| STATE. | MINERALS. | |||||||||||||
| Silver. | Gold. | Copper. | Lead. | Tin. | Mer- cury. | Iron. | Coal. | Petro- leum. | Zinc. | Anti- mony. | Sulphur. | Bis- muth. | Salt. | |
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| Chihuahua | " | " | " | " | " | " | ||||||||
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| Durango | " | " | " | " | " | " | ||||||||
| Guanajuato | " | " | " | " | ||||||||||
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| Jalisco | " | " | " | " | " | " | ||||||||
| Lower California | " | " | " | " | " | |||||||||
| Mexico | " | " | " | |||||||||||
| Michoacan | " | " | " | " | " | " | ||||||||
| Nuevo Leon | " | " | " | |||||||||||
| Oaxaca | " | " | " | " | " | |||||||||
| Puebla | " | " | " | " | " | |||||||||
| Querétaro | " | " | " | " | " | " | " | |||||||
| San Luis Potosi | " | " | " | " | " | |||||||||
| Sinaloa | " | " | " | |||||||||||
| Sonora | " | " | " | " | " | " | " | |||||||
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| Tepic | " | " | " | " | " | " | " | |||||||
| Vera Cruz | " | " | " | " | " | " | ||||||||
| Zacatecas | " | " | " | " | " | " | ||||||||
The geological formation of the country does not bear special relation to the deposits of metalliferous minerals, which are distributed in many parts of the great zone. In general terms it may be said that the abundance of the ores rather than their richness characterises the mines of Mexico and is the source of their wealth. Those which have most steadily produced bullion generally consisted of a main lode containing enormous quantities of low-grade ore of about 60 ounces per ton; and typical of these are the mines of Guanajuato, Pachuca, Querétaro, Zacatecas, and others. The ores, however, are not always low-grade, for great bonanzas of exceedingly rich ore were encountered, making rapid fortunes for their discoverers.
Silver.—The main lodes in those places enumerated have ranged up to hundreds of feet in width, and form the most potent silver-ore deposits upon the globe. Their extensions in length and depth bear out their importance as metal-producing sources. Thus the Mellado vein, of Guanajuato, measures, in places, more than 300 feet in width; with workings ten miles in length, and extending to a present depth of nearly 2,000 feet. The Veta Madre, or "mother lode," ranges from 30 feet to 165 feet in width; whilst others of the famous lodes reach 50 to 100 feet. As to the ore-values, Humboldt, who visited Guanajuato in the height of its production, at the beginning of the nineteenth century, assigned as his calculation a value equal to about 80 ounces of silver per ton for the whole lode. For portions of the ore-bodies, and for many of the great bonanzas, much higher values have obtained, silver up to 7,000 ounces per ton having been encountered; whilst ores of 1,100 ounces have been frequently exported to Great Britain.
The almost fabulous wealth obtained from the silver mines has been shown in the foregoing pages, and these mines are far from being exhausted at the present day. The importance of the Pachuca mines is shown by the statement that they produce six million ounces of silver and 30,000 ounces of gold yearly. Of the population of the city, of forty thousand souls, seven thousand are employed underground.
All of the Mexican states are silver bearing, although those which contain the famous mines are the most important, as:—Sonora, Chihuahua, Sinaloa, Zacatecas, San Luis Potosi, Guanajuato, Querétaro, Hidalgo (Pachuca), Mexico. All these states contain numerous mining districts—cities, towns, camps—which it would take too much space here to enumerate. With the exception of the few modern installations most of the mines are worked by the primitive Mexican system of winding up the ore in raw-hide sacks, hauled by means of cables made from maguey fibre, upon a mule-actuated windlass—the malacate. In some cases the miners carry huge pieces of ore on their backs, from 100 lbs. to 200 lbs. in weight, along the galleries to the shaft. Interior transport and haulage are primitive.
