In prospecting a country for Prospecting for valuable minerals wealth, it is most important to search very systematically and carefully among the sands and rocks of river beds, in dry creeks, and at the bottom of valleys, as well as on the sea-shore. Not only does the action of running water and glaciers grind down masses and particles, and, through the never-changing law of gravity, deposit the debris on the lower ground : but also, as on the shores of California, Oregon, New Zealand, and elsewhere, the tides of the ocean distribute the disintegrated heavy metals in a regular fashion. In looking to find gold, the prospector should observe the characteristics of loose rocks found in ravines or gulches, more especially in eddies or dry waterholes where heavy matter is left during freshets, such as are of frequent occurrence in mountainous districts ; for the holes and channels and fissures in the solid rock over which a stream runs, or has run, are frequently well worth examining. All earthy deposits being the result of either chemical or mechanical action, they usually serve as a guide to the nature of the constituent parts of the earth’s crust in the immediate neighbourhood.
Prospecting for heavy metals left in the form of a deposit is based on one and the same rules, and, consequently, the search for the precious metal gold may be selected as an exemplification of the method. In searching the sands washed down by rivers, it is well to bear in mind that if the bed of a river flowing through an open country yields fine gold dust, it will probably yield larger dust or grains nearer the mountains from which the stream runs, and grains of gold far along the stream may suggest nuggets nearer the source ; because the water which has washed the gold-bearing matter from the lodes in the mountains has washed it, so to speak, down an inclined plane, leaving in its course the heavy particles and transporting the lighter farther away. The richest deposits are often those where the current has been broken by a change of descent or direction, and where a turning is abrupt, so that on one side of the stream is a cliff and on the other a gentle slope; the latter may be very rich in heavy metals. Sometimes there are several of these bends with slopes opposite cliffs, and in these slopes there is more chance of discovering gold than in places where the course of the stream is a straight one. The termination of a mountain chain, too, offers a likely site for alluvial diggings. Very commonly in a canon or gulch, where gold grains are found deposited in the lowest parts along which the river or creek runs, an accumulation of boulders or gravel may be noticed higher up the sides of the range, and more or less parallel to the bed of the creek. Portions of such deposits should be carefully examined by the eye (and by the magnifying glass), and by washing in a basin at the nearest water as the gold-bearing matter, whether carried there in a past age by running water or glacier, may contain rich gold layers close to the “ bed-rock ” on which the debris rests. Should there be several distinct deposits, the deepest layer of each period is generally the most lucrative. When alluvial ground is made up of rather loose gravel mixed with boulders or lumps of rock, the gold along with other heavy substances will be found underneath the bulk of the coarse deposits, and either remains near to or on the “bed-rock” or mixed with clay ; so that the earthy matter just over the “bed-rock ” ought to claim much more attention than that elsewhere.
If the clay is likely to contain the precious metal, it ought to be washed very carefully. In prospecting a stream, should the flow of water hinder digging operations, the course of the stream must be diverted by means of back trenches, cut so that the water may flow through them ; in this manner the bed may be laid bare, and then the largo rocks or boulders can be easily removed and the finer gravel thoroughly washed by running water. It is advisable to remember that when gold in alluvial ground occurs, the chances are that auriferous lodes—not necessarily payable to work, yet, perhaps, of a far more permanent source of wealth than the gravels will prove —traverse the neighbouring elevations of land, and consequently the country round about should be searched for veins.
In the search for mineral veins or deposits other than alluvial, it is not advisable for a prospector to trouble himself about the comparatively recent formations nor modern volcanic rocks ; for, although certain deposits do occur in the former, and rich auriferous deposits have been worked in Australia and California under formations capped by the latter, it is well to bear in mind that, excepting certain deposits of iron, copper, zinc, lead and surface diggings, the metal-bearing minerals are chiefly mined for in the rocks of an older date than those of the Coal measures, though some, as in California, Transylvania, and Hungary, belong to a more recent period. It must also be remembered that a granite, diorite, andesite, or metamorphic rock (schist, quartzite.) country is always worth prospecting.
