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

I Bayonne Metallogenic Belt of Porphyry Mo and
Cu-Mo-W-Zn Skarn Deposits (Belt BA)
Southern British Columbia
The Bayonne metallogenic belt of porphyry Mo and Cu-Mo-W-Zn skam deposits (fig. 62; tables 3,4) occurs in southern
British Columbia and is hosted in the mid-Cretaceous Bayonne Plutonic Suite which is the extreme, southern part of the Omineca-
Selwyn plutonic belt. The intrusions typically are S-type, felsic, enriched in large-ion lithophile elements, and have initial Sr ratios
in the range 0.71 0 to 0.740 (Armstrong, 1988). Most of the suite forms roughly equant, plutons and large stocks of mainly
granodiorite or granite; the stocks are strongly discordant with the wall rocks of the Quesnellia and Kootenay terranes and the
North American Craton Margin. The significant deposits in the belt are porphyry Mo deposits at Boss Mountain and Trout Lake, a
W skarn deposit at Emerald-Invincible, a Zn-Pb skarn and manto deposit at Mineral King, a Mo skarn deposit at Red Mountain
Moly (Coxey, Novelty, Nevada), and a Cu-Au skarn deposit at Phoenix-Greenwood (table 4) (Nokleberg and others 1997a, b,
1998).
Boss Mountain Porphyry Mo Deposit
The Boss Mountain porphyry Mo deposit consists of molybdenite in quartz veins, fracture zones and in collapse breccias
which are hosted by a granodiorite phase of the composite Early Jurassic Takornkane batholith which is intruded by the mid-
Cretaceous Boss Mountain stock (Soregaroli and Nelson, 1976; MacDonald and others, 1995). The emplacement of the stock was
accompanied by rhyolite dikes, brecciation and multiple stages of veining and Mo deposition. Molybdenite was mined from a
sheeted vein system which describes a partial annulus centered upon the apical region of the stock. Alteration assemblages
consists of garnet, hornblende, biotite, sericite, potassium feldspar, chlorite and talc. Pyrite forms a 1.5 km-wide halo. Between
1965 and 1971, about 2.97 million tonnes were milled with an average grade of 0.26% Mo. Between 1974 and 1980, 3.6 million
tonnes were milled with an average grade of 0.188% Mo. Estimated remaining reserves are 3.84 million tonnes grading 0.135%
Mo (Soregaroli and Nelson, 1976; MacDonald and others, 1995).
Trout Lake Porphyry Mo Deposit
The Trout Lake porphyry Mo deposit consists of molybdenite and pyrite in quartz veins, and also scheelite, pyrrhotite,
chalcopyrite, with lesser amounts of galena, sphalerite and tetrahedrite in peripheral skarns (Boyle and Leitch, 1983; Linnen and
others, 1995). The deposit is hosted mainly in limestone, schist, and quartzite of the Paleozoic Lardeau Group. A minor part of the
deposit is hosted in altered granodiorite and tonalite of the Late Cretaceous Trout Lake stock which forms part of the Bayonne
Plutonic Suite. Skarn calc-silicate alteration includes prograde clinopyroxene-garnet, and retrograde tremolite-clinozoisite with
scheelite. Potassic (biotite) alteration overprints retrograde skarn and forms envelopes around quartz-albite Mo veins in skam and
homfels, whereas K-feldspar replaces plagioclase in the intrusion. The highest Mo grades are associated with the later quartz-K-
feldspar-muscovite alteration. Estimated resources are 49 million tonnes I grading 0.19% Mo (Boyle and Leitch, 1983; Linnen and
others, 1995).
Red Mountain Mo Skam Deposit
The Red Mountain Mo skarn deposit (Coxey, Novelty, Giant) consists of molybdenite, pyrrhotite, chalcopyrite,
arsenopyrite, scheelite, pyrite, magnetite, bismuthinite, galena and sphalerite which occur in veins, disseminations and shears
within skarn and contact-metamorphosed siltstone and breccia of the Pennsylvanian to Permian Mount Roberts Formation (Ray
and Webster, 199 1 ; Ray and Dawson, 1998). The small porphyritic intrusions of granite and granodiorite are interpreted to be
associated with, and a late phase of the Early to Middle Jurassic subvolcanic, monzonite Rossland intrusion which is associated
with large Au-bearing pyrrhotite-chalcopyrite vein deposits of the adjacent Rossland district (Hoy and others, 1998). An
alternative interpretation is that the intrusions associated with the deposit are part of the mid-Cretaceous Bayonne Plutonic Suite.
At Coxey, molybdenite and minor scheelite are associated with a prograde assemblage of pyroxene-garnet-vesuvianite and a
retrograde assemblage of epidote-actinolite-chlorite. The Novelty and Giant Mo skarns contain abundant arsenopyrite, and minor
pyrrhotite, pyrite, chalcopyrite, cobaltite, bismuthinite, native Bi, and Au. The Novelty deposit also contains some uraninite.
Estimated production and reserves are 1.3 1 million tonnes grading 0.20% Mo (Ray and Webster, 199 1 ; Ray and Dawson, 1998).
Emerald-Invincible W-Mo Skarn Deposit
The Emerald-Invincible W-Mo skarn deposit consists of scheelite, wolframite, molybdenite, pyrrhotite, pyrite and
chalcopyrite which generally occur as disseminations, but locally occur as massive lenses with pyrite and pyrrhotite with
associated gold (Ray and Websler, 1991; Dawson and others, 1991). The deposit is hosted in the Early Cambrian Laib Formation
along the contact of the Reeves Member Limestone with the Emerald Member argillite, as well as along the contact of the
limestone with the Cretaceous Emerald and Dodger Stocks. The skam consists of garnet, diopside, tourmaline, powellite, calcite,
biotite, and K-feldspar. Sericite alteration is predominant; but kaolinite, tremolite and silica alteration also occur. The Emerald
deposit has produced approximately 7,4 16 tonnes of Mo-W concentrate. The Pb-Zn deposits at the nearby Jersey and Emerald