USGS Professional Paper 1697 - Alaska Resources Library

208 Metallogenesis and Tectonics of the Russian Far East, Alaska, and the Canadian Cordillera
percent WO 3. The Iutin deposit has produced significant W
and Sn in past years, but is now inoperative.
Svetloe Sn-Quartz Vein Deposit
The Svetloe Sn-quartz vein deposit (Lugov, 1986; Kuleshov,
Pristavko, and Plyashkevich, 1988) consists of en-echelon
sets of quartz veins and veinlets that form two zones that
diverge to the southeast. Each zone contains several tens of
larger veins, which vary from 0.2 to 1.5 m thick and are several
hundreds of meters long, and about one hundred smaller veins.
The ore is dominated by Sn minerals with abundant sulfide
minerals that occur over a buried stock of greisenized granite.
The veins are hosted in metamorphosed Triassic sandstone and
shale and are cut by granite porphyry and aplite dikes of the
Cretaceous Iultin complex. Successive mineral assemblages
are (1) topaz-fluorite-muscovite greisen, (2) cassiterite-wolframite-quartz
assemblage with topaz, löellingite, and fluorite
(the most productive assemblage), (3) arsenopyrite-quartz with
cassiterite and native bismuth, (4) stannite-chalcopyrite with
small amounts of bismuthinite, sphalerite, galena, pyrrhotite,
and bornite, (5) scheelite-fluorite-albite with chlorite, pyrite,
marcasite, and cassiterite, and (6) fluorite-calcite with kaolinite.
A complex cassiterite-wolframite assemblage is dominant
in the upper portion of the deposit, whereas W minerals are
dominant at depth. The deposit is of medium size and has been
mined from 1979 to the mid-1990’s.
Valkumei Sn Silicate-Sulfide Vein Deposit
The Valkumei Sn silicate-sulfide vein deposit (Lugov,
Makeev, and Potapova, 1972; Lugov, 1986) consists of simple
and complex veins, mineralized zones, and less common linear
stockworks. The deposit occurs mainly within the marginal
zone of the Late Cretaceous Pevek pluton, composed of granite,
adamellite, and granodiorite, and to a lesser degree in Cretaceous
sandstone and shale that host the pluton. Mineralization occurs in
a north-northwest-trending zone alone the contact of the pluton.
The ore bodies commonly consist of a conjugate system of (1)
major north-south veins and feathered veinlets, and (2) a zone of
approximately east-west- and northwest-trending veins. Seventy
minerals occur in the deposit but the majority of the veins are
composed dominantly of tourmaline with quartz, chlorite, albite,
arsenopyrite, cassiterite, pyrrhotite, chalcopyrite, stannite, sphalerite,
stibnite, fluorite, and various carbonates. The ore bodies
are vertically extensive. The cassiterite-quartz-tourmaline veins
are replaced by sulfide veins at depth. The deposit is large, was
discovered in 1935, and has been mined from 1941 to the mid-
1990’s. The average grade is 0.4 to 1.2 percent Sn.
Chechekuyum Pb-Zn Skarn Deposit
The Chechekuyum Pb-Zn skarn deposit (G.A. Zhukov
and others, written commun., 1953) dips gently, is about 18 m
thick and 30 m long along strike, and is composed of pyrrhotite,
sphalerite, galena, chalcopyrite, magnetite, pyrite, niccolite,
marcasite, calcite, garnet, diopside, and quartz. The skarn occurs
along a fracture zone in Middle Devonian limestone, which is
overlain by Late Cretaceous felsic extrusive rocks and intruded
by granite porphyry and spessartite dikes. Massive and disseminated
pyrrhotite ore occurs in the hanging wall. Massive galena
and less abundant sphalerite-galena ore occur in the middle
part of the skarn. Sparse massive sphalerite ore is prominent in
the footwall. The skarn also contains sparsely disseminated ore
minerals. The skarn contains anomalous Sn, Cd, Co, Bi, and Ag.
The deposit is judged as small.
Metallogenic Belt Formed During Late Mesozoic
Collision and Accretion of Chukotka
Superterrane, Russian Northeast
Chukotka Metallogenic Belt of Au Quartz Vein
and Related Deposits (Belt CH), Northern Part of
Russian Northeast
The Chukotka metallogenic belt of Au quartz vein, Sn
and Sn-W polymetallic vein, and minor associated Sn greisen
deposits (fig. 79; tables 3, 4) occurs in the northern part of the
Russian Northeast (Goryachev, 1998, 2003) in the central and
western parts of the Paleozoic and early Mesozoic Chukotka
passive-continental-margin terrane (Nokleberg and others,
1994c, 1997c). The significant deposits in the belt are (table 4)
(Nokleberg and others 1997a,b, 1998): Au quartz vein deposits
at Dvoinoi, Karalveem, Lenotap, Ozernoe, Ryveem, Sredne-
Ichuveem, and Svetlin; Sn quartz vein deposits at Chaantal,
Svetloe, and Tenkergin; and a Sn-W polymetallic vein and
greisen deposit at Iultin.
Au Quartz Vein Deposits
The Au quartz vein and associated Au shear zone deposits
occur in the Anyui and Chauna subterranes of the Chukotka
passive continental-margin terrane (fig. 79). The significant
deposits are at Karalveem, Ozernoe, Sredne-Ichuveem,
Draznyaschy, Upryamy, and Lenotap. The Au-quartz vein
deposits and Au shear zones deposits generally occur in anticlinal
structures formed in Triassic siltstone, shale, and sandstone
that are intruded by widespread Triassic gabbro-diabase
sills and by Early Cretaceous granitic dikes. The Au deposits
are controlled by major, north-west-trending faults and feathering
fault zones that formed during low-grade, greenschist
facies metamorphism. A few Au-quartz vein deposits also
occur in thrust zones in middle Paleozoic clastic and carbonate
rocks and in Late Jurassic and Early Cretaceous volcanic
and sedimentary rocks. The Au quartz vein and Au shear zone
deposits of the Chukotka metallogenic belt are probably the
main lode source for numerous placer Au deposits of northern
Chukotka. However, in detail, the known lode Au deposits do
not correspond to the known large placer Au deposits. This
observation suggests that undiscovered Au quartz vein or other
types of undiscovered deposits may exist in the region.