USGS Professional Paper 1697 - Alaska Resources Library

144 Metallogenesis and Tectonics of the Russian Far East, Alaska, and the Canadian Cordillera
that rank as some of the world’s largest native platinum specimens.
In 1998 and 1999, about 75 kg PGE were recovered
from chromite lodes during pilot tests studies The Kondyor
deposit is one of the most important sources of platinum in the
Russian Federation.
Origin of and Tectonic Controls for Kondyor
Metallogenic Belt
Controversy exists about the age and tectonic environment
for the mafic and ultramafic rocks that host the Kondyor and
similar deposits. The host rocks were originally interpreted as
an integral part to the Late Proterozoic and older cratonal rocks
of the Stanovoy block of the North Asian Craton. However,
A.I. Khanchuk (written commun., 1994) interprets the mafic
and ultramafic rocks as Jurassic, because the intrusions are
similar in composition to other Jurassic massifs of the Ariadny
igneous belt. However, this belt is herein interpreted as forming
in the mid-Cretaceous along with the Algama metallogenic
belt, described above. Unpublished K-Ar isotopic ages for the
zoned mafic-ultramafic intrusions in the Kondyor metallogenic
belt range from 60 to 110 to 160 Ma (A.M. Lennikov, written
commun., 1993). An Ar-Ar isotopic age of 127 Ma (Early
Cretaceous) was recently obtained for the alkalic mafic and
ultramafic igneous rocks at Ingagli (Dalrymple and others,
1995), that may be part of the same igneous belt that hosts the
Kondyor metallogenic belt. The interplate intrusions of the
Kondyor metallogenic belt are herein interpreted as having
been emplaced along a deep-seated, continental-margin transform
fault during the Early Cretaceous, when the margin of the
North Asian Craton was being deformed during collision and
accretion of outboard terranes.
Metallogenic Belts Formed During Late
Mesozoic 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 clastic-sediment-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, 1997c).
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 cover an area of more
than 1,000 km 2 (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 that commonly contains disseminated Au in very
small quartz veinlets and rarely in small veins (Moiseenko,
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 mining 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 Au 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, Ivanov, and Bundtzen, 1994) consists of Aubearing
veins. The ore minerals are 3 percent 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 as much as 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 114 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
and accretionary-wedge terranes occur in large nappes. During