Getting Gold:
A practical treatise for prospectors, miners and students
Written by J.C.F. Johnson, F.G.S. (1898)
Chapter I
GETTING GOLD - INTRODUCTION
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 & GENERAL
It is purposed in this chapter to deal specially with the operation of searching for valuable mineral by individuals or small working parties.
It is well known that much disappointment and loss accrue through lack of knowledge by prospectors, who with all their enterprise and energy are often very ignorant, not only of the probable locality, mode of occurrence, and widely differing appearance of the various valuable minerals, but also of the best means of locating and testing the ores when found. It is for the information of such as these that this chapter is mainly intended, not for scientists or miners of large experience.
All of us who have had much to do with mining know that the majority of the best mineral finds have been made by the purest accident; often by men who had no mining knowledge whatever; and that many valuable discoveries have been delayed, or, when made, abandoned as not payable, from the same cause—ignorance of the rudiments of mineralogy and mining. I have frequently been asked by prospectors, when inspecting new mineral fields, what rudimentary knowledge will be most useful to them and how it can be best obtained.
If a man can spare the time a course of lessons at some accredited school of mines will be, undoubtedly, the best possible training; but if he asks what books he should read in order to obtain some primary technical instruction, I reply: First, an introductory text-book of geology, which will tell him in the simplest and plainest language all he absolutely requires to know on this important subject. Every prospector should understand elementary geology so far as general knowledge of the history of the structure of the earth's crust and of the several actions that have taken place in the past, or are now in operation, modifying its conditions. He may with advantage go a few steps further and learn to classify the various formations into systems, groups, and series: but he can acquire all that he need absolutely know from this useful little 2s. 6d. book. Next, it is advisable to learn something about the occurrence and appearance of the valuable minerals and the formations in which they are found. For all practical purposes I can recommend Cox and Ratte's "Mines and Minerals," one of the Technical Education series of New South Wales, which deals largely with the subject from an Australian standpoint, and is therefore particularly valuable to the Australian miner, but which will be found applicable to most other gold-bearing countries. I must not, however, omit to mention an admirably compiled multum in parvo volume prepared by Mr. G. Goyder, jun., Government Assayer and Assay Instructor at the School of Mines, Adelaide. It is called the "Prospectors' Pocketbook," costs only one shilling, is well bound, and of handy size to carry. In brief, plain language it describes how a man, having learned a little of assaying, may cheaply provide himself with a portable assay plant, and fluxes, and also gives considerable general information on the subject of minerals, their occurrence and treatment.[*]
[*] Another excellent and really practical book is Prof. Cole's "Practical Aids in Geology" (second edition), 10s. 6d.
It may here be stated that some twelve years ago I did a large amount of practical silver assaying on the Barrier (Broken Hill), which was not then so accessible a place as it is now, and got closely correct results from a number of different mines, with an extemporised plant almost amusing in its simplicity. All I took from Adelaide were a small set of scales capable of determining the weight of a button down to 20 ozs. to the ton, a piece of cheese cloth to make a screen or sieve, a tin ring 1 1/2 in. diameter, by 1/2 in. high, a small brass door knob to use as a cupel mould, and some powdered borax, carbonate of soda, and argol for fluxes; while for reducing lead I had recourse to the lining of a tea-chest, which lead contains no silver—John Chinaman takes good care of that. My mortar was a jam tin, without top or bottom, placed on an anvil; the pestle a short steel drill. The blacksmith at Mundi Mundi Station made me a small wrought iron crucible, also a pair of bent tongs from a piece of fencing-wire. The manager gave me a small common red flower pot for a muffle, and with the smith's forge (the fire built round with a few blocks of talcose schist) for a furnace, my plant was complete. I burned and crushed bones to make my bone-dust for cupelling, and thus provided made nearly forty assays, some of which were afterwards checked in Adelaide, in each instance coming as close as check assays generally do. Nowadays one can purchase cheaply a very effective portable plant, or after a few lessons a man may by practice make himself so proficient with the blowpipe as to obtain assay results sufficiently accurate for most practical purposes.
