Insights into ore genesis of Ni-Cu-PGE sulfide deposits of the Noril’sk Province (Russia): Evidence from copper and sulfur isotopes

Abstract

Abstract Combined Cu–S isotope data for Ni-Cu-PGE sufides from the economic deposits hosted in the Noril’sk-1, Talnakh and Kharaelakh intrusions, from the subeconomic deposits in the Chernogorsk, Zub-Marksheider, and Vologochan intrusions, and from the non-economic occurrences in the Nizhny Talnakh intrusion in the Noril’sk Province (Russia), and the J-M Reef in the Stillwater Complex (USA), are presented for the first time. Most sulfide samples including the ores from the Talnakh intrusion and the Stillwater Complex have a restricted range of δ 65 Cu values from − 1.1‰ to 0‰, whereas those from the Kharaelakh and Noril’sk-1 intrusions have more variable δ 65 Cu values of − 2.3‰ to 1.0‰. Samples from the three economic deposits in the Noril’sk Province have distinct mean δ 65 Cu values of –1.56 ± 0.27‰ for Kharaelakh, –0.55 ± 0.41‰ for Talnakh and 0.23 ± 0.28‰ for Noril’sk-1, consistent with those for carbonaceous chondrite and iron meteorites. The variation of δ 65 Cu values is interpreted to represent a primary signature of the ores, although a magmatic fractionation of Cu isotopes and/or assimilation from an external source cannot be ruled out, particularly in the case of the Kharaelakh ores. Collectively the eight investigated intrusions have an overall sulfur δ 34 S range from − 0.7‰ to 13.8‰. Disseminated and massive ores of the same intrusion have similar δ 34 S values. The disseminated and massive ores of the Khraelakh intrusion have a mean δ 34 S value of 12.57 ± 0.54‰ and 12.76 ± 0.42‰, respectively, which are distinctly different from those of the disseminated (10.97 ± 0.44‰) and massive ores (10.88 ± 0.77‰) of the Talnakh intrusion. The different δ 34 S values of the intrusions may be attributed to sulfur fractionation in deep-seated magma chambers rather than at shallow levels or the present emplacement site. The mean δ 34 S value of the disseminated ores from the subeconomic Ni-Cu-PGE deposits and non-economic occurrences spans over 10.5‰, averaging 0.39‰ with a standard deviation of 1.55‰ for the highly contaminated Zub-Marksheider rocks, 6.38 ± 1.89‰ for Nizhny Talnakh, 6.90 ± 1.17‰ for Vologochan and 10.86 ± 0.43‰ for Chernogorsk. Samples from the Zub-Marksheider intrusion have mantle-like S isotope signatures, consistent with a deep-seated origin. Although individual mineralized instrusions have a restricted range the overall trend they define of falling δ 34 S with rising δ 65 Cu values might be a useful indicator of the economic potential of Ni-Cu-PGE sulfide deposits.