584 MINING IKDUSTE^. 



Ounces of fine gold, per . Percentage paid of the value 



ton of 2,000 pounds. of the gold and copper. 



10 60 



9 58 



8 - 55 



7 52| 



6 50 



6 45 



4 ... 40 



3 30 



2 20 



■ In calculating the value of ore, according to the above scale, the ounce of 

 fine gold is reckoned at $20, coin, and the unit of copper at $2. The copper 

 unit, however, is to be reckoned on the English ton, and as the ores are as- 

 sayed and purchased by the short ton, a deduction of 12 per cent, is made on 

 the copper assay. Thus, if an ore is found to contain 8 per cent, or units of 

 copper, worth, according to the above scale, $16, a deduction of 12 per cent, 

 is made to adapt it to the English ton. Moreover, the copper is determined 

 by wet assay, from which W per cent, is to be deducted for working loss, so 

 that, if the percentage of copper contained in an ore does not exceed W, no 

 account is made of it in estimating its value. 



In addition to the above, the silver is paid for at the rate of 75 cents per 

 ounce, after deducting from the number of ounces contained per ton as many 

 ounces as there are units of copper, a rule said to be enforced at the Swansea 

 works. These values are all in coin ; they are paid in currency, allowing the 

 premium that rules at Central City on the day of settlement, usually 4 per 

 cent, below the rate at New York. 



As the great bulk of ores produced from the veins about Central City 

 are essentially gold-bearing, these Smelting Works have comparatively little 

 occasion to treat true silver ores, or such as are chiefly valuable for their sil- 

 ver, and carrying little or no gold. The proportion of this class of ore has 

 increased, however, of late, especially since the discovery of rich silver-bear- 

 ing veins, a mile or thereabouts below Black Hawk, in the neighborhood of 

 Slaughter-house Gulch, and it is reported that a furnace, specially designed 



