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

interpreted as forming in a submarine volcanic environment of a reducing or euxinic marine basin containing abundant organic
matter and sulfate reducing bacteria.
Fish Lake Gabbroic Ni-Cu Deposit
The Fish Lake gabbroic Ni-Cu deposit (Stout, 1976; Nokleberg and others, 1984; I.M. Lange and W.J. Nokleberg,
written comrnun., 1985; Nokleberg and others, 1991) consists disseminated and wispy-layered chromite, in serpentinized olivine
cumulate. The deposit occurs in a zone up to 15 km long along strike, and ranges up to 2 km wide. Isolated grab samples contain
greater than 0.5% Cr and up to 0.3% Ni, and local anomalous Cu and Ni in stream-sediment and rock samples. The gabbroic Ni-
Cu deposit is hosted in small- to moderate size gabbro plutons and local cumulate mafic and ultramafic rocks. The mafic and
ultramafic rocks intrude the Nikolai Greenstone and older rocks, and are interpreted as co-magmatic with the mafic magmas which
formed the Middle and Late Triassic Nikolai Greenstone (Nokleberg and others, 1994d, 2000).
Wellgreen Gabbroic Ni-Cu Deposit
The Wellgreen gabbroic Ni-Cu deposit (fig. 36) (Campbell, 1976; Hulbert and others, 1988; EMR Canada, 1989; Mining
Review, 1991) consists of massive pyrrhotite, pentlandite, chalcopyrite and magnetite lenses which are scattered along the
footwall contact of a steeply dipping fault zone in gabbroic rocks of the Late Triassic Quill Creek Complex. In the Yukon
Territory, the belt includes the Canalask deposit at White River (Bremes, 1994) in which Cu-Ni sulfides generally occur as
disseminations in mafic dikes and peridotite. The deposit is medium size and has estimated reserves of 50 million tonnes grading
0.36% Ni, 0.35% Cu, 0.5 lg/t Pt, 0.34 g/t Pd. The deposit occurs in a 130-km-long belt of Ni-Cu-Co-PGE occurrences which,
along with host gabbroic bodies, are interpreted as Late Triassic.
L
N
Quill Creek Complex
(Late Tnasslc)
Mass~ve sulfides
D~ssemlnated
a Pendobte
Stallon Creek Formallon
(Pennsylvan~an)
I
Quartz~te
0 50 M
- \ I
Figure 36. Wellgreen gabbroic Ni-Cu deposit, Eastern Alaska Range metallogenic belt. Schematic cross section through East Zone.
Adapted from Hulbert and others (1998).
Origin of and Tectonic Controls for
Eastern and Western Alaska Range
Metallogenic Belt
The gabbroic Ni-Cu and PGE deposits in the Eastern Alaska Range metallogenic belt are hosted in gabbro and ultramafic
sills and plutons which are interpreted as coeval with, and genetically related to the mainly Late Triassic Nikolai Nikolai
Greenstone (Nokleberg and others, 1994d). The Nikolai Greenstone, which forms a major part of the Wrangellia superterrane,
consists mainly of massive, subaerial, amygdaloidal basalt flows, lesser pillow basalt flows, and thin beds of argillite, chert, and
mafic volcaniclastic rocks which are up to 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);