Hafnium isotope composition of zircons from dunites of the Nizhny Tagil and Guli Massifs (Russia)

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Results of dating of thorianite and baddeleyite from carbonatites of the Guli Massif, Russia

The isotopic–geochronological features of thorianite and baddeleyite from carbonatites of the Guli massif, located within Maimecha–Kotui province in the north of the Siberian Platform, are characterized for the first time. The economic complex platinum-group element (PGE) and gold placer deposits are closely related to the Guli massif. Similar geochronological data for thorianite (250.1 ± 2.9 Ma, MSWD = 0.09, n = 36) and baddeleyite (250.8 ± 1.2 Ma, MSWD = 0.2, n = 6) obtained by two different methods indicate that carbonatites were formed close to the Permian–Triassic boundary and are synchronous with tholeiitic flood basalts of the Siberian Platform.4 page(s

Hafnium-neodymium constraints on source heterogeneity of the economic ultramafic-mafic Noril'sk-1 intrusion (Russia)

The ultramafic-mafic Noril'sk-1 intrusion in Polar Siberia (Russia) hosts one of the world's major platinum-group-element (PGE)-CuNi sulphide deposits. In situ Hf-isotope analyses of zircon and baddeleyite, combined with whole-rock Nd-isotope results, identify three distinct clusters of HfNd isotope values restricted to different lithological units (e.g., gabbro-diorite, unmineralised layered sequence gabbros, and mineralised portions, represented by ultramafic and taxitic-textured rocks). Hf-isotope signatures of zircon and baddeleyite from unmineralized mafic rocks (εHf from 7.3±1.1 to 11.4±0.3) reflect the dominant role of mantle-derived magmas and suggest that a juvenile mantle was one of the main sources for the ultramafic-mafic Noril'sk-1 intrusion. The less radiogenic Hf-isotope values for zircons from mineralised rocks (εHf from 4.9±1.4 to 6.4±1.2) and gabbro-diorite (εHf-1.2±1.9) are indicative of involvement of distinct source components, possibly equivalent to a subcontinental lithospheric mantle and a continental crust, respectively. The significant range in the initial ¹⁷⁶Hf/¹⁷⁷Hf values of unmineralised rocks and mineralised lithologies indicates interaction of distinct magma sources during formation of the Noril'sk-1 intrusion. Our new findings, in conjunction with whole-rock Nd-isotope results, imply that economic intrusions hosting PGE-CuNi deposits of the Noril'sk area have a far more complex magmatic history than is commonly assumed.11 page(s

U-Pb age and Hf-Nd-Sr-Cu-S isotope systematics of the Binyuda and Dyumtaley ore-bearing intrusions (Taimyr, Russia)

We present for the first time U-Pb age data and Hf-Nd-Sr-Cu-S isotope signatures for lithologies and associated sulphide ores from the Binyuda and Dyumtaley ultramafic-mafic intrusions located in the limits of the Taimyr Peninsula (Russian Arctic). Zircons are characterized by similar U-Pb ages (245.7 ± 12 Ma at Binyuda and 256.2 ± 0.89 Ma at Dyumtaley), indicating for their close temporal relationship with tholeiite-basalt magmatism of the Siberian Platform. Silicate materials show distinct Hf-Nd-Sr isotope signatures (εHf = -3.8 ± 1.3, ɛNd = -3.8±0.4 and87Sr/86Sri = 0.70588 ± 0.00013 at Binyuda and εHf = 9.5 ± 2.5, ɛNd = 4.2 ± 0.7 and87Sr/86Sri = 0.70474 ± 0.00020 at Dyumtaley). The determined Hf-Nd-Sr variability is interpreted to represent a primary source signature of the lithological units. An important role of the juvenile component is clearly pronounced for the Dyumtaley intrusion, whereas a major contribution from a subcontinental mantle or essentially crustal source is inferred for the Binyuda intrusion. These signatures clearly manifest deviation from those typical of the ore-bearing intrusions from the Noril’sk Province, characterized by protracted magmatic evolution with significant time span of zircon and baddeleyite U-Pb ages (from ca. 350 to 230 Ma), relatively constant εNd values (ca. +1 ± 0.5), highly heterogeneous εHf (from -2.3 to 16.3) and87Sr/86Sri (from 0.70552 to 0.70798). In terms of Cu-isotopes, the majority of the analyzed sulphide samples fall within a tight cluster of δ65Cu values (-0.66 ± 0.24‰ at Binyuda and 0.4 ± 0.1‰ at Dyumtaley), characteristic of the ores from the economic Ni-Cu-PGE deposits at Talnakh. In contrast, notable difference in δ34 S values typifies sulphide ores at Binyuda and Dyumtaley (1.5 ± 0.4 and 11.4 ± 0.6‰ respectively). We suggest that the Cu-S isotope characteristics of the sulphide ores reflect their primary signature rather than a result of mixed sources or magmatic fractionation of stable isotopes. However, the latter possibility cannot be ruled out for heavy S isotope composition of sulphide ore at Dyumtaley. Samples of the disseminated sulphide ore from the Dyumtaley intrusion approach δ34S-δ65Cu parameters of the economic ores at Talnakh (Noril’sk Province) and might be considered as the most prospective for targeting the massive Ni-Cu-PGE sulphide ores

Chemical and isotopic composition of Os-rich allois and sulfides from the Evander Goldfield of the Witwatersrand Basin (South Africa)

We firstly report compositional and isotope-geochemical characteristics of Ru-Os-Ir(-Pt) alloys, Ru-Os sulfides and polycomponent solid solutions of the system Ru-Os-Ir-Pt (±Fe) derived from the Kimberley Reef within Evander Goldfield of the Witwatersrand Basin (South Africa). The study employed electron microprobe analysis and laser ablation attached to multiple collector inductively coupled plasma mass spectrometry. The obtained results are consistent with: 1) high-temperature formation of the studied platinum-group minerals, 2) sub- hondritic Archean source of platinum-group elements, 3) similarity of the initial Os-isotope composition in coexisting Os-rich alloys and Ru-Os sulfides and 4) significant Os-isotope variations in individual Ru-Os-Ir alloys, Ru-Os sulfides and polycomponent solid solutions of the Ru-Os-Ir-Pt (±Fe) system. 187Os/188Os ages are used to discriminate between different models of noble metal mineralization origin within the Witwatersrand basin