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Stikine, Galore Creek

British Columbia, Canada

Main commodities: Cu Au
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The Stikine or Galore Creek creek group of alkalic porphyry copper-gold deposits are located in north-western British Columbia, Canada, 97 km NNE of Wrangell, Alaska (USA) and 1030 km NW of Vancouver (#Location: 57° 07'N, 131° 27'W).

Published reserve and production figures include:

   125 Mt @ 1.06% Cu, 0.4 g/t Au (Geol. Res. 1984, Dawson,1991), incuding,
     an open pit resource of 27.23 Mt @ 0.97% Cu, 0.37 g/t Au, 7.5 g/t Ag.

Galore Creek resources in 1992 (Enns, et al. 1995) were as follows:

    Central - 233.9 Mt @ 0.67% Cu, 0.35 g/t Au, 7 g/t Ag
    Southwest - 42.4 Mt @ 0.55% Cu, 1.03 g/t Au, 7 g/t Ag
    North Junction - 7.7 Mt @ 1.50 % Cu
    TOTAL - 284 Mt @ 0.67% Cu

Overall Galore Creek project resource in April 2012 were (Novagold Resources Inc., website, 2012):

    814.7 Mt @ 0.50% Cu, 0.31 g/t Au, 5.21 g/t Ag (total Measured and Indicated resource)
    346.6 Mt @ 0.42% Cu, 0.24 g/t Au, 4.28 g/t Ag (total Inferred resource)

This deposit is located within the Stikine Arch at the western margin of the Intermontaine Belt, and is 7 km east of the Coast Plutonic Complex. The Stikine Arch is a north-easterly trending salient of metamorphic rocks that formed a positive tectonic element during much of the Medsozoic. The Galore Creek area includes three main lithologic units, as follows: i). Palaeozoic and Middle Triassic metamorphic rocks - comprising Permian and older metamorphics, Permian crystalline marbles and a thin unit of Middle Triassic siltstones; ii). Upper Triassic volcanic and sedimentary rocks - unmetamorphosed augite andesite and basaltic andesite breccia, flows and tuffs with intercalated sandstones and siltstones; and iii). intrusive rocks of various ages - including Upper Triassic to Lower Jurassic syenite stocks and dykes, quartz diorite and granodiorite stocks and at least one large batholith. Jurassic and Lower Cretaceous quartz diorite, granodiorite and a variety of other intrusives make up the Coast Plutonic Complex to the west.

Mineralisation in the main central zone at the Stikine/Galore Creek deposit is associated with multiple phases of Jurassic syenite porphyries present as dykes and plugs forming the 5x2.5 km Galore Creek syenite complex. The syenites can be divided into pre, syn and post-ore (Marr, 1991). At least four intrusive phases are most closely associated with the copper deposits, while six other phases are recognized but are peripheral to the Central zone deposit.

The deposits are hosted primarily by highly altered potassium- enriched volcanic rocks and pipe-like breccias adjacent to syenite dykes and stocks. Typically, the deposits are manto-shaped and have a north to northeast trend related to the syenite contacts and zones of structural weakness.

A series of late-mineral dykes and sills, accompanied by metal deficient propylitic alteration, transect and divide the main central zone into separate orebodies. Several relatively small magnetite cemented breccias with Cu-Au mineralisation were emplaced late in the history of the system. The enclosing mineralised rock is mainly the upper Triassic Stuhini Assemblage, composed of volcanic breccias, bedded and crystal tuff, trachyte and pseudo-leucite phonolite, in the deposit area (Allen, et al., 1976; Marr, 1991).

A number of individual bodies (at least 12) make up the main resource at Galore Creek. The Central zone is by far the largest, with dimensions of 1700 x 500 elongated along a strike of 15° and dipping steeply to the west to a depth of at least 450 m. The deposit is centred on an elongate, steeply dipping breccia pipe, the long axis of which is parallel to the trend of the deposit. The deposit is roughly tabular in shape and is composed of several parallel en echelon copper zones.

