252 BROWN A HERON: GEOLOGY AND ORE DEPOSITS OF TAVOY 



According to Dr. Morrow Campbell, as well as the acid decom- 

 position of wolfram, an alkaline decomposition also takes place. 

 This is brought about by the action of alkaline carbonates which 

 are present in ground water, and dissolve out tungstic oxide. 

 Scheelite is said to break up more readily than wolfram with all 

 natural solvents, and pearly scales of gypsum, the result of its 

 decomposition with sulphuric acid, have been observed in intimate 

 association with the residual tungstite. 1 



R. W. Gannett has carried out laboratory experiments to deter- 

 mine the effects of various solutions, such as are found in ground 

 water, on tungsten minerals, and to determine the natural reagents 

 which precipitate the metal from solutions. The minerals used 

 in the tests were scheelite, ferberite, wolframite and hiibnerite, and 

 the following conclusions are given amongst his results : — 



(1) Carbonate solutions had no apparent effect on any of the 



tungsten minerals. 



(2) Alkali hydroxide solutions had no effect on scheelite, but 



dissolved tungsten from wolframite. 



(3) Sulphuric acid alone, and in combination with sulphates 



of lime, soda, manganese, and ferrous iron, dissolved 

 portions of all the minerals. 



(4) Humic acids are inactive. 



(5) Except by sodium hydroxide, scheelite is more readily 



attacked than ferberite or wolframite. 



(6) Calcium tungstate is precipitated from solutions by lime 



salts when slightly acid, but the precipitation of tungsten 

 is incomplete. 



(7) Acids partially precipitate the tungsten as tungstic acid. 



(8) Ferrous tungstate is not precipitated in acid solution, but 



is precipitated in slightly alkaline solution ; the reaction 

 is nearly complete. 



" The evidence of the experiments, on the whole, is that tungsten 

 minerals are somewhat soluble. The field evidence seems to point 

 to the same conclusion." 2 



In these paragraphs we have attempted to describe the results 

 of ordinary processes of weathering on tungsten ores in a tropical 

 climato with a very heavy rainfall. Whether identical or nearly- 



1 J. Morrow Campbell (9), pp. 25—29. 



2 R. W. Gannett. " Exporimenta relating to the Enrichment of Tungsten Ore«." 

 Econ. Geol, Vol. XIV, No. 1, 1919, pp. 68—78. 



