Rossiter W. Raymond

“ The consumption of mercury in the Washoe process may be considered chiefly a mechanical loss, and only to a limited extent a chemical one. The pan amalgamation of slimes and refractory ores, with the addition of large proportions of copper sulphate and salt, involves a greater loss of mercury.—Refractory ores, not suitable for “raw” amalgamation by the Washoe or the patio process, are treated in many localities by the Freiberg process, consisting in the chlorination of the ore by roasting with salt, and its subsequent amalgamation. ”

“ A very promising field for silver mining is found in the state of Sinaloa and along the western slope of the Sierra Madre of Durango and Chihuahua. The port of Mazatlan is the base of supplies. Sinaloa is well wooded and watered; the ores are largely true silver ores, which can be treated by the Freiberg or the modified Washoe process. Some of the mines in the interior are exporting rich silver ores to Europe; others are reported to be earning good profits with stamp mills. Central America has no silver mines that are worked to much extent ”

“ The veins of Catorce are in limestone supposed to be of carboniferous age. The greatest proportion of silver in every mining district of Mexico is obtained from the sulphuret of silver, an ore of gray color disseminated through the quartz matrix in minute particles and more or less combined with other metals. The other varieties of argentiferous ores are numerous, but comparatively small in quantity; they are the chloride of silver, ruby silver, native silver, argentiferous pyrites, and argentiferous galena. The comparative quantities of these at the different mines are very variable. ”

“ A small quantity of iron, chromium, cobalt, or nickel imparts great hardness to silver. Steel may be made to retain about 1/500 of its weight of silver, which is said to improve its quality; the alloy is called silver-steel. Combined with mercury, silver forms a most brilliant amalgam for mirrors. An alloy of 20 to 30 parts of silver with 30 of nickel and 50 of copper is said to be equal in all respects to the ordinary standard silver, which is 9 parts of silver with 1 of copper. Small coins have been made in Switzerland of an alloy of silver and copper with 10 per cent. ”

“ Oxidized ores are usually poor in silver, but the carbonate, &c., occurring in the limestone of New Mexico, Utah, and the Eureka district, Nevada, are exceptions, being smelted in large quantities for lead and silver. The peculiar ore known as stetefeldtite, which occurs abundantly in Nevada, is an oxidized but massive mineral containing antimony and other base metals, and often very rich in silver. ”

“ At a very high temperature it is volatile. Melting silver mechanically absorbs 20 volumes of oxygen, which in solidifying it expels, sometimes with sufficient force to throw off particles of metal. Alloyed with 1 or 2 per cent. of copper or with gold, it apparently loses this property. Silver is oxidized neither by exposure at ordinary temperature to dry or moist air, nor by heating in air; but it burns to an oxide when melted upon charcoal in the oxyhydrogen flame, or when exposed to a galvanic current of great intensity, or to ozone. ”

“ Pure zinc blende is usually poor in silver, but is frequently found in intimate association with true silver ores or native silver, and particularly with argentiferous galena; and in some notable instances the blende is richer than the galena.—The mechanical concentration of silver ores by water is attended with heavy loss, by reason of their usual association with base ores of nearly the same specific gravity, and their property of cleaving when crushed into fine scales and splinters or dust, which are usually carried away by the current. ”

“ The silver produced in Great Britain is extracted from an argentiferous lead, to the amount of 550,000 to 700,000 oz. annually (in 1872, 628,000 oz.) . The celebrated Kongsberg mines in Norway, discovered in 1623, have been worked almost continually since. The ore occurs in parallel belts of rock, intercalated in gneiss and crystalline schists, and impregnated with sulphides of iron, copper, zinc, and sometimes lead, cobalt, and silver. Fissure veins traverse these belts occasionally, and are argentiferous at the intersection only. Beautiful specimens of native silver occur. ”

“ Very pure silver occurs with the native copper at Lake Superior. The most famous masses of native silver, several of which exceeded 500 lbs., have been found at the mines of Kongsberg in Norway, of Freiberg, Schneeberg, and Johann-Georgenstadt in Saxony, and in the Bohemian, Hungarian, Peruvian, and Mexican mines. In the silver mines of Nevada, Idaho, and Utah it is not uncommon, though it has not been found in large masses. Silver amalgam occurs in small quantities in some European mines, and contains 26 to 35 per cent. of silver, the remainder being mercury. ”

