New Mexico Mineral Symposium — Abstracts

Earlier this year I spent the morning collecting specimens at the Mina del Tiro. I found several unusual minerals that I could not identify. I was aware of the "black wulfenite" that was previously reported there, but did not know much more. I searched the Internet to locate information on the occurrence from the prehistoric workings, but only found historical information about the mine. I did find the mineral data listed on www.mindat.org. I also found that wulfenite from the locality was mentioned by Ray DeMark, at the 1998 New Mexico Mineral symposium. The Internet did not reveal much more about the mysterious "black wulfenite." Several weeks later I traveled to Socorro to New Mexico Tech, to plunder the dusty files of symposiums past. All I was able to find was the title page of an abstract presented by Robert R. Cobban in 1983. "Black wulfenite from the Mina del Tiro, Cerrillos Hills, New Mexico"; that was it, just the title, nothing else. Only those persons present during this talk may still recall what Mr. Cobban had to say about the mysterious habit and color of this occurrence of wulfenite. I was unable to locate the author; I'm sure Mr. Cobban could answer several questions I still have on the subject.

So I decided, as a novice mineral collector, to study and report on the subject myself. I employed the assistance of, The Eveleth Encyclopedia of Mining History. Bob quickly located a box full of data on the Mina del Tiro, (Mine of the Shaft) also known by Mina de la Tierra, (Mine of the Earth). The file also contained a study by A. H. Warren, archaeologist for the Laboratory of Anthropology at Museum of New Mexico. In her report to Occidental Minerals Corporation she details the geology and the significance of the mine's prehistoric past. Her work pointed out the archaeological importance of the site and the fact that the native miners did not mine for the riches buried there, but for wealth, the minerals added to their culture. The first miners' only interests in the mines, were for the clay, galena, and turquoise deposits. Her work in 1974 helped contribute to recent discoveries as to how the mineral was used. Archaeological studies show that the ore was heated, then ground into a fine powder, and sodium carbonate also found in the area was added. This combination was then used as glaze in pot decoration. The bulk of her work still sits unpublished at the Museum of Santa Fe waiting to reveal more secrets from the past. The Mina del Tiro also carries the distinction of being one of only a few mines worked by three cultures, for riches hidden beneath the earth. The prehistoric Indians of the area worked the mine for galena to be used as glaze for pottery. The pueblo Indians also mined the beautiful blue-green turquoise, prized for trading and decoration, from the ridge north of the Mina del Tiro and from nearby Mt. Chalchihuit. The native peoples mined the area uninterrupted from 1300 to 1580.

In 1581 Spanish explorers located the mines and quickly exploited the ancient claims, enslaving the native population for nearly 100 years and forcing them to work the mine for the rich silver ore discovered there. The conquistadors broke the backs of the slaves to fill the coffers of the King of Spain. At a nearby turquoise mine several Indian slaves were buried alive in a rock slide. It was reported that the Pueblo revolt of 1680 came about from this tragic incident. The Indians killed the Spaniards and drove out their monasteries, and the native peoples also tried to obliterate any sign of mining activity and their enslavement by caving in and backfilling all known workings. The Indians vowed that the Spaniards would never engage in mining activities again, and they kept that promise for two centuries. In the late 1870s American settlers began to arrive in the Los Cerrillos mining district, and prospectors discovered the abundance of mineral resources in the land surrounding the small community.

Many prospectors and mine speculators became wealthy working the mines of the Cerrillos district of Santa Fe County .This period continued from 1870 to the early 1950s. In that time the American miners discovered and removed tons of gold, silver, zinc, turquoise, and coal. In 1896 prospectors and investors were lured to the state by the Territorial Bureau of Immigration, with statements like this, "The mines of New Mexico, a mineral belt unequalled on the face of the earth for quality, quantity, or extent: four hundred miles of gold, silver, copper, lead, and coal." Today's real estate agents refer to statements like that as "PUFFING." As a result of those wildly exaggerated statements, the population of New Mexico increased by 35,000.

The very last mining activity to take place at the Mina del Tiro was a sand and gravel operation. Today the mine has been safeguarded for future archaeological study, and the surrounding area was purchased by the county of Santa Fe and turned into Cerrillos Hills Historic Park.

Geology
Between the Mina del Tiro and the Cash Entry mines and the surrounding area, a small, primary disseminated copper deposit is located. This copper deposit lies about 1 mi north of the town of Cerrillos. Rocks in the Cerrillos district consist of latitic flows and monzonitic and syenitic intrusive probably from early Tertiary age. The disseminated copper mineralization is located around a small, circular coarse-grained monzonite stock that has invaded monzonite porphyry and pink syenite. Spectrographic analysis of 1,600 surface rock samples shows that a copper anomaly forms an annular ring up to 600 ft wide nearly encircling the coarse-grained monzonite formation. This unusual area contains more than .02% copper-in-rock. In the area of the copper occurrence, the mineralization at the surface consists of green copper carbonates and silicates, malachite, and quartz. Core drilling has revealed that the mineralization consists of thin veins and disseminated grains of chalcopyrite and rare bornite. The best grades of copper mineralization are found in silicified monzonite that also contains secondary biotite. The grade of the oxidized portion of the deposit is essentially the same as that in the unoxidized portion, and virtually no secondary enrichment has occurred. As a consequence, the deposit is considered to be a primary disseminated copper deposit, the upper part of which has been slightly modified by surface oxidation. A zone of pyritization associated with strong argillic alteration and turquoise is found outside of the zone of copper mineralization.

Mineral list for the Mina del Tiro
Cerussite, descloizite, galena, hemimorphite, jarosite,linarite, plattnerite, pyromorphite, sphalerite, tetrahedrite, turquoise, and quartz.

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