110 ECONOMIC GEOLOGY OF SILVERTON QUADRANGLE, [bull. 182. 
and Yankee Girl mines, and these inclosed masses occasionally carried 
free gold. In the Zuiii it is intimately associated with pyrite and 
kaolin. The latter mineral is found associated with the ores of all 
the Red Mountain mines, sometimes occurring in the ore or serving 
as a matrix to pyrite, as in the Zuni, but more abundantly in fissures 
in the wall rock and as a direct product of the alteration of the latter. 
Although the common structure of the principal ore bodies was 
that of a solid and massive aggregate, yet there is evidence that vugs 
or cavities sometimes occurred in the unoxidized ores. Stalactites of ] 
pyrite, having the radial structure usually considered as character- 
istic of marcasite, were seen, which were said to have come from caves 
in the Genesee- Vanderbilt. Specimens of enargite from the National 
Belle mine, preserved in various cabinets, show a free development 
of clusters of radial prisms of enargite, such as could only have formed 
in open spaces. The well-crystallized specimens of polybasite which 
have come from the Red Mountain district were also probably formed 
in vugs. 
The large caves, however, such as were a feature in the upper work- 
ings of the National Belle mine, appear to have occurred above the 
ground- water surface. A few of the smaller of these caves only could 
be seen in 1899, and we are dependent upon the description of T. E. 
Schwarz 1 for knowledge of the occurrence of the oxidized or second- 
ary ores. According to him, they occurred "above a former water 
line, either attached to walls of caves as broken detached masses, or 
as a bed of clayey mud or sand, more or less completely filling the 
cave." The ores are said to have been mainly "carbonates of lead 
and iron, with iron oxides, lead sulphate, and arsenates." Kaolinite 
and zinc blende Avere common, and galena occurred as residual ker- 
nels. "Such are the ores of the National Belle, Grand Prize, and 
Vanderbilt mines. Other mines omit lead minerals and carry oxide 
and sulphide of bismuth." Several hundred pounds of this metal are 
said to have been reduced in Durango. These caves are stated to; 
have ramified through the knolls of silicified andesite, such as that 
described at the National Belle mine, which "are cut up by cross 
fractures." The following general conclusions are cited from Mr. 
Schwarz's paper: 
1. The secondary ores are richer than the sulphide ores occurring 
below them. 
2. The ores of adjoining or connecting caves are sometimes greatly 
different in grade. 
3. In some cases the formation of the caves along fracture or cleav- 
age planes is evident, but in others all traces of such planes are quite 
obliterated. 
4. The cave walls are a porous sandy quartz (see description of 
1 Trans. Am. Inst. Min. Eng., Vol. XVIII, 1890, pp. 139-145. 
