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

Metaltogenic 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 Tert~ary metallogenic belts hosting granitic-magmatism related deposits
occur in Southeastern Alaska and the southern Canadian Cord~llera (fig. 103; tables 3,4). These belts are hosted mainly in the the
Coast-North Cascade plutonic belt and correlative unlts. In alphabet~cal order, these metallogenic belts are thc Bulkey, Carmacks,
Catfish, Central-Southeastern Alaska, Fish Lake-Bralome, Gambler, and Surpnse 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, 199 1; Journeay and
Friedman, 1993). The Coast-North Cascade plutonic belt constitutes part of a laterally-extensive, Andean-type Coast continentalmargin
arc which 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, 199 1; Journeay and Friedman, 1993; Schiarizza and others, 1997). The
plutonic belt and associated metallogenic belts of granitic-magmatism 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 Polyrnetallic 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): porphyry Mo deposits at Adanac-Adera (Ruby Creek), Mount Ogden,
Red Mountain (Bug, Fox, Boswell R.), and S.Q.E. (Storie, Casmo); a porphyry Cu-Mo deposit at Sutlahine River Area (Thorn,
Kay); porphyry Mo and W- and Mo skarn deposits at Mt. Haskin West (Joem, Rain, Moly Zone), and Windy (Balsam, Star, Kuhn,
Dead Goat); and 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. 1 18) consists of molybdenite with accessory pyrite, fluorite, chalcopyrite,
scheelite, and wolfrarnite, dong with minor arsenopyrite which occur in a quartz-vein stockwork. Estimate reserves are 152
million tonnes grading 0.063% MoS2 at a cutoff grade of 0.04% 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 which is part
of the Late Cretaceous Surprise Lake Batholith (Pinsent and Christopher, 1995). The deposit exhibits silicic and potassic alteration
which occur as envelopes, up to several centimetres thick, around quartz veins. Minor uranium occurs in the deposit. The Surprise
Lake Batholith exhibits a K-Ar isotopic age of 70.6i3.8 Ma as an average of six dates. This value represents a cooling age and
differs significantly fiom a U-Pb zircon age of 83.8+5 Ma (Mihalynuk and others, 1992). Associated W-, Cu-, and Sn-greisen
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 which intrudes
amphibolite-grade, Permian and Triassic limestone, and clastic sedimentary and volcanic rocks of the Stikinia terrane ( EM
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 up to 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% MoS2. The country rocks locally contain skarns with disseminated pyrite, pyrrhotite, magnetite, and traces of sphalerite and
scheelite.