58 



BULLETIN 12, UNITED STATES NATIONAL MUSEUM. 



facilities for workiug even iu those days were good, aud during the last 

 century a considerable amount of lead was extracted, but like all other 

 regions it has its ups and downs, and at present it is only by the utmost 

 care and economy that the mines can be profitably worked. The ore 

 consists of galena scattered through maguesian limestone, and is tech- 

 nically known as disseminated ore. The ore bodies occur in irregular 

 and often very large masses, but there is no distinct line of demarca- 

 tion between the ore and the barren limestone. The galena is accom- 

 panied by pyrite, and occasionally by chalcopyrite, and these generally 

 carry cobalt and nickel. Blende is occasionally found. The amount 

 of silver in the ore is not sufficient to be of any value, varying from 1 

 to 4 ounces per ton. 



The active mines are mostly found in Madison, Jefterson, Washing- 

 ton, and St. Frau9ois Counties, the most important being the St. Joe 

 and Desloge, Bonne Terre, St. Frauyois County, and Mine La Motte, 

 Madison County. The Valle Mine, St. Frangois County, produces a 

 considerable amount of zinc. 



Owing to the peculiar nature of the ore, a large part of it has to un- 

 dergo an elaborate system of mechanical dressing to separate the galena 

 from the limestone. The system of dressing at each of the large works 

 differs in material points from the others, and two of them are very 

 fully illustrated by the collections. 



The Desloge mill is very large, and is calculated to treat 300 tons 

 of rock per day. The ore passes through Blake crushers and then 

 through rolls, and is afterwards carefully classitied, so that each set of 

 jigs treats a material of very uniform size, differing from each other set. 

 In the St. Joe mill, after passing the crushers, the ore goes through 

 but one pair of rolls, and the material is fed direct to the jigs without 

 any classification at all. 



The product of these dressing operations consists of very pure galena, 

 commonly called " mineral," aud a mixture of pyrite and galena, com- 

 monly called "sulphur." The galena carries from 70 to 75 per cent, of 

 lead, the following being actual determinations : St. Joe, September 

 10, 1884, lead, 71.30 i)er cent.; Mjue La Motte, February, 1880, lead, 

 77.43 per cent.; January, 1881, lead, 72.12 per cent.; iron, 2.37 per cent.; 

 cobalt and nickel, 1 .51 per cent. ; copper, 0.92 per cent. ; insoluble residue, 

 1.30 per cent. The following analyses represent the composition of the 

 sulphides : 



SulpJiides. 



St. Joe. 



Miae La Motte. 



Lead (Pb) 



Iron (Fe) 



Cobalt and nickel (Co and Ni) 



Insoluble residue 



Sulphur (S) 



Analysts 



Per cent. 

 21. S7 

 16.21 

 0.61 



Per cent. 

 17.17 



4.77 



Nelll. 



Per cent. 1 Per cent. 



13.34 



44.24 



4.07 



3.58 



20.37 



0.98 



40.60 



0.71 



4.40 



41.18 



Neil. 



Neill. 



