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GETTING & GOLD.
GRIFFIN’S STANDARD PUBLICATIONS.
Fourth Edition, Revised. Fully Illustrated. 21s.
=THE METALLURGY OF GOLD=. By T. KIRKE ROSE, D.Sc. Lond.,
Assoc. R.S.M., Chemist and Assayer to the Royal Mint.
“Adapted for all who are interested in the Gold Mining Industry,
being free from technicalities as far as possible, but is more
particularly of value to those engaged in the industry.”--_Cape
Times._
“A Comprehensive Practical Treatise on this important
subject.”--_The Times._
* * * * *
Medium 8vo. With numerous Plates, Maps, and Illustrations. 21s. net.
=CYANIDING GOLD AND SILVER ORES=: A Practical Treatise on the Cyanide
Process. By H. FORBES JULIAN, and EDGAR SMART, A.M.I.C.E.
“A handsome volume of 400 pages which will be a valuable book of
reference for all associated with the process.”--_Mining Journal._
* * * * *
Large Crown 8vo. Third English Edition. Fully Illustrated, 7s. 6d.
=THE CYANIDE PROCESS OF GOLD EXTRACTION=. By Professor JAMES PARK,
F.G.S., M.Inst.M.M.
“We can confidently recommend this book as a thoroughly
practical work, and congratulate the author at its continued
success.”--_Chemical News._
* * * * *
In Crown 8vo. Illustrated. Fancy Cloth Boards. Price 4s. 6d.
=GOLD SEEKING IN SOUTH AFRICA=; A Handbook of Hints for intending
Explorers, Prospectors, and Settlers. By THEO. KASSNER, Mine
Manager.
“The Prospector ought to include this book in his library of
reference, and the stay-at-home reader will be interested and
informed by its contents.”--_Mining World._
* * * * *
Third Edition, Revised. With Illustrations. Handsome cloth, 5s.
=PROSPECTING FOR MINERALS=. By S. HERBERT COX, Assoc. R.S.M., M.Inst.
M.M., F.G.S., &c.
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to those engaged in the practical work of Mining and
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* * * * *
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=METALLURGICAL ANALYSIS AND ASSAYING=: A THREE YEARS’ COURSE FOR
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A.O.S.M., and CHAS. WALKER, F.C.S.
“The publication of this volume tends to prove that the teaching
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* * * * *
In Large 4to. Library Style. Beautifully Illustrated with 20
Plates, many in Colours, and 94 Figures in the Text. £2, 2s. net.
=PRECIOUS STONES=: THEIR PROPERTIES, OCCURRENCES, AND USES. By Dr. MAX
BAUER. Translated by L. J. SPENCER, M.A. (Cantab.), F.G.S.
“The plates are remarkable for their beauty, delicacy, and
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* * * * *
London: CHARLES GRIFFIN & CO., Limited, Exeter St., Strand.
[Illustration: THE PROSPECTOR.--DISHWASHING OR PANNING
_Frontispiece_]
=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.
=THIRD EDITION.=
_=WITH 50 ILLUSTRATIONS AND 8 PLATES.=_
[Illustration: CHARLES GRIFFIN AND COMPANY LIMITED 1820]
LONDON:
CHARLES GRIFFIN AND COMPANY, Limited;
EXETER STREET, STRAND.
1904.
[_All rights reserved._]
* * * * *
PREFACE TO THE FIRST EDITION
Some 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.
* * * * *
PUBLISHERS’ NOTE TO THE THIRD EDITION
The reviewer in _Nature_ remarked on the First Edition of this book,
“It has often been said that _the practical man_ does not write books,
but There Is Here a Complete Refutation of the Calumny.” The sale of
two large editions has justified the opinion of the reviewer, and shows
that the book from the practical man is valued. The Third Edition has
been revised throughout and several new figures in the text and eight
full-page plates have been added. It is confidently hoped that this new
Edition will meet with the same kindly reception as the earlier ones.
_November_ 1904.
