126 



GEOLOGY OF TONOPAH MINING DISTRICT, NEVADA. 



drawn from this rhyolite-andesite contact at the surface near the Desert Queen 

 to the contact in the shaft has a general angle of dip of about 68. The contact 



at the surface is evidently an intrusive 

 one, being on the western side of one 

 of the intrusive lobes which radiate 

 from the main rhyolite mass of Mount 

 Oddie. 



Tonopah Mining Co. 

 SteOcrt shaft 



\ M.zpah 500 ft leve 



Desert Queen 



I '3r 



I Belmont 609 ' 

 Mf uoor,,..*.. 



Scale 

 ?oo 



ofeet 



VARIABLE ATTITUDE OF MOUNT ODDIE INTRUSIVE 

 CONTACT. 



The steep dip of the contact be- 

 tween the andesite and the intrusive 

 rhyolite at this point is in contrast 

 with the flat portion of the same con- 

 tact in -the North Star shaft, where the 

 lower surface of the rhyolite is very 

 flat, dipping toward the mountain at 

 an angle not greater than 10, although 

 the later andesite shows the same brec- 

 ciation as at the contact in the Desert 

 Queen shaft, indicating that the rhyo- 

 lite is intrusive. This difference in dip, 

 however, is in accord with other obser- 

 vations made along the contact of the 

 rhyolite, all possible variation being 

 found, the contact being sometimes flat, 

 sometimes vertical, sometimes, indeed, 

 dipping away from the mountain rather 

 than toward it, but always showing the 

 intrusive character of the rock. 



MIZPAH VEIN IN DESERT QUEEN WORKINGS. 



The Desert Queen shaft cut the 

 Mizpah fault at 512 feet, and beneath 

 it the earlier andesite. At 500 feet a 



Fio. 26. Horizontal planof mine workings, showing the rela- drift run a short distance north from 

 tlon of the vein In the Desert Queen workings to that on the 1 i i .1 \i- u i- 1, 



corresponding level of the Mizpah mine. the * haffc cut the Mizpah fault again 



and exposed an important vein (fig. 26). 



The vein is sharply cut off by the fault on the east and is much sheeted and broken 

 by the fault movement, so that its course is not immediately evident. The general 



