The herald., 1893-12-10

minerals in solution in 6ssure may
exert great influence in the dispo-
eition Of ore. What might not be
affected at a depth OF few hundred or
thousand feet might be accomplished
under the tremendous pressure of 5000
feet. Doubtless moat veins were formed
At q much greater depth than we now
see them. They have become accessi-
bic to us through the upheaval and the
erosion of what lay above them.
Lodea will more commonly be fou nd
in the neighborhood OF plutonic rocks
rocks that have solidified beneath the
surface--than near volcanic rocks, for
the resaon that lodeg of value could
only be formed at considerable depth
under solid covering. 1t is useless to
look Tor lodee in sections OF country
covered with lava and other volcanic
rocks. Paying mineral veins are much
more likely found in the older than
more recent rocks, whether sedimentary
or igneous. They are generally to he
found in places whore dikes Of igneous
rocks have been pushed up through the
sedimentsry rocks, either at the point
of contact between two kinds of rock or
Usually when a rich quartz vein has
been discovered there ia "rush" made
for extensions" ON the course of the
strike of the vein, and at times these To-
cations extend for miles. Let the miner
who does not reach the scene OF the dis
covery in time to locate fret extern
sion give no further thought to exten-
sions, but turn his attention to search
for parallel vein.. Systems of parallel
veins. more or less regular, depending
upon the nature Of the country rock,
are found in almost every quartz min
ing district Of California. The chances
for finding paying parallel vein are
often much better than for locating the
extension OF newly discovered lode.
and, as has often happened, q parallel
vein msy be found that will prove
richer than the FIRST of the system To-
Gated.
A prospector who understands his
business will nearly always do better in
an old and rich quartz mining camp
than by rambling away into unknown
regions. In every old camp where there
ie being worked large and rich vein,
there are sure to be smaller parallel
veins that will pay, and it is impossible
to know when all these have been dis
covered, particularly when the country
rock ia covered by a stratum of soil
which hides the veins in the ne;ghbor-
hood of every old camp in California.
The regularity and smoothness of the
fssures depend much upon the char
acter Of the country rock. If the over
lying rocks do not cleave we'll and regu-
larly the lodes found in them will be
bunchy, as when bodies of serpentine
lie in the line of the fssures. Fssures
are generally very much more jagged
and irregular on the cross sections of
slate or slaty rocks than those that run
parallel to the cleavage, and as the fis-
sures are 30 are the lodes with which
they are filled. The broader veins are
so much the more regular in their
course. The broadest veins are usually
the longest. The greater the length o;
vein the greater depth to which it
will probably extend.
A true fseure" vein is one which ira
verses the country rock indie pendently of
it's qualification, cutting through slaty
rocks across the course OF their cleavage.
These veins sometimes cut across dikes
OF intruded igneous rocks. They are
supposed to have been produced by
deep-seated plutonic forces. while con-
tact veins and their accompanying
groups OF parallel veins are the result of
forces acting nearer the surface.
There are contact veins which lie be-
tween two kind Of igneous rocks. A dixie
of diorite may be upheaved in such a
position as to form contact with gran
ite, or with an older dixie or diorite or
other intruded rock. In places where
there are parallel groups of veins, as on
tho smothar loda - diorjta dika oftap
forms the foot wall of one vein and
black slate OF that great mineral is in
one place the hanging and in another
the foot wall, while in many places it
forms both walls.
As regards the gold mines OF Califor.
MIA, the different kinds of rocks in the
walls of tbef veins seem to have very
little to do with the richness of their
contents. Rich deposits of gold are
found between the walls of all kinds of
rocks, and it is the same with barren
veins. Evidently we must look beyond
the enclosing walls for the source OF the
gold. Although it is good indication
to have diorite or some other igneous
rock for one of the walls OF vein, it is
not because it 10 supposed to carry gold.
Very rich veins are found in places where
both walls are slate, with no dixie or
intrusive rock in sight, bnt at the
same time diorite or some other up
heaved rock had no doubt something to
do with the formation and filling of the
veins. Intruded dikes are not contin-
uous and do not in all places come to
the surfaces. Thus they may produce
an effect upon the surface rock without
comino into viaU