194 MINING INDUSTEY. 



bitrary. It is not the same in all mines, and does not appear to have been the 

 same at all times in individual mines. The chief object of the classification 

 is to separate those ores whose mineral composition and, more especially, 

 whose high value demand a very exact and careful treatment in order to ob- 

 tain the highest possible jDercentage of their precious contents, from those of 

 lower grade, which must, by reason of their inferior value, be treated by less 

 expensive methods. 



The first class usually embraces those ores whose assa}^ value exceeds 

 $150, or, in some cases, $100, per ton. The second class, where distinguished 

 at all, is usually designed to include ores whose assay value ranges between 

 $90 and $150 per ton. The third class embraces all workable ore of lower 

 grade than the foregoing, the average assay value varying considerably in 

 different mines. 



The first-class ores form but a very small proportion of the whole. The 

 tabular statement in the foregoing chapter, showing the ore product, with the 

 actual yield per ton, of some of the principal mines during five years past, al- 

 though not complete in this respect, will serve to indicate the relative propor- 

 tions of the several classes of ore. Thus, during the year ending July 1, 

 1868, the Savage mine produced, including the amount taken out by contract- 

 ors, 87,341 tons of ore, of which 277 J tons were first-class, having an average 

 assay value of $449 40 per ton, and an average yield of $359 52. During the 

 same year 4,745 tons of second-class ore were produced, of which the average 

 assay value was, as determined by two different methods of samphng, $124 25 

 and $142 82 per ton; the average yield being $78 16. In the following year, 

 in a total product of 69,287 tons of ore, only 685 tons were distinguished as 

 first-class, having an average assay value of $275 47 ; while no assortment 

 of second-class ore was made in that year. During the year ending July 1, 

 1868, the average assay value of 78,432J tons of ore produced by the Savage 

 mine, and denominated as third-class, was, by two different methods of sam- 

 pling, respectively, $52 01 and $55 11 per ton; the average yield being 

 $37 20. In the following year the average assay value of 55,411 tons of 

 third-class ore reduced was, by the two methods of sampling, $60 29 and 

 $50 78 per ton; the average yield being $34 64. 



