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

clastic rocks are cut by numerous late Paleogene stocks, dikes, and hypabyssal granitoids. The deposit is of medium size and
averages 0.6 % 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, 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 Arnetistovoe 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, kaolinlte-quartz, and sulfide-quartz types. The main ore minerals are gold,
argentite, and kiistelite. Subordinate minerals are stephanite, stibiopearceite, aguilarite, pyrargyrite, miargyrite, freibergite,
naurnannite, and native silver. Pyrite, galena, sphalerite, and chalcopyrite are widespread and comprise up to 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
n
Unconsolidated deposits
(Quaternary)
Dacite porphyry
(Oligocene)
Diorite porphyry
(Oligocene)
Two-py roxene andesite
(Oligocene)
Dacitic andesite
(Oligocene)
kl Dacite (Oligocene)
o Quartz vein
4 Tuff (Oligocene)
, Fault
0
Contact
Figure 124. Ametistovoe Au-Ag epithermal vein deposit, Central Koryak metallogenic belt, Russian Northeast. Schematic geologic
map. Adapted from Khvorostov (1983).
are confined to altered rocks which contain a alteration of kaolinite, illite, and quartz superimposed on widespread epidote-
chlorite-carbonate propylitic alteration. The deposit is centered on a magmatic structure which is about 5 to 6 km deep. The host
volcanic rocks are Eocene and Oligocene flows with K-Ar ages of 18-24 Ma which consist mainly of andesite, andesite-basalt,
andesite-dacite, and dacite. Associated are local abundant extrusive-vent and hypabyssal rocks of similar compositions. The
deposit is controlled by: (I) a northwest- and nearly north-south-trending faults; (2) radial and concentric fractures; and (3)
extrusive and hypabyssal bodies. The deposit is large with prove reserves of 96 tomes 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.