200 GEOLOGY OF TONOPAH MINING DISTRICT, NEVADA. 



dips west at angles of 50 or 55. The shaft was, at the time of the writer's last 

 visit in the fall of 1904, about 585 feet deep, and the lower part was all in the 

 later andesite. At the surface the contact seen in the shaft outcrops 50 or 60 feet 

 east of the shaft. No mineralization was observed. 



SHAFTS AT THE CONTACT OF THE BROTJGHER DACITE. 



BIG TONO SHAFT. 



This shaft is sunk in the intrusive dacite neck on the east side of Brougher 

 Mountain. It was started in the glassy contact phase of the neck at the very 

 contact with the dacite breccia, into which the neck is intrusive. The shaft is 

 somewhat over 300 feet deep, and is entirely in the Brougher dacite. 



For a depth of about 50 feet the glassy phase persists in the shaft, below 

 which is the ordinary porphyritic phase. This indicates that with depth the shaft 

 departs from the contact, which at this point must pitch away from the mountain. 



MOLLY SHAFT. 



The Molly shaft is situated at the west end of Golden Mountain. It was 

 sunk in the summer of 1903 and was 468 feet deep when work was stopped. A 

 rough estimate of the section passed through, made by climbing down the some- 

 what tightly lagged shaft, was that the Brougher dacite occupied the upper two- 

 thirds, and the Fraction dacite breccia most of the lower third, with 25 feet of 

 later andesite at the bottom. There seems to have been some Tonopah rh3'olite- 

 dacite sheets in the Fraction dacite breccia. No water was encountered. 



As shown on the map, the shaft lies about 250 feet east of the nearest point 

 of contact of the Golden Mountain intrusive dacite neck with the older rocks. 

 This contact, therefore, has here a pitch of about 45 toward the mountain, a 

 fact which is also indicated by the inward pitch of the outcropping contact and 

 by the flow structure in the dacite at the contact for some distance to the north 

 and east. The shaft has thus passed downward out of the dacite neck into the 

 older formations. 



SHAFTS WHOLLY OK CHIEFLY IN DACITIC TUFFS. 



NEW YORK TONOPAH SHAFT. 



The New York Tonopah lies between Butler and Brougher mountains and 

 when last visited by the writer the workings consisted of only a shaft 745 feet 

 deep. At the point where the shaft was sunk the surface consists chiefly of 

 brecciated lavas and tuffs which have been referred to the glass}' Tonopah 

 rhyolite-dacite. However, the rocks belonging to this formation, when they are 

 chiefly fragmental, as they are here, are often not easily distinguishable, or 



