USGS Professional Paper 1697 - Alaska Resources Library

study) consists of lenses, from 100 to 800 m long and 2 to
12 m thick, which occur conformable to bedding. Eleven ore
bodies have been explored by drilling to a depth of 300 m.
Pyrite is the most common ore mineral; however, some ore
bodies consist of hematite-magnetite-pyrite ore. Chalcopyrite
locally comprises as much as 1 to 2 percent. The deposit
is locally contact-metasomatized into skarn by Paleozoic
granite. The deposit is interpreted as of sedimentary-exhalative
origin, which was associated with felsic seafloor
volcanism. The Kamenushinskoe deposit occurs in Cambrian
rhyolite of the Mamyn terrane. The rhyolite underlies
a basaltic and limestone sequence that contains the volcanogenic
Gar deposit.
Chagoyan Stratiform Pb-Zn Deposit
The Chagoyan stratiform Pb-Zn deposit (I.G. Khel’vas,
written commun., 1963; V.V. Ratkin, this study) consists of a
galena-sphalerite aggregate, which occurs as cement between
grains in sandstone. Veinlets are also common. The deposit is
about 270 m long and 1.0 m thick and is hosted in quartz-feldspar
sandstone, which underlies Cambrian(?) limestone and
dolomite. Galena and sphalerite are the dominant ore minerals,
with subordinate pyrite, pyrrhotite, and chalcopyrite. Post-ore
dikes and stocks of Early Cretaceous diorite and granodiorite
cut the deposit. The Mesozoic igneous rocks and the contained
stratiform ore bodies locally exhibit hydrothermal alteration
to quartz, sericite, and tourmaline. The deposit occurs on the
northern bank of the Zeya River and is small. Average grades
are 1.42 percent Pb, 5.16 percent Zn, and as much as 3,000 g/t
Ag. The deposit contains estimated reserves of 65 thousand
tonnes zinc.
Origin of and Tectonic Controls for Gar Metallogenic Belts
The rocks hosting the two Gar metallogenic belts are
interpreted as forming in a Late Proterozoic volcanic-tectonic
basin in which marine basalt to rhyolite volcanism occurred
(V.V. Ratkin, this study). The volcanogenic Fe deposits of the
Gar metallogenic belt consist of sheeted Fe layers, mainly
magnetite, which are hosted in metamorphosed Early Cambrian(?)
felsic and mafic volcanic rocks and limestone. The
stratiform Cu and Pb-Zn deposits of the Gar metallogenic belt
are hosted in Cambrian rhyolite (Cu deposits) and quartz-feldspar
sandstone (Pb-Zn deposits), which underlies Cambrian(?)
basalt and calcareous rocks. These stratified units comprise
part of the Mamyn continental-margin arc terrane (fig. 2).
These stratigraphic units and stratiform deposits are (Nokleberg
and others, 1994c, 1997c) (1) underlain by Archean(?)
gneiss and schist, granite-gneiss, gabbro, and amphibolite that
exhibit granulite facies metamorphism, and Proterozoic(?) and
Early Cambrian sequence consists of greenschist, metasandstone,
marble, quartzite, felsites, sandstone, and siltstone; and
(2) are overlain by Silurian clastic rocks and Middle Devonian
siltstone, sandstone, and limestone that are gently folded. The
tectonic origins of the stratiform sulfide deposits are poorly
understood and need further study.
Cambrian through Silurian Metallogenic Belts (570 to 408 Ma) 27
Metallogenic Belts Formed During Early Paleozoic
Sea-Floor Spreading, Regional Metamorphism,
or During Subduction-Related Volcanism
in Russian Far East Terranes
Galam Metallogenic Belt of Volcanogenic Fe,
Volcanogenic Mn, and Sedimentary P Deposits
(Belt GL), Central Part of Russian Far East
The Galam metallogenic belt of volcanogenic Fe,
volcanogenic Mn, and sedimentary P deposits (fig. 2; tables
3, 4) occurs in the central part of the Russian Far East in the
Galam accretionary wedge terrane (Shkolnik, 1973). The
significant deposit is the Gerbikanskoe volcanogenic Fe
deposit; other deposits are the North-Shantarskoe, Nelkanskoe,
Ir-Nimiiskoe-2, and Lagapskoe sedimentary P deposits;
and the Ir-Nimiiskoe-1, Milkanskoe, Galamskoe, Gerbikanskoe,
Kurumskoe, and Itmatinskoe volcanogenic Fe and Mn
deposits (table 4) (Nokleberg and others 1997a,b, 1998). The
Fe and Mn deposits occur in Cambrian beds and lenses with
chert in seafloor basins and are interpreted as forming during
seafloor hydrothermal activity that was associated with mafic
volcanism.
The sedimentary P deposits are phosphorites that formed
in limestone caps that formed in two stages on accreted seamounts,
atolls, and guyots. The older stage consisted of siliceous
deposition of phosphate coquina (for example, inarticulate
brachiopods and trilobites) in the section of those atolls.
Abrasion resulted in the formation of fragmentary trains,
including phosphorite fragments. The younger stage consists
of accumulations of phosphorite fragments. The deposits are
interpreted as being subsequently deformed and metamorphosed
during subsequent accretion of the Galam terrane.
Gerbikanskoe Volcanogenic Fe Deposit
The Gerbikanskoe volcanogenic Fe deposit (fig. 10)
(Shkolnik, 1973) consists of two zones separated by a
sequence of sandstone and siltstone. The two zones contain
approximately 30 steeply dipping sheets and lenses of magnetite
and hematite. Individual bodies are several tens of m to 5
to 7 km long, and locally occur in a closely spaced enechelon
pattern. Thickness varies from 5 to 50 m and is commonly
8 to 28 m. Fe-rich zones vary from banded to thinly banded,
lenticular banded, and bedded and consists of finely-dispersed
hematite, magnetite, and rare pyrite and chalcopyrite. The
deposit is large with an average grade of 42 to 43 percent Fe
(soluble Fe 33-53 percent); 1.8 percent Mn, and 9.6 percent P.
Origin of and Tectonic Controls for Galam Metallogenic Belt
The volcanogenic Fe deposits in the Galam metallogenic
belt consist of numerous lenticular and sheeted
magnetite bodies that consist of conformable, steeply dipping
bodies of complex composition. Magnetite bodies occur in