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

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The Orange Hill deposit contains an inferred reserve of 320 million tonnes grading 0.35% Cu and 0.02% Mo, and the
Bond Creek deposit contains an inferred reserve of 500 million tonnes grading 0.30% Cu and 0.02% Mo (Richter and others,
1975a, b). The Nabesna pluton intrudes Late Jurassic and Early Cretaceous flysch of the Gravina-Nutzotin belt. Associated skam
deposits contain disseminated andradite garnet, pyroxene, pyrite, chalcopyrite, bornite, and magnetite, and massive pyrrhotite,
pyrite, chdcopyrite, and sphderite. Also associated with the Nabesna pluton are the mined Nabesna Fe-Au and the Rambler Fe-
Au skarn deposits (Weylmd, 1943; Nokleberg and others, 1987; Newberry and others, 1997a).
Beultoff, Hamfeld, Carl Creek
Patphyty Cu DepasIts
The Baultoff, Horsfeld, and Carl Creek porphyry Cu deposits (Richter and others, 1975b) occur in three nearby areas in
the northern Wrangell Mountains. The deposits consist of pyrite and chalcopyrite which occur both in veinlets aad as
disseminations in altered Cretaceous granitoid plutons composed of quartz diorite, quartz diorite porphyry, or granite porphyry.
The altered areas associated with the deposits have dimensions up to 1,000 by 2,000 m. Alteration minerals are chlorite, sericite,
albite, pyrite; local actinolite veins and disseminations also occur. The deposits contain an estimated resource of 240 million
tonnes grading 0.2% Cu, 4.01% Mo, and trace Au (Richter and others, 1975b). The host granitoid rocks form part of the
Cretaceous Klein Creek batholith which intrudes Late Jurassic and Early to mid-cretaceous flysch of the Gravina-Nutzotin belt.
Own of end Tectonic Contnds for
Eastem-Southem Alaska Metatlogenic Belt
The Eastern-Southern Alaska metallogenic belt occurs in the central and northern part of the Wrangellia island-arc
terrane, in and adjacent to the area underlain by the Late Jurassic and Early Cretaceous Gravina-Nutzotin belt, and by the partly
coeval Kahiltna overlap assemblage (Nokkberg and others, 1995a) (fig. 49). In the Nutzotin Mountains between the Alaska
Range and Wrangell Mountains, the Gravina-Nutzotin belt consists chiefly of argillite, graywacke, and conglomerate, and a lesser
wit of andesite and basalt volcanic and volcaniclastic rocks in the Chisana Formation (Berg and others, 1972; Richter, 1976;
Richter and others, 1976). Sedimentary rocks range in the from deep marine turbidites to shallow-water and nomarine deposits.
The come clastic rocks in the Nutzotin part of the Gravina-Nutzotin belt are interpreted as derived locally fiom the underlying
Wrangellia supertenme and fiom unknown metamorphic source terranes. Metamorphism is lower greenschist bcies (Dusel-
&con and others, 1993).
The gmnitaid rocks of the Gmvina arc are partly coeval with the andesitic and basaltic voicanic and volcaniclastic rocks
I of the Early Cretaceous Chisam Formatian which occurs in the upper part of the Gravina-Nutzotin belt in the Nutzoh Mountah
in eastern-southern Alaska. The igneous rocks of the Chisana Formation are A1,0, rich, exhibit pronounced light-REE
eruichment, arr classified as tholeiitic-transitional to calc-alkalic, and are interpreted as subduction-related by Barker (1994). The
Chisana Formation is interpreted as forming in the axial part of the Gravina arc with volcanic-rock-derived flysch of the Kahiltna
overlap assemblage and Gravina-Nutmtin belt as forming along the arc flanks.
To the west, in the central and western Alaska Range and adjacent areas, the Kahiltna overlap assemblage, which is
partly coeval with the GrwiilaNutzotin belt, consists chiefly of structurally-disrupted, deep marine, partly vokaniclastic,
flyschoid graywacke and argillite. with minor amounts of chert, I~mestone, conglomerate, and andesite (Csejtey and otben, 1986;
I Jones and others, 1982, 1987; Wallace and others, 1989; Nokleberg and others, 1994d). The assemblage is mostly Euly
Cretaceous in age, but includes rocks ranging in age from Late Jurassic to locally early Late Cretaceous (Cenommhn).
Metamorphism is lower greenschist facies, but locally ranges from zeolite to amphibolite facies (Dusel-Bacon and others, 1993).
The occurrence of locally abundant volcanic rock detritus in the flysch of the Kahiltna overlap assemblage indicates that the
Gravha an: occurred sporadically across most of southern Alaska.
Together, the granitic and andesitic rocks of the Gravina-Nutzotin belt and the Kahiltna overlap assemblage define the
Gravina island arc, which is interpreted as fonning on the northern, or leading edge of the Wrangellia island-arc superternme
I during migration towards North America (Nokleberg and others, 1984, 1985,2000; Nokleberg and Lange, 1985a; Plaflter and
others, 1989; Plafker and Berg, 1994; Nokleberg and others, 2000). The Gravina arc and associated granitic magmatism deposits
are tec(onically linked to the younger part of the McHugh Complex which forms the northern part of the Chugach subduction zone
and accretionary wedge complex (Nokleberg and others, 2000). These relations reveal the long and complex history of the
WrangeUa island-arc superterrane (Nokleberg and others, 1984, 1985,2000; Nokleberg and Lange, 1985a). The Eastern-Southern
Alaska raeIztllogenic belt is herein interpreted as partly coeval with: (1) the Westem-southeastern Alaska metallogenic bek
described bdow, which is also hosted in the Late Jurassic and Early Cretaceous Gravina overlap assemblage of the Wrangellia
superterrane in Southeastern Alaska; and (2) the lsland porphyry metallogenic belt, described above, which is hosted In the
Gambisr overlap assemblage in southern British Columbia.