Metallogenesis and Tectonics of the Russian Far East, Alaska, and ...

island-arc volcanic rocks of the Nicola Assemblage of the QuesneUia island-arc terrane (Woodsworth and others, 1991). Parallel
facies belts define a west-facing arc which progresses compositionally from calc-alkaline on the west to alkaline on the east for
both volcanic and comagmetic granitoid plutoojc rocks (Mortimer, 1987). The significant deposits in the belt are: (1) porphyry
Cu-Mo deposits in the Highland Valley district (Bethlehem-JA, Valley Copper, Lomex, Highmont (Gnawed Mountain)); (2)
porphyry Cu-Mo deposits at Axe (Summers Creek), Brenda (Peachland area), and Gibraltar ~ollyanna, Granite Mt); (3) porphyry
Cu deposits at Primer (North Zone); (4) the Craigmont Cu-Fe skam 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 teme. Associsled with the youngest, innermost, and most leucocratic phases
of the batholith are late-stage dike swarms (McMillan, 1985Casselman and others, 1995). The batholith ranges from dioite and
quartz diorite at the border, to younger granodiorite in the center. Although much variation occurs, individual deposits typically
exhibit concentric zonation alteration which grades hm central sdicic alteration, to potassic, phyllic, and argillic alteration in an
intermediate zone, and to peripheral propylitic alteration (McMiUan and others, 1995). The principal deposits in the district at
Bethlehem, Valley Copper, Lomex, and Highmont have combined production and reserves o-f about 2,009 million tonne6 grading
0.45% Cu. The Highland Valley district is the largest porphyry Cu district in the Canadian Cordillera (McMih, 1985).
Valley Copper, Brenda, Axe, and Mmer
Porphyry Cu-Mo Deposits
The Valley Copper porphyry Cu-Mo deposit (fig. 40) consists of ftacnue-controlled cbrrlcupynte (prrtassic alteration) and
bornite (phyllic alteration) with minor digenite, covellite, pyrite, pymhotite, molybdenite, sphalerite and galena (h4cMifflan, 1985,
1991; Highland Valley Copper Ltd., annual report, 1991; WILE, 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 potassic zone. Combined
estimated production and reserves are 716 million tomes grading approximately 0.47% Cu, and 0.006% Mo. The deposit is hosted
in granodiorite and quartz rnonzonite 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 lbnonite,
malachite, pyrolusite, digenite, native copper and tenorite. The average thickness of the oxidized me is 33 meters.
The smaller Brenda, Axe, and Primer porphyry Cu-Mo deposits are hosted in calc-dkahe Jurassic stocks south of
Highland Valley. The Gibraltar porphyry Cu-Mo deposit (Bysoutb and others, 1995) is hosted in the calc-alkaline Granite
Mountain granodiorite pluton which intruded the Cache Crsek terrane during accretion with the tectonically-linked S-
Quesnellia island-arc terranes to the east and west, respectively. This accretion is interpreted as occuning during orocliw warping
of these terranes in the Early Jurassic prummond and others, 1976; Dawson and others, 199 1).
Brenda Porphyry Cu-Mo Deposit
As another example, the Brenda porphyry Cu-Mo deposit consists of chalcopyrite and molybdenite with minor pyrite and
magnetite which occur within veins and fractures (McMillan, 1991; Weeks and others, 1995; klINFILE, 2002). The deposit
contains estimated combined production and reserves of 164.0 million tomes grading 0.16% Cu, 0.04% Mo, 0.03 I g/t Au, and
0.63gtt Ag. The deposit is hosted in granodiorite and quartz dioritc of the Middle Jurassic Brenda Stock. Mineralization is
interpreted as occuning dwing at least five stages of vein emplacement, each with unique attitudes awl overaIl mineralogy
developed in fractures. Grade is a function of bcture density and mineralogy of the veins. Potassic alteration (K-feldspar and
biotite) accompanies sultide 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 Shrn DepasCf
The Craigmont Cu-Fe skam deposit occurs 30 km soutb of Highland Valley and consists of magnetite, hanatite and
chalcopyrite which occur as massive pods, lenses and disseminations within a calc-silicate skam assemblage which replaces
carbonate of the Nikola Assemblage (Dawson and others, 1991; MUWILE, 2002). Combined production and mserves are
estimated at 34.9 million tonnes grading 1.2 1 % Cu and 19.6% Fe. The hast rocks are calcareous v01caniclastic and reefbid
carbonate rocks of the western facies belt of the Nicola Assemblage, at their ernbayed contacts with the border phrrse of the
Guichon Creek Batholith. Younger intrusive phases in the core of he batholith host the large Highland Valley pwphyry Cu-Mo
district (Dawson and others, 1991). Production between 1962 and 1982 was 33.4 milIion tonnes grading 1.21% Cu, 0.002 gft Au
and 0.007 g/t Ag. Reserves are estimated at 1.5 million tomes grading 1.13% Cu. A 590,000 tome stockpile of magnetite ore
exists, from which approximately 45,000 to~es per year are shipped to coalfields for use in heavy mcdia separation. The deposit
age is interpreted as Early Jurassic.