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

Khatynnakh-Sala Au Quartz Vein Deposit
The Khatynnakh-Sala Au quartz vein deposit (Nekrasov, 1959, 1962; O.G. Epov and others, written commun., 1964)
occurs in anticlinal domes and is controlled by bedding-plane faults. The ore bodies include 30 veins, lenses, lenticular bodies, and
stockworks. The veins are generally not more than 1 m thick, generally 15-20 m long, and not more than 30-40 m long. Most of
the veins and host rocks are isoclinaIly folded. The host rocks include Ordovician and Silurian amphibole-mica-carbonate shale
and limestone locally metamorphosed to marble. Two levels of intensely sulfidized shale, from 0.4-6 m thick and up to 250 m
long, also occur in the deposit. Post-mineralization diabase and diorite porphyritic dikes are present, which are probably Late
Jurassic-to-Early Cretaceous in age. Besides pyrite and pyrrhotite, the ore minerals are arsenopyrite, galena, fahlore, sphalerite,
and gold. Gangue minerals constitute 95% of the deposit and include quartz, albite, ankerite, barite, and fluorite. Pyrite is altered
to pyrrhotite, and metamorphic actinolite, zoisite, biotite, sphene replace gangue minerals along with recrystallization 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
which host the Selennyakh River metallogenic belt consist of a continuous success~on of Ordovician, Early Carboniferous, and
Pennian sedimentary rocks which 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 which 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 a complex
metallogenic history (Shpikerman, 1998) of the terrane which 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 which host the Sele~yakh River metallogenic belt consist of a continuous
succession of Middle Ordovician to Middle Devonian sedimentary rocks which are about 10,000 to 12,000 km thick. The major
lithologies are continental-shelf carbonate rocks with layers of calcareous shale. Local, rift-related, middle Paleozoic alkali-mafic
and syenite intrusions also occur and have 40~r-39~r isotopic ages of 300 and 141507 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 north-central
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, 1997~1, extends almost
50 km, and varies between 20 to 30 km wide. The Tomrnot River metallogenic belt is herein correlated with the Kharnna 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 which 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 which vary from several to 25 m thick and range up to a
hundred meters long. The most important elements in the deposit are Y, Ce, La, Ta, and Nb. Some rock samples contain 0.1-0.2%
Y; 0.1-0.5% Zn; and 0.01-0.5% Nb. K-Ar isotopic studies indicate a Permian to Carboniferous age whereas U-Pb isotopic studies
indicate an age of 368 Ma (Nekrasov, 1962).