USGS Professional Paper 1697 - Alaska Resources Library

locally Late Triassic marine volcanic and sedimentary rocks,
and local mafic and ultramafic plutonic rocks (Nokleberg and
others, 1994c). The terrane occurs for about 2,000 km along the
length of the Canadian Cordillera (Nokleberg and others, 1997b,
1998). The Slide Mountain terrane is interpreted as a sequence
of oceanic crustal rocks that formed adjacent to and were
subducted under a late Paleozoic and early Mesozoic island arc
now preserved as two fragments in the Quesnellia and Stikinia
terranes (Nokleberg and others, 1994c; Monger and Nokleberg,
1996; Nokleberg and others, 2000). The Slide Mountain terrane
occurs in large blocks to small, discontinuous remnants that
are thrust over and (or) tectonically imbricated onto the Yukon-
Tanana, Kootenay, and Cassiar continental-margin terranes
and onto the North American Craton Margin (Nokleberg and
others, 1997b, 1998). The Slide Mountain terrane is interpreted
as being emplaced onto the North American Craton and Craton
Margin, along with the Stikinia, Quesnellia, and Cache Creek
terranes during a major period of Jurassic accretion (Monger
and Nokleberg, 1996). The serpentinite-hosted asbestos deposits
in the Cassiar metallogenic belt are the products of low-grade
metamorphism and alteration of ultramafic rock in the Slide
Mountain terranes. The metamorphism and alteration are herein
interpreted as occurring during either Jurassic thrusting of these
terranes onto the North American Craton Margin, or more
likely, during younger hydrothermal activity associated with
extensive Late Cretaceous granitic magmatism.
Francois Lake Metallogenic Belt of Porphyry Mo
Deposits (Belt FL), Central British Columbia
The Francois Lake metallogenic belt (fig. 49; tables 3, 4)
(Nokleberg and others, 1997b, 1998) is defined by the distribution
of porphyry Mo deposits in felsic plutons of the Francois Lake
Suite (Carter, 1982) that intrude the Stikinia, Quesnellia, and
Cache Creek terranes along the eastern part of the Skeena Arch in
central British Columbia. The Middle and Late Jurassic plutons
of the Stag Lake (171-163 Ma) and Francois Lake (157-145
Ma) Suites (White and others, 1970; Whalen and others, 1998),
with no identified coeval volcanic rocks, may correlate with the
Nelson Plutonic Suite (170-155 Ma) in the southeastern part of
the Canadian Cordillera. Both suites of intrusive rocks are herein
interpreted as emplaced during major accretion and collision of
the Stikinia-Quesnellia island arc and associated subduction-zone
complexes to the west with the North American Craton Margin.
Endako Porphyry Mo Deposit
The Endako quartz monzonite pluton of the Francois Lake
Suite hosts the Endako porphyry Mo deposit, the largest Mo
deposit in Canada with initial reserves of 280 million tonnes
grading 0.08 percent Mo. The deposit is essentially a stockwork
of quartz-molybdenite, pyrite, and magnetite veins about 350 m
wide, which extends for about 3.3 km along a west-northwesterly
axis. The Endako pluton is flanked to the north and south
by the younger Casey Alaskite and Francois Granite plutons,
respectively. Potassic and phyllic assemblages envelope quartz-
Late Jurassic Metallogenic Belts (163 to 144 Ma; figs. 48, 49) 133
molybdenite and other vein assemblages, and the host rocks are
pervasively kaolinized (Dawson and Kimura, 1972; Dawson
and others, 1991; Bysouth and Wong, 1995). Similar, but
smaller, Mo deposits occur at Nithi Mountain, Owl Lake and to
the north and northwest of Endako deposit (Dawson, 1972).
Cariboo Metallogenic Belt of Au Quartz Vein
Deposits (Belt CB), Southern British Columbia
The Cariboo metallogenic belt of Au quartz vein deposits
(fig. 49; tables 3, 4) occurs in eastern-central British Columbia
and is hosted by the Early Cambrian Downey Creek Formation
of the Barkerville subterrane of Kootenay terrane. The belt
consists of metamorphism-related, Au-quartz-sulfide lenses that
are emplaced concordantly with limestone of the Baker Member
of the Downey Creek Formation and cut by discordant quartzsulfide-gold
veins that occur mainly in the Rainbow Member
of the Downey Creek Formation (Robert and Taylor, 1989).
The significant deposits in the belt are in the Cariboo-Barkerville
district and at Frasergold (table 4) (Nokleberg and others
1997a,b, 1998). The Cariboo-Barkerville district also contains
major placer gold deposits (Nokleberg and others, 1997a).
Cariboo-Barkerville District (Cariboo Gold Quartz,
Mosquito Creek, Island Mountain) of Au Quartz
Vein Deposits
The Cariboo-Barkerville district contains three principal
mines (Cariboo Gold Quartz, Mosquito Creek, and Island
Mountain Mines) that consists of quartz-sulfide veins and
pyritic replacement lenses (Robert and Taylor, 1989; Schroeter
and Lane, 1991; MINFILE, 2002). The quartz-sulfide veins
occur in phyllite and quartzite of the Rainbow Member, usually
within 100 m of the contact with mafic volcanic rocks
and limestone of the Baker Member of the Downey Creek
Formation. Pyrite-gold lenses, which occur discontinuously in
marble bands within the Baker Member, pre-date brittle deformation,
are cut by quartz-sulfide-Au veins, and are interpreted
as synmetamorphic (Robert and Taylor, 1989; Dawson and
others, 1991). From 1933 to 1987, the three principal mines
produced 38 tonnes of Au from 2.7 million tonnes of ore grading
13.94 g/t Au and 1.87 g/t Ag. Recent exploration of the
Mountain and Bonanza Ledge deposits indicates a probable
reserve of 3,109,800 tonnes grading 2.95 g/t Au (International
Wayside Gold Mines 2003 Annual Report). The associated
Wells-Barkerville placer Au district also produced 64.8 tonnes
of Au between 1850 and 1990. The deposit age is interpreted
as Middle Jurassic through Early Cretaceous.
Frasergold Au-Quartz Vein Deposit
The Frasergold Au quartz vein deposit consists of pyrrhotite,
pyrite and coarse-grained gold and minor galena, sphalerite,
and chalcopyrite that occur in deformed quartz-carbonate
veins and stockwork stratabound in at least three stratigraphic
horizons in porphyroblastic phyllite (Eureka Resources Inc.,