Camp: in Econ. Geol. v.111, pp. 903-912,|
White, D.J., Mwenifumbo, C. J. and Salisbury, M.H., 2016 - Seismic Properties of Rocks from the Flin Flon Volcanogenic Massive Sulfide Camp: in Econ. Geol. v.111, pp. 913-931|
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