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

The apparent spatial relationship of mineralization to extensional structures suggests format~on of the Southeast Missouri
Zn-Pb deposits during major rifting and basinal subsidence along the passive North American Craton Margin. These structures
include rift-induced, synsedimentary and block faulting, uplift, basinal subsidence, resultant facles changes, reefal development,
development of karsts, brecciat~on, and basinal brine migration (Dawson and others, 1991). The common association of
hydrocarbons with Zn-Pb deposits in carbonate rocks suggests a genetic relationship between mineralization and oil maturation,
migration, and entrapment (Jackson and Beales, 1967). Although the timings of mineral deposltlon commonly are not well known
(Sangster, 1986), the two major age groups of Southeast Missouri Zn-Pb deposits are herein interpreted as forming during two
major periods of incipient rifting of the North American Continental Margin, the Late Proterozoic and early Paleozoic.
Other metallogenic belts in the Canadian Cordillera, which contain stratiform or stratabound massive sulfide deposits
which are hosted in parts or rifted fragments of the North American Craton Margin, are (in order of decreasing age): (1) Monashee
belt of Late Proterozoic SEDEX deposits; (2) Redstone belt of Late Proterozoic sediment-hosted Cu deposits (3) Cathedral belt of
Cambrian Southeast Missouri Zn-Pb deposits; (4) Churchill belt of Late Proterozoic Cu vein deposits; (5) Kootenay belt of
Cambrian SEDEX deposits; and (6) Anvil belt of Cambrian through Silurian SEDEX deposits. An important distinction occurs
between some of the metallogenic belts. Many metallogenic belts with SEDEX deposits are directly associated with mafic
volcanic rocks and hydrothermal activity whereas the metallogenic belts containing Southeast Missouri Zn-Pb deposits are not.
Dempster Metallogenic Belt of SEDEX Ba,
Sedimentary-Exhalative (SEDEX),
SEDEX Ni-Zn-PGE-Au, and Kuroko Zn-Pb-Cu
Massive Sulfide Deposits (Belt DE)
Northwestern Yukon Territory
The Dempster metallogenic belt of SEDEX Ba, SEDEX Ni-Zn-PGE-Au, and Kuroko Zn-Pb-Cu massive sulfide deposits
occurs in the northwestern Yukon Territory (fig. 17; tables 3,4) (Nokleberg and others, 1997b, 1998). The belt is hosted in the
North American Craton Margin in a sequence Devonian and Mississippian clastic strata which are part of the Earn assemblage, in
the region north of Tintina Fault and south of Dawson Fault. The significant deposits are the Rein SEDEX, Marg Kuroko massive
sulfide, and the Nick SEDEX deposits.
Rein SEDEX Ba Deposits
The Rein and several other large SEDEX deposits in the region contain barite, barytocalcite, and witherite and are hosted
in Early to Middle Devonian (late Emsian to early Eifelian) sedimentary rocks which crop our near Dempster Highway (M.J.
Orchard, written communication, 1985). None of the occurrences has measured reserves. The upper Earn Assemblage includes
beds between the Tombstone and Robert Service thrust faults previously interpreted to be Mesozoic, including the Keno Hill
quartzite, which host the large polymetallic silver vein district of Keno Hill in the Tombstone metallogenic belt.
Marg Kuroko Volcanogenic Zn-Pb-Cu Deposit
The Marg kuroko Zn-Pb-Cu-Au-Ag massive sulfide deposit consists of pyrite, sphalerite, chalcopyrite and galena with
minor arsenopyrite and tetrahedrite which occur in a quartz and barite gangue (Eaton, written commun., Archer, Cathro, and
Associates, 1989; Yukon Minfile, 1991). The deposit occurs in four stacked massive sulfide lenses which occur at the contact of
quartz-sericite-chlorite phyllite and graphitic phyllite. The deposit contains an estimated 2.097 million tonnes grading 5.0% Zn,
2.7% Pb, I.8%Cu, 65g/t Ag, 1.2 g/t Au. The host rocks are tectonically interleaved with, and overlain by the Keno Hill quartzite
of the Late Earn Assemblage, part of a Devonian and Mississippian clastic wedge (Mortensen and Thompson, 1990; Turner and
Abbott, 1990). The felsic metavolcanic rocks are interpreted as part of a Carboniferous continental-margin arc form along the
North American Craton Margin.
Nick SEDEX Ni-Zn-PGE-Au Deposit
The Nick SEDEX Ni-Zn-PGE-Au deposit consists of pyrite, vaeslte, melnikovite-type-pyrite, sphalerlte and wurtzite
which occur in a gangue of phosphatic-carbonaceous chert, amorphous silica and intergrown bitumen (Hulbert and others, 1992;
Yukon Minfile, 1992). The deposit has reserves of 900,000 tonnes grading 5.3% Ni, 0.73% Zn, and 0.8 g/t PGE, along with minor
Au. The deposit forms a thin, conformable unit at the contact between Middle and Late Devonian Earn Group. The deposit
extends laterally over a 80 krn2 basin (Hulbert and others, 1992). The host rocks are the basinal sedimentary part of a Devonian
and Mississippian clastic wedge exposed In an east-west trending syncline. The basin is Interpreted as a local trough or
embayment on the eastern margin of the Selwyn Basin. The only known deposits similar to this rare SEDEX deposit are the Ni-
Mo sulfide beds of the Yangtze Platform, China (Coveney and others, 1994).