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Chibougamau - Chapais District

Quebec, Canada

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The Chibougamau-Chapais District of central Quebec, is located some 350 km to the north-east of Val d'Or and 270 km east of Matagami, and occupies a WSW-ENE trending, ~60 km long interval, towards the eastern extremity of the Archaean Abitibi greenstone belt of the Superior Craton in southeastern Quebec, Canada (#Location: 49° 52' 18"N, 74° 19' 59"W - Merrill Island).

The district has produced in excess 85.7 Mt of ore from a range of deposits that have yielded 1.57 Mt of Cu, 176 t (5.6 Moz) of Au, 108.8 t of Ag, and 76066 t of Zn to date from a variety of styles of ore, but is mostly characterised by copper-gold vein deposits distinct from typical greenstone hosted quartz-carbonate veins.

Regional Setting

The Archaean Roy Group represents the oldest rocks within the Chapais-Chibougamau area, and consists of a 3 to 4 km thick pile of basalt to basaltic andesite, overlain by volcaniclastic and sedimentary rocks (Dimroth et al., 1984; Daigneault et al., 1990). This sequence is divided into three volcanic cycles (Leclerc et al., 2012), with voluminous basal mafic tholeiitic volcanic rocks being capped by a thin succession of calc-alkaline felsic volcanic rocks, banded iron formations, and cherts that represent regional stratigraphic markers.
    The first cycle, represented by the Chrissie Formation, has been dated at 2791.4±3.2 Ma; (David and Dion, 2010) and comprises basic lavas overlain by intermediate to felsic volcaniclastic rocks and rhyolites.
    The second cycle has been dated at ~2730 to 2720 Ma by Daigneault et al. (2004), Pilote and Guha (2006) and Leclerc et al. (2008), and resulted in the formation of an extensive subaqueous basalt plain. This cycle comprises the Obatogamau Formation (tholeiitic mafic volcanic rocks) and the Waconichi Formation, which is subdivided into five members: the lower two Lemoine and Scott members predominantly consist of porphyritic rhyolites, dacites, and andesites. The Scott Member is overlain by transitional to calc-alkaline mafic volcanic rocks, calc-alkaline volcaniclastic rocks, and turbidites of the regional Allard Member (Leclerc et al., 2011). The Portage Member is composed of Algoma-type banded iron formation and minor volcaniclastic rocks (Henry and Allard, 1979; Roy et al., 2007) and is interlayered with mafic volcanic and volcaniclastic rocks of the contemporaneous Scott Member. The Portage Member is also the northern equivalent of the Queylus Member found elsewhere in the district.
    The third cycle has been dated at ~2720 to 2705 Ma (Daigneault et al., 2004; Pilote and Guha, 2006; Leclerc et al., 2008), and is interpreted to represent an emerging volcanic arc built on the remnants of the older volcanic rocks (Daigneault et al., 2004). The lowermost sections of this cycle comprises basalt and basaltic andesite flows and sills, and intermediate to felsic volcaniclastic rock of the Bruneau (or Gilman) Formation overlain by the Blondeau Formation, a sequence of intermediate to felsic flows, sills and volcanic derived metasediments and felsic volcaniclastic deposits considered to be the remnants of variably preserved volcanic edifices (Couture, 1986; Pilote, 1986; Côté-Mantha, 2009). The uppermost unit are the intermediate-felsic volcanic rocks of the "Scorpio" Formation. These cycle 3 volcanic rocks are genetically related to the Chibougamau Pluton (Racicot, 1980, 1981; Racicot et al., 1984; Daigneault and Allard, 1990) described below.
    The Roy Group was intruded by subvolcanic gabbro sills and mafic-ultramafic (anorthosite, pyroxenite) rocks of the 2728.3±1.5 Ma Lac Doré Complex (Mortensen, 1993) and the 2717±1 Ma peridotite, gabbro, pyroxenite, leucogabbro and diorite of the Cummings Complex (Mortensen, 1993; Bédard et al., 2009).
    This district is cored by a series of synvolcanic plutons, e.g., the Chibougamau pluton, a polyphase, tonalitic-dioritic, calcalkaline intrusion emplaced into the Doré Lake Complex at around 2718 Ma (Krogh, 1982; Pilote et al., 1996; Joanisse, 1998). It includes 2718±2 and 2716±2.5 Ma diorite (Krogh, 1982; Joanisse, 1998) and 2714±2.5 and 2715±1 Ma synvolcanic diorite and tonalite dykes (Pilote et al., 1997). The Chibougamau pluton is in turn intruded by younger (2705.1±1.5 Ma) syntectonic felsic dykes (David et al., 2011) and leucotonalite dated at 2701.7±2.9 Ma (McNicoll et al., 2008). Small satellite plutons (e.g., the 2707.6±1.4 Ma Lac Line tonalite; Côté-Mantha, 2009; Côté-Mantha et al., 2012) and 2712±8 Ma quartz and feldspar phyric intrusions (Mortensen, 1993) are coeval with the late pulses of volcanic activity within the Roy Group.
    The upper contact of the Roy Group with overlying sedimentary rocks of the <2691.7±2.9 Ma Opémisca Group (David Côté, 2007) and the <2707.3±2.3 Ma Caopatina Formation (David et al., 2006) is marked by east-west trending faults and a regional unconformity (Mueller et al., 1989; Daigneault, 1991), although to the north of Chibougamau the contact is locally depositional (Moisan, 1992). The sedimentary rocks of the Opémisca Group are interpreted to represent two depositional cycles of repeated terrigenous and shallow marine sedimentation in a backarc or marginal basin, derived from the erosion of a tectonically uplifted hinterland contemporaneous with high K, andesitic (shoshonitic) to basaltic volcanism (Mueller and Dimroth, 1987; Mueller et al., 1989) and alkaline plutonism. These comprise the Daubrée and overlying Stella formations, both of which are composed of conglomerates, sandstones and argillites.
    The Proterozoic Chibougamau Formation, which comprises conglomerates and argillites (interpreted as "glaciogene"), unconformably overlies Archaean rocks, and are probable correlates of the Huronian Gowganda Formation of Ontario (Long, 1974, 1981), (Allard et al., 1979). Deposition occurred prior to intrusion of the Nipissing dolerite dykes at approximately 2150 Ma (Morris, 1977). The formation is folded (Long, 1981) and brecciated along reactivated NE-trending fault zones (Daigneault, 1991).

