TUNGSTEN MINERALS. 



209 



Modes of occurrence in Tavoy. 



Wolfram and cassiterite occur in Tavoy as segregation deposits 

 in muscovite granite ; in pegmatite veins with quartz, felspar, mica, 

 fluorite, scheelite, molybdenite and sulphides of iron, copper and 

 lead, the last named being rare ; in quartz veins with mica (practically 

 always), fluorite (often), molybdenite (sometimes), pyrite (practically 

 always), chalcopyrite (sometimes), pyrrhotite (in some cases), galena 

 (rare), arsenopyrite (rare), zinc blende (rare), bismuth (rare), bis- 

 muthinite (rare) and topaz (in one case only) ; in greisens with mica 

 and pyrite. Wolfram and cassiterite occur in residual, detrital. 

 and talus deposits. Cassiterite occurs in alluvial and placer deposits. 



It is stated in text books that the Tavoyan field is characterised 

 by the universal presence of tourmaline and that columbite is a 

 common mineral in it. These statements are not correct. Tourmaline 

 has never been found with either wolfram or cassiterite up to the 

 present time in Tavoy. Tourmaline pegmatites occur but they do not 

 contain metallic minerals in Tavoy and do not belong to the same 

 period as the mineral-bearing veins. One small specimen of 

 columbite was discovered in a pegmatite in the north of the 

 district in 1918. Tin's rock contained neither wolfram nor cassiterite 

 and the mineral is entirely absent from the vein association as 

 far as We know. 



In the following pages the more important vein minerals are 

 described. 



MINERALOGY OF TAVOY. 



Important Vein Minerals. 



Wolfram is a black mineral rarely occurring with a good outward 

 crystal form. Beautiful crystals have how- 

 ever been obtained from a drusy lode at 

 Kanbauk. 

 It is not uncommon to find parts of both large and small imperfectly 

 formed crystals embedded in quartz, though it is practically im- 

 possible to separate them from the matrix. In any large collection 

 of roughly broken ore, pieces of wolfram showing one or more crystal 

 faces can be picked out, and imperfect crystals with rounded edges 

 are sometimes seen in concentrates from detrital deposits. But 

 by far the largest quantity of wolfram occurs as irregular aggre- 

 gates of the mineral showing no outward crystal forms, and varying 



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