“Without entering into a discussion concerning the formation and origin of veins, about which so much speculation has been rife and so many theories propounded, it suffices to say that certain laws applying to veins in one district apply also, more or less, to those in another. For instance, in any particular district the mineral-bearing lodes generally follow the same direction, that is to say their planes have the same compass-bearing, and consequently are parallel, notwithstanding a considerable distance may separate one lodo from the next nearest to it. In some mining districts, a second series of veins runs right across the first and principal; these lodes, however, are either of a different nature of mineral to that of the first, or if of the same, poorer in quality. It is well to recollect that a true mineral vein, where it exists, is not likely to be isolated; it rather represents, in a poorer or richer degree, many more within reach, and which constitute a “ mineral belt.” For this reason, the explorer should not set his affections too much on any one “ claim ” until he has to his own satisfaction, if means and time allow, considered the whole district with its numerous lodes as a mineral-bearing one.
In the search for mineral veins, the prospector should study the general geological features of the country, the sections of road cuttings, landslips, precipitous cliffs, the sides of valleys, the sections of banks exposed to view (by the action of water or other denuding agency), river-beds, dry channels and gorges. If he find “likely” stones in a creek or valley, he should travel up it until he notices that similarly constituted stones cease to be seen, and then start up the hill-side to discover the parent rock from which they became detached. Very frequently, while at the base of a hill or mountain, there is a deposit in the form of soil washed down from the more elevated ground, higher up there is “ drift ” in the form of boulders and detritus, intervening between the surface and the original bed-rock, and thus obscuring the solid rock formation from view.
However, by taking note of the various undulations and avoiding such places where common sense suggests that “ drift ” would naturally accumulate, the prospector may come across “outcrops,” especially in the steep sides of gulleys and backbones of ridges; and, failing this, he may, by travelling towards the summit of any range of hills, be sure, as he approaches the top, to find less “ drift ” to thwart his investigations. At the same time, though he ought not to be too eager to commence work with his prospecting pick in “drift ” of great thickness—say ten or twenty feet —he must, for all that, carefully notice the various “ float ” stones on the surface of the hill-sides, as by doing so he can often trace the rim of a particular lode hidden from view, and, if no “ outcrop ” of the same kind of rock has attracted his attention by leaving traces in the form of detached pieces scattered about the slopes according to the law of gravity, which distributes the pieces as they have been hurled or washed down from the parent rock with a certain amount of regularity—the larger and least weather beaten ones being nearest the lode — he can leastways observe at what point up the slope the “ float ” rock ceases to be seen; then he may sink a ten-feet-deep pit, or else drive a crosscut to strike the “ body ” of that which he is in search of.
Before commencing this, he must take note of the slope on which the “ likely ” broken away rocks repose, because judgment may tell him that the parent rock is not directly under his feet, but rather to the right or left, according to the amount of inclination of the hill-side. Much unnecessary labour is often performed through not taking account of this, as one naturally imagines that the lode is just underneath the line where the greatest amount of “float” occurs, whereas it may in reality be several yards distant, probably on the ridge just a little way off, but decidedly not on the other side of it.
Sometimes, as is the case with the Transvaal conglomerate, the direction of a deposit near the outcrop may alter considerably as depth is gained ; and, where no other outcrops at a distance are observable, much wrong calculation as to future prospecting or sinking of shafts, &c., may be the result. (Fig. 1.)
Where “ faults ” occur, the course of lodes or beds may be irregular in direction on account of the dislocation of the country rock ; but if the country is made up of different kinds of layers, the deviation may frequently be easily determined by the relative position of the beds. (Figs. 2, 3, 4.)
In examining the loose rocks on the surface, the expert explorer can often form a tolerably correct notion of the nature of an underground lode, despite the fact that exposure to weather entirely alters a piece of rock which once upon a time may have been metallic in appearance before it became disconnected from its original position. So, in scaling the heights, he casts his glance in every direction, to observe if the “ country rock ” be “kindly ” for veins, and all the while keeps a sharp look out for that kind of rock known to form the matrix of a mineral vein. The matrices are chiefly quartz, flúor spar, and calc spar; generally quartz.
