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  • 1
    Publication Date: 2020-05-30
    Description: Layers rich in chromian spinel (Cr-spinel) occur in numerous differentiated and layered intrusions. These layers are often characterized by elevated and even economic concentrations of platinum-group-elements (PGEs), but only scarce sulfide mineralization. One particular type of such lithology occurs in the roof parts of the Norilsk-type differentiated intrusions (Russia) and is referred to as the “sulfide-poor PGE ores”. We investigated rocks containing variable enrichments in Cr-spinel, sulfides, and platinum-group minerals (PGMs) from two sections of the upper zone of the Norilsk-1 intrusion, with a focus on Cr-spinel. The rocks are dominated by two lithological types: (1) leucogabbro/troctolitic and (2) olivine-gabbro. Fine-grained (5–100 μm) disperse disseminations with varying modal abundances of Cr-spinel are characteristic for the rocks studied. Those abundances range from scarce mineralization through to very dense (up to 30 vol. % Cr-spinel) cloud-like accumulations. However, compact-grained accumulations and cumulate-like textures, which are typical for chromitites of layered intrusions, are not characteristic for the studied rocks. Instead, the disseminations exhibit chain- and trail-like alignments of Cr-spinel grains, which cross the boundaries between enclosing silicates, and sub-circular arrangements. The study revealed millimeter-scaled patchy distribution of Cr-spinel compositions within a given dissemination with Cr-spinel chemistry being strongly correlated with a kind of the enclosing silicate. (1) In unaltered rocks, plagioclase hosts more magnesian Cr-spinel (Mg# 30–60), while Cr-spinel in mafic minerals is less magnesian (Mg# 18–35). (2) In altered rocks, more magnesian Cr-spinel is hosted by less altered silicates, while strongly altered silicates mainly host less magnesian Cr-spinel. Systematics of trivalent cations exhibits divergent trends, even on a scale of a thin section, and depends on a kind of hosting lithology. Leucogabbro/troctolite lithologies contain Cr-spinel with anomalously low Fe3+ and extremely high Ti contents, whereas Cr-spinel from olivine-gabbro lithologies have moderate Fe3+ and moderately-high Ti contents. It is envisaged that crystallization of Cr-spinel and their host rocks occurred from viscous mingled magmas, which had different compositions and redox state. Subsequent processes involved (1) high-temperature re-equilibration of Cr-spinel with enclosing silicates and (2) post-magmatic alteration and partial recrystallization of Cr-spinel. During these processes, Cr-spinel was losing Mg and Al and gaining Fe and Ti. These chemical trends are generally coincident with those established for other intrusions worldwide, but the upper zone of the Norilsk-1 intrusion seems to possess an exceptional variety of Cr-spinel compositions, not recorded elsewhere.
    Electronic ISSN: 2075-163X
    Topics: Geosciences
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  • 2
  • 3
    Publication Date: 2023-06-07
    Description: Abstract
    Description: This dataset comprises the analyses of the intraoceanic arc rocks of the Olyutorsky terrain: major elements, minor elements, platinum-group elements, Rb-Sr, Sm-Nd, Lu-Hf and Pb-Pd isotopic systems. Samples are late Cretaceous in age and comprise picrites from the Tumrok and Valaginsky Ranges, and picrites, magnesian basalts and basalts from the Koryak Highlands. Major elements were measured by XRF, minor/trace elements by ICP-MS at the University of Tasmania (in 2019) and the Russian Geological Institute (in 2015); platinum-group elements were measured by ICP-MS using the Ni sulfide fire assay-isotope dilution method at the Seoul National University. Radiogenic (Sr-Nd-Hf-Pb) isotope compositions were determined at the University of Melbourne and the Institute of the Earth’s Crust, Irkutsk, using multi-collector ICP-MS in 2019. A subset of these data were originally published as a supplement to Kutyrev et al. (2021), Primitive high-K intraoceanic arc magmas of Eastern Kamchatka: Implications for Paleo-Pacific tectonics and magmatism in the Cretaceous, Earth-Science Reviews 220, 103703, https://doi.org/10.1016/j.earscirev.2021.103703. This work was funded by the Ministry of Science and Higher Education of the Russian Federation (Grant No. 075-15-2019-1883), The National Research Foundation (NRF) of Korea (Grant No. 2019R1A2C1009809A) and the Russian Science Foundation (Grant No. 21-17-00122).
    Description: Other
    Description: The DIGIS geochemical data repository is a research data repository in the Earth Sciences domain with a specific focus on geochemical data. The repository archives, publishes and makes accessible user-contributed, peer-reviewed research data in standardised form (EarthChem Team, 2022) that fall within the scope of the GEOROC database. All submissions of new data will be considered for inclusion in the GEOROC database. It is hosted at GFZ Data Services through a collaboration between the Digital Geochemical Data Infrastructure (DIGIS) for GEOROC 2.0 (http://digis.geo.uni-goettingen.de) and the GFZ German Research Centre for Geosciences.
    Keywords: major elements ; minor elements ; platinum-group elements ; Rb-Sr isotopes ; Sm-Nd isotopes ; Lu-Hf isotopes ; Pb-Pb isotopes ; magnesian basalts ; basalts ; picrites ; EARTH SCIENCE 〉 SOLID EARTH 〉 GEOCHEMISTRY ; Phanerozoic 〉 Mesozoic 〉 Cretaceous 〉 Late/Upper Cretaceous
    Type: Dataset , Dataset
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