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this great vein is gold-bearing throughout its whole course, or that even a notable proportion of the quartz which rises into peaks and mountains between Mariposa and Amador counties is auriferous. It is only here and there at wide intervals that mines can be found which can be worked with a profit. Mr. Rémond enumerates twenty as being found in the region which he examined, many of which are undoubtedly still experimental enterprises, and may yet be abandoned.
The yield of the quartz from the mines situated on this great vein is generally low and somewhat under the average of the Calif rnia quartz, but the goldbearing portion of the vein is always of greater width than elsewhere, and the quartz can be mined at less expense than in those veins which are narrow and encased in the harder varieties of metamorphic rock.
The gross production of the Pine Tree and Josephine mines has been, undoubtedly, very large, though it is utterly impossible to state, with any degree of approximation, what it was previous to 1860. Since June, 1860, the quartz from these two mines has been treated at the Benton mills, on the Merced river, and from the time they commenced running until March of the following year the gross yield was about $155,000. The quartz near the surface paid much better than that which has been worked at the Benton mills. Not only does it
Not only does it appear to have been absolutely somewhat richer, but, owing to the decomposition of the sulpburets which existed in the Josephine rock in large proportions, it lent itself to a more ready amalgamation. Also, as it was worked in a ten-stamp mill, of comparatively small capacity to the Benton mills, which have sixty-four stamps, the mining superintendent was able to select his quartz with much more ease, and send only the better quality to the mill. The quartz from these mines in 1860 averaged about $9 per ton, and gradually grew poorer as the richer portions of the vein were worked out. The cost of mining, milling, and transportation amounted to about $5 50 per ton. This amount of $9 per ton is what was actually obtained in the mill, although there seems every reason to suppose that much more gold than that was really contained in the quartz, and, in fact, more has been lost and allowed to run to waste than has been secured. On several occasions attempts have been made to ascertain what proportion was lost and what saved, and it would appear that in the case of this quartz not more than forty per cent. of the gold actually contained in it was saved in the process of milling. The cause of this appears to be almost entirely owing to the very fine state of subdivision in which it exists, for very few specimens show any gold visible to the naked eye. Experiments are now being conducted on the Mariposa estate which seem to confirm this view, for on treating the quartz which formerly only returned $10 or $15 per ton, by more careful methods of amalgamation, it has been made to yield between $40 and $50. It is not to be
presumed from this statement that all the vein consists of quartz of this richness; but there is a large amount which will certainly yield, by improved processes of treatment, much more than it has ever been possible to obtain from it by the ordinary rough method.
3.-NORTHERN MINING DISTRICTS.
As we proceed northward from Mariposa county, the next most interesting mine we meet with, situated upon the “Great Vein," is the App, near Jamestown, a few miles from Sonora, the county seat of Tuolumne. This mine has been worked almost uninterruptedly for nine years. The average yield of the quartz has been at the rate of $15 52 per ton, and the expenses of mining and milling have not exceeded $7 47 per ton. The yearly yield during this period has varied from $13 26 to $19 47 per ton, and the lowest monthly return was at the rate of $12 15; but even then a considerable profit was realized over and above the expenses. The lower works of this mine now present as fine an appearance as they have ever done, and when we regard the length of time during which it has been successfully worked, the great regularity of the yield of the quartz, and the various characters of permanency which the vein preserves, we have strong reasons for arguing that it will prove as persistent in depth as almost any other mine in California. In its external characters the quartz from this mine resembles very much that taken from the Pine Tree mine. The greater proportion, however, of the gold which it contains is in such a fine state of subdivision that it rarely happens that any of it is visible to the naked eye, and undoubtedly a great deal escapes amalgamation and is lost. By more thorough treatment in the mill, there seems every reason to suppose