194 GEOLOGY OF TONOPAH MINING DISTRICT, NEVADA. 



hard white rhyolite. It is located about 200 feet south of the contact of the 

 rhvolite with the later andesite. This contact is exposed in a short trench and 

 in a pit about 8 feet deep, and the rhyolite is seen to be intrusive into the 

 andesite, with an approximately perpendicular contact (fig. 72). This, together 

 with the depth of the Belmont shaft, indicates that it is being sunk in the 

 Rushton Hill neck (which is a part of and is connected with the Mount Oddie 

 neck) at a point where the contact is very steep. 



RESCUE SHAFT. 



The Rescue shaft is located south of Mount Oddie, about one-fourth of 

 a mile southeast of the Desert Queen shaft. It is near the contact of the white 

 rhyolite which makes up Mount Oddie and Rushton Hill with the later andesite. 

 The contact is exposed at the surface, about 120 feet north of the shaft, and 

 here has a general east-west strike and a southerly dip of from 45 to 60. The 

 contact is intrusive and there is some slight brecciation of the intrusive rock in 

 the bends of the lobes which jut into the intruded rock, showing squeezing of the 

 upflowing lava at these points. 



The shaft, which starts in the later andesite, cuts the same contact as has 

 been described in outcrop, at a depth of 60 feet. This contact pitches in the 

 shaft about 45 to the south. From this point to a depth of 410 feet, which 

 the shaft had attained at the time of the writer's visit in November, 1904, the 

 rock was entirely white rhyolite of the Oddie Mountain type. From this it 

 will be seen that the shaft is being sunk in the intrusive rhyolite neck. 



Water has been encountered in this shaft (see p. 105). 



EXPLORATIONS ON VEINS AT THE CONTACT OF THE TONOPAH 



RHYOLJTE-DACITE. 



MIZPAH EXTENSION SHAFT. 

 LATER ANDESITE AT TOP OF SHAFT. 



The Mizpah Extension shaft is sunk in the hollow between the two white 

 rhyolite intrusions of Mount Oddie and Ararat Mountain. The later andesite 

 outcrops between these two intrusions, and on account of its relative softness 

 has been worn away to form the depression separating the two hills. The 

 shaft was started in this later andesite, and continued in it down to a depth of 

 about 200 feet. The rock is of a general purplish color, with large white feldspars 

 and biotite phenocrysts. At a depth of about 200 feet, however, a variety of 

 this is tine grained, black, almost basaltic looking, and is fresher than the rest 

 of the rock, which is sometimes considerably decomposed. 