CONTENTS
CHAPTER I
INTRODUCTORY. GETTING GOLD
Gold--Poetical and historical references--Its wide
distribution--Remains of ancient works--Old appliances--Modern
appliances anticipated--Labours of alchemists--Deposition
similar to common minerals--How first obtained--The Pactolian
annual miracle--Mode of working auriferous sand and
lodes--Principal sources of gold supply--Transvaal
production--Californian production--Real date of discovery in
Australia--State encouragement for new discoveries--Obstacles
in early Australian production--Australasian production to
date--The world’s wealth--Nuggets--Modern methods--Hydraulicing
cheapest--Definition of “lode”--Igneous and aqueous theories
contrasted--Difference between reef and alluvial gold--Mining
terms explained--Usual exploitation and
treatment--Operations--Stamp battery--Its advantages as
crusher--Usual milling operations pp. 1-12
CHAPTER II
GOLD PROSPECTING
(ALLUVIAL AND GENERAL)
Ignorance of prospectors--Chapter specially addressed to the
inexperienced--Valuable finds mostly accidents--Best way to
obtain elementary knowledge--An assaying experience--What a
prospector should know--Usual geological conditions of most
minerals--Unwise to follow theories blindly--Instances of
unlikely occurrences of gold--Importance of examining
outcrops--Curious matrices for gold--Alluvial and reef
gold--Hints to prospectors--Prospecting for alluvial
gold--Tin dish--Dry blowing--Size of prospecting
shaft--Intricacy of deep leads--How to recognise true
bottom--Gold bearing “gutters”--Difference in working
shallow and wet ground pp. 13-21
CHAPTER III
LODE OR REEF PROSPECTING
Likeliest localities for reefs--Similarity of indications of
minerals--Where first prospecting is done--A practical
example--Ironstone “blows”--Their true origin--Igneous theory
untenable--Usual trend of lodes in Australia--Exceptions
to the rule--Instances of rich deposits apart from
lodes--Sinuosity of lodes--How to trace lodes
demonstrated--Examine all indications--How to recognise gold,
silver, copper, tin--How to ascertain their value--Caution
in sinking--Where to prospect in case of parallel lodes--Usual
underlie in Australia--Size of prospecting shaft--Tip for
mullock--How to distinguish gold from pyrites or
mica--Estimating value from prospect--How to pan--An
amalgamating assay method--Author’s device when antimony
present--Battery, best test--Silver and tin indications--Lode
tin, stream tin, difficulty of recognising tin--Lode tin
always near granite--Minerals often mistaken for tin--How
to discriminate--Tin in Westralia pp. 22-33
CHAPTER IV
THE GENESIOLOGY OF GOLD
(AURIFEROUS LODES)
Igneous theory formerly strongly upheld--Quotation from
Rosales--His arguments combated--Hydro-thermal action--Its
evidences in New Zealand--Professor Lobley’s theory--Author’s
deposition theory confirmed--Later works--Conclusions of
Le Conte--Metamorphic slates and earlier Silurian strata
theory--Format ion of mineral lodes--What was gold
originally?--Metal or metallic salt--Silicate hypothesis
preferred--Explanation of sulphides and silicates of
gold--Bischof’s interesting experiment--Skey’s and other
deposition experiments--How gold took its metallic form--The
Comstock lode--Occurrence of gold in shutes explained--Why
lode junctions are usually rich--Cox’s theory--Instances
of lodes re-forming--Gold as natural sulphide--Newbery’s
theory of gold in pyritous lodes--Probable occurrence in
pyritous ores as sulphide pp. 34-47
CHAPTER V
THE GENESIOLOGY OF GOLD
(AURIFEROUS DRIFTS)
Derivation and occurrence--Old diggers’ “growing”
theory--Deposition experiment illustrating nature--Denudation
