Transcriber's Note: Minor typographical errors have been corrected
without note. Irregularities and inconsistencies in the text have
been retained as printed.
Subscripted text is indicated with curly braces: {2}.
Words printed in italics are marked with underlines: _italics_.
THE A B C OF MINING
_A Handbook for Prospectors_
TREATING FULLY OF EXPLORATORY AND PREPARATORY WORK OF THE PHYSICAL
PROPERTIES OF ORES, FIELD GEOLOGY, THE OCCURRENCE AND ASSOCIATIONS OF
MINERALS, METHODS OF CHEMICAL ANALYSIS AND ASSAY, BLOW-PIPE TESTS,
PROMISING INDICATIONS, AND SIMPLE METHODS OF WORKING VALUABLE
DEPOSITS, TOGETHER WITH CHAPTERS ON QUARTZ AND HYDRAULIC MINING AND
ESPECIAL DETAILED INFORMATION ON PLACER MINING, WITH AN ADDENDA ON
CAMP LIFE AND MEDICAL HINTS.
BY
CHARLES A. BRAMBLE, D.L.S.,
Late of the Editorial Staff of "The Engineering and Mining Journal,"
and formerly a Crown Lands and Mineral Surveyor for the Dominion of
Canada.
_ILLUSTRATED._
CHICAGO AND NEW YORK:
RAND, McNALLY & COMPANY,
PUBLISHERS.
Copyright, 1898, by Rand, McNally & Co.
PREFACE.
Owing to recent rich discoveries in more than one mining field,
hundreds of shrewd, intelligent men without experience in prospecting
are turning their attention to that arduous pursuit--to such this book
is offered as a safe guide.
A complex subject has been treated as simply as its nature permitted,
and when a scientific term could not be avoided, the explanation in
the glossary has been offered.
CHARLES A. BRAMBLE, D.L.S.
PREFACE TO SECOND EDITION.
A steady demand for this work has shown that it fills a want, and
serves the purpose for which it was written. In issuing this second
edition, a few compositors' errors that had crept in, owing to the
author being in a very remote region while the book was going through
the press, have been corrected, but no material changes in the text
were found desirable.
CONTENTS.
THE A B C OF MINING.
PAGE
Chapter I--Prospecting, 7
II--How to Test for Minerals, 38
III--Blow-Pipe Tests, 65
IV--Economic Ores and Minerals, 75
V--Mining, 100
VI--Camp Life, 143
VII--Surveying, 155
VIII--Floating a Company, 161
IX--Medical Hints, 165
X--Dynamite, 168
XI--Atomic Weights, 170
XII--Odds and Ends, 172
Glossary, 181
A B C OF MINING.
CHAPTER I.
PROSPECTING.
Many men seem to think that should their destinies lead them into
parts of the world where there is mineral wealth they will have little
chance of discovering the deposits without the technical education of
a mining engineer. This is wrong. The fact is that the sphere of the
prospector does not cover that of the engineer. The work of the one
ends where that of the other begins, and many of the most successful
discoverers of metallic wealth have been entirely ignorant of the
methods by which a great mine should be opened, developed, and worked.
A few simple tools and a not very deep knowledge of assaying, with an
observant eye and a brain quick to deduce inferences from what that
eye has seen, are the most valuable assets of a prospector. In time he
will gain experience, and experience will teach him much that he could
not learn in any college nor from any book. Each mining district
differs from every other, and it has been found that certain rules
which hold good in one region, and guide the seeker after wealth to
the hidden treasure that has been stored up for eons of time, do not
apply in another region.
To show what may be done with imperfect, improvised apparatus, an
Australian assayer, who has since become famous, started up country in
his youth with the following meager outfit: A cheap pair of scales, a
piece of cheese cloth, a tin ring 1-1/2 inches by 1/2 inch, a small
brass door-knob, some powdered borax, some carbonate of soda and
argol, a few pounds of lead lining taken from a tea chest, an empty
jam pot, a short steel drill, a red flower pot. With this modest
collection of implements he made forty assays of gold ores that turned
out to be correct when repeated in a laboratory.
About the best advice that can be given to a man who has determined to
go to some out of the way region where there is a possibility of his
discovering minerals is to recommend him to visit the nearest museum
and gain an acquaintance with the common rocks. Should he be unable to
do this he had better provide himself with small, inexpensive
specimens from the shop of some dealer. It is almost impossible to
teach a beginner to distinguish the various rocks by any amount of
printed instruction; the only way to learn to recognize them is to
handle them and note carefully their color, weight, and the minerals
that go to make them up. The explorer should be able to recognize at a
glance, or at any rate after a very short inspection, the sedimentary
rocks, such as sandstone and limestone; the metamorphic rocks, that
is, rocks that have been altered by the agency of great subterranean
heat in ages long past, and which were probably stratified rocks at
one period, such as granite and gneiss, and the truly igneous
rocks--trap, diabase, diorite, etc. He must know also that mysterious
rock which the western miner calls porphyry, and to which is ascribed
most wonderful virtues in the way of ore attraction; while dolerite
and dolomite must be to him familiar terms and substances. This sounds
easy enough but the student will find that a good deal of hard work is
necessary before he can readily recognize each of these rocks.
