300 Packard— Occurrence of Copper in Western Idaho. 
copper solution. In the thin section brown biotite and quartz 
are much more abundant than in the specimens just described, 
but the predominating plagioclase feldspars and the fragments 
of green hornblende indicate the dioritic character of the rock. 
The biotite is seen undergoing bleaching and an alteration to a 
green mineral. 
Diorite must also occur in the mountains north of the copper 
mines, for a specimen taken from a mass of rocky débris on the 
trail which passes throngh the Seven Devils, and perhaps 
eight miles from the mines, proved to be diorite when exam- 
ined in thin section. 
The diorite of the copper locality is bounded on its western 
side by a zone of a garnet-epidote rock and the bornite is found 
in this rock in kidneys and larger masses. At the Peacock 
mine the ore and garnet rock appeared to dip towards the 
diorite. West of the garnet rock appears an igneous rock the 
character of which is yet undetermined. Crystalline limestone 
accompanied with garnet rock crosses the diorite to the north- 
east at about a mile south of the Peacock mine. Mines are 
established at this contact also. The distance from end to end 
of the copper belt may be three miles or more in a direct line. 
The copper ore, except at the Victoria mine, is associated with 
the metamorphic- or metamorphosed-garnet rock, which is, in 
some places, more than a hundred feet thick, but at the Vic- 
toria mine the bornite occurs in a vein which is in the body of 
the diorite although near its contact with an eruptive rock and 
outside of the garnet belt. 
Copper and iron (as sulphides forming bornite) are not the 
only metals due to the diorite. The bornite carries silver, 
sometimes up to twenty ounces per ton, and native gold is 
occasionally found in it. The gravel of the diorite is washed 
for gold, and a quartz vein carrying a little gold is “ located ” 
near the contact of diorite and basalt. A little galena has 
been noticed. It was at this place that the molybdate of lime, 
described as powellite,* was found four years ago. 
* This Journal, xli, 138, 1891. 
Washington, D. C., June 19, 1895. 
