Charles George Warnford Lock.

Economic mining: a practical handbook for the miner, the metallurgist and ... online

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It may be well to remark, however, that in a new district it is
advisable to let a very thorough surface prospecting precede the use
of a diamond drill, because if no or but little gold can be found at or
near the surface in the neighbourhood of quartz reef outcroppings, it
is very unlikely that sinking will be adequately rewarded.

Diamond drilling plants are made to drill upwards of 3000 ft.,

B 2



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4 ECONOMIC MINING,

and of various sizes, in accordance with the length of drill holes for
which they are designed.

The construction of drilling plants and the uses of the various
forms of tools are fully described and illustrated in • Mining and Ore-
dressing Machinery,' but passing reference may here be made to the

very useful hand-power
diamond boring ma-
chine invented by Crce-
lius, made by Richard
Schram & Co., London,
and illustrated in Fig. 1.
This machine is in-
tended and well adapted
for prospecting pur-
poses, for proving the
existence of mineral
lodes, for tapping water
in old workings, &c.,
where it would be diffi-
cult to use steam power.
Holes can be bored up
to 300 ft deep at any
angle from the vertical
to the horizontal, or in-
clined upwards. It can
be arranged to bore
holes underground.

The power is trans-
mitted through the
horizontal spindle A
and bevel wheels B, to
the boring spindle C,
through which the bor-
ing rods D pass. The
machine can be driven
at about 60 to 70 rev.
a minute. The advance
motion is obtained by a
weighted lever acting
upon a toothed wheel E,
with which is connected
a wire rope passing
round a pulley F, which
is attached to the bore-
spindle. The other end
of the rope is fixed to
the frame of the ma-




Fio. 1.— Hand-power Diamond Boring Machine.



chine. The crown G is set with diamonds of about 1 carat each in
the usual way. The crown for ordinary purposes is \\ in. diam., and
makes a core of 1 in. diam. Larger holes can, however, be bored
with this machine if necessary. The crown G is screwed into the



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PROSPECTING, 5

core-barrel H, which is 3 ft. long ; and the core-barrel is screwed into
the boring rods, which are 4^ ft. long and are provided with screwed
oonpliogs.

Water for washing away the dSbri» and keeping the diamond
crown cool, is supplied through the boring rods by a small hand force-
pnmp ; about 1 gal. of water a minute is required. From 2 to 4 men
are required to work the machine, according to the depth of hole;
and the speed obtainable varies from 5i^ to 13 ft. per shift of 8 hours,
according to the hardness of the rock passed through. The total
weight of the machine with 200 ft. of bonng rods and all the neces-
sary tools for working it is 14 cwt., and it can be taken to pieces for
transport, so that no piece weighs more than 150 lb.

The cost of diamond drilling per foot is dependent upon the cha-
racter of the ground, cost of power, labour, &c. The speed made
exceeds sometimes 60 ft. per 24 hours. A good rate, however, allowing
for loss of time incident to the operation, for depths of 200 to 700 ft.,
in rock of favourable character, would be 20 to 40 ft. per 24 hours.
The most favourable kinds of rock are those which are homogeneous
in their structure. Fissured rocks, or those in which cavities occur,
are not favourable for drilling, owing to the liability of breaking the
bit and rods, and the consequent delay. Hard rocks, if homogeneous,
are favourable ; but in very hard rocks the progress is less rapid and
the wear of the carbons (diamonds) is greater than in softer homo-
geneous rocks.

At the present price of diamonds, a bit of 8 carbons, weighing
17| carats, costs about 50Z. The consumption of diamonds is not so
much due to the gradual abrasion incident to the grinding, as to
breakage by pressure against the face of the rock.

The average cost of drilling is variously stated. In the United
States, under ordinary conditions, it is estimated to range between
4i, and 8«. per foot. The averages of costs of boring in Victoria,
Australia, in 1891, are officially quoted as below. They cover an
aggregate of over 27,000 ft. in gold prospecting, and over 14,000 ft.
in coal prospecting. In the case of the gold prospecting, the wear
and tear of diamonds was responsible for about one-third of the total
cost; in the case of coal prospecting, this item only amounted to
one-fifth of the totaL The average costs were : —

Per foot

1 diamond drills (inolusive of cost of wear

and tear of diamonds) Oil SJ

other boring machines on contract .. .. 5 7^

/T^i _„, ^^. (diamond drills (inclusive of cost of wear

Ooalproepectmg.. | and tear ol diamonds) 10 4i

Ayerage coat per ft. for all descriptions of boring 11

The use of corundum instead of diamonds is proposed as an
economy.

