SILYEE MmiNG IK COLORADO. 623 



upper macliiiies and one of the lower, immediately in front of it, are furnished 

 with No. 6 sieves for washing the coarser material, while the other two, 

 upper and lower, are furnished with No. 10 sieves for the finer stuff. The 

 ore that enters upon the upper sieves is therefore rewashed on the lower 

 sieves, in order to insure a more effective separation. The overflow of the 

 two upper sieves, of either degree of fineness, that is, the material discharged 

 at q, is washed again upon one of the lower sieves of the same degree of fine- 

 ness, the overflow from that sieve being worthless gangue, while that which 

 passes through the sieve is second-quality ore, or blende and copper mixed. 

 The stufi" that passes through the two upper sieves, of either degree of fine- 

 ness, is delivered from the outlet pipes, o, and comes upon the remaining 

 sieve of corresponding degree of fineness, the material which passes through 

 that sieve being of first quality, while the overflow, at $", is of second quality. 

 By this arrangement there are three products obtained : first, the pure galena, 

 which is almost entirely free from other mineral; second, the zincblende and 

 gray copper, mixed with heavy spar and quartz, almost free from galena; and 

 third, the gangue, which is very clean and free from valuable mineral. 



The eight sieves, or four double machines, are capable of treating 20 to 

 30 tons of ore per day; and as the stuff is all washed twice, the capacity of 

 each double machine, for a single washing, is from 10 to 15 tons per day. 



While the Scotch hearths were in use the dressed galena was smelted, 

 yielding about 50 or 60 per cent, of its weight in metal, which was shipped 

 to Newark for the extraction of silver. It contained, on the average, be- 

 tween $300 and $400 per ton. The total shipment from this source amounted 

 to about 10 tons. The costs of transportation were about as follows: 



Freight to Greorgetown, per ton $20 00 



Freight thence to Cheyenne, per ton 20 00 



Freight to Newark, per ton 37 00 



Making in all 77 00 



The costs of separation of the silver from the rich lead were stated at 

 $6, making $83, and with lead at 9 cents per pound, or $180 per ton, the 

 balance remaining for costs of mining and reducing was $97 per ton, which, 

 according to Mr. Collom's estimates, based on the experience already gained, 

 would be a sufficient allowance under regular and continuous operation. 