that the yield could be largely increased. Experiments have been lately instituted—and they would appear to confirm this statement-most fully showing that by more careful amalgamation the quartz, in some instances, can be made to yield from 50 per cent. to 140 per cent. more gold without a corresponding increase in the expense of treatment. Attention is now being given to this important matter throughout California, and experiments are being made in several mills to ascertain to what extent the gold is lost in the process of treatment, and how far it will be economical to erect new machinery for the purpose of saving it. The gold which is contained in the auriferous quartz exists either in such minute particles as to be quite invisible, and not distinguishable from the quartz itself, else in pieces of larger size, which can be readily seen and separated by pulverization and washing, or by the simplest forms of amalgamation, or else combined, probably mechanically, with the sulphurets of iron, zinc, and lead. In the first and last cases it is amalgamated with great difficulty, and it rarely happens in any of the mills of California that more than a small proportion of the gold is saved. When, however, it is in the state of free gold, as in the second instance, a notable proportion is secured by the most simple methods, and it is not likely that additional machinery would increase the yield sufficiently to pay for its cost. In the quartz from a vein upon the Mariposa estate, known as the
Mariposa," there are but comparatively few sulphurets present, and from repeated assays made from the tailings from the mill it would appear that almost 90 per cent. of the gold contained in the quartz was secured, while at the Benton mills, working upon Pine Tree quartz, only between 30 or 40 per cent. was saved. In this connection it may not be uninteresting to show what has been done in this direction in other countries, and how far it is possible to increase the yield of very refractory gold-bearing ores by careful working and skilful treatment. One of the oldest, and, when we consider the rebellious character of the ores, one of the most successful gold mines in the world is that of St. John Del Rey, in Brazil. The company now in possession has been in operation thirty-six years, and though, like nearly every other mining company, it has had its full share of ups and downs, the general results obtained have been most satisfactory to the shareholders, and it was only through the most careful,, economical management of both the mining and milling departments that this end has been arrived at. There is no quartz mine in California which has ores in any quantity of so complex a nature or of so difficult a treatment as those of St. John Del Rey. They consist principally of specular iron mixed with sulphuret of iron, magnetic pyrites and quartz. The auriferous mass at this mine is about forty-four feet in width, and, like most of the gold-bearing veins of California, dips with the rocks in the vicinity at an angle of about 450 to the southeast. *
The vertical depth upon which this deposit has been worked is now 1,068 feet. Before the present company came into possession it had been worked for a hundred years, and was considered exhausted.
A recent number of the London Mining Journal gives some interesting details with regard to the present financial position of this company, and as these favorable results were only obtained by economy in the management and skilful treatment of the ores, which yield far less than the average of California quartz, I will give a condensed statement of their operations for the last thirty-six years. The effective capital of the company is £129,000, divided into 1,100 shares, and there has been paid in dividends £756,245, or £68 158. per share. There is on hand a reserve fund of £41,506, and the value of the property of the mine is estimated at £209,743, showing a total profit during the thirty-six years' working of £1,007,494. The produce of the mine during this period has been £2,902,480, and the expenses £1,894,986, or 65 3 per cent. of the gross receipts. The average yield of the ore raised and treated has been at the rate of 41 oitavas per ton of 2,240 pounds. This is equivalent to about $8 50, or $7 59 reduced to the usual Califorinia ton of 2,000 pounds. The yield for the last three years has been as follows:
* Whitney's Metallic Wealth of the United States, p 112.
1863, 5,787 oitavas per ton, at $1 89 per oitava, $10 94; 1864, 4,827 oitavas per ton, at $1 89 per oitava, $9 12; 1865, 5,479 oitavas per ton, at $1 89 per ton, $10 36.
During this period of the total amount of gold contained in the ore there was extracted the following percentage :
1863, 72.35 per cent.; 1864, 75.52 per cent.; 1865, 77.95 per cent.
