Extreme Alteration of Chevkinite-(Ce) by Pb-CO 2 -Rich Fluids: Evidence from the White Tundra Pegmatite, Keivy Massif, Kola Peninsula
An unusual hydrothermal alteration scheme was presented for chevkinite-(Ce) from the White Tundra pegmatite (2656 ± 5 Ma), Keivy massif, Kola Peninsula. Pb-CO 2 -rich fluids initially removed REE and Y from the chevkinite-(Ce), with enrichment in Pb and U. PbO abundances reaching 17.35 wt%. Continue...
| Published in: | Minerals |
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| Main Authors: | , , , , , |
| Format: | Article in Journal/Newspaper |
| Language: | English |
| Published: |
MDPI AG
2022
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| Subjects: | |
| Online Access: | https://doi.org/10.3390/min12080989 https://doaj.org/article/0ffae3f2d272462396008f61a8f2c187 |
| Summary: | An unusual hydrothermal alteration scheme was presented for chevkinite-(Ce) from the White Tundra pegmatite (2656 ± 5 Ma), Keivy massif, Kola Peninsula. Pb-CO 2 -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 UO 2 values ≤7.67 wt%, crystallized along with the chevkinite-(Ce). Aeschynite-(Y) with a lower UO 2 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-CO 2 environment, is ascribed to the fluids being acidic. |
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