The principal ore of silver is the sulphate, although native silver is also freely encountered in some districts. The ores were very generally decomposed to a depth of about 300 feet. Argentiferous galena is plentiful, and silver is freely found in conjunction with copper ores. The caliches, a chalk-like substance, easily worked, is another rich form of occurrence of the metal, and there are others less important. Various different methods of separating silver from its ores are used; the prevailing ones being those of smelting, lixiviation, and the patio process, which last has accounted for 90 per cent. of the production. Indeed, the recovery of silver by the patio process has always been one of the most important industries of Spanish-American countries, especially in Mexico, Peru, and Chile. In Mexico it has been employed continuously since the year 1557, when it was invented by Medina at the hacienda Purisima Grande. This was the first application of amalgamation to silver ores, and permitted the treatment of the vast quantities of low-grade ores, which did not pay to smelt. To-day great quantities of ore are still treated by this method. The process is too well known to require much description here. Its main points of advantage are the simplicity—in practice, for its chemistry is complicated in theory—of its methods and appliances. The principal agents employed may be said to be mercury and horseflesh, or rather mule-flesh; the mercury forming an amalgam with the precious metals under the incorporation brought about by the trampling hoofs of the mules. The trampling and incorporation of the torta, or charge of pounded ore, mercury, water, salt, copper sulphate, and other constituents, mixed into a paste, was originally performed by barefooted natives, but the practice of using mules for the purpose came from Peru, in 1783, as before mentioned. The patio, as its name implies, consists of a paved yard upon which the crushed mineral is treated. This is in some cases of very large capacity, one of the most important in the country, that of the Guadalupe works at Pachuca, which treats nearly a thousand tons of ore a week, being as large as the plaza of a city. Upon this the torta is spread, and bands of a dozen mules, or mules and horses, harnessed together, are driven up and down from morning till afternoon, through the slushy mass. The animals are then bathed to remove the chemicals, but notwithstanding this the work is deleterious, and they last but a few years—the old ones but a few months—as they become poisoned by the copper sulphate. At some of the haciendas of Pachuca six hundred horses are employed in this work, and the total throughout the country is considerable. Constant efforts have been made for the use of mechanical appliances, to take the place of the equine mixer, but these have not been found to give the same efficiency. The process is typical of the country and the race—time, space, and material are plentiful, and labour is cheap, and horses—well, they were made for man's use! The innate tendency of the Spanish-Americans to do without mechanical appliances also is indulged.
The growth of the silver-producing industry of recent years is shown by the returns, giving approximately a value of seven million Mexican dollars for 1890 and fifty million for 1902, for export alone. The total value of the silver production for 1907 was eight million sterling, which was more than that of the United States, and so Mexico led the world in that year.
Gold.—The gold which was formerly produced in Mexico has come principally from the silver ores, with which it is generally associated, and has been obtained from the amalgamation of these. More recently gold-bearing quartz lodes are being worked, and are producing important quantities of gold. Among the foremost of these are the mines of the district of El Oro, in the State of Mexico, somewhat less than a hundred miles to the north-west of the capital. They produced in 1905 about ten million dollars in gold, or about 800,000 dollars per month. Whilst Mexico has not generally been looked upon as a gold-producing country, it is undoubtedly the case that it will, under the present rate of development, rank among the foremost of these. At present Mexico holds sixth place with a production for 1907 of 3¾ millions sterling. Gold-bearing lodes are being discovered and worked in most of the States, and thousands of such deposits are being prospected, or awaiting such, whilst numerous crushing plants are treating ores in those districts most accessible to the railways. The enterprise known as El Oro Mining and Railway Company may be looked upon as a well-managed and prosperous concern, controlled by British capital. It was first acquired by a British company in 1815, and it is stated that it yielded five or six million pounds sterling of gold. Later it was abandoned, taken up in 1870 by native capitalists, and at the end of last century purchased by an American company, to be again acquired by British interests in 1899. The enterprise controls a large area of ground of more than 500 acres, a short railway to the Mexican National Line, and some valuable forests which afford fuel. With its battery of 200 stamps and large cyaniding mills, it has a capacity for ore treatment of 20,000 tons per month. The yield per ton of ore is given for 1900 at slightly under £3 per ton, at a cost of about 25s., and for 1907 35s. per ton, at a cost of slightly under 20s. The tonnage treated for these years were 53,500 tons and 263,000 tons respectively, and all the intervening years show the steady increase. The output for 1907 was more than a million tons of ore, due to the added capacity of the new stamp mill, whilst the monthly profits for that year and for 1908 fluctuated between £14,000 and £18,000.
Other successful enterprises of El Oro region are the Somera Gold Mining Company, affiliated with the foregoing, and the Mexico Mines of El Oro. The latter company's mill has a capacity of 250 tons of ore daily, and the recent monthly profits have been, it is stated, upwards of £15,000. These are also controlled by British capitalists, as is the "Esperanza" Mine of El Oro, it is stated, which has produced since 1895 a value of 4½ millions sterling, with a profit of nearly 2½ millions. The "Dos Estrellas" Mine is yet another example of this successful district. It is said to have made profits since 1902 of 2½ millions sterling, and to have ore for future work in large quantities. It is interesting to note that this excellent performance has been made on ground which had been condemned by mining experts![34]