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Title: Getting Gold
Author: J. C. F. Johnson
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Etext prepared by Dagny, dagnyj@hotmail.com
and John Bickers, jbickers@ihug.co.nz
GETTING GOLD:
A PRACTICAL TREATISE
FOR
PROSPECTORS, MINERS, AND STUDENTS.
BY
J. C. F. JOHNSON, F. G. S.,
MEMBER OF THE AUST. INST. OF MINING ENGINEERS;
AUTHOR OF
"PRACTICAL MINING," "THE GENESIOLOGY OF GOLD," ETC.
PREPARER'S NOTE
This text was prepared from a 1898 edition, published by Charles
Griffin & Company, Limited; Exeter Street, Strand, London. It is
the second edition, revised. Numerous drawings and diagrams have
been omitted.
PREFACE
Some six years ago the author published a small book entitled
"Practical Mining," designed specially for the use of those
engaged in the always fascinating, though not as invariably
profitable, pursuit of "Getting Gold." Of this ten thousand copies
were sold, nearly all in Australasia, and the work is now out of
print. The London /Mining Journal/ of September 9th, 1891, said of
it: "We have seldom seen a book in which so much interesting
matter combined with useful information is given in so small a
space."
The gold-mining industry has grown considerably since 1891, and it
appeared to the writer that the present would be a propitious time
to bring out a similar work, but with a considerably enlarged
scope. What has been aimed at is to make "Getting Gold" a
compendium, in specially concrete form, of useful information
respecting the processes of winning from the soil and the after-
treatment of gold and gold ores, including some original practical
discoveries by the author. Practical information, original and
selected, is given to mining company directors, mine managers,
quartz mill operators, and prospectors. In "Rules of Thumb,"
chapters XI. and XII., will be found a large number of useful
hints on subjects directly and indirectly connected with gold-
mining.
The author's mining experience extends back thirty years and he
therefore ventures to believe with some degree of confidence that
the information, original or compiled, which the book contains,
will be found both useful and profitable to those who are in any
capacity interested in the gold-mining industry.
J. C. F. J.
LONDON, November, 1896.
GETTING GOLD
CHAPTER I
INTRODUCTORY
GOLD is a name to charm by. It is desired by all nations, and is the
one metal the supply of which never exceeds the demand. Some one has
aptly said, "Gold is the most potent substance on the surface of our
planet." Tom Hood sings:
Gold, gold, gold, gold!
Bright and yellow, hard and cold;
Molten, graven, hammered, rolled,
Heavy to get, and light to hold;
Stolen, borrowed, squandered, doled.
That this much appreciated metal is heavy to get is proved by the high
value which has been placed on it from times remote to date, and that
it is light to hold most of us know to our cost.
We read no farther than the second chapter in the Bible when we find
mention of gold. There Moses speaks of "the land of Havilah, where
there is gold"; and in Genesis, chapter xxiv., we read that Abraham's
servant gave Rebekah an earring of half a shekel weight, say 5 dwt. 13
grs., and "two bracelets of ten shekels weight," or about 4 1/2 ozs.
Then throughout the Scriptures, and, indeed, in all historic writings,
we find frequent mention of the king of metals, and always it is
spoken of as a commodity highly prized.
I have sometimes thought, however, that either we are mistaken in the
weights used by the Hebrew nation in early days, or that the
arithmetic of those times was not quite "according to Cocker." We
read, I. Kings x. and xli., that Solomon in one year received no less
than six hundred and three score and six talents of gold. If a talent
of gold was, as has been assumed, 3000 shekels of 219 grains each, the
value of the golden treasure accumulated in this one year by the
Hebrew king would have been 3,646,350 pounds sterling. Considering
that the only means of "getting gold" in those days was a most
primitive mode of washing it from river sands, or a still more
difficult and laborious process of breaking the quartz from the lode
without proper tools or explosives, and then slowly grinding it by
hand labour between two stones, the amount mentioned is truly
enormous.
Of this treasure the Queen of Sheba, who came to visit the Hebrew
monarch, contributed a hundred and twenty talents, or, say, 600,000
pounds worth. Where the Land of Ophir, whence this golden lady came,
was really situated has evoked much controversy, but there is now a
general opinion that Ophir was on the east coast of Africa, somewhere
near Delagoa Bay, in the neighbourhood of the Limpopo and Sabia
rivers. It should be mentioned that the name of the "black but comely"
queen was Sabia, which may or may not be a coincidence, but it is
certainly true that the rivers of this district have produced gold
from prehistoric times till now.
The discovery of remarkable ruins in the newly acquired province of
Mashonaland, which evince a high state of civilisation in the
builders, may throw some light on this interesting subject.
The principal value of gold is as a medium of exchange, and its high
appreciation is due, first, to the fact that it is in almost universal
request; and, secondly, to its comparative scarcity; yet, oddly
enough, with the exception of that humble but serviceable metal iron,
gold is the most widely distributed metal known. Few, if any,
countries do not possess it, and in most parts of the world, civilised
and uncivilised, it is mined for and brought to market. The torrid,
temperate, and frigid zones are almost equally auriferous. Siberia,
mid-Asia, most parts of Europe, down to equatorial and southern Africa
in the Old World, and north, central, and southern America, with
Australasia, in what may be termed the New World, are all producers of
gold in payable quantities.
In the earlier ages, the principal source of the precious metal was
probably Africa, which has always been prolific in gold. To this day
there are to be seen in the southern provinces of Egypt excavations
and the remains of old mine buildings and appliances left by the
ancient gold-miners, who were mostly State prisoners. Some of these
mines were worked by the Pharaohs of, and before, the time of Moses;
and in these dreadful places thousands of Israelites were driven to
death by the taskmaster's whip. Amongst the old appliances is one
which approximated very closely to the amalgamating, or blanket table,
of a modern quartz mill.
The grinding was done between two stones, and possibly by means of
such primitive mechanism as is used to-day by the natives of Korea.
The Korean Mill is simply a large hard stone to which a rocking motion
is given by manual power by means of the bamboo handles while the ore
is crushed between the upper and basement stone.
Solomon says "there is no new thing under the sun"; certainly there is
much that is not absolutely new in appliances for gold extraction. I
lately learned that the principle of one of our newest concentrating
machines, the Frue vanner, was known in India and the East centuries
ago; and we have it on good authority--that of Pliny--that gold saving
by amalgamation with mercury was practised before the Christian era.
It will not be surprising then if, ere long, some one claims to have
invented the Korean Mill, with improvements.
Few subjects in mineralogical science have evoked more controversy
than the origin of gold. In the Middle Ages, and, indeed, down to the
time of that great philosopher, Sir Isaac Newton, who was himself
bitten with the craze, it was widely believed that, by what was known
as transmutation, the baser metals might be changed to gold; and much
time and trouble were expended in attempts to make gold--needless to
say without the desired result. Doubtless, however, many valuable
additions to chemical science, and also some useful metallic alloys,
were thus discovered.
The latest startling statement on this subject comes from, of course,
the wonderland of the world, America. In a recently published journal
it is said that a scientific metallurgist there has succeeded in
producing absolutely pure gold, which stands all tests, from silver.
Needless to say, if this were true, at all events the much vexed hi-
metallic question would be solved at once and for all time.
It is now admitted by all specialists that the royal metal, though
differing in material respects in its mode of occurrence from its
useful but more plebeian brethren of the mineral kingdom, has yet been
deposited under similar conditions from mineral salts held in
solution.
The first mode of obtaining this much desired metal was doubtless by
washing the sand of rivers which flowed through auriferous strata.
Some of these, such as the Lydian stream, Pactolus, were supposed to
renew their golden stores miraculously each year. What really happened
was that the winter floods detached portions of auriferous drift from
the banks, which, being disintegrated by the rush and flow of the
water, would naturally deposit in the still reaches and eddies any
gold that might be contained therein.
The mode of washing was exactly that carried on by the natives in some
districts of Africa to-day. A wooden bowl was partly filled with
auriferous sand and mud, and, standing knee-deep in the stream, the
operator added a little water, and caused the contents of the bowl to
take a circular motion, somewhat as the modern digger does with his
tin dish, with this difference, that his ancient prototype allowed the
water and lighter particles to escape over the rim as he swirled the
stuff round and round. I presume, in finishing the operation, he
collected the golden grains by gently lapping the water over the
reduced material, much as we do now.
I have already spoken of the mode in which auriferous lode-stuff was
treated in early times--i.e., by grinding between stones. This is also
practised in Africa to-day, and we have seen that the Koreans, with
Mongolian acuteness, have gone a step farther, and pulverise the
quartz by rocking one stone on another. In South America the arrastra
is still used, which is simply the application of horse or mule power
to the stone-grinding process, with use of mercury.
The principal sources of the gold supply of the modern world have
been, first, South America, Transylvania in Europe, Siberia in Asia,
California in North America, and Australia. Africa has always produced
gold from time immemorial.
The later development in the Johannesburg district, Transvaal, which
has absorbed during the last few years so many millions of English
capital, is now, after much difficulty and disappointment--thanks to
British pluck and skill--producing splendidly. The yield for 1896 was
2,281,874 ounces--a yield never before equalled by lode-mining from
one field.
In the year 1847 gold was discovered in California, at Sutor's
sawmill, Sacramento Valley, where, on the water being cut off, yellow
specks and small nuggets were found in the tail race. The enormous
"rush" which followed is a matter of history and the subject of many
romances, though the truth has, in this instance, been stranger than
fiction.
The yield of the precious metal in California since that date up to
1888 amounts to 256,000,000 pounds.
Following close on the American discovery came that of Australia, the
credit of which has usually been accorded to Hargraves, a returned
Californian digger, who washed out payable gold at Lewis Ponds Creek,
near Bathurst, in 1851. But there is now no reason to doubt that gold
had previously been discovered in several parts of that great island
continent. It may be news to many that the first gold mine worked in
Australia was opened about twelve miles from Adelaide city, S.A., in
the year 1848. This mine was called the Victoria; several of the
Company's scrip are preserved in the Public Library; but some two
years previous to this a man named Edward Proven had found gold in the
same neighbourhood.
Most Governments nowadays encourage in every possible way the
discovery of gold-fields, and rewards ranging from hundreds to
thousands of pounds are given to successful prospectors of new
auriferous districts. The reward the New South Wales authorities meted
out to a wretched convict, who early in this century had dared to find
gold, was a hundred lashes vigorously laid on to his already
excoriated back. The man then very naturally admitted that the alleged
discovery was a fraud, and that the nugget produced was a melted down
brass candlestick. One would have imagined that even in those
unenlightened days it would not have been difficult to have found a
scientist sufficiently well informed to put a little nitric acid on
the supposed nugget, and so determine whether it was the genuine
article, without skinning a live man first to ascertain. My belief is
that the unfortunate fellow really found gold, but, as Mr. Deas
Thompson, the then Colonial Secretary, afterwards told Hargraves in
discouraging his reported discovery, "You must remember that as soon
as Australia becomes known as a gold-producing country it is utterly
spoiled as a receptacle for convicts."
This, then, was the secret of the unwillingness of the authorities to
encourage the search for gold, and it is after all due to the fact
that the search was ultimately successful beyond all precedent, that
Australia has been for so many years relieved of the curse of
convictism, and has ceased once and for all to be a depot for the
scoundrelism of Britain--"Hurrah for the bright red gold!"
Since the year 1851 to date the value of the gold raised in the
Australasian colonies has realised the enormous amount of nearly
550,000,000 pounds. One cannot help wondering where it all goes.
Mulhall gives the existing money of the world at 2437 million pounds,
of which 846 millions are paper, 801 millions silver, and 790 millions
gold. From 1830 to 1880 the world consumed by melting down plate,
etc., 4230 tons of silver more than it mined. From 1800 to 1870 the
value of gold was about 15 1/2 times that of silver. From 1870 to 1880
it was 167 times the value of silver and now exceeds it over twenty
times. In 1700 the world had 301 million pounds of money; in 1800, 568
million pounds; and in 1860, 1180 million pounds sterling.
The gold first worked for in Australia, as in other places, was of
course alluvial, by which is usually understood loose gold in nuggets,
specks, and dust, lying in drifts which were once the beds of long
extinct streams and rivers, or possibly the moraines of glaciers, as
in New Zealand.
Further on the differences will be mentioned between "alluvial" and
"reef" or lode gold, for that there is a difference in origin in many
occurrences, is, I think, provable. I hold, and hold strongly, that
true alluvial gold is not always derived from the disintegration of
lodes or reefs. For instance, the "Welcome Nugget" certainly never
came from a reef. No such mass of gold, or anything approaching it,
has ever yet been taken from a quartz matrix. It was found at Bakery
Hill, Ballarat, in 1858, weight 2195 ozs., and sold for 10,500 pounds.
This was above its actual value.
The "Welcome Stranger," a still larger mass of gold, was found amongst
the roots of a tree at Dunolly, Victoria, in 1869, by two starved out
"fossickers" named Deeson and Oates. The weight of this, the largest
authenticated nugget ever found was 2268 1/2 ozs., and it was sold for
10,000 pounds, but it was rendered useless as a specimen by the
finders, who spent a night burning it to remove the adhering quartz.
But the ordinary digger neither hopes nor expects to unearth such
treasures as these. He is content to gather together by means of
puddling machine, cradle, long tom, or even puddling tub and tin dish,
the scales, specks, dust, and occasional small nuggets ordinarily met
with in alluvial "washes."
Having sunk to the "wash," or "drift," the digger, by means of one or
more of the appliances mentioned above, proceeds to separate the gold
from the clay and gravel in which it is found. Of course in large
alluvial claims, where capital is employed, such appliances are
superseded by steam puddles, buddles, and other machinery, and
sometimes mercury is used to amalgamate the gold when very fine.
Hydraulicing is the cheapest form of alluvial mining, but can only be
profitably carried out where extensive drifts, which can be worked as
quarry faces, and unlimited water exist in the same neighbourhood.
When such conditions obtain a few grains of gold to the yard or ton
will pay handsomely.
Lode or reef mining, is a more expensive and complicated process,
requiring much skill and capital. First, let me explain what a lode
really is. The American term is "ledge," and it is not inappropriate
or inexpressive. Imagine then a ledge, or kerbstone, continuing to
unknown depths in the earth at any angle varying from perpendicular to
nearly horizontal. This kerbstone is totally distinct from the rocks
which enclose it; those on one side may be slate, on the other,
sandstone; but the lode, separated usually by a small band of soft
material known to miners as "casing," or fluccan," preserves always an
independent existence, and in many instances is practically bottomless
so far as human exploration is concerned.
There are, however, reefs or lodes which are not persistent in depth.
Sometimes the lode formation is found only in the upper and newer
strata, and cuts out when, say, the basic rocks (such as granite,
etc.) are reached. Again, there is a form of lode known among miners
as a "gash" vein. It is sometimes met with in the older crystalline
slates, particularly when the lode runs conformably with the cleavage
of the rock.
Much ignorance is displayed on the subject of lode formation and the
deposition of metals therein, even by mining men of long experience.
Many still insist that lodes, particularly those containing gold, are
of igneous origin, and point to the black and brown ferro-manganic
outcrops in confirmation. It must be admitted that often the upper
portions of a lode present a strong appearance of fire agency, but
exactly the same appearance can be caused by oxidation of iron and
manganese in water.
It may now be accepted as a proven fact that no true lode has been
formed, or its metals deposited except by aqueous action. That is to
say, the bulk of the lode and all its metalliferous contents were once
held in solution in subterranean waters, which were ejected by geysers
or simply filtered into fissures formed either by the shrinkage of the
earth's crust in process of cooling or by volcanic force.
It is not contended that the effect of the internal fires had no
influence on the formation of metalliferous veins, indeed, it is
certain that they had, but the action was what is termed hydrothermal
(hot water); and such action we may see in progress to-day in New
Zealand, where hot springs stream or spout above the surface, when the
silica and lime impregnated water, reduced in heat and released from
pressure, begins forthwith to deposit the minerals previously held in
solution. Hence the formation of the wondrous Pink and White Terrace,
destroyed by volcanic action some eight years since, which grew almost
while you watched; so rapidly was the silica deposited that a dead
beetle or ti-tree twig left in the translucent blue water for a few
days became completely coated and petrified.
Gold differs in its mode of occurrence from other metals in many
respects; but there is no doubt that it was once held in aqueous
solution and deposited in its metallic form by electro-chemical
action. It is true we do not find oxides, carbonates, or bromides of
gold in Nature, nor can we feel quite sure that gold now exists
naturally as a sulphide, chloride, or silicate, though the presumption
is strongly that it does. If so, the deposition of the gold may be
ceaselessly progressing.
Generally reef gold is finer as to size of the particles, and, as a
rule, inferior in quality to alluvial. Thus, in addition to the extra
labor entailed in breaking into one of the hardest of rocks, quartz,
the /madre de oro/ ("mother of gold") of the Spaniards, there is the
additional labour required to pulverise the rock so as to set free the
tiniest particles of the noble metal it so jealously guards. There is
also the additional difficult operation of saving and gathering
together these small specks, and so producing the massive cakes and
bars of gold in their marketable state.
Having found payable gold in quartz on the surface, the would-be miner
has next to ascertain two things. First, the strike or course of the
lode; and secondly, its underlie, or dip. The strike, or course, is
the direction which the lode takes lengthwise.
In Australia the term "underlie" is used to designate the angle from
the perpendicular at which the lode lies in its enclosing rocks, and
by "dip" the angle at which it dips or inclines lengthwise on its
course. Thus, at one point the cap of a lode may appear on the
surface, and some distance further the cap may be hundreds of feet
below. Usually a shaft is sunk in the reef to prove the underlie, and
a level, or levels, driven on the course to ascertain its direction
underground, also if the gold extends, and if so, how far. This being
proved, next a vertical shaft is sunk on the hanging or upper wall
side, and the reef is either tapped thereby, or a cross-cut driven to
intersect it.
We will now assume that our miners have found their lode payable, and
have some hundreds of tons of good gold-bearing stone in sight or at
the surface. They must next provide a reducing plant. Of means for
crushing or triturating quartz there is no lack, and every year gives
us fresh inventions for the purpose, each one better than that which
preceded it, according to its inventor. Most practical men, however,
prefer to continue the use of the stamper battery, which is virtually
a pestle and mortar on a large scale. Why we adhere to this form of
pulverising machine is that, though somewhat wasteful of power, it is
easily understood, its wearing parts are cheaply and expeditiously
replaced, and it is so strong that even the most perversely stupid
workman cannot easily break it or put it out of order.
The stone, being pounded into sand of such degree of fineness as the
gold requires, passes through a perforated iron plate called a
"grating," or "screen," on to an inclined surface of copper plates
faced with mercury, having small troughs, or "riffles," containing
mercury, placed at certain distances apart.
The crushed quartz is carried over these copper "tables," as they are
termed, thence over the blanket tables--that is, inclined planes
covered with coarse serge, blankets, or other flocculent material--so
that the heavy particles may be caught in the hairs, or is passed over
vanners or concentrating machines. The resulting "concentrates" are
washed off from time to time and reserved for secondary treatment.
To begin with, they are roasted to get rid of the sulphur, arsenic,
etc., which would interfere with the amalgamation or lixiviation, and
then either ground to impalpable fineness in one of the many
triturating pans with mercury, or treated by chlorine or potassium
cyanide.
If, however, we are merely amalgamating, then at stated periods the
battery and pans are cleaned out, the amalgam rubbed or scraped from
the copper plates and raised from the troughs and riffles. It is then
squeezed through chamois leather, or good calico will do as well, and
retorted in a large iron retort, the nozzle of which is kept in water
so as to convert the mercury vapour again to the metallic form. The
result is a spongy cake of gold, which is either sold as "retorted"
gold or smelted into bars.
The other and more scientific methods of extracting the precious metal
from its matrices, such as lixiviation or leaching, by means of
solvents (chlorine, cyanogen, hyposulphite of soda, etc.), will be
more fully described later on.
CHAPTER II
GOLD PROSPECTING--ALLUVIAL AND GENERAL
It is purposed in this chapter to deal specially with the operation of
searching for valuable mineral by individuals or small working
parties.
It is well known that much disappointment and loss accrue through lack
of knowledge by prospectors, who with all their enterprise and energy
are often very ignorant, not only of the probable locality, mode of
occurrence, and widely differing appearance of the various valuable
minerals, but also of the best means of locating and testing the ores
when found. It is for the information of such as these that this
chapter is mainly intended, not for scientists or miners of large
experience.
All of us who have had much to do with mining know that the majority
of the best mineral finds have been made by the purest accident; often
by men who had no mining knowledge whatever; and that many valuable
discoveries have been delayed, or, when made, abandoned as not
payable, from the same cause--ignorance of the rudiments of mineralogy
and mining. I have frequently been asked by prospectors, when
inspecting new mineral fields, what rudimentary knowledge will be most
useful to them and how it can be best obtained.
If a man can spare the time a course of lessons at some accredited
school of mines will be, undoubtedly, the best possible training; but
if he asks what books he should read in order to obtain some primary
technical instruction, I reply: First, an introductory text-book of
geology, which will tell him in the simplest and plainest language all
he absolutely requires to know on this important subject. Every
prospector should understand elementary geology so far as general
knowledge of the history of the structure of the earth's crust and of
the several actions that have taken place in the past, or are now in
operation, modifying its conditions. He may with advantage go a few
steps further and learn to classify the various formations into
systems, groups, and series: but he can acquire all that he need
absolutely know from this useful little 2s. 6d. book. Next, it is
advisable to learn something about the occurrence and appearance of
the valuable minerals and the formations in which they are found. For
all practical purposes I can recommend Cox and Ratte's "Mines and
Minerals," one of the Technical Education series of New South Wales,
which deals largely with the subject from an Australian standpoint,
and is therefore particularly valuable to the Australian miner, but
which will be found applicable to most other gold-bearing countries. I
must not, however, omit to mention an admirably compiled /multum in
parvo/ volume prepared by Mr. G. Goyder, jun., Government Assayer and
Assay Instructor at the School of Mines, Adelaide. It is called the
"Prospectors' Pocketbook," costs only one shilling, is well bound, and
of handy size to carry. In brief, plain language it describes how a
man, having learned a little of assaying, may cheaply provide himself
with a portable assay plant, and fluxes, and also gives considerable
general information on the subject of minerals, their occurrence and
treatment.[*]
[*] Another excellent and really practical book is Prof. Cole's
"Practical Aids in Geology" (second edition), 10s. 6d.
It may here be stated that some twelve years ago I did a large amount
of practical silver assaying on the Barrier (Broken Hill), which was
not then so accessible a place as it is now, and got closely correct
results from a number of different mines, with an extemporised plant
almost amusing in its simplicity. All I took from Adelaide were a
small set of scales capable of determining the weight of a button down
to 20 ozs. to the ton, a piece of cheese cloth to make a screen or
sieve, a tin ring 1 l/2 in. diameter, by 1/2 in. high, a small brass
door knob to use as a cupel mould, and some powdered borax, carbonate
of soda, and argol for fluxes; while for reducing lead I had recourse
to the lining of a tea-chest, which lead contains no silver--John
Chinaman takes good care of that. My mortar was a jam tin, without top
or bottom, placed on an anvil; the pestle a short steel drill. The
blacksmith at Mundi Mundi Station made me a small wrought iron
crucible, also a pair of bent tongs from a piece of fencing-wire. The
manager gave me a small common red flower pot for a muffle, and with
the smith's forge (the fire built round with a few blocks of talcose
schist) for a furnace, my plant was complete. I burned and crushed
bones to make my bone-dust for cupelling, and thus provided made
nearly forty assays, some of which were afterwards checked in
Adelaide, in each instance coming as close as check assays generally
do. Nowadays one can purchase cheaply a very effective portable plant,
or after a few lessons a man may by practice make himself so
proficient with the blowpipe as to obtain assay results sufficiently
accurate for most practical purposes.
Coming then to the actual work of prospecting. What the prospector
requires to know is, first, the usual locality of occurrence of the
more valuable minerals; secondly, their appearance; thirdly, a simple
mode of testing. With respect to occurrence, the older sandy and clay
slates, chlorite slates, micaceous, and hornblendic schists,
particularly at or near their junction with the intrusive granite and
diorite, generally form the most likely geological country for the
finding of mineral lodes, particularly gold, silver and tin. But those
who have been engaged in practical mining for long, finding by
experience that no two mineral fields are exactly alike in all their
characteristics, have come to the conclusion that it is unwise to form
theories as to why metals should or should not be found in certain
enclosing rocks or matrices. Some of the best reef gold got in
Victoria has been obtained in dead white, milky-looking quartz almost
destitute of base metal. In South Australia reef gold is almost
invariably associated with iron, either as oxide, as "gossan;" or
ferruginous calcite, "limonite;" or granular silica, conglomerated by
iron, the "ironstone" which forms the capping or outcrop of many of
our reefs, and which is often rich in gold.
But to show that it is unsafe to decide off-hand in what class of
matrix metals will or will not be found, I may say that in my own
experience I have seen payable gold in the following materials:--
Quartz, dense and milky, also in quartz of nearly every colour and
appearance, saccharoidal, crystalline, nay, even in clear glass-like
six-sided prismatic crystals, and associated with silver, copper,
lead, arsenic, iron as sulphide, oxide, carbonate, and tungstate,
antimony, bismuth, nickel, zinc, lead, and other metals in one form or
another; in slate, quartzite, mica schist, granite, diorite, porphyry,
felsite, calcite, dolomite, common carbonate of iron, siliceous sinter
from a hot spring, as at Mount Morgan; as alluvial gold in drifts
formed of almost all these materials; and once, perhaps the most
curious matrix of all, a small piece of apparently alluvial gold,
naturally imbedded in a shaly piece of coal. This specimen, I think,
is in the Sydney Museum. One thing, however, the prospector may make
sure of: he will always find gold more or less intimately associated
with silica (Quartz) in one or other of its many forms, just as he
will always find cassiterite (oxide of tin) in the neighbourhood of
granite containing muscovite (white mica), which so many people will
persist in terming talc. It is stated to be a fact that tin has never
been found more than about two miles from such granite.
From what has been said of its widely divergent occurrences it will be
admitted that the Cornish miners' saying with regard to metals
generally applies with great force to gold: "Where it is, there it
is": and "Cousin Jack" adds, with pathetic emphasis, "and where it is
generally, there I ain't."
I have already spoken of the geological "country rock" in which red
gold is most likely to be discovered--i.e., the junction of the slates
and schists with the igneous or metamorphic (altered) rocks, or in
this vicinity. Old river beds formed of gravelly drifts in the same
neighbourhood may probably contain alluvial gold, or shallow deposits
of "wash" on hillsides and in valleys will often carry good surface
gold. This is sometimes due to the denudation, or wearing away, of the
hills containing quartz-veins--that is, where the alluvial gold really
was derived from such veins, which, popular opinion to the contrary,
is not always the case.
Much disappointment and loss of time and money may sometimes be
prevented if prospectors will realise that /all/ alluvial gold does
not come from the quartz veins or reefs; and that following up an
alluvial lead, no matter how rich, will not inevitably develop a
payable gold lode. Sometimes gold, evidently of reef origin, is found
in the alluvial; but in that case it is generally fine as regards the
size of the particles, more or less sharp-edged, or crystalline in
form if recently shed; while such gold is often of poorer quality than
the true alluvial which occurs in mammillary (breast-like) nuggets,
and is of a higher degree of purity as gold.
The ordinary non-scientific digger will do well to give credence to
this view of the case, and will often thereby save himself much
useless trouble. Sometimes also the alluvial gold, coarser in size
than true reef-born alluvial, is derived almost /in situ/ from small
quartz "leaders," or veins, which the grinding down of the face of the
slates has exposed; these leaders in time being also broken and worn,
set free the gold they have contained, which does not, as a rule,
travel far, but sometimes becomes water-worn by the rubbing over it of
the disintegrated fragments of rock.
But the heavy, true alluvial gold, in great pure masses, mammillary,
or botryoidal (like a bunch of grapes) in shape, have assuredly been
formed by accretion on some metallic base, from gold salts in
solution, probably chloride, but possibly sulphide.
Nuggets, properly so-called, are never found in quartz lodes; but, as
will be shown later, a true nugget having all the characteristics of
so-called water-worn alluvial may be artificially formed on a small
piece of galena, or pyrites, by simply suspending the base metal by a
thread in a vessel containing a weak solution of chloride of gold in
which a few hard-wood chips are thrown.
Prospecting for alluvial gold at shallow depths is a comparatively
easy process, requiring no great amount of technical knowledge.
Usually the first gold is got at or near the surface and then traced
to deep leads, if such exist.
At Mount Brown Goldfield, N.S.W., in 1881, I saw claimholders turning
out to work equipped only with a small broom made of twigs and a tin
dish. With the broom they carefully swept out the crevices of the
decomposed slate as it was exposed on the surface, and putting the
resulting dust and fragments into the tin dish proceeded to dry blow
it.
The /modus operandi/ is as follows: The operator takes the dish about
half full of dirt, and standing with his back or side to the wind, if
there be any, begins throwing the stuff up and catching it, or
sometimes slowly pouring it from one dish to another, the wind in
either case carrying away the finer particles. He then proceeds to
reduce the quantity by carefully extracting the larger fragments of
rock, till eventually he has only a handful or so of moderately fine
"dirt" which contains any gold there may be. If in good sized nuggets
it is picked out, if in smaller pieces or fine grains the digger
slowly blows the sand and dust aside with his breath, leaving the gold
exposed. This process is both tedious and unhealthy, and of course can
only be carried out with very dry surface dirt. The stuff in which the
gold occurred at Mount Brown was composed of broken slate with a few
angular fragments of quartz. Yet, strange to say, the gold was
invariably waterworn in appearance.
Dry blowing is now much in vogue on the West Australian fields owing
to the scarcity of water; but the great objection is first, the large
amount of dust the unfortunate dry blower has to carry about his
person, and secondly, that the peck of dirt which is supposed to last
most men a life time has to be made a continuous meal of every day.
For wet alluvial prospecting the appliances, besides pick and shovel,
are puddling tub, tin dish, and cradle; the latter, a man handy with
tools can easily make for himself.
In sinking, the digger should be careful to avoid making his shaft
inconveniently small, and not to waste his energy by sinking a large
"new chum" hole, which usually starts by being about three times too
large for the requirements at the surface, but narrows in like a
funnel at 10 feet or less. A shaft, say 4 feet by 2 feet 6 inches and
sunk plumb, the ends being half rounded, is large enough for all
requirements to a considerable depth, though I have seen smart men,
when they were in a hurry to reach the drift, get down in a shaft even
less in size.
