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

margin arc superterrane. The volcanic-tectonic depression is filled with mid- Cretaceous, intermediate-composition volcanic rocks
and overlying Late Cretaceous tuff and rhyolite lava. The volcanic rocks range from 1.5 to 3.0 krn thick. The volcanic rocks rest
on a basement Proterozoic metamorphic rocks of the Bureya superterrane. The intrusive rocks of the Khingan-Okhotsk belt in this
area are dominantly granite and are comagmatic with the volcanic rocks. The granitoid rocks of the Khingan-Okhotsk belt are
interpreted as subduction-related, calc-alkalic igneous rocks. which include both S- and 1-type granites.
The Khingan continental-margin arc (ko) is herein interpreted as forming from oblique subduction of the ancestral Pacific
Ocean plate. Fragments of this plate are interpreted as occurring in tectonically interwoven fragments of the Amur River (AM),
Khabarovsk (KB; younger Early Cretaceous part), and Kiselevka-Manoma accretionary-wedge terranes (Natal'in, 199 1, 1993;
Nokleberg and others, 1994a; Sengor and Natal'in, 1996a, b). This tectonic pairing is based on: (1) occurrence of accretionary-
wedge terranes outboard (oceanward) of, and parallel to the various parts of the Khinghan arc; (2) formation of melange structures
during the Early and mid-Cretaceous (Natal'in, 1991; Nokleberg and others, 1994a; Vrublevsky and others, 1988; Nechaev and
others, 1996); and (3) where not disrupted by extensive Cretaceous movement along the Central Sihote-Aline strike-slip fault,
dipping of melange structures and bounding faults toward and beneath the igneous units of the arc (Natal'in, 1993). Formation of
the Khingan arc and associated subduction is generally interpreted as ending in the late mid-Cretaceous when oblique subduction
changed into sinistral-slip faulting along the outboard margin of the arc (Nokleberg and others, 2000).
Metallogenic Belts Formed in Late Mesozoic
Collision and Accretion of Island Arcs, and
Transform Continetnal-Margin Faulting,
Russian Northwest, Western and
Northern Alaska, and Northern
Canadian Cordillera
Anadyr River Metallogenic Belt of
Au Quartz Vein and Associated Deposits
(Belt AD) Eastern Part of Russian Northeast
The Anadyr metallogenic belt of sparse Au quartz vein deposits occurs in the eastern part of the Russian Northeast in the
Anadyr region (fig. 61, tables 3,4) (Nokleberg and others, 1997b, 1998). The significant deposits are at Vaegi and Nutekin.
Significant associated placer Au districts occur at Kenkeren, Otrozhny, and Pekulney (Nokleberg and others, 1997b. 1998). The
knowledge of associated lode deposits is poor, although placer Au deposits were discovered in the Zolotoy Range in 1902. The
placer Au districts overlie island arc and oceanic crust terranes which occur in intricate fold, thrust, and nappe structures.
The lode sources for the placer Au deposits are interpreted as: (1) various Au quartz and sulfide-quartz vein which
containing feldspar, carbonate minerals, epidote, chlorite, and other minerals; and (2) various mineralized zones in Paleozoic and
Mesozoic clastic rocks, chert, volcanogenic rocks which are intruded by Late Cretaceous calc-alkaline magmatism. Some Au
occurrences are associated with PGE deposits which occur in silica-carbonate metasomatic rocks in serpentinite melange. Two
small Au quartz vein occurrences are at Vaegi and Nutekin. Both are hosted in the Mainitskiy island-arc terrane (Nokleberg and
others, 1997b, 1998).
The lode Au deposits of the Anadyr metallogenic belt are tentatively interpreted as forming mostly during late Early
Cretaceous accretion and associated metamorphism and deformation of the Mainitskiy arc that includes the Mainitskiy and West
Pekulney island-arc terranes and the Penzhina-Anadyr accretionary wedge or subduction-zone terranes (Nokleberg and others,
1994c, 1997c; 2000).
Vaegi Au Quartz Vein Occurrence
The small Vaegi Au quartz vein occurrence (M.N. Zakharov and V.P. Vasilenko, written comrnun., 1977) consists of thin
quartz and carbonate-quartz veins and veinlets which contain disseminated gold, hematite, pyrite, and chalcopyrite with spare
arsenopyrite. The deposit is hosted in Paleozoic and supposed Proterozoic intermediate metavolcanic rocks. Gold-cinnabar
intergrowths occur in nearby heavy mineral placers which have been mined. The deposit occurs in a nappe of early Paleozoic and
possibly older metavolcanic rocks which display both greenschist facies metamorphism and extensive host rock replacement by
sulfide minerals and quartz, and which may have potential for vein and disseminated Au deposits (Ivanov and others, 1989).
Nutekin Au Quartz Vein Occurrence
The small Nutekin Au quartz vein occurrence (V.P. Vasilenko, written comrnun., 1977) consists of steeply-dipping
quartz and quartz-carbonate veins which grade into zones of silicified and sulfidized veinlets along strike. The deposits trend
northwest and are up to 500 m long. The Au-bearing veins occur in early Mesozoic, and less frequently Early Cretaceous, clastic
sedimentary rocks. The highest Au contents are in veins within Paleogene dolerite dikes. The Au is associated with rare
disseminated pyrite and arsenopyrite, and is marked by high Hg content. The deposit occurs in the axial portion of a horst-
anticlinorium structure.