Structure

North-, NW- and NE-striking synvolcanic and synmagmatic structures (D0), with <150 m lengths (Bouchard, 1986; Pilote, 1986), were followed by three Archaean deformation events (D1-D3) and late (D4) structures, attributed by Daigneault and Allard (1984) and Daigneault et al. (1990) to the Mesoproterozoic Grenvillian orogenic cycle (Davidson, 1995). Fairly widespread F1 folds have north-south axial surfaces.
    The dominant east-west structural and stratigraphic trend of the Chapais-Chibougamau area, which extends westward to the Matagami area, parallels the regionally pervasive, steeply dipping S
2 schistosity which is axial planar to F2a isoclinal folds. The F2a axial planes are locally reoriented by crosscutting transcurrent to transpressional shear zones (Leclerc, 2011). "Dome and basin" and type 3 fold interference patterns (Ramsay, 1967) are the result of interaction between F2a and F1 folds at all scales (Dimroth et al., 1986; Daigneault and Allard, 1990).
    Regional east-west deformation corridors (e.g., Faribault, Antoinette, Lac Sauvage, Kapunapotagen and Guercheville corridors) are characterised by steeply north- and south-dipping reverse shear zones that are contemporaneous with SE-trending dextral shears (Daigneault and Allard, 1990).
    While the NE-SW trending sinistral Gwillim and Taché shear zones crosscut the east-west shears, they were developed during the same regional north-south D
2 shortening event. F2a folds adjacent to the Gwillim and Taché shear zones are refolded by tight to isoclinal folds with E-W axial surface (F2b) resulting from progressive deformation during displacement along these shear zones (Leclerc, 2011). Stratigraphic relationships and age dating constrains D2 deformation, and gold deposits in the southern Abitibi greenstone belt to being no older than 2680 Ma (Percival, 2007; Bateman et al., 2008).
    The dextral, NE-striking Lac Doré-McKenzie shear zone cuts earlier east-west D
2 shear zones and F2a, and is attributed to a third event, D3, which predated emplacement of the 2411 to 2405 Ma (Krogh, 1994) Palaeoproterozoic du Chef dyke swarm (Ernst et al., 1996). Near the Grenville Front tectonic zone, a NNE-SSW cleavage (S4) overprints ENE-WSW oriented S2 schistosity, and is attributed to Mesoproterozoic Grenvillian deformation (D4). The NNE-striking shears were reactivated during Grenvillian deformation and late, NNE-striking faults are also attributed to D4et al., 1990).

