Getting Gold
by
J. C. F. Johnson
Part 1 out of 3
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Etext prepared by Dagny, dagnyj@hotmail.com
and John Bickers, jbickers@ihug.co.nz
GETTING GOLD:
A PRACTICAL TREATISE
FOR
PROSPECTORS, MINERS, AND STUDENTS.
BY
J. C. F. JOHNSON, F. G. S.,
MEMBER OF THE AUST. INST. OF MINING ENGINEERS;
AUTHOR OF
"PRACTICAL MINING," "THE GENESIOLOGY OF GOLD," ETC.
PREPARER'S NOTE
This text was prepared from a 1898 edition, published by Charles
Griffin & Company, Limited; Exeter Street, Strand, London. It is
the second edition, revised. Numerous drawings and diagrams have
been omitted.
PREFACE
Some six years ago the author published a small book entitled
"Practical Mining," designed specially for the use of those
engaged in the always fascinating, though not as invariably
profitable, pursuit of "Getting Gold." Of this ten thousand copies
were sold, nearly all in Australasia, and the work is now out of
print. The London /Mining Journal/ of September 9th, 1891, said of
it: "We have seldom seen a book in which so much interesting
matter combined with useful information is given in so small a
space."
The gold-mining industry has grown considerably since 1891, and it
appeared to the writer that the present would be a propitious time
to bring out a similar work, but with a considerably enlarged
scope. What has been aimed at is to make "Getting Gold" a
compendium, in specially concrete form, of useful information
respecting the processes of winning from the soil and the after-
treatment of gold and gold ores, including some original practical
discoveries by the author. Practical information, original and
selected, is given to mining company directors, mine managers,
quartz mill operators, and prospectors. In "Rules of Thumb,"
chapters XI. and XII., will be found a large number of useful
hints on subjects directly and indirectly connected with gold-
mining.
The author's mining experience extends back thirty years and he
therefore ventures to believe with some degree of confidence that
the information, original or compiled, which the book contains,
will be found both useful and profitable to those who are in any
capacity interested in the gold-mining industry.
J. C. F. J.
LONDON, November, 1896.
GETTING GOLD
CHAPTER I
INTRODUCTORY
GOLD is a name to charm by. It is desired by all nations, and is the
one metal the supply of which never exceeds the demand. Some one has
aptly said, "Gold is the most potent substance on the surface of our
planet." Tom Hood sings:
Gold, gold, gold, gold!
Bright and yellow, hard and cold;
Molten, graven, hammered, rolled,
Heavy to get, and light to hold;
Stolen, borrowed, squandered, doled.
That this much appreciated metal is heavy to get is proved by the high
value which has been placed on it from times remote to date, and that
it is light to hold most of us know to our cost.
We read no farther than the second chapter in the Bible when we find
mention of gold. There Moses speaks of "the land of Havilah, where
there is gold"; and in Genesis, chapter xxiv., we read that Abraham's
servant gave Rebekah an earring of half a shekel weight, say 5 dwt. 13
grs., and "two bracelets of ten shekels weight," or about 4 1/2 ozs.
Then throughout the Scriptures, and, indeed, in all historic writings,
we find frequent mention of the king of metals, and always it is
spoken of as a commodity highly prized.
I have sometimes thought, however, that either we are mistaken in the
weights used by the Hebrew nation in early days, or that the
arithmetic of those times was not quite "according to Cocker." We
read, I. Kings x. and xli., that Solomon in one year received no less
than six hundred and three score and six talents of gold. If a talent
of gold was, as has been assumed, 3000 shekels of 219 grains each, the
value of the golden treasure accumulated in this one year by the
Hebrew king would have been 3,646,350 pounds sterling. Considering
that the only means of "getting gold" in those days was a most
primitive mode of washing it from river sands, or a still more
difficult and laborious process of breaking the quartz from the lode
without proper tools or explosives, and then slowly grinding it by
hand labour between two stones, the amount mentioned is truly
enormous.
Of this treasure the Queen of Sheba, who came to visit the Hebrew
monarch, contributed a hundred and twenty talents, or, say, 600,000
pounds worth. Where the Land of Ophir, whence this golden lady came,
was really situated has evoked much controversy, but there is now a
general opinion that Ophir was on the east coast of Africa, somewhere
near Delagoa Bay, in the neighbourhood of the Limpopo and Sabia
rivers. It should be mentioned that the name of the "black but comely"
queen was Sabia, which may or may not be a coincidence, but it is
certainly true that the rivers of this district have produced gold
from prehistoric times till now.
The discovery of remarkable ruins in the newly acquired province of
Mashonaland, which evince a high state of civilisation in the
builders, may throw some light on this interesting subject.
The principal value of gold is as a medium of exchange, and its high
appreciation is due, first, to the fact that it is in almost universal
request; and, secondly, to its comparative scarcity; yet, oddly
enough, with the exception of that humble but serviceable metal iron,
gold is the most widely distributed metal known. Few, if any,
countries do not possess it, and in most parts of the world, civilised
and uncivilised, it is mined for and brought to market. The torrid,
temperate, and frigid zones are almost equally auriferous. Siberia,
mid-Asia, most parts of Europe, down to equatorial and southern Africa
in the Old World, and north, central, and southern America, with
Australasia, in what may be termed the New World, are all producers of
gold in payable quantities.
In the earlier ages, the principal source of the precious metal was
probably Africa, which has always been prolific in gold. To this day
there are to be seen in the southern provinces of Egypt excavations
and the remains of old mine buildings and appliances left by the
ancient gold-miners, who were mostly State prisoners. Some of these
mines were worked by the Pharaohs of, and before, the time of Moses;
and in these dreadful places thousands of Israelites were driven to
death by the taskmaster's whip. Amongst the old appliances is one
which approximated very closely to the amalgamating, or blanket table,
of a modern quartz mill.
The grinding was done between two stones, and possibly by means of
such primitive mechanism as is used to-day by the natives of Korea.
The Korean Mill is simply a large hard stone to which a rocking motion
is given by manual power by means of the bamboo handles while the ore
is crushed between the upper and basement stone.
Solomon says "there is no new thing under the sun"; certainly there is
much that is not absolutely new in appliances for gold extraction. I
lately learned that the principle of one of our newest concentrating
machines, the Frue vanner, was known in India and the East centuries
ago; and we have it on good authority--that of Pliny--that gold saving
by amalgamation with mercury was practised before the Christian era.
It will not be surprising then if, ere long, some one claims to have
invented the Korean Mill, with improvements.
Few subjects in mineralogical science have evoked more controversy
than the origin of gold. In the Middle Ages, and, indeed, down to the
time of that great philosopher, Sir Isaac Newton, who was himself
bitten with the craze, it was widely believed that, by what was known
as transmutation, the baser metals might be changed to gold; and much
time and trouble were expended in attempts to make gold--needless to
say without the desired result. Doubtless, however, many valuable
additions to chemical science, and also some useful metallic alloys,
were thus discovered.
The latest startling statement on this subject comes from, of course,
the wonderland of the world, America. In a recently published journal
it is said that a scientific metallurgist there has succeeded in
producing absolutely pure gold, which stands all tests, from silver.
Needless to say, if this were true, at all events the much vexed hi-
metallic question would be solved at once and for all time.
It is now admitted by all specialists that the royal metal, though
differing in material respects in its mode of occurrence from its
useful but more plebeian brethren of the mineral kingdom, has yet been
deposited under similar conditions from mineral salts held in
solution.
The first mode of obtaining this much desired metal was doubtless by
washing the sand of rivers which flowed through auriferous strata.
Some of these, such as the Lydian stream, Pactolus, were supposed to
renew their golden stores miraculously each year. What really happened
was that the winter floods detached portions of auriferous drift from
the banks, which, being disintegrated by the rush and flow of the
water, would naturally deposit in the still reaches and eddies any
gold that might be contained therein.
The mode of washing was exactly that carried on by the natives in some
districts of Africa to-day. A wooden bowl was partly filled with
auriferous sand and mud, and, standing knee-deep in the stream, the
operator added a little water, and caused the contents of the bowl to
take a circular motion, somewhat as the modern digger does with his
tin dish, with this difference, that his ancient prototype allowed the
water and lighter particles to escape over the rim as he swirled the
stuff round and round. I presume, in finishing the operation, he
collected the golden grains by gently lapping the water over the
reduced material, much as we do now.
I have already spoken of the mode in which auriferous lode-stuff was
treated in early times--i.e., by grinding between stones. This is also
practised in Africa to-day, and we have seen that the Koreans, with
Mongolian acuteness, have gone a step farther, and pulverise the
quartz by rocking one stone on another. In South America the arrastra
is still used, which is simply the application of horse or mule power
to the stone-grinding process, with use of mercury.
The principal sources of the gold supply of the modern world have
been, first, South America, Transylvania in Europe, Siberia in Asia,
California in North America, and Australia. Africa has always produced
gold from time immemorial.
The later development in the Johannesburg district, Transvaal, which
has absorbed during the last few years so many millions of English
capital, is now, after much difficulty and disappointment--thanks to
British pluck and skill--producing splendidly. The yield for 1896 was
2,281,874 ounces--a yield never before equalled by lode-mining from
one field.
In the year 1847 gold was discovered in California, at Sutor's
sawmill, Sacramento Valley, where, on the water being cut off, yellow
specks and small nuggets were found in the tail race. The enormous
"rush" which followed is a matter of history and the subject of many
romances, though the truth has, in this instance, been stranger than
fiction.
The yield of the precious metal in California since that date up to
1888 amounts to 256,000,000 pounds.
Following close on the American discovery came that of Australia, the
credit of which has usually been accorded to Hargraves, a returned
Californian digger, who washed out payable gold at Lewis Ponds Creek,
near Bathurst, in 1851. But there is now no reason to doubt that gold
had previously been discovered in several parts of that great island
continent. It may be news to many that the first gold mine worked in
Australia was opened about twelve miles from Adelaide city, S.A., in
the year 1848. This mine was called the Victoria; several of the
Company's scrip are preserved in the Public Library; but some two
years previous to this a man named Edward Proven had found gold in the
same neighbourhood.
Most Governments nowadays encourage in every possible way the
discovery of gold-fields, and rewards ranging from hundreds to
thousands of pounds are given to successful prospectors of new
auriferous districts. The reward the New South Wales authorities meted
out to a wretched convict, who early in this century had dared to find
gold, was a hundred lashes vigorously laid on to his already
excoriated back. The man then very naturally admitted that the alleged
discovery was a fraud, and that the nugget produced was a melted down
brass candlestick. One would have imagined that even in those
unenlightened days it would not have been difficult to have found a
scientist sufficiently well informed to put a little nitric acid on
the supposed nugget, and so determine whether it was the genuine
article, without skinning a live man first to ascertain. My belief is
that the unfortunate fellow really found gold, but, as Mr. Deas
Thompson, the then Colonial Secretary, afterwards told Hargraves in
discouraging his reported discovery, "You must remember that as soon
as Australia becomes known as a gold-producing country it is utterly
spoiled as a receptacle for convicts."
This, then, was the secret of the unwillingness of the authorities to
encourage the search for gold, and it is after all due to the fact
that the search was ultimately successful beyond all precedent, that
Australia has been for so many years relieved of the curse of
convictism, and has ceased once and for all to be a depot for the
scoundrelism of Britain--"Hurrah for the bright red gold!"
Since the year 1851 to date the value of the gold raised in the
Australasian colonies has realised the enormous amount of nearly
550,000,000 pounds. One cannot help wondering where it all goes.
