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

Sentachan Clastic-Sediment-Hosted Au-Sb Deposit
The Sentachan clast~c-sediment-hosted Au-Sb deposit (Shur, 1985; Indolev and others, 1980; V.V. Maslennikov, written
commun., 1985) consists of two rod-like veins which vary from 85 to 200 m long and up to 3.1 m thick which occur in northwest-
striking shear zones in northwest-trending faults which are part of the Adycha-Taryn fault zone. The veins are hosted in Late
Triassic (Norian and Rbaetian) clastic rocks which are deformed northwest-trending gently-plunging folds parallel to the fault.
The main minerals are stibnite and quartz; subordinate minerals are ankerite, muscovite, pyrite, arsenopyrite, dickite, and
hydromica. Rare minerals are sphalerite, gold, chalcostibnite, berthierite, tetrahedrite, zinkenite, jamesonite, aurostibnite, and
chalcopyrite. The wallrocks exhibit silicic, carbonate, hydromica, and dickite alteration. The grade varies from 3.2 to 40.3% Sb.
Mined and proven reserves total 100,000 tonnes Sb, making the Sentachan Au-Sb deposit one of Asia's largest Sb deposits.
Ak-Altyn Au-Ag Epithermal Vein Deposit
The small Ak-Altyn Au-Ag epithermal vein deposit (Yu.A. Vladimirtseva, written commun., 1985) consists of quartz and
quartz-carbonate veins, up to 2 to 3 m thick and stringers which occur in a zone 10-30 m wide and 150 m long. The deposit is
hosted in gently-dipping Middle Triassic (Ladinian) tenigenous rocks which are intruded by Early Cretaceous diorite porphyritic
dikes. The ore is dominated by fine-grained quartz (chalcedony) with sparse sulfides (about I%), including galena, sphalerite,
chalcopyrite, arsenopyrite, and pyrite. Gold fineness is low. Average grades are 0.2-60.4 g/t Au; and 0.1-1% combined Ag, Hg,
Pb, Sb, Zn, As, and Cu.
Eastern Asia-Arctic Metallogenlc Belt:
Omsukchan Zone of Sn Polymetallic Vein,
Sn SilicateSulfide, Porphyry Sn,
Au-Ag Epithermal Vein, Porphyry Mo-Cu,
and Associated Depostts (Bett EAOM)
Southeastern Part of Russian Northeast
The Omsukchan metallogenic zone (fig. 79; tables 3,4) occurs in the southeastern part of the Russian Northeast and
forms an extensive transverse (orthogonal) branch of the East Asian-Arctic metallogenic belt. The zone occurs in and near the
Okhotsk-Chukotka volcanic-plutonic belt (Nokleberg and others, 1994c, 19Wc), is more 150 km long, and ranges from 10 to 15
up to 60 to 70 krn wide. The significmt deposits in the zone are Sn polymetallic vein deposit8 at Maly Ken and Trood, Sn silicate
sulfide vein deposits at Egorlyk, Galimoe, Khataren-Industrial, and Okhotnichie, Au-Ag epithermal vein deposits at Arylakh,
Dukat, and Rogovik, porphyry Sn deposits at Ircha, Nevskoe, and Novy Djagyn, and Sb-Au and polymetallic vein deposits at
Elombal, Mechta, Tidit, and Yakor (table 4) (Nokleberg and others 1997a, b, 1998). Mainly Sn and Ag polymetallic vein, and W,
Au, and Co vein deposits occur in the northern and middle parts of the belt, whereas mainly Au-Ag epithemal vein and porphyry
Mo-Cu deposits occur In the southern part.
The Omsukchan metalbgeaic belt occurs in a unique, local extensional tectonic environment in continental crust up to 52
km thick, which in herein interpreted as forming in the back-arc portion of the Okhotsk-Chukotka volcanic-plutonic belt. The rifttrough
is filled by Early Cretaceous volcanic and sedimentary sequences of continental coal-bearing malasse which are
unconformably overlain by Atbian through Cenomanian andesite, rhyolite, and ignhbrite. Tbe total thickness is greater than
3,000 m. The lower part of the molasse includes the Aptian Ascoldin Formation which is composed of hie-siliceous, ultrapotassic
rhyolite. The plutonic rocks associated with the metallogenic belt are dominated by the potarrsic biotite granite of the
Omsukchan Complex wbich has a K-AT isotopic age of approximately 90 Ma, and a RbSr wholarock isochron age of 80 Ma
(Goryachev, 1998).
The significant Sn and Sn-Ag deposits, mainly Sn polymetallic vein, Sn silicate-sulfide, and porphyry Sn deposit types,
are at Nevskoe, Galimoa, lrcha, Khataren-Lndustrial, Trood, Novy Djagyn, and Maly Ken. Some of these deposits were recently
discovered. Most of the numerous, small, but rich and quickly exploited Sn deposits were exhausted in the 1940's. Various types
of Sn deposits are associated with the Omsukchan granite and comagmatic extrusive-subvolcanic complexes. At depths, these Sn
deposits are associated mainly with granitoid plutonic rocks. At intermediate levels, the Sn deposits are associated with volcanic
and plutonic rocks. Near the surface, the Sn deposits are associated with volcanic~ocks, and consist mainly of Sn-Ag deposits, and
associated Ag-polymelallic and Au-Ag epithermal vein depasits. The significant Ag-polymetallic veh deposits are at Mechta and
Tidit.
Nevskoe Porphyry Sn Deposit
The Nevskoe porphyry Sn deposit (Lugov, Makeev, and Potapova, 1972; Lugov, 19
complexly intergrown pyrophyllite, topaz, quartz, muscovite, and cassiterite. Also widespread
arsenopyrite, chalcopyrite, galena, sphalerite, pyrite, pynhotite, marcasite, tetrahedrite-tennan
Semseyite, guanajuatite, laitakarite, silver, zunyite, apatite, fluorite and other minerals are rare. Sn content decreases with depth, as
does topaz and pyrophyllite; quartz content increases with depth. The deposit occurs in a district which extends north-northwest
along a zone of intensely h-actured Early Cretaceous claslic sedimentary rocks. The zone has surface dimensions of 180 by 350 m.