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The layered intrusions of the Monchegorsk Complex (MC) - Monchetundra, Monchegorsk Pluton, Vuruchuaivench, and a few small intrusions of the same age are located within the south inner corner of the Paleoproterozoic Pechenga - Imandra - Varzuga rift-transform system. The MC intrudes Achaean gneisses of the Kola-Belomorian complex and in turn is overlaid by volcano-sedimentary rocks of the Imandra - Varzuga series. The Monchegorsk pluton has a long history and is well known owing to Cu-Ni sulfide veins (exhausted by the late 60s). On the contrary, only little information is available until now on several newly discovered PGE occurrences in its frame.
Firstly it is explored high-grade PGE-deposit in altered, quartz-bearing gabbronorite of the Vuruchuaivench massif. The most common PGM are the minerals of Pd-Ni-As, Pd-As-Sb, Pd-Te-Bi systems and sperrylite. PGM obviously formed due the processes of a metasomatic alteration of primary sulfide and silicate parageneses by magmatic fluids at the final stages of the massif formation, possibly accompanied by hydrothermal influxes of As and Sb from volcano-sedimentary rocks of the Imandra - Varzuga rift zone.
The Monchetundra and Monchegorsk massifs bound along the Monchetundra regional fault expressed by high permeable shear zone, which consists of a number of steeply dipping faulted slices composing of more or less altered rocks ranging from dunite and chromitite to gabbronorite. The variable multi-stage PGM assemblages have been found in the two PGE-occurrences of the Monchetundra fault zone - the low-grade South Sopcha occurrence in brecciated mafic and ultramafic rocks, and remobilized the East-Monchetundra PGE occurrence within sheared mafic-ultramafic cumulates with very irregular PGE distribution. PGM association from suites of alternate pyroxenite and gabbronorite with minor peridotite consists of sperrylite, PGE-sulfarsenides, and minerals of Pd-Pt-Te-Bi, Pd-Sb-As, Pd-Ni-As, Pd-Sn, Pd-Pb systems. The most common PGM within serpentinized ultramafics are isoferroplatinum and Pt-Pd-Fe-Cu alloys with lesser laurite, sperrylite, PGE-sulfarsenides and Pt-Pd-bismuthtellurides. Pt-Pd-Fe-Cu alloys are replaced by Pt-Pd-Cu-Fe-S and then by Cu-Pt-Pd-Fe-O phases along fissures and grain boundaries.
There is some regularity in distribution of PGM and their assemblages in the MC. Composition of the PGM assemblages within PGE-bearing bodies strongly varies depending on ore-bearing rock types and both fluid-hydrothermal and tectonic processes. Thus, primary PGM assemblage from reef-like low-grade PGE-occurrences was appeared as a result of magmatic crystallization and intercumulus fluid-hydrothermal activity. Subsequent fluid-hydrothermal and tectonic processes gave rise to a multistage redistribution of PGE and their associations. The most intense processes of PGE remobilization, concentration and redistribution occurred within and around the Monchetundra Fault Zone.
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