154 



GEOLOGY OF TONOPAH MINING DISTRICT, NEVADA. 



^V-^J- ^.'fracture' breccia 



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Earlier :-;andesite A /' 



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reallj- due to a fault of very great displacement is shown by the occurrence 

 underground along it of a thick friction breccia containing fragments of later 

 andesite, of granitic rock, and of the adjacent rocks. 



On the 115-foot level the main Wandering Boy fault is well developed (fig. 44). 

 The small 6-inch vein followed on this level shows a repeated breakdown to the 

 southwest a.s the main fault is approached, a movement corresponding to the chief 

 normal faulting. Besides this there are horizontal grooves along the main fault 

 plane, and similar striations are found on it where it is cut in the shaft below at 

 a depth of 185 feet. Furthermore, on the 115-foot level, the vein is bent and 



dragged to the northwest along the fault plane 

 (fig.44), and here the dip becomes north instead of 

 south, as normal. These phenomena show a hori- 

 zontal movement to the northwest on the southwest 

 side of the fault, and the reversal of the dip shows 

 some differential or torsional movement. The striae 

 on a fault plane indicate the last movement, the 

 records of previous and often more important move- 

 ments being erased by each new one. The combined 

 result of all the movements indicated, therefore, is 

 that the block on the southwest side of the fault has 

 moved downward, and also to a less degree (probably) 

 northwestward, along the fault plane. This hori- 

 zontal movement is also shown in the Fraction, where 

 the northwest faults (see p. 144) are probably auxiliary 

 slips related to the Wandering Boy system. In the 

 Fraction, especially on the 300-foot level, important 

 horizontal movement is registered by the striation. 





100 



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Scale 

 o 



CROSS FAULTING ON THE 300-FOOT LEVEL. 



100 feet 



Fiu. . Vertical section on the Wan 

 defing Boy shaft, showing the main 

 Wandering Boy fault. 



Complicated faulting is shown in the 300-foot level 

 of the Wandering Boy. The main workings consist of 

 two drifts run at right angles, one running nearly east 

 and the other south. The vein shown in this level has a thickness of 3 or 4 feet, 

 strikes northeast or east-northeast, and dips southeast at an angle of 30 or 40. 

 The east drift, therefore, runs somewhat diagonally to the strike of the vein, 

 though more nearly along it, while the south drift also runs diagonally though 

 somewhat more across the strike (fig. 48). The vertical section along the east 

 drift is given in fig. 45, that along the south drift in fig. 46. Near the end of 

 the south drift a short east drift has been run, following a portion of the vein, 

 and the vertical section along this drift is given in fig. 47. In fig. 45 it is shown 



