spurr.] OCCURRENCE OF ORES IN THE VEINS. 23 
Iii the Montana Tonopah the chief vein shows in places a breccia- 
tion and subsequent cementation. Both the original material and 
the subsequent cement are«of quartz and rich black silver ores, and 
seem to have been deposited under about the same conditions. The 
inference is that the strain which originally produced the fracture 
zones kept on during their cementation by the circulating mineral- 
izing waters, and that in this case this strain resulted in the local 
shattering of the cement and the subsequent healing by similar 
materials. 
Primary ores. — At the time of the writer's first investigation of 
Tonopah, in the autumn of 1902, only the oxidized ores of the upper 
levels of the Mizpah were available for examination. From a micro- 
scopic study of these he found that the original metallic mineral was 
still present in minute grains. It was black in color, and he supposed 
it to be a rich silver sulphide. Subsequent to this investigation the 
primary sulphide ores were found in the Montana Tonopah mine, and 
the correctness of the forecast above mentioned was shown. In the 
Montana Tonopah the ores are quartz veins carrying in places very 
large amounts of the rich black antimonial sulphide of silver, steph- 
anite. This stephanite is undoubtedly primary. Besides the quartz, 
as gangue mineral, there is another having a milky appearance, 
but otherwise looking much like the quartz. This is a variety of 
orthoclase (valencianite). Some of the stephanite may contain some 
copper, making it a kind of polybasite. Chalcopyrite is very com- 
monly present and is probably, in part at least, primary, although 
this is not certain. 
Secondary sulphides. — Throughout the Tonopah district argentite 
and rub} 7 silver occur in greater or less abundance, sometimes adding 
considerably to the value of ores, but they do not occur in such quan- 
tities as the stephanite ores or the oxidized products. Wherever 
found the argentite and the ruby silver are unquestionably secondary, 
having formed from the alteration of the stephanite. They occur 
along cracks in the primary sulphide ore and are occasionally found in 
the oxidized or semioxidized ore. The chalcopyrite above mentioned, 
as observed in the Montana Tonopah ore, seems to occur chiefly as 
small streaks cutting the original stephanite ore, giving it the appear- 
ance of being secondary to the latter. In some cases it occurs along 
cracks and is undoubtedly secondary. It is very likely that some at 
least of this mineral has been formed from the copper contained in 
the cupriferous silver sulphide. Some pyrite is also undoubtedly 
secondary. Pyrite, however, is relatively rare in these ores — much 
more so than in the country rock. 
Oxidized ores. — In the Mizpah vein the oxidized zone extends nearly 
down to the 700-foot level. Observation shows, however, that the 
limit of oxidation is extremely irregular. For example, the oxidation 
extends much deeper along the vein than some distance away from it 
