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

individual flows range from 5 cm to more than 15 m thick. The Late Triassic mafic volcanic and sedimentary rocks of the NikoAai
Greenstone also host the Besshi massive sulfide deposit at Denali.
In the southwesternmost Yukon Territory, the Wellgreen and associated deposits of the Eastern and Western Alaska
Range metallogenic belt occur in gabbroic bodies which intrude the Pennsylvanian Skolai assemblage, part of the Wrangellia
sequence of the Wrangellia superterrane (Campbell, 1960; Read and Monger, 1976; Nokleberg and others, 1994~. 1997c; Hulbert,
1994). The Skolai assemblage IS overlain by m d y Late Triassic halt of the Nikolai Greenstone and by Late Triassic carbonate
rock (Nokleberg and others, 1994c, 1997~). In this area, the gabbro bodies hosting the Wellgreen deposit, and similar gabbroic Ni-
Cu deposits in the same area, are also interpreted as coeval with tbe Late Triassic Nikolai Greenstone. This suite of mak flows
and related units, and mafic and ultramaf~ shallow intrusive to plutonic rocks are interpreted as forming during eitber a shortlived
period of back-arc rifting or hol spof (oceanic plume) activity within the Talkeefna-Bonanza island arc in Wrangellia
superterrane (Nokleberg md Lange, 1985a; Nokleberg and others, 1985a; 1987,1994c, d, 2000; Plafker and others, 1989).
Also occurring in part of the Eastern Alaska Range metallogenic belt in the Yukon Tenitory are generally subeconomic
volcanic redbed Cu deposits which are hosted in the predominantly subaerial tholeiitic basalt of the Late Triassic Karmutsen
Formation, part of the Wrangellia sequence of the Wrangellia superterrane (Read and Monger, 1976). Significant volcanic redbed
Cu-Ag deposits at Silver City and Johobo consist of stratabound lenses of native Cu, chalcocite, bornite, chalcopyrite and pyrite
(Sinclair and others, 1979; Carriere and others, 1981). The origin of these deposits is not well understood Kirkham (1996a. b)
proposed that the deposits formed dwhg early-stage burial metamorphism, analogous to diagenesis in sedimentary Cu deposits.
Also in the Yukon Tenitory, the Eastem and Western Alaska Range metallogenic belt conrains sparse stratifonn gypsum deposits,
as at Bullion Creek, which me hosted in lhdone of the Late Triassic Nizina Formation, also part of a structurally displaced
fragment of the Alexander sequence of the Wranpb superkrranc (Monger and others, 1991; Noklebeq and others, 1994c,
1997~).
Alexander Metallogenic Belt of Volcanogenic Cu-PMn
and Carbonate-Hosted Masshre SuHSde Deposits,
Southeastern Alaska (Belt AX)
The Alexander metauogenic belt of volcanogenic and carbonate-hosted massive sulfide and associated deposits (fig. 32;
tables 3,4) occurs for about 750 km along the length of Southeaslern Alaska. The metallogenic belt is hosted in the early
Paleozoic (and older) to Late Triassic Alexander sequence of the Wrangellia summe (Nokleberg and others, 19946, 1997~).
The belt contains volcanic- a ~ carbonate-hosted d
massive sulfide deposits, and bedded barite deposits. The significant deposits in
the belt (tables 3,4): are the Windy Craggy massive sulfide deposit (Alsek River area, British Columbia): he Glacier Creek,
Greens Creek, Khayyam, Kupreaoof Isbod, Niblack, and Orange Point kuroko massive sulfide deposits (Dawson and others,
199 1 ; Nokleberg and others, 1994c, 1997a, b, 1998,2000; Newberry and ochers, 1997); the Castle Island, Hainw, and Lime Point
bedded barite deposits (Nokleberg and others, 1994e,1997a, b, 1998; Schmidt, 1997b); and the Moonshine arbanate-hosted
massive sulfide deposit (Herreid and others, 1978; Noklebergaad others 1997% b, 1998).
Windy Craggy Cu-Co Massive Sult7de Depalt
The world-class Windy Craggy deposit (fig. 37) occurs in the Tatshashhi River area, northern BriW Columbia, Canada,
and consists of one or more pyrrhotite, pyrite a d chalcopyrite massive sulfide bodies which are hosted in Late Triassic submasine,
tholeiitic to calcalkaine basalt flows, with lesser intercalated siltstone, chert, argillite, and limestone, and nmerow diorite dikes
and sills which cut footwall units (EMR Canada, 1989; Scheter and Lane, 1991; G. Hzuper, written c omm, 1992; Maclntyre
and others, 1993). Both zones have adjacent sulfide stringer stockworks. The deposit contains reserves of 265 million toones
grading 1.44% Cu, 0.07% Co and 0.20 g/t Au. Five additional stratiform Cu occurrences were discovered in tht are in 1992. The
deposit age is interpreted as Late Triassic on the basis of Norian conodonts in limestone fiom h e deposit (M. t&hud, written
comrnun., 1983). The host rocks are intruded by calc-* diorite sills and dikes, and overhh by calc-alkaline pillow basalt at
least 1,500 m thick. The large. Cu-bearing pyrite-pyrrhotite massive sulfide bodies are folded, faulted, and sheared. The de&t is
transitional between Cyprus and Besshi volcanogenic massive sulfide deposit types.
Greens Creek Kuroko Zn-Pb-Cu Massive
Sulfide Deposit
The Greens Creek Kuroko Zn-Pb-Cu massive sulfide dcposit (fig. 38) occurs on Adntiralg lshd and consists of
sphalerite, galena, chalcopyri.te, and tetrahedrite in a pyrite-rich matrix. The sulfides occur in massive pods, bands, laminations,
and disseminations, and are associaled with pyrilc&mte-chert exhalite (Berg, 1984; Wells and ofhem, 1986; Brew and others,
1991 ; Newbeny and others, 1997). The structural hanging wall ~ontatns chdorite- and sencite-baring metssedknmtafy rocks. The
structural footwall contains black graphitic argiLlitc. "Black ore" forms w extensive blanket dmt, and is composed of he
grained pyrite, sphalerite, galena, and Ag-rich sulfosah fs intions in black carbonaceous exhalite and strgillite. "White ore"
occurs along edges of ~ W ~ Vsulfide G pods srnd is composed of minot tetrahedrite, pyrite, galena, and sphalerite in laminations,
stringers, or disseminations in massive chert, carbonate rocks. QT sulfate-rich exbalite. Local veins occur below the massive
sulfides and contain bornlte, chalcopyrite, and gold. The veins my constilute brine conduits. The and host rocks are