COMPARISON WITH SIMILAR ORE DEPOSITS ELSEWHERE. 271 



due to disseminated argentite, which is the principal ore mineral and is accompanied 

 by gold, probably free. Bunches of stephanite, polybasite, and ruby silver were also 

 found. In the bonanzas, near the surface, chlorides and native silver occurred. 

 Frequently the ore grew base, and carried large quantities of galena, zinc blende, etc. 



Pyrite occurs abundantly both in the altered country rock and in the ore. The 

 mineralizing solutions are thought to have derived their heat from volcanic rocks, 

 and thus the general phenomena are classed as due to solfataric action, but the 

 materials precipitated, including the ores, are thought to have been derived from 

 the decomposed wall rock. 



The workable bodies or bonanzas represent the smaller portion of the lode. 

 The value of the ore in them ranges from $15 a ton to (very locally) several 

 thousand dollars. They are encountered at various depths, from the surface down 

 to 3,000 feet. The vein down to nearly 2,000 feet contained 16 workable ore 

 bodies, while below this level the ore has proved mostly low grade. One large 

 bonanza (that of the C. & C. and Con. Virginia) extends vertically from about 

 1,250 to 1,950 feet below the surface, and has a greatest diameter of about 1,100 

 feet. It yielded about one-tenth the product of the lode." The ore minerals 

 were chiefly stephanite, argentite, and gold, the latter probably free. 



The source of the heated waters which are encountered in the mines, and 

 which are thought to have accomplished the rock alteration and ore deposition, is 

 concluded from thermal surveys to be not less than 2 miles deep, and the heat 

 and the active reagents, such as carbonic and sulphydric acids, are thought to 

 have had a volcanic origin, while the waters may have had an atmospheric source. 

 The waters above 800 feet had a temperature of about 70 F., while from about 

 1,000 feet down hot waters of above 100 F., rising under pressure, were 

 repeatedly encountered. 



The Comstock district is similar to Tonopah in respect to the character and 

 age of the rocks in which the lode lies (Tertiar}- andesites), in their "propy- 

 litic" alteration, in the nature of the gangue and ore, and in the occurrence of 

 the rich ores in irregular " bonanzas." The chief distinction is that the Comstock 

 consists of a single very strong lode, while at Tonopah there are a number, of 

 less size. 



SILVER CITY AXD DE 1AMAR DISTRICTS, IDAHO. 



Another region having many striking peculiarities in common with Tonopah 

 lies about 400 miles due north of Tonopah. The districts of Silver City and De 

 Lamar (5 miles apart) are situated in the Ohwyee Range, in southwestern Idaho.* 

 The range has a granite core, almost covered by Miocene rhyolite and basaltic 



n This ore averaged about $80 per ton, with silver at 31.29 per ounce. 

 fcLindgren, W., Twentieth Ann. Kept. U. S. Geol. Survey, pt. 3, pp. 107-188. 



