USGS Professional Paper 1697 - Alaska Resources Library

266 Metallogenesis and Tectonics of the Russian Far East, Alaska, and the Canadian Cordillera
about 1,000 km and is composed mainly of Sn polymetallic,
Au-Ag epithermal, Hg-Sb vein, and porphyry Mo-Cu deposits.
The significant deposits in the belt are (table 4) (Nokleberg
and others 1997a,b, 1998) (1) Sn polymetallic vein deposits at
Ainatvetkin, Berezovaya, Khrustal (Khrustalnoe), Parkhonai,
Reznikov, and Unnei, (2) Au-Ag epithermal vein deposits at
Ametistovoe, Ivolga, Orlovka, and Sprut, (3) volcanic-hosted
Hg deposits at Agranai and Lamut, (4) clastic sediment-hosted
Hg or hot-spring Hg? deposits at Krassnaya Gorka, Lyapganai,
and Neptun, (5) silica-carbonate Hg deposits at Pervenets and
Tamvatney, and (6) porphyry Cu-Mo deposits at Kuibiveen,
Lalankytap, and Rzhavy.
The metallogenic belt is hosted in or near the calc-alkaline
magmatic rocks of the western part of the Kamchatka-
Koryak volcanic belt (fig. 102) (Pozdeev, 1986, 1990; Filatova,
1988; Nokleberg and others, 1994c, 1997c). Various,
isolated ring, volcanic-plutonic, and volcanic structures host
about a third of the metallogenic belt. The Kamchatka-Koryak
volcanic belt unconformably overlie nappes and thrust slices
of previous-accreted flysch, island arc, and ophiolite terranes.
The Sn polymetallic and Au-Ag epithermal vein deposits
occur mainly along the southern flank of the metallogenic belt
in a region underlain by a thick crust composed of a granitic
and metamorphic rocks as much as 40 km thick. The northern
part of the belt consists of the Parkhonai district, which
contains Sn, Au-Ag, Sb, and Hg polymetallic vein, and clasticsediment-hosted
Hg deposits. The Central Koryak metallogenic
belt also has potential for undiscovered Sn lode deposits.
Sn polymetallic Deposits
The Sn polymetallic vein deposits are hosted by metasedimentary
rocks, silicic and intermediate volcanic rocks, and
granite porphyry and rhyolite stocks and dikes that occur
above concealed granitic batholiths (Lashtabeg and others,
1987). The significant Sn polymetallic deposits are at Ainatvetkin,
Reznikov, Khrustal, and Unnei. The deposits tend to be
enriched in Ag, In, Bi, and sometimes Au.
Ainatvetkin Sn polymetallic Deposit
The Sn polymetallic deposit at Ainatvetkin (Lugov and
others, 1974; Lugov, ed., 1986) consists of cassiterite-bearing
sulfide-chlorite-quartz veins and fracture zones that are as
much as a few hundred m long and are 1.0 to 6.0 m thick. The
ore minerals are cassiterite, magnetite, pyrrhotite, chalcopyrite,
galena, sphalerite, arsenopyrite, wolframite, scheelite,
pyrite, stannite, canfieldite, pyrargyrite, gold, and native
copper. The cassiterite-chlorite-quartz veins and fracture
zones contain as much as 10 percent sulfide minerals. Most
economically important are brecciated zones with fragments
of metasomatically altered rocks and quartz-chlorite cement
with sulfides. The deposit is hosted in complexly-folded Late
Cretaceous (Santonian through Campanian) sandstone and
shale that is overlain by Late Eocene and Oligocene rhyolite,
rhyodacite, rhyodacite tuff, and ignimbrite. The Late Cretaceous
clastic rocks are cut by numerous late Paleogene stocks,
dikes, and hypabyssal granitoids. The deposit is of medium
size and averages 0.6 percent Sn.
Ag-Au and Au-Ag Epithermal Vein Deposits
Various Ag-Au and Au-Ag epithermal vein deposits
also occur in the Central Koryak metallogenic belt, and as at
Ametistovoe, Ivolga, and Sprut, are related to intermediate
composition subvolcanic complexes (Khvorostov and Zaitsev,
1983). These epithermal deposits are vertically and lateral
zoned with respect to the Sn and Sn-Ag deposits.
Ametistovoe Au-Ag Epithermal Vein Deposit
The Ametistovoe Au-Ag epithermal vein deposit (fig. 124)
(Khvorostov, 1983; V.P. Khvorostov, written commun., 1986;
Benevolskyi and others, 1992) contains two types of ore bodies—(1)
ore pipes with small subparallel veins and veinlets, and
(2) steeply dipping veins and zones. The veins are hundreds of
meters long and several meters thick; the zones are several tens
of meters thick. The veins are composed of quartz, kaolinitequartz,
and sulfide-quartz types. The main ore minerals are gold,
argentite, and küstelite. Subordinate minerals are stephanite,
stibiopearceite, aguilarite, pyrargyrite, miargyrite, freibergite,
naumannite, and native silver. Pyrite, galena, sphalerite, and
chalcopyrite are widespread and are as much as 20 to 30 percent
of some veins. The gangue minerals are quartz, kaolinite,
adularia, and chlorite. The Au:Ag ratio averages 1:3. The richest
ore bodies are confined to altered rocks that contain a alteration
of kaolinite, illite, and quartz superimposed on widespread epidote-chlorite-carbonate
propylitic alteration. The deposit is centered
on a magmatic structure that is about 5 to 6 km deep. The
host volcanic rocks are Eocene and Oligocene flows with K-Ar
ages of 18 to 24 Ma that consist mainly of andesite, andesitebasalt,
andesite-dacite, and dacite. Associated are local abundant
extrusive-vent and hypabyssal rocks of similar compositions.
The deposit is controlled by (1) a northwest- and nearly northsouth-trending
faults, (2) radial and concentric fractures, and (3)
extrusive and hypabyssal bodies. The deposit is large with prove
reserves of 96 tonnes Au. The average grade of the Ametistovoe
deposit is 16 g/t Au. The area around the Ametistovoe deposit
has considerable potential for discovery of additional deposits.
Hg Deposits
Hg deposits occur throughout the Central Koryak metallogenic
belt, with more abundant deposits in the southern and
northern extreme parts of the belt. Extensive mineralized fault
zones contain cinnabar, stibnite and realgar that are associated
with intermediate-composition, small intrusions and dikes
that intrude Late Cretaceous through Paleogene sandstone and
shale. Significant clastic sediment-hosted Hg deposits are at
Lyapganai, Neptun, and Krassnaya Gorka.
Lyapganai Clastic Sediment-Hosted Hg Deposit
The clastic sediment-hosted Hg deposit at Lyapganai
(Tarasenko and Titov, 1970; Babkin, 1975; Vlasov, 1977) con-