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Sherridon District - Sherridon, Bob Lake, Jungle Lake |
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Manitoba, Canada |
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Cu Zn Au Ag
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Super Porphyry Cu and Au
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IOCG Deposits - 70 papers
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All papers now Open Access.
Available as Full Text for direct download or on request. |
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The Sherridon and sub-economic Bob Lake, Jungle Lake, Park Lake and Fidelity volcanic hosted massive sulphide (VHMS) zinc-lead-copper deposits, are located ~600 km NNW of Winnipeg and 60 km NE of Flin Flon in northern Manitoba, Canada, (#Location: 55° 8' 12"N, 101° 6' 30"W).
Geological Setting
The regional and district scale setting and context of this group of deposits is described in the separate Flin Flon-Glennie Complex VHMS Deposits - Overview record.
The original discovery of mineralisation at Sherridon was made by Philip Sherlett in 1922. Sherritt Gordon Mines Limited, formed in 1927 to mine the deposit, commenced mining in April 1931 and continued to June 1932 when operations were suspended. Production resumed on August 1937. The mine was operated for an eight month period (April to November) each year and was closed for the winter months, until September 20, 1951 when mining was finally terminated.
The Sherridon deposit is hosted by rocks of the Sherridon Group within the large, highly metamorphosed, east-west trending, paragneiss dominated Kisseynew Domain of the Trans Hudson orogen. The Sherridon and underlying Nokomis Group have been correlated with the Missi and Amisk groups respectively of the Flin Flon-Glennie Complex that hosts the VHMS deposits of the Flin Flon and Snow Lake districts to the south, as detailed in the separate Flin Flon-Glennie Complex VHMS Deposits record. The boundary between the Flin Flon Glennie Complex and the Kisseynew Domain is defined by the biotite-sillimanite-almandine isograd. In addition, the rocks to the north of this isograd in the Kisseynew Domain, have a higher sedimentary and lower volcanic facies content than their equivalents to the south in the Flin Flon-Glennie Complex.
In the vicinity of the Sherridon deposit, the Sherridon Group defines a crescent shaped, 15 x 5 km, basinal structure, surrounded by Nokomis Group rocks. Sherridon is on the western limb of this structure. Interference folding from the three episodes of deformation recognised have influenced this structural geometry. F1 is represented by small isoclinal folds in the foliation plane, followed by F2 recumbent folding with axial planes dipping north, and F3 folds with axial planes trending northwesterly.
The sequence within the host Sherridon Group, is as follows (after Froese and Goetz, 1980), from the basal contact with the underlying quartz-plagioclase-biotite paragneisses of the Nokomis Group:
• Calc-silicate gneiss - layered, fine to medium grained rock containing quartz, andesine-labradorite and hornblende, with bands of K feldspar, biotite, scapolite, diopside and calcite.
• Fine to medium grained, quartz-rich gneiss, composed of quartz, oligoclase-andesine, microcline, biotite and almandine. This is the most abundant facies of the Sherridon Group. This unit also contains lenses of pelitic schists (fine to medium grained quartz, oligoclase-andesine, biotite, almandine, sillimanite and locally cordierite), calc-silicates and both layered and massive amphibolite. Copper-zinc sulphides are found along two stratigraphic horizons within this unit, in quartz-rich gneisses. These horizons are marked by discontinuous lenses of massive sulphides and intermittent zones of disseminated sulphides. Locally, sulphide mineralisation is associated with cordierite-anthophyllite rocks. The lower of the two suphide bearing horizons hosts the Sherridon deposits.
• Impure marble and calc-silicate gneiss of the type described for the basal unit.
• Well foliated, fine grained biotite-garnet schist.
• Upper quartz-rich gneiss, similar to the base lithology in the second unit.
The Sherridon Group was intruded by massive to weakly foliated, medium grained gabbro, pyroxenite, late stage, weakly foliated medium grained granodiorite. Masses of felsic pegmatite are present throughout the area.
Parts of the Sherridon orebodies have been remobilised into masses of pegmatite. The iron sulphide in the remobilised ore is typically pyrite. Intrusion of the pegmatite post-dates metamorphism.
Near the base of the Sherridon Group, rocks have a higher biotite content and display compositional layering on a scale of 10 to 30 cm. Higher in the sequence, they become more felsic and layering becomes indistinct. Locally the grain size becomes coarser and a few incipient granitic segregations are present, whilst quartz-sillimanite nodules occur in some layers.
Disseminated pyrrhotite in cherty parts of calc-silicate rocks is very common in the Sherridon Group, particularly in the calcsilicate layer at the base of the group. This type of sulphide occurrence is characteristically devoid of copper and zinc.
The lower of the two sulphide bearing quartz-rich gneisses that hosts the Sherridon deposits, can be traced north to Singsing Lake, where disseminated chalcopyrite has been encountered ~5.5 km north of Sherridon. The sequence then swings east around a D3 fold nose, and can be traced to the Park Lake deposit, 3.5 km east of Singsing Lake. From there it becomes indistinct but apparently continues to the Jungle Lake deposit, 6 km further east.
