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

27,200 tonnes, yielding 93,300 g Au, 3.1 million g Ag, 45,400 kg Cu, 1 13,500 kg Pb, 9,080 kg Zn, and 3,500 units (3 18,000 kg)
W03. The veins occur in a shear zone, schist inclusion, and mylonitic gneiss derived from the Triassic Texas Creek Granodiorite
of the informally named Coast plutonic-metamorphic complex of Brew and Ford (1 984).
Sumdum Chief Au Quartz Vein Deposit
The Surndum Chief Au quartz vein deposit consists of two quartz-calcite fissure veins that contain gold, auriferous pyrite,
galena, sphalerite, chalcopyrite, and arsenopyrite (Brew and Grybeck, 1984; Kimball and others, 1984; Goldfarb and others, 1988,
1991, 1997). Gold is unevenly distributed and occurs mainly in pockets where small veins intersect the main veins. Mining
produced about 750,000 g each of Ag and Au from ore that averaged about 13.7 g/t Au. The veins, up to 6 m thick, occur in upper
Paleozoic(?) or Mesozoic graphitic slate and marble of the informally named Coast plutonic-metamorphic complex of Brew and
Ford ( 1984).
Treadwell Au Quartz Vein Deposit
The large Treadwell Au quartz vein deposit consists of disseminated sulfides in quartz and quartz-calcite vein systems in
shattered albite sills and dikes. The veins contain sparse gold, pyrite, magnetite, molybdenite, chalcopyrite, galena, sphalerite, and
tehahedrite. The best ore grade is associated with abundant quartz and calcite veinlets (Light and others, 1989; Goldfarb and
others, 1991, 1997). Mining produced about 90.1 million grn Au fiom 25 million tonnes of ore. The albite sills and dikes are
Eocene and intrude Jurassic(?) and Early Cretaceous(?) slate and greenstone derived from basaltic tuff or agglomerate (part of the
Treadwell Slate in the Gravina-Nutzotin belt). Some ore forms a zone at least 1,100 m long in slate inclusions and in adjacent wall
rock. The deposit was mined fiom above sea level to 790 m beneath sea level in Gastineau Channel from 1885 to 1922 when most
workings flooded during a catashophic influx of sea water.
Origin of and Tectonic Controls for
Juneau Metallogenic Belt
The Juneau metallogenic belt is hosted in a wide variety of metamorphosed sedimentary, volcanic, and plutonic rocks
which occur adjacent to a complex series of faults between the Alexander and Wrangellia sequences of the Wrangellia
superterrane (Nokleberg and others, 2000), the Gravina sequence (Gravina-Nutzotin-Gambier overlap assemblage), and in syn- to
post-accretionary granitoid plutonic rocks, including the foliated tonalite sill of Southeastern Alaska (Brew and Ford, 1984). Late
Paleozoic and early Mesozoic metasedimentary and metavolcanic rocks host the Jualin (Berg, 1984) and Kensington (Bundtzen
and others, 1988) deposits in the Berner Bay district, and the Sumdum Chief (Kimball and others, 1984) and Sea Level deposits.
Flysch of the Gravina-Gambier overlap assemblage hosts the Treadwell group of quartz-sulfide-gold deposits, across the
Gastineau Channel from the Alaska-Juneau mine (Spencer, 1905), and the Gold Standard and Goldstream deposits. Hydrothermal
muscovite from Au-bearing veins from the Alaska-Juneau mine has been dated at about 54 to 57 Ma (Haeussler and others, 1995;
Goldfarb and others, 1997). As described above for the origin of the Chugach Mountains, Baranof, and Maclaren metallogenic
belts, the Au quartz veins of the Juneau metallogenic belt are interpreted as forming in response to subduction of the spreading
KuIa-Farallon Ridge beneath the southern Alaska continental margin (Plafker and others, 1989; Bradley and others, 1993;
Haeussler and Nelson, 1993; Haeussler and others, 1995; Goldfarb and others, 1995; 1997; Goldfarb, 1997).
Metallogenic Belts Formed During
Early Tertiary Spreading Along
Kula-Farallon Oceanic Ridge, Southern
and Southeastern Alaska
Prince William Sound Metallogenic Belt of
Besshi and Cyprus Massive Sulfide Deposits
(Belt PW) EasternSouthern Alaska
The Prince William Sound metallogenic belt of Besshi and Cyprus massive sulfide deposits (fig. 103; tables 3,4) occurs
in the Prince William Sound district along the eastern and northern margins in eastem-southern Alaska. The metallogenic belt is
hosted in the southern margin of the Chugach and the Prince William accretionary wedge-turbidite terranes (Jones and others,
1987; Nokleberg and others, 1994c, 1997~). The significant deposits in the belt are (table 4) (Crowe and others, 1992; Newbeny
and others, 1997; Nokleberg and others 1997a, b, 1998): Besshi massive sulfide deposits at Beatson (Latouche), Ellamar, Fidalgo-
Alaska, Midas, and Schlosser, and Cyprus massive sulfide deposits at Copper Bullion (Rua Cove), Knight Island (Pandora),
Standard Copper, and Threeman. Many of these deposits were producing mines in the early part of the 20Ih century.