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, Norilsk province, Russia

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 ( (super 187) Os/ (super 188) Os = 0.1283 + or - 0.0054, gamma Os (sub (t)) = 1.1) and disseminated ( (super 187) Os/ (super 188) Os = 0.1331 + or - 0.0052, gamma Os (sub (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., (super 187) Os/ (super 188) Os = 0.1366 + or - 0.0037, gamma Os (sub (t)) = 7.6 and (super 187) Os/ (super 188) Os = 0.1350 + or - 0.0036, gamma Os (sub (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 (delta (super 34) S) of disseminated and massive PGE-Cu-Ni sulfide ores at Kharaelakh (12.2 + or - 0.5 per mil and 12.7 + or - 0.1 per mil, respectively) are notably different from those at Talnakh (10.8 + or - 0.1 per mil and 10.9 + or - 0.1 per mil, respectively), indicative of distinct involvement of heavy sulfur during formation of PGE-Cu-Ni sulfide ores. The restricted range of delta (super 34) S values can be employed as useful fingerprint in the assessment of the potential of prospective ore deposits.