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 —
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5.1 Regional geology 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. l995a), and referenced as the Polmak - Opukasjarvi - Pasvik - Pechenga - lmandra/Varzuga Ust'Ponoy greenstone belt in some ofthe Westernliterature (e.g. Melezhik et al. 1995). This belt traverses the northeastem part of the Fennoscandian shield for a distance of about 700 km (Fig. 5.I). 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 ofthe 2.5-2.4Ga intrusions of Northem Finland - see Chapter 9). Rifting started in the eastem 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 I. 75-1.70 Ga and the belt, especially the southem part, suffered intense deformation and greenschist to amphibolite metamorphism (Smolkin at al. 1995a). Several Ni sulfide deposits and/or prospects occur within and adjacent to the Pechenga-Varzuga belt. They are concentrated primarily in and around the Pechenga and Imandra-Varzuga structures. Gorbunov et al. (l985a) subdivided them in two groups, according age and type of host intrusion. The first group (deposits of the Allarechka, NE Pechenga and Monchegorsk area - see Yakolev et al. 1981; Gorbunov et al. 1985b) are related to the Early Karelian (~2.5 Ga) layered intrusions of Mt Generalskaya type, that consist of peridotite, pyroxenite and gabbronorite. A. J. Naldrett, Magmatic Sulfide Deposits © Springer-Verlag Berlin Heidelberg 2004
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5 Deposits of the Pechenga area, Russia 36"
~ Paleozoic alkaline
~ intrusions (Khibiny
and Lovozero plutons)
EJ
ß
67"
0
100
30"
36 • White Sea
Early Proterozo ic Pechenga-Varzuga sedimentary-volcanic bell Early Proterozoic mafic-ultramafic intrusions Ni camps: 1 = Pechenga; 2 = Allarechka ; 3 NE Pechenga; 4 = Lovnoozero; 5 = Monchegorsk; 6 = Pana and Fedorova Tundra
=
Fig. 5.1. Schematic geological map of the Pechenga Structure. Simplified after Papunen and Gorbunov ( 1985) with modified legend
The intrusions hosting these deposits occur within faults, either at the margins of greenstone belts (Monchegorsk) or in gneisses forming the basement to the belt (Allarechka and NE Pechenga). The second group comprises the Late Karelian (about 2.0 Ga) deposits that are associated with wehrlite-pyroxenite-gabbro intrusive rocks and the related ferropicritic volcanic suite. The second group, particularly those at
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