32 TIN MINING IN PERAK. 



nically susj^euded mercuiy containing, of course, a certain 

 proportion of gold, remaining in the tin -sand after treatment. 

 These difficulties could be got over in a great measure by 

 crushing the tin- sand down to an uniform powder, but this 

 would cost money for the milling and would lead to a very 

 serious loss of tin by its sliming. As already mentioned, there 

 is always iron pyrites present in the auriferous tin -ore, and 

 unless it is roasted this would sicken and flour the mercury and 

 consequently increase both sources of loss. 



One method of amalgamation was tried at Klian Bharu by 

 Mr. W. H. Wellington some two years ago, but no details of the 

 experiment seem to have been made known. In this process the 

 tin -sand, water and mercury were put into a barrel, which was 

 revolved for a certain time, then the contents were turned out 

 and sent with a stream of water through a sluice box furnished 

 with " riffles " and mercury traps. The best chance of succeeding 

 with this class of ore would appear to be to present the mercury 

 to the gold on plates of copper, so as to endeavour to minimise 

 the loss of mercury due to mixing with the heavy grains of 

 tin -sand. 



The chlorination is effective in a small way in the labor- 

 atory. It is carried out by damping the ore and then passing- 

 chlorine gas through the mass, or circulating chlorine water 

 through it. The chlorine dissolves the gold which is afterwards 

 deposited from the solution by sulj)hate of iron, or by passing it 

 through charcoal filters. The results are very satisfactory, but 

 the tin -sand has to be roasted in a very perfect way or the 

 iron in it dissolves and then precipitates the gold as fast as 

 it is brought into solution by the chlorine. The roasting and 

 the trouble in preparing and handling the chlorine gas would 

 appear to render this process unsuitable for the purpose of 

 treating the auriferous tin - sand. 



The third alternative, that is the cyanide process, ajDpeared 

 to meet the requirements of the case in a most satisfactory 

 manner. As applied to this class of ore the process is as follows. 

 The ore is put dry into vats furnished Avith filter beds. A weak 

 solution of one per cent or less of cyanide of potassium is used. 

 It is run on and allowed to soak, and at intervals it is drawn 

 off and pumped up on to the top of the vat again. The leaching 

 is continued until such time as it has been found by experience 

 that the largest grains of gold are dissolved. The solution is 

 then run through a box containing fine zinc shavings, on which 

 the gold dej30sits. A second charge of a weaker solution is then 

 run through the tin -sand and the zinc box and afterwards 

 plain water washes follow as long as gold deposits in the 