Chalcopyrite is the main Cu mineral in all of the deposits. Bornite is locally abundant, although overall, the chalcopyrite:bornite ratio is 10:1. Hypogene chalcocite is rare. The bulk of the mineralisation is within meta-volcanics and breccias. The style of mineralisation is considered to be intermediate between skarn and porphyry. Much of the chalcopyrite occurs as massive zones and disseminations and the pyrite content is low. Copper and gold are concentrated as replacement zones in limy horizons and are accompanied by abundant garnet, although sulphide and associated gangue minerals also commonly fill fractures and stockworks in the meta-volcanics. As in most porphyry deposits, alteration includes K-feldspar flooding, hydrothermal biotite and magnetite, and there are cross-cutting anhydrite veins. Away from the bornite rich zones, the most abundant sulphide is pyrite, which is ubiquitous, locally comprising up to 5 to 10%. In addition to pyrite, magnetite and hematite there is lesser sphalerite, minor galena, chalcocite and molybdenite, and traces of tennantite, native silver, native gold, tetrahedrite and scheelite. The metavolcanics contain 10% or more anhydrite.

The main phase of mineralisation is characterised by bornite-magnetite and chalcopyrite-magnetite assemblages accompanied by intense potassium silicate alteration. The best grade gold accompanies the bornite rich ore. Later diatreme brecciation is common (Marr, 1991). Within and near the intrusive complex, volcanic rocks are slightly to intensely metasomatised. Almost all rocks have undergone weak to intense pervasive potash metasomatism, particularly in and around Cu bearing zones. However, many of the rocks may originally have been orthoclase rich trachyte and phonolite. In places K-feldspathisation has converted syenites and meta-volcanic rocks into pink, white, grey and orange rocks composed almost completely of orthoclase. K-feldspar also occurs as a vein mineral. Zoned orthoclase phenocrysts in many porphyries are replaced by white and pink microcline which obliterates the zones. Hydrothermal biotite forms fine to coarse grains and aggregates disseminated throughout the volcanics and dark syenite porphyry. Andradite-grossularite occurs as irregular grains disseminated in meta-volcanics and locally in syenite porphyries. Garnet occurs in veinlets, vugs and breccia interstices (Allen, et al., 1976).

No obvious mineral zoning had been observed in 1976 (Allen, et al., 1976). Rocks composed alsmost entirely of K-feldspar are prominent in the north and south of the Central Zone, biotite occurs in various amounts throughout all mineralised meta-volcanics, but appears to be concentrated in andesitic or basaltic units rather than the more K-feldspar rich units. Biotite zones parallel syenite dykes. Garnet occurs throughout much of the Central Zone, except in the extreme north and south. It is particularly abundant in the north, where it forms up to 50% of meta-volcanic rocks as massive replacements and breccia vug fillings. Garnet decreases away from breccia zones. Magnetite and pyrite parallel each other in distribution within the Central Zone. Disseminated magnetite occurs in a belt lying to the west, but includes the northern part of the deposit. Prograde diopside-garnet skarn-like alteration accompanies mineralisation with fragmental volcanic formation in the footwall. More than 1% pyrite occurs mainly to the east. Bornite is found in four separate areas in the Central Zone, with no apparent controls on its distribution (Allen, et al., 1976; Marr, 1991).

The most recent source geological information used to prepare this summary was dated: 1996.    
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:
Allen D G, Panteleyev A and Armstrong A T,  1976 - Galore Creek: in Sutherland Brown A (Ed.), 1976 Porphyry Deposits of the Canadian Cordillera, Canadian Institute of Mining and Metallurgy,   Special Volume 15, pp 402-414
Byrne K and Tosdal R M,  2014 - Genesis of the Late Triassic Southwest Zone Breccia-Hosted Alkalic Porphyry Cu-Au Deposit, Galore Creek, British Columbia, Canada: in    Econ. Geol.   v.109 pp. 915-938
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.
Micko J, Tosdal R M, Bissig T, Chamberlain C M and Simpson K A,  2014 - Hydrothermal Alteration and Mineralization of the Galore Creek Alkalic Cu-Au Porphyry Deposit, Northwestern British Columbia, Canada : in    Econ. Geol.   v.109 pp. 891-914


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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