Coming then to the actual work of prospecting. What the prospector requires to know is, first, the usual locality of occurrence of the more valuable minerals; secondly, their appearance; thirdly, a simple mode of testing. With respect to occurrence, the older sandy and clay slates, chlorite slates, micaceous, and hornblendic schists, particularly at or near their junction with the intrusive granite and diorite, generally form the most likely geological country for the finding of mineral lodes, particularly gold, silver and tin. But those who have been engaged in practical mining for long, finding by experience that no two mineral fields are exactly alike in all their characteristics, have come to the conclusion that it is unwise to form theories as to why metals should or should not be found in certain enclosing rocks or matrices. Some of the best reef gold got in Victoria has been obtained in dead white, milky-looking quartz almost destitute of base metal. In South Australia reef gold is almost invariably associated with iron, either as oxide, as "gossan;" or ferruginous calcite, "limonite;" or granular silica, conglomerated by iron, the "ironstone" which forms the capping or outcrop of many of our reefs, and which is often rich in gold.
But to show that it is unsafe to decide off-hand in what class of matrix metals will or will not be found, I may say that in my own experience I have seen payable gold in the following materials:—
Quartz, dense and milky, also in quartz of nearly every colour and appearance, saccharoidal, crystalline, nay, even in clear glass-like six-sided prismatic crystals, and associated with silver, copper, lead, arsenic, iron as sulphide, oxide, carbonate, and tungstate, antimony, bismuth, nickel, zinc, lead, and other metals in one form or another; in slate, quartzite, mica schist, granite, diorite, porphyry, felsite, calcite, dolomite, common carbonate of iron, siliceous sinter from a hot spring, as at Mount Morgan; as alluvial gold in drifts formed of almost all these materials; and once, perhaps the most curious matrix of all, a small piece of apparently alluvial gold, naturally imbedded in a shaly piece of coal. This specimen, I think, is in the Sydney Museum. One thing, however, the prospector may make sure of: he will always find gold more or less intimately associated with silica (Quartz) in one or other of its many forms, just as he will always find cassiterite (oxide of tin) in the neighbourhood of granite containing muscovite (white mica), which so many people will persist in terming talc. It is stated to be a fact that tin has never been found more than about two miles from such granite.
From what has been said of its widely divergent occurrences it will be admitted that the Cornish miners' saying with regard to metals generally applies with great force to gold: "Where it is, there it is": and "Cousin Jack" adds, with pathetic emphasis, "and where it is generally, there I ain't."
I have already spoken of the geological "country rock" in which red gold is most likely to be discovered—i.e., the junction of the slates and schists with the igneous or metamorphic (altered) rocks, or in this vicinity. Old river beds formed of gravelly drifts in the same neighbourhood may probably contain alluvial gold, or shallow deposits of "wash" on hillsides and in valleys will often carry good surface gold. This is sometimes due to the denudation, or wearing away, of the hills containing quartz-veins—that is, where the alluvial gold really was derived from such veins, which, popular opinion to the contrary, is not always the case.
Much disappointment and loss of time and money may sometimes be prevented if prospectors will realise that all alluvial gold does not come from the quartz veins or reefs; and that following up an alluvial lead, no matter how rich, will not inevitably develop a payable gold lode. Sometimes gold, evidently of reef origin, is found in the alluvial; but in that case it is generally fine as regards the size of the particles, more or less sharp-edged, or crystalline in form if recently shed; while such gold is often of poorer quality than the true alluvial which occurs in mammillary (breast-like) nuggets, and is of a higher degree of purity as gold.
The ordinary non-scientific digger will do well to give credence to this view of the case, and will often thereby save himself much useless trouble. Sometimes also the alluvial gold, coarser in size than true reef-born alluvial, is derived almost in situ from small quartz "leaders," or veins, which the grinding down of the face of the slates has exposed; these leaders in time being also broken and worn, set free the gold they have contained, which does not, as a rule, travel far, but sometimes becomes water-worn by the rubbing over it of the disintegrated fragments of rock.
