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Clear Lake, Sue Claims

Yukon Territory, Canada

Main commodities: Zn Pb Ag
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The Clear Lake (previously Sue Claims) sediment hosted Zn-Pb-Ag deposit is located 80 km NW of Faro, 65 km east of Pelly Crossing, 90 km NE of Carmacks and 225 km north of Whitehorse in the Yukon Territory, in northwestern Canada .

Exploration tenements were first taken out in 1965 following the discovery of the Faro Anvil deposits. After an EM survey, six EM anomalies were outlined and drilled, with one hole intersecting 0.45 m of massive pyrite. The claims were allowed to lapse. The area was re-staked in 1974 as the Sue Claims and extensive bulldozer trenching, geophysical surveying and diamond drilling undertaken. The main sulphide body was discovered in 1978 while drilling a 3 mgal residual gravity anomaly. The gravity anomaly coincides with magnetic and EM responses and is situated beside a small acidic lake containing geochemically anomalous lake bottom sediments which assayed up to 1.9% Zn, 1.2 ppm Ag, and 20 to 40 ppm Cu. A subtle gossan was later recognized over the target.

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The deposit lies close to the southwestern margin of the Selwyn Basin, and is transected by the continental scale, NW-SE trending, dextral, Eocene Tintina Fault. It is hosted by the carbonaceous argillite, siltstone, chert and tuff of the Devonian to Lower Devonian Earn Group on the margin of the McEvoy platform which marks the southwestern margin of the deeper Selwyn Basin. The underlying succession within the Selwyn basin includes the Late Neoproterozoic to Lower Cambrian Hyland Group, which comprises gritty clastic rocks and carbonates of the Yusezyu Formation (>500 m) and the overlying maroon shale and minor sandstone of the Narchilla Formation (0 to 630 m). These are succeeded by the Lower Cambrian Gull Lake Formation (0 to 400 m) which comprises grey-brown to rust weathering, dark blue-grey to lustrous grey phyllite to quartz-muscovite-biotite schist, minor marble and calc-silicates, and rare amphibolite. These are, in turn, overlain by the Cambro-Ordovician Rabbitkettle Formation, which comprises from 200 to possibly 800 m of white to buff weathering strata dominated by argillaceous limestone and siltstone, comprising various proportions of the lower Vangorda facies (500 m) calcareous phyllite, Twopete facies (600 to 800 m) siltstone and Gold Creek facies (270 m) siltstone and limestone. These are overlain by the basaltic volcanic rocks of the Menzie Creek Formation (>400 m). The succeeding Ordovician to Silurian Road River Group includes black siliceous shale and chert of the Duo Lake Formation (175 to 200 m) and orange to rust weathering pale green to blue grey pyritic argillite to siltstone of the Steel Formation (250 m). The Road River Group is overlain by the well bedded black cherts and argillites of the Early to Late Devonian Portrait Lake Formation (200 m), the basal unit of the Earn Group, followed by the Devonian to Lower Carboniferous upper member, the Prevost Formation (>500 m) cherts, chert bearing conglomerate, sandstone, argillites and limestone.

The deposit area is cut by the NW-SE trending Tintina Fault. To the NE of the fault, the Selwyn Basin sequence is represented by phyllite of the Lower Cambrian Mt Mye Formation, an informal unit within the Gull Lake Formation, and calcareous phyllite and limestone of the Cambrian to Ordovician Vangorda facies of the Rabbitkettle Formation. SE of the fault, the parautochthonous sequence comprises the Ordovician to Lower Devonian Road River Group shale, and the Devonian to Mississippian Earn Group clastic rocks which host the Clear Lake deposit. The deposit is masked by 5 to 26 m of glacial overburden, and the geology has only been delineated from drillholes, trenches and interpretations of geophysical data.

The deposit has a sigmoidal shape. It is ~1000 m long, dipping steeply to the east with a width of up to 120 m, but pinches out at depth. Bouma sequences in drill core indicate that it is overturned. Sulphide minerals are laminated and are largely of framboidal pyrite which is slumped and fragmented in places, comprising ~30 Mt of massive sulphides, predominantly pyrite. The best drill intersection returned 13 m of 18.3% Zn, 2.15% Pb and 58.6 g/t Ag. Tuffaceous rocks intercalated with the sulphides reach a thickness of 30 m in the stratigraphically footwall to the main massive sulphide lens. The tuff has pyroclastic textures, with both matrix and fragments predominantly altered to soft grey clay, with local concretions of galena, sphalerite, barite, siderite and calcite.

The overturned footwall tuff is stratigraphically overlain by argillite which is silicified to a depth of 90 m below the deposit. The overturned stratigraphic hanging wall is occupied by an argillite that is extensively silicified to resembles mottled to laminated chert. Both the hanging wall and footwall argillite carry irregular pyrite stringers and masses throughout. In several drillholes, massive barite appears to be peripheral to, and forms a partial cap over the deposit. Barite and tuff lenses intersected at depth suggest potential for another sulphide lens below the main orebody.

A trace element study of the tuffaceous rocks (J. Morin of DIAND) showed high Ti and P contents and high K2O/Na2O ratios, suggesting an alkaline volcanic environment. The deposit is inferred to have accompanied Devonian rifting. Interpreted worm tubes replaced by quartz and calcite, which are surrounded and partly replaced by sphalerite and pyrite, have been found in drill core, and the sulphides are believed to have precipitated from a hydrothermal fluid of >350°C.

Published underground Mineral Resources total (SRK consulting report for Copper Ridge Explorations, February 2010):
    Inferred Resource - 5.57 Mt @ 11.4% Zn, 2% Pb, 38.01 g/t Ag; -or-
    Inferred Resource - 7.765 Mt @ 7.6% Zn, 1.08% Pb, 22 g/t Ag; 4% Pb+Zn cutoff, Pb and Ag capped to 1.5% and 60 g/t respectively.

The contents of this summary are largely drawn from the Yukon Geological Survey's Integrated Data System (YGSIDS) viewed October, 2018.

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

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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