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in every climate, the distribution of silver has been very unequal; sometimes concentrated in one point, and at other times disseminated in the gangue, and allied with other metals. Sometimes in the midst of the poorest minerals we find very considerable masses of native silver; a phenomenon which appears to depend on a particular operation of chemical affinities, with the mode of action, and laws of which we are completely ignorant. The silver in place of being concealed in galenae, or in pyrites in a small degree argentiferous, or of being distributed throughout all the mass of the vein over a great extent, is collected into a single mass. In that case the riches of a point may be considered as the principal cause of the poverty of the neighbouring minerals; and hence we may conceive why the richest parts of a vein are found separated from one another by portions of gangue almost altogether destitute of metals. In Mexico, as well as in Hungary, large masses of native silver and glaserz, appear only in a reniform shape (par rognons ;) the com: posed rocks exhibit the same phenomena as the masses of veins. When we examine wit
care the structure of granites, syenites, and porphyries, we discover the effects of a particular attraction in the chrystals of Mica, amphibole and felspar, of which a great nun
WOL. III. M
ber are accumulated in one point, while the neighbouring parts are almost entirely destitute. Although the New Continent, however, has not hitherto exhibited native silver in such considerable blocks as the Old, this metal is found more abundantly in a state of perfect purity in Peru and Mexico, than in any other quarter of the globe. In laying down this opinion, I am not considering the native silver which appears in the form of lamellae, branches, or cylindrical filaments in the mines of Guantahajo, Potosi, and Gualgayoc, or in Batopilas, Zacatecas, and Ramos. I found my opinion rather on the enormous abundance of minerals called pacos and colorados, in which silver is not mineralized, but disseminated in such small particles, that they can only be perceived by means of a microscope. The result of the investigations made by Don Fausto d'Elhuyar, the director general of the mines of Mexico, and by several members of the superior council of mines, is, that in uniting together all the silver minerals annually extracted, it would be found from the mixture, that their mean riches is from 0.0018 to 0.0025 of silver, that is to say in the common language of miners, that a quintal of ore (of one hundred pounds, or 16,000 ounces) contains from three to four
ounces of silver. This important result is confirmed by the testimony of an inhabitant of Zacatecas, who had the direction of considerable metallic operations, in several districts of mines of New Spain, and who has lately published a very interesting work, on the American amalgamation. M. Garces”, whom we have already had occasion to quote, expressly says, “ that the great mass of “ Mexican minerals is so poor, that the three “ millions of marcs of silver annually produced “ by the kingdom in good years, are extracted “ from ten millions of quintals of mineral, “ partly smelted, and partly amalgamated.” According to these numbers, the mean riches would only amount to 24 ounces per quintal, a result which differs very much from the assertion of a traveller, very estimable in other respectsf, who relates that the veins of New Spain are of such extraordinary wealth, that the natives never think of working them when the minerals contain less than a third of their weight in silver, or seventy marcs per quintal. As the most erroneous ideas
* Nueva Theorica del beneficio de los metales, por Don Joseph Garces y Eguia, Perito facultativo de minas y primario de beneficios de la mineria de Zacatecas (Mexico, 1802,) p. 121 & 125.
t The Jesuit Och (Murrs Nachrichten vom Spanischen America, t. i. p. 236.)
have been spread through Europe respecting the contents of the minerals of America, I shall procecd to give a more minute description of the districts of mines of Guanaxuato, Tasco, and Pachuca, which I had occasion to visit. At Guanaxuato, the mine of the count de la Valenciana produced between the 1st January, 1787, and the 11th June, 1791, the sum of 1,737,052 marcs of silver, which were extracted from 84,368 montones of minerals. In the table" containing the general state of the mine, a monton is estimated at 32 quintals, or at 9:38 cargas; from whence it follows that the mean riches of the minerals, was, twenty years ago 5% ounces of silver per quintal. Applying the same calculation to the
* Estado de la mina Valenciana, remitido por mano del Ercellentiss. Senor virey de Nueva España al Secretario de Estado Don Antonio Valdes. (Manuscript.) I have followed the numbers contained in the table drawn up by Don Joseph Quixano, the administrator of Valenciana. A monton (a heap of minerals reduced to powder) is reckoned at 35 quintals at Guanaxuato; at thirty at the Real del Monte, Pachuca, Zultepeque, and Tasco; at Zacatecas and Sombrerete, at 20; at Fresnillo at 18; and at 15 quintals at Bolaños. The carga is generally estimated at Guanaxuato at 14 arrobas; so that 10 cargas amount there to a monton (Garces, p. 92.) As the wealth of the ore is determined from the contents of the monton, the exact knowledge of the measure is of great importance in metallurgical calculations. . .
produce of the single year 1791, we shall find 9% ounces per quintal. At this period, when the mine was in the most flourishing condition, in the total mass of minerals there Were:
ršes of rich minerals (polvillos and Xabones,) containing per quintal - - - - - - - - 22 3 1$$e of rich minerals (apolvillado.) - - - - 9 3 ##$s of rich minerals (blanco bueno) - - - - 3 1 1$$$ of poor minerals (granzas, tierras ordina. rias, &c.) - - - - - - - - - - - - 8
The quantity of rich minerals, was consequently to that of the poor minerals, nearly in the proportion of 3 to 14. The minerals which only contained 3 ounces per quintal, supplied in 1791 (we are always speaking of the mine of Valenciana alone) more than 20,0000 marcs of silver, while there was a sufficient quantity of rich minerals, to yield a produce of more than 400,000 marcs. At present, the mean nealth of the whole vein of Guanaxuato may be estimated at 4 ounces of silver, per quintal of minerals. The South West part of the vein, which intersects the mine of Rayas, yields, however minerals, of which the contents generally amount to more than 8 IIlarCS.
In the district of the mines of Pachuca,