But the heavy, true alluvial gold, in great pure masses, mammillary, or botryoidal (like a bunch of grapes) in shape, have assuredly been formed by accretion on some metallic base, from gold salts in solution, probably chloride, but possibly sulphide.
Nuggets, properly so-called, are never found in quartz lodes; but, as will be shown later, a true nugget having all the characteristics of so-called water-worn alluvial may be artificially formed on a small piece of galena, or pyrites, by simply suspending the base metal by a thread in a vessel containing a weak solution of chloride of gold in which a few hard-wood chips are thrown.
Prospecting for alluvial gold at shallow depths is a comparatively easy process, requiring no great amount of technical knowledge. Usually the first gold is got at or near the surface and then traced to deep leads, if such exist.
At Mount Brown Goldfield, N.S.W., in 1881, I saw claimholders turning out to work equipped only with a small broom made of twigs and a tin dish. With the broom they carefully swept out the crevices of the decomposed slate as it was exposed on the surface, and putting the resulting dust and fragments into the tin dish proceeded to dry blow it.
The modus operandi is as follows: The operator takes the dish about half full of dirt, and standing with his back or side to the wind, if there be any, begins throwing the stuff up and catching it, or sometimes slowly pouring it from one dish to another, the wind in either case carrying away the finer particles. He then proceeds to reduce the quantity by carefully extracting the larger fragments of rock, till eventually he has only a handful or so of moderately fine "dirt" which contains any gold there may be. If in good sized nuggets it is picked out, if in smaller pieces or fine grains the digger slowly blows the sand and dust aside with his breath, leaving the gold exposed. This process is both tedious and unhealthy, and of course can only be carried out with very dry surface dirt. The stuff in which the gold occurred at Mount Brown was composed of broken slate with a few angular fragments of quartz. Yet, strange to say, the gold was invariably waterworn in appearance.
Dry blowing is now much in vogue on the West Australian fields owing to the scarcity of water; but the great objection is first, the large amount of dust the unfortunate dry blower has to carry about his person, and secondly, that the peck of dirt which is supposed to last most men a life time has to be made a continuous meal of every day.
For wet alluvial prospecting the appliances, besides pick and shovel, are puddling tub, tin dish, and cradle; the latter, a man handy with tools can easily make for himself.
In sinking, the digger should be careful to avoid making his shaft inconveniently small, and not to waste his energy by sinking a large "new chum" hole, which usually starts by being about three times too large for the requirements at the surface, but narrows in like a funnel at 10 feet or less. A shaft, say 4 feet by 2 feet 6 inches and sunk plumb, the ends being half rounded, is large enough for all requirements to a considerable depth, though I have seen smart men, when they were in a hurry to reach the drift, get down in a shaft even less in size.
The novice who is trying to follow or to find a deep lead must fully understand that the present bed of the surface river may not, in fact seldom does, indicate the ancient watercourses long since buried either by volcanic or diluvial action, which contain the rich auriferous deposits for which he is seeking; and much judgment and considerable underground exploration are often required to decide on the true course of leads. Only by a careful consideration of all the geological surroundings can an approximate idea be obtained from surface inspection alone; and the whole probable conditions which led to the present contour of the country must be carefully taken into account.
How am I to know the true bottom when I see it? asks the inexperienced digger. Well, nothing but long experience and intelligent observation will prevent mistakes at times, particularly in deep ground; but as a general rule, though it may sound paradoxical, you may know the bottom by the top.
That is, we will assume you are sinking in, say, 10 to 12 feet ground in a gully on the bank of which the country rock is exposed, and is, say, for instance, a clay slate or sandy slate set at a certain angle; then, in all probability, unless there be a distinct fault or change in the country rock between the slate outcrop and your shaft, the bottom will be a similar slate, standing at the same angle; and this will very probably be overlaid by a deposit of pipeclay, formed by the decomposition of the slates.
