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

stibnite vein deposits in the Bridge River mining camp are related to stocks and dikes of the early Tertiary Bendor suite with
isotopic ages of 70 to 65 Ma (Leitch and others, 1989; Church, 1995). These deposits occur to the northeast of the Bralorne
district. Several other Sb-Au polymetallic vein deposits occur in the mining camp and are associated with the Late Cretaceous and
early Tertiary Bendor pluton, Robson stock, and related intrusions (Leitch and others, 1989). Also occurring in the belt are
porphyry Cu deposits, as at Empress, which locally grade to high-sulphidation epithermal vein systems in the easternmost partr of
the Coast Plutonic Complex, directly on strike from the coeval Bralorne deposit (McMillan, 1983). The belt also includes
porphyry Mo and Cu-Mo occurrences which are associated with Eocene stocks which occur along major dextral strike-slip faults.
The porphyry Cu-Mo and related deposits in the metallogenic belt are associated with Late Cretaceous porphyry dikes and
stocks which are coeval with the adjacent eastern margin of the Coast Plutonic Complex and intrude metasedimentary rocks of the
Methow terrane (Leitch and others, 1989). These granitoid rocks are part of the extensive Late Cretaceous and early Tertiary
Coast-North Cascade plutonic belt which occurs along the western and central parts of the Canadian Cordillera for several
thousand krn (Nokleberg and others, 1994c, 1997c; Monger and Nokleberg, 1996). The significant deposits in the belt are (table 4)
(Nokleberg and others 1997a, b, 1998): porphyry Cu-Mo deposits at Fish Lake, Giant Copper (Canam, A.M.), and Poison
Mountain (Copper Giant); and Au quartz vein deposits at Bralorne, Pioneer (Bridge River area), and Carolin. The Maggie
(Bonaparte River) deposit occurs along the margin of the belt.
Bralorne and Pioneer Au Quartz Vein Deposits
The Bralorne and Pioneer mines of the Bralorne district, and the smaller Wayside and BRX mines, are typically large,
continuous, mesothermal Au-quartz-sulfide veins which range from 1 to 2 m wide, and consist commonly of quartz, calcite, free
gold, arsenopyrite, pyrite, and lesser sphalerite, galena, scheelite, chalcopyrite and molybdenlte (Leitch and others, 1989). The
veins are lenticular and plunge steeply within a steeply-dipping major shear zone named the Cadwallader Break. The deposits
have major metals of Au-W-Mo-As and Au/Ag ratios of 2 to 5. A district-wide mineral zoning varies from high-temperature Au-
As-W-Mo through intermediate Sb-Ag-Au-As, to low-temperature Sb-Hg vein assemblages (Woodsworth and others, 1977). The
southwest to northeast zonation is interpreted as forming in the thermal aureole of Late Cretaceous to early Tertiary plutons of the
Coast Plutonic Complex. The Bralorne deposit is associated with Late Cretaceous (86-91 Ma) porphyry dikes. The Bralorne-
Pioneer district mines produced 129.96 tomes Au between 1899 and 1978 from 7.3 19 million tonnes ore (Dawson and others,
1991). Proven and probable reserves for Bralorne in 1991 were 965,000 tonnes grading 9.3 g/t Au (MINFILE, 2002).
Fish Lake Porphyry Cu-Au (Ag-Mo-Zn) Deposit
The Fish Lake porphyry Cu-Au (Ag-Mo-Zn) deposit consists of pyrite and chalcopyrite with minor molybdenite, bornite,
sphalerite and tetrahedrite which occur in stockwork veins (EMR Canada, 1989; McMillan, 1991 ; Taseko Mines Ltd., news
release, May 4, 1993; Caira and others, 1995; MINFILE, 2002). The deposit is hosted mainly in: (I) contact metamorphosed Early
Cretaceous(?) andesite flows and volcaniclastic rocks which occur in an embayment in a porphyritic quartz diorite stock; (2) an
associated, east-west-elongated complex of subparallel quartz-feldspar porphyry dikes; and (3) disseminations in a Late
Cretaceous quartz-diorite porphyry and in adjacent contact-metamorphosed Early Cretaceous sedimentary and volcanic rocks
(McMillan, 1991; Taseko Mines Ltd., news release, May 4, 1993). The quartz diorite stock exhibits a U-Pb zircon isotopic age of
about 80 Ma (Schiarizza and Riddell, 1997), and the biotite hornfels exhibits a K-Ar whole-rock isotopic age of 77.2 Ma
(Wolfhard, 1976). The principal orebody is ovoid shaped with dimensions of 1500 m by 800 m and a maximum depth of 880 m.
Estimated resource are 1,148 million tonnes grading 0.22% Cu and 0.41 g/t Au (Wolfhard, 1976; McMillan, 1991; Caira and
others, 1995).
Maggie Porphyry Cu-Mo Deposit
The Maggie (Bonaparte River) porphyry Cu-Mo deposit consists of chalcopyrite and molybdenite occurring in fine
disseminations in quartz veins and in host rock, and in narrow veinlets in or bordering quartz and calcite veins. The deposit is
hosted by the early Tertiary Maggie quartz monzonite stock, with a K-Ar isotopic age of 61 Ma, which intrudes metasedimentary
and metavolcanic rocks of Cache Creek terrane (Miller, 1976). The stock occurs several tens of kilometers east of other plutons in
the Fish Lake-Bralorne metallogenic belt. Chalcopyrite and molybdenite occur in quartz veins and are disseminated in the stock.
High Cu and Mo grades occur in overlapping potassic and phyllic alteration, and lower Cu and Mo grades occur in phyllic and
argilIic alteration. Estimated resources are 181 million tonnes grading 0.28% Cu and 0.029% MoSz (Miller, 1976).
Poison Mountain Porphyry Cu-Mo (Ag-Au) Deposit.
The Poison Mountain Cu-Mo (Ag-Au) porphyry deposit consists of pyrite, chalcopyrite, molybdenite, and bornite which
occur in veinlets, fracture fillings and disseminations (Brown, 1995; MINFILE, 2002). The deposit is concentrated at the contacts
between a quartz diorite porphyry stock and dikes, with isotopic ages of 59 Ma, and contact-metamorphosed Early Cretaceous
graywacke of the Jackass Mountain Group which is part of the Methow terrane. The deposit is surrounded by concentric zones of
potassic, phyllic, and propylitic alteration. Concentric zones of copper sulfide and minor oxide minerals surround a barren
granodiorite core. Estimated reserves, at 0.15% Cu cut-off, are: (1) in the oxide zone, 40.2 million tonnes grading 0.228% CU (s),