USGS Professional Paper 1697 - Alaska Resources Library

superterrane, consists mainly of massive, subaerial amygdaloidal
basalt flows, lesser pillow basalt flows, and thin beds of
argillite, chert, and mafic volcaniclastic rocks that are as much
as 4,350 m thick (Nokleberg and others, 1994c, d, 2000).
The flows are predominantly intermixed aa, pahoehoe, and
pillow basalt flows with minor interlayered chert and argillite
(Nokleberg and others, 1994d); individual flows range from 5
cm to more than 15 m thick. The Late Triassic mafic volcanic
and sedimentary rocks of the Nikolai 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 that intrude
the Pennsylvanian Skolai assemblage, part of the Wrangellia
sequence of the Wrangellia superterrane (Campbell,
1960; Read and Monger, 1976; Nokleberg and others, 1994c,
1997c; Hulbert, 1994). The Skolai assemblage is overlain by
mainly Late Triassic basalt of the Nikolai Greenstone and by
Late Triassic carbonate rock (Nokleberg and others, 1994c,
1997c). 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 the Late Triassic Nikolai
Greenstone. This suite of mafic flows and related units and
mafic and ultramafic shallow intrusive to plutonic rocks are
interpreted as forming during either a short-lived period of
back-arc rifting or hot spot (oceanic plume) activity within
the Talkeetna-Bonanza island arc in Wrangellia superterrane
(Nokleberg and Lange, 1985a; Nokleberg and others, 1985a;
1987, 1994c, d, 2000; Plafker and others, 1989).
S
0
Quill Creek Complex
(Late Triassic)
Massive sulfides
Disseminated
sulfides
Peridotite
Station Creek Formation
(Pennsylvanian)
Quartzite
50 m Contact
Figure 36. Wellgreen gabbroic Ni-Cu deposit, eastern Alaska
Range metallogenic belt. Schematic cross section through East
Zone. Adapted from Hulbert and others (1998). See figure 32 and
table 4 for location.
N
Late Triassic Metallogenic Belts (230 to 208 Ma; fig. 32) 87
Also occurring in part of the Eastern Alaska Range metallogenic
belt in the Yukon Territory are generally subeconomic
volcanic redbed Cu deposits that 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 during early-stage burial metamorphism,
analogous to diagenesis in sedimentary Cu deposits.
Also in the Yukon Territory, the eastern and western Alaska
Range metallogenic belt contains sparse stratiform gypsum
deposits, as at Bullion Creek, which are hosted in limestone of
the Late Triassic Nizina Formation, also part of a structurally
displaced fragment of the Alexander sequence of the Wrangellia
superterrane (Monger and others, 1991; Nokleberg and others,
1994c, 1997c).
Alexander Metallogenic Belt of Volcanogenic
Cu-Pb-Zn and Carbonate-Hosted Massive Sulfide
Deposits, Southeastern Alaska (Belt AX)
The Alexander metallogenic 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 southeastern Alaska. The metallogenic belt is hosted in
the early Paleozoic (and older) to Late Triassic Alexander
sequence of the Wrangellia superterrane (Nokleberg and others,
1994c, 1997c). The belt contains volcanic- and carbonatehosted
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); the Glacier Creek, Greens Creek, Khayyam,
Kupreanof Island, Niblack, and Orange Point kuroko massive
sulfide deposits (Dawson and others, 1991; Nokleberg and
others, 1994c, 1997a,b, 1998, 2000; Newberry and others,
1997); the Castle Island, Haines, and Lime Point bedded
barite deposits (Nokleberg and others, 1994c, 1997a,b, 1998;
Schmidt, 1997b); and the Moonshine carbonate-hosted massive
sulfide deposit (Herreid and others, 1978; Nokleberg and
others 1997a,b, 1998).
Windy Craggy Cu-Co Massive Sulfide Deposit
The world-class Windy Craggy deposit (fig. 37) occurs in
the Tatshenshini River area, northern British Columbia, Canada,
and consists of one or more pyrrhotite, pyrite and chalcopyrite
massive sulfide bodies that are hosted in Late Triassic submarine,
tholeiitic to calcalkaine basalt flows, with lesser intercalated
siltstone, chert, argillite, and limestone, and numerous
diorite dikes and sills that cut footwall units (EMR Canada,
1989; Schroeter and Lane, 1991; G. Harper, written commun.,
1992; MacIntyre and others, 1993). Both zones have adjacent