REE mineralization in alkaline rhyolites of the Pechalninsky ore field (North-East of Russia)

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Abstract

For the first time (by methods Scanning Electron microscopy, X-ray spectral microanalysis and cathodoluminescence method) REE mineralization studies have been conducted in alkaline rhyolites of the Pechalninsky ore field (North-East of Russia), a potentially larger-volume source of HREE. It is shown that in the direction of fluidity, thin interlayers composed of crystalline aggregates of pyroxenes and/or amphiboles impregnated with a silicate substance alternate in the rock, and ribbon-like thin strips and lace separations of Fe, Ti, and Mn hydroxides that have replaced titanomagnetite (relict secretions of which are partially preserved). Microcrystalline aggregates of pyroxenes and/or amphiboles contain the finest inclusions of REE secretions (5–7 microns), the determination of mineral species of the latter is difficult due to the small particle sizes. Scanning electron microscopy (EMF) has determined that these secretions are REE phosphates. Concentrically zonal and radially radiant REE secretions have been revealed in the relics of titanomagnetite crystals. The first ones are represented by silicates enriched with Yt and REE. In them, the content of REE varies unevenly from the center to the edge. Radially radiant aggregates are represented by oxides and/or carbonates containing REE (La, Ce and Nd predominate). The results obtained can be used in the development of enrichment technology.

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About the authors

A. V. Grigorieva

Institute of Geology of Ore Deposits, Petrography, Mineralogy and Geochemistry of the Russian Academy of Sciences

Author for correspondence.
Email: grig357@mail.ru
Russian Federation, Moscow, 119017 Moscow, Staromonetny per., 35

A. V. Volkov

Institute of Geology of Ore Deposits, Petrography, Mineralogy and Geochemistry of the Russian Academy of Sciences

Email: grig357@mail.ru

Corresponding Member of the Russian Academy of Sciences

Russian Federation, Moscow, 119017 Moscow, Staromonetny per., 35

N. V. Sidorova

Institute of Geology of Ore Deposits, Petrography, Mineralogy and Geochemistry of the Russian Academy of Sciences

Email: grig357@mail.ru
Russian Federation, Moscow, 119017 Moscow, Staromonetny per., 35

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2. Fig. 1. Geological map of the Pechalninskoye ore field according to [7, 8], enlarged fragment. 1 – Early-Middle Jurassic black shale strata (J1-2); 2 – Late Cretaceous alkaline volcanics (K2); 3 – Late Cretaceous granites (Gr); 4 – Pechalninskoye ore occurrence: a – rare metal and REE mineralization; b – epithermal Au–Ag mineralization.

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3. Fig. 2. Textures of mineralized REE trachyrhyolites of the Pechalninsky ore field. Photographs of the studied samples (a–i): a – fluidal trachyrhyolite (sample d–22), b – photograph of thin section (d–22), c – fluidal trachyrhyolite (sample 933), g – photograph of thin section (933), thin-layered trachyrhyolite (sample 994-A89), d – photograph of thin section (994-A89), g – fluidal trachyrhyolite (sample PE-15-2), i – photograph of thin section (PE-15-2).

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4. Fig. 3. Photographs (a–c) and scanning spectrum of ribbon-shaped and lacy segregations of Fe, Mn and Ti hydroxides with small inclusions of REE minerals, the sizes of which do not exceed 10 μm, in alkaline rhyolites of the Pechalninsky ore field (sample D-22).

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5. Fig. 4. Chemical composition and distribution of REE over the area of ​​a large Ce phosphate deposit. Photo in characteristic X-rays.

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6. Fig. 5. Morphology of the precipitate and chemical composition of REE precipitates in titanomagnetite crystals (sample 993).

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