It is even more necessary that he should learn the metals thoroughly.
Each one differs from all the rest in some particular. Often this
difference will be an obscure one, but to the careful investigator the
recognition of the substance will be in the end certain. They may
differ in weight, in color, in hardness, in a dozen different ways, so
that to the man who has made a study of this subject a determination
is always possible.
On account of the wonderful discoveries in the Canadian Northwest and
in Alaska, the eyes of thousands are turned towards those fields.
Wonderfully rich placer ground has already been found and there can be
no reason to doubt that very much larger areas remain unproved. Where
this gold comes from is an open question; geologists, mineralogists
and chemists, not to mention mining engineers and practical
prospectors, have disputed over the source of the gold already found,
but it must be confessed that there are almost as many theories as
there are disputants. Could it be known with certainty how and under
what conditions the gold got where it is found, the problem of seeking
for it might be made easier. Unfortunately this is not the case, and
all prospecting for the home of the precious metal is more or less a
groping in the dark. We do know that the heaviest particles of gold do
not travel far from where they were first deposited, because gold is
so enormously heavy--its specific gravity being about nineteen times
that of water--it seeks the bottom of the stream and stays there. It
is not an invariable rule that the gold increases in coarseness as the
stream is ascended, but it is a very general one. On some rivers rich
and poor stretches of gold-bearing gravel succeed one another as the
explorer makes his way up or down stream. This is difficult to account
for, but in many cases is believed to be caused by the modern river
robbing the bed of some one or more ancient water-courses whose beds
crossed the valley of the present stream. This may or may not be the
case. We only know that the miners who found coarse gold on the lower
regions of such rivers as the Frazer were miserably disappointed when
they reached stretches near the source and found nothing but flour
gold. This same feature has been noticed in some of the Alaskan
rivers. It is quite within the bounds of probability that no very rich
quartz veins exist in Alaska. It does not follow from the richness of
the placers that the gold is derived from very rich quartz lodes,
because this amount of gold may really represent the product of a vast
amount of rock that has been ground to powder and washed away in the
course of ages. The gold would not travel far, and the deposits being
unearthed to-day have been accumulating in these northern streams
since the world was young; water-courses are nature's ground sluices.
It is possible that one stream has cut through the drainage of
another. Sometimes this has impoverished the first and enriched the
second, while in other cases the reverse has obtained. Upheavals have
formed faults[1] and fractured the strata, and the gold may have been
deposited by solution in these fractures. Often the soil will have
been washed away from near the top of the mountain, so that layers of
stratified rock are seen to be duplicated on each side while they are
covered at the summit. The prospector keeps his eye open as he goes
along and notes carefully the character of the fragments of rock he
finds in the streams. Quartz, diorite, diabase, and porphyry pebbles
are grounds for expecting a profitable result, but of course there is
no certainty of such a happy issue. As soon as the district begins to
be fairly well known certain discoveries are made that invariably
render prospecting easier. Local peculiarities are noted; certain
characters are found to be common to the ore-bearing bodies or
deposits; the lines of deposits become known, and a good deal of light
is then shed upon a very difficult problem. As a rule, when the
fragments of quartz, pyrite, chalcopyrite, or galena are rough, they
have not traveled far, and the lode from which they have been derived
should be close at hand. Water and attrition soon round these minerals
on their sharp edges, and thus show that they have come from some
little distance.
[1] Dislocation of the strata.
In some countries, especially where vegetation is scanty, the outcrop
of a body of mineral may be traced by a difference in the vegetation.
In South Africa a chain of pools usually follows the course of a line
fault, which in its turn marks where an intrusive lode carrying
mineral separates two different formations. As a rule, any heavy
mineral is worth investigating. Even in remote regions silver,
mercury, tin, nickel, platinum, copper, and several other metals are
worth paying attention to. If they are too far away from the railroad
or the steamboat to-day they may not be so next year, for civilization
advances with giant stride in these days and never faster than when
transportation companies are reaching forth to some newly discovered
mineral field.
One of the greatest drawbacks to prospecting in the North is the dense
growths of moss and forest that cover the ground. In most of the
Western states, in South Africa, and in Australia this drawback does
not exist and prospecting was by that much the easier. However, as a
compensation, there is abundant water in Alaska and the Northwest,
while it was and is almost entirely absent in several other regions
that possess immense bodies of ore which are not available for this
very reason.
Quartz has been called the mother of gold, and certainly quartz and
gold are inseparably connected to-day. As to where gold may be found
the best reply that can be given is in the words of the old miner,
who, when asked that question, said: "Where it be's; there it be's,"
and then added, "and there ben't I."
Although most prospectors travel alone from sheer necessity, there can
be no doubt that three or four men forming a party and working
together have the advantage. They can do their work cheaper, more
thoroughly, and more surely. By co-operating they may carry a more
complete outfit. Should any accident happen help is at hand, whereas
the solitary wanderer often dies as the result of some accident that
would have been trivial had he had a companion. Three or four claims
may be worked in conjunction with one another at far less
proportionate expense than a single one could.
