What could be responsible for this phenomenon of alteration or contamination of Na-Amphibole (Arfvedsonite) around some of its parts?
Note that this same slide;
1. Contains dispersed grains of Scheelite (Wolfranite ore) in other places
2. The characteristics cleavage pattern of amphibole are closed spaced around the alteration/contamination.
3. Another crystal occurring as accessory is probably titanite
Dear Kayode, the grey mineral with the high relief in your upper left photograph looks like sphene, even though it is not idiomorphic. Please also have a look at the paper by Soloviev & Kryazhev (2018) in Ore Geology Reviews 101: 700-724 which describes some W deposits in the Tien Shan belt. Kind regards Daniel
Indeed, as Daniel Müller suggests, the high relief is typical of sphene, yet, in my experience sphehe is always brown, not withish. Do you have access at all to an SEM with EDS? Even a table top instrument would do. If so, just 'zap' it and get a qualitative compostion. That's what I would do. Btw. have a look at this: https://wgnhs.uwex.edu/minerals/15437/
Yes Giulio Francesco Solferino , I have access to SEM EDS. Your suggestion has helped me solve the problem. Thank you
Could I ask, whether it turned out to be sphene in the end?
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