USGS Professional Paper 1697 - Alaska Resources Library

64 Metallogenesis and Tectonics of the Russian Far East, Alaska, and the Canadian Cordillera
1983) consists of a very fine grained mixture of mainly pyrite
and marcasite and lesser sphalerite, chalcopyrite, galena, and
pyrrhotite in a gangue of siderite, calcite, quartz, and dolomite.
The sulfides and gangue occur in massive, lenticular
sulfide bodies, as replacements of carbonate-rich beds, and as
fracture fillings, mainly in chert and siltstone. The host rocks
are a Triassic and (or) Jurassic age sequence of chert, dolomite,
siltstone, shale, volcanic graywacke, conglomerate, and
aquagene tuff and are overlain by an upper sequence of pillow
basalt, agglomerate, and breccia. At least six individual sulfide
bodies are known. The main sulfide bodies may be proximal
to basaltic flow fronts. The highest chalcopyrite concentrations
occur in the basal parts of bodies. Minor sphalerite occurs in
or near the hanging wall. Extensive hydrothermal alteration
occurs in the footwall but is absent in hanging wall. The basalt
displays high background Cu values of 250 to 300 g/t. The
deposit contains an estimated several hundred thousand tonnes
of unknown grade. Individual samples contain as much as 5
percent Cu and average about 2 percent Cu and 1 percent Zn.
Origin of and Tectonic Controls for Mystic Metallogenic Belt
The Mystic metallogenic belt is hosted in the Mystic
and Nixon passive continental margin terranes that consist of
a complexly deformed but partly coherent, long-lived stratigraphic
succession, including Devonian through Pennsylvanian
carbonate and clastic sedimentary rock, Permian flysch
and chert, and Triassic(?) pillow basalt (Nokleberg and others,
1994c, 1997c): Recent studies report early to middle Paleozoic
fauna in these terranes that are typical of taxa that occur in
similar age units in the Kolyma region in the Russian Northeast
and suggest that these three terranes were rifted from the
Siberian continent (North Asian Craton Margin) (Blodgett
and Brease, 1997; Blodgett, 1998; Fryda and Blodgett, 1998;
Dumoulin and others, 1998, 1999; Blodgett and Boucot,
1999). The Mississippian and older parts of these terranes
have a stratigraphy that is similar to the North Asian Craton
Margin (NSV). Accordingly, these Mississippian and older
parts of these terranes and their Mississippian and older lode
SEDEX bedded barite deposits and metallogenic belts are
herein interpreted as being derived from rifting of the North
Asian Craton Margin (NSV) (Nokleberg and others, 2000).
Coeval metallogenic belts with similar origin deposits residing
in the Russian Northeast include the Urultun and Sudar
Rivers, Selennyakh River, and Sette-Daban, and Yarkhodon
belts (table 3). The tectonic origin of the younger Triassic(?)
Besshi(?) and Cyprus massive sulfide deposits in the Mystic
metallogenic belt, as at Shellebarger, is not clear.
Northern Cordillera Metallogenic Belt of
Southeast Missouri Zn-Pb Deposits (Belt NCO)
Central Yukon Territory
The Northern Cordillera metallogenic belt of Proterozoic
and early Paleozoic Southeast Missouri Zn-Pb deposits (fig.
17; tables 3, 4) occurs in the east-central Yukon-Territory and
western Northwest Territories and is hosted in an extensive
pericratonic platformal sequence in the North American
Craton Margin. The major Proterozoic deposits are at Gayna
River and Goz Creek. The major early Paleozoic deposit is
at Bear-Twit; other examples are at Gayna River, Goz Creek
area (Barrier Reef), and Rusty Springs (Termuende) (table 4)
(Nokleberg and others 1997a,b, 1998).
Gayna River Southeast Missouri Zn-Pb Deposit.
The Gayna River Southeast Missouri Zn-Pb deposit consists
of sphalerite with minor pyrite and galena that occur in
breccias and as tabular replacement bodies in Late Proterozoic
shallow water carbonate of the Little Dal Group (Mackenzie
Mountain Assemblage; Hardy, 1979; Aitken, 1991; Hewton,
1982; EMR Canada, 1989). Sphalerite and lesser galena occur
as disseminations in breccias that formed as slumps over the
flanks of stromatolitic reefs. Sphalerite is also concentrated
in solution-collapse and fault-related crackle breccias. The
Gayna River district contains 18 deposits and more than 100
occurrences. Several deposits exceed 1 million tonnes grading
10 percent combined Zn and Pb.
Goz Creek (Barrier Reef) Southeast Missouri Zn-Pb Deposit
Deposits in the Goz Creek area consist of sphalerite with
minor galena, pyrite and boulangerite that occur as fracture and
breccia filling and disseminations (EMR Canada, 1989; Dawson
and others, 1991; Fritz and others, 1991). The deposit contains
estimated reserves of 2.49 million tonnes grading 11 percent
combined Zn and Pb. The deposits occur in both stratigraphically
and tectonically controlled zones in pervasively silicified sandy
dolostone. Smithsonite occurs as weathering product of sphalerite.
The deposit age is interpreted to be Late Proterozoic. Other
Southeast Missouri Pb-Zn districts hosted by Late Proterozoic
dolostone include Nadaleen Mountain, south of Goz Creek, and
Coal Creek Dome, north of Dawson.
Bear-Twit Southeast Missouri Zn-Pb District.
The Bear-Twit Southeast Missouri Zn-Pb district consists
of galena and sphalerite with minor tetrahedrite that occur in
brecciated dolomitized shallow water (reef) carbonates of the
Early Devonian Whittaker, Delorme and Camsell Formations
(Dawson, 1975; Archer Cathro and Associates, unpub. company
report, 1978; EMR Canada, 1989). The deposit contains
estimated reserves of 8 million tonnes grading 5.4 percent Zn,
2.6 percent Pb, and 0.5 g/t Ag. The deposit occurs in cross-cutting
fractures, breccia matrices, fossil replacement, and also as
disseminations in dolomite. The deposit age is interpreted as
Early Devonian. In the Godlin Lakes region, numerous deposits
are hosted by orange-weathering ferroan dolostone of the
Early Cambrian Sekwi Formation (Dawson, 1975). The Rusty
Springs deposit in northwestern Yukon is an Ag-rich Southeast
Missouri Pb-Zn deposit hosted by brecciated dolostone of the
Middle Devonian Ogilvie Formation.