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

immed by wehrlite, olivine-magnetite pyroxenite, and gabbro. Chromite-bearing dunite zones contain up to 100 g/t Pt (Kozin and
others, 1999).
The Seinavsky pluton occurs 7 krn northeast of the Galmeononsky pluton. and covers an area of about 40 km'. Dunite
constitutes about 20 percent of pluton and the rest is mainly wehrlite and pyroxenite (Melkomukov and Zaitsev, 1999). A
40
~ r / isotopic ~ ~ age ~ of r 60-73.9 Ma has been obtained for the pluton (Bundtzen and others, 2003b). Chromite-rich dunite grades
up to 12 g/t Pt, and pyroxenite contains up to1 g/t Pd (Kozin and others, 1999). The PGE mineral the pluton and associated placer
deposits is isoferroplatinum. Occurring in the region are native osmium, iridium, ruthenium, and platosmiridium which comprise
a few percent of the total PGE. About 4% gold occurs in concentrates along with PGE arsenides and alloys (Melkomukov and
Zaitsev, 1999; Bundtzen and Sidorov, 1998).
Since 1994, rich PGE placers have been mined in six streams which radially drain both complexes. Approximately 18.1
tonnes PGE were mined from 1994 to 1998 (Kozin and others. 1999). Production in 2000 was approximately 3.4 tonnes PGE (A.
Koslov, written commun., 2000). The production from the Galmeononsky-Seinavsky district comprises a considerable percentage
of total Russian PGE production.
Origin of and Tectonic Controls for
Koryak Highlands Metallogenic Belt
The zoned mafic-ultramafic plutons which host the Koryak Highlands metallogenic belt intrude the Late Cretaceous
volcanogenic-sedimentary rocks of the Olyutorka subterrane of the Olyutorka-Kamchatka terrane (Nokleberg and others, 1994c,
1997~). The Olyutorka subterrane consists of a major sequence of late Mesozoic and early Cenozoic island arc volcanic and
sedimentary rocks and occurs in a large nappe which is obducted onto the Ukelayat subterrane of the West Kamchatka turbidite
basin terrane (Nokleberg and others, 1994c, 1997~). The Olyutorka subterrane consists of: (1) a lower part composed of volcanic
and siliceous oceanic rocks (Alb~an to Campanian Vatyn series); and (2) an upper part of Maastrichtian to Paleocene volcanic and
clastic island arc deposits (Achayvayarn and lvtiginskaya formations). The subterrane is locally intruded by zoned intrusives range
Gom dunite to clinopyroxenite to gabbro. The succession from pluton cores to margins is generally dunite which grades into
pyroxenite which grades into gabbro and gabbro-diabase. Lntrusion occurred in the latest Cretaceous and the plutons are
interpreted as the deep-level, magmatic roots of an island arc (Bogdanov and others, 1987). The available geologic and petrologic
and geochemical data indicate that the zoned PGE-bearing plutons formed in a marginal-oceanic basin and frontal island arc
during subduction of an oceanic plate (Bogdanov and others, 1987). Recent isotopic studies suggest intrusion of the zoned maficultramafic
plutons in the Late Cretaceous, as young as 71 Ma (Kepezhinskas and others, 1993; Sidorov and others, 1997;
Bundtzen and Sidorov, 1998). The Olyutorka-Kamchatka terrane is interpreted as an island arc rock sequence underlain by
oceanic crust. The Olyutorka subterrane is intricately faulted with, and thrust over the nearly coeval, Late Cretaceous and
Paleogene Ukelayat turbidite basin subterrane of the West Kamchatka turbidite basin terrane to the northwest (fig. 79). The Late
Cretaceous to early Tertiary Olyutorka-Kamchatka island-arc terrane is was tectonically linked to the Vetlovskiy accretionarywedge
terrane (Nokleberg and others, 2000).
Kepezhinskas and others (1993) interpret that the zoned mafic-ultramafic complexes near Epilchak Lake at the northern
end of metallogenic belt were emplaced as part of calc-alkaline magmas related to Late Cretaceous subduction during a short
period of crustal extension. They interpret tha the mafic Late Cretaceous lavas which crop out near Epilchak Lake and in the
Galmeononsky-Seinavsky areas @art of the Olyutorka-Kamchatka island arc terrane) may be co-magmatic with the zoned maficultramafic
plutons. Preliminary Ar-Ar isotopic ages fiom the Epilchak Lake and Galmeononsky zoned plutonic bodies range fiom
69 to 71 Ma (P.W. Layer, written communication, 1998).
Vatyn Metallogenic Belt of
Volcanogenic Mn and Fe Deposits (Belt VT)
Southeastern Part of Russian Northeast
The Vatyn metallogenic belt of volcanogenic Mn and Fe deposits (fig. 79; tables 3,4) occurs in the southeastern part of
the Russian Northeast. The belt occurs in several fragments, strikes east-west, is up to 680 krn long, and ranges from 5 up to 100
km wide. The belt is hosted mainly in the oceanic crustal and ophiolite rocks of the Late Carboniferous through Early Jurassic and
Cretaceous Olyutorka-Kamchatka island-arc terrane, and to a lesser extent in the Yanranay accretionary-wedge terrane (Nokleberg
and others, 1994c, 1997~). In basalt flows in the Yanranay accretionary wedge-oceanic terrane are small occurrences of cherthosted
Fe- and Mn-bearing layers and crusts which occur at the surfaces of basalt flows. The significant deposit in the belt is the
ltchayvayam volcanogenic Mn deposit (table 4) (Nokleberg and others 1997a, b, 1998).
ltchayvayam Volcanogenic Mn Deposit
The Itchayvayam and similar deposits in the metallogenic belt (Egiazarov and others, 1965) occur in a sequence of chert
and basalt. The deposits consist of massive, patchy, and brecciated Mn ores which occur as concordant, lens-like bodies 1 to 30 m
long and 0.3 to 10 m thick which are hosted in siliceous rocks. The main ore mineral is braunite, but pyrolusite occurs locally. Mn
also occurs in veins of metamorphic origin which range from 2 to 10 m long and contain 11 to 47 % Mn. The deposits occur in the
Albian-Campanian Vatyn Formation which contains abundant basalt and chert.