Metallogenesis and Tectonics of the Russian Far East, Alaska, and ...

Chechekuyum Pb-Zn Skarn Deposit
The Chechekuyum Pb-Zn skarn deposit (G.A. Zhukov and others, written comrnun., 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,
1997~). 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 Iullin.
Au Quartz Vein Deposits
The Au quartz vein and associated Au shear zones 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 which 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 which 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
zones 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 which undiscovered A11 quartz vein or other types of undiscovered deposits may exist in the region.
Karalveem Au Quartz Vein Deposit
The only commercial Au quartz vein deposit at Karalveem (fig. 98) (Olshevsky, 1974, 1976, 1984; Davidenko, 1975,
1980; Skalatsky and Yakovlev, 1983) consists of numerous longitudinal, transverse, and diagonal, steeply-dipping ladder quartz
veins up to several meters thick which occur in Triassic gabbro-diabase sills, especially near contacts with Triassic sandstone and
shale. The sedimentary rocks and sills are strongly deformed into narrow, steep, northwest-trending folds. The ore bodies are
controlled by strike-slip faults associated with the folding. Host rocks exhibit greenschist facies metamorphism. The Au quartz
veins consist of 95-97% quartz with segregations of arsenopyrite and lenses of scheelite, albite, ankerite, and muscovite. Also
widespread are calcite, dolomite, white mica, galena, native gold, aquamarine, sphalerite, pyrite, and pyrrhotite. Gold occurs
mainly in bluish-gray quartz veinlets in a matrix of coarse-grain quartz and arsenopyrite, in the upper horizons of the deposit.
Silica-carbonate and sulfide alteration occur adjacent to ore zones. Near the surface, quartz veins often host druse-like
intergrowths of large, well-crystallized quartz and isometric gold crystals. Coarse-grained masses of gold, and less common
dendritic gold, up to 1 cm diameter, are characteristic of the deposit. At depth, the gold occurs mainly as fine, dispersed masses in
arsenopyrite. The deposit is of medium size, and has been prospected and developed preparatory to mining.
Origin of and Tectonic Controls for
Chukotka Metallogenic Belt
The Au quartz vein and Au shear zones deposits of the Chukotka metallogenic belt are herein interpreted as forming in
the Late Cretaceous during regional deformation and associated metamorphism and anatectic granite magmatism (Goryachev,
1998, 2003) which occurred during a major period of collision and accretion of the Chukotka terrane (Nokleberg and others,
2000). Preceding the accretion was: (1) Early Cretaceous opening of the Canada (Arctic Ocean) Basin; (2) migration of the
Chukotka superterrane to the southwest; and (3) closure of the late Paleozoic(?) and early Mesozoic South Anyui Ocean. After