Great Bear Magmatic Zone - Sue Dianne, NICO, Port Radium - Echo Bay, Eldorado

Northwest Territories, Canada

Main commodities: Co Ag U Au Bi Cu
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The NICO and Sue-Dianne Co, Au, Bi, Cu and Ag deposits are significant IOCG or 'iron oxide-alkali-calcic alteration' system 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. The historic Echo Bay and Eldorado uranium-silver mines are also on the margin of the Great Bear Magmatic Zone and represent late high-level epithermal mineralisation related to another iron oxide-alkali-calcic alteration system, ~250 km north to NNW of Sue Dianne, in the Port Radium district, on the eastern shore of the Great Bear Lake.

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.

Echo Bay, Eldorado and a number of other small mines and prospects comprise polymetallic vein-like deposits containing Ag-Ni, Co arsenide, Bi and U, are hosted by Palaeoproterozoic sedimentary and volcanic rocks of the Echo Bay Group occurring in roof pendants within the Late Palaeoproterozoic Great Bear Magmatic Zone. Like NICO and Sue-Dianne, these deposits are located in the western volcanic corridor along the northeastern limit of the late-stage, 1.85 Ga A-type granites of the greater complex (Hayward and Corriveau, 2014).
  The mineralised veins are hosted by a series of green and red banded andesitic tuffaceous and aphanitic rocks that are partly porphyritic, with varying degrees of silicification. The volcanic rocks on the margins of the pendants are thermally metamorphosed, but reducing markedly in degree away from the intrusive contacts. Mineralisation is found within veins towards the centre of the pendants and occur within veined host volcanic rocks which are heavily sulphide-impregnated. The veins are located in splays and tension-fractures emanating from the primary controlling fault. Ore occurs in three steeply dipping veins that average ~0.5 m in thickness, are ~1500 m in length and persist to depths of >400 m. Several vein types have been recognised, including i). quartz ± carbonate; ii). quartz-hematite ±carbonate; and iii). quartz ±carbonate + chalcopyrite ±pyrite. Quartz appeared first in all veins, followed by hematite and then sulphides. Most contain carbonate, usually siderite which is younger. Where sulphides and carbonate are present the sulphides usually accompany the latter. Calcite and siderite are common and frequently also contain chalcopyrite. Locally, siderite veins cut those with quartz-siderite-sulphide. Veins also contain pitchblende, native silver, native bismuth and minor base metal sulphides as well as Co-Ni arsenides. The veins are surrounded by a halo of feldspar, hematite, chlorite and carbonate. The mineralisation has a generalised paragenesis of U → Ag+arsenides → Bi sulphides → sulphosalts, although there are variations. Silver minerals include native silver, argentite, argentiferous galena and acanthite. A number of copper, zinc, nickel and cobalt sulphides also occur within the veins. Multiple breccia generations along the edge of, or within veins, indicate repeated injection and deposition. This is supported by fluid inclusions which show veins were deposited during at least five stages of hydrothermal activity by saline fluids containing 15 to 35 wt.% NaCl equiv. at temperatures of 90 to 450°C (Reardon, 1992; Gasparini, 1984; Badham, 1975; Schiller, 1964).
  The Eldorado deposit at Port Radium was found when a prospector discovered high-grade pitchblende and silver at Eldorado. Eldorado Gold Mines Limited started operations as a radium mine in 1932, extracting radium from pitchblende for medical use. The mine closed in 1940 due to competition from Europe. In 1939, ore from Eldorado had been used in the first chain reaction experiments and the deposit became valuable as a rich source of uranium oxide. Eldorado Gold Mines Limited secured a contract with the United States military early in 1942, but was subsequently secretly expropriated and transferred to the Canadian Government in 1943-1944 and renamed Eldorado Mining and Refining Limited. Uranium ore from the mine was used in the atomic bomb developments of 1945. Uranium mining continued after World War II until the mine became unprofitable due to increased competition and its isolated location, and by 1960 the original Eldorado Mine was exhausted and closed. The estimated 1.7 million tonnes of radioactive mine tailings at Port Radium were rehabilitated by 2007.
  The Echo Bay deposits were found in 1930 and underground development constructed for exploration by the Canadian Mining and Smelting Company. It was not worked seriously until 1964, when Northwest Explorers Limited, taking advantage of the old Port Radium settlement of Eldorado Mining and Refining Limited and using the old camp and mill to recover silver and copper from the Echo Bay Mine. Production ceased in 1975. The same company then reopened the old Eldorado Mine workings and produced more silver and copper until 1981 when low silver prices closed the mine for good.

The most recent source geological information used to prepare this summary was dated: 2010.    
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:
Acosta-Gongora, P., Gleeson, S.A., Samson, I.M., Corriveau, L., Ootes, L., Jackson, S.E., Taylor, B.E. and Girard, I.,  2018 - Origin of sulfur and crustal recycling of copper in polymetallic (Cu-Au-Co-Bi-U ± Ag) iron-oxide-dominated systems of the Great Bear Magmatic Zone, NWT, Canada: in    Mineralium Deposita   v.53 pp. 353-376.
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
Porter T M,  2010 - Current Understanding of Iron Oxide Associated-Alkali Altered Mineralised Systems: Part II, A Review: in Porter T M, (Ed),  2010 Hydrothermal Iron Oxide Copper-Gold and Related Deposits: A Global Perspective, PGC Publishing, Adelaide   v.3 pp. 33-106
Zhu, Z.,  2016 - Gold in iron oxide copper-gold deposits: in    Ore Geology Reviews   v.72, pp. 37-42.

   References in PGC Publishing Books: 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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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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