New Mexico Mineral Symposium — Abstracts

The native silver occurrence at Batopilas, Chihuahua, Mexico, is like very few other deposits in the world. This deposit is grouped in a class of deposits known as "Five-Element Veins" (Lefebure 1996), characterized by native silver in a calcite host, with associated arsenic, cobalt, nickel, +/- bismuth, and uranium. Other examples of this type of silver deposit are: Cobalt, Ontario; Silver Islet, Ontario; Port Radium, Northwest Territories; Black Hawk, New Mexico, Erzgebirge district, Germany, and Kongsberg, Norway.

History
The name "Batopilas" is most likely derived from the Raramuri words Ba-cho¬tigori, the language of the Tarahumara Indians, which means "by the river." The Tarahumara almost certainly had known of silver in the area for a long time before a Spanish soldier/explorer found silver by the Batopilas River in 1632 and the Spanish exploration party took specimens of the silver back to Mexico City and then shipped them to the King of Spain.

Only small bits of local records are available from the period before 1845 because of two large fires that ravaged the area—the first in 1740 and the second in 1845. Most of what is known comes from documents in the Colonial Archives in Madrid.

1730—Rafael Alonzo de Pastrana opened the Nuestra Senora de Pilar mine and is said to have extracted an average of 40,000 pesos of silver per year "for many years." According to local legend he invited the Bishop of Durango to preside at his daughter's wedding, and Pastrana had the streets from the hotel to the Church paved with silver ingots. The Bishop is reported to have been aghast at this display of worldly pride but was quick to thank Pastrana for his "generous donation to the church." Pastrana died in 1760, by which time the main pocket of silver had been mined out and large portions of the mine were said to have caved.

1775—Cristobal Perez obtained the rights to the San Antonio mine and mined a large pocket of silver, making many millions of dollars over a 14-year period. By the time his son died in 1814 the entire fortune had been squandered.

1790—Angel Bustamante came to Batopilas as a merchant, eventually acquiring the Carmen mine (part of the San Miguel – Santo Domingo vein complex). Angel returned to Spain and "purchased" the title "Marquis de Batopilas" while his employees continued to operate the Carmen until the early 1800s.

In the 1820s the Spanish were expelled from Mexico after the Mexican War of Independence. Following expulsion of the Spanish, many mining districts in Mexico became dormant as no capital was available for operations. In 1820 the San Antonio mine was officially abandoned, leaving the Cata and Martinez mines as the last operations in the district. Some mines at Batopilas must have continued to produce high-grade ore during this difficult period as several excellent native silver specimens from this period survive (see below).

By 1842 Dona Natividad Ortiz, a woman of "strong character," began acquiring properties and re-opening mines with the help of a Tarahumara Indian associate named "Avila." In less than 10 years she had acquired and re-opened the Santo Domingo, San Nestor, Animas, Todos Santos, San Pedro, and La Aurora.

Doña Ortiz sold the San Antonio to Manuel Mendozona in 1852, and he proceeded to drive the San Miguel Tunnel, near river level, below the San Antonio workings. Mendozona died before the tunnel was completed, and the property was sold to John R. Robinson. Robinson was an American mining engineer who completed the tunnel to the San Antonio vein, encountering a "blind vein" in the process. This structure did not show good indications of silver where it was encountered, but following the weak showings resulted in the discovery of a large bonanza that earned the vein the name "Veta Grande."

In 1859 Mr. George Le-Brun acquired the Pastrana and Cata mines and started a tunnel below the historic workings of the Pastrana around 1861. In 1866 Koels reported that the lower tunnel was in ore in a structure 17 feet wide and that Le-Brun was negotiating the sale of 50% interest in the mine for $300,000. Not much else is known except that the mine was abandoned (in ore!) due to flooding. The Le-Brun tunnel has recently been excavated and shown to crosscut about 90 meters to the vein, then drift along it for 400 meters. There is a long crosscut to the west, probably exploring for an additional structure, and several stopes above the level, indicating that ore was mined from above this level. A small winze was driven into the vein about midway along the vein, but its depth cannot be determined because it remains flooded.

