84 



GEOLOGY OF TONOPAH MINING DISTRICT, NEVADA. 

 VEINS DUE CHIEFLY TO REPLACEMENT. 



That the circulation channel was in practically every case a fracture zone and 

 not an open fissure is shown by the study of the veins, which reveals all stages 

 in the change from a fracture zone in porphyry to a solid quartz vein. In many 

 cases the vein consists simply of a zone of more or less altered andesite, not 

 essentially different, except, perhaps, for a somewhat greater silicification, from 



N 



I > 



North Star Shaft a 



Tonopah Extension Shaft 



i MacNamara Shaft 



Montana Tonopah Shaft B 



Tonopah Mining Company 

 a Main Shaft 



:.'lzpah Vein 



West End Shaft 



B Fractlon No.l Shaft 

 Fraction No.2 Shaft x^y 



B Wandering Boy Shaft 



Fraction NoJ Shaft 



B Silver Top Shaft 

 Stone Cabin Shaft 



Valley View 

 Vein Group 



Gold Hill Shaft 



Tonopah City Shaft 



300 200 100 



California 



Tonop.'ih 

 " Shft_ 



FIG. 12. Map showing outcropping veins of Tonopah. 



the andesite which forms the walls. This zone is cut by parallel fractures having 

 the same strike and dip as the walls, and the walls themselves are nothing more 

 than stronger fractures of the same kind. In the next stage, where part of this 

 fractured zone becomes altered to quartz, the main wall fractures have been the 

 most favorable for water circulation, so that sometimes a hanging-wall streak of 

 quartz and a foot-wall streak are found with only altered andesite between. 