The novice who is trying to follow or to find a deep lead must fully
understand that the present bed of the surface river may not, in fact
seldom does, indicate the ancient watercourses long since buried
either by volcanic or diluvial action, which contain the rich
auriferous deposits for which he is seeking; and much judgment and
considerable underground exploration are often required to decide on
the true course of leads. Only by a careful consideration of all the
geological surroundings can an approximate idea be obtained from
surface inspection alone; and the whole probable conditions which led
to the present contour of the country must be carefully taken into
account.
How am I to know the true bottom when I see it? asks the inexperienced
digger. Well, nothing but long experience and intelligent observation
will prevent mistakes at times, particularly in deep ground; but as a
general rule, though it may sound paradoxical, you may know the bottom
by the top.
That is, we will assume you are sinking in, say, 10 to 12 feet ground
in a gully on the bank of which the country rock is exposed, and is,
say, for instance, a clay slate or sandy slate set at a certain angle;
then, in all probability, unless there be a distinct fault or change
in the country rock between the slate outcrop and your shaft, the
bottom will be a similar slate, standing at the same angle; and this
will very probably be overlaid by a deposit of pipeclay, formed by the
decomposition of the slates.
From the crevices of these slates, sometimes penetrating to a
considerable distance, you may get gold, but it is useless attempting
to sink through them. If the outcropping strata be a soft calcareous
(limy) sandstone or soft felspathic rock, and that be also the true
bottom, great care should be exercised or one is apt to sink through
the bottom, which may be very loose and decomposed. I have known
mistakes made in this way when many feet have been sunk, and driven
through what was actually bed rock, though so soft as to deceive even
men of experience. The formation, however, must be the guide, and
except in some specially difficult cases, a man can soon tell when he
is really on bed rock or "bottom."
On an alluvial lead the object of every one is to "get on the gutter,"
that is, to reach the lowest part of the old underground watercourse,
through which for centuries the gold may have been accretionising from
the percolation of the mineral-impregnated water; or, when derived
from reefs or broken down leaders, the flow of water has acted as a
natural sluice wherein the gold is therefore most thickly collected.
Sometimes the lead runs for miles and is of considerable width, at
others it is irregular, and the gold-bearing "gutter" small and hard
to find. In many instances, for reasons not readily apparent, the best
gold is not found exactly at the lowest portion of these narrow
gutters, but a little way up the sides. This fact should be taken into
consideration in prospecting new ground, for many times a claim has
been deserted after cleaning up the "bottom," and another man has got
far better gold considerably higher up on the sides of the gutter. For
shallow alluvial deposits, where a man quickly works out his 30 by 30
feet claim, it may be cheaper at times to "paddock" the whole ground--
that is, take all away from surface to bottom, but if he is in wet
ground and he has to drive, great care should be taken to properly
secure the roof by means of timber. How this may best be done the
local circumstances only can decide.
CHAPTER III
LODE OR REEF PROSPECTING
The preceding chapter dealt more especially with prospecting as
carried on in alluvial fields. I shall now treat of preliminary mining
on lodes or "reefs."
As has already been stated, the likeliest localities for the
occurrence of metalliferous deposits are at or near the junction of
the older sedimentary formations with the igneous or intrusive rocks,
such as granites, diorites, etc. In searching for payable lodes,
whether of gold, silver, copper, or even tin in some forms of
occurrence, the indications are often very similar. The first
prospecting is usually done on the hilltops or ridges, because, owing
to denudation by ice or water which have bared the bedrock, the
outcrops are there more exposed, and thence the lodes are followed
down through the alluvial covered plains, partly by their "strike" or
"trend," and sometimes by other indicating evidences, which the
practical miner has learned to know.
For instance, a lesson in tracing the lode in a grass covered country
was taught me many years ago by an old prospector who had struck good
gold in the reef at a point some distance to the east of what had been
considered the true course. I asked him why he had opened the ground
in that particular place. Said he, "Some folks don't use their eyes.
You stand here and look towards that claim on the rise where the reef
was last struck. Now, don't you see there is almost a track betwixt
here and there where the grass and herbage is more withered than on
either side? Why? Well, because the hard quartz lode is close to the
surface all the way, and there is no great depth of soil to hold the
moisture and make the grass grow."
I have found this simple lesson in practical prospecting of use since.
But the strike or course of a quartz reef is more often indicated by
outcrops, either of the silica itself or ironstone "blows," as the
miners call them, but the term is a misnomer, as it argues the easily
disproved igneous theory of veins of ejection, meaning thereby that
the quartz with its metalliferous contents was thrown out in a molten
state from the interior of the earth. This has in no case occurred,
and the theory is an impossible one. True lodes are veins of injection
formed by the infiltration of silicated waters carrying the metals
also in solution. This water filled the fissures caused either by the
cooling of the earth's crust, or formed by sudden upheavals of the
igneous rocks.
Sometimes in alluvial ground the trend of the reef will be revealed by
a track of quartz fragments, more or less thickly distributed on the
surface and through the superincumbent soil. Follow these along, and
at some point, if the lode be continuous, a portion of its solid mass
will generally be found to protrude and can then again be prospected.
There is no rule as to the trend or strike of lodes, except that a
greater number are found taking a northerly and southerly course than
one which is easterly and westerly. At all events, such is the case in
Australia, but it cannot be said that either has the advantage in
being more productive. Some of the richest mines in Australasia have
been in lodes running easterly and westerly, while gold, tin, and
copper, in great quantity and of high percentage to the ton, have been
got in such mines as Mount Morgan, Mount Bischoff, and the Burra,
where there are no lodes properly so-called at all.
Mount Morgan is the richest and most productive gold mine in
Australasia and amongst the best in the world.
Its yield for 1895 was 128,699 oz. of gold, valued at 528,700 pounds.
Dividends paid in 1895, 300,000 pounds.
This mine was opened in 1886. Up to May 31, 1897, the total yield was
1,631,981 ozs. of gold, sold at 6,712,187 pounds, from which 4,400,000
pounds have been paid in dividends. (See /Mining Journal/, for Oct. 9,
1897.)
Mount Morgan shareholders have, in other words, divided over 43 1/2
tons of standard gold.
The Burra Burra Mine, about 100 miles from Adelaide, in a direction a
little to the east of north, was found in 1845 by a shepherd named
Pickett. It is singularly situated on bald hills standing 130 feet
above the surrounding country. The ores obtained from this copper mine
had been chiefly red oxides, very rich blue and green carbonates,
including malachite, and also native copper. The discovery of this
mine, supporting, as it did at one time, a large population, marked a
new era in the history of the colony. The capital invested in it was
12,320 pounds in 5 pound shares, and no subsequent call was ever made
upon the shareholders. The total amount paid in dividends was 800,000
pounds. After being worked by the original owners for some years the
mine was sold to a new company, but during the last few years it has
not been worked, owing in some degree to the low price of copper and
also to the fact that the deposit then being worked apparently became
exhausted. For many years the average yield was from 10,000 to 13,000
tons of ore, averaging 22 to 23 per cent of copper. It is stated that,
during the twenty-nine and a half years in which the mine was worked,
the company expended 2,241,167 in general expenses. The output of ore
during the same period amounted to 234,648 tons, equal to 51,622 tons
of copper. This, at the average price of copper, amounted to a money
value of 4,749,224 pounds. The mine stopped working in 1877.
Mount Bischoff, Tasmania, has produced, since the formation of the
Company to December 1895, 47,263 tons of tin ore. It is still in full
work and likely to be for years to come.
Each of these immense metalliferous deposits was found outcropping on
the summit of a hill of comparatively low altitude. There are no true
walls nor can the ore be traced away from the hill in lode form. These
occurrences are generally held to be due to hydrothermal or geyser
action.
Then again lodes are often very erratic in their course. Slides and
faults throw them far from their true line, and sometimes the lode is
represented by a number of lenticular (double-pointed in section)
masses of quartz of greater or less length, either continuing point to
point or overlapping, "splicing," as the miners call it. Such
formations are very common in West Australia. All this has to be
considered and taken into account when tracing the run of stone.
This tyro also must carefully remember that in rough country where the
lode strikes across hills and valleys, the line of the cap or outcrop
will apparently be very sinuous owing to the rises and depressions of
the surface. Many people even now do not understand that true lodes or
reefs are portions of rock or material differing from the surrounding
and enclosing strata, and continuing down to unknown depths at varying
angles. Therefore, if you have a north and south lode outcropping on a
hill and crossing an east and west valley, the said lode, underlying
east, when you have traced its outcrop to the lowest point in the
valley, between the two hills, will be found to be a greater or less
distance, according to the angle of its dip or underlie, to the east
of the outcrop on the hill where it was first seen. If it be followed
up the next hill it will come again to the west, the amount of
apparent deviation being regulated by the height of the hills and
depth of the valley.
A simple demonstration will make this plain. Take a piece of half-inch
pine board, 2 ft. long and 9 in. wide, and imagine this to be a lode;
now cut a half circle out of it from the upper edge with a fret saw
and lean the board say at an angle of 45 degrees to the left, look
along the top edge, which you are to consider as the outcrop on the
high ground, the bottom of the cut being the outcrop in the valley,
and it will be seen that the lowest portion of the cut is some inches
to the right; so it is with the lode, and in rough country very nice
judgment is required to trace the true course.
For indications, never pass an ironstone "blow" without examination.
Remember the pregnant Cornish saying with regard to mining and the
current aphorism, "The iron hat covers the golden head." "Cousin
Jack," put it "Iron rides a good horse." The ironstone outcrop may
cover a gold, silver, copper or tin lode.
If you are searching for gold, the presence of the royal metal should
be apparent on trial with the pestle and mortar; if silver, either by
sight in one of its various forms or by assay, blowpipe or otherwise;
copper will reveal itself by its peculiar colour, green or blue
carbonates, red oxides, or metallic copper. It is an easy metal to
prospect for, and its percentage is not difficult to determine
approximately. Tin is more difficult to identify, as it varies so
greatly in appearance.
Having found your lode and ascertained its course, you want next to
ascertain its value. As a rule (and one which it will be well to
remember) if you cannot find payable metal, particularly in gold
"reef" prospecting, at or near the surface, it is not worth while to
sink, unless, of course, you design to strike a shoot of metal which
some one has prospected before you. The idea is exploded that
auriferous lodes necessarily improve in value with depth. The fact is
that the metal in any lode is not, as a rule, equally continuous in
any direction, but occurs in shoots dipping at various angles in the
length of the lode, in bunches or sometimes in horizontal layers.
Nothing but actual exploiting with pick, powder, and brains,
particularly brains, will determine this point.
Where there are several parallel lodes and a rich shoot has been found
in one and the length of the payable ore ascertained, the neighbouring
lodes should be carefully prospected opposite to the rich spot, as
often similar valuable deposits will thus be found. Having ascertained
that you have, say, a gold reef payable at surface and for a
reasonable distance along its course, you next want to ascertain its
underlie or dip, and how far the payable gold goes down.
As a general rule in many parts of Australia--though by no means an
inflexible rule--a reef running east of north and west of south will
underlie east; if west of north and east of south it will go down to
the westward and so round the points of the compass till you come to
east and west; when if the strike of the lodes in the neighbourhood
has come round from north-east to east and west the underlie will be
to the south; if the contrary was the case, to the north. It is
surprising how often this mode of occurrence will be found to obtain.
But I cannot too strongly caution the prospector not to trust to
theory but to prove his lode and his metal by following it down on the
underlie. "Stick to your gold" is an excellent motto. As a general
thing it is only when the lode has been proved by an underlie shaft to
water level and explored by driving on its course for a reasonable
distance that one need begin to think of vertical shafts and the
scientific laying out of the mine.
A first prospecting shaft need not usually be more than 5 ft. by 3 ft.
or even 5 ft. by 2 ft. 6 in., particularly in dry country. One may
often see in hard country stupid fellows wasting time, labour, and
explosives in sinking huge excavations as much as 10 ft. by 8 ft. in
solid rock, sometimes following down 6 inches of quartz.
When your shaft is sunk a few feet, you should begin to log up the top
for at least 3 ft. or 4 ft., so as to get a tip for your "mullock" and
lode stuff. This is done by getting a number of logs, say 6 inches
diameter, lay one 7 ft. log on each side of your shaft, cut two
notches in it 6 ft. apart opposite the ends of the shaft, lay across
it a 5 ft. log similarly notched, so making a frame like a large
Oxford picture frame. Continue this by piling one set above another
till the desired height is attained, and on the top construct a rough
platform and erect your windlass. If you have an iron handle and axle
I need not tell you how to set up a windlass, but where timber is
scarce you may put together the winding appliance described in the
chapter headed "Rules of Thumb."
If you have "struck it rich" you will have the pleasure of seeing your
primitive windlass grow to a "whip, a "whim," and eventually to a big
powerful engine, with its huge drum and Eiffel tower-like "poppet
heads," or "derrick," with their great spindle pulley wheels revolving
at dizzy speed high in air.
"How shall I know if I have payable gold so as to save time and
trouble in sinking?" says the novice. Truly it is a most important
part of the prospector's art, whether he be searching for alluvial or
reef gold, stream or lode tin, copper, or other valuable metal.
I presume you know gold when you see it?
If you don't, and the doubtful particle is coarse enough, take a
needle and stick the point into the questionable specimen. If gold the
steel point will readily prick it; if pyrites or yellow mica the point
will glance off or only scratch it.
The great importance of the first prospect from the reef is well shown
by the breathless intensity with which the two bearded, bronzed
pioneer prospectors in some trackless Australian wild bend over the
pan in which the senior "mate" is slowly reducing the sample of
powdered lode stuff. How eagerly they examine the last pinch of "black
sand" in the corner of the dish. Prosperity and easy times, or poverty
and more "hard graft" shall shortly be revealed in the last dexterous
turn of the pan. Let us hope it is a "pay prospect."
The learner, if he be far afield and without appliances of any kind,
can only guess his prospect. An old prospector will judge from six
ounces of stuff within a few pennyweights what will be the yield of a
ton. I have seen many a good prospect broken with the head of a pick
and panned in a shovel, but for reef prospecting you should have a
pestle and mortar. The handiest for travelling is a mortar made from a
mercury bottle cut in half, and a not too heavy wrought iron pestle
with a hardened face. To be particular you require a fine screen in
order to get your stuff to regulated fineness. The best for the
prospector, who is often on the move, is made from a piece of
cheesecloth stretched over a small hoop.
If you would be more particular take a small spring balance or an
improvised scale, such as is described in Mr. Goyder's excellent
little book, p. 14, which will enable you to weigh down to one-
thousandth of a grain. It is often desirable to burn your stone before
crushing, as it is thus more easily triturated and will reveal all its
gold; but remember, that if it originally contained much pyrites,
unless a similar course is adopted when treated in the battery, some
of the gold will be lost in the pyrites.
Having crushed your gangue to a fine powder you proceed to pan it off
in a similar manner to that of washing out alluvial earth, except that
in prospecting quartz one has to be much more particular, as the gold
is usually finer. The pan is taken in both hands, and enough water to
cover the prospect by a few inches is admitted. The whole is then
swirled round, and the dirty water poured off from time to time till
the residue is clean quartz sand and heavy metal. Then the pan is
gently tipped, and a side to side motion is given to it, thus causing
the heavier contents to settle down in the corner. Next the water is
carefully lapped in over the side, the pan being now tilted at a
greater angle until the lighter particles are all washed away. The pan
is then once more righted, and very little water is passed over the
pinch of heavy mineral a few times, when the gold will be revealed in
a streak along the bottom. In this operation, as in all others, only
practice will make perfect, and a few practical lessons are worth
whole pages of written instruction.
To make an amalgamating assay that will prove the amount of gold which
can be got from a ton of your lode, take a number of samples from
different parts, both length and breadth. The drillings from the
blasting bore-holes collected make the best test. When finely
triturated weigh off one or two pounds, place in a black iron pan (it
must not be tinned), with 4 ozs. of mercury, 4 ozs. salt, 4 ozs. soda,
and about half a gallon of boiling water; then, with a stick, stir the
pulp constantly, occasionally swirling the dish as in panning off,
till you feel certain that every particle of the gangue has come in
contact with the mercury; then carefully pan off into another dish so
as to lose no mercury. Having got your amalgam clean squeeze it
through a piece of chamois leather, though a good quality of new
calico previously wetted will do as well. The resulting pill of hard
amalgam can then be wrapped in a piece of brown paper, placed on an
old shovel, and the mercury driven off over a hot fire; or a clay
tobacco pipe, the mouth being stopped with clay, makes a good retort
(see "Rules of Thumb," pipe and potato retorting). The residue will be
retorted gold, which, on being weighed and the result multiplied by
2240 for a 1 lb. assay, or by 1120 for 2 lb., will give the amount of
gold per ton which an ordinary battery might be expected to save. Thus
1 grain to the pound, 2240 lbs. to the ton, would show that the stuff
contained 4 oz. 13 dwt. 8 gr. per ton.
If there should be much base metal in your sample such as say stibnite
(sulphide of antimony), a most troublesome combination to the
amalgamator--instead of the formula mentioned above add to your
mercury about one dwt. of zinc shavings or clippings, and to your
water sufficient sulphuric acid to bring it to about the strength of
vinegar (weaker, if anything, not stronger), place your material
preferably in an earthenware or enamelled basin if procurable, but
iron will do, and intimately mix by stirring and shaking till all
particles have had an opportunity to combine with the mercury. Retort
as before described. This device is my own invention.
The only genuine test after all is the battery, and that, owing to
various causes, is often by no means satisfactory. First, there is a
strong, almost unconquerable temptation to select the stone, thus
making the testing of a few tons give an unduly high average; but more
often the trouble is the other way. The stuff is sent to be treated at
some inefficient battery with worn-out boxes, shaky foundations, and
uneven tables, sometimes with the plates not half amalgamated, or
coated with impurities, the whole concern superintended by a man who
knows as little about the treatment of auriferous quartz by the
amalgamating or any other processes as a dingo does of the
differential calculus. Result: 3 dwt. to the ton in the retort, 30
dwt. in the tailings, and a payable claim declared a "duffer."
When the lode is really rich, particularly if it be carrying coarse
gold, and owing to rough country, or distance, a good battery is not
available, excellent results in a small way may be obtained by the
somewhat laborious, but simple, process of "dollying." A dolly is a
one man power single stamp battery, or rather an extra sized pestle
and mortar (see "Rules of Thumb").
Silver lodes and lodes which frequently carry more or less gold, are
often found beneath the dark ironstone "blows," composed of
conglomerates held together by ferric and manganic oxides; or, where
the ore is galena, the surface indications will frequently be a
whitish limey track sometimes extending for miles, and nodules or
"slugs" of that ore will generally be found on the surface from place
to place. Most silver ores are easily recognisable, and readily tested
by means of the blowpipe or simple fire assay. Sometimes the silver on
being tested is found to contain a considerable percentage of gold as
in the great Comstock lode in Nevada. Ore from the big Broken Hill
silver load, New South Wales, also contains an appreciable quantity of
the more precious metal. A natural alloy of gold containing 20 per
cent silver, termed electrum, is the lowest grade of the noble metal.
Tin, lode, and stream, or alluvial, occurs only as an oxide, termed
cassiterite, and yet you can well appreciate the compliment one
Cornish miner pays to another whose cleverness he wishes to commend,
when he says of him, "Aw, he do know tin," when you look at a
representative collection of tin ores. In various shapes, from sharp-
edged crystals to mammillary-shaped nuggets of wood-tin; from masses
of 30 lbs. weight to a fine sand, like gunpowder, in colour black,
brown, grey, yellow, red, ruby, white, and sometimes a mingling of
several colours, it does require much judgment to know tin.
Stream tin is generally associated with alluvial gold. When such is
the case there is no difficulty in saving the gold if you save the
tin, for the yellow metal is of much greater specific gravity. As the
natural tin is an oxide, and therefore not susceptible to
amalgamation, the gold can be readily separated by means of mercury.
Lode tin sometimes occurs in similar quartz veins to those in which
gold is got, and is occasionally associated with gold. Tin is also
found, as at Eurieowie, in dykes, composed of quartz crystals and
large scales of white mica, traversing the older slates. A similar
occurrence takes place at Mount Shoobridge and at Bynoe Harbour, in
the Northern Territory of South Australia; indeed, one could not
readily separate the stone from these three places if it were mixed.
As before stated tin will never be found far from granite, and that
granite must have white mica as one of its constituents. It is seldom
found in the darker coloured rocks, or in limestone country, but it
sometimes occurs in gneiss, mica schist, and chlorite schist. Numerous
other minerals are at times mistaken for tin, the most common of which
are tourmaline or schorl, garnet, wolfram (which is a tungstate of
iron with manganese), rutile or titanic acid, blackjack or zinc
blende, together with magnetic, titanic, and specular iron in fine
grains.
This rough and ready mode of determining whether the ore is tin is by
weight and by scratching or crushing, when, what is called the
"streak" is obtained. The colour of the tin streak is whitey-grey,
which, when once known, is not easily mistaken. The specific gravity
is about 7.0. Wolfram, which is most like it, is a little heavier,
from 7.0 to 7.5, but its streak is red, brown, or blackish-brown.
Rutile is much lighter, 4.2, and the streak light-brown; tourmaline is
only 3.2. Blackjack is 4.3, and its streak yellowish-white.
I have seen several pounds weight to the dish got in some of the New
South Wales shallow sinking tin-fields, and, as a rule, payable gold
was also present. Fourteen years ago I told Western Australian people,
when on a visit to that colony, that the neighbourhood of the Darling
range would produce rich tin. Lately this had been proved to be the
case, and I look forward to a great development of the tin mining
industry in the south-western portion of Westralia.
The tin "wash" in question may also contain gold, as the country rock
of the neighbourhood is such as gold is usually found in.[*]
[*] Since this book was in the printers' hands, the discovery of
payable gold has been reported from this district. A detailed
discussion of methods of prospecting will be found in chapter ii.
Of Le Neve Foster's "Ore and Stone Mining," and Mr. S. Herbert
Cox's "Handbook for Prospectors."
CHAPTER IV
THE GENESIOLOGY OF GOLD--AURIFEROUS LODES
Up to a comparatively recent time it was considered heretical for any
one to advance the theory that gold had been deposited where found by
any other agency than that of fire. As late as 1860 Mr. Henry Rosales
convinced himself, and apparently the Victorian Government also, that
quartz veins with their enclosed metal had been ejected from the
interior of the earth in a molten state. His essay, which is very
ingenious and cleverly written, obtained a prize which the Government
had offered, but probably Mr. Rosales himself would not adduce the
same arguments in support of the volcanic or igneous theory to-day.
His phraseology is very technical; so much so that the ordinary
inquirer will find it somewhat difficult to follow his reasoning or
understand his arguments, which have apparently been founded only on
the occurrence of gold in some of the earlier discovered quartz lodes,
and the conclusions at which he arrived are not borne out by later
experience. He says:--"While, however, there are not apparent signs of
mechanical disturbances, during the long period that elapsed from the
cooling of the earth's surface to the deposition of the Silurian and
Cambrian systems, it is to be presumed that the internal igneous
activity of the earth's crust was in full force, so that on the inner
side of it, in obedience to the laws of specific gravity, chemical
attraction, and centrifugal force, a great segregation of silica in a
molten state took place. This molten silica continually accumulating,
spreading, and pressing against the horizontal Cambro-Silurian beds
during a long period at length forced its way through the
superincumbent strata in all directions; and it is abundantly evident,
under the conditions of this force and the resistance offered to its
action, that the line it would and must choose would be along any
continuous and slightly inclined diagonal, at times crossing the
strata of the schists, though generally preferring to develop itself
and egress between the cleavage planes and dividing seams of the
different schistose beds."
He goes on to say, "Another argument to the same end (i.e., the
igneous origin) may be shown from the fact that the auriferous quartz
lodes have exercised a manifest metamorphic action on the adjacent
walls or casing; they have done so partly in a mineralogical sense,
but generally there has been a metamorphic alteration of the rock."
Mr. Rosales then tells his readers, what we all know must be the case,
that the gold would be volatilised by the heat, as would be also the
other metals, which he says, were in the form of arseniurets and
sulphurets; but he fails to explain how the sublimated metals
afterwards reassumed their metallic form. Seeing that, in most cases,
they would be hermetically enclosed in molten and quickly solidifying
silica they could not be acted on to any great extent by aqueous
agency. Neither does Mr. Rosales's theory account at all for
auriferous lodes; which below water level are composed of a solid mass
of sulphide of iron with traces of other sulphides, gold, calcspar,
and a comparatively small percentage of silica. Nor will it
satisfactorily explain the auriferous antimonial silica veins of the
New England district, New South Wales, in which quantities of angular
and unaltered fragments of slate from the enclosing rocks are found
imbedded in the quartz.
With respect to the metamorphism of the enclosing rocks to a greater
degree of hardness, which Mr. Rosales considered was due to heat, it
should be remembered that these rocks in their original state were
much softer and more readily fusible than the quartz, consequently all
would have been molten and mingled together instead of showing as a
rule clearly defined walls. It is much more rational to suppose that
the increased hardness imparted to the slates and schists at or near
their contact with the lode is due to an infiltration of silica from
the silicated solution which at one time filled the fissure. Few
scientists can now be found to advance the purely igneous theory of
lode formation, though it must be admitted that volcanic action has
probably had much influence not only in the formation of mineral
veins, but also on the occurrence of the minerals therein. But the
action was hydrothermal, just such as was seen in course of operation
in New Zealand a few years ago when, in the Rotomahana district, one
could actually see the growing of the marvellous White and Pink
Terraces formed by the release of silica from the boiling water
exuding from the hot springs, which water, so soon as the heat and
pressure were removed, began to deposit its silica very rapidly; while
at the Thames Gold-field, in the same country hot, silicated water
continuously boiled out of the walls of some of the lodes after the
quartz had been removed and re-deposited a siliceous sinter thereon.
On this subject I note the recently published opinions of Professor
Lobley, a gentleman whose scientific reputation entitles his
utterances to respect, but who, when he contends that gold is not
found in the products of volcanic action is, I venture to think,
arguing from insufficient premises. Certainly his theories do not hold
good either in Australasia or America where gold is often, nay, more
usually, found at, or near, either present or past regions of volcanic
action.
It is always gratifying to have one's theories confirmed by men whose
opinions carry weight in the scientific world. About seventeen years
ago I first published certain theories on gold deposition, which, even
then, were held by many practical men, and some scientists, to be open
to question. Of late years, however, the theory of gold occurrence by
deposition from mineral salts has been accepted by all but the "mining
experts" who infest and afflict the gold mining camps of the world.
These opine that gold ought to occur in "pockets" only (meaning
thereby their own).
Recently Professor Joseph Le Conte, at a meeting of the American
Institute of Mining Engineers, criticised a notable essay on the
"Genesis of Ore Deposits," by Bergrath F. Posepny. The Professor's
general conclusions are:
1. "Ore deposits, using the term in its widest sense, may take place
from any kinds of waters, but especially from alkaline solutions, for
these are the natural solvents of metallic sulphides, and metallic
sulphides are usually the original form of such deposits."
2. "They may take place from waters at any temperature and any
pressure, but mainly from those at high temperature and under heavy
pressure, because, on account of their great solvent power, such
waters are heavily freighted with metals."
3. "The depositing waters may be moving in any direction, up-coming,
horizontally moving, or even sometimes down-going, but mainly up-
coming; because by losing heat and pressure at every step such waters
are sure to deposit abundantly."
4. "Deposits may take place in any kind of waterways--in open
fissures, in incipient fissures, joints, cracks, and even in porous
sandstone, but especially in great open fissures, because these are
the main highways of ascending waters from the greatest depths."
5. "Deposits may be found in many regions and in many kinds of rocks,
but mainly in mountain regions, and in metamorphic and igneous rocks,
because the thermosphere is nearer the surface, and ready access
thereto through great fissures is found mostly in these regions and in
these rocks."
These views are in accordance with nearly all modern research into
this interesting and fruitful subject.
Among the theories which they discredit is that ore bodies may usually
be assumed to become richer in depth. As applied to gold lodes the
teaching of experience does not bear out this view.
If it be taken into account that the time in which most of our
auriferous siliceous lodes were formed was probably that indicated in
Genesis as before the first day or period when "the earth was without
form and void, and darkness was upon the face of the deep," it will be
realised that the action we behold now taking place in a small way in
volcanic regions, was probably then almost universal. The crust of the
earth had cooled sufficiently to permit water to lie on its surface,
probably in hot shallow seas, like the late Lake Rotomahana. Plutonic
action would be very general, and volcanic mud, ash, and sand would be
ejected and spread far and wide, which, sinking to the bottom of the
water, may possibly be the origin of what we now designate the azoic
or metamorphic slates and schists, as also the early Cambrian and
Silurian strata. These, from the superincumbent weight and internal
heat, became compacted, and, in some cases, crystallised, while at the
same time, from the ingress of the surface waters to the heated
regions below, probably millions of geysers were spouting their
mineral impregnated waters in all directions; and in places where the
crust was thin, explosions of super-heated steam caused huge
upheavals, rifts, and chasms, into which these waters returned, to be
again ejected, or to be the cause of further explosions. Later, as the
cooling-process continued, there would be shrinkages of the earth's
crust causing other fissures; intrusive granites further dislocated
and upheaved the slates. About this age, probably, when really dry
land began to appear, came the first formation of mineral lodes, and
the waters, heavily charged with silicates, carbonates of lime,
sulphides, etc., in solution, commenced to deposit their contents in
solid form when the heat and pressure were removed.
I am aware that part of the theory here propounded as to the probable
mode of formation of the immense sedimentary beds of the Archaic or
Azoic period is not altogether orthodox--i.e., that the origin of
these beds is largely due to the ejection of mud, sand, and ashes from
subterraneous sources, which, settling in shallow seas, were
afterwards altered to their present form. It is difficult, however, to
believe that at this very early period of geologic history so vast a
time had elapsed as would be required to account for these enormous
depositions of sediment, if they were the result only of the
degradation of previously elevated portions of the earth's surface by
water agency. Glacial action at that time would be out of the
question.
