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Finlayson Lake District - Kudz Ze Kayah, Wolverine, GP4F, Fyre Lake, Ice

Yukon Territory, Canada

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The Finlayson Lake District, which is approximately 225 km ENE of Whitehorse in southeastern Yukon Territory, Canada embraces a number of significant volcanic hosted massive sulphide (VHMS) deposits within felsic Devonian-Carboniferous volcanics, including the   Wolverine,   Kudz Ze Kayah   and   GP4F   Zn-Pb-Cu-Ag-Au,   the   Fyre Lake   Cu-Co-Au   and the   Ice   Cu rich mineralisation.

The Finlayson Lake District falls within the central section of an isolated outlier of the Yukon-Tanana and Slide Mountain terranes that is offset from the main mass of the terrane across the continental scale, north-west trending, dextral transcrurrent Tintina Fault Zone.   This offset block occurs to the north-east of that structure, bounded to the east and north by the lower to middle Palaeozoic sediments of the Selwyn Basin.   The Yukon-Tanana and Slide Mountain terranes represent a continental arc and back arc basin sequence that developed on the Devonian to Permian Pacific margin of North America.

The lithologies of the Finlayson Lake District include variably deformed and metamorphosed, foliated and lineated greenschist facies to lower amphibolite grade metasediments, metavolcanics and meta-plutonic rocks.   The metasediments and metavolcanics have been divided into three unconformity bounded sequences, from the base:

1). Grass Lakes succession - subdivided into:
 i). Unit 1 - early Carboniferous, quartz rich, non-carbonaceous metaclastics,
 ii). Fire Lake Unit - 365 to 360 Ma mafic dominated arc and back-arc volcanics, including the boninitic hosts to the "Besshi-style" Fyre Lake deposit,
 iii). Kudz Ze Kayah Unit - felsic volcanic and sediment dominated unit comprising mainly Devonian to Lower Carboniferous (Mississippian), 360 to 356 Ma felsic volcanics with variably carbonaceous sediments in the lower sections of the unit - these volcanics and associated sediments host the Kudz Ze Kayah, and GP4F VHMS deposits, and
 iv). Unit 4 - predominantly alkalic basalts and carbonaceous sediments.   Contemporaneously with the Kudz Ze Kayah Unit and Unit 4 there are 360±1 Ma Devono-Carboniferous K feldspar porphyritic to megacrystic granites of the Grass Lakes Suites were emplaced and are inferred to be the intrusive equivalents of the Kudz Ze Kayah Unit volcanics.

2). Wolverine succession - composed predominantly of early Carboniferous (356 to 346 Ma) felsic volcanic and carbonaceous sediments which host the Wolverine VHMS deposit.   The sequence commences with a lower conglomeratic unit, a lower felsic volcanic dominated unit, a regional carbonaceous argillite, the immediate footwall felsic volcanic and sub-volcanic rocks of the Wolverine deposit and a hangingwall of unit of aphyric rhyolites and carbonaceous sediments grading up into basalt flows.   The Wolverine deposit is at the contact between footwall felsic volcanics and a hangingwall of either carbonaceous argillite or "exhalite" bands.

3). Campbell Range succession - composed mainly of Lower Carboniferous to Lower Permian basalt, mafic and ultramafic plutonic rocks and minor sediments.

The rocks of the Fire Lake unit are within the footwall of the Early Permian Money Creek Thrust, above which the hangingwall sequence has been displaced by at least 35 km from the ENE.   The hangingwall of the Money Creek Thrust is occupied by Upper Devonian to Lower Carboniferous meta-sedimentary and felsic to intermediate meta-volcanic rocks and granitoids, Lower Permian limestones and dark grey basinal sediments. These are in turn overlain by another thrust sheet of undeformed Late Devonian volcanic rocks of the Cleaver Lake Formation which are associated with co-magmatic felsic, mafic and ultramafic meta-plutonic rocks and an Upper Carboniferous pluton of the Simpson Range plutonic suite. The region has also been subjected to ductile deformation during the Cretaceous. To the north and east the imbricated Yukon-Tanana terrane is juxtaposed across the Jules Creek fault against the rocks of the Slide Mountain terrane which comprise the Campbell Range Formation. The mafic rocks of the Slide Mountain terrane host the Ice VMS deposit, interpretted to have formed in a Permian back arc basin.

