USGS Professional Paper 1697 - Alaska Resources Library

quartz, and is virtually not associated with sulfides. Silver
grains (0.002 to 0.016 mm) were observed in Fe-hydroxide
alteration. The deposit is medium size with reserves of 15
million tonnes grading 4.4 g/t Au and 15 g/t Ag. The deposit is
interpreted as forming in the Late Cretaceous.
Pioneer Granitoid-Related Au Deposit
The Pioneer granitoid-related Au deposit (N.E. Malyamin
and V.E. Bochkareva, written commun., 1990; V.N. Akatkin,
written commun., 1991) occurs near the margin of an Early
Cretaceous granodiorite intrusion, both within the intrusion
and in adjacent country rock of contact-metamorphosed Jurassic
sandstone and siltstone. The ore bodies consist of quartz,
quartz-feldspar, quartz-tourmaline, and quartz-carbonate veins
and zones of altered quartz-potassium feldspar-sericite-albite
rocks. The ore bodies vary from 1 to 50 m thick and in plan
branch with variable trends. The ore bodies are large, have
low Au content, and have no visible boundaries. The extent of
mineralization is determined by geochemical sampling. Both
gold and Au-sulfide bodies are recognized. The gold ore type
consists of quartz-adularia-carbonate veins, and the Au-sulfide
type consists of quartz veins with pyrite, galena, stibnite, and
Ag-sulfosalts. The deposit is small, with estimated reserves of
17.1 tonne Au, 20.1 tonne Ag, and average grades of grade 2.7
g/t Au and 5.2 g/t Ag.
Origin of and Tectonic Controls for North Bureya
Metallogenic Belt
The Umlekan-Ogodzhin volcanic-plutonic belt (Volsky,
1983; Kozlovsky, 1988), which hosts the North Bureya
metallogenic belt, consists chiefly of (1) Early Cretaceous
sandstone, conglomerate, and mudstone with sparse flora and
freshwater fauna, (2) Early Cretaceous calc-alkalic andesite,
dacite, and tuff that yield K-Ar isotopic ages of 112-135 Ma,
and (3) Late Cretaceous alkalic basalt and rhyolite. The belt
is intruded by coeval Early Cretaceous granite, granodiorite,
diorite, and monzodiorite. Some granitoid plutons are probably
Late Jurassic, or older, because derived detritus occurs in
the Early Cretaceous part of section of the Umlekan-Ogodzhin
igneous belt. This belt was deposited on Gonzha terrane and
on Mamyn and Turan terranes of Bureya superterrane after
collision of these terranes with the Tukuringra-Dzhagdinsk
terrane (Nokleberg and others, 1994c, 1997c).
The Umlekan-Ogodzhin volcanic-plutonic belt belt
constitutes part of the Umlekan continental-margin arc that is
interpreted as forming from subduction of part of the ancestral
Pacific oceanic plate that is now preserved as tectonically
interwoven fragments of the Badzhal (BD), older Jurassic, part
part of the Khabarovsk (KB), and Samarka (SMA) terranes.
This tectonic pairing is based on (1) occurrence of the accretionary-wedge
terranes outboard (oceanward) of the Umlekan
arc (fig. 48), (2) formation of mélange structures during the
Jurassic and Early Cretaceous (Nokleberg and others, 1994a;
Khanchuk and others, 1996), and (3) where not disrupted by
extensive Cretaceous and early Cenozoic movement along the
Late Jurassic Metallogenic Belts (163 to 144 Ma; figs. 48, 49) 115
Central Sihote-Aline strike-slip fault, the mélange structures
and bounding faults dip toward and beneath the igneous units
of the arc. Subduction is generally interpreted as ending in the
Early Cretaceous when extensive sinstral faulting occurred
along the subduction zone (Khanchuk and others, 1996).
Chersky-Argatass Ranges Inferred Metallogenic
Belt of Kuroko Massive Sulfide Deposits (Belt
CAR), West-Central Part of Russian Northeast
An inferred metallogenic belt of kuroko massive sulfide
deposits (fig. 48; tables 3, 4) occurs in the west-central part
of the Russian Northeast. The metallogenic belt is hosted
in Late Jurassic volcanic rocks in the Chersky and Argatass
Ranges in the Indigirka-Oloy sedimentary-volcanic assemblage
(unit io, fig .48) (Nokleberg and others, 1994c, 1997c).
The belt extends northwest for nearly 700 km and occurs in
four areas that are as much as 35 to 30 km wide each (Danilov
and others, 1990). The significant deposit is at Khotoidokh in
the northwest part of the belt (table 4) (Nokleberg and others
1997a,b, 1998).
Khotoidokh Kuroko Massive Sulfide Deposit
The Khotoidoh Kuroko massive sulfide deposit (fig. 51)
(G.G. Naumov, written commun., 1987; Danilov and others.,
1990; Dylevsky and others, 1996) consists of a steeply dipping
stratiform body of massive sulfides in a lens that is as much as
13 m wide and 450 m long. The lens is hosted in Late Jurassic
sedimentary and volcanic rocks. The deposit is underlain by
rhyolite and overlain by siltstone. The main ore minerals are
pyrite, chalcopyrite, sphalerite, galena, tetrahedrite, and barite.
Also occurring are bornite, native Au, native Ag and matildite.
The ores vary from massive to thin banded. The ore is regionally
metamorphosed, and wallrock metasomatic alteration
includes propylitic and late-stage silica and sericite alternation.
The host rocks are the Kimmeridgian Dogdin Formation
that is about 450 m thick. This formation consists of marine,
thin-bedded clastic sedimentary rocks that are interbedded
with rhyolite lava and tuff and, to a smaller extent, with basalt
and andesite-basalt. The volcanic rocks in the deposit are a
bimodal rhyolite-basalt assemblage similar to that of island
arcs. The environment of formation of the deposit is similar
to that of the Miocene Kuroko massive sulfide deposits of the
Green Tuff belt in Japan. The known reserves are 180,000
tonnes Pb, 900,000 tonnes Zn, 150,000 tonnes Cu, and about
1,000 tonnes Ag. The average grades are 5.15 percent Pb,
14.9 percent Zn, 0.7 percent Cu, 0.5-1.0 g/t Au and more than
100 g/t Ag.
Origin of and Tectonic Controls for Chersky-Argatass
Ranges Metallogenic Belt
The Chersky-Argatass Ranges metallogenic belt is hosted
in the Indigirka-Oloy sedimentary-volcanic assemblage, which
consists chiefly of shallow-marine and nonmarine late Middle