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Great Bear Magmatic Zone - Sue Dianne, NICO

NWT, Canada

Main commodities: Co Au Bi Cu
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The NICO and Sue-Dianne Co, Au, Bi, Cu and Ag deposits are significant IOCG resources in the southern section of the Great Bear Magmatic Zone in the North-west Territories of Canada. They are of Proterozoic age, exhibit similarities to the Olympic Dam orebody and are included in the Iron Oxide Copper-Gold class of deposits. Sue-Dianne is 25 km north of NICO, ~160 km NW of the City of Yellowknife.

Crustal Setting

The Great Bear Magmatic Zone (GBMZ) is located on the western margin of the exposed Canadian Shield in the Northwest Territories of Canada. It is an extensive, 1.88 to 1.84 Ga, largely felsic, volcano-plutonic complex, developed over a continental suture zone. It overlies a Palaeoproterozoic, ~2.1 to 1.88 Ga magmatic arc, the Hottah terrane, which had been accreted to the western margin of the Archaean Slave craton during the short-lived ~1.90 to 1.88 Ga Calderian orogeny (Corriveau et al. , 2010 and sources quoted therein). The GBMZ is exposed over an area of 450 x 100 km, although, magnetic data suggest it may have a total length of 1200 km below cover. Felsic and intermediate magmatism predominates, occurring as batholiths, subvolcanic intrusions and volcanic rocks, with coeval mafic magmatism as minor volcanic rocks, dykes and sills (Corriveau et al. , 2010).

The complex is cut by a series of NE trending, deeply penetrating, dextral faults that Mumin et al. , 2009 interpret to reflect southeast-directed extension. These faults host the mafic dykes mentioned above. Regional scale iron oxide-alkali altered mineralised systems are documented throughout the exposed GBMZ. The magmatism, which is interpreted to have been both a thermal catalyst and fluid source to hydrothermal activity, ceased at 1.84 Ga. The GMBZ is interpreted to represent a voluminous accumulation of continental magmas emplaced after arc-continent collision and orogenic collapse, on top of an eroded arc and suture (Hildebrand et al. , 2010).

Isotopic signatures of GBMZ volcanic and plutonic rocks do not indicate the presence of underlying Archaean crust, although magnetotelluric data reflects the upper surface of a west dipping, wedge-shaped Archaean lithospheric root extending from the Slave craton exposed to the east. At depth, the edge of this root reaches a position that is below the eastern margin of the exposed Hottah terrane. In addition, to the west, a resistive cratonic root imaged to a depth of ~200 km occurs below the Hottah terrane, with a less resistive region underlying the GBMZ, separating the two roots. Each of these discontinuities is sharply defined. The magnetotelluric data shows the Wopmay Fault Zone, which marks the eastern limit of the GMBZ, only extending to mid-crustal levels where it intersects the Archaean lithospheric wedge. The currently known IOCG systems in the GMBZ occur above some of these discontinuities. The bulk of the IOCG-style mineralisation in the GBMZ is associated with alteration systems that are developed systematically outwards from sub-volcanic intrusions i.e., unlike most IOCG mineralisation, they do exhibit a close spatial relationship with intrusions.

District-scale Alteration and Mineralisation

The NICO and Sue Dianne lie within the southern part of the of GBMZ which contains "IOCG", uranium and iron occurrences, with associated magnetite-rich, K feldspar and magnetite-to-hematite vein, breccia and replacive alteration. This mineralisation and alteration is hosted by remnants of the pre-1.88 Ga supracrustal marine metasedimentary rocks (siltstones, sub-arkosic-wacke and arenite) of the Treasure Lake Group, and by an unconformably overlying 1.86 Ga rhyolite to rhyodacitic volcanic complex (Faber Group). The Faber group is composed of thick-bedded rhyolite to rhyodacite tuffs, flows and lesser volcaniclastic rocks. It includes basal heterolithic breccias (containing clasts from the underlying sediments), massive to flow-banded, potassium feldspar-altered rhyolite (felsite), with or without magnetite laminae, overlain in turn by thick-bedded, ash-flow tuffs with lesser porphyritic flows, lapilli tuff and volcaniclastic rocks.

