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

interpreted by and as part of a extensive continental-margin arc in the Late Devonian and Early Mississippian which formed along
the margin of the North American Craton Margin (Lange and others, 1985; Mortensen. 1992; Nokleberg and others, 2000).
Small pyrite-bearing Pb-Zn-Ba lens-shaped occurrences, as at Mickey (Mortensen, 1992). are hosted in carbonaceous
schist and quartzite and Middle Mississippian felsic metatuff. These deposits are interpreted as SEDEX Zn-Pb deposits may be
correlated with slmilar-age SEDEX deposits of the Gataga metallogenic belt 1,000 km to the southeast, across the Tintina fault
(fig. 17) (Johnston and Mortensen, 1994). However, the Dawson metallogenic bell is hosted in the Yukon-Tanana terrane which is
interpreted as a rifted fragment of the North American Craton Margin (Mortensen, 1992: Monger and Nokleberg, 1996; Nokleberg
and others, 2000) whereas these metallogenic belts to the east containing SEDEX deposits are hosted in a Devonian-Mississippian
clastic wedge deposited on the North American Craton Margin (Nokleberg and others, 1997b, 1998, Sheet 4). The host rocks for
this part of the Dawson metallogenic belt are part of the Nasina assemblage which consists of Late Devonian to Middle
Mississippian mafic to felsic metavolcanic rocks, quartzite, schist, and metaplutonic rocks. The tectonic origin of this group of
deposits is unclear.
Pyrite-bearing Kuroko Pb-Zn-Cu (Au-Ba) massive sulfide occurrences, as at Lone Star (Mortensen. 1992), are hosted in
middle Permian felsic metavolcanic rocks. The host rocks are part of the Klondike schist and associated units which consist
mainly of middle Permian felsic metavolcanic and metaplutonic rocks (Mortensen, 1992). Structurally interleaved with the
metavolcanic rocks are blueschist and eclogite which are interpreted as remnants of a former subduction zone which was
tectonically linked to the volcanic arc which formed the metavolcanic rocks and associated occurrences.
Frances Lake Metallogenic Belt of Volcanogenic
Zn-Cu-Pb Massive Sulfide Deposits (Belt FR)
Southern Yukon Territory
The Frances Lake metallogenic belt of volcanogenic massive sulfide deposits (fig. 17; tables 3,4) occurs in the
southeastern Yukon Territory and is hosted in Early Mississippian felsic metavolcanic rocks and meta volcaniclastic units in the
Yukon-Tanana terrane. The kuroko massive sulfide deposits, which occur northeast of the Tintina Fault and southwest of
Finlayson Lake, are interpreted as equivalent to: (1) smaller kuroko massive sulfide occurrences in the Dawson metallogenic belt
(as at Mickey) which occur southwest of the Tintina fault and are hosted in the Nasina Assemblage (Johnston and Mortensen
1994); and (2) major kuroko volcanogenic massive sulfide deposits which occur across the Tintina fault in the Alaska Range and
Yukon-Tanana Upland metallogenic belt in East-Central Alaska. The significant deposits are at Kudz Ze Kayah and Wolverine
(table 4). Local Besshi and Cyprus volcanogenic massive sulfide deposits also occur in the belt.
Kudz Ze Kayah Kuroko Massive Sulfide Deposit
The Kudz Ze Kayah kuroko Zn-Cu-Pb massive sulfide deposit consists of pyrite-bearing massive sulfide bodies which
are associated with deformed, subvolcanic domes or thick sills which occur within felsic metavolcanic units. The deposit contains
mineable reserves of 1 1.3 million tonnes grading 5.9% Zn, 0.98% Cu, 1.5% Pb, 133 g/t Ag, and 1.34 g/t Au (Mining Review,
summer, 2000). The deposit and similar occurrences are hosted in felsic metavolcanic rocks of the Late Devonian to Middle
Mississippian Nasina Assemblage which constitutes the middle structural sequence of the Yukon-Tanana terrane (Mortensen,
1992).
Wolverine-Lynx Kuroko Massive Sulfide Deposits
The Wolverine-Lynx kuroko Zn-Cu-Pb-Ag-Au massive sulfide deposits consist of massive sulfides in a fragmental
rhyolite unit which is capped by an extensive magnetite iron formation and limy exhalite. The deposit contains estimated reserves
(Wolverine and Lynx) of 6.2 million tonnes grading 12.66% Zn, 1.3% Cu, 1.5% Pb, 350 g/t Ag, and 371 glt Au (Mining Review,
summer 2000).The deposit occurs in the Yukon-Tanana terrane about 135 krn southeast of Ross River. Yukon Territory. It is
hosted by interbedded felsic volcanics and argillite of Devonian and Mississippian age.
Origin of Tectonic Setting for
Frances Lake Metallogenic Belt
The eastern Frances Lake belt of kuroko massive sulfide deposits is hosted subvolcanic felsic domes or sills (Johnston
and Mortensen, 1994) which form lensoidal metavolcanic units which interfinger with fine-grained quartzite and carbonaceous
schist of the Devonian and Mississippian Nasina Assemblage or Nisutlin subterrane of the Yukon-Tanana terrane. The Nasina
Assemblage consists of carbonaceous quartzite, quartz-mica schist, marble, mafic and felsic metavolcanic rocks and lesser
amounts of metaplutonic rocks. These units are interpreted as part of the extensive Kootenay continental-margin igneous arc
which formed along the margin of the North American Craton Margin, subsequent to rifting of the Yukon-Tanana and related
terranes (Mortensen, 1992; Nokleberg and others, 2000). Remnants of the extensive middle Paleozoic Kootenay continental margin
arc and associated lode deposits extend for several thousand km in various metamorphosed continental margin tenanes in Northern
Alaska, East Central Alaska, the northern and southern Canadian Cordillera, and southeastern Alaska (Rubin and others, 1991; Plafker
and Berg, 1994; Nokleberg and others, 199412, 1997c; Monger and Nokleberg, 1996; Nokleberg and others. 2000). Fragments of the