But what about the metals? Whence came the metallic gold of our reefs
and drifts? What was it originally--a metal or a metallic salt, and if
the latter, what was its nature?--chloride, sulphide, or silicate,
one, or all three? I incline to the latter hypothesis. All three are
known, and the chemical conditions of the period were favorable for
their natural production. Assuming that they did exist, the task of
accounting for the mode of occurrence of our auriferous quartz lodes
is comparatively simple. Chloride of gold is at present day contained
in sea water and in some mineral waters, and would have been likely to
be more abundant during the Azoic and early Paleozoic period.
Sulphide of gold would have been produced by the action of
sulphuretted hydrogen; hence probably our auriferous pyrites lodes,
while silicate of gold might have resulted from a combination of gold
chlorides with silicic acid, and thus the frequent presence of gold in
quartz is accounted for.
A highly interesting and instructive experiment, showing how gold
might be, and probably was, deposited in quartz veins, was carried out
by Professor Bischof some years ago. He, having prepared a solution of
chloride of gold, added thereto a solution of silicate of potash,
whereupon, as he states, the yellow colour of the chloride
disappeared, and in half an hour the fluid turned blue, and a
gelatinous dark-blue precipitate appeared and adhered to the sides of
the vessel. In a few days moss-like forms were seen on the surface of
the precipitate, presumably approximating to what we know as
dendroidal gold--that is, having the appearance of moss, fern, or
twigs. After allowing the precipitate to remain undisturbed under
water for a month or two a decomposition took place, and in the
silicate of gold specks of metallic gold appeared. From this, the
Professor argues, and with good show of reason, that as we know now
that the origin of our quartz lodes was the silicates contained in
certain rocks, it is probable that a natural silicate of gold may be
combined with these silicates. If this can be demonstrated, the reason
for the almost universal occurrence of gold in quartz is made clear.
About 1870, Mr. Skey, analyst to the New Zealand Geological Survey
Department, made a number of experiments of importance in respect to
the occurrence of gold. These experiments were summarised by Sir James
Hector in an address to the Wellington Philosophical Society in 1872.
Mr. Skey's experiments disproved the view generally held that gold is
unaffected by sulphur or sulphuretted hydrogen gas, and showed that
these elements combined with avidity, and that the gold thus treated
resisted amalgamation with mercury. Mr. Skey proved the act of
absorption of sulphur by gold to be a chemical act, and that
electricity was generated in sufficient quantity and intensity during
the process to decompose metallic solutions. Sulphur in certain forms
had long been known to exercise a prejudicial effect upon the
amalgamation of gold, but this had always been attributed to the
combination of the sulphur with the quicksilver used. Now, however, it
is certain that the sulphurising of the gold must be taken into
account. We must remember that the particles of gold in the stone may
be enveloped with a film of auriferous sulphide, by which they are
protected from the solvent actions of the mercury. The sulphurisation
of the gold gives no ocular manifestation by change of colour or
perceptible increase of weight, as in the case of the formation of
sulphides of silver, lead and other metals, on account of the
extremely superficial action of the sulphur, and hence probably the
existence of the gold sulphide escaped detection by chemists.
Closely allied to this subject is the investigation of the mode in
which certain metals are reduced from their solutions by metallic
sulphides, or, in common language, the influence which the presence of
such substances as mundic and galena may exercise in effecting the
deposit of pure metals, such as gold, in mineral lodes. The close
relation which the richness of gold veins bears to the prevalence of
pyrites has been long familiar both to scientific observers and to
practical miners. The gold is an after deposit to the pyrites, and, as
Mr. Skey was the first to explain, due to its direct reducing
influences. By a series of experiments Mr. Skey proved that the
reduction of the metal was due to the direct action of the sulphide,
and showed that each grain of iron pyrites, when thoroughly oxidised,
will reduce 12 1/4 grains of gold from its solution as chloride. He
also included salts of platina and silver in this general law, and
demonstrated that solutions of any of these metals traversing a vein
rock containing certain sulphides would be decomposed, and the pure
metal deposited. We are thus enabled to comprehend the constant
association of gold, or native alloys of gold and silver, in veins
which traverse rocks containing an abundance of pyrites, whether they
have been formed as the result of either sub-aqueous volcanic outburst
or by the metamorphism of the deeper-seated strata which compose the
superficial crust of the earth.
Mr. Skey also showed by very carefully conducted experiments that the
metallic sulphides are not only better conductors of electricity than
has hitherto been supposed, but that when paired they were capable of
exhibiting strong electro-motive power. Thus, if galena and zinc
blende in acid solutions be connected in the usual manner by a voltaic
pair, sulphuretted hydrogen is evolved from the surface of the former,
and a current generated which is sufficient to reduce gold, silver or
copper from their solutions in coherent electro-plate films. The
attributing of this property of generating voltaic currents, hitherto
supposed to be almost peculiar to metals, to such sulphides as are
commonly found in metalliferous veins, further led Mr. Skey to
speculate how far the currents discovered to exist in such veins by
Mr. E. F. Fox might be produced by the gradual oxidation of mixed
sulphides, and that veins containing bands of different metallic
sulphides, bounded by continuing walls, and saturated with mineral
waters, may constitute under some circumstances a large voltaic
battery competent to produce electro-deposition of metals, and that
the order of the deposit of these mineral lodes will be found to bear
a definite relation to the order in which the sulphides rank in the
table of their electro-motive power. These researches may lead to some
clearer comprehension of the law which regulates the distribution of
auriferous veins, and may explain why in some cases the metal should
be nearly pure, while in others it is so largely alloyed with silver.
The following extract was lately clipped from a mining paper. If true,
the experiment is interesting:--
"An American scientist has just concluded a very interesting and
suggestive experiment. He took a crushed sample of rich ore from
Cripple Creek, which carried 1100 ozs. of gold per ton, and digested
it in a very weak solution of sodium chloride and sulphate of iron,
making the solution correspond as near as practicable to the waters
found in Nature. The ore was kept in a place having a temperature
little less than boiling water for six weeks, when all the gold,
except one ounce per ton, was found to have gone into solution. A few
small crystals of pyrite were then placed in the bottle of solution,
and the gold began immediately to precipitate on them. It was
noticeable, however, that the pyrite crystals which were free from
zinc, galena, or other extraneous matter received no gold precipitate.
Those which had such foreign associations were beautifully covered
with fine gold crystals."
Experimenting in a somewhat similar direction abut twelve months
since, I found that the West Australian mine water, with the addition
of an acid, was a solvent of gold. The idea of boiling it did not
occur to me, as the action was rapid in cold water.
Assuming, then, that gold originally existed as a mineral salt, when
and how did it take metallic form? Doubtless, just in the same manner
as we now (by means of well-known reagents which are common in nature)
precipitate it in the laboratory. With regard to that found in quartz
lodes finely disseminated through the gangue, the change was brought
about by the same agency which caused the silicic acid to solidify and
take the form in which we now see it in the quartz veins. Silica is
soluble in solutions of alkaline carbonates, as shown in New Zealand
geysers; the solvent action being increased by heat and pressure, so
also would be the silicate or sulphide of gold. When, however, the
waters with their contents were released from internal pressure and
began to lose their heat the gold would be precipitated together with
the salts of some other metals, and would, where the waters could
percolate, begin to accretionise, thus forming the heavy or specimen
gold of some reefs. On this class of deposition I shall have more to
say when treating of the origin of alluvial gold in the form of
nuggets.
Mr. G. F. Becker, of the United States Geological Survey, writing of
the geology of the Comstock lode, says:--"Baron Von Richthofen was of
opinion that fluorine and chlorine had played a large part of the ore
deposition in the Comstock, and this the writer is not disposed to
deny; but, on the other hand, it is plain that most of the phenomena
are sufficiently accounted for on the supposition that the agents have
been merely solutions of carbonic and hydro-sulphuric acids. These
reagents will attack the bisilicates and felspars. The result would be
carbonates and sulphides of metals, earth, alkalies, and free quartz,
but quartz and sulphides of the metals are soluble in solutions of
carbonates and sulphides of the earths and alkalies, and the essential
constituents of the ore might, therefore, readily be conveyed to
openings in the vein where they would have been deposited on relief of
pressure and diminution of temperature. An advance boring on the 3000
ft. level of the Yellow Jacket struck a powerful stream of water at
3065 ft. (in the west country), which was heavily charged with
hydrogen sulphide, and had a temperature of 170 degrees F., and there
is equal evidence of the presence of carbonic acid in the water of the
lower levels. A spring on the 2700 ft. level of the Yellow Jacket
which showed a temperature of about 150 degrees F., was found to be
depositing a sinter largely composed of carbonates."
It may be worth while here to speak of the probable reason why gold,
and indeed almost all the metals generally occur in shutes in the
lodes; and why, as is often the case, these shutes are found to be
more or less in a line with each other in parallel lodes, and why also
the junction of two lodes is frequently specially productive. The
theory with respect to these phenomena which appears most feasible is,
that at these points certain chemical action has taken place, by which
the deposition of the metals has been specially induced. Generally a
careful examination of the enclosing rocks where the shute is found
will reveal some points of difference from the enclosing rocks at
other parts of the course of the lode, and when ore shutes are found
parallel in reefs running on the same course, bands or belts of
similar country rock will be found at the productive points. From this
we may fairly reason that at these points the slow stream filling the
lode cavity met with a reagent percolating from this particular band
of rock, which caused the deposition of its metals; and, indeed, I am
strongly disposed to believe that the deposition of metals,
particularly in some loose lodes, may even now be proceeding. But as
in Nature's laboratory the processes, if certain, are slow, this
theory may be difficult to prove.
Why the junction of lodes is often found to be more richly
metalliferous than neighbouring parts is probably because there the
depositing reagents met. This theory is well put by Mr. S. Herbert
Cox, late of Sydney, in his useful book, "Mines and Minerals." He
says:--"It is a well-known fact in all mining districts that the
junctions of lodes are generally the richest points, always supposing
that this junction takes place in 'kindly country,' and the
explanation of this we think is simple on the aqueous theory of
filling of lodes. The water which is traversing two different channels
of necessity passes through different belts of country, and will thus
have different minerals in solution. As a case in point, let us
suppose that the water in one lode contained in solution carbonates of
lime, and the alkalies and silica derived form a decomposition of
felspars; and that the other, charged with hydro-sulphuric acid,
brought with it sulphide of gold dissolved in sulphide of lime. The
result of these two waters meeting would be that carbonate of lime
would be formed, hydro-sulphuric acid would be set free, and sulphide
of gold would be deposited, as well as silica, which was formerly held
in solution by the carbonic acid."
Most practical men who have given the subject attention will, I think,
be disposed to coincide with this view, though there are some who hold
that the occurrence of these parallel ore shutes and rich deposits at
the junctions of lodes is due to extraneous electrical agency. Of
this, however I have failed to find any satisfactory evidence.
There is, however, proof that lodes are actually re-forming and the
action observed is very interesting as showing how the stratification
in some lodes has come about. Instances are not wanting of the growth
of silica on the sides of the drives in mines. This was so in some of
the mines on the Thames, New Zealand, previously mentioned, where in
some cases the deposition was so rapid as to be noticeable from day to
day, whilst the big pump was actually choked by siliceous deposits. In
old auriferous workings which have been under water for years, in many
parts of the world, formations of iron and silica have been found on
the walls and roof, while in mining tunnels which have been long
unused stalactites composed of silica and calcite have formed. Then,
again, experiments made by the late Professor Cosmo Newbery, in
Victoria, showed that a distinctly appreciable amount of gold, iron,
and silica (the latter in granular form) could be extracted from solid
mine timber; which had been submerged for a considerable time.
This reaction then must be in progress at the present time, and
doubtless under certain conditions pyrites would eventually take the
place of the timber, as is the case with some of the long buried
driftwood found in Victorian deep leads. Again, we know that the water
from some copper mines is so charged with copper sulphate that if
scrap iron be thrown into it, the iron will be taken up by the
sulphuric acid, and metallic copper deposited in its place. All this
tends to prove that the deposition of metals from their salts, though
probably not now as rapid as formerly, is still ceaselessly going on
in some place or another where the necessary conditions are
favourable.
With regard to auriferous pyritic lodes, it does not appear even now
to be clear, as some scientists assert, that their gold is never found
in chemical combination with the sulphides of the base metals. On the
contrary, I think much of the evidence points in the other direction.
I have long been of opinion that it is really so held in many of the
ferro-sulphides and arsenio-ferro sulphides. On this subject Mr. T.
Atherton contributed a short article in 1891 to the /Australian Mining
Standard/ which is worthy of notice. He says, referring to an
occurrence of a Natural Sulphide of Gold: "The existence of gold, in
the form of a natural sulphide in conjunction with pyrites, has often
been advanced theoretically, as a possible occurrence; but up to the
present time has, I believe, never been established as an actual fact.
During my investigation on the ore of the Deep Creek mines, Nambucca,
New South Wales, I have found in them what I believe to be gold
existing as a natural sulphide. The lode is a large irregular one of
pure arsenical pyrites carrying, in addition to gold and silver,
nickel and cobalt. It exists in a felsite dyke immediately on the
coast. Surrounding it on all sides are micaceous schists, and in the
neighbourhood about half a mile distant is a large granite hill about
800 feet high. In the lode and its walls are large quantities of pyro-
phyllite, and in some parts of the mine there are deposits of pure
white translucent mica, but in the ore itself it is a yellow or pale
olive green, and is never absent from the pyrites.
"From the first I was much struck with the exceedingly fine state of
division in which the gold existed in the ore. After roasting and very
carefully grinding down in an agate mortar, I have never been able to
get any pieces of gold exceeding one-thousandth of an inch in
diameter, and the greater quantity is very much finer than this.
Careful dissolving of the pyrites and gangue so as to leave the gold
intact failed to find it in any larger diameter. As this was a very
unusual experience in investigations on many other kinds of pyrites, I
was led further into the matter.
"Ultimately, after a number of experiments, there was nothing left but
to test for gold existing as a natural sulphide. Taking 200 gr. of ore
from a sample assaying 17 oz. fine gold per ton, grinding it finely
and heating for some hours with yellow sodium sulphide--on decomposing
the filtrate and treating for gold I got a result at the rate of 12
oz. per ton. This was repeated several times with the same result.
"This sample came from the lode at the 140 ft. level, whilst samples
from the higher levels where the ore is more oxidised, although
carrying the gold in exactly the same degree of fineness, do not give
as high a percentage of auric sulphide.
"It would appear that all the gold in the pyrites (and I have never
found any gold existing apart from the pyrites) has originally taken
its place there as a sulphide."
Professor Newbery, who made many valuable suggestions on the subject,
says, speaking of gold in pyritous lodes:
"As it (the gold salt) may have been in the same solution that
deposited the pyrites, which probably contained its iron in the form
of proto-carbonate with sulphates, it was not easy at first to imagine
any ordinary salt of gold; but this I find can be accomplished with
very dilute solutions in the presence of an alkaline carbonate and a
large excess of carbonic acid, both of which are common constituents
of mineral waters, especially in Victoria. This is true of chloride of
gold, and if the sulphide is required in solution, it is only
necessary to charge the solution with an excess of sulphuretted
hydrogen. In this matter both sulphides may be retained in the same
solution, depositing gradually with the escape of the carbonic acid."
Pyritic lodes usually contain a considerable proportion of calcareous
matter, mostly carbonates, and consequently it appears not improbable
that the gold may remain in some instances as a sulphide, particularly
in samples of pyrites, in which it cannot be detected even by the
microscope until by calcination the iron sulphide is changed to an
oxide, wherein the gold may be seen in minute metallic specks. The
whole subject is full of interest, and careful scientific
investigation may lead to astonishing results.
CHAPTER V
THE GENESIOLOGY OF GOLD--AURIFEROUS DRIFTS
Having considered the origin of auriferous lodes, and the mode by
which in all probability the gold was conveyed to them and deposited
as a metal, it is necessary also to inquire into the derivation of the
gold of our auriferous drifts, and the reasons for its occurrence
therein.
When quite a lad on the Victorian alluvial fields, I frequently heard
old diggers assert that gold grew in the drifts where found. At the
time we understood this to mean that it grew like potatoes; and,
although not prepared with a scientific argument to prove that such
was not so, the idea was generally laughed at. I have lived to learn
that these old hard-heads were nearer the truth than possibly they
clearly realised, and that gold does actually grow or agglomerate;
and, indeed, is probably even now thus growing, though it is likely
that the chemical and electric action in the mineral waters flowing
through the drifts is not in this age nearly so active as formerly.
Most boys have tried the experiment of dipping a clean-bladed knife
into sulphate of copper, and so depositing on the steel a film of
copper, which adheres closely until worn away. This is a simple
demonstration of a hydro-metallurgical process, though probably young
hopeful is not aware of the fact; and it is really by an enlargement
of this process that our beautiful and artistic gold- and silver-
plated ware is produced.
In the great laboratory of Nature similar chemical depositions have
taken place in the past, and may still be in progress; indeed, there
is sound scientific reason to suppose that in certain localities this
is even now the case, and that in this way much of our so-called
alluvial gold has been formed, that is, by the deposition on metallic
bases of the gold held in solution.
We will, however, take, to begin with, the generally accepted theory
as to the occurrence of alluvial gold. First, let it be said, that
certain alluvial gold is unquestionably derived from the denudation of
quartz lodes. Such is the gold dust found in many Asiatic and African
rivers, in the great placer mines of California, as also the gold dust
gained from the beach sand on the west coast of New Zealand, or in the
enormous alluvial drifts of the Shoalhaven Valley, New South Wales. Of
the first, many fabulous tales are told to account for its being found
in particular spots each summer after the winter floods, and
miraculous agency was asserted, while the early beachcombers of the
Hokitika district found an equally ridiculous derivation for their
gold, which was always more plentiful after heavy weather. They
imagined that the breakers were disintegrating some abnormally rich
auriferous reefs out at sea, and that the resultant gold was washed up
on the beach.
The facts are simply, with regard to the rivers, that the winter
floods break down the drifts in the banks and agitate the auriferous
detritus, thus acting as natural sluices, and cause the metal to
accumulate in favourable spots; whilst on the New Zealand coast the
heavy seas breaking on the shingly beach, carry off the lighter
particles, leaving behind the gold, which is so much heavier. These
beaches are composed, as also are the "terraces" behind, of enormous
glacial and fluvial deposits, all containing more or less gold, and
extend inland to the foot of the mountains.
It is almost certain that the usually fine gold got by hydraulicing in
Californian canyons, in the gullies of the New Zealand Alps, and the
great New South Wales drifts, is largely the result of the attrition
of the boulders and gravel of moraines, which has thus freed, to a
certain extent, the auriferous particles. But when we find large
nuggety masses of high carat gold in the beds of dead rivers, another
origin has to be sought.
As previously stated, there is fair reason to assume that at least
three salts of gold have existed, and, possibly, may still be found in
Nature--silicate, sulphide, and chloride. All of these are soluble and
in the presence of certain reagents, also existing naturally, can be
deposited in metallic form. Therefore, if, as is contended, reef gold
was formed with the reefs from solutions in mineral waters, by
inferential reasoning it can be shown that much of our alluvial gold
was similarly derived.
The commonly accepted theory, however, is that the alluvial matter of
our drifts has been ground out of the solid siliceous lodes by glacial
and fluvial action, and that the auriferous leads have been formed by
the natural sluicing operations of former streams. To this, however,
there are several insuperable objections.
First, how comes it that alluvial gold is usually superior in purity
to the "reef" gold immediately adjacent? Second, why is it that masses
of gold, such as the huge nuggets found in Victoria and New South
Wales, have never been discovered in lodes? Third, how is it that
these heavy masses which, from their specific gravity, should be found
only at the very bottom of the drifts, if placed by water action, are
sometimes found in all positions from the surface to the bottom of the
"wash"? And, lastly, why is it that when an alluvial lead is traced up
to, or down from, an auriferous reef, that the light, angular gold
lies close to the roof, while the heavy masses are often placed much
farther away? Any one who has worked a ground sluice knows how
extremely difficult it is with a strong head of water to shift from
its position an ounce of solid gold. What, then, would be the force
required to remove the Welcome Nugget? Under certain circumstances,
Niagara would not be equal to the task.
The generally smooth appearance of alleged alluvial gold is adduced as
an argument in favour of its having been carried by water from its
original place of deposit, and thus in transit become waterworn; while
some go so far as to say that it was shot out of the reefs in a molten
state. The latter idea has been already disposed of, but if not, it
may be dismissed with the statement that the heat which would melt
silica in the masses met with in lodes would sublimate any gold
contained, and dissipate it, not in nuggets but in fumes. With regard
to the assumed waterworn appearance of alluvial gold, I have examined
with the microscope the smooth surface of more than one apparently
waterworn nugget, and found that it was not scratched and abraded, as
would have been the case had it been really waterworn, but that it
presented the same appearance, though infinitely finer in grain, as
the surface of a piece of metal fresh from the electrical plating-
bath.
Mr. Daintree, of the Victorian Geological Survey, many years ago
discovered accidentally that gold chloride would deposit its metal on
a metallic base in the presence of any organic substance. Mr. Daintree
found that a piece of undissolved gold in a bottle containing chloride
of gold in solution had, owing to a portion of the cork having fallen
into the liquid, grown or accretionised so much that it could not be
extracted through the neck. This lead Mr. Charles Wilkinson, who has
contributed much to our scientific knowledge of metallurgy, to
experiment further in the same direction. He says: "Using the most
convenient salt of gold, the terchloride, and employing wood as the
decomposing agent, in order to imitate as closely as possible the
organic matter supposed to decompose the solution circulating through
the drifts, I first immersed a piece of cubic iron pyrites taken from
the coal formation of Cape Otway, far distant from any of our gold
rocks, and therefore less likely to contain gold than other pyrites.
The specimen (No. 1) was kept in dilute solution for about three
weeks, and is completely covered with a bright film of gold. I
afterwards filed off the gold from one side of a cube crystal to show
the pyrites itself and the thickness of the surrounding coating, which
is thicker than ordinary notepaper. If the conditions had continued
favourable for a very lengthened period, this specimen would doubtless
have formed the nucleus of a large nugget. Iron, copper, and arsenical
pyrites, antimony, galena, molybdenite, zinc blende, and wolfram were
treated in the above manner with similar results. In the above
experiments a small chip of wood was employed as the decomposing
agent. In one instance I used a piece of leather. All through the wood
and leather gold was disseminated in fine particles, and when cut
through the characteristic metallic lustre was brightly reflected. The
first six of these sulphides were also operated upon simply in the
solution without organic matter; but they remained unaltered."
Wilkinson found that when the solution of gold chloride was as strong
as, say, four grains to the ounce of water, that the pyrites or other
base began to decompose, and the iron sulphide changed to yellow
oxide, the "gossan" of our lodes, and that though the gold was
deposited, this occurred in an irregular way, and it was coated with a
dark brown powdery film something like the "black gold," often found
in drifts containing much ferruginous matter. Such were the curious
Victorian nuggets Spondulix and Lothair.
Professor Newbery also made a number of similar experiments, and
arrived at like results. He states as follows: "I placed a cube of
galena in a solution of chloride of gold, with free access of air, and
put in organic matter; gold was deposited as usual, in a bright
metallic film, apparently completely coating the cube. After a few
months the film burst along the edges of the cube, and remained in
that state with the cracks open without any further alteration in size
or form being apparent. Upon removing it a few days ago and breaking
it open, I found that a large portion of the galena had been
decomposed, forming chloride and sulphate of lead and free sulphur,
which were mixed together, encasing a small nucleus of undecomposed
sulphate of lead. The formation of these salts had exerted sufficient
force to burst open the gold coating, which upon the outside had the
mammillary form noticed by Wilkinson, while the inside was rough and
irregular with crystals forcing their way into the lead salts. Had
this action continued undisturbed, the result would have been a nugget
with a nucleus of lead salts, or if there had been a current to remove
the results of decomposition, a nugget without a nucleus of foreign
matter."
But Newbery also made another discovery which still further
establishes the probability of the accretionary growth of gold in
drifts. In the first experiments both investigators used organic
substances as the reagent to cause the deposit of gold on its base,
and in each case these substances whether woodchips, leather, or even
dead flies, were found to be so absolutely impregnated with gold as to
leave a golden skeleton when afterwards burned. Timber found in the
Ballarat deep leads has been proved to be similarly impregnated.
Newbery found that gold could also be deposited on sulphurets without
any other reagent. He says: "In our mineral sulphurets, however, we
have agents which are not only capable of reducing gold and silver
from solution, but besides are capable of locating them when so
reduced in coherent and bulky masses. Thus the aggregation of the
nuggety forms of gold from solution becomes a still more simple
matter, only one reagent being necessary, so that there is a greater
probability of such depositions obtaining than were a double process
necessary. Knowing the action of sulphides, the manner or the mode of
formation of a portion at least of these nuggets seems apparent.
Conceive a stream or river fed by springs rising in a country
intersected by auriferous reefs, and consequently in this case
carrying gold in solution; the drift of such a country must be to a
greater or lesser extent pyritous, so that the /debris/ forming the
beds of these streams or rivers will certainly contain nodules of such
matters disseminated or even stopping them in actual contact with the
flow of water. It follows, then, from what has been previously
affirmed, that there will be a reduction of gold by these nodules, and
that the metal thus reduced will be firmly attached to them, at first
in minute spangles isolated from each other, but afterwards
accumulating and connecting in a gradual manner at that point of the
pyritous mass most subject to the current until a continuous film of
some size appears. This being formed the pyrites and gold are to a
certain extent polarised, the film or irregular but connected mass of
gold forming the negative, and the pyrites the positive end of a
voltaic pair; and so according as the polarisation is advanced to
completion the further deposition of gold is changed in its manner
from an indiscriminate to an orderly and selective deposition
concentrated upon the negative or gold plate. The deposition of gold
being thus controlled, its loss by dispersion or from the crumbling
away of the sustaining pyrites is nearly or quite prevented, a
conservative effect which we could scarcely expect to obtain if
organic matter were the reducing agent. Meanwhile there is a gradual
wasting away of the pyrites or positive pole, its sulphur being
oxidised to sulphuric acid and its iron to sesquioxide of iron, or
hematite, a substance very generally associated with gold nuggets.
According to the original size of the pyritous mass, the protection it
receives from the action of oxidising substances other than gold, the
strength of the gold solution, length of exposure to it, the rate of
supply and velocity of stream, will be the size of the gold nugget. As
to the size of a pyritous mass necessary to produce in this manner a
large nugget, it is by no means considerable. A mass of common pyrites
(bisulphide of iron) weighing only 12 lbs. is competent for the
construction of the famous 'Welcome Nugget,' an Australian find having
weight equal to 152 lbs. avoirdupois. Such masses of pyrites are by no
means uncommon in our drifts or the beds of our mountain streams. Thus
we find that no straining of the imagination is required to conceive
of this mode of formation for the huge masses of gold found in
Australia in particular, such as the Welcome Nugget, 184 lbs. 9 oz.;
the Welcome Stranger, a surface nugget, 190 lbs. after smelting; the
Braidwood specimen nugget, 350 lbs., two-thirds gold; besides many
other large masses of almost virgin gold which have been obtained from
time to time in the alluvial diggings."
The author has made a number of experiments in the same direction, but
more with the idea of demonstrating how possibly gold may in certain
cases have been deposited in siliceous formations after such
formations had solidified. Some of the results were remarkable and
indeed unexpected. I found that I could produce artificial specimens
of auriferous quartz from stone which had previously contained no gold
whatever, also that it was not absolutely necessary that the stone so
treated should contain any metallic sulphides.
The following was contributed by the author and is from the
"Transactions" of the Australasian Institute of Mining Engineers for
1893:--
"THE DEPOSITION OF GOLD.
"The question as to how gold was originally deposited in our
auriferous lodes is one to which a large amount of attention has been
given, both by mineralogists and practical miners, and which has been
hotly argued by those who held the igneous theory and those who
pronounced for the aqueous theory. It was held by the former that as
gold was not probably existent in nature in any but its metallic form,
therefore it had been deposited in its siliceous matrix while in a
molten state, and many ingenious arguments were adduced in support of
this contention. Of late, however, most scientific men, and indeed
many purely empirical inquirers (using the word empirical in its
strict sense) have come to the conclusion that though the mode in
which they were composed was not always identical, all lodes,
including auriferous formations, were primarily derived from mineral-
impregnated waters which deposited their contents in fissures caused
either by the cooling of the earth's crust or by volcanic agency.
"The subject is one which has long had a special attraction for the
writer, who has published several articles thereon, wherein it was
contended that not only was gold deposited in the lodes from aqueous
solution, but that some gold found in form of nuggets had not been
derived from lodes but was nascent in its alluvial bed; and for this
proof was afforded by the fact that certain nuggets have been
unearthed having the shape of an adjacent pebble or angular fragment
of stone indented in them. Moreover, no true nugget of any great size
has ever been found in a lode such as the Welcome, 2159 oz., or the
Welcome Stranger, 2280 oz.; while it was accidentally discovered some
years ago that gold could be induced to deposit itself from its
mineral salt to the metallic state on any suitable base, such as iron
sulphide.
"Following out this fact, I have experimented with various salts of
gold, and have obtained some very remarkable results. I have found it
practicable to produce most natural looking specimens of auriferous
quartz from stone which previously, as proved by assay, contained no
gold whatever. Moreover, the gold, which penetrates the stone in a
thorough manner, assumes some of the more natural forms. It is always
more or less mammillary, but at times, owing to causes which I have
not yet quite satisfied myself upon, is decidedly dendroidal, as may
be seen in one of the specimens which I have submitted to members.
Moreover, I find it possible to moderate the colour and to produce a
specimen in which the gold shall be as ruddy yellow as in the ferro-
oxide gangue of Mount Morgan, or to tone it to the pale primrose hue
of the product of the Croydon mines.
"I note that the action of the bath in which the stone is treated has
a particularly disintegrating effect on many of the specimens. Some,
which before immersion were of a particularly flinty texture, became
in a few weeks so friable that they could be broken up by the fingers.
So far as my experiments have extended they have proved this, that it
was not essential that the silica and gold should have been deposited
at the one time in auriferous lodes. A non-auriferous siliceous
solution may have filled a fissure, and, after solidifying, some
volcanic disturbance may have forced water impregnated with a gold
salt through the interstices of the lode formation, when, if the
conditions were favourable, the gold would be deposited in metallic
forms. I prefer, for reasons which will probably be understood, not to
say exactly by what process my results are obtained, but submit
specimens for examination.
