150 The American (ieoloyist. March, 1396 
gold is frequently found with the iron. The Sorba mine lies 
wholly in limestone, but the character of the ore is very simi- 
lar. This mine, together with some others north of Darwin, 
has a fairly well defined vein form, although quite irregular. 
In the description of these silver mines no attempt will be 
made to enumerate the various complex ores resulting from 
surface alteration, ores very similar to those of other silver 
districts of the west. 
The silver-lead mines of Cerro Gordo, situated near the 
summit of the Inyo range, have produced several million dol- 
lars. The Union mine was opened to a depth of 900 feet, 
when the ore body was lost. The inclosing rock is limestone 
of Carboniferous age. Bunches of verjr rich gold ore were 
occasionally found in this mine. Quartz occurs in some of 
the deposits about Cerro Gordo. When this gangue is present 
the lead content is less important, being replaced by iron and 
copper sulphides. 
The silver-lead ores of this region have been formed, with- 
out doubt, chiefly through replacement. Although a certain 
amount of fracturing and crushing of the country rock, giv- 
ing an opportunity for the passage of solutions, must be ad- 
mitted, yet in the strict sense of the term they cannot be 
termed veins or fissure deposits. 
In exceptional instances important bodies of galena occur 
in well denned veins, the gangue of which is part quartz, as- 
sociated with sphalerite, bornite and antimonial copper ores. 
This character is best illustrated in the mines of Blind Spring 
hill near Benton, where occur many small but rich veins in 
granite. Galena is abundant here but is not as rich in silver 
as stromeyerite and tetrahedrite. The veins are regular and 
persistent. Several of them dip at a very low angle. 
Silver Bearing Sulphides of Copper, Antimony and 
Arsenic. 
These minerals are found in well defined veins, seemingly 
without regard to the character of the formation. Over much 
of the area in question they are frequently associated with 
gold bearing quartz veins, the value of the contained gold 
sometimes equalling or exceeding that of the silver. 
About the town of Panamint this class of ores occurs al- 
most exclusively. Stromeyerite and tetrahedrite with decom- 
