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

from crystalline basement of craton. The fold belt is separated from the Siberian platform by the Late Cretaceous, west-verging
Lena thrust belt (fig. 2).
Anvil Metallogenic Belt of SEDEX
(SEDEX) Zn-Pb-Ag Deposits,
Yukon Territory, Canada (Belt AN)
The Anvil metallogenic belt of sedimentary exhalative (SEDEX) Zn-Pb-Ag deposits (fig. 3; tables 3.4) occurs in the
Anvil district in the western Selwyn Basin, Yukon Territory, Canada. The deposits are hosted in the passive continental margin
rocks of the North American Craton which represent the transition from shelf to off-shelf facies. The SEDEX deposits occur in
calcareous and non-calcareous phyllites which are correlated (Jennings and Jilson, 1986) with Early Cambrian to Silurian strata in
the Howards Pass region (Gordey and Anderson, 1993) which contain Early Silurian SEDEX deposits (Howards Pass
metallogenic belt described below). The major deposits are in the Anvil district are the Faro, Vangorda Creek. Grum, Firth, DY,
and Swim (table 4) (Nokleberg and others 1997a, b, 1998).
Anvil District SEDEX Zn-Pb-Ag Deposits
The Anvil district contains six pyrite-bearing, stratiform Zn-Pb-Ag (Au-Cu-Ba) deposits and two stratiform pyritic Cu-Zn
occurrences which extend southeastward along strike for 45 km. The deposits and occurrences are hosted in distinctive, Early
Cambrian graphitic phyllite which forms a district-wide metallotect. Ore from tbe three principal deposits (Faro. Vangorda, and
Grwn) consists of massive pyrite, pyrrhotite, sphalerite, galena and marcasite with patchy barite in a siliceous gangue. Higher ore
grades are associated with barite. Pyrite-bearing massive sulfides are overlain by barite-bearing massive sulfides, and are
underlain by pyrite-bearint quartzite which grades laterally into ribbon-banded graphitic quartzite and graphitic phyllite. The Faro
deposit (fig. 12) occurs approximately 100 metres stratigraphically below the contact between phyllite and quartzite of the Early
Cambrian Mount Mye Formation and calcareous rocks of the Cambrian and Ordovician Vangorda Formation. At the northern end,
the deposit is intruded and contact metamorphosed by the Cretaceous Anvil batholith and related dikes. For the district, the
combined, pre-mining reserves were 120 million tonnes grading 5.6% Zn, 3.7% Pb, and 45-50 g/t Ag (Jennings and Jilson, 1986).
Faro, the largest deposit, ceased production in 1997. The Vangorda deposit, a smaller mine, containing 7.1 million tonnes of ore,
was largely exhausted between 1990 and 1993 (Brown and McClay, 1993), and the Gnlm mine produced 16.9 million tonnes of
ore from 1993 to 1996.
Origin of and Tectonic Controls for
Anvil Metallogenic Belt
The Anvil metallogenic belt is hosted by sedimentary rocks of western Selwyn basin which are part of the Cambrian
through Devonian passive margin of the North American Craton (Nokleberg and others, 1994c, 1997c; Monger and Nokleberg,
1996). The host sedimentary strata represent a transition from shelf to slope facies. The coincidence of southwestward thickening in
the graphitic phyllite with a linear array of alkaline basalt volcanism centers suggests which rift-related synsedimentary faults may
have served as conduits for the SEDEX fluids. However, demonstrable feeder zones have not been observed. The elongate subbasins
hosting the deposits are interpreted as forming during Middle Cambrian to Early Ordovician extension and faulting
(Jennings and Jilson, 1986). The result~ng structural conduits provided concentrated exhalative metalliferous brines in a reducing
environment in which the deposits formed. Related extensional faulting and emplacement of Middle Ordovician alkalic basalt
dikes, which occur along the eastern margin of Selwyn Bas~n and southward to Gataga Trough, may have served both as a tectonic
control on the development of the sed~mentary basins in the Anv~l and Howards Pass areas, and a source of both heat and
metal liferous brines.
The mineral assemblages, host rock age, and geologic setting for the Anvil metallogenic belt are similar to those for the
Howards Pass and Kootenay metallogenic belts of the Canadian Cordillera (described below). All three metallogenic belts are
interpreted as forming from Pb- and Zn-rich fluids resulting during rifting, volcanism, basinal subsidence, local marine
transgression, and related hydrothermal activity along the passive continental margin of the North American Craton. Rifting is
interpreted to have formed the Misty Creek Embayment in the Early to Middle Cambrian (Cecile, 1982), the Selwyn Basin in the
Late Proterozoic to Ordovician (Gabrielse, 1963), and the Meilleur River Embayment in the Early to Middle Ordovician (Morrow,
1984), with the latter event marked by alkal~c basaltic volcanism (Fritz and others, 1991). SEDEX occurrences also formed during
these events mainly in the Anvil and Howards Pass metallogen~c belts, and to a minor extent in the Misty Creek and Meilleur
River ernbayments.
Howards Pass Metallogenic Belt of Sedimentary
Exhalative Zn-Pb Deposits (Belt HP)
Eastern Yukon Territory
The Howards Pass metallogenic belt of sedimentary exhalative (SEDEX) Zn-Pb deposits (fig. 3; tables 3,4) occurs in the
eastern Yukon Territory. The belt is hosted in the Selwyn Basin which constiti~tes part of a Cambrian to Devonian passive margin