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

Cariboo Metallogenic Belt of
Au Quartz Vein Deposits (Belt CB)
Southern British Columbia
The Cariboo metallogenic belt of Au quartz vein depmits (fig. 49; tables 3,4) occurs in eatern-cend British Columbia
and is hosted by the Early Cambrian Downey Creak Formation of tbe Barkerville subterrme of Kootenay terrane. The belt
consists of metamorphism-related, Au-quartz-sulfide lenses wbich are emplaced concordantly with limestone of the Baker
Member of the Downey Creek Formation and cut by discordant quartz-sulfide-gold veins which occur mainly in the Rainbow
Member of the Downey Creek Formation (Robert and Taylor, 1989). The significant deposits in the belt are in the Cariboo-
Barkerville district and at Frasergold (table 4) (Nokleberg and others 1997a. b, 1998). The Cariboo-Barkerville district also
contains major placer gold deposits (Nokleberg and others, 1997a).
Cariboo-Barkerville Distrlct
(Cariboo Gold Quartz, Mosquito Creek,
Island Mountain) of Au Quartz Vein Deposits
The Canboo-Barkmilk dis&ict conlains three principal mines (Cariioo Gold Quartz. Mosquito Creek, and k hd
Mountain Mlnes) which consists of quartz-sulfi& veins aad pyiitic replacement lenses (Robert and Taylor, 1989; ,%hoe and
Lane, 1991; MINFILE, 2002). The quarlz-sulfide veins occur in phyllite and quartzite of tbe Rainbow Member, ustdly within
100 m of the contact with mafic volcanic rocks a d Limestone of the Baker Member of the Downey Creek Formalion. Pynte-gold
lenses, which occur discontinuously in marble bands within the Baker Member, pre-date brittle defmation, are cut by quartz-
sulfide-Au veins, and are interpreted as synrnehmorphic (Robert and Taylor, 1989; Dawson and others. 1991). From 1933-1987,
the three principal mines produced 38 tomes of Au from 2.7 million tonnes of ore grading 13.94 g/t Au and 1.87 gft Ag. Recent
exploration of the Mountain and Bonanza Ledge deposits indicates a probable reserve of 3,109,800 lonnes gradmg 2.95 gh Au
(International Wayside Gold Mines 2003 Annual Report). The associated Wells-Barkerville placer Au district also produced 64.8
tonnes of Au between 1850 and 1990. The deposit age is interpreted as Middle Jurassic through Early Cretaceous.
Frasergold Au-Quartz Vein Deposii
The Frasergold Au quartz vein deposit consists of pyrrhotite, pyrite and coarse-grained gold, and minor galena,
sphalerite, and chalcopyrite whicb occur in defarmed quartz-carbonate veins and stockwork stratabound iD at least three
stratigraphic horizons in porphyroblastic phyllite (Eureka Resources hc., annual report.1990; Mining Review, 1992; MlNFILE,
2002). Estimated resources are 12.7 million tomes grading 1.87 g/t Au. The prospect occurs 25 lun south of Quesnel Lake in
eastern British Columbia and consists of a 8-km-long zone of deformed, stratabound qutlrtz-carbonale-pyriteAu veins which are
hosted in Late Triassic phyllite ofthe Quesnellia island-arc terrane near the suture with the adjacent Kootenay tenme (Dawson
and others, 199 1).
Origin of and Tectonic Contmls for
Cariboo Metallogenic Belt
The Cariboo metallogenic belt occurs near the margin of the Kootenay tenme near the suture (major fhdt) with the
Quesnellia island-arc terranc (fig. 49, tables 3,4). The deposits in the Cariboo-Badcerville district are inhpmted a9 fohg
during chlorite- to sillimanite-grade regional metamorphism mainly in the Middle Juressic to Early Cretaceous (Andrew and
others, 1983). This event is related to the successive overthrusting of Kootenay terrane by Cllssiar, Slide Mountain, and Quesnellia
terranes during a major accretionary event (Struik, 1986). Similarly, the Frasergold Au quartz vein prospect is interpreted as
forming early in the metamorphism of the area as metamorphic segregations related to the accretion of the Quesnellia island-arc
terrane (Bloodgood, 1987).
The deposits in the Cariboo metallogenic belt are interpreted as forming during accretion of Le Quesnellia and adjacent
terranes to the North American Continental Margin because of: (1) the occurrence of the deposits near a major fault; (2) the
metamorphic textures and structures of the deposits; and (3) an age of formation which approximates the interpreted age of
accretion of the Quesnellia and adjacent tenanes, which constitute the Intermontane SuperterrouK (Monger and others, 1972,
1992), to the North American Continental Margin. A Middle to Late Jurassic period of regional metamorphism and awociated
deformation IS interpreted as the age of accretion of the Quesnellia and Stikinia island-arc tenaoes, and associated bemes, to the
North Amencan Craton Margin, after oroclinal warping of the Stkhia-Quesnellia island-arc tmmes and tectonidly-Wed
Cache Creek and Sl~de Mountain subduction-zone terranes {Monger and others, 1972,1992; Mihalynuk and athers; 1994; Monger
and Nokleberg, 1996; Noklekrg and others, 2000). Before accretion, the Qoesnellia islaad arc may have formed on the! Kootmay
terrane, a rifted and deformed fragment of the North American Craton Margin, and the coevd Stikinio island arc may have formed
on the Yukon-Tanana terrane, another rifted and deformed fragment of the North American Craton Margin (Monger and
Nokleberg, 1996; Nokleberg and others, 2000).