The various processes heretofore employed in California for amalgamating gold have been of the simplest possible description, and, although probably in a majority of instances where the gold was clean, free and uncombined with the sulphurets of iron, lead, copper, and zinc with which it is so frequently associated, these methods worked well, and the erection of expensive machinery, which would necessitate slower working, would not be warranted by the facts of the case. Yet it has often happened, particularly in those mines situated upon the course of the “Great Vein,” that quartz which has been known to contain gold in paying quantities has not yielded when treated in the mill more than sufficient to pay expenses, and sometimes has been worked at a loss. This would appear to be chiefly owing to the inefficiency of the apparatus employed to collect and save the gold, which may have been in a very fine state of subdivision, or coated with a thin film of oxide of iron arising from the decomposition of pyrites, which prevents the mercury from adhering to it without the use of more vigorous mechanical or chemical means than are usually employed.
At and near Sutter creek, in Amador county, there are several very excellent mines situated upon the course of the “Great Vein.” The most noted of these is that belonging to Messrs. Hayward & Co., and known as the Eureka. This mine has been worked for about eleven years, and has produced probably nearly as much gold as any other in California. The quartz has never averaged very high, and the principal production has been from ores of a low grade, not yielding probably more than from $10 to $15 per ton. The mine is situated at the junction of the slates and greenstone, the hanging or eastern wall of the vein being of the latter material, hard and compact, while the foot-wall is of a dark and soft argillaceous slate. The depth of the lowest workings is now 1,213 feet on the incline of the vein, which makes this shaft the deepest in the United States. The length of the underground workings is about 600 feet, and at the north and south extremities. the vein thins out rapidly. The richest portion of this vein appeared to be at a depth of between 1,000 and 1,100 feet, where the quartz is said to have yielded nearly $30 a ton. The great depth attained in this mine shows conclusively that we cannot draw any general conclusions with regard to exhaustion of quartz veins at an inconsiderable depth. It is true that in nearly every quartz mine of California the outcrop has been found to be much richer than the main body of the vein at even a short distance from the surface, but it must be borne in mind that many of the veins, and in fact a majority of them, contained gold associated with various mineral sulphurets, which were decomposed and the gold infiltrated down for some distance below the surface of the ground, causing the upper portion to appear abnormally rich. Thus the gold contained in the first few feet of the vein may be the result of the degradation of many tons of quartz and the decomposition of a large quantity of sulphurets. It is only by taking the results, afforded by the treatment of quartz during a series of months that anything like a correct average of the value of the ore can be obtained, and although this Eureka mine has probably yielded as rrgularly as any other prominent mine in California, it has been subject to great irregularities, and frequently the quartz has barely paid expenses. The popular idea that mineral-bearing veins grow richer as they are worked upon in depth, is a fallacy, and has no truth either in theory or fact; nor can we say that true veins, as distinct from veins of segregation and mineral deposits, grow poorer as we proceed downwards. I do not suppose there is a metalliferous vein in the world that is equally rich for any considerable distance, either lengthwise or up and down, and the valuable portion is almost always very limited in extent compared with the main body of the vein. Some of the silver veins of Mexico, which have produced such enormous sums, have been traced for miles, and on their course have furnished many valuable mines, but by far the greater proportion of the vein has been barren and unproductive. The Comstock vein of Nevada, which has already produced upwards of $60,000,000 worth of bullion, has been productive only over about one-seventh of its explored length.
These remarks apply with great force to the gold quartz veins of this coast. The ore exists in bunches or else in shoots or chimneys which cut the axis of the vein at every conceivable angle between the horizontal and the vertical, and these are always less than the length of the vein itself and sometimes tlian its width also.
It frequently happens that these ore-shoots have distinct terminal lines, and in these cases the experienced miner is enabled to select his ore and avoid extracting that which he knows is too poor to pay. On other occasions, huwever, it would appear that the gold is distributed without any regularity and apparently in the most capricious manner.
