USGS Professional Paper 1697 - Alaska Resources Library

248 Metallogenesis and Tectonics of the Russian Far East, Alaska, and the Canadian Cordillera
mafic plutonism (this article), or (2) possibly slightly later in
association with strike-slip dismemberment of a continentalmargin
arc (Goldfarb, 1997; Goldfarb and others, 1997, 1998).
Metallogenic Belts Formed in Late Cretaceous
and Early Tertiary Coast Continental-Margin
Arc, Southeastern Alaska, and Southern
Canadian Cordillera
An extensive suite of Late Cretaceous and early Tertiary
metallogenic belts hosting granitic-magmatism related
deposits occur in southeastern Alaska and the southern
Canadian Cordillera (fig. 103; tables 3, 4). These belts are
hosted mainly in the the Coast-North Cascade plutonic belt
and correlative units. In alphabetical order, these metallogenic
belts are the Bulkey, Carmacks, Catfish, central-southeastern
Alaska, Fish Lake-Bralorne, Gambier, and Surprise Lake belts.
The host Coast-North Cascade plutonic belt consists chiefly
of quartz diorite, granodiorite, and locally more mafic or
felsic plutons (Rubin and others, 1991; Gehrels and others,
1990; Wheeler and McFeeley, 1991; van der Heyden, 1992;
Woodsworth and others, 1992; Journeay and Friedman,
1993). The Early Late Cretaceous through early Tertiary
intrusions are interpreted as forming sequentially during
contraction, local(?) dextral transpression, and transtension,
and accompanied by regional metamorphism (Rubin and others,
1991; Journeay and Friedman, 1993). The Coast-North
Cascade plutonic belt constitutes part of a laterally-extensive,
Andean-type Coast continental-margin arc that overlaps
the Wrangellia superterrane and previously accreted, more
inboard terranes in southern Alaska and coastal Canadian
Cordillera (fig. 103) (Nokleberg and others, 1994c, 1997c;
Monger and Nokleberg, 1996). The Early Late Cretaceous
through early Tertiary intrusions were emplaced concurrently
with structures formed sequentially, first during contraction,
and subsequently during local(?) dextral transpression and
associated regional metamorphism (Woodsworth and others,
1977; Leitch and others, 1989; Rubin and others, 1991; Journeay
and Friedman, 1993; Schiarizza and others, 1997). The
plutonic belt and associated metallogenic belts of graniticmagmatism
deposits are interpreting as forming immediately
after the mid-Cretaceous accretion of the Wrangellia superterrane
and the subsequent oceanward stepping of subduction
and continental-margin magmatism (Nokleberg and others,
1994c, 1997c; Monger and Nokleberg, 1996).
Surprise Lake Metallogenic Belt of Porphyry
Mo-W-Cu, and Au-Ag Polymetallic Vein Deposits
(Belt SL), Northern British Columbia
The Surprise Lake metallogenic belt of porphyry Mo-W-
Cu and Au-Ag polymetallic vein deposits (fig. 103; tables 3, 4)
occurs in northern British Columbia and is hosted in the northwest-trending
Surprise Lake Plutonic Suite. The significant
deposit in the belt are (table 4) (Nokleberg and others 1997a,b,
1998) (1) porphyry Mo deposits at Adanac-Adera (Ruby
Creek), Mount Ogden, Red Mountain (Bug, Fox, Boswell R.),
and S.Q.E. (Storie, Casmo), (2) a porphyry Cu-Mo deposit at
Sutlahine River Area (Thorn, Kay), (3) porphyry Mo and W-
and Mo skarn deposits at Mt. Haskin West (Joem, Rain, Moly
Zone), and Windy (Balsam, Star, Kuhn, Dead Goat), and (4)
Au-Ag polymetallic vein deposits at Engineer Mine, Montana
Mountain, Venus, and Wheaton River.
Adanac-Adera Porphyry Mo Deposit
The Adanac-Adera porphyry Mo deposit (fig. 118) consists
of molybdenite with accessory pyrite, fluorite, chalcopyrite,
scheelite, and wolframite, along with minor arsenopyrite
that occur in a quartz-vein stockwork. Estimate reserves are
152 million tonnes grading 0.063 percent MoS 2 at a cutoff
grade of 0.04 percent Mo (EMR Canada, 1989; Dawson and
others, 1991; Mining Review, 1992; Pinsent and Christopher,
1995; MINFILE, 2002). The deposit is hosted by a quartz
monzonite stock that is part of the Late Cretaceous Surprise
Lake Batholith (Pinsent and Christopher, 1995). The deposit
exhibits silicic and potassic alteration that occur as envelopes,
as much as several centimetres thick, around quartz veins.
Minor uranium occurs in the deposit. The Surprise Lake
Batholith exhibits a K-Ar isotopic age of 70.6+3.8 Ma as an
average of six dates. This value represents a cooling age and
differs significantly from a U-Pb zircon age of 83.8+5 Ma
(Mihalynuk and others, 1992). Associated W-, Cu-, and Sngreisen
vein, and W and Sn (Cu, Pb, Zn) skarns occur along
contacts between the stock with limestone of Cache Creek
Assemblage (Ray and others, 1992).
Mount Ogden Porphyry Mo Deposit
The Mount Ogden porphyry Mo deposit consists of molybdenite
in an alaskite and quartz monzonite stock that intrudes
amphibolite-grade Permian and Triassic limestone and clastic
sedimentary and volcanic rocks of the Stikinia terrane (EMR
Canada, 1989; MINFILE, 2002). Molybdenite occurs mainly
in the alaskite as platy crystals in veins, in veinlets, as rosettes
in vuggy quartz, and as interstitial grains. Some molybdenite
veins range as much as 10 cm wide and occur over 30 meters.
Alteration consists of quartz-sericite, with fluorite, biotite,
minor pyrite and sphalerite. Estimated reserves are 218 million
tonnes grading 0.30 percent MoS 2. The country rocks locally
contain skarns with disseminated pyrite, pyrrhotite, magnetite,
and traces of sphalerite and scheelite.
Red Mountain Porphyry Mo Deposit
The Red Mountain porphyry Mo deposit consists of
disseminated molybdenite that occurs in a quartz stockwork
(EMR Canada, 1989; Dawson, and others, 1991; Yukon
Minfile, 1992; Sinclair, 1986). Estimated reserves are 187
million tonnes grading 0.167 percent MoS2 (with a 0.1 percent
cut-off) and 21.3 million tonnes grading 0.293 percent MoS 2