USEFUL METALS 111 



is often intimately associated with galenite and isomorphous 

 with it. All galenite is more or less argentiferous but the coarsely 

 crystallized variety like the galenite of Rossie, St. Lawrence Co., 

 N. Y., is low in its silver content, while much of the finely crystal- 

 lized galenite of the Cordilleran section is highly argentiferous. 



The last seven minerals are not important as ores of lead, but 

 the artificial massicot, minium and crocoite are important in 

 the arts and industries. Wulfenite and stolzite are interesting 

 molybdenum and tungsten salts of the metal. There are also 

 many compound minerals playing only a minor rdle in the metal- 

 lurgy of the metal. 



Origin of the Ores. As already noted, native lead is always of 

 secondary origin, the direct product of the reduction of other 

 ores. The sulphide of lead is precipitated in the laboratory 

 whenever a solution bearing H 2 S comes in contact with neutral 

 or slightly acid solutions bearing lead salts. Galenite appears 

 to have been formed in most cases from mineralized solutions 

 by hydro-chemical reactions, or by hydatogenetic reactions at 

 temperatures which are not excessively high. Mayencon has 

 reported galenite as a product of sublimation in a burning coal 

 mine, Lacroix and Zambanini both report galenite as a Vesuvian 

 sublimate formed during the eruption of April, 1906. 



Anglesite is a common oxidation derivative of galenite in the 

 presence of water or moist atmosphere. The carbonate, cerus- 

 site, is derived from the oxidation of other ores of lead in the 

 presence of carbonated waters in the upper level of ore bodies. 

 Therefore anglesite and cerussite are generally present in the 

 oxidized zone of an ore body bearing lead minerals. The rich- 

 ness of the ore varies with the extent of the decomposition that 

 has taken place. If it is limited to the breaking down of galenite 

 the ore is sometimes very rich. If the associated country rock 

 has also suffered decomposition the ore has absorbed so much 

 carbon dioxide in the formation of earthy carbonates that it is 

 often too poor in lead to pay for profitable extraction. The 

 oxides are always of secondary origin and result directly from 

 the decomposition and reduction of other lead minerals. The 

 chloride of lead, cotunnite, is a volcanic mineral produced by 

 sublimation. 



Character of the Ore Bodies. Primary galenite appears to 

 be connected with the acid intrusives of all ages. Minerals 

 which characterize ores of pneumatolytic origin are absent and 



