M1ZPAH VEIN. 



121 



its best days." This whole plan, therefore, shows, in the large sense, a single 

 bonanza, comparable in size and richness to those of the Comstock (tig. 78, p. 277). 

 As a rule, within the mine, great size of the vein coincides with increased 

 richness, although exceptionally this is not true. 



W 



Surface 



100 



B 



Scale 

 zoo 



oo feet 



FIG. 21. Diagram showing the distribution of the richer ores in the Mizpahvein. A, Distribution of the richer ores as indi- 

 cated by assays; black dots indicate assays above a certain figure; lower assays not indicated. Diagram of the Mizpah 

 vein projected on a vertical plane. The diagram indicates, roughly outlined, broad eastward-pitching shoots of rich 

 ore. B, Mizpah vein projected on a vertical section, showing slopes from which ore has been removed above 300-foot 

 level. Previous to the making of the assay plan (fig. 21, A) the distribution of these slopes indicated the eastward- 

 pitching richer shoots. 



From what has been said, it is seen that the ore shoots are primary. Along 

 certain portions of the east-west fracture zone (those portions being governed by 

 north-south striking and east-dipping fractures) the circulation of mineralizing 



aMon. U. S. Geol. Survey, vol.3, p. 10. 