"(1) Piece of previously non-gold bearing stone. Locality near
Adelaide, now showing gold freely in mammillary and dendroidal form.
"(2) Stone from New South Wales, showing gold artificially introduced
in interstices and on face.
"(3) Stone from West Australia, very glassy looking, now thoroughly
impregnated with gold; the mammillary formation being particularly
noticeable.
"(4) Somewhat laminated quartz from Victoria, containing a little
antimony sulphide. In this specimen the gold not only shows on the
surface but penetrates each of the laminations, as is proved by
breaking.
"(5) Consists of fragments of crystallised carbonate of lime from
Tarrawingee, in which the gold is deposited in spots, in appearance
like ferrous oxide, until submitted to the magnifying glass.
"The whole subject is worthy of much more time than I can possibly
give it. The importance lies in this: That having found how the much
desired metal may have been deposited in its matrix, the knowledge
should help to suggest how it may be economically extracted
therefrom."
A very remarkable nugget weighing 16 3/4 oz. was sluiced from near the
surface in one of my own mining properties at Woodside, South
Australia, some years ago, which illustrated the nuclear theory very
beautifully. This nugget is very irregular in shape, fretted and
chased as though with a jeweller's graving tool, showing plainly the
shape of the pyritous crystals on which it was formed while the
interstices were filled with red hematite iron just as found in
artificially formed nuggets on a sulphide of iron base. The author has
a nugget from the same locality weighing about 1 1/2 oz. which
exhibits in a marked degree the same characteristics, as indeed does
most of the alluvial gold found in the Mount Lofty Ranges; also a
nugget from near the centre of Australia weighing four ounces, in
which the original crystals of pyrites are reproduced in gold just as
an iron horse-shoe, placed in a launder through which cupriferously
impregnated water flows, will in time be changed to nearly pure copper
and yet retain its shape.
Now with regard to the four points I have put as to the apparent
anomalies of occurrence of alluvial gold. The reason why alluvial gold
is of finer quality as a rule than reef is probably because while gold
and silver, which have a considerable affinity for each other, were
presumably dissolved from their salts and held in solution in the same
mineral water, they would in many cases not be deposited together, for
the reason that silver is most readily deposited in the presence of
alkalies, which would be found in excess in mineral waters coming
direct from the basic rocks, while gold is induced to precipitate more
quickly in acid solutions, which would be the character of the waters
after they had been exposed to atmospheric action and to contact with
organic matters.
This, then, may explain not only the comparatively greater purity of
the alluvial gold, but also why big nuggets are found so far from
auriferous reefs, and also why heavy masses of gold have been
frequently unearthed from among the roots even of living trees, but
more particularly in drifts containing organic matter, such as ancient
timber.
All, then, that has been adduced goes to establish the belief that the
birthplace of our gold is in certain of the earlier rocks comprising
the earth's crust, and that its appearance as the metal we value so
highly is the result of electro-chemical action, such as we can
demonstrate in the laboratory.
CHAPTER VI
GOLD EXTRACTION
We now come to a highly important part of our subject, the practical
treatment of ores and matrixes for the extraction of the metals
contained. The methods employed are multitudinous, but may be divided
into four classes, namely, washing, amalgamating with mercury,
chlorinating, cyaniding and other leaching processes, and smelting.
The first is used in alluvial gold and tin workings and in preparing
some silver, copper, and other ores for smelting, and consists merely
in separating the heavier metals and minerals from their gangues by
their greater specific gravity in water. The second includes the
trituration of the gangue and the extraction of its gold or silver by
means of mercury. Chlorinating and leaching generally is a process
whereby metals are first changed by chemical action into their mineral
salts, as chloride of gold, nitrate of silver, sulphate of copper, and
being dissolved in water are afterwards redeposited in the metallic
form by means of well-known re-agents.
In really successful mining it is in the last degree important that
the mode of extraction of metals in the most scientific manner should
be thoroughly understood, but as a general rule the science of
metallurgy is but very superficially grasped even by those whose
special business it is to treat ore bodies in order to extract their
metalliferous contents, and whether in quartz crushing mill,
lixiviating, or smelting works there is much left to be desired in the
method of treating our ores.
My attention was recently attracted to an article written by Mr. F. A.
H. Rauft, M.E., from which I make the following extract:
He says, speaking of the German treatment of ores and the mode of
procedure in Australia, "It is high time that Government stepped in
and endeavoured by prompt and decisive action to bring the mining
industry upon a sound and legitimate basis. Though our ranges abound
in all kinds of minerals that might give employment to hundreds of
thousands of people, mining is carried on in a desultory, haphazard
fashion. There is no system, and the treatment of ores is of necessity
handed over to the tender mercies of men who have not even an idea of
what an intricate science metallurgy has become in older countries.
During many years of practical experience I have never known a single
instance where a lode, on being worked, gave a return according to
assay, and I have never known any mine where some of the precious
metals could not be found in the tailings or slag. The Germans employ
hundreds of men in working for zinc which produces some two or three
per cent to the ton; here the same percentage of tin could hardly be
made payable, and this, mark you, is owing not to cheaper labour
alone, but chiefly to the labour-saving appliances and the results of
the researches of such gigantic intellects as Professor Kerl and many
others, of whom we in this country never even hear. Go into any of the
great mining works of central Germany, and you may see acres covered
by machinery ingeniously constructed to clean, break, and sort, and
ultimately deliver the ores into trucks or direct into the furnace,
and the whole under the supervision of a youngster or two. When a
parcel of ore arrives at any of the works, say Freiberg or Clausthal,
it is carefully assayed by three or four different persons and then
handed over to practical experts, who are expected to produce the full
amount of previous metal according to assay; and if by any chance they
do not, a fixed percentage of the loss is deducted from their salary;
or, if the result is in excess of this assay which is more frequently
the case, a small bonus is added to their pay. Compare this system
with our own wasteful, reckless method of dealing with our precious
metals, and we may hide our heads in very shame."
All really practical men will, I think, endorse Mr. Rauft's opinion.
Well organised and conducted schools of mines will gradually
ameliorate this unsatisfactory state of things, and I hope before long
that we shall have none but qualified certificated men in our mines.
In the meantime a few practical hints, particularly on that very
difficult branch of the subject, the saving of gold, will, it is
hoped, be found of service.
The extraction of gold from the soil is an industry so old that its
first introduction is lost in the mist of ages. As before stated, gold
is one of the most widely disseminated of the metals, and man, so soon
as he had risen from the lowest forms of savagery, began to be
attracted by the kingly metal, which he found to be easily fashioned
into articles of ornament and use, and to be practically non-
corrodable.
What we now term the dish or pan, then, doubtless generally a wooden
bowl, was the appliance first used; but they had also an arrangement,
somewhat like our modern blanket tables, over which the auriferous
sand was passed by means of a stream of water. The sands of some of
the rivers from which portions of the gold supply of the old world was
derived are still washed over year after year in exactly the same
manner as was employed, probably, thousands of years ago, the labour,
very arduous, being often carried on by women, who, standing knee deep
in water, pan off the sand in wooden bowls much as the digger in
modern alluvial fields does with his tin dish. The resulting gold
often consists of but a grain or two of fine dust-gold, which is
carefully collected in quills, and so exported or traded for goods.
The digger of to-day having discovered payable alluvial dirt at such a
depth as to permit of its being profitably worked by small parties of
men with limited or no capital, procures first a half hogshead for a
puddling tub, a "cradle," or "long tom," and tin dish. The "wash
dirt," as the auriferous drift is usually termed, contains a
considerable admixture of clay of a more or less tenacious character,
and the bulk of this has to be puddled and so disintegrated before the
actual separation of the gold is attempted in the cradle or dish. This
is done in the tub by constantly stirring with a shovel, and changing
the water as it becomes charged with the floating argillaceous, or
clayey, particles. The gravel is then placed in the hopper of the
cradle which separates the larger stones and pebbles, the remainder
passing down over inclined ledges as the cradle is slowly rocked and
supplied with water. At the bottom of each ledge is a riffle to arrest
the particles of gold. Sometimes, when the gold is very fine,
amalgamated copper plates are introduced and the lower ledges are
covered with green baize to act as blanket tables and catch gold which
might otherwise be lost.
A long tom is a trough some 12 feet in length by 20 inches in width at
the upper end, widening to 30 inches at the lower end; it is about 9
inches deep and has a fall of 1 inch to a foot. An iron screen is
placed at the lower end where large stones are caught, and below this
screen is the riffle box, 12 feet long, 3 feet wide, and having the
same inclination as the upper trough. It is fitted with several
riffles in which mercury is sometimes placed.
Much more work can be done with this appliance than with the cradle,
which it superseded. Of course, the gold must be coarse and water
plentiful.
When, however, the claim is paying, and the diggings show signs of
some permanency, a puddling machine is constructed. This is described
in the chapter called "Rules of Thumb."
Hydraulicing and ground sluicing is a very cheap and effective method
of treating large quantities of auriferous drift, and, given
favourable circumstances, such as a plentiful supply of water with
good fall and extensive loose auriferous deposits, a very few grains
to the ton or load can be made to give payable returns. The water is
conveyed in flumes, or pipes to a point near where it is required,
thence in wrought iron pipes gradually reduced in size and ending in a
great nozzle somewhat like that of a fireman's hose. The "Monitor," as
it is sometimes called, is generally fixed on a movable stand, so
arranged that the strong jet of water can be directed to any point by
a simple adjustment. A "face" is formed in the drift, and the water
played against the lower portion of the ledge, which is quickly
undermined, and falls only to be washed away in the stream of water,
which is conducted through sluices with riffles, and sometimes over
considerable lengths of amalgamated copper plates. This class of
mining has been most extensively carried out in California and New
Zealand, and some districts of Victoria, but the truly enormous drifts
of the Shoalhaven district in New South Wales must in the near future
add largely to the world's gold supply. These drifts which are
auriferous from grass roots to bed rock extend for nearly fifty miles,
and are in places over 200 feet deep. Want of capital and want of
knowledge has hitherto prevented their being profitably worked on a
large scale.
The extraction of reef gold from its matrix is a much more complicated
process, and the problem how most effectively to obtain that great
desideratum--a complete separating and saving operation--is one which
taxes the skill and evokes the ingenuity of scientific men all over
the world. The difficulty is that as scarcely any two gangues, or
matrixes, are exactly alike, the treatment which is found most
effective on one mine will often not answer in another. Much also
depends on the proportion of gold to the ton of rock under treatment,
as the most scientific and perfect processes of lixiviation hitherto
adopted will not pay, even when all other conditions are favourable,
if the amount of gold is much under half an ounce to the ton and even
then will leave but a very small profit. If, however, the gold is
"free," and the lode large, a very few pennyweights (or "dollars," as
the Americans say) to the ton will pay handsomely. The mode of
extraction longest in vogue, and after all the cheapest and most
effective, for free milling ores where the gold is not too fine, is
amalgamation with mercury, which metal has a strong affinity for gold,
silver, and copper.
As to crushing appliances, I shall not say much. "Their name is legion
for they are many," and the same may be said of concentrators. It may
be old-fashioned, but I admit my predilection is still in favour of
the stamper-battery, for the reason that though it may be slower in
proportion to the power employed, it is simple and not liable to get
out of order, a great advantage when one has so often to depend on men
who bring to their work a supply principally of main strength and
stupidity. For the same reason I prefer the old draw and lift, and
plunger pumps to newer but more complicated water-lifters.
On both these points, however, I am constrained to admit that my
opinion has recently been somewhat shaken.
I have lately seen two appliances which appear to mark a new era in
the scientific progress of mining. One is the "Griffin Mill," the
other the "Lemichel Siphon Elevateur."
The first is in some respects on the principle of the Huntingdon Mill.
The latter, if the inventor may be believed and the results seem to
show he can be, will be a wonderful factor in developing not only
mining properties where a preponderance of water is the trouble, but
also in providing an automatic, and therefore extremely cheap, mode of
water-raising and supply, which in simplicity is thus far unexampled.
Atmospheric pressure alone is relied on. The well-known process of the
syphon is the basis, but with this essential difference, that a large
proportion of the water drawn up to the apex of the syphon is super-
elevated to heights regulated by the fall obtained in the outlet leg.
This elevation can be repeated almost indefinitely by returning the
waste water to the reservoirs.
The Lemichel Syphon is a wonderful, yet most simple application of
natural force. The inlet leg of the syphon is larger in diameter than
the outlet leg, and is provided at the bottom with a valve or "clack."
The outlet leg has a tap at its base. At the apex are two chambers,
with an intermediary valve, regulated by a counterpoise weighted
lever. The first chamber has also a vertical valve and pipe.
When the tap of the outlet leg is turned, the water flows as in an
ordinary syphon, but owing to the rapid automatic opening and shutting
of the valve in the first chamber about 45 per cent of the water is
diverted, and may be raised to a height of many feet above the top of
the syphon.
It need not be impressed on practical men that if this invention will
perform anything like what is claimed for it, its value can hardly be
calculated. After a careful inspection of the appliance in operation,
I believe it will do all that is stated.
Another invention is combined with this which, by a very small
expenditure of fuel, will enable the first point of atmospheric
pressure to be attained. In this way the unwatering of mines may be
very inexpensively effected, or water for irrigation purposes may be
raised from an almost level stream.
The Griffin Mill is a centrifugal motion crusher with one roller only,
which, by an ingenious application of motive force, revolves in an
opposite direction to its initial momentum, and which evolves a force
of 6000 lb. against the tire, which is only 30 inches in diameter. For
hard quartz the size should be increased by at least 6 inches. It is
claimed for this mill that it will pulverise to a gauge of 900 holes
to the square inch from 1 1/2 to 2 1/2 tons per hour, or, say roughly,
150 tons per week.
The Huntingdon mill is a good crusher and amalgamator where the
material to be operated on is comparatively soft, but does not do such
good work when the stone is of a hard flinty nature.
A No. 4 Dodge stone-breaker working about 8 hours will keep a five-
foot Huntingdon mill going 24 hours, and an automatic feeder is
essential. For that matter both are almost essential for an ordinary
stamper battery, and will certainly increase the crushing capacity and
do better work from the greater regularity of the feed.
A 10 h.-p. (nominal) engine of good type is sufficient for Huntingdon
mill, rock breaker, self-feeder and steam pump. A five-foot mill under
favourable circumstances will crush about as much as eight head of
medium weight stamps.
The Grusonwek Ball Mills, made by Krupp of Germany, also that made by
the Austral Otis Company, Melbourne, are fast and excellent crushing
triturating appliances for either wet or dry working, but are
specially suited only for ores when the gold is fine and evenly
distributed in the stone. The trituration is effected by revolving the
stone in a large cylinder together with a number of steel balls of
various sizes, the attrition of which with the rock quickly grinds it
to powder of any required degree of fineness.
More mines have been ruined by bad mill management probably than by
bad mining, though every experienced man must have seen in his time
many most flagrant instances of bungling in the latter respect. Shafts
are often sunk on the wrong side of the lode or too near or too far
away therefrom, while instances have not been wanting where the (mis)
manager has, after sinking his shaft, driven in the opposite direction
to that where the lode should be found.
A common error is that of erecting machinery before there is
sufficient ore in sight to make it certain that enough can be provided
to keep the plant going. In mines at a distance from the centre of
direction it is almost impossible to check mistakes of this
description, caused by the ignorance or over sanguineness of the mine
superintendent, and they are often as disastrous as they are
indefensible. Another fertile source of failure is the craze for
experimenting with untried inventions, alleged to be improvements on
well-known methods.
A rule in the most scientific of card games, whist, is "when in doubt
lead trumps." It might be paraphrased for mining thus: "When in doubt
about machinery use that which has been proved." Let some one else do
the experimenting.
The success of a quartz mine depends as much on favourable working
conditions as on its richness in gold. Thus it may be that a mine
carrying 5 or 6 oz. of gold to the ton but badly circumstanced as to
distance, mountainous roads, lack of wood and water, in some cases a
plethora of the latter, or irregularly faulted country, may be less
profitable than another showing only 5 or 6 dwt., but favourably
situated.
It is usually desirable to choose for the battery site, when possible,
the slope of a hill which consists of rock that will give a good
foundation for your battery.
The economical working depends greatly on the situation, which is
generally fixed more or less, in the proximity of the water. The
advantages of having ample water for battery purposes, or of using
water as a motive power, are so great that it is very often desirable
to construct a tramway of considerable length, when, by so doing, that
power can be utilised; hence most quartz mills are placed near
streams, or in valleys where catchment dams can be effectively
constructed, except, of course, in districts where much water has to
be pumped from the mine.
If water-power can be used, the water-motor will necessarily be placed
as low as possible, in order to obtain the fullest available power.
One point is essential. Special care must be taken to keep the
appliances above the flood-level. If the water in the stream is not
sufficient to carry off the tailings, the battery should be placed at
such a height as to leave sufficient slope for tailings' dumps. This
is more important when treating ore of such value that the tailings
are worth saving for secondary treatment. In this case provision
should be made for tailings, dams, or slime pits.
Whether the battery is worked by water, steam, or gas power, an ample
supply of water is absolutely necessary, at least until some
thoroughly effective mode of dry treatment is established. If it can
be possibly arranged the water should be brought in by gravitation,
and first cost is often least cost; but where this is impossible,
pumps of sufficient capacity, not only to provide the absolute
quantity used, but to meet any emergency, should be erected.
The purer the water the better it will be for amalgamating purposes,
and in cold climates it is desirable to make provision for heating the
water supplied to the battery. This can be done by means of steam from
the boiler led through the feed tanks; but where the boiler power is
not more than required, waste steam from the engine may be employed,
but care must be taken that no greasy matter comes in contact with the
plates. The exhaust steam from the engine may be utilised by carrying
it through tubes fitted in an ordinary 400 gallon tank.
Reducing appliances have often to be placed in districts where the
water supply is insufficient for the battery. When this is so every
available means must be adopted for saving the precious liquid, such
as condensing the exhaust steam from the engine. This may be done by
conducting it through a considerable length of ordinary zinc piping,
such as is used for carrying the water from house roofs. Also tailings
pits should be made, in which the tailings and slimes are allowed to
settle, and the cleared water is pumped back to be again used. These
pits should, where practicable, be cemented. It is usual, also, to
have one or two tailings dams at different levels; the tailings are
run into the upper dam, and are allowed to settle; the slimes overflow
from it into the lower dam, and are there deposited, while the cleared
water is pumped back to the battery. Arrangements are made by which
all these reservoirs can be sluiced out when they are filled with
accumulated tailings. It is well not to leave the sluicing for too
long a period, as when the slimes and tailings are set hard they are
difficult to remove.
Where a permanent reducing plant is to be erected, whatever form of
mill may be adopted, it is better for many reasons to use automatic
ore feeders. Of these the best two I have met are the "Tulloch" and
"Challenge" either of which can be adapted to any mill and both do
good work.
By their use the reducing capacity of the mill is increased, and the
feeding being regular the wear and tear is decreased, while by the
regulated feeding of the "pulp" in the battery box or mortar can be
maintained at any degree of consistency which may be found desirable,
and thus the process of amalgamation will be greatly facilitated. The
only objection which can be urged against the automatic feeder is that
the steel points of picks, gads, drills, and other tools may be
allowed to pass into the mortar or mill, and thus cause considerable
wear and tear. This, I think, can be avoided by the adoption of the
magnet device, described in "Rules of Thumb."
There are many mines where 3 to 4 dwt. of gold cover all the cost, the
excess being clear profit. In fact there are mines which with a yield
of 1 1/2 to 2 dwt. a ton, and crushing with water power, have actually
yielded large profits. On the other hand, mines which have given
extraordinary trial crushings have not paid working expenses.
Everything depends on favourable local conditions and proper
management.
Having decided what class of crushing machinery you will adopt, the
first point is to fix on the best possible site for its erection. This
requires much judgment, as success or failure may largely depend on
the position of your machinery. One good rule is to get your crusher
as reasonably high as possible, as it is cheaper to pump your feed
water a few feet higher so as to get a good clear run for your
tailings, and also to give you room to erect secondary treatment
appliances, such as concentrators and amalgamators below your copper
plates and blanket strakes.
Next, and this is most important, see that your foundations are solid
and strong. A very large number of the failures of quartz milling
plants is due to neglect of this rule.
I once knew a genius who erected a 10-Lead mill in a new district, and
who adopted the novel idea of placing a "bed log" laterally beneath
his stampers. The log was laid in a little cement bed which, when the
battery started, was not quite dry. The effect was comical to every
one but the unfortunate owners. It was certainly the liveliest, but at
the same time one of the most ineffective batteries I have seen.
In a stamp mill the foundations are usually made of hard wood logs
about 5 to 6 feet long, set on end, the bottom end resting on rock and
set round with cement concrete. These are bolted together, and the
"box" or mortar is bolted to them. The horizontal logs to carry the
"horses" or supports for the battery frame should also be of good
size, and solidly and securely bolted. The same applies to your
engine-bed, but whether it be of timber, or mason work, above all
things provide that the whole of your work is set out square and true
to save after-wear and friction.
Considerable difference of opinion exists as to the most effective
weight for stamps. My experience has been that this largely depends on
the nature of your rock, as does also the height for the drop. I have
usually found that with medium stamps, say 7 to 7 1/2 cwt. with fair
drop and lively action, about 80 falls per minute, the best results
were obtained, but the tendency of modern mill men is towards the
heavier stamps, 9 cwt. and even heavier.
To find the horse-power required to drive a battery, multiply the
weight of one stamp by the number of stamps in the battery; the height
of lift in feet by the number of lifts per minute; add one-third of
the product for friction, and the result will be the number of feet-
lbs. per minute; divide this by 33,000 which is the number of feet-
lbs. per minute equal to 1 h.-p. and the result will be the h.-p.
required. Thus if a stamp weighs 800 lb. and you have five in the box,
and each stamp has a lift of 9 in. = 0.75 ft. and strikes 80 blows per
minute, then 800 x 5 x 0.75 x 80 = 240,000; one-third of 240,000 =
80,000 which added to 240,000 = 320,000; and 320,000 divided by 33,000
= 9.7 h.-p. or 1.9 h.-p. each stamp.
The total weight of a battery, including stamper box, stampers, etc.,
may be roughly estimated at about 1 ton per stamp. Medium weight
stampers, including shank cam, disc, head, and shoe, weigh from 600 to
700 lb., and need about 3/4 h.-p. to work them.
The quantity of water required for the effective treatment of gold-
bearing rock in a stamper battery varies according to the composition
of the material to be operated upon, but generally it is more than the
inexperienced believe. For instance, "mullocky" lode stuff, containing
much clayey matter or material carrying a large percentage of heavy
metal, such as titanic iron or metallic sulphides, will need a larger
quantity of water per stamp than clean quartz. A fair average quantity
would be 750 to 1000 gallons per hour for each box of five stamps. In
general practice I have seldom found 1000 gallons per hour more than
sufficient.
As to the most effective mesh for the screen or grating no definite
rule can be given, as that depends so largely on the size of the gold
particles contained in the gangue. The finer the particles the closer
must be the mesh, and nothing but careful experiment will enable the
battery manager to decide this most important point. The American
slotted screens are best; they wear better than the punched gratings
and can be used of finer gauge. Woven steel wire gauze is employed
with good effect in some mills where especially fine trituration is
required. This class of screen requires special care as it is somewhat
fragile, but with intelligent treatment does good work.
The fall or inclination of the tables, both copper and blanket
strakes, is also regulated by the class of ore. If it should be heavy
then the fall must be steeper. A fair average drop is 3/4 inch to the
foot. Be careful that your copper tables are thoroughly water-tight,
for remember you are dealing with a very volatile metal, quicksilver;
and where water will percolate mercury will penetrate.
The blanket tables are simply a continuation of the mercury tables,
but covered with strips of coarse blanket, green baize, or other
flocculent material, intended to arrest the heavier metallic particles
which, owing to their refractory nature, have not been amalgamated.
The blanket table is, however, a very unsatisfactory concentrator at
best, and is giving place to mechanical concentrators of various
descriptions.
An ancient Egyptian gold washing table was used by the Egyptians in
treating the gold ores of Lower Egypt. The ore was first ground, it is
likely by means of some description of stone arrasts and then passed
over the sloping table with water, the gold being retained in the
riffles. In these the material would probably be mechanically
agitated. Although for its era ingenious it will be plain to practical
men that if the gold were fine the process would be very ineffective.
Possibly, but of this I have no evidence, mercury was used to retain
the gold on the riffles, as previously stated. This method of saving
the precious metal was known to the ancients.
At a mine of which I was managing director the lode was almost
entirely composed of sulphide of iron, carbonate of lime or calcspar,
with a little silica. In this case it has been found best to crush
without mercury, then run the pulp into pans, where it is
concentrated. The concentrates are calcined in a common reverberatory
furnace, and afterwards amalgamated with mercury in a special pan, the
results as to the proportion of gold extracted being very
satisfactory; but it does not therefore follow that this process would
be the most suitable in another mine where the lode stuff, though in
some respects similar, yet had points of difference.
I was lately consulted with respect to the treatment of a pyritic ore
in a very promising mine, but could not recommend the above treatment,
because though the pyrites in the gangue was similar, the bulk of the
lode consisted of silica, consequently there would be a great waste of
power in triturating the whole of the stuff to what, with regard to
much of it, would be an unnecessary degree of fineness. I am of
opinion that in cases such as this, where it is not intended to adopt
the chlorination or cyanogen process, it will be found most economical
to crush to a coarse gauge, concentrate, calcine the concentrates, and
finally amalgamate in some suitable amalgamator.
Probably for this mode of treatment Krom rolls would be found more
effective reducing agents than stampers, as with them the bulk of the
ore can be broken to any required gauge and there would consequently
be less loss in "slimes."
The great art in effective battery work is to crush your stuff to the
required fineness only, and then to provide that each particle is
brought into contact with the mercury either in box, trough, plate, or
pan. To do this the flow of water must be carefully regulated; neither
so much must be used as to carry the stuff off too quickly nor so
little as to cause the troughs and plates to choke. In cold weather
the water may be warmed by passing the feed-pipe through a tank into
which the steam from the engine exhausts, and this will be found to
keep the mercury bright and lively. But be careful no engine oil or
grease mingles with the water, as grease on the copper tables will
absolutely prevent amalgamation.
The first point, then, is to crush the gangue effectively, the degree
of fineness being regulated by the fineness of the gold itself. This
being done, then comes the question of saving the gold. If the quartz
be clean, and the gold unmixed with base metal, the difficulty is
small. All that is required is to ensure that each particle of the
Royal metal shall be brought into contact with the mercury. The main
object is to arrest the gold at the earliest possible stage;
therefore, if you are treating clean stone containing free gold,
either coarse or fine, I advise the use of mercury in the boxes, for
the reason that a considerable proportion of the gold will be caught
thereby, and settling to the bottom, or adhering to amalgamated plates
in the boxes, where such are used, will not be afterwards affected by
the crushing action, which might otherwise break up, or "flour," the
mercury. On the whole, I rather favour the use of mercury in the box
at any time, unless the ore is very refractory--that is, contains too
great a proportion of base metals, particularly sulphides of iron,
arsenic, etc., when the result will not be satisfactory, but may
entail great loss by the escape of floured mercury carrying with it
particles of gold. Here only educated intelligence, with experience,
will assist the battery manager to adopt the right system.
The crushed stuff--generally termed the "pulp"--passes from the boxes
through the "screens" or "gratings," and so on to the "tables"--i.e.,
sheets of copper amalgamated on the upper surface with mercury, and
sometimes electroplated with silver and afterwards treated with
mercury. Unless the quartz is very clean, and, consequently light, I
am opposed to the form of stamper box with mercury troughs cast in the
"lip," nor do I think that a trough under the lip is a good
arrangement, as it usually gets so choked and covered with the heavy
clinging base metals as to make it almost impossible for the gold to
come in contact with the mercury. It will be found better where the
gold is fine, or the gangue contains much base metal, to run the pulp
from the lip of the battery into a "distributor."
The distributor is a wooden box the full width of the "mortar," having
a perforated iron bottom set some three to four inches above the first
copper plate, which should come up under the lip. The effect of this
arrangement is that the pulp is dashed on the plate by the falling
water, and the gold at once coming in contact with the mercury begins
to accumulate and attract that which follows, till the amalgam becomes
piled in little crater-shaped mounds, and thus 75 per cent of the gold
is saved on the top plate.
I have tried a further adaptation of this process when treating ores
containing a large percentage of iron oxide, where the bulk of the
gold is impalpably fine, and contained in the "gossan." At the end of
the blanket table, or at any point where the crushed stuff last passes
before going to the "tailings heap," or "sludge pit," a "saver" is
placed. The saver is a strong box about 15 in. square by 3 ft. high,
one side of which is removable, but must fit tight. Nine slots are cut
inside at 4 in. apart, and into these are fitted nine square
perforated copper plates, having about eighty to a hundred 1/4 in.
holes in each; the perforations should not come opposite each other.
These plates are to be amalgamated on both sides with mercury, in
which a very little sodium has been placed (if acid ores are being
treated, zinc should be employed in place of sodium, and to prevent
the plates becoming bare, if the stuff is very poor, thick zinc
amalgam may be used with good effect; but in that case discontinue the
sodium, and occasionally, if required, say once or twice in the day,
mix an ounce of sulphuric acid in a quart of water and slowly pour it
into the launder above the saver). Underneath the "saver" you require
a few riffles, or troughs, to catch any waste mercury, but if not
overfed there should be no waste. This simple appliance, which is
automatic and requires little attention, will sometimes arrest a
considerable quantity of gold.
We now come to the subsidiary processes of battery work, the
"cleaning" of plates, and "scaling" same when it is desired to get all
the gold off them, the cleaning and retorting of amalgam, and of the
mercury, smelting gold, etc.
Plates should be tenderly treated, kept as smooth as possible, and
when cleaning up after crushing, in your own battery, the amalgam--
except, say, at half-yearly intervals--should be removed with a rubber
only; the rubber is simply a square of black indiarubber or soft pine
wood.
When crushing rich ore, and you want to get nearly all the gold off
your plates, the scraper may be resorted to. This is usually made by
the mine blacksmith from an old flat file which is cut in half, the
top turned over, beaten out to a sharp blade, and kept sharp by
touching it up on the grinding-stone. This, if carefully used, will
remove the bulk of the amalgam without injury to the plate.
