USGS Professional Paper 1697 - Alaska Resources Library

60 Metallogenesis and Tectonics of the Russian Far East, Alaska, and the Canadian Cordillera
lization of quartz. A late Paleozoic age is interpreted for the
deposit and associated metamorphism. The deposit averages
0.2 to 2 g/t Au.
Origin of and Tectonic Controls for Selennyakh River
Metallogenic Belt
The Selennyakh River metallogenic belt is hosted in the
Omulevka passive continental margin terrane. The local units
that host the Selennyakh River metallogenic belt consist of
a continuous succession of Ordovician, Early Carboniferous,
and Permian sedimentary rocks that are about 10,000 to
12,000 km thick. The major lithologies are continental-shelf
carbonate rocks with layers of deep-marine limestone and
shale. The stratabound Hg and Au deposits, which are the
major element of the Selennykh River belt, are hosted in Middle
Ordovician and Lower Silurian limestone and dolomite
that ranges from 300 to 500 m thick. The ore-bearing carbonate
stratum is overlapped by calcareous shale (Shpikerman,
1998). Local middle Paleozoic mafic and syenite intrusions
also occur. The younger, Carboniferous and Permian stratiform
deposits are interpreted as forming during a short-lived
rifting event within the Omulevka terrane.
The diversity of deposit types in the Selennyakh River
metallogenic belt is interpreted as the result of the complex
metallogenic history (Shpikerman, 1998) of the terrane
that consisted of (1) subsurface mineralization occurring in
artesian thermal basins associated with Late Devonian rifting,
thereby forming Southeast Missouri Zn-Pb and stratabound
Hg deposits, and (2) subsequent formation of veins during
intrusion and regional metamorphism of the stratabound
deposits, thereby forming Hg, Au, and Pb-Zn vein deposits.
The local units that host the Selennyakh River metallogenic
belt consist of a continuous succession of Middle Ordovician
to Middle Devonian sedimentary rocks that are about 10,000
to 12,000 km thick. The major lithologies are continentalshelf
carbonate rocks with layers of calcareous shale. Local,
rift-related, middle Paleozoic alkali-mafic and syenite intrusions
also occur and have 40Ar-39Ar isotopic ages of 300 and
141+07 Ma, respectively (Trunilina and others, 1996). The
host Omulevka terrane is interpreted as a rifted fragment of the
North Asian Craton Margin (Verkhoyansk fold belt, unit NSV;
Nokleberg and others, 1994c, 1997c; Shpikerman, 1998).
Tommot River Metallogenic Belt of Carbonatite-
Related Nb, Ta, and REE Deposits (Belt TO)
North-Central Part of Russian Northeast
The small Tommot River metallogenic belt of carbonatite-related
Nb, Ta, and REE deposits occurs in the northcentral
part of the Russian Northeast (fig. 16; tables 3, 4)
(Nokleberg and others, 1997b, 1998). The belt is hosted in the
passive continental margin Omulevka terrane of the Kolyma-
Omolon superterrane (Nokleberg and others, 1994c, 1997c),
extends almost 50 km, and varies between 20 to 30 km wide.
The Tommot River metallogenic belt is herein correlated with
the Khamna River metallogenic belt, which is hosted in the
North Asian Craton Margin (unit NAV, Verkhoyansk fold belt).
This interpretation suggests that the Omulevka terrane is a
faulted fragment of the North Asian Craton Margin.
Tommot REE Deposit
The one significant deposit in the belt at Tommot (Nekrasov,
1962; L.M. Parfenov, P.W. Layer, written commun., 1994)
consists of REE, Ta, and Nb minerals that occur in fenite,
metasomatic alkalic pegmatite, and aegirine granite and in
country rock adjacent to a zoned Late Devonian (?) alkalic
gabbroic-syenite pluton. These igneous rocks intrude early
Paleozoic slate. The 20 ore bodies at the deposit include metasomatic
veins and lenses that vary from several to 25 m thick
and are as much as a hundred meters long. The most important
elements in the deposit are Y, Ce, La, Ta, and Nb. Some rock
samples contain 0.1 to 0.2 percent Y; 0.1 to 0.5 percent Zn;
and 0.01 to 0.5 percent Nb. K-Ar isotopic studies indicate a
Permian to Carboniferous age, whereas U-Pb isotopic studies
indicate an age of 368 Ma (Nekrasov, 1962).
Origin of and Tectonic Controls for Tommot River
Metallogenic Belt
The intrusion of alkalic igneous rocks that host the Nb,
Ta and REE deposits of the Tommot River metallogenic belt
are interpreted as forming during Late Devonian rifting of
the North Asian Craton and the formation of the Omulevka
Omulevka passive continental margin terrane (Nokleberg
and others, 1997b, 1998). The alkalic igneous rocks that host
the Tommot River metallogenic belt are part of a sequence
of Mississippian igneous rocks in the terrane. The Omulevka
terrane is herein interpreted as rifted fragment of the Paleozoic
passive continental margin of North Asian Craton (Nokleberg
and others, 1994c, 1997c, 2000), which in the Khamna River
area contains a possibly similar belt of carbonatite-related Nb,
Ta, and REE deposits.
Urultun and Sudar Rivers Metallogenic Belt of
Southeast Missouri Pb-Zn, Carbonate-Hosted Hg,
Basaltic Cu, and Volcanogenic Mn Deposits (Belt
URS) West-Central Part of Russian Northeast
The Urultun and Sudar Rivers metallogenic belt of Southeast
Missouri Pb-Zn, volcanogenic-sedimentary Mn, basaltic
Cu, bedded barite, and carbonate-hosted Hg deposits (fig. 16;
tables 3, 4) occurs in three discontinuous fragments that extend
northwesterly for 170 km in the west-central part of the Russian
Northeast (Shpikerman, 1998. The southeastern portion
of the belt is in the Sudar River Basin, and the northwestern
portion of the belt is in the Late Taskan and Urultun Rivers.
The deposits occur in various parts of the Paleozoic Sudar rift
sequence in the Omulevka passive continental margin terrane