USGS Professional Paper 1697 - Alaska Resources Library

minor calcite, and sporadic pyrite and pyrrhotite. Rare arsenopyrite
and sphalerite also occur. Sampling of Fe-skarn magnetite
from the Texada Iron Mines by Webster and Ray (1990) indicate
grades of 3.14 percent Cu, 46.6 g/t Ag, and 2.8 g/t Au.
Origin of and Tectonic Controls for Island Porphyry
Metallogenic Belt
The Island Porphyry metallogenic belt is hosted in the
Jurassic volcanic and plutonic rocks that form part of the
Gambier overlap assemblage in southern British Columbia.
This group is part of the Talkeetna-Bonanza arc in the Wrangellia
superterrane (Nokleberg and others, 2000). In southern
British Columbia, the host rocks on northern Vancouver Island
consist of the Bonanza Group, and on Queen Charlotte Island,
the host rocks consist of the correlative Yakoun Group. The
Middle Jurassic volcanic and plutonic rocks, with isotopic
ages of 165 to 170 Ma, which host the Island Copper metallogenic
belt are the youngest part of the Bonanza arc, which was
initiated in the Early Jurassic (Monger and Nokleberg, 1996;
Ross and others, 1996). The Middle to Late Jurassic plutons
of the Burnaby Island suite and coeval volcanic rocks of the
Yakoun Group are a younger and northern part of the arc.
The younger, Late Jurassic part of the Island Porphyry
metallogenic belt is coeval with (1) the western-southeastern
Alaska metallogenic belt that is hosted in the Late Jurassic
and Early Cretaceous Gravina belt of the Wrangellia superterrane
in southeastern Alaska, and (2) the Eastern Alaska
Range metallogenic belt, which is hosted in the Kahiltna and
Nutzotin overlap assemblages in southern Alaska. Together,
the granitoid plutonic and andesitic volcanic rocks of the
Gravina-Nutzotin-Gambier overlap assemblage, and the
Kahiltna overlap assemblage define the Gravina island arc,
which is interpreted as forming on the northern or leading
edge of the Wrangellia island-arc terrane during migration
0 200 m
Intrusive dikes
Garnet-pyroxene skarn
Magnetite skarn
Gilles Bay granodiorite stock
(Middle Jurassic)
Marble Bay Formation (Middle
Triassic)
Texada Formation (Late and
Middle Triassic)
Fault
Contact
W E
Early Jurassic Metallogenic Belts (208 to 193 Ma; fig. 42) 103
towards North America (Nokleberg and others, 1984, 1985,
2000; Nokleberg and Lange, 1985a; Plafker and others,
1989; Plafker and Berg, 1994; Nokleberg and others, 2000).
The Gravina arc and associated granitic magmatism deposits
are tectonically linked to the younger part of the McHugh
Complex, which forms the northern part of the Chugach subduction
zone and accretionary wedge complex (Nokleberg
and others, 2000).
Metallogenic Belts Formed in Middle Mesozoic
in Stikinia-Quesnellia Island Arc
Klotassin Metallogenic Belt of Porphyry Cu-Au-
Ag Deposits (Belt KL), Southern Yukon Territory
The Klotassin metallogenic belt of porphyry Cu-Au-Ag
deposits (fig. 42; tables 3, 4) occurs in the southern Yukon Territory
and is hosted in the Klotassin Batholith. This batholith
consists of a calc-alkaline granitoid pluton that forms part of
the more extensive Klotassin Plutonic Suite, which intrudes
the Stikinia island-arc terrane in southwestern Yukon Territory
(Woodsworth and others, 1991). The significant deposits are
metamorphosed and deformed porphyry Cu-Au-Ag deposits
at Minto Copper and Williams Creek (table 4) (Nokleberg and
others 1997a,b, 1998). Both deposits are hosted in a foliated
Early Jurassic granodiorite pluton. Significant PGE prospects
occur in mafic and ultramafic plutons at Pyroxene Mountain
(Mortensen and others, 1994).
Minto Copper and Williams Creek Porphyry Cu-Au-Ag
Deposits
The Minto Copper porphyry Cu-Au-Ag deposit consists
of an assemblage of disseminated chalcopyrite, bornite,
Figure 45. Prescott body, Texada Fe skarn
deposit, Island Copper metallogenic belt,
Canadian Cordillera. Schematic cross section.
Adapted from Webster and Ray (1990).
See figure 42 and table 4 for location.