Various methods of "scaling" plates will be found among "Rules of
Thumb."
Where base metals are present in the lode stuff frequent retortings of
the mercury, say not less than once a month, will be found to have a
good effect in keeping it pure and active. For this purpose, and in
order to prevent stoppage of the machinery, a double quantity is
necessary, so that half may be used alternately. Less care is required
in retorting the mercury than in treating the amalgam, as the object
in the one case is more to cleanse the metal of impurities than to
save gold, which will for the most part have been extracted by
squeezing through the chamois leather or calico. A good strong heat
may therefore at once be applied to the retort and continued, the
effect being to oxidise the arsenic, antimony, lead, etc., which, in
the form of oxides, will not again amalgamate with the mercury, but
will either lie on its surface under the water, into which the nozzle
of the retort is inserted, or will float away on the surface of the
water. I have also found that covering the top of the mercury with a
few inches of broken charcoal when retorting has an excellent
purifying effect.
In retorting amalgam, much care and attention is required.
First, never fill the retort too full, give plenty of room for
expansion; for, when the heat is applied, the amalgam will rise like
dough in an oven, and may be forced into the discharge pipe, the
consequence being a loss of amalgam or the possible bursting of the
retort. Next, be careful in applying the heat, which should be done
gradually, commencing at the top. This is essential to prevent waste
and to turn out a good-looking cake of gold, which all battery
managers like to do, even if they purpose smelting into bars.
Sometimes special difficulties crop up in the process of separating
the gold from the amalgam. At the first "cleaning up" on the Frasers
Mine at Southern Cross, West Australia, great consternation was
excited by the appearance of the retorted gold, which, as an old miner
graphically put it, was "as black as the hind leg of a crow," and
utterly unfit for smelting, owing to the presence of base metals. Some
time after this I was largely interested in the Blackborne mine in the
same district when a similar trouble arose. This I succeeded in
surmounting, but a still more serious one was too much for me--i.e.,
the absence of payable gold in the stone. I give here an extract from
the /Australian Mining Standard/, of December 9th, 1893, with
reference to the mode of cleaning the amalgam which I adopted.
NEW METHOD OF SEPARATING GOLD FROM IMPURE AMALGAM.
I had submitted to me lately a sample of amalgam from a mine in West
Australia which amalgam had proved a complete puzzle to the manager
and amalgamator. The Mint returns showed a very large proportion of
impurity, even in the smelted gold. When retorted only, the Mint
authorities refused to take it after they had treated two cakes, one
of 119 oz., which yielded only 35 oz. 5 dwt. standard gold, and one of
140 oz., which gave 41 oz. 10 dwt. The gold smelted on the mine was
nearly as bad proportionately. Thus, 128 oz. smelted down at the Mint
to 87 oz. 8 dwt. and 109 oz. to 55 oz. 10 dwt. The impurity was
principally iron, a most unusual thing in my experience, and was due
to two causes revealed by assay of the ore and analysis of the mine
water, viz., an excess of arsenate of iron in the stone, and the
presence in large proportions of mineral salts, principally chloride
of Calcium CaCl., sodium NaCl, and magnesium MgCl2, in the mine water
used in the battery. The exact analysis of the water was as follows:--
Carbonate of Iron FeCO3 2.76 grains per gallon
Carbonate of Calcium CaCO3 7.61 grains per gallon
Sulphate of Calcium CaSO4 81.71 grains per gallon
Chloride of Calcium CaCl2 2797.84 grains per gallon
Chloride of Magnesium MgCl2 610.13 grains per gallon
Chloride of Sodium or
Common Salt NaCl 5072.65 grains per gallon
Total solid matter 8572.70 = 19.5 oz. to the gallon.
It will be seen, then, that this water is nearly four times more salt
that that of the sea. The effect of using a water of this character,
as I have previously found, is to cause the amalgamation of
considerable quantities of iron with the gold as in this case.
I received 10 oz. of amalgam, and having found what constituted its
impurities proceeded to experiment as to its treatment. When retorted
on the mine it was turned out in a black cake so impure as almost to
make it impossible to smelt properly. I found the same result on first
retorting, and after a number of experiments which need not be
recapitulated though some were fairly effective, I hit on the
following method, which was found to be most successful and will
probably be so found in other localities where similarly unfavourable
conditions prevail.
I took a small ball of amalgam, placed it in a double fold of new fine
grained calico, and after soaking in hot water put it under a powerful
press. The weight of the ball before pressing was 1583 gr. From this
383 gr. of mercury was expressed and five-eighths of a grain of gold
was retorted from this expressed mercury. The residue, in the form of
a dark, grey, and very friable cake, was powdered up between the
fingers and retorted, when it became a brown powder; it was afterwards
calcined on a flat sheet in the open air; result, 510 gr. of russet-
coloured powder. Smelted with borax, the iron oxide readily separated
with the slag; result, 311 gr. gold 871-1000 fine; a second smelting
brought this up to 914-1000 fine. Proportion of smelted gold to
amalgam, one-fifth.
The principal point about this mode of treatment is the squeezing out
of the mercury, whereby the amalgam goes into the retort in the form
of powder, thus preventing the slagging of the iron and enclosure of
the gold. The second point of importance is thorough calcining before
smelting.
Of course it would be practicable, if desired, to treat the powder
with hydrochloric acid, and thus remove all the iron, but in a large
way this would be too expensive, and my laboratory treatment, though
necessarily on a small scale, was intended to be on a practical basis.
The amalgam at this mine was in this way afterwards treated with great
success.
For the information of readers who do not understand the chemical
symbols it may be said that
FeCO3 is carbonate of iron;
CaCO3 is carbonate of calcium;
CaSO4 is sulphate of calcium;
CaCl2 is chloride of calcium;
MgCl2 is chloride of magnesium;
NaCl is chloride of sodium, or common salt.
CHAPTER VII
GOLD EXTRACTION--SECONDARY PROCESSES AND LIXIVIATION
Before any plan is adopted for treating the ore in a new mine the
management should very seriously and carefully consider the whole
circumstances of the case, taking into account the quantity and
quality of the lode stuff to be operated on, and ascertain by analysis
what are its component parts, for, as before stated, the treatment
which will yield most satisfactory results with a certain class of
gangue on one mine will sometimes, even when the material is
apparently similar, prove a disastrous failure in another. Some time
since I was glad to note that the manager of a prominent mine strongly
discountenanced the purchase of any extracting plant until he was
fully satisfied as to the character of the bulk of the ore he would
have to treat. It would be well for the pockets of shareholders and
the reputation of managers, if more of our mine superintendents
followed this prudent and sensible course.
Having treated on gold extraction with mercury by amalgamated plates
and their accessories, something must be said about secondary modes of
saving in connection with the amalgamation process. The operations
described hitherto have been the disintegration of the gold-bearing
material and the extraction therefrom of the coarser free gold. But it
must be understood that most auriferous lode stuff contains a
proportion of sulphides of various metals, wherein a part of the gold,
usually in a very finely divided state, is enclosed, and on this gold
the mercury has no influence. Also many lodes contain hard heavy
ferric ores, such as titanic iron, tungstate of iron, and hematite, in
which gold is held. In others, again, are found considerable
quantities of soft powdery iron oxide or "gossan," and compounds such
as limonite, aluminous clay, etc., which, under the action of the
crushing mill become finely divided and float off in water as
"slimes," carrying with them atoms of gold, often microscopically
small. To save the gold in such matrixes as these is an operation
which even the best of our mechanical appliances have not yet fully
accomplished.
Where there is not too great a proportion of base metals on which the
solvent will act, and when the material is rich enough in gold to pay
for the extra cost of treatment, chlorination or cyanisation are the
best modes of extraction yet practically adopted.
Presuming, however, that we are working by the amalgamation process,
and have crushed our stone and obtained the free gold, the next
requirement is an effective concentrator. Of these there are many
before the public, and some do excellent work, but do not act equally
well in all circumstances. The first and most primitive is the blanket
table, previously mentioned; but it can hardly be said to be very
effective, and requires constant attention and frequent changing and
washing of the strips of blanket.
Instead of blanket tables percussion tables are sometimes used, to
which a jerking motion is given against the flow of the water and
pulp, and by this means the heavier minerals are gathered towards the
upper part of the table, and are from thence removed from time to time
as they become concentrated.
I have seen this appliance doing fairly good work, but it is by no
means a perfect concentrator.
Another form of "shaking table" is one in which the motion is given
sideways, and this, whether amalgamated, or provided with small
riffles, or covered with blanket, keeps the pulp lively and encourages
the retention of the heavier particles, whether of gold or base metals
containing gold. There has also been devised a rocking table the
action of which is analogous to that of the ordinary miner's cradle.
This appliance, working somewhat slowly, swings on rockers from side
to side, and is usually employed in mills where, owing to the
complexity of the ore, difficulties have been met with in amalgamating
the gold. Riffles are provided and even very fine gold is sometimes
effectively recovered by their aid.
The Frue vanner will, as a rule, act well when the pulp is
sufficiently fine. It is really a adaptation of an old and simple
apparatus used in China and India for washing gold dust from the sands
of rivers. The original consisted of an endless band of strong cloth
or closely woven matting, run on two horizontal rollers placed about
seven feet apart, one being some inches lower than the other. The
upper is caused to revolve by means of a handle. The cloth is thus
dragged upwards against a small stream of water and sand fed to it by
a second man, the first man not only turning the handle but giving a
lateral motion to the band by means of a rope tied to one side.
Chinamen were working these forerunners of the Frue vanner forty years
ago in Australia, and getting fair returns.
The Frue vanner is an endless indiarubber band drawn over an inclined
table, to which a revolving and side motion is given by ingenious
automatic mechanism, the pulp being automatically fed from the upper
end, and the concentrates collected in a trough containing water in
which the band is immersed in its passage under the table; the lighter
particles wash over the lower end. The only faults with the vanner are
--first, it is rather slow; and secondly, though so ingenious it is
just a little complicated in construction for the average non-
scientific operative.
Of pan concentrators there is an enormous selection, the principle in
most being similar--i.e., a revolving muller, which triturates the
sand, so freeing the tiny golden particles and admitting of their
contact with the mercury. The mistake with respect to most of these
machines is the attempt to grind and amalgamate in one operation. Even
when the stone under treatment contains no deleterious compounds the
simple action of grinding the hard siliceous particles has a bad
effect on the quicksilver, causing it to separate into small globules,
which either oxidising or becoming coated with the impurities
contained in the ore will not reunite, but wash away in the slimes and
take with them a percentage of the gold. As a grinder and
concentrator, and in some cases as an amalgamator, when used
exclusively for either purpose, the Watson and Denny pan is effective;
but although successfully used at one mine I know, the mode there
adopted would, for reasons previously given, be very wasteful in many
other mines.
There is considerable misconception, even among men with some
practical knowledge, as to the proper function of these secondary
saving appliances; and sometimes good machines are condemned because
they will not perform work for which they were never intended. It
cannot be too clearly realized that the correct order of procedure for
extracting the gold held in combination with base metals is--first,
reduction of the particles to a uniform gauge and careful
concentration only; next, the dissipation, usually by simple
calcination, of substances in the concentrates inimical to the
thorough absorption of the gold by the mercury; and lastly, the
amalgamation of the gold and mercury.
For general purposes, where the gangue has not been crushed too fine,
I think the Duncan pan will usually be found effective in saving the
concentrates. In theory it is an enlargement of the alluvial miner's
tin dish, and the motion imparted to it is similar to the eccentric
motion of that simple separator.
The calcining may be effectively carried out in an ordinary
reverberatory furnace, the only skill required being to prevent over
roasting and so slagging the concentrates; or not sufficiently
calcining so as to remove all deleterious constituents; the subject,
however, is fully treated in Chapter VIII.
For amalgamating I prefer some form of settler to any further grinding
appliance, but I note also improvements in the rotary amalgamating
barrel, which, though slow, is, under favourable conditions, an
effective amalgamator. The introduction of steam under pressure into
an iron cylinder containing a charge of concentrates with mercury is
said to have produced good results, and I am quite prepared to believe
such would be the case, as we have long known that the application of
steam to ores in course of amalgamation facilitates the process
considerably.
Some seventeen years since I was engaged on the construction of a dry
amalgamator in which sublimated mercury was passed from a retort
through the descending gangue in a vertical cylinder, the material
thence falling through an aperture into a revolving settler, the
object being to save water on mines in dry country. The model, about
quarter size, was completed when my attention was called to an
American invention, in which the same result was stated to be attained
more effectively by blowing the mercury spray through the triturated
material by means of a steam jet. I had already encountered a
difficulty, since found so obstructive by experimentalists in the same
direction, that is, the getting of the mercury back into its liquid
metallic form. This difficulty I am now convinced can be largely
obviated by my own device of using a very weak solution of sulphuric
acid (it can hardly be too weak) and adding a small quantity of zinc
to the mercury. It is perfectly marvellous how some samples of mercury
"sickened" or "floured" by bad treatment, may be brought back to the
bright limpid metal by a judicious use of these inexpensive materials.
Thus it will probably be found practicable to crush dry and amalgamate
semi-dry by passing the material in the form of a thin pasty mass to a
settler, as in the old South American arrastra, and, by slowly
stirring, recover the mercury, and with it the bulk of the gold.
The following is from the /Australian Mining Standard/, and was headed
"Amalgamation Without Overflow":
"Recent experiments at the Ballarat School of Mines have proved that a
deliverance from difficulties is at hand from an unexpected quarter.
The despised Chilian mill and Wheeler pan, discarded at many mines,
will solve the problem, but the keynote of success is amalgamation
without overflow. Dispense with the overflow and the gold is saved.
"Two typical mines--the Great Mercury Proprietary Gold Mine, of
Kuaotunu, N.Z., the other, the Pambula, N.S.W.--have lately been
conducting a series of experiments with the object of saving their
fine gold in an economical manner. The last and best trials made by
these companies were at the Ballarat School of Mines, where
amalgamation without overflow was put to a crucial test, in each case
with the gratifying result that ninety-six per cent of the precious
metal was secured. What this means to the Great Mercury Mine, for
instance, can easily be imagined when it is understood that
notwithstanding all the latest gold-saving adjuncts during the last
six months 1260 tons of ore, worth 4l. 17s. 10 2/3d. a ton, have been
put through for a saving of 1l. 9s. 1 2/3d. only; or in other words
over two-thirds of the gold has gone to waste (for the time being) in
the tailings, and in the tailings at the present moment lie the
dividends that should have cheered shareholders' hearts.
"And now for the /modus operandi/, which, it must be remembered, is
not hedged in by big royalties to any one, rights, patent or
otherwise. The ore to be treated is first calcined, then put through a
rock-breaker or stamper battery in a perfectly dry state. If the
battery is used, ordinary precautions, of course, must be taken to
prevent waste, or the dust becoming obnoxious to the workmen. The ore
is then transferred to the Chilian mill and made to the consistency of
porridge, the quicksilver being added. When the principal work of
amalgamation is done (experience soon teaching the amount of grinding
necessary), from the Chilian mill the paste (so to say) is passed to a
Wheeler or any other good pan of a similar type, when the gold-saving
operation is completed."
This being an experiment in the same direction as my own, I tried it
on a small scale. I calcined some very troublesome ore till it was
fairly "sweet," triturated it, and having reduced it with water to
about the consistency of invalid's gruel, put it into a little berdan
pan made from a "camp oven," which I had used for treating small
quantities of concentrates, and from time to time drove a spray of
mercury, wherein a small amount of zinc had been dissolved, into the
pasty mass by means of a steam jet, added about half an ounce of
sulphuric acid and kept the pan revolving for several hours. The
result was an unusually successful amalgamation and consequent
extraction--over ninety per cent.
Steam--or to use the scientific term, hydro-thermal action--has played
such an important part in the deposition of metals that I cannot but
think that under educated intelligence it will prove a powerful agent
in their extraction. About fourteen years ago I obtained some rather
remarkable results from simply boiling auriferous ferro-sulphides in
water. There is in this alone an interesting, useful, and profitable
field for investigation and experiment.
The most scientific and perfect mode of gold extraction (when the
conditions are favourable) is lixiviation by means of chlorine,
potassium cyanide, or other aurous solvent, for by this means as much
as 98 per cent of the gold contained in suitable ores can be converted
into its mineral salt, and being dissolved in water, re-deposited in
metallic form for smelting; but lode stuff containing much lime would
not be suitable for chlorination, or the presence of a considerable
proportion of such a metal as copper, particularly in metallic form,
would be fatal to success, while cyanide of potassium will also attack
metals other than gold, and hence discount the effect of this solvent.
The earlier practical applications of chlorine to gold extraction were
known as Mears' and Plattner's processes, and consisted in placing the
material to be operated on in vats with water, and introducing
chlorine gas at the bottom, the mixture being allowed to stand for a
number of hours, the minimum about twelve, the maximum forty-eight.
The chlorinated water was then drawn off containing the gold in
solution which was deposited as a brown powder by the addition of
sulphate of iron.
Great improvements on this slow and imperfect method have been made of
late years, among the earlier of which was that of Messrs. Newbery and
Vautin. They placed the pulp with water in a gaslight revolving
cylinder, into which the chlorine was introduced, and atmospheric air
to a pressure of 60 lb. to the square inch was pumped in. The cylinder
with its contents was revolved for two hours, then the charge was
withdrawn and drained nearly dry by suction, the resultant liquid
being slowly filtered through broken charcoal on which the chloride
crystals were deposited, in appearance much like the bromo-chlorides
of silver ore seen on some of the black manganic oxides of the Barrier
silver mines. The charcoal, with its adhering chlorides, was conveyed
to the smelting-house and the gold smelted into bars of extremely pure
metal. Messrs. Newbery and Vautin claimed for their process decreased
time for the operation with increased efficiency.
At Mount Morgan, when I visited that celebrated mine, they were using
what might be termed a composite adaptation process. Their
chlorination works, the largest in the world, were putting through
1500 tons per week. The ore as it came from the mine was fed
automatically into Krom roller mills, and after being crushed and
sifted to regulation gauge was delivered into trucks and conveyed to
the roasting furnaces, and thence to cooling floors, from which it was
conveyed to the chlorinating shed. Here were long rows of revolving
barrels, on the Newbery-Vautin principle, but with this marked
difference, that the pressure in the barrel was obtained from an
excess of the gas itself, generated from a charge of chloride of lime
and sulphuric acid. On leaving the barrels the pulp ran into settling
vats, somewhat on the Plattner plan, and the clear liquid having been
drained off was passed through a charcoal filter, as adopted by
Newbery and Vautin. The manager, Mr. Wesley Hall, stated that he
estimated cost per ton was not more than 30s., and he expected shortly
to reduce that when he began making his own sulphuric acid. As he was
obtaining over 4 oz. to the ton the process was paying very well, but
it will be seen that the price would be prohibitive for poor ores
unless they could be concentrated before calcination.
The Pollok process is a newer, and stated to be a cheaper mode of
lixiviation by chlorine. It is the invention of Mr. J. H. Pollok, of
Glasgow University, and a strong Company was formed to work it. With
him the gas is produced by the admixture of bisulphate of sodium
(instead of sulphuric acid, which is a very costly chemical to
transport) and chloride of lime. Water is then pumped into a strong
receptacle containing the material for treatment and powerful
hydraulic pressure is applied. The effect is stated to be the rapid
change of the metal into its salt, which is dissolved in the water and
afterwards treated with sulphate of iron, and so made to resume its
metallic form.
It appears, however, to me that there is no essential difference in
the pressure brought to bear for the quickening of the process. In
each case it is an air cushion, induced in the one process by the
pumping in of air to a cylinder partly filled with water, and in the
other by pumping in water to a cylinder partly filled with air.
The process of extracting gold from lode stuff and tailings by means
of cyanide of potassium is now largely used and may be thus briefly
described:--It is chiefly applied to tailings, that is, crushed ore
that has already passed over the amalgamating and blanket tables. The
tailings are placed in vats, and subjected to the action of solutions
of cyanide of potassium of varying strengths down to 0.2 per cent.
These dissolve the gold, which is leached from the tailings, passed
through boxes in which it is precipitated either by means of zinc
shavings, electricity, or to the precipitant. The solution is made up
to its former strength and passed again through fresh tailings. When
the tailings contain a quantity of decomposed pyrites, partly
oxidised, the acidity caused by the freed sulphuric acid requires to
be neutralised by an alkali, caustic soda being usually employed.
When "cleaning up," the cyanide solution in the zinc precipitating
boxes is replaced by clean water. After careful washing in the box, to
cause all pure gold and zinc to fall to the bottom, the zinc shavings
are taken out. The precipitates are then collected, and after
calcination in a special furnace for the purpose of oxidising the
zinc, are smelted in the usual manner.
The following description of an electrolytic method of gold deposition
from a cyanide solution was given by Mr. A. L. Eltonhead before the
Engineers' Club of Philadelphia.
A description of the process is as follows:--"The ore is crushed to a
certain fineness, depending on the character of the gangue. It is then
placed in leaching vats, with false bottoms for filtration, similar to
other leaching plants. A solution of cyanide of potassium and other
chemicals of known percentage is run over the pulp and left to stand a
certain number of hours, depending on the amount of metal to be
extracted. It is then drained off and another charge of the same
solution is used, but of less strength, which is also drained. The
pulp is now washed with clean water, which leaches all the gold and
silver out, and leaves the tailings ready for discharge, either in
cars or sluiced away by water, if it is plentiful.
"The chemical reaction of cyanide of potassium with gold is as
follows, according to Elsner:--
2Au + 4KCy + O + H2O = 2KAuCy2 + 2KHO.
That is, a double cyanide of gold and potassium is formed.
"All filtered solutions and washings from the leaching vats are saved
and passed through a precipitating 'box' of novel construction, which
may consist either of glass, iron or wood, and be made in any shape,
either oval, round, or rectangular--if the latter, it will be about 10
ft. long, 4 ft. wide and 1 ft. high--and is partitioned off lengthwise
into five compartments. Under each partition, on the inside or bottom
of the 'box,' grooves may be cut a quarter- to a half-inch deep,
extending parallel with the partitions to serve as a reservoir for the
amalgam, and give a rolling motion to the solution as it passes along
and through the four compartments. The centre compartment is used to
hold the lead or other suitable anode and electrolyte.
"The anode is supported on a movable frame or bracket, so it may be
moved either up or down as desired, it being worked by thumb-screws at
each end.
"The electrolyte may consist of saturated solutions of soluble
alkaline metals and earth. The sides or partitions of each compartment
dip into the mercury, which must cover the 'box' evenly on the bottom
to the depth of about a half-inch.
"Amalgamated copper strips or discs are placed in contact with the
mercury and extended above it, to allow the gold and silver solution
of cyanide to come in contact.
"The electrodes are connected with the dynamo; the anode of lead being
positive and the cathode of mercury being negative. The dynamo is
started, and a current of high amperage and low voltage is generated,
generally 100 to 125 amperes, and with sufficient pressure to
decompose the electrolyte between the anode and the cathode.
"As the gas is generated at the anode, a commotion is created in the
liquid, which brings a fresh and saturated solution of electrolyte
between the electrodes for electrolysis, and makes it continuous in
its action.
"The solution of double cyanide of gold, silver, and potassium, which
has been drained from the leaching vats, is passed over the mercury in
the precipitating 'box' when the decomposition of the electrolyte by
the electric current is being accomplished, the gold and silver are
set free and unite with the mercury, and are also deposited on the
plates or discs of copper, forming amalgam, which is collected and
made marketable by the well known and tried methods. The above
solution is regenerated with cyanide of potassium by the setting free
of the metals in the passage over the 'box.'
"In using this solution again for a fresh charge of pulp, it is
reinforced to the desired percentage, or strengthened with cyanide of
potassium and other chemicals, and is always in good condition for
continuing the operation of dissolving.
"The potassium acting on the water of the solution creates nascent
hydrogen and potassium hydrate; the nascent hydrogen sets free the
metals (gold and silver), which are precipitated into the mercury and
form amalgam, leaving hydrocyanic acid; this latter combines with the
potassium hydrate of the former reaction, thus forming cyanide of
potassium. There are other reactions for which I have not at present
the chemical formulas.
"As the solution passes over the mercury, the centre compartment of
the 'box' is moved slowly longitudinally, which spreads the mercury,
the solution is agitated and comes in perfect contact with the
mercury, as well as the amalgamated plates or discs of copper,
ensuring a perfect precipitation.
"It is not always necessary to precipitate all the gold and silver
from the solution, for it is used over and over again indefinitely;
but when it is required, it can be done perfectly and cheaply in a
very short time.
"No solution leached from the pulp, containing cyanide of potassium,
gold and silver, need be run to waste, which is in itself an enormous
saving over the use of zinc shavings when handling large quantities of
pulp and solution.
"Some of the advantages the electro-chemical process has over other
cyanide processes are: Its cleanliness, quickness of action,
cheapness, and large saving of cyanide of potassium by regeneration;
not wasting the solutions, larger recovery of the gold and silver from
the solutions; the cost of recovery less; the loss of gold, silver,
and cyanide of potassium reduced to a minimum; the use of caustic
alkali in such quantity as may be desired to keep the cyanide solution
from being destroyed by the solidity of the pulp, and also sometimes
to give warmth, as a warm cyanide solution will dissolve gold and
silver quicker than a cold one. These caustic alkalies do not
interfere with or prevent the perfect precipitation of the metals. The
bullion recovered in this process is very fine, while the zinc-
precipitated bullion is only about 700 fine.
"The gold and silver is dissolved, and then precipitated in one
operation, which we know cannot be done in the 'chlorination process';
besides, the cost of plant and treatment is much less in the above-
described process.
"The electro-chemical process, which I have hastily sketched will, I
think, be the future cheap method of recovering fine or flour gold
from our mines and waste tailings or ore dumps.
"Without going into details of cost of treatment, I will state that
with a plant of a capacity of handling 10,000 tons of pulp per month,
the cost should not exceed 8s. per ton, but that may be cheapened by
labour-saving devices. There being no expensive machinery, a plant
could be very cheaply erected wherever necessary."
CHAPTER VIII
CALCINATION OR ROASTING OF ORES
The object of calcining or roasting certain ores before treatment is
to dissipate the sulphur or sulphides of arsenic, antimony, lead,
etc., which are inimical to treatment, whether by ordinary mercuric
amalgamation or lixiviation. The effect of the roasting is first to
sublimate and drive off as fumes the sulphur and a proportion of the
objectionable metals. What is left is either iron oxide, "gossan," or
the oxides of the other metals. Even lead can thus be oxidised, but
requires more care as it melts nearly as readily as antimony and is
much less volatile. The oxides in the thoroughly roasted ore will not
amalgamate with mercury, and are not acted on by chlorine or cyanogen.
To effect the oxidation of sulphur, it is necessary not only to bring
every particle of sulphur into contact with the oxygen of the air, but
also to provide adequate heat to the particles sufficient to raise
them to the temperature that will induce oxidation. No appreciable
effect follows the mere contact of air with sulphur particles at
atmospheric temperature; but if the particles be raised to a
temperature of 500 degrees Fahr., the sulphur is oxidised to the
gaseous sulphur dioxide. The same action effects the elimination of
the arsenic and antimony associated with gold and silver ores, as when
heated to a certain constant temperature these metals readily oxidise.
The science of calcination consists of the method by which the
sulphide ores, having been crushed to a proper degree of fineness, are
raised to a sufficient temperature and brought into intimate contact
with atmospheric air.
It will be obvious then that the most effective method of roasting
will be one that enables the particles to be thoroughly oxidised at
the lowest cost in fuel and in the most rapid manner.
The roasting processes in practical use may be divided into three
categories:
/First or A Process./--Roasting on a horizontal and stationary hearth,
the flame passing over a mass of ore resting on such hearth. In order
to expose the upper surface of the ore to contact with air the
material is turned over by manual labour. This furnace of the
reverberatory type is provided with side openings by which the turning
over of the ore can be manually effected, and the new ore can be
charged and afterwards withdrawn.
/Second or B Process./--Roasting in a revolving hearth placed at a
slight incline angle from the horizontal. The furnace is of
cylindrical form and is internally lined with refractory material. It
has projections that cause the powdered ore to be lifted above the
flame, and, at a certain height, to fall through the flame and so be
rapidly raised to the temperature required to effect the oxidation of
the oxidisable minerals which it is desired to extract.
The rate, or speed, of revolution of this revolving furnace obviously
depends upon the character of the ore under treatment; it may vary
from two revolutions per minute down to one revolution in thirty
minutes. Any kind of fuel is available, but that of a gaseous
character is stated to be by far the most efficient.
Any ordinary cylinder of a length of 25 ft., and a diameter of 4 ft. 6
in., inclined 1 ft. 6 in. in its length, will calcine from 24 to 48
tons per diem.
Another form of rotating furnace is one in which the axis is
horizontal. It is much shorter than the inclined type, and the feeding
and removal of the ore is effected by the opening of a retort lid door
provided at the side of the furnace. Openings provided at each end of
the furnace permit the passage of the flame through it, and the
revolution of the furnace turns over the powdered ore and brings it
into more or less sustained contact with the oxidising flame. The
exposure of the ore to this action is continued sufficiently long to
ensure the more or less complete oxidation of the ore particles.
/Third or C Process./--In this process the powdered ore is allowed to
fall in a shower from a considerable height, through the centre of a
vertical shaft up which a flame ascends; the powdered ore in falling
through the flame is heated to an oxidising temperature, and the
sulphides are thus depleted of their sulphur and become oxides.
Another modification of this direct fall or shaft furnace is that in
which the fall of the ore is checked by cross-bars or inclined plates
placed across the shaft; this causes a longer oxidising exposure of
the ore particles.
When the sulphur contents of pyritous ores are sufficiently high, and
after the ore has been initially fired with auxiliary carbonaceous
fuel, it is unnecessary, in a properly designed roasting furnace, to
add fuel to the ore to enable the heat for oxidation to be obtained.
The oxidation or burning of the sulphur will provide all the heat
necessary to maintain the continuity of the process. The temperature
necessary for effecting the elimination of both sulphur and arsenic is
not higher than that equivalent to dull red heat; and provided that
there is a sufficient mass of ore maintained in the furnace, the
potential heat resulting from the oxidation of the sulphur will alone
be adequate to provide all that is necessary to effect the
calcination.
TYPES OF FURNACES OF THE DIFFERENT CLASSES
THAT ARE IN ACTUAL USE.
