The indicator., 1897-04-24

helNeu. Nneil DOtn sides show the
same uphenval we shall probably find
the eruptive rock spread over both
| slopes and II depression or trough AT
the point where the granite takes the
opposite dip, following the trend of the
granite. and generally filled in will
lake fresh wateI) sediment. This is
the dixie. which contracted by cooling
and formed basin or lake on its sur.
| face.
"If we examine the overflow which
we find in the vicinity, not only ON the
surface, but also that which we find
| imbedded between the scdimentaries
and also the upper surface of the rocks
on which they rest, we will find whetll
cr the eruptive rocks are sufficiently
| nincralized TO make II worth while
continuing our work in the vicinity.
IN examining the granite we frc
uucntly find that after one uphcaval
had taken place other seismic disturb
ances had occurred. breaking through
| the granite floor and uphcaving it witt
all scdimcntary and cruptiVe rocks
| then lying thereon in II different direc
iion from tie first and leaving its dixie
| in the trend of the last fracture. Tn
der these circumstances it is necessary
10 examine all the eruptive rocks in
| the vicinity to ascertain which one. II
| any. of the various eruptions was the
/ mincraliZcd one, or mother of the coun
| Try, or whether there are more than
one which will pay 10 work.
This preliminary work is almost in.
variably omitted by the common pros
pector, who, consequently, has no data
on which 10 base Il belief that an ore
| body he may discover will he either
permanent or valuable, and as il is
also omitted by expert mining engi
neers or geologists who may he sent
to examine property their deduc,
tons have no more scientific accuracy
than the prospector's.
Having asccrtaincd tho fact that
mineral exists on HE surface in re:i.
sonably paving quantities, our next
step should he to discover where and
i'll what form we may expect to find
the ore in the best paying quantities.
| and in this connection we must study
the process of concentration carried on
by nature.
"All igneous rock and metals occupy
Il larger space when molten than they
do when cooled. Their contraction
causes cavities to he formed along
their lines of contact with other rocks.
and also through their mass. and
through these cavities or assures the
water from the surface percolates. car.
| rying with 1t all soluble substances
with which it is impregnated, and also
all insoluble substances which it can
carry down into the crevice
'As all igneous rocks carry Il large
percentage of silicon, or silicic acid
we find that the greater number of
Hl, I.,I .,st L.,
posted from these aqueous solutions.
as the disintegration of the eruptivc
rock would free the minerals in tive
find that the minerals are embodied in
the quartz. In this connection il,
should be stated that the last outflow of
any eruption is the most valuable. This
Is caused by the fact that the molten
bodies of highest specific gravity are
nearest the vent when formed. and are
naturally elected first of course this
need not be the case with permanent
craters. as between The times of thriI
eruption time would be allowed for the
different fluids TO resume their normal
relative positions. This last overflow
is generally elected from one side OF
the crater only. the wall being general
ly irregular in its outline, allowing the
mass to pour from the lower portion OF
the rim. and frequently its specific
gravity being SO much greater than the
preceding flows. it displaces the semi
fluid cooling mass, and travelling in II
trough of its own construction. therein
forms dikes of Il different eruptive
rock, as may he seen in Cripple Creek
''Fhe facts we want to observe most
thoroughly are in which direction the
last overflow travelled from the crater
fracture. and whether the minerIlizcd
eruptive rock has since been covered
with sedimentary rocks. as at Lead
willie. If the overflow is the upper
stratum of the carth's crust. as at Grip.
pie Creek we shall find the quartz de.
posits on the line of the dikes the rich
est ores. hui still not nearly so rich MS
the quartz formed in the mass and on
The contacts of the primary dixie still
remaining AT the era fracture.
"lf. as at the Mosquito range. we
find that The eruptive blanket over.
flows have since been covered with
sedimentaly rocks. we should deter.
mine as nearly as possible the direction
of their flow. and can then predict with
reasonable accuracy that paying ores
can he reached in any one of the blan.
kct deposits and on their lower con.
il
quantities of limestone lie above ore
deposits we may expect the concen.
tratcs in the iissures 10 he the spar FOR.
nation. Where limestone is absent.
we may expect to find quartZ. hui
whether spar or quartz are found. ;he
veins will be barren unless the ciup,
tive rocks in the vicinity have borne
the minerals from The interior of the
earth.
"A great amount has been written
about the different erllptive rocks,
which ores may be expected TO carry
mineral and which not. and they have
also been classified as mineral and non.
mineral bearing by their color. This is
also Il theory based on guess work.
and will not prove correct in Il great
many eases. The ability of Il melted
rock to float. and retain gold in proN.
unity To the earth's crust so that Ii can
he elected from a vent. depends moi
upon lis color or the presence or nh.
sence of any particular characteristics.
hut upon its specific gravity alone. and
one of the snrest indications that we
can have that gold can he found in an
cruptivc rock is the presence of crystals
of magnetic in its muss.
This metal Is so near the spccid,
gravity of gold. that no gold has ever
yet been discovered in lode or placer
without magnetic being also in the vi.
cinity. and in II gold camp its octahc.
dral crystals. glistening in the sunlight.
are the easiest seen indications of the
presence and trend of the gold belt.
'The conditions in different camps
are so varied they can scarcely he
touched upon in Il paper of this kind
from lack of time, but the prospcctor
who desires 10 follow his calling on
business lines and eliminate the ele
ment of chance. should pay less atten.
tion TO hunting for quartz float and
more to ascertnining the position OF
The dikes and blankets of cr,lptive
rnckS. the minprnIiynl unnrIz u.ill al