

CHAPTER V. 



DESCRIPTIVE GEOLOGY OF MINES AND PROSPECTS. 

 THE KNOWIST EARLIER ANDESITE VEINS. 



MIZPAH VEIN SYSTEM. 

 MIZPAH VEIN. 



EXTENT OF VEIN. 



Limitation of vein Jyy Mizpah fault. The Mizpah vein has a strong outcrop 

 (PI. XVII), extending for a distance of about 800 feet in a nearly due east-west 

 direction. Toward the east end it is broken by a number of small faults, mostly, 

 it appears, with a north-south strike and an easterly dip, by which the vein is 

 offset, now in one, now in the other direction; and it is cut off abruptly by the 

 great northwest-southeast break, which may be called the Mizpah fault (PI. 

 XVI). This fault is clearly recognizable at the surface and in the underground 

 workings on the several levels (PI. XIX), as well as in the Desert Queen, the 

 Montana Tonopah, and the North Star workings. It has a moderate dip to the 

 northeast. Wherever the veins have been followed to this fault, they have been 

 found to be cut off abruptly; and the presence of a zone of clay due to rubbing 

 or trituration, and frequently of a drag of fragments from the quartz veins 

 along this zone, give evidence of a great movement subsequent to the vein 

 formation. On the upper side of the -fault, overlying the earlier andesite in 

 which the veins lie, is the later andesite. Since the later andesite is normally 

 above the earlier andesite, a normal fault, with a downthrow on the northeast 

 side, is shown. 



Limitation of vein by Burro fault. On the west side the outcrop of the vein is 

 abruptly cut off by the Burro fault, beyond which the later andesite again outcrops. 

 This fault, traceable on the surface only by the use of the utmost skill, runs 

 northeastward. A break corresponding to this, and probably identical with it, 

 has been encountered underground in the west workings of the mine, farther 

 west than on the surface, showing that the fault dips northwestward. 



Limitation of vein by Siebert fault. The vein normally dips north at an average 

 steep angle, but alternately flattens and steepens, and is even locally overturned 

 (fig. 16). It has been followed on the dip to a depth of nearly 700 feet, where it 



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