Getting Gold by J. C. F. JohnsonA Practical Treatise for Prospectors, Miners, and Students

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
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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