Wolverine

The host rocks to the Wolverine deposit are part of the Wolverine Succession and comprise from the base:
 Unit 1 - Footwall sedimentary volcaniclastic and intrusive rocks, comprising black to grey carbonaceous argillite which grades upwards into greenish-grey quartz and feldspar crystal rhyolite volcaniclastics containing subrounded fragments of rhyolite and several percent K feldspar phenocrysts. The abundance and size of felsic volcanic fragments decrease markedly laterally away from the deposit. K feldspar-phyric rhyolite intrusives, which are 6 to 15 m thick are locally found around 20 m below the massive sulphides and represent sills emplaced contemporaneously with the massive sulphides. Similar sills are found at the same stratigraphic position at the Sable and Fisher massive sulphide occurrences 3 km to the SE and 8 km to the NW respectively. At Wolverine these have been dated at 347.8±1.3 Ma.
 Unit 2 - Interbedded argillite, rhyolite and magnetite-carbonite-sulphides, which are composed predominantly of intecalated black, graphitic argillite and massive to banded aphyric, silicified rhyolite containing millimetric quartz-pyrite veinlets. Up to 10 m thick, lenslike bands of massive sulphide occur at or near the contact between units 1 and 2, at what is known as the Wolverine Horizon, recognised regionally by the transition from quartz- and feldspar-phyric rhyolite of Unit 1, to the aphyric rhyolite of Unit 2. The hangingwall of the massive sulphide is typically composed of graphitic argillite. The massive sulphides are closely overlain by carbonate dominated 'exhalites', while 80 to 100 m higher there are laterally extensive, magnetite dominant iron formation 'exhalites' which occur over strike lengths of up to 12 km.
 Unit 3 - Fragmental rhyolite, which occurs above the uppermost iron formation where interbedded rhyolite and argillite grade into rhyolite volcaniclastics which have fragmental textures comprising sub-angular to sub-rounded cm-sized aphanitic volcanic clasts. The rhyolite has local interbeds of carbonaceous argillite.
 Unit 4 - Interbedded carbonaceous argillite, greywacke, basalt and rhyolite, with the carbonaceous argillite and black to grey, medium grained greywacke interbedded to form around 60% of the unit, with the next most common lithology being fine grained basalt, with minor felsic volcaniclastics. The upper most part of the represents the transition from the dominantly felsic volcanic rocks of the Wolverine succession to the overlying mafic volcanic unit.

The deposit comprises two discrete, tabular, Zn-Pb-rich massive sulphide lenses, the Wolverine and Lynx zones, each around 250 m long, separated to the NW and SE respectively by a 200 m long zone of Cu-rich semi-massive, replacement and sulphide-stringers known as the Hump zone. These three zones constitute the Wolverine deposit which is around 700 m long, 475 m wide and 1 to 10 m thick. It strikes NW-SE and dips at 30°NE. Locally, as in the thickest part of the Lynx zone, there are multiple sulphide bands, separated by 4 to 8 m of argillite or rhyolite. The sulphides pinch out up-dip, approximately 50 m below the surface, and persists for more than 500 m down-dip. Four discrete sulphide stringer vein zones extend up to 13 m below the Wolverine massive sulphide and Hump semi-massive zones, while another two occur on the western and south-western up-dip edge of the deposit. The stringer zones are surrounded above and laterally by chalcopyrite rich replacement style sulphide mineralisation, which grades into sphalerite replacement on the lateral margins of the massive sulphide lenses.

The massive sulphides are banded, and comprise 70 to 95% fine grained sulphides, dominantly pyrite and sphalerite, with subordinate pyrrhotite, chalcopyrite, galena, tetrahedrite and arsenopyrite and trace marcasite, native gold, meneghinite, bournonite, boulangerite and miargyrite.

The semi-massive sulphides comprise 10 to 50% sulphides which have partially or wholly replaced the host forming discrete, fine-grained, semi-massive sulphide lenses from several cm to 1 m thick. These lenses are composed of chalcopyrite, sphalerite, pyrite and minor pyrrhotite. Chalcopyrite is more abundant in the semi-massive compared to the massive sulphides and is asscoaited with chlorite alteration. Semi-massive replacement sphalerite occurs as lenses, blebs and disseminations, associated with sericite and ankerite, distal to the massive sulphides.

The stringer vein sulphides occur as 2 to 3 cm thick quartz-sulphide stringer veins which parallel the S1 foliation and comprise 5 to 10% of the rock. Individual veins are enveloped by 5 to 10 cm selvages of silicification, while groups of veins may occur within a silicified zone up to 25 cm wide which contains pyrite and sphalerite with subordinate chalcopyrite, pyrrhotite and arsenopyrite. Common gangue includes quartz, calcite, dolomite, ankerite, siderite, chlorite, biotite and muscovite.

The geologic resource at Wolverine comprises:
    6.237 Mt @ 12.7% Zn, 1.6% Pb, 1.3% Cu, 371 g/t Ag, 1.8 g/t Au (Bradshaw, et al., 2008).

