USGS Professional Paper 1697 - Alaska Resources Library

mon. The deposit is of medium size and contains an estimated
resource of 30 to 50 tonnes Au and 70 to 100 tonnes Ag. The
average grade of the Aginskoe deposit is 20 g/t Au. The deposit
is currently under development.
Kirganik Porphyry Cu Deposit
The Kirganik porphyry Cu deposit (Vlasov, 1977; A.V.
Ignatyev, written commun., 1980) consists of steeply dipping
zones of rocks with biotite-K-feldspar metasomatic alteration.
The deposit is 10 to 15 m thick, as much as 1,200 m long, and
occurs in Late Cretaceous siliceous volcanic rocks. The deposit
consists of zones of disseminated and veinlet copper and Au
minerals. The ore bodies are generally conformable with the
host rocks. The oxidized zone extends deepest in heavily fractured
rocks, to a depth of 100 to 120 m, and contains as much as
0.8 g/t Au. The richest ore is in biotite-K-feldspar-metasomatically
altered rocks. Altered rocks containing both pyroxene and
K-feldspar are practically devoid of ore. The ore minerals are
pyrite, chalcopyrite, magnetite, bornite, chalcocite, hematite,
and gold. The richest Au values occur in rich chalcosite-chalcopyrite-bornite
ore with more than 1 percent Cu. The K-Ar isotopic
age of the biotite-K-feldspar-altered rocks that host the ore
is 65 to 75 Ma. The deposit is of medium size. Average grades
are 0.1 to 1 percent Cu and 0.2 to 0.4 g/t Au in disseminated and
veinlet ore, and as much as 0.8 g/t Au in oxidized ore.
Origin of and Tectonic Controls for Central Kamchatka
Metallogenic Belt
The Central Kamchatka Volcanic and Sedimentary Basin
(Nokleberg and others, 1994c, 1997c), which hosts the Central
Kamchatka metallogenic belt, consists chiefly of late Oligocene
to Holecene volcanic and sedimentary rocks in sequences
as much as 5 km thick. The belt ranges from 20 to 70 km
wide and is about 350 km long. The volcanic and sedimentary
basin also contains mainly shallow-marine sedimentary
rocks as much as 6,000 m thick and widespread tuff, basalt,
and basaltic andesite. The basinal units overly deformed Late
Cretaceous to early Tertiary sedimentary rocks. The basin is
interpreted as a fore-arc unit of the Central Kamchatka volcanic
belt; both are interpreted as parts of the major, postaccretionary,
Northeast Asia continental-margin arc in the Russian
Far East (Nokleberg and others, 1994c, 1997c).
Alaska Peninsula and Aleutian Islands
Metallogenic Belt of Igneous Arc Deposits (Belt
AP), Western-Southern Alaska
The major Alaska Peninsula and the Aleutian Islands
metallogenic belt of igneous arc deposits (fig. 126; tables 3,
4) occurs in western-southern Alaska (Nokleberg and others,
1995a). The metallogenic belt is hosted in the area underlain or
adjacent to the middle and late Tertiary granitic and volcanic
rock of the Aleutian arc in the eastern Aleutian Islands and the
southwestern Alaska Peninsula (Nokleberg and others, 1994c,
Middle Tertiary Metallogenic Belts (20 to 10 Ma) (figs. 125, 126) 277
1997c). The arc is composed mainly of middle Tertiary to Holocene
andesite to dacite flows and tuff, shallow intrusive rocks,
small silicic stocks and sills, and associated sedimentary rocks
(Burk, 1965; Wilson, 1985). Underlying parts of the southwestern
Alaska Peninsula, almost as far west as Cold Bay, is the
mainly Mesozoic bedrock of the Peninsular island-arc terrane.
Numerous epithermal vein, polymetallic vein, and porphyry
Cu and Cu-Mo deposits occur in the metallogenic belt. The
significant deposits are (table 4) (Nokleberg and others 1997a,b,
1998) (1) epithermal vein deposits at Apollo-Sitka, Aquila, Canoe
Bay, Fog Lake (Pond), Kuy, Shumagin, and San Diego Bay, (2)
polymetallic vein deposits at Braided Creek, Sedanka (Biorka),
Cathedral Creek, and Kilokak Creek, and (3) porphyry Cu and
Mo deposits at Bee Creek, Mallard Duck Bay, Mike, Pyramid,
Rex, and Sedanka (Biorka). The epithermal and polymetallic
vein and porphyry deposits of the Alaska Peninsula and Aleutian
Islands belt occur over a distance of more than 800 km. This belt
is related to the epithermal and hydrothermal activity associated
with the late-magmatic stages of Tertiary and Quaternary hypabyssal
plutonic and associated volcanic centers. These centers
are along part of the Aleutian arc, one of the classic continentalmargin
arcs along the rim of the Circum-Pacific rim.
Pyramid Porphyry Cu Deposit
The Pyramid porphyry Cu deposit (Armstong and others,
1976; Hollister, 1978; Wilson and Cox, 1983; G.L. Anderson,
written commun., 1984; R.L. Detterman, oral commun., 1986)
occurs in the southwestern Alaska Peninsula and consists of
disseminated molybdenite and chalcopyrite(?) in a Fe-stained
dacite porphyry stock of late Tertiary age. A zonal alteration
pattern is defined by a core of secondary biotite, containing
about 3 to 10 percent magnetite, which grades outward into
an envelope of quartz-sericite alteration. Fractures adjacent
to the stock are filled with sericite. Local extensive oxidation
and supergene enrichment by chalcocite and covellite occur in
a blanket as much as 100 m thick. The deposit is centered on
a 3 km2 area within the stock and contains a resource of 110
million tonnes grading 0.4 percent Cu, 0.03 percent Mo and
trace Au (G.L. Anderson, written commun., 1984). The host
stocks and dikes, and several smaller stocks that occur nearby
all intrude the fine-grained clastic rocks of the Late Cretaceous
Hoodoo Formation and the Paleocene or Eocene to Oligocene
Stepovak(?) or Tolstoi(?) Formation. The sedimentary rocks
are contact metamorphosed adjacent to the stocks.
Bee Creek Porphyry Cu Deposit
The Bee Creek porphyry Cu deposit consists of chalcopyrite,
pyrite, and traces of molybdenite in contact-metamorphosed
Jurassic and Cretaceous sedimentary rocks that are
intruded by a small tonalite porphyry stock of Tertiary age
(Cox and others, 1981). The deposit, located on the Alaska
Peninsula 25 km northeast of Chignik Lagoon, was discovered
by Bear Creek Mining Company in cooperation with Bristol
Bay Native Corporation in the late 1970’s (E.D. Fields, written
commun., 1977).The contact-metamorphosed sedimentary