USGS Professional Paper 1697 - Alaska Resources Library

(NX, DL, MY), Viliga (VL), and Zolotogorskiy (ZL) passive
continental-margin terranes and the Avekova (AK), Kilbuck-Idono
(KI), Okhotsk (OK), and Omolon (OM) cratonal terranes. Derived
from the Devonian continental-margin arc that formed along the
margins of the North Asian Craton Margin were the Beryozovka
(BE), Oloy (OL), and Yarakvaam (YA) terranes (fig. 29). Derived
from the North American Craton Margin (NAM) were the Kootenay
(KO) and Yukon-Tanana (YT) passive continental-margin
terranes. Accompanying the rifting was formation of the Northwestern
Berezovka River (BE), Brooks Range (NBR), Dempster
(DE), Finlayson Lake (FL), Gataga (GA), Northern Cordillera
(NCO), Macmillan Pass (MP), older part of Mystic (MY), Selennyakh
River (SEL), Sette-Daban (SD), Southern Rocky Mountain
(SRM), Tommot River (TO), and Urultun and Sudar Rivers (URS)
metallogenic belts, which all contain massive sulfide, carbonatiterelated
Nb, Ta, and REE, and related deposits.
(2) Movement along a series of oblique-sinistral rifts
resulted in the separation of North Asian and North American
Cratons and Cratons Margins.
(3) The Kedon continental margin arc and associated
subduction zone continued activity along the margin of the North
Asian Craton and Craton Margin (NSC, NSV) until about the
late Early Mississippian. Associated with the arc was subduction
of the older part of the Galam (GL) accretionary wedge terrane.
Remnants of the arc are preserved in the part of the North Asian
Craton and Craton Margin (NSC, NSV, KN, units that overlie
parts of the Okhotsk (OK), Akekova (AK), Omolon (OM) cratonal
terranes, (3) the Oloy (OL) and Yarakvaam (YA) island-arc
terranes, and the Beryozovka (BE) turbidite-basin terrane.
(4) The Sicker island arc, which formed in the Devonian
along most of the length of the Wrangellia superterrane
(WRA) ceased activity. Insufficient data exist to ascertain the
relative positions of the Wrangellia superterrane.
Metallogenic Belt Formed During Mississippian-Pennsylvanian
Back-Arc Spreading Along
North American Craton Margin
Northwestern Brooks Range Metallogenic Belt
of SEDEX Zn-Pb, Bedded Barite, Kuroko Massive
Sulfide, and Sulfide Vein Deposits (Belt NBR),
Northwestern Alaska
The major Northwestern Brooks Range metallogenic
belt of large SEDEX Zn-Pb-Ag (SEDEX), kuroko massive
sulfide, bedded barite, and sulfide vein deposits (fig. 17;
tables 3, 4) occurs in northwestern Alaska. The metallogenic
belt is hosted in the Kagvik sequence in the Endicott Mountains
passive continental margin terrane of the Arctic Alaska
superterrane (Nokleberg and others, 1994c, 1997c). The belt
extends along strike for more than 200 km. Locally associated
with the SEDEX deposits are vein sulfide deposits. The larger
SEDEX Zn-Pb-Ag deposits are at Lik and the Red Dog Creek
deposit, a world-class mine of zinc and lead (Schmidt, 1997a),
Mississippian Metallogenic Belts (360 to 320 Ma; figs. 16, 17) 73
and the Drenchwater Creek kuroko-massive sulfide deposit
(Nokleberg and Winkler, 1982; Lange and others, 1985). Other
deposits in the belt are the Hannum Creek metamorphosed
SEDEX Zn-Pb? deposit, the Omar Kipushi Cu-Pb-Zn deposit,
the Frost, Story Creek, and Whoopee Creek Cu-Zn-Pb-Ba
sulfide vein deposits, and the Nimiuktuk bedded barite deposit
(table 4) (Nokleberg and others 1997a,b, 1998).
Red Dog Creek SEDEX Zn-Pb Deposit
The Red Dog Creek SEDEX Zn-Pb-Ag deposit (fig. 39)
(Tailleur, 1970; Plahuta, 1978; Booth, 1983; Joseph T. Plahuta,
L.E. Young, J.S. Modene, and D.W. Moore, written commun.,
1984; Lange and others, 1985; Moore and others, 1986;
Schmidt, 1997a; Schmidt and Zierenberg, 1988; Bundtzen and
others, 1996) consists of disseminated and massive sphalerite,
galena, pyrite, and barite in Mississippian and Pennsylvanian
shale, chert, and silica exhalite of the Kuna Formation. The
deposit is 1,600 m long and as much as 150 m thick and occurs
near the base of the Kuna Formation. Barite-rich lenses, as
much as 50 m thick locally cap the deposit. The sulfide minerals
occur as disseminated sulfides in organic-rich siliceous
shale, coarse-grained sulfide veins, fine-grained, fragmentaltextured
to indistinctly bedded sulfides,; and silica exhalite
lenses. Minor hydrothermal alteration consists of silicification
and decarbonatization of shale. A small, propylitically altered
diorite plug or hydrothermally altered pyroxene andesite flow
occurs at north end of deposit. Prior to mining, which began
in 1990, the Main deposit was estimated to contain 85 million
tonnes grading 17.1 percent Zn, 5 percent Pb, and 82 g/t
Ag. By the end of 1999, the four SEDEX deposits at Red Dog
(Main, Aggaluk, Hill Top, Anarrag) contained an estimated
142.3 million tonnes grading 15.8 percent Zn, 4.3 percent Pb,
and 83 g/t Ag (Swainbank and Szumigla, 2000) The host rocks
and deposit are extensively structurally imbricated along many
subhorizontal thrust faults. Graywacke of the Cretaceous Okpikruak
Formation structurally underlies deposit.
Drenchwater Creek SEDEX Zn-Pb and (or) Kuroko
Massive Sulfide Deposit
The Drenchwater Creek SEDEX Zn-Pb and (or) kuroko massive
sulfide deposit consists of disseminated and massive sphalerite,
galena, pyrite, and barite in Mississippian shale, chert, tuff, and
quartz-exhalite of the Kagvik sequence (Nokleberg and Winkler,
1982; Lange and others, 1985). Volcanic sandstone and keratophyre
are locally abundant. The sulfides occur as disseminations
in chert, disseminations and massive aggregates in quartz-exhalite,
and as sparse, remobilized disseminations in sulfide-quartz veins
crosscutting cleavage in shale and chert. Locally extensive hydrothermal
alteration of chert and shale is accompanied by extensive
replacement by kaolinite, montmorillonite, sericite, prehnite, fluorite,
actinolite, chlorite, calcite, and quartz. Grab samples contain
more than 1 percent Zn, 2 percent Pb, and 150 g/t Ag. The deposit
is as much as 1,800 m long and as much as 50 m thick. The host
rocks and deposit are extensively faulted and structurally imbricated
by many thrust faults that dip moderately south