USGS Professional Paper 1697 - Alaska Resources Library

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. (2) In the late Miocene, Au quartz-adularia epithermal
vein deposits, as at Rodnikovoe and Asacha deposits,
formed 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 the deposits may be Pliocene; 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 epithermal Au-Ag mineralization in
Kamchatka—(1) Late Cretaceous Okhotsk-Chukotka Belt
(Sergeevka deposit), (2) the middle Tertiary Koryak-Western
Kamchatka Belt (including the Ametistovoe deposit with a
K-Ar isotopic age of 41.4 Ma), (3) the late Tertiary Central
Kamchatka belt (including the Zolotoy deposit 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 7.4 to 0.9
Ma). An overview of the major Au-Ag epithermal vein deposits
of the Kamchatka was published by Petrenko (1999).
AsachinskoeAu-Ag Epithermal Vein Deposit
The AsachinskoeAu Au-Ag epithermal vein deposit
(Shchepot’ev, 1989; I.D. Petrenko, written commun., 1991;
A.I. Pozdeev, written commun., 1991; Petrenko, 1999;Okrugin
and others, 2002) consists of a zone of quartz-adularia veins
that occur along a north-south trending, strike-slip fault. Veins
split and pinch out in tuff and andesitic lava. Ore body is a
nearly flat-lying band, gently dipping to the south, and conformable
to the hypabyssal host rocks. Ore exhibits colloformbanded
structure. Ore minerals are less than 1 percent of the
veins. Ore mineral assemblages are: gold-hydromica, goldnaumanite-polybasite,
and gold-adularia-quartz. Major ore
minerals are pyrite, gold, selenium polybasite, and naumanite.
Deposit occurs in center of a hypabyssal dacite dome at the
intersection of three large linear faults. Deposit associated with
hypabyssal volcanic rocks that are inferred in cross-section.
A K-Ar isotopic age for the deposit is 4 Ma (Takahashi and
others, 2001). The deposit is medium size with as much as 20
g/t Au and 40 to 50 g/t Ag. Estimated reserve are 1.56 million
tonnes averaging 35 g/t Au and 62 g/t Ag.
Mutnovskoe Au-Ag Epithermal Vein Deposit
The Mutnovskoe Au-Ag epithermal vein deposit
(Shchepot’ev, 1989; I.D. Petrenko, written commun., 1991;
Middle Tertiary Metallogenic Belts (20 to 10 Ma) (figs. 125, 126) 275
Lattanzi and others, 1995; Petrenko, 1999;Okrugin and others,
2002) 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 that 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 from 10 to 18 percent sulfides. On the less weathered
northern flank, the deposit is sulfide-poor and contains 0.2 to 2
percent base metals. The major ore assemblages are gold- tennantite-tetrahedrite,
gold-argentite-pearsite, and chlorite-galenasphalerite.
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, and sphalerite 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 deposit is of medium size. Average grades are as much as
3 g/t Au and 10 g/t Ag. Proven reserves are to the north are 1.8
million tonnes of ore averaging 16 g/t Au and 315 g/t Ag, and
to the south are 5.2 million tonnes of ore averaging 12.4 g/t
Au, 1,300 g/t Ag, and 69,000 tonnes combined Pb and Zn. The
deposit contains an estimated resource of about 20 tonnes Au.
Rodnikovoe Au Quartz-Adularia Epithermal Vein Deposit
The Rodnikovoe Au quartz-adularia epithermal vein
deposit (I.D. Shchepot’ev, 1989; D. Petrenko, written commun.,
1991; Petrenko, 1999) consists of a major vein and
related quartz and quartz-carbonate veins and veinlets that
cut the apical part of a gabbro-diorite intrusion. In addition to
gold, the veins and veinlets contain goldfieldite, silver sulfosalts,
and argentite. Gold fineness is 400 to 600. Alteration
includes propylitic (chlorite-carbonate and epidote-chlorite
facies), kaolinitic, quartz-hydromica alteration with montmorillonite,
and silicic with quartz and pyrite. The altered rocks are
laterally zoned. The ore occurs in a complex vein system with
several funnel-shaped ore shoots that narrow with depth. The
shoots dip 30 to 50° south. The vertical extent of mineralization
is less than 150 m. High Au concentrations (25-30 g/t Au)
occur in upper levels of ore bodies. The quartz-adularia veins
are Late Miocene with K-Ar ages of approximately 0.9 to 1.1
Ma (Takahashi and others, 2001). The deposit is of medium
size. Average grades are as much as 11.3 g/t Au and 40 to 50 g/t
Ag. The estimated reserves are 40 tonnes gold and 356 tonnes
silver with an average grade of 11.0 g/t Au and 98.0 g/t Ag.
Origin of and Tectonic Controls for East Kamchatka
Metallogenic Belt
The Central Kamchatka volcanic belt that hosts the East
Kamchatka metallogenic belt consists chiefly of Eocene to
Quaternary thick, gently dipping andesite, dacite, and rhyolite
strata, which are interlayered with sandstone, siltstone, and