Ore Deposits

The deposits of the district range from:
i). Volcanogenic massive sulphide deposits with Cu, Zn and Ag, e.g., Astoria (Zn-Cu); Bruneau (Cu-Au-Ag-Zn); Lemoine (Zn-Cu-Ag-Au); Lempira (Au-Ag-Zn-Cu); Scott (Zn-Cu-Ag-Au); Lac des Vents/Chesbar (Cu) - VHMS deposits in the district are closely linked to the NNW- to NNE-striking synvolcanic faults developed in volcanic rocks of the Roy Group. Deposits occur in all three volcanic cycles of the Roy Group (as outlined above) and are usually located in strata deposited at the end of the volcanic cycle near the interface from tholeiitic to transitional mafic volcanic rocks and tholeiitic to calc-alkaline felsic rocks (Lafrance et al., 2006; Leclerc et al., 2008, 2011). Chemical and clastic sedimentary units commonly cap the volcaniclastic rocks in the uppermost part of volcanic cycles, accompanied in various areas by pervasive silica-chlorite-epidote alteration and Cu-Zn rich mineralisation (Trudeau, 1981; Guha et al., 1988; Côté-Mantha, 2009). The best example of such alteration has a width of <800 m, but considerable lateral extent (>30 km), and correspond to well-defined positive magnetic and electromagnetic anomalies. Individual deposits comprise massive pyrite-pyrrhotite ± sphalerite and chalcopyrite resulting in discontinuous Zn and Cu mineralisation.
    In the first cycle, the Astoria (Zn-Cu) deposit, near the top of the Chrissie Formation comprises a ~10 Mt massive sulphide body which is up to 20 m thick.
    Deposits within the second cycle included the Lemoine Mine (0.758 Mt @ 4.2 wt.% Cu, 9.56 wt.% Zn, 4.2 g/t Au, 83.38 g/t Ag; Lafrance et al., 2006) within the Waconichi Formation, occurring as a massive sulphide lens and stockwork development formed in the uppermost part of the tholeiitic, porphyritic rhyolites, near or at the contact with overlying transitional to calc-alkaline mafic volcanic rocks of the Lemoine Member (Lafrance et al., 2006; Roy et al., 2007). The Scott deposit, on the opposite (northern) side of the Lac Doré Complex (3.6 Mt @ 1.1 wt.% Cu, 5.2 wt.% Zn, 0.3 g/t Au, 36 g/t Ag; Salmon, 2010), comprises complexly deformed massive sulphide lenses and stringers, hosted in a sequence of coherent felsic to intermediate volcanic rocks similar to the Lemoine Member, but attributed to the Scott Member.
    In the third cycle, the Bruneau deposit (0.063 Mt @ 1.52% Cu, 15.09 g/t Ag, 0.69 g/t Au; Lacroix, 1988), is located 15 km NE of Chibougamau. It is hosted by massive to pillowed basalts of the Bruneau Formation that are intruded by gabbro sills and quartz and felspar porphyritic sills (Trudeau, 1981; Leclerc et al., 2011). Mineralisation comprised chalcopyrite-pyrite veins and stringers containing minor quartz and carbonate. The veins were emplaced in north-south oriented fractures developed at the contact between basalts and a thick gabbro sill (Prochnau, 1968). Some 4500 t of ore averaging 1 wt.% Cu were extracted from a disseminated pyrite-pyrrhotite-chalcopyrite stratabound orebody associated with silicified and epidote-rich, medium to coarse rhyolitic lapilli tuff. This unit is overlain by two massive magnetite±pyrite±chalcopyrite ironstones intervals that are 40 and 80 cm thick, separated by a 1 m thick laminated chert (Leclerc et al., 2011b). In the Chapais area, the 8-5 zone of the Cooke mine is a small pyrrhotite-chalcopyrite-sphalerite massive sulphide lens located at the interface between rhyolites and volcaniclastic rocks of the Blondeau Formation, at the base of the Bourbeau sill (Bélanger, 1979b; Dubé and Guha, 1989).
ii). Synmagmatic Fe-Ti-V and Ni-Cu-platinum group element (PGE) mineralisation in mafic to ultramafic layered complexes and sills - Rhythmically layered Ti-rich semi-massive to massive magnetite and ilmenite intervals occur within a 200 m thick interval of magnetite-dominant and magnetite-rich gabbros of the lowermost Layered zone or Series of the Lac Doré Complex (Allard, 1976, 2002; Girard and Allard, 1998; Taner et al., 2002). This interval hosts the McKenzie Bay (or Lac Doré) Fe-Ti-V deposit (Allard, 1967, 1976, 2002), with an estimated 450 Mt @ 1.4 to 1.6 wt.% V
2O5 (Taner et al., 2002) or 102 Mt @ 35% magnetite, 17.4% ilmenite and 0.50% V2O5 (Pacific Ore Mining website, 2012). This deposit and other nearby Fe-Ti-V occurrences are preferentially located on the steeply dipping south limb of a regional anticline that is cored by the Chibougamau pluton (Allard, 2002). The deposit occurs adjacent to an offset in a 16 km long, NE-SW trending positive magnetic anomaly. Other Fe-Ti-V occurrences located along strike also correspond to similar breaks or offsets of the strongly magnetic layers. Gabbros of the Lac Doré Complex and pyroxenite of the Cummings Complex contain anomalous, but not economic Ni-Cu±PGE levels (Leclerc et al., 2012).