Sampling the Ore Body. - A most important step in determining the
value of a mineral deposit is to adopt a correct system of sampling.

For the sake of example, let us assume it to be a vein, with an
average width of about 4 ft., varying say from 1 to 6 ft. Commencing
at the bottom level, take from the face of one of the drifts across the



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6 ECONOMIC MINING.

entire width of vein sample No. 1. To obtain this sample, break
down 16 to 30 lb. of vein matter, allowing the broken rock to fall
upon a piece of rough canvas stretched upon the floor of the drift*
In selecting this sample, aim to break down, as nearly as possible,
rock to represent the average character of the material at this point.
Waste as well as clean ore occurring in the vein must be included in
the sample. The 15 to 30 lb. of rook thus broken down are spalled
upon the canvas, and quartered so as to obtain a sample of 4 to 6 lb.
This sample is sacked, marked "No. 1," and sealed. The locality
from which the sample is selected, the width of the vein at that
point, &c., are noted.

In a similar manner sample No. 2 is taken, extending from point
at which sample No. 1 was taken, across the vein towards the shaft,
a distance of 10 to 15 ft. About the same quantity of material is
broken down, and the sample is selected in the same manner as sample
No. 1. This sample is likewise sacked, marked, and sealed.

Where there is a pinch in the vein, or where the vein is filled
with waste, or where the rock is obviously of a grade too low to be
profitably worked, it is not necessary to take a sample, but a note is
made describing the condition of the ground at the point where no
sample was taken.

In this way samples are taken from all parts of the mine, the
winzes, upraises, backs of the stopes, drifts, shafts, &c., where there
are exposures of ore.

These samples are all kept separate, and their values are sepa-
rately determined. The values of the samples thus .obtained are
indicated on a diagram of the mine. The extent and method of
occurrence of the ore body is thus graphically illustrated, and it can
be readily seen whether or not it increases in length with increase
of depth ; likewise the continuous or spotted oondition of the ore
becomes apparent.

Determination of the cost of mining and milling having been
made from investigation of the conditions of the mine, the delimita-
tion or definition of the ore body and the amount of ore in the mine,
can be readily ascertained.

In many wide veins the pay ore does not extetid across the entire
width of the vein, but is confined to a streak near the foot or hanging
wall of the fissure. Sometimes, but more rarely, this streak occurs
near the middle of the fissure. This pay streak is sometimes wide
enough to be stoped profitably, whereas the stoping of the entire
width of the vein would not pay.

In sampling such veins, where the ore body is not of even value,
the sample should not be taken across the entire width. In such
cases a sample should be selected for a width of 4 to 10 ft., beginning
at the foot wall, and sampling towards the hanging wall. This
sample should be marked "A." Another sample, selected for the
same width as " A," should be taken from the uppermost part of the
streak toward the hanging wall. This sample should be marked " B."
In this way the entire width of the ledge is sampled, and separate
tests are made of these samples to ascertain the width of any workable
pay streak, if such pay streak exists.



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PROSPECTING. 7

These samples. A, B, C, &c., are further marked by numbers as
" 1 A," " 1 B," vVc, to indicsate the points from which they were taken
along the strike and dip of the vein.

In this way the miner can determine in what part of his vein the
pay ore lies, and to what distance this pay ore extends in length,
depth, asd width. From such data, the value of the property can be
estimated as far as developments extend, and predictions, to a great
degree reliable, may be made as to the result of future developments
upon the vein, based upon the character of the deposit as far as
explorations extend. Of course, good judgment, based upon extensive
experience, greatly enhances the accuracy of these predictions.

Tetixng Auriferous Samples. — The determination of the value of an
auriferous quartz is usually made by means of the horn spoon, in
which a few ounces of pulverised quartz or vein-filling is horned
out, and an estimate is made of the yield of the quartz in free gold.
Sometimes 1 lb. or more of the quartz is panned out in a miners' pan/
and the value of the ore in free gold per ton is estimated from the
quantity of gold saved in the pan. As a rule the amount of pulp
taken for the test is not determined by weighing, nor is the quantity
of gold saved ascertained by weighing, but is judged simply by the eye.

