Mineralogy and genesis of pyrochlore-apatitite from The Good Hope Carbonatite, Ontario: A potential Nb deposit

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Marco E. Ciriotti
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Iscritto il: ven 25 giu, 2004 11:31
Località: via San Pietro, 55 I-10073 Devesi/Cirié TO - Italy
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Mineralogy and genesis of pyrochlore-apatitite from The Good Hope Carbonatite, Ontario: A potential Nb deposit

Messaggio da Marco E. Ciriotti » sab 05 ott, 2019 5:07

Prossima pubblicazione.

Referenza:
▪ Mitchell, R.H., Wahl, R., Cohen, A. (2020): Mineralogy and genesis of pyrochlore-apatitite from The Good Hope Carbonatite, Ontario: A potential Nb deposit. Mineralogical Magazine, 84, (in press).

Abstract:
The Good Hope carbonatite is located adjacent to the Prairie Lake alkaline rock-carbonatite complex in northwestern Ontario. The occurrence is a heterolithic breccia consisting of diverse calcite, dolomite and ferrodolomite carbonatites containing clasts of magnesio-arfvedsonite + potassium feldspar, phlogopite + potassium feldspar together with pyrochlore-bearing apatitite clasts. The apatitite occurs as angular, boudinaged and schlieren clasts up to 5 cm in maximum dimensions. In these pyrochlore occurs principally as euhedral single crystals (0.1 - 1.5 cm) and can comprise up to 25 vol.% of the clasts. Individual clasts contain compositionally- and texturally-distinct suites of pyrochlore. The pyrochlores are hosted by small prismatic crystals of apatite (~ 100 - 500 μm x 10 - 25 μm) that are commonly flow-aligned and in some instances occur as folds. Allotriogranular cumulate textures are not evident in the apatitites. The fluorapatite does not exhibit BSE-compositional zonation, although UV and cathodoluminescence imagery shows distinct cores with thin (< 50 μm) overgrowths. Apatite lacks fluid or solid inclusions of other minerals. The apatite is rich in Sr (7030 - 13000 ppm) and rare earth elements and exhibits depletions in La, Ce, Pr and Nd (La/NdCN ratios (0.73-1.14) relative to apatite in cumulate apatitites (La/NdCN > 1.5) in the adjacent Prairie Lake complex. The pyrochlore are primarily Na-Ca-pyrochlore of relatively uniform composition and minor Sr contents (< 2 wt.% SrO). Irregular resorbed cores of some pyrochlores are A-site deficient (> 50%) and enriched in Sr (6 - 10 wt.% SrO), BaO (0.5 - 3.5 wt.%), Ta2O5 (1 - 2 wt.%) and UO2 (0.5 - 2 wt.%). Many of the pyrochlores exhibit oscillatory zoning. Experimental data on the phase relationships of haplocarbonatite melts predicts the formation of apatite and pyrochlore as the initial liquidus phases in such systems. However, the texture of the clasts indicates that pyrochlore and apatite did not crystallize together and it is concluded that pyrochlores formed in one magma have been mechanically mixed with a different apatite-rich magma. Segregation of the apatite-pyrochlore assemblage followed by lithification resulted in the apatitites, which were disrupted and fragmented by subsequent batches of diverse carbonatites. The genesis of the pyrochlore apatitites is considered to be a process of magma mixing and not simple in situ crystallization.
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: Mineralogy and genesis of pyrochlore-apatitite from The Good Hope Carbonatite, Ontario: A potential Nb deposit

Messaggio da Marco E. Ciriotti » gio 26 mar, 2020 17:27

Pubblicazione effettuata.

Referenza:
▪ Mitchell, R.H., Wahl, R., Cohen, A. (2020): Mineralogy and genesis of pyrochlore-apatitite from The Good Hope Carbonatite, Ontario: A potential Nb deposit. Mineralogical Magazine, 84, 81-91.
Marco E. Ciriotti

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

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