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Getting Gold: A Practical Treatise for Prospectors, Miners and Students

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Title: Getting Gold: A Practical Treatise for Prospectors, Miners and Students

Author: J. C. F. Johnson


        
Release date: April 13, 2006 [eBook #3679]

Language: English

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Credits: Produced by Dagny; John Bickers; David Widger


*** START OF THE PROJECT GUTENBERG EBOOK GETTING GOLD: A PRACTICAL TREATISE FOR PROSPECTORS, MINERS AND STUDENTS ***




Produced by Dagny; John Bickers





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 1/2 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 wor

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