Chief Quartz-Mills.—The most productive quartz-mill in the state is the Benton mill, on Fremont's Ranch, in Mariposa county. It is also the largest, having forty-eight stamps. There are four mills on the estate, with ninety-one stamps in all, and their average yield per month is sixty thousand dollars. A railroad four miles long, conveys the quartz from the lode to the mills. The Allison quartz mine in Nevada county, produces forty thousand dollars per month. The Sierra Buttes quartz-mill, twelve miles from Downieville, yields about fifteen thousand dollars per month. These last mills run night and day, and crush and amalgamate ten thousand tons of rock a year, or twenty-eight tons per day. Forty men are employed, twenty-five to quarry the rock, five in the mill to attend to the stamps and amalgamation, one to do carpentry, one for blacksmithing, and eight for getting out timber, transporting quartz, and so forth. The cost of quarrying, crushing and amalgamating a ton of rock, is six dollars. The wages of the men are from fifty to seventy dollars per month with boarding. The average wages is sixty dollars. About ten miles eastward of Sonora, in Tuolumne county, are some rich veins of auriferous quartz, the most prominent of which are the Soulsby and Blakeslee lodes. The Soulsby mill produced forty thousand dollars in three weeks, when it commenced work in 1858, but it has not been so profitable of late.
Silver Mining.—Silver mining has not yet been established fairly as a business in California. The silver ores of Washoe were discovered in 1859, and mining has been fairly commenced there, but the mines of Esmeralda and Coso, within the limits of this state, were not found until the summer of 1860, and up to the present time no mills have been established there.
Silver mining differs much from gold mining. Gold is always found as a metal, never as an ore, and the separation from the accompanying vein-stone with which it is mixed mechanically, is much more simple and easy than the reduction of the argentiferous ores in which the silver is chemically combined with base substances, for which it has a strong affinity. Chemical knowledge and chemical processes are more necessary in mining for silver than for gold; and while all auriferous quartz is of the same kind, and may be treated in the same manner, there are many different kinds of silver ores, each of which requires a peculiar treatment. The reduction of silver ore costs on an average, from three to five times as much as the reduction of auriferous quartz.
The silver ore of Esmeralda and Coso is a sulphuret of silver, nearly all the veins having the same material, though the amount of it scattered through the vein-stone differs greatly in different lodes. In some veins there is much free gold, that is, little specks of metallic gold which can be separated from the other material in the same manner that gold is separated from auriferous quartz. The methods of reducing silver ore are so numerous and complex, and vary so much in different districts and under different circumstances, that it is impossible to know now what process will be used in Esmeralda and Coso, the resources of which places have been so little studied. Besides it is said that new processes for reducing silver ore have been invented, far superior to all the old methods; and these processes are kept secret. It is therefore unnecessary that I should go into a long description of the various processes practised elsewhere. Silver ore after pulverization is smelted by mixing with it fifty per cent. of lead in metal or ore, and ten per cent. of iron, and exposing the whole to a heat sufficient to melt the silver which runs off. The metal thus obtained is not pure but contains much lead, which is driven off by heat while the silver is kept in a molten condition for a period of four or six hours. The cost of smelting in California at present, is about one hundred and twenty-five dollars per ton. In most of the other methods of reducing silver ore, the ore is roasted to drive off the sulphur. In the barrel amalgamation, which has been used at Washoe, and will probably be used at Esmeralda also, half a ton of ore, after being pulverized and roasted, three hundred pounds of water, and one hundred pounds of wrought iron, in little fragments, are put into a barrel, which revolves on a perpendicular axis. At the end of two hours the mass has taken the consistence of thick cream, when five hundred pounds of quicksilver are put in, and after the barrel has revolved four hours more, the amalgamation is complete. More water is now poured in; the barrel revolves very slowly to let the amalgam all settle to the bottom, the mud runs off through a cock four inches above the bottom, and the mercury and amalgam are then drawn off through a little hole in the bottom of the barrel.
Quicksilver Mining.—The ore from which quicksilver is obtained is a sulphuret. The sulphur is driven off by heat, and the metal, which rises in fumes from the ore, is collected by condensation. The miners are Cornishmen and Mexicans. The ore is in large masses underground, not in a connected vein of regular thickness; and after one mass is exhausted, much labor is often vainly spent in search of another. There are, however, usually little seams of ore running from one large deposit to another, and it is the business of the mining captains to observe these veins closely, and trace them up when a "fault" occurs. There are no scientific rules for finding the ore; and the business of searching for the large deposits is never intrusted to educated mining engineers, but always to mining captains, who have themselves been laborers, and have learned by experience where to seek. The New Almaden mine produces two hundred and twenty thousand pounds of metal in a month. The hacienda, or reducing establishment of the mining company, has fourteen brick furnaces, each fifty feet long, twelve feet high, and twelve feet wide. At one end of each furnace is the fire chamber, which may be nine cubic feet inside; next to that is the ore chamber of about the same size; and beyond that is the condensing chamber, in which there are a number of partitions alternately running up from the bottom and down from the top, with a space for the fumes to pass, their course being up and down, and up and down again, and so on, for a distance of thirty feet to the chimney, which is forty feet high. In the bottom of the condensing chamber is water. The walls between the fire chamber and the ore chamber, and between the latter and the condensing chamber, are built with open spaces, so that the heat, smoke and fumes can pass through. The ore is placed in the ore chamber in such a manner as to leave many open spaces. The heat drives off the sulphur and mercury of the ore in fumes, which in passing through the condensing chambers, deposit the mercury, and the smoke and sulphur escape through the chimney. In the Enriqueta and Guadalupe mines the quicksilver is condensed in a close iron retort, and the sulphur is absorbed by quicklime.
Copper ore is dug from several mines in California, but it is all exported to be smelted elsewhere.
Platinum.—Platinum, iridium and osmium, three white metals of about the same specific gravity with gold, are found with the latter metal in the placers in the basin of the Klamath and Trinity Rivers. Their particles are usually fine scales, very rarely reaching a quarter of an ounce in weight, and the largest piece of either ever found was less than an ounce and a half. They cannot be separated from the gold by washing, but they do not unite with quicksilver, and therefore they are separated from the more precious metal by amalgamation. They have no regular market in the state; miners never make them the chief object of search, and they have not been studied, so it is not known to what extent they might be obtained.