Mineralogical and geochemical feature of the disseminated ores of the southern part of the Noril'sk 1 deposit

The new data on the composition of disseminated sulphide ore in the southern part of the Noril'sk 1 deposit are obtained. It was found that a sulfur-poor assemblage: as Fe-rich (cubanite, mackinawite) and Cu-rich (talnakhite, bornite, chalcocite, native copper) minerals due to the evolution of two different fractions of sulphide melt is characteristic of picritic gabbro-dolerite. It has been formed at relatively low sulfur activity (lgfS2 range from −12 to −11). And a high-sulfur assemblage (monoclinic pyrrhotite, pyrite and Ni-rich pentlandite) formed at higher sulfur activity (lgfS2 range from −10.5 to −10) due to the pyrrhotite-chalcopyrite fractionation of the sulphide melt is characteristic of olivine gabbro-dolerite. The ratios of Ni/Cu in the rocks decrease from picritic (Ni/Cu = 1.24 average) to olivine gabbro- dolerites (Ni/Cu = 0.69 average). But the Ni/Fe ratios in pentlandite are increasing down the cross-section due to increase of sulfur fugacity during the evolution of ore-forming system. The Pd-parageneses vary along the cross-section top down as follows: Sn → Pb → As → Bi(Te) in picritic gabbro-dolerite and Sn → Sb → As → Te(Bi) in olivine gabbro-dolerite. There is a clear correlation between the sulfide and PGM assemblage and the type of the host rocks.