Nature's preparation for the reception of great ore deposits is
somewhat as follows: The crust of the earth is prepared for the
reception of the metals by great outbursts of igneous or melted rocks;
the metals themselves being carried in suspension in the heated water
that everywhere traverses the strata. These metals are deposited in
the veins as soon as the waters begin to cool, and the pressure to
which they were subjected from deep down in the earth's crust is
removed. A great mineral country is usually marked by the outcrops of
the veins being persistent in their courses and traceable for many
miles, though very probably many breaks may occur in these outcrops.
The rocks associated with great ore bodies are lime, porphyry,
granite, shales, slates, quartzites, and diabase. Fragments of mineral
and gangue, known to the miners as float, may be littered over the
hills and encumber the courses of the stream. A central line of
eruption may often be traced by masses of altered rock, and beds of
lava or other volcanic products. We find the granite has been melted
and the limestone has acquired magnesia, and thus become dolomatized.
Whenever a heavy deposit of pyrites, or mundic, is found mineral
probably exists below. The cubes of pyrite are not always valueless,
they may contain gold in addition to the iron and sulphur. When the
pyrites decay under the influence of the weather, and leave the quartz
honeycombed, these cavities often contain concentrated gold; for which
reason you often get a higher assay from the surface than from any
point lower down in the vein. In sinking the shaft soon gets below
this altered quartz and the ores are then combined with sulphur. They
have become sulphides, and are harder to treat. The prospector should
therefore act very cautiously when trying to develop a mine with a
small capital behind him; because, although the first ore may be
adapted for stamping, he may find, before he has gone down fifty feet,
that it can only be treated in a smelter, and that all the money he
has put into crushing apparatus is wasted.
Without the prospector there would be no mining and the world would
yet be in the stone age. He is not appreciated at anything like his
real worth. He requires ability and experience, push and perseverance.
Prospecting is a search for valuable minerals. He may not be very
deeply learned in either geology or mineralogy, but he must have a
keen eye and good natural powers of observation.
There are some sixty or seventy elements in the world, and the most
common is oxygen. Nearly all the coloring matter of rocks comes from
iron. Wind, frost, rain, snow, and heat, cause a crumbling of the
different rocks, and running water wears them away, and carries off
and distributes the particles. By this agency, and by floating ice,
they are often removed to long distances. The action of internal heat
renews the deposits of mineral by eruption, or by hot springs, but
this means of renewal was much more powerful in the past than it is
now.
Organic matter found in the crust of the earth was derived from
animals or vegetables. Coal is a legacy from forests that flourished
ages ago, while petroleum is all that remains of vast schools of
fishes that swarmed in Devonian seas.
Stratified rocks are either sand, clay, or calcareous, which means
lime-bearing. In their natural position they were horizontal, but
owing to subsequent volcanic action they are, in some localities,
tilted at all conceivable angles. The eruptive rocks have burst
through them in places, changed their character, divided them by
intrusive masses, and generally enriched them with mineral deposits.
Everything now known points to the theory that the contents of veins
were deposited in the lodes by infiltration. In a few instances famous
mines have no veins, but are literally hills of mineral; they are then
of low grade, but much more remunerative than average high grade
mines, owing the vast quantity of ore, and the ease with which it can
be mined. The famous Treadwell mine, on Douglas Island, Alaska, has
ore that is worth less than four dollars a ton, but it is quarried,
and 640 stamps work day and night. There is about a dollar a ton
profit, and hundreds of thousands of tons are treated annually. The
tin mine known as Mount Bischoff, in Tasmania, and the Burra copper
mine in Australia are other instances. Each of these deposits was
found as an outcropping on the bare top of a low hill, and none of
them has walls.
A fault may throw the vein up or down, and a good deal of exploration
may have to be done before it is recovered.
A lenticular vein consists of a series of double pointed ore bodies
like lenses which may be strung out, overlapping, or not.
The outcrop of a vein is never the same as its strike, except on a
level surface.
A stringer of ore branching off from the main vein is known as a
chute, shoot, or chimney.
In developing a ledge or lode, first find out what the ore is. Gold is
shown in the mortar, especially after roasting. Silver may be
recognized at sight, or by assay tests, or blow pipe; copper, by its
vivid colors,--green or blue for carbonate and red for oxide or
metallic copper. The ore often differs in various parts of the vein.
Explore your lode along the surface, across, and down its dip. When
you find it continuous it will be time enough to think of a vertical
shaft. The top of a shaft must be timbered with logs, so as to give
sufficient fall to get rid of the mineral when it is hoisted.
The first thing the prospector has to consider is his outfit. The more
complete this is the better, but ninety-nine times out of a hundred
the difficulties of transportation in a wild region are so enormous
that he will have to do without a great many things that he would like
to have. He must endeavor to make up for the lack of tools by
ingenuity; then he may get along fairly well. A pan, he must have. In
this he will wash carefully all his samples. Then, a flask of
quicksilver is more precious to him even than gold; for, having it, he
can resort to pan-amalgamation, which will save the precious metal
even when it is in minute particles.