"A" OR REVERBERATORY CLASS.
The construction of this furnace has already been sufficiently
described. If the roasting is performed in a muffle chamber, the
arrangement employed by Messrs. Leach and Neal, Limited, of Derby, and
designed by Mr. B. H. Thwaite, C.E., can be advantageously employed in
this furnace, which is fired with gaseous fuel. The sensible heat of
the waste gases is utilised to heat the air employed for combustion;
and by a controllable arrangement of combustion, a flame of over 100
feet in length is obtained, with the result that the furnace from end
to end is maintained at a uniform temperature. By this system, and
with gaseous fuel firing, a very considerable economy in fuel and in
repairs to furnace, and a superior roasting effect, have been
obtained.
Where the ordinary reverberatory hearth is fired with solid coal from
an end grate, the temperature is at its maximum near the firing end,
and tails off at the extreme gas outlet end. The ores in this furnace
should therefore be fed in at the colder end of the hearth and be
gradually worked or "rabbled" forward to the firing end.
One disadvantage of the reverberatory furnace is the fact that it is
impossible to avoid the incursion of air during the manual rabbling
action, and this tends to cool the furnace.
The cost of roasting, to obtain the more or less complete oxidation,
or what is known in mining parlance as a "sweet roast" (because a
perfectly roasted ore is nearly odourless) varies considerably, the
variation depending of course upon the character of the ore and the
cost of labour and fuel.
There are several modifications of the reverberatory furnace in use,
designed mechanically to effect the rabbling. One of the most
successful is that known as the Horse-shoe furnace. In plan the hearth
of the furnace resembles a horse-shoe.
The stirring of the ore over the hearth is effected by means of
carriages fixed in the centre of the furnace and having laterally
projecting arms, carrying stirrers, that move along the hearth and
turn over the pulverised ore.
In operation, half the carriages are traversing the furnace, and half
are resting in the cooling space, so that a control over the
temperature of the stirrers is established.
This furnace is stated to be more economical in labour than other
mechanically stirred reverberatory furnaces, and there is also said to
be an economy in fuel.
Usually the mechanical stirring furnaces give trouble and should be
avoided, but the horse-shoe type possesses qualifications worthy of
consideration.
"B."--THE REVOLVING CYLINDER FURNACE.
Of these the best known to me are: The Howell-White, the Bruckner, the
Thwaite-Denny, and the Molesworth.
The Bruckner is a cylinder, turning on the horizontal axis and carried
by four rollers.
The batch of ore usually charged into the two charging hoppers weighs
about four tons. When the two charging doors are brought under the
hopper mouth, the contents of the hopper fall directly into the
cylinder.
The ends or throats of the furnace are reduced just sufficiently to
allow the flame evolved from a grated furnace to pass completely
through the cylinder.
A characteristic size for this Bruckner furnace is one having a length
of 12 feet and a diameter of 6 feet. A furnace of this capacity will
have an inclusive weight (iron and brickwork) of 15 tons.
The time of operation, with the Bruckner, will vary with the character
of the ore under treatment and the nature of the fuel employed. Four
hours is the minimum and twelve hours should be the maximum time of
operation.
By the addition of common salt with the batch of ore, such of its
constituents as are amenable to the action of chlorine are chlorinated
as well as freed from sulphur.
Where the ore contains any considerable quantity of silver which
should be saved, the addition of the salt is necessary as the silver
is very liable to become so oxidised in the process of roasting as to
render its after treatment almost impossible. I know a case in point
where an average of nearly five ounces of silver to the ton, at that
time worth 30s., was lost owing to ignorance on this subject. Had the
ore been calcined with salt, NaCl, the bulk of this silver would have
been amalgamated and thus saved. It was the extraordinary fineness of
the gold saved by amalgamation as against my tests of the ore by fire
assay that put me on the track of a most indefensible loss.
/The Howell-White Furnace./--This furnace consists of a cast iron
revolving cylinder, averaging 25 feet in length and 4 ft. 4 in. in
diameter, which revolves on four friction rollers, resting on truck
wheels, rotated by ordinary gearing.
The power required for effecting the revolution should not exceed four
indicated horse-power.
The cylinder is internally lined with firebrick, projecting pieces
causing the powdered ore to be raised over the flame through which it
showers, and is thereby subjected to the influence of heat and to
direct contact oxidation.
The inclination of the cylinder, which is variable, promotes the
gradual descension of the ore from the higher to the lower end. It is
fed into the upper end, by a special form of feed hopper, and is
discharged into a pit at the lower end, from which the ore can be
withdrawn at any time.
The gross weight of the furnace, which is, however, made in segments
to be afterwards bolted together, is some ninety to one hundred tons.
The furnace is fired with coal on a grated hearth, built at the lower
end; it is more economical both in fuel and in labour than an ordinary
reverberatory furnace.
/The Thwaite-Denny Revolving Furnace./--This new type of furnace,
which is fired with gaseous fuel, is stated to combine the advantages
of the Stetefeldt, the Howell-White, and the Bruckner.
It is constructed as follows:--Three short cylinders, conical in shape
and of graduated dimensions, are superimposed one over the other,
their ends terminating in two vertical shafts of brickwork, by which
the three cylinders are connected. The powdered ore is fed into the
uppermost cylinder and gravitates through the series. The highest
cylinder is the largest in diameter, the lowest the smallest.
The gas flame, burnt in a Bunsen arrangement, enters the smallest end
of the lowest cylinder and passes through it; then returns through the
series and the ore is reduced by the expulsion of its sulphur,
arsenic, etc., as it descends from the top to the bottom. The top
cylinder is made larger than the one below it and the middle cylinder
is made larger than the lowest one in proportion to the increased bulk
of gases and ore.
The powdered ore in descending through the cylinders is lifted up and
showers through the flame, falling in its descent a distance of over
1000 feet. By the time it reaches the bottom the ore is thoroughly
roasted.
Provision is made for the introduction of separate supplies of air and
gas into each cylinder; this enables the oxidising treatment to be
controlled exactly as desired so as to effect the best results with
all kinds of ore. Each cylinder is driven from its own independent
gearing, and the speed of each cylinder can be varied at will.
The output of this type of furnace, the operations of which appear to
be more controllable than those of similar appliances, depends, of
course, upon the nature of the ore, but may be considered to range
within the limits of twelve to fifty tons in twenty-four hours, and
the cost of roasting will vary from 2s. 6d. to 4s. per ton, depending
upon the quality of ore and of fuel.
The gaseous fuel generating system permits not only the absolute
control over the temperature in the furnace, but the use of the
commonest kinds of coal, and even charcoal is available.
The power required to drive the Thwaite-Denny furnace is four
indicated horse-power.
/The Molesworth Furnace/ also is a revolving cylindrical appliance,
which, to say the least of it, is in many respects novel and
ingenious. It consists of a slightly cone-shaped, cast-iron cylinder
about fourteen feet long, the outlet end being the larger to allow for
the expansion of the gases. Internal studs are so arranged as to keep
the ore agitated; and spiral flanges convey it to the outlet end
continually, shooting it across the cylinder. The cylinder is encased
in a brick furnace. The firing is provided from /outside/, the
inventor maintaining that the products of combustion are inimical to
rapid oxidisation, to specially promote which he introduces an excess
of oxygen produced in a small retort set in the roof of the furnace
and fed from time to time with small quantities of nitrate of soda and
sulphuric acid. Ores containing much sulphur virtually calcine
themselves. I have seen this appliance doing good work. The
difficulties appeared to be principally mechanical.
There are other furnaces which work with outside heat, but I have not
seen them in action.
"C."--SHAFT TYPE OF FURNACE
In one form of this furnace, instead of allowing the ore to descend in
a direct clear fall the descent is impeded by inclined planes placed
at different levels in the height of the shaft, the ore descending
from one plane to the other.
/The Stetefeldt Shaft Furnace./--Although very expensive in first
cost, has many advantages. No motive power is required and the
structure of the furnace is of a durable character. Its disadvantages
are:--Want of control, and the occasionally imperfect character of the
roasting originating therefrom.
Three sizes of Stetefeldt's furnaces are constructed:
The largest will roast from 40 to 80 tons per diem.
The intermediate will roast from 20 to 40 tons per diem.
The smallest will roast from 10 to 20 tons per diem.
A good furnace should bring down the sulphur contents even of
concentrates so as to be innocuous to mercuric amalgamation. The
sulphur left in the ore should never be allowed to exceed two per
cent.
A forty per cent pyritous or other sulphide ore should be roasted in a
revolving furnace in thirty to forty minutes, and without any
auxiliary fuel.
For ordinary purposes a 40-foot chimney is adequate for furnace work;
such a chimney four feet square inside at the base, tapering to 2' 6"
at the summit, will require 12,000 red bricks, and 1500 fire-bricks
for an internal lining to a height of 12 feet from the base of the
chimney shaft.
When second-hand Lancashire or Cornish boiler flues are available,
they make admirable and inexpensive chimneys. The advantage of
wrought-iron or steel chimneys lies in the convenience of removal and
erection. They should be made in sections of 20 feet long, three steel
wire guy-ropes attached to a ring, riveted to a ring two-thirds of the
height of the chimney, and attached to holdfasts driven into the
ground; tightening couplings should be provided for each wire.
Flue dust depositing chambers should be built in the line of the flues
between the furnace and the chimney; they consist simply of carefully
built brick chambers, with openings to enable workmen to enter and
rapidly clear away the deposited matters. The chambers, three or four
times the cross sectional area of the chimney flue, and ten to twenty
feet long, can be built of brickwork, set in cement; the walls are
provided with a cavity, filled with sand or Portland cement, so that
there will be no danger of the incursion of air. In all furnace work
the greatest possible precautions should be taken to prevent the least
cracking of either joints or bricks. It is surprising how much the
inadequate draft of a good chimney is due to cracks or orifices in the
flues; and therefore a competent furnace-man should see to it that his
flues are thoroughly sound, and free from openings through which the
air can enter.[*]
[*] For full details of the most recent improvements in the cyanide
process and in other methods of extraction, the reader is referred
to Dr. T. K. Rose's "Metallurgy of Gold," third edition.
CHAPTER IX
MOTOR POWER AND ITS TRANSMISSION
It is unnecessary to describe methods by which power for mining
purposes has been obtained--that is, up to within the last five years
--beyond a general statement, that when water power has been available
in the immediate locality of the mine, this cheap natural source of
power has been called upon to do duty. Steam has been the alternative
agent of power production applied in many different ways, but
labouring under as many disadvantages, chief of which are lack of
water, scarcity of fuel and cost of transit of machinery. Sometimes
condensing steam-engines have been employed. For the generation of
steam the semi-portable and semi-tubular have been the type of boiler
that has most usually been brought into service. Needless to say, when
highly mineralised mine water only is available the adoption of this
class of boiler is attended with anything but satisfactory results.
Recently, however, there is strong evidence that where steam is the
power agent to be employed the water-tube type of boiler is likely to
be employed, and to the exclusion of all other forms of apparatus for
the generation of steam. The advantages of this type, particularly the
tubulous form (or a small water tube), made as it is in sections,
offers unrivalled facilities for transport service. The heaviest parts
need not exceed 3 cwt. in weight, and require neither heavy nor yet
expensive brickwork foundations.
WATERLESS POWER.
The difficulties in finding water to drive a steam plant are often of
such a serious character as to involve the abandonment of many payable
mines; therefore, a motive power that does not require the aqueous
agent will be a welcome boon.
It will be a source of gratification to many a gold-claim holder to
know that practical science has enabled motive power to be produced
without the necessity of water, except a certain very small quantity,
which once supplied will not require to be renewed, unless to
compensate for the loss due to atmospheric evaporation.
Any carbonaceous fuel, such as, say, lignite, coal, or charcoal, can
be employed. The latter can be easily produced by the method described
in the Chapter on "Rules of Thumb," or by building a kiln by piling
together a number of trunks of trees, or fairly large-sized branches,
cut so that they can be built up in a compact form. The pile, after
being covered with earth, is then lighted from the base, and if there
are no inlets for the air except the limited proportion required for
the smouldering fire at the base, the whole of the timber will be
gradually carbonised to charcoal of good quality, which is available
for the waterless power plant.
The waterless power plant consists of two divisions: First, a gas
generating plant; secondly, an internal combustion or gas engine in
which the gas is burnt, producing by thermo-dynamic action the motive
power required. The system known as the Thwaite Power Gas System is
not only practically independent of the use of water, but its
efficiency in converting fuel heat into work is so high that no
existing steam plant will be able to compete with it.
The weight of raw timber, afterwards to be converted into charcoal,
that will be required to produce an effective horse-power for one hour
equals 7 lb.
If coal is the fuel 1 1/3 lb. per E.H.P. for one hour's run.
If lignite is the fuel 2 1/2 lb. per E.H.P. for one hour's run.
The plant is simple to work, and as no steam boiler is required the
danger of explosions is removed. No expensive chimney is necessary for
the waterless power plant.
Where petroleum oil can be cheaply obtained, say for twopence per
gallon, one of the Otto Cycle Oil Engines, for powers up to 20
indicated horse-power, can be advantageously employed.
These engines have the advantage of being a self-contained power,
requiring neither chimney nor steam boiler, and may be said to be a
waterless power. The objection is the necessity to rely upon oil as
fuel, and the dangers attending the storage of oil. A good oil engine
should not require to use more than a pint of refined petroleum per
indicated horse-power working for one hour.
Fortunately for the mining industry electricity, that magic and
mysterious agency, has come to its assistance, in permitting motive
power to be transmitted over distances of even as much as 100 miles
with comparatively little loss of the original power energy.
Given, that on a coal or lignite field, or at a waterfall, 100 horse-
power is developed by the combustion of fuel or by the fall of water
driving a turbine, this power can be electrically transmitted to a
mine or GROUP OF MINES, say 100 miles away, with only a loss of some
30 horse-power. For twenty miles the loss on transmission should not
exceed 15 horse-power so that 70 and 85 horse-power respectively are
available at the mines. No other system offers such remarkable
efficiencies of power transmission. The new Multiphase Alternating
Electric Generating and Power Transmission System is indeed so perfect
as to leave practically no margin for improvement.
The multiphase electric motor can be directly applied to the stamp
battery and ore-breaker driving-shaft and to the shaft of the
amalgamating pans.
APPROXIMATE POWER REQUIRED TO DRIVE THE MACHINERY OF A MINE.
Rock breaker 10 effective horse-power
Amalgamating pan 5 effective horse-power
Grinding pan 6 effective horse-power
Single stamp of 750 lb. dropping
90 times per minute 1.25 effective horse-power
Settlers 4 effective horse-power
Ordinary hoisting lift 20 effective horse-power
Allow 10 per cent in addition for overcoming friction.
Besides this electrical distribution power, which should not cost more
than three farthings per effective horse-power per hour, the
electrical energy can be employed for lighting the drives and the
shafts of the mine. The modern electrical mine lamps leave little to
be desired. Also it is anticipated that once the few existing
difficulties have been surmounted electric drilling will supplant all
other methods.
Electric power can be employed for pumping, for shot firing, for
hauling, and for innumerable purposes in a mine.
Electricity lends itself most advantageously to so many and varied
processes, even in accelerating the influence of cyanide solutions on
gold, and in effecting the magnetic influence on metallic particles in
separating processes; while applied to haulage purposes, either on
aerial lines or on tram or railroads, it is an immediate and striking
success.
It is anticipated that in the near future the mines on the Randt,
South Africa, will be electrically driven from a coalfield generating
station located on the coalfields some thirty miles from Johannesburg.
Such a plant made up of small multiples of highly efficient machines
will enable mine-owners to obtain a reliable power to any extent at
immediate command and at a reasonable charge in proportion to the
power used. This wholesale supply of power will be a godsend to a new
field, enabling the opening up to be greatly expedited; and no
climatic difficulties, such as dry seasons, or floods, need interfere
with the regular running of the machinery. The same system of power-
generation at a central station is to be applied to supply power to
the mines of Western Australia.
CHAPTER X
COMPANY FORMATION AND OPERATIONS
All the world over, the operation of winning from the soil and
rendering marketable the many valuable ores and mine products which
abound is daily becoming more and more a scientific business which
cannot be too carefully entered into or too skilfully conducted. The
days of the dolly and windlass, of the puddler, cradle, and tin dish,
are rapidly receding; and mining, either in lode or alluvial working,
is being more generally recognised as one of the exact sciences. In
the past, mining has been carried on in a very haphazard fashion, to
which much of its non-success may be attributed.
But the dawn of better days has arrived, and with the advent of
schools of mines and technical colleges there will in future be less
excuse for ignorance in this most important industry.
This chapter will be devoted to Company formation and working, in
which mistakes leading to very serious consequences daily occur.
It is not necessary to go deeply into the question why, in the mining
industry more than any other, it should be deemed desirable as a
general rule to carry on operations by means of public Companies, but,
as a matter of fact, few names can be mentioned of men who mine
extensively single handed. Yet, risky as it is, mining can hardly be
said to be more subject to unpreventable vicissitudes than, say,
pastoral pursuits, in which private individuals risk, and often lose
or make, enormous sums of money.
However, it is with Mining Companies we are now dealing, and with the
errors made in the formation and after conduct of these Associations.
The initial mistake most often made is that sufficient working capital
is not called up or provided in the floating of the Company. Promoters
trust to get sufficient from the ground forthwith to ensure further
development; the consequence being that, as nearly 99 per cent of
mining properties require a very considerable expenditure of capital
before permanent profits can be relied on, the inexperienced
shareholders who started with inflated hopes of enormous returns and
immediate dividends become disheartened and forfeit their shares by
refusing to pay calls, and thus many good properties are sacrificed.
In England, the companies are often floated fully paid-up, but the
same initial error of providing too little money for the equipment and
effective working of the mine is usually fallen into.
Again, far too many Companies are floated on the report of some self-
styled mining expert, often a man, who, like the schoolmaster of the
last century, has qualified for the position by failing in every other
business he has attempted. These men acquire a few geological and
mining phrases, and by more or less skilfully interlarding these with
statements of large lodes and big returns they supply reports
seductive enough to float the most worthless properties and cause the
waste of thousands of pounds. But the trouble does not end here.
When the Company is to be formed, some lawyer, competent or otherwise,
is instructed to prepare articles of association, rules, etc.; which,
three times out of four, is accomplished by a liberal employment of
scissors and paste. Such rules may, or may not, be suited to the
requirements of the organisation. Generally no one troubles much about
the matter, though on these rules depends the future efficient working
of the Company, and sometimes its very existence.
Then Directors have to be appointed, and these are seldom selected
because of any special knowledge of mining they may possess, but as a
rule simply because they are large shareholders or prominent men whose
names look well in a prospectus. These gentlemen forthwith engage a
Secretary, usually on the grounds that he is the person who has
tendered lowest, to provide office accommodation and keep the
accounts; and not from any particular knowledge he has of the true
requirements of the position.
The way in which some Directors contrive to spend their shareholders'
money is humorously commented on by a Westralian paper which describes
a great machinery consignment lately landed in the neighbourhood of
the Boulder Kalgoorlie.
"It would seem as if the purchaser had been let loose blindfold in a
prehistoric material-founder's old iron yard, and having bought up the
whole stock, had shipped it off. The feature of the entire
antediluvian show is the liberal allowance of material devoted to
destruction. Massive kibbles, such as were used in coal mines half a
century ago, are arranged alongside a winding engine, built in the
middle of the century, and evidently designed for hauling the kibbles
from a depth of 1000 feet. Nothing less than horse-power will stir the
trucks for underground use, and their design is distinctly of the
antique type. The engine is built to correspond--of a kind that might
have served to raise into position the pillars of Baalbec, and the
mass of metal in it fairly raises a blush to the iron cheek of frailer
modern constructions. The one grand use to which this monster could be
put would be to employ it as a kedge for the Australian continent in
the event of it dragging its present anchors and drifting down south,
but as modern mining machinery the whole consignment is worth no more
than its value as scrap-iron, which in its present position is a
fraction or two less than nothing."
Next, a man to manage the mine has to be obtained, and some one is
placed in charge, of whose capabilities the Directors have no direct
knowledge. Being profoundly ignorant of practical mining they are
incompetent to examine him as to his qualifications, or to check his
mode of working, so as to ascertain whether he is acting rightly or
not. All they have to rely on are some certificates often too
carelessly given and too easily obtained. Finally, quite a large
proportion of the allottees of shares have merely applied for them
with the intention of selling out on the first opportunity at a
premium, hence they have no special interest in the actual working of
the mine.
Now let us look at the prospects of the Association thus formed. The
legal Manager or Secretary, often a young and inexperienced man, knows
little more than how to keep an ordinary set of books, and not always
that. He is quite ignorant of the actual requirements of the mine, or
what is a fair price to pay for labour, appliances, or material. He
cannot check the expenditure of the Mining Manager, who may be a rogue
or a fool or both, for we have had samples of all sorts to our sorrow.
The Directors are in like case. Even where the information is honestly
supplied, they cannot judge whether the work is being properly carried
out or is costing a fair price, and the Mining Manager is left to his
own devices, with no one to check him nor any with whom he can consult
in specially difficult cases. Thus matters drift to the almost certain
conclusion of voluntary or compulsory winding up; and so many a good
property is ruined, and promising mines, which have never had a
reasonable trial, are condemned as worthless. But let us ask, would
any other business, even such as are less subject to unforeseen
vicissitudes than mining, succeed under similar circumstances?
It is now very generally agreed that to the profitable development of
mining new countries, at all events, must look mainly for prosperity,
while other industries are growing. Therefore, we cannot too seriously
consider how we may soonest make our mines successful.
What is the remedy for the unsatisfactory state of affairs we have
experienced? The answer is a more practical system of working from the
inception. Although it may evoke some difference of opinion I consider
it both justifiable and desirable that the State should take some
oversight of mining matters, at all events in the case of public
Companies. It would be a salutary rule that the promoters of any
mining undertaking should, before they are allowed to place it on the
market, obtain and pay for the services of a competent Government
Mining Inspector, who need not necessarily be a Government officer,
but might, like licensed surveyors, be granted a certificate of
competency either by a School of Mines or by some qualified Board of
Examiners. The certificate of such Inspector that the property was as
represented, should be given before the prospectus was issued. It is
arguable whether even further oversight might not be properly be taken
by the State and the report of a qualified officer be compulsory that
the property was reasonably worth the value placed upon it in the
prospectus.
Probably it will be contended that such restrictions would be an undue
interference with private rights, and the old aphorism about a fool
and his folly will be quoted. There are doubtless fools so infatuated
that if they were brayed in a ten hundred-weight stamp-battery the
"foolishness that had not departed from them" would give a highly
payable percentage to the ton. Yet the State in other matters tries by
numerous laws to protect such from their folly. A man may not sell a
load of wood without the certificate from a licensed weighbridge or a
loaf of bread without, if required, having to prove its weight; and we
send those to gaol who practise on the credulity and cupidity of fools
by means of the "confidence trick." Why not, therefore, where
interests which may be said to be national are involved, endeavour to
ensure fair dealing?
Then with regard to the men who are to manage the mines, seeing that a
man may not become captain or mate of a river steamboat without some
certificate on competency, nor drive her engines before he has passed
an examination to prove his fitness, surely it is not too much to say
that the mine manager or engineer, to whose care are often confided
the lives of hundreds of men, and the expenditure of thousands of
pounds, should be required to obtain a recognised diploma to prove his
qualifications. The examinations might be made comparatively easy at
first, but afterwards, when by the establishment of Schools and Mines
the facilities have been afforded for men to thoroughly qualify, the
standard should be raised; and after a date to be fixed no man should
be permitted to assume the charge of a mine or become one of its
officers without a proper certificate of competency from some
recognised School of Mines or Technical College. The effect of such a
regulation would in a few years produce most beneficial results.
In New Zealand, whose "progressive" legislature I do not generally
commend, they have, in the matter of mine management, at all events,
taken a step in the right direction. There a mine manager, before he
obtains his certificate, must have served at least two years
underground, and has to pass through a severe examination, lasting for
days, in all subjects relating to mining and machinery connected with
mining. In addition, he must prove his capacity by making an
underground survey, and then plotting his work. The examination is a
stiff one, as may be judged from the fact that between 1886 and 1891,
only 27 candidates passed. Then the conditions were made easier, and
from that date to 1895, 19 passed. Of the 46 students who gained
first-class honours, 30 have left for South Africa or Australia, in
both of which countries New Zealand certificated men are held in high
estimation.
But returning to the formation of the Company, care should be taken in
appointing Directors that at least one member of the Board is selected
on account of his special technical knowledge of mining, and others
for their special business capacity. The ornamental men with high
sounding names should not be required in legitimate ventures. Also, it
is most important that the business Manager or Secretary should be a
specially qualified man, who by experience has learned what are the
requirements of a mine doing a certain amount of work, so that a
proper check may be kept on the expenses. The more Companies such a
Secretary has the better, as one qualified man can supervise a large
staff of clerks, who would themselves be qualifying for similar work,
and gaining a useful and varied experience of mining business. An
office of this description having charge of a large number of mines
is, in its way, a technical school, and lads trained therein would be
in demand as mine pursers, a very responsible and necessary officer in
a big mine.
With respect to the men to whom the actual mining and treatment of
ores and machinery is committed the greatest mistakes of the past have
been that too much has been required from one man, a combination not
to be found probably in one man in a thousand. Such Admirable
Crichtons are rare in any profession or business, and that of mining
is no exception. Men who profess too much are to be distrusted. Your
best men are they who concentrate their energies and intellects in
special directions. The Mining Manager should, if possible, be chosen
from men holding certificates of competency from some technical mining
school and, of course, should, in addition, have some practical
experience, not necessarily as Head Manager. He should understand
practical mine surveying and calculation of quantities, be able to
dial and plot out his workings, and prepare an intelligible plan
thereof for the use of the Directors, and should understand sufficient
of physics, particularly pneumatics and hydraulics, to ensure
thoroughly efficient pumping operations without loss of power from
unnecessarily heavy appliances. Any other scientific knowledge
applicable to his business which he may have acquired will tell in his
favour, but he must, above all things, be a thoroughly practical man.
Such men will in time be more readily procurable, as boys who have
passed through the various Schools of Mines will be sent to learn
their business practically at the mines just as we now, having given a
lad a course of naval instruction, send him to sea to learn the
practical part of his life's work.
But, of course, more is wanted on a mine than a man who can direct the
sinking of shafts, driving of levels, and stoping of the lode. Much
loss and disappointment have resulted in the past from unsuitable,
ineffective, or badly designed and erected machinery, whether for
working the mine or treating the ores. To obviate this defect a first-
class mining engineer is required.
Then, also, day by day we are more surely learning that mining in all
its branches is a science, and that the treatment of ores and
extraction of the metals is daily becoming more and more the work of
the laboratory rather than of the rule-of-thumb procedure of the past.
Every mine, whether it be of gold, silver, tin, copper, or other
metal, requires the supervision of a thoroughly qualified metallurgist
and chemist, and one who is conversant with the newest processes for
the extraction of the metals from their ores and matrices.
It has then been stated that to ensure effective working each mine
requires, in addition to competent directors, a business manager,
mining-manager, and assistants, engineer, chemist, and metallurgist,
with assistant assayers, etc., all highly qualified men. But it will
be asked, how are many struggling mines in sparsely populated
countries to obtain the services of all these eminent scientists? The
reply is by co-operation. One of the most ruinous mistakes of the past
has been that each little mining venture has started on an independent
course, with different management, separate machinery, etc. Can it
then be wondered at that our gold-mining is not always successful?
Under a co-operative system all that each individual mine would
require would be a qualified, practical miner capable of opening and
securing the ground in a miner-like manner, and a good working
engineer; and in gold-mining, where the gold is free in its matrix, a
professional amalgamator, or lixiviator. For the rest, half a dozen or
more mines may collectively retain the services of a mine manager of
high attainments as general inspector and superintendent, and the same
system could be adopted with respect to an advising metallurgist and
an engineer. For gold, as indeed for other metals, a central
extracting works, where the ores could be scientifically treated in
quantity, might be erected at joint cost, or might easily be arranged
for as a separate business.
A very fruitful cause of failure is the fatuous tendency of directors
and mine managers to adopt new processes and inventions simply because
they are new. As an inventor in a small way myself, and one who is
always on the watch for improved methods, I do not wish to discourage
intelligent progress; but the greatest care should be exercised by
those having the control of the money of shareholders in mining
properties before adopting any new machinery or process.
We have seen, and unfortunately shall see, many a promising mining
company brought to grief by this popular error. The directors of
mining companies might, to use an American saying, "paste this in
their hats" as a useful and safe aphorism. "LET OTHERS DO THE
EXPERIMENTING; WE ARE WILLING TO PAY ONLY FOR PROVED IMPROVEMENTS." I
can cordially endorse every word of the following extracts from
Messrs. McDermott and Duffield's admirable little work, "Losses in
Gold Amalgamation."
"Some directors of mining companies are naturally inclined to listen
to the specious promises of inventors of novel processes and new
machinery, forgetting their own personal disadvantage in any argument
on such matters, and assuming a confidence in the logic of their own
conclusions, while they ignore the fruitful experience of thousands of
practical men who are engaged in the mining business. The repeated
failures of directors in sending out new machinery to their mines
ought by this time to be a sufficient warning against increasing risks
that are at once natural and unavoidable, and to deter them from
plunging their shareholders into experiments which, in ninety-nine
cases out of a hundred, result in nothing but excessive and needless
expenses.
"It is certain that new machines and new processes are, and will be,
given attention by mining men in proportion to their probable merits;
but the proper place for experiments is in a mill already as
successful as under known processes it can be made. In a new
enterprise, even when the expense of an experiment is undertaken by
the inventor, the loss to the mine-owner in case of failure must be
very great, both in time and general running expenses. Directors
should not believe that a willingness to risk cash in proving an
invention is necessarily any proof of value of the same; it is only a
measure of the faith of the inventor, which is hardly a safe standard
to risk shareholders' money by.
"The variety of modifications in approved processes ought at least to
suggest the desirability of exhausting the known, before drawing on
the unknown and purely speculative. It should also be borne in mind
that what might appear at first sight to be new processes, and even
new machinery, are, in fact, often nothing but old contrivances and
plausible theories long ago exploded among practical men.