iii). Synmagmatic, early polymetallic gold bearing sulphide veins with associated Ag, Zn, Pb, As and Sb, e.g., Brosman (Au-Ag-Cu); Béarmac II (Au-Cu-Ag); David Ouest (Au-Ag-Zn-Cu); Dulieux (Au-Cu-Ag); Islet Scott (Au-Zn); Silver Tower (Au-Ag-Zn-Cu) - Between the Antoinette (an east-west, south vergent thrust) and the Gwillim (an ENE-WSW dextral structure) shear zones (north of Chibougamau), sinistral north-south-, NNW- and NNE-striking synvolcanic faults offset volcanosedimentary rocks of the Roy Group, comagmatic gabbro sills and the Cummings mafic-ultramafic sills (Pilote, 1986, 1987; Côté-Mantha, 2009; Côté-Mantha et al., 2012), and host Au-Ag veins with subordinate Cu-Zn-Pb. These faults are cut by reverse east-west-trending D
2 ductile shear zones, while ~2.72 Ga Pb-Pb model ages for mineralisation at the Berrigan deposit hosted by these structures (Thorpe et al., 1981, 1984) also support a synvolcanic origin for the mineralisation. Other similar structures host Au-Ag-Cu-Zn-Pb polymetallic veins in the the Blondeau Formation, Chibougamau pluton (e.g., the Béarmac II deposit at the intersection of D1 sinistral-reverse and D2 dextral-reverse shear zones).
    Alteration includes propylitic to sodic-potassic and chlorite assemblages in volcanic rocks and in mafic-ultramafic to intermediate intrusive rocks, sericite in felsic intrusive and volcanic rocks, and tourmaline alteration in a brecciated tonalite (Pilote, 1986, 1987; Côté-Mantha, 2009; Côté-Mantha et al., 2012). These assemblages are interpreted to suggests a contribution from magmatic-hydrothermal fluids related to proximal synvolcanic felsic intrusions (i.e., the Chibougamau and Lac Line plutons).
    None of these veins has been mined to any significant degree.
iv). Chibougamau-type Cu-Au-veins, which comprise two variants, namely: a). pyrite-chalcopyrite-pyrrhotite-sphalerite-galena shear veins within SE-trending, dextral D
2 shear zones [e.g., Cedar Bay (Cu-Au); Chib Kayrand (Cu-Au); Copper Cliff (Cu-Au-Ag); Copper Rand (Cu-Au); Fosse Merrill (Cu-Au); Jaculet (Cu-Au-Ag); Kokko Creek (Cu-Au); Merrill Island (Cu-Au); Obalski (Cu-Au-Ag); Principale (Cu-Au)], and b). massive pyrite-chalcopyrite-pyrrhotite and magnetite veins in the Henderson-Portage shear zone that is parallel to the D3 NE-SW dextral Lac Doré-McKenzie shear zone [e.g., Henderson I & II (Cu-Au); Portage (Cu-Au-Ag)]; (Pilote et al., 1995; Tessier et al., 1995).
    At the Merrill mine, 2714±32 Ma; (Pilote et al., 1997) diorite dykes intrude the gabbroic anorthosite of the Lac Doré Complex. Both are cut by veins, veinlets, and disseminated pyrrhotite-chalcopyrite-pyrite, which are in turn cut by 2715.2±0.7 Ma porphyritic tonalite dykes (Pilote et al., 1997) that are coeval with the the Chibougamau pluton. These tonalite dykes occur within, and are deformed by SE-striking D
2 shear zones, suggesting some D2 shears reactivate earlier structures.
    Pilote et al. (1995, 2006) regarded the spatial relationships of the veins with pre-D
2 porphyritic tonalite dykes, the kilometre-scale halos of phyllic and propylitic alteration and hundred metre-scale breccia zones with stockworks, veins and disseminations of pyrite-pyrrhotite and chalcopyrite-molybdenite on both flanks of the Lac Doré Complex (e.g., Lac Clark, Queylus breccia, Devlin and Corner Bay prospects; see Fig. 2) to be clear evidence of Cu-Au-Mo porphyry-type mineralisation. However, within the more structurally complex corridors such evidence is obliterated by transformation of protoliths into mylonitic schists and by bulk flattening strain, such as conjugate shear bands, that may have been superimposed upon earlier non-coaxial fabrics, and physically and chemically re-distributed the mineralised zone into post-depositional shears.
    Production from the more significant deposits include:
        Bateman Bay, from 1969 to 1971 - 0.512 Mt 2.09% Cu, 3.09 g/t Au (Lacroix,1988),
        Cedar Bay, from 1958 to 1990 - 3.878 Mt 1.56% Cu, 3.22 g/t Au (Lacroix,1988),
        Chib Kayrand, from 1965 to 1972 - 0.114 Mt @ 1.36% Cu, 0.44 g/t Au (Lacroix,1988),
        Copper Cliff, from 1970 to 1974 - 0.864 Mt @ 1.6% Cu, 6.50 g/t Ag, 0.96 g/t Au (Lacroix,1988),
        Copper Rand, from 1959 to 1997 - 14.901 Mt @ 1.8% Cu, 2.76 g/t Au (Moorhead et al., 2009),
        Fosse Merrill, from 1958 to 1981 - 7.897 Mt@ 1.77% Cu, 0.60 g/t Au (Moorhead et al., 2009),
        Jaculet, from 1960 to 1971 - 1.091 Mt @ 1.84% Cu, 6.85 g/t Ag, 1.44 g/t Au (Lacroix (1988),
