USGS Professional Paper 1697 - Alaska Resources Library

282 Metallogenesis and Tectonics of the Russian Far East, Alaska, and the Canadian Cordillera
pylitized as much as epidote-chlorite facies, and are locally
silicified. Propylitized granodiorite and diorite crops out in the
middle part of the mineralized area. Alteration was the result
of sulfate and halogene-acid hydrothermal solutions. The age
of mineralization is late Miocene(?).
Valentinovskoe Kuroko Cu-Pb-Zn Deposit
The Valentinovskoe kuroko Cu-Pb-Zn deposit (Neverov,
1964) consists of two steeply dipping , thin, lens-like deposits,
as much as 150 m long. Two ore types exist: (1) The most
common type consists of massive, fine-grained sphalerite,
galena, chalcopyrite, chalcocite, tetrahedrite, melnikovite,
barite, gypsum, quartz, chalcedony, chlorite, sericite, and
calcite. This ore contains approximately 1 percent Cu, 1.5 to
1.7 percent Pb, and 10 to 13 percent Zn. (2) The less common
ore type consists of pyrite, sphalerite, and chalcopyrite
with galena and other sulfides. This ore contains as much as 4
percent Cu, 10 to 16 percent Zn, and 1 to 1.7 percent Pb. The
deposit occurs in early Miocene rhyolite, dacite, andesite, and
andesitic tuff with chert interbeds. The host rocks are propylitized
or sericitized and are part of a submarine tuff complex.
The deposit is small with average grades of 1 percent Cu, 1.5
to 1.7 percent Pb, and 10 to 13 percent Zn in fine-grained ore,
and locally as much as 4 percent Cu, 10 to 16 percent Zn, and
1 to 1.7 percent Pb.
Origin of and Tectonic Controls for Kuril Metallogenic Belt
The Kuril volcanic arc, which hosts the Kuril metallogenic
belt, consists chiefly of tuff, breccia, andesite, basalt,
and local hypabyssal and plutonic rocks including gabbro,
diorite, and diabase (Nokleberg and others, 1994c). The arc
occurs as large Quaternary active volcanoes that are tectonically
linked to middle Tertiary through Holocene subduction
of the western margin of the Pacific oceanic plate (Nokleberg
and others, 1994c, 1997c).
Summary of Metallogenic and
Tectonic History
The preceding analysis of the metallogenesis and tectonics
of the Russian Far East, Alaska, and the Canadian Cordillera
reveals a series of metallogenic belts, which formed during a
complicated geologic history. The metallogenic belts are hosted
in older rock units of tectonostratigraphic terranes, along suture
zones between accreted terranes, or in overlap assemblages of
continental-margin igneous arcs. Metallogenic belts formed
before accretion (preaccretion) are interpreted as forming in the
early history of terranes and are inherently linked to the older
geology and tectonic history of the host rocks. Accretionary
metallogenic belts are interpreted as forming during collision
of terranes with continental margins, resulting in varying
amounts of regional metamorphism, anatectic granites, and
associated lode deposits. Postaccretionary metallogenic belts
are interpreted as forming mainly in parts of continental-margin
arcs that overlie craton or craton margin terranes.
Preaccretionary Metallogenic Belts
Several major and minor metallogenic belts of deposits
hosted in mafic and ultramafic rocks occur in the Russian
Far East, Alaska, and the Canadian Cordillera. The principal
deposits are hornblende peridotite Cu-Ni, anorthosite-hosted
apatite Ti-Fe, gabbroic Ni-Cu, hornblende peridotite Cu-Ni,
podiform Cr, serpentinite-hosted asbestos, stratiform Zr,
zoned mafic-ultramafic Ti, and zoned mafic-ultramafic PGE
deposits. These deposits and host rocks are interpreted as
forming mainly in oceanic tectonic environments, including
basal-island-arc, ophiolite, oceanic-ridge, seamount, and
subduction-zone environments. A few deposits are interpreted
as rarely forming in continental rift environments. Subsequent
to formation, most of these ocean-derived metallogenic belts
and their host rocks migrated and were accreted to the margin
of the North Asian Craton Margin or North American Craton
Margin. Several of the metallogenic belts occur in thin, but
extensive sheets of obducted ophiolites that were thrust onto
the Paleozoic and early Mesozoic continental-margin terranes
of the Russian Northeast and northern Alaska. In island-arc
terranes, these mafic-ultramafic-related deposits occur mainly
in deep-level mafic to ultramafic plutons, some of which are
concentrically zoned.
Several major preaccretionary metallogenic belts of stratiform
and stratabound massive sulfide and associated deposits
occur in Russian Far East, Alaska, and the Canadian Cordillera.
The principal deposits types are Austrian Alps W, basaltic
Cu, bedded barite, Besshi massive sulfide, carbonate-hosted
Hg, carbonate-related Nb, Ta, and REE, Cyprus massive sulfide,
ironstone (Superior Fe), Kipushi Cu-Pb-Zn, Korean Pb-
Zn, Kuroko massive sulfide, Zn-Pb SEDEX, sandstone-hosted
U, sediment-hosted Cu deposits, sedimentary P, volcanogenic
Mn and Fe, Southeast Missouri Pb-Zn, shoshonite-hosted Cu,
and stratabound Hg and Au. This wide variety of stratiform
and stratabound deposits and associated deposits are formed
in a wide variety of tectonic environments, including continental-margin,
island-arc, seamount, ophiolite, and continental-rift
environments. These and the other deposit types listed
above also occur in accreted fragments of continental-margin,
cratonal, island-arc, oceanic, ophiolite, and subduction-zone
terranes. Major suites of stratiform and stratabound sulfide
deposits also occur in the North Asian Craton Margin (unit
NSV, Verkhoyansk fold belt) and in the North American Craton
Margin (unit NAC).
Several major and minor preaccretionary metallogenic
belts of felsic-magmatism-related deposits occur in the Russian
Far East, Alaska, and the Canadian Cordillera. The principal
deposit types are Au-Ag epithermal vein, Cu-Au skarn, felsic
plutonic REE, Fe-Au skarn, fluorite greisen, Pb-Zn skarn,
polymetallic vein, porphyry Cu, porphyry Cu-Mo, Sn greisen,
and Sn vein. These deposits are hosted mainly in continental-