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The method of treating silver ores is practically the same in all the mining centers of the country. The ore is first passed through a crusher and then separated by hand, Indian women being employed for this purpose, for which they are paid from 35 to 55 cents in Bolivian money per day, equal to from 20 to 35 cents in United States currency. Ores having 50 and more marcs per cajon, or, say, 165 ounces troy per ton and above, are placed in 100-pound sacks and shipped to Europe, while the lower-grade metals, down to 20 marcs per cajon, or yielding, say, 65 ounces of silver per ton, are treated at the mines, while all ores carrying less than 65 ounces are generally rejected as worthless. The first process here employed consists in milling the ore.

Milling the ore.—The mills used for this purpose are of three