NEW YORK ACADEMY OF SCIENCES 639 



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 resulting ton of copper in order to afford enough 

 to pay for separation. Now in a five per cent, ore of copper 

 we have a concentration 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 circumstances down to one tenth of an ounce in 

 the ton, but the run of ores is from a fourth ounce, or five dollars, 

 to an ounce, or twenty dollars. Ores of course sometimes reach a 

 number of ounces. In copper or lead ores even a twentieth of 

 an ounce may be an object, and in favorably situated gravels to 

 which the hydraulic method maybe applied, even as little as seven 

 to ten cents in the cubic yard may be recovered, or some such value 

 as a two-hundredth to a three-hundredth 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 with the rocks, though not so striking 

 a one as in the case of other metals. But the great change 

 necessary in aluminum is in the method of combination. It is 

 so tightly locked up in silicates in the rocks as to preclude direct 

 extraction by any known method. 



