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

interpreted as forming in the Jurassic and Early Cretaceous and is tectonically linked to the Goodnews sub&tio=e teim~~
(Box and Patton, 1989; Decker and others, 1994; Plafker and Berg. 1994; Nokleberg and others, 2000).
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Yukon River Metallogenic Belt of
v
Podiform Cr Deposits (Belt .. .
YR)
, I 4 HY- .* r*
West-Central Alaska 'I 'l
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The Yukon Rlver metallogenic beil of podrfom Cr deposits (fig. 49; tables 3 .4>~&s atohglhe sduthenidadk of the
Yukon-Koyukuk Basin in west-central Alaska (Foley and others, 1982, 1997). As in the %them Brooks Range metallogenic belt
of podiform Cr deposits to the north, the metallogenic belt is hosted in the upper structural level of the Angayucham oceani~ and
subduction-zone terrane which is interpreted as the basal part of the Koyukuk island arc (Noldeberg and others, 1994c, 1997c,
2000; Patton and others, 1994). The Yukon River metallogenic belt extends for several hundred kilometers. The principal deposits
in the northeastern part of this belt are at Caribou Mountain, Lower Kanuti River, and Holonada, and the significant deposits in
the southwestern pan of this belt at Mount Hunt and byuh Hills are in the Toziba and Innok? areas (table 4) (Nokleberg and Bq
others 1997a, b, 1998). - .
-.
Kaiyuh Hills Podiform Cr Deposit
The Kaiyuh Hills podiform Cr deposif (Loney and Himmelberg, 1984; Foley aid others, 1984, 1997) consists of banw
and disseminated chrormte from 1 cm to 1 m thick which occur m fresb and serpenthized Jurassic(?) dunite of the Kaiyuh Hills
ultramafic belt. The dunite interlayered wilh harzburgite tectonite. The largest deposit covers an area of1 by 100 m, and consisfs of
massive chromite containing an estimated 5,000 tonnes Cr203. Lesser occ
Metallurgical grade chromite containing 46% Cr203 is present. The deposit c
in one deposit. Surface samples from the largest deposit average 60% Cr&
Origin of and Tectonic Controls for
Yukon River Metallogenic Belt
Along the southern margin of the Brooks Range, the Angayucham oceanic te
striking, south-dipping thrust sheet which extends for several hundred km, and in sparse
structural level of the Angayucham subduction zone twrane in West-Central alaska (fig.
klippen are thrust along north-dipping faults over the highly deformed metamorph
metasedimentary, metavolcanic, and lesser metagranitoid rocks of tbe Ruby me
south. To north is the Late Jurassic and Early Cretaceous Koyukuk Island-rn
1994). The thrust sllces of ultramafic rocks in the highest structural level of th
an ophiolite which consitutes the base of the Koyukuk idand arc (Loney and Himrnelberg, 19
and others, 1994). This interpretation suggests that the Yukon hver metdogenic belt of pod^
subduction-related intrusion of mafic-ultramafie plutons into the bad part of
and others, 1993; Goldfarb, 1997; Nokleberg sad others. 2000).
Metallogenic Belts Formed in Late Mesozoic
Gravina Island Arc in Southern Alaska and
Canadian Cordillera
EasternSouthern Alaska Metallogenic Belt of
Granitic Magmatism Deposits (Belt ESA)
EasternSouthern Alaska
The major Eastem-Southem Alaska metallogenic belt of granitic magmatism depos~ts (fig. 49; tables 3,4) conta~n!
porphyry Cu, Mo, and Au, polymekllic vein, and FcAu skam deposits (Nokleberg and others, 1995a). The metallogenic b~.. ,.
hosted in the northern part of tbe Wrangellia island-arc superterdne, in and adjacent to the area underlain by the Late Jurassic t
mid-Cretaceous Gravina-Nutzotin belt and coeval granitoid plutonic rocks (Nokleberg and others, 1994c, 1995a, 1997~). This .
igneous belt was designated as part of a volcanic-plutonic arc by Richter and others (19751, has been called the Nutzotin-
Chichagof belt by Hudson (1983), the Chisana arc by Plafker and others (1989), and the Gravina arc by Stanley and others (I-.
This igneous belt extends for a few hundred kilometers within and parallel to the northern margin of the Wrangellia island arc
superterrane. The deposits of the Eastern-Southern Alaska metallogenic belt are associated with Early to mid-Cretaceous granitoid
rocks, mainly granite and granodiorite (Miller, 1994). Most of the nt-anitoid rocks are calc-alkaline and intermediate in
compbsition: fhe significant deposits are the ~abesna (fig 56) and-~ambler Fe-Au ska
Au-Cu deposit, the Bond Creek-Orange Hill, and London
deposit (table 4) (Nokleberg a d others 1997a, b, 1998).
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