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

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-Temtory 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 which 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 which 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% 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 which occur as frach~re
and breccia filling and disseminations (EMR Canada, 1989; Dawson and others, 1991; Fritz and others. 199 1). The deposit
contains estimated reserves of 2.49 million tonnes grading 11% 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 which occur in
brecciated dolomitized shallow water (reef) carbonates of the Early Devonian Whittaker, Delorme and Camsell Formations
(Dawson, 1975; Archer Cathro and Associates, unpublished company report, 1978; EMR Canada, 1989). The deposit contains
estimated reserves of 8 million tonnes grading 5.4% Zn, 2.6% 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, are 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.
Origin of and Tectonic Controls for
Northern Cordillera Metallogenic Belt
The deposits in the Northern Cordilleran metallogenic belt are classic Southeast Missouri Pb-Zn deposits composed of
sphalerite, galena, and pyrite, with a gangue of dolomite, quartz, calcite and barite, and lesser gypsum. fluorite, chalcopyrite, and
pyrobiturnen. These minerals occur in vugs, pores, burrows, various sedimentary and tectonic breccias, and minor to major
fractures. Secondary dolomite commonly accompanies mineralization. Zn: Pb ratios average 10: 1, and Ag and Fe contents are
low. The deposit form is highly irregular and usually discordant on a local scale, but stratabound on a district scale. The deposit
sizes range from a few tens of thousands to about 10 million tonnes, and grades range from 3 to 10% combined Zn and Pb in
larger deposits to about 50% combined Zn and Pb in small bodies (Dawson and others, 1991). Remote location and lack of
infrastructure has limited drilling and development to only a few of the several hundred known occurrences.
The Late Proterozoic to Middle Devonian passive part of the North American Craton Margin consists of a miogeoclinal
sedimentary prism which is segmented into two contrasting facies belts. To the northeast are shallow water sandstone, dolostone
and limestone which define the Mackenzie Platform, whereas to the southwest are turbiditic sandstone, deep-water limestone,
shale and chert which define the Selwyn Basin. Sedimentary lithofacies exerted a primary control upon the localization of pre-
accretionary sediment-hosted mineral deposits. Minor occurrences of Southeast Missouri Pb-Zn deposits are a common feature of
carbonate rocks of all ages in the North American miogeocline; however, significant deposits commonly are localized along the
carbonate-shale facies changes near the tectonically-unstable, western margin of Late Proterozoic to early Paleozoic platformal
carbonate successions.