When we consider the richness of the veins, the length of time that some of the mines have been worked, and the amount of gold annually produced, the most important quartz mining region of California is without any doubt that of Grass valley, in Nevada county. Here mines have been worked uninterruptedly since 1851. It is true there have been periods when the interest was more than usually depressed and several of the mines, which are now regarded as being among the best, were thought to be exhausted, and abandoned for the time being, but in many instances when work was resumed new bodies of gold-bearing quartz were opened up which proved rich and valuable. The veins in this district, and particularly those which have been the most productive, are noted for their narrowness as well as for the richHess of the quartz. They are incased in a hard metamorphic rock, and the expenses of mining are, as a general thing, higher here than anywhere else in California, amodnting, as they do in some instances, to from $20 to $26 per ton. Within the last fourteen years the total production from the quartz mines of the Grass Valley district has not been far from $23,000,000. The most prolific vein has been that situated upon Massachusetts and Gold Hill, which alone has produced more than $7,000,000 worth of gold during this time from a lode which will only average a foot or fourteen inches in width.
The "Eureka" is another prominent and leading mine in this vicinity. One great feature of interest connected with it is the gradual improvement of the quartz as greater depth has been attained upon the vein, which varies in width from three to four feet. This mine was first worked in 1854, and more or less ever since that period. About one year ago the property changed hands, and since that time the yield of the mine has been greater than at any previous time. When this vein was first worked and down to a depth of about thirtyfive feet from the surface, the yield of the quartz was from $6 to $12 per ton, which but little more than paid expenses. Below this level the value of the quartz rapidly increased from $14 to $21, and at the one hundred foot level the quartz paid at the rate of $28 ; at the two hundred foot level the average was about $37, and now, between the second, and third levels or three hundred feet from the surface the average yield has been during the last four months at the rate of over $60 per ton. The quartz contains from two to three per cent. of sulphurets of iron, which are said to assay generally about $300 per ton, and are regarded as being among the richest in Grass valley. These sulphurets are worked by parties in the neighborhood, who charge $50 per ton and return whatever gold is extracted to the proprietors of the mine. During the four months which preceded the first of October the mine produced 42,227 & tons of quartz, which yielded $255,072 55, and the expenses of mining and milling were $67,320 83, leaving as profit $187,751 72. The average yield of the quartz during the period was at the rate of $60 33 per ton. During the whole year the amount of quartz worked was 11,3758 tons, which produced $526,431 41, at an expense of $168,389 23, leaving as profit for the whole year $368,042 18. The average yield per ton was $47 15, and the average cost of mining and milling was $13 75, leaving a profit of $33 40 per ton.
4.-MINING IN THE SIERRAS; MILLS, EXPENSES, &c.
In thus dismissing the Grass Valley district with only a brief description of two of its leading mines, I do not intend to detract at all from its past, present, or future importance, for there is no region in California, or probably upon the Pacific coast, where, by a careful study of the numerous veins in this neighborhood, so much information could be obtained which would throw light upon the vexed questions relating to gold mining and the metallurgical treatment of the quartz.
As we proceed north from Nevada county, the next most important quartz mining district is in the mountainous region round about Downieville, the county seat of Sierra. The placer mines in this vicinity have been exceedingly rich, and surpassed only by those in Nevada county in extent and permanence. Quartz mining, however, has received but comparatively little attention until within the last few years, probably owing to the rugged nature of the country and the severity of the climate during the winter months.
The most noted mine in this county, as well as the one which has produced most largely, is that known as the Sierra Buttes. This mine is about fourteen miles from Downieville, at an elevation of probably not less than 7,000 feet above the sea. The vein is enclosed in a hard metamorphic slate, and varies in width from six to thirty feet. In the process of working, the whole thickness of the vein is not removed, and the richer portions, which lie next the 'foot-wall, are sent to the mill. The average width of this more productive streak is about twelve feet. The depth upon which this vein has been worked is not far from 750 feet, and the quartz in the lower portion of the mine is said to pay as well as that taken from the upper works. Quartz from near the surface of this vein was worked in arrastras as early as 1851, but the first mill was erected in 1853. The present owners have been in possession of the property since 1857, and the yield of the mine has been, during the last nine years, approximately as follows:
$51,000 $15,000 $36,000
55,000 15,000 40,000 1859..
88,000 20,000 68,000