AGES OF THE VOLCANIC BOCKS. 

 CONCLUSION. 



71 



It may be provisionally concluded that the volcanic rocks at Tonopah, from 

 the earlier andesites to the Brougher dacites and the rhyolites, were erupted 

 between the early Miocene and some time in the first half of the Pliocene. 



The following, then, is the sequence of events as deciphered for the vicinity 

 of Tonopah (fig. 10): 



Hypothet- Hypothet- Earlier Later Dacite 

 ical deep- ical deep- andeatte. andesite. breccia, 

 seated seated 

 granite, limestone. 



Tonopah Lake beds. Faults, 

 rhyollte- 

 daelte. 



Later da- Earlier ande- 

 cite and site veins 

 rhyolite {lesser veins 

 intrii- belonging to 

 slons. other periods 

 not repre- 

 sented). 



FIG. 10. Ideal cross section of Tonopah rocks. (This section does not represent any particular place, and is simply 

 intended to illustrate the geologic conditionsa-s described in the text.) 



Sequence of formations and erent-s in the vicinity of Tonopah. 

 Earlier andesite. 

 Fracturing. 



Vein formation. Primary minerals, quartz, adularia (valencianite), carbonates of lime, 

 magnesium, and manganese, stephanite, polybasite, argentite, silver selenide, galena, pyrite, 

 chalcopyrite, etc. Values good; gold and silver, silver predominant. 

 Erosion. 

 Later andesite. 

 Probable erosion. 

 Heller dacite. 

 Fraction dacite breccia. 



Tonopah, rhyolite-dacite breccias, flows, and dikes, intermingled with slightly stratified or 

 unstratified pumiceous or tuffaceous fragmental material. 



Vein formation. Primary minerals, quartz, pyrite, barite. Values usually relatively low; 

 gold and silver, gold apt to predominate. 



