White Pine news weekly mining review. [volume] (East Ely, Nev.) 1910-1920, 1911-03-19
VALUATIONS Of
M|N|NCPROPERTY
HOW TO APPROACH GENERAL
FACTORS RELATING TO THE
UNDETERMINABLE PROFITS
N UNEMPLOYED AREAS.

be won from the ore or that In
place. Ore is rarely, If ever, con-
~tinuous and of the same uniform
thickness for long distance, as some
coal seams, but 1t commonly occurs
in lenses or irregular bodies, with
thin or even nearly barren intervals.
Measurement of these lenses in the
course of examination give an ap-
proximate idea of the amount of ore
in sight in the mine.
Ore is not of the same value
throughout a mine; in some parts it
Is oxidized, in others IL is in its ORR
ginal, hard, crystalline or sulphide
condition; OF 1t may here and there
contain an admixture of either en-
riching or impoyerishing minerals:
hence a few grab samples will not
show the value of the ore through
out the mine, but many samples have
TO be Systematically taken at differ
ent points. Pay streaks" may have
to be sampled separately from mill
dirt or low grade ore, and an esti-
mate made of the value of each
separately or both collectively. The
same applies TO portions of the vein
that have an admixture of other
ores The sampling of all these may
ultimately give a fair idea of the sun
total or general value of the ore OF
the mine. The sampling may be
by simple assays or by mill tests and
smelter runs, or all of these.
Ore bodies in a vain may locally
contain rich patches of such a min
eral as gray copper" notorious for
its high silver values. Other parts of
the vein may entirely lack this en-
riehing element and contain inferior
or refractory ores, such as zinc
blende or some form of low grade
pyrites. or some obnoxious mineral
like barite or iron carbonate. Hence,
in summing up the general value of
the ore in place these local rich and
poor, or undesirable, admixtures
should be taken into consideration.
The ease or difficulty with which
such ores may be mined is an i'm
portant factor as we'll as the hard
ness or ~softness of the rocky matrix
containing them. A soft. oxidized
ore can be mined in decomposed rock
much easier than an original sui
phide contained In a matrix OF hard
unoxidized quartz. Added TO this Is
10 be considered the width of the
vein and ore body between walls. If
narrow. a great deal Of gangue mat
ter and barren country rock Will
have to be dug out with the ore to
make the workings wide enough and
accessible to the methods used in
development. What will ii cost per
foot to mine this ore, and is the ore
wide or rich enough TO stand profit
ably this cost are cogent questions.
Suppose by careful sampling and
measurement of the ore bodies. both
in width and length, an approximate
value of the ore in the development
workings OF the mine is attained.
The next question is the prospective
profit to be derived from the assum-
ed extension of this ore beyond yisi-
BILE exposure in the mine or beyond
all important developments. How
much available ore Is there likely to
be In the hill II the present works
are continued. An approximate esti-
mate of this may be formed by fol-
lowing up the outerops of the vein
on the hillside and getting some idea
by means of the prospect holes open
ed on them at various intervals. Is
there the same ore In these and of
much the same assay value as that
found in the developed mine. and are
the geological features Identical or
different? AT best there can be no
positive opinion, but only a reason
able assumption as to the probable
future of the ore of the property
within certain limits. Thus an ore
body may be assumed from surface
signs to be reasonably continuous, or
like that in the workings for a few
hundred feet, but when IL comes to
prophesying for thousands of feet
the case may be merely a matter OF
speculation. The same may apply to
ore in depth below the present work
ings; 1t may be reasonably assumed
to continue down and preserve much
the same character for 100 feet or
so, but no one can state positively
what 1t may do at 900 feet or more.
Among unforeseen variations that
may happen Is that an ore body may
entirely change character with
depth; thus some celebrated mines
have begun as gold or silver produ-
GERS and with depth have become
copper or zine mines, or vice versa,
Ores, again, within a few feet of the
surface are commonly oxidized and
may abound In free-milling or easily
treated mineral, but In depth such
inevitably pass into the %sulphide or
primitive crystalline condition and
may not only materially change In
values and character but may re-
quire an entirely different treatment.
An ore near the surface may be free
milling. with depth IL will probably
need smelling, cyaniding or some
other process.
In the Ease of a number OF parallel
veins on a property, although these
may have very nearly the same
geological conditions and may have
been formed and filled at the same