TY - JOUR

T1 - Unique Cu-rich sulphide ores of the Southern-2 orebody in the Talnakh Intrusion, Noril'sk area (Russia)

T2 - Geochemistry, mineralogy and conditions of crystallization

AU - Tolstykh, Nadezhda

AU - Krivolutskaya, Nadezhda

AU - Safonova, Inna

AU - Shapovalova, Mariya

AU - Zhitova, Liudmila

AU - Abersteiner, Adam

N1 - Publisher Copyright: © 2020 Elsevier B.V. Copyright: Copyright 2020 Elsevier B.V., All rights reserved.

PY - 2020/7

Y1 - 2020/7

N2 - We present new geochemical and mineralogical data from the Southern-2 orebody, located in the South-Western branch of the Talnakh intrusion (Russia) and composed of massive and disseminated sulphides. The Southern-2 orebody consists dominantly of chalcopyrite along with lesser pentlandite and subordinate cubanite, bornite and pyrrhotite, and differs from Cu-rich ores of the Oktyabr'sky deposit due to the absence of moikhukite-talnakhite assemblages. Ores from the Southern-2 orebody are highly enriched in copper, nickel and platinum-group elements (PGEs): Cu up to 28.12 and 10.58 wt%, Ni up to 6.29 and 2.45 wt%, and Pt + Pd up to 220 and 173 ppm in the massive and disseminated ores respectively. The ratios of Cu/Ni = 3.85–7.34 in massive and 2.64–6.58 in disseminated ores. The ratios of the platinum to iridium group elements (PPGE/IPGE) reaches more than 40000. These features indicate an extremely different degree of fractionation of the sulphide melt during the formation of ores. The sequence of crystallization of the PGE minerals (PGMs) on the basis of textural information was as follows: Pt-Pd-Sn (rustenburgite, atokite) → Pd-Cu-Sn (stannopalladinite) → Pt-Fe-Cu-Ni (tetraferroplatinum) → Pd-Ni-As (majakite) → Pd-As (palladoarsenide) → Pd-Pb(Bi) (zvyagintsevite, polarite and Pd5Pb3 unnamed phase) → Au-Cu-Pd (tetra-auricupride and auricupride) → Au-Ag alloys. This is consistent with experimental data on PGE minerals. The PGM assemblage was caused by the evolution of a significantly fractionated sulphide melt that was enriched in Cu, Ni, Pt, Pd, Pb and Au, and as a result produced minerals with peculiar compositions (e.g., Cu-rich stannopalladinite, Pb-rich polarite, Ni-rich palladoarsenide), which do not occur in other ores. Furthermore, Pt-Fe-Cu-Ni alloys are abundant and sperrylite is absent, which is a very common phase in all ores of the Noril'sk area. The composition of pentlandite with Ni/(Ni + Fe) ratios ranging from 0.48 to 0.68 indicates that it formed between 560 °C (Ni-poor) to 500 °C (Ni-rich) and −10.5 to −7 lgfS2, respectively. The PGMs and Au-minerals were formed at temperatures ranging from 550 to 225 °C. The specificity of sulphide (with PGMs) association is due to the evolution of the Cu-rich (and Ni-rich) melt under elevated sulphur fugacity conditions. The mechanism of filter-pressing, which precipitated sulphide drops at the bottom of the chamber, and penetration of sulphide melts into the country rocks is supported by the same geochemical composition of disseminated and massive ores.

AB - We present new geochemical and mineralogical data from the Southern-2 orebody, located in the South-Western branch of the Talnakh intrusion (Russia) and composed of massive and disseminated sulphides. The Southern-2 orebody consists dominantly of chalcopyrite along with lesser pentlandite and subordinate cubanite, bornite and pyrrhotite, and differs from Cu-rich ores of the Oktyabr'sky deposit due to the absence of moikhukite-talnakhite assemblages. Ores from the Southern-2 orebody are highly enriched in copper, nickel and platinum-group elements (PGEs): Cu up to 28.12 and 10.58 wt%, Ni up to 6.29 and 2.45 wt%, and Pt + Pd up to 220 and 173 ppm in the massive and disseminated ores respectively. The ratios of Cu/Ni = 3.85–7.34 in massive and 2.64–6.58 in disseminated ores. The ratios of the platinum to iridium group elements (PPGE/IPGE) reaches more than 40000. These features indicate an extremely different degree of fractionation of the sulphide melt during the formation of ores. The sequence of crystallization of the PGE minerals (PGMs) on the basis of textural information was as follows: Pt-Pd-Sn (rustenburgite, atokite) → Pd-Cu-Sn (stannopalladinite) → Pt-Fe-Cu-Ni (tetraferroplatinum) → Pd-Ni-As (majakite) → Pd-As (palladoarsenide) → Pd-Pb(Bi) (zvyagintsevite, polarite and Pd5Pb3 unnamed phase) → Au-Cu-Pd (tetra-auricupride and auricupride) → Au-Ag alloys. This is consistent with experimental data on PGE minerals. The PGM assemblage was caused by the evolution of a significantly fractionated sulphide melt that was enriched in Cu, Ni, Pt, Pd, Pb and Au, and as a result produced minerals with peculiar compositions (e.g., Cu-rich stannopalladinite, Pb-rich polarite, Ni-rich palladoarsenide), which do not occur in other ores. Furthermore, Pt-Fe-Cu-Ni alloys are abundant and sperrylite is absent, which is a very common phase in all ores of the Noril'sk area. The composition of pentlandite with Ni/(Ni + Fe) ratios ranging from 0.48 to 0.68 indicates that it formed between 560 °C (Ni-poor) to 500 °C (Ni-rich) and −10.5 to −7 lgfS2, respectively. The PGMs and Au-minerals were formed at temperatures ranging from 550 to 225 °C. The specificity of sulphide (with PGMs) association is due to the evolution of the Cu-rich (and Ni-rich) melt under elevated sulphur fugacity conditions. The mechanism of filter-pressing, which precipitated sulphide drops at the bottom of the chamber, and penetration of sulphide melts into the country rocks is supported by the same geochemical composition of disseminated and massive ores.

KW - Cu-Ni ores

KW - Minerals of platinum-group elements

KW - Noril'sk region

KW - PGE

KW - Southern-2 orebody

KW - Talnakh intrusion

KW - SYSTEM

KW - COPPER-NICKEL

KW - PLACER DEPOSITS

KW - GROUP-ELEMENT MINERALIZATION

KW - PLATINUM-GROUP ELEMENTS

KW - PGE MINERALIZATION

KW - FRACTIONAL CRYSTALLIZATION

KW - PHASE-RELATIONS

KW - NI

KW - ELECTRON-PROBE MICROANALYSIS

UR - http://www.scopus.com/inward/record.url?scp=85083338829&partnerID=8YFLogxK

U2 - 10.1016/j.oregeorev.2020.103525

DO - 10.1016/j.oregeorev.2020.103525

M3 - Review article

AN - SCOPUS:85083338829

VL - 122

JO - Ore Geology Reviews

JF - Ore Geology Reviews

SN - 0169-1368

M1 - 103525

ER -