The Wallace miner. [volume] (Wallace, Idaho) 1907-current, 1918-05-02

case OF slow-leaching minerals, 1t is
because the engineer believes that
lower down the values were original
ly more richly deposited.
In the case Of most copper prop
critics, where the surface showings are
favorable, 1t Is very seldom that COM
mercial mineral Is developed until the
zone Of secondary enrichment has been
reached. and this is always at some
depth For that reason copper prop
critics with good surface Indications,
although no ore may be usually in
sight, represent good prospect.
Large bodies of low-grade ore can be
estimated much closer than those In
which the mineral occurs in punches
or pockets of high grade, not only be-
toriy and at a low cost with churn or
diamond drills, but also because they
can be expected to continue in value
and quantity.
Fissure deposits, perhaps more than
those Of any other character, offer con-
siderable data for fairly definite es-
innate of the depth to which they can
be expected to go. 1t has been found
in the opening up and development of
these deposits that the depth to which
they extend has some relation to the
length of the deposit. This relation,
as commonly found by engineers, is a
ratio Of about to 1; in other words.
II the deposit Is 500 feet long the vein
may reasonably be expected to extend
to a depth of about 500 feet. AS far
as has been determined the width Of
the ore body has no relation to the
length or depth of the deposit. This
suggestion, however. as well as any Of
the foregoing. cannot be considered a
hard and fast rule, and for that reason
should be used with discretion.
The task of valuation of property
would be easy II all surface showings
or outcrops which resemble those Of a
producing mine positively indicated
the same mineral content, tonnage and
other factors as in the producing mine
which they resemble, but if exceptions
are considered as proving any rule,
the exceptions to this rule would prove
it oftener than the examples which are
found agreeing with it. In other
words, although the majority of pro-
ducing mines do have outcrops or sur
face showings which are comparative
ly similar in their respective classes,
1t does not mean that a prospect hav-
ing similar surface showings will nee
essarily develop into a producing
mine. The common saying among
miners that "all the rocks necessary
to make mine are present, but very
little, If any, mineral is present" is
only too true, and it is this factor
which makes it difficult for any two
men to, form the same estimate of
prospect; the valuation may range
from zero to a bonanza.
This is particularly true with pros
poets which are located in regions
where there has never been a produc-
ing mine developed, where. nothing
but the geological factors can be con-
sidered. If. on the other hand. there
are mines which have produced or are
producing near at hand in that section
the task Of valuation is much simpli-
fed providing the prospect lies in the
same zone and has the same geological
features as that of the producing mine.
Much data from the developed mine
can be used in helping to form an
opinion of the prospect, and as Is COM
monty known. this fact has been re-
sponsible for the purchase and dew
elopment of some of the largest mines
in the world.
The above represent some of the
geological factors which may aid in
forming an opinion Of a prospect, and
are of particular service to an exper-
fenced man who has learned them on
the ground around producing mines,
where the gradual changes in the ore
bodies from the surface are visible
permitting a thorough inspection of
them, When studied in this way they
are seldom forgotten and are great
aid to the engineer should he see an
outcrop whose geological features are
similar to that Of a producing mine
with which he is acquainted.
Since the valuation of a prospect
usually depends upon the value of the
ore at or near the surface more than
any other factor, the first thing to
he done after careful inspection of
all exposed parts of the deposit has
been made in the taking of samples.
The values obtained from the as
says of these samples are used for
making the calculations for the esti-
mate, and for this reason each sample,
when assayed. should be run either |
duplicate or triplicate, so as to elm
nate any chances Of error which |
night arise.
AT the time the samples are being
AIKEN it is good policy to take spec
mems of the rocks from the outcrop
md from the surrounding rocks as
veil as the country rock These are
alter used to make study of the geol-
gy Of the property to determine the
manner of ore deposition.
The deposit Is also surveyed at this
ime, map being made from the sur