This process may be described as follows: A pound or two of the ore in
powder is placed in the pan and water is added until the mass becomes
a thin pulp. One ounce of quicksilver and a small piece of that deadly
poison, known to the chemist as cyanide of potash, and as prussic acid
to the ordinary man, should be added, and the mass should be stirred
thoroughly, for two hours if you can stand it. Then turn in water and
wash off the dirt and the amalgam will be found in the bottom of the
pan. This you must collect very carefully. You should have a square
piece of chamois skin or a piece of strong white cotton cloth. In
either case the amalgam is put in the center of this square and the
cloth twisted until all the superfluous quicksilver is pressed out and
your amalgam remains nearly free from mercury. This amalgam placed on
a shovel and held over a brisk fire will soon show the yellow color of
gold. If you have no mould you may make one of clay, put your gold
therein with a little borax, and very soon, the fire being hot enough,
you will have a tiny ingot of the precious metal. But most prospectors
are satisfied when they have obtained their sponge gold, and do not
carry their operations further in these rough and ready tests.
The prospector of to-day is often a very different man from his
predecessor of a generation ago. The old gold hunter used to sally
forth armed with a pick, shovel and pan, and usually a very little
grub. In his stead men are now taking the field who have had the
benefits of a thorough education, both practical and theoretical, and
provided with all the equipment necessary for their work. Some of
these men carry an outfit somewhat as follows: An iron mortar holding
half a gallon, together with a pestle a rough scale for pulp, a more
delicate one showing troy grains and pennyweights, a 40-mesh sieve, a
burro furnace and muffle, one cupel mould, a couple of dozen
scorifiers, tongs to handle the cupel and scorifiers, two annealing
cups, a spirit lamp, a dozen test tubes, a pouring mould, five or six
pounds of borax and about as much carbonate of soda, five pounds of
bone ash, ditto of granulated lead, a pint of nitric acid, ditto of
hydrochloric acid, ditto sulphuric acid, ditto of ammonia, twice as
much alcohol and two pounds or so of granulated zinc.
As a blow pipe outfit he will take a blow pipe, spirit lamp, nitrate
of cobalt in solution, cyanide of potash, yellow prussiate of potash,
red prussiate of potash, a sheet or two of filtering paper and a
couple of three-inch glass filters. With this outfit he can determine
any mineral he may come across.
By patience and observation the man who starts out to take up
prospecting as a road to fortune may easily master the rudiments of
his business. It will not take him long to become familiar with the
commoner rocks, and the more valuable ores. His own rough tests in the
field must be confirmed by competent assayers upon his return to
civilization, and in this matter he should be very guarded. The most
reliable assays are made either at the different government assay
offices or by some of the large metallurgical works whose reputation
is world wide. Prospecting is hard work, but the life is healthy and
full of excitement, only the explorer should have courage, hope, and
good temper, for each and every one will be as necessary in his chosen
vocation as his pan and pick.
When alluvial or placer gold has been found it is reasonable to
suppose that the vein from which it was derived may also reward
diligent search, for it is undoubtedly true that most placer gold has
come from quartz veins. This, however, is believed not to be
invariably the case, a recent school of mineralogists contending that
pure masses of alluvial gold have been formed from the accretion or
growth of the gold deposited from certain gold salts. This is in any
case probably exceptional, and the prospector who finds gold in gravel
should seek in the adjacent country for the quartz lodes from which it
came.
Important deposits may be expected at or about the line of
unconformability where slates, shales, quartzites, sandstones,
limestones, schists and other sedimentary deposits are pierced by
intrusive masses of igneous rocks.
Veins filling the cracks that once existed between two differing rocks
are known as contact veins. Such veins are often very rich. Curiously
enough large masses of true igneous rock rarely contain valuable
deposits of mineral, but where such intrusive masses cut dikes or
walls of porphyry, or diorite, the region is worthy of careful
investigation.
[Illustration: POCKET LENS.]
In an open country the prospector should keep to the hill tops if on
the lookout for veins, as the outcrops show more distinctly on the
bare ridges, but alluvial deposits are only found in valleys and along
the borders of streams. In any case, much of the northern part of this
continent can only be prospected by following the streams, on account
of the dense growth of forest with which the soil is covered. The true
line of strike of a vein can be determined only on a level stretch.
The line of strike and the line of dip are always at right angles to
one another; the outcrop may follow the strike or it may not.
A pick, shovel, and pan, are absolutely necessary to a prospector's
proper equipment. A good pocket lens, cheesecloth screen, and small
iron pestle and mortar are often useful. The pan is the most essential
part of the outfit, and is always bright from use.
The regular gold miner's pan is 13-3/4 inches in diameter across the
top, 10 inches across the bottom and 2-1/8 inches deep. The best are
made of sheet iron and have a joint around the bottom rim which is of
some assistance in retaining the spangles of gold.