Such methods are obviously very unreliable, especially where
gold ores of various localities are being tested, since the fineness or
coarseness of the gold may vary so far as to make the estimate by
the eye of the weight of the gold but little better than guesswork.
A far better system is the following : —

Take a sample of 10 to 20 lb., the more the better. Select it
without discrimination, so as to obtain a sample of the average cha«
racter of the material of the vein where the sample is taken. Crush
all this ore to about the size of walnuts, and from this lot by " quar-*
tering down " take a «ample of about 3 lb. Pulverise this sample so
as to pass it through a 4b-mesh sieve. From this, by further quar-
tering, select a sample of 1 lb. to be tested as follows : —

Having covered the hands with rubber or other gloves to prevent
the introduction of greasy substances into the water used in panning,
weigh out the sample (1 lb.), then work it down carefully in the
batea or pan, preferably the batea, until most of the sands have been
washed off; then add a few drops of mercury, which bring in contact
with the gold by rubbing it throughout the pulp. Collect the small
amalgam, and boil it slowly in nitrio acid in a test-tube until the
mercury disappears.

llie application of heat (spirit-lamp) hastens the process by dis-
solving the mercury. Pour out carefully the acid, and wash out with
water all traces of acid left in the test-tube ; then pour the gold
carefully into an annealing cup, and heat over spirit-lamp until the
gold is thoroughly dry, when weigh it. This gives the amount of
tree gold per pound of ore, from which the free gold per ton may be
readily calculated.

An approximation as to the fineness of the gold can be made by
the eye sufficiently accurate for these tests.

Instead of *' cutting" the amalgam by the use of nitric acid, the
mercury may be volatilised by the blowpipe.



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8 ECONOMIC MINING.

The tailings from this sample should be saved, and the snlphurets
collected by washing off the sands. The snlphnrets are to be then
weighed; from this weight the percentage contained in the ore is
ascertained, and an assay is made to determine their value per ton.

A few small vials with cai-efully weighed amounts of gold will be
found usefal for comparison with the pannings made upon the field.
Such measures materially improve the guesswork otherwise practiaed.

Sampling Base Ores, — The sampling of the ores of the base metalfi
is an equally important matter. For illustration let us take a lO-ton
pile of 10 per cent, copper-ore, prepared for market. It will conaist
of masses generally the size of one's fist, smaller pieces, and even of
dust. Procure a clean, tight floor or pavement, an iron mortar and
pestle, a shovel, a small hammer, a piece of iron for an anvil, a broom,
and a wheelbarrow, barrel, or box.

Begin by shovelling the pile roughly into the form of a flattened
cone or flattened pyramid. Make a trench straight through the pile,
cutting it into two nearly equal parts ; again by a trench, at right
angles to the first, divide these halves into four nearly equal quarters.
A part of the ore taken from these trenches will form the sample
required. Proceed as follows : —

Having the wheelbarrow ready, begin at the middle of any side of
the made-up pile and cut the first trench. Cast the first shovelful to
the right, the second to the left, the third into the wheelbarrow.
Bepeat this order of shovelling until the barrow is full ; then empty
it upon the weUnswept floor intended to receive the sample. Continue
in the same way until the trench has passed through the pile, when
there will result two rather long and narrow piles. Begin the seoond
treoch, extending it across the middle of the two piles, casting the
first shovelful right, the second left, the third into the barrow. Pro-
ceed in the same way as with the first trench. When done, you will
have shovelled about 6000 lb. of ore. As every third shovelful was
thrown into the banow, there will result about 2000 lb. of sample
upon the floor. That this is a fair sample of the original pile is baued
upon the assumption that each third shovelful thrown into the barrow
was like the first and seoond ones cast into the piles. The hypothesis
is reasonable and freely to be trusted.

