Lead isotopic evidence for the origin of 1.8-1.4 Ga ores and granitoids in the southeastern part of the Fennoscandian Shield

Abstract

New data for the lead isotopic composition of galena from ore deposits related to 1.8-1.4 Ga granitoids in the southeastern part of the Fennoscandian Shield are presented and discussed together with earlier published information on granitoids and associated ore deposits. Two types of sulphide deposits genetically related to the granites can be recognized based on general metallogenetic features and isotopic composition: granite-hosted deposits (including Sn-bearing greisen veins in rapakivi granites) and peri-intrusive deposits (including contact-metasomatic skarn deposits like Pitkäranta and Gruvåsen). In addition, epigenetic deposits with a spatial but not a genetic link to the granites occur at various sites. An important metallogenetic belt related to 1.7-1.5 Ga granitoids can be followed in an east-west direction across the shield from lake Siljan in Sweden to Salmi at lake Ladoga. Within this belt, a major difference in metal derivation can be recognized: ore deposits southwest of the Raahe-Ladoga line, i.e. in areas without Archaean basement, indicate metal derivation from remelted 1.9 Ga Svecofennian crust whereas ore deposits in areas underlain by Archaean rock units indicate metal derivation from highly metamorphosed Archaean sources.