1H8 GEOLOGY OF TONOPAH MINING DISTRICT, NEVADA. 



VEINS. 



Some of the broken fragments in the fault zone show a small quantity of 

 material that is probably black silver .sulphide. 



On the 450-foot level a small quartz vein, a few inches thick, with an east- 

 southeast strike, and a northerly dip (45 to 60), was followed. This has a gangue 

 of quartz, with some calcite, and contains pyrite. In some places good values 

 are shown. On the 650-foot level, a short distance south of the shaft, in very 

 dense, and tine-grained earlier 1 andesite, a ledge of 3 feet of mixed quartz and 

 altered andesite has been cut. This quartz contains argentite and shows some 

 good values. 



MONTANA TONOPAH VEIN SYSTEM. 

 MONTANA TONAPAH MINE. ' 



ABSENCE OF VEINN IX THE LATER ANDESITE. 



The Montana Tonopah shaft was sunk in the later andesite, on the northeast 

 or upper side of the Mizpah fault (PL XVI). It passed through 372 feet of the 

 later andesite before reaching the fault. Most of this rock was extraordinarily 

 decomposed and thoroughly bleached, while much was intensely brecciated, con- 

 taining hard bowlders in a clayey matrix, with strong fractures and slickensided 

 surfaces. This indicates a great deal of faulting, of which no measure could be 

 obtained. 



Above the Mizpah fault only small veinlets of calcite and quartz were encoun- 

 tered, but 4 feet below the fault a heavy quartz vein in the earlier andesite was 

 encountered and followed in the shaft to a depth of 392 feet, where the first 

 mine level was made. The other main levels are at 460, 512, 612, and 765 feet. 



The Mizpah fault was cut in a northeast drift on the 392-foot level, as shown 

 in fig. 58, at a point about 60 feet from the shaft; it was also encountered in 

 the 512-foot level, as shown in PL XXII. Its strike and dip are therefore fairly 

 well determined; the strike is about N. 55 W., and the dip is northeast, at an 

 angle of about 29. The later andesite has been found on the northeast or upper 

 side of this fault, at all depths thus far examined, both in this mine and in 

 neighboring OUCH. 



This rock (the later andesite) has been extensively explored, both in this 

 mine (as in the drift on the 512-foot level connecting the Montana Tonopah and 

 North Star shafts) and in others, but no veins of size and value have been found, 

 nor anything that does not confirm the theory that the principal veins are older 

 than the later andesite. 



