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Locality of columbite from Madagascar - Analalava vs. Tsaramanga

Posted by Pavel Kartashov  
avatar Locality of columbite from Madagascar - Analalava vs. Tsaramanga
July 12, 2012 12:25AM
    
I'd received crystaline cluster labeled as "Ferrocolumbite from Analalava district, Sofia region, Mahajanga pr., Madagascar".



But locality [www.mindat.org] don't contain any pagmatite minerals but only mineralized basaltic effusive rocks.
Fromother hand, here was uploaded photo very similar crystal - [www.mindat.org]

Other very similar crystals we see in classic pegmatite occurrence [www.mindat.org]
Compare my specimen with [www.mindat.org]

I am confused...sad smileyconfused smileysad smiley

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.
Re: Locality of columbite from Madagascar - Analalava vs. Tsaramanga
July 12, 2012 08:09AM
    
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.
Re: Locality of columbite from Madagascar - Analalava vs. Tsaramanga
July 12, 2012 08:54AM
    
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