RARE EARTH PHOSPHATES IN THE KERCH CAVIAR IRONSTONES
A.V. Nekipelova1, E.V. Sokol1, S.N. Kokh1, P.V. Khvorov2
1V.S. Sobolev Institute of Geology and Mineralogy, Siberian Branch of the Russian Academy of Sciences, pr. Akademika Koptyuga 3, Novosibirsk, 630090, Russia
2South Urals Federal Research Center of Mineralogy and Geoecology, Ural Branch of the Russian Academy of Sciences, Ilmeny Reserve, Miass, 456317, Russia
Keywords: Kerch ooidal ironstones, rare earth elements (REE), authigenic LREE phosphates, Pr, Nd, rhabdophane, tristramite, unconventional REE resources
Abstract
The mineralogy and contents of major and trace elements (including REE+Y) in bulk samples and separate size fractions of caviar-like ironstones from the Kamysh-Burun deposit (Kerch iron province) are studied to estimate the contributions of different REE+Y species to the total budget. The analyzed ore samples contain MREE adsorbed on Fe3+-(oxy)hydroxides, as well as LREE authigenic phosphates. The predominant rhabdophane-type (Ce(PO4)nH2O) phases are enriched in La, Pr, Nd, and Ca, depleted in Ce, and free from Th. The REE carriers belong to solid solution series of two main types: LREE(PO4)·nH2O - (Ca,Ce,Th)(PO4)·H2O (rhabdophane-like phase and brockite) or LREE(PO4)·nH2O - (Ca,U,Fe3+)((PO4),(SO4))·2H2O (rhabdophane-like phase and tristramite). REE phosphates occur most often in the ≤ 0.25 mm fractions of ironstones, where average and maximum ΣREE contents ( Xav = 606-1954 ppm; Xmax = 769-3011 ppm) are comparable with the respective amounts in the Chinese industrial clay-type REE deposits. The Kerch ores are commercially attractive unconventional resources of highly demanded Pr and Nd: they can be extracted at relatively low costs, due to high Pr/Ce and Nd/Ce ratios, while low Th and U reduce the environmental risks from stockpiled wastes.
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