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Izok |
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Nunavut, Canada |
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Cu Zn Ag Pb
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Super Porphyry Cu and Au
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IOCG Deposits - 70 papers
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All papers now Open Access.
Available as Full Text for direct download or on request. |
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The Izok copper-zinc deposit lies beneath Izok Lake and is located 360 km north of Yellowknife, 265 km south of Kugluktuk (Coppermine) and 80 km west of the Lupin Mine site in Nunavut Territory, northern Canada (#Location: 65° 37' 52" N, 112° 47' 56"W).
The Izok deposit is located in the northern part of the Slave craton in the northwestern Canadian Shield. Much of the central and western parts of the craton are underlain by a contiguous Paleo- to Mesoarchaean (4.03-2.9 Ga), largely crystalline basement complex, dominated by foliated to gneissic tonalites, diorites and granodiorites. These old rocks are overlain by Neoarchaean supracrustal sequences, and heavily intruded and reworked by plutonic suites ranging in age from 2.72 to 2.67 Ga synvolcanic plutons to 2.59 to -2.58 Ga late-orogenic batholithic granites.
The supracrustal sequences are collectively known as the Yellowknife Supergroup, and comprise: i). an early, around 2.8 Ga cover sequence comprising quartzite and banded iron formation, ii). a thick dominantly tholeiitic greenstone sequence of approximately 2.7 Ga in age, iii). a younger 2.69 to 2.61 Ga arc-like sequences, iv). extensive 2.68 to 2.62 Ga turbidite blankets of the Burwash Basin, and v). syn-orogenic conglomerates deposited at approximately 2.6 Ga.
During subsequent orogenesis, the supracrustal sequences were telescoped, thickened, and multiply folded between around 2.65 and 2.58 Ga, with a peak in crustal anatexis between 2.59 and 2.58 Ga
The Izok deposit is hosted within the Point Lake Volcanic Belt, a north trending belt of the 2.69 to 2.61 Ga arc-like sequences which followed the 2.7 Ga basaltic volcanism and rifting within the Slave craton. During this period most parts of the Slave craton showed a transition to such calc-alkaline volcanism characterised by abundant felsic and intermediate volcanic rocks, calc-alkaline basaltic rocks, and intercalated volcaniclastic sedimentary rocks. These volcanic arc sequences and the associated subvolcanic plutons, are interpreted to have formed in part on top of the attenuated basement and in progressively widening, juvenile, back-arc-like basins.
The Point Lake Volcanic Belt is composed of Archaean mafic to felsic volcanic rocks and subordinate sediments which have been subjected to polyphase Archaean deformation and regionally metamorphosed. The deposit is hosted by the Point Lake Formation of the Yellowknife Supergroup and lies within the Izok sub-belt, a north-east to north trending "arm" of volcanic rocks which branches off the eastern side of the Point Lake Belt just north of Itchen Lake.
The Point Lake Formation is overlain by the Itchen and Contwoyto Formation meta-turbidites of the Burwash Basin, which outcrop some 2 km south-east of Izok. Approximately 2 km south-west of Izok, a suite of siliceous gneisses is exposed, representing a felsic volcanic sequence with intercalated sediments. Within 1 km to the north and east of Izok, a mixed sedimentary-volcanic sequence, also belonging to the Yellowknife Supergroup rocks, is intruded by numerous, Neoarchaean granitic sheets, creating lit-par-lit gneisses. These granitic bodies coalesce into the Rockinghorse Batholith about 2 km north-east of Izok.
The Izok deposit is hosted within and near the top of a thick sequence of rhyolitic and dacitic flows and tuffs which have been metamorphosed to felsic gneisses near the top of a thick pile of felsic pyroclastic rocks. This pile is conformably underlain by similar rocks, and toward the edges of the Central Zone of the orebody is underlain by rhyolitic agglomerate.
The hanging wall package includes additional, conformably overlying, felsic volcanoclastics, dacitic and basaltic flows, thin sulphide rich iron formation and turbiditic sediments (represented by a pyritic muscovite schist). The felsic volcanics are intruded by syn to late hydrothermal dacite and gabbro dykes (amphibolitic metagabbro), both of which are feeders to overlying flows, while minor mafic gneisses in the hangingwall are probably derived from intermediate to mafic tuffs. An amphibolite and massive to pillowed, mafic to intermediate flows unconformably overlie the felsic pile.
