High Lake

Nunavut, Canada

Main commodities: Cu Zn Au Ag Pb
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The High Lake copper-zinc deposits are located in the Kitikmeot region of Nunavut, northern Canada, approximately 550 km NNE of Yellowknife, NWT, 175km ESE of Kugluktuk (Coppermine) and approximately 45 km south of the Coronation Gulf coast of the Arctic Ocean (#Location: 67° 23' N, 110° 51' W).

The High Lake volcanic hosted massive sulphide (VHMS) deposits are located in the High Lake Greenstone Belt in the northern part of the Slave craton in the north-western 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.

Unlike nearly all known massive sulphide deposits in this part of the Slave craton which are within the 2.69 to 2.61 Ga arc-like sequences, the High Lake deposits are associated with bimodal volcanic rocks of the older approximately 2.7 Ga greenstone sequence of the High Lake Greenstone Belt. This greenstone belt, which extends for 140 km south from the Coronation Gulf coast and varies from 5 to 30 km in width, contains numerous Cu, Zn, Pb, Au and Ag showings, including the High Lake AB & D Zones.

The greenstone sequence comprises a thick, extensive sequence of tholeiitic basalts, with minor komatiite and rhyolite tuff intercalations, representing an active volcanic rift environment, with bimodal volcanism and minor aprons of volcaniclastic sedimentary rocks. A younger, late Neoarchaean, granitic batholith is exposed approximately 3 km east of the deposits. Deformational history involving at least two phases of Archaean folding is obscured by intense northerly shearing and common north-westerly faulting. The Kennarctic River, 1 km east of the deposit, traces a regional, north-trending shear zone.

The AB Zone is located on the western shore of High Lake, 600 m north of the D Zone and comprises a series of sub-conformable, Cu-rich, stringer-dominated sulphide lenses, striking northeast and plunging north, within intensely altered rocks. The AB Zone is essentially a single 150 x 75 x 75 m deposit divided by a 25 m wide north trending dolerite dyke. The 300 m long A Zone is the larger of the two and comprises stringer type mineralisation, with copper rich massive sulphide lenses in its core. Stratigraphically it is located below the more massive mineralisation of the 150 m long B Zone. Both zones are hosted by hydrothermally altered felsic lapilli, ash and crystal tuffs with alteration being more intense in the A Zone. Mineralisation consists of pyrite, magnetite, pyrrhotite, chalcopyrite, sphalerite, and galena. The Zn content increases westward, toward the stratigraphic top of the combined zone.

These deposits occur within a 200 m wide, north-south striking and steeply dipping unit of altered and sheared, felsic and intermediate pyroclastics (comprising dacite and siliceous rhyolite clasts in an andesitic to dacitic matrix). A rhyolitic flow and narrow beds or lenses of carbonate-cemented felsic breccia are interbedded with the pyroclastics of the host unit to the east of the deposits. This host unit is underlain to the east by massive, pillowed and tuffaceous andesites and dacites, and overlain to the northwest by rhyolite or rhyodacite tuffs.

The AB Zone is sheared and cut by faults. A 1 m wide, late Proterozoic dolerite dyke cuts north through the deposit area, while a similar 10 m wide dyke follows a NW-trending fault through both the AB and D Zones, offsetting the latter by about 40 m dextrally.

The D Zone is hosted by the same 200 m wide unit of altered and sheared, felsic and intermediate pyroclastics as the AB Zone described above and is located approximately 600 m south of the AB Zone. It strikes at approximately 30° and dips steeply to the west. It is a 100 m long by 100 m down dip polymetallic deposit that ranges from 18 m thick near surface to 60 m at depth. The deposit comprises finely disseminated, and locally stringer sulphides and four separate lenses of banded massive sulphide hosted by altered felsic ash and lapilli tuffs. The mineralisation consists of pyrite, chalcopyrite, sphalerite, magnetite and galena. Generally, narrow bands of sphalerite and chalcopyrite respectively produced a zinc rich western portion and a copper rich eastern portion which grade into stringer type mineralisation to the east. Footwall alteration is characterised by chloritisation with local quartz-pyrite-sericite-chlorite and dalmationite of chlorite ± sericite spots, in sericitised, silicified rock. The hanging wall has been subjected to phyllic quartz-pyrite-sericite alteration, with local carbonate and actinolite-tremolite zones.

The E and C Zones which are 180 m east, and approximately 300 m north of the D Zone respectively, generally contain 'low' base metal grades.

The West Zone is approximately 1.5 km west of the D Zone and comprises of two parallel lenses of massive sulphide mineralisation, the Main West Zone, and the much smaller 007 Zone. Both are hosted by steeply west dipping altered felsic ash and lapilli tuffs. The Main Zone has a strike length of approximately 250 m and plunges to a depth of >700 m.

Less than 75 m to the west of the AB Zone and approximately 125 m west of D Zone, there is a major elongate, mixed intrusion trending parallel to stratigraphy for a number of kilometres, dominantly composed of amphibolite and gabbro with numerous volcanic inclusions. In the vicinity of the orebody this intrusion has a granodioritic to dioritic composition and is thought to be responsible for contact metamorphic effects in the volcanics which range from hornblende-hornfels metamorphism and recrystallisation, to the development of dalmatianite in the already-altered ore host.

Published reserve and resource figures include (Wolfden Resources Inc., 2006):

    AB Zone, indicated resource - 2.8 Mt @ 4.08% Cu, 0.57% Zn, 0.03% Pb, 0.58 g/t Au, 28.23 g/t Ag
    D Zone, indicated resource - 2.3 Mt @ 1.67% Cu, 3.51% Zn, 0.29% Pb, 0.43 g/t Au, 51.68 g/t Ag
    West Zone, indicated resource - 12.1 Mt @ 1.94% Cu, 3.97% Zn, 0.38% Pb, 1.13 g/t Au, 82.70 g/t Ag
    Total indicated resource - 17.2 Mt @ 2.25% Cu, 3.35% Zn, 0.31% Pb, 0.95 g/t Au, 69.72 g/t Ag.

The most recent source geological information used to prepare this summary 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.

  References & Additional Information

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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