40 KEMP'S ORE DEPOSITS. 



to have been carried down in solution with ferrous and ferric sul- 

 phates, which were decomposed by feldspar, while the precious 

 metal was thrown down. The ore bodies lie in the Summit district, 

 Rio Grande County, Colorado. (R. C. Hills, Proc. Colo. Sci. Soc., 

 Vol. I., p. 32 ; S. F. Emmons, quoting Hills, Engineering and Min- 

 ing Journal, June 9, 1883.) 



1.05.07. The waters of mines which have opened up and ex- 

 posed sulphides to oxidation are often charged with sulphuric acid 

 and even metallic salts. This is especially true of mines in copper 

 sulphides, and the pumps are much corroded. In instances con- 

 siderable metallic copper has been removed by passing the mine 

 drainage over scrap-iron, as at Ducktown, Tenn., and as has been 

 lately introduced experimentally at Butte, Mont. Mine timbers 

 have been preserved very long periods by the deposition of copper 

 on them, from their reducing action on the solutions. Pumps and 

 timbers placed by the Romans in the Rio Tinto mines, in Spain, 

 are still in good preservation. Even gold has been detected in 

 Australian mine waters. (See School of Mines Quarterly, Vol. 

 XL, p. 364, for review of literature bearing on this subject.) 



1.05.08. Electrical Activity. A theoretical agent for the pre- 

 cipitation of ores in veins, which was a great favorite among the 

 writers fifty or sixty years ago, was electrical action, and careful 

 experiments were made in England and Germany to detect it. By 

 connecting the opposite ends of a vein with a wire, in which was a 

 galvanometer, the attempt was made again and again to establish 

 the existence of galvanic action. At times the results gave some 

 grounds for belief ; but at others they were contradictory or un- 

 certain, 'so that no very definite or reliable conclusions were 

 established. Other experiments were made in Germany about 

 1844, by Reich, while lately quite elaborate investigations have 

 been carried out by Dr. Carl Barns on the Comstock Lode, and at 

 Eureka, Nev. Great difficulties are met in preserving the neces- 

 sary insulation throughout the wet and devious underground work- 

 ings, and amid such surroundings in detecting the currents, which 

 would be necessarily small. With Barus the thesis was not alone 

 to establish a galvanic action, such as might be a precipitating 

 agency, but also to observe what effect, if any, was exerted by the 

 intervention of an ore body on the normal terrestrial currents. 

 Had this latter been proved of sufficient amount, the existence of 

 such bodies might be indicated by plotting electrical observations. 

 While in some respects of interest, the results of Dr. Barus are not 