        Kokko Creek, from 1960 to 1975 - 0.751 Mt @ 1.98% Cu, 0.31 g/t Au (Lacroix, 1988),
        Merrill Island, from 1958 to 1981 - 2.506 Mt @ 1.46% Cu, 0.40 g/t Au (Lacroix, 1988),
        Obalski, from 1964 to 1965 - 0.075 Mt @ 1.2% Cu, 6.04 g/t Ag, 2.60 g/t Au (Lacroix, 1988),
        Principale, from 1955 to 1975 - 4.845 Mt @ 1.82% Cu, 1.53 g/t Au (Lacroix, 1988),
        Quebec Chibougamau gold field, from 1963 to 1971 - 0.212 Mt @ 1.8% Cu, 9.26 g/t Ag, 2.81 g/t Au (Lacroix, 1988),
        Henderson I, from 1959 to 1971 - 1.650 Mt @ 2.23% Cu, 1.40 g/t Au (Lacroix, 1988),
        Henderson II, from 1960 to 1988 - 8.316 Mt @ 1.78% Cu, 1.57 g/t Au (Lacroix, 1988),
        Portage, from 1960 to 1997 - 5.636 Mt @ 1.77% Cu, 3.59 g/t Ag, 3.91 g/t Au (Lacroix, 1988; Gaudreault et al., 1988).
        Zone S-3, from 1985 to 1989 - 0.287 Mt @ 0.37% Cu, 3.11 g/t Au (Lacroix, 1988),
    For a total of 53.536 Mt of ore.
v). Shear zone-hosted Au deposits (including Opemiska-type Cu-Au veins) - shear zone-hosted Au deposits occur within ductile to brittle-ductile east-west reverse shear zones, and in coeval conjugate NW-SE and NE-SE shear zones in broad east-west oriented deformation corridors. Gold is accompanied by pyrite±chalcopyrite±magnetite in a gangue of quartz-calcite-Fe carbonate-chlorite±tourmaline. Within mineralised shear zones, the volcanosedimentary country rocks have been transformed into mylonitic chlorite-sericite-carbonate-magnetite schists over widths of tens of metres. They are characterised by strong Fe carbonate alteration with epidote-magnetite-fuchsite in the core and chlorite-calcite-magnetite on the peripheries of the shear (Guha et al., 1988; Dubé and Gosselin, 2007). Shear zones are generally present as narrow, <5 m wide corridors with sharp contacts between the sheared schists and undeformed competent rocks such as tonalite of the Chibougamau pluton or granophyres of the Lac Doré Complex. Country rocks hosting mineralisation are very variable, including almost all significant Archaean lithologies within the district from gabbro to diorite and tonalite as well as mafic and felsic volcanic rocks and felsic sills. Most Au occurrences located in areas where shear zones are cut by numerous NE to NNE cross shear zones (Dion and Maltais, 1998; Dion and Guha, 1994).
    Shear zone-hosted Au deposits are preferentially developed within regional east-west striking deformation corridors, and along NNE-striking sinistral shear zones, while "Opemiska type" Cu-Au veins occur within regionally overturned anticlines in mafic sills of the Cummings Complex.
    Opemiska-type Cu-Au veins in the Chapais area occur within east-west oriented reverse D
2 shear zones that parallel the axial surface of the F2b Beaver Lake anticline in the upper gabbro of the Ventures sill. These veins are also reoriented into NW-SE D2 shear zones and faults. At the Springer mine, the ore comprises semimassive to massive chalcopyrite-magnetite-quartz-carbonate±pyrite veins and veinlets in a subophitic gabbro. The gabbro between east-west trending D2 shear zones contains veins and veinlets with east-west and subordinate NW-SE strikes (Leclerc et al., 2011). To the south of Chapais, the F2a Campbell anticline is offset sinistrally by the Gwillim shear zone.
    Field mapping (Leclerc et al., 2011) and structural geology/aeromagnetic image interpretation (Harris et al., 2009; Leclerc, 2011) suggest that Opemiska-type Cu-Au vein distribution is linked to regional D
2 deformation, as the mineralisation is found within veins developed in F2b folds that refold F2a structures as the result of progressive deformation during sinistral displacement along the NW-SE trending Gwillim shear zone.
    Production from the more significant deposits include:
     - Shear zone-hosted gold deposits
        Lac Gwillim, from 1980 to 1984 - 0.254 Mt @ 4.56 g/t Ag, 4.79 g/t Au (Rive et al. 1985; Lavergne 1985),
        Joe Mann, from 1956 to 1959, 1974 to 1975 and 1987 to 2007 - 4.754 Mt @ 8.26 g/t Au (Houle et al. 2008),
        Norbeau, from 1964 to 1969 - 0.380 Mt @ 1.88 g/t Ag, 13.98 g/t Au (Lavergne 1985),
        Cooke, from 1976 to 1989 - 1.973 Mt @ 0.66% Cu, 5.04 g/t Au (Lacroix, 1988),
     - Opemiska type Cu-Au veins
        Springer, from 1953 to 1991 - 12.965 Mt @ 2.54% Cu, 0.28 g/t Ag, 0.48 g/t Au (Lacroix, 1988),
        Perry, from 1965 to 1991 - 9.042 Mt @ 2.19% Cu, 0.11 g/t Ag, 0.02 g/t Au (Lacroix, 1988),
        Robitaille, from 1969 to 1972 - 0.188 Mt @ 2.04% Cu, 11.21 g/t Ag, 0.53 g/t Au (Lacroix, 1988),
    For a total of 29.556 Mt of ore.

