The Seattle post-intelligencer. [volume] (Seattle, Wash. Terr. [Wash.]) 1888-1914, 1899-12-11
How to Determine the Value Of
Ore Bodies in q Mine.
SYSTEMS READILY LEARNED.
Peculisritics Of Mineral Deposits
Which Make the Estimate OF
Their Value Difncult-Four sys-
tcms That Are Useful IN Trying
to Ascertain the worth Of . Mine
--latest Advices From Republic.

veloped mining property, or blindly puts
his money into prospect on the strength
of specimens shown by smooth-tongued
promoter. has little idea usually OF the
value Of the rock that has already come
out OF the hole In the ground, and no
idea of how to determine the value OF
what Is left. The pretty specimens seen
on the desk OF some mining company do
not, as rule. resemble the dingy, mud
covered rock that the prospective In
weston, In case he takes the trouble ITO
see what the mine looks like" finds at
the head OF some drift. or In the breast
of some stope. The miner who shows
him about will not point out the poorest
rock to him. Consequently, he either
goes into the matter blindly, regarding
all mining as a gamble anyway, or,
more cautious, employs some expert who
may or may not be trustworthy. only
rarely, as q rule, does the investor en-
ploy a siillful and reliable mining engi-
neer to determine the value and amount
of the ore exposed; yet 1t is in this mat
ter Of sampling and measuring the
amount and value of pay ore in sight
that the greatest mistakes are made
in precious metal mining and the worst
frauds are worked on the public
Ore deposits. as a rule. are not sharply
defined areas with regular outlines and
of uniform character. A deposit may
have no well-defined boundaries, ana It's
values may gradually fall of on either
side OF a rich central portion till they
are too low to pay for mining. The out
lines Of the deposit are sometimes regu-
lar, but generally are extremely irregu-
lar, with richer portions running on into
tho lower grade rock surrounding them
Instead Of being of uniform value, de-
posit generally has richer and ieaner
streaks. This particularly applies to
true vein deposits, where quartz vein
six feet wide may have near each wall,
or through it's center, streak OF high
grade ore a few inches wide worth hun
dreds of dollars ton: while the great
body of the vein Is not worth 80. Some
OF the copper bearing lodes show similar
streaks. An arnygdaloid belt ten or nj
teen Aeet thick may carry much native
copper along its contact with other beds,
while the rest of the belt Is frequently
so poor as to barely pay for working.
Such variations Of character may take
place not only along tolerably even
planes, but the rich ores may be appar-
emily concentrated around centers
Four Systems for Sampling.
sampling any kind of an ore body. then,
is evidently a matter of time and trouble.
Prospectdrs. even the most honest. are
prone to give values based on analysis
OF some picked specimens rather than
on average of all ores exposed. Inere
have been a number of companies float
ed in Eastern cities this year which, the
promoters stated, had ore OF fabulous
richness, yet investigators could nnd
nothing but few outcrops OF doubtful
value or some holes in the ground, into
which selected specimens from some other
mine had been dumped.
In case the investor wishes to make
a personal test of what he Is buying and
try his hand at sampling, there are four
general systems open to him. all OF which
are frequently used on the same property:
l. With a pick or prospector's hammer
a great number of small samples may
be quickly and roughly taken along lines
at short intervals across the face of each
plane section of ore exposed The speci-
mems should be taken systematically. An
expert may be deceived by appearances
and a man Of thorough honesty may UNI
consciously chip on the best-iooking
portions of the vein. continuous
groove should be made the length OF the
section, or small bits Clipped or at inter-
walls Of an inch or SO.
g. A lesser number of large samples
may be taken with care and precision
from aIopx lines at wider intervals.
g. Mi1l-runs may be made. In this
system few samples are taken SO large
that each can be milled by itself, and
furnish enough bullion to clean up. Each
sample is taken from ore from several
parts of the vein, to make 1T representa-
tive, and is shipped to nearby mill,
smelter or sampling works.
A. A rough method of ascertaining the
value of the gold veins is to take large
number of very small samples, pulverize
them, and by panning in miners gold
nan. estimating the amount of gold In the
rock. This method is adapted only for
free-milling ores.
Merits of the Several Methods.
The first method is the quickest and
easiest to use in claims at remote points.
The samples have to be assayed separate
". but they are quickly taken, and the
assaying can sometimes be done on the
SPOT with a portable outfit When the
rock varies in hardness, and the bits
Clipped off are of different sizes, the
results may be unreliable. This system
is not to be trusted where thin streaks
of very high grade ore lie in a wide body
Of low grade rock. The system is well
adapted for sampl.ng ore bodies that must
be mined on large scale, and has been
much used in the soft hematite deposits
of the Lake Superior iron region. The
system is applicable, also. where rich ore
Is in thin sheet, and IS used for daily
working in mine where quick, IL rough,
approximations are needed AS one speci-
be large errors in any single sample, but
this is balanced by the great number of
samples taken.
The second system is particularly adapt
ed for ores so hard as to require blast
Ing, and for ore bodies which vary great
" in value, and have the values distrib-
uted without system. The samples taken
may be from fifty pounds to fifty tons;
but should be large enough to represent
all variations along the line of the cut
1t is reduced by pulver.zing and dividing
by successive quarterings TO a size suit
able for handy transportation to an as
say office 1t Is advisable to take from
the last quartering two samples, sending
each to different assayer, as a check.
The third system is impracr.cable in
the case of prospects in new country,
and is used only when there is mill or
samrllng works close at hand, on account
OF the high cost of carrying the necessary
amount of ore any distance. The ex-
pense of making such tests Is great. and
taI y.n&t for Iats TWIN