Fluor spar (fluate of lime) is favourable for lead and copper, calc spar for lead and silver ; but quartz is very nearly the universal matrix of veins in a mineral country, and thus it is that quartz rock should be especially searched for. Very frequently the pieces of quartz broken away from the lode and also the surface portion of the lode are honeycombed. Having been exposed to the influence of the atmosphere and moisture, most of the metalliferous parts once existing in the cavities, and similar to what one might expect to find a few fathoms downwards on the vein, have been decomposed, and so, instead of filling up the honeycomb cavities of the surface quartz, have merely left traces in the form of stains. This only applies to the metallic portions oxidizable, for it is in the surface of honeycombed auriferous rock that the unmistakable yellow specks may be seen in the cells once filled up with iron or copper pyrites or other metallic compound associated with the precious metal. Gold and silver in the native state (the former very much more so than the latter, which becomes tarnished) weather the effects of the elements much better than most metals, and can be recognised in the native condition ; but experience alone can acquaint one with the variously shaded blacks, reds, greens, browns, greys, &c., which the metallic sulphides have left behind as oxides and carbonates. One of the best surface indications is the honeycombed rock brown with iron oxide.
The iron oxide is really the result of the decomposition of iron pyrites; and in the lode with this at “grass roots,” iron pyrites would be found deeper down. Having thus traced the honeycombed quartz—the pieces of which are less angular and smoother the farther away they lie from the lode—or other likely matrix rocks up the hill or mountain side to some outcropping rock (often forming a distinct ridge) from which it has been hurled down, or to where the detached pieces cease to be noticed, the prospector may dig a trench at right angles, if possible, to the lode, in order to examine its character, the nature of the vein and the gangue, and to find the bounding walls, viz. the upper or hanging wall, and the lower or foot-wall, as well as to note the direction or “ strike ” of the lode; he must notwithstanding, for the sake of accuracy, “ sink ” a “ prospecting shaft” a few feet deeper than the bottom of the trench, as the inclination of the lode near the surface is most misleading, on account of the body of ore having been distorted from its original shape. When once the probable direction of the lode is ascertained, the positions where it is desirable that other pits, lower down or higher up the hill or on the other side of a valley, should be sunk so as to test the continuity of the vein, are settled. Should the prospect of the vein being a continuous one seem favourable, and the surface “ assays ” turn out well, development of the claim may be attended to.
At the same time, no person should be led away by such a hope as that “ the deeper the vein the more payable the ore “; for, as a fact, though certain lead and copper veins do improve by depth, and also very many gold-bearing lodes —for instance, those in Grass Valley, California, which seem to be as rich at 1,000 feet deep as at the surface—very many do deteriorate in value; nor is it prudent to attach too much affection on any particular lode, until the surrounding country has in some measure been examined. Besides, it is now a recognised fact that veins vary in quality and nature according to the strata they pass through.
Even if the prospects look bright, a person who goes in for mining ought not to be too sanguine of success, for mineral veins are most apt to disappoint; frequently do they “ pinch out” between hard rocks, or end in a “ pocket,” or become changed in character and value when least expected. To err on the safe side, it is just as well for a happy possessor to make sure that at least the surface rock “ assays ” payably, simply because his money and time are of too much worth to admit of the expensive and sometimes apparently endless labour involved in developing work. A capitalist may risk some of his quickly amassed gains in following up research in the hope of some day increasing his capital, although he quite understands how thoroughly the game is a chance one ; but the ordinary miner should avoid uncertainties much more than he usually does.
That a lode carries gold and silver or any other valuable metal in some form or other, is not sufficient data to lean upon in the estimation of its worth. Oftentimes the gold, for instance, is distributed in the form of very fine powder invisible to the eye and covered with a rusty film (due to sulphides or arsenides, oxide of iron or manganese, and sometimes to sulphate of copper and iron); and in consequence, though the “ assay ” may be favourable, the extraction of the precious metal from the ore by the amalgamation is not satisfactory, as the mercury “ sickens ” or “ flours.” Again, the value of a body of ore, though it may be rich in precious or valuable metals, depends in a measure upon the nature of the other constituents, especially when the ore has to be smelted. Antimony or arsenic, in not very great quantities either, may render an otherwise valuable ore useless so far as profitable smelting is concerned. Before digging operations are commenced, the pieces of rock from the lode should be examined, and, if such is possible, by a reliable assayer, who, if he suspects the presence of precious metals, will, by scorification or melting in a crucible, and afterwards by cupellation method, determine the amount of gold and silver per ton of a similar rock, and, without undertaking a careful quantitative analysis of the other associated metallic compounds, will, from the slag in the scorifier