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By: Alfredo Terrazas, Mining Engineer, October 1968

Mining in Mexico dates back to the days of the Aztec Empire when Hernán Cortés conquered it in 1521, metals were already being produced. So much so that Cortés writes in his memoirs “that in the Great Tenoxtitlén Market, the metals: gold, silver, copper and tin were being sold; that marvelous vases and jewelry were also on display; that the smiths from Cholula and Atzcapotzalco were the most famous; that cutting instruments of hard copper were available; and that cinnabar – mercury sulphide – was used as a pigment”.

The Aztecs, without any doubt, obtained most of the metals from river sands, but some did come from vein outcrops. These were mined by chiseling and hammering or by building fires against them and, when well heated, quenching with water in order to break up the ore. The products from these operations were then concentrated and, in turn, smelted to obtain the pure metals. However, and in spite of the primitive methods, the production of gold and silver was fabulous for the time. It is generally believed that the early producers were the Districts of: Oaxaca, Zimapán, Pachuca and Taxco.


This District was located in the southern part of the Chichimeca Indian Empire which covered the central part of the now Republic of Mexico. The Chichimecas were ferocious warriors and for this reason Guanajuato was not overrun by the Spaniards until 1529 when Nuño de Guzman, with “a great show of force” took it over. However, it was kept under continuous harassment by the Indians.

For this very reason, the discovery of its gold and silver deposits did not occur until 1548. It is recorded that a driver of a mule-train, on his way to the recently-discovered ore deposits in Zacatecas, found streaks of melted silver in some of the rocks around their camp-fire which was located near the Cerro de Cubilete (where the monumental statue to Christ the King stands now). The origin of the rocks very likely would correspond to some point within the now important La Luz Mining District.

The mule-driver, named Juan de Rayas, was so enthusiastic about his find, that he remained in the District to discover, two years later (1550), the outcrop of what is now the famous Rayas Mine, in the Mother Lode of the Guanajuato District.

Unfortunately, and because of the frequent incursions of the Chichimecas, mining did not take root soon. It required 50 years of hard fighting, in which the armour and war implements of the Spaniards finally conquered the brave Indians. As a result, a peace treaty was signed in 1598, whereby the Spaniards obliged themselves to feed and clothe the Indians; they, for their part, agreed to be obedient and promised “to help to subdue the rebellious and troublesome”. In this connection, it is only fair to mention here that the priests, headed by Vasco de Quiroga, deserve a lot of credit for this settlement.
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With this now peaceful climate, the District prospered rapidly and to the extent that in 1619 King Philip III granted the locality the title of “Noble and Loyal Village of Santa Fe de Guanajuato”.

Another event of great practical importance occurred when don José de Sardaneta y Legaspi introduced, in 1726, the use of black powder to blast rock. With this explosive available it became possible to greatly increase the production of ore from the mines.

In this same year - 1726 - the sinking of the Rayas Shaft was started but the project was soon abandoned because of the great amount of water encountered. The sinking of this shaft was not renewed until 1805 and was finally completed in 1833, to a depth of 400m (1312 ft). It is octagonal and 11.31m (37.2 ft) in diameter. It cost 1,700,000 pesos - a great outlay of money for those days.

In 1760, an adventurer of Spanish descent, named Antonio Obregon y Alcocer, no doubt fascinated by the ore found in the Rayas mine, undertook to sink an exploration winze in the Mother Lode, at a distance of 2000m (6560 ft) north-west from that mine. At this point the vein was sterile. He was just acting on a dream.

By 1766, he had sunk 80m (262 ft) along the dip of the vein, without even finding any encouraging indications. By this time he had spent all of his money and what he could borrow with his most fantastic stories. Nevertheless, he persisted and, after many disappointments, was finally able to find an associate, don Pedro Luciano Otero, one of the owners of the Rayas Mine who, together with others, provided funds to continue the “wild cat” exploration.

With his new association, his luck changed and, by 1768, silver mineralization started to appear. In 1771, “immense masses of silver sulphide, mixed with native and ruby silver were found” - a dream that became true!

After this most lucky discovery it did not take long for don Antonio Obregon y Alcocer to become wealthy as well as famous. He was soon considered to be one of the richest men in the world, and was honored with the title of Count of Valenciana, because his mine was then reputed to be producing one third of the silver in the world.

With ample funds available, mining operations were actively continued at Valenciana. By 1771, the Santo Cristo de Burgos shaft had been sunk 150m (492 ft) at a cost of 95,000 pesos. The San Antonio shaft, so named in honour of the Count, was 227m (744 ft) in depth by 1775, with an outlay of 397,000 pesos. The first large bonanza from the Valenciana Mine was hoisted up this shaft.

Unfortunately, the operation could not continue to be “rosy” forever. On the 14th of June, 1780, a great tragedy occurred, when an exploration drift from the San Antonio Mine unexpectedly connected with existing workings in the Santo Cristo Mine that were full of water, generating an air-blast that killed 250 miners. A most tragic occurrence!

Not long after this sad event, in 1786, the Count of Valenciana died, and his partner, Pedro Luciano Otero soon followed him, in 1788. But luckily the operations were actively continued by their descendants.

In the same year, 1788, the beautiful Valenciana Church was completed. It had been started in 1775. It cost 391,292 pesos and 6 reales (75 centavos) – very precise accounting! It is of interest to mention that the main contribution towards its construction was provided by the miners themselves, by working over-time without pay, either mining rich ore to be sold for the purpose, or actually helping with its construction.

Another great event in the Village of Guanajuato took place when, in 1791, the King of Spain – Philip V – bestowed on the congregation the title of “Ciudad (City) of Guanajuato” in consideration of, amongst many others, its “flourishing situation”.

