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

Klukwan-Duke Metallogenic Bett of
Mafic-Ultramafic Ti-Fe-Cr-PGE Deposits
Southeastern Alaska (Belt KL)
The Klukwan-Duke metallogenic belt of zoned mafic-ultramafic Ti-Fe-Cr-PGE deposits (fig. 49; tables 3.4) occurs
along the length of Southeastern Alaska horn Klukwan, near Haines, in the north, to Duke Island in the south (Taylor, 1967;
Brew, 1993; Hirnmelberg and Loney, 1995; Foley and others, 1997). Tbe deposits occur in a suite of zoned, Alaskan-type maficultramafic
plutons of mainly mid-Cretaceous age (100 to 110 Ma) which constitute a long, discontinuous suite of zoned plutgns
which intrude the flysch of the Late Jurassic and Early Cretaceous Gmvina-Nutzotin-Gambier volcanic-plutonic-sedimentary belt.
This belt, whlch forms a major overlap assemblage, occurs along the length of the Wrangellia island arc superterrane (Nokleberg
and others, 1994c, 1997~). The significant deposits (table 4) are at Union Bay, Klukwan, and Haines, and lesser deposits are at
Funter Bay, Duke Island, Snettisham, and Union Bay (NoWeberg and others 1997% b, 1998).
Union Bay Zoned Mafic-Ultranafic Fe-Cr-PGE Deposit
The Union Bay zoned mafic-ultramafic Fe-Cr-PGE deposit (fig. 58) (Ruckmick and Noble, 1959; Berg, 1984; Brew and
others, 1991; Himmelberg and Loney, 1995; Foley and others, 1997) consists of magnetite and chromite which are dissemin8te.d in
dunite; chromite also occur as discontinuous stringers in dunite. The deposit is hosted in a mid-Cretaceous, concentrically z$ed
mafic-ultramafic complex which has a dunite core, named the Union Bay ultrdc pluton. The dunite occurs in a pipe and 6
lopolith in center of the ultramafic pluton. Peridotite also occurs with dunite; pyroxenite and hornblende py-roxenite on the '
periphery of the pluton. The phton intrudes the Late Jurassic and Early Cretaceous flysch of Gravina-Nutzotin overlap ;
assemblage. Magnetite and chromite form primary segregations, and PGE also occurs with chromite and magnetite in dunit4
Hand- picked specimens of chromite average 0.093 glt Pt, 0.200 g/t Pd, 0.062 g/t Rh and 0.21 5 gft Ir. The deposit is large an
contains an estimated 1,000 million tonnes grading 18 to 20% Fe. The deposit may also contain V.
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Figure 58. Union Bay zoned mafic-ullramafic FeCr-PGE deposit, Klukwan-Duke metallogenic belt. Southeastern Alaska. ~&&atic
geologic map. Adapted from Hirnmelberg and Loney (1995).
Klukwan Zoned hfafic-Ultramafic Fe-Ti Deposit
The KIukwan Zoned mafic-ultramafic Fe-Ti deposit (Wells and Thorne, 1953; Robertson, 1956; MacKevsn and obrs,
1974; Berg, 1984; Still, 1984; Wells and others, )986; Brew and othm, 1991; Foley and others, 1997) consists of titaniferok
magnetite accompanied by minor chalcopyrite, hematite, pyrite, pyrrhotite, spinel, and leucoxeae which occur either as
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