USGS Professional Paper 1697 - Alaska Resources Library

196 Metallogenesis and Tectonics of the Russian Far East, Alaska, and the Canadian Cordillera
arc terrane and to a lesser extent in the Yanranay accretionarywedge
terrane (Nokleberg and others, 1994c, 1997c). In basalt
flows in the Yanranay accretionary-wedge-oceanic terrane
are small occurrences of chert-hosted Fe- and Mn-bearing
layers and crusts that occur at the surfaces of basalt flows. The
significant deposit in the belt is the Itchayvayam volcanogenic
Mn deposit (table 4) (Nokleberg and others 1997a,b, 1998).
Itchayvayam Volcanogenic Mn Deposit
The Itchayvayam and similar deposits in the metallogenic
belt (Egiazarov and others, 1965) occur in a sequence of chert
and basalt. The deposits consist of massive, patchy, and brecciated
Mn ores that occur as concordant, lens-like bodies 1 to
30 m long and 0.3 to 10 m thick that are hosted in siliceous
rocks. The main ore mineral is braunite, but pyrolusite occurs
locally. Mn also occurs in veins of metamorphic origin that
range from 2 to 10 m long and contain 11 to 47 percent Mn.
The deposits occur in the Albian-Campanian Vatyn Formation,
which contains abundant basalt and chert.
Origin of and Tectonic Controls for Vatyn Metallogenic Belt
The volcanogenic Mn and Fe deposits of the Vatyn metallogenic
belt are interpreted as forming in a deep marginalsea
or oceanic basin environment during submarine basalt
eruption as part of the Olyutorka subterrane of the Olyutorka-
Kamchatka island-arc terrane (fig. 79), which is described in
the above section on the Koryak Highlands metallogenic belt.
After deposition, the Mn and Fe deposits were metamorphosed
and locally redeposited as crosscutting veins (Kolyasnikov and
Kulish, 1988).
Eastern Asia-Arctic Metallogenic Belt Formed in
Late Mesozoic Part of Okhotsk-Chukotka
Continental-Margin Arc, Russian Northeast
General Setting of Metallogenic Zones in Eastern
Asia-Arctic Metallogenic Belt
The major Eastern Asia-Arctic metallogenic belt of igneous-arc-related
lode deposits occurs for several thousand kilometers
along the eastern margin of the Russian Northeast (fig.
79, tables 3, 4). The mineral deposits of the belt occur in and
(or) are adjacent to the Cretaceous and early Tertiary Okhotsk-
Chukotka volcanic-plutonic belt (Gelman, 1986; Nokleberg and
others, 1994c, 1997c). The major deposit types in the belt are
porphyry Cu-Mo, Au-Ag epithermal vein, disseminated Au-sulfide,
granitoid-related Au, Sn-Ag polymetallic vein, porphyry,
and skarn, Hg, Sb, and associated deposits. The Eastern Asia-
Arctic metallogenic belt includes the rear, frontal, and perivolcanic
zones of the Okhotsk-Chukotka volcanic-plutonic belt.
The major Eastern Asia-Arctic metallogenic belt is
subdivided into smaller metallogenic zones that each exhibit
a distinctive suite of felsic-magmatism-related lode depos-
its (fig. 79; table 4). In alphabetical order, the zones are the
Anyui-Beringov, Chaun-Seward, Chukotka, Dogdo-Erikit,
Koni Yablon, Okhotsk, Omusukchan, Verkhne-Kolyma, and
Verkhne-Yukonsky. These distinctive suites of lode deposits
in each zone are defined or subdivided on the basis of (1) the
terrane(s) that locally underlies the zone, (2) the occurrence
of longitudinal and orthogonal faults that trend north-south or
northwest, and (3) regional magmatic zonation of the Okhotsk-
Chukotka volcanic-plutonic belt (fig. 79). In some cases, the
longitudinal and orthogonal faults extend several hundreds of
kilometers to the northwest away from the northeast-trending
mass of the Okhotsk-Chukotka volcanic-plutonic belt;
Origin of and Tectonic Controls for Eastern
Asia-Arctic Metallogenic Belt
The Eastern Asia-Arctic metallogenic belt is hosted in or
near the Okhotsk-Chukotka volcanic-plutonic belt, which constitutes
a major Early Cretaceous, Late Cretaceous, and locally
Paleocene age assemblage that overlaps previously accreted
terranes. The igneous belt extends for 3,000 km along western
margin of Sea of Okhotsk, and across the Bering Straits
into the Seward Peninsula (figs. 79, 80) and consists mainly
of gently dipping basalt, andesite-basalt, andesite, dacite,
rhyolite, and tuff (Nokleberg and others, 1994c, 1997c). Rare
beds of nonmarine clastic rocks, with conglomerate, grit, and
sandstone, occur at the base. The belt also contains local widespread
silicic volcanic rock (mainly ignimbrites) and associated
tonalite, quartz-diorite, and spar granite. To the northwest,
into the continent, Late Cretaceous plutonic rocks grade into
subalkalic and alkalic granite. The Paleocene part of the igneous
belt locally consists mainly of plateau theoleiitic basalt.
The Okhotsk-Chukotka belt overlies the southeastern
margin of the North Asian Craton and the Kolyma-Omolon
superterrane, as well as the Chukotka, Kony-Murgal, Okhotsk,
Seward, South-Anyui, and Zolotogorskiy terranes of the Russian
Northeast (fig. 79). The Okhotsk-Chukotka belt is interpreted
as a Pacific-facing, continental-margin arc that formed
the Albian through Campanian and locally Paleocene boundary
of northeastern Asia. The frontal part of the Okhotsk-
Chukotka volcanic-plutonic belt is dominated by basalt, and
the rear zone is dominated by andesite and rhyolite. Coeval
granitic through gabbroic intrusions also occur in the rear zone
(Bely, 1977, 1978; Filatova, 1988). The Okhotsk-Chukotka
belt is equivalent to the East Sikhote-Alin volcanic-plutonic
belt (unit es) in the Russian Southeast (fig. 79). Together, these
two igneous belts constitute a major continental-margin arc of
Cretaceous and early Tertiary age that were tectonically linked
subduction-zone assemblages. To the north, the Okhotsk-
Chukotka igneous belt was tectonically linked to the Ekonay
oceanic crust and the West Kamchatka turbidite basin and
Yanranay accretionary-wedge terranes; to the south, the East
Sikhote-Alin igneous belt was tectonically linked to the Aniva,
Hikada, and Nabilsky accretionary-wedge and subductionzone
terranes (Nokleberg and others, 2000).