The Chevrier gold deposit is located in the northeastern part of the Abitibi Subprovince, ~30 km south of Chibougamau, within the Chevrier volcanic centre (CVC) of the southern Chibougamau District. This calc-alkaline volcanic centre evolved from mafic to felsic in a submarine environment and comprises a 5 to 6 km thick pile of volcaniclastic rocks and lava flows, interdigitated with mafic volcanic rocks and numerous gabbro sills. The Chevrier deposit is spatially associated with the uppermost unit which is composed predominantly of massive dacite to rhyolite, dated at 2730 Ma.
    The Chevrier deposit is divided in two zones: i). The North Zone, which is composed of high-grade, discordant quartz-carbonate veins and disseminated pyrite mostly within melanocratic gabbro dykes, with a resource of ~3.7 Mt @ 5.42 g/t Au (Inmet Mining, unpublished report, 1994) and ii). The South Zone, within a low-grade, concordant pyrite envelope associated with quartz-carbonate-pyrite stockwork veinlets, with a total estimated resource of 230 Mt @ 0.34 g/t Au (Inmet Mining, unpublished report, 1994). The North Zone is interpreted to represent a greater depth of formation than the South Zone which has characteristics of eipzonal deposition.
    Both zones are strongly deformed with well developed carbonate, sericite and chlorite alteration. Although these zones share many features characteristic of orogenic deposits, the overprinting of the deposit by structures associated with the major deformation events suggests that mineralisation was pre-deformation. In addition, felsic dykes associated with the formation of the CVC crosscut auriferous veins and zones, further suggesting a synvolcanic timing for the gold emplacement.
    The Chevrier deposit is classified as a noncarbonate-hosted stockwork and disseminated deposit and shows many similarities with the strata-bound manto gold deposits of the Coastal Belt of Chile (e.g., Andacollo). Dating of mineralisation indicates ore emplacement more than 25 Ma before the onset of the orogeny affecting this part of the Abitibi subprovince.

