132 ECONOMIC GEOLOGY OF SILVERTON QUADRANGLE. [.bull. 182. 
Camp Bird mines it is also associated with pale-yellow sphalerite and 
fluorite. Some specimens were seen from the Sunnyside Extension 
mine in which the gold occurred as implanted crystals on quartz and 
was therefore of later age than the latter. 
Unfortunately there are at present few opportunities for studying 
the occurrence of proustite and argontite in the Silverton quadrangle. 
In the Ridgway mine much of the argentite occurs implanted on, or 
wedged between, the quartz crystals of small vugs, and was the last 
mineral to crystallize. It has been the universal experience in the 
Silverton district that argentite, proustite, and polybasite are not 
found below a very moderate depth. The data at hand do not permit 
of a definite statement as to the depth at which these rich argentifer- 
ous minerals change to low-grade ore, but the indications are that it 
is less than 1,000 feet, although it is well known that in other regions 
some of these minerals extend to greater depths. It is probable, 
although not at present demonstrable, that in the Silverton region 
proustite, argentite, and polybasite are of secondar}' origin and indi- 
cate a zone of enrichment of the kind to which Emmons ' and Weed 2 
have recently called attention. 
The downward change from galena through richly argentiferous cop- 
per ores to chalcopyrite and pyrite, which was found to be a character- 
istic feature of many of the Red Mountain mines, is a case of paragenesis 
on a large scale, which will be discussed in the following section on 
the origin of ores. The origin of the rhodonite, which is so abundant 
in many of the lodes of the northern half of the quadrangle, and its 
exact relation to the quartz and ore which accompany it constitute a 
puzzling problem, for which no satisfactory solution has been found. 
Such a solution must account for the presence of large lenticular or 
partition-like masses of rhodonite, carrying a few specks of low-grade 
ore, and dividing the ore bodies longitudinally into two or more parts, 
and for the presence of patches and stringers of rhodonite. In the 
Saratoga mine rhodonite has formed by metasomatic replacement of 
limestone. It is possible that in such lodes as the Sunnyside the large, 
solid masses of rhodonite within the vein may represent metasomat- 
ically altered horses of country rock. This, however, is merely a 
hypothesis, which requires confirmation before acceptance. It has 
undoubtedly been deposited also in open fissures as a true vein 
mineral. 
ORIGIN OF THE LODE AND STOCK ORES. 
That the ores of the Silverton quadrangle were deposited from 
aqueous solution is a proposition which, in the light of present knowl- 
edge, needs no special demonstration. They were precipitated partly 
J The secondary enrichment of ore deposits: Trans. Am. Inst. Min. Eng.. Vol. XXX. 1900, 
pp. 177-217. 
2 Enrichment of mineral veins by later metallic sulphides: Bull. Geol. Soc. Am., Vol. XI, 1900. 
pp. 179-20(5. 
