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Identity HelpType of Pyrochlore

2nd Oct 2017 02:21 UTCReiner Mielke Expert

Is it possible to narrow down what species of pyrochlore this might be from this analysis? It is from here: https://www.mindat.org/loc-246802.html

Thank You.

2nd Oct 2017 02:32 UTCPavel Kartashov Manager

Any pyrochlore unable to contain so much iron. If this impurity is represented by ilmetie, this would able to explain elevated Ti content. Try to obtain pure spectrum.

2nd Oct 2017 13:12 UTCJohan Kjellman Expert

I was also jumping at the high Fe.

cheers

2nd Oct 2017 20:02 UTCJeff Weissman Expert

Both fluorcalciopyrochlore, (Ca,Na)2(Nb,Ti)2O6F, and hydrocalciopyrochlore, (Ca,Na,U,□)2(Nb,Ti)2O6(OH), can accept titanium as impurities in the B site, according to the formulas listed here on MinDat. As Pavel suggests, and also Johan, the iron is unlikely to occur at these levels in a pyrochlore structure - I think we are looking at a mixture of hematite and/or magnetite (and possibly and/or ilmenite) with a uranian- titanian-pyrochlore. Without further analysis impossible to tell what the fluorine or hydroxyl content may be. Pavel, what are the maximum levels of U and Ti that can be accommodated in the pyrochlore structure?

Could the U and Ti (and Fe) be in brannerite instead?

2nd Oct 2017 21:46 UTCRichard Gunter Expert

Hi Jeff:

The Ti impurities in Pyrochlore can be a function of petrogenesis. A carbonatite Pyrochlore such as this sample may have a different Ti impurity level than a pegmatitic Pyrochlore such as the McDonald Mine Hydrocalciopyrochlore with 13.5 wt % TiO2 in the structure.

2nd Oct 2017 22:58 UTCPavel Kartashov Manager

Usual early carbonatitic pyrochlore group member is hattchetolite with (U+Th)O₂ ~25-26 mas.%, enriched with Ti and Ta. At later stages of hydrotermal alteration it changed by usual Low-ti and -Ta and almost U-free pyrochlore sensu stricto.

I am think, this pyrochlore is close to hatchettolite with admixture of an iron phase. Some Ta is hidden under Si peak. But its real content some low for typical hatchettolites (absence Ta peaks at 8.2 and 9.4 keV). In old kind times it would be named simple betafite.

The highest UO₂ content observed by me personally was 53 mas.% - https://www.mindat.org/photo-230522.html (the lower spectrum), and I am sure that this isn't the limit.

The highest TiO₂ content observed by me personally was in oxyuranbetafite (https://www.mindat.org/photo-355613.html). I don't remember weight percentage now and will look for it tomorrow.

3rd Oct 2017 00:59 UTCReiner Mielke Expert

The analysis was done on a single octahedron of pyrochlore, however the pyrochlore is associated with magnetite. Maybe there is some magnetite on the surface?

3rd Oct 2017 01:55 UTCPavel Kartashov Manager

It is rather limonite films on surface. You may to wash the same crystal in hot solution of EDTA or in HNO₃ and reanalyze it.

Here is the same particle of elpidite in intergrowth with synchisite-(Nd):

initial

after night into cold EDTA solution

and after 15 min into 1m HNO₃

Finally only zircon grains remained the brightest in BSE phase (initially they were invisible besides of more bright synchisite inclusions).

3rd Oct 2017 02:46 UTCReiner Mielke Expert

Hello Pavel,

Limonite makes more sense. There was also pyrrhotite present which probably oxidized in the drying process ( after having removed calcite with HCl) and ended up on the pyrochlore.

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