USGS Professional Paper 1697 - Alaska Resources Library

106 Metallogenesis and Tectonics of the Russian Far East, Alaska, and the Canadian Cordillera
can Craton Margin (Gehrels and others, 1990; Monger and
Nokleberg, 1996; Nokleberg and others, 1994c, 1997c, 2000).
Several other metallogenic belts are herein interpreted as
forming during granitic magmatism associated with formation
of the Stikinia and Quesnellia island arcs, including the
Copper Mountain (North), Galore Creek, Guichon, Klotassin,
Texas Creek, and Toodoggone belts.
Coast Mountains Metallogenic Belt of Volcanogenic
Cu-Zn-Au-Ag Massive Sulfide Deposits
(Belt CM), Northern British Columbia
The Coast Mountains metallogenic belt of volcanogenic
massive sulfide deposits (fig. 42; tables 3, 4) occurs in the
western limb of the oroclinally warped Stikinia island-arc terrane.
To the west, the belt and terrane are borded by, and in part,
intruded by plutons along the eastern edge of the Coast Plutonic
Complex. The metallogenic belt contains a variety of significant
kuroko, Cyprus, and Besshi massive sulfide deposits (Nokleberg
and others, 1997a,b). The significant deposits are the Tulsequah
Chief and Eskay Creek kuroko Zn-Cu-Pb-Au-Ag massive
sulfide deposits, the Granduc Besshi massive sulfide deposit,
and the Alice Arm Silver and Anyox districts of Cyprus massive
sulfide deposits (table 4) (Nokleberg and others 1997a,b, 1998).
The Coast metallogenic belt contains a variety of volcanogenic
massive sulfide deposits of various ages. The following
are major rock sequences host volcanogenic massive
sulfide deposits in the Stikinia terrane: (1) the middle to upper
Paleozoic Stikine assemblage, which contains interbedded volcanic
arc, carbonate and fine-grained clastic rocks, (2) the Late
Triassic Stuhini and Takla Groups that unconformably overlie
the Stikine assemblage, and contain volcanic arc rocks and
interfingering clastic rocks that are intruded by coeval granitoids,
and (3) the unconformably-overlying, Early Jurassic
Hazelton and Spatzizi Groups, and the Takwahoni Formation
that contain andesitic volcanic rocks and intercalated sedimentary
rocks. The Stikinia island-arc terrane is interpreted as
forming on the deformed continental-margin strata of Yukon-
Tanana terrane, which may be a rifted fragment of the North
American Craton Margin (Gehrels and others, 1990; Monger
and Nokleberg, 1996; Nokleberg and others, 1994c, 1997c).
Tulsequah Chief Kuroko Massive Sulfide Deposit
The Tulsequah Chief kuroko Zn-Cu-Au-Ag-Pb volcanogenic
massive sulfide deposit consists of massive to disseminated
pyrite, sphalerite, chalcopyrite, and galena, with minor
tennantite and tetrahedrite in conformable lenses that occur
between a hanging wall of dacite tuff and a footwall sequence
of basalt and andesite flows. The volcanic rocks constitute
a bimodal sequence within the Devonian and Mississippian
Mount Eaton series of the Stuhini Group. The occurrence of
several stacked ore lenses with repeated bimodal volcanic and
sedimentary rocks indicate that several rifting events occurred
in a local basin that was part of a mature island arc (Sebert and
Barrett, 1996). Production from 1951 to 1957 was 574,000
tonnes. The deposit has reserves of 8.8 million tonnes of ore
grading 6.42 percent Zn, 1.3 percent Cu. 1.21 percent Pb, 2.1
g/t Au and 106.4 g/t Ag. (Dawson and others, 1991; Redfern
Resources Ltd., summary report,1995)
Granduc Besshi Massive Sulfide Deposit
The Granduc Besshi Cu (Ag-Au-Co) deposit consists of
several overlapping, tabular sulfide lenses hosted in pelagic
sedimentary rocks and turbidites that are underlain by basalt
and andesite flows, within the Late Triassic Stuhini Group
(Grove, 1986; Dawson and others, 1991; MINFILE, 2002).
The host rocks are intruded by Jurassic to Tertiary granitoid
plutons of the Coast Plutonic Complex. The deposit contains
reserves of 32.5 million tonnes grading 1.93 percent Cu, 7 g/t
Ag and 0.13 g/t Au. A Besshi-type exhalative origin is supported
by laterally extensive, well-bedded ore lenses, dominantly
sedimentary host rock, and ore minerals. The deposition
is interpreted as occurring in a sedimentary basin adjacent to
the Stuhini island arc.
Eskay Creek Kuroko Massive Sulfide Deposit
The Eskay Creek Ag-Au polymetallic kuroko massive
sulfide deposit consists of sphalerite, tetrahedrite, boulangerite,
and bournonite with minor pyrite and galena that occur as stratabound
and stratiform massive, semi-massive and disseminated
layers in carbonaceous and tuffaceous mudstone of the Lower
Jurassic Mount Dilworth Formation of the Hazelton Assemblage
(EMR Canada, 1989; Prime Equities Inc., 1991; Mac-
Donald, 1992; Sherlock and others, 1999; MINFILE, 2002).
Gold and silver occur as electrum grains (5 to 80 microns)
within fractured sphalerite, commonly in contact with galena.
The deposit has estimated reserves of 3.9 million tonnes grading
26 g/t Au and 986 g/t Ag. The 21B zone has reserves 1.04
million tonnes grading 63.8 g/t Au and 2567 g/t Ag, and the
109 zone, a coeval epithermal vein deposit, has reserves of 0.97
million tonnes grading 9.6 g/t Au and 127 g/t Ag.
Alice Arm Silver District of Massive Sulfide Deposits
The Alice Arm Silver district, which contains the Dolly
Varden, North Star, and other kuroko Ag-Pb-Zn deposits, is
hosted in Early Jurassic calc-alkaline volcanic rocks of the
Hazelton Group. The deposits consists of pyrite, sphalerite,
galena, tetrahedrite, pyrargyrite and some native silver in
barite-Ag-rich sulfide lenses (Devlin and Godwin, 1986; EMR
Canada, 1989; Mining Review, 1992). The various deposits are
interpreted as structurally displaced parts of a once continuous
massive sulfide zone. The combined production and reserves for
the Alice Arm Silver district are 2.91 million tonnes grading 390
g/t Ag, 0.53 percent Pb, and 0.82 percent Zn.
Anyox Cyprus Massive Sulfide Deposit
The Anyox Cyprus Cu-Ag-Au district contains the Hidden
Creek and Bonanza deposits and five other occurrences. The