USGS Professional Paper 1697 - Alaska Resources Library

258 Metallogenesis and Tectonics of the Russian Far East, Alaska, and the Canadian Cordillera
Porphyry Mo Deposits Associated with Alice Arm
Intrusions of Nanika Plutonic Suite
The Alice Arm Intrusions of the Nanika Plutonic Suite,
which occur along the eastern margin of the Coast Plutonic
Complex, consist of small granite to quartz monzonite porphyry
stocks that intrude clastic rocks of the Late Jurassic
Bowser Assemblage at the intersections of north-northwest
and east-northeast faults (Carter, 1982). The major porphyry
deposits are the Ajax porphyry Mo, Bell Moly porphyry Mo-
W, and Kitsault (B.C. Moly) porphyry Mo (Ag, Pb, Zn, Cu).
Ajax Porphyry Mo Deposit
The Ajax porphyry Mo deposit consists of molybdenum
in a quartz-vein stockwork, which is hosted in an Eocene
quartz monzonite porphyry intrusion and in adjacent contactmetamorphosed
Jurassic argillaceous rocks (Soregaroli and
Sutherland Brown, 1976; EMR Canada, 1989; MINFILE,
2002). The deposit occurs in four small, closely spaced
plutons. Estimated reserves are 178.5 million tonnes grading
0.121 percent MoS 2. Total reserves are 417.3 million tonnes
grading 0.09 percent MoS 2 with a very high stripping ratio.
The porphyry intrusion exhibits a K-Ar biotite isotopic age of
54.0 Ma age.
Bell Moly Porphyry Mo-W Deposit
The Bell Moly porphyry Mo-W deposit consists of
molybdenite and minor scheelite that occur in a quartz vein
stockwork in an Eocene quartz monzonite porphyry and in
adjacent biotite hornfels in Jurassic metasedimentary and
metavolcanic rocks (Carter, 1982; EMR Canada, 1989). Estimated
reserves are 106 million tonnes grading 0.09 percent
MoS 2. The deposit occurs in a crescent-shaped zone around
the eastern portion of the stock.
Kitsault (B.C. Moly) Porphyry Mo Deposit
The Kitsault (B.C. Moly) porphyry Mo (Ag-Pb-Zn-Cu)
deposit consists of molybdenite in quartz-vein stockworks
that are related to an Eocene quartz monzonite and quartz
diorite stock that intrudes Late-Jurassic and Early Cretaceous
siltstone and graywacke of the Bowser Assemblage (Carter,
1982; Steininger, 1985; EMR Canada, 1989; Hodgson, 1995;
MINFILE, 2002). The veinlets are cut by quartz veins, as
much as 3 m wide, and contain pyrite, galena, sphalerite,
scheelite, chalcopyrite, tetrahedrite and pyrrhotite. Molybdenum-bearing
rocks form a ring structure around the stock
in quartz veinlets. At least five stock phases are recognized.
Several stages of ores are associated with intramineral dikes.
The porphyry exhibits a K-Ar isotopic age of 53.7 Ma. Estimated
combined production and reserves are 113.3 million
tonnes grading 0.184 percent MoS 2. Between 1967 and 1972
production was 9.3 million tonnes grading 0.112 percent
MoS 2. Estimated reserves in 1989 were 104 million tonnes
grading 0.19 percent MoS 2.
Ag Polymetallic Vein Deposits Associated with Goosly
Plutonic Suite
The Goosly Plutonic Suite consists of small alkaline gabbro,
syenomonzonite, and quartz monzonite stocks that occur
near the western end of Francois Lake. The suite intrudes Late
Cretaceous volcanic and clastic rocks of the Skeena Assemblage
and is associated with subvolcanic to Eocene volcanic
centers (Church, 1971). The major Ag polymetallic vein deposits
are at Equity Silver (Sam Goosly) and Prosperity-Porter Id.
Equity Silver (Sam Goosly) Ag Polymetallic Vein Deposit
The Equity Silver (Sam Goosly) Ag deposit is an unusual
polymetallic stockwork and vein deposit that consists of pyrite,
chalcopyrite, pyrrhotite, and tetrahedrite, and minor sphalerite,
galena, and silver sulfosalts that are accompanied by argillic
alteration (Carter, 1982; Cyr and others, 1984; Northern Miner,
March 28,1988; Schroeter and Lane, 1991; Panteleyev, 1995;
MINFILE, 2002). The sulfides occur in veins, disseminations,
and massive sulfide replacement bodies, as much as 120 m
thick, that are located in tabular fracture zones roughly parallel
to stratigraphy. Estimated combined production and reserves
are 32.1 million tonnes grading 71.3 g/t Ag and 3.90 g/t Au.
The mine closed in 1984; estimated remaining reserves are
5,915,454 tonnes grading 72.01 g/t Ag, 0.82 g/t Au, and 0.22
percent Cu. Estimated total Au content of combined production
and reserves is 16.9 tonnes. The deposit age is poorly
constrained and is younger than the host Late Cretaceous units
and older than the Goosly Lake intrusions. The deposit occurs
between a granitic stock (with a K-Ar isotopic age of 58 Ma)
and a gabbro-monzonite stock (with a K-Ar isotopic age of 48
Ma). The plutonic rocks are part of the Goosly Lake Intrusions
and intrude sedimentary and pyroclastic rocks of the Cretaceous
Skeena Assemblage. The deposit is interpreted by Panteleyev
(1995) as a subvolcanic Cu-Au-Ag deposit, which commonly
occurs near or above a porphyry Cu hydrothermal system.
Prosperity-Porter Idaho Ag Polymetallic Vein Deposit
The Prosperity-Porter Idaho deposit, an important past
silver producer, consists of a set of narrow polymetallic Ag veins
hosted in volcanic rocks of the Hazelton Assemblage, which
is related to the Hyder biotite granodiorite pluton. The pluton
is part of an Eocene granitoid suite in the northeastern Coast
Plutonic Complex (Woodsworth and others, 1991). From 1922
to 1950 the mine at the deposit produced 2.36 million ounces
of Ag. Estimated reserves are 826,277 tonnes grading 669 g/t
Ag and 5 percent Pb+Zn (Schroeter and Lane, 1991). Related
silver mines in the Stewart region are those at Idaho and Indian
(Alldrick, 1985; Alldrick and others, 1987).
Porphyry Cu-Au-Ag Deposits Associated with Babine
Plutonic Suite
The Eocene Babine Plutonic Suite, which consists of distinctive,
small biotite feldspar granodiorite to quartz diorite porphyry