Belogub, Elena V.;
Shilovskikh, Vladimir V.;
Novoselov, Konstantin A.;
Blinov, Ivan A.;
Filippova, Ksenia A.
Authigenic rhabdophane from brown iron ore of the oxidation zone of the Babaryk massive sulfide occurrence (South Urals): scanning electron microscope (SEM) and electron backscattered diffraction (EBSD) study
Sie können Bookmarks mittels Listen verwalten, loggen Sie sich dafür bitte in Ihr SLUB Benutzerkonto ein.
Medientyp:
E-Artikel
Titel:
Authigenic rhabdophane from brown iron ore of the oxidation zone of the Babaryk massive sulfide occurrence (South Urals): scanning electron microscope (SEM) and electron backscattered diffraction (EBSD) study
Beteiligte:
Belogub, Elena V.;
Shilovskikh, Vladimir V.;
Novoselov, Konstantin A.;
Blinov, Ivan A.;
Filippova, Ksenia A.
Erschienen:
Copernicus GmbH, 2021
Erschienen in:
European Journal of Mineralogy, 33 (2021) 5, Seite 605-620
Beschreibung:
Abstract. Rhabdophane(Ce0.34−0.43Nd0.13−0.14Ca0.06−0.29La0.08−0.11Y0.05−0.12Pr0.03−0.05Sm0.02−0.05Gd0.02−0.05Fe0−0.04Dy0.00-0.01)0.97-1.01((P0.69−0.96S0.04−0.31)1.00O4)⚫H2O is found in a Fe3+-oxyhydroxide nodule (brown iron ore)collected from the upper part of the oxidation profile of the Babarykmassive sulfide occurrence (South Urals, Russia) at a 1.6 m depth. Thestructural and microtextural features of rhabdophane are revealed byelectron backscattered diffraction (EBSD); the chemical composition anddistribution of the main components are determined on a scanning electronmicroscope (SEM) equipped with an energy-dispersive analyzer (EDA); the bulkcontents of rare earth elements (REEs) and other elements in rock samples are analyzed usinginductively coupled plasma mass spectrometry (ICP-MS). Rhabdophane formsspherulitic aggregates up to 35 µm in size with a fine-grained coreand radial radiant rims composed of prismatic crystals. The chaoticallyoriented aggregates of its particles of various sizes including prismaticcrystals and spherulitic intergrowths also fill fractures up to 200 µm long and 20–30 µm thick in goethite. The zonal radial radiantstructure of the rhabdophane aggregates and their occurrence in fractures ofgoethite unambiguously indicate the authigenic origin of rhabdophane. Thechemically heterogeneous rhabdophane grains always contain Y, Ca and S andrarely Fe and Sr and are Th- or U-free. Contrasting zonation of Ca, S and Ycontents is characteristic of spherulites. The band contrast of the EBSDpatterns shows a good crystallinity of prismatic crystals regardless of thechemical composition even for Ca–S-rich zones. On the other hand, the Ca-and S-rich fine-grained centers of the spherulites do not yield anydistinguishable diffraction patterns. There is a strong negative correlationin pairs (Ca+Sr)–P and (REEs+Y)–S and a positive correlation inpairs (Ca+Sr)–S and (REEs+Y)–P, which indicates the isomorphismaccording to the scheme (REEs+Y)3+ + (PO4)3−↔ (Ca+Sr)2+ + (SO4)2−. Thus, the chemicalcomposition of rhabdophane does not completely correspond to therhabdophane–tristramite/brockite series because of the absence oftetravalent U or Th. In contrast to similar samples from the deeper part ofthe oxidation zone, the brown iron ore with rhabdophane is enriched in light rare earth elements (LREEs)and P. The REEs were probably sourced from ore-bearing volcanomictic rocks,while P could also have been derived from the soil. The enrichment in REEs and Pand the formation of rhabdophane are related to the alternation of dry and wetperiods, the P input, and sorption–desorption of REEs fromFe3+ oxyhydroxides and/or clay minerals due to pH changes and variablecomposition of pore water.