The Bob Lake deposit, 3.5 km SW of Jungle Lake (and 5.5 km NE of Sherridon), marks the second mineralised horizon, which extends to the east to include several showings between Bob Lake and Star Lake (8 km to the east). The Fidelity deposit appears to lie on the same horizon, although the continuation of this horizon to the west towards that deposit is not well defined.
At Sherridon, two orebodies, East and West, were developed along a local lithological contact between gneissic quartzite (meta-arkose) and an overlying garnetiferous hornblende gneiss, both members of the Sherridon group (Farley, 1949). The contact had been intruded by a pegmatite sill, with numerous offshoots breaking through the footwall gneiss and hanging wall quartzite. The pegmatite is composed of white to pinkish plagioclase, colourless to pink quartz and muscovite mica. Some greyish white calcite is also present. According to Farley (1949), the deposit was localised along and within a pegmatite sill that intruded along the shear zone at the contact of the gneissic quartzite and hornblende gneiss. The emplacement of the deposit was considered to be a sulphide replacement of the tabular sill-like pegmatite mass and in many of its dyke-like offshoots breaking through the footwall gneiss and hanging wall quartzite. Approximately 25% of the Sherridon production was mined from such offshoot orebodies. These bodies were all localised within pegmatite masses that had intruded and occupied folded structures in the hanging wall hornblende gneiss (Farley, 1949). Pegmatite residuals, occurring as unreplaced fragments, were prominent throughout the ore zone (Farley, 1949).
An alternative interpretation of the formation of the deposit, is that, the temperatures and pressures producing the metamorphic assemblage above the biotite-sillimanite-almandine isograd in the Kisseynew Domain, which were also sufficient to generate the migmatites found in the host sequence, partially melted the pre-existing sulphide body and physically redistributed the melt within the shear zone and crosscutting structures on the deposit margin (cf., the Broken Hill deposit in Australia). The pegmatite may represent the segregated silicate gangue melt, which was also redistributed and reacted with the sulphide melt during recrystallisation (Porter, 2014 - suggestion).
The total length of the mineralised contact zone was ~5 km, with a barren gap of 1100 m along strike between the East and West orebodies. The West orebody was relatively regular, persisting over a strike length of 2400 m, with a thickness that averaged 4.7 m. The deposit extended down dip for ~450 m (Farley, 1949) and had an average grade of 2.76% Zn, 2.91% Cu, plus a low grade zone containing 0.80% Zn, 1.40% Cu (Davies et al., 1962). In contrast, the East orebody was much more lenticular, and the thickness was accordingly more variable and was locally much thicker than the West orebody, but averaged 4.6 m. It had a strike length of 1300 m, but a maximum width of only 76 m (Farley, 1949) and an average grade of 5.78% Zn, 2.14% Cu (Davies et al., 1962).
The deposit strikes NW to NNW, with variable dips. At the NW end, it dips 30°NE, flattening down dip to a low angle. South-easterly along the deposit, the dip steepens and at the East Shaft, the orientation is steeply to the SW. To explain these variations, Bruce (1929) suggested that at Sherridon, the host unit had been dragged into a sharp fold, the axis of which plunged at an angle of between 20 and 25° nearly due east. Overall, the deposit is conformable to the host gneisses, apart from the dyke-like offshoots which cross the structure as described above.
The ore consisted of a coarse aggregate of massive to disseminated sulphides, which include, in order of abundance, were pyrite, pyrrhotite, chalcopyrite, sphalerite (marmatite), minor cubanite, rare arsenopyrite and small amounts of gold and silver. Pyrite was approximately twice as plentiful as pyrrhotite. Pyrrhotite is replaced by the chalcopyrite and sphalerite. Small amounts of late stage marcasite is recorded and galena was also present.
The non-metallic gangue recognised are quartz, amphibole, possibly actinolite, chlorite, garnet, biotite and scapolite. Quartz is quite abundant in the ore, mostly as rounded particles which have rough surfaces as if they had been etched. The insoluble gangue content of the ore-bearing material averaged 35% (Farley, 1949)
Reserve + production figures for these deposits are as follows:
• Sherridon - 7.739 Mt @ 2.37% Cu, 2.28% Zn, 0.63 g/t Au, 18.96 g/t Ag,
• Bob Lake 2.42 Mt @ 1.33% Cu, 1.18% Zn,
• Jungle Lake 3.76 Mt @ 1.42% Cu, 1.1% Zn.
The most recent source geological information used to prepare this decription was dated: 1980.
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.
Sherridon Jungle Lake
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Porter GeoConsultancy Pty Ltd (PorterGeo) provides access to this database at no charge. It is largely based on scientific papers and reports in the public domain, and was current when the sources consulted were published. While PorterGeo endeavour to ensure the information was accurate at the time of compilation and subsequent updating, PorterGeo, its employees and servants: i). do not warrant, or make any representation regarding the use, or results of the use of the information contained herein as to its correctness, accuracy, currency, or otherwise; and ii). expressly disclaim all liability or responsibility to any person using the information or conclusions contained herein.
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