Sulfur-bearing monazite-(Ce) from the Eureka carbonatite, Namibia

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Marco E. Ciriotti
Messaggi: 26570
Iscritto il: ven 25 giu, 2004 11:31
Località: via San Pietro, 55 I-10073 Devesi/Cirié TO - Italy
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Sulfur-bearing monazite-(Ce) from the Eureka carbonatite, Namibia

Messaggio da Marco E. Ciriotti » mer 11 dic, 2019 9:42

Prossima pubblicazione.

Referenza:
▪ Broom-Fendley, S., Smith, M., Andrade, M.B., Ray, S., Banks, D.A., Loye, E., Atencio, D., Pickles, J.R., Wall, F. (2020): Sulfur-bearing monazite-(Ce) from the Eureka carbonatite, Namibia: oxidation state, substitution mechanism, and formation conditions. Mineralogical Magazine, 84, (in press).

Abstract:
Sulfur-bearing monazite-(Ce) occurs in silicified carbonatite at Eureka, Namibia, forming rims up to ~0.5 mm thick on earlier-formed monazite-(Ce) megacrysts. We present X-ray photoelectron spectroscopy (XPS) data demonstrating that sulfur is predominantly accommodated in monazite-(Ce) as sulfate, via a clino-anhydrite-type coupled substitution mechanism. Minor sulfide and sulfite peaks in the XPS spectra, however, also indicate that more complex substitution mechanisms incorporating S2- and S4+ are possible. Incorporation of S6+ through clino-anhydrite-type substitution results in an excess of M2+ cations, which previous workers have suggested is accommodated by auxiliary substitution of OH- for O2-. However, Raman data show no indication of OH-, and instead we suggest charge imbalance is accommodated through F- substituting for O2-. The accommodation of S in the monazite-(Ce) results in considerable structural distortion that may account for relatively high contents of ions with radii beyond those normally found in monazite-(Ce), such as the heavy rare earth elements (REE), Mo, Zr and V. In contrast to S-bearing monazite-(Ce) in other carbonatites, S-bearing monazite-(Ce) at Eureka formed via a dissolution-precipitation mechanism during prolonged weathering, with S derived from an aeolian source. While large S-bearing monazite-(Ce) grains are likely to be rare in the geological record, formation of secondary S-bearing monazite-(Ce) in these conditions may be a feasible mineral for dating palaeo-weathering horizons.
Marco E. Ciriotti

«Things are interesting only in so far as they relate themselves to other things»

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Marco E. Ciriotti
Messaggi: 26570
Iscritto il: ven 25 giu, 2004 11:31
Località: via San Pietro, 55 I-10073 Devesi/Cirié TO - Italy
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Re: Sulfur-bearing monazite-(Ce) from the Eureka carbonatite, Namibia

Messaggio da Marco E. Ciriotti » gio 26 mar, 2020 17:36

Pubblicazione effettuata.

Referenza:
▪ Broom-Fendley, S., Smith, M., Andrade, M.B., Ray, S., Banks, D.A., Loye, E., Atencio, D., Pickles, J.R., Wall, F. (2020): Sulfur-bearing monazite-(Ce) from the Eureka carbonatite, Namibia: oxidation state, substitution mechanism, and formation conditions. Mineralogical Magazine, 84, 35-48.
Marco E. Ciriotti

«Things are interesting only in so far as they relate themselves to other things»

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