From the crevices of these slates, sometimes penetrating to a considerable distance, you may get gold, but it is useless attempting to sink through them. If the outcropping strata be a soft calcareous (limy) sandstone or soft felspathic rock, and that be also the true bottom, great care should be exercised or one is apt to sink through the bottom, which may be very loose and decomposed. I have known mistakes made in this way when many feet have been sunk, and driven through what was actually bed rock, though so soft as to deceive even men of experience. The formation, however, must be the guide, and except in some specially difficult cases, a man can soon tell when he is really on bed rock or "bottom."
On an alluvial lead the object of every one is to "get on the gutter," that is, to reach the lowest part of the old underground watercourse, through which for centuries the gold may have been accretionising from the percolation of the mineral-impregnated water; or, when derived from reefs or broken down leaders, the flow of water has acted as a natural sluice wherein the gold is therefore most thickly collected. Sometimes the lead runs for miles and is of considerable width, at others it is irregular, and the gold-bearing "gutter" small and hard to find. In many instances, for reasons not readily apparent, the best gold is not found exactly at the lowest portion of these narrow gutters, but a little way up the sides. This fact should be taken into consideration in prospecting new ground, for many times a claim has been deserted after cleaning up the "bottom," and another man has got far better gold considerably higher up on the sides of the gutter. For shallow alluvial deposits, where a man quickly works out his 30 by 30 feet claim, it may be cheaper at times to "paddock" the whole ground—that is, take all away from surface to bottom, but if he is in wet ground and he has to drive, great care should be taken to properly secure the roof by means of timber. How this may best be done the local circumstances only can decide.
Chapter III
LODE OR REEF PROSPECTING
The preceding chapter dealt more especially with prospecting as carried on in alluvial fields. I shall now treat of preliminary mining on lodes or "reefs."
As has already been stated, the likeliest localities for the occurrence of metalliferous deposits are at or near the junction of the older sedimentary formations with the igneous or intrusive rocks, such as granites, diorites, etc. In searching for payable lodes, whether of gold, silver, copper, or even tin in some forms of occurrence, the indications are often very similar. The first prospecting is usually done on the hilltops or ridges, because, owing to denudation by ice or water which have bared the bedrock, the outcrops are there more exposed, and thence the lodes are followed down through the alluvial covered plains, partly by their "strike" or "trend," and sometimes by other indicating evidences, which the practical miner has learned to know.
For instance, a lesson in tracing the lode in a grass covered country was taught me many years ago by an old prospector who had struck good gold in the reef at a point some distance to the east of what had been considered the true course. I asked him why he had opened the ground in that particular place. Said he, "Some folks don't use their eyes. You stand here and look towards that claim on the rise where the reef was last struck. Now, don't you see there is almost a track betwixt here and there where the grass and herbage is more withered than on either side? Why? Well, because the hard quartz lode is close to the surface all the way, and there is no great depth of soil to hold the moisture and make the grass grow."
I have found this simple lesson in practical prospecting of use since. But the strike or course of a quartz reef is more often indicated by outcrops, either of the silica itself or ironstone "blows," as the miners call them, but the term is a misnomer, as it argues the easily disproved igneous theory of veins of ejection, meaning thereby that the quartz with its metalliferous contents was thrown out in a molten state from the interior of the earth. This has in no case occurred, and the theory is an impossible one. True lodes are veins of injection formed by the infiltration of silicated waters carrying the metals also in solution. This water filled the fissures caused either by the cooling of the earth's crust, or formed by sudden upheavals of the igneous rocks.
Sometimes in alluvial ground the trend of the reef will be revealed by a track of quartz fragments, more or less thickly distributed on the surface and through the superincumbent soil. Follow these along, and at some point, if the lode be continuous, a portion of its solid mass will generally be found to protrude and can then again be prospected.
There is no rule as to the trend or strike of lodes, except that a greater number are found taking a northerly and southerly course than one which is easterly and westerly. At all events, such is the case in Australia, but it cannot be said that either has the advantage in being more productive. Some of the richest mines in Australasia have been in lodes running easterly and westerly, while gold, tin, and copper, in great quantity and of high percentage to the ton, have been got in such mines as Mount Morgan, Mount Bischoff, and the Burra, where there are no lodes properly so-called at all.
