Part 1 (1/2)
Hittel on Gold Mines and Mining.
by John S. Hittell.
_Chief Industry._--Mining is the chief industry of California. It employs more men and pays larger average wages than any other branch of physical labor. Although it has been gradually decreasing in the amount of its production, in the profits to the individuals engaged in it, and in its relative importance in the business of the state, it is yet and will long continue to be the largest source of our wealth, and the basis to support the other kinds of occupation.
_Metals obtained._--Our mines now wrought are of gold, silver, quicksilver, copper and coal. Ores of tin, lead, and antimony in large veins, beds of sulphur, alum and asphaltum; lakes of borax and springs of sulphate of magnesia, are also found in the state, but they are not wrought at the present time, though they will probably all become valuable in a few years. Platinum, iridium, and osmium are obtained with the gold in some of the placer mines, but are never found alone, nor are they ever the main object sought by the miner. The annual yield of our gold mines is about forty millions of dollars, of our quicksilver two millions of dollars. Our silver, copper and coal mines have been opened within a year, and their value is yet unknown. All our other mining is of little importance as compared with the gold.
_Gold Mines._--Our gold mines are divided into placer and quartz. In the former, the metal is found imbedded in layers of earthy matter, such as clay, sand and gravel; in the latter it is incased in veins of rock. The methods of mining must be adapted to the size of the particles of gold, and the nature of the material in which they are found. In placer mining, the earthy matter containing the gold, called the ”pay-dirt,” is washed in water, which dissolves the clay and carries it off in solution, and the current sweeps away the sand, gravel and stones, while the gold, by reason of the higher specific gravity, remains in the channel or is caught with quicksilver. In quartz mining the auriferous rock is ground to a very fine powder, the gold in which is caught in quicksilver, or on the rough surface of a blanket, over which the fine material is borne by a stream of water.
About two-thirds of our gold is obtained from the placers, and one-third from the quartz.
A mine is defined and generally understood to mean ”a subterraneous work or excavation for obtaining metals, metallic ores or mineral substances;” but this definition does not apply to our placer mines, which are places where gold is taken from diluvial or alluvial deposits. Most of the work is not subterraneous; it is done in the full light of day. In some of the claims the pay-dirt lies within two feet of the surface; in others it lies much deeper, but all the superinc.u.mbent matter is swept away.
Water is the great agent of the placer miner; it is the element of his power; its amount is the measure of his work, and its cost is the measure of his profit. With an abundance of water he can wash every thing; without water he can do little or nothing. Placer mining is almost entirely mechanical, and of such a kind that no accuracy of workmans.h.i.+p or scientific or literary education is necessary to mastery in it. Amalgamation is a chemical process it is true, but it is so simple that after a few days' experience, the rudest laborer will manage it as well as the most thorough chemist.
It is impossible to ascertain the amount of gold which has been taken from the mines of California. Records have been kept of the sums manifested at the San Francisco Custom House, for exportation, and deposited for coinage in the mints of the United States; and there is also some knowledge of the amounts sent in bars and dust to England; but we have no account of the sums carried by pa.s.sengers to foreign countries and coined elsewhere than at London, or used as jewelry, or of the amount now in circulation in this state. According to the books of the Custom House of San Francisco, the sums manifested for export were as follows:
In 1849, $4,921,250; in 1850, $27,676,346; in 1851, $42,582,695; in 1852, $46,586,134; in 1853, $57,331,034; in 1854, $51,328,653; in 1855, $45,182,631; in 1856, $48,887,543; in 1857, $48,976,697; in 1858, $47,548,025; in 1859, $47,640,462; in 1860, $42,303,345; in 1861, $40,639,089; a total of $551,603,904 in twelve years.
The exportation of gold commenced in 1848, but we have no record of the sums sent away in that year. Previous to 1854 very large sums were carried away by pa.s.sengers, who gave no statement at the Custom House; since that year, the manifests show the exportation correctly within a few millions. I am entirely satisfied that the total gold yield of California has been not less than seven hundred millions of dollars; but I have not room here to state the reasons for this opinion. My estimate is considerably less than that of most business men of the state, and less than that made by Hunt's _Merchants' Magazine_. There was undoubtedly a regular increase in the annual yield of the mines from 1848 to the end of 1853; and there has been a gradual decrease since the beginning of 1854--a decrease perhaps not very regular but still certain. Since 1854 considerable sums exported from San Francisco, and included in our tables, came from mines beyond the limits of California, such as the mines in Southern Oregon, in the eastern part of Was.h.i.+ngton Territory, in British Columbia, and in Nevada Territory; and while the California gold yield has been decreasing, these extraneous supplies have been increasing. Several millions must be deducted from the annual s.h.i.+pments since 1858, for foreign gold. The gold yield will undoubtedly continue to fall, but to what point and at what rate no one can know. I believe that in 1870, the yield will not exceed thirty millions of dollars.
