USGS Professional Paper 1697 - Alaska Resources Library

stocks and dikes, is associated with several porphyry Cu-Au
mines and significant prospects in central British Columbia. The
suite consists of a northwest-trending belt of multiple intrusions
of stocks, dikes, and breccias that are fault-controlled (Kirkham,
1971) and interpreted as the loci of volcanic centres for equivalent
extrusive rocks in the area (Carter, 1982). The major porphyry
Cu-Au-Ag deposits are at Bell Copper, Granisle, and Morrison.
These deposits exhibit: (1) an annular zoning of sulfide minerals
and associated potassic to phyllic to argillic alteration (Carson
and Jambor, 1974), and (2) high precious-metal contents that
are characteristic of classic (nonplutonic) calc-alkaline porphyry
deposits (Sinclair, and others, 1982). Other deposits in the Babine
Lake district (Carter and others, 1995) are the Dorothy porphyry
Cu-Mo deposit, which is hosted in a feldspar porphyry dike, and
the Hearne Hill Cu-Au breccia pipe, which is associated with a
biotite-feldspar porphyry plug (Ogryzlo and others, 1995).
Bell Copper Porphyry Cu-Au (Mo) Deposit
The Bell Copper porphyry Cu-Au (Mo) deposit (fig.
121) consists of chalcopyrite and lesser bornite that occur as
Limit of Alteration
Pyrite Halo
Babine
Lake
0 50 m
Late Cretaceous and Early Tertiary Metallogenic Belts (84 to 52 Ma) (figs. 102, 103) 259
Bell Pit
disseminations and in quartz lenses and stockwork veinlets.
Estimated combined production and reserves are 71.75 million
tonnes grading 0.46 percent Cu, 0.23 g/t Au, 0.48 g/t Ag, and
0.006 percent Mo (Carson and others, 1976; Noranda Inc.,
annual report, 1990; Butrenchuk, 1991; Diron and others,
1995; MINFILE, 2002). The deposit is hosted in biotite-feldspar
porphyry of the Eocene Babine Plutonic Suite and the
adjacent Jurassic metasedimentary rocks and metavolcanic
rocks of the Hazelton Group. A K-Ar biotite isotopic age of
51.0 Ma for the porphyry is interpreted as the age of deposit.
The deposit exhibits pervasive potassic (mainly biotite)
alteration with a surrounding, concentric halo of chlorite and
sericite-carbonate alteration. The alteration coincides with a
2-km-wide pyrite halo that surrounds the deposit (Dirom and
others, 1995). A supergene chalcocite zone caps the deposit
and extends to depths of 50 to 70 meters. Higher Cu grades
occur in a 60 to 90 m-thick, flat-lying area that is connected to
a central pipe-like zone that is centered on the western contact
of the intrusion. Past production was 28.7 million tonnes grading
0.46 percent Cu.
EOCENE
BABINE IGNEOUS SUITE
Post stockwork biotite plagioclase porphyry
dike, black, hard
Quartz,biotite, plagioclase porphyry
White. Post stockwork
Explosion breccia. Boulders and cobbles
of BFP in a tuffaceous matrix
Biotite plagioclase porphyry, moderate to pervasive
quartz-sericite-pyrtie alteration in quartz stockwork
Biotite plagioclase porphyry, biotite magnetite
alteration and biotite plagioclase porphyry
Undivided
Rhyolite and rhyodacite with spares plagioclase
phenocrysts in dikes, plugs, and dome
CRETACEOUS
SKEENA GROUP (Albian?)
Intermediate fragmental volcanic rocks
Black shale, siltstone, pale green tuff
JURASSIC
Hazelton group
Smithers Formation (Bajocian)
Dark brown graywacke, highly fossiliferous
Nilkitkwa Formation? (Pliensbachian)
Intermediate volcanic and volcaniclastic rock,
and brick red tuff
Telkwa Formation (Sinemurian)
Kotsine Facies (marine)
Dark green marine tuff, sandstone
Green and grey intermediate volcanic and
volcaniclastic rocks, amydaloidal basalt
Contact
Figure 121. Bell Copper porphyry Cu-Au deposit, Skeena metallogenic belt, Canadian Cordillera. Schematic geologic
map of area around open pit and alteration halos. Adapted from Butrenchuk (1991). See figure 103 and table 4 for location.