Having the sample, proceed with it after the regulation method,
as follows : —

Spread it thinly on the floor ; now examine it. If there be any
lumps which look larger than the general run, place the anvil upon
the pile, and between that and the hammer break those lumps. The
next step is to thoroughly well mix the sample. Begin at one edge
of it and shovel the ore over upon itself. Move around to the opposite
side of the pile, and from that side shovel the ore again upon itself
and back into its original place upon the floor. Having it well
mixed, form it into a flattened cone and sweep all the dust upon and
around the pile. You have now to halve and quarter the sample as
follows : —

Commence at any point and shovel a road through the centre of
the pile, casting the shovelfuls alternately right and left as you pro-
ceed. This movement will result in cutting the pile into two elon-



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PROSPECTING. 9

gated nearly eqoal ones. Beginning at the middle of one of them,
shovel a road through it in the same way as before. And in precisely
the same way cut the other pile in two ; sweep upon each pile the
dost belonging to it. These movements will result in four piles.

If the sample were well mixed, as directed, then will each of the
quarters. A, B, 0, D, have the same, composition as all the others. But
if, upon inspecting them, you judge one or another to be poorer or
richer than the other, you will then have sufficient evidence that the
work has been badly performed. In that condition of affairs mix well
together all the piles, and once more halve and quarter them. Having
made all the quarters of the same composition, it follows that any two
of them may safely be accepted as representing the original 2000 lb.
of rough sample. This opens a road leading in the right direction,
sinoe it enables us finally to get rid of half the sample. We may cast
out two of the quarters and retain the other two for the sample. It
is a matter of indifference which two are retained, say A and B.
Bemove from the floor C and D, together with the dust belonging to
them.

We have again to break the larger stones, until there remain
none larger than walnuts. Place the anvil between the piles, within
easy reach of them. Take a stone from A, break it ; take one from B,
break that. Continue in this way, taking stones alternately from
each pile, until all are reduced to the size stated. By proceeding in
this way, the sample is more or less mixed while being broken.
Complete the mixing as before, by shovelling all the sample to and fro
over the floor. Form it once more into a flattened cone, and sweep
the dust upon and around it. Divide the cone into two halves, and
those into four quarters as before. You have now to reject
two of these quarters. The unwritten law of the sampler says
that it must be those holding the positions A and B, because those
were retained in the last quartering. Eemove A and B from the
floor, retaining C and D for the sample. These would now weigh
about 600 lb.

Proceeding as before, break down the lumps of ore until none is
left larger than, say, 1-in. cubes. Again mix well the sample, make
it into a pile, sweep up the dust, halve and quarter the pile. Beject
two quarters (C and D of course), retain two« as in former quar-
terings.

Once more break the lumps, this time down to ^in. cubes. Mix
well the sample, make it into a pile, sweep up the dust, halve and
quarter ; reject two quarters. The two quarters retained would weigh
abont 125 lb. Break it down until comparable to fine gravel and coarse
fiand. Mix and quarter onoe more.

The two quarters this time retained would weigh about 60 lb.
With the mortar and pestle break this to something approaching
ooaree sand. Again mix and quarter. The quarters this time re-
tained are to be ground yet finer, mixed, and quartered.

If you have no mortar and pestle, the hammer and anvil may be
rafastituted throughout. After getting the material into the form of
coarse sand, it is best to mix and quarter it upon a sheet of paper,
even an old newspaper.



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lo ECONOMIC MINING.

At this point the sample would weigh about 15 lb. ; its larger
grains would be in size like coarse sand. It would be safe now,
without further breaking, to mix and quarter it twice, or until its
weight did not exceed 4 lb. Run this through the mortar, and then
mix and quarter it twice, or down to 1 lb. weight, (^rind this to
something approaching powder, and, for the last time, mix and quarter
it. Have ready six wide-mouth 1-oz. bottles. Place them in a line,
side by side, upon a sheet of paper. From the <»ther paper pour the
ground sample in a small stream, to and fro across the months of
the bottles, until they are all full up to their shoulderj$. Cork, seal,
and label them, and the sampling is done.

It does not matter of what solid a sample may consist, or how much
or how little it may be, it should be worked down in the manner just
detailed.

