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

Goldfarb (197) who interprets that the Arctic metallogenic belt as forming during a long-protracted, 100-m.y.-long event which
included formation of SEDEX zinc-Jead deposits in the Northwestern Brooks Range metallogenic belt (described below).
Brooks Range (Chandalar) Metallogenic Belt of
Granitic Magmatism Deposits (Belt BR)
Northern Alaska
The Brooks Range metallogenic belt of granitic magmatism deposits (fig. 17; tables 3,4), mainly porphyry, polymetallic
vein, and skarn deposits, occurs in the core of the Brooks Range in northern Alaska (Nokleberg and others, 1995a, 1997b, 1998).
The metallogenic belt is hosted in the Coldfoot. Hammond, and North Slope terranes of the Arctic Alaska si~perterrane (Moore
and others, 1992, 1994; Nokleberg and others, 1994c, 1997~). The belt is discontinuous, but extends for over 900 km along the
length of the Brooks Range. The significant deposits in the belt are: the Mount Igikpak and Arrigetch Peaks polymetallic vein, Au
quartz vein, Sn skarn, Cu-Pb-Zn skarn deposits; the AM (Ernie Lake), Galena Creek, Porcupine Lake, and Romanzof Mountains
polymetallic vein deposits; the Jim-Montana Cu-Zn skarn deposit; the Sukakpak Mountain Sb-Zu vein deposit; the Victor, Venus,
Evelyn Lee, and Ebo porphyry Cu and Cu skarn deposits; the Geroe Creek porphyry Cu-Mo deposit; the Esotuk Glacier Pb-Zn
skarn and fluorite vein deposit; and the Bear Mountain porphyry Mo deposit (table 4) (Nokleberg and others 1997a, b, 1998).
These significant deposits occur in two groups described below: a major group in the central Brooks Range, and a minor group in
the northeastern Brooks Range. In the northeastern Brooks Range, the belt is sometimes referred to as the Chandalar belt
(Newbeny and others, 1997a, b).
Vein, Skarn, and Porphyry Deposits
Central Brooks Range
Significant deposits in the central Brooks Range part of the belt are at Mount Igikpak and Arrigetch Peaks, Sukakpak
Mountain, Victor, and Geroe Creek. These deposits include polymetallic quartz veins containing base-metal sulfides, Sn skarns
containing both disseminated cassiterite and base-metal sulfides, Cu-Pb-Zn skarns containing disseminated Fe and base-metal
sulfides, and porphyry Cu and Mo deposits (Nokleberg and others, 1995a).
The Victor and associated porphyry Cu and Cu skarn deposits at Venus, Evelyn Lee, and Ebo (DeYoung, 1978; Donald
Grybeck, written cornmun., 1984; Newbeny and others, 1997a) consist of veinlet and disseminated chalcopyrite, bornite,
molybdenite, and pyrite in schistose Devonian granodiorite porphyry which intrudes either the Silurian and Devonian Skajit
Limestone or older marble. calc-schist, and pelitic schist. The skarn minerals are mainly garnet, magnetite, and diopside, and
retrograde vein and replacement epidote, amphibole, chlorite, calcite, and quartz. The skarns were subsequently regionally
metamorphosed during the Mesozoic. Skarns in marble adjacent to plutonic rocks contain vugs containing interstitial bornite,
chalcopyrite, bornite, chalcocite, pyrite, magnetite, and some digenite. Zones in granitoid rocks up to 30 m wide contain up to
0.4% Cu. Grab samples of skarn contain up to 5.5% Cu, 0.4 1 g/t Au, and 0.29 g/t Ag.
The felsic-magmatism-related deposits in the central Brooks Range are hosted in a structurally complex and
polymetamorphosed assemblage of Devonian or older carbonate rocks, including Silurian and Devonian polymetamorphosed
limestone, calc-schist, quartz-mica schist, and quartzite, which is intruded by mainly Late Devonian gneissic granitoid rocks which
together with the metasedimentary rocks constitute the Hammond passive continental margin terrane of the Arctic Alaska
superterrane (Moore and others, 1992).
Skarn, Vein, and Porphyry Deposits
Northeastern Brooks Range
Significant deposits in the Brooks Range metallogenic belt in the northeastern Brooks Range are a cluster of Pb-Zn skarn,
fluorite vein, polymetallic vein, and porphyry Cu deposits at Esotuk Glacier, Porcupine Lake, Romanzof Mountains. and Galena
Creek (Nokleberg and others, 1995a). This part of the belt is sometimes referred to as the Chandalar belt (Newberry and others,
1997a, b).
The Romanzof Mountains polymetallic vein and Pb-Zn skarn deposit (Brosge and Reiser, 1968; Grybeck, 1977; Sable,
1977; W.P. Brosge, oral commun., 1984; Newbeny and others, 1997a) consists of numerous scattered mineral occurrences of
polymetallic sulfides. The most common types of deposits are: (1) zones of disseminated galena, sphalerite, chalcopyrite and
pyrite, locally with Au and Ag, in Devonian(?) granite; (2) Pb-Zn skarn in marble with disseminated magnetite, pyrite, pyrrhotite,
sphalerite, and galena in gangue of carbonate, clinopyroxene, epidote, amphibole, beryl, tourmaline, and fluorite; (3) disseminated
galena, sphalerite, chalcopyrite, and (or) molybdenite in quartz veins along sheared contact in in Devonian(?) granite; and (4) local
fluorite greisen in in Devonian(?) granite. Grab samples contain up to 0.15% Sn. The skarns and quartz veins occur in
Precambrian marble and calc-schist of the Neruokpuk Quartzite at the periphery of the Silurian or Early Devonian Okpilak
(granite) batholith.
These felsic-magmatism-related deposits are hosted in a variety of Paleozoic and late Proterozoic metasedimentary rock
which consist mainly of marble, calc-schist, limestone, quartzite, and greenstone of the North Slope passive continental margin
terrane (part of the Arctic Alaska superterrane) where intruded by Devonian gneissose granite plutons (Newbeny and others,
1997a). The paucity of deposits in the northeastern Brooks Range most likely reflects the limited geological exploration of the