Mount Morgan is the richest and most productive gold mine in Australasia and amongst the best in the world.
Its yield for 1895 was 128,699 oz. of gold, valued at 528,700 pounds. Dividends paid in 1895, 300,000 pounds.
This mine was opened in 1886. Up to May 31, 1897, the total yield was 1,631,981 ozs. of gold, sold at 6,712,187 pounds, from which 4,400,000 pounds have been paid in dividends. (See Mining Journal, for Oct. 9, 1897.)
Mount Morgan shareholders have, in other words, divided over 43 1/2 tons of standard gold.
The Burra Burra Mine, about 100 miles from Adelaide, in a direction a little to the east of north, was found in 1845 by a shepherd named Pickett. It is singularly situated on bald hills standing 130 feet above the surrounding country. The ores obtained from this copper mine had been chiefly red oxides, very rich blue and green carbonates, including malachite, and also native copper. The discovery of this mine, supporting, as it did at one time, a large population, marked a new era in the history of the colony. The capital invested in it was 12,320 pounds in 5 pound shares, and no subsequent call was ever made upon the shareholders. The total amount paid in dividends was 800,000 pounds. After being worked by the original owners for some years the mine was sold to a new company, but during the last few years it has not been worked, owing in some degree to the low price of copper and also to the fact that the deposit then being worked apparently became exhausted. For many years the average yield was from 10,000 to 13,000 tons of ore, averaging 22 to 23 per cent of copper. It is stated that, during the twenty-nine and a half years in which the mine was worked, the company expended 2,241,167 in general expenses. The output of ore during the same period amounted to 234,648 tons, equal to 51,622 tons of copper. This, at the average price of copper, amounted to a money value of 4,749,224 pounds. The mine stopped working in 1877.
Mount Bischoff, Tasmania, has produced, since the formation of the Company to December 1895, 47,263 tons of tin ore. It is still in full work and likely to be for years to come.
Each of these immense metalliferous deposits was found outcropping on the summit of a hill of comparatively low altitude. There are no true walls nor can the ore be traced away from the hill in lode form. These occurrences are generally held to be due to hydrothermal or geyser action.
Then again lodes are often very erratic in their course. Slides and faults throw them far from their true line, and sometimes the lode is represented by a number of lenticular (double-pointed in section) masses of quartz of greater or less length, either continuing point to point or overlapping, "splicing," as the miners call it. Such formations are very common in West Australia. All this has to be considered and taken into account when tracing the run of stone.
This tyro also must carefully remember that in rough country where the lode strikes across hills and valleys, the line of the cap or outcrop will apparently be very sinuous owing to the rises and depressions of the surface. Many people even now do not understand that true lodes or reefs are portions of rock or material differing from the surrounding and enclosing strata, and continuing down to unknown depths at varying angles. Therefore, if you have a north and south lode outcropping on a hill and crossing an east and west valley, the said lode, underlying east, when you have traced its outcrop to the lowest point in the valley, between the two hills, will be found to be a greater or less distance, according to the angle of its dip or underlie, to the east of the outcrop on the hill where it was first seen. If it be followed up the next hill it will come again to the west, the amount of apparent deviation being regulated by the height of the hills and depth of the valley.
A simple demonstration will make this plain. Take a piece of half-inch pine board, 2 ft. long and 9 in. wide, and imagine this to be a lode; now cut a half circle out of it from the upper edge with a fret saw and lean the board say at an angle of 45 degrees to the left, look along the top edge, which you are to consider as the outcrop on the high ground, the bottom of the cut being the outcrop in the valley, and it will be seen that the lowest portion of the cut is some inches to the right; so it is with the lode, and in rough country very nice judgment is required to trace the true course.
For indications, never pass an ironstone "blow" without examination. Remember the pregnant Cornish saying with regard to mining and the current aphorism, "The iron hat covers the golden head." "Cousin Jack," put it "Iron rides a good horse." The ironstone outcrop may cover a gold, silver, copper or tin lode.
If you are searching for gold, the presence of the royal metal should be apparent on trial with the pestle and mortar; if silver, either by sight in one of its various forms or by assay, blowpipe or otherwise; copper will reveal itself by its peculiar colour, green or blue carbonates, red oxides, or metallic copper. It is an easy metal to prospect for, and its percentage is not difficult to determine approximately. Tin is more difficult to identify, as it varies so greatly in appearance.
Having found your lode and ascertained its course, you want next to ascertain its value. As a rule (and one which it will be well to remember) if you cannot find payable metal, particularly in gold "reef" prospecting, at or near the surface, it is not worth while to sink, unless, of course, you design to strike a shoot of metal which some one has prospected before you. The idea is exploded that auriferous lodes necessarily improve in value with depth. The fact is that the metal in any lode is not, as a rule, equally continuous in any direction, but occurs in shoots dipping at various angles in the length of the lode, in bunches or sometimes in horizontal layers. Nothing but actual exploiting with pick, powder, and brains, particularly brains, will determine this point.
Where there are several parallel lodes and a rich shoot has been found in one and the length of the payable ore ascertained, the neighbouring lodes should be carefully prospected opposite to the rich spot, as often similar valuable deposits will thus be found. Having ascertained that you have, say, a gold reef payable at surface and for a reasonable distance along its course, you next want to ascertain its underlie or dip, and how far the payable gold goes down.
As a general rule in many parts of Australia—though by no means an inflexible rule—a reef running east of north and west of south will underlie east; if west of north and east of south it will go down to the westward and so round the points of the compass till you come to east and west; when if the strike of the lodes in the neighbourhood has come round from north-east to east and west the underlie will be to the south; if the contrary was the case, to the north. It is surprising how often this mode of occurrence will be found to obtain. But I cannot too strongly caution the prospector not to trust to theory but to prove his lode and his metal by following it down on the underlie. "Stick to your gold" is an excellent motto. As a general thing it is only when the lode has been proved by an underlie shaft to water level and explored by driving on its course for a reasonable distance that one need begin to think of vertical shafts and the scientific laying out of the mine.
A first prospecting shaft need not usually be more than 5 ft. by 3 ft. or even 5 ft. by 2 ft. 6 in., particularly in dry country. One may often see in hard country stupid fellows wasting time, labour, and explosives in sinking huge excavations as much as 10 ft. by 8 ft. in solid rock, sometimes following down 6 inches of quartz.
When your shaft is sunk a few feet, you should begin to log up the top for at least 3 ft. or 4 ft., so as to get a tip for your "mullock" and lode stuff. This is done by getting a number of logs, say 6 inches diameter, lay one 7 ft. log on each side of your shaft, cut two notches in it 6 ft. apart opposite the ends of the shaft, lay across it a 5 ft. log similarly notched, so making a frame like a large Oxford picture frame. Continue this by piling one set above another till the desired height is attained, and on the top construct a rough platform and erect your windlass. If you have an iron handle and axle I need not tell you how to set up a windlass, but where timber is scarce you may put together the winding appliance described in the chapter headed "Rules of Thumb."
If you have "struck it rich" you will have the pleasure of seeing your primitive windlass grow to a "whip," a "whim," and eventually to a big powerful engine, with its huge drum and Eiffel tower-like "poppet heads," or "derrick," with their great spindle pulley wheels revolving at dizzy speed high in air.
"How shall I know if I have payable gold so as to save time and trouble in sinking?" says the novice. Truly it is a most important part of the prospector's art, whether he be searching for alluvial or reef gold, stream or lode tin, copper, or other valuable metal.
I presume you know gold when you see it?
If you don't, and the doubtful particle is coarse enough, take a needle and stick the point into the questionable specimen. If gold the steel point will readily prick it; if pyrites or yellow mica the point will glance off or only scratch it.
The great importance of the first prospect from the reef is well shown by the breathless intensity with which the two bearded, bronzed pioneer prospectors in some trackless Australian wild bend over the pan in which the senior "mate" is slowly reducing the sample of powdered lode stuff. How eagerly they examine the last pinch of "black sand" in the corner of the dish. Prosperity and easy times, or poverty and more "hard graft" shall shortly be revealed in the last dexterous turn of the pan. Let us hope it is a "pay prospect."
The learner, if he be far afield and without appliances of any kind, can only guess his prospect. An old prospector will judge from six ounces of stuff within a few pennyweights what will be the yield of a ton. I have seen many a good prospect broken with the head of a pick and panned in a shovel, but for reef prospecting you should have a pestle and mortar. The handiest for travelling is a mortar made from a mercury bottle cut in half, and a not too heavy wrought iron pestle with a hardened face. To be particular you require a fine screen in order to get your stuff to regulated fineness. The best for the prospector, who is often on the move, is made from a piece of cheesecloth stretched over a small hoop.
If you would be more particular take a small spring balance or an improvised scale, such as is described in Mr. Goyder's excellent little book, p. 14, which will enable you to weigh down to one-thousandth of a grain. It is often desirable to burn your stone before crushing, as it is thus more easily triturated and will reveal all its gold; but remember, that if it originally contained much pyrites, unless a similar course is adopted when treated in the battery, some of the gold will be lost in the pyrites.
Having crushed your gangue to a fine powder you proceed to pan it off in a similar manner to that of washing out alluvial earth, except that in prospecting quartz one has to be much more particular, as the gold is usually finer. The pan is taken in both hands, and enough water to cover the prospect by a few inches is admitted. The whole is then swirled round, and the dirty water poured off from time to time till the residue is clean quartz sand and heavy metal. Then the pan is gently tipped, and a side to side motion is given to it, thus causing the heavier contents to settle down in the corner. Next the water is carefully lapped in over the side, the pan being now tilted at a greater angle until the lighter particles are all washed away. The pan is then once more righted, and very little water is passed over the pinch of heavy mineral a few times, when the gold will be revealed in a streak along the bottom. In this operation, as in all others, only practice will make perfect, and a few practical lessons are worth whole pages of written instruction.
To make an amalgamating assay that will prove the amount of gold which can be got from a ton of your lode, take a number of samples from different parts, both length and breadth. The drillings from the blasting bore-holes collected make the best test. When finely triturated weigh off one or two pounds, place in a black iron pan (it must not be tinned), with 4 ozs. of mercury, 4 ozs. salt, 4 ozs. soda, and about half a gallon of boiling water; then, with a stick, stir the pulp constantly, occasionally swirling the dish as in panning off, till you feel certain that every particle of the gangue has come in contact with the mercury; then carefully pan off into another dish so as to lose no mercury. Having got your amalgam clean squeeze it through a piece of chamois leather, though a good quality of new calico previously wetted will do as well. The resulting pill of hard amalgam can then be wrapped in a piece of brown paper, placed on an old shovel, and the mercury driven off over a hot fire; or a clay tobacco pipe, the mouth being stopped with clay, makes a good retort (see "Rules of Thumb," pipe and potato retorting). The residue will be retorted gold, which, on being weighed and the result multiplied by 2240 for a 1 lb. assay, or by 1120 for 2 lb., will give the amount of gold per ton which an ordinary battery might be expected to save. Thus 1 grain to the pound, 2240 lbs. to the ton, would show that the stuff contained 4 oz. 13 dwt. 8 gr. per ton.
If there should be much base metal in your sample such as say stibnite (sulphide of antimony), a most troublesome combination to the amalgamator—instead of the formula mentioned above add to your mercury about one dwt. of zinc shavings or clippings, and to your water sufficient sulphuric acid to bring it to about the strength of vinegar (weaker, if anything, not stronger), place your material preferably in an earthenware or enamelled basin if procurable, but iron will do, and intimately mix by stirring and shaking till all particles have had an opportunity to combine with the mercury. Retort as before described. This device is my own invention.
The only genuine test after all is the battery, and that, owing to various causes, is often by no means satisfactory. First, there is a strong, almost unconquerable temptation to select the stone, thus making the testing of a few tons give an unduly high average; but more often the trouble is the other way. The stuff is sent to be treated at some inefficient battery with worn-out boxes, shaky foundations, and uneven tables, sometimes with the plates not half amalgamated, or coated with impurities, the whole concern superintended by a man who knows as little about the treatment of auriferous quartz by the amalgamating or any other processes as a dingo does of the differential calculus. Result: 3 dwt. to the ton in the retort, 30 dwt. in the tailings, and a payable claim declared a "duffer."
When the lode is really rich, particularly if it be carrying coarse gold, and owing to rough country, or distance, a good battery is not available, excellent results in a small way may be obtained by the somewhat laborious, but simple, process of "dollying." A dolly is a one man power single stamp battery, or rather an extra sized pestle and mortar (see "Rules of Thumb").
Silver lodes and lodes which frequently carry more or less gold, are often found beneath the dark ironstone "blows," composed of conglomerates held together by ferric and manganic oxides; or, where the ore is galena, the surface indications will frequently be a whitish limey track sometimes extending for miles, and nodules or "slugs" of that ore will generally be found on the surface from place to place. Most silver ores are easily recognisable, and readily tested by means of the blowpipe or simple fire assay. Sometimes the silver on being tested is found to contain a considerable percentage of gold as in the great Comstock lode in Nevada. Ore from the big Broken Hill silver load, New South Wales, also contains an appreciable quantity of the more precious metal. A natural alloy of gold containing 20 per cent silver, termed electrum, is the lowest grade of the noble metal.
Tin, lode, and stream, or alluvial, occurs only as an oxide, termed cassiterite, and yet you can well appreciate the compliment one Cornish miner pays to another whose cleverness he wishes to commend, when he says of him, "Aw, he do know tin," when you look at a representative collection of tin ores. In various shapes, from sharp-edged crystals to mammillary-shaped nuggets of wood-tin; from masses of 30 lbs. weight to a fine sand, like gunpowder, in colour black, brown, grey, yellow, red, ruby, white, and sometimes a mingling of several colours, it does require much judgment to know tin.
Stream tin is generally associated with alluvial gold. When such is the case there is no difficulty in saving the gold if you save the tin, for the yellow metal is of much greater specific gravity. As the natural tin is an oxide, and therefore not susceptible to amalgamation, the gold can be readily separated by means of mercury.
Lode tin sometimes occurs in similar quartz veins to those in which gold is got, and is occasionally associated with gold. Tin is also found, as at Eurieowie, in dykes, composed of quartz crystals and large scales of white mica, traversing the older slates. A similar occurrence takes place at Mount Shoobridge and at Bynoe Harbour, in the Northern Territory of South Australia; indeed, one could not readily separate the stone from these three places if it were mixed. As before stated tin will never be found far from granite, and that granite must have white mica as one of its constituents. It is seldom found in the darker coloured rocks, or in limestone country, but it sometimes occurs in gneiss, mica schist, and chlorite schist. Numerous other minerals are at times mistaken for tin, the most common of which are tourmaline or schorl, garnet, wolfram (which is a tungstate of iron with manganese), rutile or titanic acid, blackjack or zinc blende, together with magnetic, titanic, and specular iron in fine grains.
This rough and ready mode of determining whether the ore is tin is by weight and by scratching or crushing, when, what is called the "streak" is obtained. The colour of the tin streak is whitey-grey, which, when once known, is not easily mistaken. The specific gravity is about 7.0. Wolfram, which is most like it, is a little heavier, from 7.0 to 7.5, but its streak is red, brown, or blackish-brown. Rutile is much lighter, 4.2, and the streak light-brown; tourmaline is only 3.2. Blackjack is 4.3, and its streak yellowish-white.
I have seen several pounds weight to the dish got in some of the New South Wales shallow sinking tin-fields, and, as a rule, payable gold was also present. Fourteen years ago I told Western Australian people, when on a visit to that colony, that the neighbourhood of the Darling range would produce rich tin. Lately this had been proved to be the case, and I look forward to a great development of the tin mining industry in the south-western portion of Westralia.
The tin "wash" in question may also contain gold, as the country rock of the neighbourhood is such as gold is usually found in.[*]