"Many mining companies have been ruined, without any reference to
their mines, through men deciding on the reasonableness of new process
and machinery who have no knowledge of the business in hand. It is
assumed often, that if an inventor or manufacturer of new machinery
will agree to guarantee success, or take no pay if not successful, the
company takes no risk. In actual fact a whole year is wasted in most
cases, failure spoils the reputation of the company, running expenses
have continued, and further working capital cannot be raised, because
all concerned have lost confidence by the failure to obtain returns
promised. All this in addition to the regular, unavoidable risks of
mining itself, which may, at any moment during the year lost, call for
increased expenses and increased faith in ultimate success. To the
mining man who makes money by the business, the natural risks of
mining is all he will take; it is sufficient; and when he invests more
money in machinery he takes good care that he takes no chances of
either failure or delay.
"The following are rules which no mining company or individual mine-
owner can afford to neglect.
"(1) The risk should be confined to mining. No body of directors is
justified in taking a shareholder's money and investing it in new
processes or machinery when the subscription was simply for a mining
venture. Directors are invariably incapable of deciding whether a so-
called improvement in machinery or process is really so or not, and
the reasonable course is to follow established precedents.
"(2) The risk of selecting an incompetent manager should be reduced to
minimum by taking a man with a successful record in the particular
work to be done. The manager selected should be prohibited, as much as
the directors, from experimenting with new methods or machinery. A
really experienced man will require no check in this direction, as he
will not risk ruining his reputation.
"(3) The only time for a company to experiment is when the mine is
paying well by the usual methods, and the treasury is in a condition
to speculate a little in possible improvements without jeopardising
regular returns."
Probably this is the best place to insert another word of warning to
directors who are not mining specialists, and also to investors in
gold mining shares. Assays of auriferous lode material are almost
invariably worthless as a guide in the real value of the stone in
quantity. The one way to decide this is by battery treatment in bulk,
and then only after many tons have been put through. The reason is
obvious. First, the prospector or company promoter, if he knows it, is
not in the least likely to pick the worst piece of stone in the heap
for assay; and, secondly, even should the sample be selected with the
sole object of getting a fair result, no living man can judge the
value of a gold lode by the result of treatment of an ounce of stone.
So when you see it stated that Messrs. Oro and Gildenstein, the
celebrated assayers, have found that a sample of rock from the Golden
Mint Mine, Golconda, assays at the rate of 2,546 oz. 13 dwt. and 21
gr. to the ton, and that there are thousands of tons of similar stone
in sight, the statement should be received with due caution. The assay
is doubtless correct, but the deductions therefrom are most
misleading.
A few words of advice also to directors of mine-purchasing companies
and syndicates, of which there are now so many in existence, may
probably be found of value. It is not good policy as a general rule to
buy entirely undeveloped properties, unless such have been inspected
by your own man, who is both competent and trustworthy, and who should
have indeed an interest in the profits. Large areas, although so
popular in England, do not compensate for large bodies of payable ore;
the most remunerative mine is generally one of comparatively small
area, but containing a large lode formation of payable but often low
grade, ore.
It is worse still, of course, to buy a practically worked out mine,
though this too is sometimes done. It must be remembered that mining,
though often so profitable, is nevertheless a destructive industry,
thus differing from agriculture, which is productive, and
manufactures, which are constructive. Every ton of stone broken and
treated from even the best gold mine in the world makes that mine the
poorer by one ton of valuable material; thus, to buy a mining property
on its past reputation for productiveness is, as a rule, questionable
policy, unless you know there is sufficient good ore in sight to cover
the purchase cost and leave a profit.
One of the greatest causes of non-success of gold-mining ventures,
particularly when worked by public companies, is the lack of actual
personal supervision, and hence, among other troubles, is that ultra-
objectionable one--gold stealing from the mills, or, in alluvial
mining, from the tail races. As to the former, the following appeared
in 1893 in the London /Mining Journal/, and is, I think, worthy of the
close consideration of mine directors in all parts of the world:--
"No one that has not experienced the evil of gold thieving from
reduction mills can have any idea of the pernicious element it is, and
the difficulty, once that it has got 'well hold,' of rooting it out.
It permeates every class of society in the district connected with the
industry, and managers, amalgamators, assayers, accountants, aye, even
bank officials, are 'all on the job' to 'get a bit' while there is an
opportunity. To exterminate the hateful monster requires on the part
of the mine proprietors combined, stern and drastic measures
undertaken under the personal supervision of one or more of their
directors, and in many instances necessitating the removal of the
whole of the official staff."
The writer narrates how about twenty years ago he was led to suspect
that in an Australian mine running forty head of stamps, in which he
held a controlling interest, the owners were being defrauded of about
a fourth of the gold really contained in the ore, and the successful
steps taken to check the robbery.
"We first of all dispensed with the services of the general manager,
and then issued the following instructions to the mine and mill
managers, I remaining at the mine to see them carried out until I
substituted a practical local man as agent, who afterwards carried on
the work most efficiently:--
"(a) Both of these officials to keep separate books and accounts; in
other words, to be distinct departments.
"(b) The ore formerly was all thrown together and put through the
mill. I subdivided it into four classes, A, B, C, and D, representing
deep levels north and upper levels north, deep levels south and upper
levels south, and allotted to each class ten heads of stamps at the
mill.
"(c) The mine manager to try three prospects, forenoon and afternoon
of each day, from the dumps of each of the four classes and record in
a book to be kept for that purpose the estimated mill yield of each
one.
"(d) The mill manager was required to do the same at the mill and keep
his record.
"(e) There were four underground bosses in each shift, twelve in all.
I had a book fixed at the top of the shaft in which I required each of
these men, at the expiry of every shift, to record any change in the
faces of the quartz and particularly in regard to quality.
"(f) Having divided the ore into four classes I instructed the
amalgamators, of which there were two in each shift, six in all, that
I required the amalgam from each to be kept separate, with the object
of ascertaining what each part of the mine produced.
"(g) I procured padlocks for the covering boards of the mercury tables
and gave the keys to the amalgamators with instructions that they were
not to hand them over to any one except the exchange shift without my
written authority, and instructed them that they should clean down the
plates every three hours, and after cleaning down the amalgam, buckets
to be placed in the cleaning room, which I instructed to be kept
locked and the key in charge of the watchman night and day.
"(h) The whole of the amalgam taken from the plates during each
twenty-four hours to be cleaned and squeezed by the two amalgamators
on duty every forenoon at nine o'clock in the presence of the mill
manager, who should weigh each lot and enter it in a book to be kept
for the purpose, and the entry to be signed by the mill manager and
both amalgamators as witnesses.
"(i) Every alternate Friday the mortars (boxes) to be cleaned out; the
work to be commenced punctually at eight A.M. by the six amalgamators
in the presence of the mill manager, assisted by the three amalgam
cleaning room watchmen and the four battery feeders on duty,
prohibiting any of them from leaving until the cleaning up was
finished, and the amalgam cleaned, squeezed and weighed, and the
amount entered by the mill manager in the record look and attested by
the amalgamators.
"I think the intelligent readers (particularly those with a knowledge
of the business) will see the drift of the above regulations, viz.,
for there to be any peculation the whole of the battery staff--
fourteen in all--would have to participate in it, and the number was
too many to keep a secret. Formerly the amalgam cleaning room was
sacred to the mill manager, and on announcing to that official the new
instructions he at once tendered his resignation in a tone of offended
dignity, immediately followed by that of the mine manager. It is a
significant fact that shortly afterwards these two officials purchased
a large mill and other property at a cost of ten thousand pounds, and
that the mine yielded for the following three years during which I was
connected with it an average of over 17 dwt. to the ton, as against
formerly 10 to 12 dwt.
"The reader must draw his own conclusions. I used to make it a
practice to visit the mine daily and prospect the ore, and having the
mine and mill managers' daily prospecting as a guide as well as my
own, every man at the mill knew it was impossible for them to thieve
without my detecting it; moreover, I made it a rule to discharge any
of the mill employees that I discovered were interested in any small
private claims.
"The crux of the whole thing is having a practical miner at the head
of affairs, and it is impossible for him to thieve if the work is
carried out in the manner I have described."
To bring the whole matter to a conclusion. It may be taken as a safe
axiom that to make gold mining in the mine as distinct from mining on
the Stock Exchange really profitable the same system of economy, of
practical supervision, and scientific knowledge which is now adopted
in all other businesses must be applied to the raising and extraction
of the metal. Then, and not till then, will genuine mining take the
place to which it is entitled amongst our industries.
CHAPTER XI
RULES OF THUMB
This chapter has been headed as above because a number of the rules
and recipes given are simply practical expedients, not too closely
scientific. My endeavour has been to supply practical and useful
information in language as free from technicalities as possible, so as
to adapt it to the ordinary miner, mill operator and prospector, many
of whom have had no scientific training. Some of the expedients are
original devices educed by what we are told is the mother of
inventions; others are hints given by practical old prospectors who
had met with difficulties which would be the despair of a man brought
up within reach of forge, foundry, machine shop, or tradesmen
generally. There are many highly ingenious and useful contrivances
besides these I have given.
LIVING PLACES
The health of the prospector, especially in a new country, depends
largely on his housing--in which particular many men are foolishly
careless, for although they are aware that they will be camped out for
long periods, yet all the shelter they rely on is a miserable calico
tent, often without a "fly," while in some cases they sometimes even
sleep on the wet, or dusty, ground. Such persons fully deserve the ill
health which sooner or later overtakes them. A little forethought and
very moderate ingenuity would render their camp comparatively healthy
and comfortable.
In summer the tent is the hottest, and in winter the coldest of
domiciles. The "pizie" or "adobie" hut, or, where practicable, the
"dugout," are much to be preferred, especially the latter. "Pizie" or
"adobie" is simply surface soil kneaded with water and either moulded
between boards like concrete, to construct the walls, or made into
large sun-dried bricks. Salt water should not be used, as it causes
the wall to be affected by every change of weather. A properly
constructed house of this material, where the walls are protected by
overhanging eaves, are practically everlasting, and the former have
been standing for centuries. There are buildings of pizie or adobie in
Mexico, California and Australia which are as good as new, although
the latter were built nearly a century ago.
Adobie dwellings are warm in winter and cool in summer, and can be
kept clean and healthy by occasional coatings of lime whitewash.
The dugout is even more simple in construction. A cutting, say ten
feet wide, is put into the base of a hill for say twelve feet until
the back wall is, say, ten feet high, the sides starting from nothing
to that height. The front and such portion as is required of the side
walls are next constructed of pizie or rough stone, with mud mortar,
and the roof either gabled or skillion of bough, grass, or reed
thatch, and covered with pizie, over which is sometimes put another
thin layer of thatch to prevent the pizie being washed away by heavy
rain. Nothing can be more snug and comfortable than such a house,
unless the cows, as Mark Twain narrates, make things "monotonous" by
persistently tumbling down the chimney.
When the Burra copper mines were in full work in Australia, the banks
of the Burra Creek were honeycombed like a rabbit warren with the
"dugout homes" of the Cornish miners. The ruins of these old dugouts
now extend for miles, and look something like an uncovered Pompeii.
When water is scarce and the tent has to be retained, much can be done
to make the camp snug. I occupied a very comfortable camp once, of
which my then partner, a Dane, was the architect. We called it "The
Bungalow," and it was constructed as follows: First we set up our
tent, 10 ft. by 8 ft., formed of calico, but lined with green baize,
and covered with a well set fly.
Next we put in four substantial forked posts about 10 ft. high and 15
ft. apart, with securely fixed cross pieces, and on the top was laid a
rough flat roof of brush thatch; the sides were then treated in the
same way, but not so thickly, being merely intended as a breakwind.
The tent with its two comfortable bunks was placed a little to one
side, the remaining space being used as a dining and sitting room all
through the summer. Except in occasional seasons of heavy rain, when
we were saved the trouble of washing our dishes, the tent was only
used for sleeping purposes, and as a storehouse for clothes and
perishable provisions. I have "dwelt in marble halls" since then, but
never was food sweeter or sleep sounder than in the old bush bungalow.
A BUSH BED
To make a comfortable bush bedplace, take four forked posts about 3
ft. 6 in. long and 2 to 3 in. in diameter at the top; mark out your
bedplace accurately and put a post at each corner, about 1 ft. in the
ground. Take two poles about 7 ft. long, and having procured two
strong five-bushel corn sacks, cut holes in the bottom corners, put
the poles through, bringing the mouths of the sacks together, and
secure them there with a strong stitch or two. Put your poles on the
upright forked sticks, and you have a couch that even Sancho Panza
would have envied. It is as well to fix stretchers or cross stays
between the posts at head and foot.
In malarial countries, sleeping on the ground is distinctly dangerous,
and as such districts are usually thickly timbered, the Northern
Territory hammock is an admirable device, more particularly where
mosquitoes abound.
NORTHERN TERRITORY HAMMOCK
This hammock, which is almost a standing bedplace when rigged, is
constructed as follows:--To a piece of strong canvas 7 feet long and 2
1/2 feet wide, put a broad hem, say 3 1/2 inches wide at each end.
Into this hem run a rough stick, about 2 feet 8 inches by 2 inches
diameter. Round the centre of the stick pass a piece of strong three-
quarter inch rope, 8 to 10 feet long and knot it, so as to leave a
short end in which a metal eye is inserted. To each end of the two
sticks a piece of quarter-inch lashing, about 6 feet long, is securely
attached.
To make the mosquito covering take 18 feet of ordinary strong cheese
cloth, and two pieces of strong calico of the same size as the canvas
bed; put hems in the ends of the upper one large enough to take half-
inch sticks, to all four extremities of which 8 feet of whipcord is to
be attached. The calico forms the top and bottom of what we used to
call the "meat safe," the sides being of cheese cloth. A small,
flapped opening is left on the lower side. When once inside you are
quite safe from mosquito bites.
To rig the above, two trees are chosen 7 to 8 feet apart, or two
stayed poles can be erected if no trees are available. The bed is
rigged about 3 feet from the ground by taking the rope round the trees
or poles, and pulling the canvas taut by means of the metal eyelet.
Then the lashings at the extremities of the sticks are fixed about 3
feet further up the trees and you have a bed something between a
hammock and a standing bed. The mosquito net is fixed above the
hammock in a similar manner, except that it does not require the
centre stay.
An old friend of mine once had a rather startling experience which
caused him to swear by the Northern Territory hammock. He was camped
near the banks of a muddy creek on the Daly River, and had fortunately
hung his "meat safe" about four feet high. The night was very dark,
and some hours after retiring he heard a crash among his tin camp
utensils, and the noise of some animal moving below him. Thinking his
visitor was a stray "dingo," or wild dog, he gave a yell to frighten
the brute away, and hearing it go, he calmly went to sleep again. Had
he known who his caller really was, he would not have felt so
comfortable. In the morning on the damp ground below, he found the
tracks of a fourteen foot alligator, which was also out prospecting,
but which, fortunately, had not thought of investigating the "meat
safe."
PURIFYING WATER
There is not a more fertile disease distributor, particularly in a new
country, than water. The uninitiated generally take it for granted
that so long as water looks clear it is necessarily pure and
wholesome; as a matter of fact the contrary is more usually the case,
except in very well watered countries, and such, as a rule, are not
those in which gold is most plentifully got by the average prospector.
I have seen foolish fellows, who were parched with a long tramp, drink
water in quantity in which living organisms could be seen with the
naked eye, without taking even the ordinary precaution of straining it
through a piece of linen. If they contracted hydatids, typhoid fever,
or other ailments, which thin our mining camps of the strong, lusty,
careless youths, who could wonder?
The best of all means of purifying water from organic substances is to
boil it. If it be very bad, add carbon in the form of the charcoal
from your camp fire. If it be thick, you may, with advantage, add a
little of the ash also.
I once rode forty-five miles with nearly beaten horses to a native
well, or rock hole, to find water, the next stage being over fifty
miles further. The well was found, but the water in it was very bad;
for in it was the body of a dead kangaroo which had apparently been
there for weeks. The wretched horses, half frantic with thirst, did
manage to drink a few mouthfuls, but we could not. I filled our
largest billycan, holding about a gallon, slung it over the fire and
added, as the wood burnt down, charcoal, till the top was covered to a
depth of two inches. With the charcoal there was, of course, a little
ash containing bi-carbonate of potassium. The effect was marvellous.
So soon as the horrible soup came to the boil, the impurities
coagulated, and after keeping it at boiling temperature for about half
an hour, it was removed from the fire, the cinders skimmed out, and
the water allowed to settle, which it did very quickly. It was then
decanted off into an ordinary prospector's pan, and some used to make
tea (the flavour of which can be better imagined than described); the
remainder was allowed to stand all night, a few pieces of charcoal
being added. In the morning it was bright, clear, and absolutely
sweet. This experience is worth knowing as many a bad attack of
typhoid and other fevers would be averted if practical precautions of
this kind were only used.
TO OBTAIN WATER FROM ROOTS
The greatest necessity of animal life is water. There are, however,
vast areas of the earth's surface where this most precious element is
lamentably lacking, and such, unfortunately, is the case in many rich
auriferous districts.
To the practical man there are many indications of water. These, of
course, vary in different countries. Sometimes it is the herbage, but
probably, the best of all is the presence of carnivorous animals and
birds. These are never found far from water. In Australia the not
over-loved wily old crow is a pretty sure indicator of water within
reasonable distance--water may be extracted from the roots of the
Mallee (/Eucalyptus dumosa/ and /gracilis/)--the Box (/Eucalyptus
hemiphloia/) and the Water Bush (/Hakea leucoptera/). To extract it
the roots are dug up, cut into lengths of about a foot, and placed
upright in a can; the lower ends being a few inches above the bottom.
It is simply astonishing how much wholesome, if at times somewhat
astringent, water may thus be obtained in a few hours, particularly at
night.
/Hakea leucoptera/. "Pins and needles."--Maiden, in his work "Useful
Native Plants of Australia," says: "In an experiment on a water-
yielding /Hakea/, the first root, about half an inch in diameter and
six or eight feet long, yielded quickly, and in large drops about a
wine-glass full of really excellent water."
This valuable, though not particularly ornamental shrub (for it never
attains to the dimensions of a tree), is found, to the best of my
belief, in all parts of Australia, although it is said to be absent
from West Australia. As to this I don't feel quite sure. I have seen
it "from the centre of the sea" as far west as Streaky Bay, and
believe I have seen it further West still. Considering the great
similarity of much of the flora of South Africa to that of Australia,
it is probable that some species of the water-bearing /Hakea/ might be
found there. It can readily be recognised by its acicular, needle-like
leaves, and more particularly by its peculiarly shaped seed vessel,
which resembles the pattern on an old-fashioned Indian shawl.
If the water found is too impure for drinking purposes and the trouble
arises from visible animalculae only, straining through a pocket-
handkerchief is better than nothing; the carbon filter is better
still; but nothing is so effective as boiling. A carbon filter is a
tube with a wad of compressed carbon inserted, through which the water
is sucked, but as a rule clay-coloured water is comparatively
innocuous, but beware of the bright, limpid water of long stagnant
rock water-holes.
TO MAKE AN EFFECTIVE FILTER
Take a nail-can, keg, cask, or any other vessel, or even an ordinary
wooden case (well tarred inside, if possible, to make it water-tight).
Make a hole or several holes in the bottom, and set it over a tank or
bucket. Into the bottom of the filter put (1) a few inches of washed
broken stone; (2) about four inches of charcoal; (3) say three inches
of clean coarse sand (if not to hand you can manufacture it by
crushing quartz with your pestle and mortar), and (4) alternate layers
of charcoal and sand until the vessel is half filled. Fill the top
half with water, and renew from time to time, and you have a filter
which is as effective as the best London made article. /But it is
better to boil your water whether you filter afterwards or not./
Clear the inside of the water-cask frequently, and occasionally add to
the water a little Condy's fluid, as it destroys organic matter. A
useful cement for stopping leaky places in casks is made as follows:
Tallow 25 parts, lard 40 parts, sifted wood ash 25 parts. Mix together
by heating, and apply with a knife blade which has just been heated.
CANVAS WATER BAGS
Are easily made, and are very handy for carrying small supplies of
drinking-water when prospecting in a dry country; they have the
advantage of keeping the water cool in the hottest weather, by reason
on the evaporation. The mouthpiece is made of the neck of a bottle
securely sewn in.
MEDICINE CASE
Medicine is also a matter well worthy of thought. The author's worst
enemy would not call him a mollycoddle, yet he has never travelled in
far wilds without carrying something in the way of medicine. First,
then, on this subject, it cannot be too often reiterated that if
common Epsom salts were a guinea an ounce instead of a penny the
medicine would be valued accordingly, but it is somewhat bulky. What I
especially recommend, however, is a small pocket-case of the more
commonly known homeopathic remedies, "Mother tinctures," which are
small, light, and portable, with a small simple book of instructions.
Though generally an allopath in practice, I once saved my own life,
and have certainly helped others by a little knowledge in diagnosing
complaints and having simple homeopathic remedies at hand to be used
in the first stages of what might otherwise have been serious
illnesses.
PRODUCING FIRE
Every one has heard, and most believe, that fire may be easily
produced by rubbing together two pieces of wood. I have seen it done
by natives, but they seldom make use of the operation, which is
generally laborious, preferring to carry lighted fire sticks for
miles. I have never succeeded in the experiment.
Sometimes, however, it is almost a matter of life or death to be able
to produce fire. The back of a pocket knife, or an old file with a
fragment of flint, quartz, or pyrites struck smartly together over the
remains of a burnt piece of calico, will in deft hands produce a spark
which can be fanned to a glow, and so ignite other material, till a
fire is produced.
Also it may not be generally known that he who carries a watch carries
a "burning glass" with which he can, in clear weather, produce fire at
will. All that is required is to remove the glass of your watch and
carefully three parts fill it with water (salt or fresh). This forms a
lens which, held steadily, will easily ignite any light, dry,
inflammable substance.
When firearms are carried, cut a cartridge so that only about a
quarter of the charge of powder remains. Damp some powder and rub it
on a small piece of dry cotton cloth or well-rubbed brown paper. Push
a loose pellet of this into the barrel, insert your half cartridge,
fire at the ground, when the wad will readily ignite, and can be blown
into flame.
TO COPY CORRESPONDENCE
The prospector is not usually a business man; hence in dealing with
business men who, like Hamlet, are "indifferent honest," he frequently
comes to grief through not having a copy of his correspondence. It is
most desirable, therefore, either to carry a carbon paper duplicating
book and a stylus, or by adding a little sugar to good ordinary black
ink you may make a copying ink; then with the aid of a "yellow back"
octavo novel, two pieces of board, and some ordinary tissue paper, you
may take a copy of any letter you send.
TO PROVIDE A SIMPLE TELEGRAPHIC CODE
Buy a couple of cheap small dictionaries of the same edition, send one
to your correspondent with an intimation that he is to read up or down
so many words from the one indicated when receiving a message. Thus,
if I want to say "Claim is looking well," I take a shilling
dictionary, send a copy to my correspondent with the intimation that
the real word is seven down, and telegraph--"Civilian looking weird;"
this, if looked up in Worcester's little pocket dictionary, for
instance, will read "Claim looking well." Any dictionary will do, so
long as both parties have a copy and understand which is the right
word. By arrangement this plan can be varied from time to time if you
have any idea that your code can be read by others.
A SERVICEABLE SOAP
Wood ashes from the camp fire are boiled from day to day in a small
quantity of water, and allowed to settle, the clear liquid being
decanted off. When the required quantity of weak lye has been
accumulated, evaporate by boiling, till a sufficient degree of
strength has been obtained. Now melt down some mutton fat, and, while
hot, add to the boiling lye. Continue boiling and stirring till the
mixture is about the consistency of thick porridge, pour into any
convenient flat vessel, and let it stand till cool. If you have any
resin in store, a little powdered and added gradually to the melting
tallow, before mixing with the lye, will stiffen your soap.
TO CROSS A FLOODED STREAM
Take a half-gallon, or larger, tin "billy can," enclose it in a strong
cotton handkerchief or cotton cloth, knotting same over the lid,
invert, and, taking the knot in the hand, you have a floating
appliance which will sustain you in any water, whether you are a
swimmer or not. The high silk hat of civilisation would act as well as
the can, but these are not usually found far afield.
TO MAKE A HIDE BUCKET
At times when prospecting in an "incline" or "underlay" shaft,
particularly where the walls of the lode are irregular, a hide bucket
will be found preferable to an iron one. The mode of manufacture is as
follows: Procure an ox hide, "green," if possible; if dry, it should
be soaked until quite soft. Cut some thin strips of hide for sewing or
lacing. Now shape a bag or pocket of size sufficient to hold about a
hundredweight of stone, and by puncturing the edges with a knife,
marline-spike, or other pointed tool, sew together; make a handle of
twisted or pleated hide, and having filled your bucket with dry sand
or earth let it stand till the whole is quite dry, when it will be
properly distended and will maintain its shape until worn out.
TO MAKE A "SLUSH LAMP"
Where candles are scarce and kerosine is not, a "slush lamp" is a
useful substitute. Take an old but sound quart tin pannikin, half fill
it with sand or earth, and prepare a thin stick of pine, round which
wrap a strip of soft cotton cloth. The stick should be about half an
inch longer than the depth of the pannikin. Melt some waste fat, fill
the pannikin therewith, push the stick down into the earth at the
bottom, and you have a light, which, if not equal to the electric or
incandescent gas burner, is quite serviceable. In Australia the soft
velvety core of the "bottle brush," /Banksia marginata/, is often used
instead of the cotton wick.
CHAPTER XII
RULES OF THUMB
MINING APPLIANCES AND METHODS
A TEMPORARY FORGE
What prospector has not at times been troubled for the want of a
forge? To steel or harden a pick or sharpen a drill is comparatively
easy, but there is often a difficulty in getting a forge. Big single
action bellows are sometimes bought at great expense, and some
ingenious fellows have made an imitation of the blacksmith's bellows
by means of sheepskins and rough boards.
With inadequate material and appliances to hand, the following will be
found easier to construct and more lasting when constructed. Only a
single piece of iron is required, and, at a pinch, one could even
dispense with that by using a slab of talcose material, roughly
shaping a hearth therein and making a hole for the blast. First,
construct a framing about the height of an ordinary smith's forge.
This can made with saplings and bark, or better still, if available,
out of an empty packing case about three feet square. Fill the frame
or case with slightly damped earth and ram it tight, leaving the usual
hollow hearth. Then form a chamber below the perforated hearth opening
to the rear. Now construct a centrifugal fan, such as is used for the
ventilation of shallow shafts and workings. Set this up behind the
hearth and revolve by means of a wooden multiplying wheel. A piece of
ordinary washing line rope, or sash line rope, well resined if resin
can be got--but pitch, tar, or wax will do by adding a little fine
dust to prevent sticking--is used as a belt. With very rough materials
a handy man can thus make a forge that will answer ordinary
requirements.--N.B. Do not use clay for your hearth bed unless you can
get a highly aluminous clay, and can give it full time to dry before
the forge fire is lit. Ordinary surface soil, not too sandy, acts
well, if damped and rammed thoroughly. Of course, if you can get an
iron nozzle for your blower the whole operation is simplified.
SIMPLE WAY OF MAKING CHARCOAL
Dig a pit 5 feet square by 3 feet deep and fill with fuel. After
lighting, see that the pit is kept full. The hot embers will gradually
sink to the bottom. The fuel should be kept burning fiercely until the
pit seems almost full, when more fuel should be added, raising the
heap about a foot above the level of the ground. The earth dug out of
the pit should then be shovelled back over the burning mass. After
leaving it to cool for 24 hours the pit will be found nearly full of
charcoal. About one-quarter the weight of the dry fuel used should be
recovered in charcoal.
ROUGH SMELTING ON THE MINE
Rough smelting on the mine is effected with a flux of borax, carbonate
of soda, or, as I have often done, with some powdered white glass.
When the gold is smelted and the flux has settled down quietly in a
liquid state, the bulk of the latter may be removed, to facilitate
pouring into the mould, by dipping an iron rod alternately into the
flux and then into a little water, and knocking off the ball of
congealed flux which adheres after each dip. This flux should,
however, be crushed with a pestle and mortar and panned off, as, in
certain cases, it may contain tiny globules of gold.
MISFIRES IN BLASTING
One of the most common sources of accident in mining operations is due
either to carelessness or to the use of defective material in
blasting. A shot misses, generally for one of two reasons; either the
explosive, the cap, or the fuse (most often the latter), is inferior
or defective; or the charging is incompletely performed. Sometimes the
fuse is not placed properly in the detonator, or the detonator is not
properly enclosed in the cartridge, or the fuse is injured by improper
tamping. If several shots have been fired together, particularly at
the change of a "shift," the men who have to remove the broken
material may in so doing explode the missed charge. Or, more
inexcusable still, men will often be so foolish as to try to clear out
the drill hole and remove the missed cartridge. When a charge is known
to have missed all that is necessary to do in order to discharge it
safely is to remove a few inches of "tamping" from the top of the
drill hole, place in the bore a plug of dynamite with cap and fuse
attached, put an inch or two of tamping over it and fire, when the
missed charge will also be exploded. Of course, judgment must be used
and the depth of the drill taken into consideration. As a rule, miners
use far more tamping than is at all requisite. The action of the
charge will generally be found quite as effective with a few inches of
covering matter as with a foot or more, while the exploding of misfire
cartridges is rendered simple, as no removal of tamping is required
before placing the top "plug" in case of misfire.
TO PREVENT LOSS OF RICH SPECIMENS IN BLASTING
When blasting the cap of a lode, particularly on rich shutes of gold,
the rock is apt to fly, and rich specimens may be thrown far afield
and so be lost. A simple way of avoiding this is to procure a quantity
of boughs, which tie into loose bundles, placing the leafy parts
alternately end for end. Before firing, pile these bundles over the
blast and, if care is used, very few stones will fly. The same device
may be used in wide shallow shafts.
A SIMPLE MODE OF RETORTING SMALL QUANTITIES OF AMALGAM
Clean your amalgam and squeeze it as hard as possible through strong
calico or chamois leather. Take a large sound potato, cut off about a
quarter from one end and scoop out a hole in the centre about twice as
big as the ball of amalgam. Procure a piece of flat iron--an old spade
will do as well as anything--insert the amalgam, and, having placed
the potato, cut side downwards, thereon, put the plate of iron on the
forge, heat up first gently, then stronger, till separation has taken
place, when the gold will be found in a bright clean button on the
plate and the mercury in fine globules in the potato, from which it
can be re-collected by breaking up the partly or wholly cooked tuber
under water in an enamelled or ordinary crockery basin.
