184 GEOLOGY OF TONOPAH MINING DISTRICT, NEVADA. 



for the most part. The main shaft passes through this contact between the 

 385-foot level and the bottom, which is at a depth of 485 feet, and from the 

 bottom a north drift runs out about 100 feet to the contact again. The heavy 

 silicitication resulting in the formation of jaspery barren quartz, especially near 

 the contact, is shown also on this level. 



This contact was followed upward from the 385-foot level by means of an 

 incline for some distance, and showed more or less of the same rhyolitic quartz. 

 The dip of this silicified contact is less than that of the Tonopah Extension vein 

 in the earlier andesite, so that very likely these may come together at a greater 

 depth, in which case the barren jaspery portion of the Tonopah Extension vein 

 will unite with the similar quartz in the rhyolite -dacite, with which it has 

 undoubtedly a common origin. In this eventuality, however, the productive 

 portion of the Tonopah Extension vein may be cut off. 



The relative position of the Tonopah Extension vein in regard to that of 

 other known veins of similar character is shown in fig. 70. 



OTHER EXPLORATORY WORKINGS WHOLLY OR PARTLY IN EARLIER 



ANDESITE. 



WEST END WORKINGS. 

 OUTCROP OF WEST END FAULT. 



As the map (PI. XVI) shows, the West End shaft is near the contact of the 

 Fraction dacite breccia on the southwest and the later andesite on the northeast. 

 This contact follows a straight line, and was judged, from a study of the surface 

 only, to be due to faulting. By projecting the known outcrops of the Gold Hill, 

 and the Wandering Boy faults it is seen that they would normally come together 

 in the vicinity of the West End shaft. Here they probably unite to form a 

 fault which is a direct continuation of the Gold Hill fault, and which is thought 

 to have been recognized farther on, in the line separating the later andesite 

 from the Fraction dacite breccia, in the vicinity of the MacNamara shaft. This 

 united fault may be called the West End fault. In general this fault appears to be 

 downthrown on the southwest, for the Fraction dacite breccia on this side is 

 younger than the later andesite on the northeast. Moreover, both the Gold 

 Hill and the Wandering Boy faults are downthrown on the southwest side. 



RHYOLITE INTRUSION ALONG FAULT. 



Near the West End shaft are seen rugged outcrops of dark-weathering 

 rhyolite, which belong to a dike or neck of rhyolite that has ascended along the 

 fault plane. Where encountered in the mine workings this rhyolite is white, 

 and of the same type as the rhyolite of Mount Oddie, and is probably of the same 

 age and origin. 



