Archean gneisses cropping out on islands in the White Sea and its coast in northern Karelia host widespread bodies of Early Proterozoic metamorphosed gabbroids. Carbonate-silicate veins hosted in these metabasite bodies and constrained to their contacts with the gneisses contain Fe-Cu sulfides, whose concentrations occasionally reach economic levels. The dominant gangue minerals are plagioclase, quartz, carbonates, and chlorite. The formation stages of the veins correspond to the transition from the early quartz-plagioclase to late quartz-carbonate associations with chlorite and sulfides. The early (high-temperature) stage is discernible in the wall-rock amphibolite aureoles, which were formed at temperature of about 550-650 degrees C (estimates by the TWQ method). This stage corresponds to the quartz-plagioclase association in the marginal zones of the veins. The transition to the late stage and the formation of veined quartz-carbonate (+/- biotite) associations occurred at temperatures of 540 degrees C and lower, judging by the calcite-dolomite associations. The further development of the quartz-chlorite-carbonate and sulfide associations in the veins and wallrock amphibolites corresponded to a temperature decrease to 350 degrees C and below, as evaluated with the application of chlorite thermometers. The veins and wall-rock amphibolitization may have been induced by metamorphic fluids during the latest retrograde metamorphic stage in the Early Proterozoic.
