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

ecently been studied (Kirillov, 1991,1993). Insufficient data preclude determining the origin of the Ulkan melnllogenic belt. The
Ulkan belt is coeval anorthosite to the south which is interpreted as forming in a Mesoproterozoic rift-related v~lcanic-plutonic
cenler.
BWyakohan Metallogedo Belt of
SedirnentSlosed Cu and
Basaltic Cu Deposlls (Belt 81)
Sowhwegtern Part of Russian NoM~east
The Bilyakchan metallagenic belt of sediment-hosted Cu and basalt Cu deposits (fig. 2; tables 3,4) occurs in the
southwestern part of theRussian Northeast in Proterozoic rocks of the Verkhoyansk fold belt (unit NSV) that cbnztitutt~ the NoHh
Asian Crato~ Margin (Nokleberg and others, 1994c, 1997b, c, 1995; Shpikerman, 1998). The belt strikes north-nodetast for 350
km along the westem foMed margin of the Okhotsk cratonal terrane and is about 50 km wide. The deposit3 occur in
metamorphosed sandstone a d basalt of the Riphean and Vendian Bilyakchan sequence with a thiche-u of 3,100 m (Kutyrev and
others, 1986). The Bilyakchan metallogenic belt is correlated with the tectonically-displaced Oroek metalkogenic belt of ironslone
and sedimenthosted Cu deposits which is described above.
Dzhegdag B ~Iffc Cu and Severny Uy Occurrences
Basaltic Cu occurrences, as at Dzhagdag, occur in the lower part of the sequence. The Dzfiagdag deposit c~sisls of two
layers of late Ripheam (Vendian) arnygdaloidal basalt, intercalated with tuff and sandstone, which contain (3-bearing horizons
which are 0.4-5 m thick and contain finely disseminated to small masses of chalcocite, bornite, native copper, cuprite, covellite,
and malachite (Kutyrev md others. 1988). The basaltic Cu deposits and the hosting basalts are interpreted aa forming during
rifting on a shallow-submerged scarp of the western Okhotsk cratonal terrane. The sediment-hosted (sendstone) Cu occurrences,
as at Severny Uy and Borong, occur at higher stratigraphic levels. The Severny Uy deposit consists of Cu-bearing horizons &om I
to 3 m thick and occur in Late Riphean (Vendian) quartz- and polymictic sandstone and siltstone (Kulyrev and otkers, 1986). The
deposit contains fine disseminations and pockets of massive pyrite, chalcopyrite, bornite, chalcocite, and hematite. The sedimenthosted
Cu deposits and tbe bast sandstones are interpreted as forming during erosion of volcanic rocks with basaltic Cu dm&. Origin of end Tectonic Contrdf for
Bilyakchn Metallogenic Belt
The southwestern par! of the North Asia Craton Margin (Verkhoyansk fold belt, unit NSV), which boa the Bilyakchan
metaligenic belt., consisls of the following major units: (1) Middle to Late Riphean shelf limestone, sandstone, Pnd shale with a
cambiead thickness of more thiln 3 km; and (2) Late Riphean to Late Vendian clastic and volcanic rocks, mduding variegated
conglomerate, srtndarona, silbtonc, basalt, and rare rhyolite. The late Riphean (Vendian) sedimentary and volcanic rockwMcb host
the Cu &posh are interpreted as fming in a rift-related depression which formed in the transition between a continental shelf
and adjacent onshore am, with the Siberian paleocontinental passive margin. The rift-related sedimentary cocks and Cu deposits
were suhequtntly deformed into gentle folds and metamorphosed at greenschist facies. Sedimentary rocks of the fold belt are
epparently tectonically detached fiom crystalline basement of craton. In this region, the Verkhoyansk fold kllis separated from
he North Asian Craton by a west-verging thrust fault.
Kllbuck MsWtqpnlc Eelt of Ironstone
{Superior Fe) Deposits f Belt KI)
SouthweSkrn Alwka
The Kilbuck metallogenic belt of ironstone (probable Superior Fe type) deposits (fig. 3; tables 3,4) occurs in
southwestern Alaska. The metallogenic belt is hosted in the Kilbuck-Idono cratonal terrane which occurs in two dif~~atinuous
6agments separated along the dextral-slip Nixon Fork fault (fig. 3). The one known occurrence is at Canyon Cnak (table 4)
(Noldebetg aad others 19974 b, 1998).
The Canyon Creek ironstone (Superior Fe) occurrence consists of rhythmically-layered hematite, magsahte, and siderite
in layers up lo 4 cm thick which occur in bleached Early Proterozoic quartzite (Bruce Hickok, T.K. Bindtzen, andML. Miller,
written commun., 1992). The host rocks are mainly quartzite, garnet-biotite schist, meta felsic volcanic rocks, and amphibolite
which are me~orphosed at amphibolite facies. The occurrence is about 150 m long, but is poorly exposed.
The Wbuck-Idono terrane which hosts the Canyon Creek ironstone (banded Fe formation) occurrence wnsiats chicfly of
rnctmnorpbosed diorite, tonalite, trondhjemite, and granite orthogneiss, subordinate amphibolite, and minor metsedimentary
roch (Box and others, 1993; Miller and others, 1991). The metasedimentary rocks of the terrane are mainly quartz-mica schist,
marble, garnet amphlbolltc, and minor banded iron formation. The metaplutonic rocks of the terrane yield Early Proterozoit (2.06
to 2.07 Ga) U-Pb zirconages of emplacement (Box and others, 1990; Miller and others, 1991). The Kilbuck-lho terrmu may be
a displaced cratodd kagment of either the North America Craton or the North Asian Craton. The Kilbuck-ldono t m is
wsibly