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

Origin of and Tectonic Controls for
Ust-Belaya Metallogenic Belt
The Ust-Belaya metallogenic belt is hosted in ophiolite which is a tecto
or subduction zone subterrane which forms the northemiart of the Penzhina-Anadvr' Lane (fin. 31). his-ust-~elava s&terrke
L - - -
consists mainly of a large early Paleozoic ophiolite with areal extent exceeding i,000 km . Extensive zones of chrornite
deposits are confined to dunites which occur together with peridotite, metagabbro, amphiilite, and gabbro. The subteme
consists of the following tectonic sheets which are distinguished by contrasting lithologies (Nokleberg and others, 19!24c, 1997~).
(1) The Otrozhnaya sheet is composed of an ophiolite which contains metamorphosed ultramafic rocks, gabbro, diabase, basalt,
and volcanic breccia, and an overlying sequence of chert, calcareous sandstone, tuff, and limestone which yield Middle and Late
Devonian and Early Carboniferous faunas. The Otrozhnaya sheet is intruded by diabase, plagiogranite, and diorite dikes which
yield K-Ar ages of 180 to 304 Ma. (2) An unnamed sheet is composed of serpentinite melange. (3) The Mavrina sheet is
composed of shallow-marine sandstone and siltstone and interlayered conglomerate and limestone which yield a Middle Jurassic
fauna. And (4) an uppermost sheet is composed of interlayered sandstone, siltstone, and mudstone which yield an Late Jurassic to
Early Cretaceous fauna. The Penzhina-Anadyr' terrane is interpreted as accretionary wedge or subduction zone unit which
contains fragments of oceanic lithosphere, now preserved as ophiolites. The Penzhina-Anadyr' subduction zone t m e is
tectonically linked to the Late Jurassic part of the Kony-Murgal island-arc tarane (Nokleberg and others, 2000).
Metallogenic Belts Formed in Late Paleozoic
Skolai Island Arc in Wrangellia Superterrane
Alaska Range-Wrangell Mountains
Metallogenic Belt of Granltlc Magmatism
Deposits (Belt ARW) Central and Eastem-
Southern Alaska
The Alaska Range-Wrangell Mountains metallogenic belt of granitic magmatism deposits (fig. 32; tables 3,4) (mainly
porphyry, polymetallic vein, and skam deposits) occurs in the Alaska Range and the Nutzotin and Wrangell Mountains in central
and eastem-southem Alaska (Nokleberg and others, 1995a). The metallogenic belt is hosted in the late Paleozoic part of the
Wrangellia sequence of the Wrangellia island-arc terrane which contains late Paleozoic volcanic and granitoid rocks (Nokleberg
and others, 1994c, 1997~). The significant deposits are the Rainy Creek Cu-Ag skam deposit, and the Chistochina deposits, and
smaller occurrences or prospects as the Rainbow Mountain and Slate Creek porphyry Cu deposits (table 4) (Nokleberg and others
1997a, b, 1998). Farther to the southeast in the Nutzotin and Wrangellia Mountains, similar small, subvolcanic intrusions occur in
the Permian and Pennsylvanian Slana Spur, Hazen Creek, and Station Creek Formations, and in the Tetelna Volcanics (kchter,
1975; MacKevett, 1978).
Rainy Creek CU-Ag Skarn District
The Rainy Creek Cu-Ag skarn deposit (Rose, 1966; Lange and others, 198 1; Nokleberg and others, 1984, 199 1)
comprises a zone about 10 krn ling and ui to 5 km wide which contains scattered garnet-pyroxene &am bodies which have
disseminated to small masses of chalcopyhe and bornite, minor sphalerite, galena, magnetite, secondary Cu-minerals, and sparse
gold. The deposits occur in faulted lenses of marble of the Pennsylvanian and Permian Slana Spur Formation adjacent to late
Paleozoic(?) metagabbro, rnetadiabase, and hypabyssal meta-andesite intrusive rocks. Local disseminated sulfides also occur in
meta-andesite. The sulfide-bearing bodies and adjacent wall rocks are locally intensely faulted. Grab samples contain up to 5.6%
Cu, 300 g/t Ag, 1.2 g/t Au, 0.07% Zn.
Chistochina District
The Chistochina porphyry Cu and polymetallic vein deposit (Richter, 1966; Rainier J. Newbarry, written wmmua, 1985)
contains several small areas containing galena, pyrite, chalcopyrite, tetrahedrite, and gold in quartz veins, small masses, and
disseminations in margins of the Pennsylvanian and Pennian Ahtell quartz diorite pluton and in adjacent volcanic and sedimentary
rocks of the Pennsylvanian and Permian Slana Spur Formation. The quartz veins range up to 10 m wide, locally contain massive
barite, calcite, and cerussite, and occur over an area about 5 km long and 3 km wide. The district also contains small Cu-Au and
Pb-Zn skams. Grab samples contain up to 20% Pb, 1.4% Cu, 21 gft Ag, 1.4 g/t Au.
Origin of and Tectonic Controls for Alaske Range-
Wrangell Mountains Metallogenic Belt
The Alaska Range-Wrangell Mountains metallogenic belt is hosted by granitoid plutons and associated volcanic rocks of
the Pennsylvanian and Early Permian Skolai arc (Nokleberg and others, 1984, 1985; 1995a; Nokleberg and Lange, 1985, 1994d;
Plafker and others, 1989). The Skolai arc forms a lithologically variable suite of volcanic and plutonic: rocks which is
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