LEAD ORES. The principal ore of lead is galena (PbS), which contains S6.0 per cent. of metal. The sulphate (anglesite), the carbonate (cerusite), and the phosphate (pyromorphite) are occasionally found in sntlicient quantities to warrant exploitation: while the arsenate, chro mate, vanadate, molybdate, and oxide have little metallurgical importance. Galena always con tains some silver and usually a little arsenic, antimony, copper, zinc, and gold. When the content of silver reaches several ounces a ton, the ore is known as argentiferous galena. and is treated for the separation of the metals. Galena is a widely disseminated mineral, although it rarely occurs in large deposits. Along the At lantic border of the United States there are numerous localities where it is found in veins that cut through the Archaean and Paleozoic rocks, the gangue material being quartz or calcite. These deposits have not been worked, however, for many years, owing to the great abundance of rich ores in the Western States. One of the most productive mining regions is in Southeastern _Missouri. The ore is dissemi
nated in limestone through a thickness of about 200 feet, and it bars been taken out in enormous quantities from the workings at Nine La Motte, Doe Run, and Bonne Terre. Galena associated with zinc blende is found in Illinois. Wisconsin, and Iowa in proximity to the Mississippi' River, and also in southwestern Missouri in Jasper and Newton counties, and across the Kansas border in Cherokee County. The argentife•ous lead ores of the Rocky Mountain States are the principal sources of supply at the present time. The ore bodies are found in carboniferous lime stone, for the most part along the contact with sheets of porphyry; they yield hard and soft ores containing eerusite and silver chloride. In the deeper workings the oxidized ores give way to the unchanged sulphides. Lead-silver mines are operated at several localities in Utah. Large quantities of lead in crude form are imported into the United States from Mexico and British Columbia and refined by Western smelters.