In 1880 Alexander Robey Shepherd arrived in Batopilas after leaving Washington D.C. bankrupt and in disgrace after being ousted from being the first, last, and only, "Governor" D.C. ever had. Shepherd and associates raised enough funds to pay John Robinson $600,000 for the San Miguel in 1880. (Robinson used this money to buy the majority of the Santa Eulalia district outside Chihuahua City, although he never successfully operated there). Through his friendship with Mexican President Porfirio Diaz, Shepherd acquired a government concession that gave him control of most of the open ground in the district and an inside track on controlling/ acquiring 350 mining claims covering 31 square kilometers. Shepherd formed the Consolidated Batopilas Mining Company in 1881 and ran the company until his death in 1902. Shepherd returned to Washington in 1887 and commissioned the Gorham Silver Company to produce fifteen silver "Batopilas flasks" featuring embossed views of various features of the Batopilas Valley and mines. These were distributed to friends in 1888 with five given to Mexican government officials, and 10 to Americans. One sold recently for $11,000. Shepherd died in Batopilas in 1902 and was returned to Washington D.C. for burial. Shepherd's sons continued to manage the operations in Batopilas until 1913 when Pancho Villa's soldiers ruined the equipment and ran the gringos out of Mexico. Shepherd's sons briefly resumed operations late in the teens but ceased mining operations in 1920. They kept control of the claims and again attempted a revival in the mid-1930s, which collapsed in the face of fears of government expropriation of metals following seizure of all petroleum rights in 1936.

Shepherd added about $2 million in municipal and mine improvements—stamp mills, concentrators, major development tunnels including the 2.14 kilometer Porfirio Diaz tunnel, and a hydroelectric plant: Batopilas was the second city in Mexico to have electricity, following Mexico City. Other improvements included a masonry aqueduct nearly 6 kilometers long, amalgamation and retorting facilities, a foundry capable of making castings up to 2,500 pounds, a hospital, schools, a bridge over the river, and an aerial tram 800 meters long (from the San Miguel mine to the San Antonio Hacienda.) During Shepherd's era the population of Batopilas increased from 400 to 5,000 habitants, and it was considered a fine place to live. The locals still speak of the lost grandeur of Batopilas. The "hacienda" that Shepherd constructed as his residence and beneficiation plant stood until it was stripped for scrap iron in the 1950s. It is now in ruins, but many of the Shepherd-era improvements are still standing, most notably the aqueduct that is still used by the city for water.

The Santo Domingo Silver Company extracted about 800,000 ounces of silver from the Santo Domingo mine from 1922-1929. This was one property never controlled by Mr. Shepherd and associates.

During the 1970s a small mill was installed but failed, as it was not appropriate for Batopilas native silver ores. In the 1980s an attempt was made to leach some ore at the Pastrana mine with cyanide, but this too was a failure.

Currently the district is under the control of MAG Silver Corporation (96%), who run an active ongoing exploration program. This exploration program's target is finding entirely new silver lodes in unexploited parts of the district, not the small amounts of material left by previous operations.

The best estimate for the total district historic production to 1880 is Dahlgren (1883) who indicated that between 200 and 300 million ounces of silver were mined during the first two centuries of operation (1632-1845), but admits that data for the very high grade "bonanza" deposits are grossly incomplete. The best production records for the district are from the Shepherd era when roughly 1 million ounces a year were produced from ores averaging 30 ounces per ton (Shepherd 1935). This average masks the fact that 75% of this total came from less than 10% of the tonnage produced, in other words ores grading over 200 ounces per ton! It is reported that in the first years after Shepherd began mining $1 million was paid to investors as dividends, but later correspondence from disgruntled shareholders indicates that most of the profits went to support Shepherd's lavish lifestyle as the "King of Batopilas."

Until 1977 all equipment and supplies to Batopilas arrived by mule train, from Creel, Cuauhternoc, and Chihuahua City. Likewise, during Shepherd's time all of the bullion was shipped out monthly by mule, with 50-100 bars per month (each bar weighing 60-75 pounds and worth about $12,000 at today's silver price) going to the Banco Minero in Chihuahua. Production delivered to Chihuahua averaged around 80,000 to 120,000 ounces per month or around a million ounces a year in the mid-1880s to around 1913. In 1943 a road was built to La Bufa, 12 kilometers upstream from Batopilas, to provide access to the Carmen mine (source of many chalcopyrite and copper in calcite specimens); the last 12 kilometers were not built until 1977, but today access to the district is easy for most vehicles.

Mining
Batopilas has been known for very rich deposits of mainly native silver for considerable time. It is estimated that 75-80% of all silver extracted from the Batopilas district occurred as native silver in very rich pockets or "clavos" (shoots). One example of these comes from the San Miguel group where a "pocket" in the vein measured 1 meter x 8 meters x 12 meters and yielded 2 million ounces of silver. This would represent 5.93 cubic meters of silver—in a mined area of 96 cubic meters or 6.18% silver. Another is from the Santo Domingo mine and represents one of the largest pockets ever recorded in the district at around 100 meters long and up to 3 meters wide. There are several types of veins described in the Batopilas district by Brodie 1909; Krieger 1935; and Wilkerson 1988.

