New Mexico Mineral Symposium — Abstracts

In 1517 when Francisco Hernandez de Cordoba landed on the Yucatan Peninsula, he encountered the vestiges of the once-vast Mayan civilization. The Maya used substantial precious metals in decorative items as well as sacred ceremonial effigies. There was considerably more gold than silver in these objects, because the native gold could be worked without further refining, and the silver in this region is generally confined to complex minerals and not readily available in its native state. Cordoba returned to Cuba telling of the great wealth of gold in the region as demonstrated by the objects that he had seen in the Yucatan. Two years later, on March 13, 1519, Hernando Cortez landed at what is now Vera Cruz on the eastern gulf shore. Along with him, he brought 10 stallions, five mares, and at least one case of smallpox. This date signifies the beginning of the end of the Aztec, Inca, and other Native American civilizations in Latin America. In the vicinity of Vera Cruz, Cortez encountered the thriving Aztec civilization ruled by Montezuma II. The Aztec at first thought that Cortez and his followers were the reincarnation of their God—Quetzalcoatl, but soon determined that these "gueros" (light skinned people) were really there to conquer and plunder their people. By November 1519, Montezuma was a captive of the Spanish, and was then killed by his own people June 30, 1520 while trying to "calm" a crowd of Aztecs, lead by his son Cuauhternoc, as they drove Cortez and the invaders from the city. Cortez returned to capture the city on August 13, 1521, and, with a relatively small force, defeated a civilization of approximately 25 million. On October 15, 1522, Hernando Cortez was appointed governor of Mexico and thus began the reign of the Spanish Empire in the Americas.

Explorers, prospectors, and conquerors were sent out from Mexico City to find the sources of the "Aztec Gold." What they discovered instead was a vast wealth of silver. During the next few years many of the "world class" silver districts of Mexico were "discovered." At least the conquistadores took credit for their discovery, because there is evidence in many districts that the indigenous people had known of these areas for years. The discovery of this vast wealth in silver financed the Spanish Empire for a long period of time, and to this day, the mines of Mexico and Peru are the world's leading producers of silver. Silver production in Mexico has been affected by political events as well as technology.

TAXCO (Guerrero)-1522
The conquistadores Juan de La Cabra, Juan Salcedo, and Muriel and Hernan Cortez began mining silver from the Socavon de Rey (Mina del Pedregal) in 1534. Sporadic mining continued until 1747. In 1802 there were several "bonanza" discoveries in the district, but metallurgical problems curtailed major production. In 1920 American Smelting and Refining Company (ASARCO) constructed a floatation plant to treat sulfide ores followed by amalgamation. The property is currently controlled by Industrial Minera Mexico, S.A. (IIVIMSA), and in the late 1980s was producing 3,000 tons per day. It has recently been put back into production after being idle for several years due to depressed metals prices.

PACHUCA (Hidalgo)-1524
This area is located about 60 mi north of Mexico City and includes three areas (Pachuca, Real del Monte, and Moran). This is one of the most famous and productive areas in Mexico. The area represents a confluence of the effects of technology as well as politics on the mining industry in Mexico. The mines were worked continuously from 1524 to 1733, when they were abandoned because of high water flow. Drainage tunnels were constructed, and the mines reopened continuing production for an additional 140 yrs.

GUANAJUATO (Guanajuato)-1529
This district was known as early as 1529, but Juan Rayas, a muleskinner, filed the first recorded claim in 1548. On April 15, 1558, work began on the Mellado shaft resulting in the discovery of the Veta Madre. This vein system underlies the eastern half of the city, and mining continues to the present (555 yrs). By the early 1600s the mines were well developed and many mines had been discovered and developed (Cata, Mellano, Rayas, and Sirena). In 1726 Don Jose de Sardaneta y Legaspi substantially increased production with the introduction of gunpowder to break rock. In 1766 the Valenciana shaft was developed to 230 m. By 1770 production had commenced in the Peregrina, El Monte, San Nicolas, Santa Rosa, and El Cubo areas. Mining activity continued at a high level until 1821 when insurrectionists burned all mine operations, including the headframe of the Tiro Valenciana. The area became a harbor for thieves and criminals until 1868 when the Valenciana was reopened and pumped using a Cornish steam hoist and leather buckets.

FRESNILLO (Zacatecas)-1553
The Fresnillo deposits were discovered shortly after the mineralization at Zacatecas by Francisco de Ibarra by miners traveling from Zacatecas to Sombrerete along the "Camino Real." They noticed a prominent hill on the western skyline and found rich silver ores in outcrop on the flanks of the hill. The hill became known as Cerro Proatio, after Diego Fernandez de Proario, who discovered some of the first small veins in the area. Mining activities in the area continued unti11757 when they were suspended because of water problems in the mines. The mines became property of the government in 1830 and reopened with prison labor in 1833, until production was halted because of cholera and lack of capital. An English company, Compania Zacatecano-Mexicana, took over operations in 1835 and installed two Cornish pumps. The Fresnillo Company was founded in 1910 in New York and leased the mine to the English–Mexican corporation for operation. The two companies eventually merged as the Fresnillo Company of New York. This company began changing its structure in 1961, because the government required all foreign operations to reduce their ownership to 49% by 1975. Indust-has Penoles acquired the 51% majority ownership and ultimately bought the remaining 49% in 1996. However, the mine is still operated as Compania Fresnillo today.

CHARCAS (San Luis Potosi)-1570
There were small mine workings being operated as early as 1570, but the main area of production was not discovered until 1583. Open cut operations in the area of the San Bartolo shaft yielded as much as 1.5 kg / ton silver.

