Amador ledger., 1900-12-07
CALIFORNIA GOLD DEPOSITS
One Of the Principal Dykes
Is In Amador.
HANGING WALL OF KEYSTONE FORMED BY DYKE
Branch Dykes.-Examination of Aur-
ferrous Dyke In Nevada
County.

Two of the principal auriferous dykes
in California are the Amador Diabase
dyke, Amador county, and the Eureka
Idaho and Maryland Diabase dykes in
Nevada county.
| The two richest and most continuous.
ly producing mines as yet met with in
California have been found in connec.
tion with those two dykes. The
Eureka, Idaho and Maryland dyke
forming the hanging walls of those
mines which may be classed as one and
the Amador dyke which forms the
hanging wall of the keystone mine.
Attached to this report is ''plan ol
the great Amador quartz vein," show.
ing the position of the different claims
and the course of the dyke. It was
surveyed by Mr.. ]. Brown and OBJ.
tanned for the Bureau through the
kindness of the Surveyor General.
Macdonald, Esq, president of the
Keystone Company, kindly furnished
me with surface plan of the keystone
mine, showing the course and width OF
the dyke and adjoining claims. He
also gave me plans of the different
levels which show much better than l
can describe the way in which the
auriferous quartz and pyritic matter
occurs. They are to be seen at the
Library of the Bureau.
The intrusion of dyke matter be-
tween the cleavage of the slate and the
influence of that and the planes OF
stratification or bedding upon the pro-
ductiveness of the deposits is a very
interesting study.
| The course of the Amador dyke and
the strike of the cleavage of the slate
are nearly the same, running in one
given direction of the compass over
nearly the whole of the ground 1 have
examined.
In the Library of the Bureau will
also be found plan of the surface To-
cation and longitudinal section of all
the underground workings from the
Oneida to the Lincoln mine. 1t was
surveyed under my direction many
years ago, Q872), but shows the line or
zone of productiveness of the mines ut
that time.
At Quail Hill, Calaveras county, and
near Lincoln, Placer county, where
copper ore was met with in the slate
rock, intruded small dykes are found
sometimes between the cleavage of the
states and on the sides of these dykes a
few inches of ferrugenous matter is
occasionally met with rich in gold.
The Amador dyke, like those in the
north of England and elsewhere, may
be traced for long distance and on its
sides are found the auriferous deposits
called the ''Mother Lode" TO the
west and east of the dyke is argillaceous
slate, forming tine foot wall of most of
the so called lodes or veins.
/ Branch dykes occur at different
points but the rock in them has been
very much altered, as at the zeile and
other mines. The course of such
branches continue the same as the
strike of the cleavage in the states,
though the dip of the cleavage is not
so regular.
have collected and roughly cut a
very large number of sections from this
dyke, but finding the rocks above the
the Keystone to be less altered than at
any other point, 1 selected specimens
from them, had slices made for micro
scopical examination and sections cut
for microscopical determination. No.
l plate is a photograph of one of the
slices made for microscopical examina-
tion, and think it shows the character
of the rock well, and will be better un-
derstood by my fellow miners than any
plate from microscopic sections
have selected two microscopic Sec
tions of the rock taken from the Key
stone mine, one cut exceedingly thin
and the other only sufficiently SO to
show distinctly the different colors in
the rock. They are both in the COL
lection of the Bureau.
The results of the examination of a
specimen of rock from 1000 foot level
OF the Keystone mine (which results
have been checked, or passed upon by
some of the members OF the London
Geological Society Of which l am q
member) are as follows:
A basic igneous rock of dark green
ish color, specific gravity, $500; con-
tained SILICA, 44.45 per cent. Under
the microscope the following minerals
were observed: Oligoclase, albite,
anorthite, chlorite, pyroxene (angite),
|labradorite, and as accessories pyrite
and magnetic.
The mineral is rather coarse grained
and somewhat porphyritic as crystals
OF oligoclase were observed Gn the Sec
tion) imbedded ins a compact matrix.
The mineral may be classified as a
diabase somewhat porphyritic).
The Eureka, Idaho and Maryland
Diabase dyke in Nevada county is first
seen short distance west of the
Eureka claim, it can be traced east
ward through the Eureka, Idaho and
Maryland ground. The Idaho Com
pany have from the 900 foot level
driven a crosscut south for distance,
/ heliave. of soma GOO feet into their