The Weiser signal. [volume] (Weiser, Idaho) 1890-1904, 1900-06-28
DR.. RI PACKARD'S REPORT
On the Seven Devils, Made Espe-
cially for the Smithsonian Insti-

Lulc.
The Seven Devils is the name (of
rough frontier origin) gwen to a
range, or group, Of mountains on the
extreme 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 a 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
precipitious, is formed by range on
the Oregon side called the Eagle
Mountains. The few sharply point
ed, precipitious peaks which are the
Seven Devils proper and have given
their name to the whole group, have
an altitude of over 1000 fit. They
are of igneous origin and attracted
the attention of prospectors many
years ago, who found gold in the
streams issuing from their domain
and copper in the mountains adjoin-
ing them. The only occurrence of
copper of importance which has so
far been exploited 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 yet determined
extent The copper occurs as Dor
mite, and the principal mine of the
locality is named the Peacock, from
the nature of the ore The igneous
rock, which evidently has genetc
relation to the copper deposits, has
the general appearance of a granite,
and has always been so called. 1t is
gravisl- white in color, and in hand
specimens does resemble a biotite
granite without muscovlte. 1t wealth
ers 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 filled with bould-
ers of this rock several fit in diamet-
er, 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 whitsh rock, where ex-
posed and in the boulders, is seen to
contain areas of darker color which
vary in size from 2 to 3 inches to as
many feet in diameter, and impress
one at first as being intrusions of
some other rock. The igneous rock,
one would say, is evidently the cause,
if not the source, of the copper de-
posts found on its contact and in
veins in its substance, and it became
a matter of curiosity to examine it's
neurological and chemical character.
Specimens were, accordingly, pro-
cured from points about mile and
a half apart, one on the wagon road
leading to the mines (on White
Monument hilD and the other at the
Victoria mine on the northern limit
of the mines where the mountain de-
scends abruptly to form one side of
Deep Canyon creek. The slightly
darker appearance of the rock at the
latter place indicates that its compost
ton varies somewhat from point to
point 1t is also an assumption that
the whole mass is continuous for the
distance mentioned Indeed flow
of basalt intervenes at one point, but
the extent of the flow is undetermin-
ed.
The thin sections from these speci-
mems show that the rock has the fol |
lowing structure and compositions:
The structure is that of granite. The
stout, tubular, triclinic feldspars
largely predominant. Many of them
are turbid. Interstitial quartz is
present. The ferromagnesan min
erals are hypidiomorphic green, pleo-
chroic hornblende, and some brown
bolite, also limited by the adjoining
feldspars Apatite crystals, zircons,
and some isometric granules of ore
were also observed. A section from
one of the inclusions described above
showed the same meteorological COM
position as the lighter colored rock,
but the structure shows cataclastic
areas. Green hornblendss, with in
trusions, and triclinic feld-pars, APP
pear in the midst of the comminuted
crystals The section also shows
biotite, with intrusions, limited by
the adjoining felspars, aud the ore
particles are much more numerous
than in the lighter colored rock
Zonal structure of the feldspars was
also noticeable in both sections The
rock, therefore, as shown by these
sections, is diorite. Its analysis
gave:
lgnillon. ....... 90
SiOs Sulphur, Oxygen). 80. =. SO SO
AL n Eo n (Aluminum.N ozct