MINING METHODS. 315 



ore would then pass through a set of heavy-duty type crushing 

 rolls set to reduce everything to about | inch and less, and it is 

 thought that at this stage a considerable proportion of the values 

 would be released. A conical trommel screen would then divide 

 the material into three grades :— 



(1) Minus 10 mesh to join the product from a second set of 



rolls for table concentration. 



(2) Phis 10 mesh Minus \ inch to go to jigs. 



(3) Plus I inch to the second set of rolls. 



The heads from the jigs should produce a fairly clean concentrate 

 and the tailings will join the oversize from the screen and be further 

 reduced through the second set of rolls to ^ inch and less, making 

 suitable feed for Wilfley tables. The ground material will be either 

 classified or sized by further screening to several grades so that 

 each Wilfley table will work on an even feed which admits of the 

 most efficient concentration. 



Regarding the percentage of mineral extracted by such a plant 

 this would vary according to the ore treated. Some engineers 

 would grind the tailings again and pass them over further tables 

 and concentrators, as in spite of the attempt to avoid sliming by 

 coarse crushing and the elimination of coarse mineral at the different 

 stages of classification and regrinding, the tailings will account for 

 a large percentage of loss. 



Mr. Marks suggests, in the case of Tavoy concentrates, that instead 

 of attempting to reduce the tailings further, a poorer or dirtier 

 concentrate be produced and everything be put through a magnetic 

 separator. He believes that with a well-equipped modern plant 

 on these lines good work could be done and a high percentage of the 

 mineral contents extracted. 1 



Conclusions.— The perfect cleavage which wolfram possesses re- 

 sults in its breaking down to thin mica-like plates when it is powdered 

 or ground. By the action of stamps these naturally become 

 slimed, and while a certain amount of such slimes may be recovered 

 by modern slime tables, canvas tables and other devices, the loss 

 is undoubtedly very high. We have watched experiments 



in more than one experimental stamp battery erected in Tavoy, 

 and it appears to us to be preferable to adopt a practice in which a 



»G. N. Marka, (18), pp. 28-29. 



