The Weiser signal. [volume] (Weiser, Idaho) 1890-1904, 1895-11-07
A, Article on Occurrence of Copper in Western
Idaho.


A, Article on Occurrence of Copper in Western
Idaho.
ByR. L. Packard, in American Journal of Science.
The Seven Devils is the name (of
rough frontier origin given to a range
or group of mountains on the extreme
western border of Idaho where that
state is separated from Oregon by the
Snake river on its northerly course to
empty into the Columbia. The river
runs through deep gorge as it passes
the mountains, the east side of which
is formed by members of the Seven
Devils group, while the western side
or wall, which is very precipitous, is
formed by range on the Oregon side
called the Eagle mountains. The few
sharply pointed, precipitous peaks
which are the Seven Devils proper
and have given their name to the
whole group have an altitude of over
seven thousand feet. They are of
igneous origin and attracted the at
tention of prospectors many years
ago, who found gold in the streams
issuing from their domain and copper
in the mountains adjoining them
The only occurrence of copper of
Importance which has so far been ex-
plotted is found in the southern part
of the range and is confined to the
neighborhood of body of whitish
granite rock of very considerable but
not not yet determined extent. The
copper occurs as bornite and the prin-
cipal mine of the locality is named
the Peacock, from the nature of the
ore. The igneous rock, which evil
IDENTIFY has a genetic relation to the
copper deposits, has the general APP
pearance of a granite and has always
been so called 1t is grayish white
in color, and in hand specimens does
resemble a biotite granite without
muscovite. 1t weathers into rounded
blocks which are sometimes met with
in isolated groups, and at one point
on the wagon road leading up from
the Snake river to the copper mines,
and about mile from the latter, the
head of a small ravine is filed with
powders of this rock several feet in
diameter which give the appearance
of having been purposely rolled into
the place. Water runs down among
these rocks at some distance out of
sight.
The whitish rock, where exposed,
and in the powders, is seen to con
tain areas of darker color which
vary in size from two to three inches
to as many feet in diameter and i'm
press one at first as being incluslons
of some other rock.
This igneous rock, one would say,
was evidently the cause, if not the
source, of the copper deposits founc
on it's contact and in veins in its sub
stance, and it became matter O
curiosity to examine its mineraloglca
and chemical character. Specimens
were, accordingly, procured IRON
points about a mile and half apart
one ON the wagon road leading to thu
mines lat the White Monument hilD
and the other at the Victoria mine OF
the northern limit of the mines wher
the mountain descends abruptly t.
form one side of Deep Creek canyon
The slightly darker appearance OF til
rock at the latter place indicates tina
its composition varies somewhat fror
point to point. 1t is also an assump
ton that the whole mass is contlnuou
for the distance mentioned. lndee
a flow of basalt intervenes at on
point, but the extent of the How
undetermined.
The thin sections from these spec
mems show that the rock has the fol
. lowing structure and composition
The structure is that of granite. In
stout, tabular, triclinic feldspars large
ly predominant. Many of them ar
turbid. Interstltial quartz is present
The ferromagnesian minerals al
hypidiomorphic, green, pleochro'
hornblende, and some brown biotlt'
also limited by the adjoining felC
spars. Apatite crystals, zlrcons, an
some isometric granules of ore wei
also observed. A section from Oh
of the inclusions described aboN
showed the same neurological con
position as the lighter colored roc
hut the structure shows cataclast
areas Green hornblendes, with l