THE PALEOPROTEROZOIC ORE-BEARING FERROPICRITIC VOLCANIC-PLUTONIC ASSOCIATION: PETROLOGY AND GEOCHEMISTRY (Kola region, Russia)
V.F. Smol’kin1, A.V. Mokrushin2,3
1Vernadsky State Geological Museum of the Russian Academy of Sciences, Moscow, Russia
2Geological Institute, Kola Science Centre of the Russian Academy of Sciences, Apatity, Russia
3Apatity branch of Murmansk Arctic University, Apatity, Russia
Keywords: Paleoproterozoic, gabbro, clinopyroxene, wehrlite, ferropicrite, dike, sulphide Cu-Ni ore deposit, geochemistry, isotopes, genesis, Pechenga, Russia
Abstract
Located in the north-west of the Murmansk Region, the sulphide Cu-Ni ore deposits were discovered in the 1930s. Nowadays they provide approximately 8-10% of the nickel mining in Russia. The deposits are spatially associated with serpentinite massifs, which have long been assigned to either the ophiolitic complex or basalt magma differentiates. The magma is regionally represented by wide-spread fields of pillow lavas and gabbro-diabase sills. The ultramafic ferropicritic volcanic rocks, which alternate in cross-section with lavas and basaltic tuffs, were discovered in the 1970s. Initially the ore-bearing massifs were intrusions composed of peridotite (wehrlite), clinopyroxenite, and gabbro, which were tectonically metamorphosed during the Svecofennian orogeny. Based on petrological, geochemical, and isotopic research, scientists have proved that ferropicritic volcanic rocks and ore-bearing intrusions are genetically bonded. This paper concerns the processes of differentiation of all the ferropicritic magma facies, i.e., intrusive (ore and ore-free intrusions), volcanogenic (massive and pillow lavas, stratified flows, sills), and dike ones (dike bodies, cross-cutting intrusions, and dike swarms in the Archean surrounding host rocks). Their relations, time and sequence of formation have been revealed. We also discuss the role that the processes of contamination and assimilation of the Archean basement rocks and hosting sulphide carbonaceous schists have played in sulphide ore formation.
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