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Identity HelpChevkinite - location help needed

22nd Jun 2014 21:05 UTCChristopher O'Neill

Hello,

This seems to be an older specimen that was originally acquired as gadolinite however, I send a sample for EDS analysis and it came back as Chevkinite.

To me it seems to match the specimens from the Urals in Russia, with the internal reddish orange reflections as in: http://www.mindat.org/photo-90962.html

I was wondering if anyone out there was familiar enough with Chevkinite to help with identifying the proper location?

There is some Al in the formula, I was wondering if this can be used to help with the location as well.

I can provide a few more pictures if needed.

22nd Jun 2014 21:41 UTCReiner Mielke Expert

The high aluminum I would say suggests you have a mixture containing allanite-ce. Was there no locality info with the sample?

22nd Jun 2014 23:12 UTCChristopher O'Neill

Reiner,

Norway, however the label stated gadolinite as well.

The matrix (see pic) doesn't appear to be like the other Norway chevkinites, but then again I am totally unfamiliar with this mineral and its various assemblages.

Chris

23rd Jun 2014 00:51 UTCReiner Mielke Expert

Is that matrix or an alteration crust? Do you have a side view of the sample. What is the mineralogy of the matrix? Also there are a lot of gadolinite localities in Norway and very few pictures of matrix so it could still have come from Norway just that the species ID was wrong because it was based on visual.

23rd Jun 2014 03:47 UTCChristopher O'Neill

Reiner,

Here are additional photos and close-ups of the orange matrix.

It does seem botryoidal-like in some areas and fine grained powdery in others. I have no idea as to what it might be.

23rd Jun 2014 12:08 UTCKnut Edvard Larsen 🌟 Manager

"The matrix doesn't appear to be like the other Norway chevkinites"

Yes, all known chevkinites from Norway has been found in alkaline syenites or in syenite pegmatites (the first was found in 1970s) and has a different matrix. The alteration crust suggest a granite pegmatite.

Is there more infomation on the label ? Year of acquisition, name of dealer ?

23rd Jun 2014 15:21 UTCChristopher O'Neill

Thanks Knut,

Sorry, I don't have any other details regarding this specific specimen however, it was part of a flat of old specimens dating from the 1950's or earlier so this may rule out Norway.

Visually, this specimen seems a closer match to the Russian specimens.

Looking at http://www.mindat.org/photo-210251.html - it shows an orange alteration crust from syenite-pegmatite.

As Pavel Kartshov mentions in the details for his Russian specimens:

"alteration rim, composed by mixture of yellow Th-rich Bastnasite-(Ce) and black tabular Ilmenite."

Perhaps the next step would be to have the alteration crust analyzed.

Chris

23rd Jun 2014 15:26 UTCReiner Mielke Expert

Looks like an alteration crust so it really isn't the matrix. In other words there is no evidence to suggest that it isn't from Norway so I would stay with that.

23rd Jun 2014 18:18 UTCChristopher O'Neill

Reiner,

Yes I understand however, the specimens I picked up which included this chevkinite were from the 1950's which precedes the discovery of the Norway occurrence mentioned by Knut in 1970's.

If I have the alteration crust analyzed and it indicates Th-rich Bastnasite-(Ce), it may help determine the locality.

Regards,

Chris

23rd Jun 2014 18:31 UTCReiner Mielke Expert

The name gadolinite may have been applied to the sample much later, obviously incorrectly, but that does not mean the specimen could not have been found in Norway in the 1950's. It is just that they didn't know what it was at the time.

23rd Jun 2014 18:46 UTCChristopher O'Neill

Reiner,

Yes, that could be a possibility as well (sorry, I didn't think of that).

I was wondering that if Pavel did some analysis work on the alteration crust, he may also have done an analysis on the chevkinite, and if so, I was curious if it showed the presence of Al.

I will reach out in a PM.

I will also send out the alteration crust for analysis.

Thanks again,

Chris

23rd Jun 2014 21:12 UTCReiner Mielke Expert

Sending out the crust for analysis is going to raise a whole lot more questions then it will provide answers. However it will be interesting to see what it contains. Those metamict minerals are a real pain in the ass to try and pin down without detailed quantitative analysis even then sometimes the results are inconclusive. I have a glassy metamict mineral that looks homogeneous but turned out to be a mixture of at least 4 different minerals, and one of the phases could not be identified.

