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

Metallogenic Belts Formed in
Middle Mesozoic Stikinia-Quesnellia
Island Arc
Galore Creek Metallogenic Belt of
Porphyry Cu-Au Deposits (Belt GL)
Northern British Columbia
The Galore Creek metallogenic belt of porphyry Cu-Au deposits (fig 32; tables 3,4) occurs in northem British Columbia and
is hosted in alkaline granitoid plutons which are coeval and comagmatic with volcanic, volcaniclastic and subordinate sedimentary
rocks of the Late Triassic Stuhini Group of the northern Stikinia terrane. The significant deposits are the Galore Creek, Gnat Lake,
and Red Chris porphyry Cu, porphyry Cu-Au, and Cu-Au skarn deposits (table 4) (Nokleberg and others 1997a, b, 1998).
Galore Creek Alkalic Porphyry Cu-Au Deposit
The Galore Creek alkalic porphyry Cu-Au deposit consists of chalcopyrite, pyrite, bornite and magnetite which occur as
disseminations, skams, coarse replacements, and fracture fillings in syenitic porphyry and breccias and the Late Triassic Stuhini
Group metasedimentary and metavolcanic rocks (Allen and others, 1976; EMR Canada, 1989; Dawson and others, 1991; Mining
Review, 1992, J. Mortensen, written cornrnun., 1993; Ems and others, 1995). The deposit contains estimated reserves of 125
million tonnes grading 1.06% Cu, 7.7 g/t Ag, and 0.4 g/t Au. Approximately 80% of deposit consists of altered skarn and
replacements along contacts between syenite intrusives and Triassic volcanic and sedimentary rock. A U-Pb zircon isotopic age of
210 Ma is reported for the intramineral syenite porphyry. The porphyry is typical of undersaturated, feldspathoid-bearing subclass
of alkalic porphyry deposits.
The Galore Creek deposit is hosted in volcanic rocks of the Stuhini Formation. The rocks are dominantly augite and
plagioclase phyric basalt and andesite flows, fragmental rocks and less abundant feldspathoid-bearing flows. Prograde Cu skams,
which occurs in calcareous pyroclastic, volcaniclastic, and shoshonite volcanic rocks adjacent to contacts of pseudoleucite-phyric
syenite dikes, constitutes about 80% of ore reserves in the Central Zone. Potassic alteration assemblages of orthoclase and biotite,
which occur in or adjacent to potassic host rocks, are replaced by a calcic skarn assemblage of zoned andradite, diopside, Fe-rich
epidote, and vesuvianite along with chalcopyrite, bomite, pyrite, and magnetite, and minor chalcocite, sphalerite, and galena.
Retrograde assemblages consist of anhydrite, chlorite, sericite, calcite, gypsum, and fluorite (Dawson and Kirkham, 1996).
The Southwest Zone consists of disseminated chalcopyrite in a late-stage, diatreme breccia and adjacent orthoclase
porphyry. The North Junction and other satellite deposits consist of disseminated chalcopyrite and bornite in volcanic rocks.
Reserves calculated in 1992 are: Central Zone -233.9 million tonnes gading 0.67% Cu, 0.35 g/t Au, and 7 g/t Ag; Southwest Zone
-42.4 million tonnes grading 0.55% Cu, 1.03 g/t Au, and 7 g/t Ag; and North Junction - 7.7 million tonnes grading 1.5% Cu.
Red Chris Porphyry Cu-Au Deposit
The Red Chris alkalic porphyry Cu-Au deposit consists of a stockwork and a set of sheeted-veins containing quartz,
pyrite, chalcopyrite, and increasing bornite at depth. The deposit is hosted in an elongate porphyritic monzonite stock emplaced
within the Late Triassic alkaline volcanic and volcaniclastic rocks of either the Stuhini, Group (EMR Canada, 1989; American
Bullion Minerals Ltd., news release, Jan. 1995; Newell and Peatfield, 1995; Ash and others, 1997). The monzonite exhibits an
isotopic age of 203+1.3 Ma (Friedman and Ash, 1997). An early K-Na alteration stage of orthoclase-albite-biotite with variable
quartz- sericite, was succeeded by pervasive quartz-ankerite-sericite-pyrite alteration. Pyrite occurs as a halo to the steeply dipping
deposit which is both controlled and offset by east-northeast trending subvertical faults. The deposit contains estimated resources
of 320 million tonnes grading 0.38% Cu and 0.30 g/t Au (American Bullion Minerals, news release, Jan., 1995). A minimum K-
Ar isotopic age of mineralization of 195 Ma (Early Jurassic) is obtained from a post-mineral dike (Newell and Peatfield, 1995).
Subvolcanic complexes similar to the Red stock occur at the Rose and Groat Creek porphyry Cu-Au prospects which are located
10 km northwest, and 25 krn southwest of Red Chris, respectively (Newell and Peatfield, 1995). Porphyry Cu-Au prospects at
June and Stikine in the Gnat Lake area are hosted in quartz monzonite and granodiorite phases of the Hotailuh Batholith
(Panteleyev, 1977).
Origin of and Tectonic Controls for
Galore Creek Metallogenic Belt
The Galore Creek metallogenic belt of porphyry Cu-Au deposits is hosted in and adjacent to a Late Triassic (2 10 Ma)
center of alkaline volcanism, contemporaneous with multi- phase intrusion and magmatic- hydrothermal activity, and late diatreme
breccias, which together probably contributed to the high Cu and Au contents at Galore Creek relative to other alkaline porphyry
systems as at Cat Face in British Columbia (Enns and others, 1995). The Galore Creek metallogenic belt is part of the subduction
related Stikinia island arc (Monger and Nokleberg, 1996; Nokleberg and others, 2000). Isotopic ages indicate intrusion of host
granitoid plutons and formation of associated mineral deposits from the Late Triassic to the Early Jurassic. This age represents the
main and final part of subduction-related igneous building of the Stikinia island arc, just before accretion of the Stikinia terrane,