A more primitive instrument than the pan is the batea. This requires
more skill than the pan, and is much in favor with South American
miners. It is made of hard wood, 20 inches in diameter, 2-1/2 inches
deep in the center, inside measurement, and sloping gradually to
nothing at the sides.
The horn spoon has been handed on from antiquity. It is made from a
black ox horn, at least a black one is the best as it shows the gold
better; it is eight to ten inches long by three inches wide, cut off
obliquely.
When gold is suspected in quartz, but there is visible to the naked
eye more or less iron, copper, and other base metals, it is well to
crush the quartz into coarse fragments. Roast on a shovel or other
convenient tool over a hot fire, and finally pulverize in the mortar.
If panned it will now reveal much of its gold, while, had these
measures not been taken, the sample might have given negative results
and been declared valueless.
After pulverizing, the ore should be passed through the cheese cloth
screen before panning. If the approximate value of the ore is sought,
the sample must be dried and weighed before crushing; and the
resulting gold weighed. Thus:
Sample is to 2,000 lbs. as gold found is to Ans.
About 13 cubic feet of quartz weigh a ton before being disturbed; when
broken to medium sized lumps 20 cubic feet may be taken as
representing a ton. Although experience teaches the miner to estimate
very closely the value of his sample, it is better for the tyro to
have a small pair of scales with grain weights. A grain of gold, if
tolerably pure, is equal to four cents. Above all things avoid the too
common error of panning the pick of the rock, as a false estimate is
bound to follow and only too probably eventual loss.
A yard of gravel before being dug makes one and a half yards
afterwards. A pan of dirt is usually about 20 pounds, although it is
not well to fill quite full in actual work.
Many a valuable mine has been found by following up "float" ore. Float
is detached fragments of the vein or gangue, and it becomes more and
more abundant as the lode is approached until it finally ceases
abruptly. This indicates that the vein has been reached or passed, and
a trench dug throughout the alluvial soil at right angles to the
assumed line of the vein will probably reveal it. The float and
mineral of course drift down hill; if the side of the mountain be
saddle-shaped the float will spread out like a fan as it washes down,
but if concave the force of gravity will concentrate it within a
narrow space in the ravine. Float found at the foot of a hill has
come, as a rule, from that hill. The nearer the vein the less worn
will be the edges of the float and mineral. The gangue or vein-rock in
which the metal is found may be calcite or calc spar, fluor spar,
heavy spar or baryta, or quartz. Gold is almost always found in this
last matrix. The upper parts of most quartz lodes are usually
oxidized, that is to say, the atmosphere has acted upon the iron
pyrites, freeing the sulphur and staining the quartz yellow, red, or
brown, by oxide of iron. This is known as "gossan" or the "iron hat."
Such quartz is frequently honeycombed and rotten. Below the water
level these veins run to sulphides in which decomposition has not set
in, and the gold contained in the quartz is no longer "free milling,"
i.e. will not give up its gold to mercury without a preliminary
treatment.
Whenever the explorer comes across a mass of gossan he should sink a
trial shaft to the vein, as it is almost certain that below the
oxidized sulphides a body of mineral exists likely to encourage mining
operations.
Native gold is malleable, will flatten out under the hammer, and a
steel knife will cut it with ease. It almost invariably contains
silver, sometimes to the extent of one-fifth. A little practice will
enable the prospector to recognize it, for there is but one king
metal. Much gold is derived from copper and iron pyrites, and silver
and lead ores are a very large source of supply.
Gold is found in gravel of every variety, from finest pipe-clay to
boulders weighing tons. Sometimes volcanic eruptions have covered
these deposits since the ancient rivers laid them down, and in many
cases their courses do not in the least agree with the valleys of the
shrunken streams that have replaced them.
Gold may be distributed through the whole thickness of a bed, but
ninety-nine times out of a hundred the richest layer of gravel is just
above the bed rock upon which all the gravel rests. Gold may even be
found among the grass roots, especially in dry localities where there
has been little water to carry it downward. When the bed rock consists
of upturned slates the gold frequently penetrates it for some little
distance.
Sand is nearly always poorer than gravel.
The experience of miners in the Victoria gold fields is that gold is
always found on the bars or points, and not in the deep pools and
bends.
The great difficulty with which any but the very finest particles of
gold can be moved by water accounts for the value of the deposits
depending largely upon the local rocks. It is very fortunate that
gold's specific gravity is so great, for were it less its recovery
would be much more difficult. The sluices and other apparatus of the
miner are really nothing but the operations of nature imitated on a
much smaller scale. There is one thing, however, time, that nature can
afford to expend in prodigious periods, while man must not waste a
single minute.
It not being possible to point out where the ancient river beds lie,
smothered as they are by hundreds of feet of overlying drift, lava,
and other later deposits, the only feasible plan is a series of boring
with the diamond drill.
When gold has been discovered the finder must act with the greatest
prudence, for even gold may be bought too dear. The surest test is a
mill run, that is passing 10 to 50 tons through all the operations of
crushing, milling, roasting, amalgamating, etc., and so ascertaining
what returns are likely to be obtainable when the deposit is worked on
a commercial scale. True sampling is necessary. All parts of the vein
should be included, and the lode cross-cut by galleries in more than
one spot. It is the very great necessity of these expensive
preparatory explorations that has given rise to the saying, "Quartz
mining is for rich men."