24th Jun 2014 21:32 UTCChristopher O'Neill

Reiner,

Yea, I think you are right about that - could be a pain but interesting to see what he comes up with. I never heard back from Pav....

Chris

25th Jun 2014 08:22 UTCPavel Kartashov Manager

What is the size of the specimen? Size has importance in this case.;-)

What about EDX spectrum, I never met chevkinites with so high contents of Al and Ca. Usual content of CaO in real chevkinites is below 2 mas.%. So there are two possibilities - chevkinite-allanite mixture was analysed, or this is the largest in the world sample of alumoperrierite (one its micrograin was described from Antarctica by Roy Macdonald). I am more tend to the first version.

What about alteration products, my specimen was described in article, which will be published in Mineralogical Magazine soon. Essential there is graphical intergrowth of bastnasite and ilmenite. In other words, during hydrothermal alteration of this chevkinite only silicon was eliminated (replaced by carbonate), while all other constituents (REEs, Fe,Ti) were immobile in this process.

On your specimen the alteration rim is completely different origin - it isn't hydrotermal, but connected with usual weathering in very superficial conditions.

If the specimen is large (more than 1-2 cm), I would bet for Madagascar origin of it.

26th Jun 2014 22:29 UTCChristopher O'Neill

Pavel,

Thanks very much for your reply.

This specimen is 6 x 5 x 2 cm. I thought that if you had done some analysis on your chevkinites, they might have had similar Al and Ca, but it doesn't look that way.

I could send a sample to Attard for EDX, unless you know of someone else.

How do you figure Madagascar as the location? Is that based on both size and alteration?

Regards,

Chris

27th Jun 2014 02:09 UTCPavel Kartashov Manager

I had analyzed a lot of chevkinites. And most of them contains less than 1 mas.% CaO. Typical content of Al₂O₃ for the specie is within limits of 0.2 mas.%.

From specimen http://www.mindat.org/photo-210251.html were made more than 20 analyses and it contains 2.82 vas.% CaO and 0.17 mas.% Al₂O₃. May be only Th content in it is too elevated. Look Macdonald R, Bagiński B, Kartashov P, Zozulya D, Dzierżanowski P Chevkinite-group minerals from Russia and Mongolia: new compositional data from fenites, metasomatites and ore deposits, - Mineralogical Magazine 06/2012; 76(3):535–549

Largest chevkinites from Ural never didn't exeed 6 cm in maximal direction. Whole crystals. In literature I was able to found only 5 cm size xls mentioned. You have 6x5 cm fragment. This is absolutely untypical for Ural.

Besides that we have not too hot and warm climate for such deep alteration of LREE-silicates. Some similar I had observe only on britholites from Sakhariok massif / Western Keivy massif boundary- 1-2 mm thick bastnasite crusts. Chevkinites from the same rocks are fresh - hydrated but not replaced with carbonates.

Madagascar pegmatites are famous by their extralarge crystals of rare-metal minerals.

27th Jun 2014 22:05 UTCChristopher O'Neill

Thanks again Pavel and to all who contributed,

I would like to post this specimen with the locality as follows: Madagascar - unless you think there is a specific province or district that it might fall under.

I will eventually have the alteration crust analyzed and perhaps that might (or might not) help with a definitive location.

Thanks for all of your help and input,

Chris

30th Jun 2014 09:23 UTCKnut Edvard Larsen 🌟 Manager

In 1950s The Commisariat à l`Energie Atomique did an extensive exploration of pegmatites in Madagascar and several specimens also went to collectors worldwide among them possible some checvkinites.

It might be from Madagascar, but that's just only a qualified guess.

The photos has been approved for your gallery. I also took the liberty to add a note in the caption, linked it to this thread.

30th Jun 2014 12:35 UTCLefteris Rantos Expert

http://www.mindat.org/photo-616922.html Striking similarity...

