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Vol. 20 (2017 year), No. 1, DOI: 10.21443/1560-9278-2017-20-1/1
Kompanchenko A. A., Voloshin A. V., Sidorov M. Yu.
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–1, 300 cm–1, 391 cm–1, 480 cm–1, 552 cm–1, 681 cm–1, and 995 cm–1, diagnostic bands of lepidocrocite – 252 cm–1, 381 cm–1, 528 cm–1, and 652 cm–1. Discovered small crystals in the lepidocrocite veins have been diagnosed as magnetite, with diagnostic bands at 678 cm–1, 549 cm–1, and 316 cm–1. 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–1 and 403 cm–1) and marcasite bands (323 cm–1 and 386 cm–1). 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]2– vibrations in the range of 990–1 010 cm–1, and vibrations of the H–O–H in the range of 3 000–4 000 cm–1 and 1 500–1 700 cm–1 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.
(in Russian, ñòð.9, fig. 5, tables. 3, ref 7, Adobe PDF, Adobe PDF 0 Kb)
Vol. 21 (2018 year), No. 1, DOI: 10.21443/1560-9278-2018-21-1
Kozlov E. N., Fomina E. N., Sidorov M. Yu., Kirkin V. V.
Genesis of apocarbonatitic titanium metasomatites of the Petyayan-vara rare-earth occurrence (Vuoriyarvi, the Kola Region)
The objects of the study are apocarbonatitic titanium metasomatites ("titanium carbonatites") associated with the rare earth carbonatites of the Petyayan-Vara area of the Vuoriyarvi complex (the Kola region). In this paper, the following mechanism for the formation of these rocks has been substantiated based on the agreed results of mineralogical and geochemical studies. Prior to the onset of carbonatite genesis, a fluorine-enriched fluid phase originated in the lower horizons of the complex passed along the deep-permeating fracture system of several hundred meters length up to the level of the modern erosion surface. It transported Al, Fe2+, Mg, Ti, P into the pyroxenites and Si, Ca and Na out of them, as a result of which the pyroxenites were transformed into giant-grained phlogopite rocks – glimmerites. The most probable source of this fluid is alkaline aluminosilicate magma. Then carbonate melts intruded along the same fractures. In the course of carbonatite genesis, F-fluid caused a local migration of K, Al, Si, Fe, P, Ti, Nb, Ta, Zr, Hf and HREE out of glimmerites into igneous dolomite carbonatites, which led to the formation of apocarbonatitic titanium metasomatites. They represent several paragenetic associations superimposed on each other, the mineral composition and the formation sequence of which correspond to the metasomatic column zones directly observed within the contact "carbonatite – altered pyroxenite". The separation of HFSE and REE is controlled by the same metasomatic column: Ti, Nb and Ta were accumulated in titanium carbonatites, i. e. in associations of the frontal and intermediate zones, and Zr, Hf and HREE – in apatitized fields corresponding to the rear zone of the column. Accordingly, the fractionation of these elements occurred due to the "fluid – rock" interaction. Subsequently, the same long-lived fractures served as a channel for REE-Sr-Ba-S fluids, but the recrystallization caused by K-Al-Si-Ti-F-metasomatism made titanium carbonatites dense and fine-grained in texture, what, in most cases, "protected" these rocks from the influences of later processes.
(in Russian, ñòð.13, fig. 5, tables. 0, ref 26, adobe PDF, adobe PDF 0 Kb)