RICHES OF ORES. 175 from the mixture, that their mean produce is from 0.0018 to 0.0025 of silver, that is to say, in the common language of miners, that one hundred pounds of ore, or 1200 ounces troy, contain 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 expressly says, "that the 66 great mass of Mexican ores is so poor, that the "1,878,400lbs. troy of silver annually produced by "the kingdom in good years, are extracted from 66 500,000 tons of mineral, partly smelted, and "partly amalgamated." According to these numbers, the mean riches would only amount to 48 ounces per ton, a result which differs very much from the assertion of a traveller, very estimable in other respects, who relates that the veins of New Spain are of such extraordinary wealth, tnat the natives never think of working them when the minerals contain less than a third of their weight in silver, or 43lbs. troy per cwt.* As the most erroneous ideas have * These accounts of the produce of metal from the ores, seem to imply throughout that the calculation is made on the whole mass of stuff drawn out of the mines, and not upon what we should call in England the clean ores. The processes of dressing or washing in Mexico seem to be so imperfect, that by the improvements that would naturally be introduced, the ores would probably be reduced to a very different state; more rich in been spread through Europe respecting the contents of the ores of America, I shall proceed 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 1,034,500lbs. troy of silver, which were extracted from 84,368 montones of ores. In the table * containing the general state of the mine, a monton is estimated at 32 cwt.; from whence it follows that the mean riches of the minerals was twenty years ago 102 ounces of silver per ton. Applying the same calculation to the produce of the single year 1791, we shall find 186 ounces per ton. At this period, when the mine was in the most flourishing condition, in the total mass of ores there were: produce, though smaller in quantity. Much advantage may be expected from attention to this circumstance.-J. T. * Estado de la mina Valenciana, remitido por mano del Excellentiss. Señor 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 the Valenciana. A monton (a heap of ores reduced to powder) is reckoned at 35 cwt. at Guanaxuato; at 30 at the Real del Monte, Pachuca, Zultepeque, and Tasco; at Zacatecas and Sombrerete, at 20; at Fresnillo at 18; and at 15 at Bolaños. 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. RICHES OF ORES. 177 Too of rich ores (polvillos and xabones), containing 1000 of rich ores (blanco bueno) 815 of poor ores (granzas, tierras ordinarias, &c.) 1000 Oz. 3360 The quantity of rich ores was consequently, to that of the poor ores, nearly in the proportion of 3 to 14. The ores which only contained 60 ounces per ton, supplied in 1791 (we are always speaking of the Valenciana mine alone) more than 123,508lbs. troy of silver; while there was a sufficient quantity of rich ores (from 60 to 3,360 ounces per ton) to yield a produce of more than 247,000lbs. troy. At present, the mean richness of the whole vein of Guanaxuato may be estimated at 80 ounces of silver per ton of ores. 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 450 ounces per ton. In the district of the mines of Pachuca, they divide the produce of the vein of Biscaina into three classes, of which the richness varied in 1803 from 32 to 160 ounces per monton of 30 quintals. The minerals of the first class, which are the richest, contain from 144 to 160; and those of the second class, from 56 to 80 ounces troy. The poorest ores which form the third class are only computed at 32 ounces of silver per monton. The result is, that the good contains 100 ounces; the middling 80 ounces; and the worst about 50 ounces of silver per ton. In the district of mines of Tasco, the minerals of Tehuilotepec contain in a tarea of four montones or 5 tons, 15lbs. troy of silver; those of Guautla yield 45; their mean wealth is consequently about 50 ounces of silver per ton of minerals. It is not then, as has been too long believed, from the intrinsic richness of the ores, but rather from the great abundance in which they are found in the bowels of the earth, and the facility with which they can be wrought, that the mines of America are to be distinguished from those of Europe *. The three districts of mines which we have just alluded to, furnish alone about 500,000lbs. of silver, and from the whole of these data we cannot entertain a doubt that the mean contents of the Mexican ores do not amount, as we have already stated, to more than from 60 to 80 ounces of silver per ton. Hence these ores, though somewhat richer than those of Freiberg, contain much less silver than the ores of Annaberg, Johann-Georgenstadt, Marienberg, and other districts of the Obergebirge in Saxony. From 1789 to 1799, there have been extracted communibus annis from the mines of the district of Freiberg, 7,838 tons, which have yielded 30,230lbs. troy of silver; so that the mean contents *The silver ores of Peru do not in general appear to be richer than those of Mexico: the contents are estimated not by the monton, but by the caxon (chest), which contains 24 cargas, reckoning each carga at ten arrobas or 250lbs. At Potosi, the mean richness of the minerals is ; in the mines of Pasco, 1 ounces per 100lbs. MEAN RICHES OF ORES. 179 were 25 ounces per ton of minerals. But in the mines of the Obergebirge the mean riches have amounted to 200, and at very fortunate periods even to 300 ounces per ton. We have thus taken a general view of the rocks in which the principal mines of New Spain are found; we have examined on what points, in what latitudes, and at what elevations above the level of the sea, nature has collected the greatest quantity of metallic wealth; and we have indicated the ores which furnish the immense quantity of silver which annually flows from the one continent to the other. It remains for us to afford some details relative to the most considerable mining operations. We shall confine ourselves to three of these groups of mines which we have already described, to the central group, and those of Tasco and Biscaina. Those who know the state of mining in Europe will be struck with the contrast between the great mines of Mexico, for example, those of the Valenciana, Rayas, and Tereros, and the mines which are considered as very rich in Saxony, the Harz, and Hungary. Could the latter be transported to the midst of the great works of Guanaxuato, Catorce, or the Real del Monte, their wealth, and the quantity of their produce, would appear as insignificant to the inhabitants of America, as the height of the Pyrenees compared with the Cordilleras. |