USGS Professional Paper 1697 - Alaska Resources Library

46 Metallogenesis and Tectonics of the Russian Far East, Alaska, and the Canadian Cordillera
from several tens of meters to 1,300 m long. The veins and
stockworks are hosted in Middle to Late Devonian or Early
Carboniferous volcanic rocks of the Kedon series. The veins
occur along fractures, mainly in extrusive andesite breccia of a
volcanic vent, and more rarely, in hypabyssal dacite-porphyry
bodies and felsic extrusive rocks. The ore minerals include
gold, chalcopyrite, argentite, polybasite, galena, sphalerite,
pyrite, hematite, Mn-oxides, stromeyerite, tetrahedrite, native
silver, and tellurides. The gangue minerals are quartz and
adularia, with lesser calcite, dolomite, rhodochrosite, and
barite. Au and Ag is associated with Hg, Cu, Mo, Pb, Zn, Mn,
and As. The deposit exhibits propylitic and quartz-sericite
alteration. The Au-Ag ore bodies are controlled by arcuate
faults that occur around a volcano-tectonic depression over a
basement composed of Archean metamorphic rocks and early
Paleozoic(?) carbonate and clastic sedimentary rocks. Adularia
from quartz veins has been dated by K-Ar isotopic studies as
268 Ma and by Rb-Sr isotopic studies as 251 Ma. More recent
K-Ar dating of adularia from Au-bearing veins yields an age
of 318 Ma. The deposit is medium size, and grade ranges from
0.5 to 273 g/t Au and 26.3 to 4,978 g/t Ag.
Origin of and Tectonic Controls for Kedon Metallogenic Belt
The Omolon cratonal terrane, which hosts the Kedon
metallogenic belt, consists of a long-lived succession of
Archean to Early Proterozoic crystalline basement and Middle
Proterozoic through middle Paleozoic miogeoclinal sedimentary
rocks (Nokleberg and others, 1994c, 1997c). The younger
part of the stratigraphy consists of unconformably overlying,
widespread, gently-dipping Middle and Late Devonian
calc-alkalic lava and rhyolite tuff, and Early Carboniferous
trachyte, trachyandesite, and basalt, which are interlayered
with nonmarine sandstone, conglomerate, and siltstone. These
rocks constitute the Kedon arc of Shpikerman (1998). The
felsic-magmatism-related lode deposits and host rocks of the
Kedon metallogenic belt are interpreted as forming in the
Kedon continental-margin magmatic arc, which formed in
the Late Devonian. Subsequent to the Kedon arc, the Omolon
terrane is interpreted having been rifted from the North Asian
Craton (Nokleberg and others, 2000; Shpikerman, 1998).
Eastern Seward Peninsula (Kiwalik Mountain)
Metallogenic Belt of Kuroko Massive Sulfide
Deposits (Belt ES) Northwestern Alaska
The Eastern Seward Peninsula metallogenic belt of
kuroko massive sulfide deposits occurs in the Kiwalik Mountain
region of the Seward Peninsula in northwestern Alaska
(fig. 17; tables 3, 4) (Nokleberg and others, 1997b, 1998). The
metallogenic belt is hosted in a thin, tectonically-transposed
unit of middle Paleozoic(?) felsic schists and metavolcanic
rocks of the Seward metamorphosed continental margin terrane
(Nokleberg and others, 1994c, 1997c). Two small occurrences
on the west flank of Kiwalik Mountain consist of chalcopyrite,
galena, tetrahedrite, and sphalerite in layers and as disseminations.
The layers range from 0.2 to 2 m thick and occur parallel
to compositional layering in a 200 meter-thick section of
metafelsite, button schist, and metatuff. The Kiwalik Mountain
belt are interpreted as the extension of the Arctic metallogenic
belt of kuroko massive sulfide deposits described below (T.K.
Bundtzen and Thomas Crafford, written commun., 1991).
Arctic Metallogenic Belt of Kuroko and Kipushi
Massive Sulfide Deposits (Belt AT) Northern Alaska
The extensive Arctic metallogenic belt of major kuroko
massive sulfide deposits (tables 3, 4), which contains the Ambler
district, and one Kipushi Cu-Pb-Zn deposit, occurs along an
east-west trend for about 260 km along the southern flank of the
Brooks Range in northern Alaska (fig. 17). The metallogenic belt
is hosted in a sequence of metavolcanic and sedimentary rocks
that occur in both the Coldfoot metamorphosed continentalmargin
terrane of the southern Brooks Range and in the Nome
Group in the southern Seward Peninsula in the Seward metamorphosed
continental-margin terrane (Nokleberg and others, 1994c,
1997c; Schmidt, 1997b). The Arctic kuroko massive sulfide and
the Ruby Creek Kipushi Cu-Pb-Zn (fig. 22) deposits occur in
the Ambler district (Hitzman and others, 1986); other kuroko
massive sulfide deposits of the district are at Smucker, Michigan
Creek, BT, Jerri Creek, Sun, and Roosevelt Creek prospects
(table 4) (Nokleberg and others 1997a,b, 1998).
Arctic Kuroko Massive Sulfide Deposit
The Arctic kuroko massive sulfide deposit (Wiltse, 1975;
Sichermann and others, 1976; Hitzman and others, 1982;
Schmidt, 1983; Schmidt, 1986, 1988; Hitzman and others,
1986) consists of stratiform, semimassive to massive chalcopyrite
and sphalerite accompanied by lesser pyrite, minor pyrrhotite,
galena, tetrahedrite, arsenopyrite, and traces of bornite,
magnetite, and hematite. The deposit occurs in a thick horizon,
which has an areal extent of about 900 by 1,050 m, and in two
thinner horizons above the main horizon. The sulfides form
multiple lenses as much as 15 m thick over stratigraphic interval
of 6 to 80 m. The gangue minerals are mainly calcite, dolomite,
barite, quartz, and mica. Locally abundant chlorite, phlogopitetalc-barite,
and pyrite-calcite-white mica occur in hydrothermally-altered
wall rocks overlying, underlying, and interlayered
with sulfide mineralization. The alteration is interpreted as
occurring during rapid influx of cold seawater into a hot hydrothermal
vent system. The deposit contains an estimated 37 million
tonnes grading 4.0 percent Cu, 5.5 percent Zn, 0.8 percent
Pb, 47 g/t Ag, 0.62 g/t Au. The deposit is hosted in part of the
Devonian and Mississippian Ambler sequence. The main horizon
of sulfides is hosted in mainly graphitic pelitic schist and
metarhyolite porphyry derived from submarine ash-flow tuff.
Origin of and Tectonic Controls for Arctic Metallogenic Belt
The kuroko massive sulfide deposits in the Arctic metallogenic
belt are hosted in or occur adjacent to submarine