of quartz lodes theory--Examples of its probability--Nuggets
require other explanation--Deposition, most rational
theory--Usual alluvial theory combated--Daintree’s and
Wilkinson’s deposition experiments--Spondulix and Lothair
nuggets--Newbery’s deposition experiments--Nugget form
explained--Author’s experiments in manufacture of golden
quartz--Extract from author’s “Deposition of
Gold”--Remarkable nugget--Reason of superiority of alluvial
gold pp. 48-58
CHAPTER VI
GOLD EXTRACTION
Division of methods of treating ores--Scientific extraction
indispensable--Superficial knowledge--German and Australian
methods compared--Schools of Mines--Antiquity of gold
working--Miner’s equipment--Tub, cradle, long tom--How
operated--Hydraulic mining--Extensive Australian
drifts--Extraction of reef gold--Amalgamation--Crushing
appliances--Preference for stampers--The Lemichel
syphon--The Griffin mill--The Huntingdon mill--Dodge
crusher--Krupp Grusonwerk Ball Mill--Premature plant
erecting--Danger of untried processes--Double faulted
lode--Automatic ore feeders--Machinery site--Foundations
for battery--Weight of stamps--Power and water required
for battery--Selection of screen--Fall of tables--Ancient
Egyptian gold washing table--Blanket tables--Successful
treatment of refractory ore in Australia--Methods vary
with ore--Importance of even crushing--Points _re_
crushing--Best form of stamper box--Cleaning plates--Form
of scraper--Retorting amalgam--Special difficulties, how
to overcome them pp. 59-86
CHAPTER VII
GOLD EXTRACTION
(SECONDARY PROCESSES AND LIXIVIATION)
Choosing the plant---Various ores and their
constituents--Amalgamation--Various concentrators--Percussion
tables--Frue vanner--Pan concentration--Simultaneous grinding
and amalgamating condemned--Watson and Denny pan--Good
machines often condemned--Procedure in ore treatment--Duncan
pan--Calcining--Rotatory amalgamator--Steaming
concentrates--Dry amalgamation--Sulphuric acid and sickened
mercury--Amalgamation without overflow--Experiments--Steam
as an agent in gold extraction--Lixiviation by
chlorine--Various processes--Mount Morgan--Cyanide process pp. 87-99
CHAPTER VIII
CALCINATION OR “ROASTING” OF ORES
Effect of roasting--Various methods--Reverberatory
furnaces--Howell, White, Brückner, Thwaite-Denny, and
Molesworth types of revolving cylinder furnaces--Shaft
type--The Stetefeldt furnace--Chimneys--Depositing chambers pp. 100-108
CHAPTER IX
MOTOR POWER AND ITS TRANSMISSION
Water and steam power--Waterless power plant described--Oil
engines--Electric transmission--Advantages of electric
power--Its possibilities pp. 109-112
CHAPTER X
COMPANY FORMATION AND OPERATIONS
Mining becoming a scientific business--Initial mistakes in
public companies--Self-styled mining experts--How articles
of association are compiled--How directors and officials
are chosen--The usual consequences--Remedies--State
inspectors--Certificates for mine managers--Directors--
Specialists in various branches advisable--Qualifications
of mine managers--Economic advantages of co-operation--Joint
central extraction works--Folly of adopting untried new
processes without full knowledge--Pertinent
quotation--Warning to directors--Robbing mills--How
prevented--Conclusion pp. 113-126
CHAPTER XI
RULES OF THUMB
Living places--A bush bed--Northern Territory
hammock--Purifying water--To obtain water from roots--An
effective filter--Canvas water-bag--Medicine case--Producing
fire--To copy correspondence--Simple telegraphic code--A
serviceable soap--To cross a flooded stream--To make a hide
bucket--To make a “slush lamp” pp. 127-139
CHAPTER XII
RULES OF THUMB
(MINING APPLIANCES AND METHODS)