A word may be added as to larger and rougher ore piles than
have yet been mentioned* It is not unusual to have a pile of 100 or
200 tons to sample. Such piles are apt to consist of lumps larger than
a man's head, together with masses of all smaller sizes. Where a pile
is formed by dumping ore uniformly upon its top, the likelihood is
that the pile is homogeneous. In such a case it is safe to make short
cuts into it at several points around its base, and to consider as sample
the ore so got. It is safer to make one cut through the pile, retaining
as sample each third shovelful, as in the case of the copper ore just
considered. In forming ore piles of the weights given, it is a good
custom to put upon a separate platform each tenth or twentieth
barrow-loaa coming from the mine ; the small pile will prove a fairly
good sample of the large one. But no matter how it may be got, the
rough sample is to be broken and mixed and proceeded with after the
regulation method.

A very ingenious and efficient mechanical sampler was recently
described and shown at a meeting of the Institution of Mining and
Metallurgy.*

Beveling. — When the value of a sample of a mineral deposit has
been determined, the next consideration for the prospector is laying
out the development work he proposes to do, to ascertain the extent
and permanency of the ore body.

In the first instance, the exploratory work should as nearly as
possible be confined to those portions of the property which give the
most encouraging indications. The Mexican system of developing
consists in closely following the discovered ore body ; and when this
fails, their explorations, if continued at all, are confined to the neigh-
bourhood of ore bodies already proved.

This method has obvious merits in avoiding any appreciable ex-
penditure on profitless deadwork, and in multiplying the chanpes of
striking subsidiary veins and bunches of ore.

The character of the exploratory work is chiefly determined by
the situation of the ore body to be prospected, and by the local topo-
graphical features. Where practicable, adits are preferable to shafts,
especially in a country where veins carry much water. In addition

• T. Clarkson, •* Tlie Sampling of Ores and Tailings," Trans. Inst. Min. and
Met., ii. 229.



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PROSPECTING. II

to the expense obviated by tunnels in draining the mine, the cost of
extracting the ore is very greatly diminished as compared with that
attending hoisting through shafts. Much greater depth upon the
Teiu may be reached without it being necessary to resort to the
erection of a hobting plant, than where the ores are extracted through
ftbaftB.

Where possible, tunnels are run upon the vein. In some places,
notwithstanding the fact that the topography admits of tunnelling,
bhonld it be necessary to run a long croi>scut tunnel (tunnel not run
upon the vein), or should the flat character of the country prevent the
attainment of sufficient depth upon the vein to compensate for the
expense of tunnelling, the vein should be prospected, other circum-
Btanoes admitting (absence of great amount of water in vein), by
shafts. The inclined shaft following the dip of the vein is generally
adopted in prospecting the mines of California, the better to examine
the character of ground being developed, and also, because it is
oraally cheaper to sink such shafts than vertical shafts outside of the
vein formation.

The adoption of the best system of prospecting, whether by tunnels
or shafts, must be determined by local conditions, and only after
careful consideration of all the questions involved. Too often lack of
discrimination in this matter involves the useless expenditure of much
time and money, as well as often the accomplishment of but nugatory
n«alt8.

The pay ore, as previously explained, often occurs disposed with
more or lei« irregularity through the veins along its course as well as
its dip. Several pay shoots of variable extent and pitch may likewise
occur in the same vein and upon the same property. In order to
ascertain the location, as well as the extent of these bodies of pay ore,
exploratory work must be carried out. Such work should be syste-
inatically conducted, and the character of ground thus prospected be
recorded upon a map of the underground developments of the mine.
The developments by drifts, raises, stopes, &o., and the approximate
width of the vein, should be monthly recorded upon such a map.
Without a working map no scientific system of prospecting can be
conducted. Such data, if comprehended by the superintendent, are of
iDestimable value in laying out his work. To prospect the ground,
drifts and crosscuts are run, and winzes and raises are made.

The character of the ground will determine the most economical
method of its exploration ; but these explorations should be so planned
as to cover the most ground with the least amount of exploratory
work, and the work should be so laid out as to avoid the duplication
of results. This seems axiomatic, but frequently long drifts are run
in ground, the character of which had already been so satisfactorily
established by other work as to be susceptible of reliable determi-
nation by sinking a winze from an upper level to prove the absence of
ore bodies. Therefore, hi ground in which the chances of dis-
covering valuable ore bodies are very slight, this tendency to run
drifts too frequently is to . be avoided. There are few mines where
much money has not been thrown away by fruitless exploration of



Online LibraryCharles George Warnford LockEconomic mining: a practical handbook for the miner, the metallurgist and ... → online text (page 2 of 76)