Mulhall gives the existing money of the world at 2437 million pounds,
of which 846 millions are paper, 801 millions silver, and 790 millions
gold. From 1830 to 1880 the world consumed by melting down plate,
etc., 4230 tons of silver more than it mined. From 1800 to 1870 the
value of gold was about 15 1/2 times that of silver. From 1870 to 1880
it was 167 times the value of silver and now exceeds it over twenty
times. In 1700 the world had 301 million pounds of money; in 1800, 568
million pounds; and in 1860, 1180 million pounds sterling.
The gold first worked for in Australia, as in other places, was of
course alluvial, by which is usually understood loose gold in nuggets,
specks, and dust, lying in drifts which were once the beds of long
extinct streams and rivers, or possibly the moraines of glaciers, as
in New Zealand.
Further on the differences will be mentioned between "alluvial" and
"reef" or lode gold, for that there is a difference in origin in many
occurrences, is, I think, provable. I hold, and hold strongly, that
true alluvial gold is not always derived from the disintegration of
lodes or reefs. For instance, the "Welcome Nugget" certainly never
came from a reef. No such mass of gold, or anything approaching it,
has ever yet been taken from a quartz matrix. It was found at Bakery
Hill, Ballarat, in 1858, weight 2195 ozs., and sold for 10,500 pounds.
This was above its actual value.
The "Welcome Stranger," a still larger mass of gold, was found amongst
the roots of a tree at Dunolly, Victoria, in 1869, by two starved out
"fossickers" named Deeson and Oates. The weight of this, the largest
authenticated nugget ever found was 2268 1/2 ozs., and it was sold for
10,000 pounds, but it was rendered useless as a specimen by the
finders, who spent a night burning it to remove the adhering quartz.
But the ordinary digger neither hopes nor expects to unearth such
treasures as these. He is content to gather together by means of
puddling machine, cradle, long tom, or even puddling tub and tin dish,
the scales, specks, dust, and occasional small nuggets ordinarily met
with in alluvial "washes."
Having sunk to the "wash," or "drift," the digger, by means of one or
more of the appliances mentioned above, proceeds to separate the gold
from the clay and gravel in which it is found. Of course in large
alluvial claims, where capital is employed, such appliances are
superseded by steam puddles, buddles, and other machinery, and
sometimes mercury is used to amalgamate the gold when very fine.
Hydraulicing is the cheapest form of alluvial mining, but can only be
profitably carried out where extensive drifts, which can be worked as
quarry faces, and unlimited water exist in the same neighbourhood.
When such conditions obtain a few grains of gold to the yard or ton
will pay handsomely.
Lode or reef mining, is a more expensive and complicated process,
requiring much skill and capital. First, let me explain what a lode
really is. The American term is "ledge," and it is not inappropriate
or inexpressive. Imagine then a ledge, or kerbstone, continuing to
unknown depths in the earth at any angle varying from perpendicular to
nearly horizontal. This kerbstone is totally distinct from the rocks
which enclose it; those on one side may be slate, on the other,
sandstone; but the lode, separated usually by a small band of soft
material known to miners as "casing," or fluccan," preserves always an
independent existence, and in many instances is practically bottomless
so far as human exploration is concerned.
There are, however, reefs or lodes which are not persistent in depth.
Sometimes the lode formation is found only in the upper and newer
strata, and cuts out when, say, the basic rocks (such as granite,
etc.) are reached. Again, there is a form of lode known among miners
as a "gash" vein. It is sometimes met with in the older crystalline
slates, particularly when the lode runs conformably with the cleavage
of the rock.
Much ignorance is displayed on the subject of lode formation and the
deposition of metals therein, even by mining men of long experience.
Many still insist that lodes, particularly those containing gold, are
of igneous origin, and point to the black and brown ferro-manganic
outcrops in confirmation. It must be admitted that often the upper
portions of a lode present a strong appearance of fire agency, but
exactly the same appearance can be caused by oxidation of iron and
manganese in water.
It may now be accepted as a proven fact that no true lode has been
formed, or its metals deposited except by aqueous action. That is to
say, the bulk of the lode and all its metalliferous contents were once
held in solution in subterranean waters, which were ejected by geysers
or simply filtered into fissures formed either by the shrinkage of the
earth's crust in process of cooling or by volcanic force.
It is not contended that the effect of the internal fires had no
influence on the formation of metalliferous veins, indeed, it is
certain that they had, but the action was what is termed hydrothermal
(hot water); and such action we may see in progress to-day in New
Zealand, where hot springs stream or spout above the surface, when the
silica and lime impregnated water, reduced in heat and released from
pressure, begins forthwith to deposit the minerals previously held in
solution. Hence the formation of the wondrous Pink and White Terrace,
destroyed by volcanic action some eight years since, which grew almost
while you watched; so rapidly was the silica deposited that a dead
beetle or ti-tree twig left in the translucent blue water for a few
days became completely coated and petrified.
Gold differs in its mode of occurrence from other metals in many
respects; but there is no doubt that it was once held in aqueous
solution and deposited in its metallic form by electro-chemical
action. It is true we do not find oxides, carbonates, or bromides of
gold in Nature, nor can we feel quite sure that gold now exists
naturally as a sulphide, chloride, or silicate, though the presumption
is strongly that it does. If so, the deposition of the gold may be
ceaselessly progressing.
Generally reef gold is finer as to size of the particles, and, as a
rule, inferior in quality to alluvial. Thus, in addition to the extra
labor entailed in breaking into one of the hardest of rocks, quartz,
the /madre de oro/ ("mother of gold") of the Spaniards, there is the
additional labour required to pulverise the rock so as to set free the
tiniest particles of the noble metal it so jealously guards. There is
also the additional difficult operation of saving and gathering
together these small specks, and so producing the massive cakes and
bars of gold in their marketable state.
Having found payable gold in quartz on the surface, the would-be miner
has next to ascertain two things. First, the strike or course of the
lode; and secondly, its underlie, or dip. The strike, or course, is
the direction which the lode takes lengthwise.
In Australia the term "underlie" is used to designate the angle from
the perpendicular at which the lode lies in its enclosing rocks, and
by "dip" the angle at which it dips or inclines lengthwise on its
course. Thus, at one point the cap of a lode may appear on the
surface, and some distance further the cap may be hundreds of feet
below. Usually a shaft is sunk in the reef to prove the underlie, and
a level, or levels, driven on the course to ascertain its direction
underground, also if the gold extends, and if so, how far. This being
proved, next a vertical shaft is sunk on the hanging or upper wall
side, and the reef is either tapped thereby, or a cross-cut driven to
intersect it.
We will now assume that our miners have found their lode payable, and
have some hundreds of tons of good gold-bearing stone in sight or at
the surface. They must next provide a reducing plant. Of means for
crushing or triturating quartz there is no lack, and every year gives
us fresh inventions for the purpose, each one better than that which
preceded it, according to its inventor. Most practical men, however,
prefer to continue the use of the stamper battery, which is virtually
a pestle and mortar on a large scale. Why we adhere to this form of
pulverising machine is that, though somewhat wasteful of power, it is
easily understood, its wearing parts are cheaply and expeditiously
replaced, and it is so strong that even the most perversely stupid
workman cannot easily break it or put it out of order.
The stone, being pounded into sand of such degree of fineness as the
gold requires, passes through a perforated iron plate called a
"grating," or "screen," on to an inclined surface of copper plates
faced with mercury, having small troughs, or "riffles," containing
mercury, placed at certain distances apart.
The crushed quartz is carried over these copper "tables," as they are
termed, thence over the blanket tables--that is, inclined planes
covered with coarse serge, blankets, or other flocculent material--so
that the heavy particles may be caught in the hairs, or is passed over
vanners or concentrating machines. The resulting "concentrates" are
washed off from time to time and reserved for secondary treatment.
To begin with, they are roasted to get rid of the sulphur, arsenic,
etc., which would interfere with the amalgamation or lixiviation, and
then either ground to impalpable fineness in one of the many
triturating pans with mercury, or treated by chlorine or potassium
cyanide.
If, however, we are merely amalgamating, then at stated periods the
battery and pans are cleaned out, the amalgam rubbed or scraped from
the copper plates and raised from the troughs and riffles. It is then
squeezed through chamois leather, or good calico will do as well, and
retorted in a large iron retort, the nozzle of which is kept in water
so as to convert the mercury vapour again to the metallic form. The
result is a spongy cake of gold, which is either sold as "retorted"
gold or smelted into bars.
The other and more scientific methods of extracting the precious metal
from its matrices, such as lixiviation or leaching, by means of
solvents (chlorine, cyanogen, hyposulphite of soda, etc.), will be
more fully described later on.
CHAPTER II
GOLD PROSPECTING--ALLUVIAL AND GENERAL
It is purposed in this chapter to deal specially with the operation of
searching for valuable mineral by individuals or small working
parties.
It is well known that much disappointment and loss accrue through lack
of knowledge by prospectors, who with all their enterprise and energy
are often very ignorant, not only of the probable locality, mode of
occurrence, and widely differing appearance of the various valuable
minerals, but also of the best means of locating and testing the ores
when found. It is for the information of such as these that this
chapter is mainly intended, not for scientists or miners of large
experience.
All of us who have had much to do with mining know that the majority
of the best mineral finds have been made by the purest accident; often
by men who had no mining knowledge whatever; and that many valuable
discoveries have been delayed, or, when made, abandoned as not
payable, from the same cause--ignorance of the rudiments of mineralogy
and mining. I have frequently been asked by prospectors, when
inspecting new mineral fields, what rudimentary knowledge will be most
useful to them and how it can be best obtained.
If a man can spare the time a course of lessons at some accredited
school of mines will be, undoubtedly, the best possible training; but
if he asks what books he should read in order to obtain some primary
technical instruction, I reply: First, an introductory text-book of
geology, which will tell him in the simplest and plainest language all
he absolutely requires to know on this important subject. Every
prospector should understand elementary geology so far as general
knowledge of the history of the structure of the earth's crust and of
the several actions that have taken place in the past, or are now in
operation, modifying its conditions. He may with advantage go a few
steps further and learn to classify the various formations into
systems, groups, and series: but he can acquire all that he need
absolutely know from this useful little 2s. 6d. book. Next, it is
advisable to learn something about the occurrence and appearance of
the valuable minerals and the formations in which they are found. For
all practical purposes I can recommend Cox and Ratte's "Mines and
Minerals," one of the Technical Education series of New South Wales,
which deals largely with the subject from an Australian standpoint,
and is therefore particularly valuable to the Australian miner, but
which will be found applicable to most other gold-bearing countries. I
must not, however, omit to mention an admirably compiled /multum in
parvo/ volume prepared by Mr. G. Goyder, jun., Government Assayer and
Assay Instructor at the School of Mines, Adelaide. It is called the
"Prospectors' Pocketbook," costs only one shilling, is well bound, and
of handy size to carry. In brief, plain language it describes how a
man, having learned a little of assaying, may cheaply provide himself
with a portable assay plant, and fluxes, and also gives considerable
general information on the subject of minerals, their occurrence and
treatment.[*]
[*] Another excellent and really practical book is Prof. Cole's
"Practical Aids in Geology" (second edition), 10s. 6d.
