FMF - Friends of Minerals Forum, discussion and message board

[alex chaus]

Dear FMF members,
I have got some geological information about prospecting performed 35 years ago in Terskey Range (Tian-Shan mountains, Kyrgyzstan). It was discovered 25 pegmatite veins, three of them came up with analyzes of abnormal high Ce-Li mineralization.
Visual field mineralogical examination result was as follows: light blue feldspar (amazonite type), smoky quarts, violet and blue mica, light white mica (muscovite), schorl tourmaline.
Analyzes results dictated to call that as pollucite – spodumene- lepidolite mineral association.
The question is: could we expect to find colored tourmaline varieties (elbaite, rubellite, polychrome one)?
The site is quite remote and difficult to access (3600-3900 m a.s.l.), so it should be a reason for such a trip.
Any ideas will be very much appreciate.
Alex

[Riccardo Modanesi]

Hi Alex!
I think the best thing you can do is seeing on Mindat site and looking for Kyrgyzystan and Tian Shan. if the deposit is interesting (and for sure it is, according to your description), you will find it easily!
Greetings from Italy by Riccardo.

[Jesse Fisher]

The presence of spodumene, lepidolite and pollucite is in keeping with what one might expect from an LCT-type pegmatite. This suggests that you may have a good chance to find colored tourmaline as well. Schorl temds to turn to elbaite (or other polychrome varieties of tourmaline) in a low iron environment. The presence of other Fe-bearing minerals such as biotite and almandine-spessartine would be negative indicators, but you do not mention these. Whether the pegmatites also have mairolitic cavities is another issue, and perhaps only resolved by field exploration.

[alex chaus]

Hi, Riccardo and Jesse!
Thank you for reply. I have already check available geological information about that region. It is quite poor, especially items related to non-ore minerals.
I see the rarity of that mineralization style in simultaneous presence of amazonite and Ce-Li (minor Be) minerals. I hope I have checked mindat.org attentively and found no images of colored tourmalines with amazonite (or vice-versa) in a single specimen.
Published information about amazonite minerals and alteration in former SU area never mentioned colored tourmaline with association with amazonite (as far as I know).
For the Middle Tian-Shan area (in the border of Kyrgyzstan) I know only about one occurrence of polychrome and rubellite tourmaline – Sary-Jazz region (rick cassiterite deposit in altered pegmatite or greizen rock with amazonite), Sughoi Dol massif – but for that particular place amazonite was found about 10 km aside with lepidolite (rich), albite, quarts (common), no shorl.
So, presence of shorl and amazonite makes me a little bit concern.
Alex

[Jesse Fisher]

To my experience, the occurrence of amazonite is more typical of NYF type pegmatites (for example, the Pike's Peak area of Colorado), which rarely have colored tourmaline (elbaite, etc), or for that matter, other Li-bearing minerals. Topaz and/or beryl are sometimes associated, however. If you have reports of both amazonite and Li-bearing minerals, I think some serious fieldwork is in order. Not always the most economical recommendation for such a remote local, but maybe the only option.

[alex chaus]

[Jesse Fisher]

I've never seen one.

[Steve Maslansky]

I have been doing geological and geochemical work in the Pikes Peak batholith for a few years, particularly in the Lake George Ring Complex. The presence of schorl in the amazonite bearing pegs is very rare and found as small crystals in the microcline. I have never seen colored elbaite. The only reference to elbaite being found in the area, that I have knowledge of, is the Foord-Martin paper (MR, Dec 1979) which reported "schorl-elbaite in needle-like aggregates as much as a 1 cm or more in length...color is black to blue-green." Pearl reported large tourmaline "suns' from the Royal Gorge area but these are not associated with amazonite bearing pegmatites.

[alex chaus]

Is it possible that normal LCT- type pegmatites were effected by later amazonite alteration superposed? If so, could colored tourmaline be changed to shorl?
Many evidences tell about multi-stage complicated process of those pegmatite formation. On the geologic map there are some later intrusions shown after original pre-Cambrian one in the close neighborhood.

[Steve Maslansky]

I am not sure if your last comment was referring to the geological map for your Kyrgyzstan site or for the Pikes Peak batholith. If you are talking about Colorado then yes there were some later stage stocks that were intruded both internally and marginally into the larger batholith. Several of these smaller plutons are of a different composition, sodic versus potassic. The pegs are younger still, and are miarolitic, NYF-Rare Earth Element, typical of A-type granitic systems. That said you could be dealing with a mixed NYF and LCT system where fluid contamination is bringing in Li and B. I find it interesting your mentioning of pollucite, which indicates a highly fractionated LCT pegmatite. You may want to check with Dr. David London, pegmatite expert at University of Oklahoma (dlondon(at)ou(dor)edu) to see if elbaite and amazonite can occur together. I sure would like to see one of those.

[alex chaus]

[Jesse Fisher]

Have you, in fact, confirmed that the mineral in question is amazonite (blue/green microcline) and not a bluish variety of albite? Albite (cleavelandite habit) is a major constituent of LCT type pegmatites and can sometimes have a distinctly blue color. This would be more in keeping with the presence of lepidolite, spodumene and pollucite. What are the other associated minerals?

Another recommendation would be contacting Dr. Skip Simmons of University of New Orleans. He has considerable field experience with LCT type pegmatites from a number of locations including Maine and Madagascar.

[alex chaus]