Structurally controlled iron oxide mineralization in the Iron Range Mountain and Mount Thompson region, British Columbia

Structurally controlled iron oxide alteration occurs within and along the Iron Range fault, a steeply west-dipping normal fault. Iron oxide alteration occurs as massive lenses, breccia infilling, and veins in a cataclastic quartz-albite breccia. Textures in thin section suggest multiple episodes of magnetite, hematite, quartz, and pyrite growth. Fluid-inclusion studies indicate two dominant, twophase fluid-inclusion assemblages within predominantly quartz and albite, i.e. brine + H2O vapour and brine + CO2 vapour. Chlorite thermometry from six microprobe analyses indicates temperatures of 275 to 325°C. The voluminous early sodic and relatively limited potassic alteration accompanied by ironoxide-rich and sulphide-poor alteration in the Iron Range deposit appears to be consistent with basinal brine fl uid-source models (with no magmatic component) for iron oxide-copper-gold-type mineralization.