UBC Undergraduate Research

Structural Setting of Argentiferous Veins, Cariboo Gold District, East-Central British Columbia Gavin, Rachel A.

Abstract

The Cariboo Gold District (CGD) in east-central British Columbia is a hotbed for gold exploration and production. The Cariboo gold rush began in the late 1850s with the discovery of placer-gold in streams near Likely and the Wells-Barkerville area, and lode-gold was discovered not long after. To date, the CGD has yielded an estimated 118 - 134 tonnes of gold (Levson and Giles, 1993). Although structural controls appear to be similar throughout the CGD, not all mineralized veins are gold-bearing. Silver Mine, Penny Creek, and Cariboo Hudson are three veins in a cluster of argentiferous quartz veins, located 23 km southeast of Barkerville Gold Mines’ Cow Mountain deposit; these veins are dominated by silver, copper, lead, zinc and tungsten minerals with little to no gold mineralization. The Silver Mine vein is the best-exposed vein in the cluster and is the focal point of this study. The Silver Mine vein is a 2 m wide, steeply-dipping, north-northeast striking, fault-filling Ag-W polymetallic quartz-carbonate vein hosted within the Hardscrabble Mountain succession of the Barkerville subterrane. Structural analysis of the Silver Mine and surrounding veins suggest it may be a ‘strike vein’, similar to the B.C. Vein situated 23 km northwest. The Silver Mine vein may have formed by exploiting a preexisting thrust fault and, under sustained northeast-directed regional shortening, gradually rotating and continuously reactivating an area of rheological contrast at a high angle to the inferred direction of maximum regional stress. Relatively fresh lamprophyre dikes, some containing xenoliths of quartz vein fragments, intrude close to and cross-cut the vein at Silver Mine; Ar⁴⁰/Ar³⁹ geochronology confirms that these intrusions are ~20 Mya younger than the vein. The Au-Ag-Pb-Zn ± Cu-W tenor of Silver Mine and nearby veins is distinct from the Au ± Pb-Bi tenor of ore in veins in the Wells-Barkerville camp. Many of the Ag-W polymetallic veins are located within, or very near to, the relatively more carbonaceous and fissile Hardscrabble Mountain Succession, whereas Au veins tend to be hosted by the Downey Succession. Host rock lithology may be an important factor in vein ore mineralogy.

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