548 MINING INDTJSTEY. 



a limited extent, or are being introduced, but without having yet come into 

 general favor. 



In the follovi^ing pages the principal methods above referred to will be 

 described with sufficient detail to give an idea of their general character, after 

 which some of the other processes may be briefly noticed. As the great bulk 

 of the ore raised from the mines is treated by crushing and amalgamation, the 

 operations of the stamping mills will be taken up first. 



Milling. — The ore designed for treatment by this method is first reduced 

 to fragments of a suitable size for feeding to the stamps, which is done either 

 by hand or by a stone-breaking machine. Blake's Eock-breaker or Dodge's 

 Crusher are used more generally than other machines for this purpose in Col- 

 orado. The rock is then supplied to the stamps. 



The general character and method of arrangement of crushing or stamp- 

 ing machinery, as used in Nevada, has been already described in a foregoing 

 chapter. The mills of Colorado are similar, in many respects, to those of 

 Nevada. It will, therefore, be unnecessary to describe in detail all the various 

 parts of machinery that are common to mills of this sort, and a brief notice of 

 some of the characteristic features of those in Colorado will be sufficient here. 

 The drawings on Plate XXXIII illustrate many of the details of construction 

 of a Colorado crushing mill for the treatment of gold-bearing rock. The 

 case illustrated is a battery in the Trust Mill, on Lake Gulch, under the 

 management of Mr. H. B. Brastow. The reference table on the plate will 

 make the drawings intelligible without further explanation. 



The Colorado milling machinery has been mostly supplied from Chi- 

 cago, though the machine shops of other western cities are somewhat repre- 

 sented. The stamps, as a general rule, are heavier, run more slowly, and wdth 

 greater fall than is usual in the mills of California and Nevada. Some of 

 them weigh 900 pounds each, and although the mills of most recent con- 

 struction have generally adopted a 500-pound or 600-pound stamp, the aver- 

 age is probably somewhat higher than that at present. Some run with as 

 low a gpeed as 15 drops per minute ; others as high as 40 ; while the average 

 will probably not exceed 28. The fall is from 12 to 18 inches. The re- 

 volving stamp is in general use. The high mortars, having the bottom and 

 sides cast in one piece, so generally used in Nevada and California, are not 



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