This same year of 1791, the now famous Valenciana Shaft was started, and was finished in 1816, after 25 years of hard work. It was a most difficult undertaking in every respect. It is 9.22m (30 ft) in diameter, and 500m (1640 ft) in depth. The cost was around 1,000,000 pesos.

The Valenciana Shaft, together with the Rayas Shaft previously mentioned, stand out as prodigious undertakings for that time. I consider them as outstanding monuments, to the owners, who financed the undertakings and, in great measure, to the workmen who gave all they had: health, and in many cases their life, to accomplish these most difficult and perilous jobs.

Now comes another most disastrous event. No sooner was the shaft ready for operation, when all of its installations were burnt down by insurgent Francisco Ortiz. He was acting on orders from Francisco Javier Mina, a famous Spanish adventurer who was fighting for the cause of Independence of México. This motive was, of course, that of preventing the Spaniards from securing additional means of continuing the domination of México, which finally only lasted until 1821.

With the destruction of the installations at the Valenciana Shaft, the water soon rose to a level of 155m (508 ft) below the collar, drowning most of the mine workings, thus practically losing all of its production.

In view of this serious situation, the second Count of Valenciana, then in charge of operations, lost no time in finding the means of solving the problem. By 1823, he had contracted with an English concern for the unwatering of the shaft by means of steam pumps; but, most unfortunately, they failed to do the job.

Following this effort, don Lucas Alamán organized, in 1825, an Anglo-Mexican company, using 8 horse whims. This method was used while sinking the shaft but, for unknown reasons, it failed after 17 months of desperate endeavour.

After these unsuccessful attempts, conditions in the mining community were disastrous. By 1827, this once most flourishing community had become so destitute “that it became a shelter for criminals and thieves”; misery was manifest, as could be ascertained by the important fact, in those days, that the Valenciana Church “had only one chaplain instead of four as before”.

These generally bad conditions prevailed until 1868, when the House of Rul, with funds originating from a bonanza they were enjoying in one of their mines located in the La Luz District, renewed operations in Valenciana, under the management of don Francisco Glennie.

The water level at that time was only 63m below the collar. On this occasion, the unwatering was done with 4 steam hoists brought from England, and leather buckets.

At long last, these installations were successful and by 1888 a production of 50 tons per day of picked ore was being obtained. This time they unwatered to a depth of 530m (1738 ft), where they were following very rich stringers on the foot-wall side of the Mother Lode. One of these workings, known as La Merced winze, was the most famous but, to their great regret, it struck a sudden rush of water which, in no time, drowned the mine. It occurred on “Ash Wednesday” in the year of 1891. After the above mentioned disaster, great efforts were made to continue operations in the higher levels, but this procedure had to be abandoned in 1898, because of absolutely inadequate ventilating conditions.

Before going into events pertaining to the XX Century, I should mention here that all the ore produced to this date was treated metallurgically, by the “Patio Process”. This was invented in Pachuca, by Bartolomé de Medina in 1555. It was an empirical amalgamating process, consisting of the mixture of the ground mineral with salt, roasted iron and copper pyrites, lime and vegetable ash. Then, mercury was added to collect the gold and silver as an amalgam.

The grinding was done in “arrastras” (heavy hard rocks dragged by animals around a post); and the mixing with the reagents was carried on for days in large “patios” (wherefrom the name of the process) by treading it over and over with horses or mules.

XX CENTURY (1900-1968)

In the early part of the Century, American promoters came to Guanajuato lured, no doubt, by the much-publicised stories about the great “bonanzas” exploited in the past.

These promoters managed to organize several stock companies to re-open some of the most noted old mines. Their study no doubt showed that there were available large tonnages of rejected mineral from the old operations and, perhaps, some fresh ore in pillars.

At the time, they had a most valuable advantage over previous operations, in that the ore could be treated by the then recently discovered “Cyanide Process”. It rendered considerably greater recoveries than the old “Patio” system and at a very significantly lower cost.

With plenty of old fills that could be cheaply exploited and treated, they operated the mines for some 30 years with, I believe, fair profits. However, they failed to do exploration work and disregarded the maintenance and modernization of their equipment.

In this manner, by 1935, when labour demanded better wages and working conditions, they were caught entirely unprepared, deciding to turn the properties over to the workmen in payment of their legal demands.
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However by 1947, help was found in the shape of small loans from several branches of the Federal Government. These were devoted principally to short-range explorations and to the most needed repairs and renewals that allowed us to continue operations with some hopes for improvement.

From 1966 to 1968 we have been able to obtain more important loans for specific purposes:

  1. that of draining the Cata and Rayas Mines another 100m (328 ft) and Valenciana 200m (656 ft) to reach the lowest workings which we esteem to have good ore possibilities,
  2. Increase the capacity of our installations in order to be able to treat 500 tons per day, instead of 400 tons, and
  3. For general improvements and additions to our general equipment.
  4. It may be interesting to know that the monumental shafts of Rayas and Valenciana are being drained by submergible pumps made in México, that need no other heavy installations than the hanging of a pipeline to raise the water to the surface. Our expectations are that, at these lower horizons, we are likely to find old fills and pillars of payable ore and some virgin ore-bodies, as a result of our explorations. This would certainly improve our situations.

    Before closing, it is interesting to mention here that the hoists now in use at the Valenciana and Rayas shafts are the same that came from England, in 1868, to unwater the Valenciana Shaft. The only innovation is that they have been electrified.

    Now, to close this information, it is of great interest to record that the production of gold and silver from Guanajuato up to 1967, as obtained from the best sources available, is as follows:

    GOLD: 133 Tons w / a present value of 143,179,820.00 pesos
    SILVER: 30,596 Tons w / a “ “ 2,002,385,817.00 pesos
    Total 2,145,565,637.00 pesos

    ALFREDO TERRAZAS, Mining Engineer

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