Quartz-barite-galena-sphalerite veins with +/ - silver usually as acanthite.

Calcite-silver veins—These may have minor quartz, galena and sphalerite but mainly consist of native silver and acanthite in a matrix of highly fluorescent manganoan calcite. There are also trace amounts of nickel-cobalt arsenides in these veins.

Chlorite-actinolite-silver veins—These veins contain sheared mafic rocks that have altered to actinolite-chlorite. Silver is present as native silver with minor amounts of galena and sphalerite.

Quartz-pyrite-molybdenite veins—These veins contain no silver minerals and only minor galena +/- sphalerite.

As the mining developed, large masses of silver were encountered in the calcite-silver veins, and the miners developed terminology to describe the different types of material encountered.
In the mine the silver was described as follows by its physical characteristics related to mining (Koels 1866).

1st Massive—Plata Maciza—This material had to be hammered out or cut by chisels: it would not break.
2nd Wire—Plata Alambrada—This material was composed of wires of variable thickness, which separated by pounding; when very fine and near together it was called plata broza, which yields 50 to 65% silver by weight.
3rd Nails—Plata de clavos—Silver in the shape of nails of variable thickness.
4th Leaves—Plata de Hoja—Silver in the shape of leaves or sheets.
5th Lumps—Bolas de Plata—These are masses of silver that may not show much silver from the outside, but can be essentially solid silver inside.
6th Sulphurets—Metal de Azogue —This material shows small patches of silver usually as sulfosalts. Silver was extracted from this by mercury (azogue) amalgamation.

The classes of ore at Batopilas were also determined by mineralogical characteristics as follows (Randolph 18816):

Bodoque—Chloride of silver consisting of very rich earths near the surface. Plata Negra—Highly crystallized and very rich "black silver" or acanthite. Cardenilla—Highly crystallized and very rich "ruby silver" or proustite.

Plata Fuerte—Massive native silver in pieces weighing several hundred pounds.

Brosa—One-third calcite and two-thirds native silver (19,450 ounces per ton); running $20,000 a ton ($ 233,400 at $12.00 per ounce Ag). Large quantities of this were produced in the 1880s in the San Miguel mines.

Chispedo—Two-thirds calcite and one third native silver (9,725 ounces per ton); running $10,000 a ton ($ 116,700 at $ 12.00 per ounce Ag). Found accompanying Brosa silver.

Plata de Clavos—Calcite containing scattered nails and ferns of silver; running $500 to $5,000 a ton ($5,800 to $58,000 at $12.00 Ag) and resulting from the hand dressing of Brosa and Chispedo.

Azogues—Amalgamating ores, containing finely disseminated silver, and running $50 to $500 a ton ($5,800 to $58,000 at $12.00 per ounce Ag), in large quantities and containing strings and "bonanzitas" of brosa and chispedo of great value.

Ore grade material was broken by hand with hammers and later by stamp mills. The ores were processed by either direct smelting (very high grade ores) or by mixing with salt and mercury (patio process amalgamation). The metal was formed into bars and shipped to Chihuahua.
Mining started on the
vein outcroppings high on the hills both north and south of the Rio Batopilas. As mining proceeded to depth, getting the ore to the surface on workers' backs became too arduous, so some mines installed hoists that were operated by horses or mules. Some still continued human haulage, however. It was not until after Shepherd consolidated the district and started the Porfirio Diaz tunnel that the production from the upper mines (Roncesvalles, Todos Santos, and others) had the opportunity to let gravity work for instead of against them. Shepherd worked on this access tunnel for 14 years commencing in May 1885 and finishing in February 1899. However, plans to continue this tunnel an additional 4 kilometers to the west and access the lower workings of the Camuchin and Descubridora areas never materialized.

Specimens
Joel Roberts Poinsett, the first American minister to Mexico (and who popularized the familiar Christmas foliage now known as "poinsettia") acquired several excellent native silver specimens during his 1822-1830 tenure that he gave to the American Philosophical Society. Most are fist-sized pieces of brosa, but one example of stout wires to 3 cm long and another of stout elongate crystals to 5 cm long were included in his gift.

The earliest recorded specimen sales from Batopilas were from an 1886 auction, but Koels (1866) noted, "All of the different classes turn out the most beautiful specimens, which serve to adorn cabinets, and are frequently purchased for more than their intrinsic value." The collection belonging to A. Dohrmann Esq. of San Francisco was auctioned in Philadelphia at the Davis and Harvey Art Gallery on December 13-15, 1886. The collection consisted of 1,867 mineral specimens, of which 212 were silvers, with over 100 from Batopilas. Specimens from the Pastrana mine accounted for 73 of the Batopilas specimens.

