Another cause will necessarily act on the production of silver, and that is the very abundance of gold. When silver is found to be more in demand, fresh activity will ensue, both in reopening old galleries, which have been closed as not sufficiently remunerative, and in pushing on the work in those actually in operation. If the mines, feeding the present supply, are becoming exhausted, and other sources are not forthcoming, in a few years silver will reach the price of gold, or the value of gold will descend to that of silver; but as the limits of silver working are but the price of labour, the power of machinery, and the application of science, so, every increase in the quantity of gold which is not caused by accidental circumstances, or by an extraordinary demand, must produce a corresponding increase in the production of silver. Is not this a fact which we have been witnessing since 1850? Who can venture to affirm that Californian gold has had no influence in stimulating the workings of silver in Mexico and Chili? Besides this, the extraction of gold is generally accompanied with a production of silver. Silver mines are not always auriferous, and the richest in gold contain but a small quantity of it, but gold mines are almost always argentiferous. The proportion of silver in a “nugget” of gold is about ⅛th in California, ¹⁄₁₀th in Siberia, and ⅕th in New South Wales. So that for every [173]four kilogrammes of gold in Australia, there is about one of silver. This is an important fact resulting from chemical analysis.
The production of silver is in the course of increase. Will that of gold be kept up? It is reasonable to entertain considerable doubt on this point. In Siberia we have seen it retrograde since 1847. The extraction appears stationary—perhaps rather on the decrease in California. Australia alone, with gold fields yet unexplored, appears likely to produce much more than heretofore. Auriferous strata may be discovered elsewhere, and add to the general stock. Combining these various circumstances, we incline to the opinion that the quantities now forming the annual production of gold will not be diminished for a certain number of years; but when the miners have exhausted the gatherings from the alluvial deposits, and it becomes necessary to seek the golden ore in the rocks and mountains, in which nature appears during the various revolutions and convulsions of the world, to have deposited it; then the working of the mines will depend upon the amount of capital and the degree of science, which may hereafter be brought to bear on that description of enterprize.
In a paper read in 1848, before the Royal Institution of London, Sir Roderick Murchison remarks that the principal deposits of gold are found in auriferous “detritus,” and that the same degree of success must not be expected to ensue from exploring the veins, which are ramified through the quartz rock. The result hitherto shown in California fully confirms this theory, as is shown in the following letter from an engineer at St. Francisco, dated 4th April last, after an expedition amongst the localities occupied by the gold diggers:—
“I send you the result of experiments made upon fragments of rock. In each we have operated upon three tons of quartz, reduced to powder, and carefully worked by amalgamation. We have made five experiments upon as many veins in the county of Bath, which is situated between l’Yuba and the River de la Plume. No. 1 has produced [174]3 dollars 53 cents per ton; No. 2, [175]9 dollars 50 cents; Nos. 3 and 4, [176]11 dollars each; and No. 5, [177]17 dollars.
“In the county of Nevada, experiments have been made on four different points. The first has given [178]15 dollars per ton; the second, scarcely any gold; the third, [179]14 dollars per ton—this mine, upon which a company had established works, has been abandoned;—and the fourth has given [180]59 dollars, the vein being of an extraordinary richness, and having yielded large returns to the proprietors.
“In the county of Eldorado, three different veins did not give a larger return than [181]17 dollars per ton; a fourth equalled the richness of No. 4, in the adjoining county.
“In the county of Mariposa, out of eight experiments, three veins gave hardly [182]3 to 7 dollars per ton; three more gave [183]7 to 20 dollars; one gave [184]24 dollars; and one more, [185]38. The two last veins have attracted miners, who are going to work them. No enterprize requires a more careful and a more expensive examination than an auriferous quartz mine. A good vein, yielding [186]36 dollars per ton, may be considered, by moderate people, as worth working; sometimes they are found much richer; but out of all the quartz-crushing mills which have been set up in California, I do not think that one-third are used for mines which are yielding, for any continued period, [187]30 dollars the ton; so that one-half of the works of this nature are suspended.”
From the above account, it would appear that a vein of quartz, to be considered productive, should give 36 dollars, or [188]192 francs per ton. This return represents a weight of 55 grammes upon 1000 kilogrammes, or 5½ parts of gold out of 100,000 parts of quartz. Mineral of iron stone will give 10 to 15 of metal per 100; and the production by melting is infinitely less troublesome or expensive than the extraction of gold. In Australia, it was at first supposed, after an analysis of some ounces of quartz, taken from Mount Ophir, that the ton would yield more than £1100 sterling; but these experiments, made on so small a scale, are of little value. It is not likely that Australia, when the miners find themselves reduced to the necessity of working the quartz rocks, will show any considerable increase of yield over California.