Mt Polley - Caribou, Bell, Springer, Wight

British Columbia, Canada

Main commodities: Cu Au
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The Mt Polley porphyry copper-gold operation is located in central British Columbia, Canada. A central plant services a series of pits, including the original Caribou-Bell, as well as the newer Springer and Wight deposits, all within a 2 km radius.

At the Cariboo-Bell deposit an alkalic porphyry of the Copper Mountain Suite, comprises a sub-volcanic, multiple phase, syenitic laccolith of earliest middle Jurassic age, emplaced in a trachy-basalt eruptive centre. The intrusive complex includes a pre-ore syeno-diorite phase followed by a monzonite porphyry and the development of an intrusive breccia which apparently provided the ground-preparation. This was followed by post-ore monzonite porphyry and an augite porphyry. The intrusive complex cuts the upper part of the comagmatic Upper Triassic Takla Group which is composed of green augite trachy-basalt flows and volcaniclastics and purple analcite trachy-basalt flows as illustrated on Figure 30 (Hodgson, etal., 1976, Dawson, etal., 1991).

Mineralisation is concentrated in two adjoining intrusive breccias near the top of the syenite laccolith. The western is oval shaped in plan and dips steeply to the west. It has a diameter of around 450 m and drilled vertical extent of at least 275 m. The eastern is lenticular to tabular, being 1100 m long and 200 to 400 m wide, and dips moderately to the east. Together they are interpreted as a pipe and associated sill-like offshoot. Both consist of monzonite and syeno-diorite fragments in a syenite matrix (Hodgson, etal., 1976).

The principal minerals are magnetite (4 to 8%) and auriferous chalcopyrite (1 to 3%), which occur as disseminations and veinlets, and in cavities in the breccia. Native gold occurs as microscopic inclusions within chalcopyrite. Locally the magnetite is massive and forms a breccia, particularly along the southern margin of the deposit. Pyrite is abundant (up to 6%) in an elongate umbrella, east of, or above the breccias and the mineralisation, forming a partial halo with dimensions of 4500 x 1000 m at surface which coincides with the epidote alteration. Pervasive salmon pink potash feldspar with biotite and diopside alteration over an area with a diameter of 900 m coincides with the breccias, surrounded successively by brown garnet-epidote and epidote alteration zones in both the intrusives and the volcanics. Prehnite, zeolites and carbonates are common in and around the mineralised breccias. Biotite occurs as disseminations and as clusters, books and veinlets (Hodgson, etal., 1976, Dawson, etal., 1991).

Total Proven and Probable reserves in 2005:  44 Mt @ 0.45% Cu, 0.30 g/t Au.
      mainly in the Wight, Bell and Springer open pits
Measured and indicated resources were:   68.5 Mt @ 0.37% Cu, 0.26 g/t Au,
Inferred resources were 28 Mt @ 0.03% Cu, 0.27 g/t Au, primarily contained in the Springer deposit.

Measured+Indicated Resource, 2010, @ 0.25% Cu eq. cutoff for the Boundary/Zuke, Northeast, Springer, Junction,Bell, C2, Southeast and Pond bodies:     167.7 Mt @ 0.317% Cu, 0.293 g/t Au, (Imperial Metals website),
Inferred Resource, same deposits and cutoff:   3.66 Mt @ 0.317% Cu, 0.168 g/t Au, (Imperial Metals website),
Proven+Probable Reserve, 2010, @ 0.25% Cu eq.     40.5 Mt @ 0.318% Cu, 0.282 g/t Au, (Imperial Metals website),

The most recent source geological information used to prepare this summary was dated: 2005.    
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.

  References & Additional Information
   Selected References:
Bath A B, Logan J M and Kamenetsky V S,  2006 - Apatite in Cu-sulfide ore from the Mount Polley alkalic porphyry, BC Canada - Abstract: in    Geochimica et Cosmochimica Acta   v70 p A40
Logan, J.M. and Mihalynuk, M.G.,  2014 - Tectonic Controls on Early Mesozoic Paired Alkaline Porphyry Deposit Belts (Cu-Au ± Ag-Pt-Pd-Mo) Within the Canadian Cordillera : in    Econ. Geol.   v.109, pp. 827-858.
Pass H E, Cooke D R, Davidson G, Maas R, Dipple G, Rees C, Lee Ferreira, Taylor C and Deyell C L  2014 - Isotope Geochemistry of the Northeast Zone, Mount Polley Alkalic Cu-Au-Ag Porphyry Deposit, British Columbia: A Case for Carbonate Assimilation : in    Econ. Geol.   v.109 pp. 859-890
Pisiak, L.K., Canil, D., Lacourse, T., Plouffe, A. and Ferbey, T.,  2017 - Magnetite as an Indicator Mineral in the Exploration of Porphyry Deposits: A Case Study in Till near the Mount Polley Cu-Au Deposit, British Columbia, Canada: in    Econ. Geol.   v.112, pp. 919-940.

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 takes no responsibility what-so-ever for inaccurate or out of date data, information or interpretations.

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