GOLD EXTRACTION PROCESSES. 497 



especially after the coarser particles of gold have been 

 removed by amalgamation. Certain deposits of complex 

 ores, above the average in richness, are at present left 

 untouched for want of a process by which they can be 

 treated. 



The cost of treatment of gold ores by the processes de- 

 scribed above of course varies enormously with the locality 

 and the special conditions of the case. Under favourable 

 conditions the following may indicate approximately the 

 minimum amount of gold which must be present in an ore, 

 in order that it may be treated at a profit by the most 

 suitable process. Auriferous sand, washed in the miner's 

 pan, must contain about one part of gold in 100,000 or say 

 six pennyweights per ton of ore. When the sluice is used, 

 the sand being excavated and carried to the sluice by hand 

 labour, as in Siberia, there must be at least one part of 

 gold in 2,500,000 parts of sand or six grains to the ton. 

 When the hydraulic method is possible, only one part in 

 18,000,000 may be enough, or three-fourths of a grain of gold 

 per ton, a proportion about equal to that which Liversedge 1 

 found to exist in the sea water off the east coast of 

 Australia. If the gold is contained in quartz, the cost of 

 mining and of crushing the stuff makes the whole process 

 of treatment far more expensive. Excluding the cost of 

 mining, however, the cost of crushing and amalgamation 

 requires the presence of at least one part of gold in 

 400,000, or say one and a half dwts. per ton. The cost of 

 chlorination is equal to not less than one part of gold in 

 200,000 of ore or three dwts. per ton, although if only 

 applied to concentrates, the cost per ton of the original ore 

 may be trifling. Lastly, the cyanide process might be 

 applied to the crushed tailings from the amalgamation 

 process if they contain more than one part of gold in 

 600,000 or one dwt. per ton. If the ore has to be crushed, 

 it must of course be richer. As stated above, these 

 estimates apply only when the conditions are the most 

 favourable. In general, such poor ores could not be worked 

 at a profit. 



1 Proc. Roy. Soc. of MS. W., 1895. 

 35 



