USGS Professional Paper 1697 - Alaska Resources Library

potassic zone. Combined estimated production and reserves
are 716 million tonnes grading approximately 0.47 percent Cu,
and 0.006 percent Mo. The deposit is hosted in granodiorite
and quartz monzonite of the Bethsaida phase of the Guichon
Creek Batholith. Minor amounts of Fe-Sb sulfide (gudmundite)
and native gold are reported. An oxidized halo ranging in
thickness from 0.3 to 100 meters consists of limonite, malachite,
pyrolusite, digenite, native copper, and tenorite. The
average thickness of the oxidized zone is 33 meters.
The smaller Brenda, Axe, and Primer porphyry Cu-Mo deposits
are hosted in calc-alkaline Jurassic stocks south of Highland
Valley. The Gibraltar porphyry Cu-Mo deposit (Bysouth and others,
1995) is hosted in the calc-alkaline Granite Mountain granodiorite
pluton, which intruded the Cache Creek terrane during accretion
with the tectonically-linked Stikinia Quesnellia island-arc terranes
to the east and west, respectively. This accretion is interpreted as
occurring during oroclinal warping of these terranes in the Early
Jurassic (Drummond and others, 1976; Dawson and others, 1991).
Brenda Porphyry Cu-Mo Deposit
As another example, the Brenda porphyry Cu-Mo deposit
consists of chalcopyrite and molybdenite with minor pyrite
and magnetite that occur within veins and fractures (McMillan,
1991; Weeks and others, 1995; MINFILE, 2002). The deposit
contains estimated combined production and reserves of 164.0
million tonnes grading 0.16 percent Cu, 0.04 percent Mo, 0.031
g/t Au, and 0.63g/t Ag. The deposit is hosted in granodiorite and
quartz diorite of the Middle Jurassic Brenda Stock. Mineralization
is interpreted as occurring during at least five stages of vein
emplacement, each with unique attitudes and overall mineralogy
developed in fractures. Grade is a function of fracture density
and mineralogy of the veins. Potassic alteration (K-feldspar and
SW Garnet/Pyroxene Ratio
1:2 1:3
Approximate
open pit limit
NE
Toronto
Stock
Garnet/Pyroxene Ratio
1:1 1:2
Contact
Fault
Bend in
section
Au > 3 g/t
Epidote
Scapolite
Marble line
Silicification
Late Triassic Metallogenic Belts (230 to 208 Ma; fig. 32) 95
biotite) accompanies sulfide mineralization. K-Ar hornblende
ages are 176 Ma for the Brenda Stock and K-Ar biotite ages of
146 Ma is interpreted as the age of deposit.
Craigmont Cu-Fe Skarn Deposit
The Craigmont Cu-Fe skarn deposit occurs 30 km south of
Highland Valley and consists of magnetite, hematite and chalcopyrite
that occur as massive pods, lenses, and disseminations
within a calc-silicate skarn assemblage that replaces carbonate
the Nicola Assemblage (Dawson and others, 1991; MINFILE,
2002). Combined production and reserves are estimated at 34.9
million tonnes grading 1.21 percent Cu and 19.6 percent Fe.
The host rocks are calcareous volcaniclastic and reefoid carbonate
rocks of the western facies belt of the Nicola Assemblage
at their embayed contacts with the border phase of the Guichon
Creek Batholith. Younger intrusive phases in the core of the
batholith host the large Highland Valley porphyry Cu-Mo district
(Dawson and others, 1991). Production between 1962 and
1982 was 33.4 million tonnes grading 1.21 percent Cu, 0.002
g/t Au and 0.007 g/t Ag. Reserves are estimated at 1.5 million
tonnes grading 1.13 percent Cu. A 500,000 tonne stockpile of
magnetite ore exists, from which approximately 45,000 tonnes
per year are shipped to coalfields for use in heavy media separation.
The deposit age is interpreted as Early Jurassic.
Hedley Au Skarn Deposit
The Hedley Au-Ag skarn deposit consists of pyrrhotite,
arsenopyrite, pyrite, chalcopyrite and sphalerite with trace
galena, native Bi, native Au, electrum, tetrahedrite, native Cu,
molybdenite and cobaltite (Ray and Webster, 1991; Ettlinger
and others, 1992; Ray and others, 1993; Ray and Dawson,
1994) (fig. 41 for Nickel Plate part of deposit). The deposit
0 100 m
Early Jurassic
Hedley intrusion: quartz
diorite, diorite, gabbro
Late Triassic
Hedley Formation
Sunnyside Limestone
Figure 41. Nickel Plate Au
skarn deposit, Hedley Camp,
Guichon metallogenic belt,
Canadian Cordillera. Schematic
cross section. Adapted from
Dawson (1996b). See figure 32
and table 4 for location.