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Giant quartz veins occur along brittle faults in the ca. 1865 Ma Great Bear magmatic zone. They comprise two or more generations of subparallel veins and stockworks in zones as much as 100 m wide and 10 km long. They contain local concentrations of hematite/specularite, pyrite, copper sulphides, and pitchblende. Fluid inclusions in the veins at two uranium showings, Crowfoot and Ted, were examined. The homogenization temperatures (Th) range from 96 to 217°C for Type I (2-phase liquid-rich) inclusions at Crowfoot, and from 122 to 169°C for Types I and III (3-phase liquid-rich) inclusions at Ted. Type II (2-phase vapour-rich) inclusions yield grossly different Th (228 445°C range), which do not represent true Th, but do suggest fluid mixing, as does the wide salinity range from 0.18 to 31.6 weight per cent NaCl equivalent. These data are consistent with the formation of the veins in a tensional epizonal environment.

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