Granitoids of the Marian River Batholith underlie and intrude the Treasure Lake Group, and are source plutons for, and partially intrude the volcanic rocks of the Faber Group. Sub-volcanic porphyry stocks and bimodal porphyritic dyke swarms link the Marion River batholith with zones of economic mineralisation at Sue-Dianne and NICO respectively. At both of these deposits, the IOCG alteration was temporally coeval with extrusion of these GBMZ volcanic rocks.

The Sue-Dianne copper-gold-silver deposit is hosted by a structurally controlled hydrothermal breccia complex, constrained entirely within the pre-existing 400 m wide, northeast-trending, Dianne Lake fault zone, where it intersects the north trending MAR fault (Goad et al. , 2000). Textural evidence indicates these structures were active both during and after mineralisation. The breccia complex was developed within well-preserved rhyodacite ignimbrite sheets of the Faber Group (Gandhi, 1989). Hydrothermal brecciation emanates from the apex of an albitised porphyry stock low in the complex, extending upwards for approximately 300 m to where it is assumed to have breached the palaeosurface. These breccias are now capped by an interpreted fall-back breccia and palaeoregolith. Breccia clasts are strongly altered to K feldspar ±epidote, chlorite, hematite and sulphide, and are composed of rounded to sub-angular fragments of welded and crystal tuff, and occasionally of altered porphyry stock. The core of the complex comprises both clast- and matrix-supported breccia, and grades progressively outwards into structurally controlled fracture breccia. The hydrothermal matrix is composed of magnetite, hematite, K feldspar, chlorite, epidote, garnet, fluorite, chalcopyrite and pyrite. Distal hydrothermal effects take the form of giant quartz veins, stockwork and breccia complexes, and pervasive silicification, accompanied by minor K feldspar, epidote, sericite and/or hematite. At depth, the core of the deposit is barren magnetite-pyrite, grading upwards to magnetite-hematite-chlorite-epidote-fluorite-andradite-chalcopyrite matrix breccias. The peripheral and structurally higher levels of the system are dominated by hematite with bornite mineralisation (Goad et al. , 2000; Mumin et al. , 2010; Corriveau et al. , 2010).

At NICO, which is 25 km south of Sue-Dianne, economic mineralisation occurs over a vertical stratigraphic interval of ~300 m, from the base of the Faber Group volcanic rocks where minor mineralisation is hosted, downward into the Treasure Lake Group, predominantly within strongly altered siltstone and arkose. Mineralisation occurs as a series of subparallel stratabound lenses, individually up to ~50 m in intense hydrothermal iron oxide (dominantly magnetite)- hornblende-biotite-K feldspar ±tourmaline ±carbonate, carbonate-magnetite or K feldspar replacement alteration, and by veins, stockworks and breccias. At depths of >300 m, metasediments are hornfelsed, possibly through contact metamorphism by the immediately underlying Marion River Batholith. There is a general outward progression of alteration, from core to periphery, of albite, magnetite±pyrrhotite or pyrite, magnetite-hornblende-biotite-tourmaline, hematite-hornblende-biotite, biotite, K feldspar and distal sericite. The most peripheral and/or youngest hydrothermal effects include giant quartz complexes and quartz-epidote veining and alteration. Brecciation and intense K feldspar and other alteration styles are common at the interface of porphyritic dykes and altered sediments and within some of the mineralisation zones (Corriveau et al. , 2010). Gold, cobalt, bismuth and copper mineralisation is thought to have been introduced in two phases: (1) an early iron oxide event dominated by magnetite with minor chalcopyrite, native bismuth and possibly some gold; and (2) the main economic mineralisation during a later overprinting phase, mainly of cobaltian arsenopyrite, cobaltite, bismuthinite, native gold, gold-bismuth-tellurium alloys and pyrite±chalcopyrite (Corriveau et al. , 2010).