SANTA EULALIA (Chihuahua)-1593
Santa Eulalia has been in continuous production for nearly 300 yrs from 1703 to the present, and ranks as one of Mexico's chief silver and base metal producers with over a half billion ounces of silver recovered. The city of Chihuahua was built by Spanish pioneers on the riches emanating from Santa Eulalia over the first 100 yrs of mining, and, although modern industry now dominates Chihuahua's economy, the grand cathedral and palatial mansions of the old part of the city bear mute testimony to the wealth Santa Eulalia produced for those lucky enough to own the mines and not have to work in them.

Significant production from the district did not begin until the early 1700s, but the initial discovery of mineralization is shrouded in myth, romance, and speculation. Several authors have suggested that, long before the Spanish conquest of Mexico, indigenous peoples may have accidentally discovered that silver and lead could be obtained from mineralized outcrops in the district. The mineralogy of the oxide ores would permit this, but no hard archaeological evidence for it exists. It is very likely that the indigenes found small pods of gaudy copper oxide mineralization along the southern San Antonio graben and mined it, with attendant ochre, for ornamentation.

From 1709 to 1737, the district yielded a quarter of the silver produced in all of Mexico and remained the country's largest single silver producer until 1790. By 1790 over 4 million tons of ore had been produced with grades that averaged 700 grams per mega ton of silver. Ores from some mines were extremely high grade.

MAPIMI [Ojuela] (Durango)-1598
The mineralization at the Ojuela mine was first discovered in 1598 by Spanish explorers who noticed the iron-stained outcrops on the canyon walls. There are three possible derivations of the name "Ojuela":

1) The mine may have been named for a missionary, Don Pedro de Ojuela.
2) The name is possibly for a hole resembling the eye of a needle (ojuela, "little eye") visible on the north canyon wall at the mouth of the mine.
3) The third possible derivation of the name is from hojuela, an old Spanish mining term for argentiferous galena of a leafy texture. The local miners consider this to be the source for the name.

The Ojuela mine and others in the district operated until the beginning of the Mexican Revolution in 1810 and produced at very low levels under the new government from 1821 to 1867. It was closed from 1867 to 1884. Commercial mining at the Ojuela mine continued, somewhat sporadically, until the 1940s. Currently the Ojuela mine is operated solely for mineral specimens.

In 1899, the district had 216 miners and produced $4 million (1899 dollars) of ore. The German investors received $100,000 per month during the 1890s and 1900s. During this period 6% of the total mine production in Mexico came from the Mapimi district.

There are 126 known mineral species from the Ojuela mine, and the mine is the type locality for five of them (lotharmeyerite, mapimite, metakottigite, ojuelaite, paradamite) and the cotype locality for one (scrutinyite). The mine has nearly 450 km of workings.

BATOPILAS (Chihuahua)-1632
High-grade native silver outcrops in the Batopilas district were discovered around 1630, and production records begin in 1632. The district contains more than 65 mines, and it experienced three major periods of activity during which approximately 300,000,000 oz of silver were produced from 1632-1732, 1790-1819, and 1862-1914. A.R. Sheperd, former governor of Washington DC, ran the last of these, which was the most sophisticated and organized. Sheperd was a good friend of Porfirio Diaz, president of Mexico from 1880 to 1910, who gave him carte blanche for the area. Sheperd opened the mines on a systematic basis and used the proceeds to establish a fiefdom in the area. He was very successful but used a large percentage of the profits to build himself a palatial residence and support a lavish lifestyle. Sheperd died in 1902, and his sons took over until their world came to an end in about 1911 when Pancho Villa and company arrived in the area in search of silver and gold to support the revolution. The Sheperds refused to co-operate, and Pancho devastated the area, including the hydroelectric plant that drove the pumps that kept dry the deep workings where the mining was focused. Pancho and company did work the nearby Cerro Colorado deposit for gold, which made it difficult for more than minor clandestine work to continue at Batopilas. An attempt was made to put the mines back into production after the revolution, but the destruction of the power plant made it impossible to pump out the deep workings. It is believed that these efforts were directed to pillar and offshoots in the parts of the veins above the water table. Sheperd's son attempted to revive interest in the district in 1935 but was unsuccessful. There are almost no production records from 1920 to 1975, so it is reasonable to infer that whatever work was undertaken during this period consisted of minor high-grading. From the late 1970s to the early 1980s, miners reopened the New Nevada mine and hit a high-grade breccia pipe that yielded a significant amount of native silver. This work ended when the bottom dropped out of the silver market in 1983, leaving the lower extension of this body untouched. An under-funded, but well-directed program in the early 1980s drove into the hanging wall of the Roncesvalles fault vein and hit a vein carrying native silver ore. This was the first discovery of mineralization in the hanging wall of this structure, but it was not systematically followed up. No mining activity of note has occurred since 1983.

NAICA (Chihuahua)-1794
This district was discovered in 1794, and small-scale mining occurred in 1828, but operations on the early oxide ores were limited to the "rainy seasons" because there was no water available. In 1892 Compania Minera de Naica began commercial operations but suspended operations in 1911 as the mine reached the ground water level. In 1954 the Fresnillo Company acquired the mine, and they erected a 400-ton per day sulfide processing plant to process sulfide ores discovered beneath the historic oxide zones. By 1985 the mine was serviced by a 3,000-ton per day plant, which has been expanded to produce approximately 100,000 tons per month by cut-and-fill mining techniques recovering gold, silver, copper, lead, zinc, and small amounts of tungsten and cadmium.

BOLEO (Baja California South)-1868
The Boleo was first exploited by the French El Boleo Company and produced 13.6 million metric tonnes of mineral containing 500,000 metric tonnes of copper. Most of the production occurred from 1886 to 1947; the underground workings total nearly 600 km.