250 BROWN & HERON: GEOLOGY AND ORE DEPOSITS OF TAVOY. 



are no true wolfram placers or anything resembling thorn, if the 

 word be used to mean stream-borne and watersorted alluvium. 

 Wolfram does occur at the foot of slopes where the eluvial deposits 

 of the hill sides merge into the true placers of the valley bottoms, 

 but long before the clays, sands and gravel deposits have been 

 sorted out and classified by running water, the wolfram has dis- 

 appeared, though it comes from the same veins as the tin ore. 

 in which it occurs almost invariably in considerably greater 

 quantities. The only wolfram found in the alluvial deposits proper 

 is tightly enclosed in quartz, to which it owes its preservation, as 

 the solutions from the decomposing soil, or the river water itself, 

 cannot penetrate to it. Such a stability is clearly an accidental 

 one. 



The rapidity with which wolfram disappears is remarkable, 

 and is accounted for by its perfect cleavage, resulting in its disinte- 

 gration on movement and the production of a comminuted form 

 eminently suited for chemical decomposition. 



Again, observations on weathered outcrops of veins prove that 

 wolfram is readily leached. Sometimes nothing is left but the 

 empty spaces once occupied by the crystals, at other times these 

 are filled with oxides of iron and manganese, or with a bloom of 

 yellow tungstite. The ready oxidation of the sulphide associates 

 of the wolfram produce acid solutions which attack the mineral, 

 while the mechanical effect of their removal opens up a path for 

 deeper-seated chemical action. 



Dr. W. R. Jones has maintained that in Siam and the Malay 



States as well as Lower Burma, all countries possessing a moist, 

 tropical climate, it is common to find wolfram so weathered that 

 only deposits of the oxides and hydroxides of manganese and of 

 iron remain. In some cases the product left after the weathering 

 is almost a pure manganese mineral, in others it is limonite, in still 

 others only the mineral tungstite. The character of the decom- 

 position he believes depends on : — 



(a) the original composition of the wolfram and 

 (6) the composition of the water acting on it. 



He gives an analysis of a manganese deposit taken from a wolfram 

 vein. It occurred as a patch in the vein and gave place on both 



