THE PROBLEM OF THE METALLIFEEOUS VEINS. 191 



The nature of the ore is also a factor of prime importance. Some 

 compounds yield the metals readily and cheaply, while others, which 

 in the case of the precious metals are often called base ores, require 

 complicated and it may be expensive metallurgical treatment. The 

 association of metals is likewise of the highest importance. Copper 

 or lead, for example, greatly facilitates the extraction of gold and 

 silver, Avhereas zinc in large quantities is a hindrance. Conditions 

 also change. An ore which may have been valueless in earlj^ days 

 may prove a rich source of profit in later years and under improved 

 conditions. For instance, from 1870 for over twenty-five years 

 Bingham Canyon in Utah yielded lead-silver ores and minor deposits 

 of gold. It was known that in some mines low-grade and base ores 

 of copper and gold existed, but the fact was carefully concealed, 

 and in at least one instance the shaft into them was filled up, lest a 

 general knowledge of the fact should unfavorably affect the value 

 of the property. To-day, however, these ores are eagerly sought and 

 their extraction and treatment in thousands of tons daily are paying 

 good returns on verv large capitalization. Another factor is the 

 exj)ense of extraction. If simple and inexpensive methods are pos- 

 sible, the area of profitable treatment is greatly widened. Thus gold 

 may need little else than a stream of water or even a blast of air, 

 Avhereas iron and copper require huge furnaces and vast supplies of 

 coke and fluxes. 



Iron ores are of little value in any part of the world unless they 

 contain a minimum of 35 per cent iron when the}" enter the furnace, 

 but if they are distributed in amounts of 10 to 20 per cent in exten- 

 sive masses of loose or easily crushed rock in such condition that 

 they can be cheaply concentrated up to rich percentages, they may 

 be profitably treated and a product with 50 per cent iron or higher 

 be sent to the furnaces. Nevertheless, speaking for the civilized 

 world at large, it holds true that as an iron ore enters the furnace it 

 can not have less than 35 per cent, and in America, with our rich and 

 pure deposits on Lake Superior, two-thirds of our supply ranges from 

 60 to 65 per cent. 



As regards copper, a minimum working percentage amid favorable 

 conditions and with enormous quantities is usually about 3 per cent, 

 but in the altogether exceptional deposits of the native metal in the 

 Lake Superior region copper rock as low as three-fourths of 1 per 

 cent has been profitably treated. This or any similar result could 

 only be accomplished Avith exceptionally efficient management and 

 with a copper rock such as is practically known only on Lake 

 Superior. With the usual type of ore, not enriched by gold or silver, 

 2 per cent is the extreme, and in remote localities 5 to 10 may some- 

 times be too poor. 



