USGS Professional Paper 1697 - Alaska Resources Library

94 Metallogenesis and Tectonics of the Russian Far East, Alaska, and the Canadian Cordillera
belts, many of the porphyry Cu-Au deposits occur in alkaline
plutons. Isotopic ages indicate intrusion of host granitoid
plutons and formation of associated mineral deposits occurred
from about 207 to 197 Ma in the Late Triassic and Early
Jurassic (Ross and others, 1995; Stanley and others, 1995).
This age represents the end of subduction-related igneous
building of Quesnellia island arc, just before accretion of the
Quesnellia terrane, along the with tectonically related Stikinia
island arc and Cache Creek and Slide Mountain subductionzone
terranes, onto the North American Craton Margin (Monger
and Nokleberg, 1996; Nokleberg and others, 2000).
Guichon Metallogenic Belt of Porphyry
Cu-Mo-Au and Au Skarn Deposits (Belt GU),
Southern British Columbia
The Guichon metallogenic belt of porphyry Cu-Mo-Au and
Au skarn deposits (fig. 32; tables 3, 4) occurs in southern British
Columbia and is associated with the Guichon Suite of numerous
large calc-alkaline granitoid plutons hosted by the western
Quesnellia island-arc terrane. The Guichon Suite has close
spatial and temporal affinities with the Late Triassic and Early
Jurassic island-arc volcanic rocks of the Nicola Assemblage of
the Quesnellia island-arc terrane (Woodsworth and others, 1991).
Parallel facies belts define a west-facing arc that progresses
compositionally from calc-alkaline on the west to alkaline on the
east for both volcanic and comagmatic granitoid plutonic rocks
(Mortimer, 1987). The significant deposits in the belt are (1)
porphyry Cu-Mo deposits in the Highland Valley district (Bethlehem-JA,
Valley Copper, Lornex, Highmont (Gnawed Mountain)),
(2) porphyry Cu-Mo deposits at Axe (Summers Creek), Brenda
(Peachland area), and Gibraltar (Pollyanna, Granite Mt), (3) porphyry
Cu deposits at Primer (North Zone), (4) the Craigmont Cu-
F
F
Rockslide
Tertiary sedimentary and
volcanic rock
Tertiary conglomerate
Silicic reentrant fringe zone
Fault
0.36% 0.36% 0.36% Cu Cu Cu
F
0.3 0.36% .36% Cu Cu C
Lornex
Fault
Zone
Overburden
Fe skarn deposit, and (5) the Hedley Camp (Nickel Plate, Mascot)
Au skarn deposit (table 4) (Nokleberg and others 1997a,b, 1998).
Highland Valley District (Bethlehem, Valley Copper,
Lornex, Highmont ) of Porphyry Cu-Mo Deposits
The Highland Valley district contains large porphyry Cu-Mo
deposits, which occur in the calc-alkaline, composite Guichon
Creek Batholith in the southern Quesnellia terrane. Associated
with the youngest, innermost, and most leucocratic phases of the
batholith are late-stage dike swarms (McMillan, 1985; Casselman
and others, 1995). The batholith ranges from diorite and
quartz diorite at the border to younger granodiorite in the center.
Although much variation occurs, individual deposits typically
exhibit concentric zonation alteration that grades from central
silicic alteration, to potassic, phyllic, and argillic alteration in an
intermediate zone and to peripheral propylitic alteration (McMillan
and others, 1995). The principal deposits in the district at
Bethlehem, Valley Copper, Lornex, and Highmont have combined
production and reserves of about 2,000 million tonnes grading
0.45 percent Cu. The Highland Valley district is the largest porphyry
Cu district in the Canadian Cordillera (McMillan, 1985).
Valley Copper, Brenda, Axe, and Primer Porphyry Cu-Mo
Deposits
The Valley Copper porphyry Cu-Mo deposit (fig. 40)
consists of fracture-controlled chalcopyrite (potassic alteration)
and bornite (phyllic alteration) with minor digenite, covellite,
pyrite, pyrrhotite, molybdenite, sphalerite, and galena
(McMillan, 1985, 1991; Highland Valley Copper Ltd., annual
report, 1991; MINFILE, 2002). The linkages between sulfide
minerals and alteration types are not clear because chalcopyrite
also occurs in the phyllic zone and bornite occurs in the
0 200 m
Silicic reentrant zone
Bethsaida salt-and-pepper
granodiorite
Bethsaida granodiorite
Bethlehem granodiorite
Contact
1,000 m
500 m
Figure 40. Valley Copper porphyry
Cu-Mo deposit, Guichon
metallogenic belt, Canadian
Cordillera. Schematic cross
section. Adapted from McMillian
and others (1995). Line of
section bears 060° to right.
See figure 32 and table 4 for
location.