“ When granulated by falling molten into water, it acquires a rough but exceedingly beautiful surface. Reduced from the chloride in the humid way, it appears as a gray, spongy powder. It crystallizes in cubes and octahedrons when allowed to cool from the molten condition or precipitated from solution for instance, by copper or zinc. Sometimes it is precipitated black by the galvanic current or by zinc. In hardness and strength it is superior to gold and inferior to copper; a slight alloy of copper hardens and strengthens it. In malleability and ductility it is inferior to gold only. (See Metal.) ”

“ The ore is first crushed and then ground fine in arrastras. If gold is present, 50 or 60 per cent. of it may be saved by introducing silver or copper amalgam into the arrastra. Ores containing pyrites, antimony, or arsenic are incompletely roasted, to break up the combination of silver with these elements. The presence of silver sulphide does hot necessitate roasting as a preliminary for patio amalgamation. ”

“ The mining districts of Owyhee in Idaho, and Unionville, Reese River, Belmont, Pioche, White Pine, and Eureka in Nevada, have been the scenes of successive excitements, and are still productive. In Eureka district, as in the principal districts of Utah, and some of those in Montana, Colorado, New Mexico, and California, argentiferous cerussite and galena are smelted, to produce work lead containing silver. ”

“ This is also formed when compounds of silver oxide are decomposed by organic acids.—Silver may be easily alloyed by melting with most metals. The alloys with base metals are in general not useful enough to counterbalance the cost of the silver. The alloy with copper, which in subordinate quantity enhances the valuable qualities of the silver, is an exception. The alloys with lead and zinc, serving an important purpose in metallurgy, will be mentioned further on. An alloy of 100 parts of aluminum with 5 of silver gives a handsome white malleable compound, susceptible of high polish. ”

“ The smelting processes are mostly based upon the capacity of metallic lead, as well as its oxide and sulphate, to separate silver under fusion from its combinations, the liberated silver alloying itself with an excess of lead and accumulating in the metallic bath in the hearth of the furnace. ”

“ In the absence of better fuel, llama dung is employed for roasting at several establishments. But the country is full of undeveloped veins, and coal has been discovered in abundance, while railroads are rapidly extending into the interior. In Bolivia, besides the mines of Potosí, are those of Portugalete in the province of Chichas, celebrated for the richness of their ores, which produce six to eight times as much silver to the ton as those of Potosí. Other mines are worked in the same district. ”

“ Other mining districts in Peru are Gualanca in the province of Huamalies, Pasco, Lucanas, and Huantajaya. Cerro de Pasco has been especially famous for its large production. A town is built upon the site of the mines, and the openings to many of them are through the houses of the miners. The production of Peru until within a few years was very small, probably not more than $2,500,000 annually, and it is a very difficult field for mining. Roads, mules, labor, and fuel are all wanting. ”

“ The Schemnitz mines were first opened more than 800 years ago, and have been worked to a depth of more than 1,200 ft. Near Schemnitz are the mining districts of Kremnitz and Neusohl. The Joachimsthal mines in Bohemia are very ancient, very deep (nearly or quite 2,000 ft.) , and have been very productive, but now yield an insignificant amount of silver. This district belongs to the Erzgebirge, a chain of mountains composed of crystalline rocks, on the border of Saxony, in which kingdom it includes the four mining districts of Altenberg (tin) , Freiberg, Marienberg, and Schwarzenberg. ”

“ A peculiar method of amalgamation pursued in Chili avoids the chloridizing roasting, substituting a humid chlorination by means of copper dichloride (Kröncke's process) . It is highly praised, but not yet widely employed. ”

“ The ore suitable for this process (usually containing silver sulphide or chloride and native silver, with little antimony, arsenic, base sulphides, in a gangue of quartz) is first crushed in a stamp mill, similar in most respects to that employed for gold-bearing quartz. (See Gold.) The screens which regulate the size of the crushed particles are of wire cloth with 40 to 60 meshes to the inch, or of Russia sheet iron, perforated with holes 1/40 to 1/24 in. ”

“ It declined in productiveness at the beginning of this century, was suspended in 1810 on account of the war of independence, reopened in 1822 by the Anglo-Mexican company, and abandoned after much expenditure to the Mexican owners. It is the deepest mine in the country, and the lower workings are now flooded. ”