SCIENCE. 



17 



ment the ores of the more important metals 

 should have at least the above percent- 

 ag'es, but that we may grasp the relations 

 correctly, it must be appreciated that local 

 conditions affect the limits. Thus in a 

 remote situation and with high charges for 

 transportation an ore may be outside profit- 

 able treatment, although it may contain 

 several times the percentages of those more 

 favorably situated. Iron ores in particular 

 which are distant from centers of popula- 

 tion, are valueless unless cheap transporta- 

 tion on a very large scale can be developed, 

 while gold in an almost inaccessible region, 

 like the Klondike, may yield a rich reward, 

 even when in quantities which, if expressed 

 in percentages, are almost inappreciable. 



The nature of the ore is also a factor of 

 prime importance. Some compounds yield 

 the metals readily and cheaply, while 

 others, Avhich in the case of the precious 



"Average of eight eruptives from Missouri, 

 Anals. by J. D. Robertson. Report on Lead and 

 Zinc, Mo. Geol. Surv., II., 479. 



"Average of six different rocks, embracing 

 eighteen assays; S. F. Emmons, Monograph XII., 

 U. S. Geol. Surv., 591. 



' One rock, a quartz porphyry, not certain the 

 rock was not enriched. J. D. Curtis, U. S. Geol. 

 Surv., Mono. VII., 136. 



" Same reference as under 6. The zinc was de- 

 termined in but two samples. 



" Same reference as under 6, but p. 594. 



"S. F. Emmons, XVII. Ann. Rep. U. S. Geol. 

 Survey, Part II., p. 471. 



"A. Simundi in Tenth Census, XIII., 54. 



metals are often called base ores, require 

 complicated and it may be expensive metal- 

 lurgical treatment. The association of 

 metals is likewise of the highest importance. 

 Copper or lead, for example, greatly facili- 

 tates the extraction of gold and silver, 

 whereas zinc in large quantities is a hin- 

 drance. Conditions also change. An ore 

 which may have been valueless in early 

 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 Avas 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 extrac- 

 tion and treatment in thousands of tons 

 daily are paying good returns on Very large 

 capitalization. Another factor is the ex- 

 pense of extraction. If simple and inex- 

 pensive methods are possible, the area of 

 profitable treatment is greatly widened. 

 Thus gold may n6ed little else than a 

 stream of water or even a blast of air, 

 whereas iron and copper require huge fur- 

 naces and vast supplies of coke and fluxes. 

 Iron ores are of little value in any part 

 of the world unless they contain a mini- 

 mum of 35 per cent, iron when they enter 

 the furnace, but if they are distributed in 

 amounts of 10-20 per cent., in extensive 

 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 



