114 ECONOMIC GEOLOGY 



instances have been reported from Sardinia, England, and 

 Westphalia. 



The mineralizing solutions in most cases of metasomatic galen- 

 ite belong to the descending ground- water currents. There are, 

 however, examples of metasomatic replacement deposits that have 

 resulted from the action of heated solutions rising from below 

 in accordance with the theory of the ascensionists. Both of these 

 deposits usually occur in limestones which interact upon percola- 

 ting waters charged with solutions of lead salts. The limestones 

 did not originally contain the galenite. Its source was some 

 associated igneous rock or sulphide-bearing sediment. Alkaline 

 sulphides may have aided in effecting the solution of the lead, and 

 the lead in solution was doubtless transported as a sulphide and 

 deposited in the place of the dissolved limestone. 



Galenite is usually associated with several other minerals, 

 common among which are calcite, dolomite, siderite, sphalerite, 

 pyrite, rhodonite and quartz, as shown in Fig. 73. 



Geographical Distribution. Lead in its various ores is widely 

 distributed. The mineral galenite is found in almost all countries, 

 but few are of great importance. It occurs in the United States, 

 England and Sweden in limestones. In the Harz Mountains 

 it occupies veins in clay slate; in Freiberg it occurs in veins in 

 gneiss; in Spain as veins in granite. 



The United States is the largest producer of lead. The Ameri- 

 can area may be divided into three distinct fields: the Appala- 

 chian; the Missippi River belt, and the Cordilleran region. 



(1) The first district is of the least importance. It extends 

 from Alabama on the south to Maine on the north. The ores 

 are associated with Cambrian or Cambro-Ordovician metamor- 

 phics. The belt comprises a highly folded and often faulted 

 series of crystalline schists and limestones. In Pennsylvania 

 galenite occurs in many places in these crystallines and is often 

 argentiferous, varying from $2 to $2000 per ton in silver. Lan- 

 caster, Chester, Northumberland and Wayne Counties are most 

 important sections. In New York, at Rossie, St. Lawrence Co., 

 galenite occurs in veins 3 or 4 ft. in width. The crystals are 

 often very large and assiciated with a calcite gangue. In Vir- 

 ginia the terranes associated with lead at Austin's Mines and 

 Sterling are Cambrian and Ordovician. It is not likely that any 

 of these localities in the Appalachain belt will ever become great 

 producers of this useful metal (Fig. 74). 