_Placer Mines._--Placer mines are divided into many cla.s.sifications.
The first and most important is into deep and shallow. In the former the pay-dirt is found deep, twenty feet or more beneath the surface; in the latter, near the surface. The shallow or surface diggings are chiefly found in the beds of ravines and gullies, in the bars of rivers, and in shallow flats; the deep diggings are in hills and deep flats. The pay-dirt is usually covered by layers of barren dirt, which is sometimes washed, and sometimes left undisturbed, while the pay-dirt is taken out from beneath it through tunnels or shafts. So far as our present information goes, we have reason to believe that no gold country ever possessed so large an extent of paying placer mines, with the pay-dirt so near the surface, and with so many facilities for working them as California. In Australia the diggings are very deep and spotted, that is, the gold is unevenly distributed, and the supply of water for mining is scanty. In Siberia the winter is terribly cold during six months of the year. In Brazil the diggings were not so extensive nor so rich as in this state. Here we have numerous large streams coming down through the mining districts, very large bodies of pay-dirt, and a mild climate.
After dividing placers into deep and shallow, the next cla.s.sification will be according to their topographical position, as into hill, flat, bench, bar, river-bed, ancient river-bed, and gulch mines. Hill diggings are those where the pay-dirt is in or under a hill. Flat diggings are in a flat. Bench diggings are in a ”bench” or narrow table on the side of a hill above a river. Benches of this kind are not uncommon in California, and they often indicate the place where the stream ran in some very remote age. Bars are low collections of sand and gravel at the side of a river and above its surface at low water.
River-bed claims are those beneath the surface of the river at low water, and access is obtained to them only by removing the water from the bed by flumes or ditches. Ancient river-bed claims are those of which the gold was deposited by streams in places where no streams now exist. Gulch claims are those in gullies which have no water, save during a small part of the year. A ”claim” is the mining land owned or held by one man or a company.
The placer mines are again cla.s.sified according to the manner in which, or the instruments with which they are wrought. There are sluice claims, hydraulic claims, tunnel claims, dry was.h.i.+ng, dry digging, and knife claims. In 1849 and 1850, the main cla.s.sification of the placers was into wet diggings and dry diggings, the former meaning mines in the bars and beds of rivers, and dry diggings were those in gullies and flats where water could be obtained only part of the year or not at all. That cla.s.sification was made while nearly all the mining was done near the surface, before the great deposits of pay-dirt in the hills had been discovered, and before ditches, sluices, and the hydraulic process had been introduced. The cla.s.s of mines then known as the ”dry diggings,” and which for several years furnished nearly half of the gold yield of the state, are now, with a few unimportant exceptions, exhausted, or left to the attention of the Chinamen.
The purpose of all placer miners is not to catch all the gold in the dirt which they wash, but to catch the greatest possible quant.i.ty within a given time. It is not supposed that any process used in gold mining catches all the metal. Part of it is lost; in some processes a considerable proportion. The general estimate in California is, that one-twentieth of the gold in the dirt which is washed is lost. Many of the particles are so very small as to be invisible to the naked eye, and so light that their specific gravity does not avail to prevent them from being carried away by the water like sand. The larger pieces will sink to the bottom and resist the force of the water; the smaller the particles, the greater the danger that it will be borne away. Many devices have been tried to catch all the gold, but none have succeeded perfectly, and some which have caught a portion of what escaped from the ordinary modes of mining, have been found to cost more than their yield. The miner does not grieve about that which he cannot catch. He is not careful to catch all that he could. His purpose is to draw the largest possible revenue per day from his claim. He does not intend to spend many years in mining, or if he does, he has become thriftless and improvident. In either case, he wishes to derive the utmost immediate profit from his mine. If his claim contain a dollar to the ton, and he can save five dollars by slowly was.h.i.+ng only six tons in a day, while he might make ten dollars by rapidly was.h.i.+ng fifteen tons in a day, he will prefer the latter result, though he will loose twice as much of the precious metal by the fast as by the slow mode of working. The object of the miner is the practical dispatch of work, and his success will depend to a great extent upon the amount of dirt which he can wash within a given s.p.a.ce of time. He regrets that any of the gold should be wasted, but his regret is because it escapes from his sluice and his pocket, rather than because it is lost to industry and commerce.
