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Locality of columbite from Madagascar - Analalava vs. Tsaramanga

Posted by Pavel Kartashov  
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Pavel Kartashov July 12, 2012 01:25AM
I'd received crystaline cluster labeled as "Ferrocolumbite from Analalava district, Sofia region, Mahajanga pr., Madagascar".

But locality http://www.mindat.org/loc-157722.html don't contain any pagmatite minerals but only mineralized basaltic effusive rocks.
Fromother hand, here was uploaded photo very similar crystal - http://www.mindat.org/photo-149304.html

Other very similar crystals we see in classic pegmatite occurrence http://www.mindat.org/loc-27803.html
Compare my specimen with http://www.mindat.org/gallery.php?loc=27803&min=1112

I am confused...:-(:-S:-(

By the way my mineral in reality is Sc-bearing ferroan and titanoan Manganocolumbite. It contains inclusions of quartz, microcline, films of bastnasite-(La), pseudomorphoses of bismuthite after bismuthinite and overgrown by minute tetragonal prismes similar to xenotime.
open | download - MINS6922_COLU_i.jpg (94.3 KB)
open | download - MINS6922_COLU_0.jpg (84 KB)
open | download - MINS6922_COLU_1.jpg (136.3 KB)
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Knut Edvard Larsen July 12, 2012 09:09AM
The labelling of these as coming from Analalava District, Sofia Region are highly doubtful, i i would say a misnomer.
The geology of the Analalava District consist, as you say, only of cretaceous basaltic roks and jurassique-cretaceous and tertiary sedimentary layers. The columbites like these come from precambrian granite pegmatites (55o MA) from the socle of the Madagascar highland. There are so far as I know no granite pegmatites in the Analalava district,. and none marked on the geological maps of the area.

There is a granite pegmatite field with Beryl-Columbite subtype LCT pegmatites in the neighbour District of Analalava, in the Bealanana District , along the River Meavarano wich produced some columbite in the 1950s, but I have not seen these.

Your sample looks indeed very similar to samples from Tsaramanga. I have several in my collection, collected at the Tsaramanga pegmatite. Together with these I found also bismutite pseudomorphs after bismuthinite etc.

But , of course i can't say with a 100% certainty that your specimen is from Tsaramanga. It may come from another locality- but not Analalava District.
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Knut Edvard Larsen July 12, 2012 09:54AM
Message sent about http://www.mindat.org/photo-149304.html
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Pavel Kartashov January 10, 2015 02:20AM
Michel never answers messages and complaints.:-D But it looks like, that we both had the same source of material.
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