THE DECOMPOSITION OF WOLFRAM. 249 



Jn a general way the depths that are reached by gold-bearing 

 veins arc indicated by the length of their outcrops, but tungsten 

 deposits whose outcrops are comparatively small seem to reach 

 relatively greater depths, especially those that have pegmatitic 

 characteristics. 1 



THE DECOMPOSITION OF WOLFRAM. 



Very erroneous ideas are prevalent in literature regarding the 

 behaviour of the natural tungstates of iron and manganese on 

 exposure to the action of water or air. Thus, W. H. Emmons 

 classes tungsten as a metal that dissolves very slowly when its ores 

 are exposed at or near the surface and subjected to the action of 

 water and air. He considers them as stable ores comparable, say 

 with cassiterite, for he places both tin and tungsten in the same 

 division of his classification, along with gold (in part), bismuth, 

 chromium and molybdenum. 2 



R. H. Eastall writes :— " The outstanding feature of the tungsten 

 minerals is their great stability and resistance to any kind of chemical 

 or mechanical alteration. Hence, like cassiterite and gold, they 

 are particularly prone to occur in both residual and alluvial deposits. 

 In many of the published descriptions, and especially in the technical 

 journals, a good deal of confusion is found to exist between the 

 residual deposits, where the material is still more or less in place, 

 and the true alluvial or transported deposits. From their stability 

 and high density it also follows that the tungsten minerals are 

 specially liable to occur as placers and other forms of transported 

 deposits. The same properties also lead to a natural concentra- 

 tion in such deposits, especially in the lowermost layers, resting 

 on the bed rock, and in natural riffles. In this respect both wolfram 

 and scheelite behave like stream-tin, gold and platinum. Jn fact, 

 the properties of wolfram are so like those of cassiterite that their 

 separation by mechanical processes is very difficult, and it was 

 not until the introduction of magnetic separation that this difficulty 

 was overcome/' 3 



A large portion of the wolfram produced in Tavoy is won by 

 hydraulic methods from residual and detrital deposits, but there 



1 Hess, loc. cit., pp. 62-63. 



2 W. H. Emmons, Min. Sd. Press, March 31st 1917. 



3 K. H. Rastall. " Tho Gonesis of Tungsten Ores," Geol. Mag., N. S. Dec. VI, Vol. V, 

 1918, pp. 367-368. 