The pre-production reserves at NICO (Fortune Minerals Limited news release, January 14, 2010) were:
    31.7 Mt at 0.91 g/t Au, 0.12% Co, 0.16% Bi, 0.04 % Cu ;

The Sue-Dianne Cu-Au-Ag breccia complex has an NI 43-101 compliant resource (Hennessey and Puritch, 2008) of:
    8.4 Mt @ 0.80% Cu, 0.07 g/t Au, 3.2 g/t Ag

The most recent source geological information used to prepare this summary was dated: 2012.     Record last updated: 17/7/2013
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
 References to this deposit in the PGC Literature Collection:
Corriveau, L., Montreuil, J.-F. and Potter, E.G.,  2016 - Alteration Facies Linkages Among Iron Oxide Copper-Gold, Iron Oxide-Apatite, and Affiliated Deposits in the Great Bear Magmatic Zone, Northwest Territories, Canada: in    Econ. Geol.   v.111, pp. 2045-2072.
Enkin, R.J., Corriveau, L. and Hayward, N.,  2016 - Metasomatic Alteration Control of Petrophysical Properties in the Great Bear Magmatic Zone (Northwest Territories, Canada): in    Econ. Geol.   v.111, pp. 2073-2085.
Goad R E, Mumin A H, Duke N A, Neale K L and Mulligan D L,  2000 - Geology of the Proterozoic Iron Oxide-Hosted, NICO Cobalt-Gold-Bismuth, and Sue-Dianne Copper-Silver Deposits, Southern Great Bear Magmatic Zone, Northwest Territories, Canada: in Porter T M (Ed), 2000 Hydrothermal Iron Oxide Copper-Gold & Related Deposits: A Global Perspective PGC Publishing, Adelaide   v.1 pp. 249-267
Hayward, N., Corriveau, L., Craven, J.A. and Enkin, R.J.,   2016 - Geophysical Signature of the NICO Au-Co-Bi-Cu Deposit and Its Iron Oxide-Alkali Alteration System, Northwest Territories, Canada: in    Econ. Geol.   v.111, pp. 2087-2109.
Montreuil, J.-F., Corriveau, L. and Davis, W.J.,   2016 - Tectonomagmatic Evolution of the Southern Great Bear Magmatic Zone (Northwest Territories, Canada): Implications for the Genesis of Iron Oxide-Alkali–Altered Hydrothermal Systems: in    Econ. Geol.   v.111, pp. 2111-2138.
Montreuil, J.-F., Corriveau, L., Potter, E.G. and De Toni, A.F.,  2016 - On the Relationship Between Alteration Facies and Metal Endowment of Iron Oxide-Alkali-Altered Systems, Southern Great Bear Magmatic Zone (Canada): in    Econ. Geol.   v.111, pp. 2139-2168.
Montreuil, J-F., Corriveau, L. and Potter, E.G.,  2015 - Formation of albitite-hosted uranium within IOCG systems: the Southern Breccia, Great Bear magmatic zone, Northwest Territories, Canada: in    Mineralium Deposita   v.50 pp. 293-325

 References to this deposit in PGC Publications: Want any of our books ? Pricelist
Goad R E, Mumin A H, Duke N A, Neale K L, Mulligan D L, 2000 - Geology of the Proterozoic Iron Oxide-Hosted Nico Cobalt-Gold-Bismuth, and Sue-Dianne Copper-Silver Deposits, Southern Great Bear Magmatic Zone, Northwest Territories, Canada,   in  Porter T M, (Ed.),  Hydrothermal Iron Oxide Copper-Gold & Related Deposits: A Global Perspective,  v1  pp 249-267
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