Precambrian metallogeny related to tectonics in the eastern part of the Baltic Shield
Abstract The bulk of the eastern Baltic Shield is underlain by Archaean continental crust composed of three segments with varying tectonic settings. • - The Kola Peninsula Province consists of granulite-gneiss terrain with Fe, NiCu deposits; greenstone belts with NiCu, BIF and REE deposits; a highly deformed volcanic-sedimentary basin with kyanite deposits and Late Archaean gabbroanorthosite intrusions hosting FeTiV ores. • - The Karelian Province is a typical granite-greenstone belt terrain. The greenstone belts were formed during the Lopian orogeny (2.9-2.6 Ga) in tectonic environments resembling rifts and island arcs. They contain NiCu and massive pyrite deposits with Cu mineralizations, and BIF deposits. Late orogenic granites host Mo, CuMo deposits of the porphyry type. • - The Belomorian Province is a region of granulite-gneiss and granite-greenstone belt terrains reworked tectonically and metamorphically during the Lopian and Svecofennian orogenies (2.0–1.75 Ga) which involved continent-continent collision. Here, muscovite and rare metals-muscovite pegmatite deposits are related to Svecofennian igneous and metamorphic processes. In the Early Proterozoic the main metallogenic events were associated with intracontinental rift structures of the Karelian stage (2.5-2.0 Ga) in the Kuolajarvi-Vetrenny Poyas zone and the Monchegorsk-Fedorova-Pana Toundri zone and of the Svecofennian stage (2.0–1.8 Ga) in the Pechenga-Imandra-Varzuga zone. The above mentioned zones contain major NiCu, PGE and Ti deposits hosted by layered intrusions (2.45-2.35 Ga) and gabbro-wehrlites (2.0–1.9 Ga), and Cu and Au mineralizations hosted by metavolcanic rocks. Epicontinental sediments of the Jatulian Group (2.2-2.0 Ga) in a slightly deformed within-plate basin contain Cu, CuCo and schungite deposits. The Early Proterozoic Svecofennian Province is represented by the Ladoga belt only. Metamorphic zoning, thrusts, deformation and granite-gneiss domes developed, and some Cu, CuZn, FeTi, W and graphite mineralizations formed there. The tectonic setting of the Ladoga belt is interpreted as that of a deformed shelf deposit on a rifted and passive continental margin. In addition to this an abortive continental-rift belt with rapakivi granite intrusions (1.65-1.55 Ga) developed along the southern boundary of the Baltic Shield. Sn and SnCuZnFe deposits and fluorite and rare-metal mineralizations are associated with these granites.