Montana oil and mining journal. [volume] (Great Falls, Mont.) 1931-1953, 1940-06-01

tiOn of polished mineral surfaces
search in the field of microscopy
DR. s. r. b. Cooke stated TO-DAY II
Dr Cooke. research professor OF
pi,eral dressing at the Montana
school of Mines. stated that such
research has been curtailed al the
echool owing to the limited budget
rrovided for such work. This OBJ
etacIe was overcome through CO.
oneration with the Work Projects
administration whose employees
built the machines under the dlrec-
.ioD of DR. Cooke and his predeces-
sor Or A. NJ Gaudin. Details oil
the cooperative program were
drawn up by Dr.. Francis A. nom
son nresident of the School OF
Mines. and w T. Beaumont VINO -
in charge of the Research and rec
ords section Of the Work PfoJecls
administration.
Mineral dressing is defined by
recent number of the Mining Con
eress Journal as the processing OF
Nv minerals to yield marketable
nrodnrts (and waste) by means
tbat do not destroy the physical ana
cbemioal identity of the minerals.
princinles OF physics and OF physl-
cal chemistry lie at the root OF
everv individual process employed
in mineral dressing, I'LL
Among machines necessary loi
modern testing are DrlqueltlIs
press and a polishing machlhe ~
prepare samples OF ore ana otheI
mineral products for microscopic
examination. -,
Two initial steps usually are TAX
on in testing an ore for its amen
ability TO concentration, chemical
ANALYSIS and microscopic analysis.
chemical analysis yields direct m
formation concerning the quantities
of the various elements present III
ore. Microscopic analysis Identifies
mineral entities in which these ele-
ments occur.
Dr. Cooke points out as an eX-
ample body of iron minerals I
which chemical analysis shows to /
contain 35 per cent iron and 40 (
per cent silica. Such information
Yields no hint regarding minerals
in which iron occurs which IS nee
essarv before concentration tests
may be applied A careful miner
illogical examination, and certainly I
a microscopic examination, may
show that the iron-bearing mineral
is "a magnetic. (2) hematite
(3) limonite or geophite or t4)
a mixture of these minerals.
With the information provided
by the microscope the engineer may
outline several possible methods of
concentration If the iron mineral is
magnetic, then magnetic concen-
traItion may possibly be applied. If
the iron mineral is hematite or
limotite, some method of gravity
concentration such as washing,
jogging or tabling may be neces-
sary.
The microscope will give still
further information than the pure
" qualitative one of mineral con-
stitution. Ores almost invariably
consist of interlocking grains OF
gangue or worthless mineral and
valuable mineral The size to
which the ore must be crushed or
ground to completely free, within
economic limits, the valuable from
the worthless material is referred
to as the "size of liberation Sew 9
eral methods are available to eval- t
uate the size of liberation but the f
most rapid method is by means of +
the microscope The size of the in e
dividual grains of mineral is related Q
to the size of liberation. In general, a
the finer gained ore the finer that b
ore must be ground to liberate the p
minerals. The size of liberation plays a
a very important role in deciding
the type of treatment which is best g
suited to the concentration of the
ore. c
Sometimes microscopic examina- \
lions finally yield commercial re- a
suits totally unlocked for at the \
beginning of the examination Dr.. f
Cooke cites one striking example. i,
The mineral substance came from F
an eastern state and had been @
worked for its tale content for many a
years. The owners stated that TO the z
best of their belief, the gangue
was dolOmite, a relatively worth
less mineral A brief microscopic
examination of the ore showed that
the gangue consisted of magnesite.
an economically valuable substance o
provided that ii could be easily a
separated from the tale A closer p
examination of the ore demon n
strated the presence of relatively n
gersdorffite, both minerals contain
ing considerable quantities of nick
ell. In the light of this information r
successful concentration tests were S
made. A mill was subsequently, e. p
rected and is at present recovering d
all of the minerals as 90 tale flo
tation concentrates, 90 nickel c
bearing CAVITY concentrates and i
CD magnesite flotation tailings {
which are directly marketable
For the Identification of opaque .
minerals, it is necessary to prepare
sections which are essentially plane
highly polished, show little relief
and retain no fractures or scratch
es caused by the grinding process.
A briquetting press is used to Sc
cure specimens of regular shape.
These may be conveniently held in
an automatic polishing machine :