Metallogenesis and Tectonics of the Russian Far East, Alaska, and ...

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The Coast metallogenic belt contains a variety of volcanogenic massive sulfide deposits of various ages. Following are
the major rock sequences which 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 Group and Takla Group, which unconformably overlie the Stikine assemblage, and contain volcanic arc rocks and
interfingering clastic rocks which are intruded by coeval granitoids; and (3) the unconformably-overlying, Early Jurassic Hazelton
and Spatzizi Groups, and the Takwahoni Formation which 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, 1997~).
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 which 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 which several rifting events occurred in a local basin which 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% Zn, 1.3% Cu. 1.2 1 % Pb, 2.1 g/t Au and 106.4 g/t Ag. (Dawson and others, 199 1 ;
Redfem 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 which 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% 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 boumonite with minor pyrite and galena which 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; MacDonald, 1992; Sherlock and others, 1999; MINFILE, 2002). Gold and silver
occur as electrurn grains (5 to 80 microns) within fractured sphalerite, commonly in contact with galena. The deposit has estimated
reserves3.9 million tonnes grading 26 g/t Au and 986 g/t Ag. The 2 1B 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 2.9 1 million tonnes grading 390 g/t Ag, 0.53%
Pb, and 0.82% 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
deposits and occurrences consist of lenticular to sheet-like ore bodies of pyrite and pyrrhotite, lesser chalcopyrite, and minor
sphalerite and magnetite (Grove, 1986; EMR Canada, 1989; Hoy, 1991; Smith, 1993). Combined production and reserves are 26.7
million tonnes grading 1.48% Cu, 9.6 g/t Ag, and 0.17 g/t Au. The deposits and occurrences are located near the contact between
volcanic and sedimentary rocks in a roof pendant of tholeiitic mafic volcanic rocks and overlying turbidites which are intruded by
the Coast Plutonic Complex. Host rock geochemistry indicates formation along an ocean ridge. The host strata are interpreted as
Early and Middle Jurassic volcanic and sedimentary units of the Stikinia terrane (Macdonald and others, 1996).
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