The Wallace miner. [volume] (Wallace, Idaho) 1907-current, 1918-08-01

the line between the ore and wal
rock is distinct, sometimes separate,
by "gouge" or miners tale" Wher
no chrome ore is found in the wal
rock Immediately adjoining the or,
body. and gouge is present, it may in.
dictate that the original wall rock ha,
been removed by displacement. TIL,
ore along the wall may be fluted o,
grooved, and If the disturbance has
been sufficient, the ore body may be
coarsely fractured, or even so finely
crushed as to make it friable, that is
capable of being disintegrated by
compression in the hand. otherwise
If no chrome is present in the wall
rock, 1t may be due to earlier genetio
causes. Some magmas were undoubt-
edly more fluid than others, Just as
some smelter slags run freely while
Others are so sluggish that they freeze
readily at the tuyeres. In a partic-
ularly fluid magma there would be
floW currents just as there are in wa
ter, these tending to carry away
chromite particles which had not yet
been consolidated with the main mass
of chromite. For this reason | con-
clude that the largest deposits of
chrome We're probably formed in mag
mas relatively free from flow currents.
| Chrome ore is always found in basic
igneous rocks, such as peridotite or it's
altered form, serpentine. This is
probably because chromium is more
soluble in basic than in acid magmas.
Distribution of Chrome in Deposits.
All parts of chrome deposits are not
OF equal grade. The question has been
asked What may be expected to be
the highest grader In most deposits
the ore near the walls or the bottom
is less pure than that in the main ore
body. However, there is much var
iation; and there is no rule to follow.
This irregularity probably results from
minor influences during the period of
formation The principal impurity is
not necessarily silica; it may be iron,
magnesia, or alumina. If iron be pre-
sent as magnetic, the ore may be
heavy and black, and may appear to
the eye to be high grade, yet actually
low in chronic oxide Some good ore
is found with a film of magnesium
carbonate, or silicate, so that it is
white in appearance, and such ore has
been condemned for that reason, be-
cause it was considered to contain too
much silica. 1t is important to rem
ember this: You cannot make an
optical analysis of chrome ore.
Field Determination of Chromite.
FRniliarize yourself with the ap-
pearance of typical chrome ore.
Scratch a piece of the suspected ore
with a knife, deep enough to pene-
trate any surface film of foreign ma
terial. If the streak is dark brown,
the material may be chrome. If the
prospector will provide himself with
spirit lamp, tw oinches of platinum
wire fused into the end of a short
glass tube, and an ounce of bOrax, he
can make a fair determination. The
operation is as follows: Crush a small
piece of the ore to a powder; bend a
small loop at the end of the platinum
wire; heat the wire in the flame, and
Ill 4 in hA hnp
stick to the. loop. Melt this in the
flame, and continue dipping in the
powdered borax and melting it until
the loop has become filled with bead
of colorless borax glass. Heat the
bead to redness, and, while hot, place
it against the crushed ore until a few
particles adhere to the bead. Hold
this in the flame until the particles are
entirely dissolved in the borax, allow
it to cool, and then the bead, if chrom-
ium is present, will have a bright
green color Having determined that
chromium is present, send the sample
to reputable chemist and ask him
to determine the amount of chronic
oxide and silica. The ore buyer must
know the percentages of these two
materials before he can 60 further.
Minerals Mistaken for Chromite.
Magnetic, or magnetic iron ore is,
frequently mistaken for chrome one.
It is dense black, highly magnetic, and
of about the same weight as chromite.
1t is much harder, however, and can
be scratched with a pocket KNIT only
with difficulty, and it does not show
the brown streak. 1t may be dis
tinguished also by crushing to the
size of a pea. If it can be picked up
by a magnet it is not chromite.
Hematite, another ore of iron, Is
sometimes mistaken for chromite. 1t
is usually softer, and has a reddish
brown streak, quite different from that
of chromite
Hornblende-p icrite, a rock that Is
dark-gr to black, and quite heavy,
Is frequently found in chrome dis
tricts. Hornblende may be similar
in appearance. The simple way to
distinguish these rocks from chromite
is to scratch them with a pocket knife;
the streak is grayish to greenish-
white.