Deposits of the Pechenga area, Russia

The deposits of the Pechenga area are associated with a major Early Proterozoic rift system that is referred to in Russia as the Pechenga-Varzuga sedimentary-volcanic belt (e.g. Smolkin et al. 1995a), and referenced as the Polmak — Opukasjarvi — Pasvik — Pechenga — Imandra/Varzuga — Ust’Ponoy greenstone belt in some of the Western literature (e.g. Melezhik et al. 1995). This belt traverses the northeastern part of the Fennoscandian shield for a distance of about 700 km (Fig. 5.1). It includes a series of depressions filled by Early Proterozoic sedimentary and volcanic rocks (the Polmak, Pasvik, Pechenga, Imandra-Varzuga and Ust’Ponoy Structures) that occur within a reactivated Archean basement, that is cut by dikes and granitoid intrusions in intervening areas. The belt developed at about 2.3 Ga, after the emplacement and partial erosion of a series of peridotitegabbronoritic layered intrusions, (Mt. Generalskaya, Monchegorsk, Pana and Fedorova Tundra which are the equivalents of the 2.5–2.4Ga intrusions of Northern Finland — see Chapter 9). Rifting started in the eastern and central parts of the Imandra-Varzuga structure and propagated to the west. The greatest amount of spreading along the rift occurred in the Pechenga area (Smolkin 1992, 1993, 1997). Northwest-oriented compression took place from 1.75–1.70 Ga and the belt, especially the southern part, suffered intense deformation and greenschist to amphibolite metamorphism (Smolkin at al. 1995a).