USGS Professional Paper 1697 - Alaska Resources Library

34 Metallogenesis and Tectonics of the Russian Far East, Alaska, and the Canadian Cordillera
of Zn-Pb-Fe sulfides were deposited synchronously with Early
Silurian (Norford and Orchard, 1983) carbonaceous and limy
mudstone and chert. The Howards Pass metallogenic belt is
interpreted as forming from Pb- and Zn-rich fluids resulting
during rifting, volcanism, basinal subsidence, local marine
transgression, and related hydrothermal activity (Goodfellow
and Jonasson, 1986; Dawson and others, 1991). The fluids
were discharged episodically into a stable, starved marine basin
during restricted seawater circulation and resultant formation of
sulphidic, anoxic bottom waters. The mineral assemblages, host
rock age, and geologic setting for the Howards Pass metallogenic
belt are similar to those for the Anvil and Kootenay metallogenic
belts of the northern and southern Canadian Cordillera
(described above and below, respectively). All three 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.
Kootenay Metallogenic Belt of Carbonate of
Sediment-Hosted Deposits (Belt KO), Southern
British Columbia
The Kootenay metallogenic belt of carbonate or sedimenthosted
(SEDEX) Zn-Pb deposits (fig. 3; tables 3, 4) occurs
in southeastern British Columbia. The deposits are hosted in
metamorphosed and intensely deformed siliceous clastic,
carbonate, volcanic, and plutonic rocks of the Kootenay metamorphosed
continental margin terrane. This metamorphosed
continental margin terrane occurs between the North America
Craton Margin and to the east, and the accreted island arc
Quesnellia terrane to the west (fig. 3). Some of the older sedimentary
rock units, notably the middle Paleozoic Eagle Bay
Assemblage in Kootenay and Shuswap regions of southeastern
British Columbia, can probably be stratigraphically correlated
with units in the North America Craton Margin (Monger and
Nokleberg, 1996). The significant deposits in the metallogenic
belt are the Mastadon, Jersey, Duncan Lake area, H.B.
(Zincton), and Reeves-MacDonald (Reemac) deposits (table 4)
(Nokleberg and others 1997a,b, 1998).
Mastadon SEDEX Pb-Zn(?) Deposit
The Mastadon SEDEX Pb-Zn (?) deposit consists of
pyrite, arsenopyrite, sphalerite, galena and sulfosalts that occur
in bands, lenses, and stringers from 0.1 to 12 m wide (Mining
Review, 1992). The hanging wall part of the deposit consists of
disseminated sphalerite, galena, and pyrite; the footwall part of
deposit consists of massive arsenopyrite, sphalerite and pyrite.
Ore minerals are concentrated along the contact between phyllite
and limestone. Au is refractory and associated with arsenopyrite.
The deposit contains estimated production and reserves of 12.27
million tonnes grading 4.9 percent Zn, 2.3 percent Pb, and 62 g/t
Au. The deposit is hosted in Early Cambrian Hamill Formation
quartzite and Badshot Formation with limestone forming the
footwall. The deposit origin is poorly understood.
Jersey SEDEX Pb-Zn Deposit
The Jersey deposit consists of fine-grained sphalerite
and galena with pyrite, pyrrhotite and minor arsenopyrite in
five ore bands ranging from 0.30 to 9 meters thick (Fyles and
Hewlett, 1959; Sangster, 1986; MacIntyre, 1991). Sulfides
occur more abundantly in fold troughs relative to fold crests.
Cd is associated with sphalerite, Ag with galena. The deposit
has produced 7.7 million tonnes grading 3.49 percent Zn, 1.65
percent Pb, 3.08 g/t Ag. The deposit is hosted in the folded
Reeves Member dolomite of the Early Cambrian Laib Formation,
and may be a SEDEX Pb-Zn deposit.
H.B. (Zincton) Pb-Zn SEDEX Deposit
The H.B. (Zincton) Pb-Zn SEDEX deposit consists of
pyrite and sphalerite that occur in narrow bands, irregular
lenses or disseminations in dolomite of the Early Cambrian
Reeves Formation (Sangster, 1986; MacIntyre, 1991; Hoy,
1982b; MINFILE, 2002). Local cross-zones contain finegrained
massive sulfides that commonly occur as matrix in a
coarse breccia. The breccia zones are related to thrust faults
and are interpreted as secondary structures. Much of the
dolomite in the West orebody is altered to talc. The deposit
has produced 6.7 million tonnes grading 3.91 percent Zn, 0.74
percent Pb, 4.42 g/t Ag.
Origin of and Tectonic Setting for Kootenay
Metallogenic Belt
The Kootenay metallogenic belt of Zn-Pb SEDEX
deposits is hosted in platformal, Early Cambrian carbonate
rocks in the Kootenay metamorphosed continental margin
terrane. The deposits commonly consist of bands and
lenses of sphalerite, galena, and pyrite, both conformable
and discordant to often isoclinally folded and regionally
metamorphosed dolostone of the Badshot, Reeves, and Laib
formations. Along with their host rocks, these deposits were
deformed prior to deposition of unconformably overlying
strata of the Carboniferous Milford Assemblage (Monger and
others, 1991). The age of the carbonate-hosed deposits is not
known with certainty and may be either SEDEX or highlydeformed
replacement deposits in Early Cambrian carbonate
rock. The mineral assemblages, host rock age, and geologic
setting for the Kootenay metallogenic belt are similar to
those for the Anvil and Howards Pass metallogenic belts of
the northern Canadian Cordillera as described above. All
three 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. Episodic rifting in the Cambrian through Ordovician
is interpreted as opening several sedimentary basins in the
Canadian Cordillera, such as the Selwyn Basin, with related
formation of Zn-Pb SEDEX deposits, which are similar to
those in the Kootenay metallogenic belt.