COLLECTIONS IN ECONOMIC GEOLOGY AND METALLURGY. 41 



(f)!) Cenissite, massive, impure. Eureka Consolidated Mine, Eureka district, 

 Eureka County, Nevada. ( 15523. ) 



(5'J) Cerussite, massive, impure. Eureka Consoli.lated Mine, Eureka district, 

 Eureka County, Nevada. (65371.) 



(5:?) Cerusflite, massiv(% impure. Cbaney Mine, Bradsliaw district, Heavfir County, 

 Ur.ah. (HCmI.) 



(54) Cerussite, massivts, iiiumrc. Kiiiiua Mine, Little Cottonwood district. Salt 

 Lake County, Utah. (Irf045.) 



(55) Cerussite, impure, in powder. Counuouly called sand caroonate. Rebellion 

 Miue, Pinyon Hill, Summit County, Utah. (55350.) 



(56) Cerussite, impure, in powder. Very rich, 1,490 ounces silver per ton. Com- 

 monly called sand carbonate. Matchless Miue. Leadville, Lake County. Colorado. 

 (56435.) 



(.57) Cerussite, impure, in powder. Verj' rich, 2,704 ounces silver per ton. (Join- 

 monly called sand carbonate. Robert E. Lee Miue, Leadville, Lake County, Colo- 

 rado. (.50437.) 



(58) Cerussite, crystalline powder, containing also crystals of wulfonite. Com- 

 monly called sand carbonate. Eureka district. Eureka County, Nevada. (30566.) 



The Smelting of Base Bullion. 



Ill carrying on the smelting of base bullion it is necessary to have 

 a sufficient supply of ores carrying a suitable percentage of lead, if ores 

 carrying high percentages are available, then ores with only a small per- 

 centage, or none at all, may be mixed with them. Ores low in lead are 

 known as dry ores. The smelting operation is generally carried on in a 

 shaft furnace, the use of the reverberatory furnaces being mainly con- 

 fined to ores carrying, in addition to the lead and silver, a considerable 

 percentage of copper. Ores that exist in the oxidized state and those 

 containing only a small percentage of sulphur are smelted directly, but 

 if the ore is mainly a sulphide it must be subjected to a previous roasting 

 operation to remove the greater portion of the sulphur. This roasting 

 also removes some arsenic and antimony. 



The most suitable ores for the operation are those containing only 

 lead and silver minerals with quartz. It is seldom, however, that a 

 large supply of such ores can be obtained, various other metals which 

 influence more or less the smelting operation, the most objectionable of 

 which is zinc, being frequently found in the ore. Various other gangues 

 besides quartz are common, the most important being oxides of iron, 

 calcite, and barite. The first two of these can be mixed with great ad- 

 vantage with quartzose ores, since the iron and lime will neutralize the 

 silica, but the latter is quite objectionable. 



The process of roasting the sulphide ores is carried out in two ways, 

 depending on the character of the ore and its physical condition. If the 

 ore is in lumps it is roasted in brick stalls, only sufficient fuel being used 

 to start a vigorous combustion of the suli)hur, the operation being com- 

 pleted by the heat furnished from the burning of the sulphur, if, how- 

 ever, the ore is in the form of a powder, it is roasted in reverberatory 

 furnaces, which are heated by flame, either from wood, .soft coal, or gas. 

 The ore is introduced at the coldest end of the furnace and is gradually 



