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

iotite-magnetite-chalcopyrite-molybdenite, main-stage quartz-chalcopyrite-molybdenite and magnetite-actinolite-plagioclase
veining, and a late-stage, peripheral assemblage of chlorite-sericite-clay-epidote-chalcopyrite-pyrite (Leitch and others, 1995). The
mineralized dikes are interpreted as coeval and cogenetic with the adjacent Rupert stock to the east (Ross and others, 1996). Late
stage porphyry dikes and associated breccia contain an advanced argillic alteration assemblage of kaolinite, pyrophyllite, sericite
and dumortierite, similar to advanced alteration assemblages of silica, clay, pyrophyllite, diaspore, zunyite, and alunite in volcanic
rocks of the Bonanza Group at Mount McIntosh and Pemberton Hills. These units are interpreted by Panteleyev and Koyanagi
(1994 ) as high levels of alteration related to a stock hosting porphyry Cu-Mo deposits as at Hushamu (Dasler and others, 1995).
Fe and Cu-Fe-Au Skarns in lsland Porphyry
Metallogenic Belt
Significant skarn Fe and skarn Cu deposits are hosted mainly by limestone of the Late Triassic Quatsino Formation on
Vancouver and Texada Islands, the equivalent Kunga Formation on the Queen Charlotte Islands, and to a lesser degree, by
volcanic rocks of the underlying Karmutsen Formation. Skarn deposits rich in iron and some deposits containing significant
copper and precious metals, commonly occur along contacts of the above strata with granitoid plutons of the Jurassic Island Suite.
Magnetite, chalcopyrite, bornite, pyrite, pyrrhotite and molybdenite are associated with the prograde skarn assemblage of grandite
garnet, diopside, wollastonite and epidote. Significant concentrations of base and precious metals may be associated with the
retrograde assemblage of actinolite, tremolite, epidote, quartz, chlorite and calcite (Dawson and Kirkham, 1996). The deposit size
ranges up to 30 million tonnes grading 40-50% Fe. Important past iron producers were Tasu, Jedway, Burnaby Iron, Brynnor, and
Texada Island. Significant copper skarns are Coast Copper and Marble Bay.
Texada lron Fe Skarn Deposit
Texada lron Fe skarn deposit consists of massive magnetite skarn mineralization which occurs as replacement bodies at
the Prescott (fig. 45), Yellow Kid, and Paxton mines (Webster and Ray, 1990; Ray and Webster, 1997; MINFILE, 2002). The
deposits produced an estimated 17.6 million tonnes grading 61% Fe. The deposits are hosted in limestone of the Late Triassic
Quatsino Formation, at or near contacts with quartz monzonite of the Middle Jurassic Gillies Stock which has an U-Pb zircon
isotopic age of 178 Ma. The deposits consist of massive magnetite and associated garnet, pyroxene, epidote, amphibole, minor
calcite, and sporadic pyrite and pyrrhotite. Rare arsenopyrite and sphalerite also occur. Sampling of Fe-skam magnetite from the
Texada lron Mines by Webster and Ray (1990) indicate grades of 3.14% Cu, 46.6 g/t Ag, and 2.8 g/t Au.
[ Garnet-pyroxene skam
Gilles Bay granodiorite stock
(Middle Jurassic)
Figure 45. Prescott body, Texada Fe skarn deposit, Island Porphyry metallogenic belt, Canadian Cordillera. Schematic cross
section. Adapted from Webster and Ray (1990).