18 



SCIENCE. 



[N. S. Vol. XXIII. No. 575. 



America with our rich and pure deposits 

 on Lake Siiperior two thirds of our supply 

 ranges from 60-65 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 excep- 

 tional deposits of the native metal in the 

 Lake Superior region, copper-rock as low 

 as three fourths of one per cent, has been 

 profitably treated. This or any similar re- 

 sult could only be accomplished with excep- 

 tionally efficient management and with a 

 copper rock such as is practically only 

 known on Lake Superior. With the usual 

 type of ore, not enriched by gold or silver, 

 two per cent, is the extreme and in remote 

 localities five, to ten may sometimes be too 

 poor. 



In southeast Missouri, lead ores are 

 profitably mined which have 5-10 per cent, 

 lead, but they are concentrated to 65-70 

 per cent, before going to the furnace. 



Zinc ores at the furnace ought not to 

 yield less than 25-30 per cent., and when 

 concentrated or selected they range up to 

 60 per cent. 



The precious metals are expressed in 

 troy ounces to the ton avoirdupois. A troy 

 ounce in a ton is one three-hundredths of 

 one per cent., and the amount is, therefore, 

 very small when stated in percentages. If 

 it be appreciated that in round numbers 

 silver is now worth fifty to sixty cents an 

 ounce and gold twenty dollars, some grasp 

 may be had of values. Silver rarely oc- 

 curs by itself. On the contrary, it is ob- 

 tained in association with lead and copper, 

 and the ores are, as a rule, treated pri- 

 marily for these base metals, and then from 

 the latter the precious metals are later 

 separated. In the base ores there ought 

 to be enough silver to yield a minimum 

 of five dollars or ten ounces in the result- 

 ing ,ton of copper in order to afford enough 

 to pay for separation. Now in a five 



per cent, ore of copper we have a con- 

 centration of twenty tons of ore to yield 

 one ton of pig, or, more correctly stated, 

 so as to allow for losses, twenty-one tons 

 to one. We must, therefore, have at 

 least ten ounces of silver in the twenty- 

 one tons, which implies a minimum of 

 about one half ounce per ton. Smelters 

 will only pay a miner for the silver 

 if he has over one half ounce per ton in 

 a copper' ore. In a pig of lead, usually 

 called base bullion, it is necessary for 

 profitable extraction to have fifteen ounces 

 of silver. For smelting a lead ore we must 

 possess at least ten per cent, lead and may 

 have seventy. It is, therefore, obvious 

 that from two to twenty ounces silver must 

 be present in the ton of lead ore. The 

 common ranges are ten to fifty ounces or 

 one thirtieth to one sixth of one per cent. 



Gold is so cheaply extracted that it may 

 be profitably obtained under favorable cir- 

 cumstances down to one tenth of an ounce 

 in the ton, but the run of ores is from one 

 fourth ounce or five dollars to one ounce 

 or twenty dollars. Ores of course some- 

 times reach a number of ounces. In cop- 

 per or lead ores even a twentieth of an 

 ounce may be an object and in favorably 

 situated gravels, to which the hydraulic 

 method may be applied, even as little as 

 seven to ten cents in the cubic yard may be 

 recovered or some such value as one two- 

 hundredths to one three-hundredths of an 

 ounce per ton. 



The tin ores as smelted contain about 70 

 per cent., but they are all concentrated 

 either by washing gravels in which the 

 percentage is one or less or else by mining, 

 crushing and dressing ore in which it 

 ranges from 1.5 to 3 per cent. The tin- 

 bearing gravels represent a concentration 

 from much leaner dissemination in the 

 parent veins and granite. Aluminum ores 

 yield as sold about 30 per cent, of the 

 metal. This is an enrichment as compared 