8th Nov 2014 19:58 UTCBruno Hermier

Hello Christopher,

I have exactly the same specimen of Chevkinite . It was labeled Gadolinite Madagascar . An EDS gave the same patern than your sample with Al and Ca . All outcrops in Madagascar are deeply weathered by tropical climate . Most of old samples have been found as loose blocks in red Laterite . Size plus weathering crust on the Chevkinite made me think it really comes from Madagascar . It comes from Syenites . Interesting is that the famous big Bastnaesites from Madagascar have their origin as secondary minerals after leaching of Chevkinite in the Syenites . Previously in the old literature these minerals were thought to come from the famous NYF granitic pegmatites of Madagascar . Here is reference of a recent paper about the subject . You will also find the probable location of your sample .

Rasoamalala 2013 . Geology of Bastnaesite and Monazite deposits in the Ambatofinandrahana area, central Madagascar : An overview

Journal of African Earth Sciences

Data base search : www.sciencedirect.com

If you like, I can send you a copy of this paper, the EDS patern and photos of my sample . I am not registered on Mindat.org better you contact me at adress bruno.hermier@edf.fr

About the story of my Chevkinite : after many years without contact, I called a work collegue who is now retired .His wife answered the phone . I learned that firemen came to pick all radioactive samples from the appartment . A special transport would come within 3 days to put all samples in nuclear waste . I rushed to save the collection of my colleague . I remembered from the 90 s that he was found of old basement of Africa and especially Madagascar and had a lot of Columbite, Euxenite, Monazite ..... Unfortunately the healf of my colleague does not allow him to tell anything about this sample . The firemen made a big mess in the boxes and labels .

Best regards

8th Nov 2014 21:03 UTCReiner Mielke Expert

Hello Bruno,

Thank God you rescued the samples!! Good work! Please make sure that doesn't happen to your collection, it would be a big loss to the mineral collecting community.

15th Nov 2014 12:23 UTCBruno Hermier

Below is the reference of the paper

Geology of bastnaesite and monazite deposits in the Ambatofinandrahana area, central part of Madagascar: An overview

V. Rasoamalala, S. Salvi, D. Béziat, J.-Ph. Ursule, M. Cuney, Ph. de Parseval, D. Guillaume, B. Moine, J. Andriamampihantona

Journal of African Earth Sciences, Volume 94, June 2014, Pages 128-140

Part 7 Metallogenic implications on page 9 " at Marovoalavo and Ifasina, Aegirine and Na Amphibole bearing Syenites contain cm and decimeter size crystals of Chevkinite . They are mainly alluvial "

You can contact me at bruno.hermier@edf.fr

15th Nov 2014 15:35 UTCKnut Eldjarn 🌟 Manager

Hello Christopher,

I will not contest the possibility that the specimen is mislabeled and comes from Madagascar. But how do you know from an EDS that it is Chevkinite and not Perrierite ? Perrierite-(Ce) was found 40 years ago in Radøy north of Bergen in Norway in large, massive pieces (see: http://www.mindat.org/loc-54551.html). It was found in a lens in a metamorphic gneiss close to the seashore, but I have not seen any pieces with an alteration rim similar to yours.

Knut Eldjarn

15th Nov 2014 16:11 UTCBruno Hermier

Geology of bastnaesite and monazite deposits in the Ambatofinandrahana area, central part of Madagascar: An overview

V. Rasoamalala, S. Salvi, D. Béziat, J.-Ph. Ursule, M. Cuney, Ph. de Parseval, D. Guillaume, B. Moine, J. Andriamampihantona

Journal of African Earth Sciences, Volume 94, June 2014, Pages 128-140

Part 7 Metallogenic implications on page 9 " at Marovoalavo and Ifasina, Aegirine and Na Amphibole bearing Syenites contain cm and decimeter size crystals of Chevkinite . They are mainly alluvial "

bruno.hermier@edf.fr

16th Nov 2014 16:24 UTCBruno Hermier

Geology of bastnaesite and monazite deposits in the Ambatofinadrahana area, central part of Madagascar: An overview

V. Rasoamalala, S. Salvi, D. Béziat, J.-Ph. Ursule, M. Cuney, Ph. de Parseval, D. Guillaume, B. Moine, J. Andriamampihantona

Journal of African Earth Sciences, Volume 94, June 2014, Pages 128-140

Part 7 Metallogenic implications on page 9 " at Marovoalavo and Ifasina, Aegirine and Na Amphibole bearing Syenites contain cm and decimeter size crystals of Chevkinite . They are mainly alluvial "

bruno.hermier@edf.fr

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