Gilpin observer., 1899-12-28
SAMPLING ORE BODIES.
Advice as to Methods OF Determing Value
Orr.

Advice as to Methods of Determing Value
of Orr.
The average man who invests in
developed mining property, or blindly
puts money into Il 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 at its New
4 York office do not, as Il rule resemble
| the dingy. undiscovered rock that the
\ prospective investor, in case he takes
the trouble =" to see what the mine
looks like" finds at the head of some
4 drift, or in the breast of some stope.
The miner who shows him about will
not point out the poorest rock to him.
| CoDsequently, he either goes into the
nXtter blindly, regarding all mining as
yEgamble anyway. or, if more cautious,
employs some expert who may or may
not be trustworthy. Only rarely. as a
1 rule, does the investor employ skill
L ful and reliable mining engineer to de
tefmlne the value and amount of the
ore exposed: yet it is in this matter of
\ Sampling and measuring the amount
AN value of pay ore in sight. that the
| greatest mistakes are made in precious
metal mining, and the worst frauds
| worked on the public.
Ore deposits, as Il rule, are not sharp
ly defined areas with regular out
! lines, and of uniform character. A de-
| post may have no well-deiined boun-
daries and its values may gradually
| fall off on either side of Il rich central
| portion till they are too low to pay
for mining. The outlines of the de-
| post are sometimes regular, but gen
eral are extremely irregular. with rich
er portions running off into the lower
grade rock surrounding them. Instead
of being of uniform value, a deposit
generally has richer and lcancr streakS.
This particularly applies to true vein
deposits, where Il quartz vein six feet
wide may be near each wall. or
through its center, Il streak of high
grade ore. Il few inches wide. worth
hundreds of dollars II ton: while the
great body of the vein is not worth
$40. Some of the copper-hearing lodes
worked by the mines mt Hancock.
Michigan. show similar streaks. An
nmygdaloid belt. ten or fifteen feet
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.
''h'h Vi tIuTitltT DlnN Iukb
place not only along tolerably even
planes. but the rich ore may be appar-
ently concentrated around centers. In
some of the great iron mines of the
Manominee range in the Lake Super
ioI'iron district. for instance the ore
Jay vary widely in its proportion of
IRON and phosphorus within Il dis
ttance of few feet; and no rule of rea-
son has ever been discovered which
would account for these changes.
Sampling any kind of an ore body.
then, is evidently a matter of time and
tNpuble. Prospectors. even the most
h0Sest, are prone to give values based
pm analysis of some specimen rather
than on average of all ores exposed
There have been n number of COM
panies tloated in eastern cities this
year which. the promoters stated. had
pre- of fabulous richness, vet inyesti-
gators could find nothing but Il few
)utcrops of doubtful value or some
ioles in the ground. into which selected
specimens from some other mine had
been dumped.
In case the investor wishes to make
4 personal test of what he is buying
md try his hand mt sampling. there are
our general systems open to him. all
bf which are frequently used on the
same property.
l. With pick or prospector's ham
>iner. Il great number of small samples
may be quickly and roughly taken
llong lines ut short intervals across the
!. ace of each plane section of ore eN-
Dosed. The specimens should be TAX
m Systematically. An expert may be
deceived by appearances and man
pf thorough honesty may unconscious
" clip off the best-looking portions of
he vein. \ continuous groove should
pc made the length of the section. or
mail bits Clipped off at intervals of
II inch or so
:. lesser number of large samples
nay he taken with care and precision
rom along lines mt wider intervals.
3IfMill-runs may he made. In this
fhem II few samples are taken so
rye that each can he millcd by itself,
nd furnish enough bullion to clean up.
Zach sample Is taken from ore from
everal parts of the vein. To make II
representative, and is shipped toane
~ mil, smeltcr or Sampling works
~ rough method of ascertalning
IN value of gold veins Is to take II
lrge number of very small samples,
ulverizc them, and by plnning in Il
liners gold pan, estimating the
mount of gold In the rock. This
lethod is adapted only for free mill
~ ores.
The iirst method is the quickest and
asicst to use in claims mt remote
oints, The samples have to he ns-
lyed separately. but they are quickly
iken, and the assaying can sometimes
g done ON the spot with portable
utit When the rock varies in hard.
css, and the bits Clipped of are of
lfIcrcnt sizes. the results may he I'M
liable. This system is not to he
'usted where thin strealis of very
lghgradc ore lie in n wide body of
w-grndc rock The system is well
laptcd for snmplIng ore bodies that