It may here be stated that some twelve years ago I did a large amount
of practical silver assaying on the Barrier (Broken Hill), which was
not then so accessible a place as it is now, and got closely correct
results from a number of different mines, with an extemporised plant
almost amusing in its simplicity. All I took from Adelaide were a
small set of scales capable of determining the weight of a button down
to 20 ozs. to the ton, a piece of cheese cloth to make a screen or
sieve, a tin ring 1 l/2 in. diameter, by 1/2 in. high, a small brass
door knob to use as a cupel mould, and some powdered borax, carbonate
of soda, and argol for fluxes; while for reducing lead I had recourse
to the lining of a tea-chest, which lead contains no silver--John
Chinaman takes good care of that. My mortar was a jam tin, without top
or bottom, placed on an anvil; the pestle a short steel drill. The
blacksmith at Mundi Mundi Station made me a small wrought iron
crucible, also a pair of bent tongs from a piece of fencing-wire. The
manager gave me a small common red flower pot for a muffle, and with
the smith's forge (the fire built round with a few blocks of talcose
schist) for a furnace, my plant was complete. I burned and crushed
bones to make my bone-dust for cupelling, and thus provided made
nearly forty assays, some of which were afterwards checked in
Adelaide, in each instance coming as close as check assays generally
do. Nowadays one can purchase cheaply a very effective portable plant,
or after a few lessons a man may by practice make himself so
proficient with the blowpipe as to obtain assay results sufficiently
accurate for most practical purposes.
Coming then to the actual work of prospecting. What the prospector
requires to know is, first, the usual locality of occurrence of the
more valuable minerals; secondly, their appearance; thirdly, a simple
mode of testing. With respect to occurrence, the older sandy and clay
slates, chlorite slates, micaceous, and hornblendic schists,
particularly at or near their junction with the intrusive granite and
diorite, generally form the most likely geological country for the
finding of mineral lodes, particularly gold, silver and tin. But those
who have been engaged in practical mining for long, finding by
experience that no two mineral fields are exactly alike in all their
characteristics, have come to the conclusion that it is unwise to form
theories as to why metals should or should not be found in certain
enclosing rocks or matrices. Some of the best reef gold got in
Victoria has been obtained in dead white, milky-looking quartz almost
destitute of base metal. In South Australia reef gold is almost
invariably associated with iron, either as oxide, as "gossan;" or
ferruginous calcite, "limonite;" or granular silica, conglomerated by
iron, the "ironstone" which forms the capping or outcrop of many of
our reefs, and which is often rich in gold.
But to show that it is unsafe to decide off-hand in what class of
matrix metals will or will not be found, I may say that in my own
experience I have seen payable gold in the following materials:--
Quartz, dense and milky, also in quartz of nearly every colour and
appearance, saccharoidal, crystalline, nay, even in clear glass-like
six-sided prismatic crystals, and associated with silver, copper,
lead, arsenic, iron as sulphide, oxide, carbonate, and tungstate,
antimony, bismuth, nickel, zinc, lead, and other metals in one form or
another; in slate, quartzite, mica schist, granite, diorite, porphyry,
felsite, calcite, dolomite, common carbonate of iron, siliceous sinter
from a hot spring, as at Mount Morgan; as alluvial gold in drifts
formed of almost all these materials; and once, perhaps the most
curious matrix of all, a small piece of apparently alluvial gold,
naturally imbedded in a shaly piece of coal. This specimen, I think,
is in the Sydney Museum. One thing, however, the prospector may make
sure of: he will always find gold more or less intimately associated
with silica (Quartz) in one or other of its many forms, just as he
will always find cassiterite (oxide of tin) in the neighbourhood of
granite containing muscovite (white mica), which so many people will
persist in terming talc. It is stated to be a fact that tin has never
been found more than about two miles from such granite.
From what has been said of its widely divergent occurrences it will be
admitted that the Cornish miners' saying with regard to metals
generally applies with great force to gold: "Where it is, there it
is": and "Cousin Jack" adds, with pathetic emphasis, "and where it is
generally, there I ain't."
I have already spoken of the geological "country rock" in which red
gold is most likely to be discovered--i.e., the junction of the slates
and schists with the igneous or metamorphic (altered) rocks, or in
this vicinity. Old river beds formed of gravelly drifts in the same
neighbourhood may probably contain alluvial gold, or shallow deposits
of "wash" on hillsides and in valleys will often carry good surface
gold. This is sometimes due to the denudation, or wearing away, of the
hills containing quartz-veins--that is, where the alluvial gold really
was derived from such veins, which, popular opinion to the contrary,
is not always the case.
Much disappointment and loss of time and money may sometimes be
prevented if prospectors will realise that /all/ alluvial gold does
not come from the quartz veins or reefs; and that following up an
alluvial lead, no matter how rich, will not inevitably develop a
payable gold lode. Sometimes gold, evidently of reef origin, is found
in the alluvial; but in that case it is generally fine as regards the
size of the particles, more or less sharp-edged, or crystalline in
form if recently shed; while such gold is often of poorer quality than
the true alluvial which occurs in mammillary (breast-like) nuggets,
and is of a higher degree of purity as gold.
The ordinary non-scientific digger will do well to give credence to
this view of the case, and will often thereby save himself much
useless trouble. Sometimes also the alluvial gold, coarser in size
than true reef-born alluvial, is derived almost /in situ/ from small
quartz "leaders," or veins, which the grinding down of the face of the
slates has exposed; these leaders in time being also broken and worn,
set free the gold they have contained, which does not, as a rule,
travel far, but sometimes becomes water-worn by the rubbing over it of
the disintegrated fragments of rock.
But the heavy, true alluvial gold, in great pure masses, mammillary,
or botryoidal (like a bunch of grapes) in shape, have assuredly been
formed by accretion on some metallic base, from gold salts in
solution, probably chloride, but possibly sulphide.
Nuggets, properly so-called, are never found in quartz lodes; but, as
will be shown later, a true nugget having all the characteristics of
so-called water-worn alluvial may be artificially formed on a small
piece of galena, or pyrites, by simply suspending the base metal by a
thread in a vessel containing a weak solution of chloride of gold in
which a few hard-wood chips are thrown.
Prospecting for alluvial gold at shallow depths is a comparatively
easy process, requiring no great amount of technical knowledge.
Usually the first gold is got at or near the surface and then traced
to deep leads, if such exist.
At Mount Brown Goldfield, N.S.W., in 1881, I saw claimholders turning
out to work equipped only with a small broom made of twigs and a tin
dish. With the broom they carefully swept out the crevices of the
decomposed slate as it was exposed on the surface, and putting the
resulting dust and fragments into the tin dish proceeded to dry blow
it.
The /modus operandi/ is as follows: The operator takes the dish about
half full of dirt, and standing with his back or side to the wind, if
there be any, begins throwing the stuff up and catching it, or
sometimes slowly pouring it from one dish to another, the wind in
either case carrying away the finer particles. He then proceeds to
reduce the quantity by carefully extracting the larger fragments of
rock, till eventually he has only a handful or so of moderately fine
"dirt" which contains any gold there may be. If in good sized nuggets
it is picked out, if in smaller pieces or fine grains the digger
slowly blows the sand and dust aside with his breath, leaving the gold
exposed. This process is both tedious and unhealthy, and of course can
only be carried out with very dry surface dirt. The stuff in which the
gold occurred at Mount Brown was composed of broken slate with a few
angular fragments of quartz. Yet, strange to say, the gold was
invariably waterworn in appearance.
Dry blowing is now much in vogue on the West Australian fields owing
to the scarcity of water; but the great objection is first, the large
amount of dust the unfortunate dry blower has to carry about his
person, and secondly, that the peck of dirt which is supposed to last
most men a life time has to be made a continuous meal of every day.
For wet alluvial prospecting the appliances, besides pick and shovel,
are puddling tub, tin dish, and cradle; the latter, a man handy with
tools can easily make for himself.
In sinking, the digger should be careful to avoid making his shaft
inconveniently small, and not to waste his energy by sinking a large
"new chum" hole, which usually starts by being about three times too
large for the requirements at the surface, but narrows in like a
funnel at 10 feet or less. A shaft, say 4 feet by 2 feet 6 inches and
sunk plumb, the ends being half rounded, is large enough for all
requirements to a considerable depth, though I have seen smart men,
when they were in a hurry to reach the drift, get down in a shaft even
less in size.
The novice who is trying to follow or to find a deep lead must fully
understand that the present bed of the surface river may not, in fact
seldom does, indicate the ancient watercourses long since buried
either by volcanic or diluvial action, which contain the rich
auriferous deposits for which he is seeking; and much judgment and
considerable underground exploration are often required to decide on
the true course of leads. Only by a careful consideration of all the
geological surroundings can an approximate idea be obtained from
surface inspection alone; and the whole probable conditions which led
to the present contour of the country must be carefully taken into
account.
How am I to know the true bottom when I see it? asks the inexperienced
digger. Well, nothing but long experience and intelligent observation
will prevent mistakes at times, particularly in deep ground; but as a
general rule, though it may sound paradoxical, you may know the bottom
by the top.
That is, we will assume you are sinking in, say, 10 to 12 feet ground
in a gully on the bank of which the country rock is exposed, and is,
say, for instance, a clay slate or sandy slate set at a certain angle;
then, in all probability, unless there be a distinct fault or change
in the country rock between the slate outcrop and your shaft, the
bottom will be a similar slate, standing at the same angle; and this
will very probably be overlaid by a deposit of pipeclay, formed by the
decomposition of the slates.
From the crevices of these slates, sometimes penetrating to a
considerable distance, you may get gold, but it is useless attempting
to sink through them. If the outcropping strata be a soft calcareous
(limy) sandstone or soft felspathic rock, and that be also the true
bottom, great care should be exercised or one is apt to sink through
the bottom, which may be very loose and decomposed. I have known
mistakes made in this way when many feet have been sunk, and driven
through what was actually bed rock, though so soft as to deceive even
men of experience. The formation, however, must be the guide, and
except in some specially difficult cases, a man can soon tell when he
is really on bed rock or "bottom."
On an alluvial lead the object of every one is to "get on the gutter,"
that is, to reach the lowest part of the old underground watercourse,
through which for centuries the gold may have been accretionising from
the percolation of the mineral-impregnated water; or, when derived
from reefs or broken down leaders, the flow of water has acted as a
natural sluice wherein the gold is therefore most thickly collected.
Sometimes the lead runs for miles and is of considerable width, at
others it is irregular, and the gold-bearing "gutter" small and hard
to find. In many instances, for reasons not readily apparent, the best
gold is not found exactly at the lowest portion of these narrow
gutters, but a little way up the sides. This fact should be taken into
consideration in prospecting new ground, for many times a claim has
been deserted after cleaning up the "bottom," and another man has got
far better gold considerably higher up on the sides of the gutter. For
shallow alluvial deposits, where a man quickly works out his 30 by 30
feet claim, it may be cheaper at times to "paddock" the whole ground--
that is, take all away from surface to bottom, but if he is in wet
ground and he has to drive, great care should be taken to properly
secure the roof by means of timber. How this may best be done the
local circumstances only can decide.
CHAPTER III
LODE OR REEF PROSPECTING
The preceding chapter dealt more especially with prospecting as
carried on in alluvial fields. I shall now treat of preliminary mining
on lodes or "reefs."
As has already been stated, the likeliest localities for the
occurrence of metalliferous deposits are at or near the junction of
the older sedimentary formations with the igneous or intrusive rocks,
such as granites, diorites, etc. In searching for payable lodes,
whether of gold, silver, copper, or even tin in some forms of
occurrence, the indications are often very similar. The first
prospecting is usually done on the hilltops or ridges, because, owing
to denudation by ice or water which have bared the bedrock, the
outcrops are there more exposed, and thence the lodes are followed
down through the alluvial covered plains, partly by their "strike" or
"trend," and sometimes by other indicating evidences, which the
practical miner has learned to know.
For instance, a lesson in tracing the lode in a grass covered country
was taught me many years ago by an old prospector who had struck good
gold in the reef at a point some distance to the east of what had been
considered the true course. I asked him why he had opened the ground
in that particular place. Said he, "Some folks don't use their eyes.
