USGS Professional Paper 1697 - Alaska Resources Library

20 Metallogenesis and Tectonics of the Russian Far East, Alaska, and the Canadian Cordillera
Assemblage and Tindir Group with Late Proterozoic tillite and
hematite iron units of the Prikolyma terrane of the Kolyma
region in eastern Siberia (Furduy, 1968). This interpretation
tentatively supports juxtaposition of Siberia and Laurentia in
the Late Proterozoic.
Metallogenic Belts Formed During Proterozoic
Rifting of North American Craton or Craton Margin
Redstone Metallogenic Belt of Sediment-Hosted
Cu-Ag Deposits (Belt RS), Central Yukon Territory
The Redstone metallogenic belt of sediment-hosted Cu-
Ag deposits (fig, 3; tables 3, 4), which occurs in the western
Mackenzie district in the central Yukon Territory, is hosted in
the dominantly clastic rocks of the Late Proterozoic Windermere
Supergroup, which is part of the North American Craton
Margin (Gabrielse and Campbell, 1991; Nokleberg and others,
1997b, 1998). The largest deposits is at Coates Lake (Redstone);
the other deposit in the belt is the June Creek (Baldwin-
Shell) deposit (table 4) (Nokleberg and others 1997a,b, 1998).
Coates Lake (Redstone) sediment-hosted Cu-Ag Deposit
The Coates Lake (Redstone) sediment-hosted Cu-Ag
deposit consists of chalcopyrite, bornite, digenite, chalcocite
and covellite as disseminations stratabound in eight repetitive
algal carbonate/evaporite sabkha sequences along a transgressive
contact with underlying continental redbeds of the
Redstone River Formation (Chartrand and others, 1989). The
deposit contains estimated reserves of 37 million tonnes grading
3.9 percent Cu and 11.3 g/t Ag. Other deposits in the belt
are at June Creek, Hayhook Lake, and Per.
Origin of and Tectonic Controls for Redstone
Metallogenic Belt
The Coates Lake deposit is the largest and best-documented
example of Kuperschiefer-type, syngenetic mineral
deposit in Canada. Typically Kuperschiefer deposits are zonally
distributed and contain disseminated sulfides at oxidationreduction
boundaries in anoxic marine sedimentary rock at the
base of a marine or large-scale saline lacustrine transgressive
cycle. The host strata either overlie or are interbedded with
continental redbeds. The redbeds, along with characteristically-associated
evaporites, are a probable source of evaporitederived
ore fluid and copper (Kirkham, 1996a).
The Redstone metallogenic belt of sediment-hosted Cu-Ag
deposits and hosting Windermere Supergroup are interpreted
as forming during a period of major Late Proterozoic rifting
along the western continental margin of North America
(Gabrielse and Campbell, 1991). The Coates Lake Group that
hosts the Coates Lake deposit is an unconformity-bounded
rift assemblage, which occupies several fault-controlled
embayments over a 300 km-long trend that is located along
the eastern limit of Late Proterozoic strata in the Mackenzie
Mountains (Jefferson and Ruelle, 1986).
Churchill Metallogenic Belt of Cu Vein Deposits
(Belt CH), Northern British Columbia
The Churchill metallogenic Belt of Cu vein deposits
occurs in the Muskwa Ranges assemblage in northern British
Columbia (fig. 3; tables 2, 3) (Nokleberg and others, 1997b,
1998). This assemblage consists of a platformal succession,
about 6-km-thick, of quartzite, carbonate rocks, and flysch
that are tentatively correlated with the Purcell (Belt) Supergroup,
which was deposited along the passive continental
margin of the North American Craton (Bell, 1968; Aitken and
McMechan, 1991). The Muskwa Ranges assemblage consists
of a lower sequence of platformal quartzite and carbonate rocks
that is about 3.5 km thick, and an upper sequence of shaley flysch,
which is about 2.5 km thick. In this area are 12 significant
Cu vein deposits that occur in clastic and impure carbonate
rocks of the Aida and Gataga formations in the Racing River-
Gataga River region (Taylor and Stott, 1973). The significant
deposit is at Churchill. Other Cu vein deposits in the Churchill
metallogenic belt are at Davis Keays, Gataga, and Fram.
Churchill (Davis Keays) Cu Vein Deposits.
The major Churchill (Davis Keays) Cu vein deposit
occurs along the Magnum vein system. The deposit consists
of chalcopyrite, pyrite, quartz, and ankerite in a zone that is
100 m wide (Preto and Tidsbury, 1971; Dawson and others,
1991). The deposit occurs in strongly folded Late Proterozoic
dolomites and slates of the Aida Formation (with K-Ar
isotopic age 780 Ma) and is intruded by diabase dikes and
sills. Overlying Cambrian basal conglomerate contains clasts
of mineralized vein material. The deposit age is interpreted as
Late Proterozoic. From 1971 to 1974, 498,00 tonnes grading
3.43 percent Cu were produced. The grade is highly variable
and discontinuous.
Origin of and Tectonic Controls for Churchill
Metallogenic Belt
The Cu vein deposits in the Churchill metallogenic belt
are associated with a northwest-striking diabase dike swarm
that crosscuts folded sedimentary rocks in the Purcell (Belt)
Supergroup that were deposited along the passive continental
margin of the North American Craton. The Cu vein deposits
are partly concordant with and intruded by genetically related
diabase dikes. However, no diabase dikes occur in the Late
Proterozoic Windermere Groas much as the west, indicating
an early Late Proterozoic age for dike emplacement and
formation of associated Cu vein deposits (Dawson and others,
1991). The Churchill metallogenic belt is interpreted as
forming in a major, Mesoproterozoic rifting event, which is
reflected in the sedimentary assemblages of the Purcell and
Wernecke Supergroups and the Muskwa Ranges assemblage.