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SMITHSONIAN MISCELLANEOUS COLLECTIONS VOL. 78 



and are without apparent direct connection with intruded granitic 

 rocks, although there probably is a connection. This class of ore is 

 comparatively simple mineralogically, consisting of silver, lead and 

 zinc minerals accompanied by only minor amounts of silicates. A 

 number of the richest and most extensive ore deposits of Mexico 

 belong to this type of ore occurrence. 



After leaving El Paso, the first district visited was Los Lamentos 

 in the northern part of the state of Chihuahua. This district con- 



FiG. 55. — The mining camp of Los Lamentos, Chihuahua. The rocks are 

 fossiliferous Cretaceous limestones. (Photograph by Foshag.) 



tains one of the few great ore deposits of Mexico that was not known 

 to the Spanish conquerors. The extremely dry and inhospitable nature 

 of the region probably accounts for this. The ore deposits are of 

 so simple a type and the relations of the ore to country rock so clear, 

 that it has become a standard for this type of occurrence. The ore 

 persistently follows the contact between a hard, dark gray lime- 

 stone and a lighter fossiliferous one, and consists of the simple lead 

 and zinc minerals without any development of silicate minerals but 

 with a surrounding aureole of recrystallized limestone. Many other 

 North Mexican ore deposits are similar, although not always so 

 simple. The mine is rich in showy minerals of both lead and zinc. 



