USGS Professional Paper 1697 - Alaska Resources Library

Metallogenic Belts Formed During Late Mesozoic Island Arcs in Russian NE and SE Alaska, and Southern Canadian Cordillera 157
the Yana-Kolyma are interpreted as forming during syncollisional
regional deformation, metamorphism, and granitoid
magmatism related with accretion of the Kolyma-Omolon
superterrane to the North Asian Craton Margin (unit NSV,
Verkhoyansk fold belt; Nokleberg and others, 2000). The Sn
vein, Sn greisen, W vein deposits, and clastic-sediment-hosted
Hg deposits of the Yana-Kolyma metallogenic belt are interpreted
as forming during intrusion of the Early Cretaceous
late-collisional (anatectic) granitoid rocks (granodiorite-granite
and granite-leucogranite associations) of the Main part of
the Verkhoyansk collisional granite belt (unit vk; Nokleberg
and others, 1994c, 1997c). Alternatively, Babkin (1975) and
Berger (1993) interpret that the clastic-sediment-hosted Hg
deposits of the Yana-Kolyma metallogenic belt formed during
a younger event in the Paleocene.
Metallogenic Belts Formed During
Late Mesozoic Island Arcs in Russian
Northeast and Southeastern Alaska,
and Southern Canadian Cordillera
Left Omolon Belt of Porphyry Mo-Cu and Mo-Cu
Skarn Deposits (Belt LO), East-Central Part of
Russian Northeast
The Left Omolon metallogenic belt of igneous-arc-related
deposits is associated with a chain of Early Cretaceous granodiorite
stocks and small bodies that trend northwest for nearly
300 km along the left side of the Omolon River Basin (fig. 61;
tables 3, 4) (Nokleberg and others, 1997b, 1998). The major
deposit types in the belt are porphyry Mo-Cu and related Mo-
Cu skarn deposits. The significant deposits are at Bebekan and
Medgora. The porphyry Mo-Cu deposits are associated with
Au-Ag and Pb-Zn vein deposits.
Bebekan Porphyry Mo-Cu Deposit
The Bebekan porphyry Mo-Cu deposit (Alekseenko,
Korobeinikov, and Sidorov, 1990) consists of a stockwork of
sulfide-quartz veinlets with disseminated molybdenite, chalcopyrite,
pyrite, sphalerite, pyrrhotite, arsenopyrite, bornite, and
covellite. The deposit occurs in an Early Cretaceous stock of
porphyritic granodiorite. The ore body is confined to silicified
and sericitized rocks marked by biotite, quartz, and orthoclase.
The ore body is about 1.5 km by 400 to 500 m in size and
coincides with the intrusion. A pyrite aureole extends about
1 km from the intrusion and coincides with a zone of propylitic
alteration of the host Late Jurassic volcanic-sedimentary
sequence. The deposit is of small to medium size and on the
average contains about 0.5 percent Mo and 0.7 percent Cu
with minor Pb, Zn, W, Au, and Ag.
Medgora Mo-Cu skarn Deposit
The Medgora Mo-Cu skarn deposit (Gorodinsky, Gulevich,
and Titov, 1978) consists of disseminated veinlets in skarn
that is associated with the Early Cretaceous Medgora granite
and granodiorite pluton. The metallic minerals are pyrite,
chalcopyrite, molybdenite, pyrrhotite, magnetite, hematite,
and sphalerite. The skarns are composed of garnet, pyroxene,
actinolite, scapolite, calcite, quartz, chlorite, epidote,
and green mica. Individual ore zones extend from 30 to 160
m. The deposit is of medium size with grades of 0.1 to 0.64
percent Mo, 0.94 to 2.94 percent Cu, and 0.4 g/t Au. The Cu
content of the ore varies from hundredths of a percent to more
than 2 percent.
Origin of and Tectonic Controls for Left Omolon
Metallogenic Belt
The Left Omolon metallogenic belt occurs along the
northeast marginal of the Omolon cratonal terrane. Two possible
tectonic settings are interpreted for the Early Cretaceous
granitic intrusions hosting this metallogenic belt—(1) The
Early Cretaceous granitic intrusions may be a transverse,
nearly orthogonal branch of the Cretaceous Okhotsk-Chukotka
volcanic-plutonic belt, or (2) the Early Cretaceous granitic
intrusives, as interpreted herein, are part of the Oloy-Svyatoy
Nos volcanic belt that constitute part of the Early Cretaceous
Oloy continental-margin magmatic arc that occurs to the
northeast of the Omolon cratonal terrane (fig. 61) (Nokleberg
and others, 1994c, 1997b, c, 1998, 2000).
Western-Southeastern Alaska Metallogenic Belt
of Granitic-Magmatism-Related Deposits (Belt
WSE), Southeastern Alaska
The western-southeastern Alaska metallogenic belt of
granitic-magmatism-related deposits (fig. 62; tables 3, 4)
occurs in southeastern Alaska and is hosted in Early to mid-
Cretaceous granitoid plutons of the Muir-Chichagof plutonic
belt that intrude the Wrangellia superterrane (Nokleberg and
others, 1995a). The significant deposits are in the Jumbo Cu-
Au skarn district, and the Bokan Mountain felsic plutonic U-
REE deposit (table 4) (Nokleberg and others 1997a,b, 1998).
Jumbo Cu-Au Skarn Deposit
The Jumbo Cu-Au skarn district includes a significant
deposit at Jumbo, several small deposits at Magnetite Cliff,
Copper Mountain, and Corbin, and lesser deposits at Late
Magnetite, Gonnason, Houghton, Green Monster, and Hetta.
All of the deposits occur within a few kilometers of the Jumbo
deposit. The Jumbo district contains an estimated 280,000
tonnes of ore grading 45 percent Fe and 0.73 percent Cu
and has produced 4.6 million kg Cu, 220,000 g Au, and 2.73
million g Ag from 111,503 tonnes of ore (Kennedy, 1953;
Herreid and others, 1978; Newberry and others, 1997). The