Many gold mines have been abandoned as unprofitable that could have
been mined at a profit had their owners been wealthy and enterprising
enough to do a great deal of expensive prospecting by diamond drill,
cross cuts, drifts and rises. In one instance that came to the
writer's knowledge a clever mining engineer cleared nearly $200,000
profit by leasing for a term of years a gold mine that was supposed to
be exhausted. A drill hole sunk less than 50 feet below the old
workings revealed a pocket of ore in the vein, and paying quartz was
found for many hundred feet below.
With the improvements in electricity made recently a cheap power has
been provided that will permit many mines to be reopened. The saving
in working expenses effected by introducing electricity is often very
large; after the plant is once installed the cost is almost nil where
turbines can be employed to furnish the power to the generators.
Machinery capable of delivering power at a distance of several miles
from the plant, may be operated at very reasonable cost as compared to
that of other prime movers.
Discoveries of many deposits that have in time been successfully mined
were the result of chance. No skill guided the finder; he merely
stumbled upon his luck just as the wayfarer once in a while hits his
toe against a well-filled pocketbook. For instance, a South Australian
squatter picked up a piece of copper ore that a wombat had thrown out
of his burrow, and the result was the discovery of the great Wallaroo
lode. The first diamond from South Africa was picked up by an ignorant
bush boy and kept with a lot of worthless pebbles in the private
collection of the boy's master; no suspicion existed of its value
until a passing trader had carried it away and obtained $2,500 for it
in Capetown. Gold was first discovered in California in 1848 by the
superintendent of a sawmill who saw it glistening in the flume.
Similarly gold was discovered in both Australia and Brazil by the
purest chance. Had not a tree been uprooted by the wind the vast
deposits of soft hematite iron ore in the Biwabic iron mines of the
Mesabi range, Minnesota, might have remained unknown for many a long
year to come. In the desolate region to the northward of Lake Huron
great stores of nickel ore exist. These mines, which may some day
regulate the price of the metal all the world over, were exposed in a
railway cutting; no one dreamed of their existence. The Redington
quicksilver mine in California was discovered by some roadmakers.
Tradition relates that the enormously rich silver mines of Potosi, in
Bolivia, were discovered by the accidental uprooting of a bush having
spangles of silver ore attached to its roots. This was in 1538, and
two hundred years later a similar streak of luck revealed the wealth
of the Catorce district of Mexico, from which in thirty years, ore to
the value of $35,000,000 was taken.
Moreover, the search for one mineral often leads to the discovery of
another. The Comstock lode was first worked for gold, and the miners
threw away the black sulphide of silver worth $3,000 to the ton. The
Broken Hill mine in Australia was claimed as a tin deposit by its
finder; it is now the greatest silver producer in Australasia. Such
instances could be multiplied almost indefinitely, chance entering
into a majority of mineral discoveries. On the other hand, it has
happened, not infrequently, that purely scientific deductions and
calculations have brought to light stores of mineral wealth.
Certain minerals are likely to be found associated. Cassiterite goes
with boron and tourmaline, topaz, fluor spar and lithia-mica; all
containing fluorine. It is also found with wolfram, chlorite and
arsenical pyrites. Magnetite is often accompanied by rocks containing
garnet, epidote and hornblende. Zinc blend and galena may occupy the
same vein, which is likely to be of baryta or heavy spar. Much galena
carries silver. Gold is associated with many metallic sulphides such
as iron, magnetic, and copper pyrites, mispickel, galena, blend,
stibnite and tetrahedrite. Gypsum accompanies salt.
Surface indications may be described as: Form of ground, color,
outcrop, decomposed and detached mineral, mineral deposits from
springs, altered or peculiar vegetation and other similar guides. A
hard quartz outcrop often stands up like a wall and is traceable for
miles. The Rainbow silver bearing lode of Butte, Montana, stood 20
feet above the surface. Soft minerals, such as clay, are cut into and
sunk below the surrounding level. Deposits of Kaolin or China clay are
usually so found.
Any special bright coloration of the rocks of a district merits
investigation. Copper gives green, blue, and red stains; iron, red or
brown; manganese, black; lead, green, yellow or white; cobalt, pink;
cinnabar or quicksilver, vermilion. The nickel deposits of New
Caledonia were made known to the world by the explorer Garnier in
1863, his curiosity having been aroused by the delicate green coating
given the rocks by an ore containing water, quartz, nickel and
magnesium.
Hard beds of shale decompose on the surface into soft clay, and a
still more noticeable change is the conversion of ores containing
sulphur into oxides. This chemical change causes the gossan or "iron
hat," for which token of underlying wealth the prospector should be
eternally watchful. This alteration may extend downward four or five
hundred feet from the surface, but in such cases the true weathering
has ceased long before the limit of discoloration is reached, and the
change of substance is due to the filtering of surface waters through
the vein.
