USGS Professional Paper 1697 - Alaska Resources Library

gold in a gangue of quartz, calcite and siderite that occur along
northeast-trending shear zones in folded metasedimentary
rocks of the Late Triassic Ymir and Early Jurassic Rossland
groups (Schroeter and Lane, 1991). The veins occur near
contacts of metasedimentary rocks intruded by granitoid dikes
of the Middle Jurassic Nelson Plutonic Suite to which the
deposits may be related (Hoy and Andrew, 1988; Hoy and
others, 1998).
Origin of and Tectonic Controls for Rossland
Metallogenic Belt
The Rossland metallogenic belt occurs in the southern
Canadian Cordillera and, on the basis of spatial, structural, and
age data, is interpreted as forming during intrusion of dikes
and plutons of the Middle and Late Jurassic Nelson Plutonic
Suite (Parrish and others, 1988; Woodsworth and others,
1991). The Nelson plutonic suite consists chiefly of granodiorite,
quartz monzonite, and local monzonite plutons that yield
isotopic ages mainly of 155 to 170 Ma with local crustal inheritance.
On the basis of structural and temporal relations, the
Nelson Plutonic Suite is interpreted as forming immediately
after a period of regional thrusting associated with accretion
Middle Eocene
Coryell Intrusions
Marron Formation
Jurassic
Nelson Intrusions
Rainy
Day
Pluton
Gertrude
Lower and Middle(?) Jurassic
Rossland Monzonite
Rossland Sill, Monzonite
Rossland Group,
Elise Formation
Early Cretaceous Metallogenic Belts (144 to 120 Ma; figs. 61, 62) 135
Red Mountain
and obduction of the Stikinia, Quesnellia, Cache Creek, and
Slide Mountain terranes and obduction of the latter two terranes
over the Yukon-Tanana, Kootenay, Cassiar terranes, and
the North American Craton Margin (Monger and Nokleberg,
1996; Nokleberg and others, 2000). This major compressional
orogenic event included regional metamorphism, deformation,
crustal thickening, anatectic magmatism, and uplift in the core
of the Canadian Cordillera. By the Late Jurassic (about 155
Ma), detritus from this emergent orogenic welt in the eastern
Canadian Cordillera was shed eastwards onto the North
American Craton Margin (Cant, 1989).
Early Cretaceous Metallogenic Belts
(144 to 120 Ma; figs. 61, 62)
Overview
The major Early Cretaceous metallogenic belts in the
Russian Far East, Alaska, and the Canadian Cordillera are
summarized in table 3 and portrayed on figures 61 and 62.
North Belt
Main Belt
Rossland
Town Site
0 500 m
Pennsylvanian & Permian
Mount Roberts Formation
Ultramafic Rocks
Breccia-skarn
molybdenite zone
Trail Pluton
Evening Star
Iron Colt
Rossland veins
Thrust fault
Normal fault
Contact
Figure 60. Rossland Au-Ag polymetallic vein and related deposits, Rossland metallogenic belt, Canadian Cordillera.
Schematic geologic map. Adapted from Hoy and Andrew (1988). See figure 49 and table 4 for location.