ELECTRICITY IN MINING 57 



A considerable amount of work is done in mines to-day 

 in the way of ventilation by electric motors, the driving of 

 ventilating fans and blowers by electricity having been found 

 to possess many advantages. In addition to the large amount 

 of work done in tunnels, there is considerable work done in 

 galleries in the way of operating the main fans or blowers 

 for the general ventilation of mines. The larger fans of this 

 class are belt driven, on account of their very low rates of 

 speed, but the smaller ones are also to be found, direct con- 

 nected to the motors. 



The amount of placer mining work that has been done 

 by electricity of late is considerable, particularly in the west- 

 ern states. The best way to afford an idea of work of this 

 character is to cite some of the later examples. 



The Gold Pan Mining company, of Breckenridge, Colo., 

 which has the largest placer mining plant in the state, if not 

 m the United States, depends chiefly- upon electricity for its 

 operation. The current is generated at a plant some 5 miles 

 from the deposits and is carried to a substation at the mine 

 at a line pressure of 10,000 volts, 3-phase alternating. It 

 is used principally for the driving of pumps and the illumina- 

 tion of the works. Large bowlders are moved by two elec- 

 trically driven portable cranes of the boom type, which use 

 alternating current from the line, without transformation, 

 and each of which is equipped with a motor capable of de- 

 veloping 30 horsepower. A large 150 horsepower constant 

 speed motor is used to drive a centrifugal pump which assists 

 in keeping the pit dry. A large machine shop, in which are 

 made the large wrought steel water mains employed in the 

 placer system, is supplied with power by a 50 horsepower 

 constant speed motor. 



In California the earliest placer mining, represented in 

 a later stage by hydraulic working, upon which legislation 

 imposed severe restrictions, has been largely superseded by 

 dredging, which appears to have developed into a ver^^ prof- 

 itable enterprise where power can be obtained cheaply. 

 In fact, it is stated that, with cheap electric power dredging, 

 land in which the gold averages less than 10 cents to the cubic 

 yard pays for treatment. 



