Yukon Territory, Canada

Main commodities: W Cu
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Cantung is a large stratabound contact metasomatic tungsten scheelite deposit in the Tungsten district of the Yukon Territory, Canada.

The deposit is hosted by a skarn assemblage (pyroxene, amphibole, garnet, pyrrhotite, biotite, clinozoisite, plagioclase and quartz) developed from Cambro-Ordovician carbonates within a dominantly pelitic Lower Palaeozoic sequence on the edge of the Selwyn Basin adjacent to a Late Cretaceous felsic intrusion.   The ore contains scheelite and lesser chalcopyrite with a high percentage of gangue pyrrhotite.

Reserves include:

    4.2 Mt @ 1.55% WO3 (Reserve, 1981, Dick & Hodgson, 1982);
    7.5 Mt @ 1.55% WO
3, 0.3% Cu (Reserve + Production, 1978, Mine visit, 1978).

The Cantung deposit is located within the Flat River Valley, at the transition between the flat lying, carbonate dominated sequence of the Mackenzie Thrust Belt/Platform, and the folded rocks of the Selwyn Basin to the west. The principal structure in the area is a major NNW trending synform centred on, and paralleling the Flat River Valley. The sediments to the south-west of the valley are folded into tight overturned folds, while those to the north-east are deformed into open upright folds with associated thrusting. The sediments of the Selwyn Basin are characterised by shales and argillites while the stratigraphic equivalents in the Mackenzie Thrust Belt are largely quartzites and dolomites.

The Cantung orebodies are hosted by sediments of the Cambrian Sekwi Formation and equivalents in the transition between these two facies in the overturned tight fold on the south-western bank of the Flat River valley. Several small granitic exposures are found in the area representing bulges and topographically exposed windows into a larger underlying Cretaceous granitoid body. The two main orebodies at Cantung are localised within the limbs of a south-east trending recumbent cross fold on the south-western limb of the main syncline following the Flat River Valley. The two ore zones are separated by the nose of the recumbent fold. The sequence in the mine area comprises the following, from the base:

Lower Argillite, which is 2700 m thick, composed of non-calcareous slate, phyllite, siltstone and fine quartzite. This is probably upper-most Proterozoic in age;
Footwall Chert (or Swiss Cheese Limestone), 60 m thick, a fine grained, bedded, pale green cherty argillite with pink garnetiferous bands, fine disseminated pyrite and fine pyrrhotite bands, which may be laminae, or massive pyrrhotite lenses. This unit hosts one of the smaller scheelite ore lenses. Away from the mine it becomes the Swiss Cheese Limestone which contains wispy lenses and pebbles of argillite, and contains Cambrian fossils;
Ore Limestone, which varies from 0 to 100 m in thickness, but has a maximum in the mine area of 60 m. Most of the known scheelite occurrences in the district are hosted by this unit. Where not mineralised it varies from a well laminated crystalline limestone to marble, to massive, poorly bedded limestone. In the orebody it carries concordant laminae of garnet and diopside, grading to massive, banded garnet diopside. The orebodies occur as a series of laterally extensive, laminated, sharply defined, concordant massive pyrrhotite beds which are 1 cm to 2 m thick;
Upper Argillite, 50 m thick, composed of grey to black calcareous argillite, shale, chert and minor limestone;
Dolomite, 600 m thick, a varied assemblage of thin to thick bedded, pale dolomite, dolomitic quartz sandstone and quartzite. These are followed by an unconformity and
Wavey Banded Limestone and Siltstone, 1200 m thick, which belongs to the upper Rabbitkettle or lower Road River Formation.

This sequence is underlain by a medium grained, fresh, biotite quartz monzonite, grading in places to granodiorite which has been dated at 110 Ma (Cretaceous). There is no obvious thermal alteration halo to the intrusive, with the skarn development being concordant within the Ore Limestone, extending for several kilometres from the intrusive.

Mineralisation occurs in three forms, namely;

Massive pyrrhotite-scheelite-chalcopyrite ore - which constitutes the bulk of the main orebody, within the thinner sections of the Ore Limestone. Ore grade scheelite occurs in a series of massive to semi-massive pyrhotite beds ranging in thickness from 1 mm concordant laminae to laminated beds up to 2 m thick. Individual sulphide lenses are composed of around 80% pyrrhotite, while these beds and laminae make up 30 to 40% of the mineralised section. Individual sulphide lenses are separated by poorly altered wall rock with up to 20% garnet and diopside bands. The gangue in the massive sulphide bands is predominatly garnet, diopside and chlorite. The scheelite is intimately associated with the pyrrhotite and occurs as laminae within the massive sulphide lenses. The main ore zone is 850 m long, 180m wide and 0 to 30 m thick. The pyrrhotite is only poorly magnetic;
Garnet-diopside tactite ore - which is the ore type in the open cut and closely resembles the low sulphide fringes of the massive sulphide ore. It comprises alternating irregular bands of diopside-hedenbergite and grossular-andradite with quartz and calcite. The garnet and diopside average 50% of the ore zone. Pyrrhotite only accounts for a few percent of the rock, with the scheelite being intimately related to it. Coarse quartz veins cut the tactite locally, carrying coarse scheelite. The open pit orebody has dimensions of 180 x 180 m, is up to 250 m thick, but averages 15 m, pinching out down dip and along strike;
Chert Ore - which occurs at the base of the Footwall Chert, associated with a zone of pyrrhotite development with associated diopside and garnet.

The most recent source geological information used to prepare this summary was dated: 1982.    
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:
Bowman J R, Covert J J, Clark A H, Mathieson G A  1985 - The CanTung E Zone Scheelite Skarn orebody, Tungsten, Northwest Territories: Oxygen, Hydrogen, and Carbon Isotope studies: in    Econ. Geol.   v80 pp 1872-1895
Dick L A, Hodgson C J  1982 - The MacTung W-Cu(Zn) contact metasomatic and related deposits of the northeastern Canadian Cordillera: in    Econ. Geol.   v77 pp 845-867
Mathieson G A, Clark A H  1984 - The Cantung E Zone Scheelite Skarn Orebody, Tungsten, Northwest Territories: a revised genetic model: in    Econ. Geol.   v79 pp 883-901
Ootes, L., Gleeson, S.A., Turner, E., Rasmussen, K., Gordey, S., Falck, H., Martel., E. and Pierce, K.,  2013 - Metallogenic Evolution of the Mackenzie and Eastern Selwyn Mountains of Canadas Northern Cordillera, Northwest Territories: A Compilation and Review: in    Geoscience Canada,   v.40, pp. 40-69, http://dx.doi.org/10.12789/geocanj.2013.40.005.

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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