| Abstrakt: |
We present δ60Ni values for black shales, determined by double-spike MC-ICP-MS. The samples comprise Paleoproterozoic Talvivaara Ni–Zn–Co–Cu black shales from Finland, Neoproterozoic black shales from the Teplá-Barrandian Unit, Czech Republic, Early Cambrian Ni–Mo-rich black shales from the Yangtze Craton, and Devonian Ni–Zn–PGE black shales from Yukon, Canada. In addition, the sample set includes a black smoker sample from the Logatchev hydrothermal field, Mid-Atlantic Ridge. The δ60Ni values vary from − 0.84 ± 0.09 to + 0.62 ± 0.04‰ (2SD) with a median of − 0.10‰ (n = 28). Ni isotopic compositions were predominantly lighter than those of abiotic terrestrial and extraterrestrial samples (0.15 and 0.27‰), mantle (0.23‰, Gall et al. 2017), present-day seawater (1.44‰, Cameron and Vance 2014), dissolved Ni from riverine input (0.84‰, Cameron and Vance 2014), ferromanganese crusts (0.9–2.5‰, Gall et al. 2013), Devonian/Mississippian organic-rich marine sediments, lower Jurassic organic-rich marine sediments (0.2–2.5‰, average 0.92‰, n = 18, Porter et al. 2014), and euxinic sediments of the Black Sea (0.14–0.51‰, Vance et al. 2016). However, the range of δ60Ni values in our black shale samples was close to that of the weathering products of mafic/ultramafic rocks (ore and soil samples) ranging from − 0.60 to + 0.30‰ (Ratié et al. 2015; Spivak-Birndorf et al. 2018), Ni-sulfide ores hosted by Archean komatiites from Australia and Canada (− 0.10 to − 1.03‰, average − 0.70‰, n = 8, Gueguen et al. 2013), and Archean Ni-rich magmatic sulfides from Zimbabwe (− 0.28 to − 0.47‰, n = 6, Hoffman et al. 2014). Based on our observations and considering the extremely low contribution of direct biological uptake of Ni, and a dominant Ni residence in early Fe/Ni-sulfides, we suggest that our mostly light Ni isotopic compositions in metal-rich black shales result from sulfidization of organic matter and Ni removal into sulfides. [ABSTRACT FROM AUTHOR] |
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