USGS Professional Paper 1697 - Alaska Resources Library

184 Metallogenesis and Tectonics of the Russian Far East, Alaska, and the Canadian Cordillera
The B skarn deposits of the Taukha metallogenic belt are
interpreted as forming early in the history of the East Sikhote-Alin
igneous belt, from about 90 to 70 Ma when part of
the Taukha terrane was overlapped by ignimbrite sequences.
Pb-Zn skarn deposits occur in the central part of the Taukha
metallogenic belt, mainly in the Dalnegorsk district, which
has produced about 40 percent of Russia’s zinc and lead. The
Pb-Zn skarn deposits are interpreted as forming after the B
skarn deposits during a later stage of postaccretion volcanism,
with K-Ar ages of 70 to 60 Ma, and composed mainly of
rhyolite and dacite. The skarn deposits generally occur in large
limestone blocks enclosed in Early Cretaceous olistostromes.
The skarns occur along the contacts between limestone and
clastic rocks and chert, and between limestone and overlying
postaccretion volcanic rocks that overlie the Early Cretaceous
olistostrome.
The Pb-Zn polymetallic vein deposits are coeval with
the Pb-Zn skarn deposits, but occur only in clastic and volcanic
rocks. Unlike the skarn deposits, the polymetallic vein
deposits contain stannite and lesser cassiterite, in addition to
mainly galena, sphalerite, and chalcopyrite. The lower levels
of the polymetallic vein deposits contain about 3 percent Ag in
galena, with much less Ag in the upper levels. Some polymetallic
vein deposits, as at Lidovskoe, occur in the apices of
granodiorite intrusions that are comagmatic with dacite. The
Map
A
Blagodatnoe
deposit
Belogorskoe
deposit
Margaritovskoe
deposit
C-5
C-2 C-2
B
C-2
Quaternary alluvial deposits
Rhyolitic tuff
Aplite dike
Andesite and diabase dike
Rhyodacite
Granite
Limestone
Contact
A Cross section
Fault
C-2 C-5
polymetallic vein deposits at Krasnogorskoe are associated
with volcanic breccias that are spatially related to a volcanic
vent. The breccias also contain syngenetic disseminated
galena, sphalerite, pyrite, and cassiterite. This relation suggests
a gradation from Pb-Zn polymetallic vein into porphyry
Sn deposits (Ratkin and others, 1990). K-Ar isotopic studies
indicate an age of about 60 Ma for the volcanic rocks hosting
the Pb-Zn polymetallic vein deposits. Sparse disseminated and
porphyry Cu deposits, as at Plastun, occur in Maastrichtian
to Danian (early Paleocene) volcanic rocks. A small Au-Ag
epithermal quartz vein deposit at Soyuz contains Ag-sulfosalts
and is hosted in Late Cretaceous rhyolite and tuff.
Dalnegorsk B Skarn Deposit
Magnetite-garnet, garnet-magnetite skarn
The major, world-class B deposit at Dalnegorsk (fig. 85)
(Ratkin, 1991; Ratkin and Watson, 1993; Layer, Ivanov, and
Bundtzen, 1994; Vasilenko and Valuy, 1998; Shkolnik and others,
2003) occurs in a thick skarn formed in a large, upturned
olistolith of bedded Triassic limestone enclosed in Early
Cretaceous clastic sedimentary rocks. The skarn extends to a
depth of approximately 1 km, where it is cut off by a granitic
intrusion. The skarn formed in two stages, with a second-stage
skarn over-printing an earlier skarn. The two stages of skarn
formation are separated in time by intrusion of intermediate-
Garnet, garnet-pyroxene, garnet-pyroxenevesuvianite,
and garnet-magnetite-cuspidine skarn
Borehole
0 300 m
B
Figure 84. Belogorskoe Fe skarn
deposit, Taukha metallogenic belt,
Russian Southeast. Adapted from
Valuy and Rostovsky (1998). See
figure 79 and table 4 for location.