USGS Professional Paper 1697 - Alaska Resources Library

166 Metallogenesis and Tectonics of the Russian Far East, Alaska, and the Canadian Cordillera
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 that
containing feldspar, carbonate minerals, epidote, chlorite, and
other minerals, and (2) various mineralized zones in Paleozoic
and Mesozoic clastic rocks, chert, volcanogenic rocks that 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 commun., 1977) consists of
thin quartz and carbonate-quartz veins and veinlets that 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 that have
been mined. The deposit occurs in a nappe of early Paleozoic
and possibly older metavolcanic rocks that display both greenschist
facies metamorphism and extensive host rock replacement
by sulfide minerals and quartz and that 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 commun., 1977) consists of steeply dipping
quartz and quartz-carbonate veins that grade into zones
of silicified and sulfidized veinlets along strike. The deposits
trend northwest and are as much as 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.
Nome Metallogenic Belt of Au Quartz Vein
Deposits (Belt NO), Seward Peninsula
The Nome metallogenic belt of Au-bearing quartz vein
deposits (fig. 62; tables 3, 4) forms a 200 km long, east-westtrending
belt along the southern part of the Seward Peninsula.
The metallogenic belt occurs along the southern margin of the
Seward metamorphosed continental-margin terrane (Nokleberg
and others, 1994c, 1997c). The most favorable mineralized
areas are associated with upper greenschist facies metamorphic
rocks. Two major concentrations of deposits occur at (table 4)
(Nokleberg and others 1997a,b, 1998) (1) Bluff and Big Hurrah
in the Solomon District, and (2) Rock Creek, Mount Distin, and
Sophia Gulch in the Nome District. In both areas, the deposits
consist mainly of mesothermal, sulfide-poor, Au-quartz deposits
in individual high-grade veins or in zones of multiple, moreor-less
enechelon, sheeted veins that generally contain lower
Au grades. The quartz veins, which typically contain minor
carbonate, albite, and oligoclase, cut shallow-dipping metamorphic
foliation. The best studied deposits in the Nome district
are at Rock Creek and Mount Distin, both immediately north
of Nome (Gamble and others, 1985; Apodaca, 1992). These
newly evaluated lodes may be examples for the rich placer Au
deposits mined in the Nome District.
In the Nome district, Bundtzen and others (1994)
recognize three major mineral deposit type—(1) early-stage
chalcopyrite-sphalerite-gold-quartz-carbonate veins, which
appear as boudins that are rolled around early fold axes
(Banger deposit), (2) Au-quartz polysulfide veins that crosscut
schistosity at low angles (Rodine, McDuffy, and Twin Mountain
deposits), and (3) brittle, Au-polysulfide-quartz-albitecarbonate
veins that crosscut schistosity at high angles (Rock
Creek, Sliscovish, Sophies Gulch deposits). The Au deposits
are thought to have formed during various stages of dewatering
of a metamorphic pile during Barrovian-type, greenschist
facies regional metamorphism and associated plutonism,