172 GEOLOGY OF TONOPAH MINING DISTRICT, NEVADA. 



and having all the characteristics of the typical quartz vein of the district. The 

 trustified vein also is not regular nor persistent, and seems to have filled uneven 

 clefts or openings in the main vein, which itself has every appearance of having 

 been formed by silicification along fracture zones in the way previously outlined 

 for the outcropping veins of Mizpah Hill (fig. 61). 



CONDITIONS OF KOKMATION OF MONTANA VEIN. 



The gangue and the metallic contents of the crustified vein are, however, of 

 exactly the same kind as those of the ordinary inclosing vein. There is no 

 reason to doubt that both portions of the vein are primary, like the different 

 depositions noted in the breccia ore. The phenomena indicate that, in this portion 

 of the vein at least, rock movement went on subsequent to the first ore depo- 

 sition and to the first cementation of the fractures by quartz, producing in places 

 a breccia, which was cemented with similar materials by vigorously circulating 

 mineralizing waters, and even forming irregular open spaces, in which the ores 

 and gangue materials were deposited in successive layers. It seems that the 

 movement continued even after the beginning of the deposition of some of these 

 crustified masses, for some of the breccia ores show fragments of very light and 

 of very black quartz, such as are characteristic of the crustified veins and not of 

 the ordinary type, intimately associated. The later part of the mineralization 

 thus indicated may have occurred at a period when the solutions were richer in the 

 metallic minerals than previously, for this portion of the vein is characterized 

 bv extremely rich ore, and some of the faces exposed in breaking down the vein 

 showed great masses of the black sulphides, constituting ore of a richness that 

 is rarely seen in such quantity. 



KATLT8 ON THE 460-FOOT LEVEL. 



As shown on fig. 60, the northeast branch vein is interrupted by a number of 

 minor slips or faults. On the east the Montana vein is sharply cut by northeast 

 faults having a southeast dip of about 35, and its eastward continuation has not 

 been found. The smaller faults of this series show that the result as seen in 

 horizontal section is an offset to the south on the east side. Such an effect might be 

 due to a variety of displacements; in this case the strong striae, pitching east at an 

 angle of 30 on the fault planes, show a diagonal downthrow on the east. According 

 to this, the continuation of the Montana vein should be offset to the south from the 

 present course. 



The relative positions of the Montana and Mizpah veins at this level are shown 

 in fig. 62. 