You stand here and look towards that claim on the rise where the reef
was last struck. Now, don't you see there is almost a track betwixt
here and there where the grass and herbage is more withered than on
either side? Why? Well, because the hard quartz lode is close to the
surface all the way, and there is no great depth of soil to hold the
moisture and make the grass grow."
I have found this simple lesson in practical prospecting of use since.
But the strike or course of a quartz reef is more often indicated by
outcrops, either of the silica itself or ironstone "blows," as the
miners call them, but the term is a misnomer, as it argues the easily
disproved igneous theory of veins of ejection, meaning thereby that
the quartz with its metalliferous contents was thrown out in a molten
state from the interior of the earth. This has in no case occurred,
and the theory is an impossible one. True lodes are veins of injection
formed by the infiltration of silicated waters carrying the metals
also in solution. This water filled the fissures caused either by the
cooling of the earth's crust, or formed by sudden upheavals of the
igneous rocks.
Sometimes in alluvial ground the trend of the reef will be revealed by
a track of quartz fragments, more or less thickly distributed on the
surface and through the superincumbent soil. Follow these along, and
at some point, if the lode be continuous, a portion of its solid mass
will generally be found to protrude and can then again be prospected.
There is no rule as to the trend or strike of lodes, except that a
greater number are found taking a northerly and southerly course than
one which is easterly and westerly. At all events, such is the case in
Australia, but it cannot be said that either has the advantage in
being more productive. Some of the richest mines in Australasia have
been in lodes running easterly and westerly, while gold, tin, and
copper, in great quantity and of high percentage to the ton, have been
got in such mines as Mount Morgan, Mount Bischoff, and the Burra,
where there are no lodes properly so-called at all.
Mount Morgan is the richest and most productive gold mine in
Australasia and amongst the best in the world.
Its yield for 1895 was 128,699 oz. of gold, valued at 528,700 pounds.
Dividends paid in 1895, 300,000 pounds.
This mine was opened in 1886. Up to May 31, 1897, the total yield was
1,631,981 ozs. of gold, sold at 6,712,187 pounds, from which 4,400,000
pounds have been paid in dividends. (See /Mining Journal/, for Oct. 9,
1897.)
Mount Morgan shareholders have, in other words, divided over 43 1/2
tons of standard gold.
The Burra Burra Mine, about 100 miles from Adelaide, in a direction a
little to the east of north, was found in 1845 by a shepherd named
Pickett. It is singularly situated on bald hills standing 130 feet
above the surrounding country. The ores obtained from this copper mine
had been chiefly red oxides, very rich blue and green carbonates,
including malachite, and also native copper. The discovery of this
mine, supporting, as it did at one time, a large population, marked a
new era in the history of the colony. The capital invested in it was
12,320 pounds in 5 pound shares, and no subsequent call was ever made
upon the shareholders. The total amount paid in dividends was 800,000
pounds. After being worked by the original owners for some years the
mine was sold to a new company, but during the last few years it has
not been worked, owing in some degree to the low price of copper and
also to the fact that the deposit then being worked apparently became
exhausted. For many years the average yield was from 10,000 to 13,000
tons of ore, averaging 22 to 23 per cent of copper. It is stated that,
during the twenty-nine and a half years in which the mine was worked,
the company expended 2,241,167 in general expenses. The output of ore
during the same period amounted to 234,648 tons, equal to 51,622 tons
of copper. This, at the average price of copper, amounted to a money
value of 4,749,224 pounds. The mine stopped working in 1877.
Mount Bischoff, Tasmania, has produced, since the formation of the
Company to December 1895, 47,263 tons of tin ore. It is still in full
work and likely to be for years to come.
Each of these immense metalliferous deposits was found outcropping on
the summit of a hill of comparatively low altitude. There are no true
walls nor can the ore be traced away from the hill in lode form. These
occurrences are generally held to be due to hydrothermal or geyser
action.
Then again lodes are often very erratic in their course. Slides and
faults throw them far from their true line, and sometimes the lode is
represented by a number of lenticular (double-pointed in section)
masses of quartz of greater or less length, either continuing point to
point or overlapping, "splicing," as the miners call it. Such
formations are very common in West Australia. All this has to be
considered and taken into account when tracing the run of stone.
This tyro also must carefully remember that in rough country where the
lode strikes across hills and valleys, the line of the cap or outcrop
will apparently be very sinuous owing to the rises and depressions of
the surface. Many people even now do not understand that true lodes or
reefs are portions of rock or material differing from the surrounding
and enclosing strata, and continuing down to unknown depths at varying
angles. Therefore, if you have a north and south lode outcropping on a
hill and crossing an east and west valley, the said lode, underlying
east, when you have traced its outcrop to the lowest point in the
valley, between the two hills, will be found to be a greater or less
distance, according to the angle of its dip or underlie, to the east
of the outcrop on the hill where it was first seen. If it be followed
up the next hill it will come again to the west, the amount of
apparent deviation being regulated by the height of the hills and
depth of the valley.
A simple demonstration will make this plain. Take a piece of half-inch
pine board, 2 ft. long and 9 in. wide, and imagine this to be a lode;
now cut a half circle out of it from the upper edge with a fret saw
and lean the board say at an angle of 45 degrees to the left, look
along the top edge, which you are to consider as the outcrop on the
high ground, the bottom of the cut being the outcrop in the valley,
and it will be seen that the lowest portion of the cut is some inches
to the right; so it is with the lode, and in rough country very nice
judgment is required to trace the true course.
For indications, never pass an ironstone "blow" without examination.
Remember the pregnant Cornish saying with regard to mining and the
current aphorism, "The iron hat covers the golden head." "Cousin
Jack," put it "Iron rides a good horse." The ironstone outcrop may
cover a gold, silver, copper or tin lode.
If you are searching for gold, the presence of the royal metal should
be apparent on trial with the pestle and mortar; if silver, either by
sight in one of its various forms or by assay, blowpipe or otherwise;
copper will reveal itself by its peculiar colour, green or blue
carbonates, red oxides, or metallic copper. It is an easy metal to
prospect for, and its percentage is not difficult to determine
approximately. Tin is more difficult to identify, as it varies so
greatly in appearance.
Having found your lode and ascertained its course, you want next to
ascertain its value. As a rule (and one which it will be well to
remember) if you cannot find payable metal, particularly in gold
"reef" prospecting, at or near the surface, it is not worth while to
sink, unless, of course, you design to strike a shoot of metal which
some one has prospected before you. The idea is exploded that
auriferous lodes necessarily improve in value with depth. The fact is
that the metal in any lode is not, as a rule, equally continuous in
any direction, but occurs in shoots dipping at various angles in the
length of the lode, in bunches or sometimes in horizontal layers.
Nothing but actual exploiting with pick, powder, and brains,
particularly brains, will determine this point.
Where there are several parallel lodes and a rich shoot has been found
in one and the length of the payable ore ascertained, the neighbouring
lodes should be carefully prospected opposite to the rich spot, as
often similar valuable deposits will thus be found. Having ascertained
that you have, say, a gold reef payable at surface and for a
reasonable distance along its course, you next want to ascertain its
underlie or dip, and how far the payable gold goes down.
As a general rule in many parts of Australia--though by no means an
inflexible rule--a reef running east of north and west of south will
underlie east; if west of north and east of south it will go down to
the westward and so round the points of the compass till you come to
east and west; when if the strike of the lodes in the neighbourhood
has come round from north-east to east and west the underlie will be
to the south; if the contrary was the case, to the north. It is
surprising how often this mode of occurrence will be found to obtain.
But I cannot too strongly caution the prospector not to trust to
theory but to prove his lode and his metal by following it down on the
underlie. "Stick to your gold" is an excellent motto. As a general
thing it is only when the lode has been proved by an underlie shaft to
water level and explored by driving on its course for a reasonable
distance that one need begin to think of vertical shafts and the
scientific laying out of the mine.
A first prospecting shaft need not usually be more than 5 ft. by 3 ft.
or even 5 ft. by 2 ft. 6 in., particularly in dry country. One may
often see in hard country stupid fellows wasting time, labour, and
explosives in sinking huge excavations as much as 10 ft. by 8 ft. in
solid rock, sometimes following down 6 inches of quartz.
When your shaft is sunk a few feet, you should begin to log up the top
for at least 3 ft. or 4 ft., so as to get a tip for your "mullock" and
lode stuff. This is done by getting a number of logs, say 6 inches
diameter, lay one 7 ft. log on each side of your shaft, cut two
notches in it 6 ft. apart opposite the ends of the shaft, lay across
it a 5 ft. log similarly notched, so making a frame like a large
Oxford picture frame. Continue this by piling one set above another
till the desired height is attained, and on the top construct a rough
platform and erect your windlass. If you have an iron handle and axle
I need not tell you how to set up a windlass, but where timber is
scarce you may put together the winding appliance described in the
chapter headed "Rules of Thumb."
If you have "struck it rich" you will have the pleasure of seeing your
primitive windlass grow to a "whip, a "whim," and eventually to a big
powerful engine, with its huge drum and Eiffel tower-like "poppet
heads," or "derrick," with their great spindle pulley wheels revolving
at dizzy speed high in air.
"How shall I know if I have payable gold so as to save time and
trouble in sinking?" says the novice. Truly it is a most important
part of the prospector's art, whether he be searching for alluvial or
reef gold, stream or lode tin, copper, or other valuable metal.
I presume you know gold when you see it?
If you don't, and the doubtful particle is coarse enough, take a
needle and stick the point into the questionable specimen. If gold the
steel point will readily prick it; if pyrites or yellow mica the point
will glance off or only scratch it.
The great importance of the first prospect from the reef is well shown
by the breathless intensity with which the two bearded, bronzed
pioneer prospectors in some trackless Australian wild bend over the
pan in which the senior "mate" is slowly reducing the sample of
powdered lode stuff. How eagerly they examine the last pinch of "black
sand" in the corner of the dish. Prosperity and easy times, or poverty
and more "hard graft" shall shortly be revealed in the last dexterous
turn of the pan. Let us hope it is a "pay prospect."
The learner, if he be far afield and without appliances of any kind,
can only guess his prospect. An old prospector will judge from six
ounces of stuff within a few pennyweights what will be the yield of a
ton. I have seen many a good prospect broken with the head of a pick
and panned in a shovel, but for reef prospecting you should have a
pestle and mortar. The handiest for travelling is a mortar made from a
mercury bottle cut in half, and a not too heavy wrought iron pestle
with a hardened face. To be particular you require a fine screen in
order to get your stuff to regulated fineness. The best for the
prospector, who is often on the move, is made from a piece of
cheesecloth stretched over a small hoop.
If you would be more particular take a small spring balance or an
improvised scale, such as is described in Mr. Goyder's excellent
little book, p. 14, which will enable you to weigh down to one-
thousandth of a grain. It is often desirable to burn your stone before
crushing, as it is thus more easily triturated and will reveal all its
gold; but remember, that if it originally contained much pyrites,
unless a similar course is adopted when treated in the battery, some
of the gold will be lost in the pyrites.
Having crushed your gangue to a fine powder you proceed to pan it off
in a similar manner to that of washing out alluvial earth, except that
in prospecting quartz one has to be much more particular, as the gold
is usually finer. The pan is taken in both hands, and enough water to
cover the prospect by a few inches is admitted. The whole is then
swirled round, and the dirty water poured off from time to time till
the residue is clean quartz sand and heavy metal. Then the pan is
gently tipped, and a side to side motion is given to it, thus causing
the heavier contents to settle down in the corner. Next the water is
carefully lapped in over the side, the pan being now tilted at a
greater angle until the lighter particles are all washed away. The pan
is then once more righted, and very little water is passed over the
pinch of heavy mineral a few times, when the gold will be revealed in
a streak along the bottom. In this operation, as in all others, only
practice will make perfect, and a few practical lessons are worth
whole pages of written instruction.
