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

occur in clastic and impure carbonate rocks of the Aida and Gataga formations in the Racing River-Gataga River region (Taylor
and Stott, 1973). The significant deposit is at Churchill. Other CLI vein deposits in the Churchill metallogenic belt are at Davis Keays,
Gataga, and Fram.
Churchill (Davis Keays) Cu Vein Deposits.
The major Churchill (Davis Keays) Cu vein deposit occurs along the Magnum vein system. The deposit consists of
chalcopyrite, pyrite, quartz. and ankerite in a zone which is 100 m wide (Preto and Tidsbury, 1971; Dawson and others. 1991).
The deposit occurs in strongly folded Late Proterozoic dolomites and slates of the Aida Formation (with K-Ar isotopic age 780
Ma), and is intruded by diabase dikes and sills. Overlying Cambrian basal conglomerate contains clasts of mineralized vein
material. The deposit age is interpreted as Late Proterozoic. From 197 1 to 1974,498,OO tonnes grading 3.43% Cu were produced.
The grade is highly variable and discontinuous.
Origin of and Tectonic Controls for
Churchill Metallogenic Belt
The Cu vein deposits in the Churchill metallogenic belt are associated with a northwest-striking diabase dike swarm
which crosscuts folded sedimentary rocks in the Purcell (Belt) Supergroup which were deposited along the passive continental
margin of the North American Craton. The Cu vein deposits are partly concordant with and intruded by genetically-related diabase
dikes. However, no diabase dikes occur in the Late Proterozoic Windermere Group to the west, indicating an early Late
Proterozoic age for dike emplacement and formation of associated Cu vein deposits (Dawson and others, 1991). The Churchill
metallogenic belt is interpreted as forming in a major, Mesoproterozoic rifling event which is reflected in the sedimentary
assemblages of the Purcell and Wernecke Supergroups and the Muskwa Ranges assemblage.
Monashee Metallogenic Belt of Sedimentary
Exhalative (SEDEX) Zn-Pb-Ag Deposits (Belt MO)
Southern British Columbia
The Monashee belt of sedimentary exhalative (SEDEX) Zn-Pb-Ag deposits (fig. 3; tables 3,4), located in southern British
Columbia in the southeastern Canadian Cordillera, is hosted in the Monashee cratonal terrane. The major SEDEX deposits (table
4) are Big Ledge, Ruddock Creek, Cottonbelt, and River Jordan (King Fissure), as well as the Neoproterozoic Mount Copeland
porphyry Mo deposit which is herein included in the metallogenic belt because the porphyry systems are part of the Monashee
cratonal terrane (Nokleberg and others 1997a, b, 1998). The SEDEX deposits and prospects are within the upper paragneiss part
of the terrane. Estimated resources range from less than 1 million to 6.5 million tonnes.
Big Ledge SEDEXZn-Pb Deposit
The Big Ledge SEDEX Zn-Pb deposit consists of sphalerite, pyrrhotite, galena, and pyrite in lenses (Hnry, 1982a;
MINFILE, 2002). The deposit contains estimated reserves of 6.5 million tonnes grading 4% Zn. The deposit is in a dark,
pyrrhotite and pyrite-rich, graphitic, calcareous schist which extends along strike for approximately 10 km. The schist is part of
paragneiss which is interpreted as the arnphibolite-grade metamorphic equivalent of the Late Proterozoic Windermere Group.
Ruddock Creek SEDEX Zn-Pb Deposit
The Ruddock Creek SEDEX Zn-Pb deposit consists several layers with banded sphalerite, pyrrhotite, galena, pyrite and
minor chalcopyrite and local barite and fluorite which occur in discontinuous lenses and layers along strike length for several
kilometers (Dawson and others, 1991; H0y, 1982a, 2001; MINFILE, 2002). The deposit has estimated reserves of approximately
5.0 million tonnes grading 7.5% Zn, 2.5% Pb and is hosted in possibly Paleoproterozoic schist, calc-silicate gneiss, quartzite and
marble.
Mount Copeland Porphyry Mo Deposit
The Mount Copeland porphyry Mo deposit consists of molybdenite, pyrite, pyrrhotite, bornite, chalcopyrite and galena
which occur along the northern boundary of a large mass of nepheline syenite gneiss flanking the southern boundary of the
Frenchman's Cap Dome, one of several gneissic domes flanking the eastern margin of the Shuswap Metamorphic Complex
(McMillan, 1973; Okulitch and others, 1981; MINFILE, 2002). The deposit has estimated reserves of 180,000 tonnes grading
1.82% MoS2 and production of 171,145 tonnes grading 0.75% MoS2. The deposit is hosted in irregular lenses of aplite and
pegmatite syenite. U-Pb zircon isotopic analysis suggests an age of 773 Ma. This age indicates the porphyry deposit formed in the
early history of the Monashee cratonal terrane prior to fragmentation and migration.