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

along the with tectonically-related Quesnellia island arc and Cache Creek subduction-zone terranes, onto the Nortb American
Craton Margin (Monger and Nokleberg, 1996; Nokleberg and others, 2000).
Sustut Metallogenic Belt of
Basaltic Cu Deposits (Belt SU)
Northern British Columbia
The Sustut metallogenic belt of basaltic Cu deposits, whlch ocam in northern British Columbia, is hosted in fhgmmtal
volcanic rocks of intermednte cqosition and interlayered sedimentary rocks of he Late TriassicTakla Group in the
northeastern part of the Stllunia ~sland-arc terrane (fig. 32; tables 3,4) (Nokleberg and others, 199%. 1998). A more extensive,
but less coherent belt could be defined to the south and west which would include minor volcanic redbgd Cu occurrences in the
overlying Hazelton Assemblage ad the Nicola Assemblage in soutberp Quepnellia island-arc terrane. In each case, the deposits
are located within emergent, subaerial parts of island-arc terranes. The significant deposit is at Sustut.
Sustut Basaltic Cu Deposit
The Sustut basaltic Cu deposit consists of a stratabod assemblage of hematite, pyrite, chalcocite, bomjte, chalcopyrite
and native copper which occurs as disseminations and as blebs and grains in the matrix of sandstone, conglomerate, tuff breccia
and lahar of the Late Triassic Takla Group (EMR Canada, 1989; Dawson and others, 1991). The deposit is a large concordant
body which is strongly zoned inward from an outer zone of pyrite, chalcopyrite, and bornite into a core of chalcocite, native
copper and hematite. The zonation is inlerpreted as reflecting the migration of ore fluids along permeable aquifers. Tbe host rocks
are sandstone, conglomerate, laher, and &green or grey tuff breccia of subaerial origin. Estimated resources are 21 million
tonnes grading 1.1 1 % Cu (Kirkham, 1996b; Harper, 1977; Mining Review, summer 2000). The grade increases in finer grained
units. Pyrite forms an incomplete envelope around Cu-bearing lenses, and bematite is ubiquitous. The deposit age is interpreted as
Late Triassic. The Northstar deposit to the south of Sustut is a faulted block of lower-grade, chalcocite-bearing sedimentary rocks
which are apparently interlayered within volcanic flows of the Takla Group (Sutherland Brown, 1968).
Origin of and Tectonic Controls for
Sustut Metallogenic Be&
The origin of basaitic Cu deposits hosted in volcanic rocks is interpreted as analogous to that for diagenetic sedimenmy
Cu deposits in sedimentary sequences. Hmver, the common presence of low-grade metamorphic minmals may also supports a
metamorphic origin (Kirkham, 1996b). h Lne Sustut metallogenic belt, the deposits are inteapreted as forming in the upper
oxidized parts of volcanic piles during shallow burial metamorphism and diagenesis (Kirkham, 1996b) which was coeval with
Late Triassic island-arc volcanism in the Stikinia and Quesnellia terranes.
Copper Mountain (North) Metallogenic Belt of
Porphyry Cu-Au Deposits (Bett CMN)
Northern British Columbia
The Copper Mountain (North) metallogenic beh of porphyry Cu-Mo-Au wits (fig. 32; tables 3,4) mlua in northern
British Columbia and is hosted in pamitoid plutonic rocks of the mainly in intermediate-cornpasition @toid plutom in the
Copper Mountain suite in the QueswIlia island-arc terrane. Most plutons in the mite are small, equant stocks with diameters
ranging up to a few kilometers. The significant deposits are the Lorraine and Mount Mulligad porphyry Cu-Au dqmsiits (table 4)
(Nokleberg and others 1997a, b, 1998).
Lorraine Porphyry Cu-Au Deposit
The Lorraine porphyry Cu-Au deposit consists of two fault-bounded zones of chalcopyrite, &mite and magoetite which
occur as disseminations in the 30- by 5-km-wide Middle Jurassic Duckling Creek Syenite Complex which is part of the largest
pluton in the Hogem Batholith of the alkalime Copper Mountain Suite (EM? Canada, 1989; Dawson and others, 1991;
Woodsworth and others, 199 1 ; Bishop and others, 1995; MINFIU, 2002). The sulfides are domay bc:minSt6d, but also
occur in veins. In the Lower Zone, sulfides occur in rnafic-rich lenses and sue zoned from chalcopyrite i- at the rim, through
chalcopyrite with minor bornite to bornite with minor chalcopyrite at the core. Magnetite is common in veinlets and as an
accessory mineral. The deposit contains an estimated resource of 9.1 million tomes g d ~ 0.70% ~ g Cu and 0.27 $/t AU (MINFILE,
2002). An Upper Zone is similar but is highly oxidized (Garnett, 1978). The Cu-Au deposit exhibits characteeisti~~ ~f both
hydrothermal and magmatic origins, and is related to orthommgmatic-hydrothermal fluid flow contemporaneous with mgmtism
and development of migmatitic fabrics(Bishop and others, 1995). Cu minerals are associated with elevated intensity of biotite,
chlorite, potassium feldspar and sericite alteration. A K-A. isotopic age of 175 91- 5 Ma (Middle Jurassic) for the syenite at
Lorrine is interpreted as a reset age; a U-Pb zircon age is abut 18 1 Ma (Bishop and others, 1995).