GOLD MINING IN COLOEADO. 567 



der available the contents of the tailings in a more perfect and less expensive 

 manner than is now done by the means generally employed. 



It has been already shown that, by the ordinary operation of crushing 

 and amalgamating, about 50 or 60 per cent, of the gold contained in the ore 

 is extracted, while nearly all the silver, and, practically, all the copper, are al- 

 lowed to be wasted. The value of these two metals, in a ton of ordinary ore, 

 is too low to admit of their profitable extraction, except by some preliminary 

 process of concentration, by means of which the valuable contents of several 

 tons are brought into one ton, that may then be treated by smelting, or other 

 suitable methods. 



Any method of concentration, however, first requires the crushing of the 

 ore, and that, in the present condition of milling experience, can hardly be 

 done better than by the best and most improved stamp mills. If, therefore, 

 the present system of crushing and amalgamating be retained, by which means 

 a considerable percentage of the free gold is obtained, and the crushed product 

 be then delivered, without rehahdling or passing out of the mill, to the best 

 kind of concentrating machinery, the concentrated product would contain not 

 only nearly all the remaining gold, but also the greater part of the silver and 

 copper, the whole of which could then be submitted to smelting, or other 

 suitable processes, by which a very large percentage of its value should be 

 profitably extracted. 



The desired improvements in concentration appears still more important 

 when it is remembered that ores vary much in character, and that, in some, 

 only a small percentage of the gold contained is readily available for amalga- 

 mation, as practiced in the battery and on the tables. Whether this be due 

 to the form in which the gold exists in the ore, or to some peculiar condition 

 of the quicksilver, or to some other cause not fully understood, may be an 

 open question; but it has often been observed by mill-men that ores having 

 an equal value, when subjected to apparently the same process, will sometimes 

 afford very different yields, some giving a high and others a low percentage of 

 the value contained. A low yield, involving, under present conditions, a large 

 loss, would be less important if, beyond the crushing and amalgamating 

 machinery, there were other ample and efficient methods of concentration 

 provided, by which the mineral that had escaped from the batteries and 