A temporary forge--Making charcoal--Rough smelting on the
mine--Misfires in blasting--To prevent loss of rich
specimens in blasting--Simple retorting of small quantities
of amalgam--Simple mode of ascertaining nominal H.-P. of
engine--Scaling copper plates--How to supply mercury and
water to mortar-boxes--Power for mills--To avoid loss in
cleaning up--Iron extractor--To silver copper plates--How to
make a dolly, rough windlass, puddler--A makeshift
pump--Squeezing amalgam--Sluice plates--Measuring inaccessible
distances--To set out a right angle with tape--Simple levelling
instruments--Levelling by aneroid barometer--To determine
heights--To find depth of shaft--Plan for re-using
water--Cooling compound for heated bearing--Cleaning greasy
plummer blocks--An excellent anti-friction compound--To
clean brass--A solvent for rust--To protect iron and steel
from rust--To keep machinery from rusting--Fire-lute--
Rope-splicing pp. 140-166
APPENDIX
1. SELECTED DATA FOR MINING MEN.
To find lost part of a vein--Calculation of ore
reserves--Hydraulics--Boring--Durability of ropes--Diamond
drilling--Notes on timber--Laying out areas--Mensuration--Mine
surveying problems--Rainfall--Belting notes--Weight and bulk of
materials--Chemical elements and their symbols, &c.--Common
names of chemical substances--Thermometer readings--Freezing,
fusing, and boiling points--Heat values of fuels--Signs and
symbols used in expressing formulas--Weights and measures--To
find contents of a tank--Sizes and weights of corrugated iron
sheets--Thickness and weight of sheet iron--Qualities of
ropes--Atmosphere--Fresh and salt water--Velocity of falling
fluids--Pressure of water--Table of squares and cubes, and
their roots--Wages and interest tables. pp. 167-193
2. AUSTRALASIAN MINING REGULATIONS pp. 194-201
INDEX pp. 203-206
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 4 dwt. 13 grs., and
“two bracelets of ten shekels weight,” or about 4½ 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 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
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 cut out of stone
very similar to the amalgamating, or blanket-table, of a modern quartz
mill (_see_ p. 79).
The grinding was done between stones, and possibly by means of such
primitive mechanism as is used to-day by the natives of Korea.
[Illustration: FIG. 1. KOREAN MILL.]
The Korean Mill is simply a large hard stone shaped as in Fig. 1, 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 bi-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 so many millions of English capital, is now, after much
difficulty and disappointment--thanks to British pluck and
skill--producing splendidly. The yield for 1898 was 4,295,609, and for
1903 2,859,477 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.
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 might have
imagined that even in those unenlightened days it would not have been
difficult to find 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 depôt for the
scoundrelism of Britain--“Hurrah for the bright red gold!”
From the year 1851 to 1897 the value of the gold raised in the
Australasian colonies realised the enormous amount of nearly
£550,000,000. 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, &c.,
4230 tons of silver more than it mined. From 1800 to 1870 the value of
gold was about 15½ times that of silver. From 1870 to 1880 it was
16·7 times the value of silver and now exceeds it over twenty times. In
1700 the world had 301 million pounds of money, and in 1860, 1180
million pounds sterling. In 1894 the current gold was worth about
£800,000,000.
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. 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 2268½ ozs., and it was sold for
£10,000, 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 puddlers, 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.
[Illustration: FIG. 2. LODE FORMATION IN SLATE AND SANDSTONE.]
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
(Fig. 2); 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, &c.)
are reached. Again, there is a form of lode known among miners as a
“gash” vein (Fig. 3). It is sometimes met with in the older crystalline
slates, particularly when the lode runs conformably with the cleavage of
the rock.
[Illustration: FIG. 3. GASH VEIN.]
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 hydro-thermal (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 White and Pink Terraces, destroyed
by volcanic action some sixteen 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
labour 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 of the lode 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,” consisting for
the most part of sulphides of iron, copper, and lead, are washed off
from time to time and reserved for secondary treatment.
First, they are roasted to get rid of the sulphur, arsenic, &c, 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 cyanogen.
If, however, we are merely amalgamating, then at stated periods the
battery and pans are cleared 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 mercurial 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, &c), will be more fully
described further on.