A display of specimens from Batopilas was at the 1893 Columbian Exposition (Worlds Fair) in Chicago. The Batopilas Mining Company displayed a 380 pound silver specimen and a primitive voltmeter showing complete connectivity across the specimen. There is no detailed description of this specimen, and it mysteriously vanished after the fair, but it probably came from either the Porfirio Diaz tunnel (Roncesvalles–Todos Santos structures) or the San Miguel mine.

After the road was completed from La Bufa in 1977 there was a large amount of specimen production by John Whitmire, and these specimens have been disseminated to collectors since that time. During this time specimen production came principally from an orebody in the Nevada Valenciana (New Nevada), discovered by Manuel Limones in the early 1970s. The mine was acquired by a consortium of four local miners—each had a day that they were allowed to work the mine, and keep their finds, without a split to the others. During this time three "pockets" were found ranging from 200 to 450 kilograms each. These specimens are characterized as spiky crystals and herringbone growths, which had to be leached from the calcite vein matrix. There are minor amounts of sphalerite, acanthite, galena, and arsenopyrite on these specimens.

Currently several "gambusinos" are still working the mines, dumps, and the river for specimens. These people then sell the specimens to the tourists or mineral collectors when they come to Batopilas.

During recent exploration activities, MAG Silver discovered a previously un¬developed vein from which 2.7 kilograms of native silver specimens were collected in geological context as part of a vein bulk sample.

Specimen production is likely to continue on a limited scale by the local gambusinos from accessible workings and the river. However, if the exploration program currently being conducted by MAG Silver is successful there is likely to be additional mining in this very productive and historic district. Specimen collecting and marketing rights remain with IMDEX Inc., vendors of the property to MAG Silver.

Mineralization in the district has been described many times in reports and the literature as spotty high-grade silver, confined to structures. Alexander Shepherd Jr. (1935) wrote, "It must be remembered that at Batopilas veins are largely barren except where major pockets occur, and the only way to find these is to mine along the veins." An incident reported by Lamb (1908) concerns a mining engineer who was sampling veins in several points in the mine in order to determine the amount of ore "in sight." Shepherd Sr. admonished him by stating,"We have no ore in sight. Just as soon as it gets in sight, we take it out of sight."

This statement remains as true today, if you think that you can go to Batopilas and get access to the old workings to find some silver you are wasting your time. In the several years that I have been working in Batopilas, there are only a few places that ANY silver could be found exposed in the workings, and this was extremely
erratic and small. The best specimens that I have been able to obtain have come from gambusinos where they have "mined" the river following the summer and winter rains. Of course, the exception to this is MAG Silver's native silver discovery, which gives considerable hope for future specimen production from the district.
 

List of Mineral Speciments in the Batopilas District Veins

Chlorite group clays 

References:

1. * The author's extensive bibliography, generated by IMDEX Inc.'s MexBib 3.4??, is available on request.
2. Brodie, W. M., 1909, History of Silver Mines of Batopilas II: Mining World, v. 30, no. 26, pp. 1201-1208.
3. Brodie, W.M., 1909, History of Silver Mines of Batopilas: Mining World, v. 30, no. 24, pp. 1105-1110.
4. Dahlgren, C. B., 1883, Historic Mines of Mexico: A Review. Privately printed, New York pp. 94-102.
5. Koels, A. E., 1866, Mineral District of Batopilas, State of Chihuahua, Mexico: Unpublished report to the Batopilas Mining Company, printed by Mining and Scientific Press, 39 pp.
6. Kreiger, Philip, 1935, Primary Native Silver ores at Batopilas, Mexico and Bullard's Peak, New Mexico: American Mineralogist, v. 20, pp. 715-723.
7. Lamb, M. R., 1908, Stories of the Batopilas Mines, Chihuahua: Engineering and Mining Journal, v. 85, pp. 689-691.
8. Lefebure, D.V., 1996, Five-Element veins Ag-Ni-Co-As+/ -(Bi,U) in selected British Columbia Mineral Deposit Profiles. British Columbia Mines Open File Report 1996-13, pp. 89-92.
9. Randolph, J.C.F., 1881b, The Silver Mines of Batopilas (Descubridora, Valenzuela, Animas, Camuchin).
10. Shepherd, A. R., Jr., 1935, A summary of the Batopilas Native Silver Mines, Their Past Production and Outlook for Future Yield: Unpublished Report, University of Arizona Library.
11. Wilkerson, G., 1988, Batopilas Mining District, Chihuahua, Mexico: Economic Geology, v. 83, pp. 1721-1736.