The Composition and Mode of Formation of the Pechenga Nickel Deposits, Kola Peninsula, Northwestern Russia

Abstract

The Pechenga Ni-sulfide deposits, in the Kola Peninsula of Russia, are associated with ferropicrite flows and intrusions. The sulfides are divided into five types: 1) disseminated sulfides within the olivine cumulate portions of the ferropicrites, 2) massive sulfides, which occur at the contact between the ferropicrites and the country-rock black schists, 3) breccia-matrix sulfides, which occur at the contact between the ferropicrites and the schists, and in some cases continue for hundreds of meters subparallel to the contact but within the footwall, 4) chalcopyrite vein or stringer sulfides, which occur in the footwall, and 5) pyrite-rich layers, concretions and lenses in the sedimentary rocks. The disseminated sulfides have similarly shaped mantle-normalized patterns of chalcophile metal abundances to those of the ferropicrites, and could have formed in equilibrium with the ferropicritic magma at moderate R factors (250). The rocks are depleted in platinum-group elements (PGE), suggesting that the magma reached sulfide saturation prior to the formation of the ores. Sulfur isotope data indicate that the S was derived from the sediments onto and into which the ferropicrites were emplaced. The high As and Sb concentrations in the sulfides may have been derived from the sediments. The massive sulfides show a wider variety of composition than the disseminated sulfides; some sulfides are enriched in Os, Ir, Ru, Rh and depleted Pt, Pd, Ag, Au, Cu, Sb, As, Se. This pattern is attributed to the accumulation of monosulfide solidsolution during crystallization of a sulfide liquid. The sedimentary sulfides are richer in As and Sb than the disseminated and massive sulfides, but poorer in all the other chalcophile elements. The breccia-matrix sulfides consist of sedimentary and ultramafic fragments in a sulfide matrix. Compared with vein sulfides from other deposits, those from Pechenga have a very unusual composition. They are not only rich in Cu and Ag, but also in Os, Ir, Ru and Rh, and they are depleted in Pt, Pd, Au, As, Sb and Se.Keywords: nickel sulfide deposits, platinum-group elements, arsenic, antimony, gold, selenium, silver, rare-earth elements, ferropicrites, sulfur isotopes, Pechenga, Russia. SOMMAIRELes gisements de nickel de Pechenga, dans la péninsule de Kola, en Russie, sont associés à des coulées et des massifs intrusifs de ferropicrite. Les sulfures de nickel se présentent en cinq associations: 1) sulfures disséminés dans les parties cumulatives des ferropicrites, 2) sulfures massifs au contact entre les ferropicrites et les schistes noirs encaissants, 3) sulfures formant la matrice de brèches de ferropicrite et de schiste, dans certains cas se prolongeant des centaines de mètres le long du contact mais invariablement situés au dessus de la paroi inférieure, 4) veines de chalcopyrite ou sulfures en veinules, dans la paroi inférieure, et 5) accumulations de pyrite formant concrétions et lentilles dans l'encaissant sédimentaire. Les sulfures disséminés possèdent des tracés de concentrations en mét...

Partitioning of Se, As, Sb, Te and Bi between monosulfide solid solution and sulfide melt – Application to magmatic sulfide deposits

“…Even though in many magmatic sulfide deposits As, Sb, Te, and Bi are important ligands in platinum-group element (PGE) minerals (Zientek et al, 1994;Barnes et al, 2001;Helmy and Mogessie, 2001;Cawthorn et al, 2002;Oberthü r et al, 2003;Prichard et al, 2004;Holwell and McDonald, 2007;Godel et al, 2007), little quantitative information is available on the behavior of these elements in magmatic systems. For example, it is not known which role they play in the enrichment of PGE in magmatic sulfide melts.…”

8: Precambrian geodynamics and ore formation: The Fennoscandian Shield

“…The intense faulting and displacement are 511 related to the late stages of rifting, probably to the 512 cooling and subsidence of the brittle layer of the 513 lithosphere after the buoyant rise of the base of the 514 lithosphere during the active rifting phase (see Ala-515 pieti and Lahtinen, 2002 The Polmak-Pechenga greenstone belt extends for 520 about 200 km from northern Finland to NW Russia. 521 The area has been intensely studied since the discov-522 ery of the Pechenga Ni-Cu deposits in the 1920s, and 523 the review here is mainly based on the work of Hanski 524 (1992), Melezhik (1996), Green and Melezhik (1999) 525 and Barnes et al (2001). The 2.3 Ga, subaerially 526 deposited, andesitic basalts of the lowermost volcanic 527 unit of the Pechenga sequence represent the next 528 episode of magmatic activity in the Fennoscandian 529 Shield (Melezhik, 1996).…”

“…The ferro-549 picrites are enriched in LILE, LREE and HFSE and 550 display similarities with the picritic volcanic rocks of 551 the Central Lapland greenstone belt discussed below. 552 Although the idea of a core signature has been sug-553 gested for the Fe-rich Archaean to Proterozoic ultra-554 mafic volcanic rocks (Puchtel et al, 1999), it has also 555 been argued that the Archaean/Proterozoic picrites 556 were 30% richer in Fe compared with modern OIB 557 since the mantle was more Fe-rich at that time (Fran-558 cis et al, 1999;Barnes et al, 2001).…”

“…3. Depositional model of the formation of the Pechenga Ni-Cu deposits after Melezhik (1996) and Barnes et al (2001 Gaál (1972Gaál ( , 1985 1097 and Puustinen et al (1995) inferred that the Group Ia 1098 intrusions were emplaced into a subvertical D 3 1099 wrench lineament, which is clearly visible along the 1100 Kotalahti belt in tectonic and geophysical maps. How-1101 ever, in detail most of the intrusions occur outside the 1102 shear zone and a genetic relationship is ambiguous.…”

The 1.88 Ga Kotalahti and Vammala nickel belts, Finland: Geochemistry of the mafic and ultramafic metavolcanic rocks

“…1). It forms part of a series of provinces or belts of broadly similar age containing nickel sulfide mineralisation and occurring along the margins of Archaean cratons, including the Pechenga and Raglan (Cape Smith) belts (Barnes et al, 2001;St.Onge et al, 1997).…”