_The Sluice._--The board-sluice is a long wooden trough, through which a constant stream of water runs, and into which the auriferous dirt is thrown. The water carries away the clay, sand, gravel and stones, and leaves the gold in the bottom of the sluice, where it is caught by its gravity and by quicksilver. The board-sluice is the great was.h.i.+ng machine, and the most important instrument used in the placer mining of California. It washes nearly all the dirt and catches nearly all the placer gold of the country. It was invented here, although it had previously been used elsewhere; it has been more extensively employed here than in any other country, and it can be used here to more advantage than elsewhere. It is not less than fifty feet long, nor less than a foot wide, made of boards. The width is usually sixteen or eighteen inches; and never exceeds five feet. The length is ordinarily several hundred and sometimes several thousand feet. It is made in sections or ”boxes” twelve or fourteen feet long. The boards are an inch and a half thick, and are sawn for that special purpose, the bottom boards being four inches wider at one end than the other. The narrow end of one box therefore fits in the wide end of another, and in that way the sluice is put together, a long succession of boxes, the lower end of each resting in the upper end of another, and not fastened together otherwise. These boxes stand upon trestles, with a descent varying from eight to eighteen inches in twelve feet. It is therefore an easy matter to put up or take down a sluice after the boxes are made, and it is not uncommon for the miners to haul their boxes from one claim to another. The descent of a sluice is usually the same throughout its length, and is called its ”grade.” If there be a fall of eight inches in twelve feet, the sluice has an ”eight-inch grade,” and if the fall be twice as great, it is a ”sixteen-inch grade.” The grade depends upon the character of the pay-dirt, the length of the sluice, and its position. The steeper the descent, the more rapidly the dirt is dissolved, but the greater the danger also that the fine particles of gold will be carried away by the water. The tougher the dirt, that is, the greater its resistance to the dissolving power of the water, the steeper, other things being equal, should be the sluice. A slow current does not dissolve tough clay, and that is the greater part of the pay-dirt, so rapidly as a swift one. The shorter the sluice, other things being equal, the smaller the grade should be. There is more danger that the fine particles of gold will be lost by a short sluice than by a longer one, and to diminish this danger, the rapidity of the current must be reduced by a small grade. The greater the amount of dirt to be washed, other things being equal, the steeper should be the grade; for a swift current will wash more dirt than a slow one. In many claims the pay-dirt is full of large stones and boulders, weighing from one hundred to five hundred pounds each, all of which must be carried away through the sluice. Some are sent down whole, and others are broken into pieces with sledge hammers before they are thrown into the box. These require a swift current and a large body of water. The larger the supply of water, the steeper the sluice is made, other things being equal. Of course economy and convenience of working require that the sluice should be near the level of the ground, and as that may be steep or level below the claim, the grade of the sluice must to some extent conform to it. There are thus a mult.i.tude of points to be taken into consideration in fixing the grade of a sluice; but a fall of less than eight or more than twenty inches, in a box of twelve feet, would be considered as unsuitable for the board-sluice. Sometimes the upper part of the sluice is made steeper so as to dissolve the dirt, and the lower part has a small grade to catch the gold. The clayey matter of ordinary pay-dirt is fully dissolved in a sluice two hundred feet long with a low grade, so the use of the boxes beyond that length is merely to catch the gold. There are claims however in which the clay is so extremely tough that it will roll in large b.a.l.l.s more than a quarter of a mile through a steep sluice with a large head of water, and come out at the lower end scarcely diminished in size.
