Re-Os AND S ISOTOPE CONSTRAINTS ON TIMING AND SOURCE HETEROGENEITY OF PGE-Cu-Ni SULFIDE ORES: A CASE STUDY AT THE TALNAKH ORE JUNCTION, NORIL'SK PROVINCE, RUSSIA

Abstract

The ultramafic–mafic Noril’sk-type intrusions in the northern part of Siberia, in Russia, host some of the world’s major economic platinum-group-element (PGE)–Cu–Ni sulfide deposits. We present the results of Re–Os and S isotope systematics of PGE–Cu–Ni sulfide ores associated with the economic Talnakh and Kharaelakh intrusions within the Talnakh ore junction, Noril’sk Province. At Kharaelakh, Re–Os isotope analyses of disseminated and massive PGE–Cu–Ni sulfide ores identify distinct sources of sulfide mineralization, with Re–Os isochron ages that cluster around 247 Ma. Different initial Os isotope compositions of massive (187Os/188Os = 0.1283 ± 0.0054, γOs(t) = 1.1) and disseminated (187Os/188Os = 0.1331 ± 0.0052, γOs(t) = 4.9) sulfide ores at Kharaelakh indicate either a less contaminated nature of the massive orebody with respect to sulfide disseminations or distinct isotope sources involved in their generation. At Talnakh, Re–Os isotope systematics of massive and disseminated ores show broadly similar patterns ( e.g., 187Os/188Os = 0.1366 ± 0.0037, γOs(t) = 7.6 and 187Os/188Os = 0.1350 ± 0.0036, γOs(t) = 6.4, respectively), indicating their similar sources, likely of mantle origin. Combined with new geochronological and isotope-geochemical data on zircon, the Re–Os isotope systematics of sulfide ores are consistent with protracted evolution of ultramafic–mafic magmas at deep-seated staging chambers in the Noril’sk region, which served as the favorable factor for accumulation of ores of unique scales and concentrations. Sulfur isotope values (δ34S) of disseminated and massive PGE–Cu–Ni sulfide ores at Kharaelakh (12.2 ± 0.5‰ and 12.7 ± 0.1‰, respectively) are notably different from those at Talnakh (10.8 ± 0.1‰ and 10.9 ± 0.1‰, respectively), indicative of distinct involvement of heavy sulfur during formation of PGE–Cu–Ni sulfide ores. The restricted range of δ34S values can be employed as useful fingerprint in the assessment of the potential of prospective ore deposits.