Gossan varies greatly in its nature. Galena becomes anglesite,
cerussite, pyromorphite and mimetite. Copper pyrite changes into
native copper, melaconite, cuprite, malachite, chessylite, or perhaps
into a phosphate, arsenate, or silicate of the metal. Carbonate of
manganese gives the black oxides and silver sulphide ores are, after
weathering, known as native silver, kerargyrite and embolite.
The ore in the gossan is very generally more valuable than it will be
below, and this is especially true of gold and silver ores. The gold
having been set free from the close embrace in which the iron pyrite
held it previous to the latter's oxidation, it is now readily caught
by quicksilver. Silver under similar conditions becomes chloride, and
likewise amalgamates without difficulty.
Seams containing native sulphur often show no trace of that element on
the surface, having weathered into a soft, white, gray or
yellowish-white granular, or pulverulent, variety of gypsum.
Veins of asbestos often decompose into a white powder found in the
crevices of the rocks; fibrous asbestos existing in the interior.
Petroleum shows in an iridescent film upon still pools, and the odor
is a sure guide to its nature.
A "dipping-needle" is valuable to the prospector on the lookout for
iron ore; by its use he may discover masses of magnetic ore and trace
their extent. As he carries the compass over the ground the needle
dips toward any iron mass he approaches; directly over the ore it
becomes vertical.
[Illustration: MINER'S DIPPING NEEDLE.]
In a wilderness country strength of body and endurance are important
qualifications. The prospector must, moreover, have such general
knowledge of geology and mineralogy as to be able to recognize all
valuable minerals and confirm his conjecture by simple tests. Pick,
shovel and pan must be handled skillfully, while the rifle, shotgun
and paddle must also be understood. For in the unsettled parts of the
country the traveler must even yet rely to some extent upon the fish
and game he may be able to secure, and every old prospector becomes a
trained hunter and camper. Knowing how to bake bread is sometimes more
valuable than much mathematics; ability to build a rough boat is often
the one hope of salvation.
In sinking a short shaft in a sunny country a large mirror, inclined
at a suitable angle over the shaft, will give sufficient light.
Lodes or veins following the general trend of the auriferous quartz
are much more likely to be rich than are those that cross it. Gold is
never distributed evenly in veins, though it may be in great beds of
low grade material; but more often rich areas alternate with barren
portions.
Where quartz veins are small and the rich pockets separated by wide
intervals of poor gangue the gravel of the district will usually be
similar in character. As this condition obtains in the upper Yukon
district as far as the gravels are concerned, it will probably be
found to hold good for the quartz leads, when they shall have been
discovered.
The more nearly the gold formation approaches to the crystalline
schists, the poorer will the quality of the gold be through the larger
percentage of silver found in it. In slates the proportion may be 22
gold to 1 silver; in schists it has been known to be a ratio of 1 to
1.
With the discovery of valuable gold-bearing gravel on the bare
hillsides of the Northwest, a vast region has been added to the area
the prospector may explore to advantage. No experience acquired in
ordinary American placer grounds is likely to be of much use in
detecting these higher gold-bearing gravels of the Yukon, but they
appear to be somewhat similar in character to the New Zealand
terraces. Terrace-prospecting requires perseverance and the use of
some brains, as it is infinitely harder than creek-prospecting. These
terraces or benches are the remains of old river beds. The whole bench
must be carefully scanned over because the gold is quite as likely to
be in one part as in the other. Sometimes it is in half a dozen
different layers one above the other. Sometimes the old river terraces
are entirely covered by landslides, and the majority of such deposits
are not likely ever to be found, as it is almost impossible to guess
at locations.
In New Zealand gold has been found on table-lands nearly 6,000 feet
above sea level, and according to recent information valuable claims
have been discovered in Alaska on the very summits of the rounded
hills on each side of El Dorado creek.
To understand how such deposits as those of the Northwest may have
been made, suppose that such a vein as that of the Idaho, which has
been worked for a depth 1,700 feet by a width of 1,000 feet, and from
which $17,000,000 have been taken, to have been worn down by glacial
or other forces. Is it not conceivable that the gold would gradually
have accumulated in the nearest canyon?
[Illustration: DOLLY.]
To obtain suitable samples of the vein a dolly is an efficient
apparatus.
This is practically a very simple, crude, stamp mill. On the end of a
solid log, firmly fixed in the ground and standing four feet or so
above the surface, a square 6-inch hole is cut in which are fitted
wrought iron bars 3 inches deep by 1/2 inch wide, and separated by
equal intervals. These bars taper below so as to permit free passage
of the pounded mineral. A wooden box surrounding the grating keeps the
ore in place. A block of wood, shod with iron, forms the stamper. The
miner hauls on the handles at every blow. The gold is saved on the
lower table.
No one of experience in mining would look for brown hematite in a
granite range, nor for black band, though such might be a likely
region for red hematite or magnatite.
