Monazite-(Ce) and xenotime-(Y) microinclusions in fluorapatite of the pegmatites from the Volta Grande mine-Minas Gerais

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Marco E. Ciriotti
Messaggi: 25910
Iscritto il: ven 25 giu, 2004 11:31
Località: via San Pietro, 55 I-10073 Devesi/Cirié TO - Italy
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Monazite-(Ce) and xenotime-(Y) microinclusions in fluorapatite of the pegmatites from the Volta Grande mine-Minas Gerais

Messaggio da Marco E. Ciriotti » mar 25 giu, 2019 12:52

Prossima pubblicazione.

Referenza:
▪ Alves, F.E.A., Neumann, R., Ávila, C.A., Leite Faulstich, F.R. (2019): Monazite-(Ce) and xenotime-(Y) microinclusions in fluorapatite of the pegmatites from the Volta Grande mine, Minas Gerais state, southeast Brazil, as witnesses of dissolution-reprecipitation process. Mineralogical Magazine, 83, (in press).

Abstract:
Fluorapatite with monazite-(Ce) and xenotime-(Y) microinclusions occurs in the lithium-caesium-tantalum (LCT) pegmatite body A of the Volta Grande mine, Minas Gerais state, Southeast Brazil. The fluorapatite displays faint zoning, detected mainly by cathodoluminescence. Electron probe (EPMA) and laser ablation (LA-ICPMS) analyses indicate that zoning in the fluorapatite corresponds to variation in Mn and rare earth element (REE) content. Such compositional variation is attributed to partial removal of the REE from the fluorapatite structure during a dissolution-reprecipitation process, forming monazite-(Ce) and xenotime-(Y) microinclusions in the REE-depleted zones of the fluorapatite. These inclusions exhibit an inherited geochemical signature, manifested by low Th and U concentrations when compared to monazite and xenotime crystallised from melts. Rhodochrosite and calcite inclusions are also associated with monazite-(Ce) and xenotime-(Y) and are probably products of the same process, recycling Ca, Mn, and CO32- from the fluorapatite through the following reaction:
[Ca(5-2a-b-1/2x),Naa,(Y + REE)a,Mnb][(PO4)3-x(CO3)x(F)] + Fluid[a(2Ca2+ + P5+) + (x-b)(Ca2+) + H2O)] → [Ca5(PO4)3(F,OH)] + a[(Y + REE)PO4] + b[Mn(CO3)] + (x-b)[Ca(CO3)] + Fluid a[Na+] (1)
Based on new fluid inclusion analyses, we propose that a hot (T > 204.5°C), salty (16 wt.% eq. NaCl, attributed to LiCl), hydrous fluid mediated the dissolution-reprecipitation of the fluorapatite. This fluid corresponds to similarly described Li-rich fluids which were suggested to have re-equilibrated the mineralogical assemblage at the Volta Grande mine.
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: 25910
Iscritto il: ven 25 giu, 2004 11:31
Località: via San Pietro, 55 I-10073 Devesi/Cirié TO - Italy
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Re: Monazite-(Ce) and xenotime-(Y) microinclusions in fluorapatite of the pegmatites from the Volta Grande mine-Minas Ge

Messaggio da Marco E. Ciriotti » lun 02 set, 2019 15:14

Pubblicazione effettuata.

Referenza:
▪ Alves, F.E.A., Neumann, R., Ávila, C.A., Leite Faulstich, F.R. (2019): Monazite-(Ce) and xenotime-(Y) microinclusions in fluorapatite of the pegmatites from the Volta Grande mine, Minas Gerais state, southeast Brazil, as witnesses of dissolution-reprecipitation process. Mineralogical Magazine, 83, 595-606.
Marco E. Ciriotti

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

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