CHAPTER IV. 



STRUCTURES AND CHARACTERISTICS OF TUNGSTEN AND TIN ORE 



DEPOSITS IN TAVOY. 



Leaving out of consideration alluvial cassiterite deposits and 

 detrital deposits containing both cassiterite and wolfram, the 

 occurrence of which is considered later, we propose to deal now with 

 the distribution, form and structures of the original ore deposits. 



Granites, aplites, pegmatites and greisens. 



The occurrence of cassiterite as an accessory mineral in some 



varieties of Tavoy granite was first discovered 



Cassiterite and wol- Dy Bleeck, 1 who records 0*15 per cent, of metal- 



fram as accessory nunc- ,. . . . •, , ,. -, 



rals in granites. he tin in a granite porphyry Irom mile 21 



on the Siam road. Since then its presence 

 has been confirmed by others. That wolfram may occur in a similar 

 situation was first definitely established by Morrow Campbell, - 

 who writes : — " In many parts of the district I have observed, as 

 original constituents of the granite, wolfram alone, cassiterite alone, 

 and also both together in varying ratios, sometimes accompanied 

 by bismuthite." A specimen of a fine-grained white granite front 

 Zinba mine, now in the Geological Museum, Calcutta, contains a 

 nest of small radiating wolfram crystals. Long rectangular black 

 crystals seen in sections of the Bolintaung granite are probably 

 wolfram. 



It is necessary to distinguish carefully between the true occur- 

 rences of cassiterite and wolfram as accessories 



Cassiterite and wol- j n granite proper, and the far commoner finds 

 tram in aplites. , , ,, , • , , ,-. ■ , ,,, c 



ol both minerals in the aphtc veins, the fine- 

 textured white rocks containing quartz, orthoclase felspar and a 

 little muscovite mica, which sometimes penetrate the main granite 

 masses and arc later than their hosts. Weathered specimens 

 of aplite from Kalonta exhibit spots of yellow tungstite left by the 

 decomposition of wolfram. 



i A. G. Bleeck (2), p. 69. 



: J. .Morrow Campbell (9), p. 3. 



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