MIZPAH EXTENSION SHAFT. 195 



RHTOLITE AND RHYOLITE-DACITE IX SHAFT. 



At a depth of 300 feet the andesite is in contact with an underlying typical 

 white rhyolite, like that of Mount Oddie. This contact strikes about N. 60 W. 

 and dips northeast at from 20 to 25. Both andesite and rhyolite have been 

 softened near the contact by circulating waters, so that their contact phenomena 

 are not observable. At a depth of about 430 feet in the shaft the rhyolite comes 

 in contact with a rock referred to the glassy Tonopah rhyolite-dacite. This 

 contact strikes N. 30 W. and dips northeast at an angle of 40, and is marked 

 by about 14 feet of wet clay, decomposed and containing bowlders. Some water 

 runs on top of this clay zone. 



VEINS AT CONTACT OF TONOPAH RHYOLITE-DACITE. 



Immediately below the contact, but in the Tonopah rhyolite-dacite, a large 

 quartz vein comes in. This vein is several feet thick, and has the same attitude 

 as the contact. Indeed, it appears to follow the contact, although it lies in the 

 rhyolite-dacite. At a depth of 500 feet a drift was run for the puipose of 

 developing this vein. The lower contact of the vein in the shaft (at 465 feet) 

 has a strike of N. 70 W. and a northeast dip of 45, but it is much natter 

 between this point and the point at which it was cut in the drift, where it 

 has, however, the same general strike. In this drift, which runs in an irregular 

 course for upward of 150 feet, the vein is displaced, not far from the shaft, by a 

 vertical fault having a strike of N. 45 E. The displacement of this fault is not 

 known, as the vein was not looked for on the southeast side. On the northeast side 

 it was drifted on for some little distance, and continued strong. This vein is an 

 ordinary quartz vein which is not very dissimilar in appearance from the average 

 vein in the earlier andesite, but which contains a notably large amount of pvrite. 

 It has locally a banded structure, which is probably due chiefly to replacement. 

 Nevertheless, the vein is ordinarily nearly barren, the highest assay obtained 

 having been about $12. The proportion of values differed from the ordinary 

 Tonopah vein in that they were about 75 per cent gold and 25 per cent silver. 



At a depth of 505 feet in the shaft another quartz vein was encountered, 

 several feet thick, with characteristics like the one above. This vein has a strike 

 of N. 55 W. and a dip of 55 to the northeast. A specimen of the wall rock 

 taken immediately below this vein proved to be andesite, probably later andesite. 

 Therefore this vein appears to occur on the under contact of the Tonopah rhyolite- 

 dacite with the later andesite, while the first-mentioned vein occurs on the upper 

 contact of the same rhyolite-dacite body. 



This rhyolite-dacite is similar to that which outcrops to the north of Ararat 

 Mountain, is like that discovered in depth in the Desert Queen and Siebert shafts. 