The deposit consists of:
i). the combined North and Central Zones, which occur as an ENE trending, 450 x 110 m trough-shaped, flat-lying, composite lens of massive sulphides which plunges at 15 to 30° ENE. It has a highly variable thickness, varying from 0 to 160 m. A 100 x 20 m copper-rich stringer zone under the western end of the Central Zone dips south at a depth of from 100 to 160 m below the surface.
ii). the Northwest Zone is centred about 250 m north-west of the Central Zone, occurring as a fairly flat-lying, 200 x 280 m lens which is 22 m thick and somewhat concave upwards, dipping shallowly north. It occurs at a depth of 30 to 130 m. Both the Central and the Northwest Zones are open-pit prospects with a stripping ratio of 3:1.
iii). the Inukshuk Zone is located approximately 400 m east of the Central Zone, and is a 300 x 150 m, ENE-trending lens which is 10 m thick and dips shallowly to the south at depths of 60 to 400 m, partially underlying Izok Lake.
The North, Central and Northwest Zones lie within north-east trending and plunging, synclinal folds. The variable thicknesses of the sulphide layers is interpreted to be partly a pre-deformation feature, which may have influenced the location of fold axes, and partly due to deformational boudinaging and necking.
Sulphides are coarse grained and massive, dominantly comprising sphalerite, chalcopyrite, pyrite and pyrrhotite, with minor galena, tetrahedrite and silver sulphosalt (polybasite?).
Above the Cu-rich stringer zone, zoning in the Central Zone consists of a massive, copper rich basal section overlain by a zinc rich band, in turn locally overlain by a Zn-Pb-rich interval. There is ample evidence of galena and chalcopyrite re-mobilisation during deformation and/or metamorphism.
Pervasive sericite-biotite alteration forms an envelope around the deposit. Silicification is less extensive and less intensely developed, while minor aluminosilicate alteration has been noted. A magnesium enriched, chlorite-cordierite-anthophyllite rock underlies a marked thinning of the Central Zone and is interpreted to represent a feeder conduit.
Published resources in 2006 (Wolfden Resources Inc., 2007) at a 2.0% Zn Equiv. cutoff, were:
Indicated resource - 14.4 Mt @ 2.52% Cu, 12.94% Zn, 1.28% Pb, 71.0 g/t Ag,
Inferred resource - 0.37 Mt @ 3.79% Cu, 6.40% Zn, 0.27% Pb, 54.2 g/t Ag.
JORC compliant mineral resources at 30 June, 2015 (MMG Mineral Resource and Ore Reserve Statement, 2015), at 4% Zn Equiv. cut-off, were:
Indicated resource - 13.5 Mt @ 2.4% Cu, 13.3% Zn, 1.4% Pb, 73.0 g/t Ag, 0.2 g/t Au;
Inferred resource - 1.2 Mt @ 1.5% Cu, 10.5% Zn, 1.3% Pb, 73 g/t Ag, 0.2 g/t Au;
TOTAL resource - 14.6 Mt @ 2.3% Cu, 13.1% Zn, 1.4% Pb, 73 g/t Ag, 0.2 g/t Au.
No ore reserves are published.
The most recent source geological information used to prepare this decription was dated: 2006.
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.
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Laakso, K., Peter, J. M., Rivard, B. and White, H. P., 2016 - Short-Wave Infrared Spectral and Geochemical Characteristics of Hydrothermal Alteration at the Archean Izok Lake Zn-Cu-Pb-Ag Volcanogenic Massive Sulfide Deposit, Nunavut, Canada: Application in Exploration Target Vectoring: in Econ. Geol. v.111, pp. 1223-1239.
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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, its employees and servants: i). do not warrant, or make any representation regarding the use, or results of the use of the information contained herein as to its correctness, accuracy, currency, or otherwise; and ii). expressly disclaim all liability or responsibility to any person using the information or conclusions contained herein.
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