COLLECTIONS IN ECONOMIC GEOLOGY AND METALLURGY. 43 



Large ainouuts of base bullion are smelted at works located in and 

 near the mining regions, and the base bullion is shipped to other works 

 for retiuiug or to separate the silver from the lead. 



COLORADO SMKI.TER. 



To illustrate the smelting of base bullion a very complete collection 

 from the works of the Colorado Smelting Company, South Pueblo, 

 Colorado, is shown. The diagram, figure 3, illustrates the process fol- 

 lowed at these works. 



The ores as received at the works are classified into oxidized and sul- 

 phureted ; the oxidized ores are further divided into basic and siliceous, 

 that is, basic ores, the gangue of which is essentially a base, and sili- 

 ceous ores, the gangue of which is essentially acid or silica. These are 

 sent directly to the shaft furnaces. The sulphureted ores are also divided 

 into basic and siliceous ; in this case, however, it is the ores that are 

 high in sulphur that are called basic, for the reason that on roasting 

 they furnish mainly oxides, which act as bases in the smelting opera- 

 tion. The siliceous sulphureted ores consist essentially of quartz, with 

 only a small amount of sulphides. They are generally very rich in silver 

 and poor in lead, being more nearly true silver ores. 



The basic sulphureted ores are separated into coarse and fine. The 

 coarse are roasted in stalls and then go to the shaft furnaces; the fine 

 are roasted in reverberatory furnaces and are sometimes fused at the 

 end of the roasting and sometimes are not. From the roasting furnaces 

 they go direct to the shaft furnaces. The siliceous sulphureted ores 

 are sometimes roasted in the fusion furnace, but they are generally sent 

 to the shaft furnace, especially when they are very rich in silver. 



The fluxes are all basic and consist of iron ores and limestone and 

 go direct to the shaft furnaces. 



The products of the smelting in the blast furnaces are: 



(1) Base bullion which goes to the market. The bullion from these fur- 

 naces holds a high position with the refineries on account of its freedom 

 from impurities, due to the purity of the ores from the Madonna mine, 

 which form a large proportion of the charge in the shaft furnaces. It 

 varies in richness, although it generally carries 300 ounces of silver 

 per ton and about an ounce of gold. It is cast into bars or pigs weigh 

 ing 98 pounds and is shipped from the furnace in car loads of 300 

 bars. 



(2) Slag, which is divided into clean, or free from lead and silver, 

 which is thrown over the dump, and impure, that is, containing lead 

 and silver, which goes back to the shaft furnace. 



(3) ]\Iatte, which goes to the roasting stalls and then back to the 

 shaft furnaces. 



(4) Speiss, which goes to the roasting stalls and then back to the 

 shaft furnaces. 



(a) Flue dust, which is mixed with lime and ores low in lead, roasted 

 in the fusion furnace, and then goes back to the shaft furnaces. 



