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

Metallogenic Belts Formed in Tertiary
Continental-Margin Arcs, Kamchatka
Peninsula, Southern Alaska, and
Southern Canadian Cordillera
East Kamchatka Metallogenic Belt of
Au-Ag Epithermal Deposits (Belt EK)
Eastern and Southern Kamchatka Peninsula
The East Kamchatka metallogenic belt of Au-Ag epithennal deposits (fig. 125; tables 3,4) occurs in the eastern and
southern parts of the Kamchatka Peninsula. The deposits are hosted in the East-Kamchatka volcanic belt which overlies late
Mesozoic and Cenozoic island-arc and terranes of accretionary-wedge terranes (Pozdeev, 1990). The Au-Ag epithermal deposits,
most of which are economic or are potentially economic, are associated mainly with Miocene volcanoes, hypabyssal bodies, and
small intrusions. The significant deposits in the belt are at Asachinskoe, Kitkhoi, Kumroch, Mutnovskoe, and Rodnikovoe (table
4) (Nokleberg and others 1997a, b, 1998).
The Au-Ag epithermal vein deposits in the East Kamchatka metallogenic belt are interpreted as forming in two stages
(Petrenko, 1999). (1) In the early Miocene, Au-Ag Zn, Pb) epithermal vein and stockwork deposits, as at Mutnovskoe,
Kumroch, and Kitkhoi, formed during eruptions of intermediate and felsic volcanic rocks and during formation of small diorite-
granodiorite intrusions (Lattanzi and others, 1995). The major metals are Au, Pb, and Zn, along with Ag and sulfosalts. And (2) in
the late Miocene, Au quartz-adularia epithermal vein deposits, as at Rodnikovoe and Asacha deposits, fonned in andesite-basaltic
piles associated with hypabyssal bodies, and in mafic, intermediate, and felsic dikes. The deposits are sulfide poor and are
associated with propyllitic alteration. Some of tbe deposits may be Piiocene; however, K-Ar isotopic studies of stockworks, dikes,
and adularia-quartz veins yield ages of 12 to 5 Ma, indicating a Miocene age. The association of sulfide-rich and sulfide-poor
epithermal deposits in the East Kamchatka metallogenic belt suggests diverse volcanic processes (Pozdeev, 1990; Lattanzi and
others, 1995). A recent study by Takahashi and others (2002) presents a 4-fold classification of e pithd Au-Ag minerahation
in Kamchatka: (1) Late Cretaceous Okhotsk-Chukotka Beb (Sergeevka deposit); (2) the middle Tertiary Koryak-Western
Kamchatka Belt (including tbe Amedstovoe deposit with a K-Ar isotopic age of 41.4 Ma); (3) the late Tertiary Central Kamchatka
belt (including the Zolotoy depsit with a K-Ar isotopic age of 17.1 Ma, and the Aginskaya deposit with a K-Ar isotopic age of
6.9 Ma); and (4) the Eastern Kamchatka belt (including the Asachinskoye, Mutnovskoe, Rodnikovoe, and Porozhistovoe deposits
with K-Ar isotopic ages 0.9-7.4 Ma). An overview of the major Au-Ag epitbermal vein deposits of the Kamchatka was published
by Petrenko (1 999).
AsachinskoeAu-Ag Epithermal Vein Deposit
The AsachinskoeAu Au-Ag epithermal vein deposit (Shchepol'ev, 1989; I.D. Petrenko, written cormnun., 1991; A.I.
Pozdeev, written cornmun., 1991; Petrenko, 1999;Okrugjn and others, 2002) consists of a zone of quartz-adularia veins tbat occur
along a north-south trending, strike-slip fault. Veins split and pinch out in Wand andesitic lava. Ure body is a nearly flat-lying
band, gently dipping to the south, and conformable to the hypabyssal host rocks. Ore exhibits colloform-banded structure. Ore
minerals comprise less than 1% of the veins. Ore mineral assemblages are: gold-hydromica, gold-naumanitepolybasite, and gold-
adularia-quartz. Major ore minerals are pyrite, gold, selenium polybasite, and naurnanite. Deposit occurs in cenbr of a bypabygsal
dacite dome at the intersection of three large linear faults. Deposit associated with hypabyssal volcanic rocks that are inferred ia
cross-section. A K-Ar isotopic age for the deposit is 4 Ma (Takahashi and others, 2001). The deposit is medium size with up to 20
g/t Au and 40-50 g/t Ag. Estimated reserve are 1.56 million tonnes averaging 35 gt't Au and 62 g/t Ag.
Mutnovskoe Au-Ag Epithermal Vein Deposlt
The Mutnovskoe Au-Ag epitbermal vein deposit (Shchepot'ev, 1989; 1.D. Petrenko, written commun., 1991; Lattanzi and
others, 1995; Petrenko, 1999;Okrugin and others, 2002) deposit occurs in the central part of a paleovolcano composed of
Oligocene-Miocene mafic- and intermediate-composition volcanic rocks. Plutonic rocks consist of Miocene diorite intrusions and
numerous dikes of varied composition. Major ore zone consists of a thick vein and some apophyses with zones of quartz veinlets
between them. Drilling indicates which ore extends to a depth of 500 m below the surface. In heavily weathered zones, generally
at the southern flank of the deposit, quartz veins contain fiom 10-18% sulfides. On the less weathered northern flank, the deposit
is sulfide-poor and contains 0.2-2% base metals. The major ore assemblages are gold- temantite-tetrahcdrite, gold-argentite-
pearsite, and chlorite-galena-sphalerite. Canfieldite, as well as the telluride minerals, hessite and altaite, also occur. The deposit is
vertically zoned, with gold, tennantite, and tetrahedrite occurring in the upper part of the veins, and chalcopyrite, galena, sphdgtitt
occurring in the lower part of the veins. The K-Ar age of mineralization for the north flank of the Mutnovskoe deposit is 3.3 Ma
and 1.1 Ma for the south flank of the deposit (Takahashi and others, 2001). The &posit is of medim size. Average grades range
up to 3 g/t Au and 10 g/t Ag. Proven reserves are to the North, 1.8 million tomes of ore averaging 16 g/t Au and 3 15 g/t Ag, and
to the South, 5.2 million tonnes of ore averaging 12.4 g/t Au, 1300 glt Ag, and 69,000 tonnes combined Pb and Zn. The deposit
contains an estimated resource of about 20 tonnes Au.