USGS Professional Paper 1697 - Alaska Resources Library

134 Metallogenesis and Tectonics of the Russian Far East, Alaska, and the Canadian Cordillera
annual report,1990; Mining Review, 1992; MINFILE, 2002).
Estimated resources are 12.7 million tonnes grading 1.87 g/t
Au. The prospect occurs 25 km south of Quesnel Lake in
eastern British Columbia and consists of a 8-km-long zone of
deformed, stratabound quartz-carbonate-pyrite-Au veins that
are hosted in Late Triassic phyllite of the Quesnellia islandarc
terrane near the suture with the adjacent Kootenay terrane
(Dawson and others, 1991).
Origin of and Tectonic Controls for Cariboo
Metallogenic Belt
The Cariboo metallogenic belt occurs near the margin
of the Kootenay terrane near the suture (major fault) with the
Quesnellia island-arc terrane (fig. 49, tables 3, 4). The deposits
in the Cariboo-Barkerville district are interpreted as forming
during chlorite- to sillimanite-grade regional metamorphism
mainly in the Middle Jurassic to Early Cretaceous (Andrew
and others, 1983). This event is related to the successive overthrusting
of Kootenay terrane by Cassiar, Slide Mountain, and
Quesnellia terranes during a major accretionary event (Struik,
1986). Similarly, the Frasergold Au quartz-vein prospect is
interpreted as forming early in the metamorphism of the area
as metamorphic segregations related to the accretion of the
Quesnellia island-arc terrane (Bloodgood, 1987).
The deposits in the Cariboo metallogenic belt are interpreted
as forming during accretion of the Quesnellia and adjacent
terranes to the North American Continental Margin because of
(1) the occurrence of the deposits near a major fault, (2) the metamorphic
textures and structures of the deposits, and (3) an age
of formation that approximates the interpreted age of accretion of
the Quesnellia and adjacent terranes, which constitute the Intermontane
Superterrane (Monger and others, 1972, 1992), to the
North American Continental Margin. A Middle to Late Jurassic
period of regional metamorphism and associated deformation is
interpreted as the age of accretion of the Quesnellia and Stikinia
island-arc terranes and associated terranes to the North American
Craton Margin, after oroclinal warping of the Stikinia-Quesnellia
island-arc terranes and tectonically linked Cache Creek and
Slide Mountain subduction-zone terranes (Monger and others,
1972, 1992; Mihalynuk and others; 1994; Monger and Nokleberg,
1996; Nokleberg and others, 2000). Before accretion, the
Quesnellia island arc may have formed on the Kootenay terrane,
a rifted and deformed fragment of the North American Craton
Margin, and the coeval Stikinia island arc may have formed on
the Yukon-Tanana terrane, another rifted and deformed fragment
of the North American Craton Margin (Monger and Nokleberg,
1996; Nokleberg and others, 2000).
Rossland Metallogenic Belt of Au-Ag
Polymetallic Vein Deposits Belt RL), Southern
British Columbia
The Rossland metallogenic belt of Au-Ag polymetallic vein
deposits (fig. 49; tables 3, 4), which occurs in southern British
Columbia is hosted in or near granitoid plutons of the Middle
Jurassic Nelson Plutonic Suite. This granitic suite represents the
oldest continental-margin arc in the Canadian Cordillera. The
plutons and vein deposits intrude the Quesnellia, Kootenay, and
Cassiar terranes and the North American Craton Margin (Hoy
and Dunne, 1992; Høy and Andrew, 1988). The significant
deposits in the belt are at Rossland Camp (Le Roi, War Eagle),
Sheep Creek (Kootenay Belle), and Ymir-Erie Creek (Yankee
Girl; table 4) (Nokleberg and others 1997a,b, 1998).
Rossland Au-Ag Polymetallic Vein Camp
The Rossland Au-Ag polymetallic vein camp (fig. 60)
occurs in three areas, the North belt, Main veins, and South
belt. Most production (greater than 80 percent) has been from
the Le Roi, Center Star, Nickel Plate, War Eagle, and Josie
mines that occur in the Main vein system (Dawson and others,
1991; Schroeter and Lane, 1991; Hoy and Dunne, 1992;
MINFILE, 2002). The Main vein deposits consist of pyrrhotite
and chalcopyrite in a gangue of quartz and calcite with an
average ore grade of 1 percent Cu. The pyrrhotite-chalcopyrite
veins are located along the margins of the intrusions, are disseminated
and associated with K and Si skarn alteration at deep
levels, grade to massive veins with minor gangue and alteration
envelopes at higher levels, and in uppermost levels, brittle
fracture-controlled veins with Pb-Zn-Ag and quartz-carbonate
gangue predominate. The veins in the Main vein system form
an enechelon set that occurs between two large north-trending
lamprophyre dikes. The veins dip steeply north and strike
070°. A structural control is inferred by growth faults that were
active during deposition of Rossland Group. Total production
from Rossland Camp between 1894 and 1941 was 7.62 million
tonnes of ore grading 15.2 g/t Au, 19 g/t Ag, resulting in extraction
of 84 tonnes of Au and 105 tonnes of Ag. The timing of
vein emplacement with respect to the plutons in the district is
not known precisely (Files, 1984; Hoy and others, 1998).
Sheep Creek Au-Ag Polymetallic Vein District
The deposits in the Sheep Creek Au-Ag polymetallic vein
district (Kootenay Belle and others) consist of an assemblage
of pyrite, sphalerite, galena, and chalcopyrite that occurs
in quartz veins within quartzite, argillite, and argillaceous
quartzite of the Nevada and Nugget members of the Early
Cambrian Quartzite Range Formation of the North American
Craton Margin (Panteleyev, 1991; Schroeter and Lane, 1991).
Estimated combined production and reserves are 1.8 million
tonnes grading 15 g/t Au and 6 g/t Ag. The veins are controlled
by northeast-trending faults that are particularly productive
where they cross the axes of two north-trending anticlines. The
deposits are interpreted as related to local dikes of the Middle
Jurassic Nelson Plutonic Suite.
Ymir-Erie Creek Au-Ag Polymetallic Vein Deposit
The Ymir-Erie Creek (Yankee Girl) Au-Ag polymetallic
vein deposits consist of pyrite, galena, sphalerite and native