Kudz Ze Kayah

This deposit is hosted by the Kudz Ze Kayah Unit, comprising a felsic volcanic and sediment dominated sequence comprising mainly Devonian to Lower Carboniferous, 360 to 356 Ma felsic volcanics with variably carbonaceous sediments in the lower sections of the unit. The deposit comprises a coherent lens of massive to semi-massive sulphides deformed into a large isoclinal synform with a fold vergence and dip to the NNE. The limbs of the isoclinal synform are known as the upper and lower lenses that show a near symmetric base-metal and hydrothermal alteration zonation around the fold axis. It extends down dip for around 300 m and has a strike lenght of approximately 750 m. The mineralisation reaches a maximum thickness of 34 m and predominantly comprises pyrite, sphalerite, minor chalcopyrite, galena, pyrrhotite, barite and trace arsenopyrite, tetrahedrite, electrum and boulangerite.

The stratigraphic footwall rocks are extensively altered with stringer and/or replacement mineralisation characterised by and upward transition of pyrite, chalcopyrite, sphalerite and galena, with white mica, chlorite and albite concentrated towards the base. The hangingwall rocks, in contrast have little visible alteration or mineralisation.

Several metre scale granitic pegmatite dykes cut the footwall meta-volcanics and massive sulphides and have chloritised margins and when in massive sulphides have associated centimetric scale sulphide recrystallisation aggregates.

The geologic resource at Kudz Ze Kayah comprises:
    13 Mt @ 5.5% Zn, 1.3% Pb, 1% Cu, 125 g/t Ag, 1.2 g/t Au (Bradshaw, et al., 2008).

GP4F

This deposit is also hosted by the Kudz Ze Kayah Unit, as descibed above and is approximately 5 km SE of Kudz Ze Kayah and 20 km west to WNW of Wolverine. Mineralisation occurs as a single, narrow, massive to semi-massive sulphide lens that dips at 30 to 35°N and is up to 3.2 m thick. The sulphides zones comprise pyrite and sphalerite, with minor galena and pyrrhotite, and trace chalcopyrite. The mineralised zone occur in an overturned homoclinal sequence. The stratigraphic footwall/structural hangingwall have a well developed hydrothermal alteration assemblage of muscovite-tourmaline-chlorite-biotite-garnet and a weakly developed base-metal zonation.

The massive sulphides of the deposit are cut with sharp margins by numerous, metre-scale, dark-grey intemediate to basalt dykes.

The geologic resource at GP4F comprises:
    1.5 Mt @ 6.4% Zn, 3.1% Pb, 0.1% Cu, 89.7 g/t Ag, 2.0 g/t Au (Bradshaw, et al., 2008).

Resources at the other Finlayson Lake deposits (Piercey, et al., 2001) amounted to:
  Fyre Lake - 8.5 Mt of Cu-Co-Au ore.
  Ice - 4.5 Mt of Cu rich ore.

For more detail consult the reference(s) listed below.

The most recent source geological information used to prepare this summary was dated: 2001.    
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:
Bradshaw G D, Rowins S M, Peter J M and Taylor B E  2008 - Genesis of the Wolverine Volcanic Sediment-Hosted Massive Sulfide Deposit, Finlayson Lake District, Yukon, Canada: Mineralogical, Mineral Chemical, Fluid Inclusion, and Sulfur Isotope Evidence: in    Econ. Geol.   v103 pp 35-60
Layton-Matthews D, Peter J M, Scott S D and Leybourne M I  2008 - Distribution, Mineralogy, and Geochemistry of Selenium in Felsic Volcanic-Hosted Massive Sulfide Deposits of the Finlayson Lake District, Yukon Territory, Canada: in    Econ. Geol.   v103 pp 61-88
Piercey S J, Peter J M, Mortensen J K, Paradis S, Murphy D C and Tucker T L  2008 - Petrology and U-Pb Geochronology of Footwall Porphyritic Rhyolites from the Wolverine Volcanogenic Massive Sulfide Deposit, Yukon, Canada: Implications for the Genesis of Massive Sulfide Deposits in Continental Margin Environments: in    Econ. Geol.   v103 pp 5-33
Piercey S J, Paradis S, Murphy D C, Mortensen J K  2001 - Geochemistry and paleotectonic setting of felsic volcanic rocks in the Finlayson Lake volcanic-hosted massive Sulfide district, Yukon, Canada: in    Econ. Geol.   v96 pp 1877-1905
Piercey, S.J. and Kamber, B.S.,  2019 - Lead Isotope Geochemistry of Shales from the Wolverine Volcanogenic Massive Sulfide Deposit, Yukon: Implications for Pb Isotope Vectoring in Exhalative Ore Systems: in    Econ. Geol.   v.114, pp. 47-66.
Piercey, S.J., Gibson, H.L., Tardif, N. and Kamber, B.S.,  2016 - Ambient Redox and Hydrothermal Environment of the Wolverine Volcanogenic Massive Sulfide Deposit, Yukon: Insights from Lithofacies and Lithogeochemistry of Mississippian Host Shales: in    Econ. Geol.   v.111, pp. 1439-1463


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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