Much of this record is summarised and paraphrased from Leclerc et al. (2012).

The most recent source geological information used to prepare this summary was dated: 2012.     Record last updated: 26/10/2012
This description is a summary from published sources, the chief of which are listed below.
© Copyright Porter GeoConsultancy Pty Ltd.   Unauthorised copying, reproduction, storage or dissemination prohibited.


Merrill Island, Chibougamau

  References & Additional Information
 References to this deposit in the PGC Literature Collection:
Cote-Mantha O, Daigneault R, Gaboury D, Chartrand F and Pilote P,  2012 - Geology, Alteration, and Origin of Archean Au-Ag-Cu Mineralization Associated with the Synvolcanic Chibougamau Pluton: The Brosman Prospect, Abitibi Greenstone Belt, Canada: in    Econ. Geol.   v.107 pp. 909-934
Leclerc F, Harris L B, Bedard J H, van Breemen O and Goulet N,  2012 - Structural and Stratigraphic Controls on Magmatic, Volcanogenic, and Shear Zone-Hosted Mineralization in the Chapais-Chibougamau Mining Camp, Northeastern Abitibi, Canada: in    Econ. Geol.   v.107 pp. 963-989
Legault, M.  and Daigneault, R.,  2006 - Synvolcanic gold mineralization within a deformation zone: the Chevrier deposit, Chibougamau, Abitibi Subprovince, Canada: in    Mineralium Deposita   v.41, pp. 203-228.
Mercier-Langevin P, Lafrance B, Becu V, Dube B, Ingrid Kjarsgaard I and Guha J,  2014 - The Lemoine Auriferous Volcanogenic Massive Sulfide Deposit, Chibougamau Camp, Abitibi Greenstone Belt, Quebec, Canada: Geology and Genesis : in    Econ. Geol.   v.109 pp. 231-269


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