28 ORE DEPOSITS OF TONOPAH, NEVADA. [bull. 219. 
waters which produced the early andesite veins were unusually active, 
and a large amount of vein formation is indicated. It is beyond 
question, therefore, that the veins thus far found are only a fraction 
of those which exist in the vicinity. These veins will be chiefly 
unoxidized, since they are protected from oxidation by capping rocks. 
In them undoubtedly large portions — probably much the larger por- 
tions — will be relatively barren quartz, in which shoots, chimneys, or 
irregular bunches of rich ore may be expected to a considerable depth. 
These quartz veins, carding silver and gold and occurring in Ter- 
tiary andesite, belong to a larger group of veins occurring in similar 
andesite and found along a north-south zone. These veins are exem- 
plified by the Comstock in Nevada and by the important district of 
Pachuca in Mexico. Probably Pachuca is the nearest analogue, and 
its description, as given by the Mexican geologist, Ordonez, may be 
of value in considering the characters of the Tonopah veins. Judging 
from these districts it is possible that in depth a rather larger propor- 
tion of the baser metals, such as copper, and possibly lead and zinc 
(although no traces of the last two have as yet been found in the 
veins), may come in, and that the values in gold and silver may 
decrease somewhat. This, however, if it happens, should do so at a 
considerable depth. 