The gold is caught in the sluice-boxes by false bottoms of various kinds. It would not do to leave the smooth boards, for the water would sweep all the gold away, and the boards themselves would soon be worn through. The most common false bottom is the longitudinal riffle-bar, which is from two to four inches thick, from three to seven inches wide, and six feet long. Two sets of these riffle-bars go into each sluice-box, the box being twice as long as the bar. A set of riffle-bars is as many as fill one half of a box. They are wedged in, from an inch to two inches apart; the wedging being used, because the bars can more readily be fastened in their places, and more easily taken up, than if nails were used. Before the work of sluicing commences, all the boxes are fitted with riffle-bars, and the bottom of the sluice is therefore full of holes from one to two inches wide, from three to seven inches deep, and six feet long. These are the places in which the gold, quicksilver, and amalgam are caught. Quicksilver is used now in nearly all the sluices, and is the more necessary the smaller the particles of gold. The large pieces of the metal would all be caught by their specific gravity without the aid of amalgamation.
The sluice-boxes having been made, and set up with the proper grade, the water is turned in. The boxes are made of the rough boards as they come from the saw, and the joints are not waterproof, but the leaks are soon stopped by the swelling of the wood, or by the dirt. The stream of water in the sluice is at least two inches deep over the bottom. The height of the sides of the boxes is from eight inches to two feet. The sluice usually runs through the claim, and the auriferous dirt is thrown in with shovels, of which from four to twenty are constantly at work. A man will throw in from two to five cubic yards of dirt in one day. The water rus.h.i.+ng over the dirt as it lies in the box, rapidly dissolves the clay and loam, and then sweeps the sand, gravel and stones down. The first dirt in the box goes to fill the s.p.a.ces between the riffle-bars. After the sluicing has been in progress a couple of hours, some quicksilver is put in at the head of the sluice, and it gradually finds its way downward, most of it stopping, however, near where it is put in.
_Amalgamation._--There are a few metals, including gold, silver, copper and tin, which, with quicksilver, form a peculiar chemical union called amalgamation, a process of great importance to the gold miner. When a piece of gold or silver is placed in mercury, the latter metal gradually penetrates through it, destroys the coherence of its particles, and form with it a ma.s.s like dough. A lump of gold as large as a bean will be soaked through in three or four days; with silver and copper the process is slower, but they are affected in the same manner.
Amalgamation, though a union of a solid with a liquid, differs much from a solution. In the latter the union is mechanical; in the former it is chemical. In the latter the solid is reduced to particles of impalpable fineness; in the former it is not. An ounce of salt will be dissolved in, and nearly equally diffused through, a pint of water; but if an ounce of gold be thrown into a pint of quicksilver, it will, after forming an amalgam with the quicksilver, remain at the bottom. We have no texture so fine that it will strain salt out of water; but the particles of gold are so coa.r.s.e in amalgam that they can easily be strained out by means of buckskin or tight cloths. However, a little gold will remain in the quicksilver--about the fiftieth part of an ounce of gold in every pound of quicksilver; and the only method of obtaining this gold is by retorting.
Quicksilver is used in gold mining for catching the small particles of metal; the large ones are caught by their weight. But many of the particles are so small that they are almost invisible to the naked eye, and when in moving water they float. Miners frequently show visitors the fineness of their gold by putting some of the dust in a vial with water, and upon shaking, the particles of metal can be seen floating about in the clear water. Riffles, and all the devices to get the benefit of specific gravity, are of little use to arrest this ”float-gold,” so amalgamation is employed. If a bit of quicksilver is put in the way of the fine gold, the two metals unite at once and make a larger bulk, which can be caught.
There is no such attraction between gold and quicksilver as there is between the magnet and iron; but when the two former metals once touch, an amalgam is immediately formed, and if the proportions of the metals be about even, they in time make a hard ma.s.s. Some gold does not amalgamate readily; in various diggings of Siskiyou county, the gold has a reddish coating, which prevents amalgamation. Grease or resin in the water used for was.h.i.+ng, is also unfavorable. So is cold. Heat is favorable, and therefore less gold is lost in summer than in winter.
Quicksilver that has been once used is considered better than that fresh from the flask.
No tinned iron or copper vessel should be used for holding or panning out amalgam, or dirt containing amalgam; since quicksilver forms an amalgam with tin and copper, and will stick to the sides of a tinned or copper pan.
In most sluices, the quicksilver is put in above the riffle-bars at various places along in the boxes, with a confidence that the great specific gravity of the metal will prevent it from being lost. The greater the quant.i.ty and proportion of fine gold, the greater the importance of the quicksilver.
The best method of catching very fine gold by amalgamation is to cover a large copper plate with mercury, and let the dirt and water, in a thickness of not more than a quarter of an inch, pa.s.s over it slowly.
There are various methods of covering copper plates with quicksilver.