Minerals of Fe in the oxidation zone of massive sulfide ore in the South Pechenga structure zone, Kola region: Identification by the Raman spectroscopy
The paper presents data on the study of iron-bearing minerals formed in the oxidation zone of massive sulfide ores. The minerals are represented by two groups: oxides, i. e. goethite and lepidocrocite, and sulfates, i. e. melanterite and rozenit. Mineral identification has been produced by Raman spectroscopy, these data have been confirmed by scanning electron microscopy and X-ray powder diffraction. The resulting Raman spectra have been compared with the spectra of the known database and the results of previous studies of these minerals. Goethite and lepidocrocite are polymorphic modifications formed under the specific conditions by the influence of special solutions. Goethite has diagnostic bands at 243 cm<sup>-1</sup>, 300 cm<sup>-1</sup>, 391 cm<sup>-1</sup>, 480 cm<sup>-1</sup>, 552 cm<sup>-1</sup>, 681 cm<sup>-1</sup>, and 995 cm<sup>-1</sup>, diagnostic bands of lepidocrocite - 252 cm<sup>-1</sup>, 381 cm<sup>-1</sup>, 528 cm<sup>-1</sup>, and 652 cm<sup>-1</sup>. Discovered small crystals in the lepidocrocite veins have been diagnosed as magnetite, with diagnostic bands at 678 cm<sup>-1</sup>, 549 cm<sup>-1</sup>, and 316 cm<sup>-1</sup>. Goethite and lepidocrocite are formed on the surface of a complex pyrrhotite-marcasite aggregate with "bird's-eye" structure. The presence of pyrite and marcasite is confirmed by Raman spectrum which has pyrite bands (343 cm<sup>-1</sup> and 403 cm<sup>-1</sup>) and marcasite bands (323 cm<sup>-1</sup> and 386 cm<sup>-1</sup>). Melanterite and rozenite are formed under the influence of surface water on sulfide ores or other readily degradable iron-bearing minerals, as well as in confined spaces with high humidity. Raman spectra of these minerals well differ from each other allowing them reliably diagnose. There are sulfate anion [SO4]<sup>2-</sup> vibrations in the range of 990-1 010 cm<sup>-1</sup>, and vibrations of the H-O-H in the range of 3 000-4 000 cm<sup>-1</sup> and 1 500-1 700 cm<sup>-1</sup> on the spectra. As a result of the research the authors can certainly confirm that Raman spectroscopy can be used as a reliable method for mineral identification.