USGS Professional Paper 1697 - Alaska Resources Library

Finlayson Lake Metallogenic Belt of SEDEX
Zn-Pb-Ag-Cu-Au Deposits (Belt FL), Southern
Yukon Territory
The Finlayson Lake metallogenic belt of SEDEX Zn-Pb-
Ag-Cu-Au deposits (fig. 17; tables 3, 4) occurs in the Selwyn
Basin of the North American Craton Margin in the Yukon
Territory. The significant deposits at Maxi and Matt Berry
(table 4) (Nokleberg and others 1997a,b, 1998) are hosted in
deformed sedimentary rocks of the Road River Group. The
stratigraphic position and age of the host rocks at Maxi are
better known than at Matt Berry.
Maxi SEDEX Zn-Pb-Ag Occurrence
The Maxi SEDEX Zn-Pb-Ag occurrence consists of
galena, sphalerite, and quartz that occur as penetratively
deformed and transformed lamellae and bands in black phyllite
in the basal Road River Group (Blusson, 1978). The sulfides
are commonly coarse grained and concentrated in minor
fold hinges, indicating mobilization during pre-Late Devonian,
regional metamorphism. A second stage of folding and thermal
metamorphism is interpreted as related to Cretaceous granitoid
plutons in the area (Blusson, 1978). No reserves or resources
are reported.
Matt Berry SEDEX Pb-Zn Deposit
The Matt Berry SEDEX deposit consists of massive
galena, sphalerite, pyrrhotite and chalcopyrite that occur with
minor antimony-silver minerals (Ostler, 1979; Bremner and
Ouellette, 1991). The deposit contains estimated reserves of
533,434 tonnes grading 6.81 percent Pb, 4.8 percent Zn, and
102.9 g/t Ag (Northern Miner, August 5, 1980). The sulfides
are concentrated with quartz, in fold noses, and in discontinuous
enechelon lenses over a strike length of 500 m. The
rocks have undergone at least three periods of deformation
and metamorphism, including thermal metamorphism along
the contacts of a Cretaceous granitoid pluton. The deposits
constitute a zone of sulfide lenses as much as 10 m thick that
are hosted by deformed black phyllite and quartz-sericite
phyllite, probably of the Paleozoic Road River Group in eastern
Selwyn Basin, Yukon. The copper and antimony minerals
are interpreted as related to local Cretaceous intrusive
activity that overprints the Paleozoic SEDEX mineralization
that formed along a Devonian and Mississippian passive
continental margin.
Origin of and Tectonic Setting for Finlayson Lake
Metallogenic Belt
The Maxi and Matt Berry deposits are interpreted as
originally stratiform SEDEX sulfides deposits, which were
deposited with black shale in the Ordovician and Silurian
Road River Group and are provisionally correlated with the
adjacent Howards Pass metallogenic belt to the northeast. The
Maxi and Matt Berry deposits were attenuated, deformed,
Middle and Late Devonian Metallogenic Belts (387 to 360 Ma; figures 16, 17) 67
remobilized, and contact metamorphosed during mid-Cretaceous
magmatism, uplift and deformation.
Liard Metallogenic Belt of Southeast Missouri
Ba-F Deposits (Belt LI) Northern British Columbia
The Liard metallogenic belt of Southeast Missouri Ba-F
deposits occurs in northern British Columbia and is hosted mainly
in early to middle Devonian shelf carbonate rocks in the North
American Craton Margin (fig. 17; tables 3, 4) (Nokleberg and
others, 1997b, 1998). The deposits are epigenetic stockworks, breccia-fillings,
replacements, and (or) veins that exhibit stratigraphic
and structural controls similar to those of Southeast Missouri
Zn-Pb deposits. The large deposits exhibit a southward lateral gradation
towards several, small Zn-Pb vein and breccia occurrences
that are hosted in a dolomite-barite-fluorite gangue (Dawson,
1983). The Ba-F deposits are herein interpreted as analogous to
Southeast Missouri Pb-Zn deposits. However, local epigenetic barite
deposits occur in the area without fluorspar and Pb-Zn sulfides.
Leguil Creek Bedded Ba Deposit
The Leguil Creek (Letain) bedded Ba deposit consists of
three stratabound zones of veins and lenses of barite that are hosed
in Cambrian to Devonian shale and siltstone (MINFILE, 2002).
The barite and host rocks are gently folded. Discordant, fault-controlled
barite vein zones range from 1 to 4 m thick. Barite sulphur
isotopic analysis indicate a Devonian age of mineralization (K.M.
Dawson, unpub. data, 1995). A SEDEX barite origin, similar to
that for the adjacent Gataga SEDEX metallogenic belt, with subsequent
tectonic remobilization, is herein proposed.
Lower Liard Southeast Missouri Ba-F and Muncho Lake
Ba Deposits
The Lower Liard Southeast Missouri Ba-F deposit consists
of fluorite with barite, witherite, barytocalciite, quartz
and calcite that occurs as veins, lenses, and breccia-fillings at
the contact between limestone of the Middle Devonian Dunedin
Formation and shale of the Besa River Formation (EMR
Canada, 1989; MINFILE, 2002). Fission-track dating suggests a
Mississippian age of mineralization (MINFILE, 2002). Massive
stratabound Ba deposits, which occur in the same region at
Muncho Lake, northern British Columbia, are not hosted by the
same strata, and may be spatially related to fluorite-free barite
replacements and breccias. The Muncho Lake Ba in northern
British Columbia deposit consists of massive, stratabound barite
that is devoid of fluorite. The barite layer overlies the Waknash
Formation and is bedded and contains local abundant sandstone
and may exhibit evaporite textures (Dan Hora, written commun.,
2000). Also occurring in the area barite veins (Butnerchuk
and Hancock, 1997; MINFILE, 2002).
Origin of and Tectonic Setting for Liard Metallogenic Belt
The Liard metallogenic belt of Southeast Missouri(?) Ba-
F deposits is hosted in Devonian passive continental-margin