The Anaconda standard. [volume] (Anaconda, Mont.) 1889-1970, 1899-08-15
WHAT IS FREE MILLING ORE2

4 writer in the British Columbia Mn
ing Record. who signs himself ''Pyrites,"
covers the free milling gold IN an interest
ing manner. He says: The question fire.
quently arises as to what is meant by a
free milling gold ore. and as the character
of ore is a matter of considerable import
ance in the purchase of a mine and in the
subsequent erection of machinery, | will
endeavor in this paper to throw some lit
tie light on the matter and render short
description of the various devices me-
chanical and chemical, by which the pre-
cious metal when in the free state, is
separated from its accompanying gangue.
Gold is found in the rocks of nearly all
ages, and it has been from the vast dis
integrated masses of these, forming the
alluvial deposits of California and other
countries. that most of the worlds gold
has SO far been obtained. But since these
deposits have. to a great extent, been
worked out, the attention of mining men
has been turned to the rocks themselves
the original source of the gold.
Most of the gold of the present day Is
extracted from the quartz veins and lodes
traversing the metamorphic rocks, the
precious metals being frequently asso-
ciated with iron pyrites, blende. arseni-
cal pyrites, carbonate of copper, etc 1t
is also found in the mineral sylvanite-a
nagyagite-and in very small quantities
with galena. II will be necessary to con-
slider in what condition gold itself exists
in the rock. We may take the following
cases:
First-In which the gold occurs clean
and practically pure, and disseminated
through the rock in grains of an appre-
ciable weight.
second-When the gold is distributed
In, Nortin 1 nal
that they have no appreciate weight.
Third-When the gold is contained in
the sulphurets of the ore--in which case
the gold occurs. not as true gold, but as
sulphide of gold--whch is black powder,
or it may occur as grains of pure gold
coated with sulphur, arsenic or some 9TH
er impurity.
Fourth-In which the gold Is contained
partly in the ore and partly in the sui
phurets.
Now, in separating the gold from its
accompanying gangue, advantage is taken
of the fact that when clean gold is
brought into direct contact with pure
quicksilver an amalgam or alloy of the
two metals is formed. the separation be-
ing formed by pulverizing the ore by
means of stamps and passing the pulp
over copper plates coated with quickSil-
yer. whereby the gold is retained on the
plates, or by other amalgamating con-
trivances. Now. if the gold in the rock
is contained in the sulphurets it exists,
as have said, as sulphide of gold, or as
minute grains coated with impurities.
This gold is not Clean" and will not
combine with the quicksilver. This,
therefore. is not a free milling ore.
Again, take the case of gold distributed
in grains so small as to have no appre-
BILE weight--in other words, flour gold.
This gold, however clean and pure it may
be. cannot be saved by battery amalgam-
alton and cannot therefore be considered
as free milling. In the case when grains
of clean. pure gold of appreciable weight
are distributed through the rock the gold
will readily amagamate. Such is a true
free milling ore.