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

intarprcted as having ken emplaced along a deep-seated, continental-margin transform fault during the Early Cretaceous, when
t k margin of the Norlh Asian Craton was being deformed during collision and accretion of outboard terranes.
Metallogenic Belts Farmed During
Late Allesozolc Closure of Mongol-Okhotsk
Ocean in Russian Southeast
Selemdzha-Kerbi Metallogenic Belt of
Au Quartz Vein Deposits and Granitoid-Related
Au Deposits (Belt SK)
Northwestern Part of Russian Southeast
The Selemdzha-Kerbi metallogenic belt of Au quartz vein, granitoid-related Au deposits, and the Talaminskoe clasticsediment-hosted
Sb-Au deposit (fig. 61; tables 3,4) occurs in the northwestern part of the Russian Southeast. The belt is hosted in
the Tukuringra-Dzhagdi subduction-zone terrane and in the Nilan subterrane of the Galam accretionary-wedge terrane (Nokleberg
and others, 1994c, 1997~).
The Au quartz vein deposits, as at Afanas'evskoe, Kharga, Ingagli, Malomyr, Sagurskoe, Tokur, and Zazubrinskoe, occur
throughout the metallogenic belt. but are mainly in three large and remote areas, the Verkhne-Selemdzha, Sophiisky, and Kerbi
mining districts which comprise an area of over 1,000 km2 (Eirish, 1991 ; (Nokleberg and others 1997a, b, 1998). The deposits are
interpreted as forming during regional metamorphism. In this area, Au was probably derived from black shale which commonly
contains disseminated Au in very small quartz veinlets and rarely in small veins (Molseenko, 1977). In the Kerbi mining district,
an exhalative origin for primary gold is interpreted because gold is concentrated near eruptive centers composed mainly of
Paleozoic marine basalt. Placer gold mines, common in all three m~ning districts, have been active for many decades. The Au
quartz vein mines at Tokur, the significant deposit in the belt, and at Petrovsko-Eleninsky occur near dike swarms where gold is
interpreted as
presumably forming just before dike intrusion. The belt also contains the Poiskovoe granitoid-related ALL deposit and the
Talaminskoe Sb-Au vein deposit (table 4).
Tokur Au Quartz Vein Deposit
The Tokur Au quartz vein deposit (Radkevich E.A., Moiseenko V.G., Molchanov P.Ya., Melnikov V.D., and Fat'yanov
I.I., 1969; Eirish, 1972; Mel'nikov V.D. and Fat'yanov I.I., 1970; Layer, lvanov, and Bundtzen, 1994) consists of Au-bearing
veins. The ore minerals comprise 3% of the veins and consist of pyrite, arsenopyrite, gold, sphalerite, galena, chalcopyrite,
pyrrhotite, tetrahedrite, tennantite, and scheelite. Sphalerite and arsenopyrite increase with depth. The gangue minerals are quartz,
adularia, sericite, chlorite, and calcite. Gold fineness ranges from 650 to 800. Vein zones normally range from 25 to 90 m thick
and carbonaceous material occurs along vein margins. The veins commonly occur conformable to bedding of host rocks and are
locally discordant. The veins range up to 800 m in length and vary from 0.2 to 0.7 m thick. The maximum depth of deposit is 500
m. The host rocks are argillite, sandstone, and quartzite, part of a structurally-deformed middle Paleozoic sequence of sandstone
and schist. The deposit is medium size; 27.1 tonnes of Au were mined between 1933 and 1940. Ar-Ar isotopic study of vein
adularia indicate an age of 1 14 Ma or Early Cretaceous which is interpreted as the age of mineralization (P.H. Layer, Ivanov, and
Bundtzen, 1994). Diorite dikes and stocks cut the veins. The dikes are interpreted as forming during the late stage of accretion
with Au having been derived from the host black shale which is also the source for placer gold.
Origin of and Tectonic Controls for
Selemdzha-Kerbi Metallogenic Belt
The Selemdzha-Kerbi metallogenic belt is interpreted as forming during Late Jurassic and Early Cretaceous collision of
the Bureya and Khanka continental-margin arc superterranes with the North Asian Craton and closure of the Mongol-Okhotsk
Ocean (Nokleberg and others, 2000). During this collision, the middle to late Paleozoic passive continental-margin clastic rocks of
the craton to the north were thrust onto the Bureya superterrane to the south. The Paleozoic clastic rocks and the lesser oceanic
tholeiite, chert, limestone, and black shale of the Tukuringra-Dzhagdi and Galam subduction zone -accretionary-wedge terranes
occur in large nappes. During collision and regional thrusting, these rock units underwent greenschist facies regional
metamorphism with late-stage formation of Au quartz vein deposits formed. Local higher-grade metamorphism occurred in
metamorphic domes.