To make an amalgamating assay that will prove the amount of gold which
can be got from a ton of your lode, take a number of samples from
different parts, both length and breadth. The drillings from the
blasting bore-holes collected make the best test. When finely
triturated weigh off one or two pounds, place in a black iron pan (it
must not be tinned), with 4 ozs. of mercury, 4 ozs. salt, 4 ozs. soda,
and about half a gallon of boiling water; then, with a stick, stir the
pulp constantly, occasionally swirling the dish as in panning off,
till you feel certain that every particle of the gangue has come in
contact with the mercury; then carefully pan off into another dish so
as to lose no mercury. Having got your amalgam clean squeeze it
through a piece of chamois leather, though a good quality of new
calico previously wetted will do as well. The resulting pill of hard
amalgam can then be wrapped in a piece of brown paper, placed on an
old shovel, and the mercury driven off over a hot fire; or a clay
tobacco pipe, the mouth being stopped with clay, makes a good retort
(see "Rules of Thumb," pipe and potato retorting). The residue will be
retorted gold, which, on being weighed and the result multiplied by
2240 for a 1 lb. assay, or by 1120 for 2 lb., will give the amount of
gold per ton which an ordinary battery might be expected to save. Thus
1 grain to the pound, 2240 lbs. to the ton, would show that the stuff
contained 4 oz. 13 dwt. 8 gr. per ton.
If there should be much base metal in your sample such as say stibnite
(sulphide of antimony), a most troublesome combination to the
amalgamator--instead of the formula mentioned above add to your
mercury about one dwt. of zinc shavings or clippings, and to your
water sufficient sulphuric acid to bring it to about the strength of
vinegar (weaker, if anything, not stronger), place your material
preferably in an earthenware or enamelled basin if procurable, but
iron will do, and intimately mix by stirring and shaking till all
particles have had an opportunity to combine with the mercury. Retort
as before described. This device is my own invention.
The only genuine test after all is the battery, and that, owing to
various causes, is often by no means satisfactory. First, there is a
strong, almost unconquerable temptation to select the stone, thus
making the testing of a few tons give an unduly high average; but more
often the trouble is the other way. The stuff is sent to be treated at
some inefficient battery with worn-out boxes, shaky foundations, and
uneven tables, sometimes with the plates not half amalgamated, or
coated with impurities, the whole concern superintended by a man who
knows as little about the treatment of auriferous quartz by the
amalgamating or any other processes as a dingo does of the
differential calculus. Result: 3 dwt. to the ton in the retort, 30
dwt. in the tailings, and a payable claim declared a "duffer."
When the lode is really rich, particularly if it be carrying coarse
gold, and owing to rough country, or distance, a good battery is not
available, excellent results in a small way may be obtained by the
somewhat laborious, but simple, process of "dollying." A dolly is a
one man power single stamp battery, or rather an extra sized pestle
and mortar (see "Rules of Thumb").
Silver lodes and lodes which frequently carry more or less gold, are
often found beneath the dark ironstone "blows," composed of
conglomerates held together by ferric and manganic oxides; or, where
the ore is galena, the surface indications will frequently be a
whitish limey track sometimes extending for miles, and nodules or
"slugs" of that ore will generally be found on the surface from place
to place. Most silver ores are easily recognisable, and readily tested
by means of the blowpipe or simple fire assay. Sometimes the silver on
being tested is found to contain a considerable percentage of gold as
in the great Comstock lode in Nevada. Ore from the big Broken Hill
silver load, New South Wales, also contains an appreciable quantity of
the more precious metal. A natural alloy of gold containing 20 per
cent silver, termed electrum, is the lowest grade of the noble metal.
Tin, lode, and stream, or alluvial, occurs only as an oxide, termed
cassiterite, and yet you can well appreciate the compliment one
Cornish miner pays to another whose cleverness he wishes to commend,
when he says of him, "Aw, he do know tin," when you look at a
representative collection of tin ores. In various shapes, from sharp-
edged crystals to mammillary-shaped nuggets of wood-tin; from masses
of 30 lbs. weight to a fine sand, like gunpowder, in colour black,
brown, grey, yellow, red, ruby, white, and sometimes a mingling of
several colours, it does require much judgment to know tin.
Stream tin is generally associated with alluvial gold. When such is
the case there is no difficulty in saving the gold if you save the
tin, for the yellow metal is of much greater specific gravity. As the
natural tin is an oxide, and therefore not susceptible to
amalgamation, the gold can be readily separated by means of mercury.
Lode tin sometimes occurs in similar quartz veins to those in which
gold is got, and is occasionally associated with gold. Tin is also
found, as at Eurieowie, in dykes, composed of quartz crystals and
large scales of white mica, traversing the older slates. A similar
occurrence takes place at Mount Shoobridge and at Bynoe Harbour, in
the Northern Territory of South Australia; indeed, one could not
readily separate the stone from these three places if it were mixed.
As before stated tin will never be found far from granite, and that
granite must have white mica as one of its constituents. It is seldom
found in the darker coloured rocks, or in limestone country, but it
sometimes occurs in gneiss, mica schist, and chlorite schist. Numerous
other minerals are at times mistaken for tin, the most common of which
are tourmaline or schorl, garnet, wolfram (which is a tungstate of
iron with manganese), rutile or titanic acid, blackjack or zinc
blende, together with magnetic, titanic, and specular iron in fine
grains.
This rough and ready mode of determining whether the ore is tin is by
weight and by scratching or crushing, when, what is called the
"streak" is obtained. The colour of the tin streak is whitey-grey,
which, when once known, is not easily mistaken. The specific gravity
is about 7.0. Wolfram, which is most like it, is a little heavier,
from 7.0 to 7.5, but its streak is red, brown, or blackish-brown.
Rutile is much lighter, 4.2, and the streak light-brown; tourmaline is
only 3.2. Blackjack is 4.3, and its streak yellowish-white.
I have seen several pounds weight to the dish got in some of the New
South Wales shallow sinking tin-fields, and, as a rule, payable gold
was also present. Fourteen years ago I told Western Australian people,
when on a visit to that colony, that the neighbourhood of the Darling
range would produce rich tin. Lately this had been proved to be the
case, and I look forward to a great development of the tin mining
industry in the south-western portion of Westralia.
The tin "wash" in question may also contain gold, as the country rock
of the neighbourhood is such as gold is usually found in.[*]
[*] Since this book was in the printers' hands, the discovery of
payable gold has been reported from this district. A detailed
discussion of methods of prospecting will be found in chapter ii.
Of Le Neve Foster's "Ore and Stone Mining," and Mr. S. Herbert
Cox's "Handbook for Prospectors."
CHAPTER IV
THE GENESIOLOGY OF GOLD--AURIFEROUS LODES
Up to a comparatively recent time it was considered heretical for any
one to advance the theory that gold had been deposited where found by
any other agency than that of fire. As late as 1860 Mr. Henry Rosales
convinced himself, and apparently the Victorian Government also, that
quartz veins with their enclosed metal had been ejected from the
interior of the earth in a molten state. His essay, which is very
ingenious and cleverly written, obtained a prize which the Government
had offered, but probably Mr. Rosales himself would not adduce the
same arguments in support of the volcanic or igneous theory to-day.
His phraseology is very technical; so much so that the ordinary
inquirer will find it somewhat difficult to follow his reasoning or
understand his arguments, which have apparently been founded only on
the occurrence of gold in some of the earlier discovered quartz lodes,
and the conclusions at which he arrived are not borne out by later
experience. He says:--"While, however, there are not apparent signs of
mechanical disturbances, during the long period that elapsed from the
cooling of the earth's surface to the deposition of the Silurian and
Cambrian systems, it is to be presumed that the internal igneous
activity of the earth's crust was in full force, so that on the inner
side of it, in obedience to the laws of specific gravity, chemical
attraction, and centrifugal force, a great segregation of silica in a
molten state took place. This molten silica continually accumulating,
spreading, and pressing against the horizontal Cambro-Silurian beds
during a long period at length forced its way through the
superincumbent strata in all directions; and it is abundantly evident,
under the conditions of this force and the resistance offered to its
action, that the line it would and must choose would be along any
continuous and slightly inclined diagonal, at times crossing the
strata of the schists, though generally preferring to develop itself
and egress between the cleavage planes and dividing seams of the
different schistose beds."
He goes on to say, "Another argument to the same end (i.e., the
igneous origin) may be shown from the fact that the auriferous quartz
lodes have exercised a manifest metamorphic action on the adjacent
walls or casing; they have done so partly in a mineralogical sense,
but generally there has been a metamorphic alteration of the rock."
Mr. Rosales then tells his readers, what we all know must be the case,
that the gold would be volatilised by the heat, as would be also the
other metals, which he says, were in the form of arseniurets and
sulphurets; but he fails to explain how the sublimated metals
afterwards reassumed their metallic form. Seeing that, in most cases,
they would be hermetically enclosed in molten and quickly solidifying
silica they could not be acted on to any great extent by aqueous
agency. Neither does Mr. Rosales's theory account at all for
auriferous lodes; which below water level are composed of a solid mass
of sulphide of iron with traces of other sulphides, gold, calcspar,
and a comparatively small percentage of silica. Nor will it
satisfactorily explain the auriferous antimonial silica veins of the
New England district, New South Wales, in which quantities of angular
and unaltered fragments of slate from the enclosing rocks are found
imbedded in the quartz.
With respect to the metamorphism of the enclosing rocks to a greater
degree of hardness, which Mr. Rosales considered was due to heat, it
should be remembered that these rocks in their original state were
much softer and more readily fusible than the quartz, consequently all
would have been molten and mingled together instead of showing as a
rule clearly defined walls. It is much more rational to suppose that
the increased hardness imparted to the slates and schists at or near
their contact with the lode is due to an infiltration of silica from
the silicated solution which at one time filled the fissure. Few
scientists can now be found to advance the purely igneous theory of
lode formation, though it must be admitted that volcanic action has
probably had much influence not only in the formation of mineral
veins, but also on the occurrence of the minerals therein. But the
action was hydrothermal, just such as was seen in course of operation
in New Zealand a few years ago when, in the Rotomahana district, one
could actually see the growing of the marvellous White and Pink
Terraces formed by the release of silica from the boiling water
exuding from the hot springs, which water, so soon as the heat and
pressure were removed, began to deposit its silica very rapidly; while
at the Thames Gold-field, in the same country hot, silicated water
continuously boiled out of the walls of some of the lodes after the
quartz had been removed and re-deposited a siliceous sinter thereon.
On this subject I note the recently published opinions of Professor
Lobley, a gentleman whose scientific reputation entitles his
utterances to respect, but who, when he contends that gold is not
found in the products of volcanic action is, I venture to think,
arguing from insufficient premises. Certainly his theories do not hold
good either in Australasia or America where gold is often, nay, more
usually, found at, or near, either present or past regions of volcanic
action.
It is always gratifying to have one's theories confirmed by men whose
opinions carry weight in the scientific world. About seventeen years
ago I first published certain theories on gold deposition, which, even
then, were held by many practical men, and some scientists, to be open
to question. Of late years, however, the theory of gold occurrence by
deposition from mineral salts has been accepted by all but the "mining
experts" who infest and afflict the gold mining camps of the world.
These opine that gold ought to occur in "pockets" only (meaning
thereby their own).