The explorer should be familiar in theory at least with the locality
where he may expect to find valuable minerals. For instance, should he
be searching for some heavy, detached substance that is usually found
in placer deposits he will keep to the low ground and examine
carefully the beds of the streams. On the other hand, should his quest
be for some ore that is more properly a component of a lode or vein he
will examine the side hills and summits where denudation will
certainly have exposed such deposits. Then he must know the appearance
of each ore, and with the methods of making rough and ready tests he
must be perfectly familiar.
Gold is always more or less intimately associated with quartz. Oxide
of tin is said never to have been found more than two miles from some
granite rock, one of the components of which was muscovite or white
mica. The junction of slates and schists with igneous or metamorphic
rocks often proves a valuable find of mineral.
Rocks for the purposes of the explorer may be grouped under three
heads: Igneous; metamorphic; stratified. The first includes lavas;
trachytes, grayish with rough fracture and mainly glassy; dark
basalts: and traps, such as greenstone. Obsidian is a volcanic glass.
Metamorphic rocks are thought to have once been stratified, but to
have been altered by heat. They comprise granite, of quartz feldspar
and mica; syenite, containing hornblende instead of mica; gneiss, like
granite, but showing lines of stratification; mica schist, made up of
mica and quartz and separating easily into layers; slates.
Stratified rocks are those deposits from water, such as sandstone,
limestone, clay, etc.
A prospecting shaft need not be of large dimensions. One 4 feet square
is amply large for any depth down to 30 feet, but it must be kept
plumb.
Sometimes shafts are sunk through the pay streak in alluvial gravel,
without it being detected. Frequent panning will guard against this
mistake.
In the Klondike region it is said early prospectors missed very rich
deposits, that have since been discovered, by stopping short of true
bed rock, being misled by a bed of harder gravel that they thought was
bottom.
Silver almost invariably carries some gold. The dark ironstone hat
already referred to is a good indication of silver ore beneath; it is
generally composed of conglomerates cemented by oxides of iron and
manganese.
Galena, which is sometimes so rich in silver as to be worth working
for that metal, may often be followed by surface indications; namely,
a white limy track with detached fragments of float ore in the surface
soil. The blowpipe or fire assay quickly determines silver ore.
Tin in lode, stream, or alluvial deposits occurs only as an oxide, but
its appearance is varied. It may be almost any color and shape. It is
always near granite, containing white mica known as muscovite.
The minerals for which it is most easily mistaken are:
Sp. gravity. Streak.
Wolfram 7 to 7-1/2 Red, brown or black.
Rutile 4.2 Light brown.
Tourmaline 3.2 Whitish.
Black Jack 4.3 Yellow, white.
The magnetic or dipping needle is used in New Jersey, as follows,
according to the State Geologist, W. H. Scranton, M.E.: "An
attraction which is confined to a very small spot and is lost in
passing a few feet from it, is most likely to be caused by a boulder
of ore or particles of magnetite with rock. An attraction which
continues on steadily in the direction of the strike of the rock for a
distance of many feet or rods, indicates a vein of ore; and if it is
positive and strongest towards the southwest, it is reasonable to
conclude that the vein begins with the attraction there. If the
attraction diminishes in going northwest, and finally dies out without
becoming negative, it indicates that the vein has continued on without
break or ending until too far off to move the compass needle. If, in
passing towards the northwest, along the line of attraction, the south
pole is drawn down, it indicates the end of the vein or an offset.
If, on continuing further, still in the same direction, positive
attraction is found, it shows that the vein is not ended, but if no
attraction is shown, there is no indication as to the continuance of
the ore.
"In crossing veins of ore from southwest to northwest, when the dip of
the rock and ore is as usual to the southeast, positive attraction is
first observed to come on gradually, and the northwest edge of the
vein is indicated by the needle suddenly showing negative attraction
just at the point of passing off it. This change of attraction will
be less marked as the depth of the vein is greater, or as the strike
is nearer north and south. The steadiness and continuance of the
attraction is a much better indication of ore than the strength or
amount of the attraction. The ore may vary in its susceptibility to
the magnetic influence from impurities in its substance; it does vary
according to the position in which it lies, that is according to its
dip and strike; and it also varies very much according to its distance
beneath the surface."
Further instructions are given in the paper from which the foregoing
extract was taken, some of which follow:
"It is sufficient to say that the first examinations are made by
passing over the ground with the compass in a northwest and southwest
direction, at intervals of a few rods, until indications of ore are
found. Then the ground should be examined more carefully by crossing
the line of attraction at intervals of a few feet, and marking the
points upon which observations have been made, and recording the
amount of attraction. Observations with the ordinary compass should be
made, and the variation of the horizontal needle be noted. In this way
materials may soon be accumulated for staking out the line of
attraction, or for constructing a map for study or reference.
"After sufficient exploration with the magnetic needle, it still
remains to prove the value of the vein by uncovering the ore,
examining its quality, measuring the size of the vein, and estimating
the cost of mining and marketing it. Uncovering should first be done
in trenches dug across the line of attraction, and carried quite down
to the rock. When the ore is in this way proved to be of value regular
mining may begin. In places where there are offsets in the ore, or
where it has been subject to bends, folds, or other irregularities, so
that the miner is at fault in what direction to proceed, explorations
may be made with the diamond drill."