Extreme alteration of chevkinite-(Ce) by Pb-CO2-rich fluids: Evidence from the White Tundra Pegmatite, Keivy Massif

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Marco E. Ciriotti
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Extreme alteration of chevkinite-(Ce) by Pb-CO2-rich fluids: Evidence from the White Tundra Pegmatite, Keivy Massif

Messaggio da Marco E. Ciriotti » gio 04 ago, 2022 11:47

Referenza:
▪ Macdonald, R., Bagiński, B., Stachowicz, M., Zozulya, D., Kotowski, J., Jokubauskas, P. (2022): Extreme Alteration of Chevkinite-(Ce) by Pb-CO2-Rich Fluids: Evidence from the White Tundra Pegmatite, Keivy Massif, Kola Peninsula. Minerals, 12, 989.

Abstract:
An unusual hydrothermal alteration scheme was presented for chevkinite-(Ce) from the White Tundra pegmatite (2656 ± 5 Ma), Keivy massif, Kola Peninsula. Pb-CO2-rich fluids initially removed REE and Y from the chevkinite-(Ce), with enrichment in Pb and U. PbO abundances reaching 17.35 wt%. Continued alteration resulted in the altered chevkinite-(Ce) being progressively transformed to a Pb-Ti-Fe-Si phase, which proved, upon EBSD analysis, to be almost totally amorphous. Pb enrichment was accompanied by a loss of LREE, especially La, relative to HREE, and the development of strong positive Ce anomalies. A notably U-rich aeschynite-(Y), with UO2 values ≤7.67 wt%, crystallized along with the chevkinite-(Ce). Aeschynite-(Y) with a lower UO2 value (3.91 wt%) and bastnäsite-(Ce) formed during alteration. The formation of bastnäsite-(Ce) rather than cerussite, which might have been expected in a high Pb-CO2 environment, is ascribed to the fluids being acidic.

NdR: probably euxenite-(Ce)...
Marco E. Ciriotti

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