Recently Professor Joseph Le Conte, at a meeting of the American
Institute of Mining Engineers, criticised a notable essay on the
"Genesis of Ore Deposits," by Bergrath F. Posepny. The Professor's
general conclusions are:
1. "Ore deposits, using the term in its widest sense, may take place
from any kinds of waters, but especially from alkaline solutions, for
these are the natural solvents of metallic sulphides, and metallic
sulphides are usually the original form of such deposits."
2. "They may take place from waters at any temperature and any
pressure, but mainly from those at high temperature and under heavy
pressure, because, on account of their great solvent power, such
waters are heavily freighted with metals."
3. "The depositing waters may be moving in any direction, up-coming,
horizontally moving, or even sometimes down-going, but mainly up-
coming; because by losing heat and pressure at every step such waters
are sure to deposit abundantly."
4. "Deposits may take place in any kind of waterways--in open
fissures, in incipient fissures, joints, cracks, and even in porous
sandstone, but especially in great open fissures, because these are
the main highways of ascending waters from the greatest depths."
5. "Deposits may be found in many regions and in many kinds of rocks,
but mainly in mountain regions, and in metamorphic and igneous rocks,
because the thermosphere is nearer the surface, and ready access
thereto through great fissures is found mostly in these regions and in
these rocks."
These views are in accordance with nearly all modern research into
this interesting and fruitful subject.
Among the theories which they discredit is that ore bodies may usually
be assumed to become richer in depth. As applied to gold lodes the
teaching of experience does not bear out this view.
If it be taken into account that the time in which most of our
auriferous siliceous lodes were formed was probably that indicated in
Genesis as before the first day or period when "the earth was without
form and void, and darkness was upon the face of the deep," it will be
realised that the action we behold now taking place in a small way in
volcanic regions, was probably then almost universal. The crust of the
earth had cooled sufficiently to permit water to lie on its surface,
probably in hot shallow seas, like the late Lake Rotomahana. Plutonic
action would be very general, and volcanic mud, ash, and sand would be
ejected and spread far and wide, which, sinking to the bottom of the
water, may possibly be the origin of what we now designate the azoic
or metamorphic slates and schists, as also the early Cambrian and
Silurian strata. These, from the superincumbent weight and internal
heat, became compacted, and, in some cases, crystallised, while at the
same time, from the ingress of the surface waters to the heated
regions below, probably millions of geysers were spouting their
mineral impregnated waters in all directions; and in places where the
crust was thin, explosions of super-heated steam caused huge
upheavals, rifts, and chasms, into which these waters returned, to be
again ejected, or to be the cause of further explosions. Later, as the
cooling-process continued, there would be shrinkages of the earth's
crust causing other fissures; intrusive granites further dislocated
and upheaved the slates. About this age, probably, when really dry
land began to appear, came the first formation of mineral lodes, and
the waters, heavily charged with silicates, carbonates of lime,
sulphides, etc., in solution, commenced to deposit their contents in
solid form when the heat and pressure were removed.
I am aware that part of the theory here propounded as to the probable
mode of formation of the immense sedimentary beds of the Archaic or
Azoic period is not altogether orthodox--i.e., that the origin of
these beds is largely due to the ejection of mud, sand, and ashes from
subterraneous sources, which, settling in shallow seas, were
afterwards altered to their present form. It is difficult, however, to
believe that at this very early period of geologic history so vast a
time had elapsed as would be required to account for these enormous
depositions of sediment, if they were the result only of the
degradation of previously elevated portions of the earth's surface by
water agency. Glacial action at that time would be out of the
question.
But what about the metals? Whence came the metallic gold of our reefs
and drifts? What was it originally--a metal or a metallic salt, and if
the latter, what was its nature?--chloride, sulphide, or silicate,
one, or all three? I incline to the latter hypothesis. All three are
known, and the chemical conditions of the period were favorable for
their natural production. Assuming that they did exist, the task of
accounting for the mode of occurrence of our auriferous quartz lodes
is comparatively simple. Chloride of gold is at present day contained
in sea water and in some mineral waters, and would have been likely to
be more abundant during the Azoic and early Paleozoic period.
Sulphide of gold would have been produced by the action of
sulphuretted hydrogen; hence probably our auriferous pyrites lodes,
while silicate of gold might have resulted from a combination of gold
chlorides with silicic acid, and thus the frequent presence of gold in
quartz is accounted for.
A highly interesting and instructive experiment, showing how gold
might be, and probably was, deposited in quartz veins, was carried out
by Professor Bischof some years ago. He, having prepared a solution of
chloride of gold, added thereto a solution of silicate of potash,
whereupon, as he states, the yellow colour of the chloride
disappeared, and in half an hour the fluid turned blue, and a
gelatinous dark-blue precipitate appeared and adhered to the sides of
the vessel. In a few days moss-like forms were seen on the surface of
the precipitate, presumably approximating to what we know as
dendroidal gold--that is, having the appearance of moss, fern, or
twigs. After allowing the precipitate to remain undisturbed under
water for a month or two a decomposition took place, and in the
silicate of gold specks of metallic gold appeared. From this, the
Professor argues, and with good show of reason, that as we know now
that the origin of our quartz lodes was the silicates contained in
certain rocks, it is probable that a natural silicate of gold may be
combined with these silicates. If this can be demonstrated, the reason
for the almost universal occurrence of gold in quartz is made clear.
About 1870, Mr. Skey, analyst to the New Zealand Geological Survey
Department, made a number of experiments of importance in respect to
the occurrence of gold. These experiments were summarised by Sir James
Hector in an address to the Wellington Philosophical Society in 1872.
Mr. Skey's experiments disproved the view generally held that gold is
unaffected by sulphur or sulphuretted hydrogen gas, and showed that
these elements combined with avidity, and that the gold thus treated
resisted amalgamation with mercury. Mr. Skey proved the act of
absorption of sulphur by gold to be a chemical act, and that
electricity was generated in sufficient quantity and intensity during
the process to decompose metallic solutions. Sulphur in certain forms
had long been known to exercise a prejudicial effect upon the
amalgamation of gold, but this had always been attributed to the
combination of the sulphur with the quicksilver used. Now, however, it
is certain that the sulphurising of the gold must be taken into
account. We must remember that the particles of gold in the stone may
be enveloped with a film of auriferous sulphide, by which they are
protected from the solvent actions of the mercury. The sulphurisation
of the gold gives no ocular manifestation by change of colour or
perceptible increase of weight, as in the case of the formation of
sulphides of silver, lead and other metals, on account of the
extremely superficial action of the sulphur, and hence probably the
existence of the gold sulphide escaped detection by chemists.
Closely allied to this subject is the investigation of the mode in
which certain metals are reduced from their solutions by metallic
sulphides, or, in common language, the influence which the presence of
such substances as mundic and galena may exercise in effecting the
deposit of pure metals, such as gold, in mineral lodes. The close
relation which the richness of gold veins bears to the prevalence of
pyrites has been long familiar both to scientific observers and to
practical miners. The gold is an after deposit to the pyrites, and, as
Mr. Skey was the first to explain, due to its direct reducing
influences. By a series of experiments Mr. Skey proved that the
reduction of the metal was due to the direct action of the sulphide,
and showed that each grain of iron pyrites, when thoroughly oxidised,
will reduce 12 1/4 grains of gold from its solution as chloride. He
also included salts of platina and silver in this general law, and
demonstrated that solutions of any of these metals traversing a vein
rock containing certain sulphides would be decomposed, and the pure
metal deposited. We are thus enabled to comprehend the constant
association of gold, or native alloys of gold and silver, in veins
which traverse rocks containing an abundance of pyrites, whether they
have been formed as the result of either sub-aqueous volcanic outburst
or by the metamorphism of the deeper-seated strata which compose the
superficial crust of the earth.
Mr. Skey also showed by very carefully conducted experiments that the
metallic sulphides are not only better conductors of electricity than
has hitherto been supposed, but that when paired they were capable of
exhibiting strong electro-motive power. Thus, if galena and zinc
blende in acid solutions be connected in the usual manner by a voltaic
pair, sulphuretted hydrogen is evolved from the surface of the former,
and a current generated which is sufficient to reduce gold, silver or
copper from their solutions in coherent electro-plate films. The
attributing of this property of generating voltaic currents, hitherto
supposed to be almost peculiar to metals, to such sulphides as are
commonly found in metalliferous veins, further led Mr. Skey to
speculate how far the currents discovered to exist in such veins by
Mr. E. F. Fox might be produced by the gradual oxidation of mixed
sulphides, and that veins containing bands of different metallic
sulphides, bounded by continuing walls, and saturated with mineral
waters, may constitute under some circumstances a large voltaic
battery competent to produce electro-deposition of metals, and that
the order of the deposit of these mineral lodes will be found to bear
a definite relation to the order in which the sulphides rank in the
table of their electro-motive power. These researches may lead to some
clearer comprehension of the law which regulates the distribution of
auriferous veins, and may explain why in some cases the metal should
be nearly pure, while in others it is so largely alloyed with silver.
The following extract was lately clipped from a mining paper. If true,
the experiment is interesting:--
"An American scientist has just concluded a very interesting and
suggestive experiment. He took a crushed sample of rich ore from
Cripple Creek, which carried 1100 ozs. of gold per ton, and digested
it in a very weak solution of sodium chloride and sulphate of iron,
making the solution correspond as near as practicable to the waters
found in Nature. The ore was kept in a place having a temperature
little less than boiling water for six weeks, when all the gold,
except one ounce per ton, was found to have gone into solution. A few
small crystals of pyrite were then placed in the bottle of solution,
and the gold began immediately to precipitate on them. It was
noticeable, however, that the pyrite crystals which were free from
zinc, galena, or other extraneous matter received no gold precipitate.
Those which had such foreign associations were beautifully covered
with fine gold crystals."
Experimenting in a somewhat similar direction abut twelve months
since, I found that the West Australian mine water, with the addition
of an acid, was a solvent of gold. The idea of boiling it did not
occur to me, as the action was rapid in cold water.
Assuming, then, that gold originally existed as a mineral salt, when
and how did it take metallic form? Doubtless, just in the same manner
as we now (by means of well-known reagents which are common in nature)
precipitate it in the laboratory. With regard to that found in quartz
lodes finely disseminated through the gangue, the change was brought
about by the same agency which caused the silicic acid to solidify and
take the form in which we now see it in the quartz veins. Silica is
soluble in solutions of alkaline carbonates, as shown in New Zealand
geysers; the solvent action being increased by heat and pressure, so
also would be the silicate or sulphide of gold. When, however, the
waters with their contents were released from internal pressure and
began to lose their heat the gold would be precipitated together with
the salts of some other metals, and would, where the waters could
percolate, begin to accretionise, thus forming the heavy or specimen
gold of some reefs. On this class of deposition I shall have more to
say when treating of the origin of alluvial gold in the form of
nuggets.
Mr. G. F. Becker, of the United States Geological Survey, writing of
the geology of the Comstock lode, says:--"Baron Von Richthofen was of
opinion that fluorine and chlorine had played a large part of the ore
deposition in the Comstock, and this the writer is not disposed to
deny; but, on the other hand, it is plain that most of the phenomena
are sufficiently accounted for on the supposition that the agents have
been merely solutions of carbonic and hydro-sulphuric acids. These
reagents will attack the bisilicates and felspars. The result would be
carbonates and sulphides of metals, earth, alkalies, and free quartz,
but quartz and sulphides of the metals are soluble in solutions of
carbonates and sulphides of the earths and alkalies, and the essential
constituents of the ore might, therefore, readily be conveyed to
openings in the vein where they would have been deposited on relief of
pressure and diminution of temperature. An advance boring on the 3000
ft. level of the Yellow Jacket struck a powerful stream of water at
3065 ft. (in the west country), which was heavily charged with
hydrogen sulphide, and had a temperature of 170 degrees F., and there
is equal evidence of the presence of carbonic acid in the water of the
lower levels. A spring on the 2700 ft. level of the Yellow Jacket
which showed a temperature of about 150 degrees F., was found to be
depositing a sinter largely composed of carbonates."
It may be worth while here to speak of the probable reason why gold,
and indeed almost all the metals generally occur in shutes in the
lodes; and why, as is often the case, these shutes are found to be
more or less in a line with each other in parallel lodes, and why also
the junction of two lodes is frequently specially productive. The
theory with respect to these phenomena which appears most feasible is,
that at these points certain chemical action has taken place, by which
the deposition of the metals has been specially induced. Generally a
careful examination of the enclosing rocks where the shute is found
will reveal some points of difference from the enclosing rocks at
other parts of the course of the lode, and when ore shutes are found
parallel in reefs running on the same course, bands or belts of
similar country rock will be found at the productive points. From this
we may fairly reason that at these points the slow stream filling the
lode cavity met with a reagent percolating from this particular band
of rock, which caused the deposition of its metals; and, indeed, I am
strongly disposed to believe that the deposition of metals,
particularly in some loose lodes, may even now be proceeding. But as
in Nature's laboratory the processes, if certain, are slow, this
theory may be difficult to prove.
Why the junction of lodes is often found to be more richly
metalliferous than neighbouring parts is probably because there the
depositing reagents met. This theory is well put by Mr. S. Herbert
Cox, late of Sydney, in his useful book, "Mines and Minerals." He
says:--"It is a well-known fact in all mining districts that the
junctions of lodes are generally the richest points, always supposing
that this junction takes place in 'kindly country,' and the
explanation of this we think is simple on the aqueous theory of
filling of lodes. The water which is traversing two different channels
of necessity passes through different belts of country, and will thus
have different minerals in solution. As a case in point, let us
suppose that the water in one lode contained in solution carbonates of
lime, and the alkalies and silica derived form a decomposition of
felspars; and that the other, charged with hydro-sulphuric acid,
brought with it sulphide of gold dissolved in sulphide of lime. The
result of these two waters meeting would be that carbonate of lime
would be formed, hydro-sulphuric acid would be set free, and sulphide
of gold would be deposited, as well as silica, which was formerly held
in solution by the carbonic acid."
Most practical men who have given the subject attention will, I think,
be disposed to coincide with this view, though there are some who hold
that the occurrence of these parallel ore shutes and rich deposits at
the junctions of lodes is due to extraneous electrical agency. Of
this, however I have failed to find any satisfactory evidence.
There is, however, proof that lodes are actually re-forming and the
action observed is very interesting as showing how the stratification
in some lodes has come about. Instances are not wanting of the growth
of silica on the sides of the drives in mines. This was so in some of
the mines on the Thames, New Zealand, previously mentioned, where in
some cases the deposition was so rapid as to be noticeable from day to
day, whilst the big pump was actually choked by siliceous deposits. In
old auriferous workings which have been under water for years, in many
parts of the world, formations of iron and silica have been found on
the walls and roof, while in mining tunnels which have been long
unused stalactites composed of silica and calcite have formed. Then,
again, experiments made by the late Professor Cosmo Newbery, in
Victoria, showed that a distinctly appreciable amount of gold, iron,
and silica (the latter in granular form) could be extracted from solid
mine timber; which had been submerged for a considerable time.
This reaction then must be in progress at the present time, and
doubtless under certain conditions pyrites would eventually take the
place of the timber, as is the case with some of the long buried
driftwood found in Victorian deep leads. Again, we know that the water
from some copper mines is so charged with copper sulphate that if
scrap iron be thrown into it, the iron will be taken up by the
sulphuric acid, and metallic copper deposited in its place. All this
tends to prove that the deposition of metals from their salts, though
probably not now as rapid as formerly, is still ceaselessly going on
in some place or another where the necessary conditions are
favourable.
With regard to auriferous pyritic lodes, it does not appear even now
to be clear, as some scientists assert, that their gold is never found
in chemical combination with the sulphides of the base metals. On the
contrary, I think much of the evidence points in the other direction.
I have long been of opinion that it is really so held in many of the
ferro-sulphides and arsenio-ferro sulphides. On this subject Mr. T.
Atherton contributed a short article in 1891 to the /Australian Mining
Standard/ which is worthy of notice. He says, referring to an
occurrence of a Natural Sulphide of Gold: "The existence of gold, in
the form of a natural sulphide in conjunction with pyrites, has often
been advanced theoretically, as a possible occurrence; but up to the
present time has, I believe, never been established as an actual fact.
During my investigation on the ore of the Deep Creek mines, Nambucca,
New South Wales, I have found in them what I believe to be gold
existing as a natural sulphide. The lode is a large irregular one of
pure arsenical pyrites carrying, in addition to gold and silver,
nickel and cobalt. It exists in a felsite dyke immediately on the
coast. Surrounding it on all sides are micaceous schists, and in the
neighbourhood about half a mile distant is a large granite hill about
800 feet high. In the lode and its walls are large quantities of pyro-
phyllite, and in some parts of the mine there are deposits of pure
white translucent mica, but in the ore itself it is a yellow or pale
olive green, and is never absent from the pyrites.
"From the first I was much struck with the exceedingly fine state of
division in which the gold existed in the ore. After roasting and very
carefully grinding down in an agate mortar, I have never been able to
get any pieces of gold exceeding one-thousandth of an inch in
diameter, and the greater quantity is very much finer than this.
Careful dissolving of the pyrites and gangue so as to leave the gold
intact failed to find it in any larger diameter. As this was a very
unusual experience in investigations on many other kinds of pyrites, I
was led further into the matter.
"Ultimately, after a number of experiments, there was nothing left but
to test for gold existing as a natural sulphide. Taking 200 gr. of ore
from a sample assaying 17 oz. fine gold per ton, grinding it finely
and heating for some hours with yellow sodium sulphide--on decomposing
the filtrate and treating for gold I got a result at the rate of 12
oz. per ton. This was repeated several times with the same result.
"This sample came from the lode at the 140 ft. level, whilst samples
from the higher levels where the ore is more oxidised, although
carrying the gold in exactly the same degree of fineness, do not give
as high a percentage of auric sulphide.
"It would appear that all the gold in the pyrites (and I have never
found any gold existing apart from the pyrites) has originally taken
its place there as a sulphide."
Professor Newbery, who made many valuable suggestions on the subject,
says, speaking of gold in pyritous lodes:
"As it (the gold salt) may have been in the same solution that
deposited the pyrites, which probably contained its iron in the form
of proto-carbonate with sulphates, it was not easy at first to imagine
any ordinary salt of gold; but this I find can be accomplished with
very dilute solutions in the presence of an alkaline carbonate and a
large excess of carbonic acid, both of which are common constituents
of mineral waters, especially in Victoria. This is true of chloride of
gold, and if the sulphide is required in solution, it is only
necessary to charge the solution with an excess of sulphuretted
hydrogen. In this matter both sulphides may be retained in the same
solution, depositing gradually with the escape of the carbonic acid."
Pyritic lodes usually contain a considerable proportion of calcareous
matter, mostly carbonates, and consequently it appears not improbable
that the gold may remain in some instances as a sulphide, particularly
in samples of pyrites, in which it cannot be detected even by the
microscope until by calcination the iron sulphide is changed to an
oxide, wherein the gold may be seen in minute metallic specks. The
whole subject is full of interest, and careful scientific
investigation may lead to astonishing results.
CHAPTER V
THE GENESIOLOGY OF GOLD--AURIFEROUS DRIFTS
Having considered the origin of auriferous lodes, and the mode by
which in all probability the gold was conveyed to them and deposited
as a metal, it is necessary also to inquire into the derivation of the
gold of our auriferous drifts, and the reasons for its occurrence
therein.
When quite a lad on the Victorian alluvial fields, I frequently heard
old diggers assert that gold grew in the drifts where found. At the
time we understood this to mean that it grew like potatoes; and,
although not prepared with a scientific argument to prove that such
was not so, the idea was generally laughed at. I have lived to learn
that these old hard-heads were nearer the truth than possibly they
clearly realised, and that gold does actually grow or agglomerate;
and, indeed, is probably even now thus growing, though it is likely
that the chemical and electric action in the mineral waters flowing
through the drifts is not in this age nearly so active as formerly.
Most boys have tried the experiment of dipping a clean-bladed knife
into sulphate of copper, and so depositing on the steel a film of
copper, which adheres closely until worn away. This is a simple
demonstration of a hydro-metallurgical process, though probably young
hopeful is not aware of the fact; and it is really by an enlargement
of this process that our beautiful and artistic gold- and silver-
plated ware is produced.
In the great laboratory of Nature similar chemical depositions have
taken place in the past, and may still be in progress; indeed, there
is sound scientific reason to suppose that in certain localities this
is even now the case, and that in this way much of our so-called
alluvial gold has been formed, that is, by the deposition on metallic
bases of the gold held in solution.
We will, however, take, to begin with, the generally accepted theory
as to the occurrence of alluvial gold. First, let it be said, that
certain alluvial gold is unquestionably derived from the denudation of
quartz lodes. Such is the gold dust found in many Asiatic and African
rivers, in the great placer mines of California, as also the gold dust
gained from the beach sand on the west coast of New Zealand, or in the
enormous alluvial drifts of the Shoalhaven Valley, New South Wales. Of
the first, many fabulous tales are told to account for its being found
in particular spots each summer after the winter floods, and
miraculous agency was asserted, while the early beachcombers of the
Hokitika district found an equally ridiculous derivation for their
gold, which was always more plentiful after heavy weather. They
imagined that the breakers were disintegrating some abnormally rich
auriferous reefs out at sea, and that the resultant gold was washed up
on the beach.
The facts are simply, with regard to the rivers, that the winter
floods break down the drifts in the banks and agitate the auriferous
detritus, thus acting as natural sluices, and cause the metal to
accumulate in favourable spots; whilst on the New Zealand coast the
heavy seas breaking on the shingly beach, carry off the lighter
particles, leaving behind the gold, which is so much heavier. These
beaches are composed, as also are the "terraces" behind, of enormous
glacial and fluvial deposits, all containing more or less gold, and
extend inland to the foot of the mountains.
It is almost certain that the usually fine gold got by hydraulicing in
Californian canyons, in the gullies of the New Zealand Alps, and the
great New South Wales drifts, is largely the result of the attrition
of the boulders and gravel of moraines, which has thus freed, to a
certain extent, the auriferous particles. But when we find large
nuggety masses of high carat gold in the beds of dead rivers, another
origin has to be sought.
As previously stated, there is fair reason to assume that at least
three salts of gold have existed, and, possibly, may still be found in
Nature--silicate, sulphide, and chloride. All of these are soluble and
in the presence of certain reagents, also existing naturally, can be
deposited in metallic form. Therefore, if, as is contended, reef gold
was formed with the reefs from solutions in mineral waters, by
inferential reasoning it can be shown that much of our alluvial gold
was similarly derived.
The commonly accepted theory, however, is that the alluvial matter of
our drifts has been ground out of the solid siliceous lodes by glacial
and fluvial action, and that the auriferous leads have been formed by
the natural sluicing operations of former streams. To this, however,
there are several insuperable objections.
First, how comes it that alluvial gold is usually superior in purity
to the "reef" gold immediately adjacent? Second, why is it that masses
of gold, such as the huge nuggets found in Victoria and New South
Wales, have never been discovered in lodes? Third, how is it that
these heavy masses which, from their specific gravity, should be found
only at the very bottom of the drifts, if placed by water action, are
sometimes found in all positions from the surface to the bottom of the
"wash"? And, lastly, why is it that when an alluvial lead is traced up
to, or down from, an auriferous reef, that the light, angular gold
lies close to the roof, while the heavy masses are often placed much
farther away? Any one who has worked a ground sluice knows how
extremely difficult it is with a strong head of water to shift from
its position an ounce of solid gold. What, then, would be the force
required to remove the Welcome Nugget? Under certain circumstances,
Niagara would not be equal to the task.
The generally smooth appearance of alleged alluvial gold is adduced as
an argument in favour of its having been carried by water from its
original place of deposit, and thus in transit become waterworn; while
some go so far as to say that it was shot out of the reefs in a molten
state. The latter idea has been already disposed of, but if not, it
may be dismissed with the statement that the heat which would melt
silica in the masses met with in lodes would sublimate any gold
contained, and dissipate it, not in nuggets but in fumes. With regard
to the assumed waterworn appearance of alluvial gold, I have examined
with the microscope the smooth surface of more than one apparently
waterworn nugget, and found that it was not scratched and abraded, as
would have been the case had it been really waterworn, but that it
presented the same appearance, though infinitely finer in grain, as
the surface of a piece of metal fresh from the electrical plating-
bath.
Mr. Daintree, of the Victorian Geological Survey, many years ago
discovered accidentally that gold chloride would deposit its metal on
a metallic base in the presence of any organic substance. Mr. Daintree
found that a piece of undissolved gold in a bottle containing chloride
of gold in solution had, owing to a portion of the cork having fallen
into the liquid, grown or accretionised so much that it could not be
extracted through the neck. This lead Mr. Charles Wilkinson, who has
contributed much to our scientific knowledge of metallurgy, to
experiment further in the same direction. He says: "Using the most
convenient salt of gold, the terchloride, and employing wood as the
decomposing agent, in order to imitate as closely as possible the
organic matter supposed to decompose the solution circulating through
the drifts, I first immersed a piece of cubic iron pyrites taken from
the coal formation of Cape Otway, far distant from any of our gold
rocks, and therefore less likely to contain gold than other pyrites.
The specimen (No. 1) was kept in dilute solution for about three
weeks, and is completely covered with a bright film of gold. I
afterwards filed off the gold from one side of a cube crystal to show
the pyrites itself and the thickness of the surrounding coating, which
is thicker than ordinary notepaper. If the conditions had continued
favourable for a very lengthened period, this specimen would doubtless
have formed the nucleus of a large nugget. Iron, copper, and arsenical
pyrites, antimony, galena, molybdenite, zinc blende, and wolfram were
treated in the above manner with similar results. In the above
experiments a small chip of wood was employed as the decomposing
agent. In one instance I used a piece of leather. All through the wood
and leather gold was disseminated in fine particles, and when cut
through the characteristic metallic lustre was brightly reflected. The
first six of these sulphides were also operated upon simply in the
solution without organic matter; but they remained unaltered."
Wilkinson found that when the solution of gold chloride was as strong
as, say, four grains to the ounce of water, that the pyrites or other
base began to decompose, and the iron sulphide changed to yellow
oxide, the "gossan" of our lodes, and that though the gold was
deposited, this occurred in an irregular way, and it was coated with a
dark brown powdery film something like the "black gold," often found
in drifts containing much ferruginous matter. Such were the curious
Victorian nuggets Spondulix and Lothair.
Professor Newbery also made a number of similar experiments, and
arrived at like results. He states as follows: "I placed a cube of
galena in a solution of chloride of gold, with free access of air, and
put in organic matter; gold was deposited as usual, in a bright
metallic film, apparently completely coating the cube. After a few
months the film burst along the edges of the cube, and remained in
that state with the cracks open without any further alteration in size
or form being apparent. Upon removing it a few days ago and breaking
it open, I found that a large portion of the galena had been
decomposed, forming chloride and sulphate of lead and free sulphur,
which were mixed together, encasing a small nucleus of undecomposed
sulphate of lead. The formation of these salts had exerted sufficient
force to burst open the gold coating, which upon the outside had the
mammillary form noticed by Wilkinson, while the inside was rough and
irregular with crystals forcing their way into the lead salts. Had
this action continued undisturbed, the result would have been a nugget
with a nucleus of lead salts, or if there had been a current to remove
the results of decomposition, a nugget without a nucleus of foreign
matter."
But Newbery also made another discovery which still further
establishes the probability of the accretionary growth of gold in
drifts. In the first experiments both investigators used organic
substances as the reagent to cause the deposit of gold on its base,
and in each case these substances whether woodchips, leather, or even
dead flies, were found to be so absolutely impregnated with gold as to
leave a golden skeleton when afterwards burned. Timber found in the
Ballarat deep leads has been proved to be similarly impregnated.
Newbery found that gold could also be deposited on sulphurets without
any other reagent. He says: "In our mineral sulphurets, however, we
have agents which are not only capable of reducing gold and silver
from solution, but besides are capable of locating them when so
reduced in coherent and bulky masses. Thus the aggregation of the
nuggety forms of gold from solution becomes a still more simple
matter, only one reagent being necessary, so that there is a greater
probability of such depositions obtaining than were a double process
necessary. Knowing the action of sulphides, the manner or the mode of
formation of a portion at least of these nuggets seems apparent.
Conceive a stream or river fed by springs rising in a country
intersected by auriferous reefs, and consequently in this case
carrying gold in solution; the drift of such a country must be to a
greater or lesser extent pyritous, so that the /debris/ forming the
beds of these streams or rivers will certainly contain nodules of such
matters disseminated or even stopping them in actual contact with the
flow of water. It follows, then, from what has been previously
affirmed, that there will be a reduction of gold by these nodules, and
that the metal thus reduced will be firmly attached to them, at first
in minute spangles isolated from each other, but afterwards
accumulating and connecting in a gradual manner at that point of the
pyritous mass most subject to the current until a continuous film of
some size appears. This being formed the pyrites and gold are to a
certain extent polarised, the film or irregular but connected mass of
gold forming the negative, and the pyrites the positive end of a
voltaic pair; and so according as the polarisation is advanced to
completion the further deposition of gold is changed in its manner
from an indiscriminate to an orderly and selective deposition
concentrated upon the negative or gold plate. The deposition of gold
being thus controlled, its loss by dispersion or from the crumbling
away of the sustaining pyrites is nearly or quite prevented, a
conservative effect which we could scarcely expect to obtain if
organic matter were the reducing agent. Meanwhile there is a gradual
wasting away of the pyrites or positive pole, its sulphur being
oxidised to sulphuric acid and its iron to sesquioxide of iron, or
hematite, a substance very generally associated with gold nuggets.
According to the original size of the pyritous mass, the protection it
receives from the action of oxidising substances other than gold, the
strength of the gold solution, length of exposure to it, the rate of
supply and velocity of stream, will be the size of the gold nugget. As
to the size of a pyritous mass necessary to produce in this manner a
large nugget, it is by no means considerable. A mass of common pyrites
(bisulphide of iron) weighing only 12 lbs. is competent for the
construction of the famous 'Welcome Nugget,' an Australian find having
weight equal to 152 lbs. avoirdupois. Such masses of pyrites are by no
means uncommon in our drifts or the beds of our mountain streams. Thus
we find that no straining of the imagination is required to conceive
of this mode of formation for the huge masses of gold found in
Australia in particular, such as the Welcome Nugget, 184 lbs. 9 oz.;
the Welcome Stranger, a surface nugget, 190 lbs. after smelting; the
Braidwood specimen nugget, 350 lbs., two-thirds gold; besides many
other large masses of almost virgin gold which have been obtained from
time to time in the alluvial diggings."
The author has made a number of experiments in the same direction, but
more with the idea of demonstrating how possibly gold may in certain
cases have been deposited in siliceous formations after such
formations had solidified. Some of the results were remarkable and
indeed unexpected. I found that I could produce artificial specimens
of auriferous quartz from stone which had previously contained no gold
whatever, also that it was not absolutely necessary that the stone so
treated should contain any metallic sulphides.
The following was contributed by the author and is from the
"Transactions" of the Australasian Institute of Mining Engineers for
1893:--
"THE DEPOSITION OF GOLD.
"The question as to how gold was originally deposited in our
auriferous lodes is one to which a large amount of attention has been
given, both by mineralogists and practical miners, and which has been
hotly argued by those who held the igneous theory and those who
pronounced for the aqueous theory. It was held by the former that as
gold was not probably existent in nature in any but its metallic form,
therefore it had been deposited in its siliceous matrix while in a
molten state, and many ingenious arguments were adduced in support of
this contention. Of late, however, most scientific men, and indeed
many purely empirical inquirers (using the word empirical in its
strict sense) have come to the conclusion that though the mode in
which they were composed was not always identical, all lodes,
including auriferous formations, were primarily derived from mineral-
impregnated waters which deposited their contents in fissures caused
either by the cooling of the earth's crust or by volcanic agency.
"The subject is one which has long had a special attraction for the
writer, who has published several articles thereon, wherein it was
contended that not only was gold deposited in the lodes from aqueous
solution, but that some gold found in form of nuggets had not been
derived from lodes but was nascent in its alluvial bed; and for this
proof was afforded by the fact that certain nuggets have been
unearthed having the shape of an adjacent pebble or angular fragment
of stone indented in them. Moreover, no true nugget of any great size
has ever been found in a lode such as the Welcome, 2159 oz., or the
Welcome Stranger, 2280 oz.; while it was accidentally discovered some
years ago that gold could be induced to deposit itself from its
mineral salt to the metallic state on any suitable base, such as iron
sulphide.
"Following out this fact, I have experimented with various salts of
gold, and have obtained some very remarkable results. I have found it
practicable to produce most natural looking specimens of auriferous
quartz from stone which previously, as proved by assay, contained no
gold whatever. Moreover, the gold, which penetrates the stone in a
thorough manner, assumes some of the more natural forms. It is always
more or less mammillary, but at times, owing to causes which I have
not yet quite satisfied myself upon, is decidedly dendroidal, as may
be seen in one of the specimens which I have submitted to members.
Moreover, I find it possible to moderate the colour and to produce a
specimen in which the gold shall be as ruddy yellow as in the ferro-
oxide gangue of Mount Morgan, or to tone it to the pale primrose hue
of the product of the Croydon mines.
"I note that the action of the bath in which the stone is treated has
a particularly disintegrating effect on many of the specimens. Some,
which before immersion were of a particularly flinty texture, became
in a few weeks so friable that they could be broken up by the fingers.
So far as my experiments have extended they have proved this, that it
was not essential that the silica and gold should have been deposited
at the one time in auriferous lodes. A non-auriferous siliceous
solution may have filled a fissure, and, after solidifying, some
volcanic disturbance may have forced water impregnated with a gold
salt through the interstices of the lode formation, when, if the
conditions were favourable, the gold would be deposited in metallic
forms. I prefer, for reasons which will probably be understood, not to
say exactly by what process my results are obtained, but submit
specimens for examination.
"(1) Piece of previously non-gold bearing stone. Locality near
Adelaide, now showing gold freely in mammillary and dendroidal form.
"(2) Stone from New South Wales, showing gold artificially introduced
in interstices and on face.
"(3) Stone from West Australia, very glassy looking, now thoroughly
impregnated with gold; the mammillary formation being particularly
noticeable.
"(4) Somewhat laminated quartz from Victoria, containing a little
antimony sulphide. In this specimen the gold not only shows on the
surface but penetrates each of the laminations, as is proved by
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