178 GEOLOGY OF TONOPAH MINING DISTRICT, NEVADA. 



level the rock is andesite, probably earlier andesite, largely altered to chlorite 

 and calcite, like that below the Siebert fault in the Mizpah shaft. The station at 

 the 1,050-foot level and a drift running southeastward from the shaft for over 200 

 feet are mainly in the Tonopah rhyolite-dacite. This rock is much silicified and 

 is in places cherty quartz. At the shaft and on the walls of the drift in this 

 formation there has formed, since the opening of the mine, a green coating. This 

 was determined by Dr. W. T. Schaller, of, the United States Geological Survey, 

 to be a basic copper sulphate, insoluble in water. The cherty quartz on which 

 this incrustation forms contains only traces of gold and silver. Since the mine is 

 perfectly dry the formation of this copper sulphate on the walls is interesting. 

 A similar incrustation forms on the quartz of the rhyolitic "veins on the 84rO-foot 

 level of the Desert Queen. It seems, so far as observed, to be a phenomenon 

 peculiar to the quartz of the Tonopah rhyolite-dacite and to have no connection 

 with gold and silver values. 



On the.- 1,050- foot level in the earlier andesite a phenomenon was noted which 

 was not observed elsewhere 1 in the camp. This is the intrusion of one body of . 

 earlier andesite by another body of the same rock. The intrusive rock is tiner 

 grained than the rock which it cut, and near the margin showed flow structure. 

 The coarser intruded rock is of the biotite-bearing variety, while the intrusive 

 rock is of .v.ery similar composition and is very typical earlier andesite. This 

 occurrence is analogous to the finding in the Tonopah City shaft of dikes of 

 Heller dacite intrusive into a body of the same rock, and signifies successive injec- 

 tions of the earlier andesite, which may very well be of slightly different types 

 as regards composition. 



VEINS. 



On the 950 foot level, north of the shaft, a vein of quartz several feet thick 

 was cut in the earlier andesite. This has a general west-northwest strike and 

 a northerly dip of 45 or 50. This vein was cut also in the 1,050-foot level 

 and is developed by an incline between the two levels. Some ore has been shipped 

 from it, having the same characteristics as the ore of the Montana Tonopah; it 

 contains polybasite, ruby silver, etc., in a white quartz gangue. This is very 

 likely the same as the Montana vein of the Montana Tonopah. 



FAULTING. 



It has not been possible to follow this vein very far along the strike or dip 

 in any one place on account of faulting, which follows the vein very nearly in 

 strike and dip but curves and becomes oblique to it. On the 950-foot level this 

 fault nan a strike whicli is more northerly thitn that of the vein, and so has cut 

 out most of the vein, leaving only a wedge. On this level the fault is below the 

 vein, bufc in following the incline down to the level below, it is found to puss 

 through the vein and to go into the hanging wall, us shown in fig. 67. 