TO RETORT SMALL QUANTITIES OF MERCURY FOR AMALGAMATING ASSAY TESTS
Get two new tobacco pipes similar in shape, with the biggest bowls and
longest stems procurable. Break off the stem of one close to the bowl
and fill the hole with well worked clay (some battery slimes make the
best luting clay). Set the stemless pipe on end in a clay bed, and
fill with amalgam, pass a bit of thin iron or copper wire beneath it,
and bend the ends of the wire upwards. Now fit the whole pipe, bowl
inverted, on to the under one, luting the edges of both well with
clay. Twist the wire over the top with a pair of nippers till the two
bowls are fitted closely together, and you have a retort that will
stand any heat necessary to thoroughly distil mercury.
A SIMPLE MODE OF ASCERTAINING THE NOMINAL HORSE-POWER OF AN ENGINE
Multiply the internal diameter of the cylinder by itself and strike off
the last figure of the quotient. The diameter is
20" X 20"
20
___
400. The H.P. is 40.
The following rules will be found more professionally accurate from an
engineering standpoint, though the term "horse-power" is not now
generally employed.
/To find the Nominal Horse-power/.--For /non-condensing/ engines:
Multiply the square of the diameter of the cylinder in inches by 7 and
divide the product by 80. For /condensing/ engines: Multiply the
square of the diameter of the cylinder in inches by 7 and divide the
product by 200.
/To find the Actual Horse-power/ of an engine, multiply the area of
the cylinder in square inches by the average effective pressure in
pounds per square inch, less 3 lb. per square inch as the frictional
allowance, and also by the speed of the piston in feet per minute,
dividing the product by 33,000, and the quotient will be the actual
horse-power.
"SCALING" COPPER PLATES
To "scale" copper plates they may be put over a charcoal or coke fire
to slowly sublimate the quicksilver. Where possible, the fireplace of
a spare boiler can be utilised, using a thin red fire. After the
entire evaporation of the quicksilver the plates should be slowly
cooled, rubbed with hydrochloric acid, and put in a damp place
overnight, then rubbed with a solution of sal ammoniac and nitre in
equal parts, and again heated slowly over a red fire. They must not be
allowed to get red hot; the proper degree of heat is indicated by the
gold scale rising in blisters, when the plates should be taken from
the fire and the gold scraped off. Any part of the plate on which the
gold has not blistered should be again rubbed with the solution and
fired. The gold scale should be collected in a glass or earthen dish
and covered with nitric acid, till all the copper is dissolved, when
the gold can be smelted in the usual way; but after it is melted
corrosive sublimate should be put in the crucible till a blue flame
ceases to be given off.
/A Second Method/
The simplest plan I know is to have a hole dug nine inches deep by
about the size of the plate to be scaled; place a brick at each
corner, and on each side, halfway between, get up a good fire; let it
burn down to strong embers, or use charcoal, then place the plate on
three bars of iron extending between the three pairs of bricks, have a
strong solution of borax ready in which soak strips of old "table
blanket," laying these over the plate and sprinkling them with the
borax solution when the plate gets too hot. After a time the deposit
of mercury and gold on the plate will assume a white, efflorescent
appearance, and may then be readily parted from the copper.
/Another Method/
Heat the plate over an open fire, to drive off the mercury; after
which, let it cool, and saturate with dilute sulphuric acid for three
hours, or longer; then sprinkle over the surface a mixture of equal
parts of common salt and sal ammoniac, and heat to redness; then cool,
and the gold scale comes off freely; the scale is then boiled in
nitric or sulphuric acid, to remove the copper, previous to melting.
Plates may be scaled about once in six months, and will under ordinary
circumstances produce about one ounce of clean gold for each
superficial foot of copper surface employed. I always paint the back
of the plate with a mixture of boiled oil and turpentine, or beeswax
dissolved in turpentine, to prevent the acid attacking the copper.
HOW TO SUPPLY MERCURY TO MORTAR BOXES
I am indebted for the following to Mr. J. M. Drake, who, speaking of
his experience on the Wentworth Mine, N.S.W., says:
"Fully 90 per cent of the gold is saved on the outside plates, only a
small quantity remaining in the mortar. The plates have a slope of 2
in. to 1 ft. No wells are used, the amalgam traps saving any
quicksilver which may leach off the plates. The quicksilver is added
every hour in the mortar. The quantity is regulated by the mill
manager in the following manner: Three pieces of wood, 8 in. wide by
12 in. long by 2 in. thick, have 32 holes 1 in. deep bored in each of
them. These holes will just take a small 2 oz. phial. The mill manager
puts the required quantity of quicksilver in each bottle and the
batteryman empties one bottle in each mortar every hour; and puts it
back in the hole upside down. Each block of wood lasts eight hours,
the duration of one man's shift." This of course is for a 20-head mill
with four mortars or "boxes."
I commend this as an excellent mode of supplying the mercury to the
boxes or mortars. The quantity to be added depends on circumstances. A
careless battery attendant will often put in too much or too little
when working without the automatic feeder. I have known an attendant
on suddenly awaking to the fact half through his shift, that he had
forgotten to put in any mercury, to then empty into the stamper box
two or three pounds weight; with what effect may be easily surmised.
HOW WATER SHOULD ENTER STAMPER BOXES
The following extract which relates to Californian Gold Mill practices
is from Bulletin No. 6 of the California State Mining Bureau. I quite
agree with the practice.
"The battery water should enter both sides of the mortar in an even
quantity, and should be sufficient to keep a fairly thick pulp which
will discharge freely through the grating or screen. About 120 cubic
feet of water per ton of crushed ore may be considered an average, or
8 to 10 cubic feet per stamp per hour.
"Screens of different materials and with different orifices are used;
the materials comprise wire cloth of brass or steel, tough Russian
sheet iron, English tinned plate, and, quite recently, aluminium
bronze. The 'aluminium bronze' plates are much longer lived than
either of the other kinds, and have the further advantage that, when
worn out, they can be sold for the value of the metal for remelting;
these plates are bought and sold by the pound, and are said to contain
95 per cent of copper and 5 per cent of aluminium. Steel screens are
not so much used, on account of their liability to rust."
I have had no experience with the aluminium bronze screen. I presume,
however, that it is used only for mills where mercury is not put in
the mortars, otherwise, it would surely become amalgamated. The same
remark applies to brass wire cloth and tinned plate. Unless the metal
of which they are composed will not readily amalgamate with mercury, I
should be chary of using new screen devices. Mercury is a most
insidious metal and is often found most unexpectedly in places in the
battery where it should not be. Probably aluminium steel would be
better than any substance mentioned. It would be hard, light, strong,
and not readily corrodible. I am not aware if it has been tried.
Under the heading of "Power for Mills" the following is taken from the
same source.
POWER FOR MILLS
"As the Pelton wheel seems to find the most frequent application in
California, it may be convenient for millmen to have the following
rule, applicable to these wheels:
"When the head of water is known in feet, multiply it by 0.0024147,
and the product is the horse-power obtainable from one miner's inch of
water.
"The power necessary for different mill parts is:
For each 850lb. stamp, dropping 6 in. 95 times per minute, 1.33 h.-p.
For each 750lb. stamp, dropping 6 in. 95 times per minute, 1.18 h.-p.
For each 650lb. stamp, dropping 6 in. 95 times per minute, 1.00 h.-p.
For an 8-inch by 10-inch Blake pattern rock-breaker 9.00 h.-p.
For a Frue or Triumph vanner, with 220 revolutions per min. 0.50 h.-p.
For a 4-feet clean-up pan, making 30 revolutions per min. 1.50 h.-p.
For an amalgamating barrel, making 30 revolutions per min. 2.50 h.-p.
For a mechanical batea, making 30 revolutions per min. 1.00 h.-p."
The writer has had small practical experience of the working of that
excellent hydraulic motor, the Pelton wheel, but if by horse-power in
the table given is meant nominal horse-power, it appears to be high.
Working with 800 cwt. stamps, 80 blows a minute, one horse-power
nominal will be found sufficient with any good modern engine, which
has no further burden than raising the stamps and pumping the feed
water. It is always well, however, particularly when providing engine
power, to err on the right side, and make provision for more than is
absolutely needed for actual battery requirements. This rule applies
with equal potency to pumping engines.
TO AVOID LOSS IN CLEANING UP
The following is a hint to quartz mill managers with respect to that
common source of loss of gold involved in the almost inevitable loss
of mercury in cleaning up operations. I have known hundreds of pounds'
worth of gold to be recovered from an old quartz mill site by the
simple process of washing up the ground under the floor.
If you cannot afford to floor the whole of the battery with smooth
concrete, at all events smoothly concrete the floor of the cleaning-up
room, and let the floor slope towards the centre: where a sink is
provided. Any lost mercury must thus find its way to the centre, where
it will collect and can be panned off from time to time. Of course an
underground drain and mercury trap must be provided.
IRON EXTRACTOR
When using self-feeders, fragments of steel tools are especially
liable to get into the battery boxes or other crushing appliance where
they sometimes cause great mischief. I believe the following plan
would be a practicable remedy for this evil.
By a belt from the cam or counter shaft, cause a powerful electric
magnet to extract all magnetic particles; then, by a simple ratchet
movement, at intervals withdraw the magnet and drop the adhering
fragments into a receptacle by automatically switching off the
electric current. A powerful ordinary horseshoe magnet might probably
do just as well, but would require to be re-magnetised from time to
time.
TO SILVER COPPER PLATES
To silver copper plates, that is, to amalgamate them on the face with
mercury, is really a most simple operation, though many batterymen
make a great mystery of it. Indeed, when I first went into a quartz
mill the process deemed necessary was not only a very tedious one, but
very dirty also.
To amalgamate with silver, in fact, to silver-plate your copper
without resort to the electro-plating bath, take any old silver
(failing that, silver coin will do, but is more expensive), and
dissolve it in somewhat dilute nitric acid, using only just sufficient
acid as will assist the process. After some hours place the ball of
amalgam in a piece of strong new calico and squeeze out any surplus
mercury.
About an ounce of silver to the foot of copper is sufficient. To apply
it on new plates use nitric acid applied with a swab to free the
surface of the copper from oxides or impurities, then rub the ball of
amalgam over the surface using some little force. It is always well
when coating copper plates with silver or zinc by means of mercury to
let them stand dry for a day or two before using, as the mercury
oxidises and the coating metal more closely adheres.
Only the very best copper plate procurable should be used for battery
tables; bad copper will always give trouble, both in the first
"curing," and after treatment. It should not be heavily rolled copper,
as the more porous the metal the more easily will the mercury
penetrate and amalgamate. I cannot agree that any good is attained by
scouring the plates with sand and alkalies, as recommended in some
books on the subject; on the contrary, I prefer the opposite mode of
treatment, and either face the plates with nitrate of silver and
nitrate of mercury, or else with sulphate of zinc and mercury, in the
form of what is called zinc amalgam. If mine water, which often
contains a little free sulphuric acid, is being used, the latter plan
is preferable.
The copper should be placed smoothly on the wooden table and secured
firmly thereto by copper tacks. If the plate should be bent or
buckled, it may be flattened by beating it with a heavy hammer, taking
care to interpose a piece of inch-thick soft wood between hammer and
plate.
To coat with mercury only, procure some nitrate of mercury. This is
easily made by placing mercury in an earthenware bowl, pouring
somewhat dilute nitric acid on it, and letting it stand till the
metallic mercury is changed to a white crystal. Dense reddish-brown
fumes will arise, which are injurious if breathed, so the operation
should be conducted either in the open air, or where there is a
draught.
Having your silvering solution ready, which is to be somewhat diluted
with water, next take two swabs, with handles about 12 inches long,
dip the first into a basin containing dilute nitric acid, and rub it
rapidly over about a foot of the surface of the plate; the oxide of
copper will be absolutely removed, and the surface of the copper
rendered pure and bright; then take the other swab, wet with the
dilute nitric of mercury, and pass it over the clean surface, rubbing
it well in. Continue this till the whole plate has a coating of
mercury. It may be well to go over it more than once. Now turn on the
water and wash the plate clean, sprinkle with metallic mercury,
rubbing it upwards until the plate will hold no more.
A basin with nitrate of mercury may be kept handy, and the plates
touched up from time to time for a few days until they get amalgamated
with gold, after which, unless you have much base metal to contend
with, they will give no further trouble.
It must be remembered, however, that an excessive use of nitric acid
will result in waste of mercury, which will be carried off in a milky
stream with the water; and also that it will cause the amalgam to
become very hard, and less active in attracting other particles of
gold.
If you are treating the plate with nitrate of silver prepared as
already mentioned, clean the plate with dilute nitric acid, rub the
surface with the ball of amalgam, following with the swab and fairly
rubbing in. It will be well to prepare the plate some days before
requiring to use it, as a better adhesion of the silver and copper
takes place than if mercury is applied at once.
To amalgamate with zinc amalgam, clean the copper plate by means of a
swab, with fairly strong sulphuric acid diluted with water; then while
wet apply the zinc-mercury mixture and well rub in. To prepare the
zinc-amalgam, clip some zinc (the lining of packing cases will do)
into small pieces and immerse them in mercury after washing them with
a little weak sulphuric acid and water to remove any coating of oxide.
When the mercury will absorb no more zinc, squeeze through chamois
leather or calico (as for silver amalgam), and well rub in. The plate
thus prepared should stand for a few days, dry, before using. If,
before amalgamation with gold takes place, oxide of copper or other
scum should rise on this plate a little very dilute sulphuric acid
will instantly remove it.
Sodium and cyanide of potassium are frequently used in dressing-
plates, but the former should be very sparingly employed, as it will
often do more harm than good by taking up all sorts of base metals
with the amalgam, and so presenting a surface which the gold will pass
over without adhering to. Where water is scarce, and is consequently
used over and over again, lime may be added to the pulp, or, if lime
is not procurable, wood ashes may be used. The effect is two-fold; the
lime not only tends to "sweeten" sulphide ores and keep the tables
clean, but also causes the water to cleanse itself more quickly of the
slimes, which will be more rapidly precipitated. When zinc amalgam is
used, alkalies would, of course, be detrimental.
When no other water than that from the mine is available, difficulties
often arise owing to the impurities it contains. These are various,
but among the most common are the soluble sulphates, and sometimes
free sulphuric acid evolved by the oxidisation of metallic sulphides.
In the presence of this difficulty, do one of two things; either
/utilise/ or /neutralise/. In certain cases, I recommend the former.
Sometime since I was treating, for gold extraction, material from a
mine which was very complex in character, and for which I coined the
term "polysynthetic." This contained about half a dozen different
sulphides. The upper parts of the lode being partially oxidised, free
sulphuric acid (H2SO4) was evolved. I therefore, following out a
former discovery, added a little metallic zinc to the mercury in the
boxes and on the plates with excellent results. When the free acid in
the ore began to give out in the lower levels I added minute
quantities of sulphuric acid to the water from time to time. I have
since found, however, that with some water, particularly West
Australian, the reaction is so feeble (probably owing to the lime and
magnesia present) as to make this mode of treatment unsuitable.
HOW TO MAKE A DOLLY
I have seen some rather elaborate dollies, intended to be worked with
amalgamating tables, but the usual prototype of the quartz mill is set
up, more or less, as follows: A tree stump, from 9 in. to a foot
diameter, is levelled off smoothly at about 2 ft. from the ground; on
this is firmly fixed a circular plate of 1/2 in. iron, say 9 in. in
diameter; a band of 3/16 in. iron, about 8 or 9 in. in height, fits
more or less closely round the plate. This is the battery box. A beam
of heavy wood, about 3 in. diameter and 6 ft. long, shod with iron, is
vertically suspended, about 9 in. above the stump, from a flexible
sapling with just sufficient spring in it to raise the pestle to the
required height. About 2 ft. from the bottom the hanging beam is
pierced with an augur hole and a rounded piece of wood, 1 1/2 in. by
18 in., is driven through to serve as a handle for the man who is to
do the pounding. His mate breaks the stone to about 2 in. gauge and
feeds the box, lifting the ring from time to time to sweep off the
triturated gangue, which he screens through a sieve into a pan and
washes off, either by means of a cradle or simply by panning. In
dollying it generally pays to burn the stone, as so much labour in
crushing is thus saved. A couple of small kilns to hold about a ton
each dug out of a clay bank will be found to save fuel where firewood
is scarce, and will more thoroughly burn the stone and dissipate the
base metals, but it must be remembered that gold from burnt stone is
liable to become so encrusted with the base metal oxides as to be
difficult to amalgamate.
ROUGH WINDLASS
Make two St. Andrew's crosses with four saplings, the upper angle
being shorter than the lower; fix these upright, one at each end of
the shaft; stay them together by cross pieces till you have
constructed something like a "horse," such as is used for sawing wood,
the crutch being a little over 3 feet high. Select a leg for a
windlass barrel, about 6 in. diameter and a foot longer than the
distance between the supports, as straight as is procurable; cut in it
two circular slots about an inch deep by 2 in. wide to fit into the
forks; at one end cut a straight slot 2 in. deep across the face. Now
get a crooked bough, as nearly the shape of a handle as nature has
produced it, and trim it into right angular shape, fit one end into
the barrel, and you have a windlass that will pull up many a ton of
stuff.
PUDDLER
This is made by excavating a circular hole about 2 ft. 9 in. deep and,
say 12 ft. in diameter. An outer and inner wall are then constructed
of slabs 2 ft. 6 in. in height to ground level, the outer wall being
thus 30 ft. and the inner 15 ft. in circumference. The circular space
between is floored with smooth hardwood slabs or boards, and the whole
made secure and water-tight. In the middle of the inner enclosure a
stout post is planted, to stand a few inches above the wall, and the
surrounding space is filled up with clay rammed tight. A strong iron
pin is inserted in the centre of the post, on which is fitted a
revolving beam, which hangs across the whole circumference of the
machine and protrudes a couple of feet or so on each side. To this
beam are attached, with short chains, a couple of drags made like V-
shaped harrows by driving a piece of red iron through a heavy frame,
shaped as a rectangular triangle.
To one end of the beam an old horse is attached, who, as he slowly
walks round the circular track, causes the harrows and drags to so
puddle the washdirt and water in the great wooden enclosure that the
clay is gradually disintegrated, and flows off with the water which is
from time to time admitted. The clean gravel is then run through a
"cradle, "long Tom," or "sluice," and the gold saved. This, of course,
is the simplest form of gold mining. In the great alluvial mines other
and more intricate appliances are used but the principle of extraction
is the same.
A MAKESHIFT PUMP
To make a temporary small "draw-lift" pump, which will work down to a
hundred feet or more if required, take a large size common suction
Douglas pump, and, after removing the top and handle, fix the pump as
close to the highest level of the water in the shaft as can be
arranged. Now make a square water-tight wooden column of slightly
greater capacity than the suction pipe, fix this to the top of the
pump, and by means of wooden rods, work the whole from the surface,
using either a longer levered handle or, with a little ingenuity,
horse-power. If you can get it the iron downpipe used to carry the
water from the guttering of houses is more easily adapted for the pipe
column; then, also, iron pump rods can be used but I have raised water
between 60 and 70 feet with a large size Douglas pump provided only
with a wooden column and rods.
SQUEEZING AMALGAM
For squeezing amalgam, strong calico, not too coarse, previously
soaked in clean water, is quite as good as ordinary chamois leather.
Some gold is fine enough to escape through either.
MERCURY EXTRACTOR
The mercury extractor or amalgam separator is a machine which is very
simple in construction, and is stated to be most efficient in
extracting quicksilver from amalgam, as it requires but from two to
three minutes to extract the bulk of the mercury from one hundred
pounds of amalgam, leaving the amalgam drier than when strained in the
ordinary way by squeezing through chamois leather or calico. The
principle is that of the De Laval cream separator--i.e., rapid
centrifugal motion. The appliance is easily put together, and as
easily taken apart. The cylinder is made of steel, and is run at a
very high rate of speed.
The general construction of the appliance is as follows: The casing or
receiver is a steel cylinder, which has a pivot at the bottom to
receive the step for an upright hollow shaft, to which a second
cylinder of smaller diameter is attached. The second cylinder is
perforated, and a fine wire cloth is inserted. The mercury, after
passing through the cloth, is discharged through the perforations.
When the machine is revolved at great speed, the mercury is forced
into the outside cylinder, leaving the amalgam, which has been first
placed in a calico or canvas bag, in a much drier state than it could
be strained by hand. While not prepared to endorse absolutely all that
is claimed for this appliance, I consider that it has mechanical
probability on its side, and that where large quantities of amalgam
have to be treated it will be found useful and effective.
SLUICE PLATES
I am indebted to Mr. F. W. Drake for the following account of sluice
plates, which I have never tried, but think the device worth
attention:
"An addition has been made to the gold-saving appliances by the
placing of what are called in America, 'sluice plates' below the
ordinary table. The pulp now flows over an amalgamating surface, 14
ft. long by 4 ft. wide, sloping 1 1/2 in. to the foot, and is then
contracted into a copper-plated sluice 15 ft. long by 14 in. wide,
having a fall of 1 in. to the foot. Our mill manager (Mr. G. C. Knapp)
advocated these sluice plates for a long time before I would consent
to a trial. I contended that as we got little or no amalgam from the
lower end of our table plates there was no gold going away capable of
being recovered by copper plates; and even if it were, narrow sluice
plates were a step in the wrong direction. If anything the
amalgamating surface should be widened to give the particles of gold a
better chance to settle. His argument was that the conditions should
be changed; by narrowing the stream and giving it less fall, gold,
which was incapable of amalgamation on the wide plates, would be
saved. We finally put one in, and it proved so successful that we now
have one at the end of each table. The per-centage recovered on the
sluice plates, of the total yield, varies, and has been as follows:--
October, 9.1 per cent; November, 6.9 per cent; December, 6.4 per cent;
January, 4.3 per cent; February, 9.3 per cent."
MEASURING INACCESSIBLE DISTANCES
To ascertain the width of a difficult gorge, a deep river, or
treacherous swamp without crossing and measuring, sight a conspicuous
object at the edge of the bank on the farther side; then as nearly
opposite and square as possible plant a stake about five feet high,
walk along the nearer margin to what you guess to be half the distance
across (exactitude in this respect is not material to the result),
there plant another stake, and continuing in a straight line put in a
third. The stakes must be equal distances apart and as nearly as
possible at a right angle to the first line. Now, carrying in hand a
fourth stake, strike a line inland at right angles to the base and as
soon as sighting over the fourth stake, you can get the fourth and
second stakes and the object on the opposite shore in line your
problem is complete. The distance between No. 4 and No. 3 stakes is
the same as that between No. 1 and the opposite bank.
TO SET OUT A RIGHT ANGLE WITH A TAPE
Measure 40 ft. on the line to which you wish to run at right angles,
and put pegs at A and B; then, with the end of the tape held carefully
at A, take 80 ft., and have the 80 ft. mark held at B. Take the 50 ft.
mark and pull from A and B until the tape lies straight and even, you
will then have the point C perpendicular to AB. Continue straight
lines by sighting over two sticks in the well-known way.
/Another method/.--Stick a pin in each corner of a square board, and
look diagonally across them, first in the direction of the line to
which you wish to run at right angles, and then for the new line sight
across the other two pins.
A SIMPLE LEVELLING INSTRUMENT
Fasten a common carpenter's square in a slit to the top of a stake by
means of a screw, and then tie a plumb-line at the angle so that it
may hang along the short arm, when the plumb-line hangs vertically and
sights may be taken over it. A carpenter's spirit-level set on an
adjustable stand will do as well. The other arm will then be a level.
Another very simple, but effective, device for finding a level line is
by means of a triangle of wood made of half-inch boards from 9 to 12
ft. long. To make the legs level, set the triangle up on fairly level
ground, suspend a plummet from the top and mark on the cross-piece
where the line touches it. Then reverse the triangle, end for end,
exactly, and mark the new line the plumb-line makes. Now make a new
mark exactly half way between the two, and when the plumb-line
coincides with this, the two legs are standing on level ground. For
short water races this is a very handy method of laying out a level
line.
TO MEASURE THE HEIGHT OF A STANDING TREE
Take a stake about your own height, and walking from the butt of the
tree to what you judge to be the height of the timber portion you
want, drive your stake into the ground till the top is level with your
eyes; now lie straight out on your back, placing your feet against the
stake, and sight a point on the tree. AB equals BC. If BC is, say 40
ft., that will be the height of your "stick of timber." Thus, much
labour may be saved in felling trees the timber portion of which may
afterwards be found to be too short for your purpose.
LEVELLING BY ANEROID BAROMETER
This should be used more for ascertaining relatively large differences
in altitudes than for purposes where any great nicety is required. For
hills under 2000 ft., the following rule will give a very close
approximation, and is easily remembered, because 55 degrees, the
assumed temperature, agrees with 55 degrees, the significant figures
in the 55,000 factor, while the fractional correction contains /two
fours/.
Observe the altitudes and also the temperatures on the Fahrenheit
thermometer at top and bottom respectively, of the hill, and take the
mean between them. Let B represent the mean altitude and b the mean
temperature. Then 55000 X B - b/B + b = height of the hill in feet for
the temperature of 55 degrees. Add 1/440 of this result for every
degree the mean temperature exceeds 55 degrees; or subtract as much
for every degree below 55 degrees.
TO DETERMINE HEIGHTS OF OBJECTS
/By Shadows/
Set up vertically a stick of known length, and measure the length of
its shadow upon a horizontal or other plane; measure also the length
of the shadow thrown by the object whose height is required. Then it
will be:--As the length of the stick's shadow is to the length of the
stick itself, so is the length of the shadow of the object to the
object's height.
/By Reflection/
Place a vessel of water upon the ground and recede from it until you
see the top of the object reflected from the surface of the water.
Then it will be:--As your horizontal distance from the point of
reflection is to the height of your eye above the reflecting surface,
so is the horizontal distance of the foot of the object from the
vessel to its altitude above the said surface.
/Instrumentally/
Read the vertical angle, and multiply its natural tangent by the
distance between instrument and foot of object; the result is the
height.
When much accuracy is not required vertical angles can be measured by
means of a quadrant of simple construction. The arc AB is a quadrant,
graduated in degrees from B to A; C, the point from which the plummet
P is suspended, being the centre of the quadrant.
/When/ the sights AC are directed towards any object, S, the degrees
in the arc, BP, are the measure of the angle of elevation, SAD, of the
object.
TO FIND THE DEPTH OF A SHAFT
/Rule/:--Square the number of seconds a stone takes to reach the
bottom and multiply by 16.
Thus, if a stone takes 5 seconds to fall to the bottom of a shaft--
5 squared = 25; and 25 X 16 = 400 feet, the required depth of shaft.
DESCRIPTION OF PLAN FOR RE-USING WATER
Where water is scarce it may be necessary to use it repeatedly. In a
case of this kind in Egypt, the Arab miners have adopted an ingenious
method which may be adapted to almost any set of conditions. At a is a
sump or water-pit; b is an inclined plane on which the mineral is
washed and whence the water escapes into a tank c; d is a conduit for
taking the water back to a; e is a conduit or lever pump for raising
the water. A certain amount of filtration could easily be managed
during the passage from c to a.
COOLING COMPOUND FOR HEATED BEARINGS
Mercurial ointment mixed with black cylinder oil and applied every
quarter of an hour, or as often as expedient. The following is also
recommended as a good cooling compound for heavy bearings:--Tallow 2
lb., plumbage 6 oz., sugar of lead 4 oz. Melt the tallow with gentle
heat and add the other ingredients, stirring until cold.
CLEANING GREASY PLUMMER BLOCKS
When, through carelessness or unpreventable cause, plummer blocks and
other detachable portions of machinery become clogged with sticky
deposits of grease and impurities, a simple mode of cleansing the same
is to take about 1000 parts by weight of boiling water, to which add
about 10 or 15 parts of ordinary washing soda. Keep the water on the
boil and place therein the portions of the machine that are to be
cleaned; this treatment has the effect of quickly loosening all
grease, oil, and dirt, after which the metal is thoroughly washed and
dried. The action of the lye is to form with the grease a soap soluble
in water. To prevent lubricating oil hardening upon the parts of the
machinery when in use, add a third part of kerosene.
AN EXCELLENT ANTI-FRICTION COMPOUND
For use on cams and stamper shanks, which will be harmless should it
drop into the mortar or stamper boxes, is graphite (black-lead) and
soft soap. When the guides are wooden, the soft soap need not be
added; black-lead made into a paste with water will act admirably.
TO CLEAN BRASS
Oxalic acid 1 oz., rotten stone 6 oz., powdered gum arabic 1/2 oz.,
sweet oil 1 oz. Rub on with a piece of rag.
A SOLVENT FOR RUST
It is often very difficult, and sometimes impossible, to remove rust
from articles made of iron. Those which are very thickly coated are
most easily cleaned by being immersed in a nearly saturated solution
of chloride of tin. The length of time they remain in this bath is
determined by the thickness of the coating of rust. Generally from
twelve to twenty-four hours is long enough.
TO PROTECT IRON AND STEEL FROM RUST
The following method is but little known, although it deserves
preference over many others. Add 7 oz. of quicklime to 1 3/4 pints of
cold water. Let the mixture stand until the supernatant fluid is
entirely clear. Then pour this off, and mix with it enough olive oil
to form a thick cream, or rather to the consistency of melted and re-
congealed butter. Grease the articles of iron or steel with this
compound, and then wrap them up in paper, or if this cannot be done,
apply the mixture somewhat more thickly.
TO KEEP MACHINERY FROM RUSTING
Take 1 oz. of camphor, dissolve it in 1 lb. of melted lard; mix with
it (after removing the scum) as much fine black-lead as will give it
an iron colour; clean the machinery, and smear it with this mixture.
After twenty-four hours rub off and clean with soft, linen cloth. This
mixture will keep machinery clean for months under ordinary
circumstances.
FIRE-LUTE
An excellent fire-lute is made of eight parts sharp sand, two parts
good clay, and one part horse-dung; mix and temper like mortar.
ROPE-SPLICING
A short splice is made by unlaying the ends of two pieces of rope to a
sufficient length, then interlaying them, draw them close and push the
strands of one under the strands of the other several times. This
splice makes a thick lump on the rope and is only used for slings,
block-straps, cables, etc.
End of The Project Gutenberg Etext of Getting Gold, by J. C. F. Johnson