Caption:
Albitized fragmental volcanic rocks (Na facies) replaced by anastomosed fronts of disseminated microcrystalline to fine magnetite of the high-temperature C-Fe facies and cut by irregular magnetite, locally porous and enclosing scheelite and accessory allanite, apatite and titanite (past-producing Northrim mine, Camsell River district, Great Bear magmatic zone). Early alteration zones are cut by low-temperature Ca-Mg-Fe facies veins and stockworks with calcite, magnetite, sulphides, chlorite, epidote and quartz that locally display K-feldspar haloes. The earlier generation of magnetite alteration is most abundant as rims on fragments.