The Wallace miner. [volume] (Wallace, Idaho) 1907-current, 1913-06-19
Geology and Minerlization Of the
Upper St. Joe River Basin, Idaho
BY ). T. eARoee. u s. c BIOLOGICAL SURVEY.
several thousand feet below the top of
the PrIchard formation.
Crushed and shsarsd Zones.

several thousand feet below the top of
the PrIchard formation.
| Crushed and shsarsd Zones.
Zones in which the rocks are shear
ed and crushed are numerous in the
areas OF complex folds These zones
are not well defined and can not be
exactly bounded and the degree Of
crushing or shearing in them is var
liant, but areas in which the quartzitic
rocks are crushed to the semblance of
a breccia may be from few hundred
feet up to mile or more across. The
shaly beds of the Newland (Wallace)
and the diabase intrusions are COM
monty sheared.
Metamorphisnn.
The sedimentary rocks and the old
err intrusive rocks are strongly meta
morphosed in about half OF the area
examined. The intensity Of the meta
norphism is least toward the north
east and increases toward the west
and south A distinction is to be made
due to the monzonitic intrusions ex-
posed near Copper Prince and the
much more intense metamorphism
partly thermal and partly dynamic
chiefly developed In the southern par
of the area, presumably due In the
main to a huge batholith that occu-
pies great areas to the south Of the
territory here considered and is prob
ably represented by the nonfoiated
granite found at the head OF
head of the Clearwater. It is doubt
less due In part also to the old gran
ties, anorthosities and diabases, now
altered to gneiss and amphibolite, but
these have suffered more metamorph-
ism than they have caused. The dia-
base, where 1t occurs apart from 9TH
er intrusive rocks can be seen to have
caused relatively slight metamorph-
ism.
The metamorphic effect of the mon
zonites Is first perceived on going
down the railway from Avery, near
the mouth Of Slate creek, where the
buff weathering blue and gray New
land beds grade into hard fine grain
ed hornstones coarsely banded and
notified In pale green and chocolate
brown. While the metamorphic nat
ure of these rocks Is not very evident
to the Impractical eye and their gen.
eral appearance family suggests that
OF the st. Regis formation. micro
scopic study shows the brown layers
to be rich in biotite and the green
layers rich in pyroxene and, amphi-
bole and proves that they are meta
calcareous sediments. Far
ther on the shaly beds of the lower
formations are represented by mica
schists even more clearly showing the
effect of contact metamorphism.
Near the western limit of the area
the metamorphism due to the mon
zonites merges with that of other orr
gin. At the east, however, the mon
zonite has had no effect and the in
crease Of metamorphism toward the
south can be clearly observed. In the
vicinity Of the state line and Pack
saddle mountain a very slight meta
Is shown by faint brown
ish banding only In some argilltes.
Toward the river some of the sandy
shales gradually become micaceous,
resembling schists and the argillites
grade into greenish and chocolate
brown hornstones, the latter thickly
studded with round grains of scapo-
lite that stand out on weathered sur
faces suggesting so many white fish
eggs.
The metamorphism in its extreme
degree is best observed in r. 4S N.
r. 4 f. The general aspect of the old
sediments and intercalated intrusive
rocks is such that they would prob I
ably be assigned to the Archaen were
t not that they are conformable with