USGS Professional Paper 1697 - Alaska Resources Library

114 Metallogenesis and Tectonics of the Russian Far East, Alaska, and the Canadian Cordillera
Metallogenic Belt Formed Along Late
Mesozoic Along Continental-Margin
Transform Fault
Ariadny Metallogenic Belt of Zoned Mafic-
Ultramafic Ti Deposits (Belt AR), Southern Part
of Russian Far East
The Ariadny metallogenic belt of zoned mafic-ultramafic
Ti deposits (fig. 48; tables 3, 4) occurs in the southern
part of the Russian Southeast only in the Samarka accretionary-wedge
terrane. The principal Ti deposits are at Katenskoe,
Ariadnoe, and Koksharovskoe (table 4) (Nokleberg and
others 1997a,b, 1998) and consist mainly of disseminated to
massive ilmenite that is hosted in layers in gabbro and pyroxenite.
Titanium-magnetite and apatite are rare. The deposits
also contains sparse PGE minerals, and sparse PGE minerals
occur in stream-sediment samples. The bodies are several
tens of m thick and several hundred m long. K-Ar isotopic
studies yield ages of 160 to 170 Ma. The petrochemical features
and mineral composition of the gabbro and pyroxenite
intrusions hosting the zoned mafic-ultramafic Ti deposits
are similar to those hosting the Kondyor PGE deposit (A.I.
Khanchuk, written commun., 1992).
The zoned intrusions that host the Ariadny metallogenic
belt consist of Late Jurassic ultramafic and gabbroic
complexes with K-Ar isotopic ages of about 160
Ma (Shcheka and Vrzhosek, 1985). The complexes are
interpreted as synvolcanic intrusives that intruded into
the turbidite deposits of the Samarka accretionary-wedge
terrane immediately before accretion of the terrane in the
Early Cretaceous (A.I. Khanchuk, written commun., 1993;
Nokleberg and others, 1994c, 1997c). Intrusion of the
Samarka terrane may have occurred in the final stages of
accretion during seaward migration of the subduction zone
(Khanchuk and Ivanov, 1999). The Middle and Late Jurassic
clastic matrix of the terrane consists of parautochthonous
turbidite and olistostromal deposits rocks that contain
fragments of mainly middle and late Paleozoic ophiolitic
rocks and greenstone, Middle Triassic chert, Early Jurassic
schist and shale, and Triassic to Jurassic clastic rocks. Olistostromes,
particularly in the northern part of the terrane,
consist of large fragments of Carboniferous to Early Permian
limestone. A fragment of the terrane occurs near the
town of Bikin, where meimechite and picrite flows occur in
a Late Jurassic (?) matrix (Philippov, 1990). The Samarka
accretionary-wedge terrane and correlative subduction-zone
units in Japan are tectonically linked to Jurassic granitoid
rocks in Korea, and with a major Jurassic to Cretaceous
volcanic-plutonic belt in southeastern China (Nokleberg
and others, 1994c, 1997c). These subduction-related units
are interpreted as offset from their tectonically-linked igneous
arcs by left-lateral movement during the Cretaceous
and Cenozoic (Nokleberg and others, 1994c, 1997c).
Metallogenic Belts Formed in Late Mesozoic
Continental Margin and Island Arc Systems in
Russian Far East
North Bureya Metallogenic Belt of Au-Ag Epithermal
Vein and Granitoid-Related Au Deposits
(Belt NB), Northwestern Part of Russian Southeast
The North Bureya metallogenic belt of Au-Ag epithermal
vein and granitoid-related Au deposits (fig. 48; tables 3, 4)
(Radkevich, 1984) occurs in the northwestern part of the Russian
Southeast. The deposits are hosted in Early Cretaceous
felsic and intermediate volcanic rocks that occur (1) mainly in
the Late Jurassic and Cretaceous Umlekan-Ogodzhin volcanicplutonic
belt, and (2) in the northern part of the Late Jurassic
to Cenozoic Late Amur sedimentary assemblage. These units
overlie the Malokhingansk and Turan terranes of the Bureya
superterrane, and the Gonzha, North Sukhotinsk, Mamyn,
and Tukuringra-Dzhagdi terranes. The volcanic rocks extend
along the boundary of the Tukuringra-Dzhagdi terrane with
the North Asia Stanovoy cratonal block. The major Au-Ag
epithermal vein deposits are at Bamskoe, Burindinskoe, and
Pokrovskoe (table 4) (Nokleberg and others 1997a,b, 1998).
A granitoid-related Au deposit is at Pioneer. Only a few
Au-Ag epithermal vein deposits are known. Several poorly
explored deposits are known in the area but are unexplored
because of extensive Cenozoic surficial deposits and swamps
(Melnikov, 1974). Numerous placer Au mines occur within
the North Bureya metallogenic belt. The gold in the placer
mines is interpreted by Gurov (1978) as being mainly derived
from Au-bearing quartz veins hosted in Late Jurassic to Early
Cretaceous sedimentary and volcanic rocks. The North Bureya
metallogenic belt is assessed to be promising for Au resources
and needs further study.
Pokrovskoe Au-Ag Epithermal Vein Deposit
The Pokrovskoe Au-Ag epithermal vein deposit
(Khomich and others, 1978; Mel’nikov, 1984; V.D. Mel’nikov,
written commun., 1993; Khomich, 1990) occurs in Late
Cretaceous andesite, dacite andesite, and related tuff. This
volcanic sequence overlies a Jurassic coal-bearing sequence
of sandstone, siltstone, and argillite. The ore bodies consist of
gently dipping quartz veins and zones of hydrothermal alteration.
Main alteration types are propylitization (albite, sericite,
calcite, chlorite, and pyrite), berezitization (quartz, sericite,
and hydromica), and argillization (kaolinite, montmorillonite,
hydromica, carbonates, quartz, and pyrite). The largest
ore bodies are gently dipping zones of altered rock, located
near the lower contact of andesitic sequence with a granodiorite
porphyry sill. Hydrothermally altered rocks consist of
quartz (25-85 percent), carbonate (2-5 percent), hydromica
(5-12 percent), adularia (as much as 5 percent), kaolinite (5-7
percent), and sulfides (less than 1 percent and mostly pyrite).
Gold is fine-grained (0.0005 to 0.032 mm), is associated with