or crucible and colour or appearance of the bone ash cupel after the operation is concluded, be able to judge approximately what proportions of the metals copper, iron, lead, antimony, zinc, &c., are mixed with the others. It is always the wisest plan to obtain a proper assay before development work is entered on. Unfortunately, this is not an easy matter in out-of-the-way places. To assay correctly means a course of training ; for this reason the author cannot conscientiously advise anyone to undertake a silver or gold assay by scorification and cupellation, nor a “ burette ” one for copper, iron, zinc, &c., until he has practised the methods under the eye of an assayer; because in all likelihood his own attempts, though they might be near the mark as to results, would more than probably be quite misleading. Still, there is no reason why an inexperienced person should not attempt to qualitatively test minerals by simple methods, nor in some instances do so quantitatively. To fly to the assistance of a chemist or a mineralogist or an assayer for every little matter of inquiry concerning minerals is not only inconvenient, but in many mining districts unsatisfactory, as there are, naturally, so many unreliable so-called authorities to be met with. Because a miner pronounces such a mineral unlike anything he has seen in Cornwall, or California, or Ballarat, and devoid of any valuable metal, the prospector need not be too ready in accepting such an opinion; for, as a rule, the knowledge of an ordinary miner, expert, perhaps, in certain matters, such as timbering tunnels, &c., is neither remarkably extensive nor always sound. Neither must he depend on the superficial conclusions of any professed expert who has arrived at such by a superficial examination, even with the help of a magnifying glass. Experience abroad tells one that not only has the ordinary miner erroneous notions about such minerals as grey copper ore, silver glance, fine and coarse grained galena, &c., but also that the most experienced mineralogist cannot for a certainty tell at first sight how much gold or silver may be concealed in a particular rock. Both of these precious metals are found in several places, which many persons might call most unlikely formations, and it is quite a common thing to handle specimen rocks worthless in appearance and yet assaying very high in gold and silver, and also handsome looking specimens that disappoint in not “running” anything to the ton in either of the precious metals. Nor can a person, unless he be a thorough expert, depend upon the appearance of certain pieces of ore for a guide as to the yield of valuable metals. Many of the silicates, carbonates, and chlorides are perfectly nonmetallic to look at, and when associated with other metals are very deceiving as to their real value. For a long time the chloride of silver deposits in Colorado were passed over without their nature being known, and so were the carbonate of lead (carrying silver) unnoticed at Leadville, which, through the discovery, in five years became a city of 30,000 inhabitants. Who would say how much per cent, of nickel there is in a particular piece of the New Caledonia hydrated silicate of nickel ore, or how much silver in the Leadville ore, or what proportion of gold is likely to be in a lump of copper pyrites or iron pyrites, unless he had made each a special study ? Therefore it is just as well that a person should be independent of the opinions of others and, to a certain extent, of his own; and, at the same time, never grudge a few shillings or dollars in obtaining the advice of a proper assayer.
Supposing that a correct assay of the lode matter has been secured or a rough one made, the prospector has still some items of significant worth to consider before he commences to build “ castles in the air,” or even continue development work. He must find out if the ground is easily worked (for in one locality though “sinking” through a soft ground only cost £2 a fathom, “ sinking ” through hard ground may cost £20 or more); if the ore to be smelted is refractory, or is capable of concentration after sorting, before it is sent away to the smelting or to the crushing and amalgamating works. He must find out exactly the price of smelting or otherwise treating the ore, taking into consideration such items as the cost of labour, the freight of ore and fluxes as well as their cost, the freight of the ores to the “ works,” &c. He must take into account the proximity or distance off of both fuel and water, as well as the obtainable quantity of each. Many spots in Arizona and New Mexico exist where the working of veins and alluvial diggings is impossible for the time present, or retarded through the absence of creeks and springs. He must remember that a lode running twenty dollars worth of metals to the ton may be of more value than another running two hundred dollars not very many miles off; that a low-grade silver ore in one locality may be of more intrinsic worth than a vein of pure silver, having the thickness of a knife blade, in another.
In brief, the character and quality of ore, as well as the probability of the continuity of the lode, the location of the mining claim, the number of acres of available fuel and timber within reach, the proximity and quantity of water, every expense attendant on carriage, smelting operations, &c., should be considered in detail before the development of any single mine merits commencement, in order to turn out a profitable concern. It has been said that in the world there are ten unprofitable mines to one profitable ; so let no one take the trouble to dive into the above considerations until he really believes that there is “ payable stuff ” to be dug out of his “ claim ” ; let him avoid the habit of reckoning the value of a property from a few picked specimens.