USGS Professional Paper 1697 - Alaska Resources Library

52 Metallogenesis and Tectonics of the Russian Far East, Alaska, and the Canadian Cordillera
in East-Central Alaska. The significant deposits are at Kudz
Ze Kayah and Wolverine (table 4). Local Besshi and Cyprus
volcanogenic massive sulfide deposits also occur in the belt.
Kudz Ze Kayah Kuroko Massive Sulfide Deposit
The Kudz Ze Kayah kuroko Zn-Cu-Pb massive sulfide deposit
consists of pyrite-bearing massive sulfide bodies that are associated
with deformed, subvolcanic domes or thick sills that occur within
felsic metavolcanic units. The deposit contains mineable reserves
of 11.3 million tonnes grading 5.9 percent Zn, 0.98 percent Cu, 1.5
percent Pb, 133 g/t Ag, and 1.34 g/t Au (Mining Review, summer
2000). The deposit and similar occurrences are hosted in felsic
metavolcanic rocks of the Late Devonian to Middle Mississippian
Nasina Assemblage, which constitutes the middle structural
sequence of the Yukon-Tanana terrane (Mortensen, 1992).
Wolverine-Lynx Kuroko Massive Sulfide Deposits
The Wolverine-Lynx kuroko Zn-Cu-Pb-Ag-Au massive
sulfide deposits consist of massive sulfides in a fragmental
rhyolite unit, which is capped by an extensive magnetite iron
formation and limy exhalite. The deposit contains estimated
reserves (Wolverine and Lynx) of 6.2 million tonnes grading
12.66 percent Zn, 1.3 percent Cu, 1.5 percent Pb, 350 g/t Ag,
and 371 g/t Au (Mining Review, summer 2000).The deposit
occurs in the Yukon-Tanana terrane about 135 km southeast of
Ross River, Yukon Territory. It is hosted by interbedded felsic
volcanics and argillite of Devonian and Mississippian age.
Origin of Tectonic Setting for Frances Lake Metallogenic Belt
The eastern Frances Lake belt of kuroko massive sulfide
deposits is hosted in subvolcanic felsic domes or sills (Johnston
and Mortensen, 1994) that form lensoidal metavolcanic units that
interfinger with fine-grained quartzite and carbonaceous schist of
the Devonian and Mississippian Nasina Assemblage or Nisutlin
subterrane of the Yukon-Tanana terrane. The Nasina Assemblage
consists of carbonaceous quartzite, quartz-mica schist, marble,
mafic and felsic metavolcanic rocks and lesser amounts of metaplutonic
rocks. These units are interpreted as part of the extensive
Kootenay continental-margin igneous arc that formed along
the margin of the North American Craton Margin, subsequent
to rifting of the Yukon-Tanana and related terranes (Mortensen,
1992; Nokleberg and others, 2000). Remnants of the extensive
middle Paleozoic Kootenay continental margin arc and associated
lode deposits extend for several thousand km in various
metamorphosed continental margin terranes in Northern Alaska,
East Central Alaska, the northern and southern Canadian Cordillera,
and southeastern Alaska (Rubin and others, 1991; Plafker
and Berg, 1994; Nokleberg and others, 1994c, 1997c; Monger
and Nokleberg, 1996; Nokleberg and others, 2000). Fragments
of the Kootenay arc include the following metallogenic belts, in
addition to the Frances Lake belt, which host kuroko massive
sulfide and related deposits (Nokleberg and others, 1997a,b,c)
(1) Arctic metallogenic belt hosted in the Coldfoot terrane in
Arctic Alaska, (2) Alaska Range and Yukon-Tanana Upland
metallogenic belt hosted in the Yukon-Tanana terrane in central
and eastern Alaska, (3) Tracy metallogenic belt hosted in the
Yukon-Tanana terrane in southeastern Alaska and western British
Columbia, and (4) Kootenay-Shuswap metallogenic belt hosted
in the Kootenay terrane in the southern Canadian Cordillera.
Tracy Metallogenic Belt of Kuroko Massive
Sulfide Deposits (Belt TR) Southeastern Alaska
and Western British Columbia
The Tracy metallogenic belt of kuroko massive sulfide
deposits (fig. 17; tables 3, 4) extends from southeastern Alaska
into western British Columbia and is hosted in Devonian and
Mississippian interlayered metavolcanic and metasedimentary
rocks of the Yukon-Tanana terrane. In this region, the Yukon-
Tanana metamorphosed continental margin terrane occurs as
two, colinear, narrow fault-bounded fragments that extend discontinuously
north-northeast for several hundred km west of the
Stikinia island-arc terrane. The significant deposits are at Alamo,
Ecstall, Packsack, Red River, Scotia, Sumdum, and Sweetheart
Ridge (table 4) (Nokleberg and others 1997a,b, 1998).
Sumdum Kuroko Zn-Cu Massive Sulfide Deposit
The Sumdum kuroko Zn-Cu massive sulfide deposit consists
of massive lenses and disseminated zones containing pyrrhotite,
pyrite, chalcopyrite, sphalerite, and lesser bornite, malachite,
azurite, and galena in bodies as much as 15 m wide (Brew
and Grybeck, 1984; Kimball and others, 1984). The deposit
contains an estimated 24 million tonnes grading 0.57 percent
Cu, 0.37 percent Zn, and 10.3 to 103 g/t Ag, assuming deposit
continues beneath the Sumdum Glacier. The zones occur parallel
to layering along the crest and flanks of an isoclinal fold in
Paleozoic or Mesozoic metasedimentary schist and gneiss at the
western edge of the informally named Coast plutonic-metamorphic
complex of Brew and Ford (1984). Local sulfide-bearing
veins(?) and fault breccia, which may postdate the stratabound
deposit, may represent remobilization of the original deposit.
Ecstall Kuroko Zn-Cu Massive Sulfide Deposit.
The Ecstall kuroko Zn-Cu massive sulfide deposit, which
consists of pyrite, chalcopyrite, sphalerite, pyrrhotite, marcasite,
and galena, occurs in two tabular massive stratabound lenses in
Middle Devonian schist and quartzite that are intruded by granitoid
gneiss. These units are part of the Nisling assemblage of the
Yukon-Tanana terrane in the Coast Plutonic Complex of British
Columbia, Canada (EMR Canada, 1989; Hoy, 1991; Allrick and
others, 2001; MINFILE, 2002). The deposit contains estimated
reserves of 6.9 million tonnes grading 0.65 percent Cu and 2.5
percent Zn. The deposit occurs in a metavolcanic sequence that is
overprinted by an intense hydrothermal alteration assemblage of
chlorite, sericite, and silica.
Origin of and Tectonic Controls for Tracy Metallogenic Belt
The Tracy metallogenic